Method for etch rate enhancement by background oxygen control in a soft

Abstract

The invention for etching a substrate containing an oxide layer reduces activated oxygen within the plasma and maintains a high soft etch rate in a series of subsequent etches. In one aspect of the invention, a second substrate, in the form of a substrate ring, is utilized in the processing chamber and is etched in conjunction with a first substrate being processed. This substrate ring is formed of a material which, when etched, reacts with activated oxygen to form a stable oxygen-containing compound which may be evacuated from the system. In another aspect of the invention, a first power level for inductively coupling energy to the plasma is determined to establish a bias voltage level at the substrate of approximately 100 Volts. A second, lower power level is then determined for producing a bias voltage level at the substrate not significantly higher than 300 Volts. With the range provided by the determined first and second power levels, an etching power level is selected for inductively coupling energy to the plasma in the range of the first and second power levels but closer to the second power level than the first power level to reduce oxygen activated in the plasma. The etching power level is also selected to establish an etch rate of the substrate in the range of approximately 300-500 .ANG./min. for a semiconductor oxide such as silicon dioxide, and 75-125 .ANG./min. for a metal oxide, which would be considered a soft etch.