EFFECTS OF GAS ADDITIVES TO THE SILICON-TO-PHOTORESIST ETCHING SELECTIVITY.

It is well known that addition of several percent of oxygen to a CF//4 plasma can increase the etch rate of both silicon and photoresist by several times. Models of silicon etching process based on the concentration of the major etchant, i. e. , F atoms, of which the production rate is enhanced by the oxygen additive, and the competition between F atoms and O atoms for active Si surface sites have been proposed and correlated with experimental data. For etching photoresist, oxygen atoms instead of fluorine atoms are mainly responsible for the etch reaction. The addition of CF//4 to the oxygen plasma can enhance the production rate of oxygen atoms. The fluorine atoms can also enhance the etch rate of photoresist via surface mechanisms. The development of plasma etching compositions that have high etch rate of silicon and low etch rate of photoresist is desirable in order to use the photoresist as an efficient and convenient mask for etching silicon.