Optical emission study of ion composition in an inductively coupled oxygen plasma

Abstract

The success of ion implantation to precisely modify substrate properties is dependent on controlling the incident ion energies to achieve the desired depth of the implanted ions. Oxygen plasmas generally contain both O+ and O2+ ions, and in plasma immersion ion implantation (PIII) of oxygen, the two will produce different concentration depth profiles due to their different energy/mass ratios. Predicting the overall profile thus requires knowledge of the relative fluxes of the two ion species. Here we investigate the feasibility of using non-invasive optical emission spectroscopy (OES) to monitor O+ and O2+ abundances in an inductively-coupled oxygen plasma. Measurements of O, O2, O+, and O2+ emission intensities were made as a function of pressure (1-30 mTorr) and power (500-2000 W). O+ emissions were very weak for all conditions examined. Emissions from both ion species peaked at the lowest pressures and at the highest power levels, but the O+/O2+ emission ratio varied little with plasma conditions.