The Influence of Temperature and Concentration on Copper Deposition Kinetics in Supercritical Carbon Dioxide
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The Influence of Temperature and Concentration on Copper Deposition Kinetics in Supercritical Carbon Dioxide
Yinfeng Zong and James J. Watkins Department of Chemical Engineering, University of Massachusetts Amherst, Amherst, MA 01003 ABSTRACT 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 CO2. Zero order kinetics over this large concentration interval likely contributes to the exceptional step coverage obtained from Cu depositions from supercritical fluids.
INTRODUCITON Copper 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[2-4]. 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[5-9]. 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.
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MATERIALS AND METHODS Bis(2,2,7-trimethyloctane-3,5-dionato)copper [Cu(TMOD)2] was obtained from Epichem, Inc. (Allentown, PA) and used as received. The chemical structure of the compound is shown in Figure 1. H2 (Ultra High Purity grade) and CO2 (Coleman grade) were obtained from Merriam Graves Corp. (Charlestown, NH). The deposition experiments were carried out in a 170 ml, custom-designed high-pressure reactor (Figure 2). The reactor consists of opposed stainless steel flanges sealed with a
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