Patent ID: 8242024

Claim:
In a substrate having a polyimide layer overlying on an substrate with an existing integrated circuit, wherein the polyimide layer having another integrated circuit on its top surface, a method of forming a multi-step staircase structure with each step tapered on the polyimide layer for metal interconnection between said two integrated circuits comprising of the following steps: disposing a layer of photoresist; applying a first photo mask to expose the photoresist with UV light and then be developed to form a photoresist pattern; a preliminary baking process on the photoresist pattern with the substrate in an convection oven at 90° C. for 30 to 50 minutes; a secondary baking process on the photoresist pattern with substrate in an convection oven at 110° C. for 30 to 50 minutes; applying an inductively coupled reactive ion etching of oxygen plasma to the polyimide layer using photoresist pattern as an etching mask; stripping the photoresist; and repeating above process with corresponding photo masks to form multi-step staircase structure by etching other tapered steps in the thickness direction until undesired portion of the polyimide layer on the substrate is completely etched, and the integrated circuit on the substrate is exposed.