JP7656465B2 - Polishing Pad - Google Patents

Description

The present invention relates to a polishing pad. In particular, it relates to a polishing pad for CMP of semiconductor devices.

In order to form multi-layer wiring with precision, the surface of materials such as semiconductor wafers must be flat for each layer. To flatten each layer, a free abrasive polishing method using a polishing pad is usually used. The free abrasive method is a method of polishing the processed surface of an object to be polished while supplying a polishing liquid (polishing slurry) between the polishing pad and the object to be polished.

Polishing pads used in semiconductor device manufacturing require that their surface have holes for holding the polishing slurry, hardness to maintain the flatness of the workpiece, and elasticity to prevent scratches on the workpiece. Polishing pads that meet these requirements have polishing surfaces made from urethane resin foam.

In recent years, Chemical Mechanical Polishing (CMP), a type of free abrasive method, has been used to flatten material surfaces with high precision. CMP is a technique that uses a polishing liquid (slurry) containing abrasives such as silica, anticorrosives, surfactants, etc. to modify the surface of the object to be polished while increasing the mechanical polishing effect of the abrasives. In CMP, the polishing liquid containing abrasives penetrates between the object to be polished and the polishing pad, allowing the object to be polished stably while the polishing pad is rotated at high speed.

Polyurethane resin foam is usually formed by curing the prepolymer containing urethane bond-containing polyisocyanate compound and the curing agent through a reaction (dry molding method). Then, this foam is sliced into sheets to form a polishing pad. In this way, the polishing pad with a hard polishing layer produced by dry molding method (hereinafter, sometimes abbreviated as hard polishing pad) has relatively small, roughly spherical bubbles formed inside the foam during polyurethane resin curing molding, so that the polishing surface of the polishing pad formed by slicing has openings (openings) that can hold slurry during polishing processing.
When using a hard polishing pad, the flatness and polishing rate of the substrate can be improved. However, due to its hardness, there is a risk of defects such as scratches occurring. In addition, in recent years, with the miniaturization of wiring width, more precise polishing is required, and there are more and more situations where it is difficult to meet with a hard polishing pad. Therefore, especially in the finishing process, a polishing pad with a soft polishing layer manufactured by a wet film formation method (hereinafter, sometimes abbreviated as a soft polishing pad) is used.
As a soft polishing pad used for the finish polishing in the CMP process, Patent Document 1 discloses a soft suede pad which is less likely to cause micro defects.

JP 2010-149259 A

However, because conventional soft polishing pads are made of soft materials, it is difficult to increase the polishing rate, so the polishing rate has been increased by incorporating fine particles such as carbon black into the soft pad or by increasing the hardness of the resin used in the pad. However, the addition of carbon black or the increase in resin hardness can lead to scratches (polishing marks) on the surface of the workpiece being polished.

The present invention was made in consideration of the above problems, and aims to provide a polishing pad that can suppress the occurrence of scratches on the surface of the workpiece to be polished and has a high polishing rate.

As a result of extensive investigations, the present inventors have found that the above object can be achieved by combining polyurethane resins having different 100% moduli, and have thus completed the present invention.
That is, the present invention includes the following aspects.
[1] A polishing pad comprising a polyurethane sheet having a plurality of teardrop-shaped bubbles and having a polishing surface for polishing an object to be polished,
The polishing pad, wherein the polyurethane resin constituting the polyurethane sheet contains a mixture of a polyurethane resin A having a 100% modulus of 3 to 12 MPa and a polyurethane resin B having a 100% modulus of 15 to 40 MPa, and the mass ratio of the polyurethane resin A to the polyurethane resin B is 100:0.1 to 100:5.
[2] The polishing pad according to [1], wherein the 100% modulus of the polyurethane resin B is at least twice the 100% modulus of the polyurethane resin A.
[3] The polishing pad according to [1] or [2], wherein the constituent polyol component of the polyurethane resin A is different from the constituent polyol component of the polyurethane resin B.
[4] The polishing pad according to any one of [1] to [3], wherein the constituent polyol component of the polyurethane resin A includes one polyol component selected from the three types of polyether polyol, polyester polyol, and polycarbonate polyol, and the constituent polyol component of the polyurethane resin B includes one other polyol component different from the one selected as the constituent polyol component of the polyurethane resin A among the three types of polyether polyol, polyester polyol, and polycarbonate polyol.
[5] The polishing pad according to any one of [1] to [4], wherein the polyurethane resin B contains a polycarbonate polyol as a constituent polyol component.
[6] The polishing pad according to any one of [1] to [5], wherein the polyurethane resin A contains a polyether polyol or a polyester polyol as a constituent polyol component.
[7] A polishing pad comprising a polyurethane sheet having a plurality of teardrop-shaped bubbles and having a polishing surface for polishing an object to be polished,
the polyurethane resin constituting the polyurethane sheet comprises a mixture of a polyurethane resin A having a 100% modulus of 3 to 12 MPa and a polyurethane resin B having a 100% modulus of 15 to 40 MPa;
the mass ratio of the polyurethane resin A to the polyurethane resin B is 100:0.1 to 100:5;
The polishing pad, wherein the polyurethane resin A contains a polyether polyol or a polyester polyol as a constituent polyol component, and the polyurethane resin B contains a polycarbonate polyol as a constituent polyol component.
[8] The polishing pad according to any one of [1] to [7], wherein the polyurethane sheet does not contain carbon black.
[9] A method for producing a polishing pad according to any one of [1] to [8],
A step of preparing a resin solution containing a mixture of a polyurethane resin A having a 100% modulus of 3 to 12 MPa and a polyurethane resin B having a 100% modulus of 15 to 40 MPa, wherein the polyurethane resin A and the polyurethane resin B are prepared so that their mass ratio is 100:0.1 to 100:5;
A method for manufacturing a polishing pad, comprising: a step of applying the resin solution to a film-forming substrate; and a step of immersing the film-forming substrate to which the solution has been applied in a coagulating liquid to coagulate the solution.

According to the present invention, it is possible to suppress the occurrence of scratches on the surface of the workpiece to be polished, and to obtain a polishing pad with a high polishing rate.

Hereinafter, an embodiment of the present invention will be described.
<<Polishing pad>>
The polishing pad of the present invention is a polishing pad comprising a polyurethane sheet having a plurality of teardrop-shaped bubbles and having a polishing surface for polishing an object to be polished, wherein the polyurethane resin constituting the polyurethane sheet comprises a mixture of polyurethane resin A having a 100% modulus of 3 to 12 MPa and polyurethane resin B having a 100% modulus of 15 to 40 MPa, and the mass ratio of polyurethane resin A to polyurethane resin B is 100:0.1 to 100:5.

<Polyurethane sheet>
The polyurethane sheet has a plurality of teardrop-shaped bubbles. The teardrop-shaped bubbles are intended to mean bubbles formed inside the polyurethane sheet by the wet film-forming method (bubbles having anisotropy and a structure in which the diameter increases from the upper part of the resin sheet to the lower part (the side in contact with the substrate)), and are distinguished from approximately spherical bubbles formed by the molding method. Therefore, the polyurethane sheet having a plurality of teardrop-shaped bubbles of the present invention can be said to be a polyurethane sheet formed by the wet film-forming method. The wet film-forming method means a method in which a resin to be formed into a film is dissolved in an organic solvent, the resin solution is applied to a sheet-like substrate, and the organic solvent is replaced by passing the resin through a coagulating liquid in which the organic solvent dissolves but the resin does not dissolve, and the resin is coagulated and dried to form a foam layer. Usually, when a polyurethane sheet is manufactured by the wet film-forming method, the escape route when the organic solvent inside the polyurethane sheet escapes into the coagulating liquid becomes a cavity, and a plurality of approximately teardrop-shaped macro bubbles (teardrop-shaped bubbles) are generated.
In the present invention, a polyurethane sheet refers to a sheet containing polyurethane resin as a main component (50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more), and is clearly distinguished from sheets containing other resins (such as silicone resins) as a main component.

(Polyurethane resin)
The polyurethane sheet contained in the polishing pad of the present invention comprises a polyurethane resin constituting the polyurethane sheet, the polyurethane resin comprising a mixture of polyurethane resin A having a 100% modulus of 3 to 12 MPa and polyurethane resin B having a 100% modulus of 15 to 40 MPa.
In the present invention, the 100% modulus is an index of the hardness of a resin, and is the value obtained by dividing the load applied to an unfoamed resin sheet when it is stretched 100% (when it is stretched to twice its original length) by the cross-sectional area. The higher this value, the harder the resin is.
The phrase "containing a mixture" of resin A and resin B refers to a urethane sheet obtained by forming a film from a mixed resin solution containing resin A and resin B using a wet film-forming method; the above concept does not include a combination sheet obtained by separately preparing a sheet made of resin A and a sheet made of resin B and bonding/laminating them together.

The 100% modulus of the polyurethane resin A is preferably from 3 to 10 MPa, more preferably from 4 to 10 MPa, and even more preferably from 6 to 9 MPa.
The 100% modulus of polyurethane resin B is preferably from 15 to 35 MPa, more preferably from 20 to 30 MPa, and even more preferably from 21 to 27 MPa.
The 100% modulus of the polyurethane resin B is preferably at least twice the 100% modulus of the polyurethane resin A, more preferably 2 to 8 times, even more preferably 2 to 6 times, even more preferably 2 to 5 times, even more preferably 2 to 4 times, and even more preferably 3 to 4 times. When the ratio of the 100% modulus is within the above range, it becomes easier to obtain a polyurethane sheet having a phase separation structure, and it becomes easier to increase the polishing rate while suppressing the increase in the rigidity of the entire polishing pad and suppressing the occurrence of polishing scratches. The 100% modulus can be easily adjusted by adjusting the type and amount of the constituent polyol component and/or the constituent polyisocyanate component.
In addition, the polyurethane sheet contained in the polishing pad of the present invention preferably has a 100% modulus of the entire resin constituting the polyurethane sheet of 13 MPa or less, more preferably 11 MPa or less, even more preferably 3 to 10 MPa, even more preferably 4 to 10 MPa, and even more preferably 6 to 9 MPa.

(Mass ratio)
In the polyurethane sheet contained in the polishing pad of the present invention, the mass ratio of polyurethane resin A to polyurethane resin B is preferably 100:0.1 to 100:5, more preferably 100:0.5 to 100:4, and even more preferably 100:1 to 100:3. When the mass ratio of polyurethane resin A to polyurethane resin B is within the above range, it is easy to increase the polishing rate while suppressing the increase in the rigidity of the entire polishing pad and suppressing the occurrence of polishing scratches.

(Polyurethane resin)
In the polishing pad of the present invention, it is preferable that the constituent polyol component of the polyurethane resin A contained in the resin constituting the polyurethane sheet is different from the constituent polyol component of the polyurethane resin B, and it is more preferable that the constituent polyol component of the polyurethane resin A contains one polyol component selected from the three types of polyether polyol, polyester polyol and polycarbonate polyol, and the constituent polyol component of the polyurethane resin B contains one other polyol component different from the one selected as the constituent polyol component of the polyurethane resin A among the three types of polyether polyol, polyester polyol and polycarbonate polyol. For example, when the polyurethane resin A contains a polyether polyol as a constituent polyol component, it is preferable that the polyurethane resin B contains a polyester polyol or a polycarbonate polyol as a constituent polyol component.
Ether bonds, ester bonds, and carbonate bonds each have different properties, and when the polyol type of polyurethane resin A is different from the polyol type of polyurethane resin B, phase separation is likely to proceed when polyurethane resin A and polyurethane resin B are used in combination. If the modulus of polyurethane resin B is high, phase separation with polyurethane resin A proceeds further, and the high-modulus, hard resin B is dispersed and exists due to phase separation, improving strength and enabling a high polishing rate to be obtained. In addition, most of the resin with advanced phase separation is composed of the low-modulus, soft resin A, and therefore the occurrence of polishing scratches can also be suppressed.

(Polyurethane resin A)
Polyurethane resin A has a 100% modulus of 3 to 12 MPa. Polyurethane resin A preferably contains one selected from the three types of polyether polyol, polyester polyol, and polycarbonate polyol as a polyol component constituting the resin (hereinafter referred to as a constituent polyol component), more preferably contains polyether polyol or polyester polyol, and even more preferably contains polyester polyol.

There are no particular limitations on the polyether polyol, and various polyether polyols can be used. Preferred examples of polyether polyols include polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene glycol (PTMG), etc. One type of polyether polyol may be used alone, or two or more types may be used in combination.

The polyester polyol is not particularly limited, and various polyester polyols can be used. Examples of preferred polyester polyols include a reaction product of ethylene glycol and adipic acid, and a reaction product of butylene glycol and adipic acid. The polyester polyols may be used alone or in combination of two or more types.

Polyurethane resin A may or may not contain polyols other than those mentioned above as constituent polyol components, but it is preferable that it does not contain any.

(Polyurethane resin B)
Polyurethane resin B has a 100% modulus of 15 to 40 MPa. Polyurethane resin B more preferably contains, as a polyol component (constituent polyol component) constituting the resin, one type of polyol component other than the one type selected as the constituent polyol component of polyurethane resin A out of the three types of polyether polyol, polyester polyol, and polycarbonate polyol, and more preferably contains polycarbonate polyol.

The polycarbonate polyol is not particularly limited, and various polycarbonate polyols can be used. Examples of preferred polycarbonate polyols include reaction products of diols such as 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol (PTMG) with dimethyl carbonate, dialkyl carbonate, diphenyl carbonate, ethylene carbonate, or diethyl carbonate. One type of polycarbonate polyol may be used alone, or two or more types may be used in combination.

Polyurethane resin B may or may not contain polyols other than those mentioned above as constituent polyol components, but it is preferable that it does not contain any.

Among these, in the polishing pad of the present invention, it is preferable that the polyurethane resin A contains polyether polyol or polyester polyol as a constituent polyol component, and the polyurethane resin B contains polycarbonate polyol as a constituent polyol, and it is more preferable that the polyurethane resin A contains polyester polyol as a constituent polyol component, and the polyurethane resin B contains polycarbonate polyol as a constituent polyol. By using the above polyol component, phase separation can be further promoted and the polishing rate can be further improved. That is, a polyurethane resin having polycarbonate polyol as a polyol component has low compatibility with polyurethane resins using polyether polyol or polyester polyol due to the high cohesive force of the carbonate group. Here, if the modulus of polyurethane resin B is sufficiently larger than that of polyurethane resin A, in addition to the polycarbonate polyol portion with high cohesiveness, the hard segment portion with high polarity increases, so that polyurethane resin A and polyurethane resin B are more likely to phase separate, and by using polyurethane resin A and polyurethane resin B in combination, a polyurethane sheet with more advanced phase separation can be obtained. The high modulus, hard resin B is dispersed through phase separation, improving strength and enabling a high polishing rate to be achieved. In addition, because the majority of the resin with advanced phase separation is made up of the low modulus, soft resin A, the occurrence of polishing scratches can also be suppressed.

(Polyisocyanate component)
There are no particular limitations on the polyisocyanate components constituting the urethane resins A and B that constitute the polyurethane sheet, and various polyisocyanate components can be used. Examples of the polyisocyanate component are not particularly limited as long as they have two or more isocyanate groups in the molecule. Examples of the diisocyanate monomer include aromatic diisocyanate monomers such as tolylene diisocyanate (TDI), MDI, xylylene diisocyanate, naphthalene-1,5-diisocyanate, p-phenylene diisocyanate, dibenzyl diisocyanate, diphenyl ether diisocyanate, m-tetramethyl xylylene diisocyanate, and p-tetramethyl xylylene diisocyanate; aromatic triisocyanate monomers such as triphenylmethane triisocyanate; alicyclic diisocyanate monomers such as hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane-4,4'-diisocyanate, hydrogenated xylylene diisocyanate, cyclohexyl-1,4-diisocyanate, and isophorone diisocyanate; and aliphatic diisocyanate monomers such as 1,4-tetramethylene diisocyanate and 1,6-hexamethylene diisocyanate. Two or more of these may be used in combination. Examples of such a polyisocyanate include polyisocyanate components that are usually used in producing polyurethane resins, such as trifunctional or higher polyisocyanurate-type polyisocyanates or biuret-type polyisocyanates, which are modified polyisocyanates based on these diisocyanate monomers.

(Other resins)
The polyurethane sheet contained in the polishing pad of the present invention may contain resins other than polyurethane resin A and polyurethane resin B within the range that does not impair the effects of the present invention, but polyurethane resin A and polyurethane resin B are preferably 50% by mass of the total resin constituting the polyurethane sheet, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 100% by mass. It is particularly preferable that the resin constituting the polyurethane sheet in the polishing pad of the present invention is a mixture of polyurethane resin A and polyurethane resin B.

(Other ingredients)
The polyurethane sheet may or may not contain inorganic fillers such as carbon black, film forming stabilizers, surfactants, etc. in addition to the above components, as long as the effects of the present invention are not impaired.
While inorganic fillers such as carbon black improve the polishing rate, they also cause polishing scratches, so it is preferable for the polyurethane sheet to contain a small amount of inorganic filler, and it is more preferable for the amount of inorganic filler to be 5 mass % or less (preferably 3 mass % or less, and more preferably 1 mass % or less), and it is even more preferable for the polyurethane sheet to contain no inorganic filler.
In addition, the polyurethane sheet preferably contains a small amount of carbon black, more preferably contains 5% by mass or less (preferably 3% by mass or less, and more preferably 1% by mass or less), and even more preferably contains no carbon black.

(Crystalline phase, amorphous phase, mesophase)
In the polishing pad of the present invention, the proportion of the crystalline phase in the polyurethane sheet is preferably 10 to 40% by mass, more preferably 15 to 30% by mass, and even more preferably 20 to 25% by mass. The proportion of the amorphous phase in the polyurethane sheet is preferably 50 to 80% by mass, more preferably 55 to 75% by mass, and even more preferably 60 to 70% by mass. The proportion of the intermediate phase in the polyurethane sheet is preferably 0 to 20% by mass, more preferably 5 to 15% by mass, and even more preferably 10 to 15% by mass. The intermediate phase is a region in which soft segments and hard segments are mixed, and a small fraction thereof indicates that the phase separation between the hard segments and the soft segments is clear. When the proportions of the crystalline phase, intermediate phase, and amorphous phase of the polyurethane sheet are within the above ranges, a phase separation structure is easily formed when polyurethane resin A and polyurethane resin B, which has poor compatibility with polyurethane resin A and a high 100% modulus, are added.
The content of the crystalline phase was determined by subjecting the polyurethane resin to pulse NMR measurement to determine the ratio of the amorphous phase, mesophase, and crystalline phase.

(Thickness)
The thickness of the polyurethane sheet in the polishing pad of the present invention is not particularly limited, but may be, for example, in the range of 0.3 to 2.0 mm, and preferably 0.6 to 1.2 mm.
The thickness can be measured using a Chopper-type thickness measuring instrument (pressure surface: circular with a diameter of 1 cm) in accordance with the Japanese Industrial Standards (JIS K6505). Specifically, the thickness is measured as follows.
Prepare a sample that is 10 cm square by 10 cm long. Place the sample on the measuring device with the surface facing up. Place a pressure surface with a load of 100 g/ ^cm2 on the sample and measure the thickness after 5 seconds. Measure 5 points on each sheet and take the average thickness. If a 10 cm square sample cannot be obtained, use the average of the 5 points.

(density)
The density of the polyurethane sheet is preferably 0.15 to 0.40 g/cm ³ , and more preferably 0.20 to 0.30 g/cm ^3. When the density is within the above range, a good balance between the polishing rate and scratch performance is achieved.

(Compressibility and Compressive Elasticity)
In this specification, the compressibility is an index of softness, and the compressive elastic modulus is an index of the ease of return to normal after compressive deformation.
The compressibility and compressive elasticity can be determined using a Chopper-type thickness gauge (pressure surface: circular with a diameter of 1 cm) in accordance with the Japanese Industrial Standards (JIS L1021). Specifically, the method is as follows.
The thickness _t0 is measured after the initial load is applied for 30 seconds from the no-load state, and then the thickness _t1 is measured after the final load is applied for 5 minutes from the thickness _t0 state. Next, all loads are removed from the thickness _t1 state, and the specimen is left for 5 minutes (to be in a no-load state), after which the initial load is again applied for 30 seconds and the thickness _t0 ' is measured.
The compression ratio can be calculated by the formula: compression ratio (%)=100×(t ₀ −t ₁ )/t ₀ (initial load is 100 g/cm ² , final load is 1120 g/cm ² ).
The compressive elastic modulus can be calculated by the formula: compressive elastic modulus (%)=100×(t ₀ '-t ₁ )/(t ₀ -t ₁ ) (initial load is 100 g/cm ² , final load is 1120 g/cm ² ).
The compressibility of the polyurethane sheet is preferably 1 to 40%, more preferably 3 to 30%, and even more preferably 5 to 20%. The compressive elasticity of the polyurethane sheet is preferably 70 to 100%, more preferably 80 to 99%, and even more preferably 90 to 98%. When the compressibility and compressive elasticity are within the above ranges, the sheet has excellent conformability to the surface of the workpiece, leading to reduced surface roughness of the workpiece.

(Shore A hardness)
In this specification, the Shore A hardness refers to a value measured in accordance with Japanese Industrial Standards (JIS K7311).
In the polishing pad of the present invention, the Shore A hardness of the polyurethane sheet is preferably 5 to 50 degrees (°), more preferably 5 to 40 degrees, even more preferably 10 to 30 degrees, and even more preferably 15 to 25 degrees. When the Shore A hardness of the polyurethane sheet is within the above range, it is easy to achieve both a high polishing rate and low polishing scratches.

(Average pore size)
In this specification, the average aperture diameter is an average value of circle-equivalent diameters calculated from the area and number of apertures by binarizing a surface image of a polyurethane sheet.
The average pore size of the polyurethane sheet in the polishing pad of the present invention is preferably within the range of 20 to 80 μm, more preferably 25 to 70 μm, even more preferably 30 to 60 μm, even more preferably 30 to 50 μm, and even more preferably 30 to 40 μm.
When the average pore size is within the above range, the retention of the slurry is good and a stable polishing rate can be obtained.

(Opening rate)
In this specification, the open area ratio means the ratio (%) of the open area to the surface (polished surface) of the polyurethane sheet.
The porosity of the polyurethane sheet in the polishing pad of the present invention is preferably within the range of 5 to 50%, more preferably 10 to 40%, even more preferably 15 to 35%, and even more preferably 20 to 30%.
When the opening ratio is within the above range, the retention of the slurry is good, and a stable polishing rate is obtained.

The polyurethane sheet in the polishing pad of the present invention has a polishing surface for polishing an object to be polished.
In the polishing pad of the present invention, the polishing surface of the polyurethane sheet and/or the surface opposite to the polishing surface may be ground (buffed) or not, but it is preferable that the polishing surface of the polyurethane sheet is ground, which results in the presence of many openings originating from microbubbles on the polishing surface, and the polishing rate can be improved by retaining the slurry in the openings.
In addition, the polishing pad of the present invention may have grooves, embossing and/or holes (punching) on the polishing surface of the polyurethane sheet. The polishing pad of the present invention may have a light transmitting portion.
The polishing pad of the present invention may be a single-layer structure consisting of only a polyurethane sheet, or may be a multi-layer structure in which a substrate is attached to the surface opposite to the polishing surface of the polyurethane sheet. Examples of the substrate include substrates made of nonwoven fabric, PET, and vinyl chloride. There is no particular restriction on the characteristics of the substrate, but it is preferable that the substrate is harder than the polyurethane sheet (e.g., has a hardness of A or D greater). By providing a layer harder than the polyurethane sheet, the polishing pad can be prevented from expanding and contracting or curving when polishing an object to be polished using a polishing pad made of a polyurethane sheet.

The polishing pad of the present invention can be suitably used to polish (e.g., wafers) to planarize them (chemical mechanical polishing (CMP)), particularly in the manufacture of semiconductor devices. Examples of materials for the polishing object include silicon, polysilicon, silicon oxide film, silicon nitride, and metals such as Cu, W, Al, Ta, and TiN. The polishing pad of the present invention can suppress the occurrence of scratches on the surface when polishing an object such as a silicon wafer, and can improve the polishing rate.

(Action)
The polishing pad of the present invention is capable of suppressing the occurrence of scratches on the surface of the workpiece to be polished and at the same time achieving a high removal rate. The reason for this is not clear, but is presumed to be as follows.
In the polishing pad of the present invention, the resin constituting the polyurethane sheet contains a mixture of two types of polyurethane resins with significantly different 100% modulus and cohesiveness, and the proportion of the polyurethane resin with the higher 100% modulus and cohesiveness is limited to a low level. This is thought to result in a high polishing rate being achieved by the contribution of the polyurethane resin with the higher modulus present in places, while the polyurethane resin with the lower modulus serves as a base to suppress the occurrence of polishing scratches.

<Method of manufacturing polishing pad>
The polishing pad of the present invention may be produced, for example, by the following method for producing a polishing pad of the present invention.
The method for producing a polishing pad of the present invention includes the steps of preparing a resin solution containing a mixture of polyurethane resin A having a 100% modulus of 3 to 12 MPa and polyurethane resin B having a 100% modulus of 15 to 40 MPa (wherein polyurethane resin A and polyurethane resin B are prepared so that the mass ratio between them is 100:0.1 to 100:5), applying the resin solution to a film-forming substrate, and immersing the film-forming substrate to which the solution has been applied in a coagulating liquid to coagulate the solution.
Each step will be described below.

(Step of preparing resin solution)
In this step, polyurethane resin A and the polyurethane resin B are dissolved in a water-miscible organic solvent in which these resins are soluble, to prepare a resin solution containing these resins.
As the polyurethane resin A and the polyurethane resin B, those described above can be used.
Examples of the organic solvent include N,N-dimethylformamide (DMF), methyl ethyl ketone, N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), acetone, and 1,3-dimethyl-2-imidazolidinone (DMI). The organic solvent may be used alone or in combination of two or more kinds. Among them, the organic solvent is preferably DMF or DMAc.
The solid content concentration of the resin solution is not particularly limited, but is preferably 15 to 50% by mass, more preferably 15 to 40% by mass, and even more preferably 20 to 35% by mass. When the solid content concentration is within the above range, the resin solution has an appropriate fluidity, and it becomes easy to apply the resin solution uniformly to the film-forming substrate.
The resin solution may contain components other than the above components as long as the effects of the present invention are not impaired.

(Step of applying resin solution to film-forming substrate)
The resin solution obtained above is continuously applied to the film-forming substrate so as to be approximately uniform, using a coating machine such as a knife coater, a reverse coater, etc. At this time, the thickness of the coating film can be adjusted by adjusting the gap (clearance) between the film-forming substrate and the die or knife of the coating machine.
The film-forming substrate may be any substrate commonly used in the art, without any particular limitations, and examples of the substrate include flexible polymer films such as polyester films and polyolefin films, nonwoven fabrics impregnated with elastic resins, etc. Among these, polyester films are preferably used.

(Step of solidifying the resin solution)
The substrate coated with the resin solution is immersed in a coagulation liquid (coagulation bath) whose main component is water, which is a poor solvent for polyurethane resin, to coagulate and regenerate the polyurethane resin.
As the solidification liquid, water, a mixed solvent of a polar organic solvent such as water and DMF, etc., is used. As the polar organic solvent, water-miscible organic solvents used to dissolve the polyurethane resin, such as DMF, DMAc, THF, DMSO, NMP, acetone, DMI, etc., can be mentioned. The concentration of the polar organic solvent in the mixed solvent is preferably 0 to 20% by mass, more preferably 1 to 20% by mass, and more preferably 5 to 15% by mass. The above-mentioned solidification liquid is preferably water or a mixed solvent of water and DMF, more preferably a mixed solvent of water and DMF.
There are no particular limitations on the temperature of the coagulation liquid or the immersion time, but it is preferable to set the temperature at 10 to 60° C., preferably 15 to 50° C., for example, for 5 to 120 minutes.
In the coagulation liquid, a dense skin layer is first formed at the interface between the applied resin solution and the coagulation liquid. Then, the organic solvent in the resin solution is exchanged with the coagulation liquid through the skin layer, and the polyurethane resin is coagulated and regenerated in a sheet shape on the film-forming substrate, thereby obtaining a resin sheet with the film-forming substrate having a plurality of teardrop-shaped bubbles formed therein.

Thereafter, the coagulated and regenerated polyurethane sheet is peeled off from the resin sheet, or is washed and dried without being peeled off.
The washing treatment removes the organic solvent remaining in the polyurethane sheet. The washing liquid used for washing includes water.
After washing, the polyurethane sheet is dried by a conventional method, for example, at 80 to 150° C. for about 5 to 60 minutes in a dryer.

If necessary, the polished surface and/or the surface opposite to the polished surface of the polyurethane sheet may be ground (buffed). The polished surface of the polyurethane sheet may be grooved, embossed, and/or perforated (punched), and a substrate may be attached to the surface opposite to the polished surface.
There is no particular limitation on the method of grinding, and any known method can be used, such as grinding with sandpaper, grinding with a buffing machine or a slicing machine, etc. Among these, the use of a buffing machine or a slicing machine is preferred because it allows a polyurethane sheet with a substantially uniform thickness to be obtained.
There is no particular limitation on the shape of the grooves and embossing, and examples thereof include a lattice type, a concentric circle type, a radial type, and the like.
When a substrate is attached to a polyurethane sheet to form a multilayer structure, the layers may be bonded and fixed together, if necessary, under pressure, using double-sided tape, adhesive, etc. There are no particular limitations on the double-sided tape or adhesive used in this case, and any double-sided tape or adhesive known in the art may be selected and used.

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

Example 1
60 parts by mass of a 30% by mass DMF solution containing a polyester polyurethane resin with a 100% modulus of 7.9 MPa, 3 parts by mass of a 10% by mass DMF solution containing a polycarbonate polyurethane resin with a 100% modulus of 24 MPa, and 35 parts by mass of DMF as a diluting solvent were mixed to obtain a polyurethane resin-containing solution. The 100% modulus of the polycarbonate polyurethane resin is 3.4 times that of the polyester polyurethane resin.
The polyester polyurethane resin was obtained by reacting a polyester diol obtained by reacting ethylene glycol and propylene glycol with adipic acid, methylenebis(4,1-phenylene)diisocyanate (MDI), and 1,4-butanediol.
The polycarbonate polyurethane resin was obtained by reacting MDI with a polycarbonate diol obtained by reacting 1,6-hexanediol with dimethyl carbonate.
The polyurethane resin-containing solution was applied to a PET film as a film-forming substrate using a knife coater, and then immersed in a coagulating liquid (water) at 18°C for 60 minutes to coagulate and regenerate the polyurethane. The polyurethane foam sheet was then washed and dried, and peeled off from the film-forming substrate to obtain a polyurethane sheet. The surface of the obtained polyurethane foam sheet was ground to a thickness of 0.82 mm. Then, a PET substrate was attached to the surface opposite to the ground surface of the polyurethane sheet using an adhesive, and a part of the polyurethane sheet was embossed with a lattice-shaped mold to obtain a polishing pad.

(Comparative Example 1)
A polishing pad having a polyurethane sheet having a thickness of 0.81 mm was obtained in the same manner as in Example 1, except that no polycarbonate polyurethane resin was used, and 100 parts by mass of a 30% by mass DMF solution containing a polyester polyurethane resin having a 100% modulus of 7.9 MPa was mixed with 55 parts by mass of DMF as a dilution solvent to obtain a polyurethane resin-containing solution.

(Comparative Example 2)
A polishing pad having a polyurethane sheet having a thickness of 0.78 mm was obtained in the same manner as in Comparative Example 1, except that 16 parts by mass of a DMF dispersion containing carbon black and having a concentration of 15% by mass was added to the polyurethane resin-containing solution of Comparative Example 1 to obtain a polyurethane resin-containing solution.

(Comparative Example 3)
A polishing pad having a polyurethane sheet having a thickness of 0.82 mm was obtained in the same manner as in Example 1, except that 11 parts by mass of a 10% by mass DMF solution containing a polycarbonate-based polyurethane resin having a 100% modulus of 24 MPa was added.

[Evaluation of physical properties of polishing pads]
The thickness, density, compressibility, compressive elasticity modulus, Shore A hardness, average pore size, and pore ratio of the polishing layer were calculated by the following methods for the polishing pads of Example 1 and Comparative Examples 1 to 3. The results are shown in Table 2.
(1) Thickness of the Polishing Layer The thickness of the polishing layer obtained in the Examples and Comparative Examples was measured in accordance with JIS K6505 using a dial gauge (minimum division 0.01 mm) with a load of 100 g/ ^cm2 . Measurements were taken at five points, the center and four corners, of a polishing layer (polyurethane sheet) measuring 10 cm long x 10 cm wide, and read to the nearest tenth (0.001 mm), and the average value was taken as the thickness (mm) of the polishing layer.
(2) Density of the abrasive layer Sample pieces (10 cm x 10 cm) were cut out from the abrasive layers (polyurethane sheets) obtained in the examples and comparative examples, and their mass _W0 (g) was measured using an electronic balance (Mettler AJ-180 model). From the thickness t (cm) measured using a thickness gauge and the mass _W0 (g), the bulk density (ρ) was calculated using the equation (ρ) = _W0 /t/100 (g/ ^cm3 ).
(3) Compressibility %, Compressive elasticity %
The compressibility and compressive modulus were measured using a Shopper-type thickness gauge (pressure surface: circular with a diameter of 1 cm) in accordance with JIS L1021. Specifically, the thickness _t0 was measured after applying an initial load for 30 seconds from a no-load state, and then the thickness t1 was measured after applying a final pressure for 30 seconds from a thickness _t0 state. All loads were removed from the thickness _t1 state, and the sample was left for 5 minutes (to be in a no-load state), after which the thickness _t0 ' was measured again after applying an initial load for 30 seconds.
Compression rate (%) = 100 x (t0 - t ₁ )/t ₀
Compressive modulus (%) = 100 x (t ₀ '-t ₁ )/(t ₀ - t ₁ )
The initial load was 100 g/cm ² and the final pressure was 1120 g/cm ² .
Measurement was performed by.
(4) Shore A Hardness The Shore A hardness was measured by cutting a polyurethane sheet sample (10 cm x 10 cm) from the polishing pad, stacking a plurality of the sample pieces to a thickness of 4.5 mm or more, and using a type A hardness tester (Japanese Industrial Standards, JIS K7311).
(5) Average Aperture Size and Aperture Ratio The average aperture size and aperture ratio were calculated by observing the polished surface of the polyurethane sheet at nine points at 100 times magnification using a scanning electron microscope (manufactured by JEOL Ltd., JMS-5500LV), and then binarizing these images using image processing software (manufactured by Nikon Corporation, ImageAnalyzer V20 LAB Ver. 1.3).
(6) 100% modulus A non-foamed polyurethane sheet was prepared, and a test piece having a dumbbell shape of No. 3 was cut out from the sheet. The tensile stress (MPa) value when the gauge length was elongated to 100% (stretched to twice the normal length) was measured at a tensile speed of 100 mm/min in accordance with JIS K 6251 (1993).

[Measurement of the proportion of each segment]
The soft segment and hard segment contents of the polished surface of each Example and Comparative Example were determined under the following conditions using pulse NMR measurement. Specifically, a sample piece of about 1 to 3 mm square was cut out from the land portion of the polishing pad that had been ground with a cutter, filled in a 10 mmφ sample tube to a height of 1 to 2 cm, and pulse NMR measurement was performed to obtain an attenuation curve. In order to match the obtained attenuation curve with the fitting curve, analysis was performed by the least squares method using a Lorentz function (straight line portion) and a Gaussian function (curved portion), and the proportions (abundance ratios (%)) of the crystalline phase, intermediate phase, and amorphous phase in the polished surface, as well as the relaxation time (T2), were determined. The fitting and analysis were performed using software attached to the following measurement device. The measurement results are shown in Table 1.
(Measurement conditions)
Apparatus: JNM-MU25, manufactured by JEOL Ltd.
Measurement magnetic field strength: 0.58T
Observation frequency: 25MHz
Observed nucleus: 1H
Measurement: Spin-spin relaxation (T2)
Measurement method: Solid Echo method Pulse width: 2.2 μs
Pulse interval: 13.0 μs
Pulse repetition time: 4.0 sec
Number of measurements: 16 Measurement temperature: 20°C

The ratio of the crystalline phase increases mainly due to the fact that the hard segments are aggregated to increase in size and depending on an increase in the amount of the hard segments.
The relaxation time of the amorphous phase increases depending on the relative increase in the highly mobile soft segments.
As a result of the pulse NMR measurement test, although there is not a large difference in the ratio of the crystalline phase to the amorphous phase between the polishing pad of Example 1 and the polishing pads of Comparative Examples 1 to 3, it can be seen that the relaxation time of the amorphous phase is longer than the others in Example 1, and phase separation is progressing. On the other hand, the relaxation time of Comparative Example 3 is shorter than the others, and it can be seen that it is progressing toward phase mixing.

(Polishing test)
Using the polishing pads of each Example and Comparative Example, 120 silicon wafers with a TEOS (tetraethoxysilane) film and 120 silicon wafers with a Cu film were polished under the following conditions, and the polishing rate and scratch resistance were evaluated. The evaluation results are shown in Table 2.

[Polishing conditions]
Polishing machine used: Ebara Corporation, product name "F-REX300"
Polishing speed (platen rotation speed): 70 rpm
Processing pressure: 176g/ ^cm2
Slurry flow rate: 200 mL / min
Dresser: 3M diamond dresser, model number "A188"
Conditioning: Ex-situ, 30N, 4 scans Polishing time: 60 seconds Polished object: silicon wafer with TEOS film and silicon wafer with Cu film Polishing slurry: 2x diluted solution of Cabot's model number "SS-25" (SS25 stock solution: pure water = 1:1 mixture)

[Polishing rate]
The polishing rate (Å/min) was calculated by dividing the thickness measured at each point by the polishing time from the average value of the thickness measured at 121 points of the TEOS film of the wafer before and after the polishing test. The thickness was measured using an optical film thickness and film quality measuring device (DBS mode of model number "ASET-F5x" manufactured by KLA Tencor Corporation).

[Evaluation of scratch resistance (presence or absence of polishing scratches)]
For the Cu film on the wafer, polishing scratches of 150 nm or more in length were counted on the surface of the Cu part of the wafer at the polishing processing number of 13, 28, 53, 78, 103, and 118 using a surface inspection device (KLA Tencor Corporation, Surfscan SP5). When the number of polishing scratches was less than 5, it was evaluated as ○, and when the number was 5 or more, it was evaluated as ×.

<Results>
As can be seen from the graph, Example 1, which contains a mixture of two types of polyurethane resins with significantly different 100% modulus, was able to achieve both a high average polishing rate and suppression of polishing scratches. In contrast, the polishing pad of Comparative Example 1, which contains only one type of polyurethane resin with a small 100% modulus, was unable to suppress polishing scratches and had a low average polishing rate. The polishing pad of Comparative Example 2 was able to improve the average polishing rate by adding carbon black to Comparative Example 1, but the polishing scratches were worse than those of Comparative Example 1. The polishing pad of Comparative Example 3, which has a higher proportion of resin B than Example 1, did not achieve sufficient results in either polishing rate or polishing scratches.

<Considerations>
From the results of the pulse NMR measurement, it can be seen that the polyurethane phase separation is advanced in the polishing pad of Example 1. It is considered that the use of a combination of two types of polyurethane resins with significantly different 100% modulus has advanced the polyurethane phase separation, thereby achieving both an improvement in the polishing rate and a reduction in polishing scratches.
In contrast, the polishing pad of Comparative Example 1 contains only polyurethane resin A with a small 100% modulus, so the crystalline phase component is the smallest and the amorphous phase component is the largest, and the resin as a whole is flexible and stretches easily, and the openings on the polishing surface are easily blocked and blunted by friction with the workpiece during polishing. As a result, it is thought that the slurry and polishing debris do not enter the openings and come into contact with the workpiece, causing scratches. On the other hand, the polishing pad of Comparative Example 3 has a shorter relaxation time for the crystalline phase, amorphous phase, and intermediate phase than the others, and the molecular mobility is limited, so it is thought that phase mixing has progressed. Since the proportion of the polyurethane resin B added is large, the resin as a whole becomes hard, and it is thought that scratches are caused due to the increased rigidity of the pad.
On the other hand, the polishing pad of Comparative Example 2 had a high removal rate due to the hardness increased by adding carbon black, but it is believed that the scratch resistance was deteriorated due to the hard carbon black particles.

The polishing pad of the present invention can suppress the occurrence of scratches on the surface of the object being polished and has a high polishing rate. Therefore, the polishing pad of the present invention has industrial applicability.

Claims (12)

A polishing pad comprising a polyurethane sheet having a plurality of teardrop-shaped bubbles and having a polishing surface for polishing an object to be polished,
The polishing pad, wherein the polyurethane resin constituting the polyurethane sheet comprises a mixture of a polyurethane resin A having a 100% modulus of 3 to 10 MPa and a polyurethane resin B having a 100% modulus of 20 to 30 MPa, and the mass ratio of the polyurethane resin A to the polyurethane resin B is 100:1 to 100:3 . The polishing pad according to claim 1, wherein the polyurethane resin constituting the polyurethane sheet comprises a mixture of a polyurethane resin A having a 100% modulus of 6 to 9 MPa and a polyurethane resin B having a 100% modulus of 21 to 27 MPa. 3. The polishing pad according to claim 1, wherein the mass ratio of the polyurethane resin A to the polyurethane resin B is 100:1 to 100:1.7. 4. The polishing pad according to claim 1, wherein the polyurethane resin A and the polyurethane resin B each have a different polyol component. The polishing pad according to any one of claims 1 to 4, wherein the constituent polyol component of the polyurethane resin A includes one polyol component selected from the three types of polyether polyol, polyester polyol, and polycarbonate polyol, and the constituent polyol component of the polyurethane resin B includes another polyol component different from the one selected as the constituent polyol component of the polyurethane resin A among the three types of polyether polyol, polyester polyol, and polycarbonate polyol. 6. The polishing pad according to claim 1 , wherein the polyurethane resin B contains a polycarbonate polyol as a constituent polyol component. 7. The polishing pad according to claim 1 , wherein the polyurethane resin A contains a polyether polyol or a polyester polyol as a constituent polyol component. A polishing pad comprising a polyurethane sheet having a plurality of teardrop-shaped bubbles and having a polishing surface for polishing an object to be polished,
the polyurethane resin constituting the polyurethane sheet comprises a mixture of a polyurethane resin A having a 100% modulus of 3 to 10 MPa and a polyurethane resin B having a 100% modulus of 20 to 30 MPa;
The mass ratio of the polyurethane resin A to the polyurethane resin B is 100:1 to 100:3 ,
The polishing pad, wherein the polyurethane resin A contains a polyether polyol or a polyester polyol as a constituent polyol component, and the polyurethane resin B contains a polycarbonate polyol as a constituent polyol component. The polishing pad according to claim 8, wherein the polyurethane resin constituting the polyurethane sheet comprises a mixture of a polyurethane resin A having a 100% modulus of 6 to 9 MPa and a polyurethane resin B having a 100% modulus of 21 to 27 MPa. 10. The polishing pad according to claim 8, wherein the mass ratio of the polyurethane resin A to the polyurethane resin B is 100:1 to 100:1.7. The polishing pad according to any one of claims 1 to 10 , wherein the polyurethane sheet does not contain carbon black. A method for producing a polishing pad according to any one of claims 1 to 11 , comprising the steps of:
A step of preparing a resin solution containing a mixture of a polyurethane resin A having a 100% modulus of 3 to 10 MPa and a polyurethane resin B having a 100% modulus of 20 to 30 MPa, wherein the polyurethane resin A and the polyurethane resin B are prepared so that the mass ratio thereof is 100:1 to 100:3 ;
A method for manufacturing a polishing pad, comprising: a step of applying the resin solution to a film-forming substrate; and a step of immersing the film-forming substrate to which the solution has been applied in a coagulating liquid to coagulate the solution.