ADSORPTION-KINETICS FOR ETHYLSILANE, DIETHYLSILANE, AND DIETHYLGERMANE ON SI(111) 7X7

The adsorption kinetics for ethylsilane (ES), diethylsilane (DES), and diethylgermane (DEG) on Si (111) 7 X 7 were studied using laser-induc ed thermal desorption (LITD) and temperature programmed desorption (TP D) techniques. The initial reactive sticking coefficients were determi ned as a function of surface temperature using LITD measurements. In t hese experiments, the ethyl coverage vs adsorption time was monitored using CH2=CH2 (ethylene) LITD signals that were produced by the beta-h ydride elimination of the surface ethyl groups, e.g. Si-CH2CH3(ad) - S i-H (ad) + CH2=CH2 (g). The initial reactive sticking coefficients wer e S0 almost-equal-to 2 X 10(-3), 4 X 10(-3), and 5 X 10(-2) for DES, E S, and DEG, respectively, at 200 K. As expected from a precursor-media ted adsorption model, the initial reactive sticking coefficients were observed to decrease with increasing surface temperature. Experiments with preadsorbed hydrogen also demonstrated that the initial reactive sticking coefficients of DES and DEG were reduced as a function of hyd rogen coverage. This behavior indicated that alkylsilane and alkylgerm ane adsorption on Si (111) 7 X 7 requires free dangling bond sites. LI TD experiments revealed that the ethyl surface coverage saturated afte r large exposures. The saturation coverage corresponded to a deposited Si or Ge coverage of THETA = 0.13 monolayer for DES and DEG and was i ndependent of surface temperature between 2 K. DEG adsorption cycles w ere used to deposit increasing amounts of Ge on Si (111) 7 x 7. The de posited coverage was examined using H2 TPD studies which indicated tha t the germanium may be forming islands. LITD experiments were also use d to monitor ethyl surface diffusion on Si (111) 7 X 7 after DES adsor ption. No evidence of significant ethyl surface mobility (D less-than- or-equal-to 1.0 X 10(-10) cm 2/s)was found for surface temperatures as high as 600 K.