Defect Engineering at the Al<sub>2</sub>O<sub>3</sub>/(010)<i>β</i>-Ga<sub>2</sub>O<sub>3</sub>Interface via Surface Treatments and Forming Gas Post-Deposition Anneals
Ahmad E. Islam, Chenyu Zhang, Kursti DeLello, David A. Muller, Kevin Leedy, Sabyasachi Ganguli, Neil Moser, Rachel Kahler, Jeremiah C. Williams, Daniel M. Dryden, Stephen E. Tetlak, Kyle J. Liddy, Andrew J. Green, Kelson D. Chabak
Abstract
High-quality dielectrics with a low defect density at the dielectric/semiconductor interface are essential for the application of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga2O3 in the next-generation power electronic devices. In this article, we demonstrate a method for reducing defect density at the Al2O3/(010) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga2O3 interface, where metal–oxide–semiconductor capacitors (MOSCAPs) were fabricated by depositing Al2O3 on the surface of (010) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga2O3 treated sequentially with piranha and buffered hydrofluoric (HF) acid. The devices also went through a post- dielectric deposition anneal (PDA) in a forming gas ambient (FG-PDA). The fabricated devices were then characterized using current–voltage and capacitance–voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> ) measurements. The quality of Al2O3 films and surfaces was also characterized using cross-sectional transmission electron microscopy (TEM), ellipsometry, and atomic force microscopy (AFM). Electrical measurements suggested low hysteresis, consistent flat-band voltage, and excellent accumulation for MOSCAPs with an interface defect density <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D} _{{\mathrm {IT}}} < 10$ </tex-math></inline-formula> 12 cm−2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> eV−1 characterized using conductance and photo-assisted <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> (PCV) methods. In some devices, PCV method created additional <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D} _{{\mathrm {IT}}}$ </tex-math></inline-formula> during characterization. Measured leakage current through Al2O3 until its breakdown was explained using a modified space-charge-limited conduction model. Control samples prepared without (or with limited) surface treatments and without forming gas PDA revealed the importance of different process components for reducing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D} _{{\mathrm {IT}}}$ </tex-math></inline-formula> . TEM images revealed interfacial crystallization as the origin of higher defect densities in the control samples.