Chromium (IV) diethylamide Cr(NEt2)4
Chromium tetrakis(diethylamide) Cr(NEt2)4 has been applied as single-source precursor for the growth of amorphous chromium carbonitride coatings at 300-520°C by low-pressure MOCVD. Nitrogen incorporation was low (3–8 at%), in agreement with thermochemical calculations. Films grown at 300°C were contaminated with organic species due to incomplete ligand elimination, according to XPS, post-annealing data and resistivity measurements. Orthorhombic ternary chromium carbonitride phase formed upon annealing at 600°C of the films grown at higher temperatures. Chromium carbonitride films exhibit a high hardness; their resistivity decreases by increasing the growth temperature The pyrolysis mechanism of Cr(NEt2)4 was studied; the quasi-equimolar HNEt2/EtN=CHMe ratio (according to quantitative 1H and 13C NMR) suggest that most of the NEt2 ligands are removed by stepwise mechanism, similar to other transition metals diethylamides used as single-source precursors in MOCVD. [959,960]
The thermodynamic analysis of Cr(NEt2)4 pyrolysis was perfromed, with the goal to predict optimum growth conditions for the hexagonal hard phase Cr2N. The calculations were based on the minimization of the Gibbs energy in the Cr-N-C-H system (input gas mixture was Cr(NEt2)4/ H2/ He); the analysis assumed that the process is controlled by the thermodynamic equilibrium and that other phenomena like kinetics and diffusion are neglected.
The calculation results assumed that the hexagonal Cr2N phase deposited by CVD at high temperature is not obtained in the explored conditions (527°C) using this single source precursor; the only chromium nitride obtained was the cubic phase CrN (only under atmospheric pressure, using a large excess of H2). The reduced pressure facilitates both the formation of chromium carbide (or carbonitride) and the contamination by free carbon. [[i]]
[i] F. Maury, J. Phys. 1V, Colloque C5, supplernent au Journal de Physique 11, Volume 5, juin 1995
Chromium (III) diisopropylamide Cr(NiPr2)3
Chromium tris(diisopropylamide) Cr(NiPr2)3 has been synthesized by methathesis reaction between chromium (III) chloride and lithium diisopropylamide:
CrCl3 + 3 LiNiPr2 → Cr(NiPr2)3 + 3 LiCl
Cr(NiPr2)3 was reported to be the best source for low-temperature (~300°C) CVD growth of chromium carbide thin films. Mirror-bright very smooth amorphous films with Cr:C ratio of 1.4:1 were obtained at 330 °C. Amorphous films were much harder and had higher resistivity than more crystallised layers obtained at higher temperatures. Annealing at 600 °C/ 10-3 Torr for 18 h resulted in layers wth compostion Cr3C2. [958]
Cr(NiPr2)3 was also reported to produce amorphous chromium carbonitride layers by CVD process under low pressure (40 Pa, ~0.3 Torr) [840]