Holding cassette for precision substrates and method for the preparation thereof

摘要

An improvement is proposed for an injection molding method for the preparation of a wafer cassette for holding single crystal silicon wafers in alignment. While such a wafer cassette has several thick-walled portions such as reinforcement ribs, each of which is provided with a positioning groove for accurate positioning of an automatic machine for loading and unloading of wafers, such thick-walled portions in the prior art cassettes are subject to thermal shrinkage or molding sink in molding so as to cause deformation of the positioning grooves disturbing reliable positioning of the automatic machine. The improvement of the invention can be accomplished by undertaking the gas-assist method in which a gas is introduced into the cavity of the metal mold so as to form hollow cavities behind the positioning grooves to thus avoid the thermal shrinkage or molding sink due to the large wall thickness.