UC Riverside

Acetamidinate precursors have shown great promise for atomic layer deposition (ALD) applications, but potentially deposit impurities that may degrade the quality of the films and hinder their practical applications. To help solve this problem, the uptake, the surface chemistry, and the effect of hydrogen coadsorption of copper(I)( N,N'-di-sec-butylacetamidinate) and N,N'-di-sec-butylacetamidine on different metals were characterized 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). The main objective of this research project has been to develop a better molecular-level understanding of the chemical reactions associated with ALD of copper metal films, to design and optimize the film deposition processes to be used in the microelectronics industry.

In our initial studies on a Ni (110) single crystal, a temperature window between approximately 350 and 450 K was identified for the ALD of Cu using the Cu acetamidinate precursor: lower temperatures are insufficient for activation of the dissociative adsorption, and higher temperatures lead to continuous decomposition beyond Cu monolayer saturation. Approximately three dosing cycles are required to reach full Cu monolayer saturation, the equivalent of a film growth rate of ~0.75 Å/cycle in ALD. Preadsorption of hydrogen on the surface does not modify any of this behavior because of its rapid desorption at temperatures below 350 K once the gas-phase _H2is removed. The surface chemistry of the Cu precursor is complex, leading to the desorption of not only hydrogen but also 2-butene and small amdine (N-sec-butylacetamidine, ^sBut-NH-C(CH₃)=NH); it seems that the amidine ligands decompose via beta-hydride elimination from one of their terminal sec-butyl moieties. The ligands of the copper acetamidinate precursors further decompose on Ni (110) surfaces at higher temperature, leading to the desorption of more hydrogen and leaving some carbon and nitrogen on the surface. The free hydrogenated amidine ligand is less reactive, and no N-sec-butylacetamidine is produced by its thermal activation, but the remaining chemistry follows similar temperature transitions. Similar results were also observed on a Cu (110) surface.

Other copper precursors, Cu-KI5 (copper (I) (N(1(dimethylvinylsiloxy)-1- methylethano)-2-imino-4-pentanoate)) and Cu(acac) ₂ (copper(II) acetylacetonate) in particular, were tested as well. Details of the results from this work are discussed.