A novel etching-oxidation fabrication method for 3D nano structures on silicon and its application to SOI symmetric waveguide and 3D taper spot size converter

A novel etching and oxidation method utilizing space effect of dry etching for three dimensional silicon structure is presented. Testing devices of SOI symmetric waveguide with ultra thick SiO2 cladding and silicon waveguide structure integrated with 3D taper spot size converter are fabricated using this method

1. Introduction

Excessive coupling loss between SMF (single mode fiber) and silicon nano wire waveguide caused by the mismatch of their optical mode field diameter causes great research interests in three dimensional SSC (Spot Size Converter) to reduce the vertical and lateral mismatch. However, conventional fabrication methods for vertical SSC include quite complicated method such as grey-scale lithography and precise alignment [1]. Even in some cases ultra thick SiO₂ cladding which is rather difficult for plane oxidation and CVD is also necessary [2]. In this paper, we are reporting a novel fabrication method for making three dimensional silicon structure and ultra thick Si_O2 cladding layer [3]. The process mainly utilizes the dry etching speed difference between varying line width patterns [4]. The method is very simple, flexible and compatible to other silicon device fabrication. The oxidation turns the etched comb shape silicon terrace to homogeneous cladding. Therefore, three dimensional silicon structures, like terrace and taper are realized. By using this process, SOI ridge waveguide with thick cladding as well as the three dimensional taper SSC can be fabricated together in one time. Fig. 1 Schematic of Silicon high mesa waveguide with thick cladding layer and 3D SSCs for coupling SMF and compound-semiconductor laser diode