5:15 PM - 5:30 PM
[15p-B8-14] The impacts of fabrication error on spectral variation of silicon grating couplers
Keywords:grating couplers, coupling efficiency, spectral variation
In optical ICs using silicon photonics technology, silicon grating couplers (GCs) which consist of periodic trench structure are most important IO devices for optical coupling with fibers. The grating pitch and depth of GC are designed to maximize coupling efficiency between GCs and fibers for a wavelength of incident light, and cross-sectional size deviations in device fabrication, however, arise spectral variation in the optical coupling.In this study, we theoretically and experimentally investigated how fabrication errors impact on GC transmission spectrum. The GCs designed for a wavelength of 1300 nm were fabricated on 300-mm-diameter 200-nm-thick SOI substrates by using 40-nm-node CMOS technology with ArF immersion lithography, and were characterized by an automated optical wafer-level probing system. In the transmission spectra via GC-fiber coupling, it was confirmed that the coupling efficiency, peak wavelength, and transmission bandwidth (1dB) for 64 GCs on a 300-mm wafer are 2.99+/-0.07 dB, 1302.3+/-1.9 nm, and 31.1+/-0.8 nm, respectively. All of the deviation values (1sigma) for these properties are quite small, compared with previous studies by using dry excimer lithography technology. We also theoretically derive relationship between grating depth shift and peak wavelength shift, and confirm the validity of the theoretical relationship in fabricated GC’s properties.As the results of the study, we showed that fabrication error in grating formation is the main cause of spectral variation of GCs, and the usage of high-resolution process technology is a practical solution to improve spectral reproducibility in order to realize low-loss optical ICs.