Silicon-nitride and silicon-oxide films were deposited by laser chemical vapor deposition (CVD) with high area selectivity. Deposition was induced by thermal reactions of source gases at laser-heated substrate surface. Area selectivity for the dielectrics varied with the composition of source gases. Using CO2 lasers, the size for nitrides deposited on quartz substrates from SiH4/NH3 mixtures was much smaller than beam sizes, and could be made as small as 15 μm
it was reduced to a few micrometers with an argon-ion laser, where the substrate was silicon. The observed thickness profile was explained by a combination of a predicted surface temperature distribution and an observed temperature dependence of deposition rates. Similar results with high area selectivity were obtained for silicon-oxide films using SiH4/N2O mixtures. However, the thickness profile of oxides was completely different for SiH4/O 2 mixtures. Silicon-nitride films could be used as microlenses with the shortest focal length being 0.6 mm. The thickness profile was modified from an as-grown bell shape to a more spherical form by wet etching
this was made possible because etch rates were not uniform in the deposits. Concave lenses can be fabricated by evaporation of quartz substrates by the CO2 laser. Laser CVD thus proved to be a useful new technique for the fabrication of microlenses.