Precursor Transport metal atom R [►- ligand Byproduct Transport ,/>l Gas Phase Reactions Adsorption A Adsorption !*[►! '^7 Decomposition r reactions ----------► R^ Desorption Nucleation Difusion Heated substrate CVD 1 Chemical Vapor Deposition Aluminum 2.27 |uQcm, easily etched, Al dissolves in Si, GaAs + Al —► AlAs + Ga Gas diffusion barriers, Al on polypropylene, food packaging = chip bags, party balloons, high optical reflectivity TIBA ß-Hydride Elimination CH. j CH3 Al below 330 «C H Al CH3 'CH, H H^ H > /CH3 CH3 Al / H2 ß-Methyl Elimination CH. I CH> above 330 «C CH, /CH3 -X H Al / H2 CVD 2 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 3 Chemical Vapor Deposition TMAA H3C H3C' -N. "CH3 CH3 ^CH3 H3C^ CH3 ^CH3 CH3 H H3C^ ^CH3 H..... 1 ^Al- -----H H^ 1 1 H^^ 1 H Al H^ J'^ ^H H H .......N H3C^ ^ VCH3 H3C (CH3)3N-A1H3 —►Al + (CH3)3N + 3/2 H2 below 100 °C CVD 4 Chemical Vapor Deposition (CH3)3N-A1H3 —►Al + (CH3)3N + 3/2 H2 below 100 °C CVD 5 Chemical Vapor Deposition Ahiminoboranes H3C. H CH3 -CH3 ___:ai^ H^ H H (CH3)3N-BH3 + 3/2 H2 + H H B / B H | H I H ^H H H 'H H 'B H H DMAH ligand redistribution [(CH3)2A1H]3-----►(CH3)3Alft + AIH3-----►Al + H2 at 280 °C, low carbon incorporation CVD Chemical Vapor Deposition Tungsten 5.6 (iQcm, 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 7 Chemical Vapor Deposition Diketonate ligands H H H3CV 0 0 KETO /CH3 H3CN O 0 H „CH, Rl R2 Name Abbreviation CH3 CH3 Feniane-2.4-dJQriate (acetylacetonatej acac CH, CF3 1,1,1 -triHuoropentane-2,4-dionate (triťluo r&acety lacetonate) tbc <=F3 CFS 1,1,1,5,5,5-hexatiuorape ntane-2 ,4-dionate (hexaf I uoroacetyl aceton ate) hfac CHa C(CH3)3 1,1 -dimethylheKarie'3ř5-dtoriate dhd C(CH3}3 C(CH3>3 2,2,6,6-letrainethyl h eftin ne- 3:5-d ionate thd CHa CH^CHfCH^l^ 6-melhylheptane-2,4-dlcnate mhd C(CH3}3 CHrtCH (CH^Jj 212l7-trimethfyloctane-3?5-diůnate trnod CDHS GeH5 1,3-di phenyl propane-1,3-dionate (dibenyzoylmethariate} dbm CVD Chemical Vapor Deposition Copper(II) hexafluoroacetylacetonate 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 F,C CF, -O o ■ x A / \ \\ Cu X -o A o--' F,C -150 °C 3 F,C. F,C .0 CF, CF Ov O + O O Cu CF, ///////////////////////////////////////// r>100 °c F'cy^YCF3 OH O H 2 (g) —>■ 2 H (ads) O I Cu° C >250 Q C C CF, CO + CF 3 /////////////////////////////////////////// ň CVD 10 Chemical Vapor Deposition Kl' i SEM of Cu film, coarse grain, high resistivity ■ " ■■■ M^te^ y£%:. 'V" f**\ 9B ^jkflbk f^ ■**j%s ■"■..J '^^' Or, / ■ \ -■. ■:U, '■ í^,*^.:* **X. ^^"1««<""^^M n B I a r. *$- í If lW*?3Ä ' * |g|&«Kfgf T&r TB. EEľťnääi CVD Chemical Vapor Deposition Growth rate of Cu films deposited from Cu(hfacac)2 with 10 torr of H2 1000 š 100 370°C 350°C 330°C 310°C i i 1 T —I- j^T r^ f^ ^ S ^d N **J -J n i 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/TfK) X 1000 CVD 12 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 14 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 15 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 16 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 17 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 18 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 19 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 /j-doping: B2H6 incorporates B into the lattice doping with atoms larger than C very difficult, «-dopants such as P or As, cannot be used for diamond, alternative dopants, such as Li CVD 20 CVD 21 Laser-enhaced CVD ArF laser Substrate ^ iAAAA Heater Heated source Vacuum chamber Si(02CCH3)4 -> Si02 + 2 0(OCCH3)2 CVD 22