1. Radiation Effects on Emerging Electronic Materials and Devices Leonard C. Feldman Vanderbilt University Department of Physics and Astronomy Vanderbilt Institute on Nanoscale Science and Engineering June 14/15, 2007 Radiation Effects in Emerging Materials Overview

2. Topics of Interest Basic radiation interaction with electronic materials-review, educational, modifications at the nanoscale Alternate Dielectrics and Gate Stacks-in all aspects-growth, spectroscopy, radiation effects SiGe devices and other “alternate substrates” (Ge, InGaAs, SiC) Strained silicon

3. Basic radiation interaction with electronic materials- review, educational, modifications at the nanoscale Tutorials and review: Interaction of x-rays with MOS devices occurs primarily via the generation of (photo) electrons in the metal and the underlying silicon. The energetic electrons (<= 10 KeV) create electron hole pairs in the dielectric which may be trapped by “processing” defects. The dielectric is too thin to incur any substantial direct defect production by the primary radiation. The outgoing electrons are too low in energy for direct displacements, but create further secondarys, and possibly defects, through bond breaking leading eventually to e-h pair production. Gate oxide Si metal MOS Schematic

4. MAJOR POINT FROM THE PREVIOUIS CONSIDERATIONS “Processing defects”, defects from the imperfection of the grown dielectric, are the primary trapping centers -nanocrystalline HfO 2 -HfO 2 /SiO 2 interface -classic defects such as oxygen vacancies, etc -Hf penetration into the SiO 2 layer and its interaction with H “Processing defects”, defects from the imperfection of the grown dielectric, are the primary trapping centers even for the higher atomic number, physically thicker HfO 2

5. Number of Hf atoms versus distance from interface 1 nm Single Hf atoms inside SiO 2 interlayer interface 2 Å 4 Å distance (Å)

6. Basic radiation interaction with electronic materials- modifications at the nanoscale Nanoscale: Basic theory of e-h pair production, particularly ε, the average energy required for e-h pair creation, is based on bulk concepts, including bulk density of states. The nanoscale thicknesses, and the new understanding of nanoscale effects calls for re-examination of these concepts. Gate oxide Si metal MOS Schematic ΔV=Q/C=N e {(dE/dx) t ox /ε} /C ε= average energy/e-h pair N e = number of electrons penetrating the dielectric

7. ε vs. E g ε= 2.6 E g + K Shockley-Klein

9. Rutgers CMOS Materials Analysis Surface/interface analysis: Ion scattering: RBS, MEIS, NRA, ERD – composition, crystallinity, depth profiles, H/D Direct, inverse and internal photoemission – electronic structure, band alignment, defects Scanning probe microscopy – topography, surface damage, electrical defects Use high resolution characterization methods to: i. Determine composition, structure and electronic properties gate stacks that use new (post-Si) materials ii. Help determine physical and chemical nature of radiation induced defects

10. SiO 2 Monolayer? Metal Electrode High- κ Dielectric SourceDrain Ge, III-V Barrier? 10nm CMOS gate ~2010? Materials stability, band alignment and defects in CMOS nanoelectronics L. Goncharova, S. Rangan, O. Celik, C.L. Hsueh, R.A. Bartynski, T. Gustafsson and E. Garfunkel Departments of Chemistry and Physics, and Institute for Advanced Materials, Devices and Nanoelectronics Rutgers University, Piscataway, NJ Collaboration: Vanderbilt, Sematech, NIST, IMEC, IBM, Intel, Bell Labs, NCSU, Penn State, Stanford, UT-Dallas, UT-Austin, Albany.… DOS SiHigh-kMetal EFEF Band edge states Defects

11. Defects in the post-Si era: Al/HfO 2 /In x Ga 1-x As Surface passivation and composition of interfacial layer High-K deposition Post-deposition annealing Metal gate effects “Normal” and radiation induced defects – nature and evolution HfO 2 5 Å InGaO x InGaAs(001) S 2- Al

13. length scales of order and defects in nano-crystalline and non-crystalline Hf-based gate dielectrics Gerry Lucovsky students and post doc: S. Lee, JP Long, H Seo and LB Fleming collaborators: J Whitten, D Aspnes, Jan Luning (SSRL), G. Bersuker and P Lysaght (Sematech) objective: determine the effect of different length scales of order for nano- and non-crystalline Hf based dielectrics on pre-existing intrinsic defects, and then on radiation (X-ray) induced defects approach i) prepare NCSU samples by plasma-CVD ii) determine electronic structure, Hf d-state relative energies, by near edge X-ray absorption, soft X-ray photoelectron spectroscopy, and vis-VUV spectroscopic ellipsometry using symmetry adopted linear combinations (SALC-FA Cotton) of atomic states as a guideline iii) study electrical properties in MOSCAPs and compare electrical and X-ray stress

14. significant results length scale, coh - coherent Hf d  – O p  -bond inter-PUC coupling phase-sep. silicates and type I coh ~ 2 nm or < 5 PUCs no J-T splittings and band-tail defects type II coh > 3 nm or > 6 PUCs J-T splittings and discrete band-edge defects asymmetric h/e trapping +/- defects X-ray stress J-T splitting 1.2 eV Hf Si oxynitrides- high Si3N4 % no inter-group Hf d  -O p  -bonding no phase-separation, but only for small range of compositions very low tunneling, ~12 (to 16-18) positive charge defects - X-ray stress HfO 2 and Hf silicates both positive/negative charged defects

15. direct bonding HfO 2 : Ge(100) electricals being studied and measurements extended to Ge(111) GeO and GeN removed during anneal resonant X-rays reveal buried interface substrate specific  -bonds SiON interface/Ge-direct

17. HfO 2 sample details State-of-the-art samples, SEMATECH, Inc. 65 nm technology node nMOSFETs with W/L = 10  m/0.2  m t phys = 7.5 nm and 3.0 nm (EOT = 1.2 nm and 0.5 nm) SiO 2 interlayer (~ 8Å) HfO 2 based nMOSFET Gate p-substrate p-well SourceDrainBody n+n+ n+n+ p+p+ Samples Experimental 10 keV X-rays, RT irradiation Function of dose Function of bias Characterization done using I-V measurements

18. HfO 2 total dose results t phys = 7.5 nmt phys = 3.0 nm Thinner dielectric traps significantly less charge S. K. Dixit et al., “ Radiation induced charge trapping in ultra-thin HfO 2 based MOSFETs”, accepted for NSREC 2007 nMOSFETs with W/L = 10  m/0.2  m

19. n-MOSFET cross-section  Carrier injection from tunneling  Si- surface condition dependent  Both electron and hole trapping observed  Predominant bulk hole trapping (radiation)  Zero bias - radiation induced trapping SiO 2 p-Si ECEC EVEV EfEf EiEi HfO 2 TiN  HfO2/TiN HfO 2 results

21. Hafnium silicates Crystallization introduces defects and shallow traps at the grain boundaries Radiation response expected to be better for silicates Limitations of HfO 2 : HfO 2 - low thermal budget ~ 500°C Nanocrystalline HfO 2 formed during PMA Dopant penetration is an issue Need for HfSiO:  Increased thermal budget to ~ 1000°C  Reduction in dielectric constant

22. RBS & CV of HfSiO/SiO 2 /p-Si films Total dielectric thickness from RBS: ~10 to 11nm Physical characterization Electrical characterization Total dielectric thickness from CV: ~12nm E 0 = 1.4 MeV 4 He E 1 = KE 0

23. Results Initial results confirm the trend (… Hf  r ) RBS results C-V results

24. TID Response of Hf 0.6 and Hf 0.3 Films Devices prepared by RPECVD; EOT ~ 4 nm Two dielectric films: Hf 0.6 (containing crystalline HfO 2 ) Hf 0.3 (amorphous) Electron trapping observed in the Hf 0.6 film under large positive bias Probable explanation: e-trapping at nanocrystalline grain boundaries

25. TID Response Comparison to Previous Hf Silicate Films TID-induced charge trapping improved compared to previous Hf silicate devices [J. A. Felix et al., IEEE Trans. Nucl. Sci., vol. 49, pp. 3191-3196, 2002] ∆N ot ~ factor of 17 smaller at 1 Mrad Reduced charge trapping indicates superior HfSiON film qualities and improvements in processing techniques

27. Facilities at Vanderbilt Physical and Electrical characterization Ion beam characterization using RBS, PIXE, channeling studies C-V measurements I-V measurements 10 keV X-ray source (in-situ bias and irradiations) 2 kV Van de Graaff electrostatic accelerator Low dose rate Ce source Radiation sources Future upgrades In-situ biased ion irradiations using H, He and Ne beams Low-temp (up to 7K) ion irradiations using a cryostat Other facilities Thermal oxidation and gate metal deposition facilities Delta Oven furnace for high temp biased anneals Wire bonder for packaging wafer level devices

28. Biased irradiations and anneals Irradiation (-2V)RT Annealing (0V) Partial recovery observed with a 0 V annealing gate bias No additional voltage shifts observed for time scales of up to 13 hours indicating the existence of residual positive charge in the oxide

29. Radiation Effects in SiGe Devices John D. Cressler and Team Investigation of the Best Path to RHBD in Bulk SiGe HBT Technologies First Cryogenic Temperature (77K) Proton Experiment of SEU in Bulk SiGe HBTs Investigation of Radiation Effects in both Bulk C-SiGe HBTs and SiGe HBTs on SOI Investigation of Radiation Effects in both SiGe nMODFETs and SiGe pMODFETs Bulk SiGe HBTs C-SiGe HBTs (npn + pnp) SiGe p/n-MODFETs

30. S. K. Dixit et al., “ Radiation induced charge trapping in ultra-thin HfO 2 based MOSFETs”, accepted for NSREC 2007 Voltage Stress and Biased Irradiation Hole injection saturates after an hour Simultaneous injection + irradiation is even worse MURI meeting June’07

32. S. K. Dixit et al., “ Radiation induced charge trapping in ultra-thin HfO 2 based MOSFETs”, accepted for NSREC 2007 CVS and biased irradiation Simultaneous injection + irradiation is even worse SiO 2 p-Si ECEC EVEV EfEf EiEi HfO 2 TiN  HfO2/TiN Hole injection - 2V bias stress Accumulation Hole injection saturates after an hour

33. S. K. Dixit et al., “ Radiation induced charge trapping in ultra-thin HfO 2 based MOSFETs”, accepted for NSREC 2007 CVS and biased irradiation Electron injection saturates Simultaneous stress + irradiation hole trapping dominates with dose SiO 2 p-Si ECEC EVEV EfEf EiEi HfO 2 TiN  HfO2/TiN Electron injection + 2V bias stress Inversion