Pa. Coon et al., ADSORPTION-KINETICS FOR ETHYLSILANE, DIETHYLSILANE, AND DIETHYLGERMANE ON SI(111) 7X7, The Journal of chemical physics, 98(9), 1993, pp. 7485-7495
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.