Carlo Cavallotti

Modeling Plasma‐Assisted Deposition of Diamond‐Like Carbon Films

A model of diamond-like carbon growth in low-pressure plasma reactors using methane as the precursor is presented. The model considers a simplified description of transport phenomena, assuming a well-mixed gas phase and a detailed kinetic mechanism consisting of gas and surface reactions. Rate constants taken om the literature were combined with others calculated using thermochemical methods. The model predicts the film growth rate and its hydrogen content as a function of substrate temperature, pressure, feed flow rate, and applied electric power. Furthermore the catalytic effect of ions on the growing surface is explained, and methyl is identified as the most important precursor to deposition. The results of the simulations were compared with three different plasma reactors described in the literature and characterized by different working conditions: an electron cyclotron resonance reactor and two radio-frequency reactors (with 13.56 and 2.0 MHz discharge frequencies).

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

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)Lu2006→u2006CuI(β-diketonate)u2006+u2006L. 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 1.5u2006×u20061014exp(−13.5/T), which is consistent with the computed rate constant.

A multiscale study of the selective MOVPE of AlxGa1-xAs in the presence of HCl

The selective deposition of Al x Ga 1-x As films on(1 0 0)substrates patterned with a SiN x mask is simulated at multiple length and time scales. First, gas-phase and surface kinetic schemes are developed to describe GaAs, AlAs and Al x Ga 1-x As deposition from TMGa, TMAl and AsH 3 in the presence of HCl. Unknown reaction kinetic constants are determined by quantum chemistry calculations of energy and structure followed by application of transition state theory. These estimated kinetic parameters and experimental values are then incorporated in finite element computations of flow, temperature, and species concentration fields in different MOVPE reactor configurations. The predicted local growth rates and gas-phase compositions are in good agreement with experimental data. The selective deposition on patterned substrates with different mask/feature ratios is also investigated with a feature scale model, coupled to the reactor scale model by imposing continuity of gas-phase concentrations and fluxes at the boundaries. The experimentally observed growth rate enhancement is reproduced quantitatively.