Sheet Resistance Increase of Shallow Doped Silicon during Native Oxidation in Air

Abstract

An increase in sheet resistance of shallow doped silicon during air exposure was investigated. Shallow phosphorus doping of silicon wafers was carried out by an atomic-layer doping process forming a pn-junction close to its surface. The sheet resistance Rs of the n+-doped layer was found not to be constant during its contact to air after the process, but showed a remarkable step-like increase with time. After the removal of native oxide by an HF-treatment a similar behavior could be observed during re-oxidation. This behavior may be associated with a layer-by-layer growth of native oxide in conjunction with a silicon consumption and deactivation of dopants in the shallow doped subsurface layer. The observation suggests studying appropriate time-dependent surface related processes by means of the simple four-point probe setup by measuring surface affected sheet resistance changes of shallow doped layers.