The kinetics and reaction mechanism for copper deposition by the hydrogen-assisted reduction of bis(2,2,7-trimethyloctane-3,5-dionato)copper(II), [Cu(tmod)2], in supercritical carbon dioxide was studied using a differential cold wall reactor. At substrate temperatures between 220 and 270 °C, the measured film growth rate ranged between 5 and 35 nm/min. The overall apparent activation energy was 51.9 kJ/mol. Film growth rate exhibited zero-order dependence on the precursor at precursor concentrations between 0.02 and 0.5 wt % Cu (tmod)2 in CO2 and a zero-order dependence on hydrogen at hydrogen concentrations greater than 0.06 wt % in CO2. Zero-order precursor dependence over large concentration ranges promotes exceptional step coverage. At lower concentrations of either reagent a 1/2-order dependence was observed. Film growth rate was negative order with respect to excess quantities of the hydrogenated ligand byproduct, (tmod)H, and film growth could be suppressed completely at (tmod)H concentrations above 1 wt %. With use of the results of the experiments, a heterogeneous reaction mechanism is proposed. Protonation of the adsorbed ligand (tmod) was found to be the rate-determining step. A Langmuir−Hinshelwood rate expression was used to correlate the data with good agreement.

The adhesion of copper films to adjacent device layers including TiN, Ta, and TaN diffusion barriers is a crucial reliability issue for integrated circuits. We report that ultrathin layers of poly(acrylic acid) (PAA) prepared on barrier surfaces or on the native oxide of Si wafers dramatically increase the interfacial adhesion of Cu films deposited by the H2 assisted reduction of bis(2,2,7-trimethyloctane-3,5-dionato)copper in supercritical carbon dioxide. Similar improvements were achieved on Si wafers using a simple vapor phase exposure of the substrate to acrylic acid prior to metallization. The deposited films and the substrate/Cu interfaces were analyzed by X-ray photoelectron spectroscopy (XPS), electron microscopy, atomic force microscopy, and variable-angle spectroscopic ellipsometry. No trace of the adhesion layer was detected at the interface, indicating it was sacrificial at the deposition conditions used. Moreover, the presence and subsequent decomposition of the PAA layer during deposition substantially reduced or eliminated metal oxides at the substrate interface. For depositions on PAA-treated Si wafers, copper was present primarily as Cu0 at the interface and Si was present only as Si0. On PAA-treated Ta substrates, XPS analysis indicated Ta was present primarily as Ta0 at the metallized interface whereas Ta2O5 dominated the interface of samples prepared without the adhesion layers. The technique can be extended to patterned substrates using adsorption of acrylic acid or thermal/UV polymerization of acrylic acid.

The kinetics of copper deposition by the hydrogen-assisted reduction of bis(2,2,7trimethyloctane-3,5-dionato)copper in supercritical carbon dioxide was studied as a function of temperature and precursor concentration. The growth rate was found to be as high as 31.5 nm/min. Experiments between 220 ºC and 270 ºC indicated an apparent activation energy of 51.9 kJ/mol. The deposition kinetics were zero order with respect to precursor at 250 ºC and 134 bar and precursor concentrations between 0.016 and 0.38 wt.% in CO 2 . Zero order kinetics over this large concentration interval likely contributes to the exceptional step coverage obtained from Cu depositions from supercritical fluids. INTRODUCITONCopper is the material of choice for interconnect structures in advanced integrated circuits due to its low electrical resistance and superior electromigration resistance. Recently, we demonstrated that high purity copper films could be deposited with exceptional step coverage within high aspect ratio features in a single step by supercritical fluid deposition (SFD)[1]. The advantages of SFD are related to the physicochemical properties of the deposition medium. Supercritical fluids (SCFs) such as carbon dioxide exhibit low viscosity, high diffusivity, zero surface tension and pressure-dependent densities that can equal or exceed those of liquid solvents. In fact, many organometallic compounds, including a wide range of CVD precursors, exhibit significant solubilities in SCFs [2][3][4]. The solubility of metal precursors in SCFs obviates precursor volatility constraints often encountered in conventional vapor phase deposition and eliminates mass transport limitations to uniform step coverage. Accordingly, SFD is essentially a hybrid technique that combines the advantages of solution-based chemistry with exceptional transport properties typical of the gas phase. Moreover, the technique can be extended to a broad range of metals and metal alloys [5][6][7][8][9].Since SFD is a new technique, little information is available regarding deposition kinetics or mechanisms. Here we report dependence of film growth rate during depositions by the hydrogen assisted reduction of bis(2,2,7-trimethyloctane-3,5-dionato)copper, [Cu(TMOD) 2 ] in carbon dioxide as a function of temperature and precursor concentration.