Reduced time high temperature processing for thyristor silicon wafers

Thyristor diffused silicon wafers are usually manufactured by means of the planar technology which requires at least three high temperature treatment stages. Two processing flow variants with only two diffusion processes above 1000/spl deg/C and without use of the planar process, have been experimented with for thyristor wafer manufacturing. In one of them, boron diffusion at 1200/spl deg/C for ten hours has been used to obtain the two blocking junctions. In the second one, a four hour diffusion at 1200/spl deg/C of aluminium for the forward blocking junction and aluminium and boron for the reverse blocking junction have been carried out. Final diffused N/sup +/PNP/sup +/ wafers have been obtained by phosphorus diffusion on the side of the wafer where the P diffused layer has a surface concentration around of 10/sup 19//cm/sup 2/. The diffusion sources were deposited as thin films at low temperature on the wafer sides. Good performance medium power thyristors have been obtained by the above processing variants. The processing flow variant where aluminium is used as doping impurity has the advantage of a shorter total time required for the high temperature treatments.