JP6697977B2 - Polishing pad and polishing method using the same - Google Patents

Description

  The present invention relates to a polishing pad and a polishing method capable of optically detecting a polishing end point in-situ when a surface of an insulating film, a conductor film or the like is flattened in the manufacture of a semiconductor or an integrated circuit.

  In a large scale integrated circuit (LSI) represented by a semiconductor memory, high integration and miniaturization of the circuit are progressing year by year. Along with this, requirements in the manufacturing process for realizing high integration and miniaturization of LSI circuits are becoming more and more complicated. Further, due to the multi-layering of semiconductor devices, there is a problem that unevenness on the wafer surface during manufacturing causes disconnection of circuits and variation in resistance value. Therefore, highly accurate flattening of the wafer surface is required.

  Further, photolithography (light projection exposure) is widely used as a technique for transferring a pattern of a photomask onto a wafer surface when manufacturing an LSI. In photolithography of a fine semiconductor integrated circuit using a short exposure wavelength, the depth of focus of exposure becomes very shallow. When fine irregularities are present on the wafer surface, the resolution of the pattern of the photomask is lowered, and therefore the wafer surface is required to be highly accurately flattened.

  The wafer surface is usually polished by a CMP polishing apparatus using chemical mechanical polishing (CMP). Referring to FIG. 3, the CMP polishing apparatus 20 includes, for example, a top supported by a carrier 17 on a surface of a polishing pad 21 bonded to an upper surface of a rotating surface plate (polishing table) 5 with an adhesive material 13. The wafer 10 adsorbed and held on the ring (holder) 6 is brought into contact with the wafer 10, and while the polishing slurry S is supplied from the slurry nozzle 7, the surface of the wafer 10 is polished by the rotation of the surface plate 5 and the top ring 6. It is configured. Further, inside the surface plate 5, a light irradiation unit 8 for detecting the polishing end point by an optical means and an optical sensor (not shown) for detecting the reflected light thereof are provided. The polishing pad 21 has a light-transmitting window 21c, and transmits the light from the light irradiating section 8 and reflects the light on the surface of the wafer 10. Then, the end point of polishing is detected by monitoring changes in the intensity of reflected light and the like. As a method for detecting the polishing end point by an optical means, for example, Patent Document 1 below discloses a method using a laser interferometer as a technique for determining the polishing end point while polishing the wafer surface.

  In order to emit light from the light irradiating section and detect the end point by the reflected light, as shown in FIG. 3, a light transmitting section such as a light transmitting window 21c is provided on at least a part of the polishing pad, and It is necessary to reflect light on the surface. For example, the following Patent Documents 2 to 4 disclose a method of detecting the end point by the reflected light from the wafer surface by using a polishing pad having a transparent window formed in a part thereof. Specifically, in Patent Document 2 and Patent Document 3 below, a light-transmitting plug (light-transmitting window) is embedded in a liquid-state non-transmissive resin, the non-transmissive resin is cured, and further sliced to form the light-transmissive window. A method of manufacturing a polishing pad having the same is disclosed. Further, Patent Document 4 discloses a polishing pad in which the polishing surface portion and the transparent window are made of the same resin. Specifically, Patent Document 4 discloses a method in which a polishing surface portion and a light-transmitting window are made of the same resin, and a portion of the light-transmitting window is made amorphous by imparting transparency by performing a rapid cooling process on the light-transmitting window. Disclosed is a method of imparting transparency to a portion forming a film by setting the reaction temperature of the portion to be different from that of other portions. Further, Patent Document 5 discloses that a light-absorbing compound is contained in a light-transmitting region for the purpose of suppressing deterioration due to ultraviolet light.

U.S. Pat. No. 5,413,941 Japanese Patent Publication No. 11-512977 US Pat. No. 5,839,796 Special table 2003-507199 gazette Japanese Patent Publication No. 2015-512799

  When a polishing pad having a light-transmitting window is used for CMP using a CMP polishing apparatus, the light transmittance of the light-transmitting window may have too high a wavelength dependency to accurately monitor the intensity of reflected light. In this case, the accuracy of end point detection may be lowered. Further, there is no means for correcting the wavelength dependence of the light transmittance of the transparent window of the polishing pad for each manufacturing lot or each polishing pad.

  An object of the present invention is to improve the accuracy of the end point detection of a polishing pad used for the end point detection using an optical means in order to solve the above problems.

One aspect of the present invention includes a polishing layer having a polishing surface as a main surface and a cushion layer laminated on the back surface of the polishing layer, and the polishing layer has at least a part of a light-transmitting region that transmits light in a thickness direction. a cushion layer has an opening in a portion corresponding to the light transmitting region, further comprising a light adjusting layer which is colored if covering the area corresponding to the back surface of the opening of the polishing layer, the light control layer, wavelength At any wavelength in the range of 350 to 700 nm, a maximum light transmittance (T1) having a light transmittance of 50% or more and being maximum and a minimum light transmittance (T2) having a minimum light transmittance are provided. The polishing pad has a difference (T1−T2) between the maximum light transmittance (T1) and the minimum light transmittance (T2) of 20% or more. According to such a polishing pad, when the polishing end point is detected by the optical means provided in the CMP polishing apparatus, the end point detection accuracy is improved by showing a clear change in the reflected light intensity. As the light adjusting layer, a layer including a resin sheet containing a coloring material such as dye, pigment, organic or inorganic fine particles is preferably used.

  Further, the polishing layer preferably has a light transmittance of 10% or more in the entire range of the wavelength of 350 to 700 nm in the entire region of the polishing surface from the viewpoint of excellent light transmittance.

  In addition, the polishing layer is made of a homogeneous thermoplastic polyurethane molded product that does not include an embedded light-transmitting plug to serve as a light-transmitting window. It is preferable in that the polishing characteristics are less likely to become unstable in doing so. Further, when such a homogeneous molded article of thermoplastic polyurethane is a molded article of a non-foamed structure having substantially no voids, it is excellent in light transmission and polishing stability.

  In addition, the light adjusting layer is disposed in the dug portion formed on the back surface of the polishing layer, so that even if the polishing layer is relatively thick, the dug portion becomes thinner than the surrounding area, so that high light It is preferable in that the transmittance can be maintained.

  Further, with respect to light in the entire range of wavelengths of 350 to 700 nm, the maximum light transmittance (T3) in which the light transmittance is 12% or more in the portion where the light adjustment layer is present and the minimum light transmittance (T4) are shown. It is preferable that the difference (T3−T4) between the maximum light transmittance (T3) and the minimum light transmittance (T4) is 10% or less. Further, with respect to light in the entire range of wavelengths of 350 to 700 nm, the minimum light transmittance (T5) and the maximum light transmittance (T6) of which the light transmittance in the portion where the light adjustment layer is present is 15% or less are shown. It is also preferable that the difference (T6-T5) between the maximum light transmittance (T6) and the minimum light transmittance (T5) is 20% or more. Although the polishing layer alone generally has a large wavelength dependency of the light transmittance, the wavelength dependency of the light transmittance is suppressed by disposing the light adjusting layer.

  In addition, the presence of a plurality of recesses such as grooves or holes at a pitch of 30 mm or less in the entire area of the polishing surface allows the polishing slurry to be uniformly and sufficiently supplied to the polishing surface while maintaining the light transmittance. At the same time, it is preferable because it is useful for preventing the discharge of polishing dust that causes scratches and the damage of the wafer due to the suction and holding of the polishing pad.

  According to another aspect of the present invention, a step of fixing any one of the above-mentioned polishing pads to a surface plate of a polishing device, and holding a material to be polished in a holder of the polishing device so as to face a polishing surface of the polishing pad. And a step of polishing the material to be polished by relatively sliding the polishing surface and the material to be polished while supplying the polishing slurry between the polishing pad and the material to be polished. A step of transmitting light to the portion where the adjustment layer is present, reflecting the light on the surface of the material to be polished, and detecting the polishing end point by detecting a change in the reflected light intensity. In such a polishing method, the accuracy of detecting the end point of the polishing pad used for detecting the end point is improved.

  According to the polishing pad of the present invention, when the polishing end point is detected by the optical means provided in the CMP polishing apparatus, the accuracy of the end point detection of the polishing pad used for the end point detection is improved.

FIG. 1 shows a schematic cross-sectional view of the polishing pad of the embodiment. FIG. 2 is an explanatory diagram illustrating CMP using the polishing pad of the embodiment. FIG. 3 is an explanatory diagram for explaining CMP using a conventional polishing pad.

  The polishing pad of this embodiment will be described with reference to FIG. FIG. 1 shows a schematic cross-sectional view of the polishing pad 11 of this embodiment. As shown in FIG. 1, the polishing pad of this embodiment has a polishing layer 1 having a polishing surface P as a main surface, and a cushion layer laminated and bonded to a back surface R of the polishing layer 1 via an adhesive layer 3. 2 and. In FIG. 1, line c-c' indicates the center line of the disk-shaped polishing pad. The polishing layer 1 has a light-transmitting region that transmits light in the thickness direction, at least in part, preferably on the entire polishing surface. The cushion layer 2 has an opening v in a portion corresponding to the light transmissive region. A dug portion 1a is formed in a region of the back surface R of the polishing layer 1 corresponding to the opening v, and the light adjusting sheet 4a is adhered to the dug portion 1a with an adhesive material layer 4b to form the light adjusting layer 4. ing. Here, the light adjusting layer 4 has a maximum light transmittance (T1) of 50% or more and a maximum light transmittance and a minimum light transmittance in any wavelength range in the wavelength range of 350 to 700 nm. The sheet having the following minimum light transmittance (T2) and having a difference (T1-T2) between the maximum light transmittance (T1) and the minimum light transmittance (T2) of 20% or more.

  The polishing layer is a resin layer having optical transparency in at least one region, preferably the entire region, so that the end point can be optically detected. Here, the light transmittance means that the light transmittance in the thickness direction is 10% or more, and preferably 12% or more, for light in the entire range of wavelengths of 350 to 700 nm. It is preferable that the polishing layer has a light-transmitting property in the entire region of the polishing surface, because the light-transmitting plug for forming the light-transmitting window may not be embedded. In the case of a non-homogeneous polishing layer where a light-transmitting plug for forming a light-transmitting window is embedded in a resin with low light-transmitting property, slurry leakage may occur around the light-transmitting plug or if it is used for a long time. Moreover, the polishing characteristics tend to be unstable. The thickness of the polishing layer is not particularly limited, but is preferably 1.0 to 2.5 mm, more preferably 1.2 to 2.2 mm, and particularly preferably 1.4 to 2.0 mm.

  Further, the relatively hard polishing layer follows the local unevenness of the surface to be polished of the material to be polished, but it is difficult to follow the warpage and waviness of the entire material to be polished. The cushion layer, which has a hardness lower than that of the polishing layer, provides a polishing pad that can realize polishing with a good balance between global flatness and local flatness by following the warpage and waviness of the entire workpiece.

  As the cushion layer, those conventionally used as a cushion layer for a polishing pad are used without particular limitation. Specific examples thereof include resin foams such as polyurethane foam and polyethylene foam, and non-woven fabrics. Among these, polyurethane foam is particularly preferable from the viewpoint of excellent flexibility and durability. The thickness of the cushion layer is not particularly limited, but 0.4 to 3 mm, further 0.5 to 2 mm, and particularly 0.6 to 1.5 mm is excellent in the balance between polishing flatness and uniformity. It is preferable from the point.

  The cushion layer has an opening for transmitting light. The shape of the opening is not particularly limited as long as it is large enough to allow the light from the light irradiation section of the polishing apparatus to pass therethrough and to detect the end point.

  The polishing layer is adhered to the cushion layer. The pressure-sensitive adhesive used for bonding the polishing layer and the cushion layer is not particularly limited, and examples thereof include acrylic-based, rubber-based, styrene-based, silicone-based, and urethane-based pressure-sensitive adhesives. The thickness of the pressure-sensitive adhesive layer that adheres the polishing layer and the cushion layer is not particularly limited, but is preferably 10 to 500 μm, and more preferably about 30 to 300 μm.

  The light adjustment layer has a maximum light transmittance (T1) of which light transmittance is 50% or more and is maximum and a minimum light transmittance of which light transmittance is minimum at any wavelength in the wavelength range of 350 to 700 nm. (T2), the difference (T1-T2) between the maximum light transmittance (T1) and the minimum light transmittance (T2) is 20% or more, and the wavelength dependence of the light transmittance is controlled. It is a layer to do.

  The maximum light transmittance (T1) is the maximum value of the light transmittance of 50% or more existing at any wavelength in the wavelength range of 350 to 700 nm. When T1 is 50% or more, sufficient light is transmitted to the light-transmitting region of the polishing layer, and the end point detection is facilitated. T1 is preferably 55% or more, more preferably 60% or more, and particularly preferably 65% or more from the viewpoint of showing a clear change in reflected light intensity. The minimum light transmittance (T2) is the minimum value of the light transmittance existing at any wavelength in the wavelength range of 350 to 700 nm.

  The difference (T1−T2) between T1 and T2 of the light control layer is 20% or more, 22% or more, 25% or more, 27% or more, that is, the maximum light transmittance (T1) and the minimum light transmittance. Since the difference (T1-T2) from the rate (T2) is large, the effect of showing a clear change in the reflected light intensity is enhanced.

  Here, the maximum light transmittance (T1) of 50% or more and the maximum light transmittance of the light adjustment layer at any wavelength in the wavelength range of 350 to 700 nm and the minimum light transmittance of which the minimum light transmittance is minimum. The transmittance (T2) is obtained by measuring the light transmittance of the member forming the light control layer in the entire wavelength range of 350 to 700 nm using a spectrophotometer "UV-2450".

  The light adjustment sheet is not particularly limited as long as it is a sheet that can realize a light adjustment layer having the above-mentioned optical characteristics, but preferably contains a resin as a main component and controls the wavelength dependence of the light transmittance as necessary. A resin sheet containing a coloring material for achieving this is preferable because it has excellent adhesion to the polishing layer. Specific examples of the resin include polyester such as polyethylene terephthalate (PET), acrylic resin, styrene resin, polyolefin, vinyl chloride resin, polycarbonate, polyamide, polyurethane and the like. Further, specific examples of the coloring material include dyes, pigments, and inorganic fine particles. The thickness of the light adjusting sheet is not particularly limited, but is preferably 0.02 to 0.5 mm, more preferably 0.05 to 0.3 mm, and particularly preferably 0.1 to 0.2 mm.

  In the polishing pad 11 of the present embodiment shown in FIG. 1, the dug portion 1a is formed in a region of the back surface R of the polishing layer 1 corresponding to the opening v, and the dug portion 1a has a surface on the surface of the polishing layer 1. The light adjusting sheet 4a is adhered via the adhesive layer 4b. Such a form is preferable in that the region of the polishing layer 1 where the dug portion 1a is formed becomes thin and the light transmittance of the region becomes high. The depth of the dug portion 1a is appropriately adjusted in relation to the thickness of the polishing layer. For example, 3 to 40%, and further 5 to 35% of the thickness of the region of the polishing layer 1 excluding the dug portion 1a. It is particularly preferably 10 to 30%. Specifically, the depth of the dug portion 1a is preferably, for example, 0.05 to 0.8 mm, more preferably 0.1 to 0.6 mm, and particularly preferably 0.2 to 0.5 mm.

  The type of the adhesive material forming the adhesive material layer 4b is not particularly limited, and examples thereof include acrylic, rubber-based, styrene-based, silicone-based, and urethane-based adhesive materials. The thickness of the pressure-sensitive adhesive layer 4b is not particularly limited, either, but is preferably about 10 to 500 μm, and more preferably about 30 to 300 μm.

  Further, the light adjusting sheet is not limited to the mode in which the light adjusting sheet is attached to the dug portion via the adhesive material layer 4b like the polishing pad 11 of the present embodiment, and covers the region corresponding to the opening v of the polishing layer 1. Other forms may be used as long as they are arranged in the. Specifically, for example, a light adjusting sheet is attached through an adhesive material layer without forming a dug portion in a region corresponding to the opening v of the polishing layer 1, or a dug portion is provided in a region corresponding to the opening v. Forming by a method such as applying a coating liquid for forming a light adjustment sheet on the back surface of the polishing layer without forming a film and drying and curing, or filling the coating liquid in the dug portion and curing. Methods and the like. In the case of adhering the light adjusting sheet with an adhesive, it can be ignored if the adhesive layer has a light transmittance of close to 100%, but if the adhesive layer shows a low light transmittance, the The laminated structure of the adjusting sheet and the pressure-sensitive adhesive layer has a maximum light transmittance (T1) of 50% or more and a maximum light transmittance in any wavelength range in the wavelength range of 350 to 700 nm, and a light transmittance. And a minimum light transmittance (T2) that minimizes, and a difference (T1-T2) between the maximum light transmittance (T1) and the minimum light transmittance (T2) is 20% or more. It shall be.

  Next, the material forming the polishing layer will be described in detail. It is preferable that the polishing layer in the present embodiment has a light-transmitting property over the entire area of the polishing surface, because it is not necessary to embed a light-transmitting plug that becomes a light-transmitting window. When the light-transmitting plug is embedded in the polishing layer, there is a tendency that slurry leakage occurs around the light-transmitting plug or the polishing characteristics become unstable when used for a long time. Specific examples of the material for obtaining the polishing layer having light transmittance in the entire area of the polishing surface include, for example, polyolefins such as polyurethane, polyethylene and polypropylene, polyesters, polyamides and polyureas, which have excellent light transmittance. Is mentioned. These may be used alone or in combination of two or more. Among these, polyurethanes such as thermoplastic polyurethanes and thermosetting polyurethanes are preferable from the viewpoint of excellent light transmission and abrasion resistance, and particularly thermoplastic polyurethanes are easy to achieve both a high polishing rate and low scratch resistance. It is preferable from the point. In this embodiment, a thermoplastic polyurethane will be described in detail as a representative example of the material of the polishing layer that can realize the above-mentioned light-transmitting polishing pad.

  The thermoplastic polyurethane used for the production of the polishing layer having a light-transmitting property over the entire area of the polishing surface is a reaction product obtained by polymerizing a raw material containing at least an amino group-free chain extender, a polymer diol and an organic diisocyanate. Is preferred. Such thermoplastic polyurethane is excellent in light transmittance.

  As the chain extender containing no amino group, a low molecular weight compound having no amino group but two hydroxyl groups and having a molecular weight of 300 or less is preferably used. Specific examples thereof include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,2-butanediol, 1,3- Butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,4-bis(β- Examples thereof include hydroxyethoxy)benzene, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, bis(β-hydroxyethyl)terephthalate and 1,9-nonanediol. These may be used alone or in combination of two or more. Among these, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, especially 1,4-butane Diol and 3-methyl-1,5-pentanediol are preferred. Further, as the chain extender, an amino group-containing chain extender may be used in combination, if necessary, as long as the effect of the present invention is not impaired.

  Specific examples of the polymer diol include polyether diols such as poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol), and poly(methyltetramethylene glycol); polybutylene adipate, poly Examples thereof include polyester diols such as caprolactone and poly(3-methyl-1,5-pentamethylene adipate); and polycarbonate diols such as polyhexamethylene carbonate diol. These may be used alone or in combination of two or more. Of these, polyether diols and polyester diols are preferable, and polyether diols are particularly preferable. The number average molecular weight of the polymeric diol is preferably 500 to 1500, more preferably 550 to 1200, and particularly preferably 600 to 1000. When the number average molecular weight of the polymer diol is too high, the light transmittance of the polishing layer tends to be lowered. On the other hand, when the number average molecular weight of the high molecular diol is too low, the hardness of the polishing layer becomes too high and polishing scratches tend to occur during polishing.

  As the organic diisocyanate, any organic diisocyanate that has been conventionally used for producing polyurethane can be used without particular limitation. Specific examples thereof include, for example, aliphatic or alicyclic diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, 4,4′-dicyclohexylmethane diisocyanate; 4,4′-diphenylmethane diisocyanate, 2,4′-tolylene diisocyanate, Aromatic diisocyanates such as 2,6'-tolylene diisocyanate and m-xylylene diisocyanate are mentioned. These may be used alone or in combination of two or more. Among these, 4,4'-diphenylmethane diisocyanate is particularly preferable in terms of excellent abrasion resistance of the resulting polishing pad.

  The content of nitrogen atoms derived from the isocyanate group of the thermoplastic polyurethane is 5.0 to 7.0% by mass, further 5.2 to 6.7% by mass, and particularly 5.4 to 6.4% by mass. Is preferred. If the content of nitrogen atoms is too low, the polishing layer tends to be too soft, and the flatness of the surface to be polished and polishing efficiency tend to decrease. On the other hand, if the content of nitrogen atoms is too high, the polishing layer tends to be too hard and scratches are likely to occur on the surface to be polished, and the light transmittance of the polishing layer tends to decrease.

  The thermoplastic polyurethane is obtained by polymerizing by a urethanization reaction using a known prepolymer method or a one-shot method, using a raw material containing at least a chain extender, a polymer diol, and an organic diisocyanate as described above. Be done. Preferably, it is obtained by a method in which the above-mentioned components are blended in a predetermined ratio in the substantial absence of a solvent, and continuous melt polymerization is performed while melt mixing using a single-screw or multi-screw extruder.

  The blending ratio of each component is appropriately adjusted according to the desired characteristics. For example, 1 mol of active hydrogen atoms contained in the polymer diol and the chain extender may be used to reduce the isocyanate group contained in the organic diisocyanate to 0. It is preferable to mix it in a ratio of 0.95 to 1.3 mol, further 0.96 to 1.1 mol, and particularly 0.97 to 1.05 mol. If the proportion of isocyanate groups contained in the organic diisocyanate is too low, the mechanical strength and abrasion resistance of the thermoplastic polyurethane tend to decrease, and if it is too high, the productivity and storage stability of the thermoplastic polyurethane are low. Tends to decline.

  Further, the thermoplastic polyurethane is a crosslinking agent, a filler, a crosslinking accelerator, a crosslinking aid, a softening agent, a tackifier, an antiaging agent, a foaming agent, if necessary, within a range that does not impair the effects of the present invention. Processing aids, adhesion promoters, inorganic fillers, organic fillers, crystal nucleating agents, heat resistance stabilizers, weather resistance stabilizers, antistatic agents, colorants, lubricants, flame retardants, flame retardant aids (antimony oxide, etc.), It may contain additives such as an anti-blooming agent, a release agent, a thickener, an antioxidant, and a conductive agent. The content ratio of the thermoplastic polyurethane additive is not particularly limited, but is preferably 50% by mass or less, more preferably 20% by mass or less, and particularly preferably 5% by mass or less.

  The thermoplastic polyurethane obtained by continuous melt polymerization as described above is formed into a sheet-like molded article by various molding methods such as extrusion molding method, injection molding method and calender molding method after being pelletized. Molded. In particular, extrusion molding using a T die is preferable in that a sheet-shaped molded product having a uniform thickness can be obtained.

The density of the molded article of thermoplastic polyurethane is preferably 1.0 g/cm ³ or more, more preferably 1.1 g/cm ³ or more, and particularly preferably 1.2 g/cm ³ or more. If the density of the molded article of thermoplastic polyurethane is too low, the polishing layer tends to be soft and the local flatness tends to decrease. Further, as the thermoplastic polyurethane, a non-foamed thermoplastic polyurethane is particularly preferable in that a light-transmitting property is not hindered by the foamed structure and a polishing layer having excellent light-transmitting property can be obtained.

  The polishing layer is finished by adjusting the size, shape, thickness and the like of the above-mentioned thermoplastic polyurethane sheet-shaped molded body by cutting, slicing, punching or the like. The thickness of the polishing layer is not particularly limited, but is preferably 1.0 to 2.5 mm, more preferably 1.2 to 2.2 mm, and particularly preferably 1.4 to 2.0 mm.

  In the polishing layer, the entire area of the polishing surface that contacts the material to be polished, including the area through which light can be transmitted in the thickness direction, is subjected to grinding processing or laser processing in a predetermined pattern such as concentric circles to form a G pattern in FIG. It is preferable to form a recess such as a groove or a hole as shown in FIG. Such recesses serve to uniformly and sufficiently supply the polishing slurry to the polishing surface, to discharge polishing debris that causes scratches, and to prevent damage to the wafer due to suction holding of the polishing pad. As the arrangement pattern of the grooves and holes, for example, concentric circles, lattices, spirals, radials, and the like, or a pattern in which a plurality of these are combined can be mentioned. Further, for example, when the concavities are formed concentrically, the pitch between the concavities is preferably 30 mm or less, more preferably 1 to 20 mm, and particularly about 2 to 10 mm. The width of the recess is preferably 0.1 to 5 mm, more preferably 0.2 to 3 mm, and particularly preferably 0.3 to 1 mm. Further, the depth of the recess is preferably 0.3 to 2 mm, more preferably 0.4 to 1.8 mm, and particularly preferably 0.5 to 1.5 mm. Further, as the cross-sectional shape of the groove, for example, a shape such as a rectangle, a trapezoid, a triangle, and a semicircle is appropriately selected according to the purpose.

  In the polishing pad of the present embodiment, the portion where the light adjustment layer is present preferably has, for example, the following optical characteristics. The first optical characteristic is that the light transmittance in the portion where the light adjusting layer is present is 12% or more, further 15% or more, and particularly 17% or more with respect to light in the entire wavelength range of 350 to 700 nm. It has such a maximum light transmittance (T3) and a minimum light transmittance (T4), and a difference (T3-T4) between the maximum light transmittance (T3) and the minimum light transmittance (T4) is 10%. It is preferably below 7%, especially below 5%. Note that T3 and T4 may match, that is, T3-T4 may be 0%.

  The second optical characteristic is that the light transmittance in the portion where the light adjusting layer is present is 15% or less, further 12% or less, and particularly 10% or less for light in the entire wavelength range of 350 to 700 nm. The minimum light transmittance (T5) and the maximum light transmittance (T6), and the difference (T6-T5) between the maximum light transmittance (T6) and the minimum light transmittance (T5) is 20% or more. Further, it is preferably 25% or more, and particularly preferably 30% or more.

  The first optical characteristic and the second optical characteristic vary depending on the configuration of the polishing apparatus, the type of the material to be polished, the required accuracy of end point detection, etc., but the first optical characteristic is usually preferable.

  In the polishing pad of the present embodiment as described above, when the polishing end point is detected by the optical means included in the CMP polishing apparatus, the end point detection accuracy is improved by showing a clear change in the reflected light intensity. .. Further, the wavelength dependence of the light transmittance can be corrected for each manufacturing lot or each polishing pad.

  Next, an example of CMP using the polishing pad 11 of the present embodiment will be described as a typical example with reference to FIG.

  A polishing apparatus 20 used for CMP using the polishing pad 11 of the present embodiment includes a circular rotating surface plate 5 for fixing the polishing pad 11 as shown in FIG. 2 and a top ring 6 for sucking and holding the wafer 10. A carrier 17 for pressing the wafer 10 against the polishing pad 11 while swinging the top ring 6 up and down, and a slurry nozzle 7 for supplying the polishing slurry S to the upper surface of the fixed polishing pad 11 are provided. The polishing pad 11 is adhered to the surface plate 5 via the adhesive layer 9. The polishing apparatus 20 is configured to rotate the surface plate 5 and the top ring 6 to press the surface to be polished of the wafer 10 against the polishing surface of the polishing pad 11 to perform polishing. The polishing apparatus 20 also includes a pad conditioner (not shown). Further, inside the surface plate 5, there are provided a light irradiation section 8 for detecting the end point of polishing by an optical means and an optical sensor (not shown) for detecting a change in intensity of the reflected light.

  In CMP using the polishing device 20, first, the polishing pad 11 is attached to the surface of the surface plate 5 via the adhesive layer 9. At this time, the polishing pad 11 is arranged so that the light irradiated by the light irradiation part 8 is incident on the part of the polishing pad 11 where the light adjustment layer 4 exists. Then, the surface plate 5 is rotated in the direction indicated by the arrow by a motor (not shown), and while flowing distilled water on the surface of the rotating polishing pad 11, for example, diamond particles are fixed on the surface of the carrier by nickel electrodeposition or the like. The pad conditioner is pressed to condition the surface of the polishing pad 11. By conditioning, the surface of the polishing pad is adjusted to have a surface roughness suitable for polishing the surface to be polished. Next, the polishing slurry s is supplied from the slurry nozzle 7 to the surface of the rotating polishing pad 11. When performing CMP, a lubricating oil, a cooling agent, etc. may be used together with the polishing slurry, if necessary. Examples of the polishing slurry include liquid media such as water and oil; abrasive grains such as silica, alumina, cerium oxide, zirconium oxide, and silicon carbide; oxidizing agents such as hydrogen peroxide solution; chelating agents such as glycine and EDTA: base A pH adjusting agent such as an acid; a polishing slurry used for CMP containing a surfactant, a dispersant such as a water-soluble polymer, and the like can be used without particular limitation.

  Then, the rotating wafer 10 attracted and held by the top ring 6 is pressed against the surface to be polished of the polishing pad 11 on which the polishing slurry s is evenly distributed, and the polishing surface and the material to be polished are relatively slid. Carry out. At this time, the light emitted from the light irradiation section 8 inside the surface plate 5 passes through the light adjusting layer 4 and the polishing layer 1 and reaches the surface to be polished of the wafer 10, and the reflected light thereof is an optical sensor not shown. Detected by. The optical sensor measures the amount of change in film thickness by, for example, monitoring the change in reflected light intensity. Then, the polishing is continued, and when a change in the reflected light intensity that causes a predetermined film thickness change amount is detected, the carrier 17 raises the top ring 6 to finish the polishing. Polishing is performed in this manner.

  Such CMP of the present embodiment is preferably used for polishing in manufacturing processes of various semiconductor devices, MEMS (Micro Electro Mechanical Systems) and the like. Examples of objects to be polished include quartz, silicon, glass, optical substrates, electronic circuit substrates, multilayer wiring substrates, hard disks, and the like. In particular, the material to be polished is preferably a silicon wafer or a semiconductor wafer. The semiconductor wafer has, for example, an insulating film such as silicon oxide, silicon nitride, or an organic polymer; a wiring material metal film such as copper, aluminum, or tungsten; a barrier metal film such as tantalum, titanium, tantalum nitride, or titanium nitride on its surface. There are things.

  Hereinafter, the present invention will be specifically described with reference to examples. The scope of the present invention is not limited to these examples.

[Example 1]
PTMG:BD:MDI=32.5:15.6: polytetramethylene glycol (PTMG) having a number average molecular weight of 850, 1,4-butanediol (BD), and 4,4′-diphenylmethane diisocyanate (MDI). A twin-screw extruder (30 mmφ, L/D=36, cylinder temperature: 75, which is used at a ratio of 51.9 (mass ratio) and rotates coaxially such that the total supply amount thereof is 300 g/min. To 260° C.) was continuously fed by a metering pump to carry out continuous melt polymerization to produce a thermoplastic polyurethane. The resulting melt of thermoplastic polyurethane was continuously extruded into water in a strand shape, then shredded into pellets with a pelletizer, and the pellets obtained were dehumidified and dried at 70° C. for 20 hours to give thermoplastic polyurethane. Manufactured. The nitrogen atom content derived from the isocyanate group calculated from the raw material mixture ratio was 5.8% by mass.

  Then, the obtained thermoplastic polyurethane was charged into a single-screw extruder (90 mmφ), and then downward at a cylinder temperature of 215 to 225° C. and a die temperature of 225° C. from a T-die having a lip width of 3.0 mm at a speed of 40 cm/min. Was extruded into a sheet having a thickness of 2.0 mm.

  The surface of this sheet is ground to form a uniform sheet having a thickness of 1.5 mm, which is cut out into a disk shape having a diameter of 510 mm, and the one side serving as the polishing surface of the disk-shaped sheet has a width of 0.5 mm and a depth of 0. Concentric circular grooves having a pitch of 0.8 mm and a pitch of 3.5 mm were formed. Then, in a portion 100 mm from the center of the surface opposite to the polishing surface (the back surface of the polishing layer), a rectangle (long side 54 mm, short side 16 mm) with a long side parallel to the diameter direction and a depth of 0.4 mm is formed. The dug portion was formed by grinding. Next, a 1.2 mm-thick polyurethane foam was attached as a cushion layer to the surface of the polishing layer opposite to the polishing surface, and the cushion layer in the region corresponding to the dug portion on the back surface of the polishing layer was cut out. To form an opening, and a polishing pad having a region through which light can pass in the thickness direction was manufactured.

  Then, in the opening of the cushion layer of the obtained polishing pad, the light adjusting sheet A1 was adhered to the back surface of the polishing layer with an adhesive having substantially no light absorbing property to form a light adjusting layer. The light adjusting sheet A1 is a resin sheet obtained by dyeing a polyethylene terephthalate (PET) sheet having a thickness of 0.1 mm with a dye, and having a maximum light transmittance (T1) of 65% at a wavelength of 350 to 700 nm as a wavelength. The minimum light transmittance (T2) of 35% is shown at 550 nm. Therefore, the difference between T1 and T2 was 30%. Regarding the light transmittance of the region of the light adjustment layer of the polishing pad, the maximum value (T3) of 20% was shown at a wavelength of 350 nm, and the minimum light transmittance (T4) of 15% at a wavelength of 350 to 700 nm was shown at 550 nm. Therefore, the difference between T3 and T4 was 5%.

  Then, the polishing pad was installed in a polishing apparatus "MIRA" manufactured by Applied Materials. And, using Asahi Diamond Industrial Co., Ltd. diamond dresser "CMP-M", while flowing ultrapure water at a flow rate of 200 mL/min, the dresser rotation speed was 120 rpm, the polishing pad rotation speed was 50 rpm, and the dresser load was 5.0 lbf. The polishing pad surface was conditioned for minutes. Next, under the conditions of a polishing pad rotation speed of 80 rpm, a wafer rotation speed of 70 rpm, and a polishing pressure of 20 kPa, polishing slurry (“PL-7105” manufactured by Fujimi Incorporated, ultra pure water, hydrogen peroxide solution (concentration: 31 mass) %) was mixed at a mass ratio of 1:2:0.09) and the SEMATECH 854 pattern wafer was polished for 130 seconds while flowing at a flow rate of 200 mL/min. In this polishing, when the copper film was removed and the barrier metal film was exposed and the reflectance of the laser light changed by 10% or more, it was evaluated that the end point could be detected. As a result of polishing the patterned wafer, a clear change in the detected laser intensity was observed at the stage when the copper film on the surface was removed, and it was possible to detect the polishing end point by light. Table 1 shows the result that the time required for removing the copper film on the surface was 85 seconds.

[Example 2]
A polishing pad was obtained and evaluated in the same manner as in Example 1 except that the light adjusting sheet A2 was used in place of the light adjusting sheet A1. The light adjusting sheet A2 is a resin sheet obtained by dyeing a PET sheet having a thickness of 0.1 mm with a dye, and has a maximum light transmittance (T1) of 80% at a wavelength of 350 to 700 nm at a wavelength of 650 nm. The minimum light transmittance (T2) of 30% is shown at 350 nm. Therefore, the difference between T1 and T2 was 50%. Regarding the light transmittance of the region of the light adjustment layer of the polishing pad, the maximum value (T6) of 35% at a wavelength of 350 to 700 nm was shown at a wavelength of 650 nm, and the minimum light transmittance (T5) of 10% was shown at 350 nm. Therefore, the difference between T6 and T5 was 25%. As a result of mounting the polishing pad on a polishing apparatus and polishing the patterned wafer, a clear change in the detected laser intensity was observed at the stage when the copper film on the surface was removed, and it was possible to detect the polishing end point by light. The time required for removing the copper film on the surface was 85 seconds.

[Example 3]
In Example 1, instead of grinding a rectangular dug portion having a depth of 0.4 mm to a portion 100 mm from the center of the surface of the polishing layer opposite to the polishing surface (back surface of the polishing layer), A polishing pad was manufactured and evaluated in the same manner except that the dug portion having a thickness of 0.05 mm was formed. Regarding the light transmittance of the region of the light adjustment layer of the polishing pad, the maximum value (T3) of 15% was shown at a wavelength of 700 nm, and the minimum light transmittance (T4) of 10% at a wavelength of 350 to 700 nm was shown at 500 nm. Therefore, the difference between T3 and T4 was 5%. As a result of mounting the polishing pad on a polishing apparatus and polishing the patterned wafer, a clear change in the detected laser intensity was observed at the stage when the copper film on the surface was removed, and it was possible to detect the polishing end point by light. The time required for removing the copper film on the surface was 87 seconds.

[Example 4]
In Example 3, a polishing pad having a light-transmitting region in the thickness direction was prepared in the same manner as in Example 3 except that concentric circular grooves were not formed on the surface of the polishing layer in the light-transmitting region. It was manufactured and evaluated. Regarding the light transmittance of the region of the light adjustment layer of the polishing pad, the maximum value (T3) of 18% was shown at a wavelength of 700 nm, and the minimum light transmittance (T4) of 12% at a wavelength of 350 to 700 nm was shown at 500 nm. Therefore, the difference between T3 and T4 was 6%. As a result of mounting the polishing pad on a polishing apparatus and polishing the patterned wafer, a clear change in the detected laser intensity was observed at the stage when the copper film on the surface was removed, and it was possible to detect the polishing end point by light. The time required for removing the copper film on the surface was 95 seconds.

[Comparative Example 1]
A polishing pad was obtained and evaluated in the same manner as in Example 1 except that the light adjusting sheet A3 was used instead of the light adjusting sheet A1. The light adjusting sheet A3 is a resin sheet obtained by dyeing a PET sheet having a thickness of 0.1 mm with a dye, and shows a maximum light transmittance (T1) of 35% at a wavelength of 600 nm and a wavelength of 350 to The minimum light transmittance (T2) of 5% at 700 nm is shown at 400 nm. Therefore, the difference between T1 and T2 was 30%. Regarding the light transmittance of the region of the light adjustment layer of the polishing pad, the maximum value (T3) of 11% was shown at a wavelength of 600 nm, and the minimum light transmittance (T4) of 1% at a wavelength of 350 to 700 nm was shown at 400 nm. Therefore, the difference between T3 and T4 was 10%. As a result of mounting the polishing pad on the polishing apparatus and polishing the patterned wafer, the change in the detected laser intensity at the stage when the copper film on the surface was removed was small and the polishing end point could not be detected by light.

[Comparative example 2]
A polishing pad was obtained and evaluated in the same manner as in Example 3 except that the light adjusting sheet A4 was used instead of the light adjusting sheet A1. The light adjusting sheet A4 is a resin sheet obtained by dyeing a PET sheet having a thickness of 0.1 mm with a dye, and shows a maximum light transmittance (T1) of 40% at a wavelength of 450 nm and a wavelength of 350 to 350 nm. The minimum light transmittance (T2) of 30% at 700 nm is shown at 700 nm. Therefore, the difference between T1 and T2 was 10%. Regarding the light transmittance of the region of the light adjustment layer of the polishing pad, the maximum value (T3) of 10% was shown at a wavelength of 500 nm, and the minimum light transmittance (T4) of 3% at a wavelength of 350 to 700 nm was shown at 350 nm. Therefore, the difference between T3 and T4 was 7%. As a result of mounting the polishing pad on the polishing apparatus and polishing the patterned wafer, the change in the detected laser intensity at the stage when the copper film on the surface was removed was small and the polishing end point could not be detected by light.

1 Polishing Layer 2 Cushion Layer 3 Adhesive Material Layer 4 Light Adjustment Layer 4a Light Adjustment Sheet 4b Adhesive Material Layer 5 Surface Plate 6 Top Ring (Holder)
7 Slurry Nozzle 8 Light Irradiation Unit 10 Wafers 11, 21 Polishing Pad 17 Carrier 20 Polishing Device

  By using the polishing pad of the present invention, it is possible to accurately inspect the material to be polished during polishing and measure the polishing end point with an optical means. Such a polishing pad is useful, for example, in chemical mechanical polishing of silicon wafers and semiconductor wafers during the manufacture of semiconductor devices.

Claims (9)

A polishing layer having a polishing surface as a main surface, and a cushion layer laminated on the back surface of the polishing layer,
The polishing layer has a light-transmissive region that transmits light in the thickness direction in at least a part thereof,
The cushion layer has an opening in a portion corresponding to the light transmissive region,
Further comprising a light adjusting layer which is colored if covering a region corresponding to the opening of the back surface of the polishing layer,
The light adjusting layer has a maximum light transmittance (T1) having a light transmittance of 50% or more and a maximum and a minimum light transmittance having a minimum light transmittance at any wavelength in a wavelength range of 350 to 700 nm. A polishing pad having a ratio (T2) and a difference (T1-T2) between the maximum light transmittance (T1) and the minimum light transmittance (T2) is 20% or more.   The polishing pad according to claim 1, wherein the light adjustment layer includes a light adjustment sheet that is a resin sheet containing a coloring material.   The polishing pad according to claim 1 or 2, wherein the polishing layer has a light transmittance of 10% or more in the entire range of a wavelength of 350 to 700 nm in the entire region of the polishing surface.   The polishing pad according to any one of claims 1 to 3, wherein the polishing layer is made of a homogeneous molded body of thermoplastic polyurethane.   The polishing pad according to any one of claims 1 to 4, wherein the light adjustment layer is provided in a dug portion on the back surface of the polishing layer.   It has a maximum light transmittance (T3) of 12% or more and a minimum light transmittance (T4) in the portion where the light adjustment layer is present for light in the entire range of wavelengths of 350 to 700 nm. The polishing pad according to claim 1, wherein a difference (T3−T4) between the maximum light transmittance (T3) and the minimum light transmittance (T4) is 10% or less.   It has a minimum light transmittance (T5) of 15% or less and a maximum light transmittance (T6) in the portion where the light adjustment layer is present for light in the entire range of wavelengths of 350 to 700 nm. The polishing pad according to any one of claims 1 to 5, wherein the difference (T6-T5) between the maximum light transmittance (T6) and the minimum light transmittance (T5) is 20% or more.   The polishing pad according to any one of claims 1 to 7, wherein a plurality of concave portions are present at a pitch of 30 mm or less in the entire area of the polishing surface. Fixing the polishing pad according to any one of claims 1 to 8 to a surface plate of a polishing apparatus;
Holding the material to be polished in a holder of a polishing device so as to face the polishing surface of the polishing pad,
While supplying a polishing slurry between the polishing pad and the material to be polished, the step of polishing the material to be polished by relatively sliding the polishing surface and the material to be polished,
A polishing method, wherein the polishing end point is detected by transmitting light to a portion where the light adjustment layer is present, reflecting the light on the surface of the material to be polished, and detecting a change in the intensity of the reflected light. .

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