Application of deep trench LISA technology on optical switch fabrication

This paper describes LISA (Lateral isolated Silicon Accelerometer) technology developed by IME, Singapore and its application on silicon vertical optical switch fabrication. Key processes in LISA technology for optical switch fabrication include deep trench etch and oxide refill to enable insulating anchors in silicon substrate, second deep trench etch to fabricate movable microstructures and metal layer covering for switch surface improvement. In this paper, Deep trench (deeper than 35 um) oxide refill process is introduced, the dielectric characteristic of the isolation is evaluated, and more than 100 V breakdown voltage is obtained, which is much higher than the requirement in optical switch driving voltage. Some process issues related to high aspect ratio trench etch and release such as notching on silicon beam top and sidewall are showed and discussed, a double spacer process is utilized accordingly to solve the issues. Besides, a mask free metal coating process is presented to improve the mirror surface and light reflectivity. The vertical optical mirrors fabricated by the LISA technology is 35 um in height and 2 um in width, the switch displacement is larger than 40 um under 35 V DC bias, the optical characteristics of the switch is under testing.