Holding pad

Abstract

To provide a holding pad that has high chemical resistance and high breaking strength, and also has low friction with a polishing object, so that it has adsorptivity while facilitating the rotation of the polishing object while being polished, enabling the object to be uniformly polished.SOLUTION: A holding pad has a holding layer containing polyester, the holding layer having a density of 0.2-0.6 g / cm3. In a holding face of the holding layer, the total area ratio of holes equal to 20 μm or more in diameter is 1% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a holding pad for polishing optical materials, semiconductor wafers, semiconductor devices, hard disk substrates, and metal and ceramic surfaces, and in particular to a holding pad for polishing hard-to-cut materials such as SiC substrates (silicon carbide wafers), GaAs (gallium arsenide) substrates, and sapphire glass. [Background technology]

[0002] Chemical mechanical polishing (CMP) is a commonly used polishing method for planarizing the surfaces of optical materials, semiconductor wafers, semiconductor devices, hard disk substrates, metals, ceramics, and the like.

[0003] A typical CMP method will be described with reference to Fig. 1. As shown in Fig. 1, in a polishing apparatus 1 for carrying out the CMP method, a polishing pad 5 (polishing pad 5 has a polishing layer) provided on a lower surface plate 6 and a holding pad 3 provided on an upper surface plate 4 rotate and press against an object to be polished 2, thereby polishing the surface of the object to be polished 2 that is in contact with the polishing surface 5A of the polishing layer. As shown in Fig. 1, polishing is carried out in the presence of a slurry S supplied to the polishing layer from a slurry supply unit 7.

[0004] Incidentally, the polishing industry as a whole is seeking highly durable holding pads that can withstand harsher polishing conditions (such as high polishing pressure and the use of highly acidic slurries) in order to improve polishing efficiency, and highly durable holding pads are particularly desired when the object to be polished is a difficult-to-cut material such as SiC.

[0005] Conventional holding pads include the wet film-formation type described in Patent Document 1, but the structure of wet film-formation type holding pads is destroyed in just a few hours under harsh conditions, or the structure of the holding surface is destroyed when the polished object is peeled off the holding surface after polishing, so they do not have sufficient durability. Examples of holding pads that are less susceptible to structural damage include holding pads made of molded hard polyurethane, as described in Patent Document 2. However, if the density is low for the purpose of cushioning, slurry erodes into the voids, reducing durability. Furthermore, under high polishing pressures, the waviness of the holding pad itself is easily transferred to the workpiece. To mitigate this, the holding pad must have sufficient adhesive force in the shear direction to allow the workpiece to rotate during polishing. However, with low-density holding pads with openings larger than a certain size on the holding surface, the unevenness of the openings creates high frictional resistance in the shear direction, preventing the workpiece from rotating smoothly and lacking sufficient adhesive force. On the other hand, if the pad is made high-density, the pad becomes hard, reducing cushioning and potentially damaging the workpiece upon contact.

[0006] Materials other than urethane, such as polyesters like PET, can be used as holding pad materials to improve chemical resistance, but fiber-based holding pads, such as those made of nonwoven fabrics or woven fabrics as described in Patent Document 3, leave something to be desired in terms of physical durability, especially under high polishing pressure conditions. Furthermore, shed fiber fragments can cause scratches. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5976623 [Patent Document 2] Patent No. 6757156 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-88456 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, no conventional holding pads satisfy all of the requirements of high durability, high adsorption (high retention), and chemical resistance. [Means for solving the problem]

[0009] As a result of extensive research, the inventors discovered that by using polyester with a void structure that meets certain requirements, it is possible to achieve higher durability and chemical resistance than urethane-based holding pads, and also to solve the problem of adsorption (retention), thereby creating the holding pad of the present invention. [1] A support pad comprising a support layer comprising polyester, The density of the support layer is 0.2 to 0.6 g / cm 3 and A holding pad, wherein the total area ratio of pores having a diameter of 20 μm or more on the holding surface of the holding layer is 1% or less. [2] The holding pad according to [1], wherein the polyester is polyethylene terephthalate. [3] The holding pad according to [1] or [2], wherein the holding layer is made of a foamed polyester sheet. [4] The holding pad according to any one of [1] to [3], wherein the total area ratio of pores having a diameter of 20 μm or more in the cross section of the holding layer is 1% or less. [5] The holding pad according to any one of [1] to [4], wherein the holding layer has a Shore D hardness of 20 to 50 degrees. [6] The holding pad according to any one of [1] to [5], wherein the holding layer has a compressibility of 0.1 to 3.0%. [7] A support pad according to any one of [1] to [6], wherein the support layer is non-fibrous. [Effects of the Invention]

[0010] The holding pad of the present invention fully satisfies the requirements of high durability, high adsorption (high retention), and chemical resistance, and furthermore, has high breaking strength and low friction with the workpiece to be polished. Therefore, while having adsorption properties, the workpiece can easily rotate during polishing, and the workpiece can be polished uniformly. [Brief explanation of the drawings]

[0011] [Figure 1]FIG. 1 is a schematic diagram of a polishing apparatus 1. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, the embodiments of the invention will be described, but the present invention is not limited to the embodiments of the invention.

[0013] <Retention pad> The support pad 3 of the present invention is a support pad including a support layer containing polyester, and the density of the support layer is 0.2 to 0.6 g / cm 3 and the total area ratio of openings having a diameter of 20 μm or larger on the supporting surface of the supporting layer is 1% or less. Here, the total area ratio of openings having a diameter of 20 μm or larger on the supporting surface of the supporting layer refers to the proportion of the total area of ​​openings having a diameter of 20 μm or larger to the total area of ​​the supporting surface.

[0014] As shown in Fig. 1, the holding pad 3 is provided on the upper surface plate 4 and includes at least a holding layer. In addition to the holding layer, the holding pad 3 can also include an adhesive layer (not shown) for adhering to the upper surface plate 4, as well as a cushion layer, but Fig. 1 shows only the holding layer of the holding pad 3, and the other layers are omitted.

[0015] <Retention layer> The retaining layer is the layer of the retaining pad 3 that comes into contact with the workpiece 2. The material of the retaining layer contains polyester as an essential component. Examples of polyesters that can be used include PET (polyethylene terephthalate), polyethylene naphthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polypropylene terephthalate, with PET being preferred in the present invention. As long as the effects of the present invention are not impaired, the material of the retaining layer may be a mixture of resins other than polyester, such as polyurethane and epoxy resin. The preferred proportion of materials other than polyester relative to the total mass of the retaining layer is, in this order, 30% or less, 20% or less, 10% or less, and 5% or less.

[0016] The polyester used as the material for the support layer may contain additives. The additives may be used within the scope of the present invention, and examples thereof include light stabilizers, antioxidants, water repellents, hydrophilic agents, and dyes, and may be used alone or in combination of two or more.

[0017] Among polyesters, polyethylene terephthalate is particularly preferred from the viewpoints of processability, chemical resistance, etc. Polyesters are generally easy to form into a predetermined shape and size depending on the polishing conditions, such as the polishing device and the workpiece, and are less likely to deteriorate even when in contact with acidic or basic slurries, tending to have a longer product life, and this tendency is even stronger for polyethylene terephthalate.

[0018] (density and pore size) The density of the retention layer is 0.2 to 0.6 g / cm 3 and the total area ratio of pores with a diameter of 20 μm or more on the holding surface of the holding layer (the surface in contact with the workpiece 2, 3A in FIG. 1) is 1% or less. The density (true density) of ordinary polyester without pores is generally 1.2 g / cm 3 However, the density of the polyester used as the material for the support layer of the present invention is 0.2 to 0.6 g / cm 3 Therefore, the support layer contains voids such as air bubbles. In addition, considering cushioning properties, the density is 0.2 to 0.5 g / cm 3 is preferred, and 0.2 to 0.4 g / cm 3 It is more preferable that:

[0019] On the support surface 3A of the support layer, the total area ratio of pores with a diameter of 20 μm or more is 1% or less. This indicates that the support surface is smooth and has very few pores with a diameter of 20 μm or more. However, the density is 0.2 to 0.6 g / cm. 3Considering this, the holding surface contains a predetermined number of very small openings. "Openings with a diameter of 20 μm or more" includes not only "circular openings with a diameter of 20 μm or more," but also "polygonal or elliptical openings with the same area as a circle with a diameter of 20 μm."

[0020] In the present invention, the pores on the holding surface, i.e., the surface that comes into contact with the workpiece 2 to be polished, are specified, but it is preferable that not only the holding surface 3A but also the cross section (i.e., the inside) when the holding layer is cut have a total area ratio of pores with a diameter of 20 μm or more of 1% or less. This indicates that there are very few bubbles with a diameter of 20 μm or more in the entire holding layer, but it is also preferable that the density is 0.2 to 0.6 g / cm 3 Considering that the amount of very small bubbles is large, this means that the liquid contains a certain amount of very small bubbles.

[0021] The support layer is preferably non-fibrous. Here, "non-fibrous" refers to a support layer material containing fibrous components such as fibers or nonwoven fabrics in an amount of 10% by mass or less relative to the total mass. The support layer more preferably contains 5% by mass or less of fibrous components, even more preferably 1% by mass or less, and particularly preferably contains no fibrous components at all (except in cases where impurities are inevitably mixed in).

[0022] The retention layer is 0.2 to 0.6 g / cm 3By satisfying the density and the total area ratio of openings equivalent to 20 μm or more on the holding surface of the holding layer being 1% or less, the slurry used during polishing is prevented from penetrating into the holding layer, thereby preventing deterioration of the holding layer. Furthermore, the presence of many small openings on the holding surface maintains the holding force of the workpiece 2. Furthermore, since the holding surface is not too smooth, it does not excessively adhere to the workpiece 2, suppressing the effects of unevenness caused by bubbles, and allowing the workpiece to be polished while rotating. Furthermore, it is preferable that the total area ratio of openings equivalent to 20 μm or more on not only the holding surface 3A but also the cross section of the holding layer when cut is 1% or less. Since the bubbles contained in the holding layer are sufficiently fine, the holding layer holding the workpiece sinks uniformly during polishing, improving flatness (polishing accuracy). The holding layer of the present invention is highly suitable for hard-to-cut materials such as SiC substrates (silicon carbide wafers), GaAs (gallium arsenide) substrates, and sapphire glass.

[0023] (Shore D hardness) The Shore D hardness of the retaining layer is not particularly limited, but is preferably 20 to 50. If the hardness is within 50 degrees, damage to the polished object 2 is suppressed, and if it is 20 degrees or more, durability tends to be high.

[0024] (Compression ratio) The compressibility of the support layer is herein an indication of the softness of the support layer. Considering cushioning properties and durability, 0.1 to 3.0% is preferable, and 0.1 to 2.0% is more preferable. This is particularly noticeable under high polishing pressure conditions, but from the viewpoint of preventing the workpiece 2 from sinking into the holding pad 3 and reducing flatness, 0.1 to 1.5% is particularly preferable. The Shore D hardness and compressibility can be adjusted by the density (porosity), etc.

[0025] The holding pad 3 shown in Figure 1 preferably has a frame material 8 on the holding surface to prevent the workpiece from falling off. Any conventionally known frame material 8 can be used, and for example, it can be made of glass fiber reinforced epoxy resin. In this specification, the holding pad 3 equipped with the frame material 8 is referred to as a holder.

[0026] The holding pad 3 may be provided with a fixing means (not shown) on the surface opposite to the holding surface 3A of the holding layer for fixing to the upper surface plate 4. Any known fixing means can be used, such as double-sided tape or adhesive.

[0027] (Polishing layer and polishing pad) The polishing pad 5 used when the holding pad 3 of the present invention is used for polishing is not particularly limited. The polishing layer of the polishing pad 5 (the layer that comes into contact with the object to be polished 2, not shown) can be suitably made of polyurethane resin, polyurea resin, or polyurethane-polyurea resin. The polishing layer can generally have a thickness of about 1 to 5 mm, and may contain hollow microspheres as needed.

[0028] (Cushion layer) The polishing pad 3 may have a cushion layer (not shown) between the polishing layer and the lower platen to ensure more uniform contact of the polishing layer with the workpiece 2. Any known cushion layer can be used in the present invention. The cushion layer 6 may be made of a resin-impregnated nonwoven fabric, a flexible material such as synthetic resin or rubber, or a foam with a cellular structure. A cushion layer made of polyurethane resin with sponge-like micro-bubbles is also preferably used.

[0029] (adhesive layer) The adhesive layer is a layer for adhering the cushion layer and the polishing layer, and is usually made of double-sided tape or adhesive, and a known adhesive layer can be used when using the holding pad 3 of the present invention. As the adhesive layer, a double-sided tape or adhesive known in the art (for example, an adhesive sheet) can be used. [Example]

[0030] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In each example and comparative example, "parts" means "parts by mass" unless otherwise specified.

[0031] Example 1 A retainer including the holding pad of Example 1 was manufactured using a retaining layer made of a foamed PET sheet (polyethylene terephthalate sheet) manufactured by Furukawa Electric Co., Ltd. (product name: "MCPET M4"), a glass fiber-reinforced epoxy resin (Gala-Epoxy) frame attached to a predetermined position on the holding surface, and double-sided tape attached to the surface opposite the holding surface. In the holding layer of the holding pad of Example 1, no pores equivalent to a bubble diameter of 20 μm or larger were observed on either the holding surface or cross section, resulting in a pore area ratio of 0%. The pore area ratio was determined by examining an approximately 1.3 mm square area of ​​the target surface under a microscope at 175x magnification, binarizing the resulting image using image processing software (Nikon Corporation, product name: "ImageAnalyzer V20 LAB Ver. 1.3"), and calculating the circle-equivalent diameter and the pore area ratio per unit area from the area of ​​each bubble. The specific properties of the holding pad of Example 1 are shown in Table 1.

[0032] (Comparative Example 1) Molded type, density 0.75g / cm 3 A holder including a holding pad of Comparative Example 1 was produced in the same manner as in Example 1, except that the polyurethane resin was used as the holding layer. The properties of the holding pad of Comparative Example 1 are shown in Table 1. The open area ratio of the holding pad of Comparative Example 1 was the same on both the holding surface and cross section.

[0033] (Comparative Example 2) Lower density than Comparative Example 1 (density 0.39 g / cm 3 A holder including a holding pad of Comparative Example 2 was produced in the same manner as in Example 1, except that a molded polyurethane resin of the type described above was used as the holding layer. The properties of the holding pad of Comparative Example 2 are shown in Table 1. The open area ratio of the holding pad of Comparative Example 2 was the same on both the holding surface and cross section.

[0034] (Chemical resistance test) Sample pieces of the material used for each support pad were immersed in a pH 2 hydrochloric acid solution at 40°C for 48 hours, and then subjected to a tensile test to measure the tensile strength at break. Here, the n value for the break strength test was 2, and the tensile elongation was measured using a Tensilon RTC universal testing machine manufactured by A&D Co., Ltd., according to the Japanese Industrial Standard (JIS K6550). Specifically, dumbbell-shaped test samples (90 mm long, 20 mm wide at the edge, 10 mm wide) were punched out of the support layer. The test samples were clamped between the upper and lower air chucks of the measuring machine, and measurements were started at a tensile speed of 100 mm / min with an initial gripping distance of 50 mm. The break strength was calculated from the value at which the measured value reached its peak (at break).

[0035] (density measurement) Density of the retention layer (g / cm 3 ) was measured in accordance with the Japanese Industrial Standard (JIS K 6505).

[0036] (D hardness measurement) The D hardness of the support layer was measured using a D-type hardness tester in accordance with the Japanese Industrial Standards (JIS-K-6253). Here, the measurement sample was obtained by stacking multiple support layers as necessary to have a total thickness of at least 4.5 mm.

[0037] (Compression ratio measurement) The compressibility can be determined using a Schopper-type thickness measuring device (pressure surface: circular with a diameter of 1 cm) in accordance with the Japanese Industrial Standards (JIS L 1021). Specifically, the method is as follows. The thickness t0 was measured after applying an initial load for 30 seconds from the no-load state, and then the thickness t1 was measured after applying a final load for 5 minutes from the thickness t0 state. The compression ratio was calculated using the formula: compression ratio (%) = 100 × (t0 - t1) / t0 (note that the initial load was 100 g / cm 2 , final load is 1120g / cm 2 (It is).

[0038] (Polishing performance evaluation) Using the holders equipped with the obtained holding pads of Example 1 and Comparative Examples 1 and 2, silicon wafers were polished under the following polishing conditions.

[0039] (polishing conditions) The conditions other than the holding pad in the abrasion test are as follows: Grinding machine used: GRIND-X PNX332B (manufactured by Okamoto Machine Tools Manufacturing Co., Ltd.) Polishing agent temperature: 22℃ Polishing platen rotation speed: 40 rpm Polishing head rotation speed: 41 rpm Polishing pressure: (external pressure) 0.016MPa (internal pressure) 0.012MPa Polishing slurry: GLANZOX 1306 (20x diluted), GLANZOX 3105 (30x diluted), GLANZOX 3111 (20x diluted) (manufactured by Fujimi Corporation) Polishing slurry flow rate: 800~1500ml / min Polishing time: 6 to 10 minutes Polished object: silicon wafer

[0040] (Adsorption force measurement) The holding surface of the holding pad was sprayed with water about five times with a spray bottle to moisten it for 15 minutes, after which the water droplets on the surface were removed and a 4-inch silicon wafer was placed on top. A 12 kg weight was then placed on top of it for one minute, after which the weight was removed. Finally, the maximum force applied when the silicon wafer was lifted was measured. The measurement device used was a Tensilon Universal Testing Machine RTC manufactured by A&D Co., Ltd.

[0041] (frictional force measurement) A 10cm square piece of glass was used as the friction object. The holding pad was left to wet for 15 minutes before measurement. The pad was sprayed with water about five times with a spray bottle to remove the moisture, and the square glass was placed on top. A 10kg weight was placed on top of the glass and pulled 8cm, and the static and dynamic friction forces were measured.

[0042] [Table 1]

[0043] The holding pad of Example 1, made of PET and substantially free of 20 μm-equivalent voids, maintained a low density and exhibited higher chemical resistance (breaking strength) than the holding pad of Comparative Example 2, made of polyurethane and having the same density and cushioning properties (D hardness). Furthermore, the holding pad of Example 1, which did not have 20 μm-equivalent pores on the holding surface, had a moderately smooth surface and therefore low frictional force. On the other hand, Comparative Examples 1 and 2, which had a predetermined adsorption force but also had predetermined pores, exhibited higher frictional force than the holding pad of Example 1. This suggests that the holding pad of Example 1 is expected to be able to adequately adsorb and hold the workpiece to prevent it from falling off, while maintaining the workpiece in a state where it can easily rotate during polishing, thereby enabling uniform polishing of the workpiece. In actual polishing performance evaluations, it was confirmed that when the holding pads of the Examples were used, the workpiece did not fall off during polishing, and the structure of the holding surface was not destroyed even when the workpiece was released at the end of polishing. [Industrial Applicability]

[0044] The present invention contributes to the manufacture and sale of polishing pads and has industrial applicability.

[0045] 1 Polishing equipment 2 Object to be polished 3 Retention pad (retention layer) 3A holding surface 4 Upper surface plate 5 polishing pads 6 Lower surface plate 7. Slurry supply device 8 Frame material S Slurry

Claims

1. A retaining pad including a retaining layer containing more than 70% by mass of foamed polyester relative to the total mass of the retaining layer, The density of the support layer is 0.2 to 0.6 g / cm ３ and The support surface of the support layer has openings with a diameter of less than 20 μm, A holding pad, wherein the holding surface of the holding layer has a total area ratio of openings with diameters of 20 μm or more of 1% or less relative to the total area of ​​the holding surface.

2. The support pad of claim 1 , wherein the polyester is polyethylene terephthalate.

3. 3. The holding pad according to claim 1, wherein the holding layer is made of a foamed polyester sheet.

4. 4. The holding pad according to claim 1, wherein a total area ratio of pores having a diameter of 20 [mu]m or more in a cross section of the holding layer is 1% or less.

5. 5. The support pad according to claim 1, wherein the support layer has a Shore D hardness of 20 to 50 degrees.

6. 6. The support pad according to claim 1, wherein the support layer has a compressibility of 0.1 to 3.0%.

7. A retaining pad described in any one of claims 1 to 6, wherein the content of fiber components in the retaining layer is 10 mass% or less relative to the total mass of the retaining layer.

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