Studies on product layers formed during etching of Si in a SF6 plasma

Abstract

Several types of experiments were performed during and after the etching of Si in a dc discharge to confirm the presence of product layers, to characterize these layers, and to determine how such layers and concomitant changes in near‐surface regions affect the rates of release of various species formed. The experiments are (1) depth profiling of Si samples etched in SF₆ plasmas, using electron spectroscopy for chemical analysis, (2) mass spectrometric study of the concentrations of various species effusing from the plasma etching cell, with emphasis on the transients arising when the plasma is ignited and extinguished, and their dependence on sample history, and (3) exposure of previously etched samples to a second discharge, supported by Ar or H₂, and mass spectrometric analysis of the species released during that process. The results show that layers on the surface undergoing etching, and changes in subsurface regions affect the etching rates; even after the etchant gas has been removed, small amounts of the product SiF₄ are released, under various conditions.