ULTRACLEAN SI SI INTERFACE FORMATION BY SURFACE PREPARATION AND DIRECT BONDING IN ULTRAHIGH-VACUUM/

Silicon surfaces have been cleaned and bonded in ultrahigh vacuum, at a pressure in the 10(-10) Torr range. The bonded interfaces show extre mely low contamination levels as measured by secondary ion mass spectr oscopy. Nevertheless, a potential barrier could be detected at the int erface by spreading resistance and current vs. temperature measurement s. This suggests that the barrier is caused by inevitable dislocation networks due to wafer misorientation, as well as residual oxygen at th e interface.