The sensitivity of electron shading damage to electron temperature, electron density and the plasma-to-wafer electron energy threshold

The electron temperature, T_e, is a well known critical parameter affecting electron shading damage (ESD). This parameter is considered important because the damaging part of the electron density comes from high energy tail of the electron energy distribution. As the size of the high energy tail is dependent upon T_e, obtaining low T_e in plasma processing is considered an important approach to reducing ESD. Recent results in metal etching (Tokashiki et al., 1998) suggest that ESD not only depends on T_e as previously suspected but also that the electron density, n_e, may play an important role. We introduce a new parameter, the electron energy threshold, and demonstrate that it may be as important as T_e or n_e in the mechanism for electron shading damage. This new parameter, E_th, is the energy threshold for electrons to reach the wafer surface and is related to the plasma potential as well as the wafer DC bias. This threshold aspect of electron shading damage could explain why a particular class of recipes (high bias power/low source power) show improved damage performance in inductively coupled plasma (ICP) etching tools (Tokashiki et al, 1998; Tabara, 1997; Hashimoto et al., 1997; Karzhavin and Wu, 1998). In addition, we provide experimental evidence obtained on an Applied Materials DPS Metal Etch Centura which supports this explanation