Precursor Transport metal atom ligand Byproduct Transport Gas Phase Reactions V + V Adsorption Adsorption Decomposition ar reactions >, -----► «►#-*R VR ^ Desorption Difusion Nucleation Heated substrate CVD CVD Reactor solution injector I precursor solution vapouriaer substrate To pressure control, fitters, pumps and exhaust heated inlet / silica reactor 111 IR heating CVD TO Q. t/J S! Q. O □- 1000 h 100 h 10 1 h Precursor ^ Temperature (*C) 150 —i— 100 —I— 50 —I— Al(0i-Pr)3 Al(0sec-Bu)s AI(OEt)^ 2.2 2.4 2.6 2.8 3,0 3.2 1000/T (K'1) CVD • i • 4 An J n.* *__*! ft *■ * u 1CU1 8ÍH ^^^ U) 'fit 5 40- —*—*- Fe(thd)3 ----------- Ni(ttid)2 Vi 20- —o_0. Zn(thd)2 H o- 100 200 300 Temp [°C] Chemical Vapor Deposition Aluminum 2.27 jaQcm, easily etched, Al dissolves in Si, GaAs + Al —► AlAs + Ga Gas diffusion barriers, Al on polypropylene, food packaging bags, party balloons, high optical reflectivity = chip TIBA ß-Hydride Elimination H CH H 3 H CH. below 330 <>C Al H H H >= < CH3 CH, Al / H2 ß-Methyl Elimination CH3 I CH3 above 330 «C Al CH. H H >= _/CH3 -\ H Al 4 H2 CVD Chemical Vapor Deposition Al deposits selectively on Al surfaces, not on Si02 Laser-induced nucleation 248 nm only surface adsorbates pyrolysed 193 nm gas phase reactions, loss of spatial selectivity control TMA large carbon incorporation, A14C3, RF plasma, laser A12(CH3)6 —► 1/2 AI4C3 + 9/2 CH4 under N2 A12(CH3)6 + 3 H2 —► 2 Al + 6 CH4 under H2 CVD Chemical Vapor Deposition TMAA 3C\ ^N^ CH3 ^CH3 H H^ ^ ,U ^H H~ H3C H3C' ~A1 "Nx H "H 'CH3 H3CV H *N~ Al H CH3 ^CH3 H H3C. H H' H3C CH3 *N- -CH3 Al-------H "N. "CH3 (CH3)3N-A1H3 —►Al + (CH3)3N + 3/2 H2 below 100 °C CVD Chemical Vapor Deposition Decomposition mechanism of TMAA on Al CH3 CH3 XN^CH3 H3C\^CH3 ~«A1 ids H3C\^CH3 H2 ,.CH3 / fast fast (CH3)3N-A1H3 —►Al + (CH3)3N + 3/2 H2 below 100 °C CVD Chemical Vapor Deposition Ahiminoboranes H3CN H CH3 ^CH3 __:ai___ H~ H H (CH3)3N-BH3 + 3/2 H2 + H B ■H H / H H | \ H I H H *H H "B H H DMAH ligand redistribution [(CH3)2A1H]3-----►(CH3)3Alfľ + AIH3-----►Al + H2 at 280 °C, low carbon incorporation CVD Chemical Vapor Deposition Tungsten 5.6 fiQcm, a high resistance to electromigration, the highest mp of all metals 3410 °C. 2 WF6 +3Si-»2W + 3 SiF4 WF6 + 3H2 ^ W + 6 HF WF6 + 3/2SiH4 -> W + 3H2 + 3/2 SiF4 W(CO)6 -> W + 6 CO CVD Diketonate Ligands H3C. H H CH O O KETO H3C CH, O /O H" ENOL H3C CK ■H+ H3C O e CH Name Abbreviation CH, CM, Pentane-2.4-dioriate actic CHj CF3 1,1,1 -tritluo rope ntane-2,4-dionate (trifluoroacetylacetonate) ttac &s CF3 1,1,1,5,5,5-hexatiuorepe ntane-2,4-dionate (hexaf I uoroacety I aceton ate) hfac CH3 C(CH3)j 1, Ví)irnůíhylhexane-3,5-dionate' dhd C(CH3>3 C(CH3)a S^.e.&Hetraniůthylhepiarie^S-dionate thd CHa O H ňO r~H L* H ^) 2 6-melhy lheplane-2,4-cf lo nate mhd C(CH3J3 'w- H "; [_■ H 1. C M-i 1 -i 2,2,7-trimetŕiylDCtan e-3?5Hľl ionate tmod CfiH5 ^&^5 1,3-di phenyl propane-1,3-dionatß dbm (dibenyzoylmethanate) Diketonate Precursors Mononuclear Polynuclear CVD Chemical Vapor Deposition Copper(II) hexafluoroacerylacetonate excellent volatility (a vapor pressure of 0.06 Torr at r. t.), low decomposition temperature, stability in air, low toxicity, commercial availability deposition on metal surfaces (Cu, Ag, Ta) the first step, which can already occur at -150 °C, a dissociation of the precursor molecules on the surface (Scheme I). An electron transfer from a metal substrate to the single occupied HOMO which has an anti-bonding character with respect to copper dxy and oxygen p orbitals weakens the Cu-O bonds and facilitates their fission. CVD Chemical Vapor Deposition Scheme I F3C CF, F3C -150 °C CF F,C .e CF, 3 F,C O^ ^O +0 o Cu CF, ///////////////////////////////////////// >100 uc H 2 (g) —► 2 H (ads) F,C nr OH O Cu° /////////////////////////////////////////// >250 oc CO + CF 3 C ň CVD Chemical Vapor Deposition SEM of Cu film, coarse grain, high resistivity ."..-■■'Y^ -TV r v^|m ■*"* ■MĚmr^ ■■■■■■ $r&F%m%-x.y" i"* ÄH»M I CVD Chemical Vapor Deposition Growth rate of Cu films deposited from Cu(hfacac)2 with 10 torr of H2 1000 O Pí o 100 370°C 350°C 330°C 310°C ^^^^^^^ 1 I t * i \ '[ ^^~^^T^~^^^ |**4" i.Xi-wL» iX.a.^iwwJ I 1 I ] [ j 1 j i 1 T^ M i i 1 1 1 mimi n 1.50 1.52 1.54 1.56 1.58 1.60 1.62 1.64 1.66 1.68 1.70 1.72 1.74 1/rCK) x looo CVD Chemical Vapor Deposition Cu(I) precursors Disproportionation to Cu(0) and Cu(II) 2 Cu(diketonate)Ln —» Cu + Cu(diketonate)2 + n L CVD Chemical Vapor Deposition Diamond films activating gas-phase carbon-containing precursor molecules: •thermal (e.g. hot filament) •plasma (D.C., R.F., or microwave) •combustion flame (oxyacetylene or plasma torches) CVD Chemical Vapor Deposition Experimental conditions: temperature 1000-1400 K the precursor gas diluted in an excess of hydrogen (typical CH4 mixing ratio ~l-2vol%) Deposited films are polycrystalline Film quality: •the ratio of sp3 (diamond) to sp2-bonded (graphite) carbon •the composition {e.g. C-C versus C-H bond content) •the crystallinity Combustion methods: high rates (100-1000 um/hr), small, localised areas, poor quality films. Hot filament and plasma methods: slower growth rates (0.1-10 um/hr), high quality films. CVD Chemical Vapor Deposition Hydrogen atoms generated by activation (thermally or via electron bombardment) H-atoms play a number of crucial roles in the CVD process: H abstraction reactions with hydrocarbons, highly reactive radicals: CH3 (stable hydrocarbon molecules do not react to cause diamond growth) radicals diffuse to the substrate surface and form C-C bonds to propagate the diamond lattice. H-atoms terminate the 'dangling' carbon bonds on the growing diamond surface, prevent cross-linking and reconstructing to a graphite-like surface. Atomic hydrogen etches both diamond and graphite but, under typical CVD conditions, the rate of diamond growth exceeds its etch rate whilst for graphite the converse is true. This is the basis for the preferential deposition of diamond rather than graphite. CVD Chemical Vapor Deposition Diamond initially nucleates as individual microcrystals, which then grow larger until they coalesce into a continuous film Enhanced nucleation by ion bombardment: damage the surface - more nucleation sites implant ions into the lattice form a carbide interlayer - glue, promotes diamond growth, aids adhesion CVD Chemical Vapor Deposition Substrates: metals, alloys, and pure elements: Little or no C Solubility or Reaction: Cu, Sn, Pb, Ag, and Au, Ge, sapphire, diamond, graphite C Diffusion: Pt, Pd, Rh, Fe, Ni, and Ti the substrate acts as a carbon sink, deposited carbon dissolves into the metal surface, large amounts of C transported into the bulk, a temporary decrease in the surface C concentration, delaying the onset of nucleation Carbide Formation: Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Co, Ni, Y, Al B, Si, Si02, quartz, Si3N4 also form carbide layers. SiC, WC, and TiC CVD Chemical Vapor Deposition Applications of diamond films: t - a heat sink for laser diodes, microwave integrated circuits active devices mounted on diamond can be packed more tightly without overheating tools - an abrasive, a coating on cutting tool inserts CVD diamond-coated tools have a longer life, cut faster and provide a better finish than conventional WC tool bits gs -protect mechanical parts, reduce lubrication gearboxes, engines, and transmissions CVD Chemical Vapor Deposition ics - protective coatings for infrared optics in harsh environments, ZnS, ZnSe, Ge: excellent IR transmission but brittle the flatness of the surface, roughness causes attenuation and scattering of the IR signal Electronic devices - doping, an insulator into a semiconductor /7-doping: B2H6 incorporates B into the lattice doping with atoms larger than C very difficult, /i-dopants such as P or As, cannot be used for diamond, alternative dopants, such as Li CVD Laser-Enhaced CVD ArF laser Substrate » wTvywPi Heater Heated source Vacuum chamber Si(02CCH3)4 -> Si02 + 2 0(OCCH3)2 CVD LPCVD of ZnO from Amínoalcoholates Mu,.N weigh \% 100 "\ 30 \ 60 \ 40 \ 20 \_________ 100 200 300 400 500 Temperature (CC) (002) (100) Loď í ' "" SEM of the film deposited by LPCVD at 500 °C. Bar = 1 um. 2 Theta (deg.) Hexagonal ZnO PDF 79-0208 CVD LPC VD of ZnO from Amínoalcoholates [MeZn(tdmap)]2 CVD CVD of YF3 from hfacac Complex Quartz surface t*Vc* C ■i o IľBOcm1 CFa o=c H CH o-c \ 1690cm'1 YF. Q Lartz surface v ol ati I e by-p ro du cts 0 OH J OH Bifo—SkOL N___-Si— OBu1 __- Buta—Si------O-------Si—OBu1 A Al Al Al CVD 41 ALD of Si02 and A1203 Films Repeat Step A A CH3 H H J| JLL J— CVD 42 TMA Reaction (aí\ Cross-Linking / Termination %# ^ ^..........., ^ @J- s i—(2)—si-H^@ír s i-@> °* Silanol Reaction ÍŘoVsi-foŘl nčn-si-rMi Insertion / Propagation 9 * ^-Si-@ @-Si-@} CVD