Reactive Sputter Etching of Thin Films for Pattern Delineation

Thin films of several metals, commonly used in integrated circuit fabrication, were reactively sputter-etched in an oxygen atmosphere with a focused ion beam. A decrease in the sputter-etch rate was observed as the partial pressure of oxygen was increased from 1.5 X 10...6 to 1 X 10-4 tort. This decrease was attributed to a buildup of a surface layer of adsorbed oxygen on the target. The partial pressure of oxygen corresponding to this decrease in sputter-etch rate of most metals was calculated on the basis of the thermodynamic properties of the compound formed. There was excellent correlation between calculated and experimental values. For integrated circuit fabrication, a suitable metal can be chosen as a thin-film mask which has a transition pressure lower than those metals on the substrate to be sputter-etched for pattern generation. This transition pressure can be predicted prior to processing.