Application of a low-pressure radio frequency discharge source to polysilicon gate etching

Abstract

We have shown that a discharge can be sustained at low pressure (≲10−3 Torr) in a single-wafer reactor using experimental quarter-wave helical resonator structures operated at radio frequencies. These discharge sources have been used to etch submicron-wide polysilicon gates with chlorine and chlorine/oxygen mixtures. Selectivities for undoped polysilicon over oxide and hard baked trilevel photoresist were 70:1 and 2.8:1, respectively, in a 75 W discharge operated at 0.1 mTorr with a Cl2/1% O2 feed gas mixture. Anisotropic profiles of 0.25 μm lines were obtained across 100 mm wafers with negligible linewidth loss. These preliminary experiments show that rf resonator discharges may offer an alternative to low-pressure microwave discharges such as those based on electron cyclotron resonance.