Study of Laser Lift-Off Process for Fabrication of GaN-Based 365-nm Ultraviolet Absorption Layer Removed Flip Chip LED

The objective of this study was to develop a fabrication process to realize feasible n-type GaN thinning on a 365-nm flip chip ultraviolet LED for enhancement of light output power. The fabrication process included isolation trench filling using epoxy-based SU-8 photoresist, aligned wafer bonding, and sapphire laser lift-off techniques. Study of laser lift-off process for successful transfer of the flip chip LED GaN epilayers to the carrier wafer using different SU-8 trench filling methods are in progress. The first method of SU-8 trench filling was implemented on a flip chip LED wafer with chip isolation defined up to n-type GaN, whereas the second method of SU-8 trench filling was implemented on a flip chip LED wafer with chip isolation defined down to the sapphire substrate. SU-8 2 and SU-8 2025 series were used for the first and second trench filling methods, respectively. In addition to SU-8 trench filling, the second method comprised Cu electroplating and planarization polishing.