PROCESSING METHOD FOR SiC SUBSTRATE

Abstract

To provide a processing method for a SiC substrate capable of forming a high-quality epitaxial growth layer on one face of the SiC substrate in the processing method for the SiC substrate including a polishing step of the SiC substrate using a polishing liquid containing permanganate ions.SOLUTION: A processing method of a SiC substrate includes: a polishing step of polishing the SiC substrate while supplying an acidic polishing liquid containing an aqueous solution, in which permanganate is dissolved, onto one face of the SiC substrate; and a cleaning step of cleaning one face of the SiC substrate after the polishing step. The cleaning step includes: a reduction cleaning step of supplying a reduction cleaning liquid capable of reducing a metal of a metal oxide and manganic acid ions of permanganate onto one face of the SiC substrate while rotating a spinner table in a state where the other face of the SiC substrate is held by the spinner table; and a pure water cleaning step of stopping the supply of the reduction cleaning liquid and then supplying pure water onto the one face of the SiC substrate while rotating the spinner table holding the other face of the SiC substrate after the reduction cleaning step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for processing a SiC substrate. [Background technology]

[0002] In recent years, power devices that have high withstand voltage and can control large currents have been attracting attention as semiconductor devices that convert and control electric power, etc. The power device is formed on one side of a single crystal substrate of silicon carbide (SiC), which has a larger band gap and higher dielectric breakdown field strength than a single crystal substrate of silicon (Si), for example.

[0003] Generally, a high-quality SiC epitaxial growth layer with reduced crystal defects is formed on one side of a substrate made of SiC single crystal (hereinafter referred to as SiC substrate), and then a power device is formed on this SiC epitaxial growth layer side.

[0004] Before forming an SiC epitaxial growth layer on one surface of a SiC substrate, it is necessary to perform chemical mechanical polishing (CMP) on the one surface of the SiC substrate in order to flatten the one surface.

[0005] Conventionally, for chemical mechanical polishing of SiC substrates, it has been proposed to use a polishing liquid containing permanganate, inorganic salts having oxidizing power, and water (see, for example, Patent Document 1).

[0006] Permanganate ionizes in the polishing solution to form permanganate ions (MnO4 - The permanganate ions function as an oxidizing agent that oxidizes the polished surface of the SiC substrate during polishing of the SiC substrate.

[0007] Recently, it has been found that polishing one side of a SiC substrate with a polishing solution containing permanganate ions can cause lattice defects, dislocations, and the like in the epitaxial growth layer, making it impossible to form a high-quality epitaxial growth layer. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2016-92246 A Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above problems, and has an object to provide a method for processing a SiC substrate, which includes a polishing step of the SiC substrate using a polishing liquid containing permanganate ions, and which is capable of forming a high-quality epitaxial growth layer on one side of the SiC substrate. [Means for solving the problem]

[0010] According to one aspect of the present invention, there is provided a method for processing a SiC substrate, the method comprising: a polishing step of polishing the SiC substrate while holding the other surface of the SiC substrate by a chuck table so that the one surface of the SiC substrate is exposed, and while bringing a polishing pad into contact with the one surface of the SiC substrate, supplying an acidic polishing liquid containing an aqueous solution in which a permanganate is dissolved to the one surface of the SiC substrate; and a cleaning step of cleaning the one surface of the SiC substrate after the polishing step. After the polishing step and before the cleaning step, particles remain on the one surface of the SiC substrate, and the particles are composed of metal oxides and the permanganate. the cleaning step includes a reduction cleaning step of supplying a reducing cleaning solution capable of reducing a metal of the metal oxide and a manganate ion of the permanganate to the one surface of the SiC substrate while rotating a spinner table with the other surface of the SiC substrate held by the spinner table, and a pure water cleaning step of supplying pure water to the one surface of the SiC substrate while rotating the spinner table holding the other surface of the SiC substrate after the reduction cleaning step and stopping the supply of the reducing cleaning solution.

[0011] Preferably, the reduction cleaning solution comprises an aqueous solution of hydroxylamine sulfate dissolved in water.

[0012] Also, preferably, the reduction cleaning liquid contains an aqueous solution in which an acid and hydrogen peroxide are dissolved in water.

[0013] Preferably, the method for processing a SiC substrate further includes, before the polishing step, a grinding step of grinding the one surface of the SiC substrate with a grinding wheel to thin the SiC substrate to a predetermined thickness. Effect of the Invention

[0014] In a method for processing a SiC substrate according to one aspect of the present invention, a SiC substrate is polished while an acidic polishing solution containing an aqueous solution in which a permanganate is dissolved is supplied (polishing step). After the polishing step, particles containing one or both of a metal oxide and a permanganate remain on one surface of the SiC substrate.

[0015] For example, particles containing one or both of manganese oxide and permanganate resulting from manganese contained in the permanganate remain on the surface of the SiC substrate, which can hinder the quality of the epitaxial growth layer.

[0016] Therefore, in the cleaning process after the polishing process, a reduction cleaning process is performed in which one side of the SiC substrate is cleaned with a reduction cleaning solution capable of reducing the metal of the metal oxide and the manganate ions of the permanganate, and after the reduction cleaning process, a pure water cleaning process is performed in which one side of the SiC substrate is cleaned with pure water.

[0017] This reduces the number of particles containing metal oxides and / or permanganates remaining on one side of the SiC substrate, and therefore reduces the occurrence of lattice defects, dislocations, and the like per unit area of ​​the SiC substrate when forming an epitaxial growth layer on the one side of the SiC substrate, making it possible to form a high-quality epitaxial growth layer. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a flow diagram of a processing method for a SiC substrate in the first embodiment. [Diagram 2] FIG. 4 is a partial cross-sectional side view showing a polishing step. [Diagram 3] FIG. 11 is a side view showing a reduction cleaning step in the cleaning process. [Figure 4] FIG. 11 is a side view showing a pure water cleaning step in the cleaning process. [Diagram 5] FIG. 11 is a side view showing a drying step in the cleaning process. [Figure 6] 1 is an image showing the number and positions of particles on one surface of a SiC substrate that has been subjected to a reduction cleaning process, a pure water cleaning process, and a drying process. [Figure 7] 11 is an image of a comparative example showing the number and positions of particles on one surface of a SiC substrate that has been subjected to a pure water washing process and a drying process. [Figure 8] FIG. 11 is a flow diagram of a processing method for a SiC substrate in a second embodiment. [Figure 9] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (First embodiment) An embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a flow diagram of a method for processing a SiC substrate 11 (see Fig. 2) in the first embodiment. In this embodiment, each step is performed in the order of a polishing step S10 and a cleaning step S20.

[0020] First, the polishing apparatus 2 used in the polishing step S10 will be described with reference to Fig. 2. The Z-axis direction shown in Fig. 2 is the height direction of the polishing apparatus 2, and is, for example, approximately parallel to the vertical direction. The +Z direction and the -Z direction are both parallel to the Z-axis direction, but are opposite directions to each other. In this specification, the +Z direction may be referred to as "up" and the -Z direction may be referred to as "down."

[0021] The polishing apparatus 2 has a chuck table 4. The chuck table 4 has a disk-shaped frame. The frame is made of, for example, non-porous ceramics (for example, non-porous alumina). A disk-shaped recess (not shown) having a diameter smaller than the diameter of the frame is formed in the center of the frame.

[0022] A disk-shaped porous plate made of porous ceramics (e.g., porous alumina) is fixed in the recess. A predetermined flow path is formed in the frame, and a suction source (not shown) such as a vacuum pump is connected to the predetermined flow path via a pipe (not shown) or the like.

[0023] When the negative pressure generated by the suction source is transmitted to the porous plate, negative pressure is generated on the upper surface of the porous plate. The annular upper surface of the frame and the circular upper surface of the porous plate are substantially flush and substantially flat, and function as a holding surface 4a for suction-holding a workpiece such as a SiC substrate 11. The holding surface 4a is disposed substantially parallel to the XY plane.

[0024] A rotation shaft 4b of the chuck table 4 is provided below the chuck table 4 and at the radial center of the chuck table 4. The rotation shaft 4b is disposed along the Z-axis direction, and the chuck table 4 is rotatable around the rotation shaft 4b.

[0025] Power is transmitted to the rotating shaft 4b from a rotation drive mechanism (not shown) such as a servo motor. When the rotation drive mechanism operates, the chuck table 4 rotates around the rotating shaft 4b. A polishing unit 6 is disposed above the holding surface 4a.

[0026] The polishing unit 6 has a cylindrical spindle housing (not shown). The longitudinal direction of the spindle housing is arranged along the Z-axis direction. A ball screw type Z-axis direction moving mechanism (not shown) is attached to the spindle housing.

[0027] The Z-axis direction moving mechanism moves the spindle housing along the Z-axis direction. The pressing force of the polishing tool 12, which will be described later, against the workpiece is adjusted by the Z-axis direction moving mechanism. A part of the cylindrical spindle 8 is rotatably accommodated in the spindle housing.

[0028] The longitudinal direction of the spindle 8 is disposed along the Z-axis direction. A rotation drive source (not shown) such as a servo motor is provided near the upper end of the spindle 8. When the rotation drive source is operated, the spindle 8 rotates.

[0029] The lower end of the spindle 8 protrudes downward beyond the spindle housing. The center of the upper surface of a disk-shaped mount 10 is fixed to the lower end of the spindle 8. A disk-shaped polishing tool 12 is attached to the lower surface of the mount 10. When the spindle 8 is rotated, the mount 10 and the polishing tool 12 rotate together.

[0030] The polishing tool 12 includes a disk-shaped base 14. The lower surface of the mount 10 contacts an upper surface 14a of the base 14, and a disk-shaped polishing pad 16 having approximately the same diameter as the base 14 is fixed to a lower surface 14b of the base 14. The polishing pad 16 has a substrate made of foamed hard polyurethane, and abrasive grains such as silica (silicon oxide, SiO2) are fixed in the substrate.

[0031] The material of the abrasive grains is not limited to silica. The abrasive grains may be made of GC (green carbon), diamond, alumina (aluminum oxide, Al2O3), ceria (cerium oxide, CeO2), cBN (cubic boron nitride), or silicon carbide (SiC).

[0032] Furthermore, the base material of the polishing pad 16 is not limited to foamed hard polyurethane, but may be formed of other foamed hard materials, or may be formed of nonwoven fabric impregnated with urethane.

[0033] As described above, the abrasive grains are fixed to the polishing pad 16 in this embodiment, but the abrasive grains do not have to be fixed to the polishing pad 16. When the abrasive grains are not fixed to the polishing pad 16, the abrasive grains are contained as free abrasive grains in the polishing liquid 18a described later.

[0034] The spindle 8, the mount 10, and the polishing tool 12 are arranged substantially concentrically. Through holes 8a, 10a, 14c, and 16a that serve as flow paths for the polishing liquid 18a are formed in the radial centers of the spindle 8, the mount 10, and the polishing tool 12, respectively.

[0035] A polishing liquid supply source 18 is connected to the through hole 8a of the spindle 8. The polishing liquid supply source 18 includes a storage tank (not shown) in which the polishing liquid 18a is stored, and a pump (not shown) for supplying the polishing liquid 18a from the storage tank.

[0036] During polishing, a polishing liquid 18a is supplied to the polishing pad 16 and the object to be polished through the through holes 8a, 10a, 14c, and 16a. The polishing liquid 18a in this embodiment is an acidic aqueous solution that does not contain abrasive grains, and in particular, is an aqueous solution in which an oxidizing agent and a pH adjuster are dissolved in pure water (solvent).

[0037] As a material that functions as an oxidizing agent in an aqueous solution, permanganates such as sodium permanganate (NaMnO4) and potassium permanganate (KMnO4) are used, but it is preferable to use sodium permanganate, which has a higher solubility than potassium permanganate. When sodium permanganate is used in the polishing liquid 18a, the polishing liquid 18a has a pale red color.

[0038] As the pH adjuster, lanthanum nitrate (La(NO3)3) or cerium nitrate (Ce(NO3)3) is used. Note that cerium nitrate in this specification refers to trivalent cerium ions (i.e., Ce 3+ ) and nitrate ions (i.e., NO 3- ) and is an ionic compound of.

[0039] By making the polishing solution 18a strongly acidic (for example, a predetermined pH value less than 3) with a pH adjuster such as lanthanum nitrate or cerium nitrate, the oxidizing ability of permanganic acid can be fully exerted. When the oxidizing ability of permanganic acid is fully exerted, the thickness of the SiC substrate 11 removed by polishing per unit time (i.e., the polishing rate) can be increased.

[0040] However, instead of lanthanum nitrate and cerium nitrate, water-soluble nitric acid compounds such as yttrium nitrate (Y(NO3)3) and zirconyl nitrate (also called zirconium oxynitrate) (ZrO(NO3)2) may be used.

[0041] Instead of the above-mentioned nitric acid-based water-soluble compounds, hydrochloric acid-based water-soluble compounds such as lanthanum chloride (LaCl3), cerium chloride (CeCl3), yttrium chloride (YCl3), zirconyl chloride (also called zirconium oxide chloride or zirconium oxychloride) (ZrOCl2), etc. may be used.

[0042] In addition, instead of the above-mentioned nitric acid-based and hydrochloric acid-based water-soluble compounds, water-soluble sulfuric acid-based compounds such as lanthanum sulfate (La2(SO4)3), cerium sulfate (Ce(SO4)2), yttrium sulfate (Y2(SO4)3), zirconyl sulfate (also called zirconium sulfate) (ZrOSO4), etc. may be used.

[0043] In polishing the SiC substrate 11, oxidation of the first surface 11a and removal of a silicon oxide layer formed by the oxidation are alternately repeated. Specifically, when the polishing liquid 18a is first supplied to the first surface 11a of the SiC substrate 11, the Si atoms on the first surface 11a side are oxidized by the oxidizing action of permanganic acid, and a silicon oxide (e.g., SiO2) layer is formed.

[0044] The C atoms of the SiC substrate 11 change into carboxyl groups, carbon dioxide, etc. The carboxyl groups react with metal ions (e.g., La 3+ , Ce 3+), and is coordinated to the abrasive grains and extracted from the SiC substrate 11. Carbon dioxide is dissolved in the polishing liquid 18a as carbonate ions, or is discharged from the polishing liquid 18a as gas.

[0045] The silicon oxide layer formed on the first surface 11a is softer than the SiC crystals. The silicon oxide layer is physically scraped off by the abrasive grains, exposing a new SiC crystal surface. Thereafter, the formation of a silicon oxide layer by oxidation and the physical scraping off of the silicon oxide layer by the abrasive grains are alternately repeated in the same manner.

[0046] The SiC substrate 11 has a disk shape and has one circular surface 11a and another circular surface 11b located opposite each other in the thickness direction. When one of the one surface 11a and the other surface 11b is a Si surface, the other is a C surface.

[0047] 2 is a partial cross-sectional side view showing the polishing step S10. In the polishing step S10, first, one surface 11b of the SiC substrate 11 is suction-held by the holding surface 4a so that the other surface 11b is exposed. Next, the chuck table 4 is disposed directly below the polishing unit 6.

[0048] Then, by moving the polishing unit 6 downward, the polishing pad 16 is pressed against the one surface 11a with a predetermined pressure, while the chuck table 4 and the spindle 8 (i.e., the polishing tool 12 attached to the spindle 8) are rotated at predetermined rotational speeds, and polishing liquid 18a is supplied from the polishing liquid supply source 18 to the one surface 11a at a predetermined flow rate.

[0049] In this manner, the surface 11a is polished while the polishing liquid 18a is supplied to the surface 11a with the polishing pad 16 in contact with the surface 11a. In the polishing step S10, for example, the Si surface of the SiC substrate 11 having a diameter of 6 inches (about 150 mm) is polished. An example of the polishing conditions is shown below.

[0050] Spindle speed: 750 rpm Chuck table rotation speed: 745 rpm Pressing force: 39.2kPa Flow rate of supplied polishing fluid: 200ml / min Polishing time: 620s

[0051] When the SiC substrate 11 is polished while supplying the above-mentioned polishing liquid 18a in the polishing step S10, particles 13 (see FIG. 3) containing one or both of a metal oxide and a permanganate remain on the one surface 11a after the polishing step S10 (and before the cleaning step S20). Note that the particles 13 are exaggerated and shown large in FIG. 3.

[0052] As a result of extensive research, the applicant has come to the conclusion that particles 13 containing manganese oxides (MnO2, MnO3, etc.) and / or permanganates (NaMnO4, etc.) resulting from the manganese contained in the permanganate remain on one surface 11a of the SiC substrate 11, and that these particles 13 are likely the cause of preventing the epitaxial growth layer from being formed on one surface 11a from being of high quality.

[0053] Therefore, in the cleaning step S20 after the polishing step S10, a reduction cleaning step S22 (see FIG. 3) is performed in which a reduction cleaning solution 21 capable of reducing the metal of the metal oxide and the permanganate ion of the permanganate is supplied to one surface 11a of the SiC substrate 11 to clean the one surface 11a, and after the reduction cleaning step S22, a pure water cleaning step S24 (see FIG. 4) is performed in which pure water 23 is supplied to the one surface 11a to clean the one surface 11a, and a drying step S26 (see FIG. 5) is performed to dry the one surface 11a.

[0054] First, the spinner cleaning device 20 used in the cleaning step S20 will be described with reference to Fig. 3. The spinner cleaning device 20 has a disk-shaped spinner table 22. The structure of the spinner table 22 is approximately the same as that of the chuck table 4 of the polishing device 2.

[0055] The spinner table 22 has a holding surface 22a that can suck and hold the other surface 11b of the SiC substrate 11 by negative pressure. The spinner table 22 is rotatable at high speed around a predetermined rotation axis 22b.

[0056] However, the diameter of holding surface 22a is smaller than the diameter of other surface 11b of SiC substrate 11. When SiC substrate 11 is held by spinner table 22, the center portion of other surface 11b of SiC substrate 11 is suction-held by holding surface 22a.

[0057] A first rotary movement mechanism 26 is provided on the radially outer side of the spinner table 22, which rotates and moves the first arm 24 within an XY plane perpendicular to the Z-axis direction.

[0058] In the reduction cleaning process S22, the first rotational movement mechanism 26 rotates and moves the first arm 24 so that the trajectory of the first nozzle 28 provided at the tip of the first arm 24 forms an arc of a predetermined length that passes through the center of the holding surface 22a.

[0059] In the reduction cleaning step S22, the reduction cleaning liquid 21 is supplied to the first nozzle 28 from the reduction cleaning liquid supply source 30 through a flow path (not shown) formed inside the first arm 24. The reduction cleaning liquid supply source 30 includes a storage tank (not shown) in which the reduction cleaning liquid 21 is stored, and a pump (not shown) for supplying the reduction cleaning liquid 21 from the storage tank.

[0060] The first nozzle 28 may inject only the reduction cleaning liquid 21, or may inject two fluids in which the reduction cleaning liquid 21 and a gas such as air (not shown) supplied from a flow path separate from the reduction cleaning liquid 21 are mixed.

[0061] The reducing cleaning solution 21 is, for example, an aqueous solution in which hydroxylamine sulfate (rational formula: (NHOH) HSO) is dissolved in pure water. For example, the reducing cleaning solution 21 is formed by dissolving 1 part by mass or more and 20 parts by mass or less (for example, 5 parts by mass) of hydroxylamine sulfate in pure water.

[0062] The reduction cleaning solution 21 may be an aqueous solution in which citric acid (ie, acid) and hydrogen peroxide are dissolved in pure water, instead of hydroxylamine sulfate, or an aqueous solution in which ascorbic acid (ie, vitamin C) is dissolved in pure water.

[0063] Either aqueous solution is capable of reducing manganese (that is, metal) in the manganese oxide constituting the particles 13 and permanganate ions in the permanganate.

[0064] When citric acid and hydrogen peroxide are used, the reduction cleaning solution 21 is formed by dissolving, for example, 1 part by mass or more and 59 parts by mass or less (e.g., 1 part by mass) of citric acid and 1 part by mass or more and 35 parts by mass or less (e.g., 5 parts by mass) of hydrogen peroxide in pure water. Note that the citric acid functions as a pH adjuster in the reduction cleaning solution 21, and the hydrogen peroxide functions as a reducing agent.

[0065] A second rotational movement mechanism 32 is provided on the opposite side of the first rotational movement mechanism 26 across the rotation shaft 22b. The second rotational movement mechanism 32 rotates and moves a second arm 34 within an XY plane perpendicular to the Z-axis direction.

[0066] In the pure water cleaning process S24, the second rotational movement mechanism 32 rotates and moves the second arm 34 so that the trajectory of the second nozzle 36 provided at the tip of the second arm 34 forms an arc of a predetermined length that passes through the center of the holding surface 22a.

[0067] The second nozzle 36 is supplied with the pure water 23 from a pure water supply source 38 through a flow path (not shown) formed inside the second arm 34. The pure water supply source 38 includes a storage tank (not shown) in which the pure water 23 is stored, and a pump (not shown) for supplying the pure water 23 from the storage tank.

[0068] The reduction cleaning step S22 will be described with reference to Fig. 3. Fig. 3 is a side view showing the reduction cleaning step S22 in the cleaning step S20. In the reduction cleaning step S22, first, the other surface 11b of the SiC substrate 11 is suction-held by the holding surface 22a so that the polished one surface 11a is exposed.

[0069] Next, while the other surface 11b is being held by suction, the spinner table 22 is rotated at high speed and the first nozzle 28 is rotated relatively slowly above the one surface 11a, while the reducing cleaning liquid 21 is supplied from the first nozzle 28 to the one surface 11a.

[0070] As a result, the manganese in the manganese oxide and / or the permanganate ions in the permanganate contained in the particles 13 are converted to divalent manganese ions (Mn 2+ ), the divalent manganese ions contained in the reduction cleaning solution 21 are removed from the first surface 11a by centrifugal force. Note that the first surface 11a, which was light red after the polishing step S10, turns substantially colorless and transparent after the reduction cleaning step S22.

[0071] In the reduction cleaning step S22, a certain number of particles 13 are completely removed from the one surface 11a, but for the remaining particles 13, some of the manganese oxides and / or permanganates contained in the particles 13 are removed. In other words, in the reduction cleaning step S22, not all of the particles 13 are removed.

[0072] In the reduction cleaning process S22, for example, the rotation speed of the spinner table 22 is set to 500 rpm, the flow rate of the reduction cleaning solution 21 is set to 20 ml / min or more and 800 ml / min or less (e.g., 300 ml / min), and the first nozzle 28 moves from the center to the outer periphery of one surface 11a of the SiC substrate 11 over 15 s, which is repeated twice.

[0073] The flow rate of the reduction cleaning solution 21 may be 100 ml / min or more and 800 ml / min or less in the case of a single fluid that is not mixed with a gas such as air, and may be 20 ml / min or more and 200 ml / min or less in the case of a dual fluid that is mixed with a gas.

[0074] After the reduction cleaning step S22, a pure water cleaning step S24 is performed. Fig. 4 is a side view showing the pure water cleaning step S24 in the cleaning step S20. In the pure water cleaning step S24, the supply of the reduction cleaning solution 21 is stopped, and then the first arm 24 is rotated and moved so that the first nozzle 28 is positioned outside the SiC substrate 11 in the radial direction of the SiC substrate 11.

[0075] In addition, while continuing to rotate the spinner table 22 with the SiC substrate 11 being suction-held, the second nozzle 36 is moved above the surface 11a, and the pure water 23 is supplied to the surface 11a from the second nozzle 36. This removes some of the particles 13 and the reducing cleaning solution 21 remaining on the surface 11a.

[0076] In the pure water cleaning process S24, for example, the rotation speed of the spinner table 22 is set to 500 rpm, the flow rate of the pure water 23 is set to 20 ml / min or more and 800 ml / min or less (e.g., 300 ml / min), and the second nozzle 36 is moved only once from the center to the outer edge of one surface 11a of the SiC substrate 11 over 30 s.

[0077] The flow rate of the pure water 23 may be 100 ml / min or more and 800 ml / min or less in the case of only the pure water 23 not mixed with a gas such as air, and may be 20 ml / min or more and 200 ml / min or less in the case of two-fluid pure water 23 mixed with a gas.

[0078] After the pure water cleaning step S24, a drying step S26 is performed. Fig. 5 is a side view showing the drying step S26 in the cleaning step S20. In the drying step S26, the supply of the pure water 23 is stopped, and then the second arm 34 is rotated so that the second nozzle 36 is positioned outside the SiC substrate 11 in the radial direction.

[0079] In addition, the spinner table 22 continues to rotate while suction-holding the SiC substrate 11. In the drying step S26, for example, the rotation speed of the spinner table 22 is set to 2000 rpm, and the rotation duration is set to 60 s.

[0080] In this embodiment, the number of particles 13 remaining on the one surface 11a can be reduced by the cleaning step S20, and therefore, when an epitaxial growth layer is formed on the one surface 11a, the occurrence of lattice defects, dislocations, and the like per unit area of ​​the SiC substrate 11 can be reduced. In other words, a high-quality epitaxial growth layer can be formed.

[0081] (Experimental Example) Next, an experimental example will be described with reference to Figures 6 and 7. As the SiC substrate 11, a mirror wafer having a diameter of 6 inches (about 150 mm) and formed of a single crystal of SiC and having an orientation flat was used.

[0082] FIG. 6 corresponds to the processing method of the first embodiment described above, and is an image showing the number and positions of particles 13 on one surface 11a that has undergone a polishing step S10 and a cleaning step S20 including a reduction cleaning step S22, a pure water cleaning step S24, and a drying step S26.

[0083] More specifically, in the experiment in which the image in Fig. 6 was obtained, similarly to the first embodiment, the first nozzle 28 was moved twice from the center to the outer periphery of one surface 11a of the SiC substrate 11 over 15 s while spraying the reducing cleaning solution 21 from the first nozzle 28, and then the second nozzle 36 was moved once over 30 s from the center to the outer periphery of one surface 11a of the SiC substrate 11 while spraying the pure water 23 from the second nozzle 36. Thereafter, a drying step S26 was performed.

[0084] In contrast, FIG. 7 is an image of a comparative example showing the number and positions of particles 13 on one surface 11a that has been subjected to a pure water cleaning step S24 and a drying step S26 without being subjected to a reduction cleaning step S22 after the polishing step S10.

[0085] However, in the comparative example shown in FIG. 7, the reduction cleaning step S22 was omitted, and therefore the time spent in the pure water cleaning step S24 was made longer than the time spent in the pure water cleaning step S24 in the experiment that produced the image in FIG. 6.

[0086] Specifically, in the pure water cleaning process S24 of the comparative example shown in FIG. 7, the second nozzle 36 was moved twice over a period of 15 s from the center to the outer periphery of one surface 11a of the SiC substrate 11 while spraying pure water 23 from the second nozzle 36, and then the second nozzle 36 was moved once over a period of 30 s from the center to the outer periphery of one surface 11a of the SiC substrate 11 while spraying pure water 23 from the second nozzle 36.

[0087] The images shown in Figures 6 and 7 were obtained by irradiating a laser beam having a wavelength of 405 nm at a predetermined angle with respect to the normal vector of the surface 11a after the drying step S26, and receiving scattered light from the surface 11a using a detector having a photomultiplier tube (PMT).

[0088] In particular, the positional relationship between the focal point of the laser beam and the detector was fixed, and then a stage (not shown) that suction-holds the other surface 11b was rotated and moved in a predetermined direction in a horizontal plane to move the focal point in a spiral on the one surface 11a. While moving the stage in this manner, scattered light from the one surface 11a was received.

[0089] In this way, an image was created in which the particles 13 remaining on the first surface 11a were visualized. For visualization of the particles 13, a wafer surface inspection device YPI-MX-SMIF manufactured and sold by Yamanashi Gijutsu Kobo Co., Ltd. was used.

[0090] The diameter of the particles 13 that can be visualized using this device is 0.1 μm or more, and the number of particles 13 having a diameter of 0.1 μm or more was counted based on the obtained image.

[0091] In the image shown in FIG. 6 corresponding to the processing method of this embodiment, the number of remaining particles 13 was 1011, whereas in the image shown in FIG. 7 corresponding to the comparative example, the number of remaining particles 13 was 5032.

[0092] If the number of particles 13 remaining on one surface 11a of the SiC substrate 11 is 1200 or less (more preferably 1000 or less), there is almost no problem with the quality of the epitaxially grown layer. In other words, the advantages of the processing method of this embodiment were confirmed through the experiments shown in Figs. 6 and 7.

[0093] Second Embodiment Next, a second embodiment will be described with reference to Fig. 8 and Fig. 9. Fig. 8 is a flow diagram of a processing method for a SiC substrate 11 in the second embodiment. The SiC substrate 11 in the second embodiment is formed by peeling it from a SiC ingot (not shown).

[0094] Specifically, the SiC substrate 11 is peeled off from a SiC ingot (not shown) starting from a fragile region (i.e., a region in which a peeling layer including a modified region and a crack propagating from the modified region is formed) formed at a predetermined depth in the ingot.

[0095] The modified region is a region formed by multiphoton absorption that occurs near the focal point of a pulsed laser beam having a wavelength (e.g., 1064 nm) that transmits through the SiC substrate 11, and in which the crystallinity has changed compared to the region not irradiated with the laser beam.

[0096] In order to form a brittle region at a predetermined depth in a SiC ingot, first, with the focal point of the laser beam described above positioned at a predetermined depth in the SiC ingot (corresponding to the thickness of the SiC substrate 11), the focal point of the laser beam and the SiC ingot are moved relatively along a first direction perpendicular to the thickness direction of the SiC ingot.

[0097] After moving the focal point across the SiC ingot along a first direction, the focal point and the SiC ingot are indexed and fed a predetermined distance relative to each other along the thickness direction of the SiC ingot and a second direction perpendicular to the first direction. Thereafter, the focal point of the laser beam and the SiC ingot are moved relatively along the first direction in the same manner.

[0098] In this manner, a peeled layer is formed over the entirety of the SiC ingot to a predetermined depth. Next, the SiC substrate 11 is peeled off from the SiC ingot. One surface 11a of the SiC substrate 11 corresponds to the surface to be peeled off that was in contact with the peeled layer of the SiC ingot.

[0099] Since the unevenness of the surface 11a after peeling is relatively large, the surface 11a is ground with a grinding wheel 50 (see FIG. 9) before the polishing step S10 to thin the SiC substrate 11 to a predetermined thickness (grinding step S5).

[0100] The grinding device 40 will be described with reference to Fig. 9. The grinding device 40 has a disk-shaped chuck table 42. The chuck table 42 has a disk-shaped frame body formed of non-porous dense ceramics or the like.

[0101] A disk-shaped recess is formed on the upper surface of the frame. A disk-shaped porous plate made of porous ceramic is fixed in the recess. The porous plate has a substantially flat bottom surface and an upper surface whose thickness increases from the periphery toward the center.

[0102] That is, the upper surface of the porous plate is a cone surface with the center protruding slightly compared to the outer periphery. However, since the amount of protrusion of the center of the upper surface of the porous plate is very small, about 10 μm to 20 μm, the upper surface of the porous plate is shown as approximately flat in FIG.

[0103] A flow path is formed on the bottom surface of the recess of the frame. Negative pressure generated by a suction source (not shown) such as a vacuum pump is transmitted to the porous plate via the flow path. The upper surface of the frame and the upper surface of the porous plate are substantially flush with each other, and function as a holding surface 42a that holds the other surface 11b of the SiC substrate 11 by suction.

[0104] A rotation shaft 42b of the chuck table 42 is provided below the chuck table 42 and at the center in the radial direction of the chuck table 42. Note that in Fig. 9, the rotation shaft 42b of the chuck table 42 is simplified and indicated by a dashed line.

[0105] The chuck table 42 is rotatably connected to a disk-shaped table base (not shown) via a bearing (not shown). This table base is supported by an inclination adjustment mechanism (not shown) that adjusts the inclination of the rotation axis 42b of the chuck table 42.

[0106] The table base is inclined at a predetermined angle with respect to the Z-axis direction so that an arc-shaped area that is part of the holding surface 42a is approximately parallel to a predetermined plane (for example, the XY plane) perpendicular to the Z-axis direction.

[0107] A through hole (not shown) is formed in the radial center of the table base, and the above-mentioned rotating shaft 42b is disposed in the through hole. Power is transmitted to the rotating shaft 42b from a rotation drive source (not shown) such as a servo motor via a belt and pulley mechanism (not shown).

[0108] A grinding unit 44 is provided above the chuck table 42. The grinding unit 44 has a cylindrical spindle housing (not shown). A part of a cylindrical spindle 46 arranged approximately parallel to the Z-axis direction is rotatably held in the spindle housing.

[0109] A rotation drive source (not shown) such as a servo motor is provided near the upper end of the spindle 46. An annular grinding wheel 50 is attached to the lower end of the spindle 46 via a disk-shaped wheel mount 48.

[0110] The grinding wheel 50 has an annular base 52 made of a metal material such as an aluminum alloy. One surface 52a of the base 52 is fixed to the wheel mount 48 by a bolt or the like. On the other surface 52b of the base 52, a plurality of grinding stones 54 are arranged at approximately equal intervals along the circumferential direction of the base 52.

[0111] Each grinding wheel 54 is formed by kneading abrasive grains such as diamond or cBN (cubic boron nitride) with a binder such as metal, ceramics, or thermosetting resin, and then molding and firing the mixture.

[0112] A grinding water supply nozzle (not shown) is provided between the grinding wheel 50 and the holding surface 42a in the Z-axis direction directly below the spindle 46. The grinding water supply nozzle supplies grinding water such as pure water to a contact area between the SiC substrate 11 and the grinding wheel 54 when the SiC substrate 11 is ground.

[0113] 9 is a partial cross-sectional side view showing the grinding step S5. In the grinding step S5, first, the other surface 11b of the SiC substrate 11 is suction-held in a state in which the center of the holding surface 42a is approximately aligned with the radial center of the SiC substrate 11. At this time, one surface 11a of the SiC substrate 11 is exposed upward.

[0114] Next, the chuck table 42 and the grinding wheel 50 are rotated, and grinding water is supplied to the area where the movement trajectories of the multiple grinding stones 54 overlap with the SiC substrate 11 in the Z-axis direction (i.e., the area to be ground), while the grinding unit 44 is moved downward at a predetermined speed for grinding.

[0115] By such in-feed grinding, substantially the entire one surface 11a of the SiC substrate 11 is ground by the grinding wheel 50. As a result, the SiC substrate 11 is thinned to a predetermined thickness. An example of the grinding conditions is shown below.

[0116] Spindle speed: 2000 rpm Chuck table rotation speed: 200 rpm Grinding feed rate: 0.1μm / s to 1.0μm / s Grinding water flow rate: 5L / min to 10L / min

[0117] After the grinding step S5, the above-mentioned polishing step S10 and cleaning step S20 are performed in sequence. As described above, the cleaning step S20 can reduce the number of particles 13 remaining on the one surface 11a, so that the occurrence of lattice defects, dislocations, and the like per unit area of ​​the SiC substrate 11 can be reduced when an epitaxial growth layer is formed on the one surface 11a.

[0118] In addition, the structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. The metal oxide constituting the particles 13 is not limited to manganese oxide, and may include oxides of other metals, such as metals contained in the pH adjuster.

[0119] A resin protective member may be attached to the other surface 11b of the SiC substrate 11, and then the grinding step S5, the polishing step S10, and the cleaning step S20 may be performed on the one surface 11a. At this time, the other surface 11b of the SiC substrate 11 is suction-held by the holding surfaces 4a, 22a, and 42a via the protective member. [Explanation of symbols]

[0120] 2: polishing device, 4: chuck table, 4a: holding surface, 4b: rotating shaft 6: polishing unit, 8: spindle, 8a: through hole 10: mount, 10a: through hole 11: SiC substrate, 11a: one surface, 11b: other surface, 13: particle 12: Polishing tool, 14: Base, 14a: Top surface, 14b: Bottom surface, 14c: Through hole 16: polishing pad, 16a: through hole, 18: polishing liquid supply source, 18a: polishing liquid 20: Spinner cleaning device 21: Reduction cleaning solution, 23: Pure water 22: spinner table, 22a: holding surface, 22b: rotating shaft 24: first arm, 26: first rotary movement mechanism, 28: first nozzle 30: Reduced cleaning solution supply source 32: second rotational movement mechanism, 34: second arm, 36: second nozzle 38: Pure water source 40: grinding device, 42: chuck table, 42a: holding surface, 42b: rotating shaft 44: Grinding unit, 46: Spindle, 48: Wheel mount 50: grinding wheel, 52: base, 52a: one side, 52b: other side, 54: grinding stone S5: Grinding process S10: Polishing process, S20: Cleaning process S22: Reduction cleaning process, S24: Pure water cleaning process, S26: Drying process

Claims

1. A method for processing a SiC substrate, comprising the steps of: a polishing step of polishing the SiC substrate while holding the other surface of the SiC substrate by a chuck table so that the one surface of the SiC substrate is exposed and contacting a polishing pad with the one surface of the SiC substrate, while supplying an acidic polishing liquid containing an aqueous solution in which a permanganate is dissolved to the one surface of the SiC substrate; a cleaning step of cleaning the one surface of the SiC substrate after the polishing step; Equipped with particles remaining on the surface after the polishing step and before the cleaning step, the particles including one or both of a metal oxide and the permanganate; The washing step comprises: a reduction cleaning step of supplying a reduction cleaning solution capable of reducing a metal of the metal oxide and a manganate ion of the permanganate to the one surface of the SiC substrate while rotating the spinner table in a state where the other surface of the SiC substrate is held by the spinner table; and a pure water cleaning step of, after the reduction cleaning step, stopping the supply of the reduction cleaning solution and then supplying pure water to the one side of the SiC substrate while rotating the spinner table holding the other side of the SiC substrate.

2. 2. The method for processing a SiC substrate according to claim 1, wherein the reducing cleaning solution contains an aqueous solution in which hydroxylamine sulfate is dissolved in water.

3. 2. The method for processing a SiC substrate according to claim 1, wherein the reducing cleaning solution contains an aqueous solution in which an acid and hydrogen peroxide are dissolved in water.

4. 4. The method for processing a SiC substrate according to claim 1, further comprising a grinding step of grinding the one surface of the SiC substrate with a grinding wheel before the polishing step to thin the SiC substrate to a predetermined thickness.

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