JP2018166143A - Method for manufacturing mask blank substrate, method for manufacturing mask blank, and method for manufacturing transcription mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a mask blank substrate, a mask blank and a transfer mask with reduced convex defects. Specifically, a method for manufacturing a mask blank substrate is obtained in which the generation of etching steps due to foreign matters attached to the surface of a glass substrate, which is a raw material for the mask blank substrate, is reduced. A method of manufacturing a mask blank substrate manufactured from a glass substrate having two main surfaces, the pH of which is greater than 9 and less than 11, and using a cleaning solution that does not contain a chelating agent. A first cleaning step for cleaning one main surface, and a second cleaning step for performing wet etching by covering the one main surface of the glass substrate with an etching solution having a pH of 11 or more and containing a chelating agent. It is a manufacturing method of the mask blank board | substrate characterized by having. [Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a mask blank substrate, a method for manufacturing a mask blank using the mask blank substrate, and a method for manufacturing a transfer mask using the mask blank. In particular, the present invention relates to a mask blank substrate manufacturing method with few defects, a mask blank manufacturing method, and a transfer mask manufacturing method.

  If there are defects on the mask blank substrate, the mask blank, and the transfer mask, a transfer defect occurs during wafer exposure using the transfer mask. Therefore, in recent years, further reduction in defects has been required for mask blank substrates, mask blanks, and transfer masks.

  A mask blank is manufactured by performing the process (thin film formation process) which forms the thin film for pattern formation on the main surface of a glass substrate by sputtering method etc. In general, the main surface of the substrate is cleaned before the thin film forming step. In this substrate cleaning, generally, cleaning is performed with a cleaning liquid having an action of etching the surface of the substrate.

  In Patent Document 1, an etchant is injected into the first main surface of the mask blank substrate having the first and second main surfaces, and the first main surface is covered with the etchant. A method for manufacturing a mask blank substrate including a wet etching step (wet etching step) is described. Patent Document 1 describes that an aqueous solution of a strongly alkaline compound having a pH of 10 or more is used as an etchant used in the wet etching process.

Japanese Patent Laying-Open No. 2015-184523

  In general, scrub cleaning or ultrasonic cleaning is performed when removing foreign substances adhering to the main surface of the mask blank substrate. Scrub cleaning is cleaning that removes foreign substances adhering to the main surface of the substrate by placing a cleaning liquid on the main surface of the substrate and bringing the cleaning brush into contact therewith. Ultrasonic cleaning is cleaning that removes foreign matter adhering to the main surface of a substrate by applying a cleaning liquid to which ultrasonic waves are applied to the surface of the substrate. In the case of scrub cleaning, there is a problem that foreign matter removed from the main surface of the substrate easily adheres to the cleaning brush and easily reattaches to the main surface of the substrate.

  In the case of ultrasonic cleaning, relatively large foreign matters (for example, a diameter of 100 nm or more) can be washed away from the main surface of the substrate by the flow of the cleaning liquid to which ultrasonic waves are applied. However, it is difficult to wash away relatively small foreign matter (for example, less than 100 nm equivalent) from the main surface of the substrate. This is due to the fact that the flow velocity of the liquid is greatly reduced in the vicinity of the main surface of the substrate due to the relationship between the liquid and the viscosity, and it is difficult to solve this problem.

  On the other hand, when manufacturing a mask blank substrate, a wet etching process as disclosed in Patent Document 1 may be performed. In the wet etching step, a foreign material adhering to the surface is removed by wet-etching the surface of the mask blank substrate using a cleaning liquid having an etching action on the mask blank substrate such as a glass substrate. In this cleaning by wet etching, foreign matters are removed together with the surface layer of the substrate, so that the relatively small foreign matters can also be removed from the main surface of the substrate.

  In this wet etching step, the foreign matter is removed by dissolving the surface layer of the substrate by dissolving the foreign matter with a cleaning solution having an etching action and removing the surface layer of the substrate. Since the wet etching is an etching having a large isotropic tendency, the wet etching proceeds so as to wrap around the surface layer of the substrate directly under the foreign matter. Then, as the contact area between the main surface of the substrate and the foreign material gradually decreases, the adhesion force of the foreign material decreases, and the foreign material rises in the cleaning liquid and is removed from the main surface of the substrate. Due to this action, even a foreign substance having a low solubility in the etching solution can be removed.

  However, even if the foreign matter is a component having a relatively high solubility in the cleaning liquid, if the size of the foreign matter is large, it takes time until the foreign matter is dissolved. In the case of a foreign substance that is a component having a low solubility in the cleaning liquid and a large size, the time until the foreign substance is weakly adhered to the main surface and floats in the etching liquid is significantly increased. In these cases, during the wet etching process, the foreign matter may serve as a mask, and an etching step due to the foreign matter may occur on the surface of the substrate. Such an etching step may adversely affect the mask blank and the transfer mask as a convex defect.

  Therefore, an object of the present invention is to obtain a mask blank substrate, a mask blank, and a transfer mask with reduced convex defects. Specifically, an object of the present invention is to obtain a method for manufacturing a mask blank substrate in which the generation of etching steps due to foreign matters attached to the surface of a glass substrate that is a raw material of the mask blank substrate is reduced. .

  In the manufacturing process of the mask blank substrate, the present inventors perform cleaning (wet etching process) for removing foreign matters on the surface of the mask blank substrate a plurality of times, particularly twice, using different cleaning liquids. The inventors have found that a method for producing a mask blank substrate can be obtained in which many foreign matters can be removed and the generation of etching steps due to foreign matters can be reduced.

  In order to solve the above problems, the present invention has the following configuration. That is, this invention is the manufacturing method of the mask blank board | substrate characterized by being the following structures 1-6, the manufacturing method of the mask blank characterized by the following structure 7, and the following structure 8 It is a manufacturing method of the transfer mask characterized by being.

(Configuration 1)
Configuration 1 of the present invention is a method for manufacturing a mask blank substrate manufactured from a glass substrate having two main surfaces, wherein the pH is greater than 9 and less than 11, and the cleaning solution does not contain a chelating agent. A first cleaning step for cleaning one main surface of the glass substrate; and a second cleaning for performing wet etching by covering the one main surface of the glass substrate with an etching solution having a pH of 11 or more and containing a chelating agent. And a process for producing a mask blank substrate.

  According to Configuration 1 of the present invention, a mask blank substrate with reduced convex defects can be obtained. Specifically, according to Configuration 1 of the present invention, it is possible to obtain a mask blank substrate manufacturing method in which the generation of etching steps due to foreign matters is reduced.

(Configuration 2)
Configuration 2 of the present invention is the mask blank according to Configuration 1, wherein the etching solution used in the second cleaning step is supplied to the one main surface of the glass substrate at a temperature higher than room temperature. It is a manufacturing method of the board | substrate.

  In the mask blank substrate manufacturing method of the present invention, the etching solution used in the second cleaning step is supplied to one main surface of the glass substrate at a temperature higher than room temperature, whereby the mask in the second cleaning step. The etching rate of the blank substrate can be increased. Thereby, the foreign material on the surface of the mask blank substrate can be more effectively removed.

(Configuration 3)
According to Structure 3 of the present invention, the etchant used in the second cleaning step contains one or more alkali agents selected from sodium hydroxide, potassium hydroxide, and tetramethylammonium. Or it is the manufacturing method of the board | substrate for 2 of mask blanks.

  According to Configuration 3 of the present invention, the etching solution used in the second cleaning step contains a predetermined alkaline agent, so that the pH of the second cleaning step can be easily set to a predetermined value. In addition, the etching rate for the glass substrate can be increased.

(Configuration 4)
Structure 4 of the present invention is the mask blank substrate manufacturing method according to any one of Structures 1 to 3, wherein the cleaning liquid used in the first cleaning step contains a surfactant.

  According to Configuration 4 of the present invention, the cleaning liquid used in the first cleaning step contains the surfactant, so that foreign substances can be more reliably removed in the first cleaning step.

(Configuration 5)
In the configuration 5 of the present invention, the cleaning liquid to which the ultrasonic wave having a frequency of 2.0 MHz to 5.0 MHz is applied from the cleaning nozzle while rotating the glass substrate in the first cleaning step is applied to the glass substrate. The mask blank substrate manufacturing method according to any one of configurations 1 to 4, wherein the mask blank substrate is supplied so as to contact the one main surface.

  According to Configuration 5 of the present invention, in the first cleaning step, the ultrasonic wave having a predetermined frequency is applied to the cleaning liquid, so that the removal of foreign matters in the first cleaning step can be performed more effectively.

(Configuration 6)
In the configuration 6 of the present invention, the second cleaning step supplies the etching solution only on the one main surface, and performs wet etching while swinging the etching solution on the one main surface. A method for manufacturing a mask blank substrate according to any one of Structures 1 to 5 is characterized.

  According to Configuration 6 of the present invention, the foreign matter on the surface of the mask blank substrate in the second cleaning step can be more effectively removed by swinging the etching solution. As a result, it is possible to more effectively prevent the occurrence of an etching step due to foreign matter.

(Configuration 7)
According to Configuration 7 of the present invention, a thin film for forming a transfer pattern is formed on the one main surface of the mask blank substrate obtained by the method for manufacturing a mask blank substrate according to any one of Configurations 1 to 6. Is a method for manufacturing a mask blank.

  According to Configuration 7 of the present invention, it is possible to obtain a mask blank in which the generation of etching steps (convex defects) due to foreign matters is reduced.

(Configuration 8)
Configuration 8 of the present invention is a method for manufacturing a transfer mask, characterized in that a transfer pattern is formed by patterning the thin film of the mask blank obtained by the method for manufacturing a mask blank described in Configuration 7.

  According to Configuration 8 of the present invention, it is possible to obtain a transfer mask in which the generation of etching steps (convex defects) due to foreign matters is reduced.

  According to the present invention, it is possible to provide a mask blank substrate, a mask blank, and a transfer mask with reduced convex defects. Specifically, according to the present invention, it is possible to provide a method for manufacturing a mask blank substrate in which the generation of etching steps due to foreign matters attached to the surface of a glass substrate that is a raw material of the mask blank substrate is reduced. it can.

It is a schematic diagram which shows an example of the washing | cleaning apparatus which can be used in the 1st washing | cleaning process of the manufacturing method of the board | substrate for mask blanks of this invention. It is a plane schematic diagram which shows an example of the washing | cleaning apparatus (wet etching apparatus) which can be used in the 2nd washing | cleaning process of the manufacturing method of the board | substrate for mask blanks of this invention, (a) is an upper surface schematic diagram, (b). Is a schematic bottom view. It is a cross-sectional schematic diagram which shows an example of the washing | cleaning apparatus (wet etching apparatus) which can be used in the 2nd washing | cleaning process of the manufacturing method of the mask blank substrate of this invention. It is a flowchart which shows an example of the 2nd washing | cleaning process of the manufacturing method of the board | substrate for mask blanks of this invention. It is a diagram illustrating a zeta potential of SiO ₂ or the like in the case of changing the pH.

  Embodiments of the present invention will be specifically described below with reference to the drawings. In addition, the following embodiment is a form at the time of actualizing this invention, Comprising: This invention is not limited within the range.

  Embodiment of this invention is a manufacturing method of the board | substrate for mask blanks manufactured from the glass substrate which has two main surfaces. The mask blank substrate manufacturing method includes a first cleaning step and a second cleaning step. Since the mask blank substrate manufacturing method includes the predetermined first cleaning step and second cleaning step, it is possible to reduce the generation of etching steps due to foreign matters in the mask blank substrate. As a result, a mask blank substrate with reduced convex defects can be obtained.

(Mask blank substrate material)
The glass substrate used for manufacturing the mask blank substrate is not particularly limited as long as it has translucency with respect to the exposure wavelength to be used. In the present invention, a synthetic quartz glass substrate and other various glass substrates (for example, soda lime glass, aluminosilicate glass, etc.) can be used. Among them, the synthetic quartz glass substrate has a high transmittance even for an ultraviolet ray having a short wavelength such as an ArF excimer laser (wavelength 193 nm), so that glass for a binary mask blank used for forming a high-definition transfer pattern. It is suitable as a glass substrate for a substrate or a phase shift mask blank.

Moreover, as a glass substrate used for a mask blank substrate, low thermal expansion glass used for a reflective mask using EUV (Extreme Ultra Violet) light as exposure light can be used. Examples of low thermal expansion glass used for the reflection type mask, for example, _SiO 2 -TiO ₂ type glass having the characteristics of low thermal expansion (binary _(SiO 2 -TiO ₂₎ and ternary _(SiO 2 -TiO ₂ -SnO ₂ etc.), for example, so-called multicomponent glasses such as SiO ₂ -Al ₂ O ₃ -Li ₂ O based crystallized glass can be used.

(Polishing process and pre-cleaning process)
In the mask blank substrate manufacturing process, after the polishing process of the glass substrate, particles existing on the main surface of the glass substrate (for example, foreign substances such as abrasive grains adhering to the glass substrate surface) are excluded. A pre-cleaning step is performed.

  The mask blank substrate (glass substrate) has two opposing main surfaces. The two opposing main surfaces are referred to as a first main surface (also referred to as “front side main surface”) and a second main surface (also referred to as “back side main surface”). A thin film for forming a transfer pattern is formed on the first main surface (front side main surface).

  In the polishing process of the glass substrate, the polishing pad is brought into contact with the main surface of the glass substrate, a polishing liquid containing abrasive grains is supplied to the surface of the glass substrate, and the glass substrate and the polishing pad are moved relatively, Polish the main surface of the glass substrate. For example, a glass substrate is pressed against a polishing surface plate to which a polishing pad is adhered, and the polishing surface plate and the glass substrate are relatively moved while supplying a polishing liquid containing polishing abrasive grains (that is, the polishing pad and the glass substrate are The main surface of the glass substrate is polished. As the abrasive grains, colloidal silica is preferably used at least in the final polishing in the precision polishing step because good smoothness and flatness of the glass substrate can be obtained. For this polishing step, for example, a planetary gear type double-side polishing apparatus or the like can be used.

  After completion of ultra-precision polishing, cleaning (pre-cleaning step) for removing colloidal silica abrasive grains is performed. Specifically, brush cleaning is performed on the main surface and end surface of the glass substrate, and then spin cleaning with pure water is performed. Instead of brush cleaning, dip cleaning performed by immersing a mask blank substrate, which is a glass substrate, in a hydrofluoric acid aqueous solution bath and / or cleaning using a detergent containing a surfactant may be performed. it can.

  After the pre-cleaning step, an inspection step for inspecting defects such as adhesion of foreign matters on the surface of the mask blank substrate can be included.

(First cleaning process)
The manufacturing method of the mask blank substrate of the present invention includes a first cleaning step. The first cleaning step includes cleaning one main surface of the glass substrate using a cleaning liquid having a pH greater than 9 and less than 11 and containing no chelating agent. This first cleaning step is a step whose main purpose is to remove relatively large foreign matters (for example, equivalent to a diameter of 100 nm or more) among foreign matters adhering to one main surface of the glass substrate. . The cleaning liquid used in the first cleaning step is a liquid that has a relatively small etching action on the glass substrate or that does not substantially etch the glass substrate. One main surface is preferably the first main surface (front side main surface). Hereinafter, the cleaning of the first main surface will be described as an example.

When a material containing SiO ₂ , such as synthetic quartz, is used as a glass substrate for manufacturing a mask blank substrate, the surface (including the first main surface) that comes into contact with the cleaning liquid of the substrate because the cleaning liquid is alkaline. The zeta potential on each surface becomes negative. Further, as the pH rises, the negative value of the zeta potential on the surface with which the substrate cleaning liquid comes into contact tends to increase. FIG. 5 shows, as an example, zeta potentials of SiO ₂ , Si, Si ₃ N ₄ , and Al ₂ O ₃ when the pH of the aqueous solution is changed. As is apparent from FIG. 5, in any of the materials, the zeta potential tends to increase in the negative direction as the pH increases. In general, in the region from acidic to about pH 8, the zeta potential shows various values depending on the material. On the other hand, in the region of pH 9 or higher, the zeta potential becomes negative regardless of the material. For example, silica fine particles are negative in the neutral region and have the same polarity as the glass substrate. For this reason, it can be estimated that once the foreign matter is detached from the glass substrate, it does not easily reattach to the glass substrate. On the other hand, the alumina fine particles are positively charged in the vicinity of neutrality, and are easily reattached to the negatively charged glass substrate even once detached. However, when the pH is increased to 9 or more, the zeta potential of a material that is easily positively charged, such as alumina, becomes negative, and it becomes difficult to reattach to the surface of the glass substrate. Accordingly, since the cleaning liquid is alkaline at a predetermined pH, the negatively charged foreign particles are subjected to repulsive force from the surface of the glass substrate due to the negative zeta potential on the surface of the glass substrate. As a result, it is possible to prevent foreign matter from adhering to the surface of the glass substrate.

  The cleaning liquid used in the first cleaning step has a pH greater than 9 and less than 11, and is alkaline. Therefore, from the above, the zeta potential of both the surface of the glass substrate (each surface including the first main surface) and the foreign material becomes negative. That is, foreign substances can be removed from the first main surface of the glass substrate by an electric repulsive force because the cleaning liquid in the first cleaning step is alkaline at a predetermined pH. Furthermore, the removed foreign matter can be prevented from reattaching to the first main surface of the glass substrate. Therefore, in the first cleaning process, it can be said that foreign matters having a relatively large size can be effectively removed from the glass substrate and reattachment to the glass substrate can be prevented.

  Moreover, the cleaning liquid used in the first cleaning step does not contain a chelating agent. As will be described later, when the cleaning liquid is alkaline and contains a chelating agent, the etching rate of the wet etching of the cleaning liquid on the glass substrate increases. Since the cleaning liquid used in the first cleaning process does not contain a chelating agent, the etching rate of wet etching on the glass substrate of the cleaning liquid used in the first cleaning process is small. Therefore, it can be said that the possibility of an etching step due to foreign matter adhering to the first main surface of the glass substrate in the first cleaning process is extremely low.

  The cleaning liquid used in the first cleaning process is an aqueous solution having a pH in a predetermined range because it contains an alkaline agent. The alkaline agent contained in the cleaning liquid can be used without limitation as long as it can bring the cleaning liquid to a predetermined pH. Examples of the alkaline agent contained in the cleaning liquid used in the first cleaning step include alkali metal hydroxides. As the alkali metal hydroxide, for example, sodium hydroxide (NaOH) and potassium hydroxide (KOH) can be preferably used from the viewpoint of availability and handling. An organic alkaline agent such as TMAH (tetramethylammonium hydroxide) can also be used.

  The cleaning liquid used in the first cleaning step preferably contains a surfactant. Since the cleaning liquid used in the first cleaning process contains a surfactant, the surface tension of the cleaning liquid is reduced, and the penetration of the cleaning liquid between the substrate and the foreign substances is promoted, so that the foreign substances are removed in the first cleaning process. Can be done more reliably.

  As the surfactant that can be included in the cleaning liquid of the first cleaning step, a commercially available surfactant can be used without limitation. From the viewpoint of more effectively removing foreign substances, the surfactant contained in the cleaning liquid used in the first cleaning step is preferably selected from an anionic surfactant and a nonionic surfactant.

  The temperature of the cleaning liquid used in the first cleaning step is preferably 5 to 35 ° C. (20 ± 15 ° C.), and more preferably 22 to 30 ° C. In addition, in this specification, 5-35 degreeC (20 +/- 15 degreeC) is also called "normal temperature."

  In the method for manufacturing a mask blank substrate of the present invention, in the first cleaning step, a cleaning liquid to which an ultrasonic wave having a frequency of 2.0 MHz to 5.0 MHz is applied from a cleaning nozzle while rotating the glass substrate is a glass substrate. It is preferable to supply so as to hit one of the main surfaces. By applying an ultrasonic wave having a predetermined frequency to the cleaning liquid in the first cleaning step, it is possible to more effectively remove foreign substances in the first cleaning step.

  When ultrasonic waves are applied to the cleaning liquid for cleaning the glass substrate, latent scratches may occur inside the glass substrate. By setting the frequency of the ultrasonic wave applied to the cleaning liquid within a predetermined range, it is possible to suppress the occurrence of latent scratches inside the glass substrate. Specifically, the surface of the glass substrate is cleaned by applying a cleaning liquid to which an ultrasonic wave having a frequency of 2.0 MHz or more is applied toward the first main surface of the glass substrate, thereby cleaning the inside of the glass substrate (particularly the substrate). The occurrence of latent scratches on the surface of the main surface can be suppressed. In addition, it is preferable to apply a cleaning liquid to which an ultrasonic wave of 2.5 MHz or higher is applied because the occurrence of latent scratches can be more reliably suppressed. Note that whether or not latent scratches have occurred inside the substrate can be confirmed by, for example, revealing the latent scratches with an alkaline chemical solution or the like.

  In addition, by applying a cleaning method for cleaning the first main surface of the glass substrate by applying a cleaning liquid to which ultrasonic waves are applied, even in a cleaning liquid to which ultrasonic waves higher than a predetermined frequency are applied, Particles present on the main surface of the substrate can be surely eliminated. In the present invention, the upper limit of the frequency of the ultrasonic wave applied to the cleaning liquid is preferably 5.0 MHz or less. If the frequency of the ultrasonic wave applied to the cleaning liquid is higher than 5.0 MHz, the particle removal rate of the first main surface of the substrate after cleaning, particularly the removal rate of relatively large particles having a particle size of 200 nm or more may be reduced. . Note that it is desirable to set the upper limit of the frequency of the ultrasonic wave applied to the cleaning liquid to 4.0 MHz or less, preferably 3.5 MHz or less because the removal rate of relatively large particles can be further improved.

  From the above, the ultrasonic wave applied to the cleaning liquid in the first cleaning step is preferably an ultrasonic wave having a frequency of 2.5 MHz to 4.0 MHz, more preferably 2.5 MHz to 3.5 MHz. It is desirable.

  FIG. 1 is a configuration diagram illustrating an example of a cleaning apparatus that can be used in the first cleaning step.

  A cleaning apparatus 310 shown in FIG. 1 is a single wafer cleaning apparatus, and includes a spin chuck 311 that holds a substrate 301 and an ultrasonic cleaning nozzle 314 provided at the tip of an arm 315. The spin chuck 311 is rotatably provided by an electric motor 312. Further, the ultrasonic cleaning nozzle 314 applies ultrasonic waves to the cleaning liquid supplied from the cleaning liquid supply device 316. The cleaning liquid to which the ultrasonic wave is applied is directly applied to the first main surface of the substrate 301 from above and supplied. At the time of cleaning, the ultrasonic cleaning nozzle 314 is configured to move (swing) from the center to the end surface of the substrate 301 by the arm 315 while rotating the substrate 301 at a predetermined number of rotations. The periphery of the spin chuck 311 is covered with a cleaning cup 313 to prevent the cleaning liquid from splashing.

  When using the above cleaning apparatus, when the ultrasonic cleaning nozzle 314 is moved (swinged) by the rotation of the arm 315, the rotation of the arm 315 is repeated within a predetermined angle range, for example, an angle range of ± 15 degrees. It is preferable to exercise.

  In the case of using the above-described cleaning apparatus, it is desirable that the number of rotations of the substrate during cleaning and the moving speed of the ultrasonic cleaning nozzle be appropriately set so that the entire substrate 301 is cleaned uniformly. In addition, the flow rate of the cleaning liquid applied to the first main surface of the substrate 301 varies slightly depending on the number of rotations of the substrate during cleaning and the moving speed of the ultrasonic cleaning nozzle, but is approximately 1.0 to 5.0 liters / minute. Particularly, it is particularly preferable to set the rate to about 1.0 to 3.0 liters / minute.

  In addition, regarding the shape of the tip of the ultrasonic cleaning nozzle 314 in the cleaning device, for example, a circular shape or a rectangular shape (such as a slit shape) can be arbitrarily used.

  As described above, in the first cleaning step, even when a cleaning method using a cleaning liquid to which ultrasonic waves are applied is applied during the cleaning of the glass substrate, the cleaning liquid to which ultrasonic waves having a predetermined frequency range are applied is applied to the substrate. By washing it against one main surface, there is no fear of latent scratches inside the glass substrate, and particles present on the main surface of the substrate can be reliably eliminated.

  In the above description, the cleaning apparatus that can be used in the first cleaning step has been described with reference to FIG. 1, but is not limited thereto. In the first cleaning step, a cleaning apparatus as shown in FIGS. 2 and 3 that can be used in the second cleaning step described later may be used.

(Second cleaning process)
The manufacturing method of the mask blank substrate of the present invention includes a second cleaning step. The second cleaning step includes wet etching by covering one main surface of the glass substrate with an etchant having a pH of 11 or more and containing a chelating agent. This second cleaning step is a step whose main purpose is to remove minute foreign matters (for example, less than 100 nm in diameter) among foreign matters adhering to one main surface of the glass substrate. One main surface is preferably the first main surface (front side main surface). Hereinafter, the cleaning of the first main surface will be described as an example.

  By performing a second cleaning step of wet etching with a cleaning liquid having a pH of 11 or more and containing a chelating agent on the first main surface of the substrate from which foreign substances have been removed by the first cleaning step, the substrate The minute foreign matter adhering to the first main surface can be lifted off.

  The cleaning liquid used in the second cleaning step is an aqueous solution containing an alkali agent and a chelating agent. The present inventors have found that the etching rate of the glass substrate is increased when a cleaning solution having a high pH (11 or more) and containing a chelating agent is used. When such a cleaning solution having a high etching rate is used as the cleaning solution in the first cleaning step, a relatively large foreign substance serves as an etching mask, resulting in a difference in the in-plane etching amount on the first main surface of the substrate. As a result, a convex defect may be newly formed on the surface. Therefore, in the first cleaning step, an alkaline cleaning liquid that does not contain a chelating agent is used to reliably remove foreign substances having a relatively large size. On the other hand, after removing foreign matters in the first cleaning step, as a second cleaning step, by washing with an alkaline cleaning solution containing a chelating agent, minute foreign matters that could not be removed in the first cleaning step can be removed. it can. In addition, the first cleaning step described above removes foreign matters having a relatively large size and prevents reattachment of foreign matters during the first cleaning step. Therefore, the etching rate is high in the second cleaning step. Even when it is used for a cleaning liquid (an aqueous solution containing an alkali agent and a chelating agent), it is possible to suppress the occurrence of an etching step due to foreign matters attached to the first main surface of the glass substrate.

  The cleaning liquid used in the second cleaning step is an aqueous solution of an alkaline compound having a pH of 11 or more. As the aqueous solution of the alkaline compound, the pH is more preferably 12 or more, and particularly preferably 13 or more. As described above, the aqueous solution of the alkaline compound makes the zeta potential of the surface of the glass substrate (each surface including the first main surface) negative. For this reason, foreign substances having the same negative zeta potential repel each other with the first main surface of the glass substrate, so that reattachment of the foreign substances can be prevented. For this reason, it is advantageous regarding the ability to remove foreign substances that the cleaning liquid has a predetermined pH.

  The cleaning liquid used in the second cleaning process is an aqueous solution having a pH in a predetermined range because it contains an alkaline agent (alkaline compound). As the kind of the alkaline compound, either an inorganic alkaline compound or an organic alkaline compound can be used. Since the cleaning liquid used in the second cleaning process has a high etching rate with respect to the glass substrate as described above, the cleaning liquid used in the second cleaning process may be referred to as an “etching liquid”.

Examples of inorganic alkaline compounds include alkali metal hydroxides (KOH, NaOH, LiOH, RbOH, and CsOH). Among these, Na ions (Na ⁺ ) and K ions (K ⁺ ) can stably coexist with silicate ions (SiO ₃ ²⁻ etc.) released from the glass substrate. Therefore, the KOH aqueous solution and the NaOH aqueous solution in which these ions are dissociated are preferable in that the etching reaction can be stably advanced.

  An aqueous solution of an organic alkaline compound can also be used as an etching solution. In the case of an organic alkaline compound, the etching solution has a pH of 11 or more, preferably a pH of 13-14.

  When an organic alkaline compound is used as the solute of the etching solution, quaternary ammonium hydroxide can be used. Specific examples include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), and tetrabutylammonium hydroxide (TBAH). From the viewpoint of ease, tetraalkylammonium hydroxide can be preferably used.

  Moreover, what has an alkoxy group is mentioned as another example of quaternary ammonium hydroxide. Specific examples include trimethylhydroxyethylammonium hydroxide, methyltri (hydroxyethyl) ammonium hydroxide, tetra (hydroxyethyl) ammonium hydroxide, and benzyltrimethylammonium hydroxide (BTMAH).

  In the case of a weak basic substance such as a compound such as tertiary alkylamine or ammonia among organic alkaline substances, the ability to etch glass is poor, so it is appropriate to use it alone as an etchant for wet etching. Not. In addition, when ammonia is used as a component of the etching solution, the ammonia is adsorbed on the surface of the glass substrate and reacts with a component of the cleaning solution (for example, sulfate ion) used in the subsequent cleaning process to produce a product (for example, ammonium sulfate). May precipitate and cause haze, which is not preferable.

  In the mask blank substrate manufacturing method of the present invention, the cleaning liquid (etching liquid) used in the second cleaning step contains one or more alkaline agents selected from sodium hydroxide, potassium hydroxide, and tetramethylammonium. Is particularly preferred. When the etching solution used in the second cleaning step contains a predetermined alkaline agent, the pH of the second cleaning step can be easily set to a predetermined value.

  A known chelating agent can be used as the chelating agent contained in the cleaning liquid (etching liquid) used in the second cleaning step. As a chelating agent, what was selected from EDTA (edetic acid), HEDP (etidronic acid), etc. can be used preferably, for example. The addition amount of the chelating agent is preferably 0.1 wt% or more.

Since the concentration of the etching solution depends on the concentration of hydroxy ions (OH ⁻ ) that contribute to the etching reaction, the concentration may be adjusted to be in the above pH range. For example, when a strong alkaline compound such as KOH or NaOH having a large dissociation constant is used, an alkaline concentration of 0.01 mol / L or more may be used. Preferably, it is 0.1 mol / L or more, and particularly preferably 1 mol / L or more. In addition, in the case of an etching solution with poor solute volatility such as NaOH and KOH, the rinsing time after etching may be prolonged, so the sum of the concentrations of inorganic alkali components should be adjusted to 3 mol / L or less. Is preferred. When the etching solution containing only the inorganic alkali component is used, the pH is 11 or more, and the preferred pH is 13-14.

  In the mask blank substrate manufacturing method of the present invention, it is preferable that the etchant used in the second cleaning step is supplied to one main surface of the glass substrate at a temperature higher than room temperature. In the present specification, as described above, the normal temperature means 20 ± 15 ° C., that is, 5 to 35 ° C. The etching liquid used in the second cleaning step is supplied to one main surface of the glass substrate at a temperature higher than room temperature, whereby the etching rate of the mask blank substrate in the second cleaning step can be increased. Thereby, the foreign material on the surface of the mask blank substrate can be more effectively removed.

  The supply temperature of the wet etching solution is higher than normal temperature, preferably 40 ° C. or higher, particularly preferably 60 ° C. or higher. In addition, when the inorganic alkaline compound which does not have volatility is used as a solute, it is preferable that the temperature of etching liquid is 95 degrees C or less. As the distance from the supply location of the etchant increases, the solute concentrates due to the volatilization of water, which is a solvent, and the concentration distribution of the etchant may occur. Preferably it is 80 degrees C or less.

  The wet etching solution has at least one etchant, and the boiling point of the etchant is preferably higher than the temperature of the etching solution. Since the boiling point of the etchant is higher than the supply temperature of the etching solution, a decrease in solubility due to a temperature rise and a decrease in concentration due to volatilization of the solute do not occur, which is preferable in terms of stabilizing the etching solution. For example, when an inorganic strong alkali component such as an alkali metal hydroxide is used as an etchant, the volatility (vapor pressure) in an environment having a high boiling point and 100 ° C. or less is very low. As described above, even if it is basically used at 95 ° C. or lower), it is difficult to cause a decrease in concentration due to solute volatilization.

  In addition, when an organic alkaline compound is used as an etchant, four methyl groups in the quaternary ammonium hydroxide are substituents, and the boiling point of tetramethylammonium hydroxide (TMAH) having a low molecular weight and a low boiling point is 130 ° C. or higher. In addition, even if a wet etching solution using a typical quaternary ammonium hydroxide as an etchant is used at a high temperature, the concentration does not easily decrease due to volatilization.

  Examples of the wet etching method in the second cleaning step include a wet etching method performed by supplying an etching solution to the surface to be etched, a spin etching method, and a spray etching method, which can be performed alone or in combination. . Among these, wet etching performed by supplying an etching solution to the surface to be etched and spin etching are effective, and a method in which both are combined is preferable. The surface of the mask blank substrate can be quickly wetted with an etching solution by spin rotation at the time of spin etching, and after being wetted, wet etching can be performed by subsequently supplying the etching solution to the substrate surface. In this way, it is possible to avoid the risk of cross contamination while preventing variation in the etching progress due to the difference in contact time with the etching solution. Furthermore, by supplying an etching solution to the surface of the substrate and performing wet etching, the amount of the etching solution to be used can be reduced.

  Further, by making the temperature of the first main surface of the substrate uniform and appropriately supplying the etching liquid to the first main surface of the substrate, the liquid film of the etching liquid on the first main surface of the substrate can be made substantially equal in thickness. In this case, the etching reaction can be progressed uniformly. When wet etching is performed by supplying an etching solution to the first main surface of the substrate, the etching solution can be etched through a state in which the etching solution is statically deposited on the entire surface of the first main surface of the substrate to be processed.

  In the second cleaning step, in order to make the in-plane distribution of the temperature of the glass substrate more uniform, for example, as described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2015-184523), A liquid such as pure water whose temperature is adjusted to a temperature higher than normal temperature can be supplied to the opposing main surface side. Thereby, the in-plane distribution of the temperature of the glass substrate is suppressed. Although the reaction rate of the etching reaction varies depending on the contact temperature between the etching solution and the glass substrate, the intensity of the etching reaction can be made uniform by suppressing the in-plane distribution of the glass substrate temperature.

  As a cleaning apparatus that can be used in the second cleaning step, a cleaning apparatus (etching apparatus) as shown in FIGS. 2 and 3 shown in Patent Document 1 can be used, but the invention is not limited to this. In the second cleaning step, a cleaning device as shown in FIG. 1 described in the first cleaning step may be used.

  In the second cleaning step, it is preferable to perform wet etching while supplying an etching solution only on one main surface and swinging the etching solution on one main surface. In this specification, “oscillation” refers to repetitive rotational movement within a predetermined angle range, for example, an angle range of ± 30 degrees (preferably, an angle range of ± 15 degrees). By swinging the etching solution, it is possible to more effectively remove foreign substances on the first main surface of the mask blank substrate in the second cleaning step. As a result, it is possible to more effectively prevent the occurrence of an etching step due to foreign matter.

  In the second cleaning step, as in the first cleaning step, an etching solution to which an ultrasonic wave having a frequency of 2.0 MHz or more and 5.0 MHz or less is applied from the etching solution supply nozzle is supplied to one main surface of the glass substrate. Can be supplied to hit.

(Rinse washing process)
After the etching by the second cleaning process, a rinse cleaning process for removing the etching solution remaining on the mask blank substrate is performed. Since the rinse cleaning step is mainly intended to remove the etching solution, at least pure water cleaning may be performed. An example of the cleaning method in the rinse cleaning step is a spin cleaning method. Preferably, an alkaline component adsorbed on the mask blank substrate surface is efficiently removed by supplying a cleaning liquid (ultrasonic cleaning liquid) to which ultrasonic waves are applied or warm water of about 40 ° C. to 60 ° C. onto the mask blank substrate. can do. Moreover, it can carry out especially effectively by performing it in combination with a spin cleaning and an ultrasonic cleaning liquid or the said warm water. In addition, it is preferable to repeat the 2nd washing | cleaning process and the washing | cleaning after the 2nd washing | cleaning (rinse washing | cleaning process) several times continuously, for example, 3-5 times.

  As described above, a mask blank substrate can be manufactured.

(Manufacture of mask blanks)
The present invention is a mask blank manufacturing method characterized in that a thin film for forming a transfer pattern is formed on one main surface of a mask blank substrate obtained by the above-described mask blank substrate manufacturing method. is there. According to the present invention, it is possible to obtain a mask blank in which the generation of etching steps (convex defects) due to foreign matters is reduced.

  A thin film is formed on the mask blank substrate after the cleaning step is completed, a light-shielding film used for the binary mask blank, a light semi-transmissive film of the halftone phase shift mask blank, or a multilayer reflective film of the reflective mask, And an additional functional film is formed in accordance with the type of the mask blank substrate and the application of the transfer mask.

(1) Binary mask blank A binary mask blank is manufactured by forming a thin film including a light-shielding film on a synthetic quartz glass substrate processed up to the wet etching step. The light-shielding film (transfer pattern thin film) is a material containing a transition metal alone or a compound selected from chromium, tantalum, ruthenium, tungsten, titanium, hafnium, molybdenum, nickel, vanadium, zirconium, niobium, palladium, rhodium, and the like. Can be formed. For example, the light shielding film can be formed of chromium or a chromium compound containing one or more elements selected from elements such as oxygen, nitrogen, and carbon in chromium. For example, the light-shielding film can be formed of a tantalum compound containing tantalum and one or more elements selected from elements such as oxygen, nitrogen, and boron.

  On the other hand, the light shielding film can be formed of a material containing a transition metal and silicon. For example, the light shielding film can be formed of a transition metal silicide compound containing transition metal and silicon containing one or more elements selected from oxygen and nitrogen. As the transition metal, molybdenum, tantalum, tungsten, titanium, hafnium, nickel, vanadium, zirconium, niobium, palladium, ruthenium, rhodium, chromium, and the like are applicable. On the other hand, the light shielding film can be formed of a material containing silicon. For example, the light shielding film can be formed of a silicon compound in which one or more elements selected from oxygen and nitrogen are added to silicon.

  Such binary mask blanks include a light-shielding film having a two-layer structure of a light-shielding layer and a front-surface antireflection layer, or a three-layer structure in which a back-surface antireflection layer is further added between the light-shielding layer and the glass substrate. . Moreover, it is good also as a composition gradient film | membrane from which the composition in the film thickness direction of a light shielding film differs continuously or in steps.

(2) Phase shift mask blank The phase shift mask blank has a form having a light semi-transmissive film (transfer pattern thin film) on the synthetic quartz glass substrate processed up to the wet etching step, and the light semi-transmissive film A halftone phase shift mask is manufactured, which is a type in which a shifter portion is provided by patterning.

  In such a phase shift mask, in order to prevent pattern defect of the glass substrate to be transferred due to the light semi-transmissive film pattern formed in the transfer region based on the light transmitted through the light semi-transmissive film, the light semi-transmissive film is formed on the glass substrate. And a light-shielding film (light-shielding band) thereon. In addition to halftone phase shift mask blanks, there are mask blanks for Levenson type phase shift masks and enhancer type phase shift masks that are glass substrate digging types in which a glass substrate is dug by etching or the like to provide a shifter portion. Can be mentioned.

  The light semi-transmissive film of the halftone phase shift mask blank transmits light having an intensity that does not substantially contribute to exposure (for example, 1% to 30%, preferably 1% to 20% with respect to the exposure wavelength). It has a predetermined phase difference (for example, 150 degrees to 200 degrees). The light semi-transmissive portion is transmitted through the light semi-transmissive portion by a light semi-transmissive portion patterned with the light semi-transmissive film and a light transmissive portion that does not have the light semi-transmissive film and transmits light having an intensity substantially contributing to exposure. The light phase is substantially inverted with respect to the phase of the light transmitted through the light transmitting portion. For this reason, light passing through the vicinity of the boundary between the light semi-transmissive portion and the light transmissive portion and entering each other's region by the diffraction phenomenon cancels each other. As a result, the contrast, that is, the resolution of the boundary portion can be improved with the light intensity at the boundary portion being substantially zero.

  Examples of the light semi-transmissive film include a material containing a transition metal and silicon, and a material containing one or more elements selected from oxygen, nitrogen, and carbon in the transition metal and silicon. As the transition metal, molybdenum, tantalum, tungsten, titanium, hafnium, nickel, vanadium, zirconium, niobium, palladium, ruthenium, rhodium, chromium, and the like are applicable.

  In the case of having a light-shielding film on the light semi-transmissive film, the material of the light semi-transmissive film contains a transition metal and silicon. It is preferable to have (having etching resistance). The light-shielding film is particularly preferably composed of chromium or a chromium compound in which elements such as oxygen, nitrogen, and carbon are added to chromium.

  Since the Levenson type phase shift mask is manufactured from a mask blank having the same configuration as the binary type mask blank, the configuration of the pattern forming thin film is the same as that of the light shielding film of the binary type mask blank. The light semi-transmissive film of the mask blank for the enhancer-type phase shift mask transmits light having an intensity that does not substantially contribute to exposure (for example, 1% to 30% with respect to the exposure wavelength). A film having a small phase difference generated in exposure light (for example, a phase difference of 30 degrees or less, preferably 0 degrees). In this respect, the light semi-transmissive film of the mask blank for the enhancer type phase shift mask is different from the light semi-transmissive film of the halftone type phase shift mask blank. The material of this light semi-transmissive film includes the same elements as the light semi-transmissive film of the halftone type phase shift mask blank, but the composition ratio and film thickness of each element have a predetermined transmittance and predetermined ratio to the exposure light. The phase difference is adjusted to be small.

  In order to form a fine pattern by reducing the thickness of the resist film, an etching mask film may be provided over the light shielding film. This etching mask film preferably has etching selectivity (etching resistance) with respect to the etching of the light shielding film. At this time, the mask blank may be manufactured in a state where the etching mask film is left on the light shielding film by providing the etching mask film with an antireflection function.

  In the case where the light shielding film is formed of the above chromium compound, the etching mask film is made of a silicon compound in which an element such as oxygen, nitrogen, and carbon is contained in silicon which is a material having etching selectivity with respect to the light shielding film. It is preferable to comprise with the material which becomes. Further, when the light shielding film is formed of the above transition metal silicide compound, tantalum compound, or silicon compound, the etching mask film is made of chromium or chromium which is a material having etching selectivity with respect to these light shielding films. It is preferable to use a material made of a chromium compound containing an element such as oxygen, nitrogen, or carbon.

  In the case of the multi-tone mask blank having the laminated structure of the semi-transmissive film and the light-shielding film, the semi-transmissive film material is the same element as the light semi-transmissive film of the halftone phase shift mask blank. In addition, materials including simple metals such as chromium, tantalum, titanium, and aluminum, or alloys thereof, or compounds thereof are also included. The composition ratio and film thickness of each element are adjusted so as to have a predetermined transmittance with respect to the exposure light. The light shielding film of the binary mask blank can also be applied to the material of the light shielding film. Further, the composition and film thickness of the light shielding film material can be adjusted so that a predetermined light shielding performance (optical density) is obtained in the laminated structure of the light shielding film and the semi-transmissive film.

  In the above various thin films, an etching stopper film having etching resistance to the light shielding film or the light semi-transmissive film may be provided between the glass substrate and the light shielding film or between the light semi-transmissive film and the light shielding film. Good. The etching stopper film may be a material that can peel off the etching mask film at the same time when the etching stopper film is etched.

(3) Reflective mask blank In the case of a reflective mask blank, low thermal expansion glass (for example, SiO ₂ —TiO ₂ glass) that has been used up to the wet etching step is used as a mask blank substrate. The thin film of the reflective mask has a structure in which a multilayer reflective film that reflects exposure light is formed on a glass substrate, and an absorber film (thin film for transfer pattern) that absorbs exposure light is formed in a pattern on the multilayer reflective film Have

  The multilayer reflective film is formed by alternately laminating high refractive index layers and low refractive index layers.

  Examples of the multilayer reflective film include Mo / Si periodic multilayer films, Ru / Si periodic multilayer films, Mo / Be periodic multilayer films, and Mo compound / Si compound periodic multilayer films in which Mo films and Si films are alternately stacked for about 40 periods. Si / Nb periodic multilayer film, Si / Mo / Ru periodic multilayer film, Si / Mo / Ru / Mo periodic multilayer film, Si / Ru / Mo / Ru periodic multilayer film, and the like. The material can be appropriately selected depending on the exposure wavelength. The absorber film has a function of absorbing exposure light such as EUV light, and for example, tantalum (Ta) alone or a material mainly composed of Ta can be preferably used.

(Manufacture of transfer masks)
The present invention is a method for manufacturing a transfer mask, characterized in that a transfer pattern is formed by patterning a thin film of a mask blank obtained by the above-described mask blank manufacturing method. According to the present invention, it is possible to obtain a transfer mask with reduced generation of etching steps (convex defects) caused by foreign matters.

  The manufacturing method of the transfer mask of the present invention includes a step of forming a transfer pattern on the thin film of the mask blank manufactured by the mask blank manufacturing method. Hereinafter, the process of manufacturing the transfer mask from the mask blank will be described. The mask blank used here is the halftone phase shift mask blank (2). This phase shift mask blank has a structure in which a light semi-transmissive film (a thin film for forming a transfer pattern) and a light shielding film are sequentially laminated on a translucent substrate. In addition, the method of manufacturing the transfer mask (phase shift mask) is an example, and the transfer mask (phase shift mask) can be manufactured even if a part of the procedure is changed.

  First, a resist film is formed on the light shielding film of the phase shift mask blank by a spin coating method. For this resist film, a chemically amplified resist for electron beam exposure drawing is preferably used. Next, a transfer pattern to be formed on the light translucent film is exposed and drawn with an electron beam on the resist film, and a predetermined process such as development is performed to form a resist pattern having the transfer pattern. Subsequently, dry etching using the resist pattern as a mask is performed on the light shielding film to form a transfer pattern to be formed on the light semi-transmissive film on the light shielding film. After dry etching, the resist pattern is removed. Next, the light semi-transmissive film is dry-etched using a light-shielding film having a transfer pattern as a mask to form a transfer pattern on the light semi-transmissive film. Subsequently, a resist film is formed again, and a pattern to be formed on the light shielding film (pattern such as a light shielding band) is exposed and drawn with an electron beam, and a predetermined process such as development is performed to form a resist pattern. The light shielding film is subjected to dry etching using a resist pattern having a pattern such as a light shielding band as a mask to form a pattern such as a light shielding band on the light shielding film. Then, a predetermined cleaning process or the like is performed to complete a transfer mask (phase shift mask).

  Hereinafter, the embodiment of the present invention will be described more specifically with reference to examples.

(Experiments 1-6)
In Experiments 1 to 6, the glass substrate was etched using a predetermined cleaning solution (etching solution), and the etching rate was measured.

(Glass substrate preparation and polishing process)
The glass substrate to be used is a synthetic quartz glass substrate (size 152.4 mm × 152.4 mm, thickness 6.35 mm). The end surface of this synthetic quartz glass substrate is chamfered and ground, and the glass substrate that has been subjected to rough polishing treatment and precision polishing with a polishing liquid containing cerium oxide abrasive grains is set on a carrier of a double-side polishing apparatus, and the following: Polishing processing (ultra-precision polishing) was performed under the conditions.
Polishing pad: Soft polisher (suede type)
Polishing liquid: colloidal silica abrasive grains (average particle diameter 100 nm) + water Processing pressure: 50 to 100 g / cm ²
Processing time: 60 minutes After the completion of ultra-precision polishing, the colloidal silica abrasive grains were removed, and the main surface and end face of the glass substrate were subjected to brush cleaning.

(Evaluation of etching rate of glass substrate)
The etching rate when the synthetic quartz glass substrate prepared as described above was wet-etched with the cleaning liquid (etching liquid) of Experiments 1 to 6 was measured. The etching rate was measured by immersing the glass substrate in a cleaning solution for 72 hours in a state where a part of the glass substrate was masked, and measuring the size of the step generated by etching after the cleaning. Table 1 shows the compositions and etching rates of the etching solutions of Experiments 1 to 6. In Table 1, “TMAH” is tetramethylammonium hydroxide and “EDTA” is edetic acid.

  As is apparent from Table 1, the etching rate when the cleaning liquid of Experiments 1 to 3 in which pH is greater than 9 and less than 11 and does not contain a chelating agent is 0.02 nm / hour or less, pH As compared with the case of the cleaning solution containing 11 or more and containing a chelating agent, it can be seen that it is considerably small. Therefore, if the cleaning liquids of Experiments 1 to 3 are used, the etching rate for the glass substrate can be reduced, so that the foreign matter can be removed without causing an etching step due to the foreign matter. Therefore, it can be said that the cleaning liquids of Experiments 1 to 3 are suitable as the cleaning liquid used in the first cleaning process.

  On the other hand, as apparent from Table 1, in the case of the cleaning liquids of Experiments 4 to 6 containing a chelating agent having a pH of 11 or more, the etching rate for the glass substrate is 0.05 nm / hour or more. It can be seen that it is relatively large. Therefore, if the cleaning liquids in Experiments 4 to 6 are used as the cleaning liquid used in the second cleaning process, the etching rate with respect to the glass substrate can be increased, so that minute foreign matters that could not be removed in the first cleaning process are removed. Can do. Therefore, it can be said that the cleaning liquids of Experiments 4 to 6 are suitable as the cleaning liquid used in the second cleaning step.

Example 1
As Example 1, a first cleaning process was performed under the conditions of Experiment 3 above, and a second cleaning process was performed under the conditions of Experiment 6 above, thereby manufacturing a mask blank substrate.

  Ten glass substrates were prepared by the same procedure as in Experiments 1 to 6 above, and ultra-precision polishing was performed. After completion of ultra-precision polishing, cleaning was performed by immersing the glass substrate in hydrofluoric acid to remove the colloidal silica abrasive grains. Next, scrub cleaning, spin cleaning with pure water, and spin drying were performed on the main surface and the end surface of the glass substrate. After spin drying, the main surface (first main surface) on the side where the thin film of the 10 glass substrates is formed, using a 60 nm sensitivity defect inspection apparatus (M6640 manufactured by Lasertec Corporation) using a laser interference confocal optical system, Defect inspection was performed. As a result, an average of 49 convex defects having a size equivalent to 100 nm or more on 10 glass substrates was detected, and an average of 1269 convex defects having a size less than 100 nm was detected.

  Next, as a first cleaning step, ultrasonic cleaning was performed on the first main surfaces of ten glass substrates using the cleaning liquid of Experiment 3 using the cleaning apparatus shown in FIG. Specifically, an ultrasonic wave having a frequency of 2.0 MHz was applied. Further, the flow rate of the cleaning liquid to which the ultrasonic wave flowing down from the ultrasonic cleaning nozzle toward the first main surface of the substrate was applied was adjusted to 1.5 liters / minute. The number of substrate rotations during cleaning and the moving speed of the cleaning nozzle were set as appropriate.

  The substrate was cleaned for 5 minutes under the above conditions. The first main surface of the glass substrate after the first cleaning step was subjected to defect inspection using the defect inspection apparatus (M6640 manufactured by Lasertec Corporation). As a result, convex defects having a size equivalent to 100 nm or more in 10 glass substrates were not detected, but 153 convex defects having a size less than 100 nm were detected on average.

  Next, the second cleaning step was performed on the first main surfaces of the ten glass substrates on which the first cleaning step described above was performed. As the cleaning liquid (wet etching liquid), the cleaning liquid of Experiment 6 was used. The etching solution was supplied at 1 L / min. 2 and 3 are schematic views of the cleaning apparatus used in the second cleaning step.

  Alkaline etching in the second cleaning step includes spin etching in which an etching solution heated to 60 ° C. is supplied to the front main surface 101 of the glass substrate 100 that is spinning, and the supply of the etching solution is stopped. Wet etching performed with the liquid film of the etching solution formed on was continuously performed.

  FIG. 4 shows a flow of the second cleaning step (including the rinse cleaning step). First, the glass substrate 100 subjected to the first cleaning process is fixed by the holding member 28 of the wet etching apparatus 1 (process S1). Next, the distance between the back side main surface (second main surface) 102 of the glass substrate 100 and the stage 12 is adjusted to 1 mm (step S2). Pure water of 60 ° C. is supplied from the hole 18 of the stage 12 toward the back main surface 102, and a liquid film flow of warm pure water 202 is formed between the back main surface 102 and the stage 12 as shown in FIG. S3). At the same time, the nozzle 37 is moved onto the glass substrate 100 by the rotation mechanism 36 and the glass substrate is rotated by spinning (step S4). Thereafter, warm pure water at 60 ° C. is supplied from the nozzle 37 to the front main surface (first main surface) 101 of the glass substrate to sufficiently warm the substrate (step S5).

  Thereafter, position adjustment is performed using a rotation mechanism and an expansion / contraction mechanism so that the tip of the nozzle 34 faces the center of the front main surface 101 of the glass substrate. At this time, the position of the nozzle 37 is adjusted in a timely manner so that the nozzle 37 and the arm 35 do not interfere (contact) with the nozzle 34 and the arm 32. Then, the turntable (stage 12) is rotated (10 rpm), hot pure water from the nozzle 37 is stopped, and an alkaline etching solution is supplied from the nozzle 34 to the front main surface 101 of the glass substrate (step S6). Next, the rotational speed of the turntable is lowered to stop the spin etching (step S7), and the supply of the alkaline etching solution is stopped (step S8).

  Then, wet etching was performed in a state where a liquid film of an etchant was formed on the front main surface 101 of the glass substrate while continuing the supply of warm pure water to the back main surface 102 (step S9). Next, the rinse process which supplies pure water on the front side main surface 101 of the glass substrate 100, and substitutes the etching liquid on the front side main surface 101 with warm pure water was performed (process S10). During this time, a liquid film flow of pure water was continuously formed on the back main surface 102 side. Warm pure water was supplied from the nozzle 37 and the nozzle 42 to the front main surface 101. The temperature of the warm pure water used for the cleaning was initially 60 ° C., and 40 ° C. when complete replacement with the alkaline etching solution was required. The nozzle 42 is provided with an ultrasonic oscillator, and the pure water supplied from the nozzle 42 is ultrasonically applied water. By using ultrasonically applied water, foreign substances and chemical components lifted off from the front main surface 101 can be efficiently removed. Ultrasonic application water was supplied onto the glass substrate 100 from the nozzle 42 at 1 L / min.

  When the cleaning process is completed, the process returns to the process of starting the spin rotation of the substrate (process S4) again (the supply of warm pure water to the back main surface 102 continues). Steps S4 to S10 are repeated three times. And when the last washing | cleaning process was completed, the glass substrate 100 was spin-dried.

  The 10th glass substrate was subjected to the second cleaning step as described above to produce a mask blank substrate. Each mask blank substrate was subjected to a defect inspection using the defect inspection apparatus (M6640 manufactured by Lasertec Corporation). No convex defect having a size equivalent to 100 nm or more in 10 glass substrates was detected, and only three convex defects having a size less than 100 nm were detected on average.

  As a result, the ten glass substrates manufactured by the method of Example 1 were able to achieve a high level of foreign matter removal in all regions of the surface subjected to the etching treatment before and after etching.

  Moreover, when the enlarged image display function of a defect inspection apparatus confirmed the enlarged image with respect to each location where the convex defect of the size equivalent to 100 nm or more was detected by the defect inspection of the glass substrate before a 1st washing | cleaning process, any glass was confirmed. Etching steps due to foreign substances adhering to the main surface of the glass substrate were not observed at the corresponding portions of the substrate.

(Comparative Example 1)
As Comparative Example 1, a mask blank substrate was manufactured in the same manner as in Example 1 except that the first cleaning process was performed under the conditions of Experiment 5 and the second cleaning process was performed under the conditions of Experiment 6.

  Defect inspection was performed using the defect inspection apparatus (M6640 manufactured by Lasertec Corporation) on the main surface (first main surface) on the side where the thin film of the 10 glass substrates before the first cleaning step was formed. As a result, 42 convex defects having a size equivalent to 100 nm or more on the 10 glass substrates of Comparative Example 1 were detected on average, and 1124 convex defects having a size less than 100 nm were detected on average.

  Next, the first cleaning step was performed on the ten glass substrates of Comparative Example 1. Defect inspection was performed on the first main surface of the glass substrate after the first cleaning step using the defect inspection apparatus (M6640 manufactured by Lasertec Corporation). As a result, an average of 8 convex defects having a size equivalent to 100 nm or more on 10 glass substrates was detected, and an average of 123 convex defects having a size less than 100 nm was detected.

  Further, the second cleaning step was performed on the ten glass substrates of Comparative Example 1. Defect inspection was performed on the first main surface of the glass substrate after the second cleaning step using the defect inspection apparatus (M6640 manufactured by Lasertec Corporation). As a result, 8 convex defects having a size equivalent to 100 nm or more on 10 glass substrates were detected on average, but only 2 convex defects having a size less than 100 nm were detected on average.

  As a result, it was found that the ten glass substrates manufactured by the method of Comparative Example 1 were not able to remove convex defects having a size equivalent to 100 nm or more. When an enlarged image was confirmed with the enlarged image display function of the defect inspection apparatus at each location where a convex defect having a size equivalent to 100 nm or more was detected, an etching step was found at the corresponding location on any glass substrate.

(Manufacture of halftone phase shift mask blanks)
A halftone phase shift mask blank was manufactured using the mask blank substrate manufactured by the method for manufacturing a mask blank substrate of Example 1.

On the first main surface of the mask blank substrate, a light semi-transmissive film made of nitrided molybdenum and silicon was first formed. Specifically, using a mixed target of molybdenum (Mo) and silicon (Si) (Mo: Si = 10 mol%: 90 mol%), mixing argon (Ar), nitrogen (N ₂ ), and helium (He). In a gas atmosphere (gas flow ratio Ar: N ₂ : He = 5: 49: 46), a gas pressure of 0.3 Pa, a DC power source power of 3.0 kW, and reactive sputtering (DC sputtering), molybdenum, silicon, and A MoSiN film made of nitrogen was formed to a thickness of 69 nm. Next, the glass substrate on which the MoSiN film was formed was subjected to a heat treatment using a heating furnace in the atmosphere at a heating temperature of 450 ° C. and a heating time of 1 hour. This MoSiN film had a transmittance of 6.16% and a phase difference of 184.4 degrees in ArF excimer laser exposure light.

The following light-shielding film was formed on the light semi-transmissive film. Specifically, a chromium (Cr) target is used as a sputtering target, and a mixed gas atmosphere of argon (Ar), carbon dioxide (CO ₂ ), nitrogen (N ₂ ), and helium (He) (gas pressure 0.2 Pa, Gas flow ratio Ar: CO ₂ : N ₂ : He = 20: 35: 10: 30), the power of the DC power source is 1.7 kW, and a 30 nm thick CrOCN layer is formed by reactive sputtering (DC sputtering). Filmed. Subsequently, a mixed gas atmosphere of argon (Ar) and nitrogen (N ₂ ) (gas pressure 0.1 Pa, gas flow rate ratio Ar: N ₂ = 25: 5) was set, and the power of the DC power supply was set to 1.7 kW. A 4 nm thick CrN layer was formed by reactive sputtering (DC sputtering). Finally, a mixed gas atmosphere of argon (Ar), carbon dioxide (CO ₂ ), nitrogen (N ₂ ), and helium (He) (gas pressure 0.2 Pa, gas flow ratio Ar: CO ₂ : N ₂ : He = 20: 35: 5: 30), the power of the DC power source is 1.7 kW, and a CrOCN layer having a film thickness of 14 nm is formed by reactive sputtering (DC sputtering). A chromium-based light shielding film was formed.

  This light-shielding film has a laminated structure with the light semi-transmissive film and is adjusted so that the optical density (OD) is 3.0 at a wavelength of 193 nm of ArF excimer laser exposure light. The surface reflectance of the light shielding film with respect to the wavelength of the exposure light was 20%.

(Manufacture of halftone phase shift masks)
First, a chemically amplified positive resist film for electron beam drawing (PRL009 manufactured by Fuji Film Electronics Materials) was formed as a resist film on the mask blank. The resist film was formed by spin coating using a spinner (rotary coating apparatus). After applying the resist film, a predetermined heat drying treatment was performed. The film thickness of the resist film was 150 nm.
Next, a desired pattern was drawn on the resist film formed on the mask blank using an electron beam drawing apparatus, and then developed with a predetermined developer to form a resist pattern.

Next, the light shielding film was etched using the resist pattern as a mask. A mixed gas of Cl ₂ and O ₂ was used as a dry etching gas. Subsequently, the light semi-transmissive film (MoSiN film) was etched to form a light semi-transmissive film pattern. A mixed gas of SF ₆ and He was used as the dry etching gas.

  Next, the remaining resist pattern is peeled off, the same resist film as above is formed again on the entire surface, and drawing is performed to form a light-shielding band on the outer periphery of the mask. A pattern was formed. Using this resist pattern as a mask, the light shielding film other than the light shielding zone region was removed by etching.

  Next, the remaining resist pattern was peeled off to obtain a phase shift mask.

  In the phase shift mask obtained as described above using the mask blank substrate of Example 1, a 45 nm half pitch fine pattern was formed with good pattern accuracy.

(Manufacture of binary mask blanks)
Using the glass substrate obtained by the mask blank substrate manufacturing method of the example, a binary mask blank was manufactured as follows. On the 1st main surface of the glass substrate of the said Example, the MoSiN film (light-shielding layer) and the MoSiN film (surface antireflection layer) were each formed as a light-shielding film. Using a mixed target of Mo and Si (Mo: Si = 13 at%: 87 at%), in a mixed gas atmosphere of Ar and N ₂ , a MoSiN film made of molybdenum, silicon, and nitrogen (film composition ratio: Mo: 9. 9 at%, Si: 66.1 at%, N: 24.0 at%) was formed with a film thickness of 47 nm.

Next, using a target of Mo: Si = 13 at%: 87 at%, a MoSiN film made of molybdenum, silicon, and nitrogen was formed to a thickness of 13 nm in a mixed gas atmosphere of Ar and N ₂ . The total thickness of the light shielding film was 60 nm.

  The optical density (OD) of the light shielding film (light shielding layer + surface antireflection layer) was 3.0 at a wavelength of 193 nm of ArF excimer laser exposure light.

Next, the following Cr etching mask film was formed on the MoSi light shielding film. Specifically, a chromium (Cr) target is used as a sputtering target, and a 5 nm thick CrN film (film) is formed by reactive sputtering (DC sputtering) in a mixed gas atmosphere of argon (Ar) and nitrogen (N ₂ ). (Composition ratio: Cr: 75.3 at%, N: 24.7 at%). Note that Rutherford backscattering analysis was used for elemental analysis of each layer of the light shielding film and the Cr-based etching mask film.

(Manufacture of binary mask for transfer)
A binary mask for transfer was manufactured using the above binary mask blank.

  First, a chemically amplified positive resist film for electron beam drawing (PRL009 manufactured by Fuji Film Electronics Materials) was formed as a resist film on the mask blank. The resist film was formed by spin coating using a spinner (rotary coating apparatus). After applying the resist film, a predetermined heat drying treatment was performed. The film thickness of the resist film was 100 nm.

  Next, a desired pattern was drawn on the resist film formed on the mask blank using an electron beam drawing apparatus, and then developed with a predetermined developer to form a resist pattern.

Next, the etching mask film was etched using the resist pattern as a mask. A mixed gas of Cl ₂ and O ₂ was used as a dry etching gas. Subsequently, the MoSi-based light-shielding film (MoSiN / MoSiN) was etched using the pattern formed on the etching mask film as a mask to form a light-shielding film pattern. As the dry etching gas, a mixed gas of SF ₆ and He was used.

  Next, the remaining resist pattern was peeled off, and the etching mask film pattern was removed by etching.

  The MoSi binary mask obtained as described above using the mask blank substrate of Example 1 had a fine pattern of 32 nm half pitch formed with good pattern accuracy.

DESCRIPTION OF SYMBOLS 1 Wet etching apparatus 10 Fluid forming means 12 Stage 14 Column 18 Hole 20 Glass substrate holding mechanism 28 Holding member 32 Arm 33 Rotating mechanism 34 Nozzle 35 Arm 36 Rotating mechanism 37 Nozzle 40 Arm 41 Rotating mechanism 42 Nozzle 100 Glass substrate (mask Blank substrate)
101 Front main surface of glass substrate (first main surface)
102 Back main surface of glass substrate (second main surface)
201 Wet etching liquid 202 Warm pure water (liquid adjusted to a temperature higher than room temperature)
301 Substrate 310 Cleaning Device 311 Spin Chuck 312 Electric Motor 313 Cleaning Cup 314 Ultrasonic Cleaning Nozzle 315 Arm 316 Cleaning Liquid Supply Device

Claims (8)

A method for manufacturing a mask blank substrate manufactured from a glass substrate having two main surfaces,
a first cleaning step of cleaning one main surface of the glass substrate using a cleaning liquid having a pH of greater than 9 and less than 11 and containing no chelating agent;
and a second cleaning step in which wet etching is performed by covering the one main surface of the glass substrate with an etchant containing a chelating agent having a pH of 11 or more, and a method for producing a mask blank substrate .   2. The method for manufacturing a mask blank substrate according to claim 1, wherein the etchant used in the second cleaning step is supplied to the one main surface of the glass substrate at a temperature higher than room temperature.   3. The mask according to claim 1, wherein the etching solution used in the second cleaning step contains one or more alkali agents selected from sodium hydroxide, potassium hydroxide, and tetramethylammonium. A method for manufacturing a blank substrate.   The method for manufacturing a mask blank substrate according to claim 1, wherein the cleaning liquid used in the first cleaning step contains a surfactant.   In the first cleaning step, the cleaning liquid applied with an ultrasonic wave having a frequency of 2.0 MHz or more and 5.0 MHz or less from a cleaning nozzle is applied to the one main surface of the glass substrate while rotating the glass substrate. The method for manufacturing a mask blank substrate according to claim 1, wherein the mask blank substrate is supplied to the mask blank.   2. The second cleaning step is characterized in that the etching solution is supplied only to the one main surface, and wet etching is performed while the etching solution on the one main surface is swung. 6. A method for producing a mask blank substrate according to any one of 5 above.   A thin film for forming a transfer pattern is formed on the one main surface of the mask blank substrate obtained by the method for manufacturing a mask blank substrate according to any one of claims 1 to 6. Mask blank manufacturing method.   A method for producing a transfer mask, comprising: patterning the thin film of a mask blank obtained by the method for producing a mask blank according to claim 7 to form a transfer pattern.