HIGH SELECTIVITY ELECTRON-CYCLOTRON RESONANCE ETCHING OF SUBMICRON POLYSILICON GATE STRUCTURES

A submicron doped polysilicon etch using a Cl2-HBr/Cl2-HBr-O2 process in a downstream electron cyclotron resonance (ECR) etcher is described. Vertical and notchless profiles were achieved at 100%-to-300% overetches. By adjusting the radio-frequency (rf) power applied to the wafer holder and by adding a slight amount of oxygen in the overetch step, a very high polysilicon to oxide selectivity of >200:1 was obtained with oxide loss minimized to <20 angstrom. In addition, this ECR polysilicon etch offers a very large process latitude with more than 60% variation in process parameters. The effects of process parameters on etch performance were investigated. A 200-wafer repeatability test demonstrated a polysilicon etch rate repeatability of +/-3.8%.