Abstract: A method of etching polysilicon using a fluorinated gas chemistry to provide an etch rate in excess of 10,000 Å/min and a photoresist selectivity of better than 3:1. The method is accomplished using a combination of a fluorinated gas and a fluorocarbon gas, e.g., 50-60 sccm of SF6, 1-40 sccm of CHF3, and 40-50 sccm of O2 with a total chamber pressure of 4-60 mTorr. The power applied to the etch chemistry to produce an etching plasma is 400-1500 watts of inductive source power (at 13.56 MHz) via an inductively coupled antenna and 200-1500 watts (at 12.56 MHz) of cathode bias power applied via a cathode electrode within a wafer support pedestal. The pedestal supporting the wafer was maintained at 0-50 degrees C.

Abstract: The present invention provides straight forward methods for plasma etching a trench having rounded top corners, or rounded bottom corners, or both in a silicon substrate. A first method for creating a rounded top corner on the etched silicon trench comprises etching both an overlying silicon oxide layer and an upper portion of the silicon substrate during a “break-through” step which immediately precedes the step in which the silicon trench is etched. The plasma feed gas for the break-through step comprises carbon and fluorine. In this method, the photoresist layer used to pattern the etch stack is preferably not removed prior to the break-through etching step. Subsequent to the break-through step, a trench is etched to a desired depth in the silicon substrate using a different plasma feed gas composition.