Junction contact materials and interfaces in Si channel devices
- PDF / 583,226 Bytes
- 4 Pages / 585 x 783 pts Page_size
- 18 Downloads / 207 Views
troduction Semiconductor to metal contact engineering and contact material development have become crucial in recent years to keep pace with the continual improvement in electronic device performance. As device dimensions shrink and device performance improves, increasing current densities in devices is causing the semiconductor-metal contacts and semiconductor junctions to severely affect the device performance. This will require new contact materials and innovative materials engineering to cater to complementary metal-oxide semiconductors (CMOS) in dual n -type and p-type contacts requirements. In addition, introduction of new device architectures such as FinFET (fin-shaped fieldeffect transistor) and nanowire FETs is also accompanied by technological challenges in contacts, such as requirements for three-dimensional contact schemes. This review focuses on some of the key issues in the development of contact materials for advanced Si CMOS technologies. Various ways to engineer highly conductive silicide contacts (see Figure 1 in the article by Wen and Chambers in this issue) for a sub-32 nm technology node will be explored. Techniques of lowering Schottky barrier height (SBH) in nickel silicide by usage of low work function metals, improved carrier concentration via dopant segregation, implanted impurity, and silicide phase modulation will be discussed, with particular
focus on the technology requirement of contact pitch scaling for a sub-32 nm technology node.
Silicide contacts Ohmic contacts to semiconductors have typically been achieved through a single metal or silicide to degenerately doped silicon. For sub-50 nm gate length, the contribution of the contact resistance Rco (or contact resistivity ρCO when normalized by area), which is the resistive component from the metal silicide to the highly doped source drain, is expected to dominate over other parasitic components.1 Yu proposed a theoretical model for thermionic field emission between the metal/silicide and silicon, which shows ρCO is directly proportional to the SBH, ϕB, and is inversely proportional to the square root of the dopant concentration, Nd, in the semiconductor.2 See Equation 1 in the introductory article of this issue.
Work function modulation While NiSi has a low Schottky barrier to p-Si(100), ϕBp, it has a complementary high Schottky barrier, ϕBn, of 0.65–0.7 eV on nSi(100), since ϕBn + ϕBp = 1.1 eV (Si bandgap). Using rare-earth metals (which have one of the lowest metal work functions), Tu et al. have shown a low ϕBn of 0.37–0.39 eV for disilicides of Dy, Er, Gd, Ho, and Y to n-Si.3 Further studies also have shown that a very high hole Schottky barrier ϕBp of 0.82 eV
Wei-Yip Loh, Sematech, Austin, TX, USA; [email protected] Brian Coss, Sematech, Austin, TX, USA; [email protected] DOI: 10.1557/mrs.2011.7
© 2011 Materials Research Society
MRS BULLETIN • VOLUME 36 • FEBRUARY 2011 • www.mrs.org/bulletin
97
JUNCTION CONTACT MATERIALS AND INTERFACES IN SI CHANNEL DEVICES
(corresponding to ϕBn ~0.27 eV assuming ϕBn =
Data Loading...
