Overview of ALD Precursors and Reaction Mechanisms Roy G. Gordon Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, U.S.A. Abstract Successful use of ALD requires suitable chemical precursors used under reaction conditions that are appropriate for them. There are many requirements for ALD precursors: sufficient volatility, thermal stability and reactivity with substrates and with the films being deposited. In addition, it is easier to produce the required vapors if the precursor is liquid at room temperature, or if it is a solid with melting point below the vaporization temperature, or if it is soluble in an inert solvent with vapor pressure similar to that of the precursor. The precursor vapor should not etch or corrode the substrate or deposited film. Ideally, the precursors should be non-flammable, non-corrosive, non-toxic, simple and non-hazardous to make and inexpensive. Presenting Author: Roy G. Gordon (gordon@chemistry.harvard.edu) Introduction to ALD Precursors and Reaction Mechanisms Tutorial for ALD 2011 Roy Gordon Harvard University 1 Outline •Elements and Materials in ALD Films •ALD Precursors for Non-Metals •Types of ALD p yp precursors for Metals •Types of ALD Reactions Types 2 ELEMENTS AND MATERIALS IN ALD FILMS 3 List of the Stable Elements by Symbol Europium Eu p Fluorine F Iron Fe Gallium Ga Gadolinium Gd Germanium Ge Hydrogen H Helium H li He H Hafnium Hf Mercury Hg Holmium Ho Iodine I Indium In Iridium Ir Potassium K Krypton Kr Lanthanum La Lithium Li Lutetium Lu Magnesium Mg Manganese g Mn Molybdenum Mo Nitrogen N Sodium Na Niobium Nb Neodymium Nd Neon Ne Nickel Ni k l Ni Oxygen O Osmium Os Phosphorus P Lead Pb Palladium Pd Praseodymium Pr Platinum Pt Rubidium Rb Rhenium Re Rhodium Rh Ruthenium Ru Sulfur S Antimony Sb y Scandium Sc Selenium Se Silicon Si Samarium Sm Tin Sn Strontium Sr Tantalum Ta T t l T Terbium Tb Tellurium Te Thallium Tl Thulium Tm Titanium Ti Tungsten W Vanadium V Xenon Xe Yttrium Y Ytterbium Yb Zinc Zn Zirconium Zr 4 Silver Ag g Aluminum Al Argon Ar Arsenic As Gold Au Boron B Barium Ba Beryllium B B lli Be Bromine Br Carbon C Calcium Ca Cadmium Cd Cerium Ce Chlorine Cl Cobalt Co Chromium Cr Cesium Cs Copper Cu Dysprosium Dy Erbium Er main group metals Periodic Table non-metals metals 13 alka aline eart metals th s Na V Nb Ta Db Pr Pa U Nd Pm Sm Np Pu Sg Bh Hs W Re Os Ir Mt Eu Mo Tc Ru Rh Pd Pt Ds Gd Am Cm Cr Mn Fe Co Ni Rb Cs alkali m metals metalloids or semi-metals 14 B 10 11 Cu Ag Au Rg Tb Bk 12 Zn Cd Hg Al Ga In Tl C Si Ge Sn Pb 15 N P As Sb Bi 16 O S Se Te Po halogens h s 1 18 17 F Cl Br I At He Ne Ar Kr Xe Rn H 2 Li 5 6 7 8 9 Be transition metals Mg 3 4 K Ca Sc Ti Sr Y Zr Ba La Hf Fr Ra Ac Rf main group metals Dy y Cf Ho Es Er Fm Tm Md Yb Lr Lu No 5 lanthanides Ce actinides Th Elements in ALD Films 18 13 B 5 V Nb Ta Db Pr Pa U Np Pu Nd Pm Sm Eu Gd Sg Bh Hs Mt Ds Rg Tb Bk Dy Cf Ho Es Er Fm Tm Md Yb Lr Lu No W Re Os Ir Pt Au Mo Tc Ru Rh Pd Ag Cd Hg Cr C Mn M Fe F Co C Ni Cu C Zn Z Ga G In Tl 6 7 8 9 10 11 12 Al C Si Ge G Sn Pb 14 15 N P As A Sb Bi 16 O S Se S Te Po 17 F Cl Br B I At He Ne Ar Kr K Xe Rn 1 M = element in at least one ALD film H 2 Li Be Na Mg 3 4 K Ca C Sc S Ti Rb Sr Y Zr Cs Ba La Hf Fr Ra Ac Rf Ce Th Am Cm Not used in ALD because the elements are = radioactive = highly toxic = inert 6 = low-volatility compounds Combinations of Elements in ALD Films ALD f films have been made with combinations of 2 or more elements within a box f Underlined elements have been deposited as pure, single elements 14 N P B C 13 O 15 N 1 O 2 O Li Be O F N P 4 O S C N O Nb Tc Ru N O Ta C O Pm Sm O Eu Si C O Gd O Tb O Dy O Ho O Er W S Re N O Os Mo N O O Rh O Ir Pt Au Hg Te Pd Ag Cd S Te Al Te V Fe Co Cr Mn S O O N O N O N O N O C Ni S 5 6 7 8 9 10 11 N O Cu S 12 NO Zn Te F S As N P Se As N P O Al N P O Si C O Ga O Ge Sb Te O In Se As Sb O Tl Ti O Tm O Yb S O Sn S B O Si P Na Mg Te 3 O F N O N K Ca S Sc Zr Ti As Hf Al O Zr Al O Hf Al O Nd O F N O N O Sb Te O Pb S Si Bi Ti N O Lu Rb Sr S Y S Si Ti O N O Ti F N Cs Ba S Si La S Si Ti Al Ti O O Ce Pr Updated table from R. Puurunen, J. Appl. Phys. 97, 121301 (2005) 7 ALD Materials by Type Oxide dielectrics Oxide conductors or semiconductors Other ternary oxides Oth t id Nitride dielectrics or semiconductors Metallic nitrides II-VI semiconductors II-VI based phosphors III-V semiconductors Fluorides Fl id Elements Other semiconductors Al2O3, TiO2, ZrO2, HfO2, Ta2O5, Nb2O5, Sc2O3, Y2O3, MgO, B2O3, SiO2, GeO La G O2, L 2O3, C O2, P Ox, Nd2O3, S 2O3, E Ox, Gd2O3, D 2O3, H 2O3, CeO PrO Sm EuO Dy Ho Er2O3, Tm2O3, Yb2O3, Lu2O3, SrTiO3, BaTiO3, PbTiO3, PbZrO3, BixTiyO, BixSiyO, SrTa2O6, SrBi2Ta2O9, YScO3, LaAlO3, NdAlO3, GdScO3, LaScO3, LaLuO3, LaYbO3, Er3Ga5O13 In2O3, In2O3:Sn, In2O3:F, In2O3:Zr, SnO2, SnO2:Sb, Sb2O3, ZnO, ZnO:Al, ZnO:B, ZnO:Ga, RuO2, RhO2, IrO2, Ga2O3, VO2, V2O5, WO3, W2O3, NiO, CuOx, FeOx, CrOx, CoOx, MnOx LaCoO LaNiO LaMnO La Ca MnO L C O3, L NiO3, L M O3, L 1-xC xM O3 BN, AlN, GaN, InN, Si3N4, Ta3N5, Cu3N, Zr3N4, Hf3N4, LaN, LuN , , , , , , , TiN, Ti-Si-N, Ti-Al-N, TaN, NbN, MoN, WNx, WNxCy, CoxN, SnxN ZnS, ZnSe, ZnTe, CaS, SrS, BaS, CdS, CdTe, MnTe, HgTe ZnS:M (M=Mn,Tb,Tm); CaS:M (M=Eu, Ce, Tb, Pb); SrS:M(M=Ce,Tb, Pb) GaAs, AlAs, AlP, InP, GaP, InAs CaF SrF MgF LaF ZnF C F2, S F2, M F2, L F3, Z F2 Ru, Pt, Ir, Pd, Rh, Ag, Cu, Ni, Co, Fe, Mn, Ta, W, Mo, Ti, Al, Si, Ge PbS, SnS, In2S3, Sb2S3, CuxS, CuGaS2, WS2, SiC, Ge2Sb2Te5 La2S3, Y2O2S TiCx, TiS2, TaCx, WCx, Ca3(PO4)2, CaCO3, organics S, Others Adapted from M. Ritala and J. Niinisto, in Chemical Vapor Deposition (Royal Society of Chemistry, 2009) 8 ALD PRECURSORS FOR NON-METALS oxygen nitrogen fluorine, carbon sulfur, selenium, tellurium phosphorus, arsenic, antimony 9 Non-Metals Important in ALD Films N = Nitrogen O = Oxygen g yg P = Phosphorus S = Sulfur Se = Selenium 18 13 B 5 V Nb Ta Db Pr Pa U Nd Sg Bh Hs W Re Os Mo Tc Ru Rh Ir Mt Eu Np Pu Cr Mn Fe Co Ni Pd Pt Ds Gd Am Cm 6 7 8 9 10 11 Cu Ag Au Rg Tb Bk Dy Cf Ho Es Er Fm Tm Md Yb Lr Lu No 10 C = Carbon F = Fluorine 1 14 15 16 17 H 2 He Li Be C 12 Zn Cd Hg Al Ga In Tl Si Ge Sn Pb NO P As Sb Bi F S Te Po Cl Ne Ar Na Mg 3 4 K Ca Sc Ti Se Br I At Kr Xe Rn Rb Sr Y Zr Cs Ba La Hf Fr Ra Ac Rf Ce Pm Sm Th ALD Precursors for Oxygen Water vapor H2O vapor, Hydrogen peroxide, H2O2, sometimes more reactive than H2O ( (always accompanied by water) y p y ) Alcohols, ROH, such as methanol CH3OH or ethanol C2H5OH Di oxygen, Di-oxygen O2, the common form of oxygen in the air Ozone, O3, a more reactive form of oxygen, made in a plasma, can flow through tubing; ( g g (always accompanied by O2) y p y Oxygen atoms, created in a plasma close to a substrate surface; so reactive that they can’t travel far through tubing without recombining to form O2 Nitrogen dioxide, NO2 (always accompanied by its dimer N2O4) 11 ALD Precursors for Nitrogen Ammonia, NH3 Hydrazine, N2H4, is more reactive than NH3, but toxic & explosive Plasma-activated NH3 is more reactive than NH3 Dinitrogen, N2, is normally unreactive under ALD conditions Plasma-activated N2 i more reactive th N2 Pl ti t d is ti than Nitric oxide, NO, can be used for nitrogen-doping of oxides 12 ALD Precursors for Carbon H H C O OH Acetylene gas C C H Formic acid vapor Carbon contained in a metal compound ALD Precursors for Fluorine Hydrogen fluoride gas, HF Fluorine Fl i contained i a metal compound such as WF6 t i d in t l d h 13 ALD Precursors for Sulfur, Sulfur Selenium and Tellurium Elemental sulfur vapor, Sn Hydrogen sulfide gas, H2S (poisonous, but sufficient warning by smell, if not chronically exposed) Hydrogen selenide gas, H2Se (very poisonous, without sufficient warning by smell) Bis(triethylsilyl)selenium, (Et3Si)2Se Bis(triethylsilyl)tellurium, (Et3Si)2Te 14 ALD Precursors for Phosphorus, Phosphorus Arsenic and Antimony phosphine gas, PH3 (very poisonous) arsine gas, AsH3 (very poisonous) antimony trichloride, SbCl3 H3C H3C N CH3 N Sb N CH3 CH3 CH3 tris(dimethylamido)antimony 15 Elemental ALD Precursors Examples: Non-metals O2, P4, S2 or S8 Metals: Mg Mn, Zn Mg, Mn Disadvantage: low volatility (metals) 18 13 B 5 V Nb Ta Db Pr Pa U Nd Sg Bh Hs W Re Os Ir Mt Eu Np Pu Mo Tc Ru Rh Cr Mn Fe Co Ni Pd Pt Ds Gd Am Cm 6 7 8 9 10 11 Cu Ag g Au Rg Tb Bk Dy Cf Ho Es Er Fm Tm Md Yb Lr Lu No 16 Advantage: high purity 1 14 C 12 Zn Cd Hg Al Ga In Tl Si Ge Sn Pb 15 N P As Sb Bi 16 O S Se Te Po 17 F Cl Br I At H 2 He Ne Ar Kr Xe Rn Li Be Na Mg 3 4 K Ca Sc Ti Rb Sr Y Zr Cs Ba La Hf Fr Ra Ac Rf Ce Pm Sm Th TYPES OF ALD PRECURSORS FOR METALS pure elements metal hydrides metal halides: f fluorides, chlorides, bromides, iodides metal-carbon bonds: alkyls, cyclopentadienyls y , y p y metal-oxygen bonds: alkoxides, beta-diketonates metal-nitrogen bonds: amides, imides, amidinates 17 Metal Compounds for ALD Most metal compounds used in ALD have 1 or 2 metal atoms, M, combined with 1 or more “ligands”, L, written as monomers MLn or dimers M2Ln, where n = 1, 2, 3, 4, 5 or 6. The ligands, L, contain 1 or more non-metal atoms. The Th metal atoms, M, may be considered to have >1 units of positive charge. t l t M b id dt h it f iti h Metals with 1 unit of positive charge M+ may be written M(I), and are said to be in oxidation state +1 +1. Metals with 2 units of positive charge M2+ may be written M(II), and are said to be in oxidation state +2, etc. 2, Most ligands used in ALD can be considered to have electrical charge -1. A few ligands, e.g. oxides (O2-) and imides ( xH2x+1)2-, have charge -2. g g ( (NC 2x 1 g The total charges of the metal and ligands in a precursor must add to zero. 18 Types of Metal Precursors for ALD R N M Alkylimides 19 Elements with Hydride ALD Precursors Hydrides are compounds of an element X and hydrogen XHn n = 1, 2, 3 or 4 18 13 B 5 V Nb Ta T Db Pr Pa U Nd Sg Bh Hs W Re R Os O Ir I Mt Eu Pu Mo Tc Ru Rh Pd Pt Ds Gd Am Cm Cr Mn Fe Co Ni 6 7 8 9 10 11 Cu Ag Au A Rg Tb Bk Dy Cf Ho Es Er Fm Tm Md Yb Lr Lu No 20 1 14 C 12 Zn Cd Hg H Al Ga In Tl Si Ge Sn Pb 15 N P As Sb Bi 16 O S Se Te Po P 17 F Cl Br I At H 2 He Ne Ar Kr Xe Rn R Li Be Na Mg 3 4 K Ca Sc Ti Rb Sr Y Zr Cs C Ba B La L Hf Fr Ra Ac Rf Ce Pm Sm Np Th Examples of Hydride Precursors H H H H Si H H H H Ge G H H Si H H SiH4 = silane Si H Si2H6 = disilane, H more reactive than silane GeH4 = germane AlH3 NMe3 = aluminum hydride – trimethylamine Disadvantages: g usually need plasma activation pyrophoric and toxic 21 Advantage: g very volatile Elements with Halide ALD Precursors MXn n = 1, 2, 3, 4, 5 or 6 halogens 18 13 B 5 V Nb Ta Db Pr Pa U Nd Sg Bh Hs W Re Os Mo Tc Ru Rh Ir Mt Eu Np Pu Cr Mn Fe Co Ni Pd Pt Ds Gd Am Cm 6 7 8 9 10 11 Cu Ag Au Rg Tb Bk Dy Cf Ho Es Er Fm Tm Md Yb Lr Lu No 22 Halides are compounds of an element M and a halogen X = F, Cl, Br or I 1 14 C 12 Zn Cd Hg Al Ga In Tl Si Ge Sn Pb 15 N P As Sb Bi 16 O S Se Te Po 17 F Cl Br I At H 2 He Ne Ar Kr Xe Rn Li Be Na Mg 3 4 K Ca Sc Ti Rb Sr Y Zr Cs Ba La Hf Fr Ra Ac Rf Ce Pm Sm Th Examples of Halide ALD Precursors Oxygen can be combined with halide ligands: WF6 = tungsten hexafluoride TiCl4 = tit i titanium t t tetrachloride hl id HfCl4 = hafnium tetrachloride VOCl3 = trichlorooxovanadium = vanadium oxide trichloride = vanadyl trichloride CrO2Cl2 = dichlorodioxochromium = chromium dichloride dioxide = chromyl dichloride GeCl2·dioxane O H2C CH2 SnCl4 = tin tetrachloride Advantages: thermally stable usually inexpensive GeCl2 H2C O 23 Disadvantages: halogen impurities in films corrosive byproducts i b d t low volatility for some elements CH2 Metal Alkyl ALD Precursors ( (CH3)3Al = trimethylaluminum y (CH3CH2)2Zn = diethylzinc H3C Zn CH3 H2 C H2 C Advantage: volatile, hi hl reactive in ALD Ad t l til highly ti i Disadvantage: hazardous, burst into flame in air (pyrophoric) H3C CH H3C Te CH CH3 CH3 iPr 2Te = diisopropyltellurium 24 Elements with Alkyl ALD Precursors 18 13 B 5 V Nb Ta Db Pr Pa U Np Pu Nd Pm Sm Eu Sg Bh Hs Mt Ds Gd Am Cm W Re Os Ir Pt Mo Tc Ru Rh Pd Ag Au Rg Tb Bk Dy Cf Ho Es Er Fm Tm Md Yb Lr Lu No Cr Mn Fe Co Ni Cu Zn Cd Hg 6 7 8 9 10 11 12 Al Ga In Tl 14 C Si Ge Sn Pb 15 N P As Sb Bi 16 O S Se Te Po 17 F Cl Br I At He Ne Ar Kr Xe Rn 1 H 2 Li Be Na Mg 3 4 K Ca Sc Ti Rb Sr Y Zr Cs Ba La Hf Fr Ra Ac Rf Ce Th 25 Cyclopentadienyl Ligands H C HC CH CH HC Cp = cyclopentadienyl MeCp = methylcyclopentadienyl CH3 H3C C C C H3C C C CH3 CH3 Me5Cp = Cp* = pentamethylcyclopentadienyl EtCp = ethylcyclopentadienyl iPrCp = isopropylcyclopentadienyl 26 Examples of Cyclopentadienyl Precursors Cp2Ni = bis(cyclopentadienyl)nickel(II) (EtCp)2Ru = bis(ethylcyclopentadienyl)ruthenium(II) (Me5Cp)2Sr = bis(pentamethylcyclopentadienyl)strontium (iPrCp)3La = tris(isopropylcyclopentadienyl)lanthanum Cp2Me2Zr = (dicyclopentadienyl)(dimethyl)zirconium (MeCp)(Me)3Pt = (methylcyclopentadienyl)(trimethyl)platinum(IV) 27 Cyclopentadienyl ALD Precursors 18 13 B 5 V Nb Ta Db Pr Pa U Np Pu Am Cm Nd Pm Sm Eu Gd Tb Bk Sg Bh Hs Mt Ds Rg Dy Cf Ho Es Er Fm Tm Md Yb Lr Lu No W Re Os Ir Pt Au Hg Mo Tc Ru Rh Pd Ag g Cd In Tl Cr Mn Fe Co Ni Cu Zn Ga Ge Sn Pb 6 7 8 9 10 11 12 Al Si P As Sb Bi C N 14 15 16 O S Se Te Po 17 F Cl Br I At He Ne Ar Kr Xe Rn 1 H 2 Li Be Na Mg 3 4 K Ca Sc Ti Rb Sr Y Zr Cs Ba La Hf Fr Ra Ac Rf Ce Th Advantages: thermally stable Disadvantages: some have low reactivity (Ni, Ru) some are solids (Ni S M I La) lid (Ni, Sr, Mg, In, L ) some have low volatility (La, Sr, Mg) 28 Alkoxide Compounds O M M C CH3 OMe = methoxy OtBu = tert-butoxy CH3 O M C H2 CH3 O O CH3 CH3 CH3 OEt = ethoxy OtPe = tert-pentoxy M H3C C CH2 CH3 M C CH3 OiPr = isopropoxy M CH3 CH O CH3 O O C H3C H2 H2 C CH3 mmp = 1-methoxy2-methyl-2-propoxy y p p y CH3 O Bu = isobutoxy M O CH3 CH i H2 C dmae = dimethylamino- M O C ethoxy H2 N CH3 CH3 O Bu = sec-butoxy M sec butoxy CH CH3 s O H2 C CH3 dmamp = 1-dimethylamino1 di h l i 2-methyl-2-propoxy H3C H2 O CH3 C M C N CH3 CH3 29 Alkoxide Compounds Used in ALD Al(OEt)3 = tris(ethoxy)aluminum = aluminum ethoxide AlMe2(OiPr) = isopropoxydimethylaluminum B(OMe)3 = tris(methoxy)boron = trimethylborate ( ) ( y) y Hf(OtBu)4 = tetra(tert-butoxy)hafnium = hafnium tert-butoxide Hf(mmp)4 = tetra(1-methoxy-2-methyl-2-propoxy)hafnium Nb(OEt)5 = penta(ethoxy)niobium = niobium ethoxide Ni(dmamp)2 = bis(1-dimethylamino-2-methyl-2-propoxy)nickel(II) Pb(OtBu)2 = bis(tert-butoxy)lead(II) = lead(II) tert-butoxide Si(OEt)4 = tetra(ethoxy)silane = tetraethylorthosilicate = TEOS Si(OtB )3OH = t i (t t b t Bu) tris(tert-butoxy)silanol ) il l Si(OtPe)3OH = tris(tert-pentoxy)silanol Ta(OEt)5 = penta(ethoxy)tantalum = tantalum ethoxide Ti(OMe)4 = tetra(methoxy)titanium = titanium methoxide Ti(OEt)4 = tetra(ethoxy)titanium = titanium ethoxide Ti(OiPr)4 = tetra(isopropoxy)titanium = titanium isopropoxide VO(OiPr)3 = tris(isopropoxy)oxovanadium = vanadyl isopropoxide 30 Elements with Alkoxide ALD Precursors 18 13 B 5 V Nb Ta Db Pr Pa U Np Pu Am Cm Nd Pm Sm Eu Gd Tb Bk Sg Bh Hs Mt Ds Rg Dy Cf Ho Es Er Fm Tm Md Yb Lr Lu No W Re Os Ir Pt Au Hg Mo Tc Ru Rh Pd Ag g Cd In Tl Cr Mn Fe Co Ni Cu Zn Ga Ge Sn Pb 6 7 8 9 10 11 12 Al Si C N P As Sb Bi 14 15 16 O S Se Te Po 17 F Cl Br I At He Ne Ar Kr Xe Rn 1 H 2 Li Be Na Mg 3 4 K Ca Sc Ti Rb Sr Y Zr Cs Ba La Hf Fr Ra Ac Rf Ce Th Advantages: reactive to water vapor => oxides Disadvantages: limited thermal stability not suitable for making nitrides not suitable for making pure metals 31 Beta-diketonate Compounds delocalized bonding picture pict re 2 C O M O CH3 C H 3C H2 C H C CH O M CH O CH3 4 equivalent ways to represent a metal acetylacetonate (acac): delocalized bonding picture 1 i t CH3 O M H3C localized bonding picture 1 i t localized bonding picture 2 i t H3C O H C H3C H C C CH3 O O M 32 Beta-diketonate Compounds CH3 C H3C O M C O M O C C F3C H C CF3 H C H3C CH3 C O H3C C CH3 CH3 H3C H C C C O O M pe a e , d o a e, o pentane-2,4-dionate, or acetylacetonate (acac) 1,1,1,5,5,5-hexafluoro, , ,5,5,5 e a uo o acetylacetonate (hfac) (more volatile) 2,2,6,6-tetramethylheptane-3,5-dionate h t 3 5 di t (thd or tmhd) (more bulky) CH3 H3 C CH3 O H C H3C O M O H2 C C H C C CH3 H3C H2 C C H2 O H2 C C H2 C C H2 CH3 O C O M CH3 octane-2,4-dionate octane-2 4-dionate (od) (lower melting point) 1-(2-methoxyethoxy)-2,2,6,6-tetramethylheptane-3,5-dionate (methd) (very bulky) 33 Beta-diketonate ALD Precursors Advantages: non-reactive non reactive to ambient air high thermal stability Disadvantages: low vapor pressure (except Cu(hfac)2) solids with high melting points low reactivity to water vapor not suitable for making nitrides Mg(thd)2 Mn(thd)3 Nd(thd)3 Ni(acac)2 Ni(thd)2 Pb(thd)2 Pd(hfac)2 Pd(thd)2 Pt(acac)2 Ru(thd)3 Ru(od)3 Sc(thd)3 Sm(thd)3 Sr(thd)2 Sr(methd)2 ( ) Tm(thd)3 Y(thd)3 Ba(thd)2 Ce(thd)4 Co(acac)2 Co(acac)3 Co(thd)3 Cr(acac)3 C( ) Cu(hfac)2 Cu(thd)2 Dy(thd)3 Er(thd)3 Eu(thd)3 Fe(acac)3 Fe(thd)3 Gd(thd)3 Ho(thd)3 ( ) Ir(acac)3 La(thd)3 34 Beta-diketonate ALD Precursors 18 13 B 5 V Nb Ta Db Pr Pa U Np Pu Nd Pm Sm Eu Sg Bh Hs Mt W Re Os Ir Pt Ds Gd Am Cm Mo Tc Ru Rh Pd Ag Au Rg Tb Bk Dy Cf Ho Es Er Fm Tm Md Yb Lr Lu No Cr Mn Fe Co Ni Cu Zn Cd Hg 6 7 8 9 10 11 12 Al Ga In Tl 14 C Si Ge Sn Pb 15 N P As Sb Bi 16 O S Se Te Po 17 F Cl Br I At He Ne Ar Kr Xe Rn 1 H 2 Li Be Na Mg 3 4 K Ca Sc Ti Rb Sr Y Zr Cs Ba La Hf Fr Ra Ac Rf Ce Th 35 Amide Ligands CH3 M CH3 H2C M N CH3 H2C M N H2C CH3 H3C Si M H3C CH3 M N C CH3 CH3 N Si CH3 CH3 CH3 CH3 CH3 CH3 N NMe2 = dimethylamino = dimethylamido NEtMe = ethylmethylamino = ethylmethylamido NEt2 = diethylamino = diethylamido N(SiMe3)2 = bis(trimethylsilyl)amido = bis(trimethylsilyl)amino NtBu = tert-butylimino = tert-butylimido 36 Amide and Imide Precursors for ALD Al(NMe2)3 = tris(dimethylamido)aluminum = Al2(NMe2)6 = hexakis(dimethylamido)dialuminum Bi[N(SiMe3)2]3 = tris(bis(trimethylsilyl)amido)bismuth [ ( ( ( y y) ) Hf(NMe2)4 = tetrakis(dimethylamido)hafnium Hf(NEtMe)4 = tetra(ethylmethylamido)hafnium = TEMAH Hf(NEt2)4 = tetrakis(diethylamido)hafnium = TDEAH La[N(SiMe3)2]3 = tris(bis(trimethylsilyl)amido)lanthanum Pr[N(SiMe3)2]3 = tris(bis(trimethylsilyl)amido)praseodymium Ta(NMe2)5 = pentakis(dimethylamido)tantalum Ta(NEt T (NEt2)5 = pentakis(diethylamido)tantalum t ki (di th l id )t t l Ta(NtBu)(NEt2)3 = (tert-butylimido)tris(diethylamido)tantalum Ti(NMe2)4 = tetrakis(dimethylamido)titanium Ti(NEtMe)4 = tetra(ethylmethylamido)titanium = TEMAT W(NtBu)2(NMe2)2 = bis(tert-butylimido)bis(dimethylamido)tungsten Zn[N(SiMe3)2]2 = bis(bis(trimethylsilyl)amido)zinc Zr(NMe2)4 = tetrakis(dimethylamido)zirconium Zr(NEtMe)4 = tetra(ethylmethylamido)zirconium = TEMAZ Zr(NEt2)4 = tetrakis(diethylamido)zirconium = TDEAZ 37 Amide and Imide Precursors for ALD 18 13 B 5 V Nb Ta Db Pr Pa U Np Pu Am Cm Nd Pm Sm Eu Gd Tb Bk Sg Bh Hs Mt Ds Rg Dy Cf Ho Es Er Fm Tm Md Yb Lr Lu No W Re Os Ir Pt Au Hg Mo M Tc T Ru R Rh Pd Ag A Cd In I Tl Cr Mn Fe Co Ni Cu Zn Ga 6 7 8 9 10 11 12 Al Si Ge Sn S Pb C N P As Sb Bi 14 15 16 O S Se Te T Po 17 F Cl Br I At He Ne Ar Kr Xe X Rn 1 H 2 Li Be Na Mg 3 4 K Ca Sc Ti Rb Sr S Y Zr Z Cs Ba La Hf Fr Ra Ac Rf Ce Th Advantages: highly reactive suitable for oxides and nitrides it bl f id d it id Disadvantages: limited thermal stability silicon impurity from silylamides ili i it f il l id 38 Amidinate Compounds 4 equivalent ways to represent a metal amidinate: localized bonding picture 1 localized bonding picture 2 R2 R1 N M N R3 R1 N M N R2 R3 delocalized bonding picture 1 delocalized bonding picture 2 R2 R1 N M N R3 R2 R1 R3 N N M R1, R2 and R3 are non-metals, usually alkyl groups CxH2x+1; other non-metals, such as silicon or nitrogen may be included. 39 Some Amidinate Ligands N,N’-dimethyl- N,N’-diethylformamidinate formamidinate (Et2fmd) (Me2fmd) N,N’-diisopropylformamidinate (iPr2fmd) N,N’-di-sec-butylacetamidinate (sBu2amd) N,N’-dimethylacetamidinate (tBu2amd) Increasing steric bulk H2 C CH2 CH3 C CH3 CH3 CH3 C N H2 M N H 3C C H3 C C N H2 H3C CH2 C N M CH3 C CH3 CH3 H3C C N H2 H2 C H3C C H2 CH2 C N M CH3 C CH3 CH3 CH3 H 3C CH3 H3 C C C N H2 N C M CH3 N’-tert-butylN-ethylacetamidinate (tBuEt-amd) N’-tert-butylN-ethylpropionamidinate (tBuEt-pmd) N’-tert-butylN-ethylbutyramidinate y (tBuEt-bmd) N-ethyl-N’tert-butylp y pentylamidinate (tBuEt-pemd) 40 Increasing flexibility leads to decreasing melting points and liquids Amidinate Compounds Used in ALD Advantages: high reactivity to water => oxides high reactivity to ammonia => nitrides high reactivity to H2S => sulfides reactive to hydrogen gas H2 => metals Disadvantages: several different ligands needed g some are solids, not liquids Lu(Et2-fmd)3 Lu(Et2-amd)3 Mg(tBu2amd)2 Mg(iPr2-amd)2 Mn(tBu2-pemd)2 Ni(tBu2-amd)2 ( ) Pr(iPr2-amd)3 Sc(Et2-amd)3 Sr(tBu2-amd)2 Ti(iPr2-amd)3 V(Et2-amd)3 V(iPr2-amd)3 Y(iP 2-amd)3 Pr d) Zn(iPr2-amd)2 Zr(Me2-fmd)4 Zr(Me2-pmd)4 pmd) Zr(Me2-bmd)4 Ag2(tBu2-amd)2 Ca(tBu2-amd)2 Co(iPr2-amd)2 Co(tBuEt-amd)2 Cr(Et2-amd)3 Cu2(iPr2-amd)2 amd) Cu2(sBu2-amd)2 Er(tBu2-amd)3 Fe(iPr2-amd)2 Fe(tBuEt-amd)2 Ga(Et2-amd)3 Gd(iPr2-amd)3 Hf(Me f d) Hf(M 2-fmd)4 Hf(Me2-pmd)4 Hf(Me2-bmd)4 La(iPr2-fmd)3 fmd) La(tBu2fmd)3 41 Amidinate ALD Precursors 18 13 B 5 V Nb Ta Db Pr Pa U Np Pu Nd Pm Sm Eu Sg Bh Hs Mt Ds Gd Am Cm W Re Os Ir Pt Mo Tc Ru Rh Pd Ag Au Rg Tb Bk Dy Cf Ho Es Er Fm Tm Md Yb Lr Lu No Cr Mn Fe Co Ni Cu Zn Cd Hg 6 7 8 9 10 11 12 Al Ga In Tl 14 C Si Ge Sn Pb 15 N P As Sb Bi 16 O S Se Te Po 17 F Cl Br I At He Ne Ar Kr Xe Rn 1 H 2 Li Be Na Mg 3 4 K Ca Sc Ti Rb Sr Y Zr Cs Ba La Hf Fr Ra Ac Rf Ce Th 42 Structures of Metal(II) Acetamidinates m m m d Ni Co Cr Fe Mg Mn Ca Sr Ba d d d p m m d d d d p m m m m m d d d p p tert-butyl2 isopropyl2 tBu-Et Inc creasing ligand bulk b n-propyl2 Increasing size of metal atom d = volatile dimer p = non-volatile polymer p y m = volatile monomer 43 Structures of Metal(III) Acetamidinates n m m m m r m r Al Cr Ga V Ti Ru Sc Lu Er Y tert-butyl2 m m m m r r m m r m m r d d d isopropyl2 m i l Et-tBu m d Gd n propyl n-propyl2 r d d d Et2 Inc creasing ligand bulk b Eu Nd Pr Ce La Bi Increasing size of metal atom d =volatile dimer d =low-volatility =lo olatilit dimer 44 n = nonexistent? m = more crowded, r = more reactive monomer, less reactive reacts with monomer, water, H2O & t O, reacts with t ith ammonia, NH3 ozone, O3 TYPES OF ALD REACTIONS ALD reactions usually transfer one atom from a surface-bound group to a vapor group, or from a vapor group to a surface-bound group (the reverse direction). The transferred atoms are usually hydrogen, oxygen, fluorine or chlorine. A few reactions transfer a whole group of atoms, not just a single atom. atoms atom 45 Examples of ALD Reactions water H-transfer reactions => metal oxides ozone O-transfer reactions => metal oxides silanol H-transfer reactions => metal silicates ammonia H transfer reactions => metal nitrides H-transfer H-reduction reactions => transition metals oxygen O-transfer reactions => noble metals (Pt, Ru, Ir) fluoride to silicon reactions => tungsten or molybdenum g y chloride to trialkylsilyl reactions => selenides or tellurides ethanolamine H-transfer reactions => incorporated organic groups 46 Oxides by Hydroxyl Exchange & Hydrolysis Hf(NMe2)4 + 2 H2O => HfO2 + 4 HNMe2 Tetrakis(dimethylamido)hafnium reacts with water to make hafnium dioxide T t ki (di th l id )h f i t ith t t k h f i di id Chemisorption by hydrogen transfer to ligands to form dimethylamine gas: Me2N Hf O NMe2 O + 2 HNMe2 + Me2N Hf NMe2 Me2N NMe2 H H O O Transfer of hydrogen from water to surface-bound dimethylamide ligands: H O + 2 HOH Hf O O H O + 2 HNMe2 Me2N NMe2 Hf O O 47 Oxides by Oxidation with Ozone Trimethylaluminum reacts with ozone to make aluminum oxide: (CH3)3Al + O3 => Al2O3 + CH4 + H2O + CO2 Hydrogen atom transfer from surface hydroxyl to ligand to form methane: CH3 H Al + Al(CH3)3 O O + 2 HCH3 O H O Oxygen atom transfer to surface ligand t f O t t f t f li d to form water and carbon di id t d b dioxide: CH3 O + O3 O OH Al O + H2O + CO2 Al O Water may not be detected because it reacts with other surface CH3 groups 48 Metal Silicates from Silanol Me2N Hf O NMe2 O + 2 HNMe2 + Me2N Hf NMe2 Me2N NMe2 Hydrogen atom transfer from surface hydroxyls to dimethylamide ligands: H H O O Hydrogen atom transfer from silanol to surface-bound dimethylamides: y g y ButO Si ButO + HO OH Si O OtBu O Hf O O + 2 HNMe2 OtBu Me2N NMe2 Hf O O Regeneration of surface hydroxyls by hydrogen from tertiary butyl groups: OC(CH3)3 Si O Hf O O O O O Hf O HO Si O + 2 H2C C CH3 CH3 OH (H3C)3CO 49 Al-doped SiO2 from AlMe3 and (tBuO)3SiOH => very large growth per cycle up to 15 nm > 50 monolayers cycle, nm, Hydrogen atom transfer from surface hydroxyl to methyl ligands: CH3 + O O (CH3)3Al Al + 2 HCH3 H H O O Hydrogen atom transfer from silanols to methyl ligands: OtBu ButO + CH3 Al Si O Al OtBu + HCH3 (tBuO)3SiOH 50 Al-doped SiO2 from AlMe3 and (tBuO)3SiOH Repeated insertions of (tB O)3SiOH i t an Al O bond R t di ti f BuO) into Al-O b d produces a siloxane polymer tethered to the surface: Si(OBut)3 ( O OBut OBut O - ButOH Al H ButO Si OBut n (ButO)3SiOH - n ButOH ButO Si(OBut)3 ( O Si O Al OBut n+1 (ButO)3Si ButO O Si Al O 51 Al-doped SiO2 from AlMe3 and (tBuO)3SiOH Elimination of isobutene by E hydrogen transfer: E-hydrogen Si(OBut)3 O ButO Si O Al H CH2 O C(CH3)2 ButO O Si O Al OH + H2C=C(CH 3)2 Si(OBut)3 Si(OBut)3 O Bu tO Si OBut O Al 52 Al-doped SiO2 from AlMe3 and (tBuO)3SiOH Siloxane polymer chains cross link by elimination of tert butanol: cross-link tert-butanol: Si(OBut)3 O Si O Al - BuOH OBut ButO Si O Al O O Si(OBut)3 Si(OBut)3 O Si O Al OBut Si(OBut)3 Bu t H O O O Bu O t Si O Al Complete crosslinking produces a solid silica layer that is impervious to diffusion of more silanol up to the aluminum catalyst, so reaction stops. p y , p 53 Al-doped SiO2 from AlMe3 and (tBuO)3SiOH Elimination of water also cross-links polymer chains: cross links Si(OBut)3 O Si O Al - H 2O O Al OBut Si ButO O O Si(OBut)3 Si(OBu t)3 O Si O Al OBu t ButO Si(OBu t)3 H O O H Si O O Al Complete crosslinking produces a solid silica l C l t li ki d lid ili layer that is impervious to th t i i i t diffusion of more silanol up to the aluminum catalyst, so reaction stops. 54 Nitrides by Chloride Exchange and Reduction TiCl4 + NH3 => TiN Cl Cl Ti N Cl N + 2 HCl + Cl Ti Cl Cl Titanium(IV) tetrachloride plus ammonia makes titanium(III) nitride: Hydrogen atom transfer from surface amides to chlorides on precursor: H N H N Hydrogen atom transfer from ammonia to surface-bound chloride ligands: Cl Ti N + 2 HNH2 H2 N Ti N N NH2 + 2 HCl Cl N Titanium in oxidation state +4 is reduced to +3 by elimination reactions: NH2 Ti N N NH2 Ti N + ? N2, H2, and/or N2H4 ? 55 H 2N N Tungsten Nitride by Exchange and Catalysis t Hydrogen transfer from surface imides to dimethylamides on precursor: BuN W Me2N NMe2 W N N + 2 Me2NH NH NH t NtBu BuN NtBu Hydrogen transfer to imides from ammonia or from tert-butyl imido group? H NC(CH3)3 W N + NH3 N N W N + 2 Me3CNH2 or Me2C=CH2 N H (H3C)3CN N Reductive elimination of nitrogen to reduce W(VI) to W(III) WN2 => WN + ½ N2 56 Metals by Reduction with H Atoms TiCl4 + 4 H => Ti + 4 HCl Titanium from titanium tetrachloride and hydrogen atoms in a plasma Hydrogen atoms on surface transfer to chlorides on precursor: Cl + TiCl4 Ti Cl + 2 HCl H H Hydrogen atoms from plasma remove chlorine as hydrogen chloride gas: Cl + 4 H H Ti H + 2 HCl Cl Ti 57 Metals by Reduction with H2 Molecules Dissociative chemisorption of copper amidinate on a copper surface: Hydrogen transfer to amidinate ligands to make copper & amidine vapor: R R' N RN R' N RN Cu Cu NR Cu + H2 Cu Cu Cu NR H Cu Cu Cu + Cu RN R' N NR H R' N RN NR Cu Cu Cu Cu Cu Cu Cu Cu 58 Noble Metals by Oxidation Reactions O M + On M M M M M O O O O M Oxygen atoms chemisorb on noble metals (platinum, ruthenium, etc.): M M M Adsorbed oxygen atoms burn ligands to form carbon dioxide and water: O + MLn M M M M M M M M M M M + CO2 + H2O O O O O M M M M 59 Tungsten Metal by Fluoride Exchange Overall reaction: WF6 + Si2H6 => W + 2 SiF3H + 2 H2 a F atom moves from WF6 vapor to liberate Si from surface: surface-WSiF2H + WFF5 => surface-WWF5 + SiFF2H 3 F atoms move from W on surface to break up Si2H6 vapor: surface-WWF2F3 + Si2H6 => surface-WWSiF2H + SiF3H + 2 H2 A very complex reaction, breaking 1 Si-Si, 5 W F and 4 Si H bonds Si Si, W-F Si-H while forming a new W-Si bond, 5 new Si-F bonds and 2 new H-H bonds 60 Tellurides by Chloride Exchange Reactions R3 R3 Si Si R3 Si Cl + (R3Si)2T Te Te Te Te Te Te Ge Ge Ge Ge Ge + R3SiCl R3 Si R3 Si Chlorine atoms on surface move to trialkylsilyl groups on tellurium: Cl Cl Cl Cl Ge Ge Ge Ge Ge G G G G G Chlorine atoms on germanium remove surface trialkylsilyl groups: Cl R3 Si + GeCl2 Te Te Te Te Te Ge Ge Ge Ge Ge Cl Cl Cl Cl Ge Ge Ge Ge Ge G G G G G + R3SiCl R3 R3 Si Si R3 Si R3 Si Te Te Te Te Te Ge Ge Ge Ge Ge 61 Adding Organic Components to ALD Films A) trimethylaluminum ) y B) ethanolamine C) maleic anhydride Adds flexibility to brittle inorganic films from S. M. George, Chem. Rev. 110, 111 (2010) 62 Problems When the Chemistry is Wrong Thermal decomposition destroys the self-limiting property of surface reactions thickness uniformity step coverage and film purity degraded uniformity, Incomplete surface reactions can incorporate ligands as impurities slow kinetics can be alleviated by longer exposure times, or l ki ti b ll i t d b l ti too low thermodynamic driving force => change precursors Incomplete step coverage need longer exposure time or higher precursor vapor pressure but may be limited by decomposition or desorption of precursor Etching by precursor or reaction byproducts mostly from halide precursors (chlorides, bromides) 63 Summary ALD precursors are available for most non-radioactive elements non radioactive Suitable reactant pairs are known for ALD of p some pure elements oxides of most elements nitrides of many elements sulfides, selenides and tellurides of some elements phosphides and arsenides of a few elements fluorides of a few elements ALD reactions usually involve e c a ge eact o s between surface groups and apo groups exchange reactions bet ee su ace g oups a d vapor g oups exchanged atoms are usually hydrogen, oxygen or halogen 64 Summary Recent Reviews of ALD Chemistry R. Puurunen, J. Appl. Phys. 97, 121301 (2005) J. Paivasaari et al., Topics in Appl. Phys. 106, 15 (2007) M. M Ritala and J. Niinisto in Chemical Vapor Deposition (Royal J Niinisto, Society of Chemistry, 2009) S. M. George, Chem. Rev. 110, 111 (2010) S. D. Elliott, Langmuir 26, 9179 (2010) 65 Acknowledgements Students and Post-docs who worked on ALD in Gordon’s Lab Yiqun Liu Yi Li Hisashi Nakagawa Jun Ni Dawen Pang Jin-Seong Park Antti Rahtu P. Venkateswara Rao Leo Rodriguez Philippe de Rouffignac Prasert Sinsermsuksakul Amethyst Smith Seigi Suh Hongtao Wang Shenglong Wang Xinwei Wang Sheng Xu Andrew P Yo sef Andre P. Yousef Supported by the US National Science Foundation, Dow, IBM and Intel 66 Titta Aaltonen Titt A lt Sean Barry Jill Becker Mike Coulter Damon Farmer Dennis Hausmann Adam Hock Jaeyeong Heo Daewon Hong Esther Kim Kyoung-ha Kim Jean Sebastien Lehn Booyong S. Lim Don Keun Lee Huazhi Li Zhengwen Li Xinye Liu