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A completely new planar method permitting step-free multilevel interconnections is proposed. The key role in this technique is played by the polyimide film which is used as insulating layers. The fluid property of the polymer solution always gives an ideal flatness to the surface of the wafer no matter how many steps are formed by preceding metallization processes. Using this planar metallization with polymer (PNIP) technique, a five-level structure which consists of five metal (aluminum) and five polyimide layers has been successfully made, The PMP structure completely eliminates the failures which result from open circuits between metal layers at crossovers and via-holes and from short circuits between metal layers through the pin-holes of insulating layers. No trace of degradation is observed in the characteristics of the MOS-FET covered with the polyimide either after heating at 150°c for 2000 hours or after a bias-temperature test at 125°c for 200 hours.