JP5147094B2 - Polymer material for polishing sheet, polishing sheet and polishing pad - Google Patents

Description

  The present invention relates to a polishing sheet and a polishing pad used when planarizing unevenness on a wafer surface by chemical mechanical polishing, and more particularly to a polishing sheet and a polishing pad in which the concentration of a metal contained in a specific metal is extremely reduced. The present invention also relates to a polymer material used for the polishing sheet and the polishing pad, and a method for manufacturing a semiconductor device.

  When manufacturing a semiconductor device, a process of forming a conductive film on the wafer surface and forming a wiring layer by photolithography, etching, or the like, a process of forming an interlayer insulating film on the wiring layer, etc. These steps are performed, and 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 advanced for the purpose of increasing the density of semiconductor integrated circuits, and along with this, technology for flattening the irregularities on the wafer surface has become important.

  As a method for flattening the irregularities on the wafer surface, a chemical mechanical polishing (hereinafter referred to as CMP) method is generally employed. CMP is a technique of polishing using a slurry-like abrasive (hereinafter referred to as slurry) in which abrasive grains are dispersed in a state where the surface to be polished of a wafer is pressed against the polishing surface of a polishing pad. As shown in FIG. 1, for example, a polishing apparatus generally used in CMP includes a polishing surface plate 2 that supports a polishing pad 1 and a support base (polishing head) 5 that supports a material to be polished (semiconductor wafer) 4. And a backing material for uniformly pressing the wafer and a supply mechanism for the abrasive 3. The polishing pad 1 is attached to the polishing surface plate 2 by attaching it with a double-sided tape, for example. The polishing surface plate 2 and the support base 5 are disposed so that the polishing pad 1 and the material to be polished 4 supported by each of the polishing surface plate 2 and the support base 5 are opposed to each other, and are provided with rotating shafts 6 and 7 respectively. Further, a pressurizing mechanism for pressing the workpiece 4 against the polishing pad 1 is provided on the support base 5 side.

When performing such a CMP process, there is a problem of metal contamination of the wafer. In the CMP process, when a wafer as a material to be polished is polished while flowing the slurry through the polishing pad, the slurry and the metal contained in the polishing pad remain on the polished wafer surface. Such metal contamination of the wafer induces a decrease in the reliability of the insulating film, generation of leakage current, abnormal film formation, etc., has a great adverse effect on the semiconductor device, and further reduces the yield. In particular, in shallow trench isolation (STI), which is the mainstream for isolating elements on a semiconductor substrate in current semiconductor manufacturing, metal contamination of the oxide film after polishing becomes a very big problem. . In STI, a predetermined shallow groove (shallow trench) is dug in the silicon wafer surface, and a SiO ₂ film is deposited and filled in the trench. Thereafter, the surface is polished to produce a region separated into oxide films. Since an element (transistor portion or the like) is manufactured in the separated region, metal contamination on the wafer surface after polishing causes a decrease in performance and reliability of the entire element. Currently, a wafer cleaning process is performed after CMP in order to reduce metal contamination of the wafer.

  However, the cleaning of the wafer has many disadvantages such as oxidation of the wiring, and it is desired to reduce the contamination by the slurry and the polishing pad. In particular, metals such as Fe ions are difficult to remove by cleaning and are likely to remain on the wafer.

  Therefore, recently, in order to solve the above problems, a polishing sheet having a high molecular weight polyethylene resin porous film having a metal impurity concentration of 100 ppm or less as a polishing layer has been proposed (Patent Document 1). Moreover, a polishing cloth for a semiconductor wafer having a zinc content of 200 ppm or less has been proposed (Patent Document 2).

  However, with the above metal impurity concentration, metal contamination of the wafer cannot be sufficiently prevented, and a load is applied to the wafer in the wafer cleaning process after CMP, and it is difficult to improve the device yield. .

  Further, a polishing pad using an organic intermolecular crosslinking agent that contains as little metal atoms as possible has been proposed (Patent Document 3).

However, the metal content concentration in the specific polishing pad is not clarified. Further, the mold is molded at the time of manufacturing the polishing pad, and it is impossible to reduce metal contamination on the wafer surface with the polishing pad.
JP 2000-343411 A International Publication No. 01/15860 Pamphlet JP 2001-308045 A

  This invention solves the said subject, Comprising: It exists in providing the polymeric material for polishing sheets, polishing sheet, and polishing pad whose content concentration of a specific metal is below a specific value (threshold value). Moreover, it is providing the manufacturing method of the semiconductor device using this polishing sheet or polishing pad.

  As a result of intensive studies in view of the above situation, the present inventors have found that the above-described problems can be solved by the following polymer materials.

  That is, the present invention is a polishing sheet polymer material used for chemical mechanical polishing, Fe content concentration is 0.3 ppm or less, Ni content concentration is 1.0 ppm or less, Cu content concentration is 0.5 ppm or less, The present invention relates to a polymeric material for an abrasive sheet, characterized in that the Zn concentration is 0.1 ppm or less and the Al content is 1.2 ppm or less.

  As shown in FIGS. 2 to 8, the present inventors have found that the degree of influence on the device yield varies greatly depending on the type and concentration of the metal contained in the polishing sheet polymer material. For example, the concentration of Fe contained in the polishing sheet polymer material greatly affects the device yield, but the concentration of Mg and Cr hardly affects the device yield. And it discovered that Fe, Ni, Cu, Zn, and Al had a big influence on the yield of a device. Furthermore, it has been found that when the concentration of each metal contained in the polymer material for polishing sheet exceeds a threshold specific to each metal, the yield of the device is extremely lowered.

  The content concentration value of each metal is a threshold value, and if any one of the above values is exceeded, the yield of the device is extremely lowered.

  In the present invention, the polymer material is at least selected from the group consisting of polyolefin resin, polyurethane resin, (meth) acrylic resin, silicon resin, fluorine resin, polyester resin, polyamide resin, polyamideimide resin, and photosensitive resin. One type of resin is preferable, and a polyurethane resin is particularly preferable.

  The present invention also relates to an abrasive sheet made of the polymer material.

  Furthermore, this invention relates to the polishing pad formed by affixing the said polishing sheet and a cushion sheet.

  By using the polishing sheet or polishing pad of the present invention, the content concentration of each metal on the wafer can be reduced. As a result, the wafer cleaning process can be performed easily, the work process can be made more efficient, the manufacturing cost can be reduced, and the load on the wafer can be reduced in the wafer cleaning process. Can be improved.

  The present invention also relates to a method for manufacturing a semiconductor device, comprising a step of polishing a surface of a semiconductor wafer using the polishing sheet or the polishing pad.

  The polymeric material for polishing sheets in the present invention has an Fe content of 0.3 ppm or less, an Ni content of 1.0 ppm or less, a Cu content of 0.5 ppm or less, and a Zn content of 0.1 ppm or less. As long as the Al concentration is 1.2 ppm or less, there is no particular limitation. In the present invention, at least one resin selected from the group consisting of polyolefin resin, polyurethane resin, (meth) acrylic resin, silicon resin, fluorine resin, polyester resin, polyamide resin, polyamideimide resin, and photosensitive resin is used. It is preferable to use it.

  Examples of the polyolefin resin include polyethylene, polypropylene, polyvinyl chloride, and polyvinylidene chloride.

  Examples of the fluororesin include polychlorotrifluoroethylene (PCTFE), perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF).

  Examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate.

  As the photosensitive resin, a photodecomposable photosensitive resin utilizing photolysis of a diazo group or an azide group, a photodimerizing photosensitive resin utilizing a photodimerization reaction of a functional group introduced into a side chain of a linear polymer, Examples include photo-radical polymerization of olefins, photoaddition reactions of thiol groups to olefins, and ring-opening addition reactions of epoxy groups.

  In order to reduce the metal content in the polymer sheet, it is preferable to use a material having as little metal content as possible in each raw material used for the resin synthesis.

  However, even if the metal content in each raw material is reduced, it is considered that the metal content in the resin increases due to the resin coming into contact with the metal in the production process.

  The method for producing the polymer material is not particularly limited and can be produced by a known method. However, in the present invention, in all steps until the polymer material is produced, the raw materials and / or reaction products thereof are used. It is preferable to manufacture using an instrument whose surface that is in direct contact with the metal is not metal. The production process of the polymer material differs depending on the type of polymer material. For example, in the case of 1) polyurethane resin, etc., raw material measurement process, filtration process, mixing process, stirring process, casting process, 2 ) In the case of a photosensitive resin or the like, there are a raw material measurement step, a mixing step, an extrusion step, and the like. It is preferable to perform each manufacturing process so that a raw material and / or its reaction product may not contact a metal directly in all these processes. Examples of the method of preventing direct contact with metal include materials used in the production process of the polymer material, for example, raw materials such as measuring containers, filters, polymerization containers, stirring blades, casting containers, extrusion apparatuses, and / or reaction products thereof. The method of using the thing whose surface which contacts a thing directly is not a metal is mentioned.

  After the production of the polymer material, when the polymer material is in a block shape, it is sliced with a slicer or the like to produce an abrasive sheet.

  Examples of the non-metal surface include those made of resin or ceramic, and non-metal-coated surfaces of the instrument. Non-metallic coatings include, but are not limited to, resin coatings, ceramic coatings, diamond coatings, and the like.

  In the case of resin coating, the resin to be coated is not particularly limited as long as it has high corrosion resistance and extremely low metal contamination. In particular, a fluororesin is preferable because it has excellent corrosion resistance and extremely low metal contamination. Specific examples of the fluororesin include PFA and PTFE.

  Among the raw material resins of the polymer material for the polishing sheet, polyurethane resin is particularly preferable because it is a material that is excellent in abrasion resistance and can obtain a polymer having desired physical properties by variously changing the raw material composition.

  A method for producing a polyurethane resin is a method comprising a step of mixing a first component containing an isocyanate group-containing compound and a second component containing an active hydrogen group-containing compound, directly with the component and / or its reaction product. It is preferable to produce using at least a polymerization vessel, a stirring blade, and a casting vessel whose surface to be contacted is not a metal.

  Usually, a metal is used for the apparatus used in manufacture of polymeric materials for abrasive sheets, such as a polyurethane resin, from a viewpoint of strength and the like. In particular, from the viewpoint of corrosion resistance and workability, iron, aluminum, copper, galvanized steel, stainless steel (stainless is generally an alloy made of Fe, Ni, Cr) or the like is used. Since the instrument is in direct contact with the raw material and its reaction product, the metal peeled off during manufacture is mixed into the raw material and its reaction product. Such metal contamination causes the concentration of the metal contained in the raw material and its reaction product to increase, so the surface portion of the instrument that is in direct contact with the raw material and its reaction product is manufactured using a non-metal material. It is preferable.

  In the present invention, the surface is preferably non-metallic coated. When resin-coated, the resin is preferably a fluororesin.

  The polyurethane resin for polishing sheets of the present invention has as a main component a first component containing an isocyanate group-containing compound and a second component containing an active hydrogen group-containing compound.

  As the isocyanate group-containing compound used in the present invention, the metal content is extremely small, and known isocyanate compounds in the field of polyurethane can be used without any particular limitation. In particular, the use of a diisocyanate compound and a derivative thereof, particularly an isocyanate prepolymer, is preferable because the resulting polyurethane foam has excellent physical properties. Incidentally, as a method for producing polyurethane, a prepolymer method and a one-shot method are known, but any method can be used in the present invention.

  Examples of the organic isocyanate usable in the present invention include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, , 5-naphthalene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate and other aromatic diisocyanates, ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 1, Aliphatic diisocyanates such as 6-hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, 4,4′-dicyclohexylmethane diisocyanate Sulfonates, isophorone diisocyanate, cycloaliphatic diisocyanates such as norbornane diisocyanate and the like. These may be used alone or in combination of two or more.

In the present invention, the isocyanate group-containing compound suitable for use as the first component is an isocyanate prepolymer which is a reaction product of the above-described isocyanate compound and an active hydrogen group-containing compound. As such an active hydrogen group-containing compound, a polyol compound or a chain extender described later is used, and an equivalent ratio NCO / H ^{* of} the isocyanate group (NCO) to the active hydrogen (H ^* ) is 1.2 to 5.0. The isocyanate prepolymer which is an oligomer having an isocyanate group terminal is produced by a heat reaction in the range of preferably 1.6 to 2.6.

  The active hydrogen group-containing compound used in the present invention is an organic compound having an extremely low metal content and having at least two active hydrogen atoms, and a compound usually referred to as a polyol compound or a chain extender in the technical field of polyurethane. It is.

  The active hydrogen group is a functional group containing hydrogen that reacts with an isocyanate group, and examples thereof include a hydroxyl group, a primary or secondary amino group, and a thiol group (SH).

  Examples of the polyol compound include those usually used in the technical field of polyurethane. Examples include polyether polyols typified by polytetramethylene ether glycol, polyethylene glycol, etc., polyester polyols typified by polybutylene adipate, polycaprolactone polyols, reactants of polyester glycols such as polycaprolactone and alkylene carbonate, etc. Polyester polycarbonate polyol obtained by reacting ethylene carbonate with polyhydric alcohol and then reacting the obtained reaction mixture with organic dicarboxylic acid, polycarbonate polyol obtained by transesterification of polyhydroxyl compound and aryl carbonate Etc. These may be used alone or in combination of two or more.

  In addition, the number average molecular weight of these polyol compounds is not particularly limited, but is preferably about 500 to 2000 from the viewpoint of the elastic characteristics of the obtained polyurethane resin. When the number average molecular weight of the polyol compound is less than 500, the polyurethane resin obtained using the polyol compound does not have sufficient elastic properties and tends to be a brittle polymer, and the abrasive sheet made of this polyurethane resin becomes too hard, and the object to be polished It may cause scratches on the surface of the material. Moreover, since it becomes easy to wear, it is not preferable from the viewpoint of the life of the polishing sheet. On the other hand, when the number average molecular weight exceeds 2000, an abrasive sheet made of a polyurethane resin obtained by using this becomes soft and it is difficult to obtain a sufficiently satisfactory planarity, which is not preferable.

  Examples of the polyol compound include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, in addition to the above-described high molecular weight polyol. 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. . These may be used alone or in combination of two or more.

  Among the active hydrogen group-containing compounds, those called chain extenders are compounds having a molecular weight of less than 500. Specifically, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, 3- Aliphatic low molecular weight glycols and triols typified by methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, trimethylolpropane, etc., 1,4-bis (2-hydroxyethoxy) benzene, m-xylylene diene Aromatic diols represented by ol, etc., 4,4′-methylenebis (o-chloroaniline), 2,6-dichloro-p-phenylenediamine, 4,4′-methylenebis (2,3-dichloroaniline) 3,5-bis (methylthio) -2,4-toluenediamine, 3,5 Bis (methylthio) -2,6-toluenediamine, 3,5-diethyltoluene-2,4-diamine, 3,5-diethyltoluene-2,6-diamine, trimethylene glycol-di-p-aminobenzoate, 1 , 2-bis (2-aminophenylthio) ethane, 4,4′-diamino-3,3′-diethyl-5,5′-dimethyldiphenylmethane, and other polyamines. These may be used alone or in combination of two or more.

  The ratio of the organic isocyanate, the polyol compound, and the chain extender in the present invention can be variously changed depending on the molecular weight of each, the desired physical properties of the polishing sheet produced from these. In order to obtain a polishing sheet having desired polishing characteristics, the number of isocyanate groups of the organic isocyanate relative to the total number of functional groups of the polyol compound and the chain extender is preferably in the range of 0.80 to 1.20, more preferably 0.99. ~ 1.15. When the number of isocyanate groups is less than 0.80, the required hardness tends not to be obtained. On the other hand, if it exceeds 1.20, poor curing due to unreacted isocyanate occurs, which tends to lower the polishing characteristics, which is not preferable.

  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.

  The polyurethane resin of the present invention is obtained by mixing and curing a first component containing an isocyanate group-containing compound and a second component containing an active hydrogen group-containing compound. In the prepolymer method, the isocyanate prepolymer becomes an isocyanate group-containing compound, and the chain extender becomes an active hydrogen group-containing compound. In the one-shot method, the organic isocyanate is an isocyanate group-containing compound, and the chain extender and the polyol compound are active hydrogen group-containing compounds. If necessary, stabilizers such as antioxidants, lubricants, pigments, fillers, antistatic agents, and other additives may be added.

  The polishing sheet (polishing layer) in the present invention is not limited to foam or non-foamed material, and can be arbitrarily changed according to the material to be polished and polishing conditions. From the standpoint of slurry retention and scratches, a fine foam is preferable.

  Examples of the foaming method of the microfoaming polyurethane resin include, but are not limited to, a method of adding fine hollow spheres, a mechanical foaming method, and a chemical foaming method. Although the above methods may be used in combination, a mechanical foaming method using a silicon surfactant which is a copolymer of polyalkylsiloxane and polyether and does not have an active hydrogen group is particularly preferable. As such a silicon surfactant, SH-192 (manufactured by Toray Dow Corning Silicon) and the like are exemplified as a suitable compound.

An example of a method for producing a fine foamed polyurethane resin will be described below. The method for producing such a polyurethane resin includes the following steps.
1) Stirring step for producing a cell dispersion of isocyanate prepolymer A silicon-based surfactant is added to the isocyanate prepolymer, and the mixture is stirred with a non-reactive gas to disperse the non-reactive gas as fine bubbles. To do. 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 above cell dispersion and mixed and stirred.
3) Curing step An isocyanate prepolymer mixed with a chain extender is cast and cured by heating.

  In this invention, it manufactures using the instrument which the surface which contacts a raw material etc. directly is not a metal at least to the said process (until a polyurethane resin is manufactured).

  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 stirrer for making non-reactive gas into fine bubbles and dispersing it in an isocyanate prepolymer containing a silicon-based surfactant, known stirrers can be used without particular limitation. Specifically, a homogenizer, a dissolver, 2 A shaft 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 bubble dispersion liquid in the stirring 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 stirring 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. .

  In the method for producing the polyurethane resin, 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. It is. 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 case of heating and post-curing, it is preferable that the nichrome heat ray or the like, which is a heated part in the oven, is not exposed but is housed in a separate chamber and isolated from the resin. In the polyurethane resin, a catalyst that promotes a known polyurethane reaction such as a tertiary amine type or an organic tin type 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.

  The polyurethane resin can be produced in a batch system in which each component is measured using a measuring container and charged into the polymerization container and stirred, or each component and a non-reactive gas are continuously supplied to the stirring device. Then, the continuous production method may be used in which the foam dispersion is fed out and stirred to produce a molded product.

  In the present invention, in the production of the polyurethane resin for abrasive sheets, it is possible to produce by using at least a polymerization vessel, a stirring blade, and a casting vessel whose surfaces that are in direct contact with the components and / or reaction products thereof are not metals. preferable. Furthermore, it is preferable to use a polyurethane raw material measuring container, a filter or the like whose surface is not metal.

  Moreover, it is preferable to wash | clean the surfaces, such as a container, before using, using the acid and alkali with a very low metal concentration.

  The polymer material for polishing sheet such as polyurethane resin thus produced has a Fe content of 0.3 ppm or less, a Ni content of 1.0 ppm or less, a Cu content of 0.5 ppm or less, Zn The content concentration of Al is 0.1 ppm or less, and the Al content concentration is 1.2 ppm or less, and the metal content is extremely low.

  The thickness of the polishing sheet in the present invention is not particularly limited, but is generally 0.8 to 2.0 mm. As a method for producing a polishing sheet of these thicknesses, the polymer material block is made to have a predetermined thickness by using a band saw type or canna type slicer, or a resin is poured into a mold having a cavity having a predetermined thickness. A curing method, a method using a coating technique or a sheet molding technique, or the like is used. In the case of the above slicer, a process of polishing the blade edge (griding) is necessary to maintain the cutting of the blade, but in that case, the blade edge is cleaned using ultrapure water or a solvent with a very low metal content after grinding. It is preferable to do. In a jig such as a metal mold, it is preferable that the metal is not exposed by coating with resin or diamond deposition.

  When the polymer material is a foam, the average cell diameter of the polishing sheet is preferably 70 μm or less, and more preferably 50 μm or less. Within this range, planarity is good.

  When the polymer material is a foam, the specific gravity of the polishing sheet is preferably 0.5 to 1.0. When the specific gravity is less than 0.5, the strength of the polishing sheet surface tends to decrease, and the planarity (flatness) of the wafer tends to decrease. On the other hand, when the ratio is larger than 1.0, the number of bubbles on the surface of the polishing sheet decreases, and planarity is good, but the polishing rate tends to decrease.

  When the polymer material is a foam, the hardness of the abrasive sheet is preferably 45 to 65 degrees as measured by an Asker D hardness meter. When Asker D hardness is less than 45 degrees, the planarity of the wafer tends to decrease. On the other hand, when the angle is greater than 65 degrees, planarity is good, but the uniformity (uniformity) of the wafer tends to decrease.

  When the polymer material is a foam, the compressibility of the abrasive sheet is preferably 0.5 to 5.0%. If the compression ratio is within the above range, both planarity and uniformity can be achieved.

  When the polymer material is a foam, the compression recovery rate of the polishing sheet is preferably 50 to 100%. When the compression recovery rate is less than 50%, as the repeated load applied to the polishing material is applied to the polishing sheet during polishing, a large change appears in the thickness of the polishing sheet, and the stability of the polishing characteristics tends to decrease.

  When the polymer material is a foam, the storage elastic modulus of the abrasive sheet is preferably 200 MPa or more under the conditions of a measurement temperature of 40 ° C. and a measurement frequency of 1 Hz. The storage elastic modulus refers to an elastic modulus measured by applying a sinusoidal vibration to a foam using a tensile test jig using a dynamic viscoelasticity measuring device. When the storage elastic modulus is less than 200 MPa, the strength of the polishing sheet surface tends to decrease and the planarity (flatness) of the wafer tends to decrease.

  It is preferable that the polishing surface of the polishing sheet that comes into contact with the material to be polished has a surface shape that holds and renews the slurry. A polishing sheet made of foam has many openings on the polishing surface, and has the function of holding and renewing the slurry. However, in order to more efficiently retain the slurry and renew the slurry, the polishing sheet is also polished. In order to prevent destruction of the material to be polished due to adsorption with the material, it is preferable that the polished surface has an uneven structure. The concavo-convex structure is not particularly limited as long as the shape holds and renews the slurry. For example, an XY lattice groove, a concentric circular groove, a through hole, a non-penetrating hole, a helical groove, an eccentric circular groove, Examples include radial grooves and combinations of these grooves. In addition, these uneven structures are generally regular, but in order to make the slurry retention and renewability desirable, the groove pitch, groove width, groove depth, etc. should be changed for each range. Is also possible.

  The production method of the concavo-convex structure is not particularly limited, for example, a method of machine cutting using a jig such as a tool of a predetermined size, pouring a resin raw material into a mold having a predetermined surface shape, For example, a method of producing by curing, a method of producing a resin by pressing it with a press plate having a predetermined surface shape, a method of producing using photolithography, a method of producing using a printing technique, a carbon dioxide laser, etc. For example, a manufacturing method using a conventional laser beam. It is preferable that the jigs such as the cutting tool and the die are subjected to diamond vapor deposition or the like to eliminate the metal exposure.

  The thickness variation of the abrasive sheet is preferably 100 μm or less. When the thickness variation exceeds 100 μm, the polishing sheet has a large waviness, and there are portions where the contact state with the material to be polished is different, which adversely affects the polishing characteristics. In order to eliminate the thickness variation of the polishing sheet, in general, the surface of the polishing sheet is dressed with a dresser in which diamond abrasive grains are electrodeposited and fused in the initial stage of polishing. As a result, the dressing time becomes longer and the production efficiency is lowered.

  Examples of a method for suppressing the variation in the thickness of the polishing sheet include a method of buffing the surface of the polishing sheet sliced to a predetermined thickness. When buffing is performed using a polishing belt or the like coated with abrasive grains, it is preferable that the polishing belt has a low metal content.

  The polishing pad of the present invention is formed by laminating the polishing sheet and a cushion sheet.

  The cushion sheet (cushion layer) supplements the characteristics of the abrasive sheet. The cushion sheet is necessary in order to achieve both planarity and uniformity in a trade-off relationship in CMP. Planarity refers to the flatness of a pattern portion when a material with minute irregularities generated during pattern formation is polished, and uniformity refers to the uniformity of the entire material to be polished. The planarity is improved by the characteristics of the polishing sheet, and the uniformity is improved by the characteristics of the cushion sheet. In the polishing pad of the present invention, the cushion sheet is softer than the polishing sheet.

  The material used for the cushion sheet is not particularly limited as long as it is softer than the abrasive sheet. For example, fiber nonwoven fabrics such as polyester nonwoven fabric, nylon nonwoven fabric and acrylic nonwoven fabric, resin impregnated nonwoven fabrics such as polyester nonwoven fabric impregnated with polyurethane, polymer resin foams such as polyurethane foam and polyethylene foam, rubber properties such as butadiene rubber and isoprene rubber Examples thereof include resins and photosensitive resins.

  Examples of means for attaching the polishing sheet and the cushion sheet include a method of sandwiching and pressing the polishing sheet and the cushion sheet with a double-sided tape. In the case of sandwiching and pressing with a double-sided tape, it is preferable to perform resin coating or the like on the press roll or the like that comes in contact with the polishing sheet or cushion sheet in order to eliminate the exposure of metal.

  The double-sided tape has a general configuration in which adhesive layers are provided on both sides of a substrate such as a nonwoven fabric or a film. In consideration of preventing the penetration of the slurry into the cushion sheet, it is preferable to use a film for the substrate. Examples of the composition of the adhesive layer include rubber adhesives and acrylic adhesives. Considering the content of metal ions, an acrylic adhesive is preferable because the metal ion content is low. In addition, since the composition of the abrasive sheet and the cushion sheet may be different, the composition of each adhesive layer of the double-sided tape can be made different so that the adhesive force of each layer can be optimized.

  As for the polishing pad of this invention, the double-sided tape may be provided in the surface which adheres to the platen of a cushion sheet. As the double-sided tape, a tape having a general configuration in which an adhesive layer is provided on both surfaces of a base material can be used as described above. As a base material, a nonwoven fabric, a film, etc. are mentioned, for example. In consideration of peeling from the platen after use of the polishing pad, it is preferable to use a film for the substrate. Examples of the composition of the adhesive layer include rubber adhesives and acrylic adhesives. Considering the content of metal ions, an acrylic adhesive is preferable because the metal ion content is low. Also, the cushion sheet and the platen often have different compositions, and the composition of each adhesive layer of the double-sided tape can be made different so that the adhesive force to the cushion sheet and the platen can be optimized.

  As a method for polishing a semiconductor wafer, a known polishing machine can be used and the polishing pad of the present invention can be mounted. In polishing, a known abrasive used for polishing a semiconductor wafer can be used without particular limitation as the abrasive supplied between the polishing layer and the semiconductor wafer. Specific examples include abrasives such as ceria and silica. Moreover, the use of a commercially available silica slurry SS21 (manufactured by Cabot Corporation) is also suitable.

  The semiconductor device is manufactured through a step of polishing the surface of the semiconductor wafer using the polishing sheet or the polishing pad. A semiconductor wafer is generally a laminate of a wiring metal and an oxide film on a silicon wafer. The method and apparatus for polishing a semiconductor wafer are not particularly limited. For example, as shown in FIG. 1, a polishing surface plate 2 that supports a polishing pad (polishing sheet) 1 and a support table (polishing head) that supports a semiconductor wafer 4. 5 and a polishing apparatus equipped with a backing material for uniformly pressing the wafer and a supply mechanism of the abrasive 3. The polishing pad 1 is attached to the polishing surface plate 2 by attaching it with a double-sided tape, for example. The polishing surface plate 2 and the support base 5 are disposed so that the polishing pad 1 and the semiconductor wafer 4 supported on each of the polishing surface plate 2 and the support table 5 face each other, and are provided with rotating shafts 6 and 7 respectively. Further, a pressurizing mechanism for pressing the semiconductor wafer 4 against the polishing pad 1 is provided on the support base 5 side. In polishing, the semiconductor wafer 4 is pressed against the polishing pad 1 while rotating the polishing surface plate 2 and the support base 5, and polishing is performed while supplying slurry. The flow rate of the slurry, the polishing load, the polishing platen rotation speed, and the wafer rotation speed are not particularly limited and are appropriately adjusted.

  As a result, the protruding portion of the surface of the semiconductor wafer 4 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. The evaluation items in Examples and the like were measured as follows.

(Average bubble diameter measurement)
A sample obtained by cutting the produced polyurethane resin foam in parallel with a microtome cutter as thin as possible to a thickness of 1 mm or less was used as a sample for measuring the average cell diameter. The sample was fixed on a slide glass, and the total bubble diameter in an arbitrary 0.2 mm × 0.2 mm range was measured using an image processing apparatus (Image Analyzer V10, manufactured by Toyobo Co., Ltd.), and the average bubble diameter was calculated. The measurement results are shown in Table 1.

(Specific gravity measurement)
This was performed according to JIS Z8807-1976. The produced polyurethane resin foam was cut into a 4 cm × 8.5 cm strip (thickness: arbitrary) and used as a sample for measuring specific gravity, and allowed to stand for 16 hours in an environment of temperature 23 ° C. ± 2 ° C. and humidity 50% ± 5%. I put it. The specific gravity was measured using a hydrometer (manufactured by Sartorius). The measurement results are shown in Table 1.

(Hardness measurement)
This was performed in accordance with JIS K6253-1997. The produced polyurethane resin foam was cut into a size of 2 cm × 2 cm (thickness: arbitrary) and used as a sample for hardness measurement, and was allowed to stand for 16 hours in an environment of temperature 23 ° C. ± 2 ° C. and humidity 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). The measurement results are shown in Table 1.

(Measurement of compression rate and compression recovery rate)
The polyurethane resin foam produced was cut into a 7 mm diameter circle (thickness: arbitrary) and used as a sample for measuring the compression rate and compression recovery rate. The temperature was 23 ° C. ± 2 ° C. and the humidity was 50% ± 5% for 40 hours. Left to stand. For the measurement, a thermal analysis measuring instrument TMA (manufactured by SEIKO INSTRUMENTS, SS6000) was used to measure the compression rate and the compression recovery rate. The measurement results are shown in Table 1. The calculation formulas for the compression rate and compression recovery rate are shown below.

Compression rate (%) = {(T1-T2) / T1} × 100
T1: Thickness of the polyurethane resin foam when a stress load of 30 kPa (300 g / cm ² ) is maintained for 60 seconds from an unloaded state on the polyurethane resin foam.
T2: The thickness of the polyurethane resin foam when a stress load of 180 kPa (1800 g / cm ² ) is maintained for 60 seconds from the state of T1.

Compression recovery rate (%) = {(T3-T2) / (T1-T2)} × 100
T1: Thickness of the polyurethane resin foam when a stress load of 30 kPa (300 g / cm ² ) is maintained for 60 seconds from an unloaded state on the polyurethane resin foam.
T2: The thickness of the polyurethane resin foam when a stress load of 180 kPa (1800 g / cm ² ) is maintained for 60 seconds from the state of T1.
T3: The thickness of the polyurethane resin foam when held for 60 seconds in a no-load state from the state of T2, and then holding a stress load of 30 kPa (300 g / cm ² ) for 60 seconds.

(Storage elastic modulus measurement)
This was performed in accordance with JIS K7198-1991. The produced polyurethane resin foam was cut into a 3 mm × 40 mm strip (thickness; arbitrary) and used as a sample for dynamic viscoelasticity measurement, and left in a container containing silica gel for 4 days under an environmental condition of 23 ° C. did. The accurate width and thickness of each sheet after cutting was measured with a micrometer. For measurement, a storage elastic modulus E ′ was measured using a dynamic viscoelastic spectrometer (manufactured by Iwamoto Seisakusho, present IS Engineering Co., Ltd.). The measurement conditions at that time are shown below. The measurement results are shown in Table 1.
<Measurement conditions>
Measurement temperature: 40 ° C
Applied strain: 0.03%
Initial load: 20g
Frequency: 1Hz

(Contained metal concentration measurement)
The produced polyurethane resin foam was carbonized and incinerated (550 ° C.), and the residue was dissolved in a 1.2N hydrochloric acid solution as a test solution. The elements in the test solution were determined by ICP emission analysis (CIROS-120, manufactured by Rigaku Corporation).
Measurement emission line of ICP emission analysis Fe: 259.940 nm, Ni: 231.604 nm, Cu: 324.754 nm, Zn: 213.856 nm, Al: 396.152 nm

(Evaluation of polishing characteristics)
Using SPP600S (manufactured by Okamoto Machine Tool Co., Ltd.) as a polishing apparatus, 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 Corporation) was added as a slurry at a flow rate of 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. In the evaluation of the planarization characteristics, after depositing a thermal oxide film of 0.5 μm on an 8-inch silicon wafer and performing predetermined patterning, an oxide film of 1 μm is deposited by p-TEOS, and an initial step of 0.5 μm is formed. A wafer with a pattern was prepared, this wafer was polished under the above-mentioned conditions, and after polishing, each step was measured to evaluate the planarization characteristics. Two steps were measured as the flattening characteristics. One is a local step, which is a step in a pattern in which lines having a width of 270 μm are arranged in a space of 30 μm, and the step after one minute was measured. The other is the amount of scraping. In the pattern in which lines with a width of 270 μm are arranged in a space of 30 μm and the pattern in which lines with a width of 30 μm are arranged in a space of 270 μm, the level difference between the above two patterns is 2000 mm or less. The amount of scraping of the 270 μm space was measured. When the numerical value of the local step is low, it indicates that the flattening speed in a certain time is high with respect to the unevenness of the oxide film caused by the pattern dependence on the wafer. Further, when the amount of scraping of the space is small, the amount of shaving of the portion that is not desired to be shaved is small and the flatness is high. The measurement results are shown in Table 2.

(Evaluation of oxide breakdown voltage)
Polishing was performed using a polishing pad on which an n-type Cz-Si wafer having a plane orientation (100) and a resistivity of 10 Ωcm was produced. As a polishing apparatus, SPP600S (manufactured by Okamoto Machine Tool Co., Ltd.) was used. As polishing conditions, silica slurry (SS12, manufactured by Cabot) was added as a slurry at a flow rate of 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. The polishing time was 2 minutes.

  The polished oxide was removed from the polished wafer using RCA cleaning and 5% diluted HF. Thereafter, dry oxidation was performed at 900 ° C. for 2 hours. The oxide film thickness at this time was about 300 mm. An Al electrode MOS capacitor was formed on this wafer, and a 5 mmφ electrode was formed thereon. Further, the back surface of the wafer was sandblasted, and gold was evaporated to form a back electrode. A lamp voltage was applied to a 5 mmφ electrode with a polarity such that the Al electrode was (+) and the back electrode was (−).

A capacitor having an oxide film applied voltage of 7.5 MV / cm or more when the leakage current density of the oxide film was 1 μA / cm ² was determined as a good product. 100 wafers were polished, and the non-defective rate was determined from the ratio of non-defective capacitors to all capacitors. Each non-defective product rate is shown in Table 2.

<Production of polishing pad>
Example 1
3000 parts by weight of filtered polyether-based prepolymer (Uniroy, Adiprene L-325; isocyanate group concentration: 2.22 meq / g), and filtered silicone-based nonionic surfactant (Toray Dow Silicone, SH192) ) 90 parts by weight were weighed using a fluorine-coated measuring container, added to a fluorine-coated polymerization container and mixed, and the reaction temperature was adjusted to 80 ° C. Using a fluorine-coated stirring blade, the mixture was vigorously stirred for about 4 minutes so that bubbles were taken into the reaction system at 900 rpm. The mixture was weighed using a fluorine-coated measuring container in which 780 parts by weight of 4,4′-methylenebis (o-chloroaniline) (Ihara Chemical Co., Ltd., Iharacamine MT) previously melted and filtered at 120 ° C. was filtered. Added. After stirring for about 4 minutes, the reaction solution was poured into a pan-type open mold (casting container) coated with fluorine. When the fluidity of the reaction solution ceased, it was placed in an oven with a nichrome heat ray part in a separate chamber and post-cured at 110 ° C. for 6 hours to obtain a polyurethane resin foam block. In all the steps so far, it was manufactured using a tool whose surface directly contacting with the raw material or the like is not metal.

  A polyurethane resin foam sheet is obtained by slicing the polyurethane resin foam block using a band saw type slicer that has been cleaned with ultrapure water (specific resistance: 12 MΩ · cm or more) after gliding the rotary blade of the slicer. It was. Next, using a buffing machine in which a polishing belt (made by Riken Corundum Co., Ltd.) in which silicon carbide is used as abrasive grains is set, the surface of the sheet is buffed to a predetermined thickness, and the thickness accuracy is adjusted. did. The buffed sheet is punched to a predetermined diameter, and a grooved machine is used to process concentric grooves with a groove width of 0.25 mm, a groove pitch of 1.50 mm, and a groove depth of 0.40 mm on the surface. Obtained. A double-sided tape (manufactured by Sekisui Chemical Co., Ltd., double tack tape) was attached to the surface of the sheet opposite to the grooved surface using a laminator. Further, the surface of a corona-treated cushion sheet (manufactured by Toray Industries, Inc., polyethylene foam, Torepef, thickness 0.8 mm) was buffed and bonded to the double-sided tape using a laminator. Further, a double-sided tape was attached to the other surface of the cushion sheet using a laminator to prepare a polishing pad.

Comparative Example 1
A polishing pad was prepared in the same manner as in Example 1 except that 2.36 mL of an FeCl ₃ · 6H ₂ O (0.01 mol / L) aqueous solution was added during stirring.

Comparative Example 2
A polishing pad was prepared in the same manner as in Example 1 except that 5.13 mL of FeCl ₃ · 6H ₂ O (0.01 mol / L) aqueous solution was added during stirring.

Comparative Example 3
A polishing pad was produced in the same manner as in Example 1 except that 0.94 mL of Ni (NO ₃ ) ₂ .6H ₂ O (0.1 mol / L) aqueous solution was added during stirring.

Comparative Example 4
A polishing pad was prepared in the same manner as in Example 1 except that 3.24 mL of an Ni (NO ₃ ) ₂ .6H ₂ O (0.1 mol / L) aqueous solution was added during stirring.

Comparative Example 5
A polishing pad was prepared in the same manner as in Example 1, except that 1.40 mL of an aqueous Cu (NO ₃ ) ₂ .3H ₂ O (0.01 mol / L) solution was added during stirring.

Comparative Example 6
A polishing pad was prepared in the same manner as in Example 1 except that 5.48 mL of an aqueous Cu (NO ₃ ) ₂ .3H ₂ O (0.01 mol / L) solution was added during stirring.

Comparative Example 7
A polishing pad was prepared in the same manner as in Example 1 except that 0.71 mL of an aqueous Zn (NO ₃ ) ₂ .6H ₂ O (0.1 mol / L) solution was added during stirring.

Comparative Example 8
A polishing pad was prepared in the same manner as in Example 1 except that 1.42 mL of an aqueous solution of Zn (NO ₃ ) ₂ .6H ₂ O (0.1 mol / L) was added during stirring.

Comparative Example 9
During _{stirring, Al (NO 3) 3 ·} 9H 2 O (0.01mol / L) except that aqueous solution was added 3.16mL was prepared polishing pad in the same manner as in Example 1.

Comparative Example 10
During _{stirring, Al (NO 3) 3 ·} 9H 2 O (0.01mol / L) except that aqueous solution was added 7.89mL was prepared polishing pad in the same manner as in Example 1.

以上に示す結果から明らかなように、特定金属の含有濃度が閾値以下であるである高分子材料からなる研磨パッドを用いて研磨することにより、研磨後のウエハの金属汚染を低減させ、半導体デバイスの歩留まりを格段に向上させることが可能となる。

As is clear from the results shown above, by polishing using a polishing pad made of a polymer material whose specific metal content is below a threshold value, metal contamination of the wafer after polishing is reduced, and the semiconductor device It is possible to significantly improve the yield.

Schematic configuration diagram showing an example of a polishing apparatus used in CMP polishing Graph showing the relationship between Fe concentration and device yield Graph showing the relationship between Ni concentration and device yield Graph showing the relationship between Cu concentration and device yield Graph showing the relationship between Zn concentration and device yield Graph showing the relationship between Al concentration and device yield Graph showing the relationship between Mg concentration and device yield Graph showing the relationship between Cr concentration and device yield

Explanation of symbols

1: Polishing pad (polishing sheet)
2: Polishing surface plate 3: Abrasive (slurry)
4: Material to be polished (semiconductor wafer)
5: Support base (polishing head)
6, 7: Rotating shaft

Claims (6)

In the polymeric material for polishing sheets used for chemical mechanical polishing, the Fe concentration is 0.3 ppm or less, the Ni content is 1.0 ppm or less, the Cu content is 0.5 ppm or less, and the Zn content is 0. A polymeric material for polishing sheets, characterized by having a concentration of 1 ppm or less and an Al concentration of 1.2 ppm or less. The polymer material is at least one resin selected from the group consisting of polyolefin resin, polyurethane resin, (meth) acrylic resin, silicon resin, fluorine resin, polyester resin, polyamide resin, polyamideimide resin, and photosensitive resin. The polymer material for abrasive sheets according to claim 1. The polymeric material for polishing sheets according to claim 1, wherein the polymeric material is a polyurethane resin. An abrasive sheet comprising the polymer material for an abrasive sheet according to claim 1. A polishing pad comprising the polishing sheet according to claim 4 and a cushion sheet. A method for producing a semiconductor device, comprising a step of polishing a surface of a semiconductor wafer using the polishing sheet according to claim 4 or the polishing pad according to claim 5.

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