Silicon wafer polishing method

Abstract

To provide a silicon wafer polishing method that can be used regardless of equipment used and has a low environmental impact.SOLUTION: When a workpiece (silicon wafer) 16 is polished using a polishing pad 18, which is an abrasive grain-containing polishing pad containing abrasive grains 36, and a polishing liquid (polishing composition) 26 containing no abrasive grains is supplied, the polishing liquid 26 contains an organic amine, water, and bubbles 58, which are nanobubbles with a particle size of 1 μm or less, but does not contain an alkaline agent or abrasive. Because the polishing composition does not contain an alkaline agent, it can be used regardless of equipment used. Furthermore, because the polishing composition does not contain an abrasive, a silicon wafer polishing method with a low environmental impact is achieved. Furthermore, because the bubbles 58 are nanometer-sized with a particle size of 1 μm or less, they easily enter between the abrasive grains of the polishing pad and the silicon wafer, adhering to the polishing debris and facilitating their removal.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a method for polishing a silicon wafer, which is used to polish one side of a silicon wafer known as a substrate for a semiconductor device, and relates to a technology that uses a polishing composition (polishing liquid) for silicon wafers that contains an organic amine and nanobubbles but does not contain an abrasive. [Background technology]

[0002] Polishing compositions consisting of an organic amine and water, or an organic amine, an alkaline agent, and water, have been used for mirror polishing of silicon wafers. For example, the polishing composition described in Patent Document 1 is one such example. Examples of the organic amine include piperazine, ethylenediamine, and diethylenetriamine. Examples of the alkaline agent include quaternary amines similar to tetramethylammonium hydroxide (TMAH), a known poison, and aqueous ammonia, which is a deleterious substance at high concentrations.

[0003] In such a polishing composition, when considering the polishing work environment and environmental load, it is desirable to use a polishing surface composition that does not contain an alkaline agent, but the polishing efficiency is better with a polishing composition that contains an alkaline agent, so there is a trade-off relationship.In addition, the alkaline component used may contain a substance designated as a deleterious substance, and may not be usable depending on the equipment used, and depending on future regulations, it may become difficult to use regardless of the equipment used.

[0004] In response to this, a polishing composition has been proposed in which microbubbles and an abrasive are added to water, as described in Patent Document 2. According to this composition, since no alkaline agent is added, the composition does not contain any designated deleterious substances, and there is no possibility that the polishing composition will be difficult to use. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication Number (WO2023 / 190604A1) [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-111094 Summary of the Invention [Problem to be solved by the invention]

[0006] However, since the polishing composition described in Patent Document 2 contains an abrasive, a large amount of used abrasive is discharged from a polishing apparatus that polishes silicon wafers using the polishing composition, which places a heavy burden on the environment.

[0007] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a method for polishing silicon wafers that can be used regardless of the equipment used and that has a low environmental impact.

[0008] The inventor of the present invention has conducted various studies based on the above circumstances, and as a result, has found that, on the premise of using a polishing pad containing abrasive grains with a small amount of discharged abrasive grains, the polishing composition supplied onto the polishing pad containing abrasive grains is composed of water to which organic amine is added, and by injecting nanobubbles of air having a diameter of nanometer order, even if the polishing composition does not contain an abrasive, a high polishing efficiency of about 286 nm / min can be obtained for silicon wafers.In addition, the polished surface of the silicon wafer can obtain a surface roughness Ra of about 0.80 nm at the best value. [Means for solving the problem]

[0009] That is, the gist of the first invention is a silicon polishing method in which a silicon wafer is polished using a polishing pad containing abrasive grains, while a polishing composition not containing abrasive grains is supplied, wherein the polishing composition contains an organic amine, water, and nanobubbles, which are bubbles with a particle size of 1 μm or less, and does not contain an alkaline agent or an abrasive.

[0010] The gist of the second invention is that in the first invention, the nanobubbles contained in the polishing composition are bubbles formed by injecting a gas into the polishing composition for a period of 15 hours or more.

[0011] The gist of the third invention is that in the second invention, the nanobubbles injected into the polishing composition are bubbles that are present within 24 hours after the gas is injected into the polishing composition.

[0012] The gist of the fourth invention is that, in the first invention, the nanobubbles injected into the polishing composition are bubbles having a diameter of less than 1 μm and having a density of 6×10 per ml. 7 It is included in numbers of 1 or more.

[0013] The gist of a fifth invention is that, in the first invention, the organic amine is ethylenediamine, piperazine, or diethylenetriamine.

[0014] The gist of the sixth invention is that, in the first invention, the organic amine is piperazine contained at a concentration of 0.05N to 0.10N.

[0015] The gist of the seventh invention is that in any one of the first to sixth inventions, the abrasive grains contained in the polishing pad containing abrasive grains are at least one of silica, ceria, zirconia, alumina, and silicon carbide. [Effects of the Invention]

[0016] According to a first aspect of the present invention, a silicon polishing method is provided in which a silicon wafer is polished using a polishing pad containing abrasive grains while supplying a polishing composition that does not contain abrasive grains. The polishing composition contains an organic amine, water, and nanobubbles (gas bubbles with a particle size of 1 μm or less), but does not contain an alkaline agent or an abrasive. Because the polishing composition does not contain an alkaline agent, the polishing composition can be used regardless of the equipment used. Furthermore, because the polishing composition does not contain an abrasive, a silicon wafer polishing method with low environmental impact is obtained. Nanobubbles are nano-sized bubbles with a particle size of 1 μm or less that easily penetrate between the abrasive grains of the polishing pad and the silicon wafer, and adhere to the polishing debris, facilitating its removal. This accelerates the removal rate and suitably reduces the roughness of the polished surface.

[0017] According to the method for polishing a silicon wafer of the second invention, the nanobubbles contained in the polishing composition are bubbles that are produced by injecting a gas into the polishing composition for a period of 15 hours or more, and therefore nanobubbles with nano-order particle diameters can be suitably obtained.

[0018] According to the method for polishing a silicon wafer of the third invention, the nanobubbles injected into the polishing composition are bubbles that have been generated within 24 hours since the gas was injected into the polishing composition, and therefore nanobubbles with nano-order particle diameters can be suitably obtained.

[0019] According to the method for polishing a silicon wafer of the fourth invention, the nanobubbles injected into the polishing composition are bubbles having a diameter of less than 1 μm and having a density of 6 × 10 per ml. 7 Since the number of particles contained is equal to or more than 1, a favorable polishing rate and polished surface roughness can be obtained.

[0020] According to the method for polishing a silicon wafer of the fifth invention, the organic amine is ethylenediamine, piperazine, or diethylenetriamine, and therefore, when dissolved in water, strong alkalinity is obtained.

[0021] According to the method for polishing silicon wafers of the sixth aspect of the present invention, the organic amine is piperazine contained at a concentration of 0.05 N to 0.10 N. Therefore, the reactivity of silicon is enhanced under the strong alkalinity caused by the organic amine, and therefore high polishing efficiency can be obtained.

[0022] According to the method for polishing silicon wafers of the seventh invention, the abrasive grains contained in the polishing pad containing abrasive grains are at least one of silica, ceria, zirconia, alumina, and silicon carbide, thereby achieving a suitable polishing efficiency. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a perspective view conceptually showing the configuration of a surface polishing apparatus for carrying out a polishing method according to an application example of the present invention; [Figure 2] 2 is a plan view for schematically explaining a rotating mechanism of an adhesive disk of the surface polishing apparatus of FIG. 1. FIG. [Figure 3] 2 is an enlarged schematic view illustrating the surface structure of the polishing pad of FIG. 1. FIG. [Figure 4] 2 is a diagram showing the chemical structure of a primary amine (ethylenediamine), which is an example of an organic amine contained in the polishing liquid used in the polishing method of FIG. 1. FIG. [Figure 5] 2 is a diagram showing the chemical structure of a secondary amine (piperazine), which is an example of an organic amine contained in the polishing liquid used in the polishing method of FIG. 1. FIG. [Figure 6] 2 is a diagram showing the chemical structure of a substance (diethylenetriamine) having a primary amine and a secondary amine, which is an example of an organic amine contained in the polishing liquid used in the polishing method of FIG. 1. FIG. [Figure 7] 2 is a plan view for schematically explaining a polishing liquid supply device including a bubble generator for injecting gas into the polishing liquid supplied to the surface polishing apparatus of FIG. 1. FIG. [Figure 8] FIG. 1 is a graph showing the relationship between the bubbling time for a polishing liquid and the nanobubble concentration in the polishing liquid. [Figure 9] FIG. 1 is a diagram showing an example of the distribution of nanobubble diameters contained in a polishing liquid. [Figure 10] FIG. 1 is a graph showing the relationship between the bubbling time of the polishing liquid and the polishing rate of the silicon wafer, obtained in Polishing Test 1 conducted by the present inventors. [Figure 11] FIG. 1 is a graph showing the relationship between the bubbling time of the polishing liquid and the surface roughness of the silicon wafer, obtained in Polishing Test 1 conducted by the present inventors. [Figure 12] FIG. 10 is a graph showing the relationship between the concentration of an organic amine contained in a polishing liquid and the polishing rate, obtained in Polishing Test 2 conducted by the present inventors. [Figure 13] FIG. 10 is a graph showing the relationship between the concentration of an organic amine contained in a polishing liquid and surface roughness, obtained in polishing test 2 conducted by the present inventors. [Figure 14] FIG. 10 is a graph showing the relationship between the type of gas contained in the polishing liquid and the polishing rate, obtained in Polishing Test 3 conducted by the present inventors. [Figure 15] FIG. 10 is a diagram showing the relationship between the type of gas contained in the polishing liquid and surface roughness, obtained in Polishing Test 3 conducted by the present inventors. DETAILED DESCRIPTION OF THE INVENTION

[0024] An application example of the present invention will be described in detail below with reference to the drawings. [Example]

[0025] Figure 1 conceptually shows the main components of a surface polishing apparatus 10 for carrying out a silicon polishing method according to one example of the present invention, with the guide roller fixing base removed. In Figure 1, the surface polishing apparatus 10 is provided with a polishing platen 12 rotatably supported about a vertical axis of rotation C1, and the polishing platen 12 is driven by a platen drive motor 14 to rotate at a constant speed in one rotation direction indicated by the arrow in Figure 1. A polishing pad 18 is affixed to the upper surface of the polishing platen 12, i.e., the surface against which a workpiece (silicon wafer) 16 is pressed.

[0026] The workpiece 16 is held on the lower surface of the application disc 20, i.e., the surface facing the polishing pad 18, and the application disc 20 presses the workpiece 16 against the polishing pad 18 with a predetermined load. A drip nozzle 22 is provided near the application disc 20 of the surface polishing device 10, and a polishing liquid (lubricant) 26, which is a polishing composition, is delivered from a polishing liquid supply device 24 and supplied onto the polishing surface plate 12.

[0027] The surface polishing apparatus 10 is optionally provided with an adjustment tool holder (not shown) that is rotatable about a rotation axis parallel to the rotation axis C1 of the polishing table 12 and that is movable in the direction of the rotation axis and in the radial direction of the polishing table 12, and an abrasive body adjustment tool (dresser or conditioner) such as a diamond wheel (not shown) that is attached to the underside of the adjustment tool holder, i.e., the surface facing the polishing pad 18. The adjustment tool holder and the abrasive body adjustment tool attached thereto are pressed against the polishing pad 18 while being rotated by an adjustment tool drive motor (not shown), and are moved back and forth in the radial direction of the polishing table 12, thereby adjusting the polishing surface of the polishing pad 18 and constantly maintaining the surface condition of the polishing pad 18 in a state suitable for polishing.

[0028] 2, at a position eccentric from the rotation axis C1 on the polishing table 12, a short cylindrical application disk 20 holds the workpiece 16, or the object to be polished, on its underside by suction, adhesion, or a holding frame, etc. The outer surface of the application disk 20 is supported by a pair of free-rotating guide rollers 30 and a drive guide roller 32 mounted on a fixed guide roller support base 28 fixed to a frame (not shown), allowing the application disk 20 to rotate about the rotation axis C2. The application disk 20 is rotated about the rotation axis C2 by the rotational force due to the difference in peripheral speed between the polishing table or polishing pad 18, while the application disk 20 is pressed against the polishing pad 18 on the polishing table 12 by the load of, for example, a weight 34, thereby polishing the workpiece 16.

[0029] The following polishing method is used for surface polishing using the surface polishing apparatus 10. The polishing platen 12 and the polishing pad 18 attached thereto, and the attachment disk 20 and the workpiece (silicon wafer) 16 held on its underside are rotated about their respective rotation axes C1 and C2 by the platen drive motor 14 and drive guide roller 32. While the polishing liquid 26, which does not contain abrasive grains 36, is supplied onto the surface of the polishing pad 18 from the drip nozzle 22 and a spray nozzle (not shown), the workpiece 16 held on the attachment disk 20 is pressed against the polishing pad 18. As a result, the polished surface of the workpiece 16, i.e., the surface facing the polishing pad 18, is polished flat by the chemical polishing action of the polishing liquid 26 and the mechanical polishing action of the abrasive grains 36 contained within and self-supplied from the polishing pad 18. The abrasive grains 36 are, for example, silica having an average particle size of approximately 80 nm.

[0030] The polishing pad 18 attached to the polishing table 12 is an abrasive grain-containing polishing pad (LHA pad) made of epoxy resin or PES resin having independent pores or interconnected pores 38 containing abrasive grains 36, as shown in Figure 3, and has dimensions of, for example, an outer diameter of approximately 300 (mm) x thickness of approximately 5 (mm).

[0031] The polishing pad 18 is formed in a disk shape and includes a matrix resin 40 made of epoxy resin or PES resin, which has either closed or interconnected pores 38, and numerous abrasive grains 36 that are filled into the interconnected pores 38 of the matrix resin 40, some of which adhere to the matrix resin 40, and some of which detach from the matrix resin 40 during polishing. For this reason, the polishing pad 18 is referred to as a semi-fixed abrasive-containing polishing pad containing the abrasive grains 36, and polishing using this abrasive-containing polishing pad is referred to as semi-fixed abrasive polishing. The polishing pad 18 is composed of, for example, approximately 32% by volume of abrasive grains 36 and approximately 33% by volume of matrix resin 40, with the remaining volume being occupied by interconnected pores 38. The interconnected pores 38 of the matrix resin 40, which is formed in a sponge or mesh-like structure, are formed to be equal to or larger than the abrasive grains 36, and numerous abrasive grains 36 are retained within the interconnected pores 38. The base resin 40 and the abrasive grains 36 are fixed to each other by a necessary and sufficient bonding force. The polishing pad 18 of this embodiment is capable of polishing the workpiece (silicon wafer) 16 by a mechanical polishing action by the abrasive grains 36 supplied by the polishing pad 18 itself, without using a slurry containing, for example, colloidal silica, and a chemical polishing action by supplying a highly alkaline polishing liquid 26 that does not contain abrasive grains.

[0032] The abrasive grains 36 are preferably silica, but other abrasive grains, such as those 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 36 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 36 exceeds 3.0 μm, abrasive grains 26 released from the matrix resin 40 during the polishing process described below are more likely to cause polishing scratches on the workpiece 16. Furthermore, if the average particle size of the polishing grains 36 is less than 0.005 (μm), the polishing grains 36 tend to aggregate, which makes it easier for polishing scratches to occur on the object being polished during polishing.

[0033] The particle size of the abrasive grains 36 is measured by a laser diffraction / scattering method, for example, using a particle size / particle size distribution analyzer, Microtrac MT3300, manufactured by Nikkiso Co., Ltd., and the average particle size is the arithmetic mean of the particle size. Particle sizes below the measurement limit of the laser diffraction / scattering method are measured by a dynamic light scattering method using, for example, a particle size / particle size distribution analyzer, Nanotrac UPA-EX250, manufactured by Nikkiso Co., Ltd.

[0034] The polishing liquid 26 corresponds to a silicon polishing composition and contains an organic amine to enhance alkalinity, water, and bubbles 58 (described below). It is highly alkaline (pH = 10.6 to 12.8) to enhance reactivity with the workpiece (silicon wafer) 16 and promote chemical polishing, and does not contain any alkaline agents designated as deleterious substances or (free) abrasive grains. The organic amine preferably has a concentration of 0.025 to 0.100 mol / L.

[0035] As the organic amine, a primary amine such as ethylenediamine having the chemical structure shown in Figure 4, a secondary amine such as piperazine having the chemical structure shown in Figure 5, or a substance having a primary amine and a secondary amine such as diethylenetriamine having the chemical structure shown in Figure 6 are preferably used. In Figures 4, 5, and 6, the portions surrounded by dashed lines indicate amino groups.

[0036] The polishing liquid supply device 24 has an in-line structure, for example, as shown in Fig. 7. The polishing liquid supply device 24 includes a tank 42 that stores the polishing liquid 26, a pump 44 that circulates the polishing liquid 26 in the tank 42, an upstream return path 46 that connects a suction port 44a of the pump 44 to the tank 42, a downstream return path 48 that connects a discharge port 44b of the pump 44 to the tank 42, and an air bubble injection device 50 inserted in the downstream return path 48. The air bubble injection device 50 includes an airtight cylindrical case 54 whose end faces are connected to the downstream return path 48 and whose side face is connected to a gas supply pipe 52, and a cylindrical ceramic filter 56 arranged to partition the space within the cylindrical case 54 into a space SL that communicates with the downstream return path 48 and through which the polishing liquid 26 passes, and an outer circumferential space SA that communicates with the gas supply pipe 52.

[0037] In the polishing liquid supply device 24, when the pump 44 causes the polishing liquid 26 in the tank 42 to flow through the upstream return path 46 and the downstream return path 48, gas such as air, oxygen, or nitrogen is supplied from the gas supply pipe 52 at a pressure higher than the discharge pressure of the pump 44, and a large number of bubbles 58 having diameters on the nano-order of less than 1 μm are generated from the inner surface of the ceramic filter 56 and mixed into the polishing liquid 26, resulting in the polishing liquid 26 containing bubbles 58 that are nanobubbles (fine bubbles) with a particle size of 1 μm or less.

[0038] As shown in FIG. 8, in the polishing liquid supply device 24, the longer the bubbling time BT, which is the time for supplying gas from the gas supply pipe 52, the higher the concentration of bubbles 58 (number of bubbles (count number) / ml) contained in the polishing liquid 26 becomes, reaching 6×10 7The bubbling time BT indicates the concentration of bubbles 58. In this example, the concentration of bubbles 58 is the value (count number) obtained by measuring the distribution of bubbles 58 using a particle size distribution analyzer SALD-7500 manufactured by Shimadzu Corporation, which uses a method of continuously detecting scattered light from an ultraviolet semiconductor laser over a wide angle, and integrating the number of bubbles constituting the distribution. Figure 9 shows an example of this bubble size distribution.

[0039] [Experimental Example] The following describes an example of an experiment conducted by the present inventors. First, using an apparatus configured similarly to the surface polishing apparatus 10 shown in Figure 1, semi-fixed abrasive polishing using a silica abrasive grain-containing polishing pad or a ceria abrasive grain-containing pad 18 and a polishing liquid 26 was performed under the polishing conditions shown below on a common sample to be polished, which was a silicon single crystal plate with a diameter of 4 inches and a thickness of 350 μm. The polishing rate PR and surface roughness Ra of the silicon wafer after the polishing test were measured using the polishing rate measurement method and surface roughness measurement method shown below.

[0040] [Polishing test conditions] · Surface grinding device: Lapmaster LP15 modified machine (3-axis grinding machine) Workpiece: 4-inch diameter silicon wafer <100> Workpiece rotation speed: 60 rpm Polishing pad: Ceria abrasive grain (LHA) pad Polishing solution: LSC-T006 (manufactured by Noritake Company, containing piperazine) (Water containing 0.10N) Polishing pad diameter: 380mmφ Silicon wafer rotation speed: 60 rpm Polishing pad rotation speed: 60 rpm Polishing pressure: 10kPa Center distance between polishing pad and workpiece: 85mm ·Polishing liquid flow rate: 10ml / min Dressing pressure, rotation speed, time: 25kPa, 60rpm, 120sec

[0041] [Nanobubble generation conditions] Bubble generation method: In-line polishing liquid supply device Bubble generation time: 0H, 15H, 30H, 60H, 90H Gas pressure: 0.15MPa Gas type: air, oxygen ·Polishing liquid flow rate: 300ml / min

[0042] [Method for measuring polishing rate] The difference in mass of the silicon wafer before and after the polishing test was determined using an analytical balance, and the polishing amount (wear thickness) was determined from the known density of the silicon wafer and the surface area of ​​the polished surface. The polishing rate PR (nm / min) was calculated by dividing the polishing amount by the polishing time.

[0043] [Surface roughness measurement method] The surface roughness of the surface profile of the polished surface of the silicon wafer after the polishing test was measured using a white light interference microscope (Hitachi High-Tech VS-1330), and the arithmetic mean roughness Ra specified in ISO25178 was calculated.

[0044] (Polishing test 1) In this polishing test 1, a polishing liquid 26 containing water and 0.10N piperazine was prepared, and a polishing test was performed in which a bubble-free polishing liquid with a bubbling time BT of 0 H was used to polish silicon wafers under the polishing processing test conditions described above. Also, a polishing test was performed in which four types of polishing liquid 26 with different bubbling times BT of 15 H, 30 H, 60 H, and 90 H were used to polish silicon wafers under the polishing processing test conditions described above for two polishing times of 30 minutes and 24 hours, and the polishing rate PR (nm / min) and surface roughness Ra (nm) of the silicon wafers were measured in each case.

[0045] Fig. 10 shows the relationship between the bubbling time BT of the polishing liquid and the polishing rate PR of silicon wafers. In Fig. 10, the polishing rates in the polishing tests of silicon wafers using four types of polishing liquids with different bubbling times BT of 15 hours, 30 hours, 60 hours, and 90 hours are all 12% or more higher than the polishing rate PR in the polishing tests of silicon wafers using a polishing liquid containing no bubbles, except for the case where the bubbling time BT is BT and the polishing time is 24 hours.

[0046] Fig. 11 shows the relationship between the bubbling time BT and the surface roughness Ra of silicon wafers. In Fig. 11, the surface roughness Ra of silicon wafers polished using four different polishing liquids with different bubbling times BT of 15H, 30H, 60H, and 90H was 34% or more lower than the surface roughness Ra of silicon wafers polished using a polishing liquid containing no bubbles.

[0047] (Polishing test 2) In this polishing test 2, three types of polishing liquid 26 having different piperazine concentrations, i.e., 0.10 N, 0.075 N, and 0.05 N, were used, and two types of polishing liquid 26 were used at 1 H and 24 H after the 15 H bubbling time BT. Polishing tests of silicon wafers were carried out under the above-mentioned polishing processing test conditions for a fixed polishing time every 30 minutes, and the polishing rate PR and surface roughness Ra of the silicon wafers were measured in each case.

[0048] Fig. 12 shows the influence of piperazine concentration and the elapsed time after bubbling of the polishing liquid on the polishing rate PR of silicon wafers. Fig. 12 shows that the polishing rate PR of a polishing liquid that has been bubbled for 15 hours is higher than the polishing rate PR of a silicon wafer using a polishing liquid that does not contain bubbles, but the lower the piperazine concentration, the lower the polishing rate PR, and the longer the elapsed time after bubbling of the polishing liquid, the lower the polishing rate PR becomes, except when the piperazine concentration is 0.05N.

[0049] Fig. 13 shows the effect of piperazine concentration and the elapsed time after bubbling of the polishing liquid on the surface roughness Ra of a silicon wafer. In Fig. 13, the surface roughness Ra of a polishing liquid that has been bubbled for 15 hours is smaller than the surface roughness Ra of a silicon wafer that uses a polishing liquid that does not contain bubbles. However, even if the piperazine concentration changes, the surface roughness Ra does not change much, and even if the elapsed time after bubbling of the polishing liquid changes, the surface roughness removal rate PR does not change at all.

[0050] (Polishing test 3) In this Polishing Test 3, a polishing test was conducted in which silicon wafers were polished under the above-mentioned polishing processing test conditions using a polishing liquid containing no bubbles and having a bubbling time BT of 0 H, and a polishing test was conducted in which silicon wafers were polished under the above-mentioned polishing processing test conditions using two types of polishing liquids into which air and oxygen were injected for a bubbling time BT of 15 H, and the polishing rate PR (nm / min) and surface roughness Ra (nm) of the silicon wafers were measured in each case.

[0051] As described above, according to the silicon wafer polishing method of this embodiment, a workpiece (silicon wafer) 16 is polished using a polishing pad 18, which is an abrasive grain-containing polishing pad containing abrasive grains 36, under the supply of a polishing liquid (polishing composition) 26 that does not contain abrasive grains. The polishing liquid 26 contains an organic amine, water, and nanobubbles 58 with a particle size of 1 μm or less, but does not contain an alkaline agent or abrasive. Because the polishing composition does not contain an alkaline agent, the polishing composition can be used regardless of the equipment used. Furthermore, because the polishing composition does not contain an abrasive, a silicon wafer polishing method with a low environmental impact is obtained. Furthermore, because the bubbles 58 are nanometer-sized with a particle size of 1 μm or less, they easily penetrate between the abrasive grains of the polishing pad and the silicon wafer, and adhere to the polishing debris, facilitating its removal. This accelerates the polishing rate and suitably reduces the roughness of the polished surface.

[0052] Furthermore, according to the method for polishing a silicon wafer of this embodiment, the bubbles 58, which are nanobubbles contained in the polishing liquid 26, are bubbles that are formed by injecting a gas into the polishing liquid 26 for a period of 15 hours or more, and therefore, the bubbles 58 are nanobubbles with particle sizes on the nano-order.

[0053] Furthermore, according to the method for polishing a silicon wafer of this embodiment, the nanobubbles injected into the polishing liquid 26 are bubbles that have been produced within 24 hours since the gas was injected into the polishing liquid 26, and therefore, nanobubbles 58 with nano-order particle diameters can be suitably obtained.

[0054] Furthermore, according to the method for polishing silicon wafers of this embodiment, the nanobubbles injected into the polishing liquid 26 are bubbles with a diameter of less than 1 μm, and the number of nanobubbles is 6×10 per ml. 7 Since the number of particles contained is equal to or more than 1, a favorable polishing rate and polished surface roughness can be obtained.

[0055] Furthermore, according to the method for polishing silicon wafers of this embodiment, the organic amine contained in the polishing liquid 26 is ethylenediamine, piperazine, or diethylenetriamine, and therefore, when dissolved in water, it becomes strongly alkaline.

[0056] Furthermore, according to the method for polishing silicon wafers of this embodiment, the organic amine contained in the polishing solution 26 is piperazine contained at a concentration of 0.05 N to 0.10 N, and therefore the reactivity of silicon is enhanced under the strong alkalinity caused by the organic amine, thereby achieving high polishing efficiency.

[0057] Furthermore, according to the method for polishing silicon wafers of this embodiment, the abrasive grains contained in the abrasive grain-containing polishing pad 18 are at least one of silica, ceria, zirconia, alumina, and silicon carbide, and therefore, favorable polishing efficiency can be obtained.

[0058] Although one embodiment of the present invention has been described above, the present invention can also be applied in other aspects.

[0059] For example, in the surface polishing apparatus 10 of the above-described embodiment, the workpiece 16 on the polishing pad 18, which is driven to rotate around the rotation axis C1, is rotated around the rotation axis C2 parallel to the rotation axis C1, but the workpiece 16 may be polished while rotating and revolving by revolving the rotation axis C2 of the workpiece 16 along an orbit around the revolution axis parallel to the rotation axis C1.

[0060] Furthermore, although epoxy resin or PES resin is used for the base resin 40, 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.

[0061] 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.

[0062] Furthermore, in the above-described embodiment, the gas is injected into the polishing liquid 26 using the in-line polishing liquid supply device 24, but other types of nanobubble generators may also be used.

[0063] Although not specifically exemplified, the present invention can be used with various modifications within the scope of the invention. [Explanation of symbols]

[0064] 10: Surface polishing device, 12: Polishing platen, 16: Workpiece (silicon wafer), 18: Polishing pad, 20: Adhesive disc, 24: Polishing liquid supply device, 26: Polishing liquid (polishing composition), 36: Polishing abrasive grains, 58: Air bubbles (nanobubbles)

Claims

1. A method for polishing silicon wafers using a polishing pad containing abrasive grains while supplying a polishing composition that does not contain abrasive grains, comprising: The polishing composition contains an organic amine, water, and nanobubbles having a particle size of 1 μm or less, and does not contain an alkali agent or an abrasive. A silicon polishing method comprising the steps of:

2. The nanobubbles contained in the polishing composition are bubbles formed by injecting a gas into the polishing composition for a period of 15 hours or more.

2. The silicon polishing method according to claim 1.

3. The nanobubbles injected into the polishing composition are bubbles that have been present for less than 24 hours since the gas was injected into the polishing composition.

3. The silicon polishing method according to claim 2.

4. The nanobubbles contained in the polishing composition are bubbles having a diameter of less than 1 μm, and the number of bubbles is 6×10 per ml. ７ Contains at least one 2. The silicon polishing method according to claim 1.

5. The organic amine is ethylenediamine, piperazine, or diethylenetriamine.

2. The silicon polishing method according to claim 1.

6. The organic amine is piperazine present at a concentration of 0.05N to 0.10N.

2. The silicon polishing method according to claim 1.

7. The abrasive grains contained in the abrasive grain-containing polishing pad are at least one of silica, ceria, zirconia, alumina, and silicon carbide.

7. The silicon polishing method according to claim 1, wherein the silicon polishing step is performed by polishing the silicon substrate.

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