JP2005197408A - Polishing pad for cmp and polishing method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing pad for CMP with which in-plane uniformity after polishing of a workpiece is sufficiently realized. <P>SOLUTION: The polishing pad for CMP 1 is formed of hard foaming polyurethane, and has an inner region 2 whose polishing face is circular, and an outer region 3 in a doughnut shape which surrounds the inner region. Bubble density of the inner region 2 is larger than that of the outer region 3. Asker D hardness of the outer region 3 and that of the inner region 2 are 45 to 70, and a hardness difference of them is three or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a polishing pad for CMP used when planarizing unevenness of an object to be polished such as a semiconductor wafer by a chemical mechanical polishing (chemical mechanical polishing or CMP) method.

  When manufacturing a semiconductor device, a process of forming a conductive layer on the wafer surface, forming a wiring layer by photolithography, etching, etc., a process of forming an interlayer insulating film on the wiring layer, etc. As a result of these steps, irregularities made of a conductor such as metal or an insulator are generated on the wafer surface. In recent years, miniaturization of wiring and multilayer wiring have been promoted for the purpose of increasing the density of semiconductor integrated circuits. Along with this, technology for flattening the unevenness of the wafer surface has become important. As a method for flattening the height difference of the device structure, a CMP method that applies mirror processing of a silicon wafer has been recently adopted.

  A polishing apparatus generally used in CMP includes, for example, a polishing surface plate that supports a polishing pad, a support base that supports an object to be polished (such as a wafer), a backing material for uniformly pressing the wafer, and polishing. An agent supply mechanism is provided. For example, the polishing pad is attached to the polishing surface plate by pasting with a double-sided tape. The polishing surface plate and the support base are arranged so that the polishing pad supported by the polishing table and the object to be polished face each other, and each has a rotation shaft. Further, the support base is provided with a pressurizing mechanism for pressing the object to be polished against the polishing pad.

  In general, in the CMP method, after dressing (grinding) a polishing pad with a dresser, the polishing plate rotation shaft and the carrier rotation shaft are rotated, and polishing slurry is supplied from the polishing slurry supply nozzle to the center of the polishing pad while polishing. Polishing is performed by pressing the object to be polished onto the polishing pad by the pressure adjusting mechanism. In such a CMP method, the relative speed with respect to the polishing surface in the vicinity of the peripheral portion of the object to be polished is higher than that in the central portion. For this reason, the polishing rate at the center of the object to be polished is slower than that at the periphery, and there is a problem that polishing is not performed uniformly.

  In Patent Document 1, in a CMP polishing pad having a plurality of concentric grooves on the polishing surface, the density of grooves in the region where the center of the object is polished is polished, and the vicinity of the periphery of the object is polished. What is higher than the region is described. Patent Document 2 describes a CMP polishing pad having a plurality of openings in a region of a polishing surface where a central portion of an object to be polished is polished. The purpose of these polishing pads is to increase the polishing capacity by increasing the amount of polishing slurry held in the area of the polishing surface that corresponds to the central part of the object to be polished, and to increase the polishing rate of the central part of the object to be polished more than the peripheral part. It is said.

However, if grooves and openings are formed unevenly on a polishing pad that is integrally formed of the same material, the physical properties of the surface change between the regions. For example, in the polishing pad of Patent Document 1, the rigidity of a polishing surface area where grooves are formed at a high density is lower than that of a low density area. The same applies to the region where the opening is provided in the polishing pad of Patent Document 2. For this reason, the conventional technique cannot sufficiently increase the polishing rate at the center of the object to be polished, and there will be a region having a different rigidity in the polishing surface. I ca n’t do it.
JP 2000-94303 A Japanese Patent No. 3425216

  The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a polishing pad for CMP in which the in-plane uniformity after polishing of the object to be polished is sufficiently achieved.

  The present invention is a CMP polishing pad made of rigid polyurethane foam, the polishing surface has a circular inner region and a donut-shaped outer region surrounding the inner region, the bubble density is larger in the inner region than in the outer region, The Asker D hardness is 45 to 70 for both the outer region and the inner region, and provides a polishing pad for CMP having a hardness difference of 3 or less.

  Further, the present invention provides a polishing pad for CMP made of rigid foamed polyurethane, the polishing surface having a circular inner region, a donut-shaped intermediate region surrounding the inner region, and a donut-shaped outer region surrounding the intermediate region, and a bubble density A polishing pad for CMP in which the intermediate region is larger than the inner region and the outer region, the Asker D hardness is 45 to 70 in both the outer region, the intermediate region, and the inner region, and the difference in hardness between the three is 3 or less. It is to provide.

  According to the polishing pad for CMP of the present invention, the polishing ability is enhanced in the region of the polishing surface corresponding to the central portion of the object to be polished, there is little variation in rigidity within the polishing surface, and in-plane uniformity after polishing is sufficient. Is envisioned.

  The polishing pad for CMP is a layered member for polishing the object to be polished. The polishing pad functions as a carrier for polishing slurry when polishing, and has a polishing surface that contacts and rubs the object to be polished. The polished surface is generally formed from a hard elastic body. The polishing surface of the CMP polishing pad of the present invention is preferably formed of foamed polyurethane. This is because foamed polyurethane is excellent in abrasion resistance, and the physical properties can be easily adjusted by variously changing the raw material composition, cell density, and the like.

  FIG. 1 is a plan view of a two-part polishing pad according to an embodiment of the present invention. The polishing surface 1 has an inner region 2 and an outer region 3. The inner area 2 is circular and the outer area 3 is a donut shape surrounding the inner area. The size of the inner region may be appropriately adjusted depending on the size of the wafer or polishing pad that is the object to be polished. Generally, the radius of the inner region is about 50 to 90%, preferably about 60 to 85% with respect to the radius of the outer region (outer radius).

The bubble density of the polishing surface 1 is larger in the inner region 2 than in the outer region 3. This is because the inner region is mainly considered to be a range where the central portion of the object to be polished comes into contact, and the bubble density is increased to increase the holding power of the polishing slurry. For example, the bubble density in the inner region is 200 to 600 / mm ² , preferably 300 to 600 / mm ² . The cell density of the outer area 0 to 400 pieces / mm ^2, preferably 100 to 400 pieces / mm ^2.

  Both the inner and outer regions have Asker D hardness of 45 to 75, preferably 50 to 65. When the semiconductor wafer is polished when the Asker D hardness is less than 45, the planarization characteristics deteriorate, and when it exceeds 75, the planarization characteristics are good, but the polishing uniformity of the semiconductor wafer deteriorates. The difference in hardness between them is 3 or less, preferably 2 or less. When the hardness difference between the two exceeds 3, the rigidity varies within the polished surface, and the in-plane uniformity after polishing becomes insufficient.

  The difference in Taber wear loss between the inner region and the outer region is 50% or less, preferably 30% or less. If the difference in the Taber wear loss between the two exceeds 50%, the thickness difference (step) between regions increases as the number of semiconductor wafers to be polished increases, which adversely affects the polishing characteristics.

  FIG. 2 is a plan view of a three-part polishing pad according to one embodiment of the present invention. The polishing surface 11 has an inner region 12, an intermediate region 13, and an outer region 14. The inner region 12 has a circular shape, the intermediate region 13 has a donut shape surrounding the inner region, and the outer region 14 has a donut shape surrounding the intermediate region 13. The sizes of the intermediate region and the inner region may be appropriately adjusted depending on the size of the wafer or polishing pad that is the object to be polished. Generally, the radius (outer radius) of the intermediate region is about 50 to 90%, preferably about 60 to 85%, relative to the radius (outer radius) of the outer region. The radius of the inner region is about 20 to 50%, preferably about 20 to 40%, relative to the radius of the outer region (outer radius). Further, the width of the intermediate region (difference between the outer radius and the inner radius) is 20 to 80%, preferably 25 to 70% of the wafer diameter.

The bubble density of the polishing surface 11 is larger in the intermediate region 13 than in the inner region 12 and the outer region 14. The intermediate region is mainly considered to be a range in contact with the central portion of the object to be polished, and this is for increasing the bubble density and increasing the holding power of the polishing slurry. For example, the bubble density in the intermediate region is 200 to 600 / mm ² , preferably 300 to 600 / mm ² . The cell density of the inner and outer regions 0 to 400 pieces / mm ^2, preferably 100 to 400 pieces / mm ^2.

  The inner region, the intermediate region, and the outer region all have an Asker D hardness of 45 to 75, preferably 50 to 65. When the semiconductor wafer is polished when the Asker D hardness is less than 45, the planarization characteristics deteriorate, and when it exceeds 75, the planarization characteristics are good, but the polishing uniformity of the semiconductor wafer deteriorates. Further, the hardness difference between the three members is 3 or less, preferably 2 or less. When the hardness difference between the two exceeds 3, the rigidity varies within the polished surface, and the in-plane uniformity after polishing becomes insufficient.

  The difference in the Taber wear loss between the middle region, the inner region and the outer region is 50% or less, preferably 30% or less. If the difference in the Taber wear loss between the two exceeds 50%, the thickness difference (step) between regions increases as the number of semiconductor wafers to be polished increases, which adversely affects the polishing characteristics. In a preferred embodiment, the inner and outer regions are formed of a rigid foamed polyurethane having the same cell density, Asker D hardness and Taber wear loss.

  In general, when the cell density is changed in a polyurethane foam resin having the same composition, physical properties such as hardness change greatly. Therefore, it is very difficult to make the hardness of the entire polishing surface uniform while changing the bubble density partially in the integrally formed polishing pad. Therefore, in the polishing pad of the present invention, for example, members having shapes and physical properties corresponding to the inner region, the intermediate region, and the outer region are separately manufactured, and these are combined so as to have the configuration shown in FIGS. Can be manufactured.

  The members corresponding to the inner region, the intermediate region, and the outer region are obtained by slicing a block of hard foamed polyurethane to a predetermined thickness to obtain an abrasive sheet and punching it into a circular or donut shape. The thickness of the abrasive sheet is generally 0.8 to 3 mm, preferably 2.5 mm.

  The polyurethane resin is composed of an organic polyisocyanate, a polyol, and a chain extender. Examples of the organic polyisocyanate used include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, 1,5- Naphthalene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, etc. Is mentioned. These may be used alone or in combination of two or more.

  Examples of the polyol used include polyester polyols represented by polytetramethylene ether glycol, polyester polyols represented by polybutylene adipate, polycaprolactone polyols, and polyesters such as polycaprolactone. A polyester polycarbonate polyol or an ethylene carbonate exemplified by a reaction product of glycol and alkylene carbonate is reacted with a polyhydric alcohol, and then the obtained reaction mixture is reacted. Examples thereof include polyester polycarbonate polyol reacted with an organic dicarboxylic acid, and polycarbonate polycarbonate obtained by transesterification of a polyhydroxyl compound with aryl carbonate. These may be used alone or in combination of two or more.

  The number average molecular weight of these polyols is not particularly limited, but is preferably 500 to 2000 from the viewpoint of the elastic properties of the resulting polyurethane.

  If the number average molecular weight of this polyol is less than 500, the polyurethane obtained by using this polyol does not have sufficient elastic properties and becomes a brittle polymer, and the polishing pad produced from this polyurethane becomes too hard and is subject to polishing. It causes scratches on the polished surface of a workpiece, which is not preferable. Moreover, since it becomes easy to wear, it is not preferable from the viewpoint of the pad life.

  When the number average molecular weight exceeds 2000, a polishing pad produced from polyurethane obtained by using this is not preferred because it becomes soft and cannot be satisfactorily flattened.

  In addition to the high molecular weight polyols described above, the polyols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol. 1,4-cyclohexanedimethanol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, 1,4-bis (2-hydroxyethoxy) benzene and other low molecular weight polyols may be used in combination. .

  The polyol may contain polytetramethylene glycol from the viewpoint of hydrolysis resistance, elastic properties, abrasion resistance, and the like. The polytetramethylene glycol may have a number average molecular weight of 500 to 1600 and a molecular weight distribution (weight average molecular weight / number average molecular weight) of less than 1.9.

  This number average molecular weight is a value determined from a hydroxyl value measured according to JIS K1557. The molecular weight distribution is a value measured under the following measurement conditions.

The molecular weight distribution is a value measured under the following measurement conditions.

  When the number average molecular weight of this tetramethylene glycol is less than 500, the polyurethane obtained by using this does not have sufficient elastic properties and becomes a brittle polymer, and the polishing pad produced from this polyurethane becomes too hard, and the polishing It causes scratches on the polished surface of the target workpiece, which is not preferable. Moreover, since it becomes easy to wear, it is not preferable from the viewpoint of the pad life.

  When the number average molecular weight exceeds 1600, a polishing pad produced from polyurethane obtained by using the number average molecular weight becomes soft and cannot be satisfactorily flattened, which is not preferable.

  Further, when the molecular weight distribution of polytetramethylene glycol is 1.9 or more, the temperature dependency of the hardness (elastic modulus) of the polyurethane obtained therefrom becomes large, and the polishing pad produced from this polyurethane has a hardness (elasticity) due to temperature. The difference in rate) becomes large. As described above, the frictional heat is generated between the polishing pad and the workpiece, so that the temperature of the polishing pad changes during polishing. Therefore, a difference occurs in the polishing characteristics, which is not preferable.

  Examples of chain extenders include polyamines exemplified by 4,4′-methylenebis (o-chloroaniline), 2,6-dichloro-p-phenylenediamine, 4,4′-methylenebis (2,3-dichloroaniline) and the like. Or the low molecular weight polyols mentioned above. These may be used alone or in combination of two or more.

  The ratio of the organic polyisocyanate, polyol, and chain extender in the polyurethane resin can be variously changed depending on the molecular weight of each and the desired physical properties of the polishing pad produced therefrom. In order to obtain a polishing pad having desired polishing characteristics, the number of isocyanate groups of the organic polyisocyanate with respect to the total number of functional groups (hydroxyl group + amino group) of the polyol and the chain extender is desirably in the range of 0.95 to 1.15. Preferably, 0.99 to 1.10.

  Further, the ratio of the high molecular weight component to the low molecular weight component in the polyol is determined by the characteristics required for the polishing pad produced therefrom.

  The polyurethane resin can be produced by applying a known urethanization technique such as a melting method or a solution method, but is preferably produced by a melting method in consideration of cost, working environment and the like.

  As a polymerization procedure for the polyurethane resin, either a prepolymer method or a one-shot method is possible, but an isocyanate-terminated prepolymer is synthesized in advance from an organic polyisocyanate and a polyol, and a chain extender is reacted therewith. The prepolymer method is common. In addition, although the isocyanate terminal prepolymer manufactured from organic polyisocyanate and a polyol is marketed, if it suits this invention, the polyurethane used by this invention is polymerized by the prepolymer method using them. It is also possible.

  In addition, stabilizers such as antioxidants, surfactants, lubricants, pigments, fillers, antistatic agents, and other additives may be added to the polyurethane resin as necessary.

  Examples of the method for producing foamed polyurethane include, but are not limited to, a method of adding hollow beads, a method of forming a foam by a mechanical foaming method, a chemical foaming method, and the like. Each method may be used in combination, but a mechanical foaming method using a silicone surfactant which is a copolymer of polyalkylsiloxane and polyether and does not have an active hydrogen group is more preferable. As such a silicone-based surfactant, SH-192 (manufactured by Toray Dow Corning Silicon) is exemplified as a suitable compound.

An example of a method for producing a closed-cell type polyurethane foam constituting the polishing layer will be described below. Such a method for producing foamed polyurethane typically includes the following steps (1) to (4).
(1) Foaming process for producing an isocyanate-terminated prepolymer cell dispersion A silicone-based surfactant is added to an isocyanate-terminated prepolymer, stirred with a non-reactive gas, and dispersed to form a fine bubble. A dispersion is obtained. When the prepolymer is solid at room temperature, it is preheated to an appropriate temperature and melted before use.
(2) Curing Agent (Chain Extender) Mixing Step A chain extender is added to the cell dispersion and mixed and stirred.
(3) Casting process An isocyanate-terminated prepolymer mixed with a chain extender is cast.
(4) Curing step The cast polymer is cured by heating.

  As the non-reactive gas used to form the fine bubbles, non-flammable gases are preferable, and specific examples include nitrogen, oxygen, carbon dioxide, rare gases such as helium and argon, and mixed gases thereof. The use of air that has been dried to remove moisture is most preferable in terms of cost.

  As a stirring device for making non-reactive gas into fine bubbles and dispersing it in an isocyanate-terminated prepolymer containing a silicone-based surfactant, known stirring devices can be used without particular limitation. Specifically, a homogenizer, a dissolver, A two-axis planetary mixer (planetary mixer) is exemplified. The shape of the stirring blade of the stirring device is not particularly limited, but the use of a whipper type stirring blade is preferable because fine bubbles can be obtained.

  In addition, it is also a preferable aspect to use a different stirring apparatus for the stirring which produces a cell dispersion in a foaming process, and the stirring which adds and mixes the chain extender in a mixing process. In particular, the stirring in the mixing step may not be stirring that forms bubbles, and it is preferable to use a stirring device that does not involve large bubbles. As such an agitator, a planetary mixer is suitable. There is no problem even if the same stirring device is used as the stirring device for the foaming step and the mixing step, and it is also preferable to adjust the stirring conditions such as adjusting the rotation speed of the stirring blade as necessary. .

  The method of making the polyurethane foam into a block is a batch method in which each component is weighed and charged into a container and stirred, or each component and a non-reactive gas are continuously supplied to the stirring device and stirred. It may be a continuous production method in which a cell dispersion is sent out to produce a molded product. In this case, heating and post-curing the foam that has been reacted until the foam dispersion is poured into the mold and no longer flows is effective in improving the physical properties of the foam and is extremely suitable. . The bubble dispersion may be poured into the mold and immediately placed in a heating oven for post-cure. Under such conditions, heat is not immediately transferred to the reaction components, so the bubble diameter does not increase. . The curing reaction is preferably performed at normal pressure because the bubble shape is stable.

  In the polyurethane resin, a catalyst that promotes a known polyurethane reaction such as tertiary amine or organotin may be used. The type and addition amount of the catalyst are selected in consideration of the flow time for pouring into a mold having a predetermined shape after the mixing step.

  Adjustment of the cell density, Asker D hardness, and Taber abrasion loss of the rigid foamed polyurethane block may be performed by methods known to those skilled in the art. For example, the bubble density can be controlled by the amount added when hollow fine particles are added. When the bubbles are mechanically formed, the bubbles can be controlled by controlling the rotation speed, shape, and time of the stirring blade when stirring, or by changing the amount of the surfactant added as an aid for forming the bubbles. Asker D hardness is adjusted by changing the raw material type of the polyurethane resin (isocyanate, polyol, chain extender, other additives) and the blending ratio thereof, or changing the bubble density. The Taber wear loss is also adjusted by a method such as changing the type and blending ratio of the raw materials and the bubble density.

  The members corresponding to the inner region, the intermediate region, and the outer region obtained in this manner are appropriately arranged and attached to the underlayer or the like to obtain the polishing pad of the present invention. As an affixing method, the method etc. which affix the said member on an adhesive tape are mentioned, for example. In addition to this, an underlayer such as a cushion layer may be provided.

  In the polishing method of the present invention, the CMP method is performed using the polishing pad of the present invention. That is, while supplying the polishing slurry to the surface of the polishing pad, the object to be polished is rotated while being pressed with a desired polishing pressure, and is swung in a direction crossing the moving direction of the polishing pad, thereby The surface of the object to be polished is polished by the chemical and mechanical action of the polishing slurry supplied between the surface of the polishing pad and the surface of the object to be polished.

For example, the CMP polishing pad described above is fixed to the platen of the polishing apparatus,
Fix the object to be polished to the polishing table support so that it faces the polishing surface of the polishing pad,
The object to be polished is brought into contact with the polishing surface of the polishing pad,
Polishing may be performed while supplying the polishing slurry.

  However, when the object to be polished is brought into contact with the polishing surface of the polishing pad, it is necessary to adjust the position of the object to be polished or the polishing pad so that the region where the bubble density of the polishing pad is high hits the center of the object to be polished. is there. That is, the number of bubbles in the polishing layer in the region where the vicinity of the center of the wafer is polished is increased compared to the region where the peripheral portion of the object is polished. As a result, the holding power of the slurry for polishing the vicinity of the center of the wafer is increased, the polishing ability is increased, and the in-plane uniformity after polishing of the object to be polished can be achieved.

  FIG. 3 is a schematic view showing the positional relationship between the object to be polished and the two-part polished surface in the polishing method of the present invention. The object to be polished 4 is pressed onto the polishing surface 1 with a desired polishing pressure. The central portion of the object to be polished hits the inner region 2 having a high bubble density, and the peripheral portion of the object to be polished hits the outer region 3 having a low bubble density. Polishing is performed by rotating the object to be polished 4 and the polishing surface 1 in directions indicated by arrows. If it does so, time for the center part of the to-be-polished body 4 to contact the inner side area | region 3 will become long compared with a peripheral part. Therefore, the polishing rate at the center of the object to be polished is higher than that at the periphery of the object to be polished.

  FIG. 4 is a schematic diagram showing the positional relationship between the object to be polished and the three-part polishing surface in the polishing method of the present invention. The object to be polished 15 is pressed onto the polishing surface 11 with a desired polishing pressure. The central part of the object to be polished is in contact with the intermediate region 13 having a high bubble density, and the peripheral part of the object to be polished is in contact with the inner region 12 and the outer region 14 having a low bubble density. Polishing is performed by rotating the object 15 and the polishing surface 11 in directions indicated by arrows. If it does so, the time for the center part of the to-be-polished body 15 to contact the intermediate | middle area | region 13 becomes long compared with a peripheral part. Therefore, the polishing rate at the center of the object to be polished is higher than that at the periphery of the object to be polished.

  A semiconductor device is manufactured through a step of polishing the surface of a semiconductor wafer using the above-described polishing method. A semiconductor wafer is generally a laminate of a wiring metal and an oxide film on a silicon wafer. As a result, the protruding portion of the surface of the semiconductor wafer is removed and polished flat. Thereafter, a semiconductor device is manufactured by dicing, bonding, packaging, or the like. The semiconductor device is used for an arithmetic processing device, a memory, and the like.

  Examples and the like specifically showing the configuration and effects of the present invention will be described below. In addition, the evaluation item in an Example etc. was measured as follows.

(Bubble density)
A cross section of the obtained polishing sheet for polishing pad was cut out with a microtome, and 200 microscopic images of the cross section were separated with an image processing apparatus image analyzer V10 (manufactured by Toyobo Co., Ltd.), and the number of bubbles per unit area was determined. The bubble density was calculated by measuring.

(Asker D hardness)
This was performed in accordance with JIS K6253-1997. A polished region cut out to a size of 2 cm × 2 cm (thickness: arbitrary) was used as a sample for hardness measurement, and was allowed to stand for 16 hours in an environment of a temperature of 23 ° C. ± 2 ° C. and a humidity of 50% ± 5%. At the time of measurement, the samples were overlapped to a thickness of 6 mm or more. The hardness was measured using a hardness meter (manufactured by Kobunshi Keiki Co., Ltd., Asker D type hardness meter).

(Taber wear loss)
The obtained abrasive sheet is subjected to an abrasion test using a Taber abrasion tester (Model 174 manufactured by Taber) under the conditions of a load of 1000 g, an abrasion wheel H-22 and 1000 revolutions, and the weight is measured by measuring the weight before and after the test. Sex was evaluated. The difference in the wear material was calculated by the following formula.

(In-plane uniformity)
SPP600S (manufactured by Okamoto Machine Tool Co., Ltd.) was used as a polishing apparatus, and polishing characteristics were evaluated using the prepared polishing pad. The polishing rate was calculated from the time obtained by polishing about 0.5 μm of a 1-μm thermal oxide film formed on an 8-inch silicon wafer. An interference type film thickness measuring device (manufactured by Otsuka Electronics Co., Ltd.) was used for measuring the thickness of the oxide film. As polishing conditions, silica slurry (SS12, manufactured by Cabot) was added as a slurry at 150 ml / min during polishing. The polishing load was 350 g / cm ² , the polishing platen rotation number was 35 rpm, and the wafer rotation number was 30 rpm. Further, the rocking speed was 1 mm / second and the rocking distance was 20 mm.

  The in-plane uniformity was calculated by the following formula from film thickness measurement values at arbitrary 25 points on the wafer. The smaller the in-plane uniformity value, the higher the wafer surface uniformity.

Preparation Example 1

Preparation of Block A In a reaction container coated with Teflon ^{(registered trademark)} , 25 kg of filtered prepolymer L325 (Uniroy, NCO% = 9.15) and filtered silicon surfactant SH192 (Toray Dow Corning Silicone) 0.75 kg), and the reaction temperature was adjusted to 80 ° C. Using a Teflon ^{(registered trademark)} -coated stirring blade, stirring was performed for 6 minutes so that air bubbles were taken into the reaction system at a rotation speed of 900 rpm (primary stirring). 6.5 kg of 4,4′-methylenebis (o-chloroaniline) previously melted at 120 ° C. and filtered (Iharacamine MT: hereinafter abbreviated as MBOCA) was added. Stirring was continued for about 1 minute (secondary stirring), and then the reaction solution was poured into a pan-type oven mold (size: 900 × 900 mm) coated with Teflon ^{(registered trademark)} . When the reaction solution lost its fluidity, it was placed in an oven, post-cured at 110 ° C. for 6 hours, and then gradually cooled to room temperature to prepare a fine-cell polyurethane foam block.

Preparation Example 2

Production of Block B A block was produced in the same manner as in Block A except that the amount of surfactant SH192 added was 2.00 kg and the primary stirring time was 4 minutes.

Preparation Example 3

Production of Block C A block was produced in the same manner as in Block A except that the amount of surfactant SH192 added was 0.75 kg and the primary stirring time was 4 minutes.

Preparation Example 4

Preparation of block D Coronate 6912 (manufactured by Nippon Polyurethane Co., Ltd., NCO% = 7.7%) 25 kg was used as a prepolymer, the amount of surfactant SH192 added was 0.75 kg, MBOCA was 5.5 kg, and the primary stirring time A block was prepared in the same manner as block A except that was set to 30 seconds.

Preparation Example 5

Production of Block E A block was produced in the same manner as in Block A except that the primary stirring time was 8 minutes in the production method of Block A.

Preparation Example 6

Preparation of Block F Same as Block A, except that 25 kg of Coronate 4099 (manufactured by Nippon Polyurethane, NCO% = 8.0%) was used as the prepolymer, MBOCA was 5.7 kg, and the primary stirring time was 3 minutes. The block was produced by the method.

Block A was sliced to a thickness of 1.5 mm with a slicer manufactured by Amitek and cut into a circle having a diameter of 420 mm to form a member in the inner region. The specific gravity of this member was 0.80, the D hardness was 50, and the bubble density was 350 / mm ² . Next, the block B was sliced to a thickness of 1.5 mm and cut into a donut shape having an inner diameter of 420 mm and an outer diameter of 600 mm to obtain a member in the outer region. The specific gravity of this member was 0.87, the D hardness was 51, and the bubble density was 240 cells / mm ² . The inner region member was arranged inside the outer region member, and a double-sided tape for affixing to the surface plate of the polishing apparatus was affixed to the back side of the polishing layer to prepare a polishing pad. A polishing test was performed using the obtained polishing pad, and the in-plane uniformity of the polished surface was evaluated. The results are shown in Table 1.

A sheet obtained from block C (specific gravity 0.87, D hardness 54, bubble density 250 / mm ² ) was used as an inner region member, and a sheet obtained from block D (specific gravity 1.05, D hardness 52, bubble density) A polishing pad was prepared in the same manner as in Example 1 using 50 pieces / mm ² ) as an outer region member, and a polishing test was performed. The test results are shown in Table 1.

A sheet obtained from the block E (specific gravity 0.73, D hardness 46, bubble density 540 / mm ² ) was used as an inner region member, and a sheet obtained from the block F (specific gravity 0.93, D hardness 46, bubble density) A polishing pad was prepared in the same manner as in Example 1 using 200 pieces / mm ² ) as an outer region member, and a polishing test was performed. The test results are shown in Table 1.

Comparative Example 1

The block C was sliced to a thickness of 1.5 mm, cut into a circle having a diameter of 600 mm, and used as a polishing layer (specific gravity 0.87, D hardness 54, bubble density 250 / mm ² ) to prepare a polishing pad. A polishing test was performed using the obtained polishing pad, and the in-plane uniformity of the polished surface was evaluated. The results are shown in Table 1.

Comparative Example 2

A sheet (specific gravity 0.80, D hardness 50, cell density) obtained from block A was obtained by using the sheet (specific gravity 0.87, D hardness 51, cell density 240 / mm ² ) obtained from block B as an inner region member. A polishing pad was prepared in the same manner as in Example 1 using 350 pieces / mm ² ) as an outer region member, and a polishing test was performed. The test results are shown in Table 1.

Block B was sliced to a thickness of 1.5 mm with a slicer manufactured by Amitek, cut into a circle with a diameter of 220 mm, and used as a member in the inner region. The specific gravity of this member was 0.87, the D hardness was 51, and the bubble density was 240 cells / mm ² . The block A was sliced to a thickness of 1.5 mm, cut into a donut shape having an inner diameter of 220 mm and an outer diameter of 420 mm, and used as an intermediate region member. The specific gravity of this member was 0.80, the D hardness was 50, and the bubble density was 350 / mm ² . Further, a sheet obtained by slicing the block B to a thickness of 1.5 mm was cut into a donut shape having an inner diameter of 420 mm and an outer diameter of 600 mm, and used as a member in the outer region.

  An intermediate region member was disposed inside the outer region member, and an inner region member was disposed inside the outer region member, and a double-sided tape for affixing to the surface plate of the polishing apparatus was affixed to the back side of the polishing layer to prepare a polishing pad. A polishing test was performed using the obtained polishing pad, and the in-plane uniformity of the polished surface was evaluated. The results are shown in Table 2.

Comparative Example 3

A sheet obtained from the block F (specific gravity 0.93, D hardness 46, cell density 200 / mm ² ) was used as an intermediate region member, and a sheet obtained from the block B (specific gravity 0.87, D hardness 51, cell density) A polishing pad was prepared by the same method as in Example 4 using 240 pieces / mm ² ) as an inner region member and an outer region member, and a polishing test was performed. The test results are shown in Table 2.

FIG. 1 is a plan view of a two-part polishing pad according to an embodiment of the present invention. FIG. 2 is a plan view of a three-part polishing pad according to one embodiment of the present invention. FIG. 3 is a schematic view showing the positional relationship between the object to be polished and the two-part polished surface in the polishing method of the present invention. FIG. 4 is a schematic diagram showing the positional relationship between the object to be polished and the three-part polishing surface in the polishing method of the present invention.

Explanation of symbols

1, 11 ... polished surface,
2, 12 ... inner region,
13 ... middle region,
3, 14 ... outer region,
4, 15: object to be polished.

Claims (9)

  A polishing pad for CMP made of rigid polyurethane foam, the polishing surface has a circular inner region and a donut-shaped outer region surrounding the inner region, and the bubble density is larger in the inner region than in the outer region, and Asker D hardness Is a polishing pad for CMP, wherein both the outer region and the inner region are 45 to 75, and the hardness difference between them is 3 or less. The polishing pad for CMP according to claim 1, wherein the bubble density in the inner region is 200 to 600 / mm ² , and the bubble density in the outer region is 0 to 400 / mm ² .   The polishing pad for CMP according to claim 1 or 2, wherein a difference in Taber wear loss between the inner region and the outer region is 50% or less.   A polishing pad for CMP made of rigid polyurethane foam has a circular inner area, a donut-shaped intermediate area surrounding the inner area, and a donut-shaped outer area surrounding the intermediate area, and the bubble density is higher in the intermediate area. Is larger than the inner region and the outer region, the Asker D hardness is 45 to 75 in the outer region, the intermediate region, and the inner region, and the hardness difference between the three is 3 or less. 5. The polishing pad for CMP according to claim 4, wherein a bubble density in the intermediate region is 200 to 600 / mm ² , and a bubble density in the inner region and the outer region is 0 to 400 / mm ² .   The polishing pad for CMP according to claim 4 or 5, wherein a difference in Taber wear loss between the intermediate region and the inner and outer regions is 50% or less. Fixing the polishing pad for CMP according to any one of claims 1 to 6 to a platen of a polishing apparatus;
Fixing the object to be polished to the support of the polishing apparatus so as to face the polishing surface of the polishing pad;
A step of bringing the object to be polished into contact with the polishing surface of the polishing pad so that a region having a high bubble density is in contact with the center of the object to be polished on the polishing surface of the polishing pad;
Polishing while supplying the polishing slurry;
A polishing method comprising:   The polishing method according to claim 7, wherein the object to be polished is a semiconductor wafer. A semiconductor device obtained by polishing by the method according to claim 8.

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