Abstract
When photoresist structures are formed by employing various lithography technologies and followed by thermal reflow treatments, the mechanism that transforms the cross-section of a photoresist structure from a rectangular-shape into a circular-shape is seen as an integral constituent of the manufacturing method of microlens arrays. However, in the case, where a residual layer is absent, a photoresist film is completely exposed to the oncoming radiation down to the interface between the photoresist film and substrate. Even in the presence of a residual layer, it has been uncertain to the author if a photoresist structure with a circular cross-sectional shape could be obtained, and be made applicable for the fabrication of a microlens array. The author then executed a set of thermal reflow treatments under various conditions using a positive-tone photoresist AZP4903 known for its capability of forming relatively thick films. As a result, it became clear that the existence of a photoresist’s residual layer has large influence on the transformation of the cross-sectional shapes of photoresist structures. These observations can be attributed to whether the bottom surface of a photoresist structure is firmly fixed on a hard substrate, or if it happens to be in contact with a soft photoresist layer which can flow comparatively freely.
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Acknowledgments
Before the author used the laser lithography system, the author received technical advices from Dr. Kenta Suzuki and Dr. Hiroshi Hiroshima of the National Institute of Advanced Industrial Science and Technology (AIST).
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Mekaru, H. Influence of residual layer on cross-sectional shape of thermal-reflowed photoresist structures. Microsyst Technol 22, 329–336 (2016). https://doi.org/10.1007/s00542-014-2389-z
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DOI: https://doi.org/10.1007/s00542-014-2389-z