ANISOTROPIC HIGHLY SELECTIVE ELECTRON-CYCLOTRON RESONANCE PLASMA-ETCHING OF POLYSILICON

High polysilicon etch rates have been obtained in combination with high etch selectivities with respect to SiO2 and photoresist in a microwave electron cyclotron resonance plasma etch reactor. The etch system is vacuum load locked, used Cl2-O2 chemistry, and employs backside helium substrate cooling with 150 mm wafer handling. Etch rates in excess of 4000 angstrom/min are obtained in undoped polysilicon with zero applied substrate bias, using Cl2 with 0.6% O2 at 3 mTorr total pressure and 700 W of 2.45 GHz input microwave power. The corresponding polysilicon-oxide selectivities are greater than 150, and the polysilicon-resist selectivity is 15-20. Half-micron polysilicon gates etched with zero applied substrate bias have vertical sidewalls and residue-free SiO2 floors. Electron and ion energy distribution measurements show that a high ion flux ( > 10 mA/cm2) and simultaneous low ion bombardment energy are controlling parameters for high rate selective etching.