METHOD OF IMPROVING OR TESTING P-N JUNCTION CHARACTERISTICS IN A SEMICONDUCTOR DEVICE

摘要

1,248,124. Semiconductor devices. HUGHES AIRCRAFT CO. 18 March, 1969 [18 March, 1968], No. 14179/69. Heading H1K. [Also in Division C7] A conductive film is selectively removed from the N-type side of a PN junction in a semiconductor body by immersing at least the junction-containing part of the body in a deplating solution, reverse-biasing the junction and applying a deplating current which tends to pass preferentially between the solution and the N-type region. In the embodiment shown Si mesa diodes are formed by epitaxial deposition of relatively weakly N-type material on an N+ type Si wafer 10 and diffusion or ion implantation of B into the deposited layer to form a P + type region 12. An Au electrode is applied to the P+-type region 12 and an Ag heat sink pad 13 is electroplated thereon. The wafer is then etched to form a plurality of mesas, and this tends to cause the redeposition of Ag across the junction. The detrimental effect of this Ag is removed by selectively deplating from the N- type region as described above in a solution of potassium cyanide, potassium carbonate, " Sel Rex " (Registered Trade Mark) silver salts and water. This process also indicates diodes in which the junction is not satisfactorily formed, since such devices tend to deplate badly and may be discarded. The wafer is then diced. The invention is equally applicable to transistors, S.C.R.'s &c.