JP2018051726A - Polishing pad and manufacturing method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing pad capable of continuously polishing an object to be polished at a stable polishing rate.SOLUTION: A polishing pad comprises a polyurethane resin sheet including: multiple tear-shaped air bubbles; and multiple micro air bubbles each having a size smaller than that of the tear-shaped air bubble, formed by a wet film formation method. The polyurethane resin sheet has a polishing surface for polishing an object to be polished. The multiple micro air bubbles are bubbles forming openings each having the diameter of 1-20 μm in an arbitrary cutting surface in a thickness direction of the polyurethane resin sheet, and a ratio of a total area of openings each having the diameter of 10-20 μm with respect to a total area of openings each having the diameter of 1-20 μm is 15-60% in an arbitrary cutting surface in the thickness direction.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a polishing pad and a method for manufacturing the same. In particular, the present invention relates to a polishing pad for polishing silicon, a hard disk, a mother glass for a liquid crystal display, a semiconductor device, and a manufacturing method thereof.

Since the surface of a material such as an optical material, a semiconductor device, a hard disk, or a glass substrate is required to be flat, a free abrasive grain type polishing using a polishing pad is performed. The free abrasive grain method is a method of polishing a processed surface of an object to be polished while supplying a slurry (polishing liquid) containing abrasive grains between a polishing pad and the object to be polished.
In various materials such as silicon, hard disk, mother glass for liquid crystal displays, and semiconductor devices, polishing using a polishing pad is performed to ensure flatness.
Polishing pads used for polishing semiconductor devices and the like are highly required to have defect-free and flattening characteristics of an object to be polished, and there are an increasing number of cases where a soft polishing pad is used mainly in a final polishing process.
In the CMP technique, it is necessary to stabilize the polishing rate from the viewpoint of improving the efficiency of productivity and improving the yield. In particular, since the polishing rate at the start of polishing is smaller than the polishing rate in a steady state, it is required to further shorten the time required for dummy polishing (start-up processing time) until the polishing rate becomes substantially constant. .
By defining the average diameter of the openings in the nap layer of the polishing cloth and increasing the area of the wall that is not open rather than the area of the hole, the start-up processing time is reduced. A soft polishing pad has been proposed (Patent Document 1).
By defining the ratio of the opening diameter of the bubbles opened on the surface of the nap layer and the distance from the surface to the deepest part of the opened bubbles, the polishing slurry can smoothly flow into, hold, and discharge during the polishing. Thus, there has been proposed a soft polishing pad that improves the polishing rate and obtains stable polishing characteristics, and shortens the start-up processing time to improve productivity (Patent Document 2).

JP 2006-075914 A JP 2007-160474 A

However, with a conventional soft polishing pad, the polishing rate fluctuates when a number of objects to be polished are polished, and a stable polishing rate cannot be obtained. Therefore, the polishing amount of the object to be polished tends to vary, and it has been difficult to keep the product quality constant.
In addition, in the conventional soft polishing pad, it still takes time for the start-up process, and further time reduction has been required.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a polishing pad capable of continuously polishing an object to be polished at a stable polishing rate and a method for manufacturing the same.
Another object of the present invention is to provide a polishing pad that can eliminate start-up processing time or make it as short as possible and a method for manufacturing the same.

In order to solve the above problems, the present invention employs the following configuration.
<1> A polishing pad comprising a polyurethane resin sheet containing a plurality of tear-shaped bubbles formed by a wet film-forming method and a plurality of microbubbles having a size smaller than the tear-shaped bubbles,
The polyurethane resin sheet has a polishing surface for polishing an object to be polished,
The micro bubbles are bubbles forming an opening having an opening diameter of 1 to 20 μm on an arbitrary cut surface in the thickness direction of the polyurethane resin sheet, and
In an arbitrary cut surface in the thickness direction, the ratio of the total area of the openings having an opening diameter of 10 to 20 μm in the total area of the openings having an opening diameter of 1 to 20 μm is 15 to 60%. The polishing pad.
<2> In the cut surface of the polyurethane resin sheet, a ratio of the number of openings having the opening diameter of 10 to 20 μm to the number of openings having the opening diameter of 1 to 20 μm is 4.5 to 30. % Of the polishing pad according to <1>.
<3> When the thickness at 20 ° C. of the polishing pad is A and the thickness at a temperature at which the polishing pad has the largest thickness is 20 to 60 ° C. <1> or <2>, wherein the polishing pad is less than 3%.
Thermal expansion coefficient X = (B−A) / A × 100
<4> The polishing pad according to any one of <1> to <3>, wherein there are 6 to 50 openings having an opening diameter of 10 to ²⁰ μm per 10,000 μm ^{2 on the} cut surface of the polyurethane resin sheet.
<5> a step of preparing a polyurethane resin-containing solution containing a polyurethane resin and cellulose acetate;
Applying the polyurethane resin-containing solution onto a film-forming substrate; and immersing the film-forming substrate on which the solution is applied in a coagulation liquid to solidify the solution;
The manufacturing method of the polishing pad in any one of <1>-<4> containing this.
<6> The production method according to <5>, wherein the polyurethane resin-containing solution is applied to a film-forming substrate with a thickness of 1.3 to 3.0 mm.
<7> The production method according to <5> or <6>, wherein the polyurethane resin-containing solution further contains a hydrophobic additive.

  The polishing pad of the present invention can polish an object to be polished continuously at a stable polishing rate. Further, the polishing pad of the present invention can eliminate the start-up processing time or shorten it as much as possible.

1 is a scanning electron microscope (SEM) image (magnification 50 times) of a cross section in the thickness direction of a polyurethane resin sheet used for the polishing pad of Comparative Example 1. FIG. FIG. 2 is an SEM image (50 × magnification) of a cross section in the thickness direction of the polyurethane resin sheet used for the polishing pad of Example 1. 3 is an SEM image (magnification 200 times) of a cross section in the thickness direction of the polyurethane resin sheet used for the polishing pad of Comparative Example 1. FIG. 4 is an SEM image (magnification 200 times) of a cross section in the thickness direction of the polyurethane resin sheet used for the polishing pad of Example 1. FIG. FIG. 5 is an SEM photograph (600 times magnification) of a cross section obtained by cutting the polyurethane resin sheet in the polishing pad of Comparative Example 1 in the thickness direction. 6 is a SEM photograph (600 times magnification) of a cross section obtained by cutting the polyurethane resin sheet in the polishing pad of Example 1 in the thickness direction. FIG. 7 shows how much the thickness increased with respect to the thickness of each polishing pad at 20 ° C. when the temperature of the polishing pad of Example 1 and Comparative Example 1 was changed within the range of 20 ° C. to 60 ° C. It is a figure which shows (thermal expansion). FIG. 8 shows how much the thickness increases with respect to the thickness of each polishing pad at 20 ° C. when the temperatures of the polishing pads of Example 2 and Comparative Examples 2 to 4 are changed within the range of 20 ° C. to 60 ° C. It is a figure which shows whether it did (thermal expansion). FIG. 9 is a diagram showing the result of the polishing rate when 1 to 100 workpieces are polished using the polishing pads of Example 1 and Comparative Example 1. The numerical value on the horizontal axis represents the number of processed objects. The numerical value on the vertical axis represents the polishing rate (the unit is Å). FIG. 10 is a diagram showing the results of the polishing rate when 1 to 100 objects to be polished are polished using the polishing pads of Example 2 and Comparative Examples 2 to 4. The horizontal axis represents the number of processed objects. The numerical value on the vertical axis represents the polishing rate (the unit is Å).

Hereinafter, modes for carrying out the present invention will be described.
In the present specification and claims, the “opening diameter” means an opening existing in the cross section when the polyurethane resin sheet is cut in an arbitrary cross section (the opening is an opening in the cross section). The equivalent circle diameter is calculated based on the area. The equivalent circle diameter is an equivalent circle diameter calculated from the area of each bubble portion by taking a cross-sectional image of a polyurethane polishing sheet, which was taken with a scanning electron microscope (SEM) at a magnification of 600, and binarized (that is, This is the diameter of the circle when the cross-sectional shape of the bubble is replaced with a circle having the same area as the area of the bubble).
The equivalent circle diameter can be obtained by the following equation.
π × (D × 1/2) ² = S
(In the formula, the equivalent circle diameter is D and the area of the opening is S.)

In the present specification and claims, the wet film forming method means that a resin to be formed is dissolved in an organic solvent, and the resin solution is applied to a sheet-like base material, and then the organic solvent is dissolved. Means a method in which the organic solvent is replaced by passing through a coagulating liquid that does not dissolve, solidified, and dried to form a bubble layer. Normally, when a polyurethane polishing sheet is produced by a wet film formation method, the formed layer is formed into a porous structure, but the mechanism is that the solvent escapes into the coagulation liquid when it solidifies through the coagulation liquid. Sometimes the passage becomes a cavity, and this cavity becomes bubbles (tears-shaped bubbles) of the polishing sheet (P in FIG. 4). At this time, along with the tear-shaped bubbles, microbubbles smaller than the tear-shaped bubbles are formed in the entire polishing sheet (M in FIG. 4, FIG. 6).
The tear-shaped bubbles are anisotropic and generally have a structure with a large diameter from the polishing layer surface to the bottom of the polishing pad. As is apparent from FIG. 4, tear-shaped bubbles have a much larger cross-sectional area or volume than microbubbles. Therefore, tear-shaped bubbles and microbubbles can be easily distinguished.
The tear-shaped bubbles have an opening diameter larger than 20 μm when the polyurethane resin sheet is cut at an arbitrary cross section in the thickness direction. Therefore, a polyurethane resin sheet containing a plurality of tear-shaped bubbles formed by a wet film forming method has a plurality of openings having an opening diameter larger than 20 μm when the polyurethane resin sheet is cut in an arbitrary cross section in the thickness direction. In other words, it can be referred to as a polyurethane resin sheet including (a tear-shaped opening). The tear-shaped bubbles may have an opening diameter of 30 μm or more, an opening diameter of 50 μm or more, or 80 μm or more when the polyurethane resin sheet is cut in an arbitrary cross section in the thickness direction. Or an opening diameter of 100 μm or more.
Further, teardrop shaped bubbles, when cutting the polyurethane resin sheet at any cross section in the thickness direction, may have a 400 [mu] m ² larger area may have a 900 .mu.m ² or more areas, may have a 2500 [mu] m ² or more areas may have 6400Myuemu ² or more areas may have 10000 ² or more areas.

In the present specification and claims, the microbubbles are dense bubbles smaller than substantially tear-shaped bubbles formed by a wet film forming method, and the polyurethane resin sheet is cut at an arbitrary cross section in the thickness direction. The bubbles form an opening having an opening diameter (equivalent circle diameter) of 1 to 20 μm.
In the present specification and claims, the thickness direction is an angle perpendicular to the surface (polishing surface) of the polyurethane polishing sheet in contact with the object to be polished, and from the polishing surface to the opposite side of the polishing surface. It means the direction toward the surface.

<< Polishing pad >>
The polishing pad of the present invention is a polishing pad comprising a polyurethane resin sheet comprising a plurality of tear-shaped bubbles formed by a wet film forming method and a plurality of microbubbles having a size smaller than the tear-shaped bubbles, The polyurethane resin sheet has a polishing surface for polishing an object to be polished, and the microbubble has an opening having an opening diameter of 1 to 20 μm at an arbitrary cut surface in the thickness direction of the polyurethane resin sheet. The total area of the openings having an opening diameter of 10 to 20 μm that occupies the total area (S1) of the openings having an opening diameter of 1 to 20 μm on the arbitrary cut surface in the thickness direction. In the polishing pad, the ratio (S2 / S1 × 100) of (S2) is 15 to 60%.

  The polyurethane resin sheet of the present invention has a plurality of tear-shaped bubbles (P in FIG. 4) and a plurality of microbubbles (M in FIG. 4, bubbles in FIG. 6). In addition, usually, microbubbles present around the tear-shaped bubbles communicate with each other in a mesh shape and have an open-cell structure in which the bubbles are formed in an open-cell shape. The polyurethane resin sheet of the present invention contains a large number of microbubbles having a large cell diameter as compared with a conventional polyurethane resin sheet. Since the size and amount of the microbubbles communicating with the tear-shaped bubbles are large, the polishing slurry can be held quickly and more polishing slurry can be stored in the region immediately below the polishing surface. Thereby, the rising processing time is advanced, and a sufficient amount of slurry can be held on the polishing surface, so that the polishing stability is excellent.

The polishing pad of the present invention has a total area of openings having an opening diameter of 10 to 20 μm occupying the total area of openings having an opening diameter of 1 to 20 μm on an arbitrary cut surface in the thickness direction of the polyurethane resin sheet. The proportion is 15-60%. The ratio is preferably 15 to 50%, more preferably 20 to 50%, even more preferably 30 to 50%, and particularly preferably 40 to 50%. When the ratio of the total area of the openings having an opening diameter of 10 to 20 μm in the total area of the openings having an opening diameter of 1 to 20 μm is within the above range, the object to be polished is continuously produced at a stable polishing rate. Can be polished. Further, the startup processing time can be eliminated or shortened as much as possible. Furthermore, the entire surface of the object to be polished can be polished without unevenness, and the polishing uniformity is excellent.
The measurement of the opening diameter of the opening in the cut surface when the polyurethane resin sheet is cut in an arbitrary cross section in the thickness direction is, for example, a scanning electron microscope (SEM) image of the cut surface (preferably the cut surface is 100 times larger). SEM images magnified to ˜1000 times, more preferably 400 to 800 times, and even more preferably about 600 times. At this time, the tear-shaped bubble may or may not exist in the measurement region of the SEM image, but it is preferable that the tear-shaped bubble does not exist.

The polishing pad of the present invention is the ratio of the number of openings having the opening diameter of 10 to 20 μm to the number of openings having an opening diameter of 1 to 20 μm in an arbitrary cut surface in the thickness direction of the polyurethane resin sheet. However, it is preferably 4.5 to 30%, more preferably 5 to 25%, even more preferably 8 to 20%, and particularly preferably 10 to 20%. When the ratio of the number of openings having an opening diameter of 10 to 20 μm to the number of openings having an opening diameter of 1 to 20 μm is within the above range, the stability of the polishing rate can be further improved.
The measurement of the number of openings in the cut surface when the polyurethane resin sheet is cut in an arbitrary cross section in the thickness direction is, for example, an SEM image of the cut surface (preferably the cut surface is 100 to 1000 times, more preferably SEM images magnified to 400 to 800 times, and even more preferably about 600 times, can be used. At this time, the tear-shaped bubble may or may not exist in the measurement region of the SEM image, but it is preferable that the tear-shaped bubble does not exist.

The polishing pad of this invention is calculated | required by a following formula, when the thickness in 20 degreeC of the said polishing pad is set to A, and the thickness in the temperature where the thickness becomes the largest among 20-60 degreeC of the said polishing pad is set to B. The thermal expansion coefficient X is preferably less than 3%, more preferably 2.8% or less, even more preferably 2.5% or less, and even more preferably 2% or less. Although there is no restriction | limiting in particular in the lower limit of the thermal expansion coefficient X, 0% may be sufficient, 0.1% may be sufficient, and 0.5% may be sufficient.
Thermal expansion coefficient X = (B−A) / A × 100
When the thermal expansion coefficient X is within the above range, even if the temperature of the polishing pad is increased by polishing frictional heat during polishing, the expansion of the polishing pad is suppressed and the form stability is excellent, so that the polishing rate stability is improved. Contribute.

The polishing pad of the present invention has 6 to 50 openings having an opening diameter of 10 to 20 μm per 10000 μm ² (that is, a cross section of 100 μm × 100 μm) on an arbitrary cut surface in the thickness direction of the polyurethane resin sheet. Preferably, 8 to 40 are present, more preferably 8 to 30 are present, even more preferably 9 to 25 are present.
In the present specification and claims, the measurement of the number of openings of 10 to ²⁰ μm in the cut surface 10000 μm ² when the polyurethane resin sheet is cut in an arbitrary cross section in the thickness direction is, for example, SEM of the cut surface. An image (preferably an SEM image in which the cut surface is enlarged 200 to 1000 times, more preferably 400 to 800 times, and even more preferably about 600 times) can be used. At this time, if a huge tear-shaped bubble is present in the measurement region, the region in which the number of openings of 10 to 20 μm can exist is substantially limited. Therefore, a tear shape is formed on the surface of the measurement region 10000 μm ² in the cut surface. Preferably no bubbles are present.
The polishing pad of the present invention has 50 to 50 openings having an opening diameter of 1 to 20 μm per 10000 μm ² (that is, a section having a cross-sectional area of 100 μm × 100 μm) in an arbitrary cut surface in the thickness direction of the polyurethane resin sheet. Preferably, 400 are present, more preferably from 70 to 400, even more preferably from 80 to 300, and even more preferably from 90 to 250.
In the present specification and claims, the measurement of the number of openings of 1 to 20 μm in the cut surface 10000 μm ² when the polyurethane resin sheet is cut in an arbitrary cross section in the thickness direction is, for example, SEM of the cut surface. It can be performed using an image (preferably an SEM image in which the cut surface is magnified 100 to 1000 times, more preferably 400 to 800 times, and even more preferably about 600 times). At this time, if a huge tear-shaped bubble is present in the measurement region, the region in which the number of openings of 1 to 20 μm can exist is substantially limited. Therefore, the tear shape is formed on the surface of the measurement region 10000 μm ² in the cut surface. Preferably no bubbles are present.

(Thickness)
Although there is no restriction | limiting in particular in the thickness of the polyurethane resin sheet in the polishing pad of this invention, For example, it is 0.80-1.50mm, Preferably it can use in 0.90-1.30mm.

The polyurethane resin sheet contains a polyurethane resin. There is no restriction | limiting in particular in the kind of polyurethane resin, What is necessary is just to select according to a use purpose from various polyurethane resins. For example, a polyester-based, polyether-based, or polycarbonate-based resin can be used.
Examples of the polyester-based resin include a polymer of a polyester polyol such as ethylene glycol or butylene glycol and adipic acid and a diisocyanate such as diphenylmethane-4,4′-diisocyanate.
Examples of polyether resins include polymers of polyether polyols such as polytetramethylene ether glycol and polypropylene glycol and isocyanates such as diphenylmethane-4,4′-diisocyanate.
Examples of the polycarbonate-based resin include a polymer of polycarbonate polyol and isocyanate such as diphenylmethane-4,4′-diisocyanate.
These resins are marketed in the market such as DIC Corporation's trade name “Chris Bon”, Sanyo Chemical Industries' product name “Samprene”, Dainichi Seika Kogyo's trade name “Rezamin”. Available resins may be used, and a resin having desired characteristics may be produced by itself.

(Modulus)
The modulus is an index representing the hardness of the resin, and is a value obtained by dividing the load applied when the non-foamed resin sheet is stretched by 100% (when stretched to twice the original length) by the cross-sectional area. (Hereinafter, it may be called 100% modulus.) The higher this value, the harder the resin.
The polyurethane resin preferably has a 100% modulus of 1 to 20 MPa, and more preferably 2 to 10 MPa. It is preferable for the 100% modulus to be within the above range because the occurrence of polishing scratches such as scratches on the object can be suppressed.

  In addition to the above components, the polyurethane resin sheet may contain cellulose acetate, a hydrophobic additive, a filler such as carbon black, a foaming aid, a surfactant, and the like.

In the polishing pad of the present invention, the polishing surface of the polyurethane resin sheet and / or the surface opposite to the polishing surface may be ground (buffed). Among these, it is preferable that the polishing surface of the polyurethane resin sheet of the polishing pad of the present invention is ground. Thereby, a large number of openings derived from microbubbles and teardrop-shaped bubbles are present on the polishing surface, and the amount of slurry retained through the openings increases the stability of the polishing rate.
In the polishing pad of the present invention, the polishing surface of the polyurethane resin sheet may be subjected to groove processing, embossing and / or hole processing (punching processing). The polishing pad of the present invention may include a light transmission part.
In addition, the polishing pad of the present invention may have a single-layer structure composed only of a polyurethane resin sheet, and may be a multi-layer in which a substrate is bonded to the surface opposite to the polishing surface of the polyurethane resin sheet (polishing layer). It may be. Examples of the base material include polyethylene terephthalate (PET), non-woven fabric impregnated with polyurethane resin, and foams such as polyethylene foam. Although there is no restriction | limiting in particular in the characteristic of a base material, It is preferable that it is harder (A hardness or D hardness is larger) from a polyurethane resin sheet from a viewpoint of form stability.

  The polishing pad of the present invention can be suitably used for polishing silicon, a hard disk, a glass substrate, a mother glass for liquid crystal display, a semiconductor wafer, a semiconductor device, etc., particularly chemical mechanical polishing (CMP) of a semiconductor device.

<< Production Method of Polishing Pad >>
The polishing pad of the present invention can be obtained, for example, by the production method of the present invention. The production method of the present invention includes a step of preparing a polyurethane resin-containing solution containing a polyurethane resin and cellulose acetate, a step of applying the polyurethane resin-containing solution on a film-forming substrate, and a film-forming substrate on which the solution is applied A step of solidifying the solution by immersing in a coagulating solution.
Hereinafter, each step will be described.

<Process for preparing polyurethane resin-containing solution>
In this step, the polyurethane resin and cellulose acetate are dissolved in a water-miscible organic solvent capable of dissolving the polyurethane resin, for example, to prepare a polyurethane resin-containing solution. Hereinafter, components that can be contained in the polyurethane resin-containing solution will be described.
(Polyurethane resin)
The polyurethane resin-containing solution contains a polyurethane resin that serves as a material for the polyurethane polishing sheet. As the polyurethane resin, the polyurethane resins mentioned in the description of the polishing pad can be used.

(Cellulose acetate)
The polyurethane resin-containing solution contains cellulose acetate in addition to the polyurethane resin. By containing cellulose acetate, the size of microbubbles can be increased, and an opening having an opening diameter of 10 to 20 μm with respect to an opening having an opening diameter of 1 to 20 μm in any cross section in the thickness direction of the polyurethane resin sheet The area ratio and the number ratio of the parts can be increased.
Cellulose acetate is preferably contained in the polyurethane resin-containing solution in an amount of 0.1 to 10 parts by mass with respect to 100 parts by mass of the polyurethane resin, more preferably 0.2 to 5 parts by mass, and 0.5 to An amount of 3 parts by weight is even more preferred.

(Organic solvent)
The organic solvent can be used without particular limitation as long as it can dissolve the polyurethane resin and is miscible with water. Examples include N, N-dimethylformamide (DMF), methyl ethyl ketone, N, N-dimethylacetamide (DMAc), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), acetone and the like. . Among these, DMF or DMAc is preferably used.
The organic solvent has a solid content concentration in the polyurethane resin-containing solution of preferably 15 to 50% by mass, more preferably 15 to 40% by mass, and even more preferably 20 to 35% by mass. It is preferable to be contained in the resin-containing solution. When the concentration is within the above range, the polyurethane resin-containing solution has appropriate fluidity, and can be uniformly applied on the film-forming substrate in the subsequent application step.

(water)
The polyurethane resin-containing solution preferably contains water in addition to the polyurethane resin and cellulose acetate. By including water, the size of the microbubbles can be further increased. In addition, film formability is improved.
It is preferable that 0.1-30 mass parts is contained with respect to 100 mass parts of polyurethane resins, it is more preferable that water is contained 1-20 mass parts, and it is still more preferable that water is contained 5-18 mass parts.

(Hydrophobic additive)
The polyurethane resin-containing solution preferably further contains a hydrophobic additive in addition to the above components. That is, it is preferable to dissolve the hydrophobic additive together with other components in an organic solvent to obtain a polyurethane resin-containing solution.
Examples of hydrophobic additives include, for example, polyoxyethylene alkyl ether, polyoxypropylene alkyl ether, polyoxyethylene polyoxypropylene alkyl ether, perfluoroalkyl ethylene oxide adduct, glycerin fatty acid ester, propylene glycol fatty acid ester, and the like. Examples thereof include nonionic surfactants, anionic surfactants such as alkyl carboxylic acids, and silicon surfactants such as silicon nonionic surfactants. Among these, it is preferable to use a silicon-based nonionic surfactant.
The hydrophobic additive is preferably contained in an amount of 0.1 to 30 parts by mass, more preferably 0.1 to 20 parts by mass, and more preferably 1 to 20 parts by mass with respect to 100 parts by mass of the polyurethane resin. Even more preferably, 3 to 18 parts by weight is even more preferred.

(Other ingredients)
The polyurethane resin-containing solution may further contain carbon black, a foaming aid, a surfactant and the like in addition to the above components.

<Application process>
The polyurethane resin-containing solution obtained above is continuously applied on the film forming substrate by, for example, a knife coater or a reverse coater so as to be substantially uniform. As a film-forming substrate, any substrate that is usually used in this technical field can be used without any particular limitation. Examples of the film forming substrate include a flexible polymer film such as a polyester film and a polyolefin film, a non-woven fabric impregnated and fixed with an elastic resin, and a polyester film is preferably used among them.
In the application step, the polyurethane resin-containing solution is preferably applied on the film formation substrate with a thickness of 1.3 to 3.0 mm, and is applied on the film formation substrate with a thickness of 1.3 to 2.5 mm. More preferably, it is even more preferable to apply the film with a thickness of 1.4 to 2.0 mm on the film forming substrate. By applying with a thickness within the above range, microbubbles are sufficiently formed, and the thickness uniformity of the formed polyurethane resin sheet can be maintained.
Although there is no restriction | limiting in particular in the method of apply | coating with the thickness within the said range, For example, it can apply | coat with the thickness within the said range by adjusting the clearance gap (clearance) of a knife coater and a film-forming base material.

<Coagulation process>
The base material on which the polyurethane resin-containing solution is applied is immersed in a coagulation liquid mainly composed of water which is a poor solvent for the polyurethane resin.
As the coagulation liquid, water, a mixed solution of water and a polar solvent such as DMF, or the like is used. Examples of the polar solvent include water-miscible organic solvents used to dissolve the polyurethane resin, such as DMF, DMAc, THF, DMSO, NMP, and acetone. The concentration of the polar solvent in the mixed solvent is preferably 0.5 to 30% by mass.
There is no restriction | limiting in particular in the temperature and immersion time of a coagulation liquid, For example, what is necessary is just to immerse for 5 to 100 minutes (preferably 40 to 80 minutes) at 5-80 degreeC (preferably 5-30 degreeC).

<Washing and drying>
The sheet-like polyurethane resin obtained by coagulation in a coagulation bath is washed and dried after being peeled off from the film-forming substrate or without being peeled off.
The organic solvent remaining in the polyurethane resin is removed by the washing treatment. An example of the cleaning liquid used for cleaning is water.
After washing, the polyurethane resin is dried. What is necessary is just to perform the drying process by the method currently performed, for example, what is necessary is just to dry in a dryer for about 5 to 60 minutes at 80-150 degreeC. A polyurethane abrasive sheet can be obtained through the above steps.

In the method for producing a polishing pad of the present invention, the polishing surface of the polyurethane resin sheet and / or the surface opposite to the polishing surface may be ground as necessary. Further, the polishing surface of the polyurethane resin sheet may be subjected to groove processing, embossing and / or hole processing (punching processing), and the substrate may be bonded to the polyurethane resin sheet. Furthermore, you may provide a light transmissive part in a polyurethane resin sheet and / or a polishing pad.
There is no restriction | limiting in particular in the method of a grinding process, It can grind by a well-known method. Specific examples include grinding with sandpaper.
There is no restriction | limiting in particular in the shape of groove processing and embossing, For example, shapes, such as a lattice type, a concentric circle type, and a radiation type, are mentioned.
When a base material is bonded to form a multilayer structure, a plurality of layers may be bonded and fixed using a double-sided tape, an adhesive, or the like while being pressurized as necessary. There is no restriction | limiting in particular in the double-sided tape and adhesive used at this time, It can select and use arbitrarily from well-known double-sided tapes and adhesives in this technical field.

  After that, a double-sided tape is applied to the surface of the polyurethane sheet opposite to the polishing surface, or the surface opposite to the surface of the base material bonded to the polyurethane sheet, and cut into a predetermined shape, preferably a disc shape. Thus, the polishing pad of the present invention is completed. The double-sided tape is not particularly limited, and any double-sided tape known in the art can be selected and used.

When the polishing pad of the present invention is used, the polishing pad is attached to the polishing surface plate of the polishing machine so that the polishing surface of the polyurethane resin sheet faces the object to be polished. Then, while supplying the abrasive slurry, the polishing surface plate is rotated to polish the processed surface of the object to be polished.
Examples of an object to be processed by the polishing pad of the present invention include a hard disk, a glass substrate, a thin display mother glass, a semiconductor wafer, and a semiconductor device. Among these, the polishing pad of the present invention is preferably used for chemical mechanical polishing (CMP) processing of a semiconductor device.

  As described above, the polishing pad of the present invention can continuously polish an object to be polished at a stable polishing rate. The reason is not clear, but is presumed as follows. That is, when a number of objects to be polished are polished, the temperature in the vicinity of the polishing surface of the polishing pad increases due to frictional heat, but the polishing pad of the present invention containing a polyurethane resin sheet having a high proportion of openings of 10 to 20 μm, Compared to a conventional polishing pad containing a polyurethane resin sheet containing the same type of polyurethane but having a low proportion of openings of 10 to 20 μm, it is less likely to thermally expand. Therefore, it is considered that the shape of the polishing pad hardly changes and a stable polishing rate can be obtained regardless of the number of objects to be polished.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these examples. Unless otherwise specified, “parts” means parts by mass.

[Comparative Example 1]
100% modulus 3.5 MPa polyester polyurethane resin-containing DMF solution (solid content concentration 30% by mass) (100 parts), DMF (40 parts), poor solvent water (2 parts), nonionic hydrophobic additive ( By mixing 5 parts), a resin-containing solution was obtained.
The obtained resin-containing solution was cast on a polyester film (thickness: 188 μm). When applying the resin solution onto the film-forming substrate, the clearance of the coating device was set to 1.4 mm. Thereafter, the polyester film casted with the resin-containing solution was immersed in a coagulation bath (coagulation liquid was water) at 18 ° C. for 60 minutes to solidify the resin-containing solution, and then washed and dried to obtain a polyurethane resin sheet. .
The skin layer side formed on the surface of the obtained polyurethane resin sheet was ground (grinding amount: 200 μm). Thereafter, a PET base material is bonded to the surface of the polyurethane resin sheet opposite to the ground surface through an adhesive, and the ground surface of the polyurethane resin sheet is embossed with a grid mold, And a double-sided tape were bonded together to obtain a polishing pad having a thickness of 1.25 mm.

[Example 1]
100% modulus 3.5 MPa polyester polyurethane resin-containing DMF solution (solid content concentration 30% by mass) (100 parts), DMF (40 parts), poor solvent water (2 parts), silicon-based nonionic surfactant (5 parts) and a 20% cellulose acetate DMF solution (2 parts) were mixed to obtain a resin-containing solution.
The obtained resin-containing solution was cast on a polyester film (thickness: 188 μm). When applying the resin solution onto the film-forming substrate, the clearance of the coating device was set to 1.4 mm. Thereafter, the polyester film casted with the resin-containing solution was immersed in a coagulation bath (coagulation liquid was water) at 18 ° C. for 60 minutes to solidify the resin-containing solution, and then washed and dried to obtain a polyurethane resin sheet. .
The skin layer side formed on the surface of the obtained polyurethane resin sheet was ground (grinding amount: 200 μm). Thereafter, a PET base material is bonded to the surface of the polyurethane resin sheet opposite to the ground surface through an adhesive, and the ground surface of the polyurethane resin sheet is embossed with a grid mold, And a double-sided tape were bonded together to obtain a polishing pad having a thickness of 1.25 mm.

[Comparative Example 2]
100% modulus 6.0MPa polyester polyurethane resin-containing DMF solution (solid content concentration 30% by mass) (100 parts), DMF (30 parts), and poor solvent water (5 parts) A solution was obtained.
A polishing pad having a thickness of 1.25 mm was produced in the same manner as in Comparative Example 1 using the obtained resin-containing solution.
[Example 2]
100% modulus 6.0 MPa polyester polyurethane resin-containing DMF solution (solid content concentration 30% by mass) (100 parts), DMF (30 parts), poor solvent water (5 parts), and 20% cellulose acetate DMF A resin-containing solution was obtained by mixing the solution (2 parts).
A polishing pad having a thickness of 1.25 mm was produced in the same manner as in Example 1 using the obtained resin-containing solution.
[Comparative Example 3]
A polishing pad having a thickness of 1.05 mm was produced in the same manner as in Comparative Example 2 except that the clearance of the coating apparatus was set to 1.2 mm.
[Comparative Example 4]
A polishing pad having a thickness of 1.050 mm was produced in the same manner as in Example 2 except that the clearance of the coating apparatus was set to 1.2 mm.

About each polishing pad of Examples 1-2 and Comparative Examples 1-4, the ratio (%) of the total area of the opening part of the opening diameter 10-20 micrometers occupied in the total area of the opening part of the opening diameter 1-20 micrometers, opening diameter 1 The ratio (%) of the number of openings having an opening diameter of 10 to 20 μm to the number of openings of ˜20 μm, the number of openings of 1 to 20 μm and 10 to 20 μm per cut surface of 10,000 μm ² , and the heat at 20 to 60 ° C. The amount of expansion (μm) and the coefficient of thermal expansion (%) at 20 to 60 ° C. were measured. The results are shown in Tables 1-2.
In addition, the measuring method of each item is as follows.

<Measurement of aperture area and numerical aperture>
(1) The ratio (%) of the total area of the openings with an opening diameter of 10 to 20 μm in the total area of the openings with an opening diameter of 1 to 20 μm, and the opening diameter of 10 to 20 μm with respect to the number of openings with an opening diameter of 1 to 20 μm Measurement of the percentage (%) of the number of openings in:
The measurement of the opening diameter and the numerical aperture of the internal cross section of the polyurethane resin sheet was carried out with a scanning electron microscope (manufactured by JEOL Ltd., JSM-5500LV). This image is binarized by image processing software (Image Analyzer V20LAB Ver. 1.3, manufactured by Nikon) to confirm the number of openings in the measurement area area 30929.883 μm ² , and from the area of each opening to the circle The equivalent diameter was calculated as the opening diameter. Nine cross-sections obtained by cutting the polyurethane resin sheet in the thickness direction were observed, and the ratio (%) of the total area of the openings having an opening diameter of 10 to 20 μm in the total area of the openings having an opening diameter of 1 to 20 μm Asked. In addition, the opening diameter is divided into 1 μm and the number of openings of each size is totaled, and the ratio (%) of the number of openings having an opening diameter of 10 to 20 μm to the number of openings having an opening diameter of 1 to 20 μm is obtained. It was. The results are shown in Tables 1-2.
At the time of measurement, the contrast was adjusted so that an opening recognizable from the SEM image can be accurately captured by binarization processing. In this example, an SEM image was taken under the conditions of an SEM magnification of 600 times, an acceleration voltage of 20 kV, a spot size of 25, and a working distance of 21 mm so that the opening can be correctly captured during binarization processing.
(2) Measurement of the number of openings of 1 to 20 μm and 10 to 20 μm per cut surface of 10,000 μm ² :
The number of openings having an opening diameter of 1 to 20 μm and the number of openings having an opening diameter of 10 to 20 μm present per 10000 μm ² cross section obtained by cutting the polyurethane resin sheet in the thickness direction was measured. The results are shown in Tables 1-2. As a measurement cross section, a cross section having no tear-shaped bubbles was selected.

<Measurement of thermal expansion amount and thermal expansion coefficient at 20 to 60 ° C.>
Using a thermomechanical analyzer “RSAIII” manufactured by TA Instruments Japan, the polishing pad from which the release paper of the double-sided tapes of Examples and Comparative Examples was peeled was cut into 8 mm width × 12 mm length and embossed. A compressive load of 100 g (104 gf / cm ² as pressure) is applied to the surface, the temperature is raised from 0 ° C. to 100 ° C. at a rate of temperature rise of 5 ° C./min, and the polishing pad is in a temperature range of 20 to 60 ° C. corresponding to the polishing temperature The thickness of was measured. Based on the value of the polishing pad thickness (A) at a room temperature of 20 ° C. and the value of the polishing pad thickness (B) at a temperature where the thermal expansion was the largest between 20 ° C. and 60 ° C. The amount of thermal expansion (displacement) was determined. Further, the thermal expansion coefficient (%) of the polishing pad was determined by (B−A) / A × 100. The measurement was performed twice, and the average value was taken as the measurement result. Note that the number of the convex portions and the area of the sample piece may be adjusted according to the emboss size and shape, and in this measurement, the convex portion is completely included, not the sample piece partially including the convex portion. Sample pieces were used. The results are shown in Tables 1-2 and FIGS.

<Evaluation>
Using the polishing pads of Examples 1 and 2 and Comparative Examples 1 to 4, polishing rate stability, polishing uniformity, and the number of start-up treatments were evaluated. The polishing rate is expressed by dividing the polishing amount, which is the difference in film thickness before and after polishing, by the polishing time, and was obtained from the average value of the thickness measurement results at 121 locations for each of the silicon wafers before and after polishing. . For the thickness measurement, an optical film thickness measuring device (manufactured by KLA Tencor, trade name “ASET-F5x”, measurement: DBS mode) was used. As an object to be polished, a substrate (uniformity (CV%) of 13%) in which tetraethoxysilane was formed on a 12-inch silicon wafer by CVD so that the insulating film had a thickness of 1 μm was used. The polishing conditions used in the above test are as follows.
・ Use polishing machine: EBARA F-REX300
Polishing pressure: 2.5 psi
・ Abrasive: Slurry for Planer CuBM ・ Abrasive temperature: room temperature ・ Work (object to be polished): 300 mmφ SIO2 (TEOS)
・ Dressing: 3M A188
・ Pad break 9N × 30min, diamond dresser 54rpm, surface plate rotation speed 80rpm, ultrapure water 200ml / min
・ Polishing platen rotation speed 70rpm, head rotation speed 71rpm, slurry flow rate 200ml / min, polishing time 60 seconds

(1) Evaluation of Polishing Rate Stability and Polishing Uniformity Each polishing rate from 1 to 100 wafers is determined, and the maximum, minimum, and average polishing rates for each polishing rate from 10 to 100 are obtained. The value and the standard deviation of the polishing rate were determined, and polishing rate variability and polishing nonuniformity were calculated by the following formulas.
Polishing rate variability (%) = (polishing rate maximum value−polishing rate minimum value) / polishing rate average value × 100
Polishing nonuniformity (%) = (polishing rate standard deviation / polishing rate average value) × 100
The lower the polishing rate variability, the higher the polishing rate stability. Moreover, it was evaluated that the lower the numerical value of the non-uniformity in polishing, the less the non-uniformity in polishing and the uniform polishing of the wafer surface, that is, the better the polishing uniformity. The results are shown in Tables 3-4.

(2) Evaluation of the number of start-up treatments It was evaluated as follows whether or not the polishing rate at the initial stage of polishing was quickly stabilized. That is, the polishing rate with respect to the number of wafers to be polished was tracked, and the number of polishing processes in which the increase in the polishing rate as a trend was not observed was defined as the “number of startup processes”. It means that the smaller the “number of start-up treatments”, the faster the polishing rate at the initial stage of polishing is stabilized. The results are shown in FIGS.

As can be seen from the results of Table 3 and FIG. 9, the polishing pad of Comparative Example 1 having a small area ratio of the opening with the opening diameter of 10 to 20 μm with respect to the total area of the opening with the opening diameter of 1 to 20 μm has a polishing rate at the initial stage of polishing. It was necessary to polish about 10 workpieces to stabilize to some extent, and the start-up property was bad (start-up processing time was long). Further, the polishing rate fluctuated greatly during polishing of 10 to 100 workpieces, and the polishing rate stability was poor. On the other hand, the polishing pad of Example 1 in which the area ratio of the opening having an opening diameter of 10 to 20 μm was as large as 45.1% did not take time to rise and was excellent in polishing rate stability. Also, the polishing uniformity was excellent.
As can be seen from the results of Table 4 and FIG. 10, the polishing pads of Comparative Examples 2 to 4 having a small area ratio of the openings having an opening diameter of 10 to 20 μm with respect to the total area of the openings having an opening diameter of 1 to 20 μm are 10 to 100 polishing pads. The polishing rate fluctuated greatly during the polishing of the workpiece, and the polishing rate stability was poor. Also, the polishing uniformity was inferior. On the other hand, the polishing pad of Example 2 in which the area ratio of the opening having an opening diameter of 10 to 20 μm was as large as 17.1% showed very small fluctuations in the polishing rate and was excellent in polishing rate stability. Also, the polishing uniformity was good.

  The polishing pad of the present invention can polish an object to be polished continuously at a stable polishing rate. Further, the startup processing time can be eliminated or shortened as much as possible. Therefore, the polishing pad and the manufacturing method thereof of the present invention have industrial applicability.

Claims (7)

A polishing pad comprising a polyurethane resin sheet containing a plurality of tear-shaped bubbles formed by a wet film formation method and a plurality of microbubbles having a smaller size than the tear-shaped bubbles,
The polyurethane resin sheet has a polishing surface for polishing an object to be polished,
The micro bubbles are bubbles forming an opening having an opening diameter of 1 to 20 μm on an arbitrary cut surface in the thickness direction of the polyurethane resin sheet, and
In an arbitrary cut surface in the thickness direction, the ratio of the total area of the openings having an opening diameter of 10 to 20 μm in the total area of the openings having an opening diameter of 1 to 20 μm is 15 to 60%. The polishing pad.   In the cut surface of the polyurethane resin sheet, a ratio of the number of openings having the opening diameter of 10 to 20 μm to the number of openings having the opening diameter of 1 to 20 μm is 4.5 to 30%. The polishing pad according to claim 1. When the thickness of the polishing pad at 20 ° C. is A, and the thickness of the polishing pad at the temperature at which the thickness is maximum between 20 ° C. and 60 ° C. is B, the coefficient of thermal expansion X calculated by the following formula is 3%. The polishing pad according to claim 1 or 2, which is less than 1.
Thermal expansion coefficient X = (B−A) / A × 100 The polishing pad according to any one of claims 1 to 3, wherein 6 to 50 openings having an opening diameter of 10 to ²⁰ µm per 10,000 µm ² are present on the cut surface of the polyurethane resin sheet. Preparing a polyurethane resin-containing solution comprising a polyurethane resin and cellulose acetate;
Applying the polyurethane resin-containing solution onto a film-forming substrate; and immersing the film-forming substrate on which the solution is applied in a coagulation liquid to solidify the solution;
The manufacturing method of the polishing pad of any one of Claims 1-4 containing this.   The manufacturing method of Claim 5 which apply | coats the said polyurethane resin containing solution on a film-forming base material with the thickness of 1.3-3.0 mm.   The production method according to claim 5 or 6, wherein the polyurethane resin-containing solution further contains a hydrophobic additive.