On the Origin of Anomalous OffCurrent Under Hot Carrier Stress in p-Channel DDDMOS Transistors With STI Structure

Abstract

This letter investigates the abnormal OFF-current behavior induced by hot carrier stress (HCS) in p-channel double diffused drain metal-oxide-semiconductor transistors with a shallow trench isolation (STI) structure. According to ISE-TCAD simulation, the electric field at the drain-side corners of the high-voltage n-well (HVNW) adjacent to the STI trench is stronger than the electric field in the channel center in width direction. Moreover, because a nitride layer acts as a buffer in STI, the electrons generated by impact ionization at the corners of the HVNW can be easily trapped in the nitride layer or at the liner oxide/nitride layer interface. Furthermore, the extension of electron trapping in STI from drain to source during HCS forms the OFF-current conductive path. Based on the charge pumping measurements at different operation conditions, this path formation is further demonstrated by the comparisons of charge pumping measurements between initial state and after HCS.