Self-organized formation of a Blazed-grating-like structure on Si(100) induced by focused ion-beam.

A new one-step method, which has been named self-organized formation, for microfabrication of blazed-grating-like structures after bombardment with a focused ion beam (FIB) with an ion energy of 50 keV and a beam current of 0.5 nA is presented. The structure is fabricated by the FIB by raster scanning (not by patterned scanning) upon a substrate of a silicon wafer, Si(100), with total scanning time of 14 min. With this method the parameters are unchanged during the whole process, unlike for the point-by-point direct writing technique, in which the exposure intensity or the electron- or ion-beam dose is changed for each point. The surface roughness of the structure, Ra, is 2.5 nm over an area of 1 mum X 1 mum. To evaluate the performance of this method we carried out a simulation, using the PCGrate program. The simulated diffraction efficiency, of diffraction order -3 working in the reflection mode, can be as much as 79.1% for the violet wavelength of 400 nm. Using a He-Ne laser as the light source produced a measured diffraction efficiency of the order of -2 of 70.4%, which is near the simulated value of 76.9% at a wavelength of 600 nm. The depth and the period of the structure can be controlled by process parameters of the FIB, such as ion energy and ion flux.