Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session W14: Focus Session: Electronic and Atomic Structures of Interfaces and Gate Stacks II |
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Sponsoring Units: FIAP Chair: Gerd Duscher, NCSU Room: LACC 403B |
Thursday, March 24, 2005 2:30PM - 3:06PM |
W14.00001: Interface phases and the future of the nanotransistor Invited Speaker: Advances in the epitaxial growth of ultra-thin films and heterojunctions have made viable new classes of device applications that may sustain the semiconductor roadmap for another decade. However, this progress will require an in-depth understanding and utilization of electronic processes at the nanoscale. One of the central issues is the role of interfaces between materials, where most of the electronic properties of the system are determined. In this talk, I will discuss recent fundamental advances in our understanding of the physics of nano-scale interfaces and introduce the concept of interface “phase”, a region of structure-specific chemical bonding that determines the properties of heterojunctions. This interface phase results in a “Coulomb buffer” that can be tuned to adjust the overall electronic properties of the system. These ideas will be elucidated through the prototypical example of the Field Effect Transistor, where the interfaces between semiconductors, oxides and metals will be analyzed in terms of the novel concepts of interface phase and Coulomb buffer. ( Work done in collaboration with M. Nunez (NCSU), R.A. McKee (ORNL) and W.J. Walker (ORNL)) [Preview Abstract] |
Thursday, March 24, 2005 3:06PM - 3:18PM |
W14.00002: Defects at Si-SiO$_2$ and internal dielectric interfaces in high-k gate stacks for Si devices Gerald Lucovsky, J.C. Phillips The performance and reliability of Si field effect transistors (FETs) are determined in large part by electronically-active defects/defect precursors at the Si-SiO$_2$, and internal SiO$_2$-high-k dielectric interfaces. Defect/defect precursor reduction is associated with bond-strain driven interfacial self-organizations taking place during high temperature, inert ambient annealing and are addressed through the application of bond constraint theory to the Si-SiO$_2$, and internal SiO$_2$-high-k dielectric interfaces. The Si-SiO$_2$ interface is crucial with respect to interface trapping, and scattering of charge carriers in the FET channels. An empirical roughness scattering parameter at this interface reflects the scale of the interfacial self-organization, $\sim$ 5 nm. The step in the average number of bonds/atom at the internal dielectric interface determines the fixed charge density, Q$_f$, at that interface, and has been reduced by more than a factor of ten by self-organizations in devices with Hf and Zr high-k dielectrics. [Preview Abstract] |
Thursday, March 24, 2005 3:18PM - 3:30PM |
W14.00003: Ab-Initio Study of the Effect of Hydrogen and Point Defects on Arsenic Segregation at Si (100)/SiO2 Interfaces Karthik Ravichandran, Wolfgang Windl, Tao Liang The previously suggested segregation model for arsenic at Si/SiO$_{2}$ interfaces based on a combined trapping/pairing model [J. Dabrowski \textit{et al}., Phys. Rev. B \textbf{65}, 245305 (2002)] requires high binding energies for interface vacancies, which our results of $\approx $ 0.2 eV cannot confirm. As an alternative explanation, we present ab-initio results which show that As and hydrogen bond with an energy gain of 1.5-3 eV with their minimum-energy position at the interface, which creates additional trapping sites for As segregation. We also find a similar situation in case of boron segregation. The inclusion of hydrogen into the modeling might thus be able to explain the differences between the previous model and experiments. [Preview Abstract] |
Thursday, March 24, 2005 3:30PM - 3:42PM |
W14.00004: Interaction of Hydrogen with Silicon-Silicon Dioxide Interfaces Renee M. Van Ginhoven, Harold P. Hjalmarson, Peter A. Schultz, Blair Tuttle Hydrogen released by ionizing radiation reacts with hydrogen- passivated Si dangling bonds at the Si-SiO$_{2}$ interface to create interface traps (Pb-centers) in Si semiconductor devices. For certain bipolar transistors the resultant gain degradation increases as the dose rate is reduced for a given total dose of ionizing radiation. This phenomenon is known as Enhanced Low Dose Rate Sensitivity (ELDRS). In this presentation, the interaction of the hydrogen with the interface and with the dangling bonds will be discussed. Our results are obtained from electronic structure calculations (SeqQuest) on supercell models of silicon dioxide and its interface with silicon. These results provide boundary conditions for hydrogen interaction with the interface that are used for continuum calculations of the interface trap density dependence on radiation dose rate. [Preview Abstract] |
Thursday, March 24, 2005 3:42PM - 4:18PM |
W14.00005: Atomic structure of novel epitaxial oxide/semiconductor interfaces Invited Speaker: Further scaling of complementary metal-oxide-silicon field-effect transistors may require alternative gate dielectrics. Ultimately, interfaces between Si and these new gate dielectrics need to be atomically abrupt, which may require epitaxial interfaces. In this presentation, we identify the interfacial atomic structure of novel epitaxial Si/oxide interfaces and address some of the challenges in obtaining high-quality heterostructures. We report atomic resolution observations of epitaxial Si/LaAlO$_{3}$ and Si/Sc$_{2}$O$_{3}$ interfaces using scanning transmission electron microscopy. An unusual interface reconstruction of the (001) LaAlO$_{3}$/Si epitaxial interface is observed, with every third La column removed from the interface plane. The interface atomic structure is discussed in the context of electrically favorable interfacial bonding between the ionic oxide and Si. Ideally, bonding at the LaAlO$_{3}$/Si interface satisfies the valence requirements of the oxide and produces no dangling Si bonds for an insulating interface. We show that electrically favorable LaAlO$_{3}$/Si interfaces may be difficult to obtain unless processing or growth provide for additional passivation. Epitaxial Sc$_{2}$O$_{3}$ with the cubic bixbyite structure on (111) Si show a high density of misfit dislocations, which relieve the lattice mismatch by forming a hexagonal network. A high-density of antiphase boundaries is observed. These defects form because films nucleate with no unique arrangement of the ordered oxygen vacancies of the bixbyite lattice relative to the Si substrate lattice. [Preview Abstract] |
Thursday, March 24, 2005 4:18PM - 4:30PM |
W14.00006: Electron Spin Resonance Observation of Si/Dielectric Interface Traps in Fully Processed Metal Gate Hafnium Oxide Field Effect Transistors Thomas Pribicko, Jason Campbell, Patrick Lenahan, Wilman Tsai Hafnium oxide is arguably the leading candidate for SiO$_{2}$ replacement in future MOS transistors. Using spin dependent recombination (SDR), we have investigated the dominating (100) Si/HfO$_{2}$ interface defects on fully processed metal/gate transistors. We find that the densities of these defects may be altered greatly by gate dielectric stressing. Transistor SDR spectra display a g-value of 2.0051when the magnetic field is perpendicular to the (100) Si surface. Although sample rotation in the magnetic field alters the average g-value, we are as yet unable to clearly resolve the SDR pattern into several anticipated lines. The observed defects appear to be similar, but probably not identical to P$_{b0}$ centers and may be a superposition of P$_{b1}$- and P$_{b0}$-like centers. After in-situ gate voltage stressing at modest gate voltages, we observed that the SDR amplitude of the (100) Si/HfO$_{2}$ interface P$_{b}$-like spectrum increases with the application of an increasing gate voltage. A hysteretic behavior in the SDR response was observed when modest negative and positive voltages were applied to the gate. This suggests that the application of modest gate voltages changes the chemical/physical nature of the observed defect. Work at Penn State was supported by the Semiconductor Research Corporation through Intel Corporation Funding. [Preview Abstract] |
Thursday, March 24, 2005 4:30PM - 4:42PM |
W14.00007: Paramagnetic Centers in Hafnium Oxide Films on Silicon Jason Ryan, Jason Campbell, Thomas Pribicko, Patrick Lenahan, John Conley, Wilman Tsai We have investigated paramagnetic defects in hafnium oxide films prepared under a fairly wide variety of processing parameters; most films were deposited with atomic layer deposition. Deposition took place on both hydrogen terminated silicon and on silicon substrates upon which a thin chemical oxide had previously been grown. In all samples, we observe Si/dielectric interface defects similar to the Si/SiO$_{2}$ interface P$_{b}$ centers. However, we note differences between the g tensors of defects observed in hydrogen terminated silicon substrate samples and those observed on the thin chemical oxide/silicon substrate samples. In hydrogen terminated substrate samples we consistently observe shifts in the g perpendicular component of the g tensor toward high values than those found in Si/SiO$_{2}$ structures. This is not necessarily the case in hafnium oxides films deposited upon very thin SiO$_{2}$ films on silicon. We also observe several paramagnetic centers in the dielectric themselves. As previously reported, we have observed a likely O$_{2}^{-}$ center. In addition, in some samples we observe a narrow ESR spectra with zero crossing g values very close to that of the free-electron g = 2.001 to 2.003. The density of these paramagnetic defects are strongly processing dependent. We speculate that these centers are within the dielectric, but very near the silicon substrate, and likely involve an unpaired electron on a silicon atom in the oxide. Work at Penn State was supported by the Semiconductor Research Corporation through Intel Corporation Funding. [Preview Abstract] |
Thursday, March 24, 2005 4:42PM - 5:18PM |
W14.00008: Atomic-scale challenges in nano-MOSFETs: Gate dielectrics and device modeling Invited Speaker: As microelectronics enters the regime of nano-scale dimensions, new materials are being introduced and new challenges emerge in modeling devices, as standard approximations break down. The channel and gate dielectric in MOSFETS present key challenges as normal Si is replaced by strained Si in the channel, Silicon-on-Insulator technology leads to the adoption of double gates, and SiO$_{2}$ is replaced by ``alternate dielectrics.'' The talk will address issues on interface structure and electronic properties of alternate dielectrics and present new results obtained by first-principles and atomic-resolution Z-contrast microscopy; address reliability issues such as negative bias temperature instability; describe mobility calculations by first-principles theory and atomic-scale interface models, and describe first-principles calculations of Fowler-Nordheim tunneling. [Preview Abstract] |
Thursday, March 24, 2005 5:18PM - 5:30PM |
W14.00009: Nitrided hafnium silicates for gate dielectrics Chang-gong Wang, Mohith Verghese, Eric Shero, Glen Wilk, Jan Willem Maes, W. Deweerd, R. Opila, J. Morais Nitrided hafnium silicate (HfSiON) gate dielectric films deposited by atomic layer chemical vapor deposition (ALCVD$^{TM})$ show excellent capacitor and transistor characteristics with both poly-Si and metal gates, which are directly correlated with local physical and chemical properties. A wide range of compositions are demonstrated, with Si/(Hf+Si) percentages from 0 to 75{\%} and uniformly distributed N levels up to 30 at. {\%}. XPS is used to distinguish the local bonding arrangements of N to Hf, Si and O. The distribution and depth profile of these N bonds is directly attributable to the observed electrical and physical properties of these films as measured by TOF-SIMS, TEM, EELS, nuclear reaction analysis and angle-resolved XPS. Using poly-silicon gate electrodes with chemical or thermal oxide underlayers, EOT values down to 1.3nm with substantial leakage reduction vs. SiO2 have been achieved using stacks with ultrathin HfSiON. Hysteresis and midgap interface density (Dit) are less than 10mV and 5X10$^{10 }$cm$^{-2}$eV$^{-1}$, respectively. Transistors (gate length of 110nm) with these ALD HfSiON films display excellent V$_{T }$stability and channel electron mobility $>$ 90{\%} of SiO2 at high Eeff. Detailed analysis on silicate compositions, the distribution of nitrogen in the interface layers, and corresponding impact on device performance will be presented. [Preview Abstract] |
Thursday, March 24, 2005 5:30PM - 5:42PM |
W14.00010: Medium Energy Ion Scattering Study of Oxygen Diffusion-Reactions in High-k Dielectrics on Si Lyudmila Goncharova, Dmitri Starodub, Robin Barnes, Eric Garfunkel, Torgny Gustafsson, Gennadi Bersuker, Brendan Foran, Pat Lysaght Understanding the thermodynamics and kinetics of film growth during fabrication of high-$\kappa $ gate stacks is vital to establish atomic level control of interfacial layers and to minimize defects. Annealing such films in different atmospheres may lead to diffusion and reactions with significant consequences on the electrical properties. We have used high-resolution medium energy ion scattering in combination with isotope tracing to investigate oxygen transport in model systems, including Hf and Ce oxides. The reaction of oxygen (p$_{O2}$=10$^{-2 }$Torr) with HfO$_{2}$(SiO$_{2})_{x}$/Si films at 500$^{o}$C was dominated by oxygen isotopic exchange (not SiO$_{2}$ interfacial growth). The oxygen exchange rate decreases with an increase of SiO$_{2}$ fraction in Hf silicate films and is almost fully suppressed (at 500$^{o}$C) for a (HfO$_{2})$:(SiO$_{2})$=1:1 film composition. This reaction saturated with time and appeared to be enhanced after film recrystallization. Annealing in a nitrogen-containing atmosphere result in reduced O$^{18}$ incorporation and exchange. In comparison to Hf dielectrics, Ce silicates exhibit rapid interface growth upon oxygen exposure. Incorporating nitrogen into the structure lowers the rate of subsequent oxygen diffusion and incorporation. [Preview Abstract] |
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