Selective area deposition of siliconhyphen;nitride and siliconhyphen;oxide by laser chemical vapor deposition and fabrication of microlenses

摘要

Siliconhyphen;nitride and siliconhyphen;oxide films were deposited by laser chemical vapor deposition (CVD) with high area selectivity. Deposition was induced by thermal reactions of source gases at laserhyphen;heated substrate surface. Area selectivity for the dielectrics varied with the composition of source gases. Using CO2lasers, the size for nitrides deposited on quartz substrates from SiH4/NH3mixtures was much smaller than beam sizes, and could be made as small as 15 mgr;m; it was reduced to a few micrometers with an argonhyphen;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 siliconhyphen;oxide films using SiH4/N2O mixtures. However, the thickness profile of oxides was completely different for SiH4/O2mixtures. Siliconhyphen;nitride films could be used as microlenses with the shortest focal length being 0.6 mm. The thickness profile was modified from an ashyphen;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 CO2laser. Laser CVD thus proved to be a useful new technique for the fabrication of microlenses.