High aspect-ratio fine-line metallization

This study is aimed at making metallic fine lines characterized with high aspect ratio. There are two methods we have developed. One is the trilevel lift-off method with submicron lithography, and the other is the lift-off method by using the commercial negative photoresist SU-8 made by IBM. First, the trilevel lift-off method is described. A pre-imidized, soluble polyimide layer of OCG Probimide 293 A is spun on a wafer with thickness 4 mu m A 120 nm thick layer of silicon oxynitride was formed on the polyimide by PECVD. A layer photoresist layer was applied and patterned This photoresist layer is used as the etching mask of silicon oxynitride by RIE with the gas CF4 plasma Similarly, the silicon oxynitride is used as the etching mask of the thick polyimide layers by RIE with the gas O-2 plasma. After metallization the pre-imidized polyimide is dissolved in methylene chloride lifting off the oxynitride and metal layers. Following this way, the submicron lithography, such as silylation technology, is suitable to make the aspect ratio up to 10 and the metal line will still have 3 mu m height The other is the lift-off method by using negative photoresist SU-8. This SU-8 is originally used as high aspect ratio molding. The linewidth of SU-8 is reduced to 2 mu m linewidth with 12 mu m height, and used as the remover to lift off after metallization This SU-8 makes the fine-line metallization of 2 mu m linewidth to achieve the aspect-ratio up to 5.