Route Toward Commercially Manufacturable Vertical GaN Devices

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
$11 ~\mu \text{m}$
-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 (
${W}_{\text {G,eff}}$
) of 180 mm and an active area of 1.4 mm2, an ON-state resistance could be achieved of 8
$\text{m}\Omega \cdot \text {cm}^{{2}}$
. By scaling the source contact length down, the device footprint could be decreased further. It is shown that for devices with a
${W}_{\text {G,eff}}$
of 60 mm this value could be further improved with best performing devices showing a 6.2
$\text{m}\Omega \cdot \text {cm}^{{2}}$
ON-state resistance.