Plane polishing method for semiconductor substrate and plane polishing device

Abstract

To provide a plane polishing method for a semiconductor substrate capable of improving polishing efficiency and obtaining a quality of a polished plane in a plane polishing process of a semiconductor substrate, and a plane polishing device.SOLUTION: A pH adjuster agent dripping device 38 is provided for dripping a pH adjusting agent AC to a polishing liquid 32. A polishing control device 40 drips the pH adjusting adhesive AC from the pH adjusting agent dripping device 38 to the polishing liquid 32 for a predetermined period from start of polishing, executes rough polishing of a semiconductor substrate 22 by rotationally driving a lower polishing pad 18 and an upper polishing pad 20 while maintaining pH of the polishing liquid 32 in a strong acid processing zone, and executes finish polishing of the semiconductor substrate 22 by rotationally driving the lower polishing pad 18 and the upper polishing pad 20 while making the pH of the polishing liquid 32 higher than the strong acid processing zone by stopping dripping the pH adjusting agent AC from the pH adjusting agent dripping device 38 until the polishing is finished after the lapse of a predetermined period. Thus, both high polishing efficiency and satisfactory surface roughness Sa can be obtained in one polishing process.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for polishing a surface of a semiconductor substrate, which are used to polish one surface of a semiconductor substrate used in a semiconductor device, and relates to a technology for successively performing rough polishing and finish polishing during polishing by changing the pH of a polishing liquid that is circulated during polishing. [Background technology]

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

[0003] According to this polishing method, the inclusion of a weak acid and its soluble salt in the polishing liquid suppresses a rapid decrease in the polishing rate caused by a sudden increase in the pH 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6301571 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the conventional method for polishing a semiconductor substrate surface, the pH of the polishing solution is prevented from rising sharply during polishing by the action of the weak acid and its soluble salt contained in the polishing solution, and the pH is raised at a constant rate. This expands the conditions under which oxidation of the semiconductor substrate by permanganate ions occurs, compared to when the polishing solution does not contain the weak acid and its soluble salt, thereby improving polishing efficiency. For this reason, it has been difficult to achieve both improved polishing efficiency for semiconductor substrates and high quality of the polished surface (low surface roughness) in a single polishing process.

[0006] The present invention has been made in light of the above circumstances, and its object is to provide a method and apparatus for polishing a semiconductor substrate surface, which can improve the polishing efficiency and provide a high-quality polished surface in the surface polishing process of a semiconductor substrate.

[0007] The present inventors have conducted extensive research in light of the above circumstances and have found that, when polishing one surface of a semiconductor substrate with a polishing pad using a circulating acidic polishing solution containing potassium permanganate, by first supplying a pH adjusting solution to the polishing solution to maintain the pH of the polishing solution at a predetermined low, strongly acidic value while polishing, and then stopping the supply of the pH adjusting solution to the polishing solution and continuing polishing, it is possible to simultaneously obtain high polishing efficiency and good surface roughness in one polishing step. The present invention was made based on this finding. [Means for solving the problem]

[0008] That is, the gist of the first invention is (1) a method for polishing a semiconductor substrate surface by using a polishing pad to polish the surface of the semiconductor substrate while circulating a polishing liquid containing permanganate and water, (2) for a predetermined period from the start of polishing, a pH adjuster is dropped into the polishing liquid to maintain the pH of the polishing liquid in the strong acid processing range while polishing, and (3) after the predetermined period has elapsed until the polishing is completed, the dropping of the pH adjuster is stopped and polishing is performed while maintaining the pH of the polishing liquid higher than the strong acid processing range while polishing.

[0009] The gist of the second invention is (1) a surface polishing apparatus for polishing a semiconductor substrate using a polishing pad under a circulating supply of a polishing solution containing permanganate and water, including (2) a pH adjuster dripping device for dripping a pH adjuster into the polishing solution, and (3) a polishing control device that, for a predetermined period from the start of polishing, drips the pH adjuster from the pH adjuster dripping device into the polishing solution to maintain the pH of the polishing solution in a strong acid processing range while rotating the polishing pad to polish the semiconductor substrate, and then, after the predetermined period has elapsed and until the polishing process is completed, stops dripping the pH adjuster from the pH adjuster dripping device and rotates the polishing pad to polish the semiconductor substrate while maintaining the pH of the polishing solution above the strong acid processing range. The permanganate is an oxoacid salt of manganese, typically potassium permanganate or sodium permanganate.

[0010] The gist of the third invention is that in the second invention, the predetermined period is a period in which the polishing time from the start of polishing is between 33% and 50% of the polishing time of the semiconductor substrate.

[0011] The gist of the fourth invention is that in the second invention, the strong acid processing region is a region where the polishing is performed using the polishing liquid having a pH of 2.5 to 3.5.

[0012] The gist of the fifth invention is that, in the second invention, the polishing liquid does not contain abrasive grains, and the polishing pad comprises a base resin having independent pores or interconnected pores formed therein, and the abrasive grains are filled into the interconnected pores of the base resin.

[0013] The gist of the sixth invention is that in the second invention, the pH adjuster is a reagent such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, or the like that adjusts the pH of the polishing liquid to the acidic side. [Effects of the Invention]

[0014] According to the first invention, the method for polishing a semiconductor substrate surface involves: For a predetermined period of time from the start of polishing, a pH adjuster is added to the polishing solution to maintain the pH of the polishing solution in the strong acid processing range; Then, after the predetermined period has elapsed and until the end of polishing, the addition of the pH adjuster is stopped, and polishing is continued while the pH of the polishing solution is raised above the strong acid processing range. That is, for the predetermined period of time from the start of polishing, the pH of the polishing solution is increased in the strong acid processing range due to the addition of the pH adjuster, and polishing is accelerated, so to speak, to perform rough polishing; Then, after the predetermined period of time has elapsed and the pH adjuster is no longer added to the polishing solution, the pH of the polishing solution rises above the strong acid processing range, so to speak, to perform finish polishing. This allows high polishing efficiency and good surface roughness to be achieved simultaneously in a single polishing process.

[0015] According to a second aspect of the present invention, a semiconductor substrate surface polishing apparatus includes a pH adjuster dripping device that drips a pH adjuster into the polishing solution. The polishing control device drips a pH adjuster from the pH adjuster dripping device into the polishing solution to maintain the pH of the polishing solution in the strong acid processing range for a predetermined period of time from the start of polishing, rotating the polishing pad to polish the semiconductor substrate. After the predetermined period has elapsed, the polishing control device stops dripping the pH adjuster from the pH adjuster dripping device and polishes the semiconductor substrate while raising the pH of the polishing solution above the strong acid processing range. That is, during the predetermined period from the start of polishing, the pH of the polishing solution containing the pH adjuster dripped into the strong acid processing range is increased to promote polishing, essentially performing rough polishing. Then, after the predetermined period has elapsed and the pH adjuster is no longer dripped into the polishing solution, the pH of the polishing solution rises above the strong acid processing range, essentially performing finish polishing. This allows for both high polishing efficiency and excellent surface roughness to be achieved in a single polishing process.

[0016] According to the surface polishing apparatus of the third invention, in the second invention, the predetermined period is a period from the start of polishing to 50% of the total polishing time of the semiconductor substrate, so that high polishing efficiency and good surface roughness can be achieved simultaneously in one polishing process. If the polishing time is less than 33%, a sufficient polishing rate cannot be obtained, and if the polishing time is more than 50%, sufficient surface quality may not be obtained.

[0017] According to the surface polishing apparatus of the fourth invention, the strong acid processing zone in the second invention is a zone where polishing is performed using a polishing solution with a pH of 2.5 to 3.5, so high polishing efficiency and good surface roughness can be achieved in one polishing process. If the pH of the strong acid processing zone exceeds 3.5, a sufficient polishing rate cannot be obtained, and if the pH of the strong acid processing zone is below 2.5, excessive oxidation may occur, adversely affecting the surface properties.

[0018] According to the surface polishing apparatus of the fifth invention, the polishing liquid in the second invention does not contain abrasive grains, and the polishing pad has a base resin having closed or interconnected pores, and abrasive grains filled in the interconnected pores of the base resin. Since the polishing liquid does not contain abrasive grains, the environmental load is reduced.

[0019] According to the surface polishing apparatus of the sixth aspect of the present invention, in the second aspect of the present invention, the pH adjuster is a reagent that adjusts the pH of the polishing liquid to the acidic side, such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc. This makes it possible to adjust the pH of the polishing liquid to 2.5 to 3.5. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a perspective view conceptually illustrating the configuration of a double-side polishing apparatus for carrying out a surface polishing method according to an embodiment of the present invention; [Figure 2] 2 is an enlarged schematic view illustrating the surface structure of the polishing pad of FIG. 1. FIG. [Figure 3] 1 is a graph showing the relationship between polishing time and the pH value of the polishing liquid, obtained through a polishing test by the present inventors. [Figure 4]1 is a table showing measured values ​​obtained by polishing tests conducted by the present inventors, for polishing tests with different dripping periods of a pH adjuster, showing 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 difference in flatness before and after polishing. [Figure 5] 5 is a bar graph showing the polishing rate for each polishing test in which the dropping period of the pH adjuster in FIG. 4 is different. [Figure 6] FIG. 5 is a graph showing the surface roughness of the Si surface and the C surface for each polishing test in which the dropping period of the pH adjuster in FIG. 4 was different. [Figure 7] 5 is a bar graph showing the TTV (Total Thickness Variation) value, i.e., the difference in flatness, before and after polishing for each polishing test in which the dropping period of the pH adjuster in FIG. 4 is different. [Figure 8] FIG. 5 is a diagram showing an overall evaluation for each polishing test in which the dropping period of the pH adjuster in FIG. 4 is different. DETAILED DESCRIPTION OF THE INVENTION

[0021] An application example of the present invention will be described in detail below with reference to the drawings. Note that in the following embodiment, the drawings are appropriately simplified or modified, and the dimensional ratios and shapes of the various parts are not necessarily drawn accurately. [Example]

[0022] In this embodiment, a double-sided polishing machine 10 shown in FIG. 1 is used as a surface polishing machine for performing a surface polishing method for a semiconductor substrate 22 such as SiC. FIG. 1 conceptually illustrates the main components of the double-sided polishing machine 10, with the guide roller fixing base removed. In FIG. 1, the double-sided polishing machine 10 includes a pair of lower polishing platens 12 and upper polishing platens 14, which are arranged facing each other and rotatable relative to each other about a vertical rotation axis C1. The lower polishing platen 12 is driven by a platen drive motor 16 to rotate at a constant speed in one rotation direction indicated by the arrow in FIG. 1, while the upper polishing platen 14 is also driven by the platen drive motor 16 to rotate in the opposite direction via a connecting mechanism (not shown). A pair of lower polishing pads 18 and upper polishing pads 20 are disposed on the opposing surfaces of the lower polishing platen 12 and upper polishing platen 14, respectively.

[0023] A circular semiconductor substrate (workpiece) 22 is rotatably held in a holding hole formed through a well-known circular carrier plate (not shown) and is sandwiched and placed 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. For example, the carrier plate has outer peripheral teeth and is arranged to mesh with a central gear and a large-diameter internal gear that are concentric with the rotation axis C1, and is configured to perform planetary motion in which the central gear or the internal gear is rotated and revolved by a carrier drive motor 24.

[0024] As shown in FIG. 2, the lower polishing pad 18 and the upper polishing pad 20 are polishing pads (LHA pads) made of epoxy resin or PES resin having independent or interconnected pores 28 containing polishing grains 26, and have dimensions of, for example, an outer diameter of 700 mmφ and a thickness of 2 mm.

[0025] The lower polishing pad 18 and the upper polishing pad 20 are formed in a disk shape and include a base resin 30 made of epoxy resin or PES resin, which has independent or interconnected pores 28, and a large number of abrasive grains 26 that are filled into the interconnected pores 28 of the base resin 30, some of which adhere to the base resin 30, and some of which separate from the base resin 30 during polishing. For this reason, the lower polishing pad 18 and the upper polishing pad 20 are referred to as semi-fixed abrasive-containing polishing pads that contain the abrasive grains 26, and polishing using such abrasive-containing polishing pads is referred to as semi-fixed abrasive polishing. The lower polishing pad 18 and the upper polishing pad 20 are composed of, for example, approximately 32 volume % abrasive grains 26, approximately 33 volume % base resin 30, and the interconnected pores 28 that occupy the remaining volume. The interconnected pores 28 of the sponge-like or mesh-like base resin 30 are formed to be equal to or larger in size than the abrasive grains 26, and a large number of the abrasive grains 26 are held within the interconnected pores 28. The base 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 are capable of polishing semiconductor substrates 22 by the mechanical polishing action of the abrasive grains 26 self-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 the abrasive grains 26, such as colloidal silica, under the circulating supply of a polishing liquid 32 that does not contain the abrasive grains 26.

[0026] The abrasive grains 26 are preferably silica, but other abrasive grains 26 containing at least one of ceria, alumina, zirconia, silicon carbide, titania, manganese compounds, barium carbonate, chromium oxide, and iron oxide may also be used. Examples of silica include fumed silica (fine silica particles obtained by burning silicon tetrachloride, chlorosilane, etc., at high temperatures in the presence of hydrogen and oxygen). The average particle size of the abrasive grains 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 exceeds 3.0 μm, polishing scratches are likely to occur on the semiconductor substrate (workpiece) 22 due to the abrasive grains 26 liberated from the matrix resin 30 during the polishing process described below. Furthermore, if the average particle size of the polishing grains 26 is less than 0.005 (μm), the polishing grains 26 tend to aggregate, and polishing scratches tend to occur during polishing on the semiconductor substrate (workpiece) 22. The particle size of the polishing grains 26 is measured by a laser diffraction / scattering method, for example, using a particle size / particle size distribution measuring device, Microtrac MT3300, manufactured by Nikkiso Co., Ltd., and the average particle size is the arithmetic mean of the particle sizes.

[0027] The polishing solution 32 contains permanganate and water, but does not contain polishing abrasive grains 26. The permanganate is an oxoacid salt of manganese, preferably represented by potassium permanganate or sodium permanganate. The polishing solution 32 contains permanganate ions (MnO2 - ) in an amount of, for example, 0.1 mass % to 20 mass %. The pH of polishing solution 32 is adjusted to a range of 2.5 to 3.5 by a pH adjuster AC. The pH adjuster AC is a reagent such as hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid that adjusts the pH of polishing solution 32 to the acidic side.

[0028] Returning to Figure 1, the double-sided polishing apparatus 10 includes a polishing liquid circulation supply device 36 that circulates the polishing liquid 32 and supplies it to the polishing surface of the semiconductor substrate 22, a pH adjuster dripping device 38 that drips a pH adjuster AC into the polishing liquid 32, and a polishing control device 40 that controls the polishing process.

[0029] The polishing liquid circulating supply device 36 is disposed below the lower polishing pad 18 and includes a receiving tank 42 for receiving the polishing liquid 32 used in polishing the semiconductor substrate 22, a discharge pipe 46 for guiding the polishing liquid 32 received by the receiving tank 42 to a polishing liquid tank 44, a supply pipe 52 for guiding the polishing liquid 32 in the receiving tank 42, which is pumped by a circulation pump 48, into a distribution tank 50, and distribution pipes 54 connected to a plurality of through holes formed at equal intervals in the circumferential direction in the bottom wall of the distribution tank 50, for supplying the polishing liquid 32 in the distribution tank 50 to a plurality of positions arranged at equal intervals in the circumferential direction on the back surface of the upper polishing pad 20. The polishing liquid 32 discharged from the distribution pipes 54 is supplied through the upper polishing pad 20 to the lower polishing pad 18 and the semiconductor substrate 22 on the lower polishing pad 18.

[0030] The pH adjuster dripping device 38 is equipped with a storage tank 56 for storing the pH adjuster AC and an adjustment valve 58 for adjusting the amount dripped from the storage tank 56 in accordance with commands from the polishing control device 40, and is attached above the polishing liquid tank 44.

[0031] The polishing control device 40 is configured, for example, by a microcomputer, processes input signals according to a pre-stored program, and controls the operation of the platen drive motor 16, the carrier drive motor 24, the circulation pump 48, and the adjustment valve 58. The polishing control device 40 functionally comprises a first polishing control unit 60 that performs polishing at high polishing efficiency by dripping a pH adjuster AC into the polishing solution 32 when the polishing time from the start of polishing is between 33% and 50% and a second polishing control unit 62 that performs finish polishing by stopping the dripping of the pH adjuster AC into the polishing solution 32.

[0032] In the double-sided polishing apparatus 10 configured as described above, for example, in response to operation of a start switch (not shown), the polishing control device 40 activates the platen drive motor 16, the carrier drive motor 24, the circulation pump 48, and the control valve 58 to begin double-sided polishing of the semiconductor substrate 22. Initially, the first polishing control unit 60 controls the control valve 58 so that the pH of the polishing solution 32 is maintained within a predetermined range, for example, a strong acid processing range of 2.5 to 3.5, and adjusts the amount of pH adjuster AC dripped into the polishing solution 32 between 33% and 50% of the polishing time from the start of polishing. During this surface polishing process in which the pH of the polishing solution 32 is maintained within the strong acid processing range of 2.5 to 3.5, double-sided polishing of the semiconductor substrate 22 is performed at a high polishing rate PR.

[0033] Next, when 33% to 50% of the total polishing time set in advance for the semiconductor substrate 22 has elapsed since the start of polishing, the second polishing control unit 62 stops the dropping of the pH adjuster AC into the polishing liquid 32 and polishes the substrate 22. In this polishing process, the pH of the polishing liquid 32 increases due to the cessation of the dropping of the pH adjuster AC, and a finish polish is performed to reduce the value of the surface roughness Sa.

[0034] (Explanation of the polishing test) The following describes polishing tests conducted by the present inventors under the following conditions. In these polishing tests, the percentages of the time for which a pH adjuster AC was added to polishing liquid 32 from the start of polishing to maintain the pH of polishing liquid 32 in the range of 2.5 to 3.5 relative to the polishing time were 0%, 17%, 33%, 50%, 67%, 83%, and 100%. Seven types of polishing tests, namely, Polishing Test 1, Polishing Test 2, Polishing Test 3, Polishing Test 4, Polishing Test 5, Polishing Test 6, and Polishing Test 7, were performed. For each of these seven polishing tests, the polishing rate PR (μm / hr), 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 following measurement methods, and the surface roughness ratio C / Si and the flatness difference (μm) were calculated.

[0035] (Polishing test conditions) Double-sided polishing machine: Speedfan 9B double-sided polishing machine Lower platen rotation speed: 30 rpm (counterclockwise) Upper surface plate rotation speed: -10 rpm (clockwise) Carrier rotation speed: -3 rpm (clockwise) Carrier revolution speed: -10 rpm (clockwise) Polishing liquid flow rate: 0.8 / min Polishing liquid capacity: 3L Polishing time: 60min Polishing solution: Potassium permanganate aqueous solution (0.25 mol / L) Material to be polished: SiC single crystal plate (4 inch diameter x 0.4 mm thick) x 3 pieces Polishing pad: Silica abrasive grain (LHA) pad pH adjuster: 10 wt% nitric acid aqueous solution Dripping speed: 0.1ml / sec

[0036] (Method for measuring pH of polishing solution 32) Using a pH measuring instrument LAQUA WQ-300 manufactured by Horiba Ltd., the pH measuring electrode of the pH measuring instrument was attached to the supply pipe 52 of the polishing liquid 32 of the double-side polishing apparatus 10, and the pH of the polishing liquid 32 supplied during polishing was measured. (Method for measuring polishing rate PR) The difference in mass of the SiC single crystal plate before and after the polishing test was determined using an analytical balance, and the amount of polishing (wear thickness) was calculated from the known density of the SiC single crystal and the surface area of ​​the polished surface. The polishing rate PR (μm / hr) was calculated by dividing the amount of polishing by the polishing time. (Surface roughness Sa measurement method) The surface profiles of the Si face (0,0,1 face) and C face (0,0,-1 face) of the SiC single crystal plate after the polishing test were measured using a scanning white light interference microscope (Hitachi High-Tech VS1330), and the arithmetic mean surface roughness Sa specified in ISO 25178 was calculated from the surface profiles. (Method for measuring flatness difference) Using a Corning flatness measuring instrument (Tropel FlatMaster 200XRA), the difference between the maximum and minimum thickness values ​​(flatness, TTV value) based on the bottom surface of the SiC single crystal plate was measured for the SiC single crystal plate before and after polishing, and the difference between these measured values ​​was calculated as the flatness difference.

[0037] FIG. 3 is a graph showing the change in pH of polishing solution 32 over time for each of Polishing Tests 1, 2, 3, 4, 5, 6, and 7. FIG. 4 is a chart 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 difference in flatness (μm) before and after polishing, obtained for each of Polishing Tests 1, 2, 3, 4, 5, 6, and 7. FIG. 5 is a bar graph showing the measured values ​​of the polishing rate PR in FIG. 4. FIG. 6 is a graph showing the measured values ​​of the surface roughness Sa of the Si surface and the C surface in FIG. 4. FIG. 7 is a bar graph showing the difference in TTV values ​​before and after polishing in FIG. 4. Finally, FIG. 8 is a diagram showing the evaluation of the values ​​shown in FIG. 4, indicated by circles, triangles, and crosses.

[0038] Regarding the polishing rate PR (μm / hr), when a pass value was 2 μm / hr or more, the polishing methods of Polishing Test 1 and Polishing Test 2 did not obtain satisfactory results, but the polishing methods of Polishing Test 3 to Polishing Test 7 obtained satisfactory results. Regarding the surface texture (Si surface roughness Sa, C surface roughness Sa, and surface roughness ratio C / Si), when the pass value was set for the Si surface roughness Sa of 0.135 nm or less, the pass value was set for the C surface roughness Sa of 0.3 nm or less, and the surface roughness ratio C / Si of 2 or less, the polishing methods of Polishing Test 5 to Polishing Test 7 did not obtain satisfactory results, but the polishing methods of Polishing Test 1 to Polishing Test 4 obtained satisfactory results. Regarding the flatness difference (μm), when a flatness difference of 0 μm or less was used as a pass value, the polishing method of Polishing Test 7 did not obtain satisfactory results, but the polishing methods of Polishing Test 1 to Polishing Test 6 obtained satisfactory results. Then, for the three types of items, evaluation of the polishing rate PR, evaluation of the surface texture, and evaluation of the flatness difference, if all three items were passed, a high overall evaluation was given with a circle, if two items were passed, a medium overall evaluation was given with a triangle, and if one item was passed, a low overall evaluation was given with an x, and as shown in the overall evaluation chart in Figure 8, the polishing methods of Polishing Test 3 and Polishing Test 4 were given a high overall evaluation. In other words, the polishing methods of Polishing Test 3 and Polishing Test 4, which used polishing methods in which the polishing time from the start of polishing was between 33% and 50% of the polishing time of the SiC substrate, achieved both high polishing efficiency and good surface roughness Sa.

[0039] As described above, in the method for polishing the surface of a semiconductor substrate 22 according to this embodiment, for a predetermined period from the start of polishing, the pH adjuster AC is added to the polishing solution 32 to maintain the pH of the polishing solution 32 in the strong acid processing range while polishing is performed. Then, after the predetermined period has elapsed and until the polishing is completed, the addition of the pH adjuster AC is stopped and the pH of the polishing solution 32 is raised above the strong acid processing range while polishing is performed. That is, for the predetermined period from the start of polishing, the pH of the polishing solution 32 is added to the polishing solution 32 in the strong acid processing range, and polishing is promoted, so to speak, to perform rough polishing. Then, after the predetermined period has elapsed and the addition of the pH adjuster AC to the polishing solution 32 is stopped, the pH of the polishing solution 32 rises above the strong acid processing range, so to speak, to perform finish polishing. This allows high polishing efficiency and good surface roughness Sa to be achieved simultaneously in a single polishing process.

[0040] Furthermore, the double-sided polishing apparatus 10 of this embodiment is provided with a pH adjuster dropping device 38 that drops a pH adjuster AC into the polishing liquid 32, and the polishing control device 40 drops the pH adjuster AC from the pH adjuster dropping device 38 into the polishing liquid 32 for a predetermined period from the start of the polishing process, thereby maintaining the pH of the polishing liquid 32 in the strong acid processing range, and rotates the lower polishing pad 18 and the upper polishing pad 20 to polish the semiconductor substrate 22, and after the predetermined period has elapsed and until the polishing process is completed, stops dropping the pH adjuster AC from the pH adjuster dropping device 38 and keeps the pH of the polishing liquid 32 higher than the strong acid processing range, while rotating the lower polishing pad 18 and the upper polishing pad 20 to polish the semiconductor substrate 22. That is, for a predetermined period from the start of polishing, polishing is promoted in a manner that roughly polishes the surface, while the pH of the polishing solution 32, into which the pH adjuster AC has been added dropwise, is kept in the strong acid processing range. Then, after a predetermined period has elapsed and the pH adjuster AC is no longer added dropwise to the polishing solution 32, the pH of the polishing solution 32 is raised above the strong acid processing range, and so-called finish polishing is performed. This makes it possible to obtain both high polishing efficiency and a satisfactory surface roughness Sa in a single polishing process.

[0041] Furthermore, in the double-side polishing apparatus 10 of this embodiment, the predetermined period is a period during which the polishing time from the start of polishing is between 33% and 50% of the total polishing time of the semiconductor substrate 22. This allows high polishing efficiency and a good surface roughness Sa to be achieved simultaneously in a single polishing process. If the polishing time is less than 33%, a sufficient polishing rate PR cannot be achieved, and if the polishing time is more than 50%, sufficient surface quality may not be achieved.

[0042] Furthermore, in the double-side polishing apparatus 10 of this embodiment, the strong acid processing zone is a zone where polishing is performed using a polishing solution with a pH of 2.5 to 3.5, so that high polishing efficiency and good surface roughness Sa can be achieved in one polishing process. If the pH of the strong acid processing zone exceeds 3.5, a sufficient polishing rate PR cannot be obtained, and if the pH of the strong acid processing zone is below 2.5, excessive oxidation may occur, adversely affecting the surface properties.

[0043] Furthermore, according to the double-side polishing apparatus 10 of this embodiment, the polishing liquid 32 does not contain abrasive grains 26, and the lower polishing pad 18 and the upper polishing pad 20 are provided with a base resin 30 having independent pores or interconnected pores 28 formed therein, and abrasive grains 26 filled in the interconnected pores 28 of the base resin 30. Since the polishing liquid 32 does not contain abrasive grains 26, the environmental load is reduced.

[0044] Furthermore, 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 this pH adjuster AC, the pH of the polishing liquid 32 can be maintained at 2.5 to 3.5.

[0045] Although one embodiment of the present invention has been described above, the present invention can also be applied in other aspects.

[0046] For example, in the double-sided polishing apparatus 10 of the above-described embodiment, SiC is polished as the semiconductor substrate 22. Instead of SiC, Si may be polished, or other compound semiconductors such as GaN, GaP, and AlGaAs may also be polished.

[0047] Furthermore, although epoxy resin or PES resin is used for the base resin 30, other resins may be used, such as at least one of rigid foamed polyurethane resin, polyamide, polyamideimide, polyimide, polyacrylonitrile, polyvinylidene fluoride, cellulose acetate, polyvinyl alcohol, polyester, polyolefin resin, and non-foamed polyurethane.

[0048] As the silica used for the abrasive grains 26, for example, fumed silica (fine silica particles obtained by burning silicon tetrachloride, chlorosilane, etc. at high temperatures in the presence of hydrogen and oxygen) is preferably used.

[0049] In the above-described embodiment, the double-side polishing machine 10 is used to polish both sides of the semiconductor substrate 22 simultaneously, but a surface polishing machine that polishes one side of the semiconductor substrate 22 may also be used.

[0050] Although not specifically exemplified, the present invention can be used with various modifications within the scope of the invention. [Explanation of symbols]

[0051] 10: Double-sided polishing machine (flat surface polishing machine) 18: Lower polishing pad (polishing pad) 20: Upper polishing pad (polishing pad) 22: Semiconductor substrate 26: Polishing grain 28:Communicating pores 30: Base resin 32: Polishing liquid 38: pH adjuster dripping device 40: Polishing control device AC: pH adjuster

Claims

1. A method for polishing a semiconductor substrate surface by polishing the surface of the semiconductor substrate using a polishing pad under circulating supply of a polishing liquid containing permanganate and water, comprising: During a predetermined period from the start of polishing, a pH adjuster is dropped into the polishing liquid to maintain the pH of the polishing liquid in a strong acid processing range while polishing is performed; After the predetermined period has elapsed, the dropping of the pH adjuster is stopped and polishing is carried out while the pH of the polishing solution is kept higher than the strong acid processing range until the polishing process is completed.

1. A method for polishing a surface of a semiconductor substrate.

2. 1. A surface polishing apparatus for a semiconductor substrate, which polishes the surface of a semiconductor substrate using a polishing pad under circulating supply of a polishing liquid containing permanganate and water, a pH adjuster dropping device that drops a pH adjuster into the polishing liquid; and a polishing control device that, for a predetermined period from the start of polishing, drops the pH adjuster from the pH adjuster dropping device into the polishing liquid to maintain the pH of the polishing liquid in a strong acid processing range, while rotating the polishing pad to perform polishing of the semiconductor substrate, and that, after the predetermined period has elapsed and until the polishing process is completed, stops dropping the pH adjuster from the pH adjuster dropping device, while maintaining the pH of the polishing liquid higher than the strong acid processing range, while rotating the polishing pad to perform polishing of the semiconductor substrate.

1. A surface polishing apparatus for semiconductor substrates.

3. The predetermined period is a period in which the polishing time from the start of polishing of the semiconductor substrate is between 33% and 50%.

3. The semiconductor substrate surface polishing apparatus according to claim 2.

4. The strong acid processing zone is a zone where the polishing is performed using the polishing liquid having a pH of 2.5 to 3.

5.

3. The semiconductor substrate surface polishing apparatus according to claim 2.

5. The polishing liquid does not contain abrasive grains, The polishing pad comprises a base resin having independent pores or interconnected pores, and the abrasive grains filled in the interconnected pores of the base resin.

3. The semiconductor substrate surface polishing apparatus according to claim 2.

6. The pH adjuster is a reagent such as hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid that adjusts the pH of the polishing liquid to the acidic side.

3. The semiconductor substrate surface polishing apparatus according to claim 2.

Images