High voltage bipolar transistor and method of fabrication

摘要

High voltage bipolar transistors built with a BiCMOS process sequence exhibit reduced gain at high current densities due to the Kirk effect. Threshold current density for the onset of the Kirk effect is reduced by the lower doping density required for high voltage operation. The widened base region at high collector current densities due to the Kirk effect extends laterally into a region with a high density of recombination sites, resulting in an increase in base current and drop in the gain. The instant invention provides a bipolar transistor in an IC with an extended unsilicided base extrinsic region in a configuration that does not significantly increase a base-emitter capacitance. Lateral extension of the base extrinsic region may be accomplished using a silicide block layer, or an extended region of the emitter-base dielectric layer. A method of fabricating an IC with the inventive bipolar transistor is also disclosed.

主权项

1. A method of forming an integrated circuit, comprising:
providing a semiconductor substrate; forming a buried layer of n or p conductivity type in the semiconductor substrate; forming an epitaxial layer of semiconductor material of the same n or p conductivity type over the buried layer; the epitaxial layer and the buried layer defining a collector of a bipolar transistor; forming regions of field oxide in a top portion of the epitaxial layer, but not a bottom portion of the epitaxial layer; forming a base layer of opposite n or p conductivity type over the epitaxial layer including over at least part of the field oxide regions; the base layer defining a base of the bipolar transistor; forming a dielectric layer over the base layer; patterning the dielectric layer to define an emitter opening; forming an emitter layer of same n or p conductivity type semiconductor material over the dielectric layer and within the emitter opening; patterning the emitter layer to remove the emitter layer overlying the field oxide regions and to remove at least part of the emitter layer overlying the base layer not overlying the field oxide portions, forming a silicide block layer over the patterned emitter layer; and patterning the silicide block layer to form monolithic silicide blocking structures around and overlapping the patterned emitter layer and extending onto the base layer; wherein the silicide blocking structures are patterned to expose the base layer overlying the at least part of the field oxide regions; doping the base layer through the emitter opening to form an emitter-base junction region of the same n or p conductivity type in the base layer; the emitter-base junction region being laterally spaced from the at least part of the field oxide regions; and the emitter layer and emitter-base junction region defining an emitter of the bipolar transistor; and forming at least one base contact region over the base layer, in a position laterally spaced from the emitter-base junction region.