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Proceedings Paper

An investigation of SU-8 resist adhesion in deep x-ray lithography of high-aspect-ratio structures
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Paper Abstract

The SU-8 negative photo resist has been recognised as an unique resist, equally useful for UV lithography and deep x-ray lithography (DXRL) applications; but it is in DXRL where SU-8 has shown a significant advantage over other resists. When compared with the common DXRL resist poly-methyl methacrylate (PMMA), SU-8 has been found to significantly reduce x-ray exposure time, processing time and cost, thus making SU-8 a strong candidate for commercial DXRL applications. Despite these advantages, several factors associated with SU-8 processing are not well understood. Resist-substrate adhesion, which is the key for successful lithography, is one such example. This paper examines the effect of substrate (silicon and graphite), seed layer (Ti/Cu/Ti, Ti/Cu, Cr/Au and Cr/Au/Cr), and the use of adhesion promoters (OmniCoat and MPTS) on the adhesion of SU-8 structures. In addition, parameters such as SU-8 thickness (450 μm, 650 μm, 900 μm) and substrate roughness values (silicon, Ra < 10 nm and Ra = 0.5 μm) have also been investigated. The results of our work highlight the importance of material selection for a given process and the relationship between the different parameters investigated. Increased stress for thicker films (> 850 μm) has lead to the delamination of SU-8 on some substrates. The adhesion has also proven to be a function of process parameters such as pre-bake (time and temperature), exposure dose, development time and post exposure bake (time and temperature). We have found that a <100> silicon wafer (Ra = 0.5 μm) containing a titanium-copper-titanium (Ti/Cu/Ti) seed layer, provided an adequately adhered resist for DXRL, while a chromium-gold (Cr/Au) seed layer on silicon (Ra = 0.5 μm) showed poor adhesion. A detailed correlation of the effect of these parameters on SU-8 adhesion will be discussed in this paper.

Paper Details

Date Published: 2 April 2004
PDF: 7 pages
Proc. SPIE 5276, Device and Process Technologies for MEMS, Microelectronics, and Photonics III, (2 April 2004); doi: 10.1117/12.521170
Show Author Affiliations
Richard L. Barber, Swinburne Univ. of Technology (Australia)
CRC for Microtechnology (Australia)
Muralidhar K. Ghantasala, Swinburne Univ. of Technology (Australia)
CRC for Microtechnology (Australia)
Ralu Divan, Argonne National Lab. (United States)
Derrick C. Mancini, Argonne National Lab. (United States)
Erol C. Harvey, Swinburne Univ. of Technology (Australia)
CRC for Microtechnology (Australia)

Published in SPIE Proceedings Vol. 5276:
Device and Process Technologies for MEMS, Microelectronics, and Photonics III
Jung-Chih Chiao; Alex J. Hariz; David N. Jamieson; Giacinta Parish; Vijay K. Varadan, Editor(s)

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