ABSTRACT
Abstract Due to their excellent thermal, mechanical and electrical properties, polyimides have been widely used as stress buffer coatings to improve the reliability of semiconductor devices. In recent years, there has been a trend away from non-photodefinable polyimides (non-PDPIs) towards photodefinable polyimides (PDPIs) because of the ability of a PDPI to simplify the stress buffer layer fabrication process, resulting in process cost reduction. Furthermore, aqueous-developable, positive-tone PDPIs are now becoming the mainstream technology due to demands such as higher resolution, further reduction in process cost, and the need for more environmentally friendly chemicals. These systems typically utilize polybenzoxazole (PBO) material that has a thermal resistance equivalent to polyimides but requires cure temperatures >300◦C to achieve optimum end-use properties. However, in order to reduce damage and improve yields on certain devices such as the next generation memory devices, a low temperature cure, less than 250◦C, is now becoming an important requirement. To meet this demand, a low temperature curable (<250◦C) aqueous-developable, positive-tone PBO has been developed by adopting an effective cure promoter without sacrificing any lithographic (140 mJ/cm2 exposure energy at 5 µm cured film thickness) or end-use properties (70% elongation). Keywords Polybenzoxazole, low temperature cure
1. Introduction
Due to their excellent thermal, mechanical and electrical properties, polyimides have been widely used as stress buffer coatings to improve the reliability of semiconductor devices [1] and, more recently, have also been used as cover coating films for wafer level chip size packages having re-routing distribution layers of copper. In recent years, the need for process cost reduction and the capability for produc-
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Figure 1. Mechanisms of positive-tone photo-definable PBO with NQD system (ICA: Indene Carboxylic Acid; TMAH: Tetramethylammonium hydroxide).
