UK SiGe Research Programme EPSRC Final Review Meeting, Thursday November 4th 2004 Electrical and Electronic Engineering Dept, Imperial College, 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

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

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!)

Deliverables in Phase I-II ( ): 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, (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 Symp Invited papers : 12 Special notice: Paper accepted for IEDM04.

Deliverables ( ): II New Grants and Collaborations 1. 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 £ 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/ /2006 $ SINANO - Network of Excellence A. Asenov, J.R. Barker,S. Roy IMEC, LETI, INFINEON, ST MICROELECTRONICS European Commission 01/ / Sub 100 nm III-V MOSFETs for Digital Applications With 14 others MOTOROLA, University of Surrey EPSRC 09/ /2006 £ 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, : £ Atomistic simulation of nanoscale devices A Asenov, J.R. Barker, S Roy EPSRC Platform grant, : £

Other stuff 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 DFT collaborations underway INDUSTRY: IBM, Intel,Toshiba NASA, Sony, Freescale…

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

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

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

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

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 Members of the SiGe consortium have carried out pioneering work in these two mainstream areas. High K: new issues

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

Mobility in UTB SOI 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 K. Ushida IEDM 02 Complexity associated with the simulation of thin body SOI MOSFETS Quantum potential variation Associated with UTB variation

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

Technology nodes 22 nm SOI 30nm Toshiba (2004) 6 nm channel

5 nm wire FINFET Taiwan Semiconductor Manufacturing company

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

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

Two recent examples High- dielectrics Scaling of MOSFETs beyond the 45nm technology node required by 2010 (ITRS) requires extremely thin SiO 2 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 HfO 2 and Al 2 O 3 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 compensate for the performance hit due to high k dielectric. 1.

Interface roughness (new non-perturbative model in excellent agreement with expt) Gaussian auto-covarianceExponential auto-covariance 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 p (2004) 2. Ab initio models Full SC Quantum

Device Structures investigated

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 Simulation of 67nm IBM Relaxed and Strained Si n-MOSFET

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, t ox =2.2nm (SiO 2 ) 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)

Universal Mobility Curve: Monte Carlo v Expt universal mobility behaviors of bulk Si and strained Si, a comparison between experiment and Monte Carlo simulation. A smoother interface for strained Si? SiSSi RMS0.5nm CL1.8nm3.0nm

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 I D -V G characteristics of the 67nm n-type bulk Si and strained Si MOSFETs (experimental data from Rim VLSI01) L. Yang, et al, Si/SiGe Heterostructure Parameters for Device Simulations, Semiconductor Science and Technology (2004)

Device Calibration – Monte Carlo Calibrated I D -V G characteristics for 67nm conventional Si and strained MOSFETs, comparison with experimental data of Rim. Larger CL For SSi Smoother interface Performance Enhancement

Problems associated with high- dielectrics (1)Lower mobility (Soft optical phonon scattering) (2)Micro crystal growth (3)Lateral oxidation at gate edge (4)Interfacial layer formation Fermi level pinning (5)Fixed charge, Flatband shift (6)Higher density of interface states (7)Reliability Iwai, ESSDERC03 Atomic level modelling Strong SO phonon scattering degrades the inversion layer carrier mobility within the MOSFET with high- gate stacks.

Adapted from: Hitachi IEDM 2003 Atomic level models needed

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 (HfO 2 EOT=2.2nm for bulk Si MOSFET)

The losses due to high k in Si are largely compensated by switching to high k in strained silicon. Monte Carlo simulations of Si MOSFET and SSi MOSFET with HfO 2 oxide See IEDM paper

Monte Carlo simulations of Si MOSFET, with Al 2 O 3 oxide I D -V G characteristics of 67nm n-type Si MOSFET, with and without soft-optical phonon scattering, from the Al 2 O 3 oxide. Note SSi Restores Performance hit

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 HfO 2 and Al 2 O 3. A device current degradation of around 25% and 10% at V G - V T =1.0V and V D =1.2V is observed for conventional and strained Si devices with a 2.2nm EOT HfO 2 or Al 2 O 3 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.

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, with industry looking for answers soon.

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

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

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

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 compete in Europe, let alone the world. Silicon technology of the type available to develop new applications and systems is BIG ENGINEERING. We need to shift away from the gentlemanly amateurism of the 1970s and 1980s which saw us lose our world lead in semiconductors. CONCLUSIONS: The future with silicon

The future with silicon The UK cannot afford not to be in silicon It will remain the platform 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 transistor or even two. Can you demonstrate any path to fabricating transistors, precisely, at low cost in 16 mm 2 and repeat this for chips?

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. Dont believe the hype!

Spintronics: similar issues to single electronics. Also scales. Wave interference devices: in your dreams! You need 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 the scale of 5 nm MOSFETs. Huge problems of fabrication and Interconnection. Absolutely no assembly method demonstrated, Unless you count DNA replication (error rate !!). 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!! 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 as engineering. If you want more emergent technologies that will replace Si Remember the characteristic of Pseudo-Science

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 tunnel devices, 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!

The future with silicon Let me tell you about the reality of the Road Map. was It is supposed to be a wish list of problems to solve in order to continue 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.

The future with silicon 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 developed using 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 new inventions. Off the shelf is simply not good enough. Of course there are problems, but there is a surfeit of routes forward

The industry needs help in the development of the next generations devices 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 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).

Not the end… New beginnings!!