Ultraclean Si/Si Interface Formation by Surface Preparation and Direct Bonding in Ultrahigh Vacuum

Abstract

Silicon surfaces have been cleaned and bonded in ultrahigh vacuum, at a pressure in the 10'° Torr range. The bonded interfaces show extremely low contamination levels as measured by secondary ion mass spectroscopy. Nevertheless, a potential barrier could be detected at the interface by spreading resistance and current vs. temperature measurements. This suggests that the barrier is caused by inevitable dislocation networks due to wafer misorientation, as well as residual oxygen at the interface.

Interface Resistivity of Directly Bonded Si Wafers

“…In a different method for bonding semiconductors, Si to Si direct bonding was performed by making contact between surfaces and raising the ambient temperature to 1000 or 1100 C. [3][4][5] Here, we call this method silicon direct bonding (SDB). According to Takagi, interfaces in Si wafers bonded by SAB behave differently from those bonded by SDB: 6) Oxygen is the major impurity in Czochralski (CZ) Si wafers and has typical concentrations of 10 17 -10 18 cm À3 .…”

“…For the electric study on bonded interfaces, the spread resistance method, current-voltage (I-V) measurement, capacitance-voltage (C-V) measurement and deep level transient spectroscopy (DLTS) were employed. For the spread resistance method, 3) bonded Si specimens should be polished to a beveled angle for scanning the interface of bonded Si wafers, although no electrodes are required on the Si wafers. In I-V, C-V, and DLTS measurements, 4,5) electrodes should be fabricated on Si wafers.…”