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Study of stress and adhesion strength in SU-8 resist layers on silicon substrate with different seed layers

[+] Author Affiliations
Richard L. Barber

Swinburne University of Technology, Industrial Research Institute Swinburne, Faculty of Engineering and Industrial Sciences and CRC for MicroTechnology, PO Box 218, Hawthorn, Victoria 3122, Australia

Muralidhar K. Ghantasala

Western Michigan University, Department of Mechanical and Aeronautical Engineering, 1903 Western Michigan Avenue, Kalamazoo, Michigan 49008

Ralu Divan

Argonne National Laboratory, Center for Nanoscale Materials, 9700 South Cass Avenue, Argonne, Illinois 60439

Derrick C. Mancini

Argonne National Laboratory, Center for Nanoscale Materials, 9700 South Cass Avenue, Argonne, Illinois 60439

Erol C. Harvey

Swinburne University of Technology, Industrial Research Institute Swinburne, Faculty of Engineering and Industrial Sciences and CRC for MicroTechnology, PO Box 218, Hawthorn, Victoria 3122, Australia

J. Micro/Nanolith. MEMS MOEMS. 6(3), 033006 (September 26, 2007). doi:10.1117/1.2778644
History: Received April 17, 2007; Revised June 01, 2007; Accepted June 12, 2007; Published September 26, 2007
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We present the details of our study on the internal stresses and adhesion strengths of SU-8 structures to different substrate seed layers. The effect of adhesion promoter—methacryloxy [propl] trimethoxysilane (MPTS), and OmniCoat—and different seed layer combinations (TiCuTi, TiCu, CrAu, and CrAuCr) was examined for internal stress and adhesion strength in 650-μm-thick SU-8 films. Increased stress and poor adhesion have led to the delamination of SU-8 in some cases. Adhesion and stress have proven to be the function of process parameters such as soft bake (time and temperature), exposure dose, post-exposure bake (time and temperature), and development time. We have found that a 100 silicon wafer containing a titanium-copper-titanium (TiCuTi) seed layer with MPTS as the adhesion promoter yielded a thick SU-8 film with a lower value of stress and consequently better adhesion for processing in deep x-ray lithography (DXRL). A detailed correlation of the effects of adhesion and internal stress on the SU-8 film is discussed. An analysis of the possible chemical bonding interactions occurring between SU-8, and its adhesion promoter and/or substrate is also presented.

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© 2007 Society of Photo-Optical Instrumentation Engineers

Citation

Richard L. Barber ; Muralidhar K. Ghantasala ; Ralu Divan ; Derrick C. Mancini and Erol C. Harvey
"Study of stress and adhesion strength in SU-8 resist layers on silicon substrate with different seed layers", J. Micro/Nanolith. MEMS MOEMS. 6(3), 033006 (September 26, 2007). ; http://dx.doi.org/10.1117/1.2778644


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