Npn/pnp fabrication process with improved alignment

Abstract

An improved merged transistor logic (I.sup.2 L) process is disclosed which provides a practical technique for forming micron to sub-micron window size devices. In a single step, the process forms all of the contact and guard ring windows in the passivation layer and then by use of selective blocking of various combinations of these windows, the various ion-implanted regions of the devices are formed with a minimum number of hot processing steps. A second embodiment of the method forms a double diffused lateral PNP device having an asymmetrically placed emitter within the base so as to enhance the injection efficiency in the vicinity of the collector. A micron to sub-micron window for the formation of all contacts and guard ring permits a merged transistor logic structure to be formed having a reduced upward NPN collector-base capacitance, lower PNP emitter-base diffusion capacitance, a lower PNP base series resistance, and an increased probability of avoiding collector-emitter pipe defects. The formation of all the windows in the passivation layer and the use of selective photoresist blocking to define the various ion-implanted regions in the device permit the practical formation of a minimum size (self-aligned contact to guard ring) MTL device with a minimum number of critical mask and hot processing steps. The advantages also apply to downward NPN and individual PNP devices.