Reduction of Defects in Ion Implanted Bipolar Transistors by Argon Back Side Damage

Abstract

The effectiveness of argon backside implants on the reduction of defects in an implanted bipolar process has been investigated. Insertion of an argon backside implant at two places in the processing sequence has been found to be beneficial. A backside implant before initial oxidation of the wafers will minimize the density of epitaxial defects for both arsenic diffused or implanted buried layers. For diffused buried layers, the backside damage offers only minimum improvement in yield because of the gettering action of the diffused arsenic itself. For implanted buried layers, the backside damage allows for higher arsenic doses and shorter etch‐back prior to epi growth, resulting in lower sheet resistance while still maintaining acceptably low defect levels. Correlation of electrical parameters and crystal defects showed that small defects in the emitter, probably dislocations generated by the implanted emitter process are responsible for “piped” transistors, leaky base emitter junctions, and poor low current beta. An argon backside implant just prior to emitter processing will reduce the density of these small defects and improve device yield.