Dependence of plasma damage on density and T/sub e/ in a decoupled plasma source metal etcher

Plasma induced damage due to metal etch is a well established and well studied problem. Work by several groups has shown that the primary mechanism is electron shading, and that current injection through the gate oxide occurs during the period when open areas in the pattern have cleared but dense areas have not, leading to latent antenna effects (Krishnan et al., 1995; Kinoshita et al., 1997; Krishnan et al., 1997). It has also been shown that damage is generally more severe in high power processes, correlating generally with higher plasma density (Colonell et al., 1997; Tabara, 1996). This observation is easily explained by more available current, if the plasma can be viewed as a current limited source. Plasma damage in general is expected to become more severe with increasing electron temperature, but this effect is less well explored, due partly to the difficulty of measuring T/sub e/. In this paper, we examine the dependence of plasma damage on pressure during the overetch. Measurements of plasma density and T/sub e/ show that reduced damage at higher pressures correlates with a drop in both density and T/sub e/; applying a simple circuit model to the data suggests that decreased T/sub e/ is the primary driver.