Segregation of copper to (100) and (111) silicon surfaces from internal Cu{sub 3}Si precipitates

Segregation of transition metal impurities to surfaces or interfaces can have detrimental or beneficial effects in silicon-based microelectronic devices. Controlled segregation of impurities to regions remote from device structures, i.e. gettering is routinely used to prevent uncontrolled segregation to critical regions which may cause failure. Internal gettering is a widely used process in which oxide precipitates and associated lattice defects provide sites for precipitation of metal-silicide phases. Segregation of impurities onto surfaces of internal microcavities has also been examined as a potential gettering process. It was observed that gettering to cavities can dissolve pre-existing internal metal silicide precipitates of Cu, Au and Ni. The energetics of copper segregation to silicon surfaces were examined by measuring the Cu coverage after equilibration between Cu on the surface and internal Cu{sub 3}Si, for which the Cu chemical potential is known. For oxide-free surfaces the Cu coverage was close to one monolayer on (111) surfaces but was much smaller on (100) surfaces. The Cu coverage was greatly reduced by oxide passivation of the surface. LEED showed the 7 x 7 structure of the clean (111) silicon surface converted to a quasiperiodic 5 x 5 structure after equilibrating with Cu{sub 3}Si. The 2 x 1more » LEED patterns for (100) surfaces indicated no change in surface structure due to the Cu{sub 3}Si. These results show that the free energy of copper in Cu{sub 3}Si is higher than that of copper on (111) surfaces but lower than that of copper on (100) surfaces.« less