Route Toward Commercially Manufacturable Vertical GaN Devices

Abstract

To make vertical GaN-based trench gateMOSFET devices commercially manufacturable, 200 mmengineered substrates with a poly-AlN core are a good sub-strate choice. The poly-AlN core, matched in thermal expan-sion to GaN, allows to grow high-quality thick GaN layers.Up to 11 mu m-thick GaN stacks were grown crack-free, withexcellent control over the wafer warp. Breakdown valuesof 900 V were reached for the vertical p/n-junction. Fulldevice processing was completed in a CMOS-compatiblepilot line without any wafer breakage, demonstrating themechanical strength of these substrates. On module level,a new gate trench profile combining a smooth sidewall andround corners, is presented. While a smooth sidewall isimportant for theON-state performance of the devices, therounded corners are beneficial for theOFF-state operation.A semi-vertical test vehicle was used to demonstrate theON-state of the fabricated power transistors. For devices withan effective gate width (WG,eff) of 180 mm and an activearea of 1.4 mm2, an ON-state resistance could be achievedof 8 m Omega<middle dot>cm(2). By scaling the source contact length down,the device footprint could be decreased further. It is shownthat for devices with a W(G,eff )of 60 mm this value could befurther improved with best performing devices showing a 6.2 m Omega<middle dot>cm(2 )ON-state resistance