JP2011044473A - Grinding device for wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grinding device for wafer that never causes a rigid wafer such as a sapphire wafer to crack even when the rigid wafer is ground to be processed thin. <P>SOLUTION: The grinding device for wafer includes a chuck table capable of rotating while holding the wafer, and a grinding means configured to rotatably hold a grinding wheel having a grindstone for grinding the wafer held by the chuck table. The chuck table includes a suction plate having a holding surface for suctionally holding the wafer and a frame having a bottom part enclosing the suction plate except the holding surface and also supporting a surface opposite to the holding surface, and a suction groove is formed at the bottom part of the frame closer at a center part than at an outer peripheral part of the suction plate such that suctional force is higher at the center part than at the outer peripheral part. The suction plate of the chuck table is linked to a suction source through the suction groove formed at the frame. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wafer grinding apparatus suitable for grinding a hard wafer having a Mohs hardness of 9 or more, such as a sapphire wafer or a silicon carbide wafer.

  A sapphire wafer in which a nitride semiconductor layer such as gallium nitride is stacked on the surface, and an optical device is formed in each region defined by the planned division lines formed in a lattice pattern, is a laser beam along the planned division lines. The optical device is divided into individual optical devices by irradiation, and the divided optical devices are used for electronic devices such as a mobile phone and a digital camera (see, for example, Japanese Patent Application Laid-Open No. 2008-6492).

  Since sapphire wafers are formed by growing a nitride semiconductor layer on a sapphire substrate suitable for epitaxial layer growth, the sapphire substrate is an indispensable material for manufacturing optical devices. After the layers are stacked, the back surface of the sapphire substrate is ground and thinned by a grinding device in order to reduce the weight, size, and improve device characteristics of the electronic device (see, for example, Japanese Patent Application Laid-Open No. 2008-23693). .

JP 2008-6492 A JP 2008-23893 A

  However, when a protective tape made of an adhesive tape is attached to the surface of the sapphire wafer and the back surface of the sapphire wafer is ground to reduce its thickness to 100 μm or less, and further to 50 μm or less, there is a problem that the sapphire substrate is cracked. . Such a problem also occurs when grinding a hard brittle substrate such as a silicon carbide substrate (SiC substrate).

  Considering this cause, it can be inferred that one of the causes is that a large number of micro cracks are generated on the ground surface of the wafer and the substrate warps in a convex shape. When the substrate is warped, the wafer is dragged in the lateral direction during grinding, and the substrate is likely to be cracked.

  The present invention has been made in view of the above points, and the object of the present invention is to grind a wafer that does not cause cracking of the substrate even if a hard brittle substrate such as a sapphire substrate is ground and thinned. Is to provide a device.

  According to the present invention, there is provided a wafer grinding apparatus comprising: a chuck table that holds and rotates a wafer; and a grinding means that rotatably supports a grinding wheel having a grinding wheel for grinding the wafer held on the chuck table. The chuck table includes a suction plate having a holding surface for sucking and holding the wafer, and a frame having a bottom portion that surrounds other than the holding surface of the suction plate and supports the opposite surface of the holding surface, A suction groove is formed at the bottom of the frame so that the suction force at the center of the suction plate is stronger at the center than at the outer periphery so that the suction at the center is stronger than the suction at the outer periphery. The wafer grinding apparatus is characterized in that the suction plate of the chuck table communicates with a suction source through a suction groove formed in the frame body.

  According to the grinding device of the present invention, the suction groove is formed at the center of the bottom part of the frame constituting the chuck table as compared with the outer peripheral part so that the suction force of the central part of the suction plate is stronger than the suction force of the outer peripheral part. Since it is formed densely in the part, the holding force for holding the wafer in the central part is increased, the warpage of the wafer during grinding is suppressed, and the wafer can be prevented from cracking.

1 is an external perspective view of a grinding apparatus according to an embodiment of the present invention. It is a surface side perspective view of a sapphire wafer. It is a back surface side perspective view of a sapphire wafer in the state where a protective tape was stuck on the surface. It is a disassembled perspective view of a chuck table. It is a perspective view of a chuck table. It is a schematic diagram which shows the suction force of the center part and outer peripheral part in a suction plate. It is a perspective view which shows the positional relationship of the chuck table and grinding wheel at the time of grinding.

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

  A grinding unit (grinding means) 10 is mounted along the pair of guide rails 8 so as to be movable in the vertical direction. The grinding 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 grinding unit 10 includes a spindle 18 rotatably accommodated in a spindle housing 12, a wheel mount 20 fixed to the tip of the spindle 18, and a plurality of grinding wheels that are screwed to the wheel mount 20 and arranged annularly. A grinding wheel 22 having an electric motor 24 for rotating the spindle 18 is included.

  The grinding apparatus 2 includes a grinding unit moving mechanism 32 including a ball screw 28 that moves the grinding unit 10 in the vertical direction along the 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 housing 4, and a chuck table mechanism 34 is disposed in the recess 4a. The chuck table mechanism 34 has a chuck table 36 and is moved in the Y-axis direction between a wafer attaching / detaching position A and a grinding position B facing the grinding unit 10 by a moving mechanism (not shown). 38 and 40 are bellows. On the front side of the housing 4, an operation panel 42 on which an operator of the grinding device 2 inputs grinding conditions and the like is disposed.

  Referring to FIG. 2, a perspective view of the sapphire wafer 11 before being ground to a predetermined thickness is shown. The sapphire wafer 11 is configured by laminating a gallium nitride layer (GaN layer) on a sapphire substrate, and a plurality of streets 13 are formed in a lattice shape on the surface 11a, and a plurality of sections partitioned by the plurality of streets 13 are formed. An optical device 15 such as an LED is formed in the region.

  The sapphire wafer 11 thus configured includes a device region 17 in which the optical device 15 is formed and an outer peripheral surplus region 19 that surrounds the device region 17. A notch 21 is formed on the outer periphery of the sapphire wafer 11 as a mark indicating the crystal orientation of the sapphire substrate.

  Prior to grinding, the protective tape 23 is attached to the surface 11a of the sapphire wafer 11 by a protective tape attaching process. Therefore, the front surface 11a of the sapphire wafer 11 is protected by the protective tape 23, and the back surface 11b is exposed as shown in FIG.

  Referring to FIG. 4, an exploded perspective view of the chuck table 36 is shown. FIG. 5 is a perspective view of the chuck table 36. The chuck table 36 includes a frame body 46 having a recess 47 formed from a metal such as SUS, and a suction plate 48 having a holding surface for sucking and holding a wafer fitted in the recess 47 of the frame body 46. .

  At the bottom 49 of the frame 46, a suction port 51, a plurality of radial grooves 53 communicated with the suction port 51, and a plurality of concentric circular grooves 55 communicated with the radial grooves 53 are formed. As is clear from FIG. 4, the circular groove 55 is formed so that its density increases toward the center. Since the density of the circular grooves 55 formed in the bottom 49 of the frame 46 increases toward the center, the suction force of the suction plate 48 becomes stronger compared to the outer periphery at the center as shown in FIG. .

  The frame body 46 of the chuck table 36 is connected to a servo motor 52 through a cylindrical connecting portion 50. The suction plate 48 fitted in the recess 47 of the frame 46 includes a circular groove 55 formed in the bottom 49 of the frame, a radial groove 53, a suction port 51, a suction path formed in the cylindrical connecting portion, and a rotary. A suction source 58 is connected via a joint 54 and a pipe 56.

  Referring to FIG. 7, a wheel mount 20 is fixed to the tip of the spindle 18, and a grinding wheel 22 is detachably attached to the wheel mount 20 with a plurality of screws 25. The grinding wheel 22 is configured by adhering a plurality of grinding wheels 26 to a free end portion of an annular base 24.

  When the sapphire wafer 11 sucked and held by the chuck table 36 is positioned at the grinding position shown in FIG. 7, the grinding wheel 22 is rotated in the same direction as the chuck table 36 while rotating the chuck table 36 in the direction of arrow a at 500 rpm, for example. That is, while rotating in the arrow b direction at, for example, 1000 rpm, the grinding unit feeding mechanism 32 is operated to bring the grinding wheel 26 into contact with the back surface 11 b of the sapphire wafer 11.

  Then, the sapphire wafer 11 is ground by feeding the grinding wheel 22 downward by a predetermined amount at a predetermined grinding feed rate (for example, 0.1 μm / s). The sapphire wafer 11 is finished to a desired thickness (for example, 50 μm) while measuring the thickness of the sapphire wafer 11 using a contact-type or non-contact-type thickness measurement gauge (not shown).

  According to the grinding apparatus of the present embodiment, the density of the concentric circular grooves 55 formed in the bottom portion 49 of the frame body 46 of the chuck table 36 is formed so as to increase toward the center of the bottom portion. The holding force for holding the sapphire wafer 11 at the center of the sapphire increases, and warping of the sapphire wafer 11 during grinding is suppressed, so that the sapphire wafer 11 can be prevented from cracking.

  The grinding device 2 of the above-described embodiment is not only suitable for grinding the sapphire wafer 11, but can be similarly applied to grinding a hard wafer having a Mohs hardness of 9 or more such as a silicon carbide wafer.

2 Grinding device 10 Grinding unit 11 Sapphire wafer 22 Grinding wheel 26 Grinding wheel 36 Chuck table 46 Frame 48 Suction plate 53 Radial groove 55 Concentric circular groove

Claims (2)

A wafer grinding apparatus comprising: a chuck table that holds a wafer and is rotatable; and a grinding means that rotatably supports a grinding wheel having a grinding wheel for grinding the wafer held on the chuck table.
The chuck table includes a suction plate having a holding surface for sucking and holding the wafer, and a frame having a bottom portion that surrounds other than the holding surface of the suction plate and supports the opposite surface of the holding surface,
A suction groove is formed at the bottom of the frame so that the suction at the center of the suction plate is stronger at the center than at the outer periphery so that the suction at the center is stronger than the suction at the outer periphery. ,
The wafer grinding apparatus, wherein the suction plate of the chuck table communicates with a suction source through a suction groove formed in the frame.   2. The wafer grinding apparatus according to claim 1, wherein the wafer comprises a sapphire wafer.

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