Paper AP+2D+EM+PS+TF-MoM9
Area-selective Deposition Achieved in a Continuous Process using Competitive Adsorption

Monday, October 21, 2019, 11:00 am, Room A214

A significant challenge for single-nm fabrication technologies is the development of area selective deposition (ASD) processes, particularly for device structures with exposed metallic and dielectric surfaces on patterned, often three dimensional, substrates. A number of techniques have been proposed and examined for ASD processes, particularly with respect to ALD, and these include the use of “permanent” blocking layers in the form of SAMs, and repetitive deposition/etch cycles. Some success has been reported with these techniques, but they possess potential drawbacks. An ideal ASD process should be fast, preferably vapor phase, and leave no residue on the non-growth surface. One technique that can possibly provide this is the use of competitive adsorption to induce area selective deposition, where a co-adsorbate is chosen that will bind much more strongly to one surface vs. another. A significant challenge concerning this approach is avoiding direct reactions between the co-adsorbate and the thin film precursor in the case of ALD, and also the co-reactant in the case of CVD. We are coupling quantum mechanical calculations of co-adsorbate/thin-film precursor/substrate interactions with experiments using our coupled micro-reactor/UHV surface analysis system. We have examined the effect of a class of unsaturated hydrocarbons as co-adsorbates on the CVD growth of ZrO₂ thin films using a Zr amido-coordination complex as the thin film precursor and O₂ as the co-reactant. The substrates were SiO₂ and Cu, and we examined the effects of both temperature, T_s = 120-240 °C, and the partial pressure of the co-adsorbate hydrocarbon. DFT calculations predict that the binding energies of these hydrocarbons are at least a factor of two larger on Cu vs. those on SiO₂. For CVD growth of ZrO₂ thin films as thick as 22 nm (growth rates of ~ 1 nm-s^-1), we find that the co-introduction of the hydrocarbon results in linear growth with time on a SiO₂ substrate, with no apparent incubation time, while essentially no growth is observed on Cu. In situ, post-deposition analysis with XPS reveals ZrO₂ thin films on SiO₂, and only adventitious carbon and less than a monolayer of Zr on the Cu surface. Consistent with a model based on competitive adsorption, we find that selectivity is eventually lost at sufficiently high substrate temperatures or sufficiently low partial pressures of the hydrocarbon co-adsorbate. Finally, we will report on the CVD growth on patterned Cu/SiO₂ substrates where we observe deposition only on those areas covered by SiO₂. We will conclude with a discussion of the promise and challenges of this approach for ASD concerning both ALD and CVD processes.