Suppressed Si precipitation at an AlSi/Si contact by the presence of thin SiO2 film on the Si substrate

Abstract

The effects of Si surface conditions on the susceptibility of Si precipitation at the AlSi (1 wt%)/Si interface have been studied. Conditions of the Si surface on which AlSi films are to be sputtered were varied by two wet cleanings, using an ammonium peroxide mixture (APM) and diluted hydrofluoric acid (HF). For AlSi/Si interfaces, Si precipitation after annealing at 400 degrees C for 2 h and that after AlSi sputtering were observed by scanning electron microscopy after removing AlSi films and by cross-sectional transmission electron microscopy (TEM) respectively. 1.0 mu m diameter contact resistance (Rc) was measured using Kelvin patterns. Complete suppression of Si precipitation at the AlSi/Si interface was observed by SEM for the APM-cleaned contacts resulting in a low and uniform Rc in a wafer, while large precipitates were observed resulting in high and non-uniform Rc for the HF-cleaned contacts. Furthermore, while Si precipitates on the substrate for the HF-cleaned AlSi/Si observed by TEM were epitaxially grown on the substrate, those precipitates for the APM-cleaned one were not grown and scarcely observed in the TEM image. Oxygen atoms formed by the APM cleaning were detected by energy dispersive X-ray spectroscopy at the AlSi/Si interface -even after annealing at 400 degrees C. A new model of the thin silicon oxide layer to suppress Si precipitation is proposed.