A Combination of Implant Shadow and Skin Effects Leading to HV Devices Failure during the ESD Event

The impacts of skin effect and base push-out effect are found as major cause of failure for high-voltage (HV) transistors during the electrostatic-discharge (ESD) zapping event. The skin effect is caused by that the ESD current or TLP current is a large time-varying current at the transistor turn-on transient. This effect occurs at the backend of transistor. So, most current is localized in the skin depth of backend from the edge. The base push-out effect is caused by the base region expands its area to the heavily doped region of collector. This effect is on the frontend of high-voltage (HV) transistor and induces the snapback occurred at the shortest collector region due to some well implants are implanted into the silicon at an angle with respect to wafer position. If the region is shadowed by photoresist (PR), it is the implant blank region. If the region is not shadowed by PR, it becomes the implant overexposure region. This induces the different reduced surface-field (RESURF) widths in different regions of the drain, which causes the collector width to differ.