Toward a unified reaction mechanism for chemical vapor deposition of copper

We report the reaction kinetics of copper chemical vapor deposition using H-2 reduction of Cu(hfac)(2) H(hfac) = 1,1,1,5,5,5-hexafluoro-2,4 pentanedione]. We observe a growth rate of 0.48 +/- 0.07 mg cm(-2) h(-1) (i.e., 9 nm min(-1)) at reference conditions of 300 degrees C substrate temperature, 40 Torr H-2 partial pressure, and 1.8 Torr Cu(hfac)(2). The dependence of growth rate on operating conditions can be described using a Langmuir-Kinshelwood rate expression with a numerator that is first-order in Cu(hfac)(2) and half-order in H-2, and a third-order denominator that includes adsorption terms for Cu(hfac)(2), H-2, and H(hfac). Optimized values for the surface reaction rate constant and the reactant adsorption coefficients are determined using nonlinear regression. On the basis of the optimized rate expression, we propose a minimum-parameter reaction mechanism for Cu(hfac)(2) reduction. The proposed rate limiting step is the surface reaction between adsorbed H and the first dissociated (hfac) ligand from adsorbed Cu(hfac)(2), leading to the desorption of H(hfac) product. The proposed mechanism also includes the major elementary steps needed to describe the competing disproportionation reaction. In particular, the rate constant for recombinative desorption of Cu(hfac)(2) obtained in the present work is remarkably consistent with previous kinetic results for Cu(hfac)(2-butyne) disproportionation.