Polyimide Planarization with Polystyrene by RIE Etch-Back

Abstract

This paper reports the results of a planarization process of polyimide which has been utilized as a passivation material in multilevel interconnection. The degree of planarization with spin-coated polyimide over metal topography is only 10–20% due to crosslinking and shrinking of the polymer during the curing process. Polystyrene used as sacrificial planarizing film can achieve <95% planarity over 100μm metal pad with 1μm height. A conformal polystyrene film can be spin-coated onto the polyimide surface without adhesion promoter. The topography of polyimide over the metal pattern can be planarized with thermal reflow of the polystyrene by baking the film below 250°C. The planarity of this sacrificial film, polystyrene, can be transferred to polyimide by etch-back without degrading the polyimide surface properties which has been examined by X-ray photoelectron spectroscopy.