FTIR STUDIES OF THE ADSORPTION/DESORPTION BEHAVIOR OF CU CHEMICAL-VAPOR-DEPOSITION PRECURSORS ON SILICA .3. REEXAMINATION OF (1,1,1,5,5,5-HEXAFLUOROACETYLACETONATO)(VINYLTRIMETHYLSILANE)COPPER(I), (HFAC)CU(VTMS)

The reaction of (hfac)Cu(VTMS) with SiO2 surfaces with varying surface concentrations of isolated and hydrogen-bonded surface hydroxyl groups and four-membered SiO rings has been investigated. The adsorbed (hfac)Cu(VTMS) (where hfac=1,1,1,5,5,5-hexafluoroacetylacetonate and VTMS=vinyltrimethylsilane) reacted with the hydrogen-bonded surface hydroxyl groups and the strained siloxane sites and interacted with the isolated surface hydroxyl groups. The VTMS ligand was completely liberated from the adsorbed compound between 125 and 175 degrees C depending on the relative ratios of the reactive surface sites. Because all SiO2 surfaces have some combination of these reactive sites, dissociation of (hfac)Cu(VTMS) to give ''(hfac)Cu'' and VTMS is always expected. Selective chemical Vapor deposition (CVD) relies on the slow nucleation of Cu on SiO2 which involves a number of steps in series including adsorption, dissociation, and reaction to give Cu atoms and physical nucleation to give stable nuclei. This suggests that selective CVD must rely on slow adsorption, dissociation, reaction, or physical nucleation to limit the formation of Cu clusters on the nongrowth, SiO2 surface. Results from this work and the literature suggest that most of these steps are slower on SiO2 than on Cu surfaces. However the rates of these steps can be increased sufficiently by increasing temperature and precursor partial pressure to result in loss of selectivity.