High etch rate and low temperature InP backside via etching using HI-based inductively coupled plasma

We have successfully demonstrated a high etch rate and low temperature backside via etching into InP using HI-based ICP. An average InP etch rate of 2.0 μm/min at a wafer temperature of 130 °C was obtained. Using this etching, 80 μm diameter backside vias were formed into 100 μm thick InP with a simple process. The vias show good profile and smooth surface over a 3-inch diameter wafer. From s-parameter measurements, the average via inductance of 12.1 pH was extracted and the inductance coincides with a calculated value. To evaluate reliability, a heat cycle test under a condition of temperature cycling from 150°C to -65°C was carried out. After testing of 100 cycles, all vias satisfied the test requirements. These results show that our InP backside via process is promising for practical applications.