Polishing solution for polishing compound semiconductor substrates

Abstract

To facilitate handling and reduce hazards to an operator compared to a strong acid polishing liquid.SOLUTION: A polishing liquid for compound semiconductor substrate polishing includes an aqueous solution in which permanganate and a water-soluble compound in which a weak acid and a group 3 element, a lanthanide or a group 4 element are combined are dissolved. Preferably, the pH of the polishing liquid is greater than or equal to 3 and less than or equal to 7. Also preferably, the concentration of permanganate is 2.50 wt% or higher. The concentration of the water-soluble compound is greater than or equal to 0.55 wt% and less than or equal to 5.50 wt%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polishing liquid for polishing a compound semiconductor substrate.

Background Art

[0002] In recent years, power devices with high breakdown voltage and capable of controlling large current have attracted attention compared to conventional devices formed using single-crystalline silicon substrates. A power device is formed, for example, on one side of a SiC (silicon carbide) single-crystalline substrate.

[0003] Before forming a device on one side of a SiC single-crystalline substrate, it is known to perform CMP (Chemical Mechanical Polishing, i.e., chemical mechanical polishing) on that one side (see, for example, Patent Document 1). In the polishing method described in Patent Document 1, while sucking and holding a SiC single-crystalline substrate on a chuck table, the SiC single-crystalline substrate is polished while supplying a polishing liquid between a fixed abrasive pad and the SiC single-crystalline substrate.

[0004] In Patent Document 1, it is described that, in particular, by using potassium permanganate (KMnO4) and ammonium cerium nitrate ((NH4)2Ce(NO3)6) in the polishing liquid, the polishing rate can be made the highest.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the polishing liquid described in Patent Document 1 is a strong acid, and its pH is, for example, 1 or more and 2 or less. Therefore, there is a problem that the handling of the polishing liquid is not easy and it involves risks for workers when used.

[0007] This invention has been made in view of the aforementioned problems, and aims to make the polishing solution easier to handle compared to strong acid polishing solutions, and to reduce the risk to workers. [Means for solving the problem]

[0008] According to one aspect of the present invention, SiC A polishing solution for substrate polishing, comprising permanganate, Zirconium acetate It is equipped with an aqueous solution in which the substance is dissolved. The concentration of the permanganate is 2.50 wt% or more, and the concentration of the zirconium acetate is 0.55 wt% or more and 5.50 wt% or less. ru SiC Polishing fluid for circuit board polishing is provided.

[0009] Preferably, the pH of the polishing solution is between 3 and 7. [Effects of the Invention]

[0011] A polishing solution for polishing compound semiconductor substrates according to one aspect of the present invention is weakly acidic due to the weak acid component constituting the water-soluble compound, making it easier to handle and reducing the risk to workers compared to a strong acid polishing solution. [Brief explanation of the drawing]

[0012] [Figure 1] This is a partial cross-sectional side view of a polishing device. [Figure 2] These are experimental results when the concentration of sodium permanganate was fixed and the concentration of zirconyl acetate was changed in steps. [Figure 3] These are experimental results when the concentration of zirconyl acetate was fixed and the concentration of sodium permanganate was changed in steps. [Modes for carrying out the invention]

[0013] An embodiment of one aspect of the present invention will be described with reference to the attached drawings. First, the polishing solution 1 of this embodiment (see Figure 1) will be described. The polishing solution 1 contains an aqueous solution in which a permanganate salt and a water-soluble compound are dissolved.

[0014] As the permanganate, sodium permanganate (NaMnO4), potassium permanganate (KMnO4), etc. are used. Note that as the permanganate, it is preferable to use sodium permanganate which has a higher solubility in water than the solubility of potassium permanganate in water.

[0015] Other examples of permanganates include permanganates containing metal cations such as silver permanganate (AgMnO4), zinc permanganate (Zn(MnO4)2), magnesium permanganate (Mg(MnO4)2), calcium permanganate (Ca(MnO4)2), barium permanganate (Ba(MnO4)2), etc.

[0016] As the water-soluble compound, (i) a water-soluble compound formed by combining a weak acid and a Group 3 element, (ii) a water-soluble compound formed by combining a weak acid and a lanthanoid, or (iii) a water-soluble compound formed by combining a weak acid and a Group 4 element is used.

[0017] Examples of weak acids include acetic acid, citric acid, carbonic acid, phosphoric acid, oxalic acid, boric acid, etc., but weak acids are not limited to only these six types.

[0018] (1) As the Group 3 element, for example, yttrium (Y) can be mentioned. (2) As the lanthanoid, for example, lanthanum (La) and cerium (Ce) can be mentioned. Also, (3) as the Group 4 element, for example, zirconium (Zr) can be mentioned, respectively.

[0019] When acetic acid (CH3COOH) is used as the weak acid, (1) yttrium acetate (Y(CH3COO)3), (2) lanthanum acetate (La(CH3COO)3), cerium acetate (Ce(CH3COO)3), and (3) zirconyl acetate (also called zirconium oxyacetate) (ZrO(CH3COO)2) are each used as the water-soluble compound.

[0020] When using citric acid (C6H8O7) as the weak acid (shown by the chemical formula instead of the empirical formula for convenience), each of (1) yttrium citrate (Y(C6H5O7)), (2) lanthanum citrate (La(C6H5O7)), cerium citrate (Ce(C6H5O7)), and (3) zirconyl citrate ((ZrO)3(C6H5O7)2) is used as a water-soluble compound.

[0021] When using carbonic acid (H2CO3) as the weak acid, each of (1) yttrium carbonate (Y2(CO3)3), (2) lanthanum carbonate (La2(CO3)3), cerium carbonate (Ce2(CO3)3), and (3) zirconyl carbonate (ZrO(CO3)) is used as a water-soluble compound.

[0022] When using phosphoric acid (H3PO4) as the weak acid, each of (1) yttrium phosphate (YPO4), (2) lanthanum phosphate (LaPO4), cerium phosphate (CePO4), and (3) zirconyl phosphate ((ZrO)3(PO4)2) is used as a water-soluble compound.

[0023] When using oxalic acid (C2O4H2) as the weak acid (shown by the chemical formula instead of the empirical formula for convenience), each of (1) yttrium oxalate (Y2(C2O4)3), (2) lanthanum oxalate (La2(C2O4)3), cerium oxalate (Ce2(C2O4)3), and (3) zirconyl oxalate (ZrO(C2O4)) is used as a water-soluble compound.

[0024] When using boric acid (H3BO3) as the weak acid (shown by the chemical formula instead of the empirical formula for convenience), each of (1) yttrium borate (YBO3), (2) lanthanum borate (LaBO3), cerium borate (CeBO3), and (3) zirconyl borate ((ZrO)3(BO3)2) is used as a water-soluble compound.

[0025] Polishing solution 1, which contains an aqueous solution of permanganate and a water-soluble compound, is weakly acidic with a pH (hydrogen ion concentration) of 3 to 7 (3 ≤ pH ≤ 7), and is used when polishing a compound semiconductor substrate (workpiece) 11, as shown in Figure 1. In other words, polishing solution 1 is for polishing compound semiconductor substrates.

[0026] The compound semiconductor substrate 11 is, for example, a silicon carbide (SiC) single crystal substrate, but it may also be a single crystal substrate of another compound semiconductor such as gallium nitride (GaN) or gallium arsenide (GaAs).

[0027] In particular, polishing solution 1 is weakly acidic and is used when polishing compound semiconductors. In contrast, silicon single crystal substrates are generally polished under alkaline conditions, so polishing solution 1 is not usually used for polishing silicon single crystal substrates.

[0028] Furthermore, in addition to the aqueous solution in which the permanganate salt and water-soluble compound described above are dissolved, polishing solution 1 may also contain additives such as pH adjusters, viscosity adjusters, rust inhibitors, and preservatives, as well as free abrasive particles (for example, silica (SiO2) abrasive particles).

[0029] Polishing solution 1 is weakly acidic due to the weak acid component that makes up the water-soluble compound, which has the advantage of being easier to handle and reducing the risk to workers compared to polishing solutions with strong acids.

[0030] Next, the mechanism for chemical mechanical polishing of a SiC single-crystal substrate, which is a compound semiconductor substrate 11, using a polishing solution 1 containing an aqueous solution of sodium permanganate (NaMnO4) and zirconyl acetate (ZrO(CH3COO)2) will be explained. Note that the mechanism described below is the applicant's speculation, and the actual mechanism may differ.

[0031] First, when polishing solution 1 is supplied to one surface 11a (see Figure 1) of the compound semiconductor substrate 11, the Si atoms on the surface 11a are oxidized by the oxidizing action of permanganate (i.e., the oxidizing agent), and an SiO2 (silicon oxide) layer is formed.

[0032] Furthermore, the carbon atoms in the SiC single crystal substrate are transformed into carboxyl groups, carbon dioxide, etc. The carboxyl group is zirconyl (ZrO 2+ ) and abrasive grains are coordinated and extracted from the compound semiconductor substrate 11. In addition, carbon dioxide is dissolved in the polishing solution 1 as carbonate ions or becomes a gas and is discharged from the polishing solution 1.

[0033] In polishing solution 1, zirconyl (ZrO) derived from zirconyl acetate 2+ ) and zirconium ions (Zr 4+ The abrasive particles act as a crosslinking agent, adsorbing and peeling off the SiO2 layer formed on one side 11a. In addition, the SiO2 layer is physically scraped off by the abrasive particles.

[0034] This exposes a new SiC crystal plane. Once the new SiC crystal plane is exposed, the following processes alternately occur: (a) the formation of an SiO2 layer by oxidation, (b) the adsorption and peeling of the SiO2 layer by zirconyl and zirconium ions, and physical removal by abrasive grains.

[0035] Furthermore, in order to proceed with polishing one side 11a using the polishing solution 1, it is necessary to allow the polishing solution 1 to exert its ability to oxidize one side 11a of the compound semiconductor substrate 11.

[0036] In this embodiment, the 11a side is primarily oxidized with permanganate. Permanganate has stronger oxidizing power at lower pH (i.e., under acidic conditions) than at higher pH (i.e., under alkaline conditions).

[0037] In this embodiment, by maintaining the polishing solution 1 at a weakly acidic state using a water-soluble compound formed by the combination of a weak acid and a transition metal element, the oxidizing ability of permanganate can be fully exhibited compared to alkaline conditions.

[0038] By the way, when using an aqueous solution of potassium permanganate and cerium ammonium nitrate, as in the conventional method, the permanganate contains ammonium ions (NH₃). 4+ It is thought that the permanganic acid in polishing solution 1 is consumed by oxidizing ) and ammonia (NH3).

[0039] Therefore, the number of permanganic acid molecules oxidizing the 11a side decreases, which is thought to relatively weaken the oxidizing ability of the permanganic acid. When oxidation on the 11a side becomes more difficult, the polishing rate is thought to decrease.

[0040] Conversely, as described above, the water-soluble compound of this embodiment does not contain ammonium ions and ammonia (i.e., approximately 0 wt%). Therefore, compared to conventional polishing solutions containing potassium permanganate and cerium ammonium nitrate, the concentrations of ammonium ions and ammonia in polishing solution 1 are less than or equal to the concentrations of Group 3 elements, lanthanides, and Group 4 elements.

[0041] For example, in the polishing solution 1 of this embodiment, the concentration of ammonium ions is below the limit of quantification by ion chromatography, and is approximately 0 wt%. However, since there is a possibility that trace amounts of ammonium ions present in the cleanroom where polishing is performed may dissolve in the polishing solution 1, the ammonium ion content in the polishing solution 1 may not be completely 0 wt%.

[0042] However, in this embodiment, basic substances and ions such as ammonia and ammonium ions are not intentionally added as raw materials during manufacturing. Therefore, in polishing solution 1, the oxidizing ability of permanganate can be fully exhibited compared to conventional polishing solutions.

[0043] Next, a method for polishing a compound semiconductor substrate 11 using polishing solution 1 will be described. First, the polishing apparatus 2 used will be described. Figure 1 is a partial cross-sectional side view of the polishing apparatus 2. Note that the Z-axis direction shown in Figure 1 is approximately parallel to the vertical direction.

[0044] The polishing apparatus 2 has a disc-shaped chuck table 4. A rotating shaft (not shown) is connected to the underside of the chuck table 4, with its longitudinal direction aligned with the Z-axis. A driven pulley (not shown) is provided on the rotating shaft.

[0045] A rotational drive source (not shown), such as a motor, is provided near the chuck table 4. A drive pulley (not shown) is provided on the output shaft of the rotational drive source. An endless belt (not shown) is stretched over the drive pulley and the driven pulley, and the power from the rotational drive source is transmitted to the rotating shaft of the chuck table 4.

[0046] When the rotary drive source operates, the chuck table 4 rotates around the axis of rotation. The chuck table 4, the rotary drive source, etc., are supported by a movable plate (not shown) that can move along a predetermined direction (for example, the X-axis direction perpendicular to the Z-axis direction).

[0047] The movable plate is movable along the X-axis direction together with the chuck table 4, rotational drive source, etc., by a ball screw type moving mechanism (not shown). The chuck table 4 has a disc-shaped frame 6 made of ceramics. A disc-shaped recess is formed on the upper part of the frame 6.

[0048] A disc-shaped porous plate 8 made of porous ceramics or the like is fixed in this recess. The upper surface of the porous plate 8 and the upper surface of the frame 6 are flush, forming a substantially flat holding surface 4a.

[0049] The porous plate 8 is connected to a suction source (not shown), such as a vacuum pump, via channels 6a and 6b formed within the frame 6. When the suction source is operated, negative pressure is transmitted to the upper surface of the porous plate 8.

[0050] A compound semiconductor substrate 11 is placed on the holding surface 4a. A circular protective tape 13 made of resin is attached to the other surface 11b of the compound semiconductor substrate 11 shown in Figure 1 to prevent contamination, impact, etc.

[0051] The compound semiconductor substrate 11 is held in place by suction on the holding surface 4a via a protective tape 13, with one side 11a, which is opposite to the other side 11b, facing upwards. A polishing unit 10 is positioned above the holding surface 4a.

[0052] The polishing unit 10 has a cylindrical spindle housing (not shown). The longitudinal direction of the spindle housing is arranged approximately parallel to the Z-axis direction. A ball screw type Z-axis movement unit (not shown) is connected to the spindle housing to move the polishing unit 10 along the Z-axis direction.

[0053] A portion of a cylindrical spindle 12 is rotatably housed within the spindle housing. The longitudinal direction of the spindle 12 is positioned approximately parallel to the Z-axis direction. A rotational drive source (not shown), such as a motor, for rotating the spindle 12 is provided on the upper portion of the spindle 12.

[0054] The center of the upper surface of a disc-shaped mount 14 is connected to the lower end of the spindle 12. The mount 14 has a diameter larger than the diameter of the holding surface 4a. A disc-shaped polishing tool 16, which has approximately the same diameter as the mount 14, is mounted on the lower surface of the mount 14.

[0055] The polishing tool 16 has a disc-shaped base (also called a platen) 18 connected to the lower surface of the mount 14. The base 18 is made of a metal such as stainless steel. A polishing pad 20, which has approximately the same diameter as the base 18, is fixed to the lower surface of the base 18.

[0056] The polishing pad 20 has a main body made of rigid foamed urethane resin. Silica abrasive grains 20a are fixed to this main body. In other words, the polishing pad 20 is a so-called fixed abrasive pad.

[0057] By the way, in the polishing pad 20, other rigid foamed resins or nonwoven fabrics may be used instead of rigid foamed urethane resin. Also, the abrasive grains 20a do not need to be fixed to the polishing pad 20. In this case, the free abrasive grains are dispersed in the polishing liquid 1.

[0058] The radial center positions of the polishing pad 20, base 18, mount 14, and spindle 12 are approximately coincident, and a cylindrical through-hole 22 is formed so as to pass through these center positions. The upper end of the through-hole 22 is connected to the polishing fluid supply source 26 by a conduit 26a.

[0059] The polishing fluid supply source 26 includes a storage tank (not shown) for the polishing fluid 1, a pump (not shown) for sending the polishing fluid 1 from the storage tank to the conduit 26a, and the like. The polishing fluid 1 supplied from the polishing fluid supply source 26 is supplied to the central part of the polishing pad 20 through the through hole 22.

[0060] In polishing using the polishing device 2, the chuck table 4 is rotated in a predetermined direction, and the spindle 12 is also rotated in a predetermined direction. For example, the rotational speed of the chuck table 4 is set to 500 rpm, and the rotational speed of the spindle 12 (i.e., the polishing tool 16) is set to 495 rpm.

[0061] In this way, by setting the speed difference so that the rotational speed of one of the chuck table 4 and spindle 12 is even and the rotational speed of the other is odd, it is possible to prevent the same area of ​​surface 11a and polishing pad 20 from continuously contacting each other for a predetermined time, as would occur if the rotational speeds of the chuck table 4 and spindle 12 were the same.

[0062] Furthermore, in this embodiment, the surface to be ground (one surface 11a) is facing upward (i.e., face up), and the polishing fluid 1 is supplied to the surface to be ground from above. Therefore, even if the chuck table 4 is set to more than 120 rpm, the polishing fluid 1 can be properly supplied to the surface to be ground.

[0063] In contrast, when the surface to be ground is facing downwards (i.e., face down), the compound semiconductor substrate 11 is placed at the position of the polishing pad 20, the polishing pad 20 is placed at the position of the chuck table 4, and polishing liquid 1 is supplied from above to a predetermined area of ​​the polishing pad 20 that is not in contact with the compound semiconductor substrate 11.

[0064] However, when the surface to be ground is facing downwards (i.e., face down), if the rotation speed of the grinding pad 20 exceeds 120 rpm, the grinding fluid 1 supplied to the grinding pad 20 is scattered radially outward by centrifugal force, so the grinding fluid 1 is not properly supplied to the surface to be ground. As a result, even if the rotation speed of the grinding pad 20 is increased, the grinding rate does not increase easily (i.e., it does not follow Preston's Law).

[0065] In this embodiment, by employing a face-up method, the polishing fluid 1 can be properly supplied to the workpiece even when rotating at high speeds exceeding 120 rpm. Furthermore, the polishing rate can be increased by increasing the rotational speed of the chuck table 4 and spindle 12. In other words, polishing that follows Preston's Law can be achieved.

[0066] During polishing, the chuck table 4 may be oscillated by a moving mechanism within a predetermined distance along a predetermined direction (for example, the X-axis direction). Specifically, the chuck table 4 is moved a predetermined distance in the +X direction, and then moved a predetermined distance in the -X direction, and this operation is repeated.

[0067] The predetermined distance is smaller than the radius of the compound semiconductor substrate 11, and more preferably smaller than 1 / 10 of the diameter of the compound semiconductor substrate 11. By oscillating the chuck table 4 in this way during polishing, there is an advantage in that the unevenness on one surface 11a can be reduced compared to when it is not oscillated.

[0068] Next, referring to Figure 2, we will explain the experimental results of polishing a SiC single crystal substrate using polishing solution 1, which contains an aqueous solution of sodium permanganate (NaMnO4) and zirconyl acetate (ZrO(CH3COO)2).

[0069] Figure 2 shows the experimental results in which the polishing rate (μm / h) and the surface roughness (Ra (nm)) of the polished surface were measured while the concentration of sodium permanganate was fixed at 2.50 wt% and the concentration of zirconyl acetate was gradually changed from 0.55 wt% to 5.50 wt%.

[0070] Silica abrasive grains (particle size 0.4 μm to 0.6 μm) were used for the abrasive grains 20a of the polishing pad 20. The polishing conditions were as follows.

[0071] Chuck table 4 rotation speed: 500 rpm Polishing pad 20 rotation speed: 495 rpm Polishing solution flow rate: 0.15 L / min Pressure from polishing pad 20: 73.5kPa Polishing time: 6 min (i.e., 360 s) Compound semiconductor substrate 11: SiC single crystal substrate Diameter of compound semiconductor substrate 11: 4 inches (approximately 100 mm) Surface to be polished: Si surface

[0072] A1 in Figure 2 is polishing solution 1, which contains 2.50 wt% sodium permanganate and 0.55 wt% zirconyl acetate. To prepare polishing solution 1, for example, 55 g of zirconyl acetate is added to a sufficient amount of pure water, then 250 g of sodium permanganate is added to this, and then this is diluted with 10 L of pure water and stirred at 100 rpm for 30 minutes using a stirrer. The pH of A1 was 4.90 at 22.4°C.

[0073] When using A1, the polishing rate was 3.28 μm / h, and the surface roughness (Ra) of one surface 11a after polishing was 0.117 nm. Ra represents the arithmetic mean roughness. Ra is defined in accordance with JIS B 0601:2013 and represents the average of the absolute values ​​of the height positions of the contour curve at a given length.

[0074] A2 in Figure 2 is polishing solution 1, containing 2.50 wt% sodium permanganate and 1.38 wt% zirconyl acetate. For example, A2 can be prepared using 138 g of zirconyl acetate in the same process as A1. The pH of A2 was 4.65 at 22.2°C. When using A2, the polishing rate was 3.75 μm / h, and the Ra of one surface 11a after polishing was 0.129 nm.

[0075] A3 in Figure 2 is polishing solution 1, containing 2.50 wt% sodium permanganate and 2.75 wt% zirconyl acetate. For example, A3 can be prepared using 275 g of zirconyl acetate in the same process as A1. The pH of A3 was 4.48 at 22.9°C. When using A3, the polishing rate was 3.91 μm / h, and the Ra of one surface 11a after polishing was 0.126 nm.

[0076] A4 in Figure 2 is polishing solution 1, containing 2.50 wt% sodium permanganate and 4.13 wt% zirconyl acetate. For example, A4 can be prepared using 413 g of zirconyl acetate in the same process as A1. The pH of A4 was 4.44 at 22.5°C. When using A4, the polishing rate was 2.96 μm / h, and the Ra of one surface 11a after polishing was 0.130 nm.

[0077] A5 in Figure 2 is polishing solution 1, containing 2.50 wt% sodium permanganate and 5.50 wt% zirconyl acetate. For example, A5 can be prepared using 550 g of zirconyl acetate in the same process as A1. The pH of A5 was 4.35 at 22.6°C. When using A5, the polishing rate was 2.52 μm / h, and the Ra of one surface 11a after polishing was 0.136 nm.

[0078] Furthermore, compared to A3, the polishing rate decreased in A4 and A5 despite an increased concentration of zirconyl acetate. Two possible reasons for this are hypothesized.

[0079] The first reason is that as the concentration of zirconyl acetate increased, the viscosity of polishing solution 1 increased, and the frictional resistance between the polishing pad 20 and surface 11a decreased, causing the polishing pad 20 to slip on surface 11a and reducing polishing efficiency. The second reason is that since the concentration of sodium permanganate was fixed at 2.50 wt%, the ability to oxidize surface 11a reached its limit.

[0080] In other words, the ability to oxidize one side 11a (i.e., the concentration of sodium permanganate) remained constant from A1 to A5, and the polishing rate increased with increasing zirconyl acetate concentration from A1 to A3. However, in A4 and A5, the increase in polishing rate associated with increasing zirconyl acetate concentration was offset by a decrease in polishing efficiency due to the slippage of the polishing pad 20.

[0081] Considering the experimental results in Figure 2, the concentration of zirconyl acetate (water-soluble compound) is preferably 0.55 wt% to 2.75 wt%, and more preferably 1.38 wt% to 2.75 wt%.

[0082] Next, referring to Figure 3, we will explain the experimental results when the zirconyl acetate concentration is fixed at 2.75 wt%. Figure 3 shows the experimental results when the zirconyl acetate concentration is fixed at 2.75 wt% and the sodium permanganate concentration is changed in steps, measuring the polishing rate (μm / h) and the surface roughness (Ra (nm)) of the polished surface. A3 shown on the far left of Figure 3 is the same as A3 in Figure 2.

[0083] Figure 3 shows that B1 is polishing solution 1, containing 5.00 wt% sodium permanganate and 2.75 wt% zirconyl acetate. B1 can be prepared using the same process as A1, but with twice the weight of sodium permanganate used. The pH of B1 was 4.54 at 22.8°C. When using B1, the polishing rate was 4.59 μm / h, and the Ra of one surface 11a after polishing was 0.122 nm.

[0084] Figure 3, B2, is polishing solution 1, containing 7.50 wt% sodium permanganate and 2.75 wt% zirconyl acetate. B2 can be prepared using three times the weight of sodium permanganate used in A1, following the same process as A1. The pH of B2 was 4.61 at 22.8°C. When using B2, the polishing rate was 5.19 μm / h, and the Ra of one surface 11a after polishing was 0.133 nm.

[0085] B3 in Figure 3 is polishing solution 1, containing 10.00 wt% sodium permanganate and 2.75 wt% zirconyl acetate. B3 can be prepared using four times the weight of sodium permanganate used in A1, following the same process as A1. The pH of B3 was 4.62 at 22.9°C. When using B3, the polishing rate was 5.99 μm / h, and the Ra of one surface 11a after polishing was 0.122 nm.

[0086] Furthermore, increasing the concentration of sodium permanganate (permanganate) does not significantly affect the viscosity of polishing solution 1. Therefore, the concentration of permanganate in polishing solution 1 may be increased depending on the desired polishing rate.

[0087] As is clear from the experimental results in Figures 2 and 3, by setting the concentration of sodium permanganate (permanganate salt) to 2.50 wt% or higher and the concentration of zirconyl acetate (water-soluble compound) to 0.55 wt% or higher and 5.50 wt% or lower, polishing to a Ra of less than 0.2 nm can be achieved on the polished surface.

[0088] Furthermore, the applicant has confirmed that virtually no scratches are formed on the polished surface when polishing using A1 to A5 and B1 to B3. In this way, by achieving polishing with Ra < 0.2 nm and virtually scratch-free, it is possible to satisfy the high specification requirements in post-polishing processes.

[0089] Of course, as mentioned above, since polishing solution 1 is weakly acidic due to the weak acid component that makes up the water-soluble compound, it has the advantage of being easier to handle and reducing the risk to workers compared to polishing solutions with strong acids.

[0090] Furthermore, the structures, methods, etc., according to the embodiments described above can be modified as appropriate without departing from the scope of the present invention. For example, the water-soluble compound used in polishing solution 1 is not limited to zirconyl acetate.

[0091] Even when using yttrium acetate, lanthanum acetate, or cerium acetate, the same mechanism as with zirconyl acetate allows for easier handling compared to strong acid polishing solutions and reduces the risk to workers.

[0092] It can be reasonably inferred that similar effects can be obtained when using water-soluble compounds such as yttrium citrate, lanthanum citrate, cerium citrate, zirconyl citrate, yttrium carbonate, lanthanum carbonate, cerium carbonate, zirconyl carbonate, yttrium phosphate, lanthanum phosphate, cerium phosphate, zirconyl phosphate, yttrium oxalate, lanthanum oxalate, cerium oxalate, zirconyl oxalate, yttrium borate, lanthanum borate, cerium borate, and zirconyl borate.

[0093] Therefore, a combination of transition metal elements from different groups may be used in polishing solution 1. That is, the transition metal elements used in polishing solution 1 only need to include at least one element from among the Group 3 elements, lanthanides, and Group 4 elements.

[0094] Incidentally, during polishing, instead of supplying the polishing liquid 1 from the through hole 22, the polishing liquid 1 may be supplied from the polishing pad 20 to the compound semiconductor substrate 11 by spraying it from a spray nozzle located radially outside the chuck table 4 onto the area on the underside of the polishing pad 20 that is not in contact with the compound semiconductor substrate 11. [Explanation of Symbols]

[0095] 1: Polishing liquid, 2: Polishing device, 4: Chuck table, 4a: Holding surface 6: Frame, 6a, 6b: Flow channels, 8: Porous plate 10: Polishing unit, 12: Spindle, 14: Mount 11: Compound semiconductor substrate, 11a: one side, 11b: the other side, 13: protective tape 16: Polishing tool, 18: Base, 20: Polishing pad, 20a: Abrasive grain, 22: Through hole 26: Polishing liquid supply source, 26a: Conduit

Claims

1. A polishing solution for polishing a SiC substrate, The solution comprises an aqueous solution containing permanganate and zirconium acetate. A polishing solution for SiC substrates, characterized in that the concentration of the permanganate is 2.50 wt% or more, and the concentration of the zirconium acetate is 0.55 wt% or more and 5.50 wt% or less.

2. The polishing solution for polishing SiC substrates according to claim 1, characterized in that the pH is 3 or higher and 7 or lower.

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