1. Field of the Invention
The present invention relates to a sheet feeding type wafer polishing machine, and specifically relates to a sheet feeding type polishing machine which processes both surfaces of the wafer and outermost periphery of the wafer (edge part) in series. More specifically the present invention relates to a sheet feeding type polishing machine which polishes both surfaces and edge part of a wafer bigger than 12 inches diameter in series, and relates to a processing method using the machine.
2. Description of the Prior Art
An electronic part such as integrated circuit (IC), large-scale integration (LSI) or very large-scale integration (VLSI) are assembled using a small piece of semiconductor device chip on which a very fine electric circuit is drawn as a main part. Said semiconductor device chip is made from a thin wafer which is prepared by slicing a mono-crystalline ingot of silicon or other compound semiconductor. Recently, the size of silicon or other compound semiconductor wafer (hereinafter shortened to wafer) is becoming bigger in response to the requirement to improve productivity and productive efficiency. Especially, in a case of silicon wafer, since the manufacturing technique of silicon mono-crystalline ingot which is the starting material is remarkably improved, big size wafers of 12 inch or 16 inch diameter are beginning to be prepared on an industrial scale.
A wafer sliced from an ingot is processed by a lapping process, an etching process and then by a polishing process to generate a mirror finish wafer, i.e. at least one surface is mirror finished. The object of a lapping process is to improve a form accuracy of as cut wafer which has uneven surface after being sliced and to form a standard surface. The object of a polishing process is to improve the surface roughness. In general, to perform good productivity and high productive efficiency, a conventional lapping or polishing machine is designed to process plural numbers of wafer at the same time. Concretely, a lapping machine which has big cast iron platens or a polishing machine which has platens with polishing pad on upper and lower part of machine are generally used, and plural numbers of wafer are held by carrier plates. At the actual processing, plural numbers of wafer held by carrier plates are put between upper and lower platens and pressed. The platens and wafer are rotated, while fluid for processing which contains fine particles of abrasive is supplied and wafers are processed. At the final mirror finishing process, usually only one necessary side surface is processed.
Along with the recent increase in growth of the wafer size, a bigger processing machine which processes plural numbers of bigger size wafers at the same time becomes necessary. However, along with the increase in size of the processing machine, not only does the requirement for form accuracy and dimensional stability of the machine become more severe, but also the handling difficulty of loading and unloading of wafers becomes more troublesome. Therefore, it becomes difficult to expect good productivity and high productive efficiency from a bigger size processing machine.
To solve the above mentioned problem of a bigger size machine, recently a sheet feeding type wafer processing machine which processes wafers one at a time is becoming popular. For example, a double-disc surface grinding machine which uses two diamond grinding wheels is used as a sheet feeding type wafer processing machine. Diamond wheels are rotated at a high rotating speed and a grinding fluid is supplied, while wafers are supplied through a feeding system. In this case, since a wafer is processed by a grinding mechanism, it is difficult to achieve the purpose of obtaining a mirror finish surface which can be obtained by polishing.
After fine and complicated electric circuit is engraved on a mirror finished surface of wafer in a device procedure, the wafer is divided into small unit chips. Before the dividing process, a wafer is processed maintaining the original circular shape, and among the key processes there are additional procedures such as washing, rinsing, drying and transferring. Through these procedures, if the shape of outermost periphery of the wafer is sharp, sheer and coarse, these Portions of the wafers contact each other or the machine and cause fine cracks which generate fine particles, or fine contamination particles cover the coarse surface of the edge part of the wafer. These generated fine particles are scattered during the latter procedure, contaminate fine processed surfaces of wafers and affect significantly the yield and the quality of products. In general, to avoid said phenomenon, the sharp outermost periphery of wafer is dulled by a beveling wheel, then the dulled part is mirror finished (edge polishing).
However, if the edge polishing is carried out at the earlier stage, the polished edge surface can be easily damaged and contaminated at the latter procedure, and causes re-contamination which affects significantly the yield and the quality of products. Namely, since the polishing of a wafer surface and an edge surface are carried out independently as different procedures, these above mentioned problems arise.