FTIR STUDIES OF THE ADSORPTION DESORPTION BEHAVIOR OF COPPER CHEMICAL-VAPOR-DEPOSITION PRECURSORS ON SILICA .1. (1,1,1,5,5,5-HEXAFLUOROACETYLACETONATO)COPPER(II)/

The reactions of Cu(hfac)(2) (where hfac = 1,1,1,5,5,5-hexafluoroacety lacetonate), a precursor for the chemical vapor deposition (CVD) of co pper, and hfacH with high-surface-area SiO2 have been investigated by transmission FTIR spectroscopy. The SiO2 surface was prepared in three different ways to produce different combinations of reactive surface functionalities. These were (I) a highly dehydroxylated surface which possessed isolated surface hydroxyl groups and four-membered siloxane rings, (II) a dehydroxylated surface which possessed both isolated and hydrogen-bonded surface hydroxyl groups, and (III) an as-loaded surfa ce, containing a higher concentration of isolated and hydrogen-bonded surface hydroxyl groups. The reagents, Cu(hfac)(2) and hfacH, were eac h dosed at low temperature (-130 degrees C) and higher temperature (25 degrees C), and their temperature-dependent behavior was investigated . The species hfacH molecularly adsorbed on surfaces I-III at -130 deg rees C and molecularly desorbed on heating to -50 degrees C on surface s II or III. However, hfacH reacted with surface I on heating to -75 d egrees C. In contrast, when surfaces II and III were treated with hfac H at 25 degrees C, no interaction was observed while reaction with sur face I was observed. Surfaces I-III when treated with Cu(hfac)(2) at - 130 degrees C gave rise to IR spectra similar to the gas-phase spectru m for this compound. On heating, Cu(hfac)(2) may aggregate on all thre e surfaces. On heating to higher temperatures (25 degrees C), Cu(hfac) (2) hydrogen-bonded with the isolated surface hydroxyl groups and reac ted with the hydrogen-bonded surface hydroxyl groups and the strained siloxane bridges on all three surfaces, exhibiting similar adsorption/ desorption characteristics (such as uptake and temperature-dependent s pectra). The changes in FTIR data observed on heating are believed to be due to interaction between the adsorbate, derived from Cu(hfac)(2) and surface oxo groups (from surface hydroxyl groups or siloxane rings ). These results are consistent with observed decomposition of Cu(hfac )(2) on SiO2 during CVD of copper. Furthermore, these data suggest tha t selective CVD onto metals in the presence of SiO2 cannot be obtained simply by changing the relative concentration of the reactive sites o n these silica surfaces because Cu(hfac)(2) reacts with both the hydro gen-bonded surface hydroxyl groups and the strained siloxane rings. It is likely that most SiO2 surfaces contain at least one of these react ive surface functional groups.