The application of chemical-mechanical polishing for planarizing a SU-8/permalloy combination used in MEMS devices

Chemical-mechanical polishing (CMP) allows the planarization of wafers with two or more materials at its surface. Subject of this investigation was to apply CMP for planarizing electroplated permalloy (NiFe 81/19) in micromolds formed by photosensitive epoxy (SU-8). This material remained in the structure as an insulation and planarization layer. This material combination was intended for fabricating magnetic Micro Electro-mechanical Systems (MEMS). For planarizing a SU-8/permalloy combination, metal CMP slurry was used in conjunction with standard CMP polishing pads. SU-8 effectively served as a polishing stop. For this reason it was necessary to optimize the SU-8 properties to exhibit an optimal hardness and wear resistance. The mechanical properties of the SU-8 depended on the thermal treatment during hard bake after development. The resulting SU-8 layer not only had a sufficient hardness to stop the removal of permalloy, but also could be planarized quite well. (C) 2003 Elsevier B.V. All rights reserved.