JP2003245861A - Polishing foam sheet and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing pad used for flattening a surface of a semiconductor device wafer, such as an interlayer insulating film and a metal wiring, which has small polishing performance variation, high polishing accuracy, and is environmentally friendly. An abrasive foam sheet and a method for producing the same are provided. SOLUTION: This is a foamed sheet in which gas having a gaseous state at normal temperature and normal pressure is used as a foaming agent to foam bubbles having an average diameter of 0.1 μm or more and less than 300 μm, and the sheet contains abrasive grains. The polishing foam sheet is characterized in that the gas in a gaseous state at normal temperature and normal pressure is carbon dioxide, nitrogen or a mixed gas thereof, and the main component of the material constituting the sheet is preferably polyurethane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing pad used for polishing semiconductors, substrates for various memory hard disks and the like, and in particular, surface flattening of a semiconductor device wafer such as an interlayer insulating film and metal wiring. The present invention relates to a polishing pad that is preferably used in.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a chemical mechanical polishing (CMP) which is a typical process used for surface flattening of a semiconductor device wafer. While rotating the platen (2) and the sample holder (5) and dropping the polishing slurry (4) containing abrasive grains through the slurry supply pipe (10), the semiconductor wafer (1) is placed on the polishing pad (6) surface. The surface of the object to be polished is flattened with high precision by pressing it against. During polishing, the surface state of the polishing pad (6) is adjusted by pressing the dressing disc (3) against the surface of the polishing pad (6) while rotating the dressing disc holder (9). Not only the polishing conditions, but also the polishing pad (6), the dressing disk (3), the polishing slurry (4), the backing material (11), the wafer fixing jig (8), and other characteristics of each component are the polishing rate and the polishing. The polishing performance represented by the subsequent flatness and the in-plane uniformity of the semiconductor wafer is affected. Among them, the influence of the polishing pad (6) and the polishing slurry (4) and the abrasive grains contained in the polishing slurry is exerted. Is extremely large.

Conventionally, a polishing pad has a single layer consisting of only a polishing layer or a polishing layer and a cushion layer, depending on the type of object to be polished such as an interlayer insulating film or metal wiring and the required level of polishing accuracy. Although a laminated structure having been combined has been used, in any structure, the polishing layer is
Broadly classified, for example, an independent foamed body represented by IC1000 (trade name) manufactured by Rodel, or a non-foamed fixed-abrasive molded body containing abrasive grains is used. In the conventional closed-cell foam, air bubbles are opened due to dressing before and during use, and abrasion of the polishing pad surface as the polishing progresses, so that the polishing slurry retaining ability is exhibited. It can be used in combination with various polishing slurries, and has been standardly used because of its high versatility. However, in the conventional closed-cell foam, for example, the density variation of the foam itself caused by the variation of the foaming state represented by the cell diameter, the cell density, the distribution state of the cells, the resin crosslink density, etc. Since it can exist inside and in the thickness direction of the foam, the conventional independent foam has a problem that the polishing performance varies with an increase in the number of processing, and the polishing accuracy varies.

On the other hand, in the fixed-abrasive molding, the abrasive particles are mixed and dispersed at the stage of molding and fixed in advance, which has the effect of suppressing fluctuations in polishing performance due to, for example, variations in density of the independent foam. Can be expected. When using a fixed-abrasive compact as the polishing layer of the polishing pad, basically no polishing slurry is used, or a slurry called abrasive-less containing no abrasive is used, but polishing with abrasive is used. Compared to the case of using a slurry, for example, there is a problem that the absolute amount of the abrasive grains is insufficient, the polishing rate is low, or the dropped abrasive grains cause the scratches at the micron level called scratches on the processed surface. It was

Due to the recent remarkable development of the electronics industry, it has evolved into transistors, ICs, LSIs and VLSIs. As the degree of integration of circuits in these semiconductor elements has rapidly increased, the design rules of semiconductor devices have become finer year by year, the depth of focus in the device manufacturing process has become shallower, and the flatness of the pattern formation surface has become more and more strict. Is coming. Along with that, CM in the future
Since the polishing accuracy required for P is further increased and the polishing performance level required for the polishing pad is inevitably increased, the problems of the conventional pad are overcome,
The advent of polishing pads that can achieve highly accurate polishing is highly desired.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to a conventional polishing pad using an independent foam, for example, a problem of variations in polishing performance, or a polishing pad using a fixed-abrasive compact, for example, dropping of abrasive grains. It is intended to solve the problem of scratches due to the like, and its purpose is to provide stable, high-precision polishing performance when used as the polishing layer of a polishing pad, and for environmentally friendly polishing. It is to provide a foamed sheet and a manufacturing method thereof.

[0007]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made extensive studies in view of the problems of the prior art, and as a result, have accomplished the present invention by the following means. That is, the present invention is
(1) As a foaming agent, a gas in a gaseous state at room temperature and pressure is used.
A foaming sheet obtained by foaming bubbles having an average diameter of 0.1 μm or more and less than 300 μm, wherein the sheet contains abrasive grains, (2) at room temperature and atmospheric pressure The foamed sheet for polishing according to the item (1), wherein the gas in a gaseous state is carbon dioxide, nitrogen or a mixed gas thereof.
(3) The foaming sheet for polishing according to the item (1) or (2), wherein the main component of the raw material constituting the sheet is polyurethane.
(4) The foaming sheet for polishing according to the item (1) or (2), wherein the main component of the raw material constituting the sheet is a copolymer of polyurethane and fluororesin and / or a mixture of polyurethane and fluororesin. , (5) A foaming sheet for polishing according to any one of (1) to (4), which comprises an acrylic-modified fluororesin as an essential component, (6) a gas in a gaseous state at room temperature and atmospheric pressure, and a high temperature. -(1) to (5) by dissolving in a resin under high pressure and / or mixing with a resin, and then exposing the resin to a pressure atmosphere lower than the pressure at the time of dissolving and / or mixing
(7) A method for producing a foaming sheet for polishing, comprising: obtaining the foaming sheet for polishing according to any one of (1) to (6), wherein the gas is in a supercritical state under high temperature and high pressure. Is a method for producing a foam sheet for polishing.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the foaming sheet for polishing of the present invention, a gas in a gaseous state at room temperature and atmospheric pressure is used as a foaming agent. The gas to be used is not particularly limited as long as it is an inert gas for the sheet raw material, and examples thereof include inorganic gas, CFC gas, organic gas such as low molecular weight hydrocarbon, and the like. Is preferred. The inorganic gas is not particularly limited as long as it is an inorganic substance that is a gas at room temperature and atmospheric pressure, and can be dissolved and / or mixed in the sheet raw material, for example, carbon dioxide, nitrogen, argon, neon, helium, Oxygen or the like is preferable, but dissolved in the sheet material and /
Alternatively, carbon dioxide and nitrogen are more preferable because they are easy to mix, are easy to handle, are environmentally friendly, and are cheaper than other foaming agents. These may be used alone or in combination of two or more. The foaming sheet for polishing of the present invention contains abrasive grains. Abrasive grains not only function as the same abrasive as the abrasive grains contained in the polishing slurry, but also play a role as a foam nuclei material when the foaming agent foams. It greatly contributes to the reduction of variations. Particularly in the present invention in which the foaming agent uses a gas in a gaseous state at room temperature and atmospheric pressure, the abrasive grains are an essential component.

The kind of abrasive grains is not particularly limited. It can be arbitrarily selected depending on the processing target, required polishing accuracy, and the like. For example, silica-based (SiO ₂ ), ceria-based (CeO ₂ ), alumina-based (Al ₂ O ₃ ), zirconia-based (ZrO ₂ ), and manganese-based (MnO ₂ , Mn).
₂ O ₃ ), titanium oxide and the like, polymethyl methacrylate, copolymers of polymethyl methacrylate and divinylbenzene, and melamine formaldehyde condensates. These may be used alone or in combination of two or more. The combination, ratio, etc. are not particularly limited. The average diameter of bubbles contained in the polishing foam sheet of the present invention is preferably 0.1 μm or more and 3
Less than 00 μm, more preferably 0.5 μm or more, 20
Less than 0 μm, most preferably 1.0 μm or more, 100 μm
It is less than m. If the average diameter of the bubbles is less than 0.1 μm, for example, during polishing, clogging is likely to occur due to agglomerates of abrasive grains contained in the polishing slurry, polishing debris, etc., and polishing performance decreases in a short time. Is not preferable because the life as a polishing pad is significantly shortened. On the contrary, 300μ
When it is m or more, the mechanical strength is significantly lowered, which is not preferable.

The foaming sheet for polishing of the present invention may be used alone as a polishing pad depending on the type of object to be polished, required polishing accuracy, or the like, or, for example, Suba400 manufactured by Rodel Co. Laminated with a soft sheet,
It can also be used as a polishing layer in a polishing pad having a laminated structure. When the foaming sheet for polishing of the present invention is used as a polishing layer in conventional polishing slurry polishing method, that is, so-called free abrasive grain CMP, both bubbles and abrasive grains coexist in the polishing layer. Complement each other's shortcomings. Specifically, the abrasive grains supplement insufficient retention and / or variation in retention of the polishing slurry due to bubbles, and contribute to stable polishing performance expression for a long time. Further, by adopting the conventional free abrasive grain method, for example, the occurrence of scratches due to the dropped abrasive grains can be suppressed. The main component of the foaming sheet material for polishing of the present invention is not particularly limited, but polyurethane, polystyrene, polyester, polypropylene, polyethylene, nylon, polyvinyl chloride, polyvinylidene chloride, polybutene, polyacetal, polyphenylene oxide, polyvinyl alcohol, polymethylmethacrylate. , Polycarbonate, polyarylate, aromatic polysulfone, polyamide, polyimide, fluororesin, ethylene-propylene resin, ethylene-ethyl acrylate resin, acrylic resin, norbornene-based resin,
For example, vinyl polyisoprene-styrene copolymer, butadiene-styrene copolymer, acrylonitrile-styrene copolymer, styrene copolymer represented by acrylonitrile-butadiene-styrene copolymer, or natural rubber, synthetic rubber, etc. Is preferred. These may be used alone, or may be mixed or copolymerized. From the viewpoint that the abrasion resistance, surface hardness, compression rate, etc. of the sheet are very well balanced and suitable for polishing, it is preferable to use polyurethane and / or a copolymer of polyurethane and fluororesin as a main component. .

The fluororesin has a high affinity for carbon dioxide in the supercritical state, and enhances the solubility of carbon dioxide.
In order to contribute to the homogenization of foaming, particularly when carbon dioxide and / or a mixed gas containing carbon dioxide is used as a foaming agent, a copolymer of polyurethane and a fluororesin is mainly used as a raw material for the foaming sheet for polishing of the present invention. More preferably, it is used as a component. Generally, in forming a foamed sheet, unevenness is generated on the sheet surface due to, for example, foaming and / or breaking of foam near the surface of the sheet. If the unevenness is severe, for example,
This causes problems such as long dressing time before polishing and / or reduction in polishing accuracy. In the polishing foam sheet of the present invention, for example, the unevenness of the sheet surface,
In other words, for the purpose of improving the surface appearance, etc., a resin modifier,
Various additives such as processing aids and plasticizers can be used. For example, an acrylic-modified fluororesin typified by Mitsubishi Rayon's thermoplastic resin modifier (trade name: METABLEN A-3000) may be mixed in advance with the raw resin and / or added at the time of sheet molding. It is very preferable because it not only improves the appearance of the surface of the sheet, but also increases the melt tension of the resin, suppresses foam breakage, and contributes to homogenization of foaming.

The method for producing the foaming sheet for polishing of the present invention is not particularly limited.
From the viewpoint of being able to produce at low cost, a gas that is in a gaseous state at room temperature and atmospheric pressure is dissolved in and / or mixed with a resin at high temperature and high pressure, and then lower than the pressure when the resin is dissolved and / or mixed. The method of exposing to a pressure atmosphere is preferable. Specifically, a preformed sheet is charged into a high-pressure container, and in a closed state, a gas in a gas state at room temperature and normal pressure, which is a foaming agent, is dissolved in the sheet at high temperature and high pressure, In addition to the method of opening the closed state and exposing it to a pressure atmosphere lower than the pressure at the time of melting, kneading the raw material resin in the extruder, the gas in the gaseous state at room temperature and atmospheric pressure which is the foaming agent is added to the molten resin. After dissolution and / or mixing with resin,
Examples of the method include, but are not limited to, a method of exposing to a pressure atmosphere lower than the pressure during melting and / or mixing through a molding die. As the extruder, a single-screw extruder, a twin-screw extruder,
Alternatively, those obtained by connecting these extruders with a connecting pipe or the like can be appropriately selected and used.

When a gas that is in a gaseous state at room temperature and pressure is dissolved in a resin and / or mixed with a resin at a high temperature and a high pressure,
It is preferable that the high temperature and high pressure is in a supercritical state of the gas. The supercritical state means a state at a critical temperature or a critical pressure or higher, for example, in the case of carbon dioxide, 30 ° C. or higher,
It is 7.3 MPa or more. In the supercritical state, it has the characteristics of lower viscosity and higher diffusivity than the liquid state, and since it has a higher density than the gas state, a large amount of gas can be quickly dissolved in the resin or mixed with the resin. It is possible because it is possible.

[0014]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the contents of the examples. <Foam sheet forming equipment> A schematic view of the foam sheet forming equipment used in the examples of the present invention is shown in FIG. Barrel diameter 50mm,
Single screw extruder (12) with L / D = 32 and barrel diameter 65m
m, L / D = 36 single-screw extruder (13) connected by a hollow single tube (19), at the tip of a tandem extruder, a molding die with a lip width of 300 mm and a lip gap of 1.0 mm (1
4) was attached. A single-screw extruder (12) is provided with a foaming agent injecting part (15) at approximately the center, and after taking out from a cylinder (17), gas pressurized by a pressure boosting pump (16) is introduced into the extruder through an injection port. Injected.

<Evaluation of Polishing Performance> As an object to be polished, a 3-inch silicon wafer on which 10000 Å of Cu was formed by electrolytic plating was prepared. Plate diameter 200 for polishing
A mm single-side polishing machine was used. A polishing pad is attached to the surface plate of the polishing machine with double-sided tape, and a diamond-coated dressing disk is used for polishing for 2 hours under the conditions of a load of 10 kPa, a surface plate rotation speed of 60 rpm, and a dressing disk holder rotation speed of 50 rpm. After dressing the pad surface, a polishing slurry (trade name: iCue5003) manufactured by Cabot Co. was poured to polish the Cu film for 1 minute. As the polishing condition, the load applied to the wafer is 350
g / cm ² , the rotation number of the platen is 70 rpm, the rotation number of the wafer is 70 rpm, and the flow rate of the polishing slurry is 200 ml / mi.
It was set to n. After the wafer after polishing was washed and dried, the Cu film thickness was measured using a sheet resistance measuring device, and the average polishing rate, variation in polishing rate within the wafer surface, and flatness were compared with those of the conventional pad.

(Example 1) Polyurethane containing titanium oxide (trade name: Resamine P) manufactured by Dainichiseika and a modifier for thermoplastic resin (trade name: METABLEN A-300, manufactured by Mitsubishi Rayon Co., Ltd.)
Pellets prepared by mixing 0) in advance with a twin-screw extruder were used as sheet raw materials, and carbon dioxide was used as a foaming agent. The raw material resin pellets were used after being dried in a tray dryer at 100 ° C. for 4 hours. Single screw extruder (1
2), the average temperature of the single-screw extruder (13) and the molding die were set to 210 ° C, 160 ° C, and 160 ° C, respectively. The pressure inside the extruder immediately after the gas injection part is 20M.
It was Pa, and it was confirmed that carbon dioxide as a foaming agent was in a supercritical state in the zone where it was dissolved in the resin and / or mixed with the resin. Width obtained 270 mm, thickness 1.1
mm foam sheet was soaked in liquid nitrogen and then fractured, and its cross section was taken with a scanning electron microscope S-2400 (HITACH
As a result of observation with (I), it was confirmed that bubbles having an average diameter of 32 μm were dispersed almost uniformly in the sheet thickness direction and the width direction. A disc having a diameter of 200 mm was cut out from the obtained foamed sheet and used alone as a polishing pad to polish a Cu film.

(Example 2) A sheet material was prepared by mixing a titanium oxide-containing polyurethane (trade name: Rezamin P) manufactured by Dainichiseika Co., Ltd. with a copolymer of polyurethane and a fluororesin (trade name: Rezamin FR). Carbon dioxide was used as a blowing agent. The raw material resin pellets were used after being dried in a tray dryer at 100 ° C. for 4 hours. The average temperatures of the single-screw extruder (12), the single-screw extruder (13) and the molding die are 210 ° C, 160 ° C and 16 ° C, respectively.
It was set to 0 ° C. The pressure inside the extruder immediately after the gas injection part was 18 MPa, and it was confirmed that carbon dioxide as a foaming agent was in a supercritical state in the zone where it was dissolved in the resin and / or mixed with the resin. The obtained foamed sheet having a width of 275 mm and a thickness of 1.1 mm was immersed in liquid nitrogen and then fractured, and its cross section was taken with a scanning electron microscope S-2400 (HI.
As a result of observation with TACHI), it was confirmed that bubbles having an average diameter of 41 μm were dispersed almost uniformly in the sheet thickness direction and the width direction. A disc having a diameter of 200 mm was cut out from the obtained foamed sheet and used alone as a polishing pad to polish a Cu film.

(Comparative Example) As a polishing pad, a pad (trade name: IC1000) manufactured by Rodel Co. was used to polish a Cu film. <Evaluation Results> In the comparison between (Example 1) and (Example 2) and (Comparative Example), no remarkable difference was observed in the polishing rate, but in contrast to (Comparative Example), (Example 1) Variations in the polishing rate in the wafer surface of Example 2 and (Example 2) were reduced, and the flatness was improved.

[0019]

The foaming agent of the present invention is a gas in a gaseous state at room temperature and atmospheric pressure, contains abrasive grains in the sheet, and has an average bubble diameter of 0.1 μm or more and less than 300 μm. When a certain foaming sheet for polishing was used as the polishing layer of the polishing pad, variation in polishing performance was reduced and polishing accuracy was improved. Further, the gas of the present invention, which is in a gaseous state at room temperature and atmospheric pressure, is dissolved in and / or mixed with a resin at high temperature and high pressure, and then the pressure atmosphere is lower than the pressure at the time of dissolving and / or mixing the resin. According to the manufacturing method which exposes below, it can be expected that this foaming sheet for polishing can be efficiently manufactured at low cost.

[Brief description of drawings]

FIG. 1 is an example of a standard process of chemical mechanical polishing (CMP).

FIG. 2 is a schematic diagram of a foamed sheet forming facility used in Examples.

[Explanation of symbols]

1 Semiconductor wafer 2 surface plate 3 dressing discs 4 Polishing slurry 5 Sample holder 6 polishing pad 7 rotation axis 8 Wafer fixing jig 9 Dressing disc holder 10 Slurry supply pipe 11 Backing material 12 Single screw extruder 13 Single screw extruder 14 Mold for molding 15 Parts for injection of foaming agents 16 Booster pump 17 cylinders 18 Raw material hopper 19 single pipe

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01L 21/304 621 H01L 21/304 622F 622 622X B29K 27:12 // B29K 27:12 75:00 75:00 B29L 7 : 00 B29L 7:00 C08L 75:00 C08L 75:00 B29C 67/22 F term (reference) 3C058 AA07 AA09 CB01 DA17 3C063 AB07 BB01 BB03 BB26 BC03 BC04 BC09 CC05 EE10 FF22 FF23 4F074 AA38 AA78 BA32 BA34 CA33 CA33 CA33 AA31 AB02 AG01 AG20 UA09 UG02 UH30 UN11

Claims (7)

[Claims] 1. A foamed sheet in which bubbles having an average diameter of 0.1 μm or more and less than 300 μm are foamed by using a gas in a gas state at room temperature and atmospheric pressure as a foaming agent, and the sheet contains abrasive grains. A foamed sheet for polishing, which is characterized by: 2. The foaming sheet for polishing according to claim 1, wherein the gas in a gaseous state at room temperature and atmospheric pressure is carbon dioxide, nitrogen or a mixed gas thereof. 3. The foaming sheet for polishing according to claim 1, wherein the main component of the raw material constituting the sheet is polyurethane. 4. The foaming sheet for polishing according to claim 1, wherein the main component of the raw material constituting the sheet is a copolymer of polyurethane and fluororesin, and / or a mixture of polyurethane and fluororesin. 5. The foaming sheet for polishing according to claim 1, which contains an acrylic-modified fluororesin as an essential component. 6. A gas that is in a gaseous state at normal temperature and pressure is
The polishing according to any one of claims 1 to 5, which is obtained by dissolving the resin in a resin under high pressure and / or mixing with the resin, and then exposing the resin to an atmosphere of a pressure lower than the pressure at the time of dissolving and / or mixing. A method for producing a foam sheet for polishing, which comprises obtaining a foam sheet. 7. The method for producing a foaming sheet for polishing according to claim 6, wherein the gas is in a supercritical state under high temperature and high pressure.