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Proceedings Paper

Optimization and characterization of ultrathick photoresist films
Author(s): Warren W. Flack; Warren P. Fan; Sylvia White
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Paper Abstract

There are in increasing number of advanced lithographic technologies that require photoresist film thickness in excess of twenty microns. For example, suppliers of microprocessors are migrating to flip chip packaging because of bond pad limitations. The flip chip application can require photoresist materials as thick as 125 micrometers for the bump-bonding step. Another application that requires ultra- thick photoresist films is micromachining. Extremely large structure heights are frequently required for micro- electrodeposition of the mechanical components such as coils, cantilevers and valves. These applications can require photoresist in excess of a hundred microns thickness. The patterning of high aspect ratio structures in these ultra-thick photoresist films is extremely challenging. The aspect ratios easily exceed those encountered in submicron lithography for standard integrated circuit (IC) manufacturing. In addition, the specific photoresist optical properties and develop characteristics degrade the critical dimension control for these ultra-thick films. The bulk absorption effect of the photoresist reduces the effective dose at the bottom of the film. This effect is exacerbated by the isotropic wet development process which produces sloped profiles. Unlike thin photoresist for IC manufacturing, lithography modeling and characterization are not readily available for ultra-thick photoresist films. The performance of several commercially available positive and negative ultra-thick photoresists is examined over a thickness range of 20 to 100 micrometers . This paper is primarily focused on the 25 micrometers film thickness using both high throughput i-line and gh-line lithography systems optimized for thick film processing. The various photoresists used in this study were selected to represent the full range of available chemistries from multiple suppliers. Basic photoresist characterization techniques for thin films are applied to the ultra-thick photoresist films. The cross sectional SEM analysis and Bossung plots were used to establish relative lithographic capabilities of each photoresist. The trade-offs between the various photoresist chemistries is reviewed and compared with the process requirements for the various applications. A future paper will discus the capabilities of these same photoresists at both 50 and 100 micrometers film thicknesses.

Paper Details

Date Published: 29 June 1998
PDF: 16 pages
Proc. SPIE 3333, Advances in Resist Technology and Processing XV, (29 June 1998); doi: 10.1117/12.312452
Show Author Affiliations
Warren W. Flack, Ultratech Stepper, Inc. (United States)
Warren P. Fan, Ultratech Stepper, Inc. (United States)
Sylvia White, Ultratech Stepper, Inc. (United States)


Published in SPIE Proceedings Vol. 3333:
Advances in Resist Technology and Processing XV
Will Conley, Editor(s)

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