Tungsten Allylimido Complexes Cl₄(RCN)W(NC₃H₅) as Single-Source CVD Precursors for WN_xC_y Thin Films. Correlation of Precursor Fragmentation to Film Properties

A mixture of the tungsten allylimido complexes Cl₄(RCN)W(NC₃H₅) (3a, R = CH₃ and 3b, R = Ph) was tested as a single-source precursor for growth of tungsten nitride (WN_x) or carbonitride (WN_xC_y) thin films. Films deposited from 3a,b below 550 °C contained amorphous β-WN_xC_y, while those deposited at higher temperatures were polycrystalline. Film growth rates from 3a,b ranged from 5 to 10 Å/min over a temperature range of 450−650 °C, and the apparent activation energy for film growth was 0.15 eV. A plot of the E_a values for deposition from Cl₄(RCN)W(NR‘) [R‘ = Ph, ⁱPr, allyl] against the N−C imido bond strengths for the analogous amines R‘NH₂ is linear, implicating cleavage of the N−C bond as the rate-determining step in film growth. The correlation of mass spectral fragmentation patterns for Cl₄(RCN)W(NR‘) with film properties such as nitrogen content supports the significance of facile N−C bond cleavage in film growth.