A quick algorithm of exposure distribution for fabrication of micro-optical structures

An approximate algorithm of exposure distribution on photoresist for the case of large exposure dose is obtained on the basis of the algorithm reported in [X. Dong, C. Du, S. Li, C. Wang, Y. Fu, Control approach for form accuracy of microlenses with continuous relief, Opt. Express 13 (2005) 1353–1360] via analyzing a PAC concentration distribution inside the photoresist. We analyzed the fabrication errors of the micro-optical structures which are caused by the approximate algorithm. The relief form error originating from the measurement errors of characteristics parameters of the photoresist is analyzed as well. A valid approach for a quick and accurate design of the exposure distribution is provided accordingly. As an example, a saw-tooth grating with 75 μm relief depth was designed and fabricated so as to verify the new algorithm. Our measurement results show that root mean square (rms) value is less than 0.81 μm. The quick algorithm can satisfy the requirements of micro-optical systems for practical applications.