27 May 1996 Thick PMMA layer formation as an x-ray imaging medium for micromachining
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Conventional resist application techniques are based on spinning a resist layer onto a mechanically dominating substrate. As thicker imaging layers are required, the integrity of the resist/substrate system is influenced by the resist thickness. The traditional LIGA approach is to form a PMMA resist sheet on the substrate by casting using a press. This method causes high stresses in the resist and at the resist/substrate interface. Another method consists of gluing or bonding a PMMA sheet with subsequent machining to a desired thickness. The stresses can be high enough to cause the resist to crack and/or separate from the substrate. In this paper, alternative and improved techniques are presented. One of these is a modified multiple coating spin-on method, suitable for producing PMMA resist thickness of 60-80 micrometers . The other method is based on bonding a solid PMMA sheet of desired thickness using an appropriate solvent. These techniques produce uniform PMMA layers with thicknesses ranging from 5 micrometers to 1500 micrometers and above. A mechanical cleaving test was used to estimate the resist/substrate bond strength and characterize the bonding solvents. Issues such as radiation swelling and thickness losses associated with latent image formation in PMMA are addressed.
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Olga Vladimirsky, Gina M. Calderon, Yuli Vladimirsky, Harish M. Manohara, "Thick PMMA layer formation as an x-ray imaging medium for micromachining", Proc. SPIE 2723, Electron-Beam, X-Ray, EUV, and Ion-Beam Submicrometer Lithographies for Manufacturing VI, (27 May 1996); doi: 10.1117/12.240489; https://doi.org/10.1117/12.240489

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