Heterogeneous recombination of atomic bromine and fluorine

Recombination coefficients (gamma) 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 gamma(Br) and gamma(F) values are compared to our previously reported measurements of gamma(Cl) [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 gamma(Br) values are similar to the gamma(Cl) values for the various surfaces. At room temperature, gamma(Br) 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, gamma(F), at room temperature, is no greater than 0.05 for all the surfaces. gamma(F) 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 gamma(Cl) (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. (C) 1999 American Vacuum Society. [S0734-2101(99)04701-6].