Gordon, Roy Gerald

Heo, Jae Yeong

Hock, Adam S.

Harvard University - DASH 

 Low Temperature Atomic Layer Deposition of Tin Dioxide, SnO\(_2\)  (Article begins on next page)The Harvard community has made this article openly available.Please share how this access benefits you. Your story matters.Citation Heo, Jaeyeong, Adam S. Hock, and Roy G. Gordon. 2010. Low temperature atomiclayer deposition of tin dioxide, SnO\(_2\). Presentation slides. 10th InternationalConference on Atomic Layer Deposition. Seoul, South Korea.Accessed February 19, 2015 10:06:41 AM ESTCitable Link http://nrs.harvard.edu/urn-3:HUL.InstRepos:8961464Terms of Use This article was downloaded from Harvard University's DASH repository, and is madeavailable under the terms and conditions applicable to Other Posted Material, as setforth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAALow Temperature Atomic Layer Low Temperature Atomic Layer Deposition of Tin Dioxide, SnO2Jaeyeong Heo, Adam S. Hock and Roy G. GordonHarvard UniversityCambridge  MA USA Cambridge, MA USAHarvard UniversityOutlineEarth-abundant, non-toxic transparent conductor: SnO2ALD process for SnO2new tin precursorgrowth per cycle growth per cycleSnO2 film propertiescompositionstructureoptical properties pp pelectrical propertiesapplicationsHarvard University 2SnO2: Transparent Conductor and Heat MirrorHi h i ibl t i i (hi h b d (E 41 V) High visible transmission (high bandgap (Eg ~ 4.1 eV)High electrical conductivity (high electron concentration and mobility) High electrical conductivity (high electron concentration and mobility)High environmental stability High environmental stabilityConstituent elements are non-toxic and abundantKnown ALD processes require high temperatures, > 200 oCor produce impure films (C, N), amorphous, low conductivityHarvard University 3Tin(II) Cyclic Stannylene as ALD PrecursorNN t-Bu t-BuN2,N3-di-tert-butyl-butane-2,3-diamido-tin(II)SnHydrocarbon ligand => high volatility (30 Torr at 60 oC)Sn-N bonds => reactive to hydrogen peroxide, H2O2Chelate structure => thermal stabilitySn N bonds   reactive to hydrogen peroxide, H2O2Synthesis and properties described by Adam Hock, Wednesday 14:15Harvard University 4Source temperature: 40 oCALD Process for SnO2Substrate temperature: 120 oC Source temperature: 40 oC Substrate temperature: 120 oCGrowth per cycle: 0.18 nm Induction period: only a few cycles80 4060 ess (nm)20Thickne0 100 200 300 4000CyclesHarvard University 5ALD Saturation CurvesIncreasing doses of cyclic tl ft iIncreasing doses of oxygen stannylene precursor for tin precursor, hydrogen peroxideRefractive index ~ 1 94 for saturated growth (3 doses)Harvard University 6Refractive index ~ 1.94 for saturated growth (3 doses)Temperature Dependence of Growth0.20 le)0.160.18te (nm/cyc0.120.14 osition Rat50 100 150 200 2500.10DepTemperature (oC)ALD window from 50 to 150 oCHarvard University 7SnOx CompositionRutherford Backscattering Spectroscopy (RBS) 0 5 1 0 1 5Energy (MeV)2.02.12.22.3o506070ield0.5 1.0 1.5Sn1.61.71.81.90 As-depo. O/Sn Rati203040NormalizedYiOCarbonSubstrateC in film1234561.5  350oC annealNumber of H2O2 doses 0 200 400 600 800 1000 1200 1400Channel010 O NNo C or N in film SnO2 for 2-3 dosesHarvard University 8X-Ray Photo-Electron Spectroscopy (XPS)No impurities detected (C, N) inside filmHarvard University 9Smooth Morphology of SnO2 Films 2.041.51.0µm02nm SiO2SnOx0.50.0-4-2200nm 200nmSi2.0 1.5 1.0 0.5 0.0µm400 l 71AFM RMS h 2 400 cycles => 71 nm RMS roughness = 2 nm< 3 % of thicknessHarvard University 10Step CoverageUniform thickness in holes with aspect ratio 50:1, grown at 50 oCHarvard University 11Polycrystalline Rutile Structure of SnO2 FilmsSiTEMelectrondiff ti(110)(101)(200)(211)(301)TEM diffractionX Ray DiffractionSnO2 5 nmX-Ray Diffraction (XRD) Harvard University 12SnO2 has Very Little Visible Absorption1.001 00.60.81.0 T Rn & Reflection0.060.080.10n = 1-T-R000.20.4 Transmission0.000.020.04 absorption200 400 600 8000.0TWavelength (nm)400 600 800Wavelength (nm)film 100 nm thick104x10105x1010 nt 2(cm-2) film 100 nm thick1x10102x10103x1010 on coefficieBand gap 4.13 eVHarvard University 132.5 3.0 3.5 4.0 4.5 5.00absorptioE (eV)Electrical Properties100cm)>105Resistivity minimum for 10-1 Resistivity ( ystoichiometric SnO2(2 to 4 doses)12345610-2Number of H2O2 dosesN-type semiconductor by Hall measurementselectron concentration ~ 1020 cm-3Harvard Universityelectron mobility ~ 6 cm2 V-1 s-114Resistivity vs. Deposition Temperature6x10-2 m)4x10-25x10-2 ivity (-cm(b)50 100 150 200 2502x10-23x10-2ResistiTemperature (oC)ii it ii t 0 0 2  h d it d t 120 C minimum resistivity 0.02 -cm when deposited at 120 oCHarvard University 15Ligand exchange of Sn precursor with hydroxylated surfaceProposed MechanismLigand exchange of Sn precursor with hydroxylated surface NSnNO OH Ht-Bu t-Bu NSnNO OH Ht-Bu t-Bu NNO OHHt-Bu t-BuSnSnO OSnO OO OSnO OO OOxidative addition of hydrogen peroxideOOH HO OH HO OH HSnO OSnSnO OSnO OSnO OSnO OHarvard University 16O OSnO O O OSnO2 is transparent semiconductor made of earth-abundant,SummarySnO2 is transparent semiconductor made of earth abundant, inexpensive, non-toxic elementsALD from a cyclic tin(II) amide and H2O2 => SnO2 2 2 2Smooth films of pure, stoichiometric, polycrystalline SnO2High optical transparency and electrical conductivity High optical transparency and electrical conductivity Successfully used in several applications:organic solar cells (with Alan Heeger UCSB) organic solar cells (with Alan Heeger, UCSB)conducting and protective coatings for plastics(with Michelle Schulberg, Physical Sciences Inc.)electron multipliers (Philippe deRouffignac,  Arradiance, to be presented on Wednesday at 13:30) Harvard University 17another possible application: thin-film transistors on plasticHall measurements done with Mark Winkler and Eric MazurAcknowledgementsHall measurements done with Mark Winkler and Eric Mazur  Support was provided by the following:Camille and Henry Dreyfus Postdoctoral Program in Environmental ChemistryAir Force Office of Scientific Research STTR under Air Force Office of Scientific Research-STTR under contract FA9550-09-C-0075Center for Nanoscale Systems (CNS), a member of the  y( ) ,National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under NSF award no ECS 0335765 CNS is Foundation under NSF award no. ECS-0335765. CNS is a part of the Faculty of Arts and Sciences and the School of Engineering and Applied Sciences at Harvard Harvard University 18University. 

Low Temperature Atomic Layer Deposition of Tin Dioxide, SnO\(_2\)

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