JP2003089056A - Workpiece thickness measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a workpiece thickness measuring method capable of preventing the detection of a thickness of a workpiece from being affected by mechanical precision of a polishing device polishing both faces simultaneously or one face of surfaces of a monocrystal silicone wafer used in a substrate for a semiconductor integrated circuit. SOLUTION: Error factors due to the wear of upper and lower lap surface plates and a drive shaft are eliminated by measuring a clearance between the upper and lower lap surface plates directly to simplify a structure and eliminate compensation factors in measurement in order to detect a thickness of the workpiece with high precision.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for simultaneously polishing one or both surfaces of a single crystal silicon wafer or the like used for a substrate for crystal, glass, ceramic, or semiconductor integrated circuit. And a polishing apparatus for performing the polishing. 2. Description of the Related Art Conventionally, according to a polishing method of an apparatus for polishing a silicon wafer, a crystal or the like, an upper and lower lap surface plate called a surface plate made of a material such as cast iron, a center gear and an internal gear are used. A gear, which is mounted on the lower lap surface plate and holds a workpiece called a carrier meshed with the two gears, performs a planetary motion of revolving while revolving, thereby turning the upper and lower surfaces of the workpiece. Polishing. [0003] At the start of the machining operation, the workpiece is set upward by moving it upward by an upper lap surface lifting device installed above the upper lap surface plate in order to attach the workpiece to the carrier. When the setting is completed, lower the upper lap surface plate, load it on the work material held by the carrier placed on the lower lap surface plate, press the work material, and lap it while supplying the abrasive. The internal gear and the center gear rotate according to a preset program so that the workpiece relatively moves on the entire surface of the surface plate. [0004] Equal pressing by the upper lap surface plate against the processing surfaces of a plurality of workpieces held by each carrier is a condition for high precision processing. However, in addition to the conventionally required high precision flatness, in recent years the thickness precision has been required, and the precision of the finished dimensions with respect to the thickness of the workpiece before processing has become important. . Therefore, there is provided a sizing device that measures the thickness of the workpiece before processing and controls the lapping operation to be completed when the workpiece reaches a specified thickness by the lap. There are various types of the sizing device.
Normally, a linear sensor that detects the movement of the center axis of the upper lap surface plate is installed, and the amount of change in the upper lap surface plate as the processing progresses is converted into the thickness of the workpiece, and this change amount is When a value corresponding to the desired thickness is obtained, the lapping operation is terminated, and a quartz oscillator having the same thickness as the workpiece is sandwiched between the upper and lower lapping plates, and the thickness changes as the processing proceeds. Is captured by the frequency of the crystal, converted into the thickness of the workpiece, and the lapping operation is terminated when the amount of change reaches a value corresponding to the desired thickness of the workpiece. [0006] However, in the conventional lapping machine as described above, the rotation of the rotating shaft of the upper lapping plate, the wear of the lapping plate, and the variation in the thickness of the workpiece. Error factors such as deformation of the lap plate due to the processing pressure overlap, and it has been impossible to accurately measure the position of the upper lap plate during lap processing. In order to solve this problem, there is a method of providing a measurement point of the height of the upper lap platen at the center of the rotating shaft.
In this case as well, the wear of the lapping plate and the causes of errors cannot be completely eliminated, and the structure becomes complicated due to interference with the rotating mechanism, so that it is difficult to provide this sizing device on an existing flat lapping plate. It is. A method of averaging the detection signal and reducing the noise in order to remove the noise of the size signal due to the swing of the lap surface plate is also considered. Due to the large swing of the lap surface plate, effective noise removal cannot be sufficiently performed by simple averaging, and there is a problem that adverse effects due to an increase in control error due to averaging become conspicuous. Therefore, the present invention is to solve the above-mentioned problems, and an object of the present invention is to directly detect the interval between the upper and lower lap platen easily by a method with a small error factor, thereby obstructing the measurement of the upper and lower lap platen. To realize a new sizing device that eliminates SUMMARY OF THE INVENTION The gap between the upper and lower lap plates is directly measured without being affected by the wear of the upper and lower lap plates, thereby eliminating error factors and simplifying the structure. In addition, by directly measuring the distance between the upper and lower lap surfaces, other error factors such as the rotation axis are eliminated, and the measurement correction factor is minimized. In addition, by eliminating consumables such as a quartz crystal unit for measurement and using a sensor having a simple structure that is strong in a processing environment, cost can be reduced and reliability can be improved. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A polishing apparatus according to the present invention will be described below with reference to the drawings. FIG. 2 is a partial cross-sectional view showing a schematic configuration of a sizing apparatus showing an example of a polishing apparatus for polishing a workpiece according to an embodiment of the present invention. In FIG. 2, reference numeral 2 denotes an upper lap surface plate, and reference numeral 3 denotes a lower lap surface plate.
The upper lap platen 2 has a nozzle 4 through which air passes toward the lower lap platen 3, and air at a constant pressure is sent from a pneumatic source 10 through a regulator 15. An air hose 7 and a nipple 11 are provided between the upper lap platen 2 and the air pressure source 10.
, And a pressure sensor 8 for detecting the pressure of air in the middle thereof is provided. When the lower lap surface plate 3, which is a tool, is rotated by a driving device (not shown), the center gear 13 and the internal gear 12 also start rotating. The air continuously sent from the nozzle hole 4 is cut off by the planetary gear movement mechanism when the air coincides with the upper surface of the rotating or revolving work piece 6. Air is sent to the upper surface of the slightly thin workpiece carrier 5. Next, air is sent to the upper surface of the lower lap surface plate 3 or the groove 14 by separating from the workpiece carrier 5. FIG.
Indicates a representative pattern repeatedly detected by the pressure sensor 8 during processing. Point A is the upper surface of the workpiece 6, and point B is
The upper surface of the carrier 5, point C is the pressure when the upper surface of the lower lap surface plate 3 is detected, point D is the pressure when the groove 14 of the lower lap surface plate is detected, and E is the pressure change amount of the distance between the lap surface plates. Is shown.
If the measured pressure data of the thickness of the workpiece is set in advance in the pressure sensor 8, a signal is sent to a control device not shown at the time when a predetermined pressure is detected, and control such as rotation stop is performed. To end. The upper lap surface plate 2 and the lower lap surface plate 3 having the nozzle holes 4 wear as the processing proceeds, but the nozzle holes also wear by the same amount, so that the surface plate distance can be accurately measured. According to the polishing apparatus of the present invention, it is possible to measure a workpiece which is not affected even if the upper lap surface plate 2 and the lower lap surface plate 3 are worn during processing. In addition, since there is little error factor by directly measuring the distance between the lap surface plates, it is possible to perform stable machining with few correction factors. There was no consumables for measurement and the cost was reduced. Since the sensor has a simple configuration, it has excellent environmental resistance, reducing costs and improving reliability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an external view of a planar polishing apparatus according to the present invention. FIG. 2 is a cross-sectional view of a concept of a measured thickness and a surface plate. FIG. 3 shows hole positions of nozzles provided on a lower platen and an upper platen. FIG. 4 shows an example of measured pressure data of a workpiece thickness. [Description of Signs] 1 Planar polishing machine 2 Upper lap surface plate 3 Lower lap surface plate 4 Nozzle hole 5 Workpiece carrier 6 Workpiece 7 Air hose 8 Pressure sensor 9 Workpiece mounting hole 10 Pneumatic pressure source 11 Nipple 12 Internal Gear 13 Center gear 14 Groove 15 Regulator A Upper surface of workpiece 6 Upper surface C of carrier 5 Pressure when detecting pressure on upper surface of lower lap platen Pressure E when detecting groove of lower lap platen E Up and down Pressure change of lap platen distance

Claims (1)

Claims: 1. An upper and lower platen as a polishing tool, or a flat polishing machine in which both or one of the grindstones rotates, machining one or both surfaces of a workpiece held between the polishing tool and the upper or lower platen. As a means for detecting the thickness of the workpiece when performing, a hole through which air can pass toward either the upper or lower platen and a sensor for detecting a change in air pressure, flow rate or flow velocity in a part of the air supply path Is a method of measuring the distance from the end face of the nozzle hole to the mating face, and using the change as the thickness of the workpiece.