JP2012218137A - Polishing pad and polishing method for plate-like body using the polishing pad - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing pad and a polishing method that does not cause chipping at the outer periphery of a plate-like body and does not impair the flatness of a polished surface.SOLUTION: The polishing pad is used while being mounted to a rotary body, and has a center of rotation and an annular polishing surface. The polishing pad is characterized in that the annular polishing surface has a width larger than the diameter of the plate-like body to be polished, and tilts in a direction away from the plate-like body to be polished outward from the center of rotation.

Description

  The present invention relates to a polishing pad and a method for polishing a plate-like object such as a wafer using the polishing pad.

  An optical device wafer is a street in which a semiconductor layer (epitaxial layer) such as gallium nitride (GaN) is formed on the surface of a sapphire substrate or SiC substrate, and a plurality of optical devices such as LEDs are formed in a lattice pattern on the semiconductor layer. It is divided and formed by (division planned line).

  The sapphire substrate has a lattice constant close to that of GaN and is suitable for the growth of GaN epitaxial layers, and is an indispensable material for the production of optical devices. In order to improve the luminance of the device, the back surface of the sapphire substrate is ground by a grinding apparatus (for example, Japanese Patent Application Laid-Open No. 2008-23693).

  However, when a plate-like object such as a sapphire substrate is ground thinly, the plate-like object may be warped and cracked. This warpage occurs when a fine crack is formed on the surface to be ground of the plate-like object by grinding. Therefore, polishing is performed on the surface to be ground of the plate-like object after grinding to remove fine cracks, thereby preventing warpage and improving the bending strength of the plate-like object.

JP 2008-23893 A JP 2002-28311 A

  However, a conventional polishing pad is mainly used in which the radius is smaller than the diameter of a plate-like object such as a wafer, and polishing is performed such that the polishing surface of the polishing pad partially covers the plate-like object. As a result, as the edge of the polishing pad passes the outer periphery of the plate-like object, the outer periphery of the plate-like object may be chipped.

  In addition, since the polishing rate differs depending on the difference in peripheral speed between the rotation center side and the outer peripheral side of the polishing pad, in the portion in contact with the rotation center side and the outer peripheral side of the polishing pad on the surface to be ground of the plate, There is a problem that the thickness after polishing is not uniform and the thickness accuracy (flatness) is deteriorated.

  The present invention has been made in view of these points, and the object of the present invention is to provide a polishing pad that does not deteriorate the flatness of the surface to be ground without causing chipping in the outer periphery of the plate-like object. And a polishing method.

  According to the first aspect of the present invention, a polishing pad used by being mounted on a rotating body has a rotation center and an annular polishing surface, and the width of the annular polishing surface is larger than the diameter of the plate-like object to be polished. In addition, a polishing pad is provided in which the annular polishing surface is inclined in a direction away from the plate-like object to be polished outward from the rotation center.

  According to the second aspect of the present invention, a polishing pad used by being mounted on a rotating body has a rotation center and a circular polishing surface, and the radius of the circular polishing surface is larger than the diameter of the plate-like object to be polished. The polishing pad is characterized in that the circular polishing surface is inclined in a direction away from the plate-like object to be polished outward from the rotation center.

  According to a third aspect of the present invention, there is provided a plate-like material polishing method using the polishing pad according to the first or second aspect, wherein the holding step of holding the surface side of the plate-like object with a chuck table having a holding surface; A polishing step of polishing the plate-like object by rotating the polishing pad around a rotation center in a state where the entire back surface of the plate-like object held by the chuck table is covered with the polishing surface of the polishing pad. There is provided a method for polishing a plate-like material.

  In the polishing method using the polishing pad of the present invention, since the polishing is performed in a state where the entire surface to be ground of the plate-like object is covered with the polishing pad, the edge of the polishing pad passes through the outer periphery of the plate-like object. Occurrence of chipping of the outer periphery of the plate-like material due to the occurrence of the above is prevented.

  In addition, since the polishing surface of the polishing pad is inclined in the direction of releasing the polishing pressure from the rotation center of the polishing pad toward the outside, the polishing rate can be made equal between the rotation center side and the outer peripheral side of the polishing pad. The thickness of the polished plate-like material can be made uniform, and the thickness accuracy (flatness) does not deteriorate.

It is a perspective view of a polish device provided with a polishing pad of an embodiment of the present invention. It is a perspective view which shows a mode that a protective tape is stuck on the surface of an optical device wafer. 3A is a bottom view of the polishing pad according to the first embodiment of the present invention, and FIG. 3B is a longitudinal sectional view of the polishing head showing the positional relationship with the wafer and mounted with the polishing pad of the first embodiment. It is. It is a longitudinal cross-sectional view explaining the grinding | polishing method of embodiment of this invention. FIG. 5A is a bottom view of the polishing pad according to the second embodiment of the present invention, and FIG. 5B is a longitudinal sectional view of the polishing head showing the positional relationship with the wafer and mounted with the polishing pad of the second embodiment. It is.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, an external perspective view of a polishing apparatus 2 equipped with the polishing pad of the present invention is shown. Reference numeral 4 denotes a base of the polishing apparatus 2, and a column 6 is erected on the rear side of the base 4. A pair of guide rails 8 extending in the vertical direction is fixed to the column 6.

  A polishing unit (polishing means) 10 is mounted along the pair of guide rails 8 so as to be movable in the vertical direction. The polishing unit 10 includes a spindle housing 12 and a support portion 14 that holds the spindle housing 12, and the support portion 14 is attached to a moving base 16 that moves up and down along a pair of guide rails 8. Yes.

  The polishing unit 10 includes a spindle (rotary body) 18 rotatably accommodated in a spindle housing 12, a motor 20 that rotationally drives the spindle 18, a head mount 22 fixed to the tip of the spindle 18, and a head mount 22. And a polishing head 24 detachably attached to the head.

  The polishing apparatus 2 includes a polishing unit feed mechanism 32 including a ball screw 28 that moves the polishing unit 10 in the vertical direction along a pair of guide rails 8 and a pulse motor 30. When the pulse motor 30 is driven, the ball screw 28 rotates and the moving base 16 is moved in the vertical direction.

  A recess 4a is formed on the upper surface of the base 4, and a chuck table mechanism 34 is disposed in the recess 4a. The chuck table mechanism 34 has a chuck table 36, and the chuck table 36 is moved in the Y-axis direction between a wafer attaching / detaching position A and a polishing position B facing the polishing unit 10 by a moving mechanism (not shown).

  38 and 40 are bellows. An operation panel 42 is provided on the front side of the base 4 so that an operator of the polishing apparatus 2 inputs polishing conditions and the like.

  Referring to FIG. 2, a perspective view showing a state where a protective tape is stuck on the surface of the optical device wafer is shown. The optical device wafer 11 is configured by laminating an epitaxial layer (semiconductor layer) 15 such as gallium nitride (GaN) on a sapphire substrate 13.

  The optical device wafer 11 has a front surface 11a on which an epitaxial layer 15 is stacked and a back surface 11b on which the sapphire substrate 13 is exposed. A plurality of optical devices 19 such as LEDs are formed in the epitaxial layer 15 by being partitioned by division lines (streets) 17 formed in a lattice pattern.

  Prior to performing the polishing method of the present invention, a back surface grinding step is performed in which the back surface 11b of the optical device wafer 11 is ground to process the optical device wafer 11 to a predetermined thickness. Before performing this back surface grinding step, a surface protection tape 21 for protecting the optical device 19 formed on the surface 11a is attached to the surface 11a of the optical device wafer 11.

  The back surface 11b of the optical device wafer 11 is ground by the grinding wheel of the grinding device while the surface protection tape 21 side is sucked and held by the chuck table of the grinding device, and the optical device wafer 11 is processed to a predetermined thickness.

  When grinding is performed, grinding strain such as fine cracks remains on the back surface 11b of the optical device wafer 11, and therefore the polishing pad of the present invention is used to remove this grinding strain and improve the bending strength of the optical device wafer 11. Polishing using is performed.

  Referring to FIG. 3A, a bottom view of the polishing pad 26 according to the first embodiment of the present invention is shown. FIG. 3B is a longitudinal sectional view showing the positional relationship between the polishing head 24 to which the polishing pad 26 of the first embodiment is mounted and the optical device wafer 11 held on the chuck table 36.

  The polishing pad 26 of this embodiment has a center hole 26a, and the polishing surface 26b is formed in an annular shape. The base 25 of the polishing head 24 also has a center hole 25 a having the same diameter as the center hole 26 a of the polishing pad 26, and the polishing head 24 is configured by adhering the polishing pad 26 to the base 25. Reference numeral 27 denotes a rotation center of the polishing head 24. The polishing pad 26 is formed of, for example, a felt grindstone in which abrasive grains are dispersed in polyurethane or felt and fixed with an appropriate bond agent.

  As apparent from FIG. 3B, the annular polishing surface 26 b of the polishing pad 26 has a width larger than the diameter of the optical device wafer 11 held on the chuck table 36. Reference numeral 37 denotes a rotation center of the chuck table 36.

  Further, the annular polishing surface 26 b of the polishing pad 26 is inclined in a direction away from the optical device wafer 11 which is an object to be ground held by the chuck table 36 from the rotation center 27 toward the outer periphery.

  In other words, the polishing pad 26 has an annular polishing surface 26b whose thickness continuously decreases from the inner periphery toward the outer periphery. The thickness difference h between the inner peripheral side and the outer peripheral side of the polishing pad 26 is set within a range of 10 to 100 μm. More preferably, h is 20-50 μm.

  Hereinafter, a method of polishing the optical device wafer 11 by the polishing head 24 to which the polishing pad 26 of the first embodiment described above is mounted will be described with reference to FIG. The polishing method of the present embodiment is preferably dry polishing performed without supplying a polishing liquid.

  Therefore, the polishing pad 26 has a hollow hole 26a for releasing frictional heat due to polishing, and the base 25 also has a hollow hole 25a. As described above, the polishing pad 26 of the present embodiment is particularly suitable for dry polishing, but can also be applied to chemical mechanical polishing (CMP) performed while supplying a polishing liquid.

  According to the polishing method of this embodiment, the chuck table 36 is moved in the direction indicated by the arrow in the state where the entire back surface 11b of the ground optical device wafer 11 sucked and held by the chuck table 36 is covered with the polishing surface 26b of the polishing pad 26. And the polishing pad 26 is rotated at different peripheral speeds in the same direction as the chuck table 36 to polish the ground back surface 11 b of the optical device wafer 11.

  Since the polishing is performed in such a manner that the back surface 11 b of the optical device wafer 11 is covered with the polishing pad 26, the optical device wafer 11 caused by the edge of the polishing pad 26 passing through the outer periphery of the optical device wafer 11. It is possible to prevent the occurrence of chipping on the outer periphery of the sheet.

  Further, since the polishing surface 26b of the polishing pad 26 is inclined in a direction in which the polishing pressure is released from the rotation center 27 of the polishing pad 26 to the outside, the polishing rate is adjusted between the inner peripheral side and the outer peripheral side of the polishing pad 26. The thickness of the optical device wafer 11 after polishing can be made uniform, and the thickness accuracy (flatness) does not deteriorate.

  Next, a polishing pad 26A according to a second embodiment of the present invention will be described with reference to FIG. 5A is a bottom view of the polishing pad 26A, and FIG. 5B is a longitudinal sectional view of the polishing head 24A on which the polishing pad 26A is mounted on the base 25A. The polishing is held by the chuck table 36. The positional relationship with the optical device wafer 11 is shown.

  The polishing pad 26A of this embodiment has a circular polishing surface 26b, and has a radius larger than the diameter of the optical device wafer 11 to be polished. Further, the polishing surface 26 b of the polishing pad 26 A is inclined in a direction away from the optical device wafer 11 held by the chuck table 36 from the rotation center 27 toward the outside.

  In other words, the polishing pad 26A has a polishing surface 26b that is inclined so that its thickness continuously decreases from the rotation center 27 toward the outer periphery. The thickness difference h between the center of the polishing pad 26A and the outermost periphery is in the range of 10 to 100 μm, more preferably 20 to 50 μm.

  The polishing pad 26A of this embodiment is preferably used for chemical mechanical polishing (CMP) because its polishing surface 26b is formed in a circular shape. However, the polishing pad 26A of this embodiment may be used for dry polishing.

  Polishing of the ground back surface 11b of the optical device wafer 11 by the polishing head 24A equipped with the polishing pad 26A of the present embodiment is the same as the polishing head 24 equipped with the polishing pad 26 of the first embodiment described above. Since the effect is the same as that of the first embodiment, the description thereof is omitted.

  In the above-described polishing method of the present invention, the example in which the present invention is applied to the polishing of the optical device wafer 11 having the sapphire substrate 13 has been described. However, the object to be polished to which the polishing method of the present invention is applied is limited to this. In addition, the polishing pad and the polishing method of the present invention can be similarly applied to polishing of plate-like materials such as SiC (silicon carbide) and general silicon wafers.

2 Polishing apparatus 10 Polishing unit 11 Optical device wafer 13 Sapphire substrate 19 Optical device 21 Surface protective tape 24 Polishing head 26, 26A Polishing pad 26b Polishing surface 36 Chuck table

Claims (3)

A polishing pad used by being mounted on a rotating body,
Having a center of rotation and an annular polishing surface;
The width of the annular polishing surface is larger than the diameter of the plate-like object to be polished, and the annular polishing surface is inclined in a direction away from the plate-like object to be polished outward from the rotation center. Polishing pad. A polishing pad used by being mounted on a rotating body,
Having a center of rotation and a circular polished surface;
The radius of the circular polishing surface is larger than the diameter of the plate to be polished, and the circular polishing surface is inclined in a direction away from the plate to be polished outward from the rotation center. Polishing pad. A plate-like material polishing method using the polishing pad according to claim 1 or 2,
A holding step for holding the surface side of the plate-like object with a chuck table having a holding surface;
A polishing step of polishing the plate-like object by rotating the polishing pad around the rotation center in a state where the entire back surface of the plate-like object held by the chuck table is covered with the polishing surface of the polishing pad;
A method for polishing a plate-like material, comprising:

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