JP2012002676A - Mask defect checking device and mask defect checking method - Google Patents

Abstract

An object of the present invention is to provide a mask defect inspection apparatus that realizes highly accurate defect detection of a mask by acquiring inspection images having different focal positions.
A light source, an illumination optical system that divides light emitted from the light source into first and second inspection light and irradiates different areas on the same surface of the mask, and first and second irradiates the mask. An imaging optical system for focusing the inspection light on the same image plane as the first and second images, and a first and second magnifying optical system for enlarging the first image and the second image, respectively The first and second image sensors that respectively capture the first and second images magnified by the first and second magnification optical systems, and the first and second image sensors that are captured by the first and second image sensors, respectively. A comparison unit that detects a defect of the mask by comparing the first and second inspection images, which are images of the second image, with a reference image, and an image plane of the first magnifying optical system A mechanism for shifting the focal position and the focal position of the second magnifying optical system relative to the image plane by a predetermined amount Mask defect inspection apparatus characterized by.
[Selection] Figure 1

Description

  The present invention relates to a mask defect inspection apparatus and a mask defect inspection method for inspecting defects of a photomask used for manufacturing a semiconductor, for example.

  Along with the high integration of semiconductor devices such as LSIs, mask patterns formed on a mask (photomask or reticle) are becoming finer. Therefore, high performance is also required for a mask defect inspection apparatus for inspecting a mask. As a mask defect inspection apparatus, there has been proposed an apparatus that detects a defect by imaging a mask with an imaging element such as a CCD and comparing the captured inspection image with a reference image.

  In order to advance the miniaturization of the mask pattern, in photolithography, for example, a Levenson-type that can draw a fine pattern by providing a dug in a mask made of glass and changing the optical distance of the exposure light. A phase shift mask is used. In addition, for example, an attempt is made to draw a fine pattern by using exposure light as EUV (Extreme Ultra Violet) light having a wavelength of about 13.5 nm and using an EUV mask corresponding to EUV exposure.

  In such a defect inspection apparatus for inspecting a mask, not only the conventional pattern defect on the mask surface, but also, for example, the difference in the amount of digging in the glass of the phase shift mask, the defect present in the blank of the EUV mask, etc. Detection of this has come to be required.

  Patent Document 1 describes a mask defect inspection apparatus that separately detects images from different areas of a mask.

JP 2009-222625 A

  In view of the above circumstances, an object of the present invention is to provide a mask defect inspection apparatus and a mask defect inspection method that realize highly accurate defect detection of a mask by acquiring inspection images having different focal positions.

  A mask defect inspection apparatus according to an aspect of the present invention includes a light source, an illumination optical system that divides the light emitted from the light source into first and second inspection lights and irradiates different regions on the same surface of the mask, An imaging optical system that forms the first and second inspection lights irradiated on the mask on the same image plane as first and second images, and the first image and the second image, The first and second magnifying optical systems that respectively magnify, the first and second image sensors that respectively capture the first and second images magnified by the first and second magnifying optical systems, A comparison unit that compares the first and second inspection images, which are images of the first and second images captured by the first and second image sensors, with a reference image to detect a defect of the mask. A focal position of the first magnifying optical system with respect to the image plane, and the second Characterized by having a shifted and the focal position relative to the image plane of the magnifying optical system by a predetermined amount mechanism.

  In the mask defect inspection apparatus according to the above aspect, it is preferable that the mechanism is a focal position adjustment unit provided in the first and second magnifying optical systems.

  In the mask defect inspection apparatus according to the above aspect, an image processing unit that superimposes the first and second inspection images, and a defect identification unit that identifies the type of the defect from the superimposed image generated by the image processing unit. In addition, it is desirable to have.

  In the mask defect inspection apparatus according to the above aspect, it is desirable that the illumination optical system is a reflection optical system with respect to the mask.

  In the mask defect inspection apparatus according to the above aspect, it is desirable that the illumination optical system is a transmission optical system with respect to the mask.

  In the mask defect inspection method of one embodiment of the present invention, the light emitted from the light source is branched into the first and second inspection lights, the different areas on the same surface of the mask are irradiated with the illumination optical system, and the mask is irradiated The first and second inspection lights thus formed are imaged on the same image plane as the first and second images by the imaging optical system, and the first image and the second image are respectively converted into the first and second images. The first and second image sensors are enlarged by the second magnifying optical system and the first and second images magnified by the first and second magnifying optical systems are shifted in focus position with respect to the image plane. The first and second inspection images, which are images of the first and second images captured by the first and second image sensors, are compared with the reference image, and the defect of the mask Is detected.

  In the mask defect inspection method of the above aspect, it is desirable to identify the type of the defect from an image obtained by superimposing the first and second inspection images.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the mask defect inspection apparatus and mask defect inspection method which implement | achieve highly accurate defect detection of a mask by acquiring the inspection image from which a focus position differs.

It is a conceptual diagram which shows the internal structure of the mask defect inspection apparatus of 1st Embodiment. It is a conceptual diagram of the expansion optical system and image sensor of the mask defect inspection apparatus of 1st Embodiment. It is a conceptual diagram which shows the internal structure of the mask defect inspection apparatus of 2nd Embodiment. It is a conceptual diagram which shows the internal structure of the mask defect inspection apparatus of 3rd Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the present specification, the pattern defect means a defect in which the reflectivity of the surface is changed from the original reflectivity, such as a chipping of a material forming the pattern on the mask. In addition, the phase defect is, for example, a local film thickness change in the multilayer film of the EUV mask, and the reflectance of the surface does not change from the original reflectance, but the phase of the light is different from the original phase. It shall mean a defect that is changing.

(First embodiment)
The mask defect inspection apparatus according to the present embodiment includes a light source, an illumination optical system that divides light emitted from the light source into first and second inspection light and irradiates different areas on the same surface of the mask, and a mask. An imaging optical system that forms the irradiated first and second inspection lights on the same image plane as first and second images, and a first image that enlarges the first image and the second image, respectively. And the second magnifying optical system, the first and second image sensors for capturing the first and second images magnified by the first and second magnifying optical systems, respectively, and the first and second images A first and second inspection images that are images of the first and second images captured by the sensor, and a comparison unit that compares the reference image with a reference image to detect a defect in the mask. A focal position with respect to the image plane of the magnifying optical system and a focal position with respect to the image plane of the second magnifying optical system are predetermined. It has a mechanism to shift by an amount.

  According to the mask defect inspection apparatus of the present embodiment, two different areas on the mask can be observed simultaneously at different focal positions (focus positions). Therefore, it becomes possible to detect more defects, and it is possible to realize highly accurate mask defect inspection.

  FIG. 1 is a conceptual diagram showing the internal configuration of the mask defect inspection apparatus according to the present embodiment.

  The mask defect inspection apparatus 100 is an apparatus that inspects a defect of the mask 10 using the mask 10 as an inspection target. The mask defect inspection apparatus 100 includes an inspection image generation unit 12, a data processing unit 14, and the like.

  The inspection image generator 12 includes a light source 16, a beam expander 18, a beam splitter 20, a first-stage collimator lens 24, a half mirror 26, an objective lens 28, an XYθ table 30, an XYθ motor 32, a displacement meter 34, and a first-stage imaging lens 36. The first collimator lens 38a, the second collimator lens 38b, the first imaging lens 40a, the second imaging lens 40b, the first image sensor 42a, the second image sensor 42b, and the first sensor circuit. 44a and a second sensor circuit 44b.

  The light source 16 is, for example, a laser light source that emits ultraviolet laser light. An illumination optical system in which the beam expander 18, the beam splitter 20, the first-stage collimator lens 24, the half mirror 26, and the objective lens 28 irradiate the mask 10 placed on the XYθ table 30 with the light emitted from the light source 16. Constitute. Here, the illumination optical system is a reflection optical system with respect to the mask.

  The objective lens 28 and the first-stage imaging lens 36 constitute an imaging optical system that forms an image on the image plane 46 with the light irradiated on the mask 10 by the illumination optical system. The first collimator lens 38a and the first imaging lens 40a constitute a first magnification optical system, and the second collimator lens 38b and the second imaging lens 40b constitute a second magnification optical system.

The beam splitter 20 is, for example, a prism, and branches the light emitted from the light source 16 into the first inspection light L ₁ and the second inspection light L ₂ . The branched inspection light is irradiated to different areas on the same surface of the mask 10. The imaging optical system forms the first inspection light L ₁ and the second inspection light L ₂ irradiated on the mask 10 on the same image plane 46 as the first image I ₁ and the second image I _2. To do.

First enlargement optical system enlarges the first image I _1. Also. Second enlarging optical system enlarges the second image I _2.

The first image sensor 42a captures the _first image I1 magnified by the first magnification optical system. The second image sensor 42b captures the _second image I2 magnified by the second magnification optical system. The first and second image sensors are, for example, CCDs, photodiode arrays, or CMOS sensors.

  The data processing unit 14 includes a CPU 50 serving as a control computer via a bus 52 serving as a data transfer line, a mass storage device 54, a main storage device 56, a printing device 58, a display device 60, a table control unit 62, and a development unit. 64, a reference unit 66, a first comparison unit 68a, a second comparison unit 68b, a position detection unit 70, and the like.

  The first comparison unit 68a compares the first inspection image captured by the first image sensor 42a and processed by the first sensor circuit 44a with the reference image to detect a mask defect. The second comparison unit 68b detects a mask defect by comparing the reference image with the second inspection image captured by the second image sensor 42b and processed by the second sensor circuit 44b. To do.

  Here, the reference image is an image obtained by capturing the same pattern in another region of the same mask, even if it is a reference image generated by the development unit 64 or the reference unit 66 using the mask design data. It doesn't matter. The former is a so-called DB (Die to Database) comparison, and the latter is a so-called DD (Die to Die) comparison.

  The mask defect inspection apparatus 100 includes a mechanism for shifting the focal position of the first magnification optical system with respect to the image plane 46 and the focal position of the second magnification optical system with respect to the image plane 46 by a predetermined amount.

  In FIG. 1, descriptions of components other than those necessary for describing the present embodiment are omitted, but the mask defect inspection apparatus 100 includes other components that are usually necessary.

  FIG. 2 is a conceptual diagram of the magnifying optical system and the image sensor of the mask defect inspection apparatus according to the present embodiment. The first magnifying optical system adjusts the focal position with respect to the image plane 46 by moving the first collimator lens 38a up and down relative to the image plane 46 in addition to the first collimator lens 38a and the first imaging lens 40a. The first focus position adjusting unit 70a is provided. The second magnifying optical system includes the second collimator lens 38b and the second imaging lens 40b, and the second collimator lens 38b is moved up and down with respect to the image plane 46, so that the focal position with respect to the image plane 46 is reached. A second focal position adjustment unit 70b for adjusting the angle.

  The first focal position adjusting unit 70a and the second focal position adjusting unit 70b are constituted by, for example, a lens driving pulse motor and its control circuit.

  By driving either one or both of the first focal position adjustment unit 70a and the second focal position adjustment unit 70b, the focal position with respect to the image plane 46 of the first magnification optical system and the second magnification It is possible to shift the focal position of the optical system with respect to the image plane 46 by a predetermined amount (a distance indicated by fd in the drawing).

  Next, the mask defect inspection method of this embodiment will be described.

  The mask 10 is automatically conveyed from an autoloader (not shown) whose drive is controlled, and is placed on the XYθ table 30. The XYθ table 30 is driven by the table control unit 62 under the control of the CPU 50. It can be moved by a drive system such as a triaxial (XY-θ) motor 32 that drives in the X-axis direction, the Y-axis direction, and the θ-direction. For example, a step motor can be used as the three-axis (XY-θ) motor 32.

The movement position of the XYθ table 30 is measured by a displacement meter 34. The light emitted from the light source 16 is branched into first and second inspection lights L ₁ and L ₂ , and different areas on the same surface of the mask 10 are irradiated with the reflective illumination optical system.

The first and second inspection lights L ₁ and L ₂ irradiated on the mask 10 are imaged on the same image plane 46 by the imaging optical system as first and second images I ₁ and I ₂ . Then, the first image and the second images I ₁ and I ₂ are magnified by the first and second magnification optical systems, respectively. At this time, before the inspection, the focal positions of the first and second magnifying optical systems with respect to the image plane 46 are shifted and fixed by a desired amount.

Then, the first and second images I ₁ and I ₂ magnified by the first and second magnification optical systems are picked up by the first and second image sensors 42 a and 42 b by shifting the focal position with respect to the image plane 46. To do. The XYθ table 30 is moved to capture the first and second images I ₁ and I ₂ while shifting the focal position over a predetermined inspection area on the mask.

The sensor circuits 44a and 44b perform data processing on the captured first and _second images I ₁ and I ₂ and output the first and second inspection images to the comparison units 68a and 68b. The comparison units 68a and 68b detect the defect of the mask 10 by comparing the first and second inspection images with the reference image.

  The displacement meter 34 sends the position data of the mask 10 on the XYθ table 30 to the position detection unit 70. In the position detection unit 70, for example, the distribution of the defect distribution on the mask 10 is performed.

  The mask 10 on the XYθ table 30 is automatically carried out of the apparatus by the autoloader after the inspection is completed. The inspection image is, for example, 8-bit unsigned data, and the light intensity of each pixel is expressed by a gradation value.

  According to the present embodiment, it is possible to simultaneously observe the same mask at different focal positions (focus positions). For example, in the Levenson-type phase shift mask, the defects on the dug glass surface and the defects on the pattern surface have different heights at which the defects exist, so the optimum focal position for detecting the defect differs. ing.

  According to the present embodiment, the focal position of the first magnifying optical system and the focal position of the second magnifying optical system are set in advance so that two focal positions considered to be optimal for each defect can be observed. Set. As a result, more defects can be detected with high throughput, and highly efficient and highly accurate mask defect inspection can be realized.

  In addition, as an example in which the optimum focal position for detecting a defect is different on the same mask surface, foreign matters on the mask surface and phase defects, pattern defects and glass in the multilayer film of the EUV mask Examples of the phase defect of the film and two foreign matters having different sizes can be given.

(Second Embodiment)
In addition to the configuration of the first embodiment, the mask defect inspection apparatus of the present embodiment further includes an image processing unit that superimposes the first and second inspection images, and a superimposed image generated by the image processing unit. The second embodiment is the same as the first embodiment except that a defect identification unit that identifies the type of defect detected from the first embodiment is provided. Accordingly, the description overlapping with the first embodiment is omitted.

  FIG. 3 is a conceptual diagram showing the internal configuration of the mask defect inspection apparatus according to the present embodiment. As shown in FIG. 3, the mask defect inspection apparatus 200 of the present embodiment includes an image processing unit 72 and a defect identification unit 74.

  The image processing unit 72 is imaged by the first image sensor 42a and processed by the first sensor circuit 44a, and is imaged by the second image sensor 42b and the second sensor circuit 44b. A process for superimposing the second inspection image data-processed in step (b) is performed. The first inspection image and the second inspection image acquired at the same time are shifted by a predetermined shift amount (distance indicated by d in the figure) in the horizontal direction as shown in FIG. The image processing unit 72 corrects the shift amount d and superimposes the first inspection image and the second inspection image corresponding to the same area on the mask.

  At this time, for example, a superimposed image is generated by calculating a difference in light intensity (gradation value) between the first inspection image and the second inspection image. Two different types of defects, such as pattern defects and phase defects, may have different contrast change directions when the focal position is shifted.

  When such information is obtained in advance, the defect identification unit 74 can identify the type of defect by checking the superimposed image of the defect position in the defect identification unit 74 for the defect detected by the comparison unit 68a or 68b. It becomes possible. For example, in the superimposed image, it is determined whether the defective portion is a dark portion or a bright portion with respect to the periphery, and the type of defect is identified.

  In addition to the first embodiment, the mask defect inspection method of this embodiment identifies the type of the defect from an image obtained by superimposing the first and second inspection images corresponding to the same region. It is.

  According to this embodiment, in addition to highly efficient and highly accurate mask defect inspection, it is also possible to identify the type of defect. In particular, this function is useful in classifying pattern defects and phase defects that have been difficult to determine conventionally.

  Note that, according to the present embodiment, two inspection images to be superimposed are acquired simultaneously. Therefore, since temporal factors such as fluctuations in the apparatus state in acquiring two inspection images can be eliminated, the accuracy of overlaying can be improved, and the defect type can be identified with higher accuracy.

  Here, the case where the difference in light intensity (gradation value) is calculated has been described as an example. However, if it is useful for identifying the defect type, other calculation processing may be performed and superimposed. Absent.

(Third embodiment)
The mask defect inspection apparatus of this embodiment is the same as that of the first embodiment except that in addition to the configuration of the first embodiment, the mask is further provided with a transmission optical system illumination optical system for the mask. is there. Accordingly, the description overlapping with the first embodiment is omitted.

  FIG. 4 is a conceptual diagram showing an internal configuration of the mask defect inspection apparatus according to the present embodiment. As shown in FIG. 4, the mask defect inspection apparatus 300 according to the present embodiment includes a transmission illumination optical system in addition to the reflection illumination optical system.

  The beam expander 18, the second beam splitter 80, the second first-stage collimator lens 84, and the condenser lens 86 transmit the light emitted from the light source 16 to the mask 10 mounted on the XYθ table 30. Configure the illumination optical system.

  The mask defect inspection apparatus 300 includes an optical path changing mirror 88 for switching between the transmission illumination optical system and the reflection illumination optical system.

  According to the present embodiment, not only in defect inspection using reflected light as inspection light but also in defect inspection using transmitted light as inspection light, two different regions on the mask are set at different focal positions (focus positions). It becomes possible to observe at the same time. Therefore, it is possible to detect more defects than in the first embodiment, and it is possible to realize highly accurate mask defect inspection.

  In the above description, what is described as “to part” and “to circuit” can be configured by a program operable by a computer. Alternatively, not only a program that is software but also a combination of software and hardware may be used. Or it may be a combination with firmware. Alternatively, it may be realized by a combination of these. When configured by a program, the program is stored in a recording medium such as a magnetic disk device, a magnetic tape device, an FD, or a ROM.

  The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. Descriptions of parts that are not directly necessary for the description of the present invention, such as a mask defect inspection apparatus and a mask defect inspection method, have been omitted, but a necessary mask defect inspection apparatus and mask defect inspection method can be appropriately selected and used. it can. In addition, all mask defect inspection apparatuses and mask defect inspection methods that include the elements of the present invention and that can be appropriately modified by those skilled in the art are included in the scope of the present invention.

  For example, the mask defect inspection apparatus may be an apparatus that includes only the transmission illumination optical system as the illumination optical system.

Further, the mechanism for shifting the focal position may be a method of moving the collimator lens, the imaging lens, and the image sensor integrally instead of moving the collimator lens.

  Further, even if the focal position adjusting unit is not necessarily provided, a mechanism in which the focal positions of the first and second magnifying optical systems are fixed in advance by a predetermined amount as an apparatus is not excluded.

  In addition, the first and second inspection images may be compared with the reference image instead of individually comparing with the reference image.

  The focal positions of the first and second magnifying optical systems have been described as being fixed during the inspection. However, for example, it is possible to take an inspection method in which the focal position is finely changed during the inspection. is there.

DESCRIPTION OF SYMBOLS 10 Mask 12 Inspection image generation part 14 Data processing part 16 Light source 18 Beam expander 20 Light beam splitting element 24 First stage collimator lens 26 Half mirror 28 Objective lens 36 First stage imaging lens 38a First collimator lens 38b Second collimator lens 40a First First imaging lens 40b Second imaging lens 42a First image sensor 42b Second image sensor 46 Image plane 68a First comparison unit 68b Second comparison unit 72 Image processing unit 74 Defect identification unit 100 Mask defect Inspection apparatus 200 Mask defect inspection apparatus 300 Mask defect inspection apparatus

Claims (8)

A light source;
An illumination optical system that divides the light emitted from the light source into first and second inspection light and irradiates different areas on the same surface of the mask;
An imaging optical system that forms the first and second inspection lights irradiated on the mask on the same image plane as first and second images;
First and second magnifying optical systems for magnifying the first image and the second image, respectively;
First and second image sensors that respectively capture first and second images magnified by the first and second magnification optical systems;
Comparison in which the first and second inspection images, which are images of the first and second images captured by the first and second image sensors, are compared with a reference image to detect a defect of the mask. And
With
A mask defect inspection apparatus comprising: a mechanism for shifting a focal position of the first magnifying optical system with respect to the image plane and a focal position of the second magnifying optical system with respect to the image plane by a predetermined amount.   The mask defect inspection apparatus according to claim 1, wherein the mechanism is a focus position adjustment unit provided in the first and second magnifying optical systems. An image processor that superimposes the first and second inspection images;
The mask defect inspection apparatus according to claim 1, further comprising: a defect identification unit that identifies the type of the defect from the superimposed image generated by the image processing unit.   4. The image processing unit generates a superimposed image by calculating a difference in light intensity between the first inspection image and the second inspection image. 5. The mask defect inspection apparatus described.   5. The mask defect inspection apparatus according to claim 1, wherein the illumination optical system is a reflection optical system with respect to the mask.   5. The mask defect inspection apparatus according to claim 1, wherein the illumination optical system is a transmission optical system with respect to the mask. The light emitted from the light source is branched into first and second inspection light and irradiated to different regions on the same surface of the mask with the illumination optical system,
The first and second inspection lights applied to the mask are imaged on the same image plane as the first and second images by an imaging optical system,
Magnifying the first image and the second image with first and second magnifying optical systems, respectively;
The first and second image sensors magnified by the first and second magnification optical systems are imaged by the first and second image sensors while shifting the focal position with respect to the image plane,
Comparing the first and second inspection images, which are images of the first and second images captured by the first and second image sensors, with a reference image to detect a defect of the mask. A mask defect inspection method characterized by the above. 8. The mask defect inspection method according to claim 7, wherein the type of the defect is identified from an image obtained by superimposing the first and second inspection images.

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