Plasma Chemistry in Etching

Abstract

Plasma etching has largely replaced wet etching for microcircuit fabrication because of its finer resolution and adaptability to increased throughput and automation. The simplest reactors consist of opposed parallel plate electrodes in a chamber that can be maintained at low pressure, typically ranging from 0.01 to 1 Torr (1.33–133 Pa). A high frequency voltage is applied between the electrodes forming a plasma. Semiconductor wafers or other substrate materials on the electrode surfaces are exposed to reactive neutral and charged species from the plasma. Some of these species combine with the substrate and form volatile products which evaporate, thereby etching the substrate. For plasmas of interest to etching, the density of charged particles is low, about 10⁹–10¹¹ cm^-3, which corresponds to one charged particle per 10⁴ to 10⁶ neutrals at 0.1 Torr.