Effect of plasma density and uniformity, electron temperature, process gas, and chamber on electron shading damage

Electron shading is a major plasma process-induced device damage mechanism in high-density etching. Patrick et al (1997) showed that although gross plasma nonuniformity can cause damage, nonuniformities seen in modern commercial etchers contribute negligible damage. Vahedi et al. (1997) derived an analytic model that clarifies the contribution of plasma and device parameters to topography induced charging. Electron temperature and plasma density are the major damage parameters for plasma. Modeling and preliminary shading coefficient measurements show that plasma nonuniformity is indeed only a small contribution. Other major factors in plasma processing induced damage relate to the device, and are the gate oxide activation electric field, effective mass constant, and gate oxide thickness. Finally, topography dependent shading parameters need to be considered. These are a function of minimum line width, aspect ratio, and antenna ratio. Protection diodes and transient fuses (Krishnan et al., 1998) may help mitigate shading damage effects, but do not change the charging mechanism, namely electron shading. This work examines the role of plasma parameters on V _th shifts in transistors fabricated in a flash memory process where metal 1 and/or metal 2 were etched in either a Lam TCP^TM 9600SE or Lam TCP^TM 9600PTX chamber. The plasma parameters varied were plasma density, electron temperature, and plasma uniformity. The role of chamber gap height in the 9600SE was examined and the results compared to the those in the 9600PTX. The role of a lighter ion in decreasing damage as suggested by Tabara (1998) was also examined