US Patent 8718432 Method for forming a spotsize converter

A method for forming a tapered region in a first layer of a first material is disclosed. The method comprises forming an accelerator layer of a second material on the first layer and forming a mask layer disposed on the accelerator layer. The accelerator layer is exposed to a first etch that removes the second material in a first region and laterally etches the accelerator layer along a second region to expose the first layer in the second region to the first etch. Since the time for which the first layer is exposed to the first etch in the second region is based on the progress of the lateral etch of the accelerator layer, the first etch tapers the first layer in the second region.