Technical Insight
Modular concept overcomes SiGe bipolar process problems
There is still plenty of room for improvement to the SiGe bipolar processes that are now being used by many RFIC manufacturers. Ted Johansson and Johan Pejnefors describe a process that overcomes some common problems with the base layer epitaxy.
The performance of silicon-based high-speed bipolar transistors has improved greatly during the last few years. At the 2002 IEDM meeting, IBM reported a Si-based HBT with a record cut-off frequency of 350 GHz. The basis of this technology is an epitaxially grown SiGe base layer, which makes it possible to engineer the bandgap and to achieve a narrower base than in Si-only bipolar technology. The inevitable boron out-diffusion from the base layer during high-temperature processing steps can be minimized by the addition of
