Optical emission spectroscopy of gallium phosphide plasma-enhanced atomic layer deposition

Abstract

The capability of optical emission spectroscopy for in situ study and control of plasma-enhanced atomic-layer deposition (PE-ALD) of gallium phosphide from phosphine and trimethylgallium carried by hydrogen was explored. The gas composition changing during the PE-ALD process was monitored by in situ measurements of optical emission intensity for phosphine and hydrogen lines. For PE-ALD process where phosphorus and gallium deposition steps are separated in time a negative influence of excess phosphorus accumulation on the chamber walls was observed. Indeed, the phosphorus deposited on the walls during PH3 decomposition step is etched by hydrogen plasma during the next trimethylgallium decomposition step leading to uncontrollable and unwanted conventional plasma-enhanced chemical vapor deposition. To reduce this effect, it has been proposed to introduce a step of hydrogen plasma etching, which allows one to etch excess phosphorus before the beginning of gallium deposition step and achieve atomic-layer deposition growth mode.