| AVS 66th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Friday Sessions |
| Session PS+2D+SE+TF-FrM |
| Session: | Plasma Deposition and Plasma-Enhanced Atomic Layer Deposition |
| Presenter: | Ali Okyay, OkyayTech Inc., Turkey |
| Authors: | A.K. Okyay, OkyayTech Inc., Turkey A. Mohammad, University of Connecticut D. Shukla, University of Connecticut S. Ilhom, University of Connecticut B. Johs, Film Sense LLC B.G. Willis, University of Connecticut N. Biyikli, University of Connecticut |
| Correspondent: | Click to Email |
ALD-grown films are vastly characterized via ex-situ measurements to quantify various material properties. However, gaining insight into the saturating surface reactions and growth mechanisms is only possible with real-time in-situ process monitoring of individual ALD cycles. While several in-situ measurement techniques have been employed in ALD research, in-situ ellipsometry stands out as one of the best options for real-time monitoring surface reactions. The promising potential of in-situ spectroscopic ellipsometry has already been demonstrated for a number of materials grown by remote plasma-ALD. Here, we verify that cost-effective multi-wavelength ellipsometer (MWE) can also be used effectively for real-time in-situ analysis of plasma-ALD growth cycles. We demonstrate for the first time that real-time dynamic in-situ MWE measurements convey not only accurate film deposition rate, but as well resolve single chemisorption, ligand removal, and nitrogen incorporation events with remarkable clarity. Moreover, forcing the limits for fitting the acquired in-situ MWE data, we were able to track the evolution of the optical constants of III-nitride films along the ALD cycles which indeed showed thickness-dependent behavior.
Our main motivation behind this study was twofold: (i) Analyze and compare the self-limiting growth characteristics of binary III-nitride (AlN, GaN, and InN) thin films via real-time in-situ ellipsometry and to gain insight into the ALD surface reaction mechanisms including chemical adsorption, ligand removal, and nitrogen incorporation steps. (ii) Performance evaluation of our custom designed ALD reactor featuring improved hollow-cathode plasma source by comparing our results with previous plasma-ALD grown III-nitrides.
Despite using the conventional alkyl metal precursors (trimethyaluminum, trimethyl/ethylgallium, trimethylindium) utilized also widely in MOCVD epitaxial growth, their solid-gas surface interactions with nitrogen plasma species shows notable differences, particularly with respect to substrate temperature, plasma power, plasma exposure time, and plasma gas composition. In terms of substrate temperature, AlN exhibited crystallinity at lower temperatures when compared to GaN and InN. Even at 100 °C, AlN showed crystalline behavior whereas GaN displayed amorphous character up to 200 °C. While Ar/N2/H2 composition is optimal for AlN, N2/H2 and Ar/N2 mixtures proved to be better for GaN and InN. InN experiments revealed that the inclusion of H2 gas led to mixed phase growth with substantial c-In2O3 phase. The possible surface reaction mechanisms that lead to these different growth behaviors will be discussed in detail.