ENHANCED SPUTTERING OF ONE SPECIES IN THE PROCESSING OF MULTIELEMENT THIN-FILMS

We discuss two mechanisms for enhanced selective sputtering which may strongly influence the composition of thin films deposited under energetic particle bombardment. The first mechanism occurs on sloping substrate surfaces which experience a higher fraction of material resputtered than flat surfaces. 500 eV Ar+ ion bombardment during deposition of Al-5 at. % Cu causes an increase in Cu concentration by up to a factor-of 2 on sloping surfaces. This effect is modeled with the dynamic Monte Carlo code T-DYN, which simulates film growth under ion bombardment and confirms the selective sputtering of Al. The second mechanism occurs if diffusion of the film constituents is significant, and the film is situated on top of an underlying material containing one of the film components. Enhanced sputtering of one component occurs if that component maintains a high surface concentration by diffusion or segregation. Raising the temperature of TiSi2 on (100) Si to the range in which Si atoms are mobile (500-700-degrees-C) increases the sputtering yield ratio of Si to Ti under 300 eV Ar+ bombardment to a value of 19 from the room temperature value of 2. During high rate sputter deposition, both of these mechanisms of enhanced sputtering of one species may occur, leading to phase separation and extreme concentration gradients on topographically structured surfaces.