Quantitative Analysis of Thin Films by dc Arc Optical Emission Spectroscopy

Abstract

dc arc optical emission spectroscopy was investigated as a quantitative method for measuring compositions of thin films commonly used in fabricating semiconductor devices. Thin films studied were nickel-chromium, phosphorus-silicon dioxide, and silicon-aluminum. Film samples were obtained by direct deposition onto ordinary graphite electrodes mounted in vacuum deposition chambers. Standards for each film were prepared by evaporating series of synthetic solutions approximating film compositions onto electrode tips, or by preparing appropriately weighed mixed powder standards. Calibration curves were established by burning multiple sets of these standard electrodes in a 15-A dc arc and plotting the intensity ratios for selected atomic lines of the analyte elements. Correlation of emission results with atomic absorption, electron microprobe, and gravimetric analysis showed absolute agreement to within ±3% for nickel-chromium, ± 0.3% for phosphorus-silicon dioxide, and ±0.2% for silicon-aluminum. Maximum relative percent error was 5, 10, and 12.5%, respectively. This technique has proved to be a rapid convenient process control tool in the manufacture of microelectronic devices.