Emitter-base short issue study and improvement in a low cost and high performance 0.18um SiGe BiCMOS process

This paper studied the short issue of the emitter and the base, which is frequently found in the fabrication of the SiGe HBT devices. The physical failure analysis reveals that the main reason is the formation of cobalt silicide in the emitter poly-Si sidewall. Reducing the lower electrode voltage and source power of the main etch step can reduce the byproducts accumulation during etching and improve the emitter poly-Si profile. Adjusting the etch time ratio of main etch and soft landing makes the polysilicon angle improved from less 80° to 88° and eliminate the footing issue. It is found that the PECVD film has poor coverage, and that by LPTEOS shows better coverage. And by increasing the oxide film thickness from 80nm to 160nm, the width of emitter poly (EP) sidewall spacer after etching is 105nm. Before cobalt silicide formation, the sidewall spacer width is 63nm, which can play a role of a good protection layer for the emitter polysilicon and isolate the emitter from the base of the SiGe HBT.