Investigation of failure mechanisms in low-voltage power VDMOSFETs linked with gate oxide process quality

Devices dedicated to automotive applications have to reach exacting specifications especially in terms of reliability. The burn-in HTGB test is dedicated to evaluate gate oxide integrity with gate biased under high temperature. Therefore, gate oxide quality is an exacting parameter which contributes to device reliability. This paper is based on the study of planar technology and more precisely on vertical double-diffused power MOSFETs. First of all, the purpose of this work is to correlate the gate oxide process quality and the influence of wet cleanings at silicon level on die reliability. Actually, the cleaning performed just before oxide growth is linked with gate oxide robustness as shown with GOI measurements on dedicated structures and QBD measurements on power devices. Another key point is the homogeneity of breakdown voltage due to parallel MOSFETs used in application. Probe electrical results and TEM observations has demonstrated a correlation between BVdss establishment and cleaning used on silicon surface. In conclusion, the kind of cleaning performed at silicon level before oxide growth has been identified to generate irreversible damages for power VDMOSFETs.