Polishing pad

Abstract

To prevent polishing chips from being accumulated in a transparent window W for end point detection, and prevent lowering of accuracy of the end point detection of polishing by the window W for end point detection.SOLUTION: A polishing pad 3 includes a polishing layer 3A composed of a resin having a polished surface 3a for polishing an object 2 to be polished, and a window W for end point detection which is provided on the polishing layer 3A and is composed of a transparent resin. A plurality of gaps are formed inside the polishing layer 3A, and the upper surface of the window W for end point detection is provided so as to be lower than the polished surface 3a, and a recess 12 is formed on the polished surface 3a. The recess 12 has a flat part 12a composed of the polishing layer 3A, at a position adjacent to outside the window W for end point detection.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a polishing pad, and more particularly to a polishing pad comprising a polishing layer made of resin having a polishing surface for polishing an object to be polished, and an end point detection window made of transparent resin provided in the polishing layer. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in the manufacturing process of semiconductor wafers, chemical mechanical polishing (CMP) is performed in which the surface of a semiconductor wafer is polished with a polishing pad and slurry for the purpose of planarizing the surface after forming an insulating film and forming metal wiring. Here, because over-polishing or under-polishing of the workpiece directly leads to product defects, the amount of polishing must be strictly controlled. To this end, a transparent end-point detection window is provided in the polishing pad, and the end point of polishing is detected by transmitting light through the end-point detection window (Patent Document 1). The polishing pad used in Patent Document 1 has an end point detection window formed at a position lower than the polishing surface, which reduces the occurrence of scratches caused by contact between the workpiece and the end point detection window and prevents a decrease in end point detection accuracy. On the other hand, by making the window for detecting the end point lower than the polishing surface, a recess is formed on the polishing surface. If polishing debris gets into this recess along with the slurry, the light is blocked by the polishing debris, which may reduce the accuracy of detecting the end point. Therefore, in Patent Document 1, a discharge groove is formed in the polishing surface to connect the recess with the outside of the polishing pad, and the slurry and polishing debris are discharged to the outside of the polishing surface through the discharge groove. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-152665 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the case of the polishing pad of Patent Document 1, the window for detecting the end point has the same diameter as the recess formed on the polishing surface, so that the polishing debris remains above the window for detecting the end point until it is discharged to the outside by the discharge groove, and therefore there is still a risk that the accuracy of the end point detection will decrease. In view of the above problems, the present invention provides a polishing pad capable of preventing deterioration in the accuracy of end point detection due to polishing debris. [Means for solving the problem]

[0005] That is, the polishing pad according to the invention of claim 1 comprises a polishing layer made of resin having a polishing surface for polishing an object to be polished, and an end point detection window made of transparent resin provided in the polishing layer, In a polishing pad, an upper surface of the end point detection window is provided at a position lower than the polishing surface, so that a recess is formed in the polishing surface, A plurality of voids are formed inside the polishing layer, The recess has a flat portion formed by the polishing layer at a position adjacent to the outer side of the end point detection window. Effect of the Invention

[0006] According to the polishing pad of the invention of claim 1, polishing debris that gets between the end point detection window and the workpiece is quickly moved to the flat portion formed adjacent to the end point detection window by the centrifugal force generated by the rotation of the polishing pad, since the upper surface of the end point detection window is smooth. On the other hand, due to the countless voids formed inside the polishing layer, countless tiny openings are formed on the upper surface of the flat portion formed by the polishing layer, so that polishing debris that moves through the end point detection window can be contained in the tiny openings. From the above, with the polishing pad of the present invention, it is possible to quickly remove polishing debris that has gotten between the end point detection window and the workpiece being polished from the top of the end point detection window, thereby preventing a decrease in the accuracy of end point detection. [Brief description of the drawings]

[0007] [Figure 1] 1 is a perspective view of a polishing apparatus showing an embodiment of the present invention; [Diagram 2] FIG. 2 is an enlarged plan view of a main portion of the polishing pad; [Diagram 3] Cross-sectional view of part III-III in Figure 2. [Figure 4] 5A to 5C are diagrams showing a manufacturing process of a polishing pad. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The present invention will now be described with reference to the illustrated embodiment. FIG. 1 shows a schematic diagram of a polishing apparatus 1, which polishes a thin plate-shaped workpiece 2 with a polishing pad 3 according to the present invention. The polishing apparatus 1 comprises a polishing platen 4 located on the lower side and having a polishing pad 3 fixed on its upper surface, a holding platen 5 located on the upper side and holding an object to be polished 2 on its lower surface, a slurry supplying means 6 for supplying a slurry S between the object to be polished 2 and the polishing pad 3, and a detection means 7 for detecting the progress of the polishing process. The object to be polished 2 can be a semiconductor wafer, an optical material, a silicon wafer, a glass substrate for liquid crystal displays, a semiconductor substrate, etc., but the polishing apparatus 1 of this embodiment is particularly suitable for planarizing an insulating film formed on the surface of a semiconductor wafer after the film is formed, or for forming metal wiring. When planarizing the surface of such a semiconductor wafer after the formation of an insulating film, or when forming metal wiring, it is necessary to detect the progress of the polishing process of the workpiece 2 using the detection means 7, since over-polishing or under-polishing directly leads to product defects. Therefore, a transparent end point detection window W is provided in the polishing pad 3, and the inspection light L1 irradiated by the detection means 7 passes through the window W, thereby detecting the progress of the polishing process and the end point of the process.

[0009] The polishing platen 4 and the holding platen 5 are each substantially disk-shaped and are adapted to rotate in the direction of the arrow by a driving mechanism (not shown). The holding platen 5 is provided so as to be movable up and down. When polishing the workpiece 2, the workpiece 2 is rotated while being pressed against the polishing surface 3a on the upper surface of the polishing pad 3 at a set pressure by the holding platen 5, and in this state, the slurry supply means 6 supplies the slurry S between the workpiece 2 and the polishing pad 3.

[0010] FIG. 2 shows an enlarged plan view of the polishing pad 3, and FIG. 3 shows a cross-sectional view taken along line III-III in FIG. The polishing pad 3 has a disk shape and comprises a polishing layer 3A made of resin located on the upper side, and a support layer 3B (cushion layer) made of resin adhered to the lower surface of the polishing layer 3A with an adhesive or double-sided tape, and the support layer 3B is adapted to be adhered and fixed to the polishing table 4 by means of double-sided tape or the like. As shown in FIG. 3, annular grooves 11 are formed concentrically at a required pitch on the polishing surface 3a of the polishing pad 3, and an end point detection window W made of transparent resin is provided at a predetermined position on the polishing pad 3, which transmits the inspection light L1 irradiated by the detection means 7. Each of the annular grooves 11 is set to, for example, a width of 0.4 mm and a depth of 0.8 mm, and the pitch between adjacent annular grooves 11 is set to 1.7 mm. In this embodiment, only the annular groove 11 is formed on the polishing surface 3a, but in addition to the annular groove 11, linear grooves, lattice grooves, radial grooves, and spiral grooves may be formed, or these may be combined.

[0011] The polishing layer 3A is made of polyurethane polyurea resin and has numerous minute voids formed therein, while the support layer 3B is made of a sheet-like polyurethane or resin-impregnated nonwoven fabric. The polishing layer 3A and the support layer 3B are bonded to each other by an adhesive or a double-sided tape. The lower surface of the support layer 3B is fixed to the upper surface of the polishing platen 4 by means of an adhesive or double-sided tape. The annular grooves 11 function as slurry retaining grooves for retaining the slurry S, and the slurry S discharged from the slurry supplying means 6 flows into these annular grooves 11 and is supplied to the entire polishing surface 3a.

[0012] The end point detection window W is made of a transparent resin that transmits the inspection light L1 and the reflected light L2, specifically, an elastic resin such as polyurethane is used, and the structure is designed to avoid foaming that would interfere with the inspection light L1 and the reflected light L2. More specifically, an elastic resin such as polyurethane that does not have any voids formed inside is preferable. In addition, the end point detection window W is formed, in a plan view, into an approximately rectangular shape, for example, with long sides of 40 to 70 mm and short sides of 10 to 30 mm, and is arranged so that the long sides face the radial direction of the polishing pad 3, and is fitted tightly into the polishing layer 3A. In this embodiment, the upper surface of the end-point detection window W is provided at a position lower than the polishing layer 3A, and the bottom surface is formed at the same height as the lower surface of the polishing layer 3A. The support layer 3B has a substantially rectangular through hole 3b with dimensions smaller than the end point detection window W, and the outer peripheral edge of the end point detection window W is supported from below by the opening edge portion of the through hole 3b. In addition, the end-point detection window W may have various shapes such as a square, polygon, ellipse, etc., in addition to the above-mentioned approximately rectangular shape when viewed in a plan view, and may also be formed in a circular shape with a diameter of 10 to 30 mm. Furthermore, in this embodiment, the long side of the end point detection window W is arranged to face the radial direction of the polishing pad 3, but the size, orientation, and position of the end point detection window W are not limited to the above embodiment, and multiple end point detection windows W may be provided.

[0013] As described above, the upper surface of the end-point detection window W is set lower than the polishing layer 3A, and the polishing layer 3A has a recess 12 formed at the position of the end-point detection window W. In this embodiment, a flat portion 12a is formed at the bottom of the recess 12, which is composed of the upper surface of the end point detection window W and a polishing layer 3A formed to surround the outer periphery of the end point detection window W. In particular, it is desirable to form a flat portion 12a of a certain degree of width at a position from the center of the polishing pad 3 to the outer periphery of the end point detection window W, for reasons that will be described later. It is desirable to set the dimension of the flat portion 12a, for example, so that the distance from the outer periphery of the end-point detection window W to the side surface 12b forming the recess 12 is 1 mm to 30 mm. The shape of the flat portion 12a is preferably a shape surrounding the end point detection window W, and more preferably an elliptical shape surrounding the end point detection window W as shown in this embodiment. Furthermore, in this embodiment, the flat portion 12a has approximately the same distance to the side surface 12b on both the outer and inner sides of the polishing pad 3, but by making the outer side wider, it is possible to make it easier for the flat end portion 12a on the outer side to collect polishing debris.

[0014] The recess 12 is formed by grinding (for example, to a depth of 0.9 mm) the polishing layer 3A and the end point detection window W as described below, so that the upper surface of the end point detection window W and the flat portion 12a are formed at the same height. By grinding the polishing layer 3A, a large number of tiny openings are formed on the surface of the flat portion 12a, which originate from voids formed inside the polishing layer 3A, and these openings are designed to accommodate polishing debris generated during the polishing process of the workpiece 2. The upper surface of the end point detection window W may be provided higher than the flat portion 12a (so as to protrude toward the polishing surface 3a). By doing so, it is possible to prevent polishing debris discharged from the upper portion of the end point detection window W and moved to the flat portion 12a from returning to the end point detection window W.

[0015] Furthermore, a chamfered shape 12c is formed along the opening edge at the upper portion of the side surface 12b of the recess 12. By providing this chamfered shape 12c, the effect of reducing scratches on the polished object 2 can be obtained compared to the case where the chamfered shape 12c is not formed. The chamfered shape 12c may be omitted, or may be replaced with an R-shape. Instead of these shapes, the side surface 12b of the recess 12 may be inclined so as to widen from the flat end 12a toward the polishing surface 3a, with the same effect being obtained.

[0016] As described above, a plurality of annular grooves 11 are formed concentrically on the polishing surface 3a, and several of these annular grooves 11 intersect with the recesses 12 described above. With this configuration, the slurry S flowing through the annular groove 11 flows in from the intersection between the annular groove 11 and the recess 12, and conversely, the slurry S in the recess 12 is discharged via the annular groove 11. In this embodiment, the position of the flat portion 12 a is set lower than the bottom of the annular groove 11 , so that polishing waste that has flowed into the recess 12 is prevented from flowing out into the annular groove 11 . In addition, by making the position of the flat portion 12a lower than the bottom of the annular groove 11, the annular groove formed in the surface of the end point detection window W by cutting is made to disappear by subsequent countersinking in a manufacturing process described later. As a result, diffuse reflection of light passing through the end point detection window W can be prevented compared to a case in which the annular groove is not burned away by countersinking.

[0017] The detection means 7 includes a light-emitting unit 7A that is provided below the polishing table 4 and irradiates inspection light L1 upward, a light-receiving unit 7B that receives reflected light L2 from the workpiece 2, and a control unit 7C that controls their operation and detects the progress of the polishing process and the end point where the process ends. In addition, a through hole 4a is formed in the polishing platen 4 in accordance with the position of the end point detection window W and the through hole 3b provided in the polishing pad 3, and is configured to allow the inspection light L1 and reflected light L2 to pass through. During polishing of the workpiece 2, the light-emitting unit 7A of the detection means 7 irradiates the inspection light L1 upward. The inspection light L1 passes through a transparent end-point detection window W and is reflected by the underside of the workpiece 2, and the reflected light L2 passes through the transparent end-point detection window W and is received by the light-receiving unit 7B. The control unit 7C measures the intensity of the reflected light L2 received by the light receiving unit 7B, and as the polishing of the workpiece 2 by the polishing pad 3 progresses, the intensity of the reflected light L2 changes, thereby recognizing the progress of the processing and determining the end point of the processing.

[0018] When the polishing pad 3 having the above-mentioned configuration is used to polish the object 2, the following effects can be obtained. First, the polishing apparatus 1 is operated, the workpiece 2 mounted on the holding platen 5 is pressed against the polishing pad 3 mounted on the polishing platen 4, and the holding platen 5 and the polishing platen 4 are rotated. At the same time, a slurry supplying means 6 supplies a slurry S between the object to be polished 2 and the polishing pad 3, so that the object to be polished 2 is subjected to so-called chemical mechanical polishing by the polishing pad 3 and the slurry S.

[0019] When the workpiece 2 is polished in this manner, polishing debris is generated from the workpiece 2 and the polishing pad 3, and the polishing debris flows into the annular groove 11 together with the slurry S, and then flows from the annular groove 11 into the recess 12 in which the end point detection window W is provided. The polishing debris that flows into the recess 12 gets caught between the end point detection window W and the workpiece 2 in the recess 12, but since the polishing pad 3 is rotated by the polishing table 4, the polishing debris that flows into the recess 12 tends to move toward the outer periphery of the center of the polishing pad 3 due to centrifugal force. Furthermore, since the upper surface of the end point detection window W has a structure that prevents foaming as described above, its surface roughness is 1.0 to 3.5 μm and is almost smooth, so that polishing debris does not remain on the end point detection window W but moves toward the outer periphery and onto the flat portion 12a of the recess 12. Meanwhile, minute openings resulting from voids inside the polishing layer 3A are formed on the surface of the flat portion 12a, and the surface roughness of the openings is about 3.5 to 9.0 μm, which is rougher than the end-point detection window W. Therefore, polishing debris that has moved to the flat portion 12a is accommodated in the openings. In addition, in this embodiment, the height of the flat portion 12a is set lower than the bottom of the annular groove 11, so that polishing debris from the flat portion 12a is less likely to be discharged into the annular groove 11, and it is possible to retain the polishing debris on the flat portion 12a of the recess 12.

[0020] Thus, according to the polishing pad 3 of this embodiment, even if polishing debris enters the recess 12 in which the end point detection window W is formed, it can be quickly removed to the flat portion 12a formed adjacent to the end point detection window W. As a result, it is possible to prevent scratches on the workpiece 2 caused by polishing debris, and it is also possible to prevent the polishing debris from remaining between the workpiece 2 and the end point detection window W, which would reduce the detection accuracy by the detection means 7. In other words, if polishing debris remains between the workpiece 2 and the end point detection window W, the inspection light L1 and reflected light L2 emitted by the light emitting section 7A of the detection means 7 may be obstructed by the polishing debris, making it impossible to accurately determine the end point.

[0021] Next, one embodiment of a method for manufacturing the polishing pad 3 having the above configuration will be described with reference to FIG. First, polyisocyanate, which is the material for the end point detection window W, and a hardener are mixed together, and the mixture is centrifuged and degassed to prepare a mixture. The mixture is then poured into a rectangular mold and hardened to form a transparent rectangular parallelepiped 102. Meanwhile, polyisocyanate and a curing agent, which are the materials for the polishing layer 3A, are mixed together to prepare a mixture 103, which is mixed with hollow microparticles to form voids. This mixture 103 is then poured into a mold 101 in which the rectangular parallelepiped 102 has already been placed (Figure 4(a)). As the mixture 103 hardens, a block-shaped polyurethane polyurea resin molding 104 is formed inside the formwork 101, and the transparent rectangular prism 102 is held inside the polyurethane polyurea resin molding 104 in a fixed state with no gaps (Figure 4(b)).

[0022] Next, the polyurethane polyurea resin molded body 104 is removed from the mold 101, and the polyurethane polyurea resin molded body 104 is thinly cut along a plane perpendicular to the thickness direction (FIG. 4(c)). In the sheet-like member 107 thus obtained, the polyurethane polyurea resin molded body 104 becomes the polishing layer 3A, and the rectangular parallelepiped 102 corresponds to the window W for end-point detection.

[0023] Next, one surface of the obtained sheet-like member 107 is buffed to form the polished surface 3a. Next, the annular groove 11 is formed concentrically on the polishing surface 3a by cutting, and then an end mill having a diameter larger than the short side of the rectangular solid 102 is used to perform countersinking at the position where the rectangular solid 102 corresponding to the end point detection window W is provided, by moving the end mill in the long side direction. As a result, the rectangular parallelepiped 102 and the surrounding polishing layer 3A are ground to form a recess 12 on the polishing surface 3a. Specifically, the end point detection window W and the flat portion 12a are formed at the same height on the bottom surface of the recess 12 (FIG. 4(d)). Next, the chamfered shape 12c is machined onto the opening edge of the recess 12, and a support layer 3B, which has a through hole slightly smaller than the end point detection window W at a position corresponding to the end point detection window W, is adhered to the underside of the polishing layer 3A with an adhesive or double-sided tape. Finally, the adhered polishing layer 3A and support layer 3B are cut into a circular disk shape to obtain the polishing pad 3. The above manufacturing method is based on the manufacturing method described in Patent Document 1, and other manufacturing methods described in Patent Document 1 may also be used.

[0024] In each of the above embodiments, the explanation is based on the assumption that the centers of the multiple annular grooves 11 arranged at concentric positions coincide with the center of the polishing surface 3a, but the center of the annular groove 11 may be eccentric with respect to the center of the polishing surface 3a. [Explanation of symbols]

[0025] 1 Polishing device 2 Object to be polished 3 Polishing pad 3a...polishing surface 3A Polishing layer 7 Detection means 11 Annular groove 12 Recess 12a Flat part 12b Side L1 Inspection light L2 Reflected light S Slurry W End point detection window

Claims

1. a polishing layer made of resin having a polishing surface for polishing an object to be polished, and an end point detection window made of transparent resin provided in the polishing layer; In a polishing pad, an upper surface of the end point detection window is provided at a position lower than the polishing surface, so that a recess is formed in the polishing surface, A plurality of voids are formed inside the polishing layer, The polishing pad, wherein the recess has a flat portion formed by the polishing layer at a position adjacent to the outside of the end point detection window.

2. 2. The polishing pad according to claim 1, wherein an upper surface of the end point detection window and the flat portion are at the same height.

3. 2. The polishing pad according to claim 1, wherein a concentric annular groove is formed in said polishing surface, and the height of said flat portion is lower than the bottom of said annular groove.

4. 2. The polishing pad according to claim 1, wherein the opening edge of the recess is chamfered or rounded.

5. 2. The polishing pad according to claim 1, wherein the recess has a sloped side surface.

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