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14 May 2004 Characterization of an ultrathick positive photoresist for electroplating applications
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The performance requirements for ultra-thick photoresists are rapidly increasing with the dramatic growth in new lithographic applications that require electroplating processes. Two of the main applications for ultra-thick photoresists are nanotechnology (MEMS) and advanced packaging. Flipchip packaging has become widely adopted to address electrical device performance and chip form factor considerations. The growth in the nanotechnology market is driven by a wide range of products, which include accelerometers, ink jet print heads, biomedical sensors and optical switches. Electroplating levels for these applications require a photosensitive polymer material capable of coating, exposing and plating with conventional semiconductor equipment and standard ancillary process chemicals. A single coat step to achieve the final photoresist thickness is critical to minimize the number of process steps and cycle time. For this thick layer the sidewall profile, aspect ratio, electroplating durability and subsequent stripability are all important. This study characterized a novel positive photoresist (Shin-Etsu SIPR) for use in a 100 micron thick coat for electroplating on copper. The lithographic performance of the ultra-thick positive photoresist was optimized using a broad band, 1X KARL SUSS MA150 aligner used in the proximity mode. All proximity gaps were hard set at 100 microns. Cross sectional SEM analysis, process linearity, and optimized proximity gaps were used to establish the lithographic capabilities. High aspect ratio structures were then electroplated using the optimized photoresist process to demonstrate photoresist durability and stripability. A recommended process flow is described for this photoresist and exposure tool.
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Brad K. Avrit, Edward W. Maxwell, Lisa M. Huynh, and Elliott S. Capsuto "Characterization of an ultrathick positive photoresist for electroplating applications", Proc. SPIE 5376, Advances in Resist Technology and Processing XXI, (14 May 2004);

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