Asymmetric Early Leakage Failure in Bi-Directional SCR ESD Protection Device in BCD Technology

A bi-directional silicon-controlled rectifier (Bi-SCR) electrostatic discharge (ESD) protection device consisting of a left SCR connected to the anode and a right SCR connected to the grounded cathode, which was developed for bipolar-CMOS-DMOS (BCD) technology, exhibited asymmetric early leakage failure in the device, i.e., negative ESD stress caused an earlier leakage failure as compared to positive ESD stress. The analysis of the current and voltage waveforms of transmission line pulse (TLP), technology computer-aided design (TCAD) simulations, and equivalent circuit analysis was conducted to investigate the phenomenon. The investigation shows that the vertical parasitic PNP bipolar junction transistor (BJT), which was formed by the p-type substrate, n-type epitaxial layer, and p-type high voltage p-well, played an important role in the phenomenon. Under negative ESD stress, the hole injection current from the p-type substrate was able to turn on the parasitic PNP BJT, which led to early activation of the left SCR. The current injection through the vertical parasitic PNP BJT can be suppressed by increasing the thickness of the epitaxial layer, which was confirmed by experiment. It is shown that with a sufficiently thick epitaxial layer, the early leakage failure under negative ESD stress was effectively eliminated.