REACTIONS OF DISILANE ON CU(111) - DIRECT OBSERVATION OF COMPETITIVE DISSOCIATION, DISPROPORTIONATION, AND THIN-FILM GROWTH-PROCESSES

We report a detailed study using reflection absorption infrared (RAIR) , temperature-programmed reaction (TPR), Auger electron (AES) spectros copies, and low-energy electron diffraction (LEED) of the interaction and thermolytic reactions of disilane on a Cu(111) surface. Disilane a dsorbs dissociatively on Cu(111) at temperatures as low as 90 K. At lo w coverages Si-Si and Si-H bond scissions yield two adsorbed fragments which are identified as being the SiH fragment and adsorbed H atoms, respectively. Low fluxes of disilane (less than or equal to 5 x 10(12) molecules/s) favor the formation of these dissociative adsorption pro ducts. Using higher fluxes, the exposures lead to the concomittant for mation of SiH2 and SiH3 moieties. The yields of these later species de pend very sensitively on both the absolute and relative surface covera ges of Si and H. The decomposition processes of adsorbed SiH3 and SiH2 are characterized strongly by coverage dependent kinetics. The SiH3 s pecies is stable over a limited temperature range (T < 150 K); upon he ating it undergoes sequential Si-H bond cleavages to form a surface bo und monohydride. The dihydride is stable to similar to 180 K. The mono hydride decomposes at higher temperatures (T > 250 K), leaving behind surface bound Si. The recombinative desorption of dihydrogen occurs at similar to 300 K. This bimolecular process competes with another asso ciative reaction which leads to the formation and desorption of silane (T similar to 230 K) from the surface. The amount of Si deposited on the surface depends sensitively on the surface temperature and the mag nitude of the disilane exposure. A high coverage silicide surface phas e is readily formed above the dihydrogen desorption temperature. This thin film is characterized by an ordered (root 3 x root 3)R30 degrees overlayer structure which is thermally stable over a wide range of tem peratures. At higher temperatures, where atomic mobilities are higher, the growth of multilayer intermetallic thin films can be effected.