Uptake of Copper Acetamidinate ALD Precursors on Nickel Surfaces

Abstract

The adsorption and thermal activation of copper(I)-N,N 0 -di-sec-butylacetamidinate on a Ni(110) single-crystal surface were characterized in connection with the use of that compound as a precursor for the growth of copper films via atomic layer deposition (ALD) processes. Studies were carried out under ultrahigh vacuum (UHV) conditions by using a combination of X-ray photoelectron spectroscopy (XPS), low-energy ion scattering (LEIS), and temperature-programmed desorption (TPD). A temperature window between approximately 350 and 450 K was identified for the clean deposition of the precursor on the surface: lower temperatures are insufficient for activation of the dissociative adsorption, and higher temperatures lead to continuous decomposition beyond Cu monolayer saturation. Approximately three ALD-like cycles are required to reach full Cu monolayer saturation, the equivalent of a film growth rate of approximately 0.75 A ˚/cycle. Preadsorption of hydrogen on the surface does not modify any of this behavior because of its rapid desorption at temperatures above 350 K once the gas-phase H 2 is removed. A discussion is provided on how hydrogen pressures above the mbar range are required to maintain significant steady-state coverages of hydrogen on the surface. Copper precursors leading to relatively stable organic surface intermediates are required in ALD because their clean removal can only happen in the second half-cycle of processes that rely on hydrogenation reactions.

Surface Chemistry of Copper(I) Acetamidinates in Connection with Atomic Layer Deposition (ALD) Processes

“…Finally, our initial work on the deposition of the same copper precursor on a Ni(110) single-crystal surface identified a temperature window between approximately 350 and 450 K for the deposition of the precursor on the surface: lower temperatures are insufficient for activation of the dissociative adsorption, and higher temperatures lead to continuous decomposition beyond Cu monolayer saturation. 15 That study also suggested more complex surface chemistry than on SiO 2 . Here, we provide further details on the thermal conversions involved.…”

“…15 Less clear is what may happen if the temperature used in ALD is high enough to promote the second set of reactions reported here. As indicated in Figure 4, the copper atoms start to be reduced on the surface at temperatures slightly above 300 K, a change that is quite extensive by In view of this emphasis of the need to use a hydrogenation agent in the second half of the ALD cycle, it is particularly important to identify the thermal chemistry of the ALD precursor and to evaluate the feasibility of being able to remove any possible intermediates that may form on the Q. Ma, R. G. Gordon, and F. Zaera, Surface Chemistry of Copper(I) Amidinates in...…”

“…-22 -copper(I)-N,N'-di-sec-butylacetamidinate at 350 K, a temperature above that require for N-secbutylacetamidine desorption, than at 300 K. 15 It should be noted that self-limiting uptake still occurs at 350 K, and that temperatures above ~400 K are still needed for the continuous deposition of copper by using the copper amidinate alone. 15 Less clear is what may happen if the temperature used in ALD is high enough to promote the second set of reactions reported here.…”

“…We have already reported that by 480 K the deposition of copper films using the copper amidinate precursor along is no longer self-limiting, and continues indefinitely with increasing exposures. 15 That is a definitive threshold temperature to avoid the deposition of carbon impurities.…”

“…It should be said that previous studies in our laboratory have indicated that the use of temperatures above 450 K lead to the continuous conversion of the copper acetamidinate on the surface, which means that deposition would not be strictly via an ALD process above that temperature. 15 In any case, the use of temperatures above 500 K would almost surely lead to the deposition of some carbon in the growing films.…”