Trimethylaluminum and Oxygen Atomic Layer Deposition on Hydroxyl-Free Cu(111)
- School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States
- Institute for Physical Chemistry, University of Innsbruck, A-6020 Innsbruck, Austria, Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, United States
- Institute for Physical Chemistry, University of Innsbruck, A-6020 Innsbruck, Austria
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, United States, Department of Physics, Purdue University, West Lafayette, Indiana 47907, United States
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, United States
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 Cu2S 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 Cu2O/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 Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu1+ to metallic copper (Cuo) and the formation of a copper aluminate, most likely CuAlO2. The reaction is limited by the amount of surface oxygen. After the first TMA half-cycle on Cu2O/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 Cu2O/Cu(111). High-resolution electron energy loss spectroscopy (HREELS) was used to distinguish between tetrahedrally (Altet) and octahedrally (Aloct) coordinated Al3+ in surface adlayers. TMA dosing produced an aluminum oxide film, which contained more octahedrally coordinated Al3+ (Altet/Aloct HREELS peak area ratio ≈ 0.3) than did dosing O2 (Altet/Aloct HREELS peak area ratio ≈ 0.5). After the first ALD cycle, TMA reacted with both Cu2O 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 Al2O3. O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K. The growth rate was approximately 3–4 Å/cycle for TMA+O2 ALD (O2 half-cycles at 623 K). No preferential growth of Al2O3 on the steps of Cu(111) was observed. According to STM, Al2O3 grows homogeneously on Cu(111) terraces.
- Research Organization:
- Energy Frontier Research Centers (EFRC) (United States). Institute for Atom-efficient Chemical Transformations (IACT)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- AC02-06CH11357
- OSTI ID:
- 1201001
- Alternate ID(s):
- OSTI ID: 1370209
- Journal Information:
- ACS Applied Materials and Interfaces, Journal Name: ACS Applied Materials and Interfaces Vol. 7 Journal Issue: 30; ISSN 1944-8244
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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Related Subjects
Cu(111)
trimethylaluminum (TMA)
scanning tunneling microscopy (STM)
X-ray photoelectron spectroscopy (XPS)
high-resolution electron energy loss spectroscopy (HREELS)
atomic layer deposition (ALD)
surface science
single crystal
oxides
copper
oxygen