Ion Implantation Masking Ability Degradation in High Temperature Annealed Mo Film

Unwanted depletion modes have been observed in Mo-gate MOSFET characteristics, when high-temperature annealed Mo-gate film was used as a mask for As implantation into source and drain region, in sharp contrast to enhancement mode characteristics for FETs with as-deposited Mo-gate film. Donor-type impurity incorporation in Si substrate and fast interface states generation were derived from C V characteristics for diodes fabricated by the same process as used for depletion-mode FETs. The former is considered to be due to As incorporation in the Si substrate owing to channeling through annealed Mo film resulting from improved crystallinity, and the latter to some impurity contamination in the gate oxide film due to the As knock-on effect.