Low-temperature ICPECVD of silicon nitride in SiH 4–NH 3–Ar discharges analyzed by spectroscopic ellipsometry and etch behavior in KOH and BHF

Abstract

Low-temperature (80–130°C) high-quality silicon nitride was grown on Si substrates using a SiH 4 (5% in He)/NH 3/Ar chemistry and ICPECVD technology. The influence of percentage SiH 4, temperature, chamber pressure and source power on the wet etch rate, deposition rate, refractive index at 632.8 nm and extinction coefficient at 320 nm was investigated. The SiN x films were characterized by spectroscopic ellipsometry and by the etch rate in KOH and BHF. The lowest etch rates (BHF, KOH) are found for nearly stoichiometric silicon nitride with a refractive index close to 2 and deposition rates above 40 nm min −1. The etch rates at 130 and 80°C were only two- and four-fold, respectively, higher than those for LPCVD SiN (780°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-thick silicon nitride layer at 90°C on a photoresist degrading at temperatures above 100°C. A 50-nm-thick SiN x film was used as a capacitor layer using lift-off techniques. This film showed a breakdown field strength of 4 MV cm −1. These films were also deposited on InGaAs Mesa diodes. After removal, no damage by the ICPECVD process could be found by comparing the reverse current before deposition and after removal of the SiN x film.