Method for performing a deep trench etch for a planar lightwave circuit

Abstract

A method of making an optical waveguide structure having improved thermal isolation and stress reduction. The method etches both deep trenches and shallow trenches in a single step. The method includes the step of depositing a partial top clad layer over a first and second waveguide core. An etch back is then performed on the partial top clad layer to obtain a desired thickness of the partial top clad layer. A first hard mask layer is subsequently deposited over the partial top clad layer. A set of hard masks are then formed over the first and second waveguide cores by patterning and etching the first hard mask layer. A full top clad layer is then deposited over the partial top clad layer and the set hard masks to form a top clad. A second hard mask layer is then deposited over the top clad. A deep trench area and first and second shallow trench areas are then exposed by patterning and etching the second hard mask layer. The deep trench area and the first and second shallow trench areas are then simultaneously etched to form a deep trench extending from the upper surface of the top clad to an underlying substrate, and first and second shallow trenches extending from the upper surface of the top clad to the set of hard masks. The set of hard masks and the second hard mask layer are then removed. Reactive ion etching can be used to etch the first and second hard mask layers. The hard mask layers can be amorphous silicon.