Trimethylaluminum and Oxygen Atomic Layer Deposition on Hydroxyl-Free Cu(111)

[Image: see text] Atomic layer deposition (ALD) of alumina using trimethylaluminum (TMA) has technological importance in microelectronics. This process has demonstrated a high potential in applications of protective coatings on Cu surfaces for control of diffusion of Cu in Cu(2)S films in photovoltaic devices and sintering of Cu-based nanoparticles in liquid phase hydrogenation reactions. With this motivation in mind, the reaction between TMA and oxygen was investigated on Cu(111) and Cu(2)O/Cu(111) surfaces. TMA did not adsorb on the Cu(111) surface, a result consistent with density functional theory (DFT) calculations predicting that TMA adsorption and decomposition are thermodynamically unfavorable on pure Cu(111). On the other hand, TMA readily adsorbed on the Cu(2)O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO(2). The reaction is limited by the amount of surface oxygen. After the first TMA half-cycle on Cu(2)O/Cu(111), two-dimensional (2D) islands of the aluminate were observed on the surface by scanning tunneling microscopy (STM). According to DFT calculations, TMA decomposed completely on Cu(2)O/Cu(111). High-resolution electron energy loss spectroscopy (HREELS) was used to distinguish between tetrahedrally (Al(tet)) and octahedrally (Al(oct)) coordinated Al(3+) in surface adlayers. TMA dosing produced an aluminum oxide film, which contained more octahedrally coordinated Al(3+) (Al(tet)/Al(oct) HREELS peak area ratio ≈ 0.3) than did dosing O(2) (Al(tet)/Al(oct) HREELS peak area ratio ≈ 0.5). After the first ALD cycle, TMA reacted with both Cu(2)O and aluminum oxide surfaces in the absence of hydroxyl groups until film closure by the fourth ALD cycle. Then, TMA continued to react with surface Al–O, forming stoichiometric Al(2)O(3). O(2) half-cycles at 623 K were more effective for carbon removal than O(2) half-cycles at 473 K or water half-cycles at 623 K. The growth rate was approximately 3–4 Å/cycle for TMA+O(2) ALD (O(2) half-cycles at 623 K). No preferential growth of Al(2)O(3) on the steps of Cu(111) was observed. According to STM, Al(2)O(3) grows homogeneously on Cu(111) terraces.