JP4378904B2 - Manufacturing method of semiconductor substrate and manufacturing method of field effect transistor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor substrate, a method for manufacturing a field effect transistor, a semiconductor substrate and a field effect transistor used for a high-speed MOSFET or the like.
[0002]
[Prior art]
In recent years, high-speed MOSFETs, MODFETs, and HEMTs using a strained Si layer epitaxially grown on a Si (silicon) substrate via a SiGe (silicon-germanium) layer as a channel region have been proposed. In this strained Si-FET, tensile strain is generated in the Si layer due to SiGe having a larger lattice constant than Si, so that the band structure of Si is changed, the degeneracy is solved, and the carrier mobility is increased. Therefore, by using this strained Si layer as the channel region, the speed can be increased by about 1.3 to 8 times the normal speed. Further, a normal Si substrate by the CZ method can be used as a substrate as a process, and a high-speed CMOS can be realized by a conventional CMOS process.
[0003]
However, in order to epitaxially grow the strained Si layer required as the channel region of the FET, it is necessary to epitaxially grow a high-quality SiGe layer on the Si substrate, but due to the difference in lattice constant between Si and SiGe, There was a problem with crystallinity. For this purpose, various proposals have been made in the past.
[0004]
For example, a method using a buffer layer in which the Ge composition ratio of SiGe is increased at a constant gentle slope, a method using a buffer layer in which the Ge (germanium) composition ratio is changed stepwise (stepped), and a Ge composition ratio exceeding There have been proposed a method using a buffer layer changed into a lattice shape and a method using a buffer layer in which the Ge composition ratio is changed at a constant gradient using a Si off-cut wafer (US Patent 5,442,205, US Patent 5,221,413, PCT). WO98 / 00857, JP-A-62-252046, etc.).
[0005]
In the above-described prior art, for example, in the case of using a buffer layer in which the Ge composition ratio is increased with a constant gentle slope, unevenness (so-called cross hatch) reflecting the distribution of dislocation lines occurs due to the generated dislocations. . Since this unevenness becomes a problem in the photolithography process of the device manufacturing process, conventionally, polishing is performed using a polishing process similar to that of normal Si.
[0006]
[Problems to be solved by the invention]
However, the following problems remain in the conventional technology.
That is, the SiGe layer formed by using the above-described conventional technique is in a state where the threading dislocation density and the surface roughness do not reach the level required for the device and the manufacturing process. In particular, the cross hatch does not cause uniform unevenness on the entire surface, but presents large unevenness of several tens of nanometers with a period of several μm. Such unevenness should be removed by polishing similar to normal Si. I could not.
[0007]
The present invention has been made in view of the above-described problems, and a semiconductor substrate manufacturing method, a field effect transistor manufacturing method, and a semiconductor substrate capable of improving the surface roughness by removing cross hatching on the surface of the SiGe layer It is another object of the present invention to provide a field effect transistor.
[0008]
[Means for Solving the Problems]
The present invention employs the following configuration in order to solve the above problems.
That is, the semiconductor substrate manufacturing method of the present invention is a semiconductor substrate manufacturing method in which a SiGe layer is epitaxially grown on a Si substrate,
A film forming step of epitaxially growing a SiGe layer on the Si substrate and further epitaxially growing a Si layer on the SiGe layer;
An oxide film forming step of forming an oxide film by oxidizing the entire Si layer and the upper surface of the SiGe layer in an atmospheric gas containing moisture after the film forming step;
The oxide film after the oxide film formation step is removed by etching, and the oxide film removing step of removing the Ri taken crosshatch of the semiconductor substrate surface,
A polishing step of polishing the surface of the SiGe layer after the oxide film removing step;
A post-polishing film forming step of epitaxially growing a SiGe layer on the finish-polished SiGe layer with the same Ge composition ratio as the final Ge composition ratio of the SiGe layer;
In the film forming step, a gradient composition region in which a Ge composition ratio is gradually increased toward the surface is formed in at least a part of the SiGe layer.
The present invention is a method of manufacturing a semiconductor substrate in which a SiGe layer is epitaxially grown on a Si substrate, the film forming step of epitaxially growing a SiGe layer on the Si substrate, and oxidizing the upper surface of the SiGe layer after the film forming step. An oxide film forming step for forming an oxide film, and an oxide film removing step for removing the oxide film by etching after the oxide film forming step.
[0009]
This method for manufacturing a semiconductor substrate includes an oxide film forming process for forming an oxide film by oxidizing the upper surface of the SiGe layer after the film forming process, and an oxide film removing process for removing the oxide film by etching after the oxide film forming process. Therefore, the surface roughness of the upper surface of the SiGe layer in which cross hatching occurs after film formation is improved during the oxidation process, and when the oxide film is removed, the surface of the SiGe layer having good surface roughness can be exposed.
[0010]
In the method for manufacturing a semiconductor substrate of the present invention, it is preferable that the oxide film is formed by thermally oxidizing the upper surface of the SiGe layer in an atmosphere gas containing moisture in the oxide film forming step. In this method of manufacturing a semiconductor substrate, in the oxide film forming step, the upper surface of the SiGe layer is thermally oxidized, that is, pyro-oxidized in an atmosphere gas containing moisture, so that the Ge composition ratio in the vicinity of the upper surface of the SiGe layer is increased and defects are generated. It can suppress becoming easy. That is, in thermal oxidation in an atmospheric gas not containing moisture, that is, dry oxidation, an oxide film (SiO ₂ ) not containing Ge is formed on the upper surface of the SiGe layer, and the Ge composition ratio in the vicinity of the upper surface of the SiGe layer is increased. In contrast, since pyro oxidation is performed in the present invention, Si and Ge are oxidized at approximately the same rate, so that an oxide film containing Si on the upper surface of the SiGe layer (Si ₁ Ge _1-x O ₂ ). Can be prevented, and the Ge composition ratio in the vicinity of the upper surface of the SiGe layer can be prevented from increasing.
[0011]
In addition, the method for manufacturing a semiconductor substrate of the present invention employs a technique in which a Si layer is further epitaxially grown on the SiGe layer in the film forming step. That is, in this method of manufacturing a semiconductor substrate, since the Si layer is further epitaxially grown on the SiGe layer, it is possible to prevent the surface of the SiGe layer from being roughened by the movement of Ge on the upper surface of the SiGe layer by heat in the initial stage of thermal oxidation. it can.
[0012]
In the method of manufacturing a semiconductor substrate according to the present invention, it is preferable that in the film forming step, a gradient composition region in which a Ge composition ratio is gradually increased toward the surface is formed in at least a part of the SiGe layer. That is, in this semiconductor substrate manufacturing method, a gradient composition region in which the Ge composition ratio is gradually increased toward the surface is formed in at least a part of the SiGe layer, so that the Ge composition ratio gradually increases in the gradient composition region. The dislocations easily extend in the direction along the SiGe layer, and the density of dislocations can be suppressed particularly in the surface side of the SiGe layer.
[0013]
Moreover, it is preferable that the manufacturing method of the semiconductor substrate of this invention has a grinding | polishing process which grind | polishes the said SiGe layer surface after the said oxide film removal process. That is, in this semiconductor substrate manufacturing method, the surface roughness of the SiGe layer surface is further improved by finishing and polishing the surface of the SiGe layer after the oxide film removing step.
[0014]
The semiconductor substrate of the present invention is a semiconductor substrate in which a SiGe layer is formed on a Si substrate, and is manufactured by the method for manufacturing a semiconductor substrate of the present invention. That is, since this semiconductor substrate is manufactured by the method for manufacturing a semiconductor substrate according to the present invention, it has a good surface roughness with improved surface roughness.
[0015]
The semiconductor substrate manufacturing method of the present invention is a semiconductor substrate manufacturing method in which a strained Si layer is formed on a Si substrate via a SiGe layer, and the semiconductor substrate manufactured by the above-described semiconductor substrate manufacturing method of the present invention. The strained Si layer is epitaxially grown directly on the SiGe layer or via another SiGe layer.
The semiconductor substrate of the present invention is a semiconductor substrate in which a strained Si layer is formed on a Si substrate via a SiGe layer, and is manufactured by the method for manufacturing a semiconductor substrate in which the strained Si layer of the present invention is formed. It is characterized by that.
[0016]
In these semiconductor substrate manufacturing methods and semiconductor substrates, since the strained Si layer is epitaxially grown directly on the SiGe layer or via another SiGe layer, a high-quality strained Si layer having a small surface roughness can be obtained. A semiconductor substrate suitable for an integrated circuit using a MOSFET or the like having a layer as a channel region can be obtained.
[0017]
A method for manufacturing a field effect transistor according to the present invention is a method for manufacturing a field effect transistor in which a channel region is formed in a strained Si layer epitaxially grown on a SiGe layer, the semiconductor substrate having strained Si according to the present invention. The channel region is formed in the strained Si layer of the semiconductor substrate manufactured by the manufacturing method.
The field effect transistor of the present invention is a field effect transistor in which a channel region is formed in a strained Si layer epitaxially grown on a SiGe layer, and is manufactured by the method for manufacturing a field effect transistor of the present invention. It is characterized by that.
[0018]
The field effect transistor manufacturing method and the field effect transistor are excellent because the channel region is formed in the strained Si layer of the semiconductor substrate manufactured by the method for manufacturing a semiconductor substrate having the strained Si layer of the present invention. A high-effect field-effect transistor can be obtained with a high yield by using a strained Si layer with surface roughness.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment according to the present invention will be described with reference to FIGS. 1 to 3.
[0020]
FIG. 1 shows a cross-sectional structure of a semiconductor wafer (semiconductor substrate) W of the present invention. The structure of this semiconductor wafer will be described together with its manufacturing process. On the p-type or n-type Si substrate 1, as shown in FIG. 1A and FIG. 2, the first SiGe graded composition region in which the Ge composition ratio in the layer is gradually decreased toward the surface is first. The SiGe layer 2 is epitaxially grown by, for example, a low pressure CVD method.
[0021]
Next, the second SiGe layer 3 having a constant composition ratio in the final Ge composition ratio of the first SiGe layer 2 is epitaxially grown on the first SiGe layer 2 as a relaxation layer. Further, Si is epitaxially grown on the second SiGe layer 3 to form a strained Si layer 4. The thickness of each layer is, for example, 1.5 μm for the first SiGe layer 2, 0.7 to 0.8 μm for the second SiGe layer 3, and 15 to 22 nm for the strained Si layer 4. The film formation by the low pressure CVD method uses, for example, H ₂ as a carrier gas and SiH ₄ and GeH ₄ as source gases.
[0022]
The wafer immediately after the film formation has a cross-hatch on the surface, that is, large irregularities of several tens of nanometers with a period of several μm. In order to remove this cross hatch, the wafer on which the film has been formed is then subjected to pyro-oxidation in a thermal oxidation furnace, that is, thermal oxidation treatment in an atmosphere gas containing moisture. The heat treatment temperature is set within a temperature range of 800 ° C. to 1300 ° C. As a result of this thermal oxidation treatment, the entire strained Si layer 4 is oxidized as shown in FIG. 1B, and Si and Ge are oxidized at substantially the same rate above the second SiGe layer 3. Thus, an oxide film 3a containing Ge is formed. The oxide film 3a is formed with a thickness of 100 nm or more in order to obtain a sufficient planarization effect.
[0023]
Next, the oxide film 3a is removed by etching the wafer on which the oxide film 3a is formed with hydrofluoric acid, as shown in FIG. At this time, the surface of the second SiGe layer 3 exposed by removing the oxide film 3a has a surface roughness of about 1/5 in terms of PV (Peak to Valley) compared to the wafer surface immediately after film formation. Get smaller.
[0024]
Further, the surface roughness of the wafer from which the oxide film 3a has been removed is further polished by mechanical chemical polishing (CMP: mechanochemical polishing), so that the surface roughness is further improved and the PV is reduced to 1 nm or less. be able to.
Next, a SiGe layer is epitaxially grown on the finish-polished second SiGe layer 3 with the same Ge composition ratio as the second SiGe layer 3 to increase the thickness of the second SiGe layer 3 to a predetermined thickness. Further, a strained Si layer 5 is newly epitaxially grown on the film with a thickness of about 15 to 22 nm, whereby a semiconductor wafer W provided with the strained Si layer of this embodiment is manufactured.
[0025]
As described above, in the semiconductor wafer W of the present embodiment, the upper surface of the second SiGe layer 3 is oxidized to form the oxide film 3a and the oxide film 3a is removed by etching. The resulting wafer upper surface is improved in surface roughness during the oxidation process, and when the oxide film 3a is removed, the surface of the second SiGe layer having good surface roughness can be exposed.
[0026]
Further, by pyro-oxidizing the upper surface of the second SiGe layer 3 in an atmosphere gas containing moisture, Si and Ge are oxidized at substantially the same rate, and the upper surface of the second SiGe layer 3 is oxidized containing Ge. The film 3a is formed, and the Ge composition ratio in the vicinity of the upper surface of the second SiGe layer 3 can be suppressed from becoming higher than necessary.
Further, since the strained Si layer 4 is further epitaxially grown on the second SiGe layer 3 to form a protective film before the oxide film is formed, the Ge on the upper surface of the second SiGe layer 3 is moved by the heat during thermal oxidation. The rough surface can be prevented.
[0027]
Further, since the first SiGe layer 2 is a graded composition region in which the Ge composition ratio is gradually increased toward the surface, dislocations easily extend in the direction along the first SiGe layer 2, particularly in the SiGe layer. Dislocation density can be suppressed on the surface side.
[0028]
Next, a field effect transistor (MOSFET) using the semiconductor wafer W of the present invention will be described with reference to FIG.
[0029]
FIG. 3 shows a schematic structure of the field effect transistor of the present invention. In order to manufacture this field effect transistor, the strained Si layer 5 on the surface of the semiconductor wafer W manufactured in the above manufacturing process is shown. A SiO ₂ gate oxide film 6 and a gate polysilicon film 7 are sequentially deposited thereon. Then, a gate electrode (not shown) is formed by patterning on the gate polysilicon film 7 on the portion to become the channel region.
[0030]
Next, the gate oxide film 6 is also patterned to remove portions other than those under the gate electrode. Further, an n-type or p-type source region S and drain region D are formed in a self-aligned manner in the strained Si layer 5 and the second SiGe layer 3 by ion implantation using the gate electrode as a mask. Thereafter, a source electrode and a drain electrode (not shown) are formed on the source region S and the drain region D, respectively, and an n-type or p-type MOSFET in which the strained Si layer 5 serves as a channel region is manufactured.
[0031]
In the MOSFET manufactured in this way, a channel region is formed in the strained Si layer 5 on the semiconductor wafer W manufactured by the above-described manufacturing method. Therefore, the high-quality strained Si layer 5 with improved surface roughness has high characteristics. MOSFET can be obtained with high yield.
[0032]
The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
[0033]
For example, a SiGe layer may be further formed on the strained Si layer of the semiconductor wafer of each of the above embodiments.
In each of the above embodiments, a semiconductor wafer having a SiGe layer is manufactured as a substrate for MOSFET. However, the substrate may be applied to other applications. For example, you may apply the manufacturing method and semiconductor substrate of the semiconductor substrate of this invention to the board | substrate for solar cells or an optical element. That is, the first SiGe layer and the second SiGe layer are formed on the Si substrate of each of the above-described embodiments so that the outermost surface has 65% to 100% Ge or 100% Ge, and the oxide film formation is performed. A substrate for a solar cell or an optical device may be manufactured by depositing InGaP (indium gallium phosphide), GaAs (gallium arsenide), or AlGaAs (aluminum gallium arsenide) on the surface after oxide film removal and finish polishing. In this case, a high-performance solar cell substrate with good surface roughness can be obtained.
[0034]
【The invention's effect】
The present invention has the following effects.
According to the semiconductor substrate and the method of manufacturing a semiconductor substrate of the present invention, an oxide film forming step of forming an oxide film by oxidizing the upper surface of the SiGe layer after the film forming step, and removing the oxide film by etching after the oxide film forming step. The surface roughness is improved during the oxidation process, and a substrate having a SiGe layer surface with good surface roughness can be obtained by removing the oxide film.
Furthermore, if a strained Si layer is formed on this SiGe layer, a high-quality strained Si layer having a small surface roughness can be obtained. For example, a semiconductor substrate suitable for an integrated circuit using a MOSFET having a strained Si layer as a channel region. Can be obtained.
[0035]
Further, according to the field effect transistor and the method of manufacturing a field effect transistor of the present invention, the strained Si layer of the semiconductor substrate of the present invention or the semiconductor substrate manufactured by the method of manufacturing the semiconductor substrate of the present invention is Since the channel region is formed, a high-quality MOSFET can be obtained with a high yield by a high-quality strained Si layer with good surface roughness.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a semiconductor substrate in one embodiment according to the invention in the order of steps.
FIG. 2 is a graph showing a Ge composition ratio with respect to film thicknesses of a first SiGe layer and a second SiGe layer in an embodiment according to the present invention.
FIG. 3 is a schematic cross-sectional view showing a MOSFET according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Si substrate 2 1st SiGe layer 3 2nd SiGe layer 3a Oxide film 4, 5 Strained Si layer 6 SiO ₂ Gate oxide film 7 Gate polysilicon film S Source region D Drain region W Semiconductor wafer (semiconductor substrate)

Claims (3)

A method of manufacturing a semiconductor substrate in which a SiGe layer is epitaxially grown on a Si substrate,
A film forming step of epitaxially growing a SiGe layer on the Si substrate and further epitaxially growing a Si layer on the SiGe layer;
An oxide film forming step of forming an oxide film by oxidizing the entire Si layer and the upper surface of the SiGe layer in an atmospheric gas containing moisture after the film forming step;
The oxide film after the oxide film formation step is removed by etching, and the oxide film removing step of removing the Ri taken crosshatch of the semiconductor substrate surface,
A polishing step of polishing the surface of the SiGe layer after the oxide film removing step;
A post-polishing film forming step of epitaxially growing a SiGe layer on the finish-polished SiGe layer with the same Ge composition ratio as the final Ge composition ratio of the SiGe layer;
In the method of manufacturing a semiconductor substrate, the film forming step forms a gradient composition region in which a Ge composition ratio is gradually increased toward the surface in at least a part of the SiGe layer. A method of manufacturing a semiconductor substrate in which a strained Si layer is formed on a Si substrate via a SiGe layer,
A method for manufacturing a semiconductor substrate, comprising: epitaxially growing the strained Si layer directly on the SiGe layer of the semiconductor substrate manufactured by the method for manufacturing a semiconductor substrate according to claim 1 or via another SiGe layer. A method of manufacturing a field effect transistor in which a channel region is formed in a strained Si layer epitaxially grown on a SiGe layer,
A method for manufacturing a field effect transistor, comprising forming the channel region in the strained Si layer of a semiconductor substrate manufactured by the method for manufacturing a semiconductor substrate according to claim 2.

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