Silicon nitride films for passivation of pHEMT based MMIC

Passivation of psuedomorphic high electron mobility transistor (pHEMT) based MMIC´s by silicon nitride films deposited by PECVD is reported here. These films were first optimized for passivation of MESFET´s to get desired performance. No degradation in pHEMT/MESFET characteristics like I_dss, g_m V_p and C_gs were observed while only nominal degradation was found in Schottky diode ideality factor eta and its breakdown voltage V_B. The refractive index of the films was 1.92 with 1200 A⁰ thickness. The films have high dielectric strength > 5E6 V/cm, low tensile stress < 5E9 dynes/cm² and dielectric constant 6.9 -7.1. The etch rate of the film is ~ 900 A⁰/min in BHF and fine patterns can be etched with 1-2 minutes etch time in BHF. The film composition was analyzed by FTIR and SIMS studies.