Polishing cloth

Abstract

Provided is a polishing cloth comprising a nonwoven fabric composed of fibers and a resin composition impregnated into the nonwoven fabric, wherein: said polishing cloth is provided with a polishing surface; a direction perpendicular to the polishing surface is a vertical direction; a CT image of a cross section parallel to the vertical direction is acquired; among a plurality of cross sections of the fibers in the CT image, 2% of the cross sections in a descending order of area are measurement targets; the orientation directions of fibers having the cross sections are determined from the shapes of the respective cross sections, which are the measurement targets; and when the proportion of the number of the cross sections of which the orientation directions are less than 30º with respect to the vertical direction is defined as the vertical orientation ratio (X (%)) of the fibers, the vertical orientation ratio (X (%)) is less than 12.1%.

Description

polishing cloth CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application No. 2024-134415, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to a polishing cloth.

[0003] Conventionally, semiconductor wafers and the like have been polished by a method known as chemical mechanical polishing (CMP). Chemical mechanical polishing uses a slurry containing components such as abrasive grains for mechanically polishing the workpiece and chemical components for chemically promoting the polishing. Furthermore, polishing cloths are used to polish workpieces such as wafers (see, for example, Patent Document 1). Known polishing cloths include a nonwoven fabric that forms the base of the polishing cloth and a resin composition impregnated into the nonwoven fabric. This type of polishing cloth is not only used for chemical mechanical polishing of semiconductor wafers, but is also widely used for other purposes.

[0004] Japanese Patent Application Publication No. 2021-107106

[0005] In chemical mechanical polishing using an abrasive cloth, defects such as scratches and particles may occur on the surface of the polished object after polishing. It is necessary to suppress the occurrence of these types of defects in chemical mechanical polishing using an abrasive cloth. Although various methods for imparting good surface properties to the polished object after polishing have been investigated, there is still room for improvement. Therefore, an object of the present invention is to provide an abrasive cloth that can impart good surface properties to the polished object after polishing.

[0006] The present invention provides a polishing cloth having a nonwoven fabric made of fibers and a resin composition impregnated into the nonwoven fabric, the polishing cloth having a polishing surface, the direction perpendicular to the polishing surface being the longitudinal direction, obtaining a CT image of a cross section parallel to the longitudinal direction, measuring 2% of a plurality of cross sections of the fibers in the CT image in descending order of area, determining the orientation direction of the fibers having the cross section from the shape of each of the cross sections measured, and defining the longitudinal orientation rate (X (%)) of the fibers as the percentage of the number of cross sections whose orientation direction is less than 30° to the longitudinal direction, the longitudinal orientation rate (X (%)) of the fibers is less than 12.1%.

[0007] FIG. 1 is a schematic plan view of a polishing cloth according to one embodiment. FIG. 2 is a schematic cross-sectional view showing the cross section taken along line II-II in FIG. 1. FIG. 3 is a cross-sectional view (SEM image) of the polishing cloth, and is a diagram showing the area indicated by dashed line III in FIG. 2. FIG. 4a is a schematic perspective view showing the cross-sectional shape of the fibers of the nonwoven fabric. FIG. 4b is a schematic perspective view showing the cross-sectional shape of the fibers of the nonwoven fabric. FIG. 4c is a schematic diagram showing how to determine the longitudinal orientation rate of the fibers. FIG. 5a is a cross-sectional view (SEM image) of the polishing cloth of Comparative Example 1. FIG. 5b is a CT image (fiber extraction image) of the polishing cloth of Comparative Example 1. FIG. 6a is a cross-sectional view (SEM image) of the polishing cloth of Example 1. FIG. 6b is a CT image (fiber extraction image) of the polishing cloth of Example 1. FIG. 7 is a diagram showing the reproducibility of the longitudinal orientation rate when polishing cloths are manufactured using the same manufacturing method. Fig. 8 is a diagram showing the surface roughness (viewing angle: 177 μm × 133 μm) of a wafer after polishing when a wafer is polished using a combination of a polishing cloth of an example or a comparative example and a specific slurry. Fig. 9 is a diagram showing the surface roughness (viewing angle: 177 μm × 133 μm) of a wafer after polishing when a wafer is polished using a combination of a polishing cloth of an example or a comparative example and a specific slurry. Fig. 10 is a diagram showing the surface roughness (viewing angle: 177 μm × 133 μm) of a wafer after polishing when a wafer is polished using a combination of a polishing cloth of an example or a comparative example and a specific slurry.

[0008] An embodiment of the present invention will be described below. The polishing cloth of this embodiment is suitably used, for example, for chemical mechanical polishing using a slurry containing abrasive grains. The polishing cloth is not particularly limited in its use, but can be used, for example, for chemical mechanical polishing of a wafer as the object to be polished. Examples of wafers to be polished include silicon (Si) wafers, compound wafers, and glass wafers. Examples of compound wafers include gallium oxide (Ga ２ O ３ ) wafers, gallium nitride (GaN) wafers, aluminum nitride (AlN) wafers, sapphire (Al ２ O ３ ) wafer, gallium arsenide (GaAs) wafer, indium phosphide (InP) wafer, lithium niobate (LiNbO ３ ) wafer, lithium tantalate (LiTaO ３ Examples of the glass wafer include a quartz glass wafer, an alkali glass wafer, and a borosilicate glass wafer.

[0009] As shown in FIG. 1 , the polishing cloth 1 of this embodiment has at least one surface serving as a polishing surface 1p for polishing an object to be polished. The polishing surface of the polishing cloth 1 of this embodiment has a circular outline shape in a plan view. The polishing cloth 1 of this embodiment has a back surface 1b that is the opposite surface to the polishing surface 1p. The polishing cloth 1 of this embodiment is used, for example, by rotating relative to the object to be polished while being in surface contact with the object to be polished with a slurry interposed therebetween. As will be described later, the polishing cloth 1 of this embodiment can suppress the occurrence of defects on the surface of the object to be polished after polishing because the polishing surface 1P and the object to be polished are in good contact with each other.

[0010] As shown in Figures 2 and 3, in the polishing cloth 1 of this embodiment, the direction perpendicular to the polishing surface 1p is the longitudinal direction D1, and the thickness direction of the polishing cloth 1 is the longitudinal direction D1. Furthermore, in the polishing cloth 1 of this embodiment, the direction parallel to the polishing surface 1p is the transverse direction D2. The polishing cloth 1 of this embodiment includes a nonwoven fabric 11 and a resin composition 12. The nonwoven fabric 11 serves as the base of the polishing cloth 1, and the resin composition 12 is impregnated into the nonwoven fabric 11. The resin composition 12 is impregnated into the nonwoven fabric 11 so as not to fill all of the spaces between the fibers 11f constituting the nonwoven fabric 11. More specifically, a portion of the resin composition 12 is impregnated into the nonwoven fabric 11 so as to form a thin coating that covers each of the fibers 11f constituting the nonwoven fabric 11. Furthermore, a portion of the resin composition 12 is impregnated into the nonwoven fabric 11 so as to form a resin film between two fibers 11f that are spaced apart. The polishing cloth 1 has voids 13 where neither the resin composition 12 nor the fibers 11f are present. The voids 13 are formed so as to be continuous in the vertical direction D1 and the horizontal direction D2 of the polishing cloth 1. The voids 13 that are continuous vertically and horizontally are contained in the polishing cloth 1 in a mesh-like pattern.

[0011] As also shown in Figure 3, the polishing cloth 1 of this embodiment has voids 13 formed therein so that when cut along a plane parallel to the longitudinal direction D1, multiple cross sections are scattered across the plane.

[0012] In the polishing cloth 1 of this embodiment, the fibers 11f constituting the nonwoven fabric 11 are oriented in the longitudinal direction D1 at a rate less than a predetermined rate. Fibers 11f oriented in the longitudinal direction D1 (thickness direction of the polishing cloth 1) have ends that tend to protrude perpendicularly from the polishing surface 1p and come into strong contact with the workpiece, which can cause defects on the surface of the workpiece. The polishing cloth 1 of this embodiment has a relatively small number of fibers 11f oriented in the longitudinal direction D1, which can prevent defects from occurring on the surface of the workpiece. Furthermore, when the fibers 11f are oriented in the longitudinal direction D1, the resin composition 12 can easily penetrate between the fibers 11f from the surface of the nonwoven fabric 11, which can increase the compressive strength in the thickness direction of the polishing cloth 1. The polishing cloth 1 of this embodiment has a relatively small number of fibers 11f oriented in the longitudinal direction D1 (thickness direction of the polishing cloth 1), which can prevent localized increases in compressive strength and prevent defects from occurring on the surface of the workpiece after polishing.

[0013] The polishing cloth 1 of this embodiment is configured so that, when cut on an imaginary plane parallel to the longitudinal direction D1, multiple cross sections of the fibers 11f constituting the nonwoven fabric 11 are scattered on the imaginary plane. 2% of the multiple cross sections of the fibers 11f are measured in descending order of area, and the orientation direction of the fibers 11f having these cross sections is determined from the shape of each of the cross sections measured. The longitudinal orientation rate (X(%)) of the fibers 11f is defined as the percentage of the number of cross sections whose orientation direction is less than 30° with respect to the longitudinal direction D1. The longitudinal orientation rate (X(%)) of the fibers 11f is less than 12.1%.

[0014] The cross-sectional shape of the fibers 11f can be analyzed using, for example, a computed tomography (CT) device. The acquired CT image can be, for example, a square with each side parallel to the longitudinal direction D1 and the transverse direction D2, e.g., a 2 mm square that covers the entire longitudinal direction D1 of the polishing cloth 1. In a CT image captured to form a 2 mm square, the fibers 11f are more likely to move due to external forces in areas closer to the polishing surface 1p and back surface 1b of the polishing cloth 1 than in the central portion in the thickness direction, which can cause errors. Therefore, it is desirable to exclude these areas from the area used to analyze the cross-sectional shape of the fibers 11f. Specifically, the area used to analyze the cross-sectional shape of the fibers 11f can be, for example, the area excluding 10 to 20% of the surface layer from the polishing surface 1p side and the back surface 1b side, when the thickness of the polishing cloth 1 is 100%. Furthermore, even when the thickness of the polishing pad 1 is much greater than 2 mm, the viewing angle can be adjusted so that the area for analyzing the cross section in the CT image is the area excluding 10 to 20% of the surface layer from both the polishing surface 1p side and the back surface 1b side. Analysis of the cross-sectional shape of the fiber 11f can be performed by acquiring 57 CT images so that the interplanar spacing in the horizontal direction D2 is 25 μm, for example.

[0015] Specifically, the CT images used for analysis can be obtained by extracting and visualizing the cross sections of the fibers using analysis software commercially available from Volume Graphics Co., Ltd. under the trade name "VGSTUDIO MAX" from CT data acquired using a commercially available device, for example, "X-ray CT Scanner" from Yamato Scientific Co., Ltd. The orientation of the fiber cross sections in the obtained CT images can be determined by measuring the Feret diameter in both the vertical and horizontal directions (D1, D2) of the cross section using image analysis software commercially available from Mitani Shoji Co., Ltd. under the trade name "Win Roof." Note that in CT images, multiple fiber cross sections may be observed connected. Since the image analysis software described above is equipped with a noise processing function, in this case, noise processing can be performed so that the fiber cross sections are separated, and the Feret diameter can be measured. Note that if the cross sections of several fibers are too close to each other and form a single bundle, making it difficult to separate them using noise processing, they will be treated as a single cross section.

[0016] The method for determining the orientation of the fibers 11f will be described in detail below. For example, as shown in FIG. 4a, among the cross sections of the fibers 11f seen in a CT image, for example, a fiber 11f cut nearly perpendicularly on a plane P1 parallel to the longitudinal direction D1 and having a relatively round cross section XSa, the fiber 11f can be considered to extend in the transverse direction D2. For example, as shown in FIG. 4b, a cross section XSb observed in a stretched state can be determined to have such a cross-sectional shape because the fibers 11f extend in the direction of extension of the cross section and were cut nearly parallel to the direction of extension of the fibers 11f. Typically, the cross section XSb observed in a stretched state has a larger cross-sectional area than the round cross section XSa. Therefore, the longitudinal orientation ratio (X (%)) is determined by measuring the areas of all cross sections within a measurement area set in the CT image, and then targeting the cross sections that fall within the top 2% of the largest cross-sectional areas when the total number of measured cross sections is taken as 100%.

[0017] The CT images can be taken so that the total number of cross sections for which the area is to be calculated is 5,000 or more, for a total of 57 images. In other words, the CT images can be taken so that the number of the top 2% of cross sections to be measured for Feret's diameter is 100 or more (5,000 x 2% = 100). The number of cross sections to be measured for Feret's diameter is usually higher, as the reliability of the analysis results improves. The number of cross sections to be measured may be 200 or more, 300 or more, or 500 or more. The number of cross sections to be measured in the CT images is, for example, 5,000 or less. Therefore, the total number of cross sections to be calculated for the area in the CT images may be 10,000 or more, 15,000 or more, or 25,000 or more. The total number of cross sections to be calculated for the area in the CT images is, for example, 250,000 or less.

[0018] The orientation direction of the fiber 11f can be determined from the angle θ between the diagonal line DL of the rectangle LA1, which is a rectangle LA1 whose short and long sides are parallel to the longitudinal direction D1 and the transverse direction D2, respectively, and whose four sides are each drawn to circumscribe the cross section XSb, as shown in Figure 4c, for example.

[0019] Specifically, the angle θ of the diagonal line DL, which represents the orientation direction of the fibers 11f, can be calculated by determining the Feret diameter (L1) in the longitudinal direction D1 of the cross section XSb and the Feret diameter (L2) in the transverse direction, and then calculating the arctangent (arctan) from the aspect ratio (L2 / L1) of the Feret diameters. In the polishing cloth 1 of this embodiment, when the ratio of the number of cross sections satisfying the following formula (1) is defined as the longitudinal orientation rate (X(%)) in which the fibers 11f are oriented in the longitudinal direction D1, the longitudinal orientation rate (X(%)) satisfies the following formula (2). [arctan(L2 / L1)] / π×180°<30° (1) X(%)<12.1(%) (2)

[0020] As described above, the polishing cloth 1 of this embodiment has a longitudinal fiber orientation rate (X(%)) of less than 12.1%. The longitudinal fiber orientation rate (X(%)) of the polishing cloth 1 may be, for example, less than 10.0%. The longitudinal fiber orientation rate (X(%)) may be less than 9.0%, less than 8.0%, less than 7.0%, or less than 6.0%. The longitudinal fiber orientation rate (X(%)) of the polishing cloth 1 may be, for example, 0.1% or more. The longitudinal fiber orientation rate (X(%)) may be 0.5% or more, or 1.0% or more.

[0021] It is preferable that the polishing cloth 1 has a certain degree of flexibility. The polishing cloth 1 may have an Asker C hardness of, for example, 70 or less. The Asker C hardness of the polishing cloth 1 may be 68 or less, or may be 66 or less. It is preferable that the polishing cloth 1 exhibits a certain level of resilience against pressure from the object to be polished. The polishing cloth 1 may have an Asker C hardness of, for example, 50 or more. The Asker C hardness of the polishing cloth 1 may be 54 or more, or may be 58 or more.

[0022] The Asker C hardness of the polishing cloth 1 can be confirmed by carrying out a spring hardness test specified in JIS K7312-1996 "Physical testing methods for thermosetting polyurethane elastomer moldings" using a type C testing machine. The test is carried out at 23°C, and the value (instantaneous value) immediately after the pressure surface comes into contact is measured.

[0023] The polishing cloth 1 preferably has voids 13 at a predetermined ratio inside. The polishing cloth 1 has an apparent density of, for example, 400 kg / m ３ The apparent density of the polishing cloth 1 can be, for example, 350 kg / m ３ or less, 300 kg / m ３ or less, 270 kg / m ３ The apparent density of the polishing pad 1 may be, for example, 200 kg / m or less. ３ The apparent density of the polishing cloth 1 can be 220 kg / m or more. ３ The apparent density of the polishing pad 1 can be measured based on JIS K7222:2005.

[0024] The mass per unit area of ​​the nonwoven fabric 11 that forms the base of the polishing cloth 1 is, for example, 100 g / m ２ More than 1000g / m ２ The nonwoven fabric may be, for example, a needle-punched nonwoven fabric, a spunlace nonwoven fabric, or a steam-jet nonwoven fabric, in which fibers are entangled by applying force to the fibers in the thickness direction, or a thermal-bonded nonwoven fabric or a chemical-bonded nonwoven fabric, in which fibers are bonded directly or via an adhesive. Of these, nonwoven fabrics in which fibers are entangled, such as needle-punched nonwoven fabrics, spunlace nonwoven fabrics, and steam-jet nonwoven fabrics, are preferred because the fiber density can be easily adjusted. Needle-punched nonwoven fabrics and spunlace nonwoven fabrics are particularly preferred because the fiber material can be selected relatively freely.

[0025] The longitudinal orientation rate (X (%)) of the fibers in the nonwoven fabric can be adjusted, for example, by the tension applied to the web in the transverse direction (plane direction) when forming the nonwoven fabric. Specifically, increasing the tension strengthens the orientation of the fibers in the transverse direction, and therefore, by using a nonwoven fabric produced in this way to produce a polishing cloth, a polishing cloth with a low longitudinal orientation rate (X (%)) can be obtained.

[0026] When using a nonwoven fabric in which the fibers are entangled, such as a needle-punched nonwoven fabric, the longitudinal orientation rate (X (%)) of the fibers of the polishing cloth 1 is likely to be high if a conventional manufacturing method is used. Therefore, the nonwoven fabric 11 in this embodiment is preferably manufactured under conditions for entangling the fibers that are more relaxed than usual. Specifically, for example, in the case of a needle-punched nonwoven fabric, the longitudinal orientation rate (X (%)) can be reduced by reducing the number of needle puncture points (intertwined fiber points) per unit area compared to usual. Furthermore, the longitudinal orientation rate (X (%)) can be reduced by thickening the fibers or shortening the fiber length. This is also true for spunlace nonwoven fabrics, steam-jet nonwoven fabrics, and the like.

[0027] In order to homogenize the surface quality of the polishing cloth 1 with a needle-punched nonwoven fabric, it is considered more effective to reduce the number of fibers guided by one needle by reducing the punch speed, the number of barbs provided on one needle, or the size of the barb, rather than reducing the number of needle piercing points per unit area. When attempting to reduce the longitudinal orientation rate (X (%)) in a needle-punched nonwoven fabric using such a method, it may be better to increase the number of piercing points per unit area in order to homogenize the surface quality. ２ The number of puncture points per cm can be, for example, 10 or more. ２ It may be 20 or more points / cm ２ or more, 25 locations / cm ２ It may be 30 points / cm or more. ２ or more, 35 locations / cm ２ The needle-punched nonwoven fabric may have a size of 1 cm square (1 cm ２ The number of puncture points per needle may be, for example, 200 or less.

[0028] The polishing cloth 1 of this embodiment can be a nonwoven fabric 11 containing, for example, polyester fibers or polyamide fibers. The average fineness of the nonwoven fabric 11 can be, for example, 10 dtex or less. The average fineness of the nonwoven fabric 11 may be 8 dtex or less, or 5 dtex or less. The average fineness of the nonwoven fabric 11 may be 4 dtex or less, 3 dtex or less, or 2 dtex or less. The average fineness of the nonwoven fabric is, for example, 0.1 dtex or more. The nonwoven fabric 11 may contain two or more types of fibers.

[0029] The nonwoven fabric 11 may contain a main fiber that accounts for the largest mass proportion of the fibers contained therein, and one or more types of secondary fibers other than the main fiber. One or both of the main fiber and the secondary fiber may be a modified cross-section fiber having a hollow cross-section or a star-shaped cross-section. Modified cross-section fibers have stronger stiffness (higher bending stiffness) than typical fibers with a round cross-section. Therefore, by including such fibers, the nonwoven fabric 11 can suppress longitudinal orientation of the fibers during fiber entanglement.

[0030] One or both of the main and secondary fibers may be uncrimped fibers with a crimp percentage of less than 10%, or may be crimped fibers with a crimp percentage of 10% or more. Crimped fibers have a significantly different fiber orientation from one edge to the other. Therefore, the inclusion of such fibers can reduce the longitudinal fiber orientation rate (X (%)) in the nonwoven fabric 11.

[0031] One or both of the main and secondary fibers may be ultrafine fibers having a fineness of 0.5 dtex or less. The ultrafine fibers may be what are called ultrafine fibers having a fineness of 0.3 dtex or less. Ultrafine fibers have superior flexibility compared to fibers of normal thickness. In other words, ultrafine fibers are less likely to entrain surrounding fibers when caught on barbs and guided in the longitudinal direction during needle punching or the like. Therefore, the inclusion of such fibers can reduce the longitudinal orientation rate (X (%)) of the fibers in the nonwoven fabric 11.

[0032] One or both of the main fibers and the secondary fibers may be made of a single resin composition, or may be composite fibers (conjugate fibers) in which fibers made of one resin composition are integrated with fibers made of another resin composition. The composite fibers may be of a side-by-side type or a core-sheath type. The composite fibers may be heat-fusible fibers made of resins with different melting points. By including heat-fusible fibers that exhibit heat-fusible properties when heated, the fibers can be bonded together by heat fusion. In such a nonwoven fabric, the binding force of the fibers during needle punching can be increased, preventing the fibers 11f from being oriented in the longitudinal direction D1.

[0033] The content of each of the modified cross-section fibers, crimped fibers, ultrafine fibers, and composite fibers in the nonwoven fabric can be, for example, 1% by mass or more. The content of each of these fibers may be 5% by mass or more, 10% by mass or more, 20% by mass or more, or 30% by mass or more. The content of each of these fibers can be, for example, 50% by mass or less.

[0034] Furthermore, a fiber that exhibits thermal fusion properties and has a cross-sectional shape, for example, a snowman-shaped side-by-side composite fiber, made using resin compositions with different heat shrinkage properties, can be not only a composite fiber but also a modified cross-section fiber, a crimped fiber, or a thermal fusion fiber. Furthermore, by reducing the fineness of the fiber, the fiber can also become an ultrafine fiber. The nonwoven fabric 11 may contain fibers that serve several of the above functions. In this case, by adding, for example, 15% by mass of one type of fiber that can serve as all of the modified cross-section fiber, crimped fiber, ultrafine fiber, and composite fiber, the nonwoven fabric 11 can have a content of each fiber of 15% by mass.

[0035] When a needle-punched nonwoven fabric is used as nonwoven fabric 11, a general needle-punched nonwoven fabric may be used, which is produced by depositing fibers to form a web and then needle-punching the web so that needles penetrate the web in the thickness direction. When a needle-punched nonwoven fabric is used as nonwoven fabric 11, a needle-punched nonwoven fabric may be used in which the needles are stopped from penetrating the web midway so that the barbs on the needles do not penetrate the web, thereby reducing the longitudinal orientation rate (X (%)).

[0036] In a needle-punched nonwoven fabric produced by stopping needle penetration midway, the barb reach region extends from the surface to a certain point in the thickness direction, where fiber entanglement by the barbs occurs, and the remaining region defines a barb non-reach region where fiber entanglement by the barbs does not occur. When needles penetrate from both sides of the web, both ends in the thickness direction can be defined as barb reach regions, and the central portion in the thickness direction can be defined as a barb non-reach region. The nonwoven fabric 11 constituting the polishing cloth 1 may be obtained by cutting the surface layer of the nonwoven fabric produced in this manner to remove part or all of the barb reach region. This can further reduce the longitudinal orientation rate (X (%)) of the polishing cloth 1. The removal of the surface layer of the nonwoven fabric may be performed before or after the nonwoven fabric is impregnated with the resin composition. The removal of the surface layer of the nonwoven fabric may be performed both before and after the impregnation with the resin composition.

[0037] As described above, the polishing cloth 1 of this embodiment can be manufactured by entangling fibers in the thickness direction of the web to prepare a nonwoven fabric and impregnating the nonwoven fabric 11 with the resin composition 12. The entanglement of the fibers of the web can be performed by needle punching. The entanglement of the fibers by needle punching can be performed so that the needles do not penetrate the web, and the needle punched region can be from the surface to halfway in the thickness direction. Alternatively, the polishing cloth 1 can be manufactured by removing the surface layer of the nonwoven fabric before or after impregnation with the resin composition 12, thereby removing part or all of the barb reachable region.

[0038] The resin composition 12 used to form the polishing cloth 1 together with the nonwoven fabric 11 may consist solely of resin, or may contain various additives such as functional agents and fillers in addition to resin. The resin composition 12 may contain, for example, polyurethane resin, polyamide resin, or polyvinyl alcohol resin as the base resin (the resin with the largest mass proportion). From the viewpoints of impregnation into the nonwoven fabric and adhesion to the fibers 11f constituting the nonwoven fabric 11, the base resin of the resin composition 12 is preferably a thermoplastic polyurethane resin. The resin composition 12 may contain two or more types of resin. The proportion of polyurethane resin in the total resin content of the resin composition 12 may be 80% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more. The resin contained in the resin composition 12 may essentially consist of polyurethane resin alone.

[0039] The resin composition is preferably impregnated into the nonwoven fabric by wet impregnation, which will be described later, and preferably contains a thermoplastic polyurethane resin, which is easy to use in such a method. The resin composition may also be impregnated into the nonwoven fabric by dry impregnation, which will be described later, and in that case, may contain a thermosetting polyurethane resin, which is easy to use in such a method.

[0040] The polyurethane resin may be a polyether-based polyurethane resin or a polyester-based polyurethane resin. In terms of excellent hydrolysis resistance, the polyurethane resin is preferably a polyether-based polyurethane resin, and more preferably a polyether-based polyurethane resin containing polytetramethylene glycol (PTMG) as a main structural unit. The polyether-based polyurethane resin may be a polymer containing a polyether-based polyol and a polyisocyanate compound as structural units, with these being urethane-bonded, or may be a polymer further containing a polyamine compound as a structural unit and containing a urea bond. The polyurethane resin may contain 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA) or the like as a structural unit to introduce a urea bond.

[0041] As described above, the polishing cloth 1 of this embodiment can be produced by, for example, carrying out a nonwoven fabric production step of entangling the fibers of the web to produce the nonwoven fabric 11, and an impregnation step of impregnating the produced nonwoven fabric with a resin composition containing a polyurethane resin. In the process of producing the polishing cloth 1 of this embodiment, a surface layer removal step of removing a surface layer of the nonwoven fabric may be carried out between the nonwoven fabric production step and the impregnation step and / or after the impregnation step.

[0042] The entanglement of fibers in the nonwoven fabric production process can be carried out, for example, by a needle punching method in which needle punching is carried out on a web.

[0043] In this embodiment, the needles are inserted only halfway into the web so as not to penetrate the web, and a nonwoven fabric is produced which has a barb reach region on the surface layer on the side that will become the polishing surface and further has a barb non-reach region that contacts the barb reach region from the inside in the thickness direction. An impregnation process is then carried out in which the nonwoven fabric produced in the nonwoven fabric production process is impregnated with a resin composition containing a polyurethane resin. This produces a polishing cloth in which the longitudinal orientation rate (X (%)) in the surface layer is higher than the longitudinal orientation rate (X (%)) in the central portion in the thickness direction. A surface layer removal process is then carried out in which the surface layer of the polishing cloth is removed, thereby producing a polishing cloth with a low longitudinal orientation rate (X (%)).

[0044] In the impregnation step of impregnating a nonwoven fabric with a resin composition containing a polyurethane resin, one or both of wet impregnation, in which the nonwoven fabric is impregnated with an impregnation liquid containing an aqueous solvent, and dry impregnation, in which the nonwoven fabric is impregnated with an impregnation liquid not containing an aqueous solvent, can be performed.

[0045] In wet impregnation, a polyurethane resin is first dissolved in a water-soluble organic solvent to obtain an aqueous impregnation solution. Examples of water-soluble organic solvents include dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, and dimethylacetamide. Next, a nonwoven fabric is immersed in the aqueous impregnation solution, and the nonwoven fabric immersed in the aqueous impregnation solution is then immersed in water. As a result, the water-soluble organic solvent in the aqueous impregnation solution impregnated into the nonwoven fabric is replaced with water, the polyurethane resin coagulates, and the polyurethane resin adheres to the surface of the fibers constituting the nonwoven fabric. The impregnation process in wet impregnation can be carried out so that the polyurethane resin composition, which is the cured product of the aqueous impregnation solution, covers the fibers constituting the nonwoven fabric to form a resin layer on the fiber surface. The impregnation process in wet impregnation can be carried out so that the polyurethane resin composition does not fill the voids inside the nonwoven fabric. This results in a polishing cloth with voids.

[0046] In dry impregnation, for example, a non-aqueous impregnation liquid is prepared by mixing a prepolymer having an isocyanate group as a terminal group, a curing agent, which is an organic compound having active hydrogen, and an organic solvent. Examples of the organic solvent include methyl ethyl ketone, acetone, alcohol, and ethyl acetate. In dry impregnation, a non-woven fabric is immersed in the non-aqueous impregnation liquid, and the non-woven fabric immersed in the non-aqueous impregnation liquid is heated in a drying oven. This evaporates the organic solvent, and the pre-polymer and the curing agent undergo a curing reaction. In this way, the fibers constituting the non-woven fabric are coated with a polyurethane resin composition, which is the cured product of the non-aqueous impregnation liquid. In this case, too, a polishing cloth with voids is formed by preventing the polyurethane resin composition from filling the voids inside the non-woven fabric.

[0047] In the impregnation step in the embodiment, for example, a nonwoven fabric having a resin layer formed on the fiber surface by wet impregnation may be produced, and then the nonwoven fabric may be subjected to dry impregnation. In this case, the polishing cloth comprises a first resin composition constituting a first resin layer directly covering the fibers constituting the nonwoven fabric, and a second resin composition constituting a second resin layer covering the first resin layer, and the first resin layer may be formed by wet impregnation, and the second resin layer may be formed by dry impregnation.

[0048] Wet impregnation allows for a wide range of resins to be selected, allowing for the use of flexible resins, which is advantageous in providing a soft texture to the polishing cloth to suppress defects. In wet impregnation, even if a resin film is formed between the fibers, the resin film tends to be relatively thin. Furthermore, the formed resin film tends to be a porous film with multiple through-holes penetrating in the thickness direction. Therefore, the wet process can prevent areas that are harder than the surrounding area from being formed by resin pools or resin films. Therefore, it is preferable to perform only wet impregnation in the impregnation process of this embodiment.

[0049] In this embodiment, the impregnation step produces a polishing cloth with a high longitudinal orientation rate (X (%)) in the surface layer, which allows the impregnation liquid to be impregnated well into the nonwoven fabric. Furthermore, by carrying out the surface layer removal step as described above, the polishing cloth can be finished to a state with a low longitudinal orientation rate (X (%)), and a polishing cloth that is less likely to cause defects in the workpiece can be obtained.

[0050] The impregnation process may be carried out batchwise or continuously. The batchwise impregnation process can be carried out using a nonwoven fabric that has been cut to a predetermined length in advance to form a single sheet. In the batchwise impregnation process, a method can be used in which the nonwoven fabric is immersed in a tank containing an aqueous impregnation liquid or a nonaqueous impregnation liquid. The continuous impregnation process can be carried out using a nonwoven fabric roll in which a long strip of nonwoven fabric is wound into a roll. The continuous impregnation process can be carried out by unwinding the nonwoven fabric from the nonwoven fabric roll and sequentially impregnating the unwound nonwoven fabric with an aqueous impregnation liquid or a nonaqueous impregnation liquid. In this case, tension may be applied to the nonwoven fabric as the resin composition impregnated into the nonwoven fabric solidifies. In this case, the fibers extending along the longitudinal direction D1 can be tilted in the direction of the applied tension, and the resin composition solidifies in this state, thereby maintaining the tilted state of the fibers to a certain extent or more. The tension can be applied by increasing the conveying speed of the nonwoven fabric. The conveying speed of the nonwoven fabric for applying the tension can be, for example, 1.2 times or more the normal conveying speed. The conveying speed of the nonwoven fabric may be 1.5 times or more the normal conveying speed. The specific conveying speed of the nonwoven fabric can be, for example, 1.0 m / min or more and 10.0 m / min or less, preferably 1.5 m / min or more and 5.0 m / min or less. By producing a polishing cloth in this manner, a polishing cloth with a low longitudinal orientation rate (X (%)) can be obtained. In the continuous impregnation process, tension can be applied to the nonwoven fabric in both the longitudinal direction (MD) and the width direction (TD) during solidification of the resin composition.

[0051] The polishing cloth of this embodiment can be manufactured by various methods other than the above method. The polishing cloth disclosed above is merely a limited example, and the polishing cloth of the present invention is not limited to the above-mentioned form. Furthermore, the polishing cloth of the present invention is not limited by the above-mentioned effects. The polishing cloth of the present invention can be variously modified within the scope of the gist of the present invention.

[0052] As described above, this specification includes the following disclosures: (1) A polishing cloth having a nonwoven fabric made of fibers and a resin composition impregnated into the nonwoven fabric, and having a polishing surface, wherein a direction perpendicular to the polishing surface is defined as a longitudinal direction, and CT images of cross sections parallel to the longitudinal direction are obtained, and 2% of a plurality of cross sections of the fibers in the CT image are measured in descending order of area, and the orientation direction of the fibers having the cross sections is determined from the shape of each of the cross sections measured, and when the ratio of the number of cross sections whose orientation direction is less than 30° to the longitudinal direction is defined as the longitudinal orientation rate (X(%)) of the fibers, the longitudinal orientation rate (X(%)) is less than 12.1%.

[0053] (2) The polishing cloth according to (1), having an Asker C hardness of 50 or more and 70 or less.

[0054] (3) Apparent density is 200 kg / m ３ More than 400kg / m ３ The polishing cloth according to (1) or (2) below:

[0055] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0056] Comparative Example 1: A long, strip-shaped needle-punched nonwoven fabric was prepared by needle-punching the web to penetrate the thickness direction, as in a typical product. The nonwoven fabric was impregnated with a resin composition containing a polyurethane resin by wet impregnation. The wet impregnation was carried out by immersing the nonwoven fabric in an aqueous impregnation solution at a constant conveying speed while applying tension to the nonwoven fabric. After the impregnated resin composition had fully cured, the surface layers on both sides were cut away. The cutting was carried out to a depth of 0.4 to 0.5 mm from each surface (approximately 0.9 mm in total), and the polishing cloth of Comparative Example 1 was prepared with one of the surfaces exposed by the cutting as the polishing surface.

[0057] Figure 5a shows a scanning electron microscope (SEM) photograph of the cross section of the polishing cloth of Comparative Example 1.For the polishing cloth of Comparative Example 1, 57 CT images (2.0 mm x 2.0 mm) were taken on a plane parallel to the longitudinal direction so that the plane had a surface spacing of 25 μm in the normal direction, and the top 2% (1319 pieces) of the total number of fiber cross sections present in the analysis area of ​​each image were measured in descending order of area, and the Feret diameter (L1) in the longitudinal direction and the Feret diameter (L2) in the transverse direction were obtained for all of them, and the aspect ratio (L2 / L1) of the Feret diameter was calculated.The number (n pieces) whose aspect ratio (L2 / L1) satisfies the following formula (a) was counted, and the proportion ([n / 1319] x 100%) of the total was taken as the longitudinal orientation rate (X (%)) of the fiber in the polishing cloth of Comparative Example 1. [arctan (L2 / L1)] / π×180°<30° (a) The CT image (fiber extracted image) of the polishing cloth of Comparative Example 1 is shown in Fig. 5b, and the longitudinal orientation rate (X (%)) of the polishing cloth of Comparative Example 1 was 12.3%. The polishing cloth of Comparative Example 1 also had an Asker C hardness (23°C, instantaneous value) of 56 and an apparent density of 280 kg / m ３ It was.

[0058] (Example 1) The polishing cloth of Example 1 was produced in the same manner as Comparative Example 1, except that the needles were not allowed to penetrate a web formed from fibers with an average fiber diameter approximately 0.7 times that of Comparative Example 1, resulting in a nonwoven fabric approximately 0.3 mm thicker than that of Comparative Example 1, the tension applied to the nonwoven fabric during wet impregnation was strengthened, and the cutting thickness after resin impregnation was increased by a total of just over 0.2 mm on both sides compared to Comparative Example 1, increasing the total cutting thickness from approximately 0.9 mm to approximately 1.1 mm.

[0059] FIG. 6a shows a scanning electron microscope (SEM) photograph of the cross section of the polishing cloth of Example 1. From this figure, it can be seen that the polishing cloth of Example 1 has suppressed longitudinal fiber orientation. The longitudinal orientation rate (X (%)) of the polishing cloth of Example 1 was determined in the same manner as in Comparative Example 1. However, for the polishing cloth of Example 1, the number of cross sections to be measured was 1,368. A CT image (fiber extraction image) of the polishing cloth of Example 1 is shown in FIG. 6b, and the longitudinal orientation rate (X (%)) of the polishing cloth of Example 1 was 5.2%. Furthermore, the polishing cloth of Example 1 had an Asker C hardness (23°C, instantaneous value) of 60 and an apparent density of 240 kg / m ３ It was.

[0060] (Example 2) The polishing cloth of Example 2 was produced in the same manner as Example 1, except that a nonwoven fabric approximately 0.2 mm thinner than that of Example 1 was produced using the same web as Example 1 and by not piercing the needles as in Example 1.

[0061] The polishing cloth of Example 2 had a longitudinal orientation rate (X (%)) of 7.0% (number of cross sections measured: 1503), an Asker C hardness (23°C, instantaneous value) of 62, and an apparent density of 260 kg / m ３ It was.

[0062] Example 3 A polishing cloth of Example 3 was produced in the same manner as in Example 2, except that the abrasive thickness after resin impregnation was reduced by approximately 0.2 mm in total on both sides compared to Example 2.

[0063] The polishing cloth of Example 3 had a longitudinal orientation rate (X (%)) of 7.1% (number of cross sections measured: 1,461), an Asker C hardness (23°C, instantaneous value), and an apparent density of 260 kg / m ３ was 63.

[0064] (Comparative Example 2) The polishing cloth of Comparative Example 2 was produced in the same manner as Comparative Example 1, except that a web formed of fibers with an average fiber diameter approximately 1.2 times that of Comparative Example 1 was used, the conveying speed of the nonwoven fabric during wet impregnation was approximately 0.6 times that of Comparative Example 1, and the abrasive thickness after resin impregnation was reduced by approximately 0.3 mm in total on both sides compared to Comparative Example 1.

[0065] The polishing cloth of Comparative Example 2 had a longitudinal orientation rate (X (%)) of 26.3% (number of cross sections measured: 875), an Asker C hardness (23°C, instantaneous value) of 66.5, and an apparent density of 310 kg / m ３ It was.

[0066] Comparative Example 3 A polishing cloth of Comparative Example 3 was prepared in the same manner as Comparative Example 2, except that the abrasive thickness after resin impregnation was increased by approximately 0.2 mm in total on both sides compared to Comparative Example 2.

[0067] The polishing cloth of Comparative Example 3 had a longitudinal orientation rate (X (%)) of 23.5% (number of cross sections measured: 825), an Asker C hardness (23°C, instantaneous value) of 60, and an apparent density of 300 kg / m ３ It was.

[0068] <Verification of Reproducibility> Polishing cloths were produced five times using the same method as in Comparative Example 1, and polishing cloths were produced five times using the same method as in Example 1, and the degree of variation in the longitudinal orientation rate (X (%)) was verified. For each polishing cloth, the longitudinal orientation rate (X (%)) was determined at two locations, and the average value of the two locations was taken as the longitudinal orientation rate (X (%)) of the polishing cloth. The results are shown in Figure 7. This figure shows that the adoption of a similar manufacturing method shows good reproducibility of the longitudinal orientation rate (X (%)).

[0069] <Verification of Polishing Performance 1: Number of Defects Occurring on Wafers After Polishing> Three polishing steps were performed on a wafer using three polishing cloths, and the number of surface defects on the wafer after the three polishing steps was measured using a wafer defect inspection device manufactured by KLA-Tencor, product name "Surfscan SP5." The verification was performed under the four conditions shown in Table 1 below, using the polishing cloth of Comparative Example 1, the polishing cloth of Example 1, and a commercially available NAP pad.

[0070]

[0071] <Polishing Performance Verification 2: Surface Roughness (Sa) of Wafer After Polishing> Wafers were polished with three types of slurries: a slurry with relatively high chemical etching performance (Slurry C: manufactured by Nitta DuPont, "Nanopure™ NP6610"), a slurry with relatively high mechanical polishing performance (Slurry M: manufactured by Nitta DuPont, "Nanopure™ NP8020H"), and a slurry intermediate between the two (Slurry MC: manufactured by Nitta DuPont, "Nanopure™ NP7050S"), using the polishing cloths of each Example and Comparative Example, and the surface roughness (Sa) of the wafer after polishing was measured at a field of view of 177 μm × 133 μm. Unlike "Polishing Performance Verification 1", wafer polishing was performed in only one stage.

[0072] In polishing using slurry C (a slurry with relatively high chemical etching performance), a comparison was made using three types of polishing cloths: Comparative Example 2, Example 1, and Example 2. The results are shown in FIG.

[0073] In polishing using slurry M (a slurry with relatively high mechanical polishing performance), a comparison was made using three types of polishing cloths: Comparative Example 1, Example 1, and Example 2. The results are shown in FIG.

[0074] In polishing using slurry MC (medium slurry), a comparison was made using four types of polishing cloths: Comparative Example 1, Comparative Example 2, Example 1, and Example 2. The results are shown in FIG.

[0075] <Summary> Table 2 below shows how the characteristic values ​​of the polishing pad changed when changes were made to the manufacturing conditions in each example and comparative example, with Comparative Example 1 being used as the standard.

[0076]

[0077] From the above results, it is clear that the present invention can impart good surface properties to the polished object after polishing.

[0078] 1: Polishing cloth, 1b: Back surface, 1p: Polishing surface, 11: Nonwoven fabric, 11f: Fiber, 12: Resin composition, 13: Void portion

Claims

1. A polishing cloth having a nonwoven fabric made of fibers and a resin composition impregnated into the nonwoven fabric, and having a polishing surface, wherein the direction perpendicular to the polishing surface is the longitudinal direction, and CT images of cross sections parallel to the longitudinal direction are obtained, and 2% of the cross sections of the fibers in the CT images are measured in descending order of area, and the orientation direction of the fibers in the cross sections is determined from the shape of each of the cross sections measured, and when the ratio of the number of cross sections whose orientation direction is less than 30° to the longitudinal direction is defined as the longitudinal orientation rate (X (%)) of the fibers, the longitudinal orientation rate (X (%)) is less than 12.1%.

2. The polishing cloth according to claim 1, having an Asker C hardness of 50 or more and 70 or less.

3. Apparent density is 200 kg / m ３ More than 400kg / m ３ 3. The polishing cloth according to claim 1, wherein the polishing cloth is:

Images