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UK SiGe Research Programme EPSRC Final Review Meeting, Thursday November 4th 2004

Device Modelling in the New Silicon Era & the future with silicon John Barker Nanoelectronics Research Centre Department of Elelectronics and Electrical Engineering University of Glasgow. UK SiGe Research Programme EPSRC Final Review Meeting, Thursday November 4th 2004

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UK SiGe Research Programme EPSRC Final Review Meeting, Thursday November 4th 2004

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  1. Device Modelling in the New Silicon Era & the future with silicon John Barker Nanoelectronics Research Centre Department of Elelectronics and Electrical Engineering University of Glasgow UK SiGe Research Programme EPSRC Final Review Meeting, Thursday November 4th 2004 Electrical and Electronic Engineering Dept, Imperial College,

  2. Human Resources John Barker Asen Asenov Scott Roy Jeremy Watling Savas Kaya Mirela Borici Richard Wilkins Lianfeng Yang Antonio Martinez

  3. Outline • Deliverables: Publications, Conferences, Grants, Collaborations • Context: where we are with Si and SiGe (update) • Theory and Modelling: 3D atomistic Full Band Monte Carlo, 3D Non-equilibrium Green function atomistic simulator 3D NASA codes High dielectrics Devices: conventional versus strained Si MOSFETs Nano-silicon and atomistic MOSFETs • The future with silicon(I come to bury silicon not to praise it!)

  4. Deliverables in Phase I-II (2001-2004): I Publications: > 50 (major journals inc IEEE Trans) Review paper:”The impact of interface roughness scattering and degeneracy in relaxed and strained Si n-channel MOSFETs” Solid State Electronics, 48, 1337-1346 (2004) Special mention:”I am pleased to tell you that your article, "Si/SiGe heterostructure parameters for device simulations", in Semiconductor Science and Technology, Vol 19, pp1174 (2004), has been downloaded 250 times so far.To put this into context, across all IOP journals 10% of articles were accessed over 250 times this quarter.” Conferences: IEDM, ESSDERC, Si-VLSI, ICPS26, ICPS27, VLSI02,03,04 CMMP04,SISPAD,NEGF2,MSED03,EDSSC03, EDMO,ULSI04,ICSIT04,IWCE9, SIMD-6,NPMD03, HCIS13, IWCE10,HighKWorshopAustin04,Sematech SympInvited papers: 12 Special notice: Paper accepted for IEDM’04.

  5. Deliverables (2001-2004): II New Grants and Collaborations Statistical 3D simulation of intrinsic parameter fluctuations in decananometer MOSFETS introduced by discreteness of charge and matter A Asenov, J.R. Barker, S Roy, J Watling EPSRC HPC facility EPSRC 01/10/04-30/09/04 £ 153021 Modelling the impact of high-k gate stacks on mobility device performance and intrinsic parameter fluctuations J. Watling , A. Asenov ,J.R.Barker, S. Roy; and UCL; International Sematech 09/2004-10/2006 $ 310 000 SINANO - Network of Excellence A. Asenov , J.R. Barker,S. Roy IMEC, LETI, INFINEON, ST MICROELECTRONICS European Commission 01/2004-02/2007 € 250 000 Sub 100 nm III-V MOSFETs for Digital Applications With 14 others MOTOROLA, University of Surrey EPSRC 09/2003-09/2006 £ 3000 000 Meeting the materials challenges of nano-CMOS electronics A Asenov, J.R. Barker and S Roy collaboration with University College London and NASA Ames EPSRC, 01.07.04-30.06.08: £ 354711 6. Atomistic simulation of nanoscale devices A Asenov, J.R. Barker, S Roy EPSRC Platform grant, 06.02-05.07: £ 429564

  6. Other stuff DFT collaborations underway Intel using SiGe/Si hole band model for compact studies. Sharing atomistic codes NASA 2D and 3D NEGF codes to be shared with Glasgow Our 3D atomistic NEGF codes to be shared with NASA INDUSTRY: IBM, Intel,Toshiba NASA, Sony, Freescale…

  7. 2002 Context: where we are with Si and SiGe The dramatic acceleration of the ITRS is due to the failure of conventional MOSFETs to meet the performance requirements.

  8. Intel Brute force scaling of MOSFETS will not work • Requires • Too thin oxide • Too high doping Too Hot Toshiba • Results in • High leakage • Gate oxide and band to band tunnelling • Low performance • Impurity scattering limited mobility • Intrinsic parameter variations • Random dopants and interfaces Intel 10 nm The conventional MOSFET will need a replacement somewhere between the 65 nm and the 45 nm technology nodes.POST CMOS

  9. The IBM 6 nm silicon transistor (IEDM 2002) demonstrated New Post CMOS architecture solves problem

  10. Context: where we are with Si and SiGe 2004 Research pushes MOSFET designs down to 4-5 nm High K dielectric take-up is high(gate leakage stopped dead) Some problems in old CMOS yield at 90 nm node IBM. Intel Parallel track developing: Plan A-aggressive scaling Plan B-multi-core and other architecture developments NoC/SoC SiGe and strained silicon: Huge interest: definitely on board for coming generations

  11. The Post CMOS Si developments have two mainstreams • New materials SiGe, Ge, Strained Si • Lower effective mass • Increased mobility • Reduced scattering • Higher carrier velocity • Ballistic transport Improves device performance compared to Si • New device architectures UTB SOI, Multiple gates • Better electrostatic integrity • Reduced SCE • Improved drivability • Relatively thicker oxide • Ballistic transport Allows scaling to nanometer dimensions High K: new issues Members of the SiGe consortium have carried out pioneering work in these two mainstream areas.

  12. The Post CMOS devices are immensely complex from physics and technology point of view Double-gate Fin-FET Omega-gate UTB SOI SON SiGe Quantum Strained Si Confinement Pure Ge Tunnelling High-K Non-equilibrium TiN 10 nm DG MOSFET Ballistic NiSi Metal gate Schottky S/D Atomistic Replacement gate Raised S/D Silicon is once again an exciting area for research. Huge challenge for device modelling

  13. Mobility in UTB SOI K. Ushida IEDM 02 Quantum potential variation Associated with UTB variation • Scattering from two interfaces • Surface phonons • TO phonons coupling • Remote Coulomb scattering • Interface charge scattering • Body thickness fluctuations • Material composition fluctuations • High-k composition fluctuations Complexity associated with the simulation of thin body SOI MOSFETS

  14. Device quantum effects at room temperature Gate Tunnelling B-to-B Tunnelling Quantum transport S-to-D Tunnelling Quantum Confinement And this is only one item from the list on the previous slide.

  15. Technology nodes 22 nm SOI 30nm 0.25 m2 6 nm channel Toshiba (2004)

  16. 5 nm wire FINFET Taiwan Semiconductor Manufacturing company

  17. High-k SiGe(:C) Univ. Texas Motorola LETI/STM

  18. Theory and Modelling: Tools: unique to UK Helps understand the present Helps design the future Used to iteratively design and model devices for Cons. 3D Atomistic Monte Carlo 3D Non-equilibrium Green function atomistic simulator 3D NASA codes Medici Quantum corrected Medici Planned: atomic basis sets, DFT, Quantum corrected Monte Carlo Convergence with quantum chemistry

  19. Two recent examples 1. High- dielectrics • Scaling of MOSFETs beyond the 45nm technology node required by 2010 (ITRS) requires extremely thin SiO2 gate oxides (~0.7nm) resulting in intolerably high gate leakage. • Maximise gate capacitance: • The most likely solution is the implementation of high- dielectrics such as HfO2 and Al2O3 which are the leading contenders. However, there is a fundamental drawback due to the resulting mobility degradation. Strained Si • Has already demonstrated significant enhancement for CMOS applications. It is shown here that it can compensatefor the performance hit due to high k dielectric.

  20. 2. Interface roughness(new non-perturbative model in excellent agreement with expt) Full SC Quantum Gaussian auto-covariance Exponential auto-covariance Ab initio models Parameters: RMS height, 0.5nm and Correlation Length, c=3.0nm M. Boriçi, J. R. Watling, R. Wilkins, L. Yang and J. R. Barker, J. Comp. Electronics, 2 p163-167 (2004)

  21. Device Structures investigated

  22. Simulation of 67nm IBM Relaxed and Strained Si n-MOSFET Impact of Surface Roughness Scattering • Comparison between n-type Strained Si and control Si MOSFETs: • 67nm effective channel length • Similar processing and the same doping conditions In the strained Si MOSFET: • 10nm tensile strained Si layer • Strained Si on relaxed SiGe (Ge content: 15%) K.Rim, et. al., Symposium on VLSI Technology 2001 http://www.research.ibm.com/resources/press/strainedsilicon/

  23. Strained Si n-channel MOSFET Structure Comparison between the n-type Strained Si and control Si MOSFETs: • 67nm effective channel length • Similar processing and doping conditions • Oxide thickness, tox =2.2nm (SiO2) • For the strained Si MOSFET: • 10nm strained Si layer thickness • Strained Si on relaxed SiGe (Ge content: 15%) • SiGe n-MOSFET >35% drive current enhancement • (70% high field mobility enhancement)

  24. Universal Mobility Curve: Monte Carlo v Expt A smoother interface for strained Si? ‘universal’ mobility behaviors of bulk Si and strained Si, a comparison between experiment and Monte Carlo simulation.

  25. Device Calibration – Drift Diffusion • Drift-diffusion (MEDICI™) device simulations • Concentration dependent, Caughy-Thomas and perpendicular field dependent mobility models • Corrected Si/SiGe heterostructure parameters: band gap and band offsets, effective mass, DoS and permittivity† Calibrated ID-VG characteristics of the 67nm n-type bulk Si and strained Si MOSFETs (experimental data from Rim VLSI’01) † L. Yang, et al, ‘Si/SiGe Heterostructure Parameters for Device Simulations’, Semiconductor Science and Technology (2004)

  26. Device Calibration – Monte Carlo • Larger CL • For SSi • Smoother interface PerformanceEnhancement Calibrated ID-VG characteristics for 67nm conventional Si and strained MOSFETs, comparison with experimental data of Rim.

  27. Problems associated with high- dielectrics • Lower mobility (Soft optical phonon scattering) • Micro crystal growth • Lateral oxidation at gate edge • Interfacial layer formation  Fermi level pinning • Fixed charge, Flatband shift • Higher density of interface states • Reliability Iwai, ESSDERC’03 Atomic level modelling Strong SO phonon scattering degrades the inversion layer carrier mobility within the MOSFET with high- gate stacks.

  28. Adapted from: Hitachi IEDM 2003 Atomic level models needed

  29. Remote (SO) Phonon Scattering SO phonon scattering rate in the X-valley for phonon mode 1 (absorption) as a function of energy and the distance from interface (HfO2 EOT=2.2nm for bulk Si MOSFET)

  30. Monte Carlo simulations of Si MOSFET and SSi MOSFET with HfO2 oxide The losses due to high k in Si are largely compensatedby switching to high k in strained silicon. See IEDM paper

  31. Monte Carlo simulations of Si MOSFET, with Al2O3 oxide Note SSi Restores Performance hit ID-VG characteristics of 67nm n-type Si MOSFET, with and without soft-optical phonon scattering, from the Al2O3 oxide.

  32. Summary of high K results • We have investigated the impact on the performance degradation in sub 100nm n-MOSFETs due to soft-optical phonon scattering in the presence of high- dielectrics HfO2 and Al2O3. • A device current degradation of around 25% and 10% at VG-VT=1.0V and VD=1.2V is observed for conventional and strained Si devices with a 2.2nm EOT HfO2 or Al2O3 dielectric respectively. • Results indicate that the performance degradation associated with high- gate stack MOSFETs can be compensated by the introduction of strained Si channels. • The infancy of high- gate fabrication techniques means that overall performance degradation associated with high- gate dielectrics is expected to be worse than the predictions here. More details in IEDM paper.

  33. Nano-silicon and atomistic MOSFETs New methodologies for the challenges ahead: planned or in hand. Convergence with Quantum Chemistry Atomic basis functions Density Functional Theory Non Equilibrium 3D Green Function codes Quantum corrected Monte Carlo Extensions to quantum corrected drift diffusion Convergence with Quantum Chemistry Basis for exploring hybrid technologies and Ultimately nano-molecular electronics. Huge range of new materials/device configs, withindustry looking for answers soon.

  34. The next generation Post-CMOS devices are immensely complex from physics and technology point of view Double-gate Fin-FET Omega-gate UTB SOI SON SiGe Quantum Strained Si Confinement Pure Ge Tunnelling High-K Non-equilibrium TiN 10 nm DG MOSFET Ballistic NiSi Metal gate Schottky S/D Atomistic Replacement gate Raised S/D Silicon is once again an exciting area for research. Huge challenge for device modelling

  35. Quantum simulations and Green Function Codes Exotic science discovered in advanced Si devices 10-25 nm Fluctuations indevice performance Current flow comprises open orbits + localised vortices Discovered at Glasgow, picked up by IBM, ASU

  36. Existence of vortices in total current at high T Exact model and NEGF Simulations in 3D Barker and Martinez 2004 Decoherence studies in 3D

  37. CONCLUSIONS: The future with silicon EPSRC has given the UK community the opportunity to stay in world-class competition in the technology of the century. But it will not be enough to continue to competein Europe, let alone the world. Silicon technology of the type available to develop newapplications and systems is BIG ENGINEERING. We need to shift away from the gentlemanly amateurism of the 1970s and 1980swhich saw us lose our world lead in semiconductors.

  38. The future with silicon The UK cannot afford not to be in silicon It will remain theplatform technology for at least 20 years as scaling continues. It will remain a platform for maybe >20 years beyond, by supporting System on Chip, Network on Chip, Comms on chip, Lab on chip, Smart dust, Nanorobotics, Med.Diagnostic on Chip, Nanotechnology, Hybrid organic/plastic silicon/ Some questions and observations Can you name any replacement technology? Remember: it is not good enough to demonstrate a transistoror even two. Can you demonstrate any path to fabricating 1000000000000 transistors, precisely, at low cost in 16 mm2 and repeat this for 16000000000 chips?

  39. The future with silicon What opposition? Does exotic science gave any solitions? Single Electronics: no gain, RC time constant limited,very slow Sensitive to local fluctuations. Compensating circuitry outweighs SET circuitry at 256 M level.No fabrication strategy. Nanotubes: Millie Dresselhaus let the cat out of the bag in ICPS27. Every CNT has its own name: they are all different and massively sensitive to contaminants. There is absolutely no interconnection strategy, no fabrication strategy. Even magnetic bubble logic was better advanced. Don’t believe the hype!

  40. The future with silicon Spintronics: similar issues to single electronics. Also scales. Wave interference devices: in your dreams! You need 30000 electrons just to resolve a 2 slit experiment. Scale, coherence/de-coherence. The interface between macro Micro system…… Already dismissed in the 1980s. Molecular electronics: most simple molecules are already thescale of 5 nm MOSFETs. Huge problems of fabrication and Interconnection. Absolutely no assembly method demonstrated, Unless you count DNA replication (error rate 10-5!!). 3D might just be an advantage; likely to be very slow. Nice non-competitive apps: still need to interface to silicon. Biological devices: surely not neurons or biomachines!!

  41. The future with silicon III-V MOSFETs: the window of opportunity is narrowing. At the smallest scales there is no advantage. But could integrate with silicon or germanium. (IBM, IWCE04) Silicon and SiGe are already encroaching on III-Vs for RF Quantum Computing: the idea of several bits on one electron and the mystical advantages of QC fascinates a lot of people. Ask them what real advantages it has over analogue computing? Do you really expect to control coherence/entanglement etc at room temperature? DNA computers: fascinating demos. Totally ludicrous asengineering. If you want more emergent technologies that will replace Si Remember the characteristic of Pseudo-Science

  42. The future with silicon How many more times does the UK have to get it wrong in Electronics? The issue is primarily engineering. Remember: Babbage Malvern 3D ICs in 1950s 1960s; GaAs, III-Vs, InP, Bubble logic, Gunn logic, Resonant tunneldevices, High Tc and Low Tc superconducting systems, ……. So, you whine….” It is in the Road Map; All the new stuff you disparage is IN THE ROAD MAP.” “..and the non Silicon Physics community says that silicon is dead!”

  43. The future with silicon Let me tell you about the reality of the Road Map. It is supposed to be a wish list of problems to solve in order tocontinue Moores Law. It was originally. Now manufacturers lower the targets, so that they triumphantly beat the Road Map. Usually each year at IEDM. Remember the HEAT DEATH of NMOS ? We got CMOS. Remember the recent HEAT DEATH scares of CMOS? Lots of solutions: raised S/D, Si on insulator, high k dielectrics, … What about the new emergent technology section? Mostly pie in the sky. This is where the gurus play. It is also cool for investors to know that your favourite company invests in the future. But test it: you are scientists: how much are they actually spending? Eg look at Intels CNT investment.

  44. The future with silicon Of course there are problems, but there is a surfeit of routes forward Most involve new science tightly integrated with new engineering.Of course there are limits. But not to applicable electronics. We will still want low cost super-functionality from future chips. But they will not just be memories and CPUs. New materials, new devices will be hybridised and developedusing that special economic advantage of silicon: the cost per function is likely to fall even as the functionality increases and diversifies. The next decades should be periods of great invention. We will need access to silicon fabrication to explore newinventions. Off the shelf is simply not good enough.

  45. The industry needs help in the development of the next generations devices • The technology is so complex that even the large multinationals can not afford to develop it alone (groupings for developing 65 nm node). • During the downturn the multinationals downsized their basic research capabilities and cannot deal with some of the material, device physics and modelling issues. • The companies are therefore ready to forge new relations with universities and to offer not only financial contribution but access to technologies and devices. • Strong alliances has been developed in the European scene in Framework 6 including members of the consortium (SINANO, NanoCMOS). University research is bound to play an important role in the Nano-CMOS era. The ex members of the SiGe consortium are particularly well placed due to pioneering research in materials, device physics and design, semiconductor theory and modelling and Si fabrication

  46. Not the end… New beginnings!!

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