This paper presents the meaningful consequence of a minor Wafer Fab process variability, generating on-resistance drift on low voltage vertical power N-MOSFETs dedicated to microhybrid automotive application. The originality of this paper concerns the necessity to use complementary failure analysis investigations needed to determine the origin of the failure without any possibilities to perform any fault localization. The results enabled implementation of corrections and improvement of test screening to protect customers.

This paper presents an original approach allowing determining the failure mechanism at the origin of onresistance (RDSon) drift on vertical Power N-MOSFETs, dedicated to automotive application. The studied devices failed after Temperature Cycling (TC) qualification stress. The originality of that paper concerns the necessity to use strategic Failure Analysis (FA) approaches to determine the origin of the defect, without any localization possibilities. In that perspective, an original microprobing sub-mohms resistance electrical characterization of the different conductive interfaces was performed in order to determine the failing layer. Then, physical destructive FA techniques (backside SAM, leadframe peel-off and mechanical cross-section) were combined in order to finely characterize the defect. As a result, problems in die attach layer were highlighted, confirming the electrical probing characterization. At last, root cause of this abnormal die attach will be discuss through review of assembly process parameters. These results allowed implementing corrections and improving product stress resistance.