Polishing solution for polishing compound semiconductor substrates, and method for polishing compound semiconductor substrates.

Abstract

To realize a higher polishing rate than when potassium permanganate and cerium ammonium nitrate are used as polishing liquids.SOLUTION: A polishing liquid for compound semiconductor substrate polishing includes an aqueous solution containing permanganate and a water-soluble compound containing a strong acid and a transition metal element. The transition metal element contains at least one element among a group 3 element, a lanthanoid, and a group 4 element, the concentration of ammonium ions and ammonia contained in the aqueous solution is lower than the concentration of the group 3 element, the lanthanoid, and the group 4 element.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In recent years, power devices that have higher breakdown voltage and can control large current compared to conventional devices formed using silicon single crystal substrates have attracted attention. A power device is formed, for example, on one side of a SiC (silicon carbide) single crystal substrate.

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

[0004] In Patent Document 1, it is particularly described that 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.

[0005] For example, in Patent Document 1, when the rotation speed of the polishing pad (i.e., the rotation speed of the spindle) is 495 rpm, the rotation speed of the chuck table is 500 rpm, the pressure from the polishing pad to the chuck table is 1 kgf / cm 2 and the flow rate of a polishing liquid having 3% potassium permanganate and 0.16% ammonium cerium nitrate is 0.15 L / min, it is described that a polishing rate of 197 nm / min can be achieved. In terms of the polishing rate, 197 nm / min corresponds to 11.82 μm / h. Also, in terms of pressure, 1 kgf / cm 2 corresponds to about 98 kPa.

[0006] Conventionally, the above polishing process was performed on 4-inch (approximately 100 mm) SiC single crystal substrates. However, polishing equipment for substrates with a diameter exceeding 4 inches may not be able to apply pressures exceeding 50 kPa due to the performance limitations of the equipment.

[0007] In polishing according to Preston's Law, the polishing rate increases with pressure. However, even when the pressure applied to the SiC single crystal substrate is reduced compared to conventional methods, it is required to achieve a polishing rate higher than that of conventional methods. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2012-253259 [Overview of the project] [Problems that the invention aims to solve]

[0009] This invention was made in view of the aforementioned problems, and aims to achieve a higher polishing rate than conventional methods by improving the polishing fluid. [Means for solving the problem]

[0010] According to one aspect of the present invention, Used when polishing compound semiconductor substrates with abrasive pads containing abrasive particles. A polishing solution for polishing compound semiconductor substrates, comprising an aqueous solution in which a permanganate salt, a water-soluble compound formed by the combination of a strong acid and a transition metal element are dissolved, Furthermore, it does not contain free abrasive particles, The transition metal element is a Group 3 element. and Lantanoy do The aqueous solution contains at least one of the elements, and the concentrations of ammonium ions and ammonia contained in the aqueous solution are equal to the concentrations of the Group 3 element. and The Lantanoi do Compounds with concentrations below a certain level are provided as polishing solutions for semiconductor substrates.

[0011] Preferably, the concentration of the permanganate is 0.6 wt% or more, and the concentration of the water-soluble compound is 0.3 wt% or more.

[0012] Preferably, the concentration of the permanganate is 4.8 wt% or less, and the concentration of the water-soluble compound is 2.4 wt% or less.

[0013] According to another aspect of the present invention, a method for polishing a compound semiconductor substrate comprises: a holding step of holding the compound semiconductor substrate in a chuck table of a polishing apparatus; and a polishing step of polishing the compound semiconductor substrate while supplying a polishing solution from the polishing pad to the compound semiconductor substrate with a polishing pad having abrasive particles in contact with one surface of the compound semiconductor substrate, wherein the polishing solution comprises an aqueous solution in which a permanganate salt and a water-soluble compound formed by the combination of a strong acid and a transition metal element are dissolved. Furthermore, it does not contain free abrasive particles, The transition metal element is a Group 3 element. and Lantanoy do The aqueous solution contains at least one of the elements, and the concentrations of ammonium ions and ammonia contained in the aqueous solution are equal to the concentrations of the Group 3 element. and The Lantanoi do A method for polishing compound semiconductor substrates with a concentration below a certain level is provided. [Effects of the Invention]

[0014] A polishing solution according to one aspect of the present invention comprises an aqueous solution in which a permanganate salt and a water-soluble compound formed by the combination of a strong acid and a transition metal element are dissolved. The transition metal element includes at least one element from among the Group 3 elements, lanthanides, and Group 4 elements.

[0015] In particular, the concentrations of ammonium ions and ammonia in the polishing solution are below the concentrations of oxides of Group 3 elements, lanthanides, and Group 4 elements. Therefore, compared to cases where the concentrations of ammonium ions and ammonia exceed this level, the oxidizing effect of permanganate ions on one surface of the compound semiconductor substrate can be maintained at a high level.

[0016] If one side of a compound semiconductor substrate is oxidized, the oxidized side can be smoothly scraped off with a polishing pad compared to the case where the side is not oxidized. By reducing the concentrations of ammonium ions and ammonia in this way, a higher polishing rate can be achieved compared to using potassium permanganate and cerium ammonium nitrate as the polishing liquid.

Brief Description of the Drawings

[0017] [Figure 1] It is a partial cross-sectional side view of a polishing apparatus. [Figure 2] It is a flowchart of a polishing method. [Figure 3] It is a diagram showing the experimental results of comparing a conventional polishing liquid with the polishing liquid of this embodiment.

Modes for Carrying Out the Invention

[0018] Referring to the accompanying drawings, an embodiment according to an aspect of the present invention will be described. First, the polishing liquid 1 (see FIG. 1) of this embodiment will be described. The polishing liquid 1 contains an aqueous solution in which a permanganate and a water-soluble compound are dissolved.

[0019] As the permanganate, sodium permanganate (NaMnO4), potassium permanganate (KMnO4), etc. are used. As will be described later, it is preferable to use sodium permanganate, which has a higher solubility in water than the solubility of potassium permanganate, as the permanganate.

[0020] Further, the permanganate may be a permanganate 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).

[0021] The water-soluble compounds used are (i) water-soluble compounds formed by the combination of a strong acid and a group 3 element, (ii) water-soluble compounds formed by the combination of a strong acid and a lanthanide, or (iii) water-soluble compounds formed by the combination of a strong acid and a group 4 element.

[0022] Examples of strong acids include nitric acid (HNO3), hydrochloric acid (HCl), and sulfuric acid (H2SO4), but strong acids are not limited to these three types.

[0023] (1) Examples of Group 3 elements include yttrium (Y), (2) Examples of lanthanides include lanthanum (La) and cerium (Ce), and (3) Examples of Group 4 elements include zirconium (Zr).

[0024] When nitric acid (HNO3) is used as a strong acid, (1) yttrium nitrate (Y(NO3)3), (2) lanthanum nitrate (La(NO3)3), cerium nitrate (Ce(NO3)3), and (3) zirconyl nitrate (also called zirconium oxynitrate) (ZrO(NO3)2) are used as water-soluble compounds.

[0025] When hydrochloric acid (HCl) is used as a strong acid, (1) yttrium chloride (YCl3), (2) lanthanum chloride (LaCl3), cerium chloride (CeCl3), and (3) zirconyl chloride (also called zirconium oxide or zirconium oxychloride) (ZrOCl2) are used as water-soluble compounds.

[0026] When sulfuric acid (H2SO4) is used as a strong acid, (1) yttrium sulfate (Y2(SO4)3), (2) lanthanum sulfate (La2(SO4)3), cerium sulfate (Ce(SO4)2), and (3) zirconyl sulfate (also called zirconium sulfate) (ZrOSO4) are used as water-soluble compounds.

[0027] Polishing solution 1, which contains an aqueous solution in which permanganate and a water-soluble compound are dissolved, is strongly acidic (for example, a predetermined pH of less than 3) 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.

[0028] 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).

[0029] In particular, polishing solution 1 is strongly 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.

[0030] 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).

[0031] 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 lanthanum nitrate (La(NO3)3) will be explained. Note that the mechanism described below is the applicant's speculation, and the actual mechanism may differ.

[0032] 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.

[0033] Furthermore, the carbon atoms in the SiC single crystal substrate are transformed into carboxyl groups, carbon dioxide, etc. Carboxyl groups are formed from La 3+It coordinates with the abrasive grains and is extracted from the compound semiconductor substrate 11. In addition, carbon dioxide dissolves in the polishing solution 1 as carbonate ions or becomes a gas and is discharged from the polishing solution 1.

[0034] The SiO2 layer formed on one side 11a is softer than the SiC crystal plane. As the SiO2 layer is physically removed by the abrasive grains, a new SiC crystal plane is exposed. From this point onward, the formation of the SiO2 layer by oxidation and the physical removal by the abrasive grains are repeated alternately.

[0035] Thus, in order to proceed with polishing one side 11a using the polishing solution 1, it is necessary to ensure that the polishing solution 1 fully exhibits its ability to oxidize one side 11a of the compound semiconductor substrate 11.

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

[0037] In this embodiment, by maintaining the polishing solution 1 as strongly acidic using a water-soluble compound formed by the combination of a strong acid and a transition metal element, the oxidizing ability of permanganic acid can be fully exhibited.

[0038] In contrast, 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 surface 11a decreases, which is thought to relatively weaken the oxidizing ability of the permanganic acid. When oxidation on the surface 11a becomes more difficult, the abrasive grains become less able to remove material, and as a result, 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, the polishing solution 1 does not intentionally contain basic substances or ions such as ammonia or ammonium ions as raw materials during manufacturing. Therefore, the polishing solution 1 can fully exhibit the oxidizing ability of permanganate 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. In Figure 1, the abrasive grains 20a are arranged regularly on the polishing pad 20, but in reality, the abrasive grains 20a are arranged randomly on the polishing pad 20.

[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] Figure 2 is a flowchart of the polishing method for polishing a compound semiconductor substrate 11. In this example, the compound semiconductor substrate 11 is a SiC single crystal substrate with a diameter of 6 inches (approximately 150 mm). When polishing one surface 11a, first, one compound semiconductor substrate 11 is placed on the chuck table 4 so that one surface 11a is exposed facing upwards.

[0061] Then, the other side 11b of the compound semiconductor substrate 11 is held in place by suction on the holding surface 4a (holding step S10). In this embodiment, one side 11a is a Si surface and the other side 11b is a C surface, but it is also possible for one side 11a to be a C surface and the other side 11b to be a Si surface.

[0062] Next, the polishing process S20 is performed. In the polishing process S20, 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 750 rpm, and the rotational speed of the spindle 12 (i.e., the polishing tool 16) is set to 745 rpm.

[0063] 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.

[0064] 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.

[0065] 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 shown in Figure 1, the polishing pad 20 is placed at the position of the chuck table 4 shown in Figure 1, 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.

[0066] 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 outside the grinding pad 20 by centrifugal force, and 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).

[0067] 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.

[0068] The flow rate of polishing solution 1 shall be between 0.1 L / min and 0.3 L / min (for example, 0.2 L / min). The pressure exerted by the polishing pad 20 against the compound semiconductor substrate 11 shall be between 30 kPa and 50 kPa (for example, 40 kPa).

[0069] However, since the polishing in this embodiment follows Preston's Law, the pressure may be increased or decreased as appropriate depending on the polishing method. However, for the performance of the polishing apparatus 2, the pressure should be 50 kPa or less, more preferably 40 kPa or less.

[0070] In polishing step S20, the compound semiconductor substrate 11 is polished while the polishing pad 20 is in contact with one surface 11a, the chuck table 4 and spindle 12 are rotated, and polishing liquid 1 is supplied from the polishing pad 20 to the compound semiconductor substrate 11. At this time, one surface 11a is polished according to the chemical mechanical polishing mechanism described above.

[0071] In addition, during the polishing process S20, the chuck table 4 may be oscillated along the X-axis direction within a predetermined distance range by the X-axis direction movement mechanism. That is, during the polishing process S20, the chuck table 4 may be moved a predetermined distance in the +X direction, and then moved a predetermined distance in the -X direction, and this operation may be repeated.

[0072] 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. In this embodiment, where the diameter of the compound semiconductor substrate 11 is 6 inches (approximately 150 mm), the predetermined distance is set to 10 mm.

[0073] In this way, by oscillating the chuck table 4 during the polishing process S20, there is an advantage in that one side 11a can be polished more uniformly (for example, the TTV (total thickness variation) can be reduced) compared to when it is not oscillated.

[0074] (First Experiment) Next, the first experiment will be described with reference to Figure 3. Figure 3 shows the experimental results comparing the polishing rates of conventional polishing solutions (Experimental Examples 1 and 2) and polishing solution 1 of this embodiment (Experimental Examples 3 and 4).

[0075] In Experimental Examples 1 to 4 shown in Figure 3, a fixed abrasive type polishing pad 20 was used, in which silica abrasive grains (product name: SO-E2, particle size 0.4 μm to 0.6 μm) manufactured by Admatex Co., Ltd. were fixed to a pad made of rigid foamed urethane resin. The polishing conditions were as follows.

[0076] Chuck table 4 rotation speed: 750 rpm Polishing pad 20 rotation speed: 745 rpm Polishing fluid flow rate: 0.2 L / min Pressure from polishing pad 20: 39.2 kPa Polishing time: 620s Compound semiconductor substrate 11: SiC single crystal substrate Diameter of compound semiconductor substrate 11: 6 inches (approximately 150 mm) Surface to be polished: Si surface

[0077] In Experimental Example 1 (Conventional Example), 60 g of cerium ammonium nitrate was added to a sufficient amount of pure water, and then 120 g of potassium permanganate was added to this. Next, this was diluted with 10 L of pure water, and then stirred with a stirrer at 100 rpm for 30 minutes to prepare a 10 L polishing solution in which 1.2 wt% potassium permanganate and 0.6 wt% cerium ammonium nitrate were dissolved.

[0078] In Experimental Example 2 (Conventional Example), 60 g of cerium ammonium nitrate was added to a sufficient amount of pure water, and then 120 g of sodium permanganate was added to this. Next, this was diluted with 10 L of pure water, and then stirred with a stirrer at 100 rpm for 30 minutes to prepare a 10 L polishing solution in which 1.2 wt% of sodium permanganate and 0.6 wt% of cerium ammonium nitrate were dissolved.

[0079] In Experimental Example 3 (an example of this embodiment), 79.94 g of lanthanum(III) nitrate hexahydrate was added to a sufficient amount of pure water, and then 120 g of potassium permanganate was added to this. Next, this was diluted with 10 L of pure water, and then stirred with a stirrer at 100 rpm for 30 minutes to prepare 10 L of polishing solution 1 in which 1.2 wt% of potassium permanganate and 0.6 wt% of lanthanum nitrate were dissolved.

[0080] In Experimental Example 4 (another example of this embodiment), 79.94 g of lanthanum(III) nitrate hexahydrate was added to a sufficient amount of pure water, and then 120 g of sodium permanganate was added to this. After diluting this with 10 L of pure water, the mixture was stirred at 100 rpm for 30 minutes using a stirrer to prepare 10 L of polishing solution 1 in which 1.2 wt% of sodium permanganate and 0.6 wt% of lanthanum nitrate were dissolved.

[0081] In Experimental Examples 1 to 4, a fixed abrasive type polishing pad 20 is used, so the polishing solution does not contain free abrasive particles. In other words, each concentration represents the wt% in the polishing solution that does not contain abrasive particles.

[0082] In Experimental Examples 1 to 4, the Si side of the SiC single crystal substrate was polished according to the polishing conditions described above. The polishing rate in Experimental Example 1 was 5.22 μm / h, and the polishing rate in Experimental Example 2 was 6.78 μm / h. Thus, in Experimental Examples 1 and 2, which used conventional polishing solutions, the target polishing rate of 7.00 μm / h was not achieved.

[0083] In contrast, the polishing rate in Experimental Example 3 was 8.09 μm / h, and the polishing rate in Experimental Example 4 was 8.53 μm / h, both exceeding the target polishing rate of 7.00 μm / h.

[0084] As described above, by lowering the concentrations of ammonium ions and ammonia, it is believed that a higher polishing rate was achieved compared to the conventional method of using potassium permanganate and cerium ammonium nitrate as polishing solutions.

[0085] Furthermore, the reason why using sodium permanganate resulted in a higher polishing rate compared to potassium permanganate is thought to be due to the higher solubility of sodium permanganate compared to potassium permanganate.

[0086] For example, the solubility of sodium permanganate in 100g of pure water at 25°C is 61.6g, while the solubility of potassium permanganate in 100g of pure water at 25°C is 7.5g.

[0087] It is presumed that higher solubility leads to an increase in the number of permanganate molecules, and an increase in the number of permanganate molecules makes it easier to oxidize the SiC single crystal substrate, thus leading to an increase in the polishing rate. However, this is the applicant's speculation, and the increase in the polishing rate may be due to other factors.

[0088] (Second Experiment) Next, the experimental results of polishing a SiC single crystal substrate, which is a compound semiconductor substrate 11, using polishing solution 1 containing an aqueous solution of sodium permanganate and lanthanum nitrate are shown (see Tables 1 and 2).

[0089] The polishing conditions were the same as those described above, except that the pressure from the polishing pad 20 to the compound semiconductor substrate 11 was set to 40.0 kPa. The polishing time for the Si surface was 620 s, as described above, but the polishing time for the C surface was 140 s.

[0090] Table 1 shows the polishing rates of the Si surface according to the respective concentrations of sodium permanganate and lanthanum nitrate in polishing solution 1.

[0091] [Table 1]

[0092] Table 2 shows the polishing rates of the C-surface according to the sodium permanganate and lanthanum nitrate in polishing solution 1.

[0093] [Table 2]

[0094] As is clear from Tables 1 and 2, if the concentration of sodium permanganate is 0.60 wt% or higher and the concentration of lanthanum nitrate is 0.30 wt% or higher, the target polishing rate of 7.00 μm / h can be achieved even when polishing Si surfaces, which are considered relatively difficult to polish.

[0095] Furthermore, by setting the concentration of sodium permanganate to 4.80 wt% or less and the concentration of lanthanum nitrate to 2.40 wt% or less, a sufficient polishing rate can be obtained while suppressing the increase in material costs for polishing solution 1.

[0096] 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 lanthanum nitrate.

[0097] It can be reasonably inferred that a higher polishing rate can be achieved using yttrium nitrate, cerium nitrate, and zirconyl nitrate compared to using cerium ammonium nitrate, through a similar mechanism.

[0098] Similarly, it can be reasonably inferred that using yttrium chloride, lanthanum chloride, cerium chloride, and zirconyl chloride, or yttrium sulfate, lanthanum sulfate, cerium sulfate, and zirconyl sulfate, will achieve a higher polishing rate compared to using cerium ammonium nitrate.

[0099] Therefore, a combination of transition metal elements from different groups may be used in polishing solution 1. For example, two or more types of yttrium nitrate, lanthanum nitrate, and zirconyl nitrate may be used in polishing solution 1 in appropriate combinations. In other words, 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.

[0100] Alternatively, a water-soluble compound of nitric acid and a transition metal element containing at least one element from among the Group 3 elements, lanthanides, and Group 4 elements (i.e., a nitric acid-based water-soluble compound) and a water-soluble compound of sulfuric acid and a transition metal element containing at least one element from among the Group 3 elements, lanthanides, and Group 4 elements (i.e., a sulfuric acid-based water-soluble compound) may be combined in polishing solution 1.

[0101] By the way, in the polishing process S20, 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 lower side of the polishing pad 20 that is not in contact with the compound semiconductor substrate 11. [Explanation of Symbols]

[0102] 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 S10: Holding process, S20: Polishing process

Claims

1. A polishing liquid for polishing a compound semiconductor substrate, used when polishing a compound semiconductor substrate with a polishing pad having abrasive particles, The solution comprises an aqueous solution containing a permanganate salt, a water-soluble compound formed by the combination of a strong acid and a transition metal element, and does not contain free abrasive particles. The transition metal element includes at least one element from among the Group 3 elements and the lanthanides. A polishing solution for polishing compound semiconductor substrates, characterized in that the concentrations of ammonium ions and ammonia contained in the aqueous solution are less than or equal to the concentrations of the group 3 element and the lanthanide.

2. The polishing solution for polishing a compound semiconductor substrate according to claim 1, characterized in that the concentration of the permanganate is 0.6 wt% or more, and the concentration of the water-soluble compound is 0.3 wt% or more.

3. The polishing solution for polishing a compound semiconductor substrate according to claim 1 or 2, characterized in that the concentration of the permanganate is 4.8 wt% or less, and the concentration of the water-soluble compound is 2.4 wt% or less.

4. The compound is used to polish a semiconductor substrate, and the compound is used to polish a semiconductor substrate. A holding step of holding the compound semiconductor substrate in the chuck table of the polishing apparatus, A polishing step in which a polishing pad having abrasive particles is brought into contact with one surface of the compound semiconductor substrate, and a polishing solution is supplied from the polishing pad to the compound semiconductor substrate while polishing the substrate, Equipped with, The polishing liquid is The solution comprises an aqueous solution containing a permanganate salt, a water-soluble compound formed by the combination of a strong acid and a transition metal element, and does not contain free abrasive particles. The transition metal element includes at least one element from among the Group 3 elements and the lanthanides. A method for polishing a compound semiconductor substrate, characterized in that the concentrations of ammonium ions and ammonia contained in the aqueous solution are less than or equal to the concentrations of the group 3 element and the lanthanide.

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