HYDROCARBON SURFACE-CHEMISTRY ON SI(100)

The interaction of various hydrocarbon species with the Si(100) surface has been investigated using several surface science techniques. The efficiency of carbon deposition is related to the efficiency of SiC thin film formation. The hydrocarbon species studied include acetylene (C2H2), ethylene (C2H4), and the adsorbed methyl group (CH3(a)). In the case of the chemisorption of acetylene and ethylene, the pi-bond of the olefinic molecules interacts with the dimer unit (Si2) on the Si(100)-(2 x 1) surface. One monolayer of both acetylene and ethylene on Si(100) has been achieved by saturating the surface at 105 K. and a di-sigma-bonding structure is proposed for one molecule per Si2 dimer unit at monolayer coverage. Upon heating, the majority (> 95%) of the adsorbed acetylene undergoes dissociation to produce chemisorbed carbon and H-2(g). In contrast, chemisorbed ethylene desorbs intact from Si(100) at approximately 550 K, with approximately 2% of the monolayer undergoing dissociation. The low activation energy for desorption (E(d)-degrees(C2H4) = 38 kcal mol-1) allows C2H4 to desorb prior to significant decomposition. Investigations of the thermal behavior of CH3(a) on Si(100) show that the adsorbed methyl group is stable up to approximately 600 K. At higher temperatures, CH3(a) decomposes to CH(x)(a) (x < 3) species, and subsequently liberates H-2(g), leaving carbon on the surface. Less than 1% of the adsorbed carbon species (CH(x) x less-than-or-equal-to 3) desorbs in the form of C2 hydrocarbon species upon heating. This indicates that the methyl group is an efficient source of surface carbon by thermal decomposition.