Synchrotron radiation-excited etching reactions

The present status of the research on synchrotron radiation-excited etching reactions of SiO2 and various Si surfaces initiated at the KEK-Photon Factory and at UVSOR is reviewed, although it is at a primitive stage of the development. The recent results obtained for etching reaction of SiO2/SF6 system --a) the pressure and temperature dependences of the etch rates, and b) cross-sectional profiles of the etched surfaces as a function of SF6 pressure, and c) wavelength and pressure dependence of the etch rates using pseudo-monochromatic undulator radiation--are described and the reaction mechanisms are discussed. From the results so far obtained it has been concluded that excitation of the SiO2 surface covered by reactive species such as F atoms is essential in promoting the etching reaction. The etching reactions of various Si materials by Cl2 and SF6 gases are also presented and a possible contribution of surface excitation is discussed. It has been believed that Si surfaces are etched by spontaneous reaction of the radical species formed by photodissociation of gaseous etchants. However it is pointed out that more experiments are needed to clarify the mechanisms of etching reactions of Si surfaces. (author)