EFFECT OF SILICON-OXIDE THICKNESS ON THE DIRECT SYNTHESIS OF DIMETHYLDICHLOROSILANE

The effect of silicon oxide thickness on the direct synthesis of dimet hyldichlorosilane ((CH3)(2)SiCl2, dmd) was studied by reacting Si(100) surfaces with CH3Cl. Oxide layers of 0.9, 2, 4, and 14 nm average thi cknesses were grown on Si(100) and were characterized by ellipsometry and AES. A copper catalyst (82 wt% Cu and 18 wt% Cu2O) was placed as a powder on the oxide layer and the reaction was carried out at 598 K i n 1 atm CH3Cl. Reacted surfaces were characterized by XRD, SEM, and op tical microscopy. The reacted surfaces contained Cu3Si, Cu, and Si. Th e surface with the lowest oxide coverage had the best selectivity (78 mol% (CH3)(2)SiCl2 and 22 mol% CH3SiCl3). As the oxide thickness incre ased, the selectivity for (CH3)(2)SiCl2 continuously decreased, the ov erall reaction rate for methylchlorosilane formation decreased, and th e induction time before dmd formation increased. Even after 18 h of re action, the rate and selectivity were still affected by the initial ox ide thickness on the 2-nm oxide surface, but selectivity for dmd on th e 4-nm oxide surface was the same as that on the 2-nm oxide surface. T he reaction rate on Si(100) with a 14-nm oxide layer was less than 1% of that on the Si(100) with 0.9-nm oxide. On all surfaces, square-base d pyramidal pits formed as Si were removed, and the pits were larger, for the same reaction time, for surfaces with thinner oxides. A 4-nm o xide affected the orientation of the Cu3Si phase, but on 0.9 and 2-nm oxide layers, Cu3Si was randomly oriented. (C) 1996 Academic Press, In c.