The role of kinetics in the nucleation and void formation in copper films produced by chemical vapor deposition

The heterogeneous nucleation and subsequent growth of chemical vapor deposi ted copper using hexafluoroacetylacetonate-Cu(I)-trimethylvinylsilane on ph ysical vapor deposited tantalum and chemical vapor deposited titanium nitri de was studied by means of electron microscopy and atomic force microscopy. It was found that the nucleation densities are about two orders of magnitu de higher on TiN than on Ta. This leads to an increased roughness of films deposited on Ta compared to those produced on TiN. Moreover, the Cu films o n the Ta substrate show a large number of voids, whereas no such voids were observable in the Cu films deposited on top of TiN. A simplified model for the influence of gas-surface reaction and surface self-diffusion on the sh ape of the Cu grains was developed. This model, which is supported by the e xperimental data, shows that if the grain shape changes from spherical to n onspherical before coalescence with neighboring grains, voids occur. A crit ical grain size and nucleation density of about 150 nm and 5x10(13) m(-2), respectively, were calculated for the deposition conditions used in this wo rk. (C) 2000 American Institute of Physics. [S0021-8979(00)01816-8].