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4 May 2005 Enhanced inorganic bimetallic thermal resists transparency and resolution for photomask fabrication
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Bimetallic films have been found to be promising direct write binary and grayscale photomask materials, as they turn transparent after laser exposure. Current structural analysis shows that the laser exposure is an oxidation process. The amount of the oxidized metal created during the laser writing process is related to the laser power, which in turn, determines the gray level (OD) of the exposed film. New exposure conditions have greatly increased the transparency of exposed films (down to 0.18 OD at 365 nm). Furthermore, this extended to deeper UV (300 nm). As the transparency of exposed area changes with the laser exposure power, grayscale photomasks can be created with the bimetallic films, and 3D structures can be produced in the substrate. Interference lithography has been used to investigate the bimetallic films resolution limit, which can generate much finer structures. Lines of 100-180 nm wide were successfully created on silicon and silicon dioxide. Aluminum thin films were found to turn transparent (0.28 OD) after laser exposure with high power, indicating that Al can also be a potential direct-write photomask material.
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Glenn Chapman, David Poon, Chinheng Choo, Yuqiang Tu, James Dykes, Jun Wang, Jun Peng, Willy Lennard, and Karen Kavanagh "Enhanced inorganic bimetallic thermal resists transparency and resolution for photomask fabrication", Proc. SPIE 5753, Advances in Resist Technology and Processing XXII, (4 May 2005);

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