SiO2 Tapered Etching Employing Magnetron Discharge of Fluorocarbon Gas

SiO2 tapered etching has been studied with special emphasis on the substrate temperature. A tapered etching profile was formed accompanying a polymer deposition on the side wall, and a high etching rate was obtained by lowering the substrate temperature. The polymer film deposited on the side wall was easily removed together with photoresist by O2 plasma ashing to yield a very smooth side wall in the via hole without any residual films. Experiments on polymer deposition revealed that the polymerization at as low a temperature as -70°C gives a fluorine-rich polymer film with poor durability in a plasma environment, and the etchants for SiO2 are released by ion bombardments at the interface between the polymer and the underlying SiO2 to enhance SiO2 etching.