Low-temperature ICPECVD of silicon nitride in SiH4-NH3-Ar discharges analyzed by spectroscopic ellipsometry and etch behavior in KOH and BHF

Low-temperature (80-130 degreesC) high-quality silicon nitride was grown on Si substrates using a SiH4 (5%, in He)/NH3/Ar chemistry and ICPECVD techno logy. The influence of percentage SiH4, temperature, chamber pressure and s ource power on the wet etch rate, deposition rate, refractive index at 632. 8 run and extinction coefficient at 320 nm was investigated. The SiNx films were characterized by spectroscopic ellipsometry and by the etch rate in K OH and BHF. The lowest etch rates (BHF, KOH) are found for nearly stoichiom etric silicon nitride with a refractive index close to 2 and deposition rat es above 40 nm min(-1). The etch rates at 130 and 80 degreesC were only two - and four-fold, respectively, higher than those for LPCVD SiN (780 degrees C). The mechanical stress of these films is compressive and below 0.1 GPa. To check the surface temperature during ICPECVD, we deposited a 200-nm-thic k silicon nitride layer at 90 degreesC on a photoresist degrading at temper atures above 100 degreesC. A 50-nm-thick SiNx film was used as a capacitor layer using lift-off techniques. This film showed a breakdown field strengt h of 4 MV cm(-1). These films were also deposited on InGaAs Mesa diodes. Af ter removal, no damage by the ICPECVD process could be found by comparing t he reverse current before deposition and after removal of the SiNx, film. ( C) 2001 Elsevier Science B.V. All rights reserved.