Surface Science Aspects of Etching and Wall Reactions in High Density Plasmas

Abstract

Within the last ten years or so, in response to the needs of the semiconductor processing industry, new plasma etching machines involving high density plasmas (>1011 cm-3) have been developed. The requirement that lead to this change from low density plasmas, (<1011 cm-3), to high density plasmas was a need for lower energy ion bombardment of the wafer (often <100 eV). In reactive ion etching (RIE) with low density plasmas, ion energies of several hundreds of eV are usually incident on the wafer and the damage and selectivity loss caused by these ions was found to be unacceptable in some critical applications. However decreasing the ion energy also decreases the etch yield per ion and therefore, in order to maintain the etch rates, high ion fluxes are required. Hence the need for high density plasmas. Furthermore, low pressure operation (<10 millitorr) is often needed to achieve the desired profile shape in the etched feature.