The number of lithographic applications that require ultra-thick layers of resist (>50 um) is rapidly increasing. One field in which this requirement is growing is in the field of MEMS (Micro-Electro-Mechanical-Systems) and MOEMS (Micro-Optical-Electro-Mechanical-Systems). A second is in the realm of wafer-level, advanced chip scale packaging1. For both of these fields, ultra-thick, as well as high aspect ratio, photolithography is an absolute requirement for device processing. The process optimization required to obtain high aspect ratio structures in these ultra-thick photoresist films is extremely challenging. Alignment accuracy is a critical factor in this process. Because of the thick films involved, the alignment keys between mask and wafer could be separated by more than a hundred microns. Standard microscope and objectives have limited depth of focus. Once resist thickness and separation gap exceeds the depth of focus, alignment accuracy suffers from image quality between substrate and mask. Various special microscope options have been developed for alignment of very thick resist. However, most of these processes suffered from one failing or another. This paper addresses a new method to perform true large gap alignment for these applications. True large gap alignment systems overcome these limitations by using identical focal planes for mask and wafer alignment key. Both alignment keys are focused clearly with resist thickness and separation gap of up to 500 um. This paper will present detailed experimental results of alignment accuracy obtained at different thicknesses of photoresist in a contact/proximity production aligner system.
An ever increasing need exists for thick resist layers in the processing of MEMS and for advanced packaging. Applications in the MEMS field include bulk micromachining, surface micromachining, and the actual creating of active device structures. For advanced packaging, the applications are in redistribution and passivation layers, and micromolds for metal bumps. The various applications can require resist layer thicknesses up to and exceeding 1000 micrometers . In order to properly achieve these thicknesses, appropriate coating materials were developed by manufacturers. These materials include AZ P4620, Shipley SPR220, AZ PLP100XT, JSR THB 611P, and SU-8. Finally, equipment was developed to handle these materials, in the form of specialized coating equipment and contact/proximity aligners.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.