MSE Colloquium: Theodosia Gougousi, Interface cleaning mechanism during the Atomic Layer Deposition of dielectrics on III-V semiconductors
Atomic layer deposition (ALD) is a thin film deposition technique which can be used to grow highly conformal thin films with sub-nanometer thickness control. Since its early development for the deposition of thin films for electroluminescent displays, the applications of ALD broadened into an expansive field ranging from microelectronics to biocompatible coatings. One of the most common applications is the formation of gate oxides in metal oxide semiconductor devices. During the ALD of Al2O3 from trimethyl aluminum (TMA) and H2O on GaAs, the thinning of the native oxide interfacial layer was observed.1,2 Since then, several systems exhibiting this native oxide “clean-up” behavior have been identified.3 One controversial observation was that for amine precursors the “clean-up” reaction seemed to proceed well after the native oxide surface had been covered with the formed film. To explain such observations a mechanism that will transport the surface oxides through the growing film is required.
In this talk I will present an overview of the literature data on the interface cleaning reaction for several dielectric/III-V systems and present evidence for native oxide migration in the growing film at typical processing conditions (150-250 °C). Subsequently I will present the experiments we designed to demonstrate the existence of this transport mechanism. In these experiments we coupled transmission Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) measurements to show both indirectly and directly that arsenic and gallium oxides can diffuse through 4 nm thick TiO2 films deposited on native oxide GaAs(100) surfaces at temperatures as low as 150°C. 4
1. Ye, P. D. et al. GaAs metal–oxide–semiconductor field-effect transistor with nanometer-thin dielectric grown by atomic layer deposition. Appl. Phys. Lett. 83, 180–182 (2003).
2. Frank, M. M. et al. HfO2 and Al2O3 gate dielectrics on GaAs grown by atomic layer deposition. Appl. Phys. Lett. 86, 152904 (2005).
3. Gougousi, T. Atomic layer deposition of high-k dielectrics on III–V semiconductor surfaces. Prog. Cryst. Growth Charact. Mater. 62, 1–21 (2016).
4. Henegar, A. J., Cook, A. J., Dang, P. & Gougousi, T. Native Oxide Transport and Removal During Atomic Layer Deposition of TiO2 Films on GaAs(100) Surfaces. ACS Appl. Mater. Interfaces 8, 1667–1675 (2016).
Theodosia Gougousi is a Professor in the Department of Physics at UMBC (University of Maryland, Baltimore County). She received her BS in Physics from the Aristotle University of Thessaloniki, Greece in 1990 and her MS and Ph.D. in Physics from the University of Pittsburgh in 1993 and 1996. Prior to joining the faculty at UMBC in 2004 she held postdoctoral appointments at the University of Maryland, College Park and North Carolina State University. Her research interests include the deposition mechanisms and properties of thin films, interfaces and other low dimensional materials. Her laboratory uses a combination of vacuum and high-pressure approaches to study the deposition of materials on planar and high aspect ratio topography. These techniques include Atomic Layer Deposition and Supercritical Fluid Deposition. She has authored or coauthored more than 45 journal articles, and has more than 50 contributions to conferences. She received an NSF CAREER award in 2009.