Polishing pad

Abstract

This invention provides a polishing pad that can perform polishing at a high polishing rate while maintaining high finishing accuracy, even on wafers made of difficult-to-machine materials such as LT (LiTaO3) and LN (LiNbO3), thereby reducing the time required for wafer planarization. [Solution] The polishing pad according to the present invention has a nonwoven fabric base material made of polyester fibers and nylon fibers, and a polishing layer made of water-based urethane resin and polycarbonate-based urethane resin. Spherical silica is supported by a thermosetting synthetic resin adhesive, and the compressibility of the polishing pad is 2.5% or more and 4.0% or less.

Description

Technical Field

[0001] The present invention relates to a polishing pad, and particularly to a polishing pad suitable for precision polishing of wafers made of hard and brittle materials of oxides typified by LT (LiTaO3) and LN (LiNbO3).

Background Art

[0002] A SAW filter is a filter device having a configuration in which an elastic surface wave is excited by a comb-shaped electrode having regularity formed on a thin film of a piezoelectric body or a substrate. The substrates of these SAW filters are oxide wafer materials such as LT (LiTaO3), LN (LiNbO3), and quartz. In recent years, with the multi-functionalization of mobile phones, it has become essential to miniaturize and lighten various devices. Even for SAW filters, it is required to reduce the mounting area and thickness. In addition, one of the processes necessary for manufacturing these devices is a wafer bonding process. In the wafer bonding process, in addition to the process of bonding wafers to each other, a technique for flattening the bonding surface of the wafers to be bonded is essential. Conventionally, for workpieces such as silicon wafers for semiconductor devices and LT substrates that require high shape accuracy such as high smoothness and flatness, in order to planarize the polished surface, colloidal silica with uniform particle size and a polishing pad are used, and Chemical Mechanical Polishing (CMP) is widely used to mechanically polish the polished surface with an abrasive while chemically altering the surface layer. As a polishing pad used for CMP, a porous non-woven fabric sheet obtained by impregnating a non-woven fabric felt with a urethane solution and performing a wet coagulation treatment (Patent Document 1) and the like are disclosed. Also, polishing pads and the like that can perform polishing processing at a high polishing rate while maintaining high finishing accuracy for wafers made of difficult-to-cut materials such as sapphire are also disclosed (Patent Document 2).

Prior Art Documents

Patent Documents

[0003] [Patent Document 1] Japanese Patent Application Publication No. 02-250776 [Patent Document 2] Japanese Patent Publication No. 2014-087870 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, LT (LiTaO3) and LN (LiNbO3) are brittle due to internal strain and difficult to machine due to their high hardness, requiring unique processes and know-how compared to silicon for ultra-precision machining. [Means for solving the problem]

[0005] The invention described in claim 1 is a polishing pad having a nonwoven fabric blended with polyester fibers and nylon fibers as a base material, a polishing layer made of a water-based urethane resin and a polycarbonate-based urethane resin, and spherical silica supported by a thermosetting synthetic resin adhesive, characterized in that the compressibility of the polishing pad is 2.5% or more and 4.0% or less. The invention described in claim 2 is the polishing pad according to claim 1, wherein the average particle size of the spherical silica is in the range of 2 to 12 μm. [Effects of the Invention]

[0006] The polishing pad according to the present invention can perform polishing at a high polishing rate while maintaining high finishing accuracy even on wafers made of difficult-to-machine materials such as LT (LiTaO3) and LN (LiNbO3), thereby reducing the time required for wafer planarization. [Modes for carrying out the invention]

[0007] The elements constituting the polishing pad according to the present invention are described in detail below.

[0008] The polishing pad has a fiber aggregate. The fiber aggregate is a web formed with synthetic fibers as constituent fibers. The web used for the fiber aggregate can be any of the parallel webs, cross webs, semi-random webs, and random webs produced by existing web manufacturing methods such as the carding method, air-laying method, spunbonding method, or papermaking method, and is not particularly limited, but it is preferable to produce it by the carding method or spunbonding method in order to control the density. Furthermore, it is desirable to subject the web to needle punching or water needleing in order to increase its density. One type of nonwoven fabric can be used alone from the above-mentioned types, or two or more types can be used in combination.

[0009] The fineness of the nonwoven fabric in this embodiment is not particularly limited, but from the viewpoint of reducing scratch generation during polishing, it is preferably 2 to 3 dtex.

[0010] The manufacturing method for the polishing pad of this embodiment comprises a primary impregnation step of impregnating a nonwoven fabric with a resin solution containing a first resin and drying it to obtain a resin-impregnated nonwoven fabric, and a secondary impregnation step of impregnating it with a resin solution containing a second resin.

[0011] The first resin described above can be obtained by a dry impregnation method using a solution containing an ester-based urethane resin and a polycarbonate-based urethane resin, along with a foaming agent and a solvent capable of uniformly dispersing them. In this case, the content of the polycarbonate-based urethane resin is preferably in the range of 15 to 40%.

[0012] The second resin described above is impregnated into the nonwoven fabric by dry impregnation, and the solvent can be any solvent that can uniformly disperse the spherical silica without agglomerating it using a surfactant, for example, methyl isobutyl ketone (MIBK) is preferred.

[0013] In this embodiment, the polishing pad has silica fixed in the secondary impregnation process described above. In this process, urethane resin is preferably selected because it can firmly bond the nonwoven fabric substrate and the spherical silica, and can impart high elasticity to the polishing pad. The silica mainly acts as a polishing aid in the polishing process. By supporting the silica on the nonwoven fabric substrate, it acts on the colloidal silica contained in the CMP polishing slurry, balancing the retention and discharge of the polishing slurry, thereby improving the polishing rate and finishing accuracy.

[0014] The amount of silica added is preferably 5 to 50% by weight of the entire polishing pad, and more preferably 15 to 25% by weight. If the amount is 5% by weight or less, the spherical silica will not exert its full effect as a polishing aid, and if it is 50% by weight or more, it will inhibit the adhesion of the adhesive and reduce the durability of the polishing pad.

[0015] The surfactant is used to uniformly disperse spherical silica in the solvent used to dilute the thermosetting synthetic resin adhesive without causing aggregation. Therefore, the type of surfactant is not particularly limited as long as it is soluble in the solvent used to dilute the thermosetting synthetic resin adhesive and can uniformly disperse spherical silica.

[0016] A slurry containing a curable synthetic resin adhesive, silica, and a surfactant in any proportion is added to a nonwoven fabric substrate, and the adhesive is cured. As a result, silica is uniformly dispersed and fixed to the surface of the constituent fibers of the fiber aggregate by the thermosetting synthetic resin adhesive. Methods for adding the slurry to the fiber aggregate include immersion, spraying, and coating, which may be used individually or in combination. The fiber aggregate to which the slurry has been added is then dried using a known drying method to cure the thermosetting synthetic resin adhesive. At this time, the drying must be done at a temperature that does not alter the fiber aggregate, but at a temperature that allows the thermosetting synthetic resin adhesive to cure sufficiently.

[0017] Since the polishing pad has irregularities on its surface due to the fiber aggregate, both sides are subjected to sanding and polishing to improve flatness. As a result, a polishing pad with a predetermined thickness and flatness can be obtained.

[0018] The compression ratio of the polishing pad of the present embodiment is preferably 2.5% or more and 4.0% or less. When the compression ratio is within the above range, the contact area between the polishing pad and the non-polished object becomes uniform during polishing, and an improvement in flatness can be expected.

Example

[0019] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0020] A web in which 2.2 dtex nylon fiber, 2.2 dtex polyester fiber, and 2.8 dtex polyester fiber are blended so that the blending ratio is 65:15:20 in the above order is needle-punched to obtain a non-woven fabric as a base material. An ester-based aqueous urethane resin, a polycarbonate-based aqueous urethane resin, a foaming agent, and a thickener are uniformly dispersed in water and mixed in the above order at a weight ratio of 60:14:10:1:15 to prepare a resin solution. After immersing the above non-woven fabric in the resin solution, it was uniformly impregnated into the non-woven fabric using a mangle roller (first impregnation). Then, it was dried at 150 to 165°C. An adhesive urethane resin, a urethane resin, a surfactant, a thickener, and silica are uniformly dispersed in methyl isobutyl ketone, and a prepolymer solution is prepared in the above order at a weight ratio of 25:2:21:2:1:17:32 together with a catalyst. After immersing the non-woven fabric after the above impregnation in the prepolymer solution so that silica is uniformly dispersed by a thermosetting synthetic resin-based adhesive, the prepolymer solution is uniformly impregnated into the non-woven fabric using a mangle roller and dried at 150 to 160°C to obtain a resin-impregnated non-woven fabric (second impregnation). The surface of the resin-impregnated non-woven fabric was buffed to remove the surface skin layer, thereby obtaining a polishing layer. The polishing layer was cut out into a circle with a diameter of 600 mm, and grid grooves with a pitch of 20 mm and a width of 8 mm were provided on the buffed polishing surface to obtain the target polishing pad.

[0021] Comparative Example 1 A polishing pad was obtained in the same manner as in Example 1 except that the first resin impregnation was not performed.

[0022] Polishing test Regarding the polishing pad, polishing was performed under the following polishing conditions, and a polishing measurement test was conducted. Measurement In the measurement, the polishing pad was mounted at a predetermined position on the polishing machine, and an LT (LiTaO3) wafer was used as the workpiece (object to be polished). The surface of the polishing pad was pre-dressed using a diamond dresser under dressing conditions of a pressure of 1.5 kPa, a rotation speed of 40 rpm for the polishing head and the polishing table, a supply rate of ultrapure water of 50 mL / min, and a dressing time of 5 minutes, and then used for polishing evaluation.

[0023] Polishing conditions Polishing machine used: manufactured by MAT, product name "ARW-681M" Polishing speed (rotation speed of the table): 60 rpm Processing pressure: 200 g / mm Slurry: manufactured by JGC Catalysts & Chemicals Ltd., product name "SL-45P" (stock solution: water = 1:9) Slurry flow rate: 50 mL / min Polishing time: 60 minutes Object to be polished: 4-inch LT (LiTaO3) wafer

[0024]

Table 1

Claims

1. This polishing pad is characterized by having a nonwoven fabric base material composed of polyester fibers and nylon fibers, a polishing layer made of water-based urethane resin and polycarbonate-based urethane resin, and spherical silica supported by a thermosetting synthetic resin adhesive, with a compressibility of 2.5% or more and 4.0% or less.

2. The polishing pad according to claim 1, wherein the average particle size of the spherical silica is in the range of 2 to 12 μm.

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