JP2018182248A - Polishing pad and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing pad which enables the polishing of a semiconductor wafer backside, and the formation of a gettering layer without causing fiber falling.SOLUTION: A polishing pad comprises a polyvinyl acetal-based resin foaming body impregnated with a polyurethane resin and silicon carbide as a polishing layer. The polishing pad is used to polish a semiconductor wafer backside in wet manner to form a gettering layer. The polyvinyl acetal-based resin is a polyvinyl formal-based resin. The silicon carbide is included in the polyvinyl acetal-based resin foaming body impregnated with the polyurethane resin and silicon carbide within a range of 30-70 mass%.SELECTED DRAWING: None

Description

  The present invention relates to a polishing pad and a method of manufacturing the same. In particular, the present invention relates to a polishing pad for polishing the back surface of a semiconductor wafer and a method of manufacturing the same.

When manufacturing semiconductor devices, it is necessary to form a gettering layer together with thinning and stress relief to 100 microns or less (stress relief means removal of damage generated on the wafer grinding surface by grinding) (Gettering means the collection of metal ions that contaminate the environment).
Conventionally, the gettering layer has been formed by dry polishing using a fixed abrasive type polishing pad or a grinding wheel. For example, Patent Document 1 discloses that a fixed layer serving as a gettering site for metal impurities is formed by polishing the back surface of a semiconductor wafer using fixed abrasives. Further, Patent Document 2 discloses a method of performing gettering processing by grinding the back surface of a semiconductor device with a grinding stone in which diamond abrasive grains having a particle diameter of 4 μm or less are solidified with a bonding material. Patent Document 3 discloses a processing method for suitably applying a gettering layer by polishing the back surface of a wafer with a polishing member in which abrasive grains having an average particle diameter of 5 μm or less are dispersed.

  However, since the grinding wheels and the like used in Patent Documents 1 to 3 are all used to polish (dry-polish) semiconductor wafers without using a slurry, in the formation of the gettering layer by these dry-grade polishes, dusts are generated at the time of polishing Has the disadvantage of causing In addition, when using the polishing member of Patent Document 3, it is necessary to perform thinning processing and stress relief by performing polishing and etching in the previous step of gettering formation, and there is a problem in terms of work efficiency and cost. The

  On the other hand, as a polishing pad used for wet polishing instead of dry polishing, for example, Patent Document 4 discloses a polishing pad in which abrasive grains and alkaline particles are contained in foamed polyurethane. The polishing pad uses pure water as a polishing solution to form a gettering layer on the back surface of the wafer. Patent Document 5 discloses a polishing cloth in which abrasive grains are fixed to the surface of a porous non-woven fabric obtained by impregnating a polyester felt with polyurethane.

JP, 2005-72150, A JP 2005-317846 A JP, 2007-242902, A Unexamined-Japanese-Patent No. 2010-225987 Unexamined-Japanese-Patent No. 2002-231669

However, since the polishing pad described in Patent Document 4 is made of foamed polyurethane and has independent cells, there is a problem that clogging is easily caused by polishing debris and the like. Moreover, since the resin hardness used for foaming polyurethane was high, it had the fault that the thinned wafer was easy to be broken.
In addition, when the back surface of the semiconductor wafer is polished using the polishing cloth described in Patent Document 5, the fibers of the non-woven fabric are dropped off, which causes a problem that a defect of the semiconductor wafer occurs.

  The present invention has been made in view of the above-mentioned problems of the prior art, and performs well polishing (thining processing, stress relief) of a back surface of a semiconductor wafer and formation of a gettering layer without dropping of fibers. It is an object of the present invention to provide a polishing pad that can be used.

As a result of intensive investigations for the above problems, the present inventors have used a polishing pad having a polyvinyl acetal resin foam impregnated with a polyurethane resin and silicon carbide as a polishing layer, without fibers falling off. The inventors have found that it is possible to obtain a polishing pad capable of forming a gettering layer while thinning and relieving the back surface of a semiconductor wafer and completing the present invention.
That is, the present invention provides the following.

[1] A polishing pad having a polyvinyl acetal resin foam impregnated with a polyurethane resin and silicon carbide as a polishing layer.
[2] The polishing pad according to [1], for wet polishing the back surface of a semiconductor wafer.
[3] The polishing pad according to [2], for forming a gettering layer by wet polishing the back surface of the semiconductor wafer.
[4] The polishing pad according to any one of [1] to [3], wherein the polyvinyl acetal resin is a polyvinyl formal resin.
[5] Any one of [1] to [4], wherein silicon carbide is contained in a range of 30 to 70% by mass in a polyvinyl acetal resin foam formed by impregnating a polyurethane resin and silicon carbide Polishing pad.
[6] The polishing pad according to any one of [1] to [5], wherein the particle diameter of silicon carbide is in the range of 0.3 to 5.0 μm.
[7] Any one of [1] to [6], wherein the polyvinyl acetal resin is contained in the range of 5 to 25% by mass in a polyvinyl acetal resin foam formed by impregnating a polyurethane resin and silicon carbide. The polishing pad as described in.
[8] The polyurethane resin is contained in the range of 15 to 60% by mass in the polyvinyl acetal resin foam formed by impregnating the polyurethane resin and silicon carbide, according to any one of [1] to [7] Polishing pad.
[9] The polishing pad according to any one of [1] to [8], wherein the polyvinyl acetal resin foam impregnated with a polyurethane resin and silicon carbide further contains a fluorine-based water repellent.
[10] preparing a polyurethane resin solution containing a polyurethane resin and silicon carbide,
A step of impregnating the polyvinyl acetal resin foam substrate with a polyurethane resin solution, and immersing the polyvinyl acetal resin foam substrate impregnated with the polyurethane resin solution in a coagulating liquid to coagulate the polyurethane resin,
The manufacturing method of the polishing pad in any one of [1]-[9] containing these.

  According to the present invention, it is possible to provide a polishing pad capable of polishing the back surface of a semiconductor wafer and forming a gettering layer without dropping of fibers.

<< Polishing pad >>
The polishing pad of the present invention is characterized in that it is a polishing pad having as a polishing layer a polyvinyl acetal resin foam (hereinafter sometimes referred to as polyurethane resin-containing foam) impregnated with a polyurethane resin and silicon carbide. .
In the present specification and claims, “polyvinyl acetal resin foam impregnated with polyurethane resin and silicon carbide” refers to polyvinyl acetal resin foam impregnated with a solution containing polyurethane resin and silicon carbide It also refers to those obtained by coagulating the polyurethane resin by wet coagulation treatment. The above expression distinguishes the product obtained by coagulating the polyurethane resin and the polyvinyl acetal resin after mixing the polyurethane resin dissolved in the solvent, the polyvinyl acetal resin dissolved in the solvent, and the silicon carbide. Used for
The above expression can be rephrased as, for example, a polyvinyl acetal resin foam containing polyurethane resin and silicon carbide in the foam void portion.

（式中、Ｒは水素原子又は炭素数１〜５のアルキル基を表す。）
Ｒは、水素原子又は炭素数１〜３のアルキル基であることが好ましく、水素原子であることがより好ましい。
ビニルアセタール単位は、ビニルホルマール単位（上記式中、Ｒ＝水素原子）又はビニルブチラール単位（上記式中、Ｒ＝炭素数３のアルキル基）であることが好ましく、ビニルホルマール単位であることがより好ましい。従って、ポリビニルアセタール系樹脂は、ポリビニルホルマール系樹脂又はポリビニルブチラール系樹脂が好ましく、ポリビニルホルマール系樹脂がより好ましい。 (Polyvinyl acetal resin foam)
In the polishing pad of the present invention, a polyvinyl acetal resin foam used as a substrate for containing a polyurethane resin and silicon carbide has a sponge-like structure having a void. The polyvinyl acetal resin foam can be obtained by foaming a polyvinyl acetal resin.
A polyvinyl acetal resin has a vinyl acetal unit as a basic unit (a structural unit, a repeating unit) which comprises resin. The vinyl acetal unit is preferably a unit of the following structure.

(Wherein R represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms)
R is preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and more preferably a hydrogen atom.
The vinyl acetal unit is preferably a vinyl formal unit (in the above formula, R = hydrogen atom) or a vinyl butyral unit (in the above formula, R = an alkyl group having 3 carbon atoms), and more preferably a vinyl formal unit preferable. Therefore, polyvinyl formal resin or polyvinyl butyral resin is preferable, and polyvinyl formal resin is more preferable.

The polyvinyl acetal resin can be obtained, for example, by acetalization by reacting polyvinyl alcohol with an aldehyde using an acid as a catalyst. In addition, after polyvinyl acetate is hydrolyzed to obtain polyvinyl alcohol, the obtained polyvinyl alcohol can be obtained by acetalization by reacting it with an aldehyde using an acid as a catalyst. Since it is difficult to completely react polyvinyl alcohol or polyvinyl acetate to completely convert to polyvinyl acetal, polyvinyl acetal resins are generally used as structural units (repeating units) constituting a resin, in addition to vinyl acetal units, vinyl alcohol units _{(-CH 2 -CH (OH) -} ) and / or vinyl acetate units _{(-CH 2 -CH (OCOCH 3)} -) may have.
In the present specification and claims, the "polyvinyl acetal resin" refers to a resin containing a vinyl acetal unit and optionally having a vinyl alcohol unit and / or a vinyl acetate unit.
The total of vinyl acetal units, vinyl alcohol units and vinyl acetate units in the total structural units constituting the polyvinyl acetal resin is preferably 50 mol% or more, more preferably 70 mol% or more, and 80 It is further more preferable that it is mol% or more, still more preferably 90 mol% or more, and it may be 100 mol%.
As an example of polyvinyl acetal type-resin, Bel eater A (The Aeon Co., Ltd. make, polyvinyl formal-type resin) etc. are mentioned, for example.

  In the present specification and claims, when referring to a polyvinyl acetal resin foam or a polyvinyl acetal resin foam substrate, a polyvinyl acetal as a substrate for impregnating a resin solution containing a polyurethane resin and silicon carbide. In the case of a polyvinyl acetal resin foam impregnated with a polyurethane resin and silicon carbide, it refers to a polyurethane resin and a polyurethane resin after being impregnated with a resin solution containing a polyurethane resin and silicon carbide and wet-set It refers to a polyvinyl acetal resin foam containing silicon carbide. In the case of a polyvinyl acetal resin foam substrate impregnated with a polyurethane resin solution, the polyvinyl acetal resin foam substrate in a state containing the polyurethane resin solution after the polyvinyl acetal resin foam substrate is impregnated with the polyurethane resin solution. Point to

By using a polyvinyl acetal-based resin foam as a substrate, it is possible to prevent the falling off of the fiber which causes a problem in a polishing pad having a nonwoven fabric as a substrate. In addition, the dressing allowance (the amount of shaving) at the time of dressing can be reduced, and the product life of the polishing pad can also be improved.
As a manufacturing method of polyvinyl acetal type-resin foam | form, what is necessary is just to use a well-known method, For example, it can obtain by block molding etc. by a metal mold | die by the manufacturing method of Unexamined-Japanese-Patent No. 10-338765.
In the polishing pad of the present invention, the polyvinyl acetal resin is contained in the range of 5 to 25% by mass in the polyvinyl acetal resin foam (polyurethane resin-containing foam) impregnated with a polyurethane resin and silicon carbide. It is preferable that it is included in the range of 10 to 20% by mass, and still more preferably included in the range of 12 to 18% by mass.
When the content of the polyvinyl acetal resin is in the above range, the polyvinyl acetal resin holds the polyurethane resin and the silicon carbide as the aggregate and contributes to the polishing, whereby the gettering layer can be formed.
The density of the polyvinyl acetal resin foam as a substrate, is preferably 0.05~0.20g / cm ^3, more preferably 0.05~0.15g / cm ^3, 0.06~ Even more preferably, it is 0.12 g / cm ³ . When the density of the polyvinyl acetal resin foam is within the above range, a polyurethane resin containing more silicon carbide can be impregnated into the polyvinyl acetal resin foam, and the silicon carbide content can be increased. it can.
The average cell diameter of the cells present in the polyvinyl acetal resin foam as a substrate is preferably 1 to 10000 μm, more preferably 5 to 5000 μm, and still more preferably 10 to 2000 μm, It is further more preferable that it is 50-1500 micrometers, and it is still more preferable that it is 80-1200 micrometers. The average bubble diameter is obtained, for example, by imaging the surface of the polyvinyl acetal resin foam by using a scanning electron microscope (SEM) at a magnification of 250 times and taking an image obtained by binarizing the image with image processing software. It can measure by calculating from the area.
There is no restriction | limiting in particular as thickness of the polyvinyl acetal type-resin foam as a base | substrate, For example, 1.0-20.0 mm may be sufficient and 1.5-8.0 mm may be sufficient, 2.0 It may be ~ 6.0 mm.

(Silicon carbide)
The polishing pad of the present invention comprises silicon carbide (SiC).
0.3 to 5.0 μm is preferable, 0.3 to 4.0 μm is more preferable, 0.3 to 3.0 μm is still more preferable, and the particle diameter of silicon carbide used in the polishing pad of the present invention is 0 The thickness is more preferably 0.3 to 2.0 μm, still more preferably 0.3 to 1.0 μm, still more preferably 0.4 to 0.8 μm, and particularly preferably 0.6 μm. In the present specification and claims, the "particle size" of silicon carbide means the median size.
If the particle size of silicon carbide is in the above range, defects of the silicon crystal lattice can be formed without damaging the wafer, and a gettering layer can be formed in which sufficient gettering performance can be obtained.
In the polishing pad of the present invention, silicon carbide is preferably contained in a range of 30 to 70% by mass, and more preferably contained in a range of 35 to 65% by mass in the polyurethane resin-containing foam. It is even more preferable to be included in the range of 40 to 60% by mass, and even more preferable to be included in the range of 45 to 60% by mass.
When the content of silicon carbide is in the above range, defects of the silicon crystal lattice can be formed with a sufficient density, and a gettering layer can be formed in which gettering performance can be obtained.

(Polyurethane resin)
There is no restriction | limiting in particular in the kind of polyurethane resin used as the material of the polishing pad of this invention, It can select from various polyurethane resin according to the intended purpose. For example, one or more resins of polyester type, polyether type or polycarbonate type can be used.
Examples of polyester resins include polymers of polyester polyols of ethylene glycol, butylene glycol, etc. and adipic acid, etc., and diisocyanates 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 polycarbonate resins include polymers of polycarbonate polyols and isocyanates such as diphenylmethane-4,4'-diisocyanate. These resins are commercially available under the trade names “Kurisbon” manufactured by DIC Corporation, “Samprene” manufactured by Sanyo Chemical Industries, Ltd., and “Resamine” manufactured by Dainichi Seika Kogyo Co., Ltd. Available resins may be used, or resins having desired properties may be produced by themselves.
Among these, polyether polyurethane resins having high chemical stability are particularly preferable.
In the polishing pad of the present invention, the polyurethane resin is preferably contained in the range of 15 to 60% by mass, and more preferably in the range of 20 to 55% by mass, in the polyurethane resin-containing foam. It is even more preferable to be included in the range of 25 to 45% by mass, and even more preferable to be included in the range of 25 to 40% by mass.
If the content of the polyurethane resin is in the above range, silicon carbide attached to the polyurethane resin has cushioning properties, and gettering performance can be obtained without damaging the wafer.

The polyurethane resin preferably has a resin modulus of 1.0 to 60.0 MPa, more preferably 20 to 60 MPa, and still more preferably 30 to 50 MPa. When the resin modulus is in the above range, the retention of silicon carbide is excellent, and the self-disintegrating property of the resin stabilizes the polishing characteristics.
The resin modulus is an index that represents the hardness of the resin, and is the value obtained by dividing the load applied when the non-foamed resin sheet is stretched 100% (when it is stretched twice the original length) by the cross-sectional area (Hereafter, it may be called 100% modulus.) The higher this value, the harder the resin.

(Water repellent)
The polyurethane resin-containing foam in the polishing pad of the present invention may further contain a water repellent. By including the water repellent, it is possible to suppress the swelling of the polishing pad that may occur by absorbing the slurry and water during polishing, and to suppress the temporal change of the shape of the polishing pad due to the swelling. Therefore, the temporal stability of the polishing characteristics can be improved. Examples of the water repellent include fluorine-based water repellents such as NK Guard S series (Nicca Chemical Co., Ltd.) and Klisbon Axistar SD series (DIC Company). As the water repellent, one water repellent may be used alone, or two or more water repellents may be used in combination.
The water repellent agent is preferably contained in the polyurethane resin-containing foam in the range of 0.1 to 5% by mass, more preferably in the range of 0.5 to 4% by mass, and 1 to 1 Even more preferably, it is included in the range of 3% by mass.

(Crosslinking agent)
The polyurethane resin-containing foam in the polishing pad of the present invention may further contain a crosslinking agent. By including the crosslinking agent, the polishing pad becomes hard, and swelling of the polishing pad which can be generated by absorbing the slurry and water during polishing can be suppressed, the form of the polishing pad is stabilized, and the stability of the polishing characteristics is further increased. It can be improved. Examples of the crosslinking agent include aliphatic polyisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate and hexamethylene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI) and 2,4-tolylene diisocyanate (2, Examples thereof include polyvalent isocyanate-based crosslinking agents such as aromatic polyisocyanates such as 4-TDI) and 2,6-tolylene diisocyanate (2,6-TDI).
The crosslinking agent is preferably contained in the range of 2.0 to 18.0% by mass, more preferably in the range of 6.0 to 12.0% by mass, in the polyurethane resin-containing foam. .

(Other ingredients)
The polyurethane resin-containing foam in the polishing pad of the present invention may further contain other components in addition to the above components as long as the effects of the present invention are not impaired. Other components include higher alcohols, polyether derivatives, fatty acids, fatty acid salts, cellulose derivatives, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, paraffins, organic silicones, Carbon, organic pigments, inorganic pigments, antioxidants and the like can be mentioned. When other components are included, the other components are preferably contained in the polyurethane resin-containing foam in a proportion of 10% by mass or less, and more preferably in a proportion of 3% by mass or less.

<Physical properties of polishing pad>
(density)
The polishing pad of the present invention, the density of the polyurethane resin-containing foam is preferably 0.40~0.90g / cm ^3, more preferably in the range of 0.50~0.90g / cm ³ It is still more preferable to set it as the range of 0.50-0.80 g / cm < ³ >, and it is still more preferable to set it as the range of 0.50-0.70 g / cm < ³ >. When the density of the polyurethane resin-containing foam is in the above range, the gettering layer can be easily formed on the back surface of the semiconductor wafer in contact with the polishing surface of the polishing pad.

(A hardness)
In the present specification, the A hardness means a value measured according to JIS K7311.
In the polishing pad of the present invention, the A hardness of the polyurethane resin-containing foam is preferably 50 to 100 degrees, more preferably 60 to 90 degrees, and still more preferably 70 to 90 degrees. When the A hardness is within the above range, since it is appropriately hard, it is easily scratched, and the occurrence of uneven polishing and chipping can also be reduced.

(Thickness)
The thickness of the polyurethane resin-containing foam in the polishing pad of the present invention is not particularly limited, and is, for example, about 0.5 to 10.0 mm, preferably about 1.0 to 8.0 mm, more preferably 1.5 to 6. It can be about 0 mm.

<< Other layers >>
In the polishing pad of the present invention, another layer (lower layer, support layer) may be bonded to the surface opposite to the surface (polishing surface) on which the object to be polished is polished. The kind of other layer is not specifically limited, For example, a cushioning layer can be bonded together.
In the present specification and claims, the cushion layer means a layer having the same or smaller A hardness than the polishing layer. By providing the cushion layer, the influence of the hardness and flatness of the surface plate can be mitigated, and unevenness in contact between the work and the polishing surface can be prevented. Therefore, the service life of the polishing pad can be extended, and chipping (chipping around the workpiece) can be prevented.
As a material of the cushion layer, resin-impregnated non-woven fabric, synthetic rubber, polyethylene foam, polyurethane foam or the like can be used.
The thickness of the cushion layer is not particularly limited, but is preferably 0.1 to 10 mm, and more preferably 0.5 to 3 mm or so without mechanical restriction of the polishing mechanism, and a polishing plate You can reduce the impact of

  In the case where the polishing pad forms a multilayer structure, a plurality of layers may be adhered and fixed while being pressurized if necessary using a double-sided tape, an adhesive or the like. There is no particular limitation on the double-sided tape and adhesive used in this case, and any double-sided tape and adhesive known in the art can be selected and used.

(Use)
The polishing pad of the present invention can be suitably used as a polishing pad for wet-polishing an object (object to be polished). In the present specification and claims, wet polishing is a polishing method for polishing using slurry, water or the like, and it is possible to use a polishing pad as an object (object to be polished) without using slurry, water or the like. This is clearly distinguished from dry polishing in which polishing is performed by direct contact.
The polishing pad of the present invention is a back surface of a silicon wafer, a semiconductor wafer of SiC, GaAs, GaN or the like, or a compound-based wafer such as sapphire (here, the back surface is opposite to the surface of the wafer on which the semiconductor element is formed. Can be suitably used as a polishing pad for wet polishing of a surface. Among these, the polishing pad of the present invention can be particularly suitably used as a polishing pad for wet-polishing the back surface of a silicon-based semiconductor wafer, and is for wet-polishing the back surface of the semiconductor wafer to form a gettering layer. It can be suitably used as a polishing pad of

The silicon carbide used in the present invention is very poor in handleability (high mechanical abrasiveness, poor dispersibility, high sedimentation rate, difficult waste solution treatment). Therefore, for example, when a slurry containing silicon carbide as abrasive grains is dropped onto a conventional polishing pad to form gettering on the back surface of a semiconductor wafer, it is necessary to increase the mechanical load to improve the dispersibility of silicon carbide. However, when the mechanical load is increased, silicon carbide polishes a mechanical surface such as a tube while the slurry is transported to the surface of the polishing pad through the tube or the like, resulting in contamination due to device wear. Moreover, there is also a problem that the handling itself is difficult because the silicon carbide settling speed is high.
The same problem arises when silicon carbide is internally added to a polyurethane foam polishing pad. That is, in the polyurethane foam type polishing pad, the silicon carbide needs to be mixed with the high viscosity resin, so the dispersibility of the silicon carbide is further deteriorated. Therefore, the mechanical load is increased in order to enhance the dispersibility, and mechanical wear due to silicon carbide tends to occur. As a result, contamination occurs in the polishing pad, which adversely affects polishing and gettering.
On the other hand, in the polishing pad of the present invention, since silicon carbide is contained in the polyvinyl acetal resin foam, no problem occurs when using silicon carbide in the slurry. That is, since the polishing pad of the present invention disperses silicon carbide in a resin solution and impregnates the polyvinyl acetal resin foam substrate with the resin solution, it can be uniformly dispersed without increasing the mechanical load. . As a result, there is little contamination due to device wear. There is no need to consider the settling speed of silicon carbide. Furthermore, since it is self-disintegrating, by conditioning with a dresser, the polished surface can be regenerated, and the effect of the present invention can be sustained for a long time.
The polishing pad of the present invention can be preferably produced by the following method.

<< Method of manufacturing polishing pad >>
The method for producing a polishing pad according to the present invention comprises the steps of: preparing a polyurethane resin solution containing a polyurethane resin and silicon carbide; impregnating a polyurethane resin solution into a polyvinyl acetal resin foam substrate; and polyvinyl impregnated with a polyurethane resin solution. And immersing the acetal resin foam base in a coagulating liquid to coagulate the polyurethane resin.

<Preparation process of resin solution>
In this preparation process, a polyurethane resin solution containing a polyurethane resin and silicon carbide is prepared. As a resin as a raw material, the resin described in the section of << Polishing pad >> can be used. Further, as a solvent for dissolving the resin, N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), isopropyl alcohol (IPA), methyl ethyl ketone (MEK), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO) And acetone, acetonitrile, N-methyl pyrrolidone (NMP) and the like and mixtures thereof. Among these, DMF is preferred.
The silicon carbide may be added to the solvent before the resin is dissolved in the solvent, or may be added after the resin is dissolved in the solvent. By doing so, silicon carbide can suppress aggregation and can be uniformly dispersed in a resin solution.
5-50 mass parts is preferable with respect to 100 mass parts of solvents, 10-40 mass parts is more preferable, and, as for the quantity of the polyurethane resin to be used, 15-30 mass parts is still more preferable.
The amount of silicon carbide to be used is preferably 10 to 60 parts by mass, more preferably 15 to 55 parts by mass, and still more preferably 30 to 50 parts by mass with respect to 100 parts by mass of the solvent.
In addition, in the preparation step, components other than the above components may be added. Other components include water repellents and crosslinking agents. By adding a water repellent or a crosslinking agent, it is possible to suppress swelling due to absorption of slurry or water at the time of polishing processing of the obtained polishing pad, and to maintain the shape of the polishing pad. Thereby, the stability of the polishing characteristics can be further improved. As the water repellent and the crosslinking agent, those described above in the section << Polishing pad >> can be used.
When a water repellent is added, the amount of the water repellent used is preferably 0.1 to 5 parts by mass, more preferably 0.5 to 4 parts by mass, and 1 to 3 parts by mass with respect to 100 parts by mass of the solvent. Is even more preferred.
When a crosslinking agent is added, the amount of the crosslinking agent to be used is preferably 1 to 20 parts by mass, and more preferably 5 to 15 parts by mass with respect to 100 parts by mass of the solvent.

<Impregnation process>
Next, a polyvinyl acetal resin foam base is prepared, and the polyvinyl acetal resin foam base is immersed (impregnated) in a polyurethane resin solution. As the polyvinyl acetal resin foam and the polyvinyl acetal resin constituting the foam, the polyvinyl acetal resin foam and the polyvinyl acetal resin described in the section of << Polishing Pad >> can be used. The temperature and time of the immersion treatment are not particularly limited as long as the polyurethane resin solution sufficiently penetrates into the polyvinyl acetal resin foam base, and for example, it may be immersed at about 5 to 30 ° C. for about 1 to 20 minutes.

<Coagulation process>
Next, the polyurethane resin is coagulated by a wet coagulation method.
In the wet coagulation method, a water-based coagulating liquid mainly composed of water, which is a poor solvent for a resin, is a resin-impregnated polyvinyl acetal resin foam substrate after a polyvinyl acetal resin foam substrate is impregnated with a resin solution. Is a method of coagulating and regenerating the resin by immersion in In the coagulating liquid, the solvent (for example, DMF) of the resin solution contained in the resin-impregnated polyvinyl acetal resin foam substrate and the coagulating liquid are substituted, and the polyurethane resin is coagulated and regenerated.
As the coagulating solution, water, a mixed solution of water and a polar solvent such as DMF, or the like is used. Polar solvents include water miscible organic solvents such as DMF, DMAc, THF, DMSO, NMP, acetone, IPA, ethanol, methanol and the like. Moreover, as for the density | concentration of the polar solvent in a mixed solvent, 0.01-20.0 mass% is preferable.
There is no restriction | limiting in particular in the temperature and immersion time of coagulation | solidification liquid, For example, what is necessary is just to immerse at 10-50 degreeC for 5 to 2000 minutes.

  The polishing pad obtained by the production method of the present invention has a polyvinyl acetal resin foam base impregnated with a polyurethane resin and silicon carbide and is wet-set, so that the density, hardness and / or hardness suitable for gettering layer formation are obtained. A polishing pad containing silicon carbide can be made.

<Washing and drying process>
The polyvinyl acetal resin foam base obtained by coagulating the polyurethane resin by coagulation bath treatment is washed and dried.
By the washing treatment, the solvent remaining in the polyvinyl acetal resin foam after the coagulation treatment is removed. Water may be mentioned as a washing solution used for washing.
After washing, the obtained polyvinyl acetal resin foam is subjected to drying treatment. The drying process may be carried out by a conventional method, for example, at 50 to 100 ° C. for about 20 to 1200 minutes in a dryer. Through the above steps, a polyurethane resin-containing foam (abrasive layer) can be obtained.
Moreover, after the said drying, you may perform a buff process or a slice process process on the single side | surface or both surfaces of a polyurethane resin containing foam.

<< Polishing of semiconductor wafer (Gettering layer formation) >>
In the polishing pad of the present invention, for example, the polishing pad and the semiconductor wafer of the present invention are respectively set in a polishing apparatus, and the semiconductor wafer is polished while pressing the back surface of the semiconductor wafer against the polishing pad while dropping the polishing agent onto the polishing pad. As a result, the backside polishing and gettering layer formation of the semiconductor wafer can be performed collectively in one step. As the polishing agent, dispersions of colloidal silica, alumina, zirconium oxide, diamond, boron nitride, silicon carbide and the like can be used.
In addition to the above method, after thinning and stress relief of the semiconductor wafer using an abrasive such as colloidal silica or alumina and the polishing pad of the present invention, the abrasive is changed to water or the like to obtain a semiconductor. A gettering layer can also be formed on the back of the wafer. In this method, it is possible to continuously carry out backside polishing and gettering layer formation of a semiconductor wafer using one type of polishing pad.

  In the polishing pad of the present invention, backside polishing (thinning and stress relief) of a semiconductor wafer and gettering layer formation can be performed collectively or continuously in one step. In addition, the polishing pad of the present invention is resistant to scratching and provides a good polishing rate. In addition, since the polishing pad of the present invention uses a polyvinyl acetal resin foam as a base, it is less likely to generate base waste than a polishing pad manufactured from a non-woven base, and is not fibrous even if base waste is generated. Therefore, it is easy to remove by washing. Furthermore, since the polishing pad of the present invention is used for wet polishing, dust is not generated at the time of polishing.

<< Manufacture of polishing pad >>
The polishing pad of Examples 1-2 and the comparative example 1 was manufactured using the following materials and manufacturing methods.

Example 1 Production of Polishing Pad Containing Polyvinyl Acetal Resin Foam as a Substrate
(1) Preparation of resin solution Thermoplastic polyether polyurethane resin (100% modulus: 47 MPa) in a solvent in which N, N-dimethylformamide (DMF) and isopropyl alcohol (IPA) are mixed in a ratio of 9: 1 by mass An abrasive particle-containing polyurethane resin solution was prepared by adding silicon carbide (SiC) (particle size: 0.6 μm, particle size: # 10000) as abrasive particles to a solution in which
The amount of polyurethane resin added to the solvent was 25.2 parts by mass with respect to 100 parts by mass of the solvent.
The amount of SiC added to the solvent was 43.9 parts by mass with respect to 100 parts by mass of the solvent.
(2) Impregnation step The polyurethane resin solution prepared in the above (1) in a polyvinyl acetal resin foam (polyvinyl formal resin foam, thickness: 2.111 mm, density: 0.087 g / cm ³ , cell diameter: 1000 μm) Was impregnated for 5 minutes at 25.degree.
(3) Coagulation process The polyvinyl acetal-based resin foam impregnated with the polyurethane resin solution obtained in the above (2) was wet coagulated at 20 ° C. for 1440 minutes using water as a coagulation liquid. The resin-containing polyvinyl acetal-based resin foam after wet coagulation is washed with water, dried at 80 ° C. for 480 minutes, and a double-sided tape is attached to the surface opposite to the polishing surface to obtain the polishing pad of Example 1. The

<Example 2: Production of a polishing pad containing a polyvinyl acetal resin foam as a substrate and containing a water repellent>
(1) Preparation of resin solution Thermoplastic polyether polyurethane resin (100% modulus: 47 MPa) in a solvent in which N, N-dimethylformamide (DMF) and isopropyl alcohol (IPA) are mixed in a ratio of 9: 1 by mass An abrasive particle-containing polyurethane resin solution was prepared by adding silicon carbide (SiC) (particle size: 0.6 μm, particle size: # 10000) and a fluorine-based water repellent as abrasive particles to a solution in which
The amount of polyurethane resin added to the solvent was 24.9 parts by mass with respect to 100 parts by mass of the solvent.
The amount of SiC added to the solvent was 43.3 parts by mass with respect to 100 parts by mass of the solvent.
The water repellent added to the solvent was 2.0 parts by mass with respect to 100 parts by mass of the solvent.
(2) Impregnation step The polyurethane resin solution prepared in the above (1) in a polyvinyl acetal resin foam (polyvinyl formal resin foam, thickness: 5.00 mm, density: 0.09 g / cm ³ , cell diameter: 100 μm) Was impregnated for 5 minutes at 25.degree.
(3) Coagulation process The polyvinyl acetal-based resin foam impregnated with the polyurethane resin solution obtained in the above (2) was wet coagulated at 20 ° C. for 1440 minutes using water as a coagulation liquid. The resin-containing polyvinyl acetal-based resin foam after wet coagulation is washed with water, dried at 80 ° C. for 480 minutes, and a double-sided tape is attached to the surface opposite to the polishing surface to obtain the polishing pad of Example 2. The

Comparative Example 1 Production of Polishing Pad Containing Polyester Nonwoven Fabric as Substrate
(1) Preparation of resin solution Thermoplastic polyether polyurethane resin (100% modulus: 47 MPa) in a solvent in which N, N-dimethylformamide (DMF) and isopropyl alcohol (IPA) are mixed in a ratio of 9: 1 by mass The abrasive particle-containing polyurethane resin solution was prepared by adding SiC (particle diameter: 0.6 μm, particle diameter: # 10000) as abrasive particles to a solution in which
The amount of polyurethane resin added to the solvent was 25.2 parts by mass with respect to 100 parts by mass of the solvent.
The amount of SiC added to the solvent was 43.9 parts by mass with respect to 100 parts by mass of the solvent.
(2) Impregnation process Non-woven fabric (Fujibo Ehime Co., Ltd., thickness: 4.5 mm, density: 0.126 g / cm ³ ) was impregnated for 5 minutes at 25 ° C. with the polyurethane resin solution prepared in the above (1).
(3) Coagulation process The non-woven fabric impregnated with the polyurethane resin solution obtained in (2) above was wet coagulated at 20 ° C. for 1440 minutes using water as a coagulation liquid. The resin-containing non-woven fabric after wet coagulation was washed with water, dried at 85 ° C. for 480 minutes, and a double-sided tape was attached to the surface opposite to the polishing surface to obtain a polishing pad of Comparative Example 1.

<< Physical Properties >>
The thickness, density, and A hardness of the polishing pads of Examples 1 and 2 and Comparative Example 1 were measured by the following method. The results are shown in Table 4.

(thickness)
The thickness of the polishing pad was measured according to the thickness measurement method described in Japanese Industrial Standard (JIS K6505). That is, the thickness of the polishing pad was measured when a load of 480 g / cm ² (the thickness direction of the polishing pad) was applied to the polishing pad as a load in the thickness direction. The polishing pad was cut into three pieces of 10 cm long and 10 cm wide, and the thickness of the four corners and the center part per one piece was measured using a dial gauge, and the average value of five points was made the thickness of one piece. The average thickness of the polishing pad was the average value of the thickness measured for each of the three pieces.

(Density g / cm ³ )
The weight (g) of the sample cut out to a size of a predetermined size was measured, and calculated by calculating the volume (cm ³ ) from the size.

(A hardness)
A hardness was measured according to JIS K7311.

<< Evaluation >>
Using the polishing pads of Examples 1 to 2 and Comparative Example 1, the polishing rate, the flaw density, and the presence or absence of defects and flaws were evaluated using the polishing method described below.

(Polishing method)
A silicon wafer and the polishing pad of Example 1 or 2 or Comparative Example 1 were set in a polishing apparatus (Fujitsu Machine Industry Co., Ltd .: MCP-150X), and polishing was performed while dropping an abrasive onto the polishing pad.
The polishing agent used was a mixture of COMPOL 80 (manufactured by Fujimi Incorporated, Inc.) and water at 3: 7, and 200 ml was dropped onto the polishing pad in 1 minute. The rotation speed of the platen was 80 rpm. The pressure for pressing the silicon wafer against the polishing pad by the pressure head was 300 g / cm ² . The silicon wafer used was 6 inches (diameter 152.4 mm), and the polishing time was 10 minutes.
Next, the pad surface was lightly dressed with a # 200 diamond dresser, and dropped onto a 200 ml polishing pad for 1 minute using pure water. Processing was performed under the same conditions as described above to form a gettering layer.

(Polishing rate)
Using an electronic balance for analysis (manufactured by A & D Co., Ltd .: GH-300), the difference in mass of the silicon wafer before and after polishing is measured, and the values are the Si density (g / cm ³ ) and the surface area (cm ² ) The product was divided by the product of, and the value was further corrected to μm, and then was divided by the polishing time to calculate the polishing rate (μm / min), which was evaluated according to the criteria in Table 5. The results are shown in Table 10.

(Presence of flaw density and flaws)
The surface of the silicon wafer after polishing was visually determined with an optical microscope (dark field observation magnification 200 ×) according to the criteria in Tables 6 to 7 below.
Although the wafer to which the gettering layer is applied usually looks like a mirror surface, flaws can be confirmed by applying light to the wafer, but flaws can be confirmed without applying light. Therefore, the flaw in the flaw density means a flaw that can be confirmed by applying light, and the defect flaw means a flaw that can be confirmed without applying light.
The results are shown in Table 10.

(Fiber dropout)
The surface of the silicon wafer after polishing was visually determined according to the criteria in Table 8 below with an optical microscope (dark field observation microscope magnification 200 ×). The results are shown in Table 10.

(Form stability)
Each of the polishing pads of Examples 1 to 2 and Comparative Example 1 has a thickness (dry state) after standing for 2 hours or more under conditions of 20 ± 2 ° C. and a relative humidity of 65 ± 5%, and overnight in deionized water. The thickness after immersion and swelling (wet state) was measured.
The difference in thickness between the dry and wet polishing pads was calculated, and the shape stability was determined according to the criteria in Table 9 below. The results are shown in Table 10.

  As apparent from Table 10, in the polishing pad of Comparative Example 1 in which the non-woven fabric is used as the substrate, the falling of the fibers was observed, while the polishing pad of the present invention in which the polyvinyl acetal resin foam was used as the substrate was Did not drop out (Examples 1 and 2). In addition, although the base material is a polyvinyl acetal resin foam which is completely different from the non-woven fabric, it has the same polishing rate as the polishing pad of Comparative Example 1 which uses the non-woven fabric as a base, and the flaw density suitable for the gettering layer Was recognized. Furthermore, no flaws were found. Furthermore, the polishing pad of Example 2 having a polyvinyl acetal resin foam as a substrate and containing a water repellent has a smaller difference in thickness between the polishing pad in the dry state and in the wet state than the polishing pad of Comparative Example 1, The stability was high. Therefore, it is considered that the polishing pad of Example 2 can suppress swelling of the polishing pad due to absorption of slurry and water at the time of polishing, and can suppress a temporal change in polishing characteristics due to the swelling.

  According to the present invention, it is possible to provide a polishing pad capable of polishing the back surface of a silicon wafer and forming a gettering layer without dropping of fibers. Therefore, it is very useful industrially.

Claims (10)

  A polishing pad comprising a polyvinyl acetal resin foam impregnated with a polyurethane resin and silicon carbide as a polishing layer.   The polishing pad according to claim 1, for wet polishing the back surface of a semiconductor wafer.   The polishing pad according to claim 2, for wet polishing the back surface of the semiconductor wafer to form a gettering layer.   The polishing pad according to any one of claims 1 to 3, wherein the polyvinyl acetal resin is a polyvinyl formal resin.   The polishing pad according to any one of claims 1 to 4, wherein silicon carbide is contained in the range of 30 to 70% by mass in a polyvinyl acetal resin foam formed by impregnating a polyurethane resin and silicon carbide. .   The polishing pad according to any one of claims 1 to 5, wherein the particle size of silicon carbide is in the range of 0.3 to 5.0 μm.   The polyvinyl acetal resin is contained in the range of 5-25 mass% in the polyvinyl acetal resin foam formed by making a polyurethane resin and a silicon carbide impregnate in any one of Claims 1-6. Polishing pad.   The polishing pad according to any one of claims 1 to 7, wherein the polyurethane resin is contained in the range of 15 to 60% by mass in the polyvinyl acetal resin foam formed by impregnating the polyurethane resin and silicon carbide. .   The polishing pad according to any one of claims 1 to 8, wherein the polyvinyl acetal resin foam impregnated with a polyurethane resin and silicon carbide further comprises a fluorine-based water repellent. Preparing a polyurethane resin solution comprising a polyurethane resin and silicon carbide,
A step of impregnating the polyvinyl acetal resin foam substrate with a polyurethane resin solution, and immersing the polyvinyl acetal resin foam substrate impregnated with the polyurethane resin solution in a coagulating liquid to coagulate the polyurethane resin,
The manufacturing method of the polishing pad of any one of Claims 1-9 containing these.