Laser-Induced Chemical Vapour Deposition of Silicon Carbonitride

Laser-induced Chemical Vapour Deposition of silicon carbonitride coatings and powders has been investigated using hexamethyldisilazane (HMDS) and ammonia as reactants. An industrial CW CO2-laser in parallel configuration has been used to heat up the reactant gases. HMDS dissociates in the laser beam and reactive radicals are formed which increase rapidly in molecular weight by an addition mechanism. Dense polymer-like silicon carbonitride thin films and nanosized powders are formed depending on process conditions. Powder particles are deposited on a substrate by means of a thermal gradient. The primary particle size is about 30 nm. The particles are agglomerated. Depositions are characterized with spectroscopic and chemical analysis and correlated to some important laser process parameters. The powder deposit and the thin film consist of Si-N, Si-C and Si-0 bonds according to FTIR-spectroscopy and X-ray Photo-Electron Spectroscopy. A residual amount of hydrogen is present. The material is amorphous (XRD) and has a polymer-like structure. The overall composition varies around Si0~4CO~1NO~300~2. The nitrogen content increases significantly by adding ammonia to the reactant gas flow. The high amount of oxygen is caused by hydrolysis and is a result of being exposed to air.