Evaluation of LPCVD SiNx Gate Dielectric Reliability by TDDB Measurement in Si-Substrate-Based AlGaN/GaN MIS-HEMT

Si-substrate-based AlGaN/GaN high-electron mobility power transistors with low pressure chemical vapor deposition (LPCVD) SiNx as gate isolation material are fabricated on a 6-in wafer by CMOS compatible process. The dielectric failure by forward-biased constant-voltage stress time-dependent dielectric breakdown (TDDB) measurements at various temperatures (from room temperature to 250 degrees C) and their statistical Weibull analysis are compared. Impact of gate dielectric area and multifinger on the SiNx TDDB characteristics is also discussed. Using thermal microscope imager, the leakage current spots have been identified. The mean time to failure decreases with the increasing finger numbers in exponential form. We also predict the device (W-G = 0.25 mm) with 35-nm-thick LPCVD SiNx gate dielectric can survive at a positive gate voltage of V-GS = 15 V for a 10-year time-to-breakdown lifetime (100 ppm and T = 25 degrees C) and V-GS = 7.5 V for a 10-year time-to-breakdown lifetime (100 ppm and T = 250 degrees C).