Challenges and Opportunities. Prof. J. Raynien Kwo 年

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1 Nanoelectronics Beyond Si: Challenges and Opportunities Prof. J. Raynien Kwo 年 立

2 Si CMOS Device Scaling Beyond 22 nm node High κ,, Metal gates, and High mobility channel 1947 First Transistor First First MOSFET MOSFET Metal Gate High κ gate dielectric Oxide/semiconductor interface High mobility channel Moore s Law: The number of transistors per square inch doubles every 18 months Integration of Ge, III-V with Si Shorter gate length L Thinner gate dielectrics t ox Driving force : High speed Low power consumption High package density 108Å GGG 5nm 5 nm Ge

3 Intel Transistor Scaling and Research Roadmap More non-silicon elements introduced d (production) (production-early2008) (development)

4 Major Research Subjects Enhancement of κ in the new phase through epitaxy Fundamental study by IETS for detections of phonons and defects in high κ dielectrics Room temperature ferromagnetism in cluster free, Co doped HfO 2 films

5 Can you make κ even higher? Phase Transition Engineering ---Enhancement ace etof κ in the New Phase through Epitaxy

6 Crystal structures of HfO 2 and the corresponding κ Hf O Dielectric constants * Stable phase temperature >2700 o C >1750 o C <1750 ο C The dielectric constant increases when HfO 2 structure is changed from monoclinic to other symmetry y * Xinyuan Zhao and David Vanderbrit, P.R.B. 65, , (2002).

7 Permittivity Increase of Yttrium-doped HfO 2 Through Structural Phase Transformation by Koji Kita, Kentaro Kyuno, and Akira Toriumi, Tokyo Univ. HfO 2 <1750 monoclinic κ~ >1750 cubic κ~29 >2700 tetragonal κ~70 Yttrium serves effectively as a dopant to induce a phase transformation from the monoclinic to the cubic phase even at 600 C. Yttrium-doped HfO 2 films show higher permittivity than undoped HfO 2, and the permittivity as high as 27 is obtained by 4at. % yttrium doping. The permittivity of undoped HfO 2 is reduced significantly at high temperature, t whereas thatt of 17 at. % yttrium-doped d filmshows no change even at 1000 C.

8 2x position 190 1x position 280 After deposition for 5mins Dielectric film of 4 fold symmetry in the plane After deposition for 2mins 145 Wafer rotate After reconstruction

9 HRTEM of Low Temp Growth Amorphous HfO 2 on GaAs (100) 56 Å HfO 2 A very abrupt transition from GaAs to HfO 2 over one atomic layer thickness was observed. GaAs

10 High Resolution TEM Images of Pure HfO2 on GaAs (001) An abrupt transition from GaAs to HfO2 and no interfacial layer y Coexistence of four monoclinic domains rotated by y 90º.

11 u.) Inte ensity (a X-ray Diffraction of Epitaxial HfO 2 Films Recrystalized on GaAs GaAs(002) GaAs(004) c b K H 9 a HfO 2 (002) R space K space 10-2 HfO 2 (004) L(r.l.u_GaAs) --- Monoclinic HfO 2 in R space and K space --- Forming four degenerate domains about the surface normal L HfO 2 (004) FWHM(L)= domain size 97.8 Å close to film thickness With C. H. Hsu of NSRRC

12 The Structure of HfO 2 Grown on GaAs(001) monoclinic phase a= A, b= A, c= A, β= A C D B C B Coexistence of 4 domains rotated 90º from each other A B D C B A D D A

13 The Structure of HfO 2 doped with Y 2 O 3 Grown on GaAs (100) Surface normal scan Find the peaks: (022)(400)(200)(311)(31-1)(113)(420)(133)(20-2) All peaks of film match the JCPDS of cubic phase HfO2 Use the d-spacing formula to fit the lattice parameters HfO2 doped with Y2O3 Grown on GaAs(001) is Cubic phase a=5.126a, b=5.126a, c=5.126a α=90,β=90, γ=90 (400)Phi scan (040)Phi scan

14 Comparison between Monoclinic phase and Cubic phase of HfO 2 Without doping Y 2 O 3 With doping Y 2 O L scan 200 & 220 L scan C D C B B 220 Lscan x y A B D C Monoclinic phase B A D D A Cubic phase

15 The Electrical Property of HfO 2 doped with Y 2 O 3 Grown on GaAs(001) 2 ) C(µ µf/cm k k 30k k T=110A κ= J (A/cm m 2 ) YDH/GaAs HfO 2 /GaAs E (MV/cm) Y 2 O 3 +HfO GaAs(001) V (volts)

16 Electrical properties - MBE-HfO 2 (0.8) /Y 2 O 3 (0.2) MBE-HfO 2 (0.8) /Y 2 O 3 (0.2) Annealing Temperature effects ox (pf) C o TiN/MBE-HfO 2 (0.8) /Y 2 O 3 (0.2) (~10nm)/P-Si FG 400 o C 30min 175 1k 10k 100k 10 nm TiN MBE-HfO 2 +Y 2 O 3 P-Si(100) V (voltage) F/cm 2 ) C (u MOS diodes of TiN/HfO 2.8 2(0.8) /Y 2 O 3(0.2) /p-si(100) 2.4 Different RTP conditions k ~ 30.1 k ~ 17.9 k ~ 10 J (A/cm 2 g ) x E (MV/cm) As-deposited RTP 800 o -3 C20 20s N RTP 900 o C 20s N 2 V(voltage) Increase of κ from 15 to over 30 in cubic phase!

17 Cross Sectional HRTEM Study of The Y Y-doped doped HfO2 Films in Cubic Phase Interfaces of YDH(100)/GaAs, and YDH(111)/Si are atomically sharp 11nm =[110]YDH YDH [001]YDH [1-10]YDH [001]GaAs 5nm GaAs =[110] GaAs HRTEM image of yttrium-doped HfO2 films 11 nm thick on GaAs (001). HRTEM image of yitturm-doped HfO2 films 7.5 nm thick on Si (111).

18 The Enhancement of κ through Phase Transition Engineering κ= (1 + 8π α m /3V m ) / (1 4πα m /3V m ) Clausius-Mossotti Relation Change of molar volume in Y doped HfO 2 Many high κ materials, such as HfO 2, ZrO 2, TiO 2, Ta 2 O 5, commonly have high temperature phases with a higher κ. Achieve the enhancement through phase transition engineering i by additions of dopants such as lower valence cations, followed by proper post high temperature anneals.

19 IETS Study to Detect Phonons and Defects in High κ Dielectrics But what is inside of high κ?

20 Electrical characterization / optimization -- Good News!! Low electrical leakage is common. Have Attained an EOT under nm. -- Major problems are : High interfacial state density Large trapped charge Low channel mobility Electrical stability and reliability

21 Degradation of Mobility in High κ Gate Stack Phonons may have reduced mobility seriously! Fechetti et al, JAP 90, 4587, (2001). Correction from the charge trapping effect

22 Possible Source of Mobility Degradation Fixed charge Remote-surface roughness Remote phonon Phase-separation Crystalization Interfacial dipole Interface trap Source Drain Surface roughness

23 Interactions Detectable by IETS Substrate Silicon Phonons Gate Electrode Phonons Dielectric Phonons Chemical Bonding Interfacial Structures Defects (Trap States)

24 Trap-Related Signatures in IETS I Trap Assisted Tunneling Background I-V 2 d I dv 2 Charge Trapping V Trap Assisted Tunneling Charge Trapping Wei He and T.P.Ma, APL 83,2605, (2003) ; APL 83, 5461, (2003). V

25 Inelastic Electron Tunneling Spectroscopy (IETS) Charge trapping will cause shift in the threshold voltage. Trap-assisted conduction will cause increased leakage current. Wei He and T.P.Ma, APL 83,2605, (2003) ; APL 83, 5461, (2003)

26 IET spectrum of Al/HfO 2 /Si MOS structure Al/HfO 2 /Si, vacuum 600 annealing for 3 minutes d 2 I/dV 2 (Arbit trary Unit ts) (Arbitrary Units) d 2 I/dV 2 Si TA Si LO Si TO Hf-O Al-O Al Hf-O Hf-O Hf-O Al-O -Hf Al Hf-O -Si Si-O Forward-bias (gate positive) Si-O Reverse-bias (substrate positive) Voltage (mv) APS March Meeting March 7, 2007

27 IET spectrum of Al/HfO 2 /Si MOS structure V 2 (a..u.) Wave Number [cm -1 ] (b)gate Injection Si TA Al Hf-O Hf-O Si LA Si LO Hf-O Si TO Hf-O Hf-O O-Si 1 Si-O ALD 600C N 2 d 2 I/d MBE 600 UHV MBE 600C N 2 MBE 400C Ν Monoclinic HfO 2 V bias ( m V)

28 IET spectrum of Al/HfO2/Si MOS structure u.) d 2 I/dV 2 (a. [ (a )S u bstrate injection Hf-O Si TO -1 ] W ave N umb er [cm -1 ] Si TA Al Si LA Si LO Hf-O Hf-O Hf-O ALD 600C N 2 MBE 600C UHV MBE 600C N MBE 400C N V bias (m V) Monoclinic HfO 2

29 IET Spectrum of Al/Y2O3/Si MOS Diode Cubic Y2O3

30 Determination of Physical Locations and Energy Levels of Trap in Stacked HfO 2 /Y 2 O 3 /Si Structure d 2 I/ /dv 2 (a a.u.) post-deposition annealing at 400 o C Si Charge trapping HfO 2 ~ 2nm Y 2 O 3 ~ 2nm o C Si (100) in N 1 2 ambiance for 3 min 2 Substrate t HfO 2 ~2nm Y 2 O 3 ~2nm 2 3 d t Substrate Si(100) f r d 0 ( V V ) V = V V / + t f f r ( V V ) d = d V / + V f and V r are the voltages where the charge trapping features occur in forward bias and reverse bias V bias (mv) 7 0 M. Wang et al, APL. 86, (2005) APL, 90, (2007) f r

31 Determination of Physical Locations and Energy Levels of Trap in Stacked HfO 2 /Y 2 O 3 /Si Structure Bilayer Trap V f V r V t d Sample label (mv) (mv) (mv) t /d 0 HfO 2 (1.7nm) /Y 2 O 3 (1.4nm) o C HfO 2 (1.7nm) /Y 2 O 3 (1.4nm) o C HfO 2 (1.2nm) /Y 2 O 3 (1.5nm) o C Charge trapping HfO 2 ~2nm Y 2 O 3 ~2nm 2 3 d t d0 Substrate Si(100)

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33 Can you make HfO 2 magnetic? Diluted Magnetic Oxides Observation of Room Temperature Ferromagnetic Behavior in Cluster Free, Co doped HfO 2 Films Appl. Phys. Lett. 91, (2007)

34 Introduction o and motivation o Both injection and transport of spin-polarized p carriers are necessary for the spintronic devices. Using diluted magnetic semiconductor (DMS) as the ferromagnetic contact is one way to achieve this goal. Several models such as Zener s model, bound magnetic polaron, and F-center theory were used to describe the ferromagnetism. The potential ti usage of HfO 2 as alternative ti high-κ gate dielectrics in replacing SiO 2 for nano CMOS. Giant magnetic moment in Co doped HfO 2 as reported recently. F-center Fe 3+ Fe 3+ Oxygen vacancy

35 HR-TEM Images of High T and Low-T High-T Low T Grown Films High-T g ((700 C)) g grown film Monoclinic phase o ((100 C) 00 C) g grown, o, Low-T Polycrstalline film

36 EXAFS and Magnetic Characterization of High-T (700ºC) Grown Films 50 20% of Fourier r Transform Magnitude 40 4% % 10 1% % 4% R(A) 1 st O shell + 2 nd Co shell 2.04A 2.49A 2% EXAFS of the high-t grown samples showed a progressive formation of Co 1% clusters in the film (Co = 1-20 at.%). Superparramagnetic temperature dependence. d Saturation moment increases with increasing Co doping concentration.

37 Magnetic Property of Low-T Grown Films Substrate Temperature ( ) 40~100 40~100 40~100 Doping concentration (at.%)( Ms at 10K (µ B /Co) Ms at 300K(µ B /Co) Ferromagnetic behavior was observed at both 10K and 300K. The magnetic moment decreases with increasing Co doping due to enhanced dopant dopant associations. The magnetic properties are stable after annealing in O 2 at 350 o C. Correlation between saturation magnetization with concentrations of oxygen vacancies

38 F-center Exchange Mechanism: --An electron orbital created dby an oxygen vacancy with trapped electrons is expected to correlate with magnetic spins dispersed inside the oxides. Impurity-band Exchange Model : --The hydrogenic orbital formed by donor defect (like oxygen vacancy) associated with an electron overlaps to create delocalized impurity bands. -- If the donor concentration is large enough and interacts with the magnetic cations with their 3d orbitals to form bound magnetic polarons leading to ferromagnetism. γ 3 δ p 4.3, where γ = ε(m/m*) ) δ p : polaron percolation threshold M. Coey et al, X p : cation percolation threshold, γ H : hydrogenic radius Nature Materials, 2005.

39 Theoretical Analysis Using Impurity Band Exchange Model Material ε m * /m γ γ H (nm) δ P (10-6 ) ZnO TiO SnO HfO Al 2 O δ p : Polaron percolation threshold X p : Cation percolation threshold γ Η : Hydrogenic orbital radius p and x p are two landmarks on magnetic phase diagram. Ferromagnetism occurs when δ > δ p and x < x p. δ p of HfO 2 based DMO is about Appearance of ferromagnetic insulator behavior in HfO 2 is more likely than ZnO, TiO 2 and SnO 2. Will try Y 2 O 3, ZrO 2, and Al 2 O 3 etc.

40 Major Research Topics Novel MBE template approach for ALD growth Enhancement of κ in the new phase through epitaxy Fundamental study by IETSfor detections ti of phonons and defects in high κ dielectrics Room temperature ferromagnetism in cluster free, Co doped HfO 2 films

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