Optical characterisation of silicon nitride thin films grown by novel remote plasma sputter deposition

Abstract

Silicon nitride (SiNx) thin films have been deposited by a new remote plasma deposition system HiTUS (High Target Utilisation Sputtering). The remote plasma geometry allows, pseudo separation of plasma/target-bias parameters, lower ion bombardment, and effectively eliminates poisoning, making it an attractive option for stable reactive sputtering of important electronic and photovoltaic films including silicon nitride. Transmission and absorbance measurements on glass were performed in order to evaluate the absorbance of the silicon nitride thin layer. The SiNx is produced by reactive sputtering from a silicon target in an Ar/N2 atmosphere, negating the use of silane gas in difference to the more commonly used PECVD method. A deposition rates up to 0.7 nm/s have been obtained. Control of refractive index from 1.9 to 2.3 was achieved by varying the RF target bias, meeting the requirements for silicon passivation in PV applications, with a growth rate independent of refractive index across a wide range. The carrier life time over a range of specified minority carrier densities was measured using a contactless inductively coupled photoconductance tester for 50 ohm cm 〈100〉 oriented silicon wafers coated with different types of SiNx. We found that the passivation action of the silicon nitride increased the carrier lifetime over one order of magnitude.