Process for fabricating a lateral transistor having self-aligned base and base contact

Claim 1

A process for fabricating a lateral bipolar transistor with self-aligned low resistance base contact comprising: sequentially depositing on an underlying first conductivity type layer of semiconductor material a first polycrystalline silicon layer, then a metal silicide layer; forming on the metal silicide layer a three-layer sandwich having a lower, a middle and an upper layer, the upper and lower layers of the three-layer sandwich being substantially impervious to a selected impurity, but not the middle layer; removing a portion of the upper and the middle layers to define an edge; introducing selected impurity into the middle layer through the edge to define a zone of impurity in the middle layer; removing all of the upper layer, then all of the middle layer except for the zone of impurity; removing all of the lower layer and the metal silicide layer except where each of these is overlaid by the zone of impurity, thereby to define a remaining region of the lower layer; removing all of the metal silicide layer except that portion overlaid by the remaining region, then removing all of the zone of impurity and all of the first polycrystalline silicon layer except that portion of the first polycrystalline silicon layer overlaid by the remaining region to thereby provide a metal silicide/polycrystalline silicon contact to the first conductivity type layer of semiconductor material; laterally etching the metal silicide layer and the first polycrystalline silicon layer to undercut the lower layer; forming insulating material over all of the first polycrystalline silicon layer, the metal silicide and the first conductivity type layer of semiconductor material except where the first conductivity type layer of semiconductor material is overlaid by the first polycrystalline silicon layer; removing all of the insulating material except that masked by the lower layer; and using the lower layer as a mask, introducing opposite conductivity type impurity into the first conductivity type layer of semiconductor material to thereby form a collector and an emitter of a lateral bipolar transistor.