Plane polishing method and plane polishing apparatus for semiconductor substrate

Abstract

The invention relates to a surface polishing method and a surface polishing apparatus for a semiconductor substrate. The surface polishing device is provided with: a pH adjusting agent dropping device (38) for dropping a pH adjusting agent (AC) to a polishing liquid (32); and a polishing control device (40) that performs rough polishing of the semiconductor substrate (22) by rotationally driving the lower polishing pad (18) and the upper polishing pad (20) while dropping a pH regulator (AC) from the pH regulator dropping device (38) into the polishing liquid (32) and maintaining the pH value of the polishing liquid (32) in a strong acid processing region during a predetermined period from the start of polishing processing. From the elapse of a predetermined period of time to the end of polishing processing, fine polishing of the semiconductor substrate (22) is performed by rotationally driving the lower polishing pad (18) and the upper polishing pad (20) while stopping the addition of the pH regulator AC from the pH regulator addition device (38) to make the pH value of the polishing liquid (32) higher than the strong acid processing region. As a result, both high polishing efficiency and good surface roughness (Sa) can be obtained in one polishing step.

Description

Technical Field

[0001] The present invention relates to a surface polishing method and surface polishing device for a semiconductor substrate used for polishing one side of a semiconductor substrate used in a semiconductor device, and relates to a technology for continuously performing rough polishing and fine polishing during the polishing process by changing the pH value of a polishing liquid circulated during the polishing process. Background Art

[0002] Regarding polishing semiconductor substrates (semiconductor wafers) such as SiC, there is a surface polishing method described in, for example, Patent Document 1. According to this surface polishing method, an acidic polishing liquid containing permanganate ions, a weak acid, and a soluble salt thereof, whose pH value is adjusted to 0.5 to 6 before polishing, is circulated and repeatedly supplied to the polishing surface.

[0003] According to this polishing method, by including a weak acid and a soluble salt thereof in the polishing liquid, it is possible to suppress a sharp decrease in the polishing rate caused by a sharp increase in the pH value of the polishing liquid due to oxidation of the material to be polished by permanganate ions in the polishing liquid, thereby improving the polishing efficiency of the polished surface of the semiconductor substrate.

[0004] [Prior Art Literature]

[0005] [Patent Document]

[0006] [Patent Document 1] Japanese Patent No. 6301571 Summary of the Invention

[0007] However, in the conventional surface polishing method for semiconductor substrates, the pH value of the polishing liquid is suppressed from rising sharply during polishing by the action of a weak acid and a soluble salt thereof contained in the polishing liquid, causing the pH value to rise at a constant rate. This increases the oxidation state of the semiconductor substrate caused by permanganate ions compared to a case where the polishing liquid does not contain a weak acid and a soluble salt thereof, thereby achieving improved polishing efficiency. Therefore, it is difficult to achieve both improved polishing efficiency of the semiconductor substrate and the quality of the polished surface (low surface roughness) in a single polishing step.

[0008] The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide a surface polishing method and a surface polishing apparatus for a semiconductor substrate, which can improve polishing efficiency and polished surface quality in the surface polishing process of the semiconductor substrate.

[0009] The present inventors conducted various studies based on the above situation and discovered that, when polishing one side of a semiconductor substrate using a polishing pad while cyclically using an acidic polishing slurry containing potassium permanganate, if a pH adjusting liquid is initially supplied to the polishing slurry to maintain the pH value of the polishing slurry at a predetermined low, strongly acidic value while polishing is performed, and then the supply of the pH adjusting liquid is stopped while polishing is continued, high polishing efficiency and good surface roughness can be achieved in a single polishing step. The present invention was completed based on this finding.

[0010] That is, the gist of the first invention is to provide a method for polishing a semiconductor substrate, (1) the method comprises polishing a semiconductor substrate using a polishing pad while circulating a polishing liquid containing permanganate and water, (2) polishing is performed while adding a pH adjusting agent to the polishing liquid to maintain the pH value of the polishing liquid in a strong acid processing region during a predetermined period starting from the start of the polishing process, and (3) polishing is performed while stopping the addition of the pH adjusting agent from the end of the predetermined period until the end of the polishing process to maintain the pH value of the polishing liquid higher than that in the strong acid processing region.

[0011] The second invention is directed to a surface polishing device for a semiconductor substrate, wherein (1) the polishing device is a surface polishing device for a semiconductor substrate that polishes the surface of the semiconductor substrate using a polishing pad while circulating a polishing liquid containing permanganate and water, and comprises: (2) a pH adjusting agent dripping device that drips a pH adjusting agent into the polishing liquid; and (3) a polishing control device that, during a predetermined period from the start of the polishing process, causes the pH adjusting agent to be dripped from the pH adjusting agent dripping device into the polishing liquid to maintain the pH value of the polishing liquid in a strong acid processing region while rotating the polishing pad to polish the semiconductor substrate, and, from the lapse of the predetermined period until the end of the polishing process, causes the pH adjusting agent to be dripped from the pH adjusting agent dripping device to maintain the pH value of the polishing liquid above the strong acid processing region while rotating the polishing pad to polish the semiconductor substrate. The permanganate is an oxygen-containing salt of manganese represented by potassium permanganate and sodium permanganate.

[0012] The summary of the third invention is that, in the second invention, the predetermined period is a period during which the polishing time of the semiconductor substrate is between 33% and 50% of the polishing time from the start of polishing.

[0013] The gist of the fourth invention is that, in the second invention, the strong acid processing region is a region where the polishing process is performed using the polishing liquid having a pH value of 2.5 to 3.5.

[0014] The gist of the fifth invention is that, in the second invention, the polishing liquid is a polishing liquid that does not contain polishing abrasive grains, and the polishing pad is a polishing pad having a base resin having independent pores and / or interconnected pores and the polishing abrasive grains filled in the independent pores and / or interconnected pores of the base resin.

[0015] The gist of the sixth invention is that, in the second invention, the pH adjuster is an agent such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc., which can adjust the pH value of the polishing liquid to the acidic side.

[0016] According to the first invention, a surface polishing method for a semiconductor substrate is performed while adding a pH adjusting agent to the polishing liquid to maintain the pH value of the polishing liquid in the strong acid processing region during a specified period from the start of the polishing process. Then, from the end of the specified period until the end of the polishing process, the addition of the pH adjusting agent is stopped to increase the pH value of the polishing liquid above the strong acid processing region while polishing is performed. That is, during the specified period from the start of the polishing process, the pH value of the polishing liquid after adding the pH adjusting agent is within the strong acid processing region, promoting polishing, in other words, performing rough polishing. Then, when the pH adjusting agent is stopped after the specified period, the pH value of the polishing liquid becomes higher than the strong acid processing region, in other words, performing fine polishing. Thus, high polishing efficiency and good surface roughness can be achieved in one polishing step.

[0017] According to the second invention, a surface polishing apparatus for a semiconductor substrate includes a pH adjuster dripping device for dripping a pH adjuster into a polishing liquid. A polishing control device, for a predetermined period from the start of the polishing process, causes the pH adjuster to drip from the pH adjuster dripping device into the polishing liquid, maintaining the pH value of the polishing liquid within the strong acid processing region, while rotating the polishing pad to polish the semiconductor substrate. From the elapse of the predetermined period until the end of the polishing process, the pH adjuster dripping from the pH adjuster dripping device is stopped, causing the pH value of the polishing liquid to rise above the strong acid processing region, while rotating the polishing pad to polish the semiconductor substrate. Specifically, during the predetermined period from the start of the polishing process, the pH value of the polishing liquid after the pH adjuster is dripped into the polishing liquid is within the strong acid processing region, promoting polishing, in other words, performing rough polishing. Subsequently, when the pH adjuster is no longer dripped into the polishing liquid after the predetermined period, the pH value of the polishing liquid rises above the strong acid processing region, in other words, performing fine polishing. Thus, high polishing efficiency and good surface roughness are simultaneously achieved in a single polishing step.

[0018] According to the surface polishing apparatus of the third invention, in the second invention, the predetermined period is the period during which the polishing time, calculated from the start of polishing, is between 33% and 50% of the semiconductor substrate polishing time. Therefore, high polishing efficiency and good surface roughness can be achieved simultaneously in a single polishing step. If the polishing time is less than 33%, a sufficient polishing rate cannot be achieved, while if the polishing time is greater than 50%, sufficient surface texture may not be achieved.

[0019] According to the surface polishing apparatus of the fourth invention, in the second invention, the strong acid processing zone is a zone where polishing is performed using a polishing liquid having a pH of 2.5 to 3.5. Therefore, high polishing efficiency and good surface roughness can be achieved simultaneously in a single polishing step. When the pH of the strong acid processing zone is higher than 3.5, a sufficient polishing rate cannot be achieved. When the pH of the strong acid processing zone is lower than 2.5, excessive oxidation occurs, sometimes adversely affecting surface properties.

[0020] According to the surface polishing device of the fifth invention, in the second invention, the polishing liquid does not contain abrasive grains, and the polishing pad includes a matrix resin having independent pores and / or interconnected pores formed therein, and abrasive grains filled in the independent pores and / or interconnected pores of the matrix resin. Since the polishing liquid does not contain abrasive grains, the environmental load is reduced.

[0021] According to the surface polishing apparatus of the sixth invention, in the second invention, the pH adjuster is a reagent such as hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid that can adjust the pH of the polishing liquid to the acidic side, thereby enabling the pH of the polishing liquid to be adjusted to 2.5 to 3.5. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a perspective view conceptually illustrating the configuration of a double-side polishing apparatus for implementing a surface polishing method according to an application example of the present invention.

[0023] Figure 2 It will Figure 1 Schematic diagram showing an enlarged view of the surface structure of the polishing pad.

[0024] Figure 3 This is a graph showing the relationship between polishing time and pH of the polishing liquid obtained through polishing experiments conducted by the present inventors.

[0025] Figure 4 This is a graph showing the measured values ​​of the polishing rate, the surface roughness of the Si surface, the surface roughness of the C surface, the surface roughness ratio C / Si, and the flatness difference before and after polishing in each polishing test obtained by the present inventors, each showing different pH adjuster addition periods.

[0026] Figure 5 Yes Figure 4 A bar graph showing the milling rates of various milling tests with different pH adjuster addition periods.

[0027] Figure 6 Yes Figure 4 Graph showing the surface roughness of the Si surface and the C surface in each polishing test at different pH adjuster addition periods.

[0028] Figure 7 Yes Figure 4 The bar graph shows the TTV (Total Thickness Variation) value, i.e., the flatness difference, before and after polishing for each polishing test with different pH adjuster addition periods.

[0029] Figure 8 Yes Figure 4 A graph showing the comprehensive evaluation of each grinding test in which the pH adjuster addition period was different.

[0030] Description of Reference Numerals

[0031] 10: Double-sided grinding device (flat grinding device)

[0032] 18: Lower polishing pad (polishing pad)

[0033] 20: Upper polishing pad (polishing pad)

[0034] 22: Semiconductor substrate

[0035] 26: Grinding abrasive

[0036] 28: Independent pores and / or connected pores

[0037] 30: Base material resin

[0038] 32: Grinding fluid

[0039] 38: pH regulator dosing device

[0040] 40: Grinding control device

[0041] AC: pH adjuster DETAILED DESCRIPTION

[0042] Hereinafter, an application example of the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, the drawings are appropriately simplified or deformed, and the dimensional ratios and shapes of the various parts are not necessarily accurately depicted.

[0043] [Example]

[0044] In this embodiment, a surface polishing apparatus is used as a surface polishing apparatus for performing a surface polishing method on a semiconductor substrate 22 such as SiC. Figure 1The double-sided grinding device 10 shown. Figure 1 In FIG, the guide roller fixing table is removed to conceptually illustrate the main parts of the double-side polishing device 10. Figure 1 In the double-side polishing apparatus 10, a pair of lower polishing platforms 12 and upper polishing platforms 14 are arranged to face each other and to be rotatable relative to each other around a vertical rotation axis C1. The lower polishing platform 12 is driven by a platform drive motor 16 to rotate relative to the upper polishing platform 14. Figure 1 The lower polishing platen 12 and the upper polishing platen 14 are rotated at a constant speed in one direction indicated by the arrow in FIG. 1 , and the upper polishing platen 14 is also rotated in the opposite direction by the platen drive motor 16 via a coupling mechanism (not shown). A pair of lower polishing pads 18 and upper polishing pads 20 are provided on the facing surfaces of the lower polishing platen 12 and the upper polishing platen 14, respectively.

[0045] A circular semiconductor substrate (workpiece) 22 is sandwiched between the upper surface of the lower polishing pad 18 of the lower polishing platen 12 and the lower surface of the upper polishing pad 20 of the upper polishing platen 14. This semiconductor substrate (workpiece) 22 is rotatably held within a holding hole formed through a well-known circular carrier plate (not shown). For example, the carrier plate has peripheral teeth and is meshed with a central gear concentric with the rotation axis C1 and a large-diameter internal gear. The carrier plate is configured to rotate and revolve in a planetary motion by rotating the central gear or internal gear using a carrier plate drive motor 24.

[0046] The lower polishing pad 18 and the upper polishing pad 20 are as shown in FIG. Figure 2 As shown, the polishing pad (LHA pad) is made of epoxy resin or PES resin and has independent pores and / or communicating pores 28 for accommodating polishing abrasive grains 26, and has an outer diameter of, for example ×Thickness: Approximately 2mm.

[0047] The lower polishing pad 18 and the upper polishing pad 20 are formed into a disc-shaped disk and include a matrix resin 30 made of epoxy resin or PES resin and having independent pores and / or interconnecting pores 28 formed therein, and a plurality of abrasive grains 26 that are filled within the independent pores and / or interconnecting pores 28 of the matrix resin 30 and are partially fixed to the matrix resin 30 or partially separated from the matrix resin 30 during polishing. Therefore, the lower polishing pad 18 and the upper polishing pad 20 are referred to as semi-fixed internal abrasive polishing pads containing the abrasive grains 26, and polishing using such internal abrasive polishing pads is referred to as semi-fixed abrasive polishing. For example, the lower polishing pad 18 and the upper polishing pad 20 are composed of approximately 32% by volume of the abrasive grains 26, approximately 33% by volume of the matrix resin 30, and the remaining volume of the independent pores and / or interconnecting pores 28. The independent pores and / or interconnected pores 28 of the matrix resin 30, which is formed in a sponge-like or mesh-like manner, are formed to be equal to or larger than the abrasive grains 26, and a plurality of abrasive grains 26 are retained within the independent pores and / or interconnected pores 28. The matrix resin 30 and the abrasive grains 26 are fixed to each other by a necessary and sufficient bonding force. The lower polishing pad 18 and the upper polishing pad 20 of this embodiment can polish the semiconductor substrate 22 by the mechanical polishing action of the abrasive grains 26 supplied by the lower polishing pad 18 and the upper polishing pad 20 and the chemical polishing action of the polishing liquid 32, without using a slurry containing abrasive grains 26 such as colloidal silica, for example, while circulating a polishing liquid 32 that does not contain abrasive grains 26.

[0048] Silica is preferably used for the polishing abrasive 26, but other polishing abrasives 26 may also be used, such as those containing at least one of ceria, alumina, zirconium oxide, silicon carbide, titanium dioxide, manganese compounds, barium carbonate, chromium oxide, and iron oxide. As the silica, for example, fumed silica (silica fine particles obtained by high-temperature combustion of silicon tetrachloride, chlorosilane, or the like in the presence of hydrogen and oxygen) is preferably used. The average particle size of the polishing abrasive 26 is preferably 0.005 to 3.0 μm, more preferably 0.005 to 1.0 μm, more preferably 0.02 to 0.6 μm, more preferably 0.08 to 0.5 μm, and even more preferably 0.08 to 0.3 μm. For example, if the average particle size of the abrasive grains 26 is greater than 3.0 μm, the abrasive grains 26 released from the matrix resin 30 are likely to cause grinding scratches on the semiconductor substrate (workpiece) 22 during the grinding process described later. Furthermore, if the average particle size of the abrasive grains 26 is less than 0.005 μm, the abrasive grains 26 are likely to aggregate, and grinding scratches are likely to occur on the semiconductor substrate (workpiece) 22 during the grinding process. The particle size of the abrasive grains 26 is a particle size measured using a laser diffraction-scattering method, for example, a particle size / particle size distribution measuring device, Microtrac MT3300, manufactured by Nikkiso Co., Ltd., and the so-called average particle size is the arithmetic mean of the particle sizes.

[0049] The polishing liquid 32 contains permanganate and water, and does not contain polishing abrasive particles 26. The permanganate is an oxygen-containing salt of manganese, preferably represented by potassium permanganate and sodium permanganate. The polishing liquid 32 contains, for example, 0.1% by mass or more and 20% by mass or less of permanganate ions (MnO4 - The pH value of the polishing liquid 32 is adjusted to a range of 2.5 to 3.5 using a pH adjuster AC. The pH adjuster AC is a reagent such as hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid that can adjust the pH value of the polishing liquid 32 to the acidic side.

[0050] Back to Figure 1 The double-side polishing apparatus 10 includes a polishing liquid circulation supply device 36 for circulating the polishing liquid 32 while supplying it to the polishing surface of the semiconductor substrate 22, a pH adjuster dropping device 38 for dropping a pH adjuster AC into the polishing liquid 32, and a polishing control device 40 for controlling the polishing process.

[0051] The polishing liquid circulation supply device 36 includes a receiving tank 42, located below the lower polishing pad 18, for receiving the polishing liquid 32 used to polish the semiconductor substrate 22; a discharge pipe 46, which guides the polishing liquid 32 received by the receiving tank 42 to the polishing liquid tank 44; a supply pipe 52, which guides the polishing liquid 32 in the receiving tank 42, which is pumped by a circulation pump 48, into the distribution tank 50; and a distribution pipe 54, which is connected to a plurality of through-holes formed at equal intervals in the circumferential direction in the bottom wall of the distribution tank 50 and supplies the polishing liquid 32 in the distribution tank 50 to a plurality of positions at equal intervals in the circumferential direction on the back side of the upper polishing pad 20. The polishing liquid 32 discharged from the distribution pipe 54 passes through the upper polishing pad 20 and is supplied to the lower polishing pad 18 and the semiconductor substrate 22 on the lower polishing pad 18.

[0052] The pH adjuster dripping device 38 includes a storage tank 56 for storing the pH adjuster AC and a regulating valve 58 for regulating the dripping amount from the storage tank 56 according to a command from the polishing control device 40 , and is installed above the polishing liquid tank 44 .

[0053] The polishing control device 40 is constructed, for example, using a microcomputer. It processes input signals according to a pre-stored program and controls the operation of the table drive motor 16, the carrier plate drive motor 24, the circulation pump 48, and the regulating valve 58. The polishing control device 40 functionally includes a first polishing control unit 60 that controls the addition of a pH adjuster AC to the polishing liquid 32 during the period between 33% and 50% of the polishing time from the start of polishing to achieve high-efficiency polishing, and a second polishing control unit 62 that controls the stoppage of the addition of the pH adjuster AC to the polishing liquid 32 to achieve finish polishing.

[0054] In the double-side polishing apparatus 10 configured as described above, for example, in response to the operation of a start switch (not shown), the polishing control unit 40 controls the platen drive motor 16, the carrier drive motor 24, the circulation pump 48, and the regulating valve 58 to start double-side polishing of the semiconductor substrate 22. Initially, the first polishing control unit 60 controls the regulating valve 58 to adjust the amount of pH adjuster AC added to the polishing liquid 32 during the polishing time period between 33% and 50% of the start time, so that the pH value of the polishing liquid 32 is maintained within a predetermined range, for example, the strong acid processing range of 2.5 to 3.5. During the surface polishing process in which the pH value of the polishing liquid 32 is maintained within the strong acid processing range of 2.5 to 3.5, double-side polishing of the semiconductor substrate 22 is performed at a high polishing rate PR.

[0055] Next, when 33% to 50% of the total polishing time preset for the semiconductor substrate 22 has elapsed, polishing is continued under the control of the second polishing control unit 62, with the addition of the pH adjuster AC to the polishing liquid 32 stopped. During this polishing process, the pH value of the polishing liquid 32 increases due to the cessation of the addition of the pH adjuster AC, and finish polishing is performed to reduce the surface roughness Sa.

[0056] (Explanation of grinding test)

[0057] The following describes polishing tests conducted by the present inventors under the polishing test conditions described below. In these polishing tests, seven polishing tests (i.e., Polishing Test 1, Polishing Test 2, Polishing Test 3, Polishing Test 4, Polishing Test 5, Polishing Test 6, and Polishing Test 7) ​​were performed, each with the ratio of the time the pH adjuster AC was added to the polishing liquid 32 to the polishing process time, calculated from the start of polishing, to maintain the pH value of the polishing liquid 32 within the range of 2.5 to 3.5, set to 0%, 17%, 33%, 50%, 67%, 83%, and 100%. Furthermore, in each of these seven polishing tests, the polishing rate PR (μm / hour), the surface roughness Sa of the Si surface, the surface roughness Sa of the C surface, and the flatness before and after polishing were measured using the measurement method described below. The surface roughness ratio C / Si and the flatness difference (μm) were calculated.

[0058] (Grinding test conditions)

[0059] Double-side polishing device: 9B double-side polishing machine manufactured by Spindle Farm Co., Ltd.

[0060] Rotation speed of lower platform: 30rpm (counterclockwise)

[0061] Rotation speed of upper platform: -10rpm (clockwise)

[0062] Carrier plate speed: -3rpm (clockwise)

[0063] Carrier plate revolution speed: -10rpm (clockwise)

[0064] Grinding fluid flow rate: 0.8 / min

[0065] Grinding liquid capacity: 3L

[0066] Grinding time: 60min

[0067] Grinding liquid: potassium permanganate aqueous solution (0.25mol / L)

[0068] Material to be polished: SiC single crystal plate (4 inches t) 3 pieces

[0069] Polishing pad: LHA pad with silica abrasive grains

[0070] pH adjuster: 10 wt% nitric acid aqueous solution

[0071] Dropping speed: 0.1ml / s

[0072] (Method for measuring pH value of polishing liquid 32)

[0073] A pH measuring instrument LAQUA WQ-300 manufactured by Horiba, Ltd. was used. The pH measuring electrode of the pH measuring instrument was installed in the supply pipe 52 of the polishing liquid 32 of the double-side polishing apparatus 10 to measure the pH of the polishing liquid 32 supplied during polishing.

[0074] (Measurement method of polishing rate PR)

[0075] A chemical balance was used to determine the mass difference of the SiC single crystal plate before and after the grinding test. The grinding amount (wear thickness) was determined based on the known density of the SiC single crystal and the surface area of ​​the grinding surface. The grinding rate PR (μm / hour) was calculated by dividing the grinding amount by the grinding time.

[0076] (Surface roughness Sa measurement method)

[0077] The surface profiles of the Si surface ((0,0,1) surface) and the C surface ((0,0,-1) surface) of the SiC single crystal plate after the polishing test were measured using a scanning white interference microscope (VS1330 manufactured by Hitachi High-Tech Corporation). The arithmetic mean surface roughness Sa specified in ISO 25178 was calculated based on the surface profiles.

[0078] (Measurement method of flatness difference)

[0079] Using a flatness measuring machine (Tropel FlatMaster 200XRA) manufactured by Corning Corporation, the difference between the maximum and minimum thickness values ​​(flatness, TTV value) based on the bottom surface of the SiC single crystal plate before and after polishing was measured, and the difference between these measured values ​​was calculated as the flatness difference.

[0080] Figure 3 Graphs showing changes in the pH value of the polishing liquid 32 in polishing test 1, polishing test 2, polishing test 3, polishing test 4, polishing test 5, polishing test 6, and polishing test 7. Figure 4It is a graph showing the measured values ​​of the polishing rate PR, the surface roughness Sa of the Si surface, the surface roughness Sa of the C surface, the surface roughness ratio C / Si between the surface roughness Sa of the Si surface and the surface roughness Sa of the C surface, and the flatness difference (μm) before and after polishing obtained in polishing test 1, polishing test 2, polishing test 3, polishing test 4, polishing test 5, polishing test 6, and polishing test 7, respectively. Figure 5 Shown in a bar graph Figure 4 The measured value of the polishing rate PR. Figure 6 Yes Figure 4 Graph showing the measured values ​​of surface roughness Sa of the Si surface and C surface. Figure 7 Shown in a bar graph Figure 4 The difference in TTV values ​​before and after grinding. Figure 8 It is indicated by ○, △, and × symbols. Figure 4 The numerical values ​​shown are in the figure for evaluation.

[0081] Regarding the polishing rate PR (μm / hour), when a pass value of 2 μm / hour or higher was used, satisfactory results were not obtained in the polishing methods of Polishing Tests 1 and 2, but satisfactory results were obtained in the polishing methods of Polishing Tests 3 to 7. Regarding surface properties (surface roughness Sa of the Si surface, surface roughness Sa of the C surface, and surface roughness ratio C / Si), when a pass value of 0.135 nm or less was used for the surface roughness Sa of the Si surface, 0.3 nm or less was used for the surface roughness Sa of the C surface, and 2 or less was used for the surface roughness ratio C / Si, satisfactory results were not obtained in the polishing methods of Polishing Tests 5 to 7, but satisfactory results were obtained in the polishing methods of Polishing Tests 1 to 4. Regarding the flatness difference (μm), when a pass value of 0 μm or less was used for the flatness difference, satisfactory results were not obtained in the polishing method of Polishing Test 7, but satisfactory results were obtained in the polishing methods of Polishing Tests 1 to 6. Furthermore, in the evaluation of polishing rate PR, surface texture, and flatness difference, if all three items are qualified, a high comprehensive evaluation mark of ○ is given, if two items are qualified, a medium comprehensive evaluation mark of △ is given, and if one item is qualified, a low comprehensive evaluation mark of × is given. Figure 8 As shown in the comprehensive evaluation chart, the polishing methods of Polishing Tests 3 and 4 received a high comprehensive evaluation. Specifically, the polishing methods of Polishing Tests 3 and 4, in which the polishing time from the start of polishing was between 33% and 50% of the polishing time for the SiC substrate, achieved both high polishing efficiency and good surface roughness Sa.

[0082] As described above, according to the surface polishing method of a semiconductor substrate 22 of this embodiment, polishing is performed while adding a pH adjuster AC to the polishing liquid 32 for a predetermined period from the start of the polishing process, maintaining the pH value of the polishing liquid 32 in the strong acid processing range. Subsequently, from the elapse of the predetermined period until the end of the polishing process, the addition of the pH adjuster AC is stopped, raising the pH value of the polishing liquid 32 above the strong acid processing range. Specifically, during the predetermined period from the start of the polishing process, the pH value of the polishing liquid 32 after the addition of the pH adjuster AC is within the strong acid processing range, promoting polishing, in other words, performing rough polishing. Subsequently, when the pH adjuster AC is stopped after the elapse of the predetermined period, the pH value of the polishing liquid 32 rises above the strong acid processing range, in other words, performing fine polishing. Thus, high polishing efficiency and good surface roughness Sa can be achieved simultaneously in a single polishing step.

[0083] In addition, according to the double-side polishing apparatus 10 of this embodiment, there is provided a pH adjusting agent dripping device 38 for dripping a pH adjusting agent AC into the polishing liquid 32. The polishing control device 40 causes the pH adjusting agent AC to be dripped from the pH adjusting agent dripping device 38 into the polishing liquid 32 to maintain the pH value of the polishing liquid 32 in the strong acid processing region during a predetermined period starting from the start of the polishing process, while rotating and driving the lower polishing pad 18 and the upper polishing pad 20 to perform polishing of the semiconductor substrate 22. From the lapse of the predetermined period until the end of the polishing process, the dripping of the pH adjusting agent AC from the pH adjusting agent dripping device 38 is stopped to maintain the pH value of the polishing liquid 32 higher than the strong acid processing region, while rotating and driving the lower polishing pad 18 and the upper polishing pad 20 to perform polishing of the semiconductor substrate 22. Specifically, during a predetermined period from the start of the polishing process, the pH value of the polishing liquid 32 after the pH adjuster AC is added to the polishing liquid 32 is within the strong acid processing range, promoting polishing, in other words, performing rough polishing. Subsequently, after the predetermined period has elapsed, when the pH adjuster AC is no longer added to the polishing liquid 32, the pH value of the polishing liquid 32 is raised above the strong acid processing range, in other words, performing fine polishing. Thus, high polishing efficiency and good surface roughness Sa can be simultaneously achieved in a single polishing step.

[0084] Furthermore, according to the double-side polishing apparatus 10 of this embodiment, the predetermined period is the period during which the polishing time of the semiconductor substrate 22, calculated from the start of polishing, falls between 33% and 50%. This allows high polishing efficiency and good surface roughness Sa to be achieved simultaneously in a single polishing step. If the polishing time is less than 33%, the polishing rate PR cannot be sufficiently achieved, while if the polishing time exceeds 50%, the surface texture may not be sufficiently achieved.

[0085] Furthermore, according to the double-side polishing apparatus 10 of this embodiment, the strong acid processing area is polished using a polishing liquid with a pH of 2.5 to 3.5. Therefore, high polishing efficiency and good surface roughness Sa can be achieved in a single polishing step. If the pH of the strong acid processing area is greater than 3.5, a sufficient polishing rate PR cannot be achieved. If the pH of the strong acid processing area is less than 2.5, excessive oxidation may occur, which may adversely affect surface properties.

[0086] Furthermore, according to the double-side polishing apparatus 10 of this embodiment, the polishing liquid 32 does not contain the polishing abrasive grains 26, and the lower polishing pad 18 and the upper polishing pad 20 include a matrix resin 30 having independent pores and / or communicating pores 28 formed therein, and the polishing abrasive grains 26 filling the independent pores and / or communicating pores 28 of the matrix resin 30. Since the polishing liquid 32 does not contain the polishing abrasive grains 26, the environmental load is reduced.

[0087] In the double-side polishing apparatus 10 of this embodiment, the pH adjuster AC is a reagent such as hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid that adjusts the pH of the polishing liquid 32 to the acidic side. By dripping the pH adjuster AC, the pH of the polishing liquid 32 can be maintained at 2.5 to 3.5.

[0088] One embodiment of the present invention has been described above, but the present invention can also be applied in other aspects.

[0089] For example, in the double-side polishing apparatus 10 of the embodiment, SiC is polished as the semiconductor substrate 22 to be polished. However, Si may be polished instead of SiC, or other compound semiconductors such as GaN, GaP, and AlGaAs may be polished.

[0090] In addition, epoxy resin or PES resin is used as the base resin 30, but it can also be a base resin containing other resins, such as rigid foam polyurethane resin, polyamide, polyamideimide, polyimide, polyacrylonitrile, polyvinylidene fluoride, cellulose acetate, polyvinyl alcohol, polyester, polyolefin resin and non-foamed polyurethane.

[0091] As the silicon dioxide that can be used for the polishing abrasive grains 26 , for example, fumed silica (silicon dioxide fine particles obtained by burning silicon tetrachloride, chlorosilane, or the like at high temperature in the presence of hydrogen and oxygen) is preferably used.

[0092] In the above-described embodiment, the double-side polishing apparatus 10 is used to polish both surfaces of the semiconductor substrate 22 simultaneously. However, a flat surface polishing apparatus that polishes only one surface of the semiconductor substrate 22 may be used.

[0093] Although there are no other specific examples, the present invention can be used with various modifications without departing from the scope of the present invention.

Claims

1. A method for polishing a surface of a semiconductor substrate (22), characterized in that: A method for polishing a semiconductor substrate (22) is provided, wherein the semiconductor substrate (22) is polished using polishing pads (18, 20) while a polishing liquid (32) containing permanganate and water is circulated. During a predetermined period starting from the start of the polishing process, the polishing is performed while a pH adjuster (AC) is added dropwise to the polishing liquid (32) to maintain the pH value of the polishing liquid (32) in a strong acid processing region. From the time the predetermined period has passed until the polishing process is completed, polishing is performed while stopping the dripping of the pH adjuster (AC) and making the pH value of the polishing liquid (32) higher than the strong acid processing region.

2. A surface polishing device (10) for a semiconductor substrate (22), characterized in that: A surface polishing device (10) for a semiconductor substrate (22) is provided for polishing a semiconductor substrate (22) using polishing pads (18, 20) under the circulation supply of a polishing liquid (32) containing permanganate and water, and comprises: a pH adjusting agent dropping device (38) for dropping a pH adjusting agent (AC) into the polishing liquid (32); and A polishing control device (40) which, during a specified period starting from the start of the polishing process, causes the pH adjusting agent (AC) to be dripped from the pH adjusting agent dripping device (38) to the polishing liquid (32) to maintain the pH value of the polishing liquid (32) in the strong acid processing region, while rotating the polishing pads (18, 20) to perform polishing of the semiconductor substrate (22); and from the time the specified period has passed until the polishing process is completed, stops dripping the pH adjusting agent (AC) from the pH adjusting agent dripping device (38) to make the pH value of the polishing liquid (32) higher than the strong acid processing region, while rotating the polishing pads (18, 20) to perform polishing of the semiconductor substrate (22).

3. The surface grinding device (10) for a semiconductor substrate (22) according to claim 2, characterized in that: The predetermined period is a period during which the polishing time of the semiconductor substrate (22) from the start of polishing is between 33% and 50%.

4. The surface grinding device (10) for a semiconductor substrate (22) according to claim 2, characterized in that: The strong acid processing area is an area where the polishing process is performed using the polishing liquid (32) with a pH value of 2.5 to 3.

5.

5. The surface grinding device (10) for a semiconductor substrate (22) according to claim 2, characterized in that: The grinding liquid (32) is a grinding liquid that does not contain grinding abrasive particles (26). The polishing pad (18, 20) is a polishing pad comprising a base resin (30) having independent pores and / or communicating pores (28) formed therein and the polishing abrasive grains (26) filled in the independent pores and / or communicating pores (28) of the base resin (30).

6. The surface grinding device (10) for a semiconductor substrate (22) according to claim 2, characterized in that: The pH adjuster (AC) is an agent that can adjust the pH value of the polishing liquid (32) to the acidic side.

7. The surface grinding device (10) for a semiconductor substrate (22) according to claim 6, characterized in that: The reagent comprises hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid.

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