TCAD based development of a polysilicon emitter transistor in a BiCMOS technology

Continuing advances in silicon integrated circuit technology lead to todays very large scale integrated circuits with several millions of transistors per single chip. High density and low power consumption advantage made CMOS technology to the leading silicon fabrication technology. Over the last decade the demand for higher speed and better analog circuit gave rise to the BiCMOS technology, where bipolar and MOS devices are fabricated on the same silicon substrate. For mobile telecommunication applications the advantage of low power CMOS and fast bipolar operation permit battery powered, handhold telephones. Although the principle of the BiCMOS process was invented already in the early 1970s, its importance emerged only in the late 1980s. The goal of this thesis is the development of a polysilicon BiCMOS tech¬ nology using modern TCAD simulation tools. A newly developed polysilicon bipolar transitor is integrated into a industrial CMOS technology. Comparison of simulation to measurement of electrical and physical properties show the advantages and disadvantages of modern silicon TCAD tools. This thesis describes the design ofthe bipolar transistor, the development of the fabrication process and the characterization of the resulting transistor. Prior to the actual design of the process a feasibility study is made evaluating the best possible bipolar device for the given constraints of the existing process and the targeted application. Successful integration of the process in the fabrication line is demonstrated discussing the major problems. Thanks to the process and device simulation the first fabrication resulted in functional bipolar transistors. Characterization ofthe produced polysilicon emitter bipolar transistors showed a small-signal current gain up to 3GHz.