JP2012148389A - Method for grinding hard substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for grinding a hard substrate which can grind a hard substrate without damaging the hard substrate.SOLUTION: The method for grinding a hard substrate includes: a holding step of holding the hard substrate by a holding surface of a chuck table; a positioning step of positioning the chuck table at a grinding position; a contact detection step of operating a grinder feeding device to put a grinding wheel close to the hard substrate held on the chuck table at a first grinder feeding speed, and detecting a moment in which the grinding wheel comes into contact with the hard substrate using a change in a load current value of a motor of the grinder feeding device; a separating step of operating the grinder feeding device immediately after detecting contact between the grinding wheel and the hard substrate in the contact detection step to separate the grinding wheel from the hard substrate; a grinding step of operating the grinder feeding device while feeding the grinding of the grinding wheel at a second grinder feeding speed that is lower than the first grinder feeding speed to grind the hard substrate held on the chuck table; and a grinding completion detection step of stopping the grinding when the thickness of the hard substrate reaches a desired thickness.

Description

  The present invention relates to a method for grinding a hard substrate such as a sapphire substrate or a SiC substrate.

  A street in which a semiconductor layer (epitaxial layer) such as gallium nitride (GaN) is formed on the surface of a sapphire substrate, SiC substrate, etc., and a plurality of optical devices such as LEDs are formed in a lattice shape on the semiconductor layer (division planned line) Since the optical device wafer formed by dividing the optical device wafer is relatively high in Mohs hardness and difficult to divide by a cutting blade, it is divided into individual optical devices by laser beam irradiation. It is used for electric devices such as personal computers (see, for example, Japanese Patent Application Laid-Open No. 2008-6492).

  A sapphire substrate is suitable for the growth of epitaxial layers and is an indispensable material for manufacturing optical devices, but after the epitaxial layer has grown, it is necessary to reduce the weight and size of electrical equipment and improve the brightness of optical devices. Next, the back surface of the sapphire substrate is ground by a grinding device (for example, Japanese Patent Application Laid-Open No. 2008-23693).

  The grinding device is capable of rotating a grinding wheel having a holding surface for holding a workpiece and a rotatable chuck table, and a grinding wheel provided with an annular grinding wheel for grinding the workpiece held on the chuck table. It comprises at least grinding means for supporting and grinding feed means for moving the grinding means toward and away from the chuck table, so that a plate-like workpiece can be ground to a desired thickness.

JP 2008-6492 A JP 2008-23893 A

  However, since hard substrates such as sapphire substrates and SiC substrates have high Mohs hardness and the back surface is formed in a mirror surface, the grinding wheel with diamond abrasive grains as the main component does not allow sliding grinding on the back surface of the hard substrate, There is a problem that the hard substrate is damaged by the pressure of the grinding feed.

  This invention is made | formed in view of such a point, The place made into the objective is to provide the grinding method of the hard board | substrate which can be ground without damaging a hard board | substrate.

  According to the present invention, a rotatable chuck table having a holding surface for holding a workpiece, and a grinding wheel in which a grinding wheel for grinding the workpiece held on the chuck table is arranged in an annular shape can be rotated. Grinding means for supporting the workpiece, grinding water supply means for supplying grinding water, positioning means for positioning the chuck table at a loading / unloading position for loading / unloading the workpiece and a grinding position for grinding the workpiece, and the grinding Grinding means comprising a grinding feed means having a motor for grinding and feeding the means relative to the chuck table to approach and separate, and a thickness detecting means for detecting the thickness of the workpiece held on the chuck table A method of grinding a hard substrate by an apparatus, comprising: a holding step of holding a hard substrate on a holding surface of the chuck table; and polishing the chuck table. A positioning step of positioning the position, and the grinding feed means is actuated to bring the grinding wheel closer to the hard substrate held on the chuck table at a first grinding feed speed, and the moment when the grinding wheel contacts the hard substrate. A contact detection step of detecting the load current value of the motor of the grinding feed means; and detecting the contact between the grinding wheel and the hard substrate by the contact detection step; A separation step for separating the grindstone from the hard substrate, and after performing the separation step, the grinding feed means is operated to grind feed the grinding wheel at a second grinding feed rate that is slower than the first grinding feed rate. A grinding process for grinding the hard substrate held by the chuck table, and a grinding end detection process for terminating the grinding when the hard substrate reaches a desired thickness. Grinding method of a substrate is provided.

  Preferably, the hard substrate is composed of a sapphire substrate or a SiC substrate.

  According to the grinding method of the present invention, the grinding feed means is configured at the moment when the grinding feed means is actuated to bring the grinding wheel close to the hard substrate held on the chuck table at the first grinding feed speed and contact the hard substrate. Since the detection is performed based on the change in the load current value of the motor and the grinding feed means is immediately operated to separate the grinding wheel from the hard substrate, the surface to be ground of the hard substrate is roughened by the grinding wheel.

  Therefore, when the grinding wheel is brought into contact with the hard substrate at the second grinding feed speed suitable for grinding the hard substrate, which is slower than the first grinding feed speed, the grinding wheel is well bitten and the grinding wheel is placed on the back surface of the hard substrate. Grinding can be started without sliding.

It is a perspective view of a grinding device suitable for carrying out the grinding method of the present invention. It is a perspective view of a chuck table unit and a chuck table feed mechanism. It is a perspective view which shows a mode that a protective tape is stuck on the surface of an optical device wafer. It is a disassembled perspective view which shows a holding process. It is a partial cross section side view which shows a positioning process. It is a partial cross section side view which shows a contact detection process. It is a partial cross section side view which shows a separation process. It is a partial cross section side view which shows a grinding process. It is a perspective view which shows a grinding process. It is a time chart of the load current value of the motor which comprises the grinding feed means by the grinding method of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a perspective view of a grinding apparatus 2 suitable for carrying out the grinding method of the present invention. The housing 4 of the grinding device 2 includes a base 6 and a column 8 rising vertically from the base 6.

  A pair of guide rails 12 and 14 extending in the vertical direction are fixed to the column 8. A grinding means (grinding unit) 16 is mounted along the pair of guide rails 12 and 14 so as to be movable in the vertical direction. The grinding unit 16 is attached to a moving base 18 that moves up and down along a pair of guide rails 12 and 14 via a support portion 20.

  The grinding unit 16 includes a spindle housing 22 attached to the support portion 20, a spindle 24 rotatably accommodated in the spindle housing 22, and a servo motor 26 that rotationally drives the spindle 24.

  As shown in FIG. 5, a mounter 28 is fixed to the tip of the spindle 24, and a grinding wheel 30 is screwed to the mounter 28. The grinding wheel 30 is configured by fixing a plurality of grinding wheels 34 in which diamond abrasive grains having a particle diameter of 5 to 10 μm are hardened by vitrified bonds to a free end portion of a wheel base 32.

  Grinding water is supplied to the grinding means (grinding unit) 16 via a hose 36. Preferably, pure water is used as the grinding water. As shown in FIGS. 6 to 8, the grinding water supplied from the hose 36 enters the grinding water supply hole 38 formed in the spindle 24, the space 40 formed in the mounter 28, and the wheel base 32 of the grinding wheel 30. It is supplied to the wafer 11 held on the grinding wheel 34 and the chuck table 54 via the plurality of formed grinding water supply nozzles 42.

  Referring to FIG. 1 again, the grinding apparatus 2 includes a grinding unit feeding mechanism (grinding feeding means) 44 that moves the grinding unit 16 in the vertical direction along the pair of guide rails 12 and 14. The grinding unit feed mechanism 44 includes a ball screw 46 and a pulse motor 48 fixed to one end of the ball screw 46. When the pulse motor 48 is pulse-driven, the ball screw 46 rotates and the moving base 18 is moved in the vertical direction via the nut of the ball screw 46 fixed inside the moving base 18.

  A chuck table unit 50 is disposed in the recess 10 of the base 6. As shown in FIG. 2, the chuck table unit 50 includes a support base 52 and a chuck table 54 that is rotatably disposed on the support base 52. The chuck table unit 50 further includes a cover 56 having a hole through which the chuck table 54 is inserted.

  The chuck table 54 is moved in the Y-axis direction by a chuck table moving mechanism 58 between a loading / unloading position on the front side of the apparatus for loading / unloading the wafer 11 and a grinding position on the back side of the apparatus that receives the action of the grinding means 16. . The chuck table moving mechanism 58 includes a ball screw 60 and a pulse motor 64 connected to one end of a screw shaft 62 of the ball screw 60.

  When the pulse motor 64 is pulse-driven, the screw shaft 62 of the ball screw 60 rotates, and the support base 52 having a nut screwed to the screw shaft 62 moves in the front-rear direction (Y-axis direction) of the grinding device 2. Therefore, the chuck table 54 also moves in the Y-axis direction according to the rotation direction of the pulse motor 64.

  A thickness detecting means 94 for detecting the thickness of the wafer 11 held on the chuck table 54 is disposed adjacent to the chuck table 54. The detection needle (probe) 96 of the thickness detecting means 94 is rotated between a detection position that comes into contact with the grinding surface of the wafer 11 held on the chuck table 54 and a retreat position that is away from the chuck table 54.

  As shown in FIG. 1, the pair of guide rails 66 and 68 and the chuck table moving mechanism 58 shown in FIG. 2 are covered with bellows 70 and 72. That is, the front end portion of the bellows 70 is fixed to the front wall that defines the recess 10, and the rear end portion is fixed to the front end surface of the cover 56. Further, the rear end of the bellows 72 is fixed to the column 8, and the front end thereof is fixed to the rear end surface of the cover 56.

  The base 6 includes a first wafer cassette 74, a second wafer cassette 76, a wafer transfer robot 78, a wafer temporary table 80 having a plurality of positioning pins 81, a wafer carry-in means 82, and a wafer carry-out means. 84 and cleaning means 86 are disposed. Further, an operation means 88 is provided in front of the housing 4 for an operator to input grinding conditions and the like.

  A cleaning water spray nozzle 90 that cleans the chuck table 54 is provided at the approximate center of the base 6. The cleaning water jet nozzle 90 ejects cleaning water toward the wafer after grinding held by the chuck table 54 in a state where the chuck table 54 is positioned at the wafer loading / unloading position. The concave portion 10 of the base 6 is provided with a drain port 92 for draining the grinding water containing the grinding scraps of the wafer 11 ground by the grinding wheel 32.

  Referring to FIG. 3, a perspective view of an optical device wafer 11 which is a grinding object of the grinding method of the present invention 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.

  The sapphire substrate 13 before the grinding process has a thickness of 1300 μm, for example, and the epitaxial layer 15 has a thickness of 5 μm, for example. In the epitaxial layer 15, an optical device 19 such as an LED is partitioned and formed by dividing lines (streets) 17 formed in a lattice shape.

  Prior to grinding of the back surface of the optical device wafer 11, that is, grinding of the sapphire substrate 13, a protective tape 23 is applied to the surface 11 a of the optical device wafer 11 in order to protect the optical device 19 formed on the surface 11 a of the optical device wafer 11. Is pasted.

  Therefore, in the grinding method of the present invention, as shown in FIG. 4, the optical device wafer 11 is sucked and held by the holding surface 54a of the chuck table 54 positioned at the wafer loading / unloading position with the protective tape 23 facing down. Therefore, the sapphire substrate 13 is exposed in the held state.

  Next, the chuck table moving mechanism 58 is driven to move the chuck table 54 in the Y-axis direction, and the grinding wheel 34 is positioned at a grinding position where it acts on the sapphire substrate 13 as shown in FIG.

  Next, as shown in FIG. 6, the grinding unit feed mechanism 44 is driven to perform the first grinding while rotating the chuck table 54 in the direction of arrow a at 750 rpm and rotating the grinding wheel 30 in the direction of arrow b at 1300 rpm. The grinding wheel 34 is brought close to the sapphire substrate 13 held on the chuck table 54 at a feed rate, that is, 15 μm / s, and the moment of contact with the sapphire substrate 13 is changed by a change in the load current value of the pulse motor 48 of the grinding unit feed mechanism 44. To detect.

  Since the frictional resistance is generated at the moment when the grinding wheel 34 comes into contact with the sapphire substrate 13, the load current value of the pulse motor 48 increases instantaneously at the time indicated by time t1 in FIG. For example, the load current value of 7 amperes (A) instantaneously increases to 11A.

  At the moment when the change in the load current value of the pulse motor 48 is detected, as shown in FIG. 7, the grinding unit feeding mechanism 44 is driven to move the grinding wheel 34 away from the back surface of the sapphire substrate 13 by a predetermined distance h, for example, 30 μm. A separation step is performed. In the time chart of FIG. 10, a separation process is performed between times t1 and t2 indicated by reference numeral 98.

  Since the chuck table 54 rotates at 750 rpm in the direction of the arrow a, the chuck table 54 is once or twice during the contact detection process that is detected by a change in the load current value of the pulse motor 48 of the grinding unit feed mechanism 44. It rotates and the back surface (surface to be ground) of the sapphire substrate 13 becomes rough.

  After the separation process, the grinding process is started at time t2. In this grinding step, while rotating the chuck table 54 in the direction of the arrow a at 750 rpm and rotating the grinding wheel 30 in the direction of the arrow b at 1300 rpm, the grinding unit feed mechanism 44 is driven to exceed the first grinding feed speed. The sapphire substrate 13 is ground with the grinding wheel 34 while the grinding wheel 30 is ground and fed downward at a slow second grinding feed rate, that is, 3 μm / s.

  At the start of this grinding, the grinding wheel 34 is in contact with the back surface of the sapphire substrate 13 for a very short time and the surface to be ground of the sapphire substrate 13 is roughened, so that the sapphire substrate at a second grinding feed rate suitable for grinding. When the grinding wheel 34 is brought into contact with 13, the biting becomes good, and the grinding is performed without the grinding wheel 34 sliding on the back surface of the sapphire substrate 13.

  The detection needle 96 of the thickness detecting means 94 is brought into contact with the sapphire substrate 13 to perform grinding of the sapphire substrate 13, and the grinding is finished at time t3 when the thickness of the optical device wafer 11 becomes 150 μm. The grinding process is performed between time t2 and t3 indicated by reference numeral 100 in the time chart of FIG.

  When grinding the sapphire substrate 13, as shown in FIG. 9, a ground trace showing a pattern in which a large number of arcs are radially drawn on the back surface 11 b of the optical device wafer 11, that is, the surface to be ground of the sapphire substrate 13. 25 remains.

  In the above-described embodiment, the example in which the present invention is applied to grinding of the sapphire substrate 13 has been described. However, the present invention is not limited to this, and can be similarly applied to other hard substrates such as SiC substrates. is there.

  According to the above-described embodiment, when grinding the sapphire substrate 13, the grinding unit feed mechanism 44 is driven to bring the grinding wheel 34 close to the sapphire substrate 13 held on the chuck table 54 at the first grinding feed speed. The moment when the grindstone 34 comes into contact with the sapphire substrate 13 is detected by a change in the load current value of the pulse motor 48 of the grinding unit feed mechanism 44, and then the grinding unit feed mechanism 44 is driven immediately to separate the grinding grindstone 34 from the sapphire substrate 13. Therefore, the surface to be ground of the sapphire substrate 13 is roughened.

  Therefore, when the grinding wheel 34 is brought into contact with the sapphire substrate 13 at a second grinding feed rate suitable for grinding that is slower than the first grinding feed rate, the grinding wheel 34 is well bitten, and the grinding wheel 34 is attached to the sapphire substrate 13. The sapphire substrate 13 can be ground without sliding on the back surface.

2 Grinding device 11 Optical device wafer 13 Sapphire substrate 15 Epitaxial layer 16 Grinding unit 19 Optical device 30 Grinding wheel 34 Grinding wheel 44 Grinding unit feed mechanism (grinding feed means)
48 Pulse motor 54 Chuck table 94 Thickness detection means

Claims (2)

Grinding means for rotatably supporting a grinding wheel in which a chuck table having a holding surface for holding a workpiece and rotatable and a grinding wheel for grinding the workpiece held on the chuck table are arranged in an annular shape. Grinding water supply means for supplying grinding water, positioning means for positioning the chuck table at a loading / unloading position for loading / unloading the workpiece and a grinding position for grinding the workpiece, and the grinding means for the chuck table A rigid substrate is provided by a grinding apparatus comprising a grinding feed means having a motor that moves relative to and moves away from the workpiece, and a thickness detecting means for detecting the thickness of the workpiece held on the chuck table. A method for grinding a hard substrate,
A holding step of holding the hard substrate on the holding surface of the chuck table;
A positioning step of positioning the chuck table at a grinding position;
The grinding feed means is operated to bring the grinding wheel close to the hard substrate held by the chuck table at a first grinding feed speed, and the motor of the grinding feed means at the moment when the grinding wheel comes into contact with the hard substrate. A contact detection step of detecting by a change in the load current value of
A separation step of operating the grinding feed means immediately after the contact between the grinding wheel and the hard substrate is detected by the contact detection step to separate the grinding wheel from the hard substrate;
After carrying out the separation step, the rigid substrate held on the chuck table while operating the grinding feed means and grinding and feeding the grinding wheel at a second grinding feed speed slower than the first grinding feed speed Grinding process to grind,
A grinding end detection step for finishing grinding when the hard substrate reaches a desired thickness;
A method for grinding a hard substrate, comprising:   The hard substrate grinding method according to claim 1, wherein the hard substrate is composed of a sapphire substrate or a SiC substrate.

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