Process Technology and Industrial Processes

Abstract

A quick review of the deposition methods that achieved sufficient low resistivities and comparison of these methods in terms of the capability for large area mass production will be made. At the later half our experience on two pilot runs by evaporation and magnetron sputtering machines will be described in detail. 15.1 Challenges to Lower Resistivities It was 1966 when the indium oxide doped with tin, later called as ITO, was recognized as an outstanding low resistivity transparent conductor by the work of R. Groth [1]. He and his colleagues later reported 2 Â 10 À4 O cm in 1968 [2] by spray pyrolysis from an acidic alcoholic solution of SnCl 4 and InCl 3 onto 5 mm thick borosilicate glass substrates at 500 C range. The optimal doping level of tin was 2 at.%. This triggered many extensive R & D activities all over the world toward the liquid crystal displays (LCDs), especially in the US and Japan. According to this movement we could have many findings and in-depth understandings of the ITO materials. These research works provided firm position of ITO in the LCD devices. During the very beginning of LCD development the transparent thin film electrode on both sides of liquid crystal layer was tin oxide doped with antimony, SnO 2 :Sb. Its resistivity was in some lower 10 À3 O cm at best. The first commercial LCD was applied to the calculator where the required sheet resistance was of the order of hundred ohms with a thickness less than 40 nm so as not to be seen to unaided human eyes. This means the resistivities less than 1 Â 10 À3 O cm as an essential demand from the device side. Based on this market demand sheet glass