JP5672021B2 - Manufacturing method of semiconductor substrate - Google Patents

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. Examples of 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, 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 the object of the present invention is to form a gallium nitride film using a simple single crystal silicon substrate instead of an SOI substrate as a starting substrate, and warping and cracks are prevented. An object of the present invention is to provide a suppressed semiconductor substrate and a manufacturing method thereof.

  As a result of intensive studies to solve the above problems, the inventors of the present application do not necessarily use an SOI substrate on which a single-crystal SiC layer is formed, and dislocations are transferred to a surface layer region excluding the outermost surface of the silicon substrate by ion implantation. If a layer is formed and a buffer layer such as AlN or AlGaN is formed on this silicon substrate, warpage and cracking of the silicon substrate due to a difference in lattice constant and thermal expansion coefficient from GaN can be suppressed, and finally It has been found that a GaN film having a low dislocation density can be obtained.

  The present invention is based on such technical knowledge. A semiconductor substrate according to the present invention includes a single crystal silicon substrate, a dislocation layer formed in a surface layer region excluding the outermost surface of the single crystal silicon substrate, and the single substrate. A buffer layer formed on the outermost surface of the crystalline silicon substrate, 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 dislocation layer in a surface layer region excluding the outermost surface of the single crystal silicon substrate, and a buffer on the outermost surface of the single crystal silicon substrate on which the dislocation layer is formed. A step of forming a layer; and a step of forming a gallium nitride film on the surface of the buffer layer.

  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 1 according to the present embodiment includes a single crystal silicon substrate 11, a dislocation layer 12 formed in a surface region excluding the outermost surface 11 s of the single crystal silicon substrate 11, and the surface of the dislocation layer 12. And a GaN film 14 formed on the surface of the buffer layer 12.

  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 dislocation layer 12 has an incomplete silicon crystal structure formed at a position deeper than the outermost surface 11 s of the silicon substrate 11 and contains vacancies at a high concentration, so that the growth of the buffer layer 13 and the GaN film 14 is performed. Functions as a stress relaxation layer. The dislocation layer 12 is preferably formed in a region having a depth of 0.5 μm or less from the outermost surface 11s of the silicon substrate. The dislocation layer 12 can be formed by ion implantation of argon ions or the like. As the ion implantation conditions, a single crystal structure remains on the surface of the silicon substrate in order to reduce the dislocation density in the GaN film 14. It is necessary to set acceleration energy. This is because in the acceleration energy that is made amorphous to the silicon surface, high-density dislocations exist on the surface of the silicon substrate 11, and ultimately the dislocation density of the GaN film 14 is increased.

  The surface layer of the silicon substrate 11 after the ion implantation has a disordered single crystal structure, and the crystal recovers during the heat treatment for growing the buffer layer 13 and the GaN film 14 in the MOCVD furnace. Because of the structure, it effectively acts as a stress relaxation layer during growth of the buffer layer 13 and the GaN film 14. Furthermore, according to the above ion implantation conditions, dislocations due to ion implantation do not reach the substrate surface in the heat treatment during the growth of the buffer layer 13, so that dislocations can be prevented from propagating into the buffer layer, Ultimately, the dislocation of the GaN film can be reduced.

  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.

  In contrast, in the semiconductor substrate 10 according to the present embodiment, argon or the like is ion-implanted into the silicon substrate 11 to form the dislocation layer 12, and a buffer layer 13 such as AlN or AlGaN is grown on the surface of the silicon substrate 11. Therefore, the lattice constant difference and the thermal expansion coefficient difference between silicon and GaN can be further absorbed. Therefore, the defect density of GaN can be reduced, and a high-quality GaN film 14 can be manufactured.

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

  FIG. 2 is a schematic diagram illustrating a manufacturing process of the semiconductor substrate 10.

  In the manufacture of the semiconductor substrate 10, a single crystal silicon substrate 11 is first prepared as shown in FIG. 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, as shown in FIG. 2B, a dislocation layer 12 is formed on the single crystal silicon substrate 11. The dislocation layer 12 is potentially formed by implanting argon ions having an acceleration energy of 150 KeV and a dose of 1E + 15 / cm ² from the substrate surface while the silicon substrate is heated by an ion implantation apparatus. The dislocation layer 12 becomes apparent by the subsequent heat treatment step in the MOCVD furnace. The wafer after ion implantation may be heat-treated in advance before the formation of the buffer layer 13, but in terms of cost, the heat treatment is not performed in advance, and the dislocation layer 12 is revealed by using a heat-treatment process in the MOCVD furnace. It is preferable to make it.

  Next, as shown in FIGS. 2C and 2D, a buffer layer 13 and a GaN film 14 are sequentially formed on the outermost surface 11s of the silicon substrate 11 on which the dislocation layer 12 is formed. Specifically, the silicon substrate 11 on which the dislocation layer 12 is formed is put into a MOCVD furnace, cleaned in a hydrogen-containing atmosphere of 500 ° C. or higher and 1150 ° C. or lower, and after forming an AlN film, the Ga concentration is gradually increased. An AlGaN film having a changed 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 dislocation layer 12 as the stress relaxation layer is provided between the silicon substrate 11 and the buffer layer 13, the growth of the buffer layer 13 and the GaN film 14 is performed. Thus, 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. The present invention can also be applied to an SOI substrate in addition to a normal silicon substrate.

[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, argon ions having an acceleration energy of 150 KeV and a dose of 1E + 15 / cm ² were implanted into the surface of the wafer using an ion doping apparatus.

Thereafter, the ion-implanted CZ wafer was heat-treated at 1000 ° C. for 1 hour. During the heat treatment, the amorphous layer was crystallized and dislocations were formed. It was found that the dislocations existed only inside the silicon wafer and did not penetrate to the surface. It was found that the dislocation density on the silicon wafer surface at this time was 0 / cm ² .

[Example 2]
A CZ wafer ion-implanted under the same conditions as in Example 1 was mounted in a MOCVD furnace, an AlN film was grown at a temperature of 950 ° C., and Ga concentrations were successively increased to 20%, 50%, and 80%. The AlGaN film thus formed was grown, whereby 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, as a result of measuring the warpage of the wafer, the warpage of the wafer was 25 μm or less. Furthermore, when the dislocation density on the wafer surface was measured, it was found that the dislocation density was about 1E + 9 / cm ² .

[Example 3]
A CZ wafer having the same characteristics as in Example 1 was prepared, and boron ions having an acceleration energy of 75 KeV and a dose of 1E + 15 / cm ² were implanted. Thereafter, a buffer layer 13 and a GaN film 14 were formed under the same conditions as in Example 2 to obtain a semiconductor wafer sample # 2. Thereafter, the same evaluation as in Example 2 was performed on the obtained wafer 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. Further, the warpage of the wafer was 25 μm or less.

Furthermore, when the dislocation density on the wafer surface was measured, the dislocation density was about 8E + 8 / cm ² , and it was found that the dislocation density was further reduced as compared with Sample # 1 of Example 2. This is presumably because the difference in lattice constant from the buffer layer was reduced by the entry of boron into the silicon lattice position.

[Comparative Example 1]
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 implanting argon ions into the wafer. 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 1100 ° C. by 2 μm to obtain a semiconductor wafer sample # 3. Thereafter, the same evaluation as in Example 2 was performed on the obtained wafer sample # 3. As a result, cracks having a length of 1 to 2 mm were generated on the entire circumference of the outer peripheral portion. As a result of measuring the warpage of the wafer, the warpage of the wafer was 45 μm. At this time, the dislocation density on the surface of the silicon wafer was about 5E + 9 / cm ² .

[Comparative Example 2]
A CZ wafer having the same characteristics as in Example 1 was prepared, and argon ions having an acceleration energy of 50 KeV and a dose of 1E + 15 / cm ² were implanted. 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 # 4 was obtained. Thereafter, the same evaluation as in Example 2 was performed on the obtained wafer sample # 4. As a result, the length of the crack generated in the outer peripheral portion of sample # 4 was 0.5 mm or less. Further, the warpage of the wafer was 25 μm or less. At this time, the dislocation density on the surface of the silicon wafer was about 5E + 9 / cm ^{2 as} in the case of Sample # 3.

DESCRIPTION OF SYMBOLS 10 Semiconductor substrate 11 Single crystal silicon substrate 11s Outermost surface 12 of single crystal silicon substrate Dislocation layer 13 Buffer layer 14 Gallium nitride (GaN) film

Claims (1)

Forming a dislocation layer in a surface layer region excluding an outermost surface of the single crystal silicon substrate; forming a buffer layer on the outermost surface of the single crystal silicon substrate on which the dislocation layer is formed; and a surface of the buffer layer And a step of forming a gallium nitride film .
In the step of forming the dislocation layer, argon ions having a dose of 5E + 14 atoms / cm ² or more and 5E + 17 atoms / cm ² or less are ion-implanted with an acceleration energy of 150 KeV so that dislocation does not occur on the outermost surface of the single crystal silicon substrate. The manufacturing method of the semiconductor substrate characterized by including the process to do.

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