Luigi Colombo. Texas Instruments Incorporated Dallas, TX, USA. Graphene Conference: From Research to Applications Oct 2012

Transcription

1 Luigi Colombo Texas Instruments Incorporated Dallas, TX, USA Graphene Conference: From Research to Applications Oct 2012 NPL,UK

2 UT Austin - Banerjee group UT Austin - Tutuc group UT Austin Ruoff UT Dallas - Wallace group UT Dallas - J. Kim group GIT/UT Dallas Vogel group Nano-electronic Research Initiative and NIST

3 Introduction Graphene based devices Graphene integration Graphene film growth Dielectrics thickness scaling Metal contacts contact resistance Summary

4 Performance per power density vs. gate length that the slowing of voltage scaling causes a reversal of the trend beyond 130-nm-node technology Power density vs. gate length: active and passive power density W. Haensch et al IBM J. RES. & DEV. VOL. 50 NO. 4/5 JULY/SEPTEMBER 2006

5 10 m 1 m Modern CMOS Beginning of Submicron CMOS Deep UV Litho 100 nm 10 nm >40 Years of Scaling History Every generation Feature size shrinks by 70% Transistor density doubles Wafer cost increases by 20% Chip cost comes down by 40% 90 nm in 2004 Generations occur regularly l? On average every 2.9 years over the past 40 years Recently every 2 years 32 nm in nm Presumed Limit Need a New Switch

6 Spin based devices Spin Wave Spin torque Spin FETs All spin logic Nano magnetic logic devices Tunnel FETs III-V, graphene Graphene PN Junction Devices Bilayer Pseudospin FETs(BiSFET) Lateral graphene tunneling devices

7 BiSFET Bose-Einstein Condensate High Quality SC Graphene J.J. Su and A.H. McDonald, Nat. Phys., 2008 Banerjee et al, EDL 2009 Tunneling FET: Low SS Bilayer graphene? GNR? Q. Zhang et al, EDL, 2008 P-N Junction Veselago lens switch High Quality SC Graphene V. V. Cheianov et al, Science, 2007

8 (Schematic only, cross section) section) BiSFET Schematic V Gn V n Gate Voltage (mv) V p graphene layer contacts Gate(s) V Gp p and n type graphene layers Equivalent Circuit Model Energy per switching operation per BiSFET ~ aj = 10 zj SKBanerjeeet S. K. et al., Electron Device Letters, IEEE 30, 158 (2009). F. Register, UT Austin

9 Very intriguing device will require significant process development to realize as Gr/h-BCN There could be other options, easier than lateral composition control for implementation G. Fiori et al., ACS Nano 2012

10 Graphene Growth Monolayer graphene Graphene nano ribbons (GNR) LER is a major challenge for etched GNRs Chemical pathways for growing GNRs placement challenge Bi-layer graphene Chemically inactive graphene surface is a major challenge for uniform bi-layer growth Surface modification e.g.: BCN Dielectric selection and deposition High-k scaling Low-k - scaling Lattice matched 2D crystals Metal contacts t

11 1950s Teal & Buehler Courtesy of Texas Instruments D. Edelstein, in P. Moon, et al., Intel Technology Journal 2, pp , 2008.

12 Chemical vapor deposition: Cu, Ir, Ru; Pt Plasma enhanced CVD processes: Cu Precipitation: Ni, Ru, Co, Pt, Pd Growth by desorption of Si from SiC X. Li et al, Science (2009). (Cu) P. Sutter et al., Physical Review B 80 (24) (2009). Pt N.A. Kholin et al., Surface Science (1984). Ir Karu and Beer, JAP (1966). Ni J. Sanchez-Barriga et al., Diamond and Related Materials (2010). Co J. Lee, et al, in IEDM - Technical Digest, (ICP-CVD) D. V. Badami, Nature (1962). SiC

13 Substrate t selection Metal C solubility Orientation Catalytic activity Lattice matched Dielectrics High-k, low-k? Layered compounds Process type: Growth Temperature Cold wall Hot wall Pressure Low Atmospheric (K) T T (K) Ti/(C+Ti) T (K) T (K) Cu/(C+Cu) Precursor Sources: Gases Liquids Solids Solutions Ni/(C+Ni) Ir/(C+Ir) Okamoto H., Phase Diagrams for Binary Alloys, Desk Handbook, Vol. 1, 2000

14 We can grow large area graphene Large area low defect density single crystals of graphene are most likely required to achieve the highest uniform transport properties for nano-electronic devices Can large single crystals of graphene be grown? Do we have the right substrate? Is the growth rate high enough for commercial viability? 2-D growth from a single nucleus? Can registered nuclei of graphene be created for further graphene large area crystal growth?

15 SEM TEM graphene 20 m Cu Graphene e islands 5 m Li et at. Science, 2009 Cu Cu Su urface Cove erage (%) 10 m G. B mtorr 285 mtorr 560 mtorr 0Q. Yu et 1al., Nature Materials, Time (min)

16 Grain Structure of graphene by Electron Diffraction: >2000 ED patterns Raman Isotope labeling 10 m 5 m C. Floresca, UT Dallas unpublished data Li et al., Science, 2009

17 Li et al., JACS 2011 Li et al JACS 2011 Li et al Science 2009

18 Cu substrate Pt substrate 400 m Yan Z, ACS Nano mm Y.Hao Unpublished results UT Austin L. Gao et al Nat. Comm. (2012)

19 Nucleation Graphene nuclei CH 4 + H 2 Cu Graphene Graphene domain CH 4 + H 2 Domain Growth CHx coverage CASE I: Isolated nuclei CH 4 + H 2 CASE II: Multiple nuclei CH 4 + H 2 C x H y C x H y C x H y C x H y Constant growth rate with time Infinite it exposed catalyst t C x H y C x H y C x H y Varying growth rate Finite/decreasing exposed catalyst

20 Mobility 16,400 25,000 cm2/v - for Gr/SiO 2 Mobility 27,000 45,000 cm2/v - for Gr/h-BN X. Li et al., Nano Letters (2010) Pt Petrone et al., Nano Letters (2012)

21 Very large area graphene can be grown on Cu and transferred to any substrate. PMMA Fe 3+ Acetone Si/SiO 2 Si/SiO 2 Li et al,. Nano Lett (2009) Bae et al. Nat. Nanotech. (2010)

22 Graphene grown and transferred multiple times from the same Cu foil An aqueous solution of K 2 S 2 O 8 (0.05 mm) was employed as electrolyte l t in the electrochemistry process. Wang, Y, ACS Nano 5(12), 927 (2011)

23 Single Crystal Graphene Exfoliated CVD Manchester UT Austin Shenyang UT Austin 1 m 1 mm Microns millimeters Centimeters meters Polycrystalline CVD Graphene UT Austin SKKU IBM Graphene Quartz 4 cm 23

24 Graphene surface is chemically inert Need to functionalize the surface to deposit dielectrics using non-physical deposition techniqueses Scaling of dielectrics down to ~ 1 nm needed for devices Enable a variety of dielectrics high-k, low-k and 2D dielectrics

25 Y. Xuan, et al., APL 92, (2008) Standard ALD Al 2 O 3 processes (TMA/H 2 O) lead to non-uniform deposition at step edges Need to use a nucleation layer or Nucleation strategies for ALD on graphene Thin polymer (NFC CP) layer D. B. Farmer, et. al., Nano Lett. 9(12), 4474 (2009) 1 nm e-beam Al / oxidation in air S. Kim, et. al., APL 94, 6, (2009) D. B. Farmer, et. al., APL 97(1) (2010) Evaporated PTCDA M. Hersam et. al., in press. NO 2 noncovalent functionalization functionalize the graphene surface D. B. Farmer and R. G. Gordon, Nano Lett. 6(4), 699 (2006) Y.-M. Lin, et. al., Nano Lett. 9(1), 422 (2009) O 3 functionalization But, O 3 etches of HOPG surface at 200 C B. Lee, et. al., APL 92(20), (2008) GL G. Lee, et. al., J. JPhys.Chem. C 113(32), (2009) B. Lee, et. al., APL 97(4), (2010) G. Lee, et. Al., J.Phys. Chem. C 113, 32, (2009)

26 Pirkle, A, PhD Thesis, UT Dallas 2011 CVD graphene transferred to SiO 2 Main sp 2 graphene peak is fit with an asymmetric Doniach- Sunjic line FWHM for transferred graphene: 0.88 ev FWHM for CVD graphene on Cu: 0.74 ev PMMA residue observed after transfer (states highlighted in orange) Curve fit residual error shown below data in gray PMMA residue present PMMA fit is consistent with G. Beamson, et. al., Surface and Interface Analysis 17(2), 105 (1991)

27 eight (nm) He nm z RMS = 4.23 nm x ( m ) (a) Al Adsorbed H 2 O Al 2 O 3 Adsorbed H 2 O (b) Al Al 2 O 3 Al 17 nm 0 nm Pho otoelectro on intensit ty (a.u.) Al 2 O 3 1 nm (nominal) Al deposited by on natural graphite by e-beam evaporation,oxidized idi d in 1000 mbar O 2 at t25 C O 1s x10 x10 (d) (c) (b) (a) C 1s * C-C (d) (c) (b) (a) Binding energy (ev) Al 2p Al (d) (c) (b) (a) (d) + 25 C O 2 (c) Unannealed natural graphite substrate + 1 nm Al (b) + 25 C O 2 (a) Annealed (400 C, UHV) natural graphite substrate + 1 nm Al Large (~ 5-10 nm) Al clusters explain incomplete oxidation when pre-deposition anneal is employed Cluster radius is larger than limiting oxide thickness (~ nm) 1 Further details given in Ref L. P. H. Jeurgens, et. al., JAP 92, 3, 1649 (2002) 2. A. Pirkle, et. al, APL 95(13), (2009) 27

28 Hf 1s / O 1s fit regions 1: O 1s -HfO 2 2: O 1s - Hf(OH) 3: Hf 1s Pre-deposition anneal, deposition pressure 4x10-10 mbar necessary to suppress Hf carbide formation Hf 1s O1 1s C1 1s Hf 4f Pho otoelectro on intensit ty (a.u.) HfC (c) Annealed graphite, mbar deposition (LN 2 chamber shroud cooled) (b) Annealed graphite, mbar deposition (chamber shroud not cooled) (a) Exfoliated graphite, mbar deposition (chamber shroud not cooled) Binding energy (ev) A. Pirkle, et. al, APL 95(13), (2009)

29 1 nm of HfO 2 deposited on natural graphite by evaporating Hf with 1x10-6 mbar partial pressure of O 2 in e-beam evaporation chamber Chamber base pressure 5x10-10 mbar Internal LN 2 chamber shroud cooled to minimize background residual gases (OH) Photoele ectron intensit ty (a.u.) O 1s C 1s Hf 4f 1 nm HfO 2 - reactive e-beam Natural graphite substrate AFM 1 nm HfO 2 on natural graphite Binding energy (ev) XPS No carbide detected after reactive e-beam deposition TEM 5 nm HfO 2 on natural graphite High and low magnification Low surface roughness: z rms = 0.24 nm Comparable to roughness of HfO 2 on Si spectator sample deposition images show good uniformity it (within a factor of ~2) No pinhole/short defects Pirkle, A, PhD Thesis, UT Dallas 2011 observed

30 2.2nm Oxidized Al 1.1nm 300nm 0 150nm 0 150nm 300nm 0 Oxidized Ti 2.2nm 1.1nm nm 300nm 0 150nm 300nm Provides nucleation centers for the ALD growth uniform coverage critical No detrimental effect on gate capacitance ultra-thin interfacial layer desirable Surface diffusion limits the minimum interfacial layer thickness B. Fallahazad et al. APL, 2012

31 Al 2 O 3 -TiO x dielectric on graphene scaled to ~ 2.6nm B. Fallahazad et al APL (2012) Are oxide high-k h kdielectrics ti good enough hto achieve high mobility in graphene?

32 Height (nm) CVD graphene transferred to SiO 2 using PMMA method Sample received in-situ 300 C / 3 hr vacuum anneal (P ~ 1x10-9 mbar) a) Transferred b) Annealed a) b) x ( m) x ( m) Pirkle, A, PhD Thesis, UT Dallas 2011 Pho otoelectron in ntensity (cts/ /s) 18 x (f) (e) (g) (i) (h) (i) (h) (g) (e,f) (d) C 1s (c) (b) (a) Binding energy (ev) c) Transferred CVD graphene on SiO C / 3 hr UHV anneal b) Transferred CVD graphene on SiO 2 C 1s XPS states corresponding to PMMA are largely removed AFM shows a much smoother surface RMS roughness drops from 4.6 nm to 0.6 nm upon annealing 300 C / 3 hr vacuum anneal is effective for significant removal of PMMA residue from graphene 0 a) CVD graphene on Cu

33 Chen J, ACS Nano, 2012

34 Ni/Au Ni/Au Parylene Graphene SiO 2 (90 nm) Ni/Au (a) (b) Nickel Parylene ~7 nm 5nm Graphene n++ Si substrate 1 um 5 nm SiO 2 Intens sity cps (a) Without Parylene With Parylene Raman Shift (cm -1 ) Mordi et al., Appl. Phys. Lett. 100, (2012) (b) 3 Mobility ~ 5000 cm 2 /V s nce [K] Resista nm V D = 10 mv V BG [V]

35 Exfoliated h-bn CVD FL h-bn CVD Monolayer h-bn Kim et al NL (2012) 2 nm C.R. Dean et al, Nature Nanotech, 2010 Ismach et al, ACS Nano accepted for pub

36 C 1s 1.0 PI (a.u.) HOPG + 1 nm Ni+ 500 C / 10 min anneal (UHV) HOPG + 1 nm Ni HOPG I d (ma) μm V bg (V) BE ( ev ) V d (V) XPS analysis indicates absence of carbide formation ( ~ 282 ev) at the Ni graphene interface I d -V d plots for Ni on graphene indicative of ohmic behavior higher total resistance (R) and hence higher R c A. Venugopal, Ph.D. Thesis, UT Dallas, 2012

37 Exfoliated 2 CVD grown CVD Graphene R c (k) 1 old transfer new transfer TiO x process L c = 3m W c (m) ~ 5X reduction in R c observed Residue at interface significantly contributes to R c A. Venugopal, Ph.D. Thesis, UT Dallas, 2012

38 Progress has been made in graphene growth and integration of graphene-based devices Large area polycrystalline CVD graphene Large, g a few mm, single crystal graphene Many issues remain on uniformity/roughness Need to improve contacts Scaling of dielectrics to 1 nm range H-BN shows promise but growth of reproducible uniform films is still very challenging