Overview of greyscale photolithography for microoptical elements fabrication
Cui Z., Du J., Guo Y.
The advance in microlithography has greatly helped the development of microoptical elements. Large array of microlenses can now be fabricated in the same fashion as manufacturing of integrated circuits. Because most of the microoptical elements require well-defined and continuous surface relief profile, special methods are needed to supplement to the normal microlithography to produce those relief structures. One of the techniques is grayscale lithography, including electron and laser beam direct write and grayscale photolithograhy. In this paper, the development of grayscale photolithography is reviewed, in comparison with the direct write techniques. The new development in coding method for grayscale mask is introduced. The importance of correcting non linearity in optical imaging and resist development is discussed. A discussing is also devoted to practical issues in mask fabrication, thick resist patterning and pattern transfer process.