Optical emission spectroscopy on an industrial PACVD system for titanium nitride

The optical emission spectra of an industrial PACVD process for coating of hard metal and HSS tools with titanium nitride (TiN) layers by a micro-pulsed d.c. discharge were investigated. For recording of the spectra a simple and economy-priced spectrometer with an resolution of about 0.5 nm was used. Atomic lines of H, Ar and Ar⁺, and some molecular bands of H₂, N₂, N₂⁺ and NH were found. With the resolution and sensitivity available it was not possible to clearly identify atomic lines of titanium, nitrogen or chlorine and bands of titanium nitride or titanium chlorides. Because the optical emission of the discharge comes only from species made up of five elements one can expect that many of the spectral lines are highly correlated. For that reason, principal component analysis should offer a good tool to identify those parts in the optical emission spectra which distinguish the single spectra, and which would be relevant for plasma monitoring. However, factors describing species responsible for TiN formation were not found within our experimental limits.