Highly selective sputtering of silicon from TiSi₂ at elevated temperature

Abstract

We demonstrate almost 100% selective sputtering of silicon from TiSi 2 using a combination of low energy ion bombardment and elevated temperature. TiSi2 was prepared by annealing 1000-Å-thick Ti on (100)Si in He at 635°C for 30 min to produce 2300-Å thick TiSi 2. Ion beam etching was carried out using 300 eV argon with a flux of 0.27 mA/cm2 at temperatures from 33 to 700°C. In situ sheet resistance measurements were used to monitor the decrease in silicide thickness as a function of time. Near room temperature, ion etching causes normal sputtering of the silicide. However, at temperatures of 500-700°C, the sheet resistance remains almost unchanged during ion beam etching. Analysis by Rutherford backscattering, with and without Xe markers, shows that Si atoms sputtered from the surface of these high-temperature samples are continuously replaced by Si diffusing from beneath the silicide layer. The thickness and composition of the silicide remain almost unchanged, but the dramatic change in sputtering behavior shows that the surface is enriched in Si. Compared with the room-temperature values, the absolute sputtering yield of Ti at 500-700°C is decreased by a factor of 5, and the yield of Si is increased by a factor of 2. The net result is almost 100% selective sputtering of silicon.