Selective Masking for Metal Contacts on Silicon Planar Devices

ABSTRACT

With the advent of planar transistors and monolithic integrated circuits, techniques by which a large number of individual devices on a wafer can be processed simultaneously, have become feasible. One such technique is that of selectively coating metal for ohmic contacts and interconnections for such devices.

Three different methods of coating aluminium through selective masks have been developed. One method consists of evaporating aluminum over the wafer through a precise metal mask. The mask is prepared by photoengraving techniques. In the second method, photoresist layer is left on the wafer surface except the exposed portions where contacts are desired to be fixed. Aluminium is evaporated over the complete surface. The wafer is then washed in trichloroethylene to remove the photoresist layer along with aluminium coating. The third method deals with evaporating aluminium over the wafer and etching the undesired portions of the metal by photolithographic process. Details and application of each technique is presented.