Heterogeneous recombination of atomic bromine and fluorine

Abstract

Recombination coefficients (γ) of Br and F atoms have been measured for crystalline Si, quartz, photoresist, anodized aluminum, poly-Si, WSix, tungsten and stainless steel surfaces for a range of temperatures. The γBr and γF values are compared to our previously reported measurements of γCl [G. P. Kota, J. W. Coburn, and D. B. Graves, J. Vac. Sci. Technol. A 16, 270 (1998)]. In general, the Br-, Cl- and F-atom recombination coefficients decrease as the surface temperature increases. The γBr values are similar to the γCl values for the various surfaces. At room temperature, γBr is highest (>0.4) for stainless steel and tungsten, moderate (0.1–0.4) for poly-Si, WSix and anodized Al, and lowest (<0.05) for c-Si, quartz and photoresist. However, γF, at room temperature, is no greater than 0.05 for all the surfaces. γF increases slightly as the temperature is decreased to 80 K but is still below 0.1 for all the surfaces. The recombination coefficient data as a function of temperature for all surfaces are fit to a phenomenological model developed previously for γCl (see the above reference). The model assumes that the incident halogen atoms physisorb on a surface that is saturated with chemisorbed halogen atoms. The physisorbed atoms are assumed to diffuse on the surface and either desorb before recombining or recombine and then desorb. The recombination rate is assumed to be first order in physisorbed atom coverage.