Photonic Crystal Nanocavities With an Average <italic>Q</italic> Factor of 1.9 Million Fabricated on a 300-mm-Wide SOI Wafer Using a CMOS-Compatible Process

Abstract

Electron-beam lithography allows precise photonic crystal (PC) fabrication, but is not suitable for mass production. Therefore, the development and optimization of CMOS-compatible processes is necessary to implement unique nanocavity technologies in optoelectronic circuits. We investigated the quality factors ( Q ) and the resonant wavelengths ( λ ) of PC heterostructure nanocavities fabricated by the 193-nm argon fluoride immersion lithography on a 300-mm-wide silicon-on-insulator wafer. We measured 30 cavities distributed over nine chips at various positions of the wafer. An average Q of 1.9 million was obtained for the 30 cavities, and the highest value was 2.5 million, which is the highest Q reported so far for a nanocavity fabricated by photolithography. Such high Q were realized by the improvements of the nanocavity design and the fabrication process. All nanocavities exhibited a Q of larger than 1 million and the fluctuation of the chip-averaged Q was independent of the chip location. On the other hand, the measured λ tended to shift to shorter wavelengths as the distance between the nanocavity and the substrate center increased. Among the nine chips, the difference of the chip-averaged λ was as large as 8.0 nm. We consider that a systematic shift of the average air-hole radius by several nanometers is responsible for the large fluctuation of the chip-averaged λ . These statistical studies provide important hints to accelerate the application study of PC high- Q nanocavities.