Method for manufacturing silicon carbide substrate

Abstract

To provide a method for producing a silicon carbide substrate that is less prone to generate defects.SOLUTION: A method for producing a silicon carbide substrate includes the step (S10) for preparing a silicon carbide substrate having a surface with the total density of deposition of sodium, magnesium, aluminum, potassium, and calcium being less than 1×1012 atoms / cm2 and the step (S20) for polishing the surface of the silicon carbide substrate by chemical mechanical polishing.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a silicon carbide substrate. [Background technology]

[0002] WO 2019 / 111507 (Patent Document 1) describes a process for performing chemical mechanical polishing on a silicon carbide single crystal substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 111507 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a method for manufacturing a silicon carbide substrate capable of suppressing the occurrence of defects. [Means for solving the problem]

[0005] A method for manufacturing a silicon carbide substrate according to the present disclosure includes the following steps: 12 atoms / cm 2 A silicon carbide substrate is provided having a surface that is less than 100 nm in thickness. The surface of the silicon carbide substrate is polished by a chemical mechanical polishing method.

[0006] A method for manufacturing a silicon carbide substrate according to the present disclosure includes the following steps: cleaning a surface of a silicon carbide substrate using an acid solution containing a carboxylic acid, and polishing the cleaned surface of the silicon carbide substrate by chemical mechanical polishing. Effect of the Invention

[0007] Advantageous Effects of Invention According to the present disclosure, it is possible to provide a method for manufacturing a silicon carbide substrate capable of suppressing the occurrence of defects. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a flowchart illustrating a method for manufacturing a silicon carbide substrate in accordance with the present embodiment. [Diagram 2] FIG. 2 is a flowchart for explaining the contents of the preparation process shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described.

[0010] (1) A method for manufacturing a silicon carbide substrate according to an embodiment of the present disclosure includes the following steps: 12 atoms / cm 2 A silicon carbide substrate is provided having a surface that is less than 100 nm in thickness. The surface of the silicon carbide substrate is polished by a chemical mechanical polishing method.

[0011] (2) In the method for manufacturing a silicon carbide substrate according to the above (1), in the step of preparing a silicon carbide substrate, the deposition density of calcium is 1×10 11 atoms / cm 2 It may be less than.

[0012] (3) In the method for manufacturing a silicon carbide substrate according to the above (1) or (2), the step of preparing a silicon carbide substrate further comprises: 12 atoms / cm 2 The method may include cleaning the silicon carbide substrate so that the surface roughness is less than 100 nm.

[0013] (4) In the method for manufacturing a silicon carbide substrate according to the above (3), in the cleaning step, the surface of the silicon carbide substrate may be cleaned with an acid solution.

[0014] (5) In the method for manufacturing a silicon carbide substrate according to the above (4), the acid solution may contain a carboxylic acid.

[0015] (6) In the method for manufacturing a silicon carbide substrate according to the above (5), the acid solution may contain a hydrogen peroxide solution.

[0016] (7) In the method for manufacturing a silicon carbide substrate according to any one of (1) to (6) above, in the polishing step, the silicon carbide substrate may be polished by an amount of 0.5 μm or more and 2 μm or less.

[0017] (8) In the method for manufacturing a silicon carbide substrate according to any one of the above (1) to (7), the abrasive grains used in the polishing step may contain at least one selected from the group consisting of colloidal silica, manganese oxide, and zirconium oxide.

[0018] (9) A method for manufacturing a silicon carbide substrate according to an embodiment of the present disclosure includes the steps of: cleaning a surface of a silicon carbide substrate using an acid solution containing a carboxylic acid; and polishing the cleaned surface of the silicon carbide substrate by a chemical mechanical polishing method.

[0019] (10) In the method for manufacturing a silicon carbide substrate according to the above (9), the acid solution may contain a hydrogen peroxide solution.

[0020] [Details of the embodiment of the present disclosure] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are given the same reference numerals, and the description thereof will not be repeated. In the crystallographic description in this specification, an individual orientation is indicated by [], a collective orientation by <>, an individual plane by (), and a collective plane by {}. In addition, for negative indices, a "-" (bar) is placed before the number in crystallography, but in this specification, a negative sign is placed before the number.

[0021] (Method for manufacturing silicon carbide substrate) A method for manufacturing a silicon carbide substrate according to this embodiment will be described. Fig. 1 is a flowchart for explaining the method for manufacturing a silicon carbide substrate according to this embodiment. Fig. 2 is a flowchart for explaining the contents of the preparation step shown in Fig. 1.

[0022] As shown in FIGS. 1 and 2, the method for manufacturing a silicon carbide substrate according to this embodiment mainly includes a preparing step (S10), a polishing step (S20), and a post-treatment step (S30).

[0023] First, a preparation step (S10) is performed. Specifically, as shown in FIG. 2, the preparation step (S10) mainly includes a substrate preparation step (S11), a cleaning step (S12), and a polishing pretreatment step (S13).

[0024] In the step (S11) of preparing a silicon carbide substrate as a substrate to be subjected to finish polishing, an ingot made of a silicon carbide single crystal of polytype 4H is formed, for example, by a sublimation method. After the ingot is shaped, the ingot is sliced ​​by a wire saw device. As a result, a silicon carbide single crystal substrate (also called a silicon carbide substrate) is cut out from the ingot.

[0025] The silicon carbide substrate is made of, for example, hexagonal silicon carbide of polytype 4H. The silicon carbide substrate has a first main surface and a second main surface opposite to the first main surface. The first main surface is, for example, a surface that is off-angled by 4° or less in the <11-20> direction with respect to the {0001} plane. Specifically, the first main surface may be, for example, a surface that is off-angled by about 4° or less with respect to the (0001) plane. The second main surface may be, for example, a surface that is off-angled by about 4° or less with respect to the (000-1) plane.

[0026] The silicon carbide substrate may be subjected to a chamfering process, a mechanical polishing process, etc., before the cleaning process (S12) described later is performed. Alternatively, in the substrate preparation process (S11), a silicon carbide substrate whose size, thickness, surface roughness, etc. have been adjusted may be purchased.

[0027] Next, a cleaning step (S12) is performed as the second step of the preparation step (S10). In this step (S12), the surface of the silicon carbide substrate is cleaned with an acid solution. The acid solution contains, for example, a carboxylic acid. Examples of the carboxylic acid that can be used include formic acid, acetic acid, oxalic acid, and citric acid. Furthermore, the acid solution may contain hydrogen peroxide. For example, a solution of a mixture of formic acid, hydrogen peroxide, and pure water may be used as the acid solution, or a solution of a mixture of acetic acid, hydrogen peroxide, and pure water may be used as the acid solution.

[0028] The acid solution may be a mixture of formic acid, hydrogen peroxide, and pure water in a volume ratio of formic acid:hydrogen peroxide:pure water=1:1:10. Alternatively, the acid solution may be a mixture of formic acid and pure water in a volume ratio of formic acid:pure water=1:5. In this case, the concentration of the formic acid to be mixed may be, for example, 40 wt%, and the concentration of the hydrogen peroxide to be mixed may be 30 wt%.

[0029] Also, the acid solution may be a mixture of acetic acid, hydrogen peroxide, and pure water in a volume ratio of acetic acid:hydrogen peroxide:pure water=1:1:10. Alternatively, the acid solution may be a mixture of acetic acid and pure water in a volume ratio of acetic acid:pure water=1:5. In this case, the concentration of the acetic acid to be mixed may be, for example, 30 wt%, and the concentration of the hydrogen peroxide to be mixed may be 30 wt%. In the acid solution, the volume ratio of the carboxylic acid to the pure water may be 0.05 to 0.3, or 0.1 to 0.2. In the acid solution, the volume ratio of the hydrogen peroxide to the pure water may be 0.05 to 0.3, or 0.1 to 0.2.

[0030] The acid solution may contain, for example, an inorganic acid. Examples of inorganic acids that can be used include sulfuric acid, hydrofluoric acid, hydrochloric acid, and nitric acid. As the acid solution containing sulfuric acid, a sulfuric acid / hydrogen peroxide mixture (a solution containing sulfuric acid and hydrogen peroxide) may be used. For example, a mixture of sulfuric acid, hydrogen peroxide, and pure water in a volume ratio of sulfuric acid:hydrogen peroxide:pure water=10:1:1 may be used as the sulfuric acid / hydrogen peroxide mixture. In this case, the volume ratio of sulfuric acid to hydrogen peroxide may be 5 or more and 10 or less. The concentration of the sulfuric acid to be mixed may be 70 wt% or more and 98 wt% or less. In addition, when hydrofluoric acid is used as the acid solution, the concentration of hydrofluoric acid may be 20 wt% or more and 50 wt% or less. As the acid solution containing hydrochloric acid and nitric acid, for example, aqua regia may be used.

[0031] In the cleaning step (S12), the surface of the silicon carbide substrate is cleaned with the above-mentioned acid solution, and any specific cleaning method can be adopted. For example, the acid solution may be placed in a quartz or Teflon (registered trademark) container, and the silicon carbide substrate may be immersed in the acid solution. Alternatively, the acid solution may be ejected or dropped onto the surface of the silicon carbide substrate from a nozzle or the like.

[0032] The cleaning time in the cleaning step (S12) may be, for example, 5 minutes or more and 60 minutes or less. The temperature of the acid solution may be, for example, 20° C. or more and 40° C. or less.

[0033] By the cleaning step (S12) using such an acid solution, elements such as sodium (Na), magnesium (Mg), aluminum (Al), potassium (K), and calcium (Ca) are removed from the surface of the silicon carbide substrate. As a result, the total adhesion density of sodium (Na), magnesium (Mg), aluminum (Al), potassium (K), and calcium (Ca) on the surface of the silicon carbide substrate becomes 1×10 12 atoms / cm 2 The method for measuring the adhesion density of the above-mentioned elements will be described later.

[0034] Next, a pre-polishing step (S13) is performed as the third step of the preparation step (S10). In this step (S13), for example, a water washing step is performed to remove the acid solution used in the above-mentioned cleaning step (S12) from the surface of the silicon carbide substrate with pure water. In the water washing step, for example, the silicon carbide substrate may be immersed in pure water in a quartz or Teflon container. Alternatively, the pure water may be ejected or dropped from a nozzle or the like onto the surface of the silicon carbide substrate.

[0035] Furthermore, in the above step (S13), an alkaline cleaning step may be performed to remove foreign matter such as abrasive particles adhering to the surface of the silicon carbide substrate. In this alkaline cleaning step, the surface of the silicon carbide substrate is cleaned with an alkaline solution. As the alkaline solution, for example, a liquid obtained by mixing hydrogen peroxide, tetramethylammonium hydroxide (TMAH), and pure water in a volume ratio of hydrogen peroxide:TMAH:pure water=0.5:1:20 may be used. In the alkaline cleaning step, for example, the silicon carbide substrate may be immersed in the alkaline solution in a quartz or Teflon container. Alternatively, the alkaline solution may be ejected or dropped onto the surface of the silicon carbide substrate from a nozzle or the like.

[0036] In addition, in the step (S13), a water washing step may be performed in which the alkaline solution used in the alkaline cleaning step is removed from the surface of the silicon carbide substrate by pure water. Furthermore, a drying step may be performed in which the pure water used in the water washing step is removed from the surface of the silicon carbide substrate. In the drying step, for example, spin drying may be performed in which the silicon carbide substrate is rotated and dried.

[0037] The silicon carbide substrate thus prepared in the preparation step (S10) has a total adhesion density of sodium (Na), magnesium (Mg), aluminum (Al), potassium (K), and calcium (Ca) on the surface of 1×10 12 atoms / cm 2 In addition, the adhesion density of calcium (Ca) on the surface of the silicon carbide substrate is less than 1×10 11 atoms / cm 2 It is preferable that it is less than 1000 .mu.m.

[0038] Next, a polishing step (S20) is performed as shown in FIG. 1. This step is a so-called finish polishing step, in which chemical mechanical polishing is performed on the silicon carbide substrate. The polishing liquid used in this step (S20) contains abrasive grains and liquid. The abrasive grains are, for example, colloidal silica. As the abrasive grains, for example, manganese oxide or zirconium oxide may be used. The average grain size of the abrasive grains is, for example, 40 nm. The polishing liquid contains, for example, a lubricant, an oxidizing agent, and a dispersing agent. The lubricant is, for example, a sugar such as sucrose or glucose. The lubricant may be, for example, a polyhydric alcohol. The oxidizing agent is, for example, hydrogen peroxide water. The dispersing agent contains, for example, magnesium (Mg).

[0039] The chemical mechanical polishing apparatus used in the polishing step (S20) may have an arbitrary configuration. For example, the chemical mechanical polishing apparatus may mainly have a polishing cloth provided on a platen, a polishing plate, a rotating support member, and a polishing liquid supply unit. The silicon carbide substrate is attached to the polishing plate. The polishing plate is placed on the polishing cloth. The second main surface of the silicon carbide substrate faces the polishing plate. The first main surface of the silicon carbide substrate faces the polishing cloth. The polishing cloth is, for example, a suede polishing cloth. The polishing liquid supply unit supplies the polishing liquid. The polishing liquid supplied from the polishing liquid supply unit is supplied between the first main surface of the silicon carbide substrate and the polishing cloth.

[0040] The polishing plate on which the silicon carbide substrate is attached is connected to a rotating support member. The rotating support member is rotatable in a rotational direction around a rotation axis extending in a direction perpendicular to the surface of the polishing cloth. When the rotating support member rotates around the rotation axis, the silicon carbide substrate rotates in contact with the polishing cloth. The rotation speed of the rotating support member is, for example, 60 rpm. The surface plate on which the polishing cloth is provided is also rotatable. The rotation speed of the surface plate is, for example, 60 rpm. The processing surface pressure for pressing the silicon carbide substrate against the polishing cloth is, for example, 300 g / cm. 2 The polishing time is, for example, 5 hours. The amount of the silicon carbide substrate polished in the polishing step (S20) may be not less than 0.5 μm and not more than 2 μm.

[0041] Next, as shown in FIG. 1, a post-treatment step (S30) is performed. In this step, a cleaning step is performed to remove the polishing liquid used in the polishing step (S20) from the surface of the silicon carbide substrate. In the cleaning step, the surface of the silicon carbide substrate is cleaned using, for example, an alkaline solution. Thereafter, a water washing step and a drying step are performed. In this manner, a silicon carbide substrate used for forming a semiconductor device is obtained.

[0042] (Method for measuring adhesion density of impurities) The adhesion density of elements on the surface of the silicon carbide substrate described above can be measured by the following method. First, acid is dropped onto the entire surface (first main surface) of the silicon carbide substrate using a horizontal substrate inspection device. As a result, elements such as sodium (Na), magnesium (Mg), aluminum (Al), potassium (K), and calcium (Ca) that are attached to the first main surface are taken up by the acid. Next, the entire amount of acid containing the above elements is recovered from the entire surface of the first main surface. The sample preparation is performed, for example, in a class 10 clean draft installed in a class 100 clean room.

[0043] The adhesion density of the above-mentioned elements can be measured by ICP-MS (Inductively Coupled Plasma Mass Spectrometry). For example, an ICP-MS8800 manufactured by Agillent can be used as a measuring device. The mass (ng) of the elements obtained by the measurement is divided by the atomic weight of each element to convert it into the number of moles, and then multiplied by Avogadro's number to convert it into the number of atoms. Next, the number of atoms is divided by the area of ​​the first main surface to convert it into the number of atoms per unit area. In this way, the adhesion density of the above-mentioned elements on the surface of the silicon carbide substrate can be measured.

[0044] (Action and effect) A method for manufacturing a silicon carbide substrate according to an embodiment of the present disclosure includes the following steps: 12 atoms / cm 2 A silicon carbide substrate having a surface that is less than 100 nm in diameter is prepared (step (S10)). The surface of the silicon carbide substrate is polished by chemical mechanical polishing (step (S20)).

[0045] In this manner, damage such as scratches can be sufficiently removed from the surface of the silicon carbide substrate polished by chemical mechanical polishing, and as a result, even when an epitaxial film is formed on the surface of the silicon carbide substrate, the occurrence of defects caused by the damage can be suppressed.

[0046] Here, in the silicon carbide substrate, there are cases where scratches remain on the surface even after the chemical mechanical polishing process (finish polishing process). When such scratches exist, when a silicon carbide epitaxial layer is formed on the surface of the silicon carbide substrate, defects due to the scratches also occur in the epitaxial layer.

[0047] As a result of investigating the cause of the scratches after the finish polishing step as described above, the inventors found that the scratches are caused by variations in the amount of polishing in the finish polishing step. That is, scratches (scratches) that occurred in a previous step such as a mechanical polishing step are present on the surface of the silicon carbide substrate before the finish polishing. If the amount of polishing in the finish polishing step is as designed, the scratches are almost completely removed. However, in reality, there are variations in the amount of polishing in the finish polishing step, and there are cases where the amount of polishing is insufficient and the scratches cannot be completely removed.

[0048] It is conceivable to increase the design value of the polishing amount to an extent that such variations in the polishing amount can be absorbed. However, when the polishing amount is increased in this way, the polishing rate in the finish polishing step is generally small, so the time required for the step increases. As a result, the manufacturing cost of the silicon carbide substrate increases, so it is not realistic to increase the design value of the polishing amount.

[0049] Therefore, the inventors have studied the cause of the variation in the polishing amount in the final polishing process and found that the elements attached to the surface of the silicon carbide substrate to be final polished have a large effect on the polishing amount in the final polishing process. That is, if elements such as sodium (Na), magnesium (Mg), aluminum (Al), potassium (K), and calcium (Ca) (especially elements such as light metals that become monovalent or divalent cations) are attached to the surface (polished surface) of the silicon carbide substrate before the final polishing process in which chemical mechanical polishing is performed, these elements are firmly bonded to the surface of the silicon carbide substrate. Then, in the initial stage of the final polishing process, the above elements bonded to the surface of the silicon carbide substrate act like a mask, and the surface of the silicon carbide substrate is not polished efficiently. Furthermore, since these elements are highly reactive, they react with chemical components in the polishing agent for chemical mechanical polishing before the silicon carbide substrate. As a result, these elements inhibit the chemical reaction of the polishing agent with the silicon carbide substrate. As a result, the silicon carbide substrate is not sufficiently polished in the initial stage of the finish polishing step, giving rise to a problem that the final polishing amount of the silicon carbide substrate cannot be ensured.

[0050] Based on the above findings, the inventors have attempted to reduce the adhesion density of elements such as sodium on the surface of the silicon carbide substrate before the finish polishing step, thereby progressing the polishing of the silicon carbide substrate from the early stage of the finish polishing step. As a result, they have come up with a method for manufacturing a silicon carbide substrate in which the polishing amount can be sufficiently increased (the variation in the polishing amount can be suppressed) and scratches and other damage can be sufficiently removed from the surface of the silicon carbide substrate by the finish polishing step.

[0051] In the method for manufacturing a silicon carbide substrate, in the step (S10) of preparing a silicon carbide substrate, a deposition density of calcium (Ca) on a surface of the silicon carbide substrate is set to 1×10 11 atoms / cm 2 Here, since calcium in particular adheres firmly to the surface of the silicon carbide substrate, by limiting the calcium adhesion density as described above, it is possible to suppress inhibition of polishing of the silicon carbide substrate by chemical mechanical polishing due to the calcium.

[0052] In the method for manufacturing a silicon carbide substrate, the step (S10) of preparing a silicon carbide substrate includes a step of preparing a silicon carbide substrate in such a manner that the total deposition density of sodium, magnesium, aluminum, potassium, and calcium on the surface of the silicon carbide substrate is 1×10 12 atoms / cm 2 The method may include a step (S12) of cleaning the silicon carbide substrate so that the surface of the silicon carbide substrate has a viscosity of less than 1000 nm. In the cleaning step (S12), the surface of the silicon carbide substrate may be cleaned with an acid solution.

[0053] In this case, since the above-mentioned elements such as calcium are dissolved in the acid solution, these elements can be effectively removed from the surface of the silicon carbide substrate.

[0054] In the method for manufacturing a silicon carbide substrate, the acid solution may contain a carboxylic acid. By using the acid solution containing a carboxylic acid, elements such as calcium can be effectively removed from the surface of the silicon carbide substrate.

[0055] In the method for manufacturing a silicon carbide substrate, the acid solution may contain hydrogen peroxide, which can further enhance the effect of removing elements such as calcium from the surface of the silicon carbide substrate by the acid solution.

[0056] In the method for manufacturing a silicon carbide substrate, the polishing amount of the silicon carbide substrate may be 0.5 μm or more and 2 μm or less in the polishing step (S20). In this case, flaws such as scratches formed on the surface of the silicon carbide substrate before the polishing step (S20) can be sufficiently removed.

[0057] In the method for manufacturing a silicon carbide substrate, the abrasive grains used in the polishing step (S20) may include at least one selected from the group consisting of colloidal silica, manganese oxide, and zirconium oxide, which can facilitate polishing of the silicon carbide substrate in the polishing step (S20).

[0058] A method for manufacturing a silicon carbide substrate according to an embodiment of the present disclosure includes the following steps: A surface of a silicon carbide substrate is cleaned using an acid solution containing a carboxylic acid (step (S12)). The cleaned surface of the silicon carbide substrate is polished by a chemical mechanical polishing method (step (S20)).

[0059] In this way, elements that inhibit polishing by chemical mechanical polishing, such as calcium, can be removed by the acid solution from the surface of the silicon carbide substrate before it is polished by chemical mechanical polishing. Therefore, the polishing amount in the polishing step of the silicon carbide substrate can be sufficiently secured, and the variation in the polishing amount can be suppressed. Therefore, scratches and other damage can be sufficiently removed from the surface of the silicon carbide substrate. As a result, even when an epitaxial film is formed on the surface of the silicon carbide substrate, the occurrence of defects due to the damage can be suppressed.

[0060] In the method for manufacturing a silicon carbide substrate, the acid solution may contain hydrogen peroxide, which can further enhance the effect of removing elements such as calcium from the surface of the silicon carbide substrate by the acid solution. EXAMPLES

[0061] (Sample preparation) First, silicon carbide substrates according to Sample 1 to Sample 5 were prepared. The silicon carbide substrates according to Sample 1 to Sample 4 were used as Examples. The silicon carbide substrate according to Sample 5 was used as a Comparative Example. For each of Sample 1 to Sample 5, 50 silicon carbide substrates were prepared.

[0062] The silicon carbide substrates of Samples 1 to 5 each had a diameter of 150 mm, a thickness of 340 μm to 370 μm, and a polytype of 4H. The first main surface to be polished was a surface offset by 4° in the <11-20> direction with respect to the {0001} plane.

[0063] (Treatment for each sample) A cleaning process using an acid solution was carried out for Samples 1 to 4. On the other hand, a cleaning process using an acid solution was not carried out for Sample 5. The conditions (acid solution conditions) used in the cleaning process for each sample are shown in Table 1.

[0064] [Table 1]

[0065] Conditions 1 to 4 in Table 1 are the acid solution conditions in the cleaning process for Samples 1 to 4, respectively. Table 1 shows the type of acid (A), the type of additive (B), and the volume ratio (mixture ratio) of the acid (A), additive (B), and pure water in the acid solution under each condition. The cleaning process was carried out by immersing the silicon carbide substrates for Samples 1 to 4 in the acid solution under each condition shown in Table 1. The temperature of the acid solution in the cleaning process was 30°C, and the immersion time was 30 minutes. Note that Condition 5, which is the condition for Sample 5, is indicated as "no cleaning" since the cleaning process was not carried out.

[0066] For the silicon carbide substrates of Samples 1 to 4, a water washing step was carried out after the above-mentioned cleaning step.

[0067] Thereafter, an alkaline cleaning process was carried out on the silicon carbide substrates of Samples 1 to 5 to remove foreign matter such as abrasive particles from the surfaces. In this alkaline cleaning process, the surfaces of the silicon carbide substrates were cleaned with an alkaline solution. The alkaline solution used was a mixture of hydrogen peroxide, tetramethylammonium hydroxide (TMAH), and pure water in a volume ratio of hydrogen peroxide:TMAH:pure water=0.5:1:20. In the alkaline cleaning process, the silicon carbide substrates were immersed in the alkaline solution held in a container. The temperature of the alkaline solution in the alkaline cleaning process was 28°C, and the immersion time was 30 minutes.

[0068] Next, a water washing process was performed on the silicon carbide substrates of Samples 1 to 5 to remove the alkaline solution from the surfaces. Then, a drying process was performed to remove the pure water used in the water washing process from the surfaces of the silicon carbide substrates. In the drying process, spin drying was performed to rotate and dry the silicon carbide substrates.

[0069] Next, chemical mechanical polishing (finish polishing) was performed on the first main surfaces of the silicon carbide substrates of Samples 1 to 5. The polishing liquid used in the chemical mechanical polishing contains abrasive grains and liquid. The abrasive grains are colloidal silica. The average particle size of the abrasive grains is 40 nm. The polishing liquid contains a lubricant, an oxidizing agent, and a dispersing agent. The lubricant is sucrose. The oxidizing agent is hydrogen peroxide. The dispersing agent contains magnesium (Mg).

[0070] In the chemical mechanical polishing, the rotation speed of the silicon carbide substrate pressed against the polishing cloth was 60 rpm. The surface pressure for pressing the silicon carbide substrate against the polishing cloth was 300 g / cm. 2 The polishing time was 5 hours.

[0071] Thereafter, a cleaning process was carried out to remove the polishing liquid used in the above-mentioned chemical mechanical polishing from the surface of the silicon carbide substrate. In the cleaning process, the surface of the silicon carbide substrate was cleaned using an alkaline solution. Then, a water rinsing process and a drying process were carried out.

[0072] Next, a hydrogen treatment was performed as a pretreatment on the surfaces (first main surfaces) of the silicon carbide substrates of Samples 1 to 5, and then a silicon carbide epitaxial layer was formed.

[0073] In the hydrogen treatment, first, the first main surface of the silicon carbide substrate was subjected to hydrogen treatment while the silicon carbide substrate was heated. Specifically, the silicon carbide substrate was placed in a treatment chamber. Next, the temperature of the silicon carbide substrate was increased to about 1630°C. Next, hydrogen gas was introduced into the treatment chamber. The flow rate of the hydrogen gas was adjusted to 100 slm. As a result, the first main surface of the silicon carbide substrate was etched. The etching amount was about 50 nm to 300 nm.

[0074] Next, an epitaxial growth process was carried out to form a silicon carbide epitaxial layer. In the epitaxial growth process, the processing chamber was first heated to about 1630°C. Next, a mixed gas containing silane, propane, ammonia, and hydrogen was introduced into the processing chamber. Specifically, the flow rate of the silane gas was adjusted to 115 sccm. The flow rate of the propane gas was adjusted to 57.6 sccm. The flow rate of the ammonia gas was adjusted to 2.5 x 10 -2 The flow rate of the hydrogen gas was adjusted to 100 slm. By introducing the mixed gas into the processing chamber, a silicon carbide epitaxial layer was formed by epitaxial growth on the first main surface of the silicon carbide substrate. The thickness of the silicon carbide epitaxial layer was 10 μm.

[0075] (measurement) Element Density: The deposition amount (deposition density) of elements such as sodium on the first main surface was measured immediately before chemical mechanical polishing for each of the silicon carbide substrates according to the above-mentioned Samples 1 to 5. ICP-MS was used as the measurement method.

[0076] Amount of polishing by chemical mechanical polishing (finish polishing): The amount of polishing caused by chemical mechanical polishing was measured by measuring the thickness of the silicon carbide substrates of Samples 1 to 5 before and after chemical mechanical polishing. The thickness of the silicon carbide substrate was measured using a spectral interference laser displacement meter SF-80 manufactured by Keyence Corporation.

[0077] Defect (scratch) occurrence rate after chemical mechanical polishing (finish polishing): The incidence of defects (scratches) was measured for silicon carbide substrates according to Samples 1 to 5 after the above-mentioned chemical mechanical polishing (finish polishing). The incidence of defects was measured by scanning the entire surface of the silicon carbide substrate using SICA6X manufactured by Lasertec Corporation. Among the defects detected as a result, groove-shaped defects with a length of 5 μm or more and a width of 1 μm to 10 μm were counted as the above-mentioned defects (scratches). The incidence of defects (scratch incidence) is the ratio of the number of silicon carbide substrates in which the above-mentioned defects (scratches) were detected among 50 silicon carbide substrates for each sample. The incidence of scratches (%) was calculated by the formula: (number of silicon carbide substrates in which defects (scratches) were detected)÷50×100(%).

[0078] (result) The results of the above measurements are shown in Table 2.

[0079] [Table 2]

[0080] Table 2 shows the measurement results of the adhesion density (adhesion amount) of sodium (Na), magnesium (Mg), aluminum (Al), potassium (K), and calcium (Ca) for the silicon carbide substrates of each sample, the polishing amount in chemical mechanical polishing (finish polishing), and the defect occurrence rate (scratch occurrence rate) after finish polishing. Note that the polishing amount is shown as a relative value with the polishing amount of the silicon carbide substrate of sample 1 set as 1. Also, the above-mentioned measurement results of the adhesion amount and the polishing amount are shown as average values ​​for 50 silicon carbide substrates of each sample.

[0081] As shown in Table 2, the adhesion density (amount of adhesion) of sodium on the surface of the silicon carbide substrate of Samples 1 to 5 is 38×10 9 atoms / cm 2 , 14×10 9 atoms / cm 2 , below detection limit, 10×109 atoms / cm 2 , 42×10 9 atoms / cm 2 The adhesion density (amount of adhesion) of magnesium on the surface of the silicon carbide substrate for Samples 1 to 5 was below the detection limit, 2×10 9 atoms / cm 2 , below detection limit, 82×10 9 atoms / cm 2 , 35×10 9 atoms / cm 2 It was.

[0082] The adhesion density (amount) of aluminum on the surface of the silicon carbide substrate of Samples 1 to 5 is 11×10 9 atoms / cm 2 , 11×10 9 atoms / cm 2 , below detection limit, 400×10 9 atoms / cm 2 , 510×10 9 atoms / cm 2 The deposition density (amount) of potassium on the surface of the silicon carbide substrate for Samples 1 to 5 was 1×10 9 atoms / cm 2 , below detection limit, 73×10 9 atoms / cm 2 , below the detection limit, below the detection limit.

[0083] The calcium deposition density (amount of deposition) on the surface of the silicon carbide substrate of Samples 1 to 5 is 5×10 9 atoms / cm 2 , 8×10 9 atoms / cm 2 , 84×10 9 atoms / cm 2 , 260×10 9 atoms / cm 2 , 640×10 9 atoms / cm 2The total adhesion density (total adhesion amount) of the above-mentioned elements on the surfaces of the silicon carbide substrates of Samples 1 to 5 was 55×10 9 atoms / cm 2 , 35×10 9 atoms / cm 2 , 157×10 9 atoms / cm 2 , 752×10 9 atoms / cm 2 , 1227×10 9 atoms / cm 2 It was.

[0084] The polishing amounts (relative values) in the final polishing of the silicon carbide substrates of Samples 1 to 5 were 1.0, 1.2, 0.8, 0.7, and 0.4. The defect occurrence rates after the final polishing of the silicon carbide substrates of Samples 1 to 5 were 0%, 0%, 2.5%, 2.8%, and 18.6%. The defect occurrence rates in the silicon carbide epitaxial layers showed almost the same tendency as the defect occurrence rates after the above-mentioned polishing.

[0085] As can be seen from Table 2, the total adhesion density of elements such as sodium is 1×10 12 atoms / cm 2 For Samples 1 to 4, where the total adhesion density of the above elements is less than 1×10, the polishing amount is sufficiently large, so the defect occurrence rate is relatively small. In addition, for Samples 1 to 4, the variation in the polishing amount is also small. On the other hand, for Sample 5, the total adhesion density of the above elements is less than 1×10 12 atoms / cm 2 , the polishing amount is relatively small and the occurrence rate of defects is relatively large.

[0086] From the above results, it was found that the total adhesion density of sodium (Na), magnesium (Mg), aluminum (Al), potassium (K), and calcium (Ca) on the silicon carbide substrate was 1×10 12 atoms / cm 2It was shown that by performing chemical mechanical polishing after setting the polishing pressure at less than 1000 nm, damages and defects such as scratches can be sufficiently removed from the surface of the silicon carbide substrate. Furthermore, it was shown that even when an epitaxial film is formed on the surface of the silicon carbide substrate, the occurrence of defects due to the damage can be suppressed.

[0087] The embodiments disclosed herein are illustrative in all respects and should not be considered as limiting. The basic scope of the present disclosure is indicated by the claims rather than the above-described embodiments, and it is intended to include all modifications within the scope of the claims and the meaning equivalent thereto.

Claims

1. The total adhesion density of sodium, magnesium, aluminum, potassium, and calcium is 1.0 x 10 １２ atoms / cm ２ providing a silicon carbide substrate having a surface that is less than and polishing the surface of the silicon carbide substrate by chemical mechanical polishing.

2. In the step of preparing a silicon carbide substrate, the calcium deposition density is 1×10 １１ atoms / cm ２ The method for manufacturing a silicon carbide substrate according to claim 1 , wherein the thickness of the silicon carbide substrate is less than 1 mm.

3. The step of preparing a silicon carbide substrate includes: １２ atoms / cm ２ The method for manufacturing a silicon carbide substrate according to claim 1 or 2, comprising the step of cleaning the silicon carbide substrate so that a surface roughness of the silicon carbide substrate is less than 100 nm.

4. The method for manufacturing a silicon carbide substrate according to claim 3 , wherein in said cleaning step, said surface of said silicon carbide substrate is cleaned with an acid solution.

5. The method for manufacturing a silicon carbide substrate according to claim 4 , wherein the acid solution contains a carboxylic acid.

6. The method for manufacturing a silicon carbide substrate according to claim 5 , wherein the acid solution further contains a hydrogen peroxide solution.

7. 7. The method for manufacturing a silicon carbide substrate according to claim 1, wherein in said polishing step, a polishing amount of said silicon carbide substrate is equal to or greater than 0.5 μm and equal to or less than 2 μm.

8. 8. The method for manufacturing a silicon carbide substrate according to claim 1, wherein abrasive grains used in said polishing step include at least one selected from the group consisting of colloidal silica, manganese oxide, and zirconium oxide.

9. cleaning a surface of the silicon carbide substrate with an acid solution containing a carboxylic acid; and polishing the cleaned surface of the silicon carbide substrate by a chemical mechanical polishing method.

10. The method for manufacturing a silicon carbide substrate according to claim 9 , wherein the acid solution contains hydrogen peroxide water.

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