Selective and uniform high rate etching of polysilicon in a magnetically confined microwave discharge

Abstract

An electron cyclotron resonance plasma reactor with multipolar magnetic confinement has been characterized for potential applications in polysilicon gate patterning. A two-step, low pressure, 100% Cl2 etch process is used, in which a small substrate bias is applied only during the polysilicon etch step. This system etches anisotropic profiles into undoped polysilicon with an etch rate of 4000–4500 Å/min and polysilicon–oxide etch selectivities of 150–300. The downstream ion current density and plasma potential are radially uniform to within 1% (1σ) over a 200 mm diam. The polysilicon etch rate is radially uniform to within ±2% of the mean etch rate across a 150 mm wafer.