Silicon substrate and its manufacturing method

Abstract

To provide a silicon substrate that has excellent adhesion to a diamond thin film, and ensures strong and uniform adhesion over the whole area of the substrate even if the substrate has a large diameter.SOLUTION: The present invention discloses a silicon substrate for forming a diamond thin film on the surface of the substrate. In a surface area 2 from the substrate surface to the depth 5 μm, the carbon concentration is at least 1×1017 atoms / cm3 and, as maximum value, 5×1017 atoms / cm3 or more; the oxygen concentration is 6×1017 atoms / cm3 or less; and the nitrogen concentration is 1×1014 atoms / cm3 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a silicon substrate and a manufacturing method thereof, and more particularly to a silicon substrate which has good adhesion to a diamond thin film and which can obtain strong and uniform adhesion over the entire surface of the substrate even if the substrate has a large diameter, and a manufacturing method thereof. [Background technology]

[0002] Diamond has the highest hardness of any substance, the highest thermal conductivity, and high electrical insulation. It is also a unique substance that has a wide range of transparency and chemical stability from ultraviolet to infrared. In the field of semiconductor materials, diamond is known as a material that has a band gap, a dielectric breakdown voltage, and a carrier mobility higher than those of semiconductor materials such as silicon and gallium arsenide.

[0003] In addition, the diamond can form a semiconductor thin film layer on a silicon substrate by adding impurity elements during the vapor phase synthesis of thin diamond film or by ion implantation into diamond. Therefore, by utilizing the characteristics of diamond, it is possible to realize electronic devices that were previously impossible, such as high-temperature resistant devices that function even at temperatures of 500°C or higher and ultraviolet light emitting devices.

[0004] In recent years, various methods have been attempted for forming polycrystalline diamond thin films on foreign gases by gas phase techniques, such as hot filament CVD (chemical vapor deposition), microwave plasma CVD, and DC plasma jet CVD. However, the biggest problem in coating or forming a diamond thin film on a silicon substrate using such a method is the adhesive strength between the substrate and the diamond film, and there is a problem that sufficient adhesive strength cannot be obtained with the above-mentioned method.

[0005] To address this issue, the method disclosed in Patent Document 1 has a 1×10 16 atoms / cm 3It is said that the adhesion of the diamond thin film can be improved by incorporating at least one element selected from the group consisting of boron and carbon in a concentration equal to or higher than the solid solubility limit in silicon. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2004-59342 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the inventors of the present application conducted experiments using the method disclosed in Patent Document 1, they found that defects such as curling and cracks occurred in the diamond thin film formed on the silicon substrate, making it impossible to manufacture with a good yield. That is, it was confirmed that the method disclosed in Patent Document 1 did not provide sufficient adhesion between the silicon substrate and diamond.

[0008] As a result of extensive research, the inventors of the present application discovered that by not only setting a high carbon concentration in the surface region of the silicon substrate but also keeping the oxygen and nitrogen concentrations in the surface region low, it is possible to suppress the occurrence of curling and cracking in the diamond thin film and improve the adhesion between the silicon substrate and diamond, which led to the invention.

[0009] An object of the present invention is to provide a silicon substrate which has good adhesion to a diamond thin film and which can obtain strong and uniform adhesion over the entire surface of the substrate even if the substrate diameter is large, and a method for manufacturing the same. [Means for solving the problem]

[0010] The silicon substrate according to the present invention, which has been made to solve the above problems, is a silicon substrate for forming a diamond thin film on a substrate surface, and the carbon concentration in a surface region from the substrate surface to a depth of 5 μm is at least 1×10 17 atoms / cm 3 , and the maximum value is At least 5×10 17 atoms / cm 3 in The oxygen concentration is 6×10 17 atoms / cm 3 Below, nitrogen concentration is 1×10 14 atoms / cm 3 The semiconductor device is characterized by having a SiOC-based film. In the bulk region 20 μm or deeper from the substrate surface, the carbon concentration is 1×10 16 atoms / cm 3 It is desirable that the following:

[0011] By increasing the carbon concentration in the surface region of the silicon substrate in this manner, adhesion to the diamond thin film formed on the substrate surface can be improved, and by keeping the oxygen and nitrogen concentrations in the surface region low, the incorporation of oxygen and nitrogen into the diamond thin film can be suppressed. As a result, curling or cracking of the diamond thin film can be suppressed, and strong and uniform adhesion to the diamond thin film can be obtained even if the substrate has a large diameter.

[0012] Further, a method for producing a silicon substrate according to the present invention, which has been made to solve the above-mentioned problems, is a method for producing a silicon substrate for forming a diamond thin film on a substrate surface, which comprises the steps of placing a substrate cut from a silicon single crystal in a chamber and introducing a carbon-containing gas into the chamber to perform a heat treatment, and has a carbon concentration of at least 1×10 in a surface region up to a depth of 5 μm from the substrate surface. 17 atoms / cm 3 , and the maximum value is 5 x 10 17 atoms / cm 3 The oxygen concentration is increased to 6×1017 atoms / cm 3 The nitrogen concentration is 1×10 14 atoms / cm 3 The present invention is characterized by the following formation. In the step of introducing a gas containing carbon into the chamber and performing heat treatment, the gas containing carbon is CO gas It is desirable to introduce the following. In addition, in the step of introducing a gas containing carbon into the chamber and performing the heat treatment, it is preferable to maintain the inside of the chamber at 1200° C. or higher for at least one hour. In addition, by the step of introducing a gas containing carbon into the chamber and performing heat treatment, the carbon concentration in a bulk region at a depth of 20 μm or more from the substrate surface is reduced to 1×10 16 atoms / cm 3 It is preferable to form the following:

[0013] By increasing the carbon concentration in the surface region of the silicon substrate in this manner, adhesion to the diamond thin film formed on the substrate surface can be improved, and by keeping the oxygen and nitrogen concentrations in the surface region low, the incorporation of oxygen and nitrogen into the diamond thin film can be suppressed. As a result, curling or cracking of the diamond thin film can be suppressed, and strong and uniform adhesion to the diamond thin film can be obtained even if the substrate has a large diameter. Effect of the Invention

[0014] According to the present invention, it is possible to provide a silicon substrate which has good adhesion to a diamond thin film and which can obtain strong and uniform adhesion over the entire surface of the substrate even if the substrate diameter is large, and a method for manufacturing the same. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view illustrating a silicon substrate of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing an outline of an example of a heat treatment apparatus used for manufacturing the silicon substrate of FIG. [Diagram 3] FIG. 3 is a flow chart showing the flow of a method for manufacturing a silicon substrate according to the present invention. [Figure 4] FIG. 4 is a graph showing the results of Example 1 according to the present invention. [Diagram 5] FIG. 5 is a graph showing the results of Examples 2, 3, and 4 according to the present invention. [Figure 6] FIG. 6 is a graph showing the results of Examples 5, 6, and 7 according to the present invention. [Figure 7] FIG. 7 is a graph showing the results of Example 8 according to the present invention. [Figure 8] FIG. 8 is a graph showing the results of Example 9 according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view showing a silicon substrate of the present invention. As shown in Fig. 1, a silicon substrate 1 has a surface region 2 extending from the substrate surface to a depth of 5 µm, and a bulk region 3 extending deeper than 20 µm from the substrate surface. The surface region 2 has a carbon concentration of at least 1×10 17 atoms / cm 3 The maximum carbon concentration is 5×10 17 atoms / cm 3 The oxygen concentration in the surface region 2 is 6×10 17 atoms / cm 3 and the nitrogen concentration in the surface region 2 is 1×10 14 atoms / cm 3 It is formed as follows: The carbon concentration in the bulk region 3 is 1×10 16 atoms / cm 3 It is formed as follows:

[0017] In this way, since the silicon substrate 1 is formed with a high carbon concentration in the surface region 2, when the diamond thin film 5 shown by the dashed line in FIG. 1 is formed, the adhesion between the silicon substrate 1 and the diamond thin film 5 can be improved. Furthermore, since the oxygen concentration and nitrogen concentration in the surface region 2 are low, it is possible to suppress the intrusion of oxygen and nitrogen into the diamond thin film 5 when the diamond thin film 5 is formed. As a result, the occurrence of defects such as curling and cracking of the diamond thin film 5 can be significantly suppressed compared to the conventional method, and the diamond thin film 5 can be adhered uniformly to the substrate even if the substrate has a large diameter.

[0018] Fig. 2 is a cross-sectional view showing an overview of an example of a heat treatment apparatus used to manufacture the silicon substrate of Fig. 1. As shown in Fig. 2, the heat treatment apparatus 10 includes a chamber (reaction tube) 20 having an atmospheric gas inlet 20a and an atmospheric gas outlet 20b, a plurality of lamps 30 arranged at a distance from one another in the upper part of the chamber 20, and a substrate support part 40 that supports the silicon substrate 1 in the reaction space 25 in the chamber 20. In addition, the heat treatment apparatus 10 includes a rotation means (not shown) that rotates the silicon substrate 1 around its central axis at a predetermined speed.

[0019] The substrate support 40 includes an annular susceptor 40a that supports the outer periphery of the silicon substrate 1, and a stage 40b that supports the susceptor 40a. The chamber 20 is made of, for example, quartz. The lamp 30 is made of, for example, a halogen lamp. The susceptor 40a is made of, for example, silicon. The stage 40b is made of, for example, quartz.

[0020] 2, when heat treatment is performed on a silicon substrate 1, the silicon substrate 1 is introduced into the reaction space 25 through a substrate inlet (not shown) provided in the chamber 20, and the silicon substrate 1 is supported on a susceptor 40a of a substrate support portion 40. Then, an atmospheric gas, which will be described later, is introduced through the atmospheric gas inlet 20a, and the substrate surface is irradiated with light from lamps 30 while the silicon substrate 1 is rotated by a rotating means (not shown).

[0021] The temperature control within the reaction space 25 in the heat treatment device 10 is performed by measuring the average temperature at multiple points (e.g., nine points) within the substrate surface in the radial direction of the lower part of the silicon substrate 1 using multiple radiation thermometers 50 embedded in the stage 40b of the substrate support part 40, and controlling the multiple halogen lamps 30 (individual ON-OFF control of each lamp, control of the emission intensity of the emitted light, etc.) based on the measured temperatures.

[0022] Next, a method for manufacturing a silicon substrate according to the present invention will be described with reference to the flow chart of FIG. In the method for producing a silicon substrate according to the present invention, a surface of a silicon substrate sliced ​​from a silicon single crystal ingot grown by, for example, the Czochralski method is heat-treated under predetermined production conditions.

[0023] The growth of a silicon single crystal ingot by the Czochralski method is carried out by a well-known method. That is, polycrystalline silicon filled in a quartz crucible is heated to turn it into a silicon melt, a seed crystal is brought into contact with the silicon melt from above the liquid surface, and the seed crystal and the quartz crucible are pulled up while rotating, and the diameter is expanded to the desired diameter to grow a straight body portion, thereby producing a silicon single crystal ingot.

[0024] The silicon single crystal ingot thus obtained is processed into a silicon substrate (wafer) by a well-known method (step S1). That is, a silicon single crystal ingot is sliced ​​into wafers using an inner diameter blade or a wire saw, and then processed by chamfering the outer periphery, lapping, etching, polishing, etc. to manufacture silicon substrates. Note that the processing steps described here are merely illustrative, and the present invention is not limited to these processing steps.

[0025] Next, the surface of the manufactured silicon substrate is subjected to a heat treatment under a predetermined manufacturing condition. Specifically, in a heat treatment apparatus 10 as shown in Fig. 2, the manufactured silicon substrate is placed in a chamber 20 maintained at a desired initial temperature (step S2).

[0026] After the substrate was placed, atmospheric gas having a carbon concentration of 5×10 was introduced into the chamber 20 from the atmospheric gas inlet 20a. 17 atoms / cm 3 More preferably, 1×10 18 atoms / cm 3 The above CO2 gas is introduced at a predetermined flow rate (step S3).

[0027] Then, the inside of the chamber 20 is heated by the halogen lamps 30, and heat treatment is performed at a predetermined substrate temperature (eg, 1200° C.) for a predetermined time (eg, 1 hour) (step S4). In order to control a constant gas flow and carbon concentration in the heat treatment space, the atmosphere within the chamber is exhausted from the exhaust port 20b at a predetermined flow rate.

[0028] By this heat treatment, the carbon concentration in the region (surface region 2) from the surface of the silicon substrate 1 (under the oxide film formed by the heat treatment) to a depth of 5 μm is reduced to at least 1×10 17 atoms / cm 3 The maximum carbon concentration is 5×10 17 atoms / cm 3 In addition, the carbon concentration in the region deeper than 20 μm from the surface (bulk region 3) is 1×10 16 atoms / cm 3 It is formed as follows:

[0029] In addition, the oxygen concentration in the surface region 2 is increased to 6×10 17 atoms / cm 3 and the nitrogen concentration in the surface region 2 is 1×10 14 atoms / cm 3 It is formed as follows: That is, a film having a high carbon concentration is formed on the surface region 2 of the silicon substrate 1, which makes it possible to improve the adhesion with the diamond thin film.

[0030] The carbon concentration in the surface region 2 of the silicon substrate 1 is 1×10 17atoms / cm 3 If it is smaller, the adhesion with the diamond thin film will be poor, which will cause defects in the diamond film, and this is not preferred. In addition, the carbon concentration in the bulk region 3 is 1×10 16 atoms / cm 3 If it is larger, the impurity concentration becomes high, which is not preferable.

[0031] In addition, the oxygen concentration in surface region 2 is 6×10 17 atoms / cm 3 If it is large, the amount of oxygen mixed into the diamond thin film formed on the silicon substrate 1 increases, which is undesirable. Similarly, the nitrogen concentration in the surface region is 1×10 14 atoms / cm 3 If the thickness is larger, the amount of nitrogen mixed into the diamond thin film formed on the silicon substrate 1 increases, which is undesirable.

[0032] When the high-temperature heat treatment is completed, the temperature inside the chamber is lowered to a predetermined temperature at a predetermined heating rate, and the heat treatment is terminated (step S5). Finally, the silicon substrate 1 is taken out of the chamber 20, and the oxide film formed on the substrate surface by the heat treatment is removed by HF cleaning, thereby obtaining the silicon substrate 1 of the present invention.

[0033] As described above, according to the embodiment of the present invention, by increasing the carbon concentration in the surface region 2 of the silicon substrate 1, it is possible to improve adhesion with the diamond thin film formed on the substrate surface, and by keeping the oxygen and nitrogen concentrations in the surface region 2 low, it is possible to suppress the intrusion of oxygen and nitrogen into the diamond thin film. As a result, curling or cracking of the diamond thin film can be suppressed, and strong and uniform adhesion to the diamond thin film can be obtained even if the substrate has a large diameter.

[0034] In the above embodiment, CO2 gas is introduced into the chamber as a gas containing carbon in the heat treatment, but the present invention is not limited to this, and CO gas may be introduced into the chamber. EXAMPLES

[0035] The silicon substrate and the manufacturing method thereof according to the present invention will be further described with reference to examples. In the examples, the following experiments were carried out based on the above-described embodiment.

[0036] (Experiment 1) Example 1 In Example 1, a silicon substrate with a diameter of 300 mm and a thickness of 775 μm was prepared from a silicon single crystal grown by the Czochralski method, placed in a chamber, and CO2 gas was introduced to maintain a high carbon concentration in the chamber. Then, the chamber was kept at 1200°C for 1 hour to perform heat treatment. After the heat treatment, the oxide film formed on the silicon substrate surface was removed by HF cleaning, and then a diamond film having a thickness of 5 μm was formed on the substrate surface by the hot filament CVD method. A visual appearance inspection was carried out on the diamond film thus formed, and the locations where curling, cracks, etc. occurred were measured.

[0037] Comparative Example 1 In Comparative Example 1, a silicon substrate with a diameter of 300 mm and a thickness of 775 μm was prepared in the same manner as in Example 1, and a 1×10 16 atoms / cm 3 of carbon, concentration 1×10 18 atoms / cm 3 A diamond film having a thickness of 5 μm was formed on the surface of the substrate by the hot filament CVD method. A visual appearance inspection was carried out on the diamond film thus formed, and the locations where curling, cracks, etc. occurred were measured.

[0038] The results of Example 1 and Comparative Example 1 are shown in the graph of Figure 4. In the graph of Figure 4, the vertical axis represents the number of defects in the diamond coating. From this graph, it can be seen that the number of defects in the diamond coating of Example 1 was kept low, about one-fifth of that in Comparative Example 1. In other words, it was confirmed that high adhesion between the silicon substrate and the diamond coating was obtained in Example 1.

[0039] (Experiment 2) In experiment 2, it was verified how the concentration of carbon implanted into the substrate changes depending on the temperature conditions when carbon gas is introduced into the chamber and heat treatment is performed in the present invention. Example 2 In Example 2, a silicon substrate with a diameter of 300 mm and a thickness of 775 μm was prepared as in Example 1, and placed in a chamber, and CO2 gas was introduced so that the carbon concentration in the chamber was kept high. Then, the heat treatment was performed by holding the chamber at 1000° C. for 1 hour. After the heat treatment, the oxide film formed on the surface of the silicon substrate was removed by HF cleaning. The carbon concentration was measured along the depth direction from the surface of the silicon substrate.

[0040] Example 3 In the third embodiment, the temperature in the chamber during the heat treatment was set to 1100° C. The other conditions were the same as those in the second embodiment.

[0041] Example 4 In the fourth embodiment, the temperature in the chamber during the heat treatment was set to 1200° C. The other conditions were the same as those in the third embodiment.

[0042] The results of Examples 2 to 4 are shown in the graph of Figure 5. In the graph of Figure 5, the vertical axis represents the carbon concentration (atoms / cm 3 ), and the horizontal axis indicates the depth (μm) from the substrate surface. From the graph of FIG. 5, by carrying out a heat treatment at 1200° C. for 1 hour as in Example 4, the carbon concentration in the surface region up to a depth of 5 μm was reduced to 1×10 18 atoms / cm 3In the bulk region deeper than 20 μm, the 16 atoms / cm 3 It was confirmed that this could be reduced to the following: In Example 2 (temperature 1000° C.), it was not possible to form a high carbon concentration in the surface region. From the above, it was confirmed that the heat treatment temperature should be 1200° C. or higher for at least 1 hour.

[0043] Example 5 In Example 5, the gas introduced into the chamber in the heat treatment was CO gas, the temperature was 1000° C., and the time was 1 hour. The other conditions were the same as in Example 2.

[0044] Example 6 In Example 6, the gas introduced into the chamber in the heat treatment was CO gas, the temperature was 1100° C., and the time was 1 hour. The other conditions were the same as in Example 2.

[0045] Example 7 In Example 7, the gas introduced into the chamber in the heat treatment was CO gas, the temperature was 1200° C., and the time was 1 hour. The other conditions were the same as in Example 2.

[0046] The results of Examples 5 to 7 are shown in the graph of Figure 6. In the graph of Figure 6, the vertical axis represents the carbon concentration (atoms / cm 3 ), and the horizontal axis indicates the depth (μm) from the substrate surface. From the graph of FIG. 6, by carrying out a heat treatment at 1200° C. for 1 hour as in Example 7, the carbon concentration in the surface region up to a depth of 5 μm was reduced to 1×10 18 atoms / cm 3 In the bulk region deeper than 20 μm, the 16 atoms / cm 3 It was confirmed that this could be reduced to the following: In Example 5 (temperature 1000° C.), it was not possible to form a high carbon concentration in the surface region. From the above, it was confirmed that the heat treatment temperature should be 1200° C. or higher for at least 1 hour.

[0047] (Experiment 3) In experiment 3, the distribution of oxygen (O), silicon (Si), and carbon (C) in the surface layer of the silicon substrate obtained by the present invention was measured and verified by RBS (Rutherford Backscattering Spectrometry) / NRA (Nuclear Reaction Analysis) methods. Example 8 In Example 8, a silicon substrate with a diameter of 300 mm and a thickness of 775 μm was prepared as in Example 1, and placed in a chamber, and CO2 gas was introduced so that the carbon concentration in the chamber was kept high. Then, the heat treatment was performed by holding the chamber at 1200° C. for 1 hour. The distributions of oxygen, silicon, and carbon were measured from the surface of the obtained silicon substrate along the depth direction.

[0048] The results of Example 8 are shown in the graph of Figure 7. In the graph of Figure 7, the vertical axis represents the atomic ratio, and the horizontal axis represents the depth (nm) from the substrate surface. From the graph in Figure 7, it was confirmed that a certain proportion of carbon is contained from the substrate surface to a depth of approximately 230 nm. This graph also confirmed that the film formed on the surface of the wafer heat-treated with CO2 gas is a silicon oxide film (SiO2). Furthermore, SiO2 can be easily removed by HF cleaning, and the Si surface on which diamond will be formed can be easily exposed to the surface.

[0049] In Example 9, the gas introduced into the chamber was CO gas. The other conditions were the same as in Example 8. The results of Example 9 are shown in the graph of Figure 8. In the graph of Figure 8, the vertical axis represents the atomic ratio, and the horizontal axis represents the depth (nm) from the substrate surface. From the graph in Figure 8, it was confirmed that a film containing carbon is present from the substrate surface to a depth of about 60 nm. Furthermore, from this graph it was confirmed that the film formed on the surface of the wafer heat-treated with CO gas is not a simple silicon oxide film (SiO2). In other words, it was confirmed that a SiOC-based film is formed at the interface between the SiO2 film and Si. When the SiO2 is removed by HF cleaning, a SiOC-based film remains on the surface, and this SiOC-based film aids in the formation of the diamond film and also improves the adhesion between the Si and the diamond film.

[0050] As described above, it has been confirmed that the present invention can provide a silicon substrate that has good adhesion to a diamond thin film and that has strong and highly uniform adhesion over the entire substrate surface even when the substrate diameter is large. [Explanation of symbols]

[0051] 1. Silicon substrate 2 Surface area 3. Bulk Region 5 Diamond thin film 10 Heat treatment device 20 Chamber 20a Atmospheric gas inlet 20b Atmospheric gas exhaust port 25 Reaction Space 30 Lamp 40 Substrate support

Claims

1. A silicon substrate for forming a diamond thin film on a surface thereof, In a surface region up to a depth of 5 μm from the substrate surface, The carbon concentration is at least 1×10 １７ atoms / cm 3 , and the maximum value is at least 5×10 17 atoms / cm 3 , Oxygen concentration is 6 x 10 １７ atoms / cm 3 Below, the nitrogen concentration is 1×10 １４ atoms / cm 3 is as follows: A silicon substrate having a SiOC-based film.

2. In a bulk region having a depth of 20 μm or more from the substrate surface, Carbon concentration is 1 x 10 １６ atoms / cm 3 2. The silicon substrate according to claim 1, wherein:

3. A method for manufacturing a silicon substrate for forming a diamond thin film on a substrate surface, comprising the steps of: placing a substrate cut from a silicon single crystal in a chamber; A step of introducing a gas containing carbon into the chamber and performing a heat treatment; In a surface region from the substrate surface to a depth of 5 μm, the carbon concentration is at least 1×10 １７ atoms / cm 3 , and the maximum value is at least 5×10 １７ atoms / cm 3 In addition, Oxygen concentration 6 x 10 １７ atoms / cm 3 In the following, the nitrogen concentration is 1×10 １４ atoms / cm 3 Formed as follows: The method for manufacturing a silicon substrate further comprises forming a SiOC-based film.

4. In the step of introducing a gas containing carbon into the chamber to perform heat treatment, 4. The method for producing a silicon substrate according to claim 3, wherein CO gas is introduced as the gas containing carbon.

5. In the step of introducing a gas containing carbon into the chamber to perform heat treatment, 5. The method for manufacturing a silicon substrate according to claim 3, wherein the inside of the chamber is maintained at 1200[deg.] C. or higher for at least one hour.

6. A step of introducing a gas containing carbon into the chamber and performing heat treatment, In the bulk region at a depth of 20 μm or more from the substrate surface, the carbon concentration is set to 1×10 １６ atoms / cm 3 6. The method for manufacturing a silicon substrate according to claim 3, further comprising the steps of:

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