Fabrication of an accurately vertical sidewall for optical switch applications using deep RIE and photoresist spray coating

Abstract

The authors propose a new approach for fabricating an accurately vertical sidewall by deep RIE process for optical MEMS device applications. The etching area is divided in two patterns, an outline pattern and area pattern. The first pattern defines the outline of the etching area and has a uniform pattern width of 70–80 μm to achieve accurately vertical trench etching within 0.1°. The remaining area is removed by successive second etching using another pattern. The difficulties involved with multiple deep etchings are overcome by the combination of a photoresist spray coating and the side etching effect of RIE controlled by recipe control. The fabrication of mirror structure with 90.1° sidewall is demonstrated using the above procedures. Moreover, an inverted nickel mold is exhibited using electroplating. The resulting accurately vertical sidewall is considered to be effective for achieving lower insertion loss and easier optical alignment for MEMS optical devices.