Polishing pad and wafer polishing method

Abstract

The present invention provides a polishing pad and a wafer polishing method which each make it possible to suppress generation of a scratch on a polished wafer and which each make it possible to achieve high accuracy and higher workability. A polishing pad in a wafer polishing device 10 of a double-sided polishing type can include a first polishing pad 7 and a second polishing pad 9. A wafer W is made of SiC such that one of a first surface W1 and a second surface W2 thereof is an Si surface and the other of the first surface W1 and the second surface W2 thereof is a C surface. The polishing pad includes a base material 19 which contains a binder resin and in which a plurality of pores 21, 23 are formed and polishing particles 25a, 25b which are held in the base material 19 or the pores 21, 23. The binder resin is a sulfone-based resin. The polishing particles 25a, 25b are made of silica. Durometer hardness (D) is 30-52. Density is 0.60-0.90g / cm3.

Description

Polishing pad and wafer polishing method

[0001] The present invention relates to a polishing pad and a method for polishing a wafer.

[0002] Patent Document 1 discloses a method for simultaneously polishing both sides of a SiC wafer. This wafer polishing method is used in a double-side polishing wafer polishing apparatus. This wafer polishing apparatus moves a first side of the wafer and a first polishing pad relative to each other under a predetermined surface pressure to polish the first side with the first polishing pad, and moves a second side of the wafer (the backside of the first side) relative to the second polishing pad to polish the second side with the first polishing pad. During this process, a polishing liquid containing no abrasive particles is interposed between the first side of the wafer and the first polishing pad and between the second side of the wafer and the second polishing pad.

[0003] More specifically, the wafer polishing apparatus includes a first platen, a second platen, and a carrier. The first platen has a first polishing pad extending in a direction perpendicular to an axis and is rotated about the axis. The second platen extends in a direction perpendicular to the axis and has a second polishing pad facing the first polishing pad and is rotated about the axis. The carrier extends in a direction perpendicular to the axis and has a fixing portion facing the first polishing pad and the second polishing pad, and is rotated relative to the first platen and the second platen.

[0004] The first polishing pad and the second polishing pad are abrasive grain-containing polishing pads also known as LHA (Loosely Held Abrasive) pads, which contain a binder resin, a base material in which a plurality of pores are formed, and abrasive particles held within the base material or within the pores.

[0005] In this wafer polishing method, when the first surface of the wafer is the Si surface and the second surface is the C surface, the polishing rate of the first polishing pad is set lower than that of the second polishing pad because the polishing rate of the second polishing pad is greater than that of the first surface, which makes it possible to suppress the occurrence of scratches on the wafer after polishing and achieves high workability and precision.

[0006] Patent No. 7433170

[0007] However, in the above-mentioned conventional wafer polishing method, it is necessary to use a first polishing pad and a second polishing pad with different polishing rates, which results in insufficient workability.

[0008] The present invention has been made in consideration of the above-mentioned conventional situation, and aims to solve the problem of providing a polishing pad and a wafer polishing method that can suppress the occurrence of scratches on the wafer after polishing, and that can achieve high precision and greater workability.

[0009] The polishing pad of the present invention is a polishing pad that can be used in a double-side polishing type wafer polishing apparatus that, under a predetermined surface pressure, moves a first surface of a wafer and a first polishing pad relatively to polish the first surface with the first polishing pad, and moves a second surface, which is the backside of the first surface of the wafer, and a second polishing pad relatively to polish the second surface with the first polishing pad, and can be the first polishing pad and the second polishing pad, wherein the wafer polishing apparatus comprises: a first surface platen that has the first polishing pad extending in a direction perpendicular to an axis and that is rotated about the axis; a second surface platen that extends in a direction perpendicular to the axis and has the second polishing pad facing the first polishing pad and that is rotated about the axis; and a carrier that extends in a direction perpendicular to the axis and has fixing portions that face the first polishing pad and the second polishing pad, and that is rotated relatively to the first surface platen and the second surface platen, wherein the wafer is fixed to the fixing portion so that the first surface faces the first polishing pad and the second surface faces the second polishing pad, The wafer is made of SiC, one of the first surface and the second surface being an Si-face and the other of the first surface and the second surface being a C-face; the wafer includes a base material containing a binder resin and having a plurality of pores formed therein; and abrasive particles held within the base material or the pores; the binder resin is a sulfone-based resin; the abrasive particles are made of silica; the wafer has a durometer hardness (D) of 30 to 52; and a density of 0.60 to 0.90 g / cm. 3 It is characterized in that:

[0010] Further, a wafer polishing method of the present invention uses a wafer polishing apparatus including: a first platen having a first polishing pad extending in a direction perpendicular to an axis and rotated about the axis; a second platen having a second polishing pad extending in a direction perpendicular to the axis and facing the first polishing pad and rotated about the axis; and a carrier extending in a direction perpendicular to the axis and having a fixing portion facing the first polishing pad and facing the second polishing pad, the carrier being rotated relatively to the first platen and the second platen, wherein a wafer is fixed to the fixing portion such that a first surface faces the first polishing pad and a second surface that is the back side of the first surface faces the second polishing pad, and the first surface and the first polishing pad are moved relatively to each other under a predetermined surface pressure to polish the first surface, and the second surface and the second polishing pad are moved relatively to polish the second surface, The wafer is made of SiC, one of the first surface and the second surface being an Si-face and the other of the first surface and the second surface being a C-face, the first polishing pad and the second polishing pad are the same type of polishing pads, each of which includes a base material containing a binder resin and having a plurality of pores formed therein, and abrasive particles held in the base material or the pores, the binder resin being a sulfone-based resin, the abrasive particles being made of silica, and having a durometer hardness (D) of 30 to 52, and a density of 0.60 to 0.90 g / cm 3 It is characterized in that:

[0011] According to the results of the inventors' tests, by using the above-mentioned polishing pads for the first and second polishing pads, it is possible to suppress the occurrence of scratches on the wafer after polishing and achieve high precision. Therefore, the wafer polishing method of the present invention using the polishing pad of the present invention eliminates the need to use first and second polishing pads with different polishing rates, and achieves higher workability.

[0012] The polishing pad and wafer polishing method of the present invention can suppress the occurrence of scratches on the wafer after polishing, and can also achieve high precision and improved workability.

[0013] Fig. 1 is a schematic cross-sectional view of a wafer polishing apparatus according to an embodiment. Fig. 2 is a 500x SEM photograph of the polishing pad of Example 1. Fig. 3 is a 2000x SEM photograph of a first region of the polishing pad of Example 1. Fig. 4 is a 400x SEM photograph of a second region of the polishing pad of Example 1. Fig. 5 is a 2000x SEM photograph of a second region of the polishing pad of Example 1. Fig. 6 is a schematic enlarged cross-sectional view of the polishing pads of Examples 1 to 7.

[0014] The binder resin used for the LHA pad may be polyether, rigid polyurethane foam, epoxy resin, or polyethersulfone resin, as well as fluorine-based synthetic resins such as polyvinyl fluoride, vinyl fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride, or vinylidene fluoride-hexafluoropropylene copolymer, polyethylene resin, or polymethyl methacrylate. However, according to the results of tests conducted by the inventors, sulfone-based resins are preferred for the first and second polishing pads because of their excellent chemical resistance and abrasion resistance.

[0015] The sulfone resin may be polyethersulfone (PES), polysulfone (PSU), polyphenylsulfone (PPSU), etc. The inventors confirmed the effect of the present invention using PES.

[0016] Silica is used as the abrasive particles. The LHA pad can use silica, diamond, cubic boron nitride, boron carbide, silicon carbide, alumina, zirconia, titania, ceria, manganese oxide, barium carbonate, chromium oxide, iron oxide, etc., as abrasive particles, but according to the results of tests conducted by the inventors, silica is preferred as the polishing pad to be used for the first polishing pad and the second polishing pad because it has a low Knoop hardness, is less likely to be scratched, and has excellent polishing properties.

[0017] According to the test results of the inventors, the polishing pads used for the first polishing pad and the second polishing pad should have a durometer hardness (D) of 30 to 52 and a density of 0.60 to 0.90 g / cm 3 It is preferable to set the following.

[0018] According to the results of the inventors' tests, it is preferable that the binder resin is 17.6 to 26.2% by volume, the abrasive particles are 16.3 to 24.6% by volume, and the pores are 49.2 to 66.1% by volume.

[0019] It is particularly preferable that the pores consist of micropores forming a three-dimensional network structure and large pores that are larger in volume than the micropores and communicate with numerous micropores. In this case, the polishing surface of the polishing pad has a first region without large pores and a second region with large pores. In the first region, the binder resin forms a network structure, and abrasive particles are contained within the pores. Furthermore, in the first region, the binder resin and abrasive particles are densely present. Therefore, high-efficiency polishing can be expected in the first region. On the other hand, in the second region, numerous pores exist on the surface of the large pores, and abrasive particles are discharged from each pore. Furthermore, the polishing liquid accumulates in the large pores. The abrasive particles discharged from the micropores into the large pores have a degree of freedom in the large pores during polishing. Furthermore, the large pores reduce processing resistance during double-side polishing of wafers, resulting in high-quality polished wafers and reducing wafer crushing during double-side polishing.

[0020] According to the results of the inventors' tests, it is preferable that the fine pores are 44.1 to 51.6% by volume, and the large pores are 2.7 to 15.7% by volume.

[0021] In the wafer polishing method, a polishing liquid is interposed between the wafer and the first polishing pad and between the wafer and the second polishing pad, but in the wafer polishing method of the present invention, a polishing liquid that does not contain abrasive particles can be used, which improves the cleanability of the wafer after polishing and is expected to reduce waste liquid costs.

[0022] (Examples and Comparative Examples) First, a double-side polishing type wafer polishing apparatus (9B double-side polisher) 10 shown in Figure 1 was prepared. This wafer polishing apparatus 10 includes a first platen 1, a second platen 3, and a carrier 5. The wafer polishing apparatus 10 is capable of polishing the first side W1 and the second side W2 of the wafer W simultaneously.

[0023] The first surface plate 1 is annular, and has a first annular polishing pad 7 on its underside. The second surface plate 3 is also annular and matches the first surface plate 1, and has a second annular polishing pad 9 on its upper surface. The first surface plate 1 is provided with a first rotation shaft (not shown), and the second surface plate 3 is provided with a second rotation shaft (not shown). These extend in the direction of axis X1 and are rotated around axis X1 at a predetermined speed by a drive unit 11. The first surface plate 1 and the second surface plate 3 can move toward and away from each other. The first polishing pad 7 and the second polishing pad 9 extend horizontally in a direction perpendicular to X1 and face each other.

[0024] The carrier 5 is disposed between the first polishing pad 7 and the second polishing pad 9. A driving force transmission mechanism (not shown) is provided in the carrier 5, and the driving force transmission mechanism rotates the carrier 5 relative to the first platen 1 and the second platen 3 at a predetermined speed around an axis X2 parallel to the axis X1.

[0025] The fixing portion 5a of the carrier 5 extends horizontally in a direction perpendicular to the axis X2, and faces the first polishing pad 7 and the second polishing pad 9. A wafer W is fixed to the fixing portion 5a. The carrier 5 has a plurality of fixing portions 5a, and a plurality of wafers W can be mounted thereon.

[0026] Each wafer W is made of SiC. The Si-face of the SiC is the first face W1, and the C-face of the SiC is the second face W2. The first face W1 of the wafer W faces the first polishing pad 7, and the second face W2 faces the second polishing pad 9.

[0027] An annular tray 13 is placed on the first platen 1. The tray 13 can rotate around the axis X1 together with the first platen 1. A plurality of nozzles 15 are provided on the tray 13, and each nozzle 15 is connected to a tank (not shown). Thus, polishing liquid 17 in the tank is supplied from each noble 15 into the tray 13. A plurality of supply holes 13a are formed in the tray 13, and each supply hole 13a is connected to a tube 19 extending above the first platen 1. Communication holes 1a and openings 7a are formed through the first platen 1 and the first polishing pad 7, and the polishing liquid 17 in the tray 13 can be supplied between the first polishing pad 7 and the second polishing pad 9 via the supply holes 13a, the tubes 19, the communication holes 1a, and the openings 7a.

[0028] When the wafer W is fixed to the fixing portion 5a and the wafer polishing apparatus 10 is operated, the first platen 1 and the second platen 3 approach each other, and each wafer W fixed to the fixing portion 5a of the carrier 5 and the first and second polishing pads 7 and 9 are pressed to a predetermined surface pressure, and the drive device 11 is driven to rotate the first platen 1, the second platen 3, and the carrier 5. As a result, the first surface W1 of the wafer W and the first polishing pad 7 move relative to each other at a predetermined speed to polish the first surface W1, and the second surface W2 of the wafer W and the second polishing pad 9 move relative to each other at a predetermined speed to polish the second surface W2. Then, after a predetermined time has elapsed, polishing of the first surface W1 and polishing of the second surface W2 can be completed simultaneously.

[0029] Meanwhile, the following binder resin, abrasive particles, solvent, pore-forming agent, and additives were prepared: (Binder resin) Polyethersulfone (PES) (Abrasive particles) Silica (SiO2) (average particle size: 200 nm) (Solvent) N-methyl-2-pyrrolidone (NMP) (Pore-forming agent) Granulated sugar (average particle size 200 μm) (Additive) Glycerin

[0030] The binder resin, abrasive particles, solvent, pore-forming agent, and additive components were mixed in the blending ratios (volume %) shown in Table 1 to obtain pastes. Each of the obtained pastes was used to obtain a sheet-shaped molded body using a T-die. The solvent was removed from each molded body, and the binder resin was solidified.

[0031]

[0032] The polishing surface of the obtained intermediate was dressed to produce polishing pads of Examples 1 to 7 and Comparative Example 1. A 500x SEM photograph of the polishing pad of Example 1 is shown in Figure 2. From Figure 2, it can be seen that the polishing pads of Examples 1 to 7 contain a base material containing a binder resin and having multiple pores formed therein, and abrasive particles held within the base material or the pores. It can also be seen that the pores consist of fine pores forming a three-dimensional network structure and large pores that are larger in volume than the fine pores and communicate with the fine pores. The fine pores are formed by a solvent, and the large pores are formed by granulated sugar. Glycerin is used to adjust the solubility of the binder resin in the solvent.

[0033] The physical properties of the polishing pads of Examples 1 to 7 and Comparative Example 1 were measured using durometer hardness (D), density (g / cm 3 The results are shown in Table 2.

[0034]

[0035] The pore content breakdown, i.e., the volume percent of fine pores and the volume percent of large pores, was also measured. The results are shown in Table 3.

[0036]

[0037] 3 shows a 2000x SEM photograph of the first region, where no large pores exist, in the polishing pad of Example 1. Table 4 shows the density addition (volume %) of the binder resin and the density addition (volume %) of the abrasive particles in the first region of the polishing pads of Examples 1 to 7.

[0038]

[0039] 3, it can be seen that in the first region, the binder resin forms a network structure, and the abrasive particles are contained within the pores. Furthermore, Table 4 shows that the binder resin and abrasive particles are densely present in the volume of large pores with a diameter of about 200 μm.

[0040] Meanwhile, an SEM photograph of the second region at 400x magnification is shown in Figure 4, and an SEM photograph of the second region at 2000x magnification is shown in Figure 5. Figures 4 and 5 show that large pores are formed in the second region, and that there are many pores with a diameter of about 4 μm on the surface of the large pores, and that abrasive particles are discharged through the pores.

[0041] (Test) Polishing pads of Examples 1 to 7 or Comparative Example 1 were used as the first polishing pad 7 and the second polishing pad 9 of the wafer polishing apparatus 10, and polishing tests were carried out under the following conditions: Polishing pad dimensions: doughnut shape with a diameter of 660 mm (punched out at a diameter of 200 mm from the center) Wafer W: SiC (diameter 4 inches) Polishing liquid: permanganic acid aqueous solution (not containing abrasive particles)

[0042] The polishing rate (μm / h), surface roughness Ra (nm) of the Si surface, surface roughness Ra (nm) of the C surface, machining resistance (A) converted into current value, and TTV (μm) were measured. Note that TTV is an index of thickness variation of the wafer W. A high TTV indicates a large thickness variation, and a low TTV indicates a small thickness variation. A low TTV is excellent.

[0043] The cleaning properties were evaluated by observation under an electron microscope, with the number of particles in a 5 μm × 5 μm area being rated as follows: 0 particles = ◎; 5 or less particles = ◯; 5 to 10 particles = △; and 10 or more particles = ×.

[0044] The overall evaluation was performed according to the following criteria. ◎ was evaluated as follows: the polishing rate was 1.5 μm / h or more, the surface roughness Ra of the Si surface was 0.15 nm or less, the surface roughness Ra of the C surface was 0.25 nm or less, the machining resistance was 0.40 A or less, the TTV was 1.0 μm or less, and the cleanability was ◎. 〇 was evaluated as follows: the polishing rate was 1.0 μm / h or more, the surface roughness Ra of the Si surface was 0.20 nm or less, the surface roughness Ra of the C surface was 0.30 nm or less, the machining resistance was 0.40 A or less, the TTV was 1.5 μm or less, and the cleanability was ◎ or ○. △ was evaluated as follows: the polishing rate was 1.0 μm / h or less, the surface roughness Ra of the Si surface was 0.20 nm or more, the surface roughness Ra of the C surface was 0.30 nm or more, the machining resistance was 0.40 A or more, the TTV was 1.5 μm or more, and the cleanability was ○ or △. The cases where the polishing rate was 1.0 μm / h or less, the surface roughness Ra of the Si surface was 0.20 nm or more, the surface roughness Ra of the C surface was 0.30 nm or more, the processing resistance was 0.40 A or more, the TTV was 2.0 μm or more, and the cleanability was △ or × were rated as ×. The results are shown in Table 5.

[0045]

[0046] From Table 5, it can be seen that if the polishing pads of Examples 1 to 7 are used for the first polishing pad 7 and the second polishing pad 9, it is possible to suppress the occurrence of scratches on the wafer W after polishing and achieve high accuracy, even if the wafer W is made of SiC, with the first surface W1 being an Si surface and the second surface W2 being a C surface. Therefore, it can be seen that the wafer polishing methods of Examples 1 to 7 using the polishing pads of Examples 1 to 7 eliminate the need to use first and second polishing pads with different polishing rates, and achieve higher workability.

[0047] 6, in the polishing test, the first surface W1 or the second surface W2 of the wafer W moves relative to the first polishing pad 7 or the second polishing pad 9 while being pressed against them by a predetermined force F in the presence of a polishing liquid 17. During this time, the inventors speculate that the following action occurs in the polishing pads of Examples 1 to 6, since the pores of the pads are made up of small pores 21 and large pores 23.

[0048] That is, the base material 19 has a three-dimensional network structure formed by the pores 21, and the pores 21 contain abrasive particles 25a that do not contribute to polishing. The large pores 23 have a larger volume than the pores 21 and are connected to the countless pores 21. The polishing liquid 17 accumulates in the large pores 23. The abrasive particles 25a that do not contribute to polishing within the countless pores 21 are discharged from each pore 21 into the large pores 23. The abrasive particles 25b discharged into the large pores 23 contribute to polishing of the wafer W on the polishing surface 20 while retaining their freedom. Furthermore, the binder resin and abrasive particles are densely present in the first region of the polishing surface 20. In this way, polishing is performed with high precision and efficiency.

[0049] Although the present invention has been described above with reference to the examples, it goes without saying that the present invention is not limited to the above examples and can be modified and applied as appropriate within the scope of the invention.

[0050] For example, in the above-mentioned wafer polishing apparatus 10, the first axis X1 of the first and second platens 1 and 3 is parallel to the second axis X2 of the carrier 5, but in the wafer polishing apparatus used in the polishing pad and wafer polishing method of the present invention, the axis of the first and second platens 1 and 3 may coincide with the axis of the carrier 5.

[0051] The present invention can be used in semiconductor device manufacturing equipment and the like.

[0052] W...wafer W1...first surface 7...first polishing pad W2...second surface 9...second polishing pad 10...wafer polishing apparatus X1, X2...axial center (X1...first axis, X2...second axis) 1...first surface plate 3...second surface plate 5a...fixing portion 5...carrier 19...base material 21, 23...pores (21...small pores, 23...large pores) 25a, 25b...abrasive particles

Claims

1. A polishing pad that can be the first polishing pad and the second polishing pad, used in a double-side polishing type wafer polishing apparatus that, under a predetermined surface pressure, moves a first surface of a wafer and a first polishing pad relatively to polish the first surface with the first polishing pad, and moves a second surface, which is the back side of the first surface of the wafer, and a second polishing pad relatively to polish the second surface with the first polishing pad, wherein the wafer polishing apparatus comprises: a first surface plate that has the first polishing pad extending in a direction perpendicular to an axis and is rotated about the axis; a second surface plate that extends in a direction perpendicular to the axis and has the second polishing pad facing the first polishing pad and is rotated about the axis; and a carrier that extends in a direction perpendicular to the axis and has a fixing portion that faces the first polishing pad and the second polishing pad, and is rotated relatively to the first surface plate and the second surface plate; the wafer is fixed to the fixing portion so that the first surface faces the first polishing pad and the second surface faces the second polishing pad, The wafer is made of SiC, one of the first surface and the second surface being an Si-face and the other of the first surface and the second surface being a C-face; the wafer includes a base material containing a binder resin and having a plurality of pores formed therein; and abrasive particles held within the base material or the pores; the binder resin is a sulfone-based resin; the abrasive particles are made of silica; the wafer has a durometer hardness (D) of 30 to 52; and a density of 0.60 to 0.90 g / cm. 3 A polishing pad characterized by:

2. The polishing pad according to claim 1, wherein said binder resin is polyethersulfone.

3. The polishing pad according to claim 2, wherein the binder resin is 17.6 to 26.2% by volume, the abrasive particles are 16.3 to 24.6% by volume, and the pores are 49.2 to 66.1% by volume.

4. A polishing pad according to any one of claims 1 to 3, wherein the pores consist of pores forming a three-dimensional network structure and large pores having a larger volume than the pores and communicating with the numerous pores.

5. The polishing pad according to claim 4, wherein the fine pores are 44.1 to 51.6% by volume, and the large pores are 2.7 to 15.7% by volume.

6. A wafer polishing method using a wafer polishing apparatus comprising: a first platen having a first polishing pad extending in a direction perpendicular to an axis and rotated about said axis; a second platen having a second polishing pad extending in a direction perpendicular to said axis and facing the first polishing pad and rotated about said axis; and a carrier extending in a direction perpendicular to said axis and having a fixing portion facing the first polishing pad and facing the second polishing pad, said carrier being rotated relative to said first platen and said second platen; a wafer is fixed to said fixing portion so that a first surface faces said first polishing pad and a second surface, which is the back side of said first surface, faces said second polishing pad; and the first surface and the first polishing pad are moved relatively to each other under a predetermined surface pressure to polish the first surface, and the second surface and the second polishing pad are moved relatively to polish the second surface, wherein said wafer is made of SiC, one of said first surface and said second surface is a Si-face and the other of said first surface and said second surface is a C-face; The first polishing pad and the second polishing pad are the same type of polishing pads, each including a base material containing a binder resin and having a plurality of pores formed therein, and abrasive particles held within the base material or the pores, wherein the binder resin is a sulfone-based resin, the abrasive particles are made of silica, the durometer hardness (D) is 30 to 52, and the density is 0.60 to 0.90 g / cm. 3 A wafer polishing method comprising:

7. A wafer polishing method according to claim 6, wherein a polishing liquid is interposed between the wafer and the first polishing pad and between the wafer and the second polishing pad, and the polishing liquid does not contain abrasive particles.

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