Route Toward Commercially Manufacturable Vertical GaN Devices

Abstract

To make vertical GaN-based trench gate MOSFET devices commercially manufacturable, 200 mm engineered substrates with a poly-AlN core are a good substrate choice. The poly-AlN core, matched in thermal expansion to GaN, allows to grow high-quality thick GaN layers. Up to 11 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m-thick GaN stacks were grown crack-free, with excellent control over the wafer warp. Breakdown values of 900 V were reached for the vertical p/n-junction. Full device processing was completed in a CMOS-compatible pilot line without any wafer breakage, demonstrating the mechanical strength of these substrates. On module level, a new gate trench profile combining a smooth sidewall and round corners, is presented. While a smooth sidewall is important for the ON-state performance of the devices, the rounded corners are beneficial for the OFF-state operation. A semi-vertical test vehicle was used to demonstrate the ON-state of the fabricated power transistors. For devices with an effective gate width ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{W}_{\text{G,\text{ef}\text{f}}}\text{)}$</tex-math> </inline-formula> of 180 mm and an active area of 1.4 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\text{2}}$</tex-math> </inline-formula> , an ON-state resistance could be achieved of 8 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega\cdot \text{cm}^{\text{2}}$</tex-math> </inline-formula> . By scaling the source contact length down, the device footprint could be decreased further. It is shown that for devices with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{W}_{\text{G,\text{ef}\text{f}}}$</tex-math> </inline-formula> of 60 mm this value could be further improved with best performing devices showing a 6.2 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega\cdot\text{ cm}^{\text{2}}$</tex-math> </inline-formula> ON-state resistance.