In situ mass spectral and IR studies of the role of auxiliary reagents in the enhancement of copper growth in the chemical vapor deposition of Cu(II) β-diketonate precursors

Abstract

In spite of significant scientific and technical advances, the incorporation of chemical vapor deposition (CVD) of copper into emerging microelectronics manufacturing technologies remains inhibited by key processing and reliability issues. The most critical of these issues at present centers on the need to achieve industrially acceptable growth rates in the planarized and void-free copper CVD filling of aggressive vias and trenches (such as 0.25 μm structures with aspect ratio 4 and above). In this respect, recent studies have shown that the use of auxiliary reagents such as water and alcohols can lead to an enhancement of copper growth rates for both Cu(I) and Cu(II) β-diketonate precursors. However, the mechanisms that control this enhancement remain unclear. Accordingly, in situ quadrupole mass spectroscopy and Fourier transform IR studies were performed in the present investigation, under real CVD processing conditions, to examine the role of selected solvents (2-propanol, ethanol, methanol and 2-butanol) in enhancing the Cu growth rate in the plasma-assisted CVD of Cu from Cu II (hfac) 2. (hfac 1,1,1,5,5,5-hexafluoroacetylacetonate). The results of these studies showed that these solvents contribute atomic hydrogen which assists in the Cu II (hfac) 2 reduction process and lead to a higher probability of interaction-precursor reduction and therefore higher copper growth rates. In addition, the ability of these solvents to release atomic hydrogen was investigated through experimental measurements of the IR absorbances of the OH stretching bond in the parent solvent and the CO stretching bond in the ketone or aldehyde byproducts of the conversion reaction. By examining the ratios of absorbances for the CO and OH bands for the various solvents, the concentrations of ketone or aldehyde resulting from the conversion of the various alcohols were calculated and used to determine that 2-propanol can release hydrogen more efficiently than ethanol or 2-butanol. This ability was attributed to the hydrogen-primary carbon (CH) bond in these solvents, which is significantly weaker in 2-propanol than in ethanol or 2-butanol. This study thus confirms the present authors' earlier findings concerning the appropriateness of 2-propanol for use as a solvent in the delivery of the solid Cu IIhfac) 2 in liquid form, since not only can it readily decouple from the precursor in the gas phase but it can also help enhance copper growth rates.