Continuous profile writing by electron and optical lithography

Further developments in micro-optics and diffractive optics depend on the fabrication capabilities for microstructures and profiles. One of the most interesting fields, apart from binary mask technology for multilevel patterns, is the fabrication of continuous surface profiles which offer high flexibility in the design and good optical quality of the elements fabricated. For continuous relief writing there exist several methods; an essential number of these are based on lithographic techniques. The paper reviews this type of technology regarding their merits for selected applications, and leaves out the description and discussion of other surface-profiling techniques. In detail, laser-beam writing, electron-beam writing, optical half-tone mask technology and writing by shaped optical beams are described and compared to each other. The physical background of each technique is explained as well as possible advantages and obstacles for selected applications. Separately discussed both for optical-and electron-beam lithography is the influence of the resist and its interaction with the radiation which is an essential part of all lithographic technologies. The paper is illustrated with various examples for profiles and elements in the field of micro-optics and diffractive optics.