| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF-MoM |
| Session: | ALD Precursors and Surface Reactions |
| Presenter: | Adrie Mackus, Eindhoven University of Technology, Netherlands |
| Authors: | A.J. Mackus, Eindhoven University of Technology, Netherlands C. MacIsaac, Stanford University V. Vandalon, Eindhoven University of Technology, Netherlands W.M.M. Kessels, Eindhoven University of Technology, Netherlands S.F. Bent, Stanford University |
| Correspondent: | Click to Email |
Atomic layer deposition (ALD) has become an important technique for the deposition of ultrathin and conformal films for a wide variety of applications in nanoelectronics and photovoltaics. Although the reactions mechanisms of several metal oxide ALD processes have been investigated in detail, there are still some open questions regarding the understanding of their growth characteristics. ALD typically relies on two fundamental surface reactions: (i) the adsorption of a precursor molecule at specific surface groups (e.g. hydroxyl groups) in the first half-reaction, (ii) the elimination of the precursor ligands (while new functional surface groups are formed) in the second half-reactions. In this presentation, it will be shown that the elimination of precursor ligands is often not complete, which has broad implications for the growth characteristics of binary and ternary metal oxide ALD processes.
Experimental evidence for the presence of persisting ligands after the H2O half-reaction at low temperatures (< 200 ºC) will be presented for the binary ALD processes of Al2O3 from TMA, SnO2 from TDMASn, and ZnO from DEZ. The data for Al2O3 was measured using broadband sum-frequency generation (BB-SFG) spectroscopy,1 while the SnO2 and ZnO processes were studied using Fourier transform infrared (FTIR) spectroscopy. The incomplete removal of precursor ligands will be explained based on previously reported density functional theory (DFT) studies on cooperative effects during the H2O half-reaction.2 In addition, we found that the elimination of precursor ligands is even less effective when ZnO ALD is carried out after SnO2 ALD, which likely causes the nucleation delay that has been observed for ZnO during the growth of the ternary material zinc-tin-oxide (ZTO).3,4
The consequences of the persisting ligands on the growth rate and temperature dependence of the binary ALD processes will be described. Moreover, it will be discussed that the incomplete removal of precursor ligands is expected to play an important role during many other ternary ALD processes, which can explain some of the deviating growth characteristics that have been reported.
1. V. Vandalon and W.M.M. Kessels, Appl. Phys. Lett.108, 011607 (2016)
2. M. Shirazi and S.D. Elliott, Nanoscale7, 6311 (2015)
3. M.N. Mullings et al., Thin Solid Films556, 186 (2014)
4. C. Hägglund et al., J. Vac. Sci. Technol. A 34, 021516 (2016)