Dissociation reactions of CuI(hfac)L compounds relevant to the chemical vapor deposition of copper

Abstract

Density functional theory (DFT) calculations have been performed for ligand copper bond energies of typical copper β-diketonate compounds used in chemical vapor deposition (CVD) of copper films. The molecules have the general formula CuI(hfac)L, where hfac is hexafluoroacetylacetonate, and L represents vinyltrimethylsilane (VTMS), trimethylphosphine (PMe3), 2-butyne (2-butyne), or 1,5-cyclooctadiene (COD). The DFT method is used with the three-parameter Becke exchange and the Lee–Yang–Parr correlation functionals (B3LYP) with different basis sets. The optimized structures correspond to the crystal structures determined using crystal X-ray diffraction. Two different structures, CuI(hfac)(η2-COD) and CuI(hfac)(η4-COD), are determined for the CuI(hfac)(COD) complex, the latter being more stable by ∼3 kcal mol−1. The strength of the ligand–copper interaction is studied for the reaction CuI(β-diketonate)L → CuI(β-diketonate) + L. Bond energies of 32.1, 35.6, 33.6 and 38.4 kcal mol−1 are calculated for typical Cu CVD precursors, CuI(hfac)(butyne), CuI(hfac)(COD), CuI(hfac)(VTMS) and CuI(hfac)(PMe3), respectively. The similarity between these bond energies and reported experimental activation energies for CVD suggests that the dissociation of the ligand L could be the rate determining step for the film growth under certain conditions. The rate parameters for the dissociation reaction of CuI(hfac)(VTMS) are evaluated based upon the results of the DFT calculations. A simple reaction mechanism for Cu CVD is proposed and combined with transport phenomena simulations of two reported reactors configurations. Good agreement with experimental observations is obtained with a CuI(hfac)(VTMS) dissociation rate constant of 1.5 × 1014exp(−13.5/T), which is consistent with the computed rate constant.