Micro Electro Mechanical Systems (MEMS) is a three-dimensional micro-fabrication technology based on photolithography. The fields of application are extensive and wide-ranging. Among the applications, those that have already acquired a large market include acceleration sensors for airbags of automobiles, pressure sensors for engine
control, inkjet printer heads and thin film magnetic heads. The market is expected to further expand in the optic and
biology-related fields in the future. In the MEMS field, the packaging accounts for the cost, and it is difficult to
standardize due to the low production volume of highly specific technology application. A typical application in the MEMS process would be to conduct plating and etching (Deep RIE) through an
intermediate layer of photoresist patterns, but there are cases where the photoresist itself is left therein as a permanent
film. A photoresist composed of epoxy resin as the main component can form the permanent film through a catalyst of
the optical cationic polymerizating initiator. In general, the optical cationic polymerizating initiator is of onium salt
with antimonite as the anion group due to the nature of the hardening rate or the exposure energy. This paper presents the development status of a high sensitivity permanent photoresist made of epoxy resin as the main component with non-antimonite optical cationic polymerizating initiator with concerns to the impact to the
environment and material for packaging.
In recent years, the demand of thick film photoresists for both copper metal posts and solder bump has been rising for Wafer Level Chip Size Package (WL-CSP) applications. The polymerizing negative tone photoresist, typified by Dry-film photoresist, for metal post applications is currently the mainstream method, but difficulty in removal, thickness selectivity, scaling of chip size and high definition requirements has made the development of a positive tone photoresist for thick film application a necessity. However, the sensitization of a conventional DNQ positive tone photoresist system was difficult due to the nature of the reaction mechanism. In order to meet these requirements, a study was made with a new approach with a positive tone chemically amplified photoresist system, and will be explained in detail in this paper. In general, DNQ type thick photoresist for plating process is developed from the positive tone photoresist platform for semiconductor application through optimization of resist composition and improvement of cracking during the plating process through addition of plasticizers. Inherent performance or compatibility issues with the conventional plasticizer in positive tone chemically amplified photoresist have lead to the development of plasticizer with protecting group. This modification of composition has improved the phtoresist for cracks and swelling of bumps after plating. This is the first chemically amplified photo resist designed for use in the consumer product manufacturing industry.