Study On Imaging Characteristics Of Thick Photoresists In Lithography

MEMS applications are growing rapidly in recent years. A lot of micro machining technologies are developed to fabricating MEMSs. Recently, lithograph of thick resist has been regarded as an effective and economical technology for manufacturing excellent high-aspect-ratio microstructures (HARMS). With the development of MEMSs, their structures are more and more complex, and new HARMSs need to be designed and fabricated. So, it is very necessary to simulate the imaging process of thick resist photolithograph. In the past, process controls of thick resist lithograph have been studied extensively. On the contrary, much less investigation has been done concerning its imaging transmission. Unfortunately, the existent exposure and development simulation models are only appropriate for thin film resist. Therefore, the imaging characteristics of thick resist photolithograph are investigated in this paper based on the exposing and developing theories of thin film resists.Firstly, the influences of nonlinearities in imaging process of thick resist lithography are studied. Based on the analysis, we find refractive index of resists changes during bleaching process, and the exposure parameters vary with resist thickness, so as the development parameters. Therefore, the Dill exposure model and Mack development model are improved, so that they are suitable for the simulation of thick resist lithography.In addition, the calculation errors from refractive index changes are discussed. From the simulation of PEB process, we prove that PEB could reduce standing wave effects and improve resist development profile. After analyzing the effects of standing wave effects on resist profiles, we bring forward a certain thickness andthese effects could be ignored when resist is beyond that value. Finally, the characters of thick resist profile are analyzed, and experiment results are also given.