Defect Engineering at the Al₂O₃/(010)<i>β</i>-Ga₂O₃Interface via Surface Treatments and Forming Gas Post-Deposition Anneals

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">${D} _{{\mathrm {IT}}} &lt; 10$ </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.