THE VISCOSITY OF GERMANIUM DURING SUBSTRATE RELAXATION UPON THERMAL ANNEAL

Thin-film heterostructures experience structural relaxation when subje cted to post-deposition thermal heat treatment. The rate of relaxation , elastic effects, and inelastic effects on the stress and deformation of the structure are determined by the physical properties of the mat erials, in particular, the solid-phase viscosity. During relaxation, m ovement of defects causes an increase of viscosity with time at a cons tant rate as these defects are annihilated. Experimental anneals have been performed on structures with polycrystalline silicon films on (11 1) germanium substrates, in which the substrate relaxes during thermal annealing. A numerical analysis of the experimental results has deter mined values for the viscosity and viscosity rate of (111) germanium w afers. In addition, four zones of the relaxation process have been ide ntified, and results indicate that the increasing viscosity with time has a larger effect at lower furnace ramp-up rates.