Metal Stop Laser Drilling for Blind via Holes of GaN‐on‐GaN Devices

The metal stop laser drilling of GaN‐on‐GaN devices is demonstrated using a UV sub‐nanosecond laser as a light source. By monitoring the Bremsstrahlung emission at the drilling point, metal stops with a precision higher than 1 μm are realized for vias with a depth of 100 μm. From in situ laser‐induced breakdown spectroscopy measurements, it is shown that endpoint detection is realized with high signal‐to‐noise ratio owing to the difference in the emission process between the strongly excited semiconductor and the metal. Herein, a through‐substrate electrode with a resistance of less than 5 mΩ on GaN‐on‐GaN high‐electron‐mobility transistor (HEMT) wafers is demonstrated. The fabrication of through‐substrate electrodes by this technique provides a simple process that does not require lithography or other complex processes. This process is expected to be useful in the fabrication of future GaN‐on‐GaN devices, including very thin GaN‐on‐GaN HEMTs.