High-performance silicon-germanium technology

This paper will focus on the various and ubiquitous uses of silicon-germanium (SiGe) in high-performance silicon-based semiconductor technology. SiGe can now qualify as a "mature" technology - it is almost 20 years since the first SiGe HBT work. It is 10 years since the qualification of SiGe as a manufacturable silicon technology in a high-volume silicon fabricator [1]. In the past few years the total SiGe silicon (wafer) area shipped has outstripped III-V ICs. SiGe frequencies have gone up 8× in 10 years! Starting at 47GHz, current results demonstrate f _T of 350+ GHz in f _T-optimized devices, and f _MAX of 300 GHz [2], though not at the same time. We have also achieved simultaneous f _T and f _MAX in excess of 275 GHz. These results are driving the feasibility of new markets such as 60GHz wireless LAN. The process improvements and device components that contributed to this improvement will be discussed. SiGe-based MODFETs for microwave performance have also been demonstrated [3]. In spite of the microwave losses in silicon, the metallization can be designed for good performance at microwave frequency [4]. Process design tradeoffs for microwave frequency will be discussed. In the opto-electronics realm, much progress has been made on high-speed SiGe integrated photo-detectors [5]. We will discuss process requirements for integrating photo-detectors with CMOS, as well as potential advantages. SiGe is also making inroads into silicon CMOS processor technology - the "meat and potatoes" of the high-volume silicon business. This is because more and more innovation is required to maintain Moore's law of Silicon scaling. Improvements in performance are now coming from mobility improvement in silicon by straining the inversion channel silicon layer. We will discuss two such applications. The first is use of SiGe to create uniformly-strained silicon layers and improve the mobility [6]. The second is embedded SiGe source-drains to apply non-uniform strain in the MOSFET channel. In such MOSFETs it is now possible with conventional lithography to reach gate lengths of 30nm on billions of transistors in a single chip, rivaling electron-beam lithography defined InP HEMTs - a new paradigm for the microwave world.