Hydrogen incorporation in silicon nitride films deposited by remote electron-cyclotron-resonance chemical vapor deposition

Abstract

We have studied the incorporation of hydrogen in films of silicon nitride deposited by remote electron-cyclotron-resonance chemical vapor deposition using silane (SiH4) as the silicon precursor and both ammonia (NH 3) and deuteroammonia (ND3) as nitrogen precursors. Nearly stoichiometric films of silicon nitride, with a refractive index ranging from 1.84 to 2.08, were obtained at substrate temperatures from 50 to 550°C, microwave powers from 0.5 to 2.5 kW, and NH3 (ND3) to SiH4 flow ratios from 2.5 to 10. The total hydrogen incorporation decreased linearly with increasing temperature from a maximum value of 2×1022 to 6×1021 cm-3. The amount of hydrogen incorporated in the film was independent of the microwave power and the NH3/SiH4 flow ratio, though both variables strongly influenced the hydrogen bonding configuration. The majority of the hydrogen ends up bound to the excess species in the film. Films deposited from deuteroammonia show that 70%-80% of the incorporated hydrogen originates from the ammonia precursor. Optical emission spectroscopy shows the formation of both SiD and NH in the gas phase indicating that an isotopic exchange takes place during the downstream excitation of SiH4. The relative number of N - H and Si - H bonds measured in the gas phase and in the film, as a function of the NH 3 to SiH4 flow ratio, are similar. These results suggest that the hydrogen configuration in the film may be determined primarily by gas phase chemistry. Temperature programmed desorption analysis on deposited films shows that hydrogen starts to evolve from the film at a temperature of 620°C. Films deposited at temperatures ≳350°C were found to be stable after a 920°C anneal. © 1995 American Institute of Physics.