Signal noise perturbation on automotive mixed-mode semiconductor device generated by graded substrate defect

The semiconductor technologies evolution allows greatly reducing noise impact on products and many structures have been created to reduce its effect. However, this paper presents the apparition of a noise issue during the production of a mixed-mode device dedicated to automotive applications. The research investigations concerned the fact that failure was not detected at test level but at customer level; therefore, it was determinant to understand the root cause of this failure mode to drive corrective actions in order to secure customer. The challenge was to analyse noise in Failure Analysis (FA) without fault spatial localization results. Indeed, Light Emission Microscopy (EMMI) and Thermal Laser Stimulation (ex: Soft Defect Localization - SDL) were unable to provide any defective area in the product. The lack of failing device identification led us to combine electrical and design analyses in order to define hypothesis on the failure origin. It was then possible to drive physical investigations through different approaches, using physical cross-section, Secondary Ion Mass Spectrometry (SIMS) and Scanning Capacitance Microscopy (SCM) techniques. Finally, the obtained complementary results will be discussed and an explanation of the failure mechanism will be presented as the root cause issue, allowing defining the defective step in production process.