JP2011056597A - Polishing pad, and device and method of polishing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that a polishing pad becomes swollen due to cells formed between a polishing surface plate and a polishing pad after repeating polishing. <P>SOLUTION: An upper face of a polishing layer abuts to a polishing object. A soft layer is adhered to a back face of the polishing layer. A back face of the soft layer opposite to the upper face adhered to the polishing layer is adhered to the rotating polishing surface plate. The soft layer is softer than the polishing layer, and has an open cell structure. Notches are formed on the back face of the soft layer from each of a plurality of points on a circumference with the rotation center of the polishing surface plate centered toward the outer circumference of the soft layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polishing pad that is bonded to a rotating polishing platen and polishes an object to be polished, a polishing apparatus that includes the polishing pad, and a polishing method that uses the polishing pad.

  Chemical mechanical polishing (CMP) is widely used in planarization of the surface of a semiconductor substrate, damascene method, and the like. The CMP apparatus includes a polishing surface plate and a polishing pad bonded thereon. In a state where the semiconductor wafer to be polished is in contact with the polishing pad, the semiconductor wafer is polished by rotating the polishing platen while dropping the polishing liquid on the polishing pad.

  When a large number of semiconductor wafers are polished, bubbles may enter the interface between the polishing surface plate and the polishing pad, and a part of the polishing pad may rise. When a part of the polishing pad rises, the pressure applied to the surface of the semiconductor wafer becomes non-uniform, and it becomes difficult to uniformly polish the entire surface.

  As a countermeasure against the generation of such bubbles, there has been proposed a technique for suppressing the generation of bubbles by forming a groove in the adhesive layer between the polishing pad and the polishing surface plate. As another countermeasure, a technique has been proposed in which air bubbles are pushed out by forming a groove that continues to the outer peripheral edge on the upper surface of the polishing surface plate.

JP 2000-306870 A JP 2006-239808 A

  When a groove is formed in the adhesive layer between the polishing pad and the polishing surface plate, the flatness of the upper surface of the polishing pad is lowered due to the influence of the groove. Even when grooves are formed on the polishing surface plate, the surface shape of the polishing pad may be affected by the grooves of the polishing surface plate depending on the thickness and flexibility of the polishing pad.

According to one aspect of the invention,
A polishing layer whose upper surface is in contact with the object to be polished;
Adhered to the back surface of the polishing layer opposite to the upper surface, the back surface opposite to the upper surface bonded to the polishing layer is bonded to a rotating polishing platen, softer than the polishing layer, and continuous A soft layer having a cellular structure,
A polishing pad is provided in which a notch is formed on each of a plurality of points on the circumference centering on the center of rotation of the polishing surface plate toward the outer periphery of the soft layer on the back surface of the soft layer. The

  According to another aspect of the present invention, a polishing apparatus having the above-described polishing pad and a polishing method using the above-described polishing pad are provided.

  By forming the cut in the soft layer, it is possible to suppress the phenomenon that the upper surface of the polishing pad partially swells due to the localization of bubbles.

It is a perspective view of the polish device by an example. (2A) and (2B) are a plan view and a cross-sectional view of the polishing pad according to the embodiment, respectively. (3A) is a diagram showing a planar arrangement of a polishing pad, a polishing head, and a semiconductor wafer, and (3B) is a sectional view of the polishing surface plate and the polishing pad. It is a bottom view of the metal mold | die for forming a notch in the polishing pad by an Example. It is sectional drawing for demonstrating the method to form the notch | incision of the polishing pad by an Example. It is sectional drawing of the part which the bubble generate | occur | produced of the polishing pad by a comparative example. It is a top view of the polishing pad which shows the other example of the planar shape of retraction.

  FIG. 1 is a schematic perspective view of a polishing apparatus according to an embodiment. A polishing pad 20 is bonded to the upper surface of the polishing surface plate 10. The planar shapes of the polishing surface plate 10 and the polishing pad 20 are circular. Two polishing heads 30 are disposed above the polishing surface plate 10. The polishing head 30 holds the semiconductor wafer 40 to be polished on the surface facing the polishing platen 10 and presses it against the polishing pad 20. A polishing liquid 32 is dropped from the nozzle 31 onto the upper surface of the polishing pad 20.

  The polishing surface plate 10 rotates about its center axis as the center of rotation. Each of the polishing heads 30 rotates about its central axis as a rotation center and reciprocates in the radial direction of the polishing surface plate 10.

  FIG. 2A shows a plan view of the polishing pad 20. Grooves 21 that extend radially from the vicinity of the center are formed on the surface of the polishing pad 20.

  2B is a cross-sectional view taken along one-dot chain line 2B-2B in FIG. 2A. A polishing layer 23 is bonded to the upper surface of the soft layer 22 via an adhesive layer 24. A groove 21 is formed on the upper surface of the polishing layer 23. A double-sided pressure-sensitive adhesive sheet 25 is attached to the back surface of the soft layer 22. The double-sided pressure-sensitive adhesive sheet 25 includes a base material 25A. The base material 25A is bonded to the soft layer 22 via the adhesive layer 25B. A release liner 28 is attached to the back surface of the base material 25A via an adhesive layer 25C. By peeling the release liner 28 from the double-sided pressure-sensitive adhesive sheet 25, the polishing pad 20 can be attached to the polishing surface plate (FIG. 1) via the pressure-sensitive adhesive layer 25C.

  The polishing layer 23 has a closed cell structure in which bubbles are not continuous with each other. For the polishing layer 23, for example, a hard urethane foam is used. The soft layer 22 has an open cell structure in which bubbles are continuous with each other. For the soft layer 22, a material softer than the polishing layer 23, for example, a polyurethane-impregnated polyester nonwoven fabric is used.

  As an example, the thickness of the polishing layer 23 is 1.1 to 1.4 mm, the thickness of the soft layer 22 is 1.2 to 1.4 mm, and the depth of the groove 21 is 0.4 to 0.8 mm. It is. The thickness from the back surface of the soft layer 22 to the upper surface of the polishing layer 23, that is, the total thickness of the soft layer 22, the adhesive layer 24, and the polishing layer 23 is, for example, 2.6 to 2.9 mm. The diameter of the polishing pad 20 is 750 mm, for example.

  FIG. 3A shows a plan layout of the polishing pad 20, the polishing head 30, and the semiconductor wafer 40. The planar shapes of the polishing pad 20 and the polishing head 30 are circular. The centers of the two polishing heads 30 and the center of the polishing pad 20 are arranged on one imaginary straight line. Each of the polishing heads 30 rotates and reciprocates with a constant amplitude in a direction parallel to the virtual straight line. The semiconductor wafer 40 also rotates and reciprocates following the rotation and reciprocation of the polishing head 30. Following the rotation of the polishing surface plate 10 (FIG. 1), the polishing pad 20 also rotates.

  When one of the semiconductor wafers 40 is moved to the outermost side and the polishing pad 20 rotates once, the outer peripheral line of the figure drawn on the surface of the polishing pad 20 by the semiconductor wafer 40 becomes a circumference. The region surrounded by this circumference is referred to as “polishing region” 50.

  3B is a cross-sectional view taken along one-dot chain line 3B-3B in FIG. 3A. Cuts 29 are formed in the soft layer 22 from the back side. The cut 29 penetrates the double-sided pressure-sensitive adhesive sheet 25. Further, the notch 29 does not reach the polishing layer 23.

  Returning to FIG. 3A, the description will be continued. The notches 29 extend in parallel to the radial direction from a plurality of points on the outer peripheral line of the polishing region 50 toward the outer periphery of the polishing pad 20. However, the notch 29 does not reach the edge of the polishing pad 20. In the example shown in FIG. 3A, the cuts 29 extend from each of eight points arranged at equal intervals on the outer peripheral line of the polishing region 50. That is, the cuts 29 are arranged so as to be 8 times rotationally symmetric with respect to the center of the polishing pad 20. The number of cuts 29 is not limited to eight. The number of the cuts 29 may be n (n is a natural number), and the cuts 29 may be arranged so as to be n times rotationally symmetric.

  Hereinafter, an example of the dimension of each part in the planar arrangement shown in FIG. 3A will be described. The diameter of the pad 20 is 750 mm. The diameter of the semiconductor wafer 40 is 8 inches (203 mm). The polishing head 30 includes an annular retainer ring that surrounds the semiconductor wafer 40 in plan view. The width of the retainer ring is 25 mm. For this reason, the diameter of the polishing head 30 is 253 mm. The retainer ring restrains the position of the semiconductor wafer 40 in the in-plane direction with respect to the polishing head 30.

  The diameter of the polishing region 50 is 480 to 500 mm. The width of the annular region between the polishing region 50 and the edge of the polishing pad 20 is about 125-135 mm. The length of each of the cuts 29 is 70 to 80 mm. The distance from the outer peripheral end of the notch 29 to the edge of the polishing pad 20 is 45 to 65 mm.

  Next, a method for forming the cuts 29 will be described with reference to FIGS. 4 and 5A to 5C.

  In FIG. 4, the bottom view of the metal mold | die for forming the notch 29 is shown. A blade edge 61 is attached to the bottom surface of the mold 60. The blade edge 61 is arranged so as to match the arrangement of the notches 29 shown in FIG. 3A in plan view.

  FIG. 5A shows a cross-sectional view of the polishing pad 20 before the cut is formed. A polishing layer 23 is stuck on the soft layer 22 via an adhesive layer 24. A double-sided pressure-sensitive adhesive sheet 25 is affixed to the back surface of the soft layer 24. A release liner 28 is affixed to the double-sided pressure-sensitive adhesive sheet 25.

  As shown in FIG. 5B, the mold 60 is pressed against the back surface of the polishing pad 20. Cuts 29 are formed in the release liner 28, the double-sided pressure-sensitive adhesive sheet 25, and the soft layer 22 by the cutting edge 61 of the mold 60. At this time, the cross-section of the notch 29 follows the cross-sectional shape of the cutting edge 61 and becomes a shape in which the opening is widened.

  As shown in FIG. 5C, the mold 60 is pulled away from the polishing pad 20. The opening of the cut 29 is closed by the elasticity of the soft layer 22. However, the portion where the notch 29 is formed is not adhered again, and the notch 29 remains.

  Next, the polishing method according to the embodiment will be described with reference to FIG. The release liner 28 of the polishing pad 20 in which the notch 29 shown in FIG. 5C is formed is peeled off, and the polishing pad 20 is attached to the upper surface of the polishing surface plate 10. The semiconductor wafer 40 to be polished is held by the polishing head 30 and brought into contact with the upper surface of the polishing pad 20. A polishing liquid 32 is dropped from the nozzle 31.

  While the semiconductor wafer 40 is pressed against the polishing pad 20 with a predetermined pressure, the polishing surface plate 10 and the polishing head 30 are rotated at a predetermined number of rotations, and the polishing head 30 is reciprocated in the radial direction of the polishing surface plate 10. Move. The semiconductor wafer 40 is polished by contacting the inside of the polishing region 50 of the polishing pad 20 shown in FIG. 3A with the semiconductor wafer 40.

  Next, the effect of using the polishing pad 20 according to the embodiment will be described. When polishing was repeated using the polishing pad according to the comparative example in which the cuts 29 were not formed, bubbles were concentrated in the region along the outer peripheral line of the polishing region 50, and the polishing pad was raised. As an example, under a polishing condition in which the pressure for pressing the semiconductor wafer 40 against the polishing pad 20 is 6900 Pa (6 psi) and the rotation speed of the polishing surface plate 10 and the polishing head 30 is 100 rpm, about 100 semiconductor wafers are polished. Thus, the upper surface of the polishing pad 20 was raised.

  FIG. 6 is a cross-sectional view of a portion where the swell occurs. Large bubbles 70 are generated at the interface between the polishing surface plate 10 and the double-sided pressure-sensitive adhesive sheet 25 so that the upper surface of the polishing pad 20 rises. This is presumably because bubbles uniformly distributed in the soft layer 22 having an open cell structure were concentrated in the vicinity of the outer peripheral line of the polishing region 50.

  In the case where the polishing pad 20 according to the example was used, even when 1000 semiconductor wafers were polished, bubbles having such a size that the upper surface of the polishing pad 20 was raised did not occur. Thus, by forming the notch 29 in the polishing pad 20, concentration of bubbles can be suppressed.

  In order to obtain a sufficient effect of suppressing the concentration of bubbles, the depth of the cut 29 is preferably 20% or more of the thickness of the soft layer 22. The length of the cuts 29 is preferably 10 times or more the thickness of the soft layer 22. The number of the cuts 29 is preferably 4 or more.

  In the embodiment, the notch 29 is disposed outside the polishing region 50 and is not disposed inside the polishing region 50. For this reason, even if the flatness of the upper surface of the polishing pad 20 is reduced due to the notches 29, the polishing of the semiconductor wafer is not affected by the reduction of the flatness.

  In the embodiment, the notch 29 does not reach the edge of the polishing pad 20. For this reason, the polishing liquid that has flowed to the edge of the polishing pad 20 does not enter the notch 29. In order to prevent the penetration of the polishing liquid, it is preferable that the distance from the outer peripheral end of the notch 29 to the edge of the polishing pad 20 is 5 mm or more.

  7A and 7B show other examples of the planar shape of the cuts 29. FIG. As shown in FIG. 7A, the direction of each cut 29 may be inclined with respect to the radial direction of the polishing pad 20. Further, as shown in FIG. 7B, the planar shape of the cut 29 may be a curve such as an arc.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

  The following additional notes are further disclosed with respect to the embodiment including the above examples.

(Appendix 1)
A polishing layer whose upper surface is in contact with the object to be polished;
Adhered to the back surface of the polishing layer opposite to the upper surface, the back surface opposite to the upper surface bonded to the polishing layer is bonded to a rotating polishing platen, softer than the polishing layer, and continuous A soft layer having a cellular structure,
A polishing pad in which a notch is formed in each of a plurality of points on a circumference centering on a rotation center of the polishing surface plate toward an outer periphery of the soft layer on the back surface of the soft layer.

(Appendix 2)
The polishing pad according to appendix 1, wherein the cut does not reach the end of the soft layer.

(Appendix 3)
The polishing pad according to appendix 1 or 2, wherein the depth of the cut is 20% or more and 100% or less of the thickness of the soft layer.

(Appendix 4)
A polishing surface plate that can rotate,
A polishing pad affixed to the upper surface of the polishing platen;
A polishing head for holding a wafer to be polished, rotating the wafer in contact with the polishing pad and reciprocating in the radial direction of the polishing platen;
The polishing pad is
A soft layer adhered to the polishing platen and having an open cell structure;
An adhesive layer adhered on the soft layer, and a harder polishing layer than the soft layer,
On the surface of the soft layer bonded to the polishing surface plate, a cut is formed from each of a plurality of points on the circumference centering on the rotation center of the polishing surface plate toward the outer periphery of the soft layer. Polishing equipment.

(Appendix 5)
When the polishing platen is rotated in a state where the wafer is moved to the outermost peripheral side of the polishing platen, an end portion on the inner peripheral side of the cut is positioned on the outermost peripheral line of the figure drawn by the wafer. The polishing apparatus according to appendix 4.

(Appendix 6)
The polishing apparatus according to appendix 4 or 5, wherein the cut does not reach the end of the soft layer.

(Appendix 7)
The polishing pad according to any one of appendices 4 to 6, wherein a depth of the cut is 20% or more and 100% or less of a thickness of the soft layer.

(Appendix 8)
A step of bringing a wafer to be polished into contact with a polishing pad disposed on a polishing surface plate;
And rotating the wafer while rotating the polishing pad and reciprocating in the radial direction of the polishing platen to polish the wafer,
The polishing pad is
A soft layer adhered to the polishing platen and having an open cell structure;
An adhesive layer adhered on the soft layer, and a harder polishing layer than the soft layer,
On the surface of the soft layer bonded to the polishing surface plate, a cut is formed from each of a plurality of points on the circumference centering on the rotation center of the polishing surface plate toward the outer periphery of the soft layer. Polishing method.

(Appendix 9)
When the polishing platen is rotated in a state where the wafer is moved to the outermost peripheral side of the polishing platen, an end portion on the inner peripheral side of the cut is positioned on the outermost peripheral line of the figure drawn by the wafer. The polishing method according to appendix 8.

(Appendix 10)
The polishing method according to appendix 8 or 9, wherein the notch does not reach the end of the soft layer.

DESCRIPTION OF SYMBOLS 10 Polishing surface plate 20 Polishing pad 21 Groove 22 Soft layer 23 Polishing layer 24 Adhesive layer 25 Double-sided adhesive sheet 28 Release liner 29 Cutting 30 Polishing head 31 Nozzle 32 Polishing liquid 40 Semiconductor wafer 50 Polishing area 60 Mold 61 Cutting edge

Claims (5)

A polishing layer whose upper surface is in contact with the object to be polished;
Adhered to the back surface of the polishing layer opposite to the upper surface, the back surface opposite to the upper surface bonded to the polishing layer is bonded to a rotating polishing platen, softer than the polishing layer, and continuous A soft layer having a cellular structure,
A polishing pad in which a notch is formed in each of a plurality of points on a circumference centering on a rotation center of the polishing surface plate toward an outer periphery of the soft layer on the back surface of the soft layer.   The polishing pad according to claim 1, wherein the notch does not reach the end of the soft layer.   The polishing pad according to claim 1 or 2, wherein a depth of the cut is 20% or more and 100% or less of a thickness of the soft layer. A polishing surface plate that can rotate,
A polishing pad affixed to the upper surface of the polishing platen;
A polishing head for holding a wafer to be polished, rotating the wafer in contact with the polishing pad and reciprocating in the radial direction of the polishing platen;
The polishing pad is
A soft layer adhered to the polishing platen and having an open cell structure;
An adhesive layer adhered on the soft layer, and a harder polishing layer than the soft layer,
On the surface of the soft layer bonded to the polishing surface plate, a cut is formed from each of a plurality of points on the circumference centering on the rotation center of the polishing surface plate toward the outer periphery of the soft layer. Polishing equipment. A step of bringing a wafer to be polished into contact with a polishing pad disposed on a polishing surface plate;
And rotating the wafer while rotating the polishing pad and reciprocating in the radial direction of the polishing platen to polish the wafer,
The polishing pad is
A soft layer adhered to the polishing platen and having an open cell structure;
An adhesive layer adhered on the soft layer, and a harder polishing layer than the soft layer,
On the surface of the soft layer bonded to the polishing surface plate, a cut is formed from each of a plurality of points on the circumference centering on the rotation center of the polishing surface plate toward the outer periphery of the soft layer. Polishing method.

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