Low-loss SOI photonic wires and ring resonators fabricated with deep UV lithography

We demonstrate single-mode photonic wires in silicon-on-insulator with propagation loss as low as 2.4 dB/cm, fabricated with deep ultraviolet lithography and dry etching. We have also made compact racetrack and ring resonators functioning as add-drop filters, attaining Q values larger than 3000 and low add-drop crosstalk.

I. Introduction

ONE OF THE main requirements for the further integration of photonics is a low-loss waveguide that allows for short bends. This can be done using waveguides with a high refractive index contrast confining light by total internal reflection. In these so-called photonic wires, bend radii as small as 2 are possible with low bend radiation losses. Fig. 1. SOI photonic wire waveguide. For single-mode operation, the wire width should be less than 600 nm. In such narrow high-index contrast waveguides, scattering at sidewall roughness is a severe cause of propagation loss [1]. Therefore, very accurate fabrication processes are needed. For research purposes, e-beam lithography is the preferred fabrication method. While this technique is very accurate, it is also slow. To fabricate photonic wires in Silicon-on-insulator (SOI), we opted for deep ultraviolet (DUV) lithography with an illumination wavelength of 248 nm, as used for high-end complementary metal–oxide–semiconductor manufacturing [2], [3]. DUV lithography is better suited for mass fabrication, with a lower resolution, but offering large throughput and a large field size.