Fabrication and characterization of rare earth scandate thin films prepared by pulsed laser deposition J. Schubert M. Wagner1, T. Heeg1, O. Trithaveesak1, A. Gerber1 C. Zhao2, O. Richard2, M. Caymax2 V. V. Afanas’ev3 L.F. Edge4, Y. Jia4, W. Tian4, D.G. Schlom4 1Institute of Thin Films and Interfaces and Center of Nanoelectronic Systems for Information Technology, Research Center Jülich, D-52425 Jülich, Germany 2IMEC, Kapeldreef 75, B-3001 Leuven, Belgium 3Department of Physics, University of Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium 4Penn State University, 16802 University Park, Pennsylvania, USA Institute of Thin Films and Interfaces (ISG) Outline Pulsed Laser Deposition (PLD) High-κ-dielectrics Epitaxial films Amorphous films Summary and outlook Institute of Thin Films and Interfaces (ISG) Pulsed Laser Deposition (PLD) Nearly any material can be deposited High deposition rate Stoichiometric deposition Simple setup ideal for material screening Institute of Thin Films and Interfaces (ISG) PLD: on-axis-geometry Institute of Thin Films and Interfaces (ISG) PLD: off-axis-geometry Institute of Thin Films and Interfaces (ISG) Rare-earth based oxide films Collossal magneto resistance La0.66Ca0.33MnO3 La0.33Ba0.66MnO3 Isolating materials CeO2 LaAlO3 PrGaO3, NdGaO3 GdScO3 DyScO3 LaScO3 Institute of Thin Films and Interfaces (ISG) Outline Pulsed Laser Deposition (PLD) High-κ-dielectrics Epitaxial films Amorphous films Summary and outlook Institute of Thin Films and Interfaces (ISG) High-κ-dielectrics MOSFET: Driving force in micro-/nanoelectronics [ Spektrum d. Wissenschaft, 6/2004] [ Intel/SIA roadmap; www.intel.com] Institute of Thin Films and Interfaces (ISG) High-κ-dielectrics 10 SiO 2 optical bandgap [eV] 9 8 Al 2 O 3 MgO YAlO 3 CaO 7 Y 2O 3 ZrSiO 4 Sc2O3 ZrO2 Gd2 O3 SrO Si 3 N 4 Sm2 O 3 6 5 4 LaAlO 3 SrZrO 3 HfO2 LaLuO3 3 2 0 5 10 15 20 25 30 35 40 dielectric constant D.G. Schlom und J.H. Haeni, “A Thermodynamic Approach to Selecting Alternative Gate Dielectrics“, MRS Bulletin V. 27, No. 3 (2002) Institute of Thin Films and Interfaces (ISG) Motivation RE-Scandates stable in contact with silicon high melting point ( > 2000 °C) orthorhombic crystal structure (Pbnm) Material LaScO3 CeScO3 PrScO3 NdScO3 SmScO3 EuScO3 GdScO3 TbScO3 DyScO3 HoScO3 a [Å] 5.678 5.626 5.602 5.579 5.524 5.502 5.488 5.466 5.440 5.427 b [Å] 5.787 5.787 5.770 5.770 5.750 5.750 5.746 5.727 5.713 5.714 c [Å] 8.098 8.047 8.010 7.999 7.953 7.954 7.934 7.915 7.887 7.895 Institute of Thin Films and Interfaces (ISG) 15 mm Motivation GdScO3 DyScO3 RE-Scandates dielectric constant GdScO3 (single crystal) DyScO3 (single crystal) LaScO3 (poly material) Jeff Haeni-Thesis 2002 18-30 18-35 25-68 Transmission (%) 70 GdScO3-bandgap 60 50 40 30 20 10 0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 E(eV) Seung-Gu Lim et al., JAP (91) 7, (2002), 4500-4505 Institute of Thin Films and Interfaces (ISG) 7.0 High-κ-dielectrics 10 SiO 2 optical bandgap [eV] 9 8 Al 2 O 3 MgO YAlO 3 CaO 7 Y 2O 3 ZrSiO 4 GdScO 3 Sc 2 O 3 LaAlO 3 ZrO 2 SrZrO 3 LaScO 3 Gd 2 O 3 SrO DyScO 3 Si 3 N 4 HfO 2 Sm 2 O 3 LaLuO 3 6 5 4 3 2 0 5 10 15 20 25 30 35 40 dielectric constant D.G. Schlom und J.H. Haeni, “A Thermodynamic Approach to Selecting Alternative Gate Dielectrics“, MRS Bulletin V. 27, No. 3 (2002) Institute of Thin Films and Interfaces (ISG) Typical growth conditions wave length 248 nm pulse duration 25 nsec energy 1 J / pulse energy density 3-5 J/cm2 repetition rate 10 Hz pressure > 1*10-3 mbar O2 target - substrate 6 cm substrate temperature 20°C - 1000°C sintered stoichiometric targets Institute of Thin Films and Interfaces (ISG) Outline Pulsed Laser Deposition (PLD) High-κ-dielectrics Epitaxial films Amorphous films Summary and Outlook Institute of Thin Films and Interfaces (ISG) Results: DyScO3 on SrTiO3 (100) Energy (MeV) 150 0.6 0.8 1.0 1.2 Sc Dy random O Normalized Yield Tsub 900°C d = 250 nm Dy:Sc 1:1.05 0.4 Ti 100 50 Sr channelling χmin= 3.5 % 0 200 400 600 Channel Institute of Thin Films and Interfaces (ISG) 800 1000 Ts = 900 °C a,b = 5.67 Å ∆ω 220 = 0.26° * 330 * * 220 110 Results: DyScO3 on SrTiO3 (100) Counts 900 °C 700 °C 500 °C 10 20 30 40 50 60 2θ (degrees) Institute of Thin Films and Interfaces (ISG) 70 80 Results: LaScO3 on SrTiO3 (100) Energy (MeV) 150 0.6 0.8 O 1.2 La Ti 100 50 1.0 Sc random Normalized Yield Tsub 900°C d = 350 nm La:Sc 1:1 0.4 Sr channelling χmin= 2% 0 200 400 600 Channel Institute of Thin Films and Interfaces (ISG) 800 1000 * Ts = 900 °C c = 8.26 Å a,b = 5.70 Å ∆ω 220 = 0.1° * 330 * 220 110 Results: LaScO3 on SrTiO3 (100) Counts 900 °C 600 °C 500 °C 10 20 30 40 50 2θ (degrees) 60 Institute of Thin Films and Interfaces (ISG) 70 80 Results: LaScO3 on SrTiO3 (100) LaScO3 SrTiO3 450 nm LaScO3 SrTiO3 1 nm Institute of Thin Films and Interfaces (ISG) Wei Tian (PSU) LaScO3 on SrTiO3 on Silicon (100) Energy (MeV) 100 0.4 0.6 0.8 1.0 1.2 La js_4797_r js_4797_c Normalized Yield 80 60 O Si 40 Sr Ti 20 0 200 χmin ~ 3.5 % (LSO) ∆ω (220) ~ 0.6 ° (LSO) Sc 400 600 800 1000 Channel Institute of Thin Films and Interfaces (ISG) Results: LaScO3 on SrRuO3 / SrTiO3 (100) Energy (MeV) 0.4 150 Tsub 900°C d = 350 nm 0.6 random Normalized Yield O Ti 0.8 Sr 1.0 1.2 Sc La Ru 100 50 χmin= 3% channelling 0 200 400 600 Channel Institute of Thin Films and Interfaces (ISG) 800 1000 C(V)-Measurements (f = 1 MHz) LaScO3 28 Vbd > 1MV/cm dielectric constant 27 κ = 26 LaScO3 κ = 20 DyScO3 26 GdScO3 25 fits to the values of single crystals in a,b direction 24 23 -2 -1 0 1 2 5 electric field [V/cm * 10 ] Institute of Thin Films and Interfaces (ISG) Epitaxial films • Epitaxial RE-scandate films grown by PLD • Stoichiometric transfer target substrate • Twinned orthorhombic structure • Good crystalline properties ∆ω = 0.1° (LaScO3) • κ = 26 (LaScO3) κ = 20 (DyScO3, GdScO3) Institute of Thin Films and Interfaces (ISG) Outline Pulsed Laser Deposition (PLD) High-κ-dielectrics Epitaxial films Amorphous films Summary and Outlook Institute of Thin Films and Interfaces (ISG) RBS: GdScO3 on Si Energy (MeV) 120 0.4 0.6 0.8 Si 1.0 1.2 Gd GdScO3 Normalized Yield 100 Measurement Simulation 80 O 60 Si 40 Sc 20 0 200 Tsub 500°C d = 50 nm 400 600 800 Channel Institute of Thin Films and Interfaces (ISG) 1000 SEM/TEM-micrographs On-axis-chamber Off-axis-chamber Institute of Thin Films and Interfaces (ISG) High temperature XRD Amorphous phase of DyScO3 and GdScO3 stable up to 1000°C Institute of Thin Films and Interfaces (ISG) Amorphous films: properties Internal photoemission Bandgap > 5.5 eV Bandoffsets 2 – 2.5 eV Afanas’ev, V. V.; Stesmans, A.; Zhao, C.; Caymax, M.; Heeg, T.; Schubert, J.; Jia, Y.; Schlom, D.; Lucovsky, G.: “Band alignment between (100)Si and complex rare earth/transition metal oxides“. Appl. Phys. L. Vol. 85, No. 24 (2004) Institute of Thin Films and Interfaces (ISG) Electrical measurement Au high-κ-dielectric SiO2 dhigh-κ dSiO κhigh-κ κSiO 2 2 Chigh-κ CSiO 2 p-doped Si → d EOT κ SiO = d high −κ + d SiO κ high −κ 2 Institute of Thin Films and Interfaces (ISG) 2 Ugate EOT-plots GdScO3 on Si DyScO3 on Si 20 18 measured @ 100 kHz 16 EOT [nm] 14 12 on-axis κ = 20 10 8 on-axis off-axis linear fit on-axis linear fit off-axis 6 4 off-axis κ = 16 2 0 0 10 20 30 40 50 Film thickness [nm] Institute of Thin Films and Interfaces (ISG) 60 70 C-V-curves (On-axis-chamber) 0.55 measured @ 100 kHz hold time: 3 s 0.50 2 Capacitance [µF/cm ] 0.45 0.40 DyScO3 - 5 nm 0.35 DyScO3 - 8 nm 0.30 DyScO3 - 25 nm DyScO3 - 50 nm 0.25 0.20 0.15 VFB = -0.2 to -0.4 V 0.10 0.05 0.00 -3 -2 -1 0 1 Gate voltage [V] Institute of Thin Films and Interfaces (ISG) 2 3 Leakage currents (Off-axis-chamber) Institute of Thin Films and Interfaces (ISG) Amorphous films Stability up to 1000°C (DyScO3, GdScO3) Stability up to 700°C (LaScO3) Bandgap > 5.5 eV Bandoffsets 2 – 2.5 eV On-axis-geometry: dense and smooth films κ ~ 20 Small leakage currents Scandates are promising candidates Institute of Thin Films and Interfaces (ISG) Outlook Transistors Mobility measurements Creating films with higher κ (laminates from titanates and scandates) Institute of Thin Films and Interfaces (ISG)