Diffractive optical elements obtained using electron-beam writer and reactive ion etching

Among various kinds of micro-optical elements, diffractive optical elements are especially attractive because of their functional flexibility in handling wave-front conversion, and because of their planar, compact and lightweight nature what makes them suitable for using in wide range of research, industrial and commercial applications. We present a method of fabricating 8-level DOEs with submicrometer feature sizes in a 3-step lithographic process. In each step a variable-shaped c-beam exposure system is used for writing the pattern that is transferred into substrate by reactive ion etching to form the phase profile. Using this technology several DOEs, including rectangular-apertured micro-Fresnel lens arrays and diffraction gratings were realized on quartz and GaAs wafers. The diffraction efficiencies of these elements were measured to be up to 92%. The lens arrays showed uniform focusing characteristics, and each lens exhibited a good quality of the focused wave front.