Improve Intermetal Dielectric Process for HTRB Stability in Power GaN High Electron Mobility Transistor (HEMT) by unbiased-Highly Accelerated Stress Testing (uHAST).

This study investigates a severe high-temperature reverse bias (HTRB) failure observed in GaN HEMTs, with devices failing in under 24 h. We conducted an in-depth analysis of the electrical and physical failure mechanisms, revealing that unbiased-highly accelerated stress testing (uHAST) can effectively induce dielectric delamination. The electrical and physical characteristics of devices post-delamination demonstrated a strong correlation between delamination at the nitride-polyimide interface and an increase in off-state drain leakage current (IDSS). Our findings led to the removal of a suspected process step involving the use of the reactive chemical, N-methyl-2-pyrrolidone (NMP), before and after polyimide deposition. This critical process change yielded a significant improvement in reliability; while the initial failure rate was 25% at 24 h, three lots of 260 parts subsequently survived 1000 h of HTRB stress with no failure. In conclusion, uHAST is a valuable reliability testing tool for assessing package and film adhesion, leveraging high pressure and moisture to quickly identify and troubleshoot delamination-related reliability issues.