In situ quadrupole mass spectroscopy studies of water and solvent coordination to copper(II) β-diketonate precursors: implications for the chemical vapor deposition of copper

Abstract

The incorporation of Cu(II) β-diketonates in technologically useful chemical vapor deposition (CVD) processes requires identifying the nature of the coordinated complexes that result from variations in the methods used for precursor preparation, and exploring their effects on its stability and performance. Accordingly, in situ quadrupole mass spectrometry (QMS) was employed to investigate the gas-phase evolution of various coordinated forms of Cu II(hfac) 2 and Cu II(tdf) 2, where tdf = 1,1,1,2,2,3,3,7,7,8,8,9,9,9-tetradecafluorononane-4,6-dione and hfac = hexafluoroacetylacetonate, to determine the nature of these coordinated complexes and elucidate the desorption energetics of associated additives. Careful analyses of complex fragmentation patterns during its sublimation and transport to the CVD reactor were performed under a variety of electron energies to develop an understanding of the effects of synthetic variations on precursor coordination, determine the fragmentation modes of the parent molecular ions and associated ionic fragments, and identify the mechanisms of precursor-additive interactions. In particular, it was found that Cu(hfac) 2 coordinates with water, methanol, or ethanol, but not with 2-propanol. Additionally, QMS studies of Cu(hfac) 2 seem to indicate that the use of methanol in the final recrystallization step involved in its synthesis yields a mixture of the coordinated complexes Cu II(hfac) 2 · H 2O · CH 3OH, Cu II(hfac) 2 · 2H 2O, and Cu II(hfac) 2 · 2CH 3OH. Similarly, in the case of Cu II(tdf) 2, the use of ethanol and trichloromethane appears to produce a mixture of the coordinated complexes Cu II(tdf) 2 · C 2H 5OH · H 2O, Cu II(tdf) 2 · C 2H 5OH, and Cu II(tdf) 2 · 2H 2O. By determining the temperature above which solvent molecules decoordinate from the copper precursor, reliable and reproducible processing windows were identified for the delivery of the pure precursors to the reaction zone, regardless of the synthetic technique used. It is thus shown that, by eliminating the effects of synthesis-induced variations in source coordination, copper β-diketonates can be successfully and reliably incorporated in industrially compatible CVD processes for ULSI applications without the need for costly precursor purification procedures.