ROLE OF OXYGEN IN ION-ENHANCED ETCHING OF POLY-SI AND WSIX WITH CHLORINE

Ion-enhanced etch yields of poly-Si and WSi1.66 With beams of molecula r and atomic chlorine and oxygen are reported as a function of neutral -to-ion-flux ratios. The ions used are 500 and 1000 eV Ar+ and 500 eV O-2(+)/O+. Measurements were made in a vacuum chamber with chlorine an d oxygen molecules/atoms effusing from an external discharge source as a beam and impacting the selected surface. The etch rates were measur ed using quartz-crystal microbalances onto which poly-Si and WSi1.66 w ere deposited. In the ion-flux limited regime, atomic chlorine in comp arison to molecular chlorine enhances the etch yield of poly-Si by a f actor of 4 and of WSi1.66 by a factor of 9. Therefore, the etch yield selectivity of WSi1.66 over poly-Si, which is 0.7 with molecular chlor ine, increased to 1.5 with atomic chlorine in the presence of energeti c Arf ions. The effect of neutral O/O-2 on both molecular and atomic c hlorine/Ar+ etching of poly-Si and WSi1.66 is negligible. However, wit h 500 eV oxygen ions, the etch yields of poly-Si with both Cl and Cl-2 are greatly reduced in comparison to those with 500 eV Arf. The etch yields of WSi1.66 are also lower with oxygen ions, but the reduction i s smaller than for the poly-Si case. Therefore, the etch yield selecti vity of WSi1.66 over poly-Si increases to 10 with Cl/oxygen ions. (C) 1998 American Vacuum Society. [S0734-2101(98)09804-2].