Incorporation of nitrogen into amorphous silica using a direct plasma reaction technique

Abstract

A direct plasma reaction (DPR) technique has been used to surface-nitride amorphous silica. The nitride treatment has been performed over a temperature range of 750 to 1300°C and a low-pressure range of 40 to 268 Pa using a 90:10 nitrogen-hydrogen gas mixture. The plasma is generated by an inductively coupled rf power supply and is used as both a thermal and chemical source. The effects of various process parameters such as surface temperature, gas pressure and treatment time on nitrogen content and weight loss have been studied. Nitrogen is incorporated in both molecular and structural form. A very high nitridation rate has been observed. A good agreement among the nitrogen content, weight loss and microstructures is established. Electron and X-ray diffraction studies showed the treated layers as amorphous. Microblisters form at higher temperatures and this may limit the treatment temperatures to below 900°C. The effect of post-treatment annealing has been investigated. Unlike the case of thermal nitridation, pure nitrogen has also been shown to be a good candidate for surface modification.