Flame Hydrolysis Deposition (FHD) is widely employed as a common process for fabricating passive integrated optical devices used in optical communications. It is used to deposit SiO2 films by the hydrolysis of SiCl4 in a high temperature H2-O2 flame. The planar waveguide circuit device fabricated by SiO2/Si became an improved replacement for fiber devices since it can be mass produced by employing semiconductor fabrication technology. The waveguide device size, price, productivity, and reproducibility are better than those of fiber devices. Since many processing parameters of FHD are involved in forming multicomponent amorphous silica films consisting of SiO2-B2O3-P2O5-GeO2, it has not been easy to predict the optical, mechanical, and thermal properties of deposited films from simple process parameters, such as the flow rate of source gases. Furthermore, the prediction of the final film composition becomes even more difficult after sintering at high temperature because of the evaporation of volatile dopants. The motivation of the present study was to clarify the quantitative relationship between simple processing parameters and chemical composition in sintered films. Quantitative compositional analysis of silica soot by Fourier Transformation Infrared spectroscopy (FTIR) and Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) was carried out under conditions of controlled dopant amount to obtain the quantitative composition. By measuring FTIR absorbance spectra, the compositional changes of B-O, Si-O and H2O(OH) in silica films were analyzed. The concentrations of these dopants were also measured by ICP-AES, which were then compared with the FTIR result. The final quantitative relationship between simple processing parameters and composition was deduced from the comparison between the two results.

Keywords: Optical device, FHD, PLC, silica film, FTIR