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Proceedings Paper

Process improvements for ultrathick photoresist using a broadband stepper
Author(s): Warren W. Flack; Ha-Ai Nguyen; Elliott Sean Capsuto
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Paper Abstract

There are a number of new lithographic applications that require the use of ultra-thick photoresists. Extremely large structure heights and high aspect ratios are often necessary for electroplating processes. In this situation it is important for the height of the patterned photoresist to exceed the plating height. Two of the main applications for thick photoresist are micromachining and advanced packaging. Ultra-thick photoresists are used in packaging to define the size and location of the bonds for bump bonding, while in micromachining the photoresist is used to define fluidic chambers and electroforming molds. At photoresist thickness greater than 15 microns, standard lithographic techniques become difficult in terms of performance and productivity. The bake, exposure and develop times increase dramatically as the photoresist thickness climbs. The estimated total process time for a 15 micron photoresist is approximately three times greater than that of a 1 micron photoresist. For thick films the develop time on the wafer track becomes the throughput limiter for the entire lithography cell. Therefore, reducing develop time for thick photoresist processes is critical to enhancing the lithography cell cost of ownership. In this paper we will focus on the developer chemistry and process to improve both performance and productivity for a 15 micron thick photoresist. We evaluate process changes in both normality and surfactant level of the developer. Cross sectional analysis, contrast curves, process linearity and process windows are used to establish the lithographic capabilities. It is clear that a developer and process for a thin photoresist is not necessarily optimum for a thick photoresist process. The implementation of an ultra-thick photoresist becomes more feasible in a manufacturing environment after optimizing developer chemistry and process conditions.

Paper Details

Date Published: 14 September 2001
PDF: 14 pages
Proc. SPIE 4346, Optical Microlithography XIV, (14 September 2001); doi: 10.1117/12.435796
Show Author Affiliations
Warren W. Flack, Ultratech Stepper (United States)
Ha-Ai Nguyen, Ultratech Stepper (United States)
Elliott Sean Capsuto, ShinEtsu MicroSi, Inc. (United States)


Published in SPIE Proceedings Vol. 4346:
Optical Microlithography XIV
Christopher J. Progler, Editor(s)

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