Development status of thick film photoresist for semiconductor packaging

Abstract

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.