AVS 52nd International Symposium
    Electronic Materials and Processing Monday Sessions
       Session EM-MoM

Invited Paper EM-MoM1
Electronic Properties of High-K Dielectrics and their Interfaces

Monday, October 31, 2005, 8:20 am, Room 309

Session: Electronic Properties of High-k Dielectrics and their Interfaces
Presenter: J. Robertson, University of Cambridge, UK
Correspondent: Click to Email
The continued scaling of CMOS devices means that SiO2 must be replaced as gate oxide by a dielectric of higher dielectric constant (K) to minimise gate leakage.@footnote 1@. The presently preferred candidates are HfO2, its silicates and nitrided alloys. La oxide and LaAlO3 are possible in the future. The reasons for this selection in terms of band offsets will be given,@footnote 2@ including their measurement and calculation. Despite much success in developing growth methods for high K oxides, including ALD, presently the performance of FETs with HfO2 are worse than those with SiO2 in terms of threshold voltage shifts, carrier mobility and trapped charge. This arises partly from the more complicated interface structure and greater bonding possibilities than at an Si:SiO2 interface. We show it is possible to define an ideal abrupt Si:HfO2 interface in terms of its bonding; only Hf-O and Si-O bonds or only Hf-Si bonds.@footnote 3@ In fact, a number of high symmetry and lower symmetry abrupt interfaces are possible. The structure, electronic structure and band offsets for these are given. It is then possible to define a defective interface; one containing mixed bonding. It is shown how such mixed bonding at the "back interface" between the HfO2 and poly-Si gate may be the cause of the excessive gate threshold voltages.@footnote 4@@FootnoteText@@footnote 1@ J Robertson, "High dielectric constant oxides", Euro Phys J Appl Phys 28 265 (2004) @footnote 2@ J Robertson, "Band offsets of wide band gap oxides and implications for future electronic devices", J Vac Sci Technol B 18 1785 (2000) @footnote 3@ P W Peacock, J Robertson, "Bonding, energetics and band offsets of Si-ZrO2 high-dielectric constant gate oxide interfaces", Phys Rev Letts 92 057601 (2004) @footnote 4@ K Xiong, P W Peacock, J Robertson, "Fermi level pinning and Hf-Si bonds at HfO2: poly-Si gate electrode interfaces", App Phys Lett 86 012904 (2005).