Analysis of Fourier transform infrared spectra and peak shifts in plasma-enhanced chemical vapor deposited fluorinated silica glasses

Abstract

The use of Fourier transform infrared spectroscopy was investigated to analyze fluorine dopant levels in plasma-enhanced chemical vapor deposited (PECVD) fluorinated silica glasses (FSG). The physical and electrical properties of FSG films are strongly dependent on the fluorine dopant concentrations in the film; however, peak overlaps and film thickness effects can reduce the reliability of fluorine dopant estimates. The relationships between peak positions, peak areas, FSG film thickness, physical properties, and fluorine dopant concentration levels were studied for a large number of PECVD FSG films deposited using a wide variety of process conditions. The position of the Si–F peak was found to be independent of dopant levels or film properties. Shifts of the Si–O peak to higher wave numbers were found to be dependent on the fluorine concentration in the film and on the film thickness. Peak deconvolution and curve fitting can be used to separate the effects of the two interfering peaks that make up the Si–O asymmetrical bond stretch peak. The peak area of the Si–F peak normalized to the peak area of the asymmetrical Si–O peak can give reliable quantitative estimates of fluorine dopant concentration when corrected for the effects of film thickness.