Formation of directly bonded Si/Si interfaces in ultra-high vacuum

The formation of Si/Si interfaces by surface cleaning and direct bonding in ultra-high vacuum, at a pressure in the lo-” Torr range, is presented. High bond strengths have been achieved for bonding temperatures above 450°C in the last heating step, by applying mechanical pressure. Spreading resistance measurements show features similar to conventional direct bonded interfaces. The increasing resistance at the location of the interface corresponds to approximately 5 X 10” positive elementary charges per cm2. UHV bonded interfaces with contamination levels below the SIMS detection limit can be made.