Polishing pad

Abstract

To provide a means to extend the lifespan of polishing pads. [Solution] The present invention provides a polishing pad for use in chemical mechanical polishing, wherein the polishing surface is made of polyurethane resin foam, and the polyurethane resin foam is made of a resin composition containing polyurethane resin and an antioxidant, the antioxidant is a phenolic antioxidant, and the phenolic antioxidant is a hindered phenolic antioxidant having a melting point of 45°C to 140°C, in which both sides of the phenolic hydroxyl group are substituted with tert-butyl groups.

Description

Technical Field

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[0001] The present invention relates to a polishing pad.

Background Art

[0002] Conventionally, wafers for semiconductors and the like have been polished by a method called chemical mechanical polishing (CMP). In chemical mechanical polishing, a slurry containing components such as abrasive grains for mechanically polishing the workpiece and chemical components for chemically promoting the polishing is used. Also, a polishing pad is used for polishing the workpiece such as a wafer (for example, Patent Document 1). As the polishing pad, one having a polishing surface formed of a polyurethane resin foam is known. This type of polishing pad is also widely used in chemical mechanical polishing with a workpiece other than a wafer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0006] In such polishing pads, oxidative degradation of the polyurethane resin foam due to chemical components contained in the slurry used in chemical mechanical polishing is suppressed, thus extending the service life of the polishing pads. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic plan view of a polishing pad according to one embodiment. [Figure 2] Figure 2 is a schematic side view of a polishing pad according to one embodiment. [Figure 3a] Figure 3a is a schematic plan view showing one modified example of a polishing pad. [Figure 3b] Figure 3b is a schematic plan view showing one modified example of a polishing pad. [Figure 3c] Figure 3c is a schematic plan view showing one modified example of a polishing pad. [Figure 4] Figure 4 is a magnified view (scanning electron microscope image) of the polishing surface of the polishing pad. [Modes for carrying out the invention]

[0008] The polishing pad of this embodiment is a sheet having a predetermined thickness, as shown in Figures 1 and 2. The polishing pad 1 of this embodiment is suitably used, for example, in chemical mechanical polishing using a slurry containing abrasive components and chemical components. The polishing pad 1 is not particularly limited in its applications, but can be used, for example, in chemical mechanical polishing with semiconductor wafers as the workpiece. Examples of semiconductor wafers to be polished include silicon (Si) wafers, silicon carbide (SiC) wafers, gallium oxide (Ga2O3) wafers, gallium nitride (GaN) wafers, and aluminum nitride (AlN) wafers.

[0009] The polishing pad 1 has at least one surface that is a polishing surface 1s for polishing the workpiece. The contour shape of the polishing pad 1 in this embodiment, when viewed from above, is circular. The polishing pad 1 in this embodiment has a radial direction D1 that passes through the center C of the circle and is parallel to the polishing surface 1s, and a thickness direction D2 that is perpendicular to the polishing surface 1s. The polishing pad 1 further has a circumferential direction D3 that is a direction that revolves around a virtual axis AX that passes through the center C and extends in the thickness direction D2.

[0010] The polishing pad 1 is composed of a polyurethane resin foam in its main body portion, including the polishing surface 1s. That is, in the polishing pad 1 according to this embodiment, the polishing surface 1s that polishes the object to be polished is composed of a polyurethane resin foam. Figure 2 illustrates a polishing pad 1 having a laminated structure in which the pad body 10 and the base sheet 11 are laminated in the thickness direction D2, and the base sheet 11 is laminated on the side opposite to the polishing surface 1s. However, the polishing pad 1 may be a single-layer structure consisting only of the pad body 10 made of polyurethane resin foam, or it may be a multi-layer structure in which materials other than the base sheet 11 are laminated.

[0011] The polishing pad 1 of this embodiment may have recesses 1r that are recessed from the polishing surface 1s, as shown in Figures 3a to 3c. If the polishing pad 1 has recesses 1r, a plurality of recesses 1r may be scattered on at least one side of the polishing pad 1 (the side having the polishing surface 1s), as shown in Figure 3a. The recesses 1r may extend in the circumferential direction D3 to form annular grooves, as shown in Figure 3b. The polishing pad 1 may have a plurality of annular grooves of different diameters arranged concentrically at predetermined intervals in the radial direction D1. The polishing pad 1 may have recesses 1r that form a grid of grooves, as shown in Figure 3c.

[0012] The polyurethane resin foam that makes up the pad body 10 of the polishing pad 1 is cut from a polyurethane resin foam larger than the pad body 10, and as shown in Figure 4, there are many open air bubbles 1a on the polishing surface 1s.

[0013] In the polyurethane resin foam that constitutes the pad body 10, the resin composition that makes up the resin film 1b existing between adjacent bubbles 1a contains polyurethane resin and an antioxidant. As shown in Figure 4, the bubbles 1a of the polyurethane resin foam contain open bubbles in which pores have opened in the resin film 1b and are in communication with adjacent bubbles. In particular, open bubbles that open on the polishing surface 1s and are in communication with adjacent bubbles in the thickness direction of the polishing pad 1 (bubbles located behind the bubbles that have opened on the surface) easily take in polishing debris into the bubbles, suppress the occurrence of scratches caused by polishing debris interposed between the workpiece and the polishing surface 1s, and also have excellent slurry retention, thus effectively enabling the polishing pad 1 to exhibit a high polishing rate.

[0014] In this embodiment, the polishing pad 1 preferably contains open bubbles in a predetermined proportion among the bubbles 1a that are open on the polishing surface 1s. The proportion of open bubbles among the bubbles 1a that are open on the polishing surface 1s is, for example, 5% or more based on the number of bubbles. The proportion of open bubbles may be 10% or more, 15% or more, or 20% or more. The proportion of open bubbles may be, for example, 50% or less. The proportion of open bubbles may be 40% or less. Open bubbles may be bubbles that are open on the polishing surface 1s and communicate with each other, but in this embodiment, the polishing pad 1 preferably contains open bubbles that communicate with the bubbles further inside among the bubbles that are open on the polishing surface 1s in the proportions described above. The proportion of open bubbles can be confirmed by microscopic observation at randomly selected locations on the polishing surface 1s. More specifically, for example, the magnification can be set so that approximately 25 to 100 open bubbles can be observed in one field of view, and a microscopic observation of the polished surface 1s can be performed. Microscopic observation can then be performed at multiple locations (e.g., 5 locations) with different fields of view, and the number of continuous bubbles at each location can be calculated. The obtained values ​​can then be taken as an arithmetic mean.

[0015] The deterioration of the polishing performance of the polishing pad 1 during the polishing process of the workpiece has so far been thought to be mainly due to wear of the polyurethane resin foam and clogging by polishing debris. However, in this embodiment, we have focused on the fact that oxidative degradation of the polyurethane resin foam can also be a major factor affecting the service life of the polishing pad, and we aim to extend the service life of the polishing pad 1 by suppressing this oxidative degradation.

[0016] In the polishing pad 1 of this embodiment, because it has open bubbles as described above, the proportion of the contact area between the resin film 1b and the slurry is large. If a highly oxidizing agent is contained in the slurry, the resin film 1b will be placed in an environment where it is prone to oxidative degradation. However, as mentioned above, the resin composition constituting the resin film 1b contains an antioxidant, which suppresses oxidative degradation.

[0017] In chemical mechanical polishing, a slurry containing a chemical component together with an abrasive component is used. As the chemical component, for example, oxidizing agents such as hydrogen peroxide, peracetic acid, perbenzoic acid, potassium permanganate compounds such as potassium permanganate, and ammonium persulfate can be used. The polishing pad 1 of the present embodiment is suppressed from deteriorating even in chemical mechanical polishing using potassium permanganate having a strong oxidizing power. Therefore, it can be said that the polishing pad 1 of the present embodiment is suitable for chemical mechanical polishing using such an oxidizing agent having a strong oxidizing power in order to significantly exhibit the effect.

[0018] In the oxidative degradation of a resin, the generation of peroxyl radicals by radicals and oxygen generated in the system due to heat or chemical action is the starting point. In oxidative degradation, the peroxyl radicals serve as chain carriers, and the resin is degraded in a chain reaction. As forms of resin degradation, there are cases where the resin becomes lower molecular weight and softer than the sound state due to cleavage of the molecular chain, or cases where intermolecular crosslinking occurs and the resin becomes harder than the sound state. In any case, if the polishing surface 1s is composed of a degraded resin and becomes softer or harder than the inside, the degraded resin will be relatively easily scraped off in chemical mechanical polishing, and as a result, the resin appearing on the surface after the degraded resin is removed will be newly oxidatively degraded. As antioxidants, there are known primary antioxidants that function as radical scavengers that capture generated radicals and secondary antioxidants that function as peroxide decomposing agents that decompose peroxides generated by radicals and oxygen. However, as an antioxidant used in a polishing pad in which degradation can proceed by the above mechanism, a primary antioxidant is preferred.

[0019] As primary antioxidants, phenolic and amine-based ones are known. However, in the polishing pad 1 of the present embodiment, a phenolic antioxidant is preferable. Among them, a hindered phenolic antioxidant is suitable in that it has excellent radical stabilization ability. As the hindered phenolic antioxidant, there are those in which only one of the two ortho positions of the phenolic hydroxyl group is substituted with a bulky functional group such as a tertiary butyl group and those in which both ortho positions are substituted with a functional group such as a tertiary butyl group. Although the former has a higher radical trapping ability, the phenoxy radicals after radical trapping are likely to couple and deactivate each other. Therefore, from the viewpoint of the sustainability of the antioxidant function, the latter is more preferable as the antioxidant of the present embodiment.

[0020] In the polishing pad 1 of the present embodiment, a hindered phenolic antioxidant in which both adjacent positions of the phenolic hydroxyl group are substituted with tertiary butyl groups is used from the above viewpoints. As the hindered phenolic antioxidant, many have a high melting point exceeding 200°C. However, in the present embodiment, those having a melting point of 45°C or higher and 140°C or lower are used. A low melting point means that the intermolecular binding force is relatively low compared to those with a high melting point, and it can be expected to exhibit good dispersibility in the polyurethane resin.

[0021] The melting point of the antioxidant can be determined using a differential scanning calorimeter (DSC), and it can be determined as the peak top value of the endothermic peak in the DSC curve obtained at a heating rate of 10°C / min.

[0022] The melting point of the hindered phenolic antioxidant may be, for example, 48°C or higher, or may be 50°C or higher. The melting point of the hindered phenolic antioxidant may be, for example, 138°C or lower, or may be 135°C or lower.

[0023] In this specification, hindered phenol antioxidants that meet the above requirements may be referred to as "first-class hindered phenol antioxidants," and hindered phenol antioxidants that do not meet the above requirements may be referred to as "second-class hindered phenol antioxidants." Examples of the first hindered phenol antioxidants include stearyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 4-[[4,6-bis(octylthio)-1,3,5-triazine-2-yl]amino]-2,6-di-tert-butylphenol, and 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Among these, the first hindered phenol antioxidant is preferably either (or both) 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate stearyl or pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0024] The proportion (content) of the first hindered phenol antioxidant in the resin composition is, for example, 1% by mass or more. Preferably, the proportion of the first hindered phenol antioxidant in the resin composition is 3% by mass or more, and more preferably 5% by mass or more. The proportion of the first hindered phenol antioxidant in the resin composition may exceed 5% by mass. The proportion of the first hindered phenol antioxidant in the resin composition may be, for example, 6% by mass or more, 7% by mass or more, or 8% by mass or more. The proportion (content) of the first hindered phenol antioxidant in the resin composition is, for example, 30% by mass or less. Preferably, the proportion of the first hindered phenol antioxidant in the resin composition is 28% by mass or less, and more preferably 25% by mass or less. The proportion (content) of the first hindered phenol antioxidant in the resin composition may be, for example, 20% by mass or less.

[0025] If the resin composition constituting the polyurethane resin foam contains additives in addition to the polyurethane resin and the first hindered phenol antioxidant, the first hindered phenol antioxidant may be included in the resin composition in such a proportion to the total amount of the polyurethane resin that is the value mentioned above.

[0026] In addition to polyurethane resin and the first hindered phenol antioxidant, other additives that may be included in the resin composition include, for example, other primary antioxidants such as second hindered phenol antioxidants and amine antioxidants, and secondary antioxidants such as phosphorus antioxidants and sulfur antioxidants. When the content of the first hindered phenol antioxidant in the resin composition is 100 parts by mass, the content of antioxidants other than the first hindered phenol antioxidant is, for example, 50 parts by mass or less. The content of antioxidants other than the first hindered phenol antioxidant may be 25 parts by mass or less, 10 parts by mass or less, or 5 parts by mass or less. The antioxidant contained in the resin composition may be substantially only the first hindered phenol antioxidant, and the resin composition may not contain any antioxidants other than the first hindered phenol antioxidant. When antioxidants other than the first hindered phenol antioxidant are included in the resin composition, their content may be, for example, 0.1 parts by mass or more. In this context, "content" refers to the total content of antioxidants other than the first hindered phenol antioxidant if the resin composition contains multiple types of antioxidants.

[0027] The polyurethane resin foam of this embodiment can be prepared by common methods such as the prepolymer method or the one-shot method. When the polyurethane resin foam is prepared by the prepolymer method, for example, it can be produced by a prepolymer step in which a stock solution for prepolymer containing a polyol component and a polyisocyanate component is prepared, and the polyol component and polyisocyanate component contained in the stock solution for prepolymer is reacted to prepare a prepolymer liquid containing a prepolymer; and a foaming and curing step in which a foaming curing reaction liquid containing the prepolymer liquid produced in the prepolymer step and a curing agent is prepared, and the prepolymer contained in the foaming curing reaction liquid and the curing agent are reacted to form a polyurethane resin foam.

[0028] The polishing pad 1 of this embodiment can be manufactured, for example, by preparing a strip-shaped raw material sheet wider than the base material sheet 11, foaming and curing a foaming curing reaction liquid on the raw material sheet, creating a laminated sheet in which a base material layer made of the raw material sheet and a foamed layer made of polyurethane resin foam are laminated, making the foamed layer of the laminated sheet larger in the thickness direction D2 than the pad body 10, cutting off the surface layer of the foamed layer and cutting the laminated sheet into a circular shape.

[0029] The first hindered phenol antioxidant may be added to one or both of the polyol and polyisocyanate used in the prepolymerization process to be incorporated into the polyurethane resin foam, or it may be added to one or both of the prepolymer liquid and curing agent used in the foaming and curing process to be incorporated into the polyurethane resin foam. Of these, the prepolymer liquid has a higher viscosity than the polyol and polyisocyanate used as its starting materials, and when mixed with the first hindered phenol antioxidant, it is easier to impart shear force to the first hindered phenol antioxidant through stirring, making it suitable as a dispersion medium for the first hindered phenol antioxidant in order to achieve a good dispersion state of the first hindered phenol antioxidant.

[0030] In other words, in this embodiment, the polishing surface 1s is composed of a polyurethane resin foam, the polyurethane resin foam is composed of a resin composition containing a polyurethane resin and an antioxidant, the antioxidant is a phenolic antioxidant, and the phenolic antioxidant is a hindered phenolic antioxidant (first hindered phenolic antioxidant) having a melting point of 45°C to 140°C, in which both adjacent phenolic hydroxyl groups are substituted with tert-butyl groups. In this manufacturing method for producing a polishing pad 1, it is preferable to produce the polyurethane resin foam by a prepolymer method, and to mix the hindered phenolic antioxidant (first hindered phenolic antioxidant) with the prepolymer when producing the polyurethane resin foam.

[0031] Examples of polyols used in the preparation of prepolymers include polyether polyols, polyester polyols, polyester polycarbonate polyols, and polycarbonate polyols. The polyol may also be a polyfunctional polyol polymer having three or more hydroxyl groups in its molecule.

[0032] Examples of the aforementioned polyether polyols include polytetramethylene ether glycol (PTMG), polypropylene glycol (PPG), polyethylene glycol (PEG), and ethylene oxide-added polypropylene polyol.

[0033] Examples of the polyester polyol include polyethylene adipate glycol, polybutylene adipate glycol, polycaprolactone polyol, and polyhexamethylene adipate glycol.

[0034] Examples of the polyester polycarbonate polyol include reaction products of polyester glycols such as polycaprolactone polyol and alkylene carbonates, and reaction products obtained by reacting ethylene carbonate with a polyhydric alcohol and further reacting the resulting product with an organic dicarboxylic acid.

[0035] Examples of the polycarbonate polyol include reaction products of diols such as 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene ether glycol with phosgene, diallyl carbonate (e.g., diphenyl carbonate), or cyclic carbonate (e.g., propylene carbonate).

[0036] Examples of the aforementioned polyisocyanates include aromatic diisocyanates, aliphatic isocyanates, and alicyclic isocyanates.

[0037] Examples of the aromatic isocyanates include tolylene diisocyanate (TDI), 1,5-naphthalene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, and 1,4-phenylene diisocyanate. Other examples of the aromatic isocyanates include diphenylmethane diisocyanate (MDI) and modified diphenylmethane diisocyanate (MDI).

[0038] Modified products of diphenylmethane diisocyanate (MDI) include, for example, carbodiimide-modified products, urethane-modified products, allophanate-modified products, urea-modified products, biuret-modified products, isocyanurate-modified products, and oxazolidone-modified products. Specifically, an example of such a modified product is carbodiimide-modified diphenylmethane diisocyanate (carbodiimide-modified MDI).

[0039] Examples of the aliphatic diisocyanates include ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate (HDI).

[0040] Examples of the aforementioned alicyclic diisocyanates include 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, norbornane diisocyanate, and methylenebis(4,1-cyclohexylene) diisocyanate.

[0041] The prepolymer prepared from the polyol and polyisocyanate may have isocyanate groups or hydroxyl groups at the molecular ends, but in this embodiment, it is preferable to prepare a prepolymer with isocyanate groups at the molecular ends.

[0042] Examples of the curing agent in this embodiment include polyamines and polyols.

[0043] Examples of the aforementioned polyamines include 4,4'-methylenebis(2-chloroaniline) (MOCA), 4,4'-methylenedianiline, trimethylenebis(4-aminobenzoate), 2-methyl4,6-bis(methylthio)benzene-1,3-diamine, 2-methyl4,6-bis(methylthio)-1,5-benzenediamine, 2,6-dichloro-p-phenylenediamine, 4,4'-methylenebis(2,3-dichloroaniline), Examples include 3,5-bis(methylthio)-2,4-toluenediamine, 3,5-bis(methylthio)-2,6-toluenediamine, 3,5-diethyltoluene-2,4-diamine, 3,5-diethyltoluene-2,6-diamine, trimethylene glycol-di-p-aminobenzoate, 1,2-bis(2-aminophenylthio)ethane, and 4,4'-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane.

[0044] When a polyol is used as the curing agent, the bonding structure with the prepolymer becomes a urethane bond, and when a polyamine is used, the bonding structure becomes a urea bond. In this embodiment, it is preferable to introduce a urea bond, which is more robust than a urethane bond, and it is preferable that the curing agent contains a polyamine.

[0045] The foaming curing reaction solution may contain, in addition to the prepolymer, the first hindered phenol-based antioxidant, and the curing agent, a foaming agent, a catalyst, a foam stabilizer, and the like.

[0046] Examples of the blowing agent include water, carbon dioxide, hydrocarbons or their halides, and chemical blowing agents that decompose upon heating to generate gas. Examples of chemical blowing agents include azo compounds (azodicarbonamide, azobisisobutyronitrile, diazoaminobenzene, azodicarboxylate barium, etc.), nitroso compounds (N,N'-dinitrosopentamethylenetetramine, N,N'-dinitroso-N,N'-dimethylterephthalamide, etc.), and sulfonyl hydrazide compounds [p,p'-oxybis(benzenesulfonyl hydrazide), p-toluenesulfonyl hydrazide, etc.].

[0047] Examples of the catalysts include amine-based catalysts such as N,N-dimethylaminoethyl ether, triethylenediamine, dimethylethanolamine, triethanolamine, N,N,N',N'-tetramethylhexamethylenediamine, and N-methylimidazole, as well as organometallic catalysts such as dioctyltine dilaurate.

[0048] Examples of foam stabilizers include silicone-based surfactants, fluorine-based surfactants, and ionic surfactants.

[0049] As described later, the polishing pad 1 of this embodiment has a longer service life by suppressing the oxidation of the resin by chemical components contained in the slurry. Compared to a polishing pad 1 on which the polishing surface 1s is flat and no recesses 1r are formed, a polishing pad 1 having recesses 1r can exhibit a significant effect in that it has a larger surface area and the resin is more easily oxidized.

[0050] In a polishing pad 1 whose polishing surface 1s is made of polyurethane foam, the bubbles that open toward the polishing surface 1s function to hold the slurry and contain polishing debris. However, if chemical mechanical polishing of wafers or the like is performed with a polishing pad that is prone to oxidative degradation, the resin located on the polishing surface may detach due to oxidative degradation, potentially blocking the bubbles that should function to hold the slurry and contain polishing debris. This can lead to a decrease in the polishing rate and an increased likelihood of scratches. Therefore, while conventional polishing pads would have to be replaced frequently, using the polishing pad of this embodiment allows for a longer service life of a single polishing pad, thereby reducing the frequency of polishing pad replacement in chemical mechanical polishing.

[0051] As described above, this specification includes the following disclosures: (1) A polishing pad used in chemical mechanical polishing, the polishing surface of which is made of polyurethane resin foam, The polyurethane resin foam is composed of a resin composition containing polyurethane resin and an antioxidant. The aforementioned antioxidant is a phenolic antioxidant. The polishing pad is a hindered phenolic antioxidant having a melting point of 45°C to 140°C, in which the phenolic hydroxyl groups on both sides are substituted with tert-butyl groups.

[0052] (2) The polishing pad according to (1), wherein the content of the hindered phenol-based antioxidant in the resin composition is 3% by mass or more and 30% by mass or less.

[0053] (3) The polishing pad according to (2), wherein the content of the hindered phenol-based antioxidant in the resin composition is 5% by mass or more.

[0054] (4) A polishing pad described in any of (1) to (3) above, used in chemical mechanical polishing using potassium permanganate as an oxidizing agent.

[0055] Furthermore, the polishing pads described above are merely illustrative examples, and the polishing pads according to the present invention are not limited to the above-described forms. Also, the polishing pads according to the present invention are not limited by the effects described above. Various modifications to the polishing pads according to the present invention are possible without departing from the spirit of the invention. [Examples]

[0056] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0057] (Antioxidant) The following antioxidants were prepared for evaluation. HP1-AO1: 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid stearyl (primary hindered phenol antioxidant with a melting point of 51°C) HP1-AO2: Pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (a first hindered phenol antioxidant with a melting point of approximately 120°C) HP2-AO1: 1,3,5-Tris[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (a secondary hindered phenol antioxidant with a melting point of approximately 219°C) HP2-AO2: 1,1,3-Tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane (a secondary hindered phenol antioxidant with a melting point of approximately 187°C) P-AO1:3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (phosphorus antioxidant) P-AO2: Triphenylphosphite (phosphorus-based antioxidant) BTA-AO1: Bisoctrizole (benzotriazole) HA-AO1: Bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (hindered amine)

[0058] (Confirmation of compatibility) The compatibility between the prepolymer and the antioxidant was evaluated. An evaluation solution was prepared by heating a prepolymer to 145°C and adding an antioxidant, so that the antioxidant content was 10% by mass per 200g of prepolymer. After stirring and degassing the evaluation solution, it was left to stand in an oven at 145°C for 30 minutes or more, and the compatibility between the prepolymer and the antioxidant was visually evaluated (good: ○, poor: ×). The results are shown in the table below.

[0059] [Table 1]

[0060] <Verification of oxidation suppression function: 1> Polyurethane resin foams were prepared using each antioxidant, and their resistance to aqueous solutions of potassium permanganate, an oxidizing agent used in chemical mechanical polishing, was evaluated. The evaluation was conducted by measuring the mass change of polyurethane resin foam before and after contact with potassium permanganate aqueous solution, as polyurethane that has oxidized and degraded upon contact with potassium permanganate aqueous solution will have manganese oxide attached to it and its mass will increase. The polyurethane resin foam used for evaluation was prepared by blending 100 parts by mass of prepolymer with 26.3 parts by mass of chain extender, 0.05 parts by mass of catalyst, 1 part by mass of foam stabilizer, 0.175 parts by mass of blowing agent, and 10 parts by mass of antioxidant, and curing the mixture under conditions that resulted in an R value of 0.9. A sheet was prepared by slicing the fabricated polyurethane resin foam so that the air bubbles were cut on both the front and back surfaces. A 25 mm diameter disc-shaped sample was taken from the sheet, and the disc-shaped sample was immersed in 30 mL of a 2% by mass potassium permanganate aqueous solution. After being kept at 40°C for 16 hours, it was ultrasonically cleaned for approximately 20 minutes. The mass (M1) of the disc-shaped sample after drying was measured, and the degree of mass change [mass change rate = (M1-M0) / M0 × 100%] compared to the mass (M0) of the disc-shaped sample before immersion in the potassium permanganate aqueous solution was measured. The results are shown in the table below.

[0061] [Table 2]

[0062] <Verification of oxidation suppression function: 2> Using two primary hindered phenol-based antioxidants, "HP1-AO1" and "HP1-AO2," and one secondary hindered phenol-based antioxidant, "HP2-AO2," the amount of antioxidants in polyurethane resin foam was varied, and the rate of mass change was evaluated in the same manner as in "Verification of Oxidation Inhibition Function: 1." Furthermore, the rate of mass change was evaluated in the case where no antioxidant was used, similar to "Verification of oxidation suppression function: 1". Furthermore, the various physical properties of the polyurethane resin foam (density, hardness, elastic modulus, breaking strength, and elongation at break) were also evaluated. The results are shown in the table below.

[0063] [Table 3]

[0064] From the above results, it can be seen that the rate of mass change when using the first hindered phenol antioxidant and when using the second hindered phenol antioxidant becomes significant when the antioxidant content is 3% by mass or more, and becomes even more significant when the antioxidant content is 5% by mass or more. Furthermore, it can be understood from the above results that the first hindered phenol antioxidant has little effect on the physical properties of polyurethane resin foam even when included at high concentrations and has excellent ability to suppress the oxidation of polyurethane resin, making it effective in extending the service life of polishing pads. [Explanation of Symbols]

[0065] 1: Polishing pad, 1a: Air bubble, 1b: Resin film, 1r: Recess, 1s: Polishing surface 10: Pad body, 11: Base sheet

Claims

1. A polishing pad used in chemical mechanical polishing, the polishing surface of which is made of polyurethane resin foam, The polyurethane resin foam is composed of a resin composition containing polyurethane resin and an antioxidant. The aforementioned antioxidant is a phenolic antioxidant. A polishing pad in which the phenolic antioxidant is a hindered phenolic antioxidant having a melting point of 45°C to 140°C, and in which the phenolic hydroxyl groups on both sides are substituted with tert-butyl groups.

2. The polishing pad according to claim 1, wherein the content of the hindered phenol-based antioxidant in the resin composition is 3% by mass or more and 30% by mass or less.

3. The polishing pad according to claim 2, wherein the content of the hindered phenol-based antioxidant in the resin composition is 5% by mass or more.

4. A polishing pad according to any one of claims 1 to 3, used in chemical mechanical polishing using potassium permanganate as an oxidizing agent.

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