Plasma enhanced chemical vapor deposition and characterization of boron nitride gate insulators on InP

Abstract

Thin films of boron nitride have been deposited in a plasma-enhanced chemical vapor deposition system, for use as a gate dielectric layer on InP. The InP substrates were pretreated by in situ HCl vapor etching prior to the film deposition. Borane-dimethylamine and ammonia were used as sources for boron and nitrogen. The depositions were carried out at low temperatures (320 °C), the samples being not directly exposed to the plasma which minimizes radiation damage to the substrates. The deposited films were characterized by ellipsometry, x-ray photoelectron spectroscopy, infrared and ultraviolet−visible spectroscopy. Metal-insulator-semiconductor structures were realized to evaluate the bulk dielectric and insulator−semiconductor interface properties. The growth rates are low (20 nm/h). X-ray photoelectron spectroscopy and infrared measurements showed that the layers are essentially boron nitride, with some boron excess (typically N/B≂0.8). The dielectric films were found to have an optical index n≂1.7, an optical band gap E0≂ 5.8 eV, a resistivity of about 1013 Ω cm and a dielectric constant of 3.5. Frequency dispersion, between 100 Hz and 1 MHz, of capacitance in accumulation did not exceed 10%. The interface state density was in the 1011–1012 cm−2 eV−1 range.