Anisotropic highly selective electron cyclotron resonance plasma etching of polysilicon

Abstract

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 Å/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.