1. Field of the Invention
This invention concerns a substrate flat grinding device with high rigidity including (i) a functional grinding head, (ii) a workpiece chuck rotary mechanism, (iii) a grindstone spindle tilt mechanism, and (iv) a fastening plate lifting and lowering mechanism. The functional grinding head comprises mainly a grindstone spindle capable of rotary/linear motion supported by hydrostatic bearings and a cup wheel type diamond grindstone. The workpiece chuck rotary table mechanism includes a rotary chuck table made of a porous ceramic is axial-supported by a hollow spindle equipped with hydrostatic bearings. This substrate flat grinding device improves the surface flatness of the workpieces such as bare silicon wafers, semiconductor substrates, ceramic substrates, GaAs boards, sapphire substrates, etc.
2. Background of the Invention
In a grinding for processing surface flatness of a workpiece on a rotary chuck table, a grindstone spindle equipped with a cup wheel type grindstone is rotated and lowered downward to the workpiece. The cup wheel type grindstone cuts a surface of the workpiece. In the grinding process, a tilt angle of the grindstone spindle with respect to a surface of the workpiece is changed. The feed quantity (quantity of cut-in) initially is large and gradually is made to be smaller. The tilt of the grindstone spindle is altered to prevent grinding burns and to make the distribution of the thickness of the workpiece as uniform as possible.
For example, U.S. Pat. No. 3,472,784 discloses a grinding device in which a wafer is placed onto a porous-ceramic rotary chuck table that is rotated in the horizontal plane and ground by a cup wheel type diamond grindstone attached to the lower part of a grinding spindle head that is disposed vertically, grinding devices have been proposed that have a drive means that moves the grinding spindle head and the wafer relatively in the z-axis direction, which is the perpendicular direction, a tilt means that rotates the grinding spindle head or wafer in the horizontal plane about the x-axis and y-axis, and a control means that controls the drive means and tilt means to change, either stepwise or continuously, the amount of feed of the grinding spindle head as well as the relative tilt of the grinding spindle head and the workpiece in accordance with the stage of grinding. The tilt means has a column to which is affixed a grinding spindle head raising-and-lowering means.
In Japanese unexamined patent publication H11-132232 [1999], air bearing spindles comprise a spindle main body on which is mounted a grinding grindstone that grinds the surface of the workpiece and a housing that contains radial bearings and thrust bearings that support the spindle main body with air. In an air spindle tilt adjustment mechanism, the air blowing region of the thrust bearings is partitioned into at least three regions and the pressure of the air supplied to the partitioned area blowout regions is individually adjusted, and the tilt of the spindle main body is adjusted.
In addition, in Japanese unexamined patent publication 2005-22059, a flat grinding device includes a porous-ceramic rotary chuck table that holds the workpiece, a grinding spindle head comprises a spindle equipped with a grinding wheel and is supported by air bearings and magnetic bearings that control the tilt of the grinding spindle head, sensors that detect the relative attitude of the grinding spindle with respect to the workpiece, and an attitude control means that uses detection data detected by the sensors to control the magnetic bearings to ensure that the wheel spindle assumes the preset attitude. This is done by moving the workpiece and the wheel relative to one another while the wheel is pressed against a surface of the workpiece held on the porous-ceramic rotary chuck table.
Moreover, Japanese unexamined patent application 2005-262431 discloses a grinding device including a wheel spindle equipped with a grindstone, a magnetic bearing for controlling the position of the wheel spindle, a grindstone feeding means, a rotary workpiece table, and a workpiece table feeding means which moves the workpiece table in a direction parallel to the surface to be processed. The magnetic bearing means controls the position of the grindstone spindle. The workpiece support platform feed means uses the axial-direction control current and the radial-direction control current of the magnetic bearing device, in which the stopping position of the rotating grindstone in the direction perpendicular to the surface to be processed is controlled based on the axial-direction control current of the magnetic bearing device.
Also, Japanese unexamined patent publication 2000-24805 discloses an inner cylindrical grinding device that includes a tool spindle head equipped with a grindstone, a workpiece holding means, and a feeding means that moves the grindstone of the tool spindle head toward the workpiece holding means The tool spindle head has the spindle installed through hydrostatic pressure magnetic composite bearings combining static pressure gas bearings and the magnetic bearings. Pressure sensors measuring the pressure on the bearing surface of the static pressure gas bearings are provided as a displacement measurement means that determines the displacement of the spindle, and a magnetic bearing control means is provided that determines the displacement of the spindle from the measurements of these pressure sensors and carries out magnetic force control of the magnetic bearings.
Meanwhile, although they have no particular application to grinding devices, compound (rotary/linear) actuators have been proposed that rotate or move linearly tool main shaft (spindle) that are capable of rotary/linear motion. See, for example, U.S. patent publication 2007/0222401, Japanese unexamined patent 2006-220196, Japanese unexamined patent 2004-364348, and Japanese unexamined patent publication 2006-220178.
Also known are testing devices that are equipped with a height position adjustment tool that makes use of kinematic coupling, in which male members and female members are coupled together. See for example U.S. Pat. No. 6,104,202 and Bal-tec Co., “Kinematic coupling design for the Z axis”, {on-line}, pages 430-434, {searched May 30, 2005}, Internet <URL: http://www.precisionballs.com/kinematic_repeatability.html>.
In addition, grinding spindle heads are known in which the grindstone spindle that supports the rotor of a built-in motor is supported by hydrostatic pressure thrust bearings and hydrostatic pressure radial bearings and the grindstone spindle is made of a heat pipe, the heat generated by the rotor is transmitted by the heat pipe in the longitudinal direction of the grindstone spindle, and the grinding head is supported by hydrostatic bearings as a cooling structure wherein the heat is allowed to escape to the outside from the hydrostatic bearings (see for example Japanese Unexamined patent H11-235643 [1999]). Rotary chuck tables made of porous ceramic for holding a workpiece supported by water hydrostatic pressure bearings have also been proposed (see for example U.S. patent publication 2007/0286537 and Japanese unexamined patent publication 2000-240652).
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