JP5414377B2 - Polishing pad - Google Patents

Description

  The present invention relates to a polishing pad having a plurality of grooves formed on a polishing surface for polishing an object to be polished such as a semiconductor wafer.

  For example, a chemical mechanical polishing method, so-called CMP (Chemical Mechanical Polishing), is widely adopted as a polishing method capable of forming a surface having excellent flatness in a semiconductor device manufacturing process.

  In recent years, there has been a demand for thinner semiconductor wafers due to demands for smaller and thinner semiconductor devices. For this reason, after mechanically grinding the backside of the semiconductor wafer with a grindstone, etc., the backside of the semiconductor wafer after grinding is polished by CMP for the purpose of removing grinding distortion caused by this grinding and improving the bending strength. doing.

  CMP is performed by relatively sliding the polishing pad and the object to be rotated while supplying a polishing liquid (slurry) between the polishing pad and the object to be polished (see, for example, Japanese Patent Laid-Open No. Hei. No. 3-248532).

  A nonwoven fabric is generally used as the polishing pad, and the surface of an object to be polished such as a semiconductor wafer is polished while supplying a polishing liquid (slurry) containing free abrasive grains such as silica. However, in CMP using a polishing liquid containing free abrasive grains, there is a problem that waste liquid treatment is difficult because most of the free abrasive grains remain in the waste liquid without contributing to polishing. Moreover, since the consumption of abrasive grains during polishing is usually about 3 to 4% of the entire abrasive grains, there is also a problem that most of the abrasive grains are wasted without contributing to polishing.

  In order to solve these problems, CMP using a polishing liquid that does not contain free abrasive grains (for example, an alkaline solution) and a fixed abrasive polishing pad in which abrasive grains are contained in the polishing pad is disclosed, for example, in JP-A-2005-129644. Proposed in the Gazette.

  In CMP, it is known that the polishing result depends greatly on the properties of the polishing pad and the polishing liquid. In JP-A-11-70463 and JP-A-8-216029, by providing a plurality of grooves on the polishing surface of the polishing pad and uniformly supplying the polishing liquid to the polishing surface, the polishing rate and the polishing result are obtained. A technique for improving the above is disclosed.

JP-A-3-248532 JP 2005-129644 A JP-A-11-70463 JP-A-8-216029

  However, when an object to be polished such as a semiconductor wafer is polished using a polishing pad having a plurality of grooves formed on the polishing surface, there arises a problem that chipping (edge chipping) occurs in the outer peripheral portion of the object to be polished.

  The polishing pad and the object to be polished are brought into contact with each other while being applied with a predetermined pressing force, and are relatively slid to perform polishing, but the side wall defining the groove and the polishing surface are formed to intersect each other. When the edge portion of the groove to be passed through the outer peripheral portion of the object to be polished, edge chipping is generated by colliding with the outer peripheral portion of the object to be polished.

  If edge chipping occurs on the outer periphery of the object to be polished, the object to be polished may be damaged starting from the edge chipping during conveyance or handling, which is a very serious problem.

  The present invention has been made in view of these points, and an object of the present invention is to provide a polishing pad capable of reducing chipping generated in the outer peripheral portion of an object to be polished.

According to the present invention, a polishing pad having a plurality of grooves formed on a polishing surface for polishing an object to be polished, wherein at least a part of the plurality of grooves is an edge portion on the rear side in the rotation direction of the polishing pad. In addition, a buffer portion for buffering the collision between the object to be polished and the edge portion of the groove is formed, and the polishing pad that defines the polishing surface includes at least abrasive grains and a binder that binds the abrasive grains. In addition, a polishing pad is provided in which the buffer portion does not contain abrasive grains .

  Preferably, the plurality of grooves have a radial shape, a concentric circular shape, a lattice shape, or a cylindrical shape.

  Preferably, the polishing pad includes a polishing liquid supply through-hole connected to a polishing liquid supply source in the center, and one end of each of the plurality of grooves communicates with the polishing liquid supply through-hole, and the outer peripheral direction of the polishing pad. And a plurality of concentric circular grooves formed concentrically, and the other end of the radial groove reaches at least the outermost circular groove among the plurality of concentric circular grooves. The buffer portion is formed at an edge portion of each radial groove on the rear side in the rotation direction of the polishing pad.

  According to the present invention, since the buffer portion is formed at the rear edge portion in the rotation direction of the polishing pad of at least some of the plurality of grooves formed on the polishing surface, the object to be polished and the edge of the groove It is possible to buffer the collision with the part, and it is possible to reduce the chip generated in the outer peripheral part of the object to be polished.

1 is an external perspective view of a polishing apparatus suitable for mounting the polishing pad of the present invention. It is a perspective view of the semiconductor wafer cut out from the ingot. FIG. 3A is a sectional view of the polishing pad according to the first embodiment of the present invention, and FIG. 3B is a bottom view of the polishing pad according to the first embodiment. It is a bottom view of the polishing pad of 1st Embodiment when a polishing pad and a to-be-polished object rotate in the opposite direction at the time of grinding | polishing. FIG. 5A is a cross-sectional view of the polishing pad of the second embodiment of the present invention, and FIG. 5B is a bottom view of the polishing pad of the second embodiment. FIG. 6A is an enlarged cross-sectional view of a radial groove portion of the polishing pad of the second embodiment, and FIG. 6B is an enlarged cross-sectional view showing another embodiment of the radial groove portion. It is a bottom view of the polishing pad of 3rd Embodiment of this invention. It is a bottom view of the polishing pad of 4th Embodiment of this invention. It is a figure which shows the positional relationship of a polishing pad and a to-be-polished object. It is a side view which shows a mode that the semiconductor wafer hold | maintained at the chuck table using the polishing pad of this invention is grind | polished.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a perspective view of a polishing apparatus 2 suitable for mounting the polishing pad of the present invention. Reference numeral 4 denotes a housing of the polishing apparatus 2, and a column 6 is erected on the rear side of the housing 4. A pair of guide rails (only one is shown) 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 is attached to a moving base 12 whose housing 20 moves in the vertical direction along a pair of guide rails 8.

  The polishing unit 10 includes a housing 20, a spindle (not shown) rotatably accommodated in the housing 20, a servo motor 22 that rotationally drives the spindle, and a polishing wheel 24 having a polishing pad 26 fixed to the tip of the spindle. Contains.

  The polishing unit 10 includes a polishing unit moving mechanism 18 including a ball screw 14 and a pulse motor 16 that move the polishing unit 10 up and down along a pair of guide rails 8. When the pulse motor 16 is pulse-driven, the ball screw 14 rotates and the moving base 12 is moved in the vertical direction.

  A holding table mechanism (chuck table mechanism) 28 is disposed at an intermediate portion of the housing 4, and the holding table mechanism 28 is moved in the Y-axis direction by a holding table moving mechanism (not shown). Reference numeral 30 denotes a bellows that covers the holding table mechanism.

  In the front portion of the housing 4, a first wafer cassette 32, a second wafer cassette 34, a wafer transfer robot 36, a positioning mechanism 38 having a plurality of positioning pins 40, and a wafer carry-in mechanism (loading arm) 42 are provided. A wafer unloading mechanism (unloading arm) 44 and a spinner unit 46 are disposed.

  Further, a cleaning water spray nozzle 48 for cleaning the holding table mechanism 28 is provided at the approximate center of the housing 4. The cleaning water spray nozzle 48 sprays cleaning water toward the holding table mechanism 28 in a state where the holding table mechanism 28 is positioned in the wafer loading / unloading area on the front side of the apparatus.

  Referring to FIG. 2, there is shown a perspective view of a semiconductor wafer 50 as an example of a workpiece to be polished by the polishing pad of the present invention. This semiconductor wafer 50 is an as-sliced wafer cut out from an ingot, and has a thickness of about 700 μm. Before forming a circuit such as an IC or LSI on such a semiconductor wafer 50, the front and back surfaces of the semiconductor wafer 50 are polished with the polishing pad of the present invention.

  Referring to FIG. 3A, a cross-sectional view of the polishing pad 26 of the first embodiment of the present invention is shown. FIG. 3B is a bottom view of the polishing pad 26 of the first embodiment. The cross-sectional view shown in FIG. 3A is a cross-sectional view taken along line 3A-3A in FIG.

  The polishing pad 26 includes a disc-like polishing layer 56 having a polishing surface 56a and a non-polishing surface 56b opposite to the polishing surface 56a, and a disc-like shape bonded on the polishing layer 56 with, for example, an acrylic double-sided tape. Buffer layer 52.

  Preferably, the polishing layer 56 is a fixed abrasive type polishing layer in which silica is bonded with foamed urethane, and the buffer layer 52 is made of felt. The buffer layer 52 may be made of urethane, nonwoven fabric, or the like that is softer than the polishing layer 56.

  A polishing liquid supply through hole 54 connected to a polishing liquid supply source 64 (see FIG. 10) is formed at the center of the buffer layer 52. As apparent from FIG. 3B, the polishing layer 56 has a plurality of radial grooves whose one ends communicate with the polishing liquid supply through hole 54 of the buffer layer 52 and extend radially in the outer circumferential direction of the polishing layer 56. 58 is formed. The number of the radial grooves 58 is preferably in the range of 4 to 32, more preferably 16 to 32.

  The polishing layer 56 further includes a plurality of circular grooves 56 formed concentrically. The pitch of the concentric circular grooves 60 is preferably 2 to 20 mm, and more preferably 2 to 10 mm. For example, when the pitch between the grooves is 2 mm, the width of the circular groove 60 is 1 mm.

  In FIG. 3B, arrow A indicates the direction of rotation of the polishing pad 26 during polishing, and arrow B indicates the direction of rotation of the semiconductor wafer 50. A buffer portion 62 that cushions the collision between the semiconductor wafer 50 and the edge portion of the radial groove 58 is formed at the edge portion of each radial groove 58 on the rear side in the rotation direction of the polishing pad 26.

  The buffer portion 62 is formed of soft urethane 62 as shown in FIG. 6 (A), for example. In the embodiment of FIG. 6A, the buffer portions 62 are formed on both side walls of the radial groove 58, but in the polishing pad 26 of the first embodiment, the radial groove 58 on the rear side in the rotational direction of the polishing pad 26. The buffer part 62 is formed only on the side wall part.

  The formation method of the radial groove | channel 58, the concentric circular groove | channel 60, and the buffer part 62 is as follows, for example. First, the polishing layer 56 in which the radial grooves 58 and the circular grooves 60 are not formed is attached to the buffer layer 52 with a double-sided tape or the like.

  Next, a plurality of radial grooves are formed in the polishing layer 56 by cutting or milling, and soft urethane is injected into each groove and cured. Thereafter, the radial grooves 58 are formed by leaving the soft urethane serving as a buffer portion on one side wall in the soft urethane portion. Next, concentric circular grooves 60 are formed.

  The polishing surface of the polishing layer 56 is formed by injection molding, compression press or the like. As described above, the groove is formed by cutting or milling, but may be formed by pressing by hydraulic or pneumatic press. The polishing layer 56 is composed of a fixed abrasive type polishing layer in which silica is bonded with foamed urethane, while the buffer portion 62 is made of soft urethane containing no abrasive grains.

  The polishing liquid supplied from the polishing liquid supply source 64 is supplied to the radial groove 58 of the polishing layer 56 through the polishing liquid supply through hole 54 of the buffer layer 52, and a part thereof is formed on the polishing surface 56 a of the polishing layer 56. While staying in the concentric circular groove 60, it is uniformly supplied to the entire polishing surface 56a and supplied to the surface of an object to be polished such as a semiconductor wafer.

  In the first embodiment shown in FIG. 3, the outer peripheral ends of the radial grooves 58 are terminated by the outermost circular groove 60. However, the radial grooves 58 may be extended to the outermost periphery of the polishing layer 56. . In this case, the polishing liquid is also supplied to the surface of the object to be polished from the outermost periphery of the radial groove 58.

  A preferable polishing liquid is, for example, an alkaline solution (for example, pH 12.5) that does not contain free abrasive grains, and a mixed liquid produced by mixing an aqueous ammonia solution and ethylenediaminetetraacetic acid at a predetermined ratio is used.

  Referring to FIG. 4, there is shown a modified example of the polishing pad 26 of the first embodiment described above during polishing. In this modification, the rotation direction indicated by the arrow B of the semiconductor wafer 50 during polishing is set to be opposite to the rotation direction of the polishing pad 26 indicated by the arrow A.

  Also in this modified example, the buffer portion 62 is formed only at the edge portion of the radial groove 58 of the polishing pad 26 on the rear side in the rotation direction of the polishing pad 26. Thus, by forming the buffer portion 62 formed of urethane softer than the polishing surface at the edge portion on the rear side in the rotation direction, it is possible to reduce chipping generated in the outer peripheral portion of the semiconductor wafer 50.

  Referring to FIG. 5A, a sectional view of a polishing pad 26A according to the second embodiment of the present invention is shown. FIG. 5B is a bottom view of the polishing pad 26A of the second embodiment. In the polishing pad 26A of this embodiment, the plurality of radial grooves 58 and the plurality of concentric circular grooves 60 are formed on the polishing surface 56a of the polishing layer 56A without using the buffer layer 52 of the first embodiment. Further, a polishing liquid supply through hole 54 connected to the polishing liquid supply source 64 is formed in the central portion of the polishing layer 56A.

  Furthermore, in the polishing pad 26A of the present embodiment, as best shown in the sectional view of FIG. 6A, buffer portions 62 made of soft urethane are formed on both side wall portions that define each radial groove 58. Yes.

  In this way, by forming the buffer portions 62 made of urethane softer than the polishing surface at the edge portions on both sides of each radial groove 58, chipping generated in the outer peripheral portion of the semiconductor wafer 50 that is the object to be polished is reduced. be able to. As shown in FIG. 6B, a taper 63 may be provided at the edge of the radial groove 58 as a buffer.

  Referring to FIG. 7, a bottom view of a polishing pad 26B according to a third embodiment of the present invention is shown. In the polishing pad 26B of the present embodiment, a plurality of cylindrical grooves 68 are formed on the polishing surface.

  A buffer portion 70 made of soft urethane or the like is formed on both sides of the cylindrical groove 68. The buffer portion 70 may be formed only at the rear edge portion in the rotation direction of the polishing pad 26B.

  Referring to FIG. 8, a bottom view of a polishing pad 26C according to a fourth embodiment of the present invention is shown. The polishing pad 26 </ b> C of the present embodiment has a grid-like groove 72 on the polishing surface. Buffer portions 74 made of soft urethane or the like are formed on both sides of the lattice-like grooves 72.

  Referring to FIG. 9, a positional relationship between the polishing pad 26 and the semiconductor wafer 50 as an object to be polished is shown. The entire surface of the semiconductor wafer 50 is positioned in the polishing pad 26. Preferably, the outer periphery of the semiconductor wafer 50 is positioned, for example, several mm to several tens of mm from the outer periphery of the polishing pad 26.

  Next, with reference to FIG. 10, the polishing operation of the object to be polished using the polishing pad 26 will be described. The object to be polished is a semiconductor wafer 50 'in which a plurality of devices such as IC and LSI are formed on the surface, and the back surface is ground to a predetermined thickness (for example, 50 μm) by a grinding apparatus, and a protective tape 51 is pasted on the surface. It is worn.

  The protective tape 51 side of the semiconductor wafer 50 ′ is sucked and held by the holding pad 66 of the holding table 28. Next, the polishing unit moving mechanism 18 is driven to lower the polishing pad 26, press it against the semiconductor wafer 50 ′ on the holding pad 66 with a predetermined pressure, and from the polishing liquid supply source 64 through the radial groove 58 and the circular groove 60. The polishing of the wafer 50 'is started while supplying the polishing liquid.

  At the time of this polishing, the spindle 21 of the polishing unit 10 is rotated in the direction of arrow A, for example, 200 to 600 rpm, and the holding table 28 is rotated in the direction of arrow B, for example, 200 to 600 rpm. The rotation speed of the spindle 21 and the rotation speed of the holding table 28 are approximately the same rotation speed. However, since the diameter of the polishing pad 26 is larger than the diameter of the wafer 50 ′, the polishing pad 26 is faster than the peripheral speed of the wafer 50 ′. The back surface of the wafer 50 'is polished by rotating at a large peripheral speed.

  According to the polishing pad 26 of the first embodiment described above, the polishing liquid is supplied in the radial direction of the polishing pad 26 through the radial grooves 58 formed in the polishing layer 56, and further formed on the polishing surface 56 a from the radial grooves 58. The concentric circular groove 60 is supplied.

  A portion of the polishing liquid stays in the concentric circular groove 60 formed on the polishing surface 56a of the polishing layer 56 and is uniformly supplied to the entire polishing surface 56a, so that the polishing rate is not reduced. Good polishing quality can be ensured. Since the polishing liquid stays in the concentric circular groove 60, the chemical reaction with the object to be polished can be promoted, and the polishing time can be shortened.

  Furthermore, in the polishing pad of each of the embodiments described above, at least a rear edge in the rotation direction of the polishing pad is a softer buffer than the polishing surface in some of the plurality of grooves formed on the polishing surface. Since it is formed, chipping generated in the outer peripheral portion of the object to be polished can be reduced.

2 Polishing device 10 Polishing unit 26-26C Polishing pad 28 Holding table (chuck table)
50 Semiconductor wafer 52 Buffer layer 54 Polishing liquid supply through hole 56 Polishing layer 56a Polishing surface 58 Radial groove 60 Concentric circular groove 62 Buffer part 64 Polishing liquid supply source

Claims (3)

A polishing pad having a plurality of grooves formed on a polishing surface for polishing an object to be polished,
A buffer portion for buffering a collision between an object to be polished and the edge portion of the groove is formed on an edge portion on the rear side in the rotation direction of the polishing pad of at least some of the plurality of grooves ,
The polishing pad that defines the polishing surface includes at least abrasive grains and a binder that binds the abrasive grains,
The said buffer part does not contain an abrasive grain, The polishing pad characterized by the above-mentioned .   The polishing pad according to claim 1, wherein the plurality of grooves have at least one of a radial shape, a concentric circle shape, a lattice shape, and a cylindrical shape. The polishing pad includes a polishing liquid supply through-hole connected to a polishing liquid supply source in the center,
The plurality of grooves, a plurality of radial grooves, one end of which communicates with the polishing liquid supply through hole and extends in the outer peripheral direction of the polishing pad;
A plurality of concentric circular grooves formed concentrically,
The other end of the radial groove is formed to reach the outermost circular groove among at least the plurality of concentric circular grooves,
The polishing pad according to claim 2, wherein the buffer portion is formed at an edge portion of each radial groove on the rear side in the rotation direction of the polishing pad.

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