Liquid crystal display with superposed contact holes and method of manufacturing the same

1. A method of manufacturing an in-plane switching liquid crystal display having thin film transistors on a substrate, scan lines and signal lines connected to the thin film transistors and longitudinally and latitudinally crossing each other, and common wiring formed by the same layer as the scan lines and generating electric fields substantially parallel to the substrate between a common electrode connected to the common wiring and covering the signal lines partially via an interlayer insulating film formed on the thin film transistors, and pixel electrodes connected to the thin film transistors, the method comprising the steps of:

forming a first inorganic insulating film on at least source and drain electrodes of the thin film transistors,

forming first contact holes in said first inorganic insulating film for connecting the common wiring and the common electrode to each other, and second contact holes in said first inorganic insulating film for connecting the thin film transistors and the pixel electrodes to each other using at least dry etching,

forming a second inorganic insulating film on the first inorganic insulating film,

forming third contact holes in said second inorganic insulating film so as to be superposed on the first contact holes, and fourth contact holes in said second inorganic insulating film so as to be superposed on the second contact holes,

forming a conductive film on the second inorganic insulating film,

forming the common electrode connected to the common wiring via the first and third contact holes, and

forming the pixel electrodes connected to the thin film transistors via the second and fourth contact holes,

wherein the third contact holes are formed inside the first contact holes while the fourth contact holes are formed inside said second contact holes.