Structural film characteristics related to the passivation properties of high-rate (> 0.5 nm/s) plasma deposited a-SiNx:H

This paper addresses the effects of a short high-temperature step, corresponding to the firing of the metallization on Si solar cells, on the structural and optical properties of high-rate (> 0.5 nm/s) plasma deposited a-SiNx:H films. Three different types of a-SiNx:H films were prepared using (i) a N2-SiH4 expanding thermal plasma, (ii) a NH3-SiH4 expanding thermal plasma, and (iii) a NH3-SiH4 microwave plasma. The changes in structural and optical properties of the films have been investigated before and after the high temperature step by means of elastic recoil detection, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy. The high temperature step induces significant changes in hydrogen content, mass density, and optical properties of the films and these thermally induced effects are more enhanced for Si-rich films than for N-rich films. It is found that a high density and thermal stability of the as-deposited films are crucial for obtaining good bulk passivation properties