A mass-spectroscopical study of the decomposition of Ti(NMe2)4 in a mixed Ar–H2–N2 pulsed d.c. plasma

The favourable gas-phase conditions for deposition of TiN have been determined by a mass-spectroscopic investigation of the gaseous species in an ambient of tetrakis(dimethyl-amino)titanium (TDMAT) molecules during pulsed d.c. plasma-enhanced deposition processes. The gas-phase composition was varied, at a pressure of 0.4 Torr, a temperature of 350 °C and a bias voltage of 500 V, based on an Ar, H₂, N₂ ternary diagram. The results reveal that hydrogen plays a key role in the cleavage of –NMe₂ from the central Ti atom. The addition of N₂ to the hydrogen plasma opens up the possibility for transamination reactions by NH_x formation (1<x<3), known by thermal CVD using NH₃. This addition also leads to powder formation, which seems to reach a maximum within a 100% N₂ plasma. In a nitrogen plasma, only relatively small amounts of gaseous species, like HCN, NH₂CN, and CH₃CN, are detected, which indicates that residual hydrocarbon fragments of TDMAT must be incorporated into the powder and coating. Even small amounts of Ar addition to a hydrogen plasma convert TDMAT to powder particles, which is the opposite of the densification purpose of Ar bombarment. No gaseous species, apart from small amounts of HCN, are detected, suggesting hydrocarbon-containing coatings. If Ar:H₂:N₂=1:1:1, no specific mechanism is dominant under the conditions used here. Decreasing the deposition temperature and pressure and increasing the bias voltage seem to favour the cleavage of –NMe₂ ligands.