Deposition of (Ti,Al)N thin films by organometallic chemical vapor deposition: thermodynarnic predictions and experimental results

Abstract

Ti 1 − xAl xN coatings were deposited by CVD using organometallic precursors: tetrakis dimethylamido titanium Ti(N(CH 3) 3) 4, hexakis dimethylamido dialuminum Al 2(N(CH 3) 2) 6 and ammonia as reactant gas. A preliminary thermodynarnic study allowed us to establish the ternary diagram Ti-Al-N at two temperatures (1173 K and 673 K). For the CVD thermodynarnic simulation, the metastable phase Ti 1 − xAl xN was first considered as the mixture of the stable compounds TiN fcc and AlN hcp. The calculations show that in our working range parameters there is codeposition of TiN and AlN (and consequently, of the metastable phase). Experiments were conducted at deposition temperature as low as 643 K. (Ti,Al)N thin films were characterized by SEM, TEM and EPMA. The deposition rate is about 15 nm/min. We obtained an Al/Ti ratio varying from 5:95 to 50:50. The ammonia flow rate has a significant effect on (Ti,Al)N composition and also on carbon and oxygen incorporation. The metastable cubic substitutional solid solution phase structure Ti 1 − xA xN has been identified, with a lattice parameter a = 4.15 ± 0.03 Å and nanometer-sized grains.