JP2012151401A - Semiconductor substrate and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor substrate and a method for manufacturing the same which can form a gallium nitride film by using a simple single crystal silicon substrate as a starting substrate, and which suppress warpage and a crack.SOLUTION: In a semiconductor substrate 10 which includes a single crystal silicon substrate 11, a carbon-containing silicon layer 12 formed on the surface of the single crystal silicon substrate 11, a buffer layer 13 formed on the surface of the carbon-containing silicon layer 12, and a gallium nitride film 14 formed on the surface of the buffer layer 13, the concentration of the carbon included in the carbon-containing silicon layer 12 is 1E+18 atoms/cmor more and 1E+21 atoms/cmor less, and the carbon-containing silicon layer 12 is formed by subjecting the single crystal silicon substrate 11 to a heat treatment under a propane gas atmosphere, for instance.

Description

  The present invention relates to a semiconductor substrate and a manufacturing method thereof, and more particularly to a silicon substrate on which gallium nitride is formed and a manufacturing method thereof.

  Group III nitride compound semiconductors such as gallium nitride have been used as blue LED materials, but they have excellent insulation resistance, environmental resistance, high frequency characteristics, etc. Is being actively developed. Among these, gallium nitride (GaN) has a large band gap, and has attracted attention as a power device material for high withstand voltage and high frequency.

The starting substrate material of the GaN substrate for power devices must be stable at the growth temperature of GaN and have a small lattice constant difference from GaN. The starting substrates that are currently in practical use include sapphire (Al ₂ O ₃ ) substrates, 6H, 4H silicon carbide (SiC) substrates, and the like. For example, metal organic vapor phase epitaxy (MOVPE method) on a single crystal sapphire substrate. For example, a method of epitaxially growing GaN is generally used.

  Since the sapphire substrate has a lattice constant different from that of GaN, a good single crystal film cannot be obtained even if GaN is directly epitaxially grown on the sapphire substrate. Therefore, a method is adopted in which a buffer layer of AlN or the like is grown on a sapphire substrate at a low temperature and GaN is grown after the strain of the lattice is relaxed by this buffer layer.

  However, a sapphire substrate or the like has a problem that workability is poor and expensive, and it is difficult to obtain a large-diameter substrate.

  As a method for solving this problem, an SOI (Silicon On Insulator) substrate is used as a starting substrate, a strain buffer layer is formed by ion implantation in the SOI layer, and then the SOI layer is carbonized and heat-treated to form a single crystal SiC layer. A method of using this SiC layer as a buffer layer of a GaN film has been proposed (see Patent Documents 1 and 2).

JP 2010-40737 A JP 2007-123675 A

  However, when forming a single crystal SiC layer as a buffer layer, propane gas or the like is introduced into a hydrogen gas atmosphere to carbonize the surface of the silicon substrate at a low temperature of 1100 ° C. or lower, and then silane gas and propane gas are introduced. Thus, the 3C—SiC single crystal film must be epitaxially grown at a high temperature of about 1200 ° C., which causes problems such as a decrease in productivity and occurrence of slip dislocation in the silicon substrate due to high-temperature heat treatment. In addition, in the above method, an SOI substrate is used as a growth substrate for GaN, and there is a problem that the substrate cost is very high.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to form a GaN film using a simple single crystal silicon substrate instead of an SOI substrate as a starting substrate, and suppress warpage and cracks. An object of the present invention is to provide a semiconductor substrate and a method of manufacturing the same.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present application do not necessarily use an SOI substrate on which a single crystal SiC layer is formed. On a silicon substrate carbonized at a low temperature of 1200 ° C. or lower. By forming a buffer layer such as AlN or AlGaN, it is possible to suppress warping and cracking of the silicon substrate due to a difference in lattice constant and thermal expansion coefficient from GaN, and finally obtain a GaN film having a low dislocation density. I found out that I can do it.

  The present invention is based on such technical knowledge. A semiconductor substrate according to the present invention includes a single crystal silicon substrate, a carbon-containing silicon layer formed on the surface of the single crystal silicon substrate, and the carbon-containing silicon layer. And a gallium nitride film formed on the surface of the buffer layer.

  The method for manufacturing a semiconductor substrate according to the present invention includes a step of forming a carbon-containing silicon layer on a surface of a single crystal silicon substrate, a step of forming a buffer layer on the surface of the carbon-containing silicon layer, and a surface of the buffer layer. And a step of forming a gallium nitride film.

  According to the present invention, a GaN film can be formed using a simple single crystal silicon substrate instead of an SOI substrate as a starting substrate, and a semiconductor substrate in which warpage and cracks are suppressed and a method for manufacturing the same can be provided.

It is a schematic sectional drawing which shows the structure of the semiconductor substrate by preferable embodiment of this invention. It is a schematic diagram which shows the manufacturing process of the semiconductor substrate by this embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic cross-sectional view showing the structure of a semiconductor substrate according to a preferred embodiment of the present invention.

  As shown in FIG. 1, the semiconductor substrate 10 according to the present embodiment is formed on a single crystal silicon substrate 11, a carbon-containing silicon layer 12 formed on the surface of the single crystal silicon substrate 11, and a surface of the carbon-containing silicon layer 12. And a GaN film 14 formed on the surface of the buffer layer 13.

  The silicon substrate 11 is a CZ wafer having a surface orientation (111) cut out from a silicon ingot pulled up by the Czochralski (CZ) method. Although not particularly limited, the silicon substrate 11 is doped with boron (B) as a p-type impurity or phosphorus (P) as an n-type impurity, and the silicon substrate 11 based on these impurities is used. The specific resistance is preferably 0.001 Ω · cm or more and 1000 Ω · cm or less, and more preferably 0.1 Ω · cm or less.

The initial oxygen concentration of the silicon substrate 11 is not particularly limited, and may be in the range of oxygen concentration that can be generally manufactured, and is 4 × 10 ¹⁷ atoms / cm ³ or more and 2.4 × 10 ¹⁸ atoms / cm ³ or less. . The thickness of the silicon substrate 11 is preferably thicker from the viewpoint of warping countermeasures, and preferably 0.9 mm or more and 2.5 mm or less, although it depends on the diameter of the silicon substrate.

  The carbon-containing silicon layer 12 functions as a relaxation layer that reduces the lattice constant difference between the silicon substrate 11 and the buffer layer 13. Since the lattice constant of the carbon-containing silicon layer 12 is smaller than that of single crystal silicon, the induction of defects from the interface with the buffer layer 13 can be suppressed, and the propagation of defects to the final GaN film can be reduced. .

The carbon-containing silicon layer 12 is preferably formed on the surface of the silicon substrate 11 by simultaneously introducing a silicon-containing gas such as trichlorosilane and propane gas into a furnace at 1050 ° C., for example. Alternatively, monomethylsilane or trimethylsilane gas may be introduced alone into a furnace at 1000 ° C. or lower. The carbon concentration in these silicon single crystal films is preferably 1E + 18 to 1E + 21 atms / cm ³ . This is because if the carbon concentration is too low, the effect is not exhibited, and if it is too high, defects are induced in the carbon-containing silicon layer.

  The buffer layer 13 serves to reduce the lattice constant difference between the silicon substrate 11 and the GaN film 14. The thickness of the buffer layer 13 may be about 2 μm. As the buffer layer 13, a film in which the concentration of the AlGaN buffer layer is changed after the formation of the AlN layer is grown a plurality of times, and finally a GaN film is grown by 2 μm.

  As a conventional method for forming a single crystal SiC film on the surface of the single crystal silicon substrate 11, propane gas or the like is introduced into a hydrogen gas atmosphere at a temperature of 1100 ° C. or less to carbonize only the surface layer of the silicon substrate (incomplete A method of growing a 3C—SiC single crystal film by introducing a silane gas and a propane gas at a higher temperature after forming a SiC film) is known. Although this SiC film has a small lattice constant difference, it is also used as a buffer layer for a GaN substrate, but there are problems such as a decrease in productivity and slippage due to high-temperature heat treatment.

  On the other hand, the semiconductor substrate 10 according to the present embodiment carbonizes the silicon substrate 11 at a low temperature to form a carbon-containing silicon layer 12, and a buffer layer 13 such as AlN or AlGaN is formed on the surface of the carbon-containing silicon layer 12. Thus, the lattice constant difference and the thermal expansion coefficient difference between silicon and GaN can be further absorbed. Therefore, the defect density of the GaN film can be reduced, and a high-quality GaN film can be manufactured.

  Next, a method for manufacturing the semiconductor substrate 10 will be described.

  In the manufacture of the semiconductor substrate 10, first, a single crystal silicon substrate 11 is prepared. As the single crystal silicon substrate 11, a CZ wafer having a plane orientation (111) cut out from a silicon ingot pulled up by the Czochralski (CZ) method can be used. As described above, the silicon substrate 11 preferably has a diameter of 100 mmφ or more, a thickness of 0.9 mm to 2.5 mm, and a specific resistance of 0.001 to 1000 Ω · cm. The specific resistance can be adjusted by the amount of boron and the amount of n-type dopant added to the CZ method silicon melt.

  Next, a carbon-containing silicon layer 12 is formed on the single crystal silicon substrate 11. The carbon-containing silicon layer 12 is epitaxially grown on the silicon substrate 11 by introducing a mixed gas of trichlorosilane and propane into a furnace at 1050 ° C., or monomethylsilane or trimethylsilane gas is introduced into the furnace at 1000 ° C. or less. Then, it can be formed by epitaxial growth, whereby a silicon epitaxial layer containing a high concentration of carbon can be obtained.

  The carbon-containing silicon layer 12 may be formed not by epitaxial growth but by carbonization heat treatment. For example, the carbon-containing silicon layer 12 can be formed by introducing a mixed gas of hydrogen and propane gas and performing heat treatment at 1000 ° C. or more and 1200 ° C. or less. Since single crystal SiC begins to form in a temperature range exceeding 1200 ° C., the temperature range of the heat treatment is preferably 1050 ° C. to 1150 ° C. or less, which makes it possible to form an unstable silicon carbide layer. Become.

  Next, the buffer layer 13 and the GaN film 14 are sequentially formed on the surface of the carbon-containing silicon layer 12. Specifically, the silicon substrate 11 on which the carbon-containing silicon layer 12 is formed is put into a MOCVD furnace, cleaned in a hydrogen-containing atmosphere at 500 ° C. or higher and 1150 ° C. or lower to form an AlN film, and then the Ga concentration is gradually increased. Then, an AlGaN film changed to a high concentration is grown a plurality of times. Thereafter, the final GaN film is grown by 2 μm, thereby completing the semiconductor substrate 10 according to the present embodiment.

  As described above, according to the present embodiment, since the carbon-containing silicon layer 12 as the stress relaxation layer is provided between the silicon substrate 11 and the buffer layer 13, the buffer layer 13 and the GaN film 14 During the growth, warping and cracking of the silicon substrate 11 can be suppressed, and a high-quality GaN film 14 having a low dislocation density can be formed.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, in the above embodiment, the buffer layer 13 is a multilayer film of an AlN film and an AlGaN film, but may be a single layer film made of AlN or another material. However, the buffer layer needs to take an intermediate value of the lattice constants of the carbon-containing silicon layer 12 and the GaN film 14. Furthermore, the present invention can be applied to an SOI wafer in addition to a normal silicon wafer.

[Example 1]
A boron-doped CZ wafer having a diameter of 150 mm, a plane orientation (111), a thickness of 625 μm, an initial oxygen concentration of 1.5 × 10 ¹⁸ atoms / cm ³ and a specific resistance of 10 to ²⁰ Ω · cm was prepared. Next, the wafer is heated to 1130 ° C. while flowing hydrogen gas of 60 L / min in the epitaxial growth apparatus, and then propane gas (propane concentration 10%; hydrogen gas base) 250 mL / min is flowed for 30 seconds to carbonize the wafer. Went.

  After that, the carbonized CZ wafer was mounted in an MOCVD furnace, an AlN film was grown at a temperature of 950 ° C., and then an AlGaN film with Ga concentrations of 20%, 50%, and 80% were sequentially increased. By growing, the buffer layer 13 was formed. Subsequently, a GaN film was grown by 2 μm at a temperature of 1100 ° C. to obtain a semiconductor wafer sample # 1.

As a result of observing the surface of wafer sample # 1 thus obtained with an optical microscope and measuring cracks, cracks were found in the entire outer periphery, but the length was 0.5 mm or less. It was. Moreover, when the cross section of the wafer was observed with an electron microscope, a film having a black contrast was observed on the surface of the silicon wafer. As a result of measuring this film by FT-IR, an Si—C peak (800 cm ⁻¹ ) was observed in the infrared absorption spectrum, and the carbon concentration was 1E + 18 atoms / cm ³ . Furthermore, as a result of measuring the warpage of the wafer, the warpage of the wafer was 25 μm.

[Example 2]
A CZ wafer having the same characteristics as in Example 1 was prepared, heated to 1130 ° C. while flowing hydrogen gas at 60 L / min in the epitaxial growth apparatus, held for 30 seconds, lowered to 1050 ° C., and then propane The wafer was carbonized by flowing 250 mL / min of gas (propane concentration: 10%; hydrogen gas base) and 15 L / min of trichlorosilane gas for 30 seconds. Thereafter, the buffer layer 13 and the GaN film 14 were formed under the same conditions as in Example 1, and a semiconductor wafer sample # 2 was obtained. Then, evaluation similar to Example 1 was performed with respect to obtained sample # 2.

As a result, the length of the crack generated in the outer peripheral portion of sample # 2 was 0.5 mm or less. Moreover, as a result of measuring this sample by FT-IR, the Si-C peak was observed and the carbon concentration was 1E + 18 atoms / cm ³ . Further, the warpage of the wafer was 25 μm.

[Example 3]
A CZ wafer having the same characteristics as Example 1 was prepared, heated to 1130 ° C. while flowing hydrogen gas at 60 L / min in the epitaxial growth apparatus, held for 30 seconds, lowered to 900 ° C., and then trimethyl The wafer was carbonized by flowing 200 mL / minute of silane gas for 120 seconds. Thereafter, a buffer layer 13 and a GaN film were formed under the same conditions as in Example 1 to obtain a sample # 3 of a semiconductor substrate. Thereafter, the same evaluation as in Example 1 was performed on the obtained sample # 3.

As a result, the length of the crack generated in the outer peripheral portion of sample # 3 was 0.5 mm or less. Moreover, as a result of measuring this sample by FT-IR, the Si-C peak was observed and the carbon concentration was 1E + 18 atoms / cm ³ . Further, the warpage of the wafer was 25 μm.

[Comparative Example 1]
A CZ wafer having the same characteristics as in Example 1 was prepared and used as a sample without performing carbonization, buffer layer and GaN film formation, etc., and the cross section of the wafer was observed with an electron microscope. No film with black contrast was observed. As a result of measuring this sample with FT-IR, a Si-C peak was not observed.

[Comparative Example 2]
A CZ wafer having the same characteristics as in Example 1 was prepared, and only the buffer layer 13 and the GaN film 14 were formed without subjecting this wafer to carbonization. That is, after mounting the wafer in a MOCVD furnace, an AlN film was formed at a temperature of 950 ° C., then an AlGaN film having a 20% Ga concentration was formed, and an AlGaN film having a high concentration of 50% and 80% was successively grown. . Subsequently, a GaN film was grown at 2 μm at 1100 ° C. to obtain a sample # 5 of a semiconductor substrate. Thereafter, the same evaluation as in Example 1 was performed on the obtained wafer sample # 5.

  As a result, cracks having a length of 1 to 2 mm were generated on the entire circumference of the outer peripheral portion. Further, when the cross section of the wafer was observed with an electron microscope, a film having a black contrast was not observed on the surface of the silicon wafer. As a result of measuring this sample with FT-IR, a Si-C peak was observed. Furthermore, as a result of measuring the warpage of the wafer, the warpage of the wafer was 45 μm.

DESCRIPTION OF SYMBOLS 10 Semiconductor substrate 11 Single crystal silicon substrate 12 Carbon-containing silicon layer 13 Buffer layer 14 Gallium nitride (GaN) film

Claims (7)

  A single crystal silicon substrate, a carbon-containing silicon layer formed on the surface of the single crystal silicon substrate, a buffer layer formed on the surface of the carbon-containing silicon layer, and a gallium nitride film formed on the surface of the buffer layer A semiconductor substrate comprising: 2. The semiconductor substrate according to claim 1, wherein the concentration of carbon contained in the carbon-containing silicon layer is 1E + 18 atoms / cm ³ or more and 1E + 21 atoms / cm ³ or less.   Forming a carbon-containing silicon layer on the surface of the single-crystal silicon substrate; forming a buffer layer on the surface of the carbon-containing silicon layer; and forming a gallium nitride film on the surface of the buffer layer. A method for manufacturing a semiconductor substrate.   4. The method of manufacturing a semiconductor device according to claim 3, wherein the step of forming the carbon-containing silicon layer includes a step of heat-treating the single crystal silicon substrate in a propane gas atmosphere.   4. The method of manufacturing a semiconductor device according to claim 3, wherein the step of forming the carbon-containing silicon layer includes a step of epitaxially growing the carbon-containing silicon layer using a mixed gas of trichlorosilane and propane.   4. The method of manufacturing a semiconductor device according to claim 3, wherein the step of forming the carbon-containing silicon layer includes a step of epitaxially growing the carbon-containing silicon layer using a trimethylsilane gas. 7. The method of manufacturing a semiconductor substrate according to claim 3, wherein a concentration of carbon contained in the carbon-containing silicon layer is 1E + 18 atoms / cm ³ or more and 1E + 21 atoms / cm ³ or less.

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