Nanophotonic ICs promise to play a major role in the future of opto-electronic signal processing and telecommunications. But for these devices, which consist of large numbers of wavelength-scale photonic components, to be successful, reliable and cost-effective mass-fabrication technology is needed. Photonic components, and among them photonic crystals, require a high degree of accuracy, which translates to low fabrication tolerances. Today, similar demands are made for high-end CMOS components, made of Silicon, for which a large manufacturing base is installed.
We demonstrate the fabrication of nanophotonic components, like photonic crystal waveguides and photonic wires, using state-of-the-art CMOS processing tools. The foremost of these is deep UV lithography at 248nm and 193nm, combined with dry-etch processes. To maintain compatibility with standard CMOS processes, we use Silicon-on-Insulator (SOI) as our material system. SOI is transparent at telecom wavelengths and provides a good substrate for high-index contrast optical waveguides. Moreover, recent studies have shown that nanophotonic components in SOI are less sensitive to surface roughness than similar components made in III-V semiconductor.
Although deep UV lithography cannot attain the resolution of e-beam lithography, this can be compensated with thorough process characterization, and the technique offers more speed because of its parallel nature. We will illustrate this with experimental results, and will also discuss some of the issues that have arisen in the course of this project.