JP5277722B2 - Polishing method of silicon carbide single crystal wafer surface - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an effective method of obtaining a surface of high quality by removing a layer deteriorated by processing from the surface of a silicon carbide single crystal wafer which has been rough-lapped for chemical stability, and then finish polishing. <P>SOLUTION: The polishing method efficiently provides a surface of high quality with no deteriorated layer by processing that occurs after diamond mechanical polishing, by oxidizing the surface of silicon carbide single crystal wafer that has been rough-lapped in diamond mechanical polishing, and then removing an oxide film on the surface by finish polishing. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for polishing a single crystal wafer, and more particularly, to a method for polishing a surface of a high-quality, large-sized silicon carbide single crystal wafer that is a base material for a substrate wafer such as a blue light emitting diode or an electronic device.

  Silicon carbide (SiC) has attracted attention as an environmentally resistant semiconductor material because of its physical and chemical properties such as excellent heat resistance and mechanical strength, and resistance to radiation. In recent years, the demand for SiC single crystal wafers is increasing as a substrate wafer for short wavelength optical devices from blue to ultraviolet, high frequency high voltage electronic devices, and the like. However, a crystal growth technique that can stably supply a high-quality SiC single crystal having a large area on an industrial scale has not yet been established. Therefore, practical use of SiC has been hindered despite the semiconductor materials having many advantages and possibilities as described above.

Conventionally, on a laboratory scale scale, for example, a SiC single crystal was grown by a sublimation recrystallization method (Rayleigh method) to obtain a SiC single crystal of a size capable of manufacturing a semiconductor element. However, with this method, the area of the obtained single crystal is small, and it is difficult to control its size and shape with high accuracy. Also, it is not easy to control the crystal polymorphism and impurity carrier concentration of SiC. In addition, a cubic SiC single crystal is grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using a chemical vapor deposition method (CVD method). With this method, a single crystal with a large area can be obtained, but only a SiC single crystal containing many defects (up to 10 ⁷ cm ^-2 ) can be grown due to the lattice mismatch of about 20% with the substrate. It is not easy to obtain a high-quality SiC single crystal.

  In order to solve these problems, an improved Rayleigh method for performing sublimation recrystallization using a SiC single crystal {0001} wafer as a seed crystal has been proposed (Non-patent Document 1). Since this method uses a seed crystal, the nucleation process of the crystal can be controlled, and the atmospheric pressure is controlled to about 100 Pa to 15 kPa with an inert gas to control the crystal growth rate with good reproducibility. it can. At present, SiC single crystal ingots having a diameter of 2 inches (50 mm) to 4 inches (100 mm) can be grown, processed into wafers, and used for various devices.

  When processing into a wafer, the grown ingot is processed into a cylindrical shape with a desired diameter, that is, 2 inches (50 mm) to 4 inches (100 mm), and then sliced into a wafer, and further surface-treated The process of polishing is taken.

  In surface polishing, SiC is very hard, so the surface is mechanically polished using a harder diamond or the like as an abrasive to create a flat surface. However, since many crystal defects such as dislocations are generated on the SiC wafer surface polished with diamond abrasive grains, residual stress and mechanical distortion (displacement of molecules from the position that should originally occupy) on the surface, that is, processing alteration If the layer remains, it is difficult to produce a semiconductor device with good performance on the surface. If a semiconductor element is formed on this surface, there is a high possibility that the element will not operate normally or that the performance will deteriorate significantly even if it operates.

Therefore, for example, as described in Patent Document 1 or Patent Document 2, while oxidizing the SiC wafer surface with hydrogen peroxide, manganese dioxide, manganese trioxide, etc., with chromium oxide abrasive grains, The device has been devised such as finish polishing.
JP 2001-205555 JP 2006-121111 JP Yu. M. Tairov and VF Tsvetkov, Journal of Crystal Growth, vol.52 (1981) pp.146-150

  As described above, only mechanical polishing with hard abrasive grains such as diamond leaves a work-affected layer on the SiC single crystal wafer surface, so a high-quality wafer surface suitable for semiconductor device fabrication cannot be obtained. When the work-affected layer is removed using chromium oxide or the like, chromium remains chemically bonded to the polished surface, which may cause surface metal contamination. Further, by using an oxidizing agent, the surface of the polishing apparatus exposed to the oxidizing agent is also oxidized, leading to deterioration of the apparatus in the long term. Further, the oxidizing agents manganese dioxide and manganese trioxide may cause surface metal contamination.

  Therefore, an object of the present invention is to provide a method for polishing a surface of a silicon carbide single crystal wafer that obtains a high-quality surface without causing the above-described surface metal contamination or deterioration of a polishing apparatus.

  In order to realize a high-quality large-diameter SiC single crystal wafer surface that can withstand the fabrication of high-performance semiconductor elements, the work-affected layer at the bottom of the SiC substrate surface is oxidized to a soft material without causing metal contamination. The peeling method is effective. Therefore, the present inventors conducted extensive comparative examination, observation, and analysis on the polishing conditions, and as a result, oxidized the surface of the silicon carbide single crystal wafer that was rough polished (lapped), and then oxidized the surface by finish polishing (polish). The inventors have found that removing the film is effective for removing the work-affected layer, and have completed the present invention.

That is, the present invention
(1) The surface of the silicon carbide single crystal wafer whose orientation on the wafer surface is inclined 4 ° from the Si (0001) plane to the (1-210) direction is roughly polished by mechanical polishing , and then thermally oxidized to form A method for polishing a surface of a silicon carbide single crystal wafer, wherein the oxide film is removed by finish polishing,
( 2 ) The method for polishing a silicon carbide single crystal wafer surface according to ( 1 ), wherein the thermal oxidation of the silicon carbide single crystal wafer is thermal oxidation in an oxygen gas atmosphere containing moisture,
( 3 ) The silicon carbide single crystal according to (1) or (2) , wherein the work-affected layer formed on the surface layer portion of the silicon carbide single crystal wafer is oxidized by rough polishing, and the oxidized work-affected layer is removed by finish polishing. Polishing method of crystal wafer surface,
( 4 ) The polishing method for a silicon carbide single crystal wafer surface according to any one of (1) to ( 3 ), wherein the polishing agent used in finish polishing is a polishing agent having a Knoop hardness between silicon oxide and silicon carbide.
( 5 ) The polishing method for a silicon carbide single crystal wafer surface according to ( 4 ) , wherein the abrasive is one or more selected from silica, garnet, zirconia and alumina.
It is.

  According to the polishing method of the present invention, the work-affected layer on the surface portion of the SiC substrate is oxidized and changed to soft silicon oxide without causing metal contamination, and the silicon oxide layer is removed to remove the silicon oxide layer. The SiC single crystal wafer surface does not have a damaged damaged layer of SiC, and the surface irregularity is as small as 0.3 nm or less, and a high quality surface can be obtained stably. Furthermore, it can peel and remove efficiently by using the abrasive | polishing agent located in the middle of a silicon oxide and silicon carbide.

The polishing mechanism in the present invention will be described. In the polishing process of the silicon carbide single crystal wafer surface, the surface after rough polishing (lapping) is mirror-like and flat, but a work-affected layer remains under the surface, and if it is left as it is, a semiconductor element with good performance is produced on the surface. Have difficulty. Therefore, after rough polishing, the work-affected layer below the surface is oxidized and changed to SiO _x having the same hardness as silica. As a method for oxidizing the surface, there is a method in which the surface is exposed to an oxidant. However, silicon carbide single crystal is not appropriate because oxidant molecules do not diffuse below the surface. In addition, the method of oxidizing oxygen ions on the surface of a silicon carbide single crystal wafer and oxidizing it is not suitable because the ions further damage the surface. Therefore, in order to effectively oxidize the work-affected layer after rough polishing without leaving any damage below the surface, it is best to thermally oxidize the surface.

Thermal oxidation of the SiC wafer surface can be easily realized by heating the SiC wafer in an atmospheric oxygen atmosphere containing moisture. As the atmospheric gas, wetO ₂ obtained by bubbling oxygen gas into water is used. By supplying wetO ₂ to a SiC wafer heated in an electric furnace in an atmospheric pressure atmosphere, the SiC wafer is constantly exposed to wetO ₂ and the surface portion including the work-affected layer under the SiC wafer surface is oxidized. . Since there is no particular strict limitation in this thermal oxidation process, the atmospheric pressure that can be easily realized is the best mode for the atmosphere. In other words, the SiC wafer is heated by a heater in an open quartz tube, and the atmosphere gas is heated by putting the oxygen gas supplied from the gas cylinder in hot water and adding wet moisture to wetO ₂ in the SiC wafer. It is supplied to the quartz tube and then diffused into the atmosphere. The gas flow rate is arbitrarily selected within the range of 1.7 × 10 ^{−4 to} 1.7 × 10 ⁻¹ Pa · m ³ / sec, and it is not necessary to use ultrapure water as hot water. Warm normal tap water to 40 to 100 ° C. It is the best form to use. The meaning of warming is to prevent the temperature of the SiC wafer from being lowered by supplying wetO ₂ to the quartz tube and unnecessary thermal gradients from being generated in the heating furnace. A higher temperature for heating the SiC wafer is desirable because it promotes oxidation, but if it is too high, the quartz tube may be softened and deformed. Accordingly, the best mode is a temperature range of 800 ° C. or higher and lower than 1400 ° C., desirably 1000 ° C. or higher and lower than 1200 ° C.

From the viewpoint of hardness, SiC has a Knoop hardness of 2500 (modified Mohs hardness of 13), alumina has a Knoop hardness of 2100 (modified Mohs hardness of 12), zirconia has a modified Mohs hardness of 11, and garnet has a modified Mohs hardness of 10. The Knoop hardness of silica is 750-820 (modified Mohs hardness is 5 (fused quartz) -6 (crystal)), and alumina, zirconia, garnet, and silica are much softer than SiC, so alumina, zirconia, garnet It is difficult to mechanically polish SiC with silica. In the present invention, the surface of SiC wafer is oxidized to change the surface SiC to SiO _x having a hardness equivalent to that of silica, thereby enabling efficient finish polishing. In other words, SiC C is oxidized to CO ₂ and desorbed from the SiC surface, and SiC Si remains on the surface in the form of SiO _x . By mechanically polishing and removing this SiO _x with alumina, zirconia, garnet, and silica, the surface of SiC is efficiently finish-polished and the work-affected layer is removed. In the finish polishing method of the present invention, since alumina, zirconia, garnet, and silica are softer than SiC, a work-affected layer does not remain on the surface of the SiC single crystal after the removal of SiO _x . Note that, when final polishing is performed with SiC abrasive grains, a damaged layer may be newly formed on the polished wafer surface, so SiC abrasive grains are not suitable. On the other hand, the oxidized work-affected layer can also be removed by using an abrasive in which at least two of alumina, zirconia, garnet, and silica are mixed.

  Regarding the conditions of alumina, zirconia, garnet, and silica abrasive grains, the shape is not particularly limited as long as it is a normal shape close to a sphere. There is no particular limitation on the particle size, and there is no problem using a commercial product having an average particle size in the range of 10 to 100 nm.

In the final polishing, there is no particular limitation on using a buff sold as a polishing cloth. Further, since there is no particular limitation on the relative speed between the wafer and the polishing pad, the preferable rotation condition range of the polishing surface plate is determined by the equipment capacity on the polishing apparatus side, and there is no problem. As a common sense example, there is no problem in the range of about 10 to 200 rpm. With respect to the polishing surface pressure during polishing, a larger value is advantageous because polishing efficiency increases. However, since a large polishing surface pressure imposes a load on the apparatus, it is desirable that the polishing surface pressure be small from that viewpoint. In the present invention, it has been confirmed that the surface can be polished even with a slight polishing surface pressure of about 0.01 kg / cm ^2, but polishing is performed with a large polishing surface pressure so that an excessive load is not applied to the apparatus in order to improve efficiency. The surface pressure applied in the present invention, it is widespread valid from slight polishing surface pressure of about 0.01 kg / cm ² to a large pressure of about 3.0 kg / cm ² is confirmed. More preferably, a range suitable for the apparatus configuration is good. It is more preferable that the apparatus is configured with a surface pressure in the range of 0.05 to 0.2 kg / cm ^{2 because} the polishing efficiency is not lowered and the mechanical apparatus load is not excessive.

  The amount of the work-affected layer generated by lapping depends on various conditions such as the size of the abrasive grains used in the lapping and the pressure during polishing, and the thickness of the work-affected layer can be measured by TEM observation of the wafer cross section. . That is, in the “damaged SiC layer”, SiC molecules are regularly arranged at the positions where they should be, and therefore a uniform bright image can be obtained by TEM observation. On the other hand, the “work-affected layer” has many crystal defects such as dislocations, and the TEM electron beam is scattered because the SiC molecules are shifted from the positions that should be originally occupied. Become a statue. The thickness of the work-affected layer can be estimated by how dark the TEM image is in the depth direction from the outermost surface. However, since it is difficult to accurately estimate the thickness of the work-affected layer in a non-destructive manner, a work-affected layer with a thickness equivalent to the past is generated when polished under the same conditions as the past lapping conditions during TEM observation. Assume that It should be noted that the thickness of the work-affected layer that can be estimated by TEM observation is the data of the observed part, and the entire wafer has a part with a thinner or thicker work-affected layer than the part observed by TEM. It is. Therefore, in order to completely remove the work-affected layer from the entire wafer surface, the thickness for oxidizing the surface is set to be thicker than the work-affected layer. Empirically, if the thickness of the work-affected layer estimated by TEM observation is oxidized twice, the work-affected layer is completely oxidized. The means for rough polishing (lapping) is not particularly limited, and examples thereof include mechanical polishing that is usually performed such as polishing using diamond abrasive grains.

Hereinafter, the present invention will be described with reference to examples.
First, the example which implemented this invention using the colloidal silica slurry is demonstrated. The SiC wafer is a 4H-SiC single crystal wafer having a diameter of 4 inches (100 mm), and the orientation of the wafer surface is inclined 4 ° in the (1-210) direction from the Si (0001) plane.

  The surface state of the SiC wafer before finish polishing according to the present invention was mechanically polished with diamond free abrasive grains, and the unevenness on the wafer surface was Ra = 0.8 nm as measured by AFM. The thickness of the work-affected layer was about 15 nm as evaluated by cross-sectional TEM. The surface roughness Ra is an arithmetic average roughness based on JIS B0601: 2001.

As shown in FIG. 1, oxygen gas supplied from a general-purpose oxygen cylinder is immersed in hot water heated to 80 ° C. to produce wetO _2, which is supplied to a quartz tube that is heated in a SiC wafer in an electric furnace. The flow rate was approximately 1.7 × 10 ⁻³ Pa · m ³ / sec. The furnace temperature was 1100 ° C. and heated for 2 hours. As a result, the work-affected layer under the SiC wafer surface generated in the rough polishing process was all oxidized. That is, an oxide film having a thickness of about 20 nm was formed on the Si surface side surface of the wafer, and an oxide film having a thickness of about 200 nm was formed on the C surface side surface. Therefore, all the work-affected layers are oxidized.

The Si surface of this wafer was pressed against the polishing surface plate with a polishing surface pressure of 0.2 kg / cm ² and polished by rotating the polishing surface plate at 40 rpm. The abrasive was a slurry containing a colloidal silica solid content of 20 mass%, and the pH was adjusted to a weak alkali (pH˜10). The slurry was fed by a roller pump at a rate of 1 liter per hour. The slurry discharged from the lower part of the polishing machine was recovered and circulated and supplied again to the polishing platen with a roller pump. The polishing surface plate is a buffing machine with a diameter of 15 inches (380 mm). A wafer bonding plate is affixed with a single 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm). Polished.

  As a result of polishing for 6 hours under these conditions, the work-affected layer on the surface was completely removed, and surface damage was observed with a cross-sectional TEM, but no damage was detected. In addition, when the surface irregularities were measured by AFM, Ra = 0.1 nm was found to be very excellent in flatness.

  Next, the example which implemented this invention using the alumina slurry is demonstrated. The SiC wafer is a 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm) as in the colloidal silica slurry example, and the orientation of the wafer surface is inclined 4 ° from the Si (0001) plane to the (1-210) direction. ing.

  The surface state of the SiC wafer before finish polishing according to the present invention was mechanically polished with diamond free abrasive grains, and the unevenness on the wafer surface was Ra = 0.8 nm as measured by AFM. The thickness of the work-affected layer was about 15 nm as evaluated by cross-sectional TEM.

As shown in FIG. 1, oxygen gas supplied from a general-purpose oxygen cylinder is immersed in hot water heated to 80 ° C. to produce wetO _2, which is supplied to a quartz tube that is heated in a SiC wafer in an electric furnace. The flow rate was approximately 1.7 × 10 ⁻³ Pa · m ³ / sec. The furnace temperature was 1100 ° C. and heated for 2 hours. As a result, the work-affected layer under the SiC wafer surface generated in the rough polishing process was all oxidized. That is, an oxide film having a thickness of about 20 nm was formed on the Si surface side surface of the wafer, and an oxide film having a thickness of about 200 nm was formed on the C surface side surface. Therefore, all the work-affected layers are oxidized.

The C surface of this wafer was pressed against a polishing surface plate with a polishing surface pressure of 0.2 kg / cm ² and polished by rotating the polishing surface plate at 40 rpm. The abrasive was a slurry containing alumina solid content of 20 mass%, and the pH was adjusted to a weak alkali (pH˜10). The slurry was fed by a roller pump at a rate of 1 liter per hour. The slurry discharged from the lower part of the polishing machine was recovered and circulated and supplied again to the polishing platen with a roller pump. The polishing surface plate is a buffing machine with a diameter of 15 inches (380 mm). A wafer bonding plate is affixed with a single 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm). Polished. The polishing surface plate is a buffing machine with a diameter of 15 inches (380 mm), and a 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm) is affixed to the wafer affixing plate, and one affixing plate is placed on the polishing surface plate. Polished.

  As a result of polishing for 6 hours under these conditions, the work-affected layer on the surface was completely removed, and surface damage was observed with a cross-sectional TEM, but no damage was detected. In addition, when the surface irregularities were measured by AFM, Ra = 0.1 nm was found to be very excellent in flatness.

  When reproducibility was confirmed under the same conditions, the work-affected layer was always removed from the surface after finish polishing, and the surface irregularities measured by AFM were always finished with a value of 0.3 nm or less.

  Moreover, the example which implemented this invention using the zirconia slurry is demonstrated. The SiC wafer is a 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm) as in the colloidal silica slurry example, and the orientation of the wafer surface is inclined 4 ° from the Si (0001) plane to the (1-210) direction. ing.

  The surface state of the SiC wafer before finish polishing according to the present invention was mechanically polished with diamond free abrasive grains, and the unevenness on the wafer surface was Ra = 0.8 nm as measured by AFM. The thickness of the work-affected layer was about 15 nm as evaluated by cross-sectional TEM.

As shown in FIG. 1, oxygen gas supplied from a general-purpose oxygen cylinder is immersed in hot water heated to 80 ° C. to produce wetO _2, which is supplied to a quartz tube that is heated in a SiC wafer in an electric furnace. The flow rate was approximately 1.7 × 10 ⁻³ Pa · m ³ / sec. The furnace temperature was 1100 ° C. and heated for 2 hours. As a result, the work-affected layer under the SiC wafer surface generated in the rough polishing process was all oxidized. That is, an oxide film having a thickness of about 20 nm was formed on the Si surface side surface of the wafer, and an oxide film having a thickness of about 200 nm was formed on the C surface side surface. Therefore, all the work-affected layers are oxidized.

The C surface of this wafer was pressed against a polishing surface plate with a polishing surface pressure of 0.2 kg / cm ² and polished by rotating the polishing surface plate at 40 rpm. The abrasive was a slurry containing zirconia solid content at a concentration of 20 mass%, and the pH was adjusted to a weak alkali (pH˜10). The slurry was fed by a roller pump at a rate of 1 liter per hour. The slurry discharged from the lower part of the polishing machine was recovered and circulated and supplied again to the polishing platen with a roller pump. The polishing surface plate is a buffing machine with a diameter of 15 inches (380 mm). A wafer bonding plate is affixed with a single 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm). Polished. The polishing surface plate is a buffing machine with a diameter of 15 inches (380 mm), and a 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm) is affixed to the wafer affixing plate, and one affixing plate is placed on the polishing surface plate. Polished.

  As a result of polishing for 12 hours under these conditions, the work-affected layer on the surface was completely removed, and surface damage was observed with a cross-sectional TEM, but no damage was detected. In addition, when the surface irregularities were measured by AFM, Ra = 0.1 nm was found to be very excellent in flatness.

  When reproducibility was confirmed under the same conditions, the work-affected layer was always removed from the surface after finish polishing, and the surface irregularities measured by AFM were always finished with a value of 0.3 nm or less.

  Furthermore, the example which implemented this invention using the garnet slurry is demonstrated. The SiC wafer is a 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm) as in the colloidal silica slurry example, and the orientation of the wafer surface is inclined 4 ° from the Si (0001) plane to the (1-210) direction. ing.

  The surface state of the SiC wafer before finish polishing according to the present invention was mechanically polished with diamond free abrasive grains, and the unevenness on the wafer surface was Ra = 0.8 nm as measured by AFM. The thickness of the work-affected layer was about 15 nm as evaluated by cross-sectional TEM.

As shown in FIG. 1, oxygen gas supplied from a general-purpose oxygen cylinder is immersed in hot water heated to 80 ° C. to produce wetO _2, which is supplied to a quartz tube that is heated in a SiC wafer in an electric furnace. The flow rate was approximately 1.7 × 10 ⁻³ Pa · m ³ / sec. The furnace temperature was 1100 ° C. and heated for 2 hours. As a result, the work-affected layer under the SiC wafer surface generated in the rough polishing process was all oxidized. That is, an oxide film having a thickness of about 20 nm was formed on the Si surface side surface of the wafer, and an oxide film having a thickness of about 200 nm was formed on the C surface side surface. Therefore, all the work-affected layers are oxidized.

The C surface of this wafer was pressed against a polishing surface plate with a polishing surface pressure of 0.2 kg / cm ² and polished by rotating the polishing surface plate at 40 rpm. The abrasive was a slurry containing a garnet solid content of 20 mass%, and the pH was adjusted to a weak alkali (pH˜10). The slurry was fed by a roller pump at a rate of 1 liter per hour. The slurry discharged from the lower part of the polishing machine was recovered and circulated and supplied again to the polishing platen with a roller pump. The polishing surface plate is a buffing machine with a diameter of 15 inches (380 mm). A wafer bonding plate is affixed with a single 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm). Polished. The polishing surface plate is a buffing machine with a diameter of 15 inches (380 mm), and a 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm) is affixed to the wafer affixing plate, and one affixing plate is placed on the polishing surface plate. Polished.

  As a result of polishing for 24 hours under these conditions, the work-affected layer on the surface was completely removed, and surface damage was observed with a cross-sectional TEM, but no damage was detected. In addition, when the surface irregularities were measured by AFM, Ra = 0.1 nm was found to be very excellent in flatness.

  When reproducibility was confirmed under the same conditions, the work-affected layer was always removed from the surface after finish polishing, and the surface irregularities measured by AFM were always finished with a value of 0.3 nm or less.

  Furthermore, the example which implemented this invention using the garnet slurry and the colloidal silica slurry mixed is demonstrated. The SiC wafer is a 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm) as in the colloidal silica slurry example, and the orientation of the wafer surface is inclined 4 ° from the Si (0001) plane to the (1-210) direction. ing.

  The surface state of the SiC wafer before finish polishing according to the present invention was mechanically polished with diamond free abrasive grains, and the unevenness on the wafer surface was Ra = 0.8 nm as measured by AFM. The thickness of the work-affected layer was about 15 nm as evaluated by cross-sectional TEM.

As shown in FIG. 1, oxygen gas supplied from a general-purpose oxygen cylinder is immersed in hot water heated to 80 ° C. to produce wetO _2, which is supplied to a quartz tube that is heated in a SiC wafer in an electric furnace. The flow rate was approximately 1.7 × 10 ⁻³ Pa · m ³ / sec. The furnace temperature was 1100 ° C. and heated for 2 hours. As a result, the work-affected layer under the SiC wafer surface generated in the rough polishing process was all oxidized. That is, an oxide film having a thickness of about 20 nm was formed on the Si surface side surface of the wafer, and an oxide film having a thickness of about 200 nm was formed on the C surface side surface. Therefore, all the work-affected layers are oxidized.

The Si surface of this wafer was pressed against the polishing surface plate with a polishing surface pressure of 0.2 kg / cm ² and polished by rotating the polishing surface plate at 40 rpm. The abrasive was a slurry containing a garnet solid content of 10 mass% and a colloidal silica solid content of 10 mass%, and the pH was adjusted to a weak alkali (pH to 10). The slurry was fed by a roller pump at a rate of 1 liter per hour. The slurry discharged from the lower part of the polishing machine was recovered and circulated and supplied again to the polishing platen with a roller pump. The polishing surface plate is a buffing machine with a diameter of 15 inches (380 mm). A wafer bonding plate is affixed with a single 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm). Polished. The polishing surface plate is a buffing machine with a diameter of 15 inches (380 mm), and a 4H-SiC single crystal wafer with a diameter of 4 inches (100 mm) is affixed to the wafer affixing plate, and one affixing plate is placed on the polishing surface plate. Polished.

  As a result of polishing for 3 hours under these conditions, the work-affected layer on the surface was completely removed, and surface damage was observed with a cross-sectional TEM, but no damage was detected. In addition, when the surface irregularities were measured by AFM, Ra = 0.1 nm was found to be very excellent in flatness.

  When reproducibility was confirmed under the same conditions, the work-affected layer was always removed from the surface after finish polishing, and the surface irregularities measured by AFM were always finished with a value of 0.3 nm or less.

As a conventional technique, in a polishing method using the synergistic action of colloidal silica and an alkali solution, the surface irregularities are only flattened to Ra = 0.5 to 0.8 nm as measured by AFM. At this time, the polishing surface pressure was 0.5 kg / cm ² and the rotation speed of the polishing platen was 80 rpm, and polishing was performed at a high rotation speed by applying a higher pressure than the examples of the present invention. Took more than 48 hours and the throughput deteriorated.

Moreover, as another conventional technique, when polished with chromium oxide, the polishing method using the synergistic action of colloidal silica and an alkaline solution is superior in flatness, but the surface evaluation result is the surface irregularity in AFM. The measured value was Ra = 0.4 nm. At this time, chromium oxide was rubbed into a non-woven buffing plate and held on the polishing platen, the polishing surface pressure was 0.15 kg / cm ² , and the polishing platen was rotated at 80 rpm. When the polished wafer surface was analyzed with a fluorescent X-ray analyzer (XRF), residual chromium was detected and metal contamination could be confirmed. On the other hand, no metal contamination was found on the wafer surface after polishing by the method of the present invention.
From these comparisons, the superiority of the method of the present invention is clear.

Configuration of thermal oxidizer

Claims (5)

The surface of the silicon carbide single crystal wafer, whose wafer surface orientation is inclined 4 ° in the (1-210) direction from the Si (0001) plane, is roughly polished by mechanical polishing , and then thermally oxidized to form the formed oxide film. A method for polishing a surface of a silicon carbide single crystal wafer, wherein the polishing is performed by finish polishing. Thermal oxidation of the silicon carbide single crystal wafer, a polishing method of a silicon carbide single crystal wafer surface according to claim 1 which is thermal oxidation in an oxygen gas atmosphere containing moisture. The polishing of the silicon carbide single crystal wafer surface according to claim 1 or 2 , wherein the work-affected layer formed on the surface layer portion of the silicon carbide single crystal wafer by rough polishing is oxidized, and the oxidized work-affected layer is removed by finish polishing. Method. The method for polishing a surface of a silicon carbide single crystal wafer according to any one of claims 1 to 3 , wherein the polishing agent used in finish polishing is a polishing agent having a Knoop hardness between silicon oxide and silicon carbide. The method for polishing a surface of a silicon carbide single crystal wafer according to claim 4, wherein the abrasive is one or more selected from silica, garnet, zirconia, and alumina.

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