Patterning of polyimide and metal in deep trenches

This paper presents a method to spin coat and pattern photo-sensitive polyi mide in deep grooves and cavities. The polyimide can be used as dielectric layer to isolate metal interconnects from each other and from the substrate . The advantage of using a polyimide base layer for the metallization is th at it smoothens the corners of the grooves and cavities to facilitate a goo d patterning of subsequent metal layers with standard resist process. Anoth er advantage of polyimide over oxide or nitride for passivation is that rel atively thick polyimide layers can be applied to minimize the capacitive co upling of the metallization to the substrate. The coating is performed in t wo steps. In the first step the wafer is spin coated in a conventional way in saturated solvent atmosphere and after that the wafer is rotated again, upside down to improve the uniformity of the layer. The preliminary coating with polyimide facilitates a uniform coating with standard photoresist for patterning metal layers. Additional improvement in the corner coverage is achieved by smoothening all obtuse corners by a short etch dip of the wafer in TMAH prior to polyimide coating. (C) 2001 Elsevier Science B.V. All rig hts reserved.