IMPROVEMENT OF THICKNESS UNIFORMITY OF SILICON AND SOI WAFER BY NUMERICALLY CONTROLLED LOCAL WET ETCHING

摘要

A novel ultra-precision figuring process named LWE, which utilizes chemical removal reaction between a liquid etchant and the workpiece surface, was developed for figuring the ultra-precision optical components, correcting the thickness distribution of the bulk silicon and SOI wafer, and so on. In the LWE process, removal footprint is localized by using a coaxial etchant supply and suction nozzle head, and removal volume is proportional to the dwelling time of the nozzle head on the workpiece surface. Therefore, this process enables deterministic figuring by only controlling the scanning speed distribution of the nozzle head. The machining characteristics of the silicon which were applied HF/HNO3 mixtures were investigated, and it was found that adequate addition of the hydrofluoric acid keeps the etching rate constant within ±2.5 % during the machining operation.rnThickness uniformity of the 0200 mm bulk silicon wafer was improved from 420 nm (p-v) to 150 nm (p-v) in the 0140 mm area.