TREATMENT OF AMORPHOUS SILICON

PURPOSE:To obtain a selective etching method without etching an SiN film, by adding carbon tetrachloride to sulfur hexafluoride as an etching gas species, and etching an a-Si film. CONSTITUTION:Sulfur hexafluoride (SF6) becomes fluorine radicals or fluorine ions in an etching chamber, and a-Si 4 is etched. An etching seed for carbon tetrachloride (CCl4) as etching gas is chlorine radical or chlorine ion. The etching of a-Si 4 and SiN 3 is extremely slow with such an etching species. In dry etching using mixed gas of SF6 and CCl4 the etching speed of SiN3 becomes more slower than the etching speed of a-Si 4, and a high selecting ratio is obtained. Thus the selective dry etching can be performed so that the a-Si film 4 is etched and the SiN film 3 is not etched.