Infrared (IR) external reflection spectra of phosphosilicate glass (PSG) dielectric thin films deposited on undoped silicon wafer substrates were measured at an incident angle of 15°. The IR reflection spectra of PSG thin films exhibited nonlinear or distorted spectral features arising from competing optical effects, including specular reflection and reflection‐ absorption. Quantitative analysis of the PSG IR reflection spectra was achieved by partial least squares (PLS) multivariate calibration techniques. The spectral regions used for the PLS analysis were selected to minimize the detrimental effects of competing optical effects in the IR reflection spectra. Phosphorus content and film thickness were determined with a cross‐validated standard error of prediction (SEP) of 0.10 weight percent (w/o) and 60 Å, respectively. These standard errors corresponded well to the precisions of the analytical reference methods, which were reported as 0.1 w/o for phosphorus and 30 Å for film thickness. The quantitative results achieved for these PSG thin films indicate the promise of IR external reflection spectroscopy as a method for at‐line process monitoring and quality control of dielectric thin films in the microelectronics industry.
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Franke et al. (1993) studied this question.