Polishing cloth

Abstract

To provide an abrasive cloth capable of imparting good surface properties to an object to be polished after polishing.SOLUTION: Provided is a polishing cloth which is provided with a nonwoven fabric composed of fibers and having a longitudinal direction which is a direction perpendicular to a polishing surface, and a resin composition impregnated in the nonwoven fabric, wherein 2% of the cross sections of the fibers in a CT image parallel to the longitudinal direction are measured in order from the one having the largest area, the orientation direction of the fibers having the cross sections is determined from the shapes of the individual cross sections which are measured, and the number ratio of the cross sections in which the orientation direction is less than 30 ° with respect to the longitudinal direction is less than 12.1%.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a polishing cloth. [Background technology]

[0002] 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 object to be polished and chemical components for chemically promoting the polishing. Furthermore, polishing cloths are used to polish objects 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-107106 Summary of the Invention [Problem to be solved by the invention]

[0004] Chemical mechanical polishing using an abrasive cloth can cause defects such as scratches and particles on the surface of the workpiece 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 texture to the workpiece 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 texture to the workpiece after polishing. [Means for solving the problem]

[0005] The present invention provides A polishing cloth having an abrasive surface, a vertical direction that is perpendicular to the polishing surface; A nonwoven fabric made of fibers and a resin composition impregnated into the nonwoven fabric, Acquire a CT image of a cross section parallel to the longitudinal direction; Among the multiple cross sections of the fiber in the CT image, 2% of the cross sections are measured 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 being measured; When the ratio of the number of cross sections in which the orientation direction is less than 30° to the longitudinal direction is defined as the longitudinal orientation rate (X (%)) of the fibers, the polishing cloth has a longitudinal orientation rate (X (%)) of less than 12.1%. [Effects of the Invention]

[0006] Such a polishing cloth can improve the surface quality of the object to be polished after polishing. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic plan view of a polishing pad according to one embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view taken along the line II-II in FIG. [Figure 3] FIG. 3 is a cross-sectional view (SEM image) of the polishing pad, and is a diagram that schematically shows the portion indicated by the dashed line III in FIG. [Figure 4a] FIG. 4a is a schematic perspective view showing the cross-sectional shape of fibers of a nonwoven fabric. [Figure 4b] FIG. 4b is a schematic perspective view showing the cross-sectional shape of the fibers of the nonwoven fabric. [Figure 4c] FIG. 4c is a schematic diagram showing how to determine the longitudinal orientation rate of the fibers. [Figure 5a] FIG. 5a is a cross-sectional view (SEM image) of the polishing pad of Comparative Example 1. [Figure 5b] FIG. 5b is a CT image (fiber extracted image) of the polishing cloth of Comparative Example 1. [Figure 6a] FIG. 6a is a cross-sectional view (SEM image) of the polishing cloth of Example 1. [Figure 6b] FIG. 6b is a CT image (fiber extracted image) of the polishing cloth of Example 1. [Figure 7] FIG. 7 is a graph showing the reproducibility of the longitudinal orientation rate when polishing pads are manufactured using the same manufacturing method. [Figure 8] FIG. 8 is a diagram showing the surface roughness (viewing angle: 177 μm×133 μm) of a wafer after polishing when the wafer was polished using a combination of the polishing cloths of the examples and comparative examples and a specific slurry. [Figure 9] FIG. 9 is a diagram showing the surface roughness (viewing angle: 177 μm×133 μm) of a wafer after polishing when the wafer was polished using a combination of the polishing cloths of the examples and comparative examples and a specific slurry. [Figure 10] FIG. 10 is a diagram showing the surface roughness (viewing angle: 177 μm×133 μm) of a wafer after polishing when the wafer was polished using a combination of the polishing cloths of the examples and comparative examples and a specific slurry. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of the present invention will be described below. The polishing cloth of this embodiment is suitable for use in, for example, chemical mechanical polishing using a slurry containing abrasive grains. The polishing cloth is not particularly limited in its application, but can be used, for example, in chemical mechanical polishing of wafers as the polished object. Examples of wafers to be polished include silicon (Si) wafers, compound wafers, and glass wafers. Examples of compound wafers include gallium oxide (Ga2O3) wafers, gallium nitride (GaN) wafers, aluminum nitride (AlN) wafers, sapphire (Al2O3) wafers, gallium arsenide (GaAs) wafers, indium phosphide (InP) wafers, lithium niobate (LiNbO3) wafers, and lithium tantalate (LiTaO3) wafers. Examples of glass wafers include quartz glass wafers, alkali glass wafers, and borosilicate glass wafers.

[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 in plan view. The polishing cloth 1 of this embodiment has a back surface 1b opposite 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 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 FIGS. 2 and 3, the polishing cloth 1 of this embodiment has a longitudinal direction D1 perpendicular to the polishing surface 1p and a transverse direction D2 parallel to the polishing surface 1p. 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 that make up the nonwoven fabric 11. More specifically, 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 that make up the nonwoven fabric 11. The resin composition 12 is also impregnated into the nonwoven fabric 11 so as to form a resin film between some of the fibers 11f. The polishing cloth 1 has voids 13 where neither the resin composition 12 nor the fibers 11f are present. The voids 13 are formed in a continuous mesh-like pattern in the longitudinal direction D1 and the lateral direction D2 of the polishing pad 1.

[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. The ends of the fibers 11f oriented in the longitudinal direction D1 (thickness direction of the polishing cloth 1) 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 amount 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 increases the compressive strength of the polishing cloth 1 in the thickness direction. The polishing cloth 1 of this embodiment has a relatively small amount 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. Of the multiple cross sections of the fibers 11f, 2% of the cross sections in descending order of area are measured, and the orientation direction of the fibers 11f having these cross sections is determined from the shape of each of the measured cross sections. When the ratio of the number of cross sections whose orientation direction is less than 30° with respect to the longitudinal direction D1 is defined as the longitudinal orientation rate (X(%)) of the fibers 11f, the longitudinal orientation rate (X(%)) 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 lateral direction D2, e.g., a 2 mm square that covers the entire area of ​​the polishing cloth 1 in the longitudinal direction D1. In the CT image captured to form a 2 mm square, the fibers 11f are more likely to move due to external forces near the polishing surface 1p or 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, when the thickness of the polishing cloth 1 is taken as 100%, 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 both the polishing surface 1p side and the back surface 1b side. Furthermore, even when the thickness of the polishing cloth 1 is much thicker 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, for example, by acquiring 57 CT images so that the interplanar spacing in the horizontal direction D2 is 25 μm.

[0015] Specifically, the CT images used for analysis can be obtained by extracting and visualizing fiber cross sections using analysis software commercially available from Volume Graphics, Inc. under the trade name "VGSTUDIO MAX" from CT data acquired using a commercially available device, such as Yamato Scientific Co., Ltd. (X-ray CT Scanner). 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 and D2) of the cross section using image analysis software commercially available from Mitani Shoji Co., Ltd. (Win Roof). Note that multiple fiber cross sections may appear connected in CT images. Since the image analysis software mentioned above is equipped with a noise reduction function, noise reduction can be performed to separate the fiber cross sections before measuring the Feret diameter. Note that if several fiber cross sections are too close together to form a single bundle and are difficult to separate using noise reduction, they will be treated as a single cross section.

[0016] The method for determining the orientation of the fiber 11f will be described in detail below. For example, as shown in Figure 4a, among the cross sections of the fiber 11f seen in the CT image, the fiber 11f can be considered to extend in the transverse direction D2 when the cross section XSa is cut nearly perpendicularly on a plane P1 parallel to the longitudinal direction D1 and has a relatively rounded shape. The fiber 11f can be considered to extend in the transverse direction D2 when the cross section XSb observed in a stretched state is cut nearly parallel to the direction of extension of the fiber 11f. The cross section XSb observed in a stretched state usually 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 in the top 2% of the largest cross-sectional areas when the total number of measured cross sections is taken as 100%.

[0017] The number of cross sections to be measured for Feret's diameter is set to, for example, 100 or more. That is, 57 CT images can be taken so that the total number of cross sections to be used for calculating the area is 5000 or more (5000 × 2% = 100). The reliability of the analysis results is usually improved by increasing the number of cross sections to be used for measuring Feret's diameter. The number of cross sections to be measured may be 200 or more, 300 or more, or even 500 or more. The number of cross sections to be measured in the CT image is, for example, 5000 or less. Therefore, the total number of cross sections to be used for calculating the area in the CT image may be 10,000 or more, 15,000 or more, or even 25,000 or more. The total number of cross sections to be used for calculating the area in the CT image is, for example, 250,000 or less.

[0018] The orientation direction of fiber 11f can be determined from the angle θ between the diagonal DL of 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 drawn so as to circumscribe the cross section XSb, as shown in Figure 4c, for example.

[0019] Specifically, the angle θ of the diagonal line DL representing 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 determining 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 conducting the spring hardness test specified in JIS K7312-1996 "Physical test methods for thermosetting polyurethane elastomer moldings" using a Type C testing machine. The test is conducted at 23°C, and the value (instantaneous value) is measured immediately after the pressure surface comes into contact.

[0023] The polishing cloth 1 preferably has a predetermined ratio of voids 13 formed therein. 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 or less. 3 may be less than 300 kg / m 3 may be less than 270 kg / m 3 The apparent density of the polishing cloth 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. 3The apparent density of the polishing cloth 1 can be measured in accordance with JIS K7222:2005.

[0024] The mass per unit area (basis weight) 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, so that by using a nonwoven fabric produced in this way to produce a polishing cloth, it is possible to obtain a polishing cloth with a low longitudinal orientation rate (X (%)).

[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 tends 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 also applies to spunlace nonwoven fabrics, steam-jet nonwoven fabrics, and the like.

[0027] In order to homogenize the surface quality of the polishing cloth 1 with 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 on one needle, or the size of the barb, rather than reducing the number of needle piercing points per unit area. When using such a method to reduce the longitudinal orientation rate (X (%)) in needle-punched nonwoven fabric, 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 More than 20 locations / cm 2 More than 25 locations / cm 2 More than 30 locations / cm 2 More than 35 locations / cm 2 It may be 1cm square (1cm 2 The number of puncture points per needle can 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] Nonwoven fabric 11 may contain a main fiber that accounts for the largest mass proportion of all 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 containing such fibers, nonwoven fabric 11 can suppress the longitudinal orientation of fibers during fiber entanglement.

[0030] One or both of the main and secondary fibers may be uncrimped fibers with a crimp rate of less than 10%, or may be crimped fibers with a crimp rate 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 with a fineness of 0.5 dtex or less. The ultrafine fibers may also be what are called ultrafine fibers with a fineness of 0.3 dtex or less. Ultrafine fibers are more flexible than 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 fiber orientation rate (X (%)) of 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 the side-by-side type or the 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 (superfine 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] Note that fibers that exhibit thermal fusion, such as side-by-side composite fibers with a snowman-shaped cross section made using resin compositions with different heat shrinkage properties, are not simply composite fibers, but can also be modified cross-section fibers, crimped fibers, or thermal fusion fibers. Furthermore, by reducing the fineness of such fibers, they can also become ultrafine fibers (ultrafine fibers). Nonwoven fabric 11 may contain fibers that serve several of the above functions. In this case, by including, for example, 15% by mass of one type of fiber that can serve as all of modified cross-section fibers, crimped fibers, ultrafine fibers (ultrafine fibers), and composite fibers, 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, it is possible to use a general needle-punched nonwoven fabric 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, it is also possible to use a needle-punched nonwoven fabric produced so that the needles stop penetrating the web halfway and the barbs on the needles do not penetrate the web, thereby reducing the longitudinal orientation rate (X (%)).

[0036] In needle-punched nonwoven fabrics 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 impregnation of the nonwoven fabric with the resin composition. The removal of the surface layer of the nonwoven fabric may be performed both before and after 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 area 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 area.

[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 that form 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. Of all the resins contained in the resin composition 12, the proportion of polyurethane resin may be 80 mass% or more, 90 mass% or more, 95 mass% or more, or 98 mass% or more. The resin contained in the resin composition 12 may essentially be 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 bonded via urethane bonds, 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 in which the fibers of the web are entangled to produce the nonwoven fabric 11, and an impregnation step in which the produced nonwoven fabric is impregnated 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 in which a surface layer of the nonwoven fabric is removed 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 area on the surface layer on the side that will become the polishing surface and further has a barb non-reach area that contacts the barb reach area 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 part 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 is then immersed in water. This replaces the water-soluble organic solvent in the aqueous impregnation solution impregnated into the nonwoven fabric, solidifying the polyurethane resin and adhering to the surface of the fibers that make up 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 that make up the nonwoven fabric and forms a resin layer on the fiber surface, without filling the voids inside the nonwoven fabric with the polyurethane resin composition. 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 that directly covers the fibers constituting the nonwoven fabric, and a second resin composition constituting a second resin layer that covers 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 the formation of areas that are harder than the surrounding area due to 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 (%)), resulting in a polishing cloth that is less likely to cause defects on the workpiece.

[0050] The impregnation process may be performed batchwise or continuously. In the batchwise process, a nonwoven fabric cut to a predetermined length can be used as a single sheet. The nonwoven fabric can be immersed in a tank containing an aqueous or nonaqueous impregnation liquid. In the continuous process, a long strip of nonwoven fabric can be wound into a roll. The nonwoven fabric is unwound from the roll and sequentially impregnated with an aqueous or nonaqueous impregnation liquid. 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. The resin composition solidifies in this state, maintaining the tilted state of the fibers at a certain level. The tension can be applied by increasing the conveying speed of the nonwoven fabric. The conveying speed of the nonwoven fabric for applying 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 transverse 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 an abrasive surface, a vertical direction that is perpendicular to the polishing surface; A nonwoven fabric made of fibers and a resin composition impregnated into the nonwoven fabric, Acquire a CT image of a cross section parallel to the longitudinal direction; Among the multiple cross sections of the fiber in the CT image, 2% of the cross sections are measured 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 being measured; When the ratio of the number of cross sections in which the orientation direction is less than 30° to the longitudinal direction is defined as the longitudinal orientation rate (X (%)) of the fibers, the polishing cloth has a longitudinal orientation rate (X (%)) of 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: [Example]

[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 of needle-punched nonwoven fabric was prepared by needle-punching the web so as to penetrate in the thickness direction in the same manner as in a general 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 the aqueous impregnation solution at a constant conveying speed while applying tension to the nonwoven fabric. After the impregnated resin composition was sufficiently cured, the surface layers on both sides were cut off. The cutting was carried out to a depth of 0.4 to 0.5 mm from each surface (total of about 0.9 mm), and the polishing pad of Comparative Example 1 was prepared with one of the surfaces exposed by the cutting as the polishing surface.

[0057] 5a shows a scanning electron microscope (SEM) photograph of the cross section of the polishing cloth of Comparative Example 1. 57 CT images (2.0 mm × 2.0 mm) of the polishing cloth of Comparative Example 1 on a plane parallel to the longitudinal direction were taken in the normal direction of the plane with a plane spacing of 25 μm, and of the total number of fiber cross sections present in the analysis area of ​​each image, the top 2% (1319 pieces) of cross sections in descending order of area were measured, and the Feret diameter in the longitudinal direction (L1) and the Feret diameter in the transverse direction (L2) were determined for all of them, and the aspect ratio (L2 / L1) of the Feret diameters was calculated. The number (n) of particles whose aspect ratio (L2 / L1) satisfied the following formula (a) was counted, and the percentage of the total ([n / 1319] x 100%) was taken as the longitudinal orientation rate (X (%)) of the fibers 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 has 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 pad of Example 1. It can also be seen from this figure that the polishing cloth of Example 1 has its fibers restrained from being oriented in the longitudinal direction. The longitudinal orientation rate (X (%)) of the polishing pad 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. The CT image (fiber extracted 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%. The polishing cloth of Example 1 has 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 prepared in the same manner as Example 1, except that a nonwoven fabric approximately 0.2 mm thinner than that of Example 1 was prepared using the same web as in Example 1 and not penetrating 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 The polishing cloth of Example 3 was prepared 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: 1461), 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 prepared 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 on both sides in total 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) The 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 in the same manner as in Comparative Example 1 and in the same manner as in Example 1, and the degree of variation in the longitudinal orientation rate (X (%)) was examined. For each polishing cloth, the longitudinal orientation rate (X(%)) was determined at two points, and the average value of the two points was taken as the longitudinal orientation rate (X(%)) of the polishing cloth. The results are shown in Figure 7. This figure shows that the longitudinal orientation rate (X (%)) can be reproducibly improved by using the same manufacturing method.

[0069] <Verification of polishing performance 1: Number of defects on wafers after polishing> The wafer was polished in three stages using three polishing cloths, and the surface defects of the wafer after the three polishing stages were measured using a wafer defect inspection device manufactured by KLA-Tencor, main product name "Surfscan SP5." The verification was carried out 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] [Table 1]

[0071] <Verification of polishing performance 2: Surface roughness (Sa) of wafer after polishing> Wafers were polished with the polishing cloths of each example and comparative example using 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"). The surface roughness (Sa) of the polished wafers was measured at a field of view of 177 μm × 133 μm. Unlike "Verification of Polishing Performance 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 Figure 8.

[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 Figure 9.

[0074] In polishing using slurry MC (medium slurry), comparison was carried out using four types of polishing cloths, Comparative Example 1, Comparative Example 2, Example 1, and Example 2. The results are shown in Figure 10.

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

[0076] [Table 2]

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

[0078] 1: Polishing cloth, 1b: Back, 1p: Polishing surface, 11: nonwoven fabric, 11f: fiber, 12: resin composition, 13: void portion

Claims

1. A polishing cloth having an abrasive surface, a vertical direction that is perpendicular to the polishing surface; A nonwoven fabric made of fibers and a resin composition impregnated into the nonwoven fabric, acquiring a CT image of a cross section parallel to the longitudinal direction; Among the multiple cross sections of the fiber in the CT image, 2% of the cross sections in descending order of area are selected as measurement targets, determining the orientation direction of the fibers having the cross section from the shape of each of the cross sections being measured; When the ratio of the number of cross sections in which the orientation direction is less than 30° to the longitudinal direction is defined as the longitudinal orientation rate (X (%)) of the fibers, the polishing cloth has a longitudinal orientation rate (X (%)) of less than 12.1%.

2. 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:

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