Passive Voltage Contrast (PVC) in a Scanning Electron Microscope (SEM) or a Focused Ion Beam (FIB) is a key Failure Analysis (FA) technique to highlight a leaky gate. The introduction of Silicon On Insulator (SOI) substrate in our recent automotive analog mixed-signal technology highlighted a new challenge: the Bottom Oxide (BOX) layer, by isolating the Silicon Active Area from the bulk made PVC technique less effective in finding leaky MOSFET gates. A solution involving sample preparation performed with standard FA toolset is proposed to enhance PVC on SOI substrate.

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.