Laser-lift-off of GaN-based transistors with an ultra-short-pulsed deep UV laser

Abstract

GaN-based wide bandgap transistors offer several advantages compared to silicon-based counterparts. These transistors are effective in reducing power conversion losses and find applications in various sectors, including power supplies in data centers and traction inverters for electric vehicles and other components empowering the renewable energy transformation.To fully harness the potential of GaN-based transistors, quick and reliable detachment from the growth (typically sapphire) substrate is essential. Separation avoids structural and electrical problems caused by low thermal and electrical conductivity of the growth substrate and enables flexible integration with materials that are optimal for the individual application. Furthermore, the limited scalability of sapphire substrates, attributed to handling difficulties and material costs, emphasizes the need for reliable detachment. While the conventional method employs nanosecond-pulsed excimer lasers that dissociates GaN to metallic Ga and N2-gas, this work utilizes an ultra-short-pulsed deep UV laser operating at 266 nm wavelength, which allows for precise and localized energy deposition at the sapphire-GaN interface. Single pulse picosecond processing allows to minimize parasitic heat accumulation and thermal damage to preserve the integrity of underlying layers and surrounding structures. This contribution encompasses an analysis of the threshold for gallium formation and the level of damage to the surroundings. Furthermore, it investigates the influence of bonding materials on detachment performance and discusses limits of achievable throughput.