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 A
⁰
thickness. The films have high dielectric strength > 5E6 V/cm, low tensile stress < 5E9 dynes/cm
²
and dielectric constant 6.9 -7.1. The etch rate of the film is ~ 900 A
⁰
/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.