Development of an in-situ thickness measurement technique for film growth by APCVD

Abstract
The aim is to measure in-situ the growth rate and final thickness of thin films of SnO₂ and SnO₂:F (by oxidation of (CH₃)₂SnCl₂) deposited on a glass substrate, using an Atmospheric Pressure Chemical Vapour Deposition (APCVD) lab-scale reactor. The measuring system uses an optical technique based on thin-film interference (Fresnel equations and the matrix analysis of them). At the same time, an FTIR spectrophotometer has been installed, analysing the composition of the gas phase species in the reaction zone (in-situ). Changes in the intensity of the reflectivity at each wavelength were recorded in the visible range, during the growth of the film. Assuming that the film is transparent in the visible range, the optical film thickness can be monitored for each wavelength as the film grows. Hence the film thickness can be calculated assuming the refractive index is known, and does not vary during deposition. A program was developed that reads the spectra vs. time, and translates the data into thickness vs. time for each wavelength. The final value is the median of all wavelengths. Correlations between the different species involved in the gas phase, the resistivity, emissivity and the growth parameters have been investigated.