The study of processing stimulated by synchrotron radiation (SR) started about 13 years ago. Unfortunately, for semiconductor processing, the reaction rate of this technique was considered to be too slow for practical applications. However the situation is rapidly changing as device dimensions shrink to the nanometer range, which requires high controllability and low defect densities, but is not so reliant on quick processing since much less material is involved. SR etching—which has a typical etching rate of 1–10 nm/min, capability of high-resolution etching due to the short wavelength of SR photons, high controllability, low damage production, and a clean reaction system—is considered to be extremely suitable for nanometer processing.

The benefit of SR etching is that it has unique material selectivities. However the mechanisms for the selectivity are not yet clarified. Consideration of the future application of the SR process to nanometer structure fabrication is dependent upon the development of in situ observation techniques that can evaluate the reaction surface at an atomic or molecular level. Recently we have developed an in situ observation technique: infrared reflection absorption spectroscopy using buried metal layer substrates (BML-IRRAS), which is especially suitable for in situ monitoring of beam-induced reactions on the semiconductor surface in high vacuum.