High-Performance SiGe MODFET Technology
- PDF / 638,113 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 113 Downloads / 195 Views
B7.2.1
High-Performance SiGe MODFET Technology S. J. Koester, J. O. Chu, K. L. Saenger, Q. C. Ouyang, J.A. Ott, D. F. Canaperi, J. A. Tornello, C. V. Jahnes, and S. E. Steen IBM Research Division, T. J. Watson Research Center 1101 Kitchawan Rd / Rte 134 P.O. Box 218 Yorktown Heights, NY 10598 ABSTRACT An overview of SiGe modulation-doped field-effect transistor (MODFET) technology is provided. The layer structures and mobility enhancements for both p- and n-channel modulation-doped quantum wells are described and compared to mobilities in Si/SiO2 inversion layers. Next, previous results on high-performance n- and p-MODFETs fabricated at IBM and elsewhere are reviewed, followed by recent results on laterally-scaled Si/SiGe n-MODFETs with gate lengths as small as 70 nm. We conclude with a discussion of the materials issues for the future vertical and lateral scaling of SiGe MODFETs. INTRODUCTION SiGe-based heterostructure bipolar transistors (HBTs) have been the enabling factor in establishing Si-based technology as a viable contender in the rf communications marketplace. While SiGe HBTs are an established commercial technology [1], the steady progress made on SiGe modulation-doped field-effect transistors (MODFETs) in recent years, indicates that these devices hold promise to further expand the capabilities of Si technology for rf and microwave communications applications. SiGe MODFETs are based upon the principle of using strain to provide carrier confinement and enhanced mobility to improve FET performance. The most common technique for creating these strained layers is to start with a low-defect-density relaxed Si1-xGex buffer layer (grown on a Si substrate) that can then be used as a template for subsequent strained-layer growth [2]. Strained Si layers grown on relaxed SiGe are under biaxial tensile strain, which splits the six-fold conduction-band degeneracy, reducing the in-plane electron effective mass as well as the intervalley scattering rate [3]. The strain splitting also leads to a staggered band alignment, with the formation of a potential well for electrons [4]. Similarly, a thin Si1-yGey layer grown on Si1-xGex (y > x) will be under biaxial compressive strain, leading to splitting in the valence band, reducing inter-band scattering and improving the hole mobility [5]. The band offset created by the strain also produces a confining potential for holes [4]. SiGe MODFETs specifically utilize this carrier confinement to implement the well-known III-V technique of modulation doping [6], whereby the quantum well is separated from dopants in one or both of the barrier regions by a thin undoped spacer layer. This technique efficiently populates the quantum well with minimal additional ionized impurity scattering, and eliminates the adverse effects of surface roughness scattering that occur in surface-channel MOSFETs. In the following section, a description of Si/SiGe/Ge modulation-doped quantum wells and the mobility enhancement that can be obtained in these layer structures is provided.
B7.2.2
MOBILITY ENH
Data Loading...
