Basic steps in the VD process Precursor Transport metal atom ligand Gas Phase eactions + Adsorption Adsorption Decomposition reactions + Desorption Difusion Nucleation eated substrate VD 1
uminum 2.27 µωcm, easily etched, dissolves in Si, GaAs + As + Ga Gas diffusion barriers, on polypropylene, food packaging = chip bags, party balloons, high optical reflectivity TIBA β-ydride Elimination 3 3 3 below 330 o 3 3 3 2 β-methyl Elimination 3 3 3 above 330 o 3 3 2 VD 2
deposits selectively on surfaces, not on Si 2 Laser-induced nucleation 248 nm only surface adsorbates pyrolysed 193 nm gas phase reactions, loss of spatial selectivity control TMA large carbon incorporation, 4 3, F plasma, laser 2 ( 3 ) 6 1/2 4 3 + 9/2 4 under N 2 2 ( 3 ) 6 + 3 2 2 + 6 4 under 2 VD 3
TMAA 3 N 3 3 3 N 3 3 3 N 3 3 3 3 N 3 3 3 N 3 ( 3 ) 3 N- 3 + ( 3 ) 3 N + 3/2 2 below 100 VD 4
Decomposition mechanism of TMAA on ( 3 ) 3 N- 3 + ( 3 ) 3 N + 3/2 2 below 100 VD 5
uminoboranes 3 N 3 3 ( 3 ) 3 N-B 3 + 3/2 2 + B B B B DMA ligand redistribution [( 3 ) 2 ] 3 ( 3 ) 3 + 3 + 2 at 280, low carbon incorporation VD 6
Tungsten 5.6 µωcm, a high resistance to electromigration, the highest mp of all metals 3410. 2 WF 6 + 3 Si 2 W + 3 SiF 4 WF 6 + 3 2 W + 6 F WF 6 + 3/2 Si 4 W + 3 2 + 3/2 SiF 4 W() 6 W + 6 VD 7
3 3 3 3 Diketonate ligands KET ENL 3 3 - + 3 3 VD 8
opper(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 (u, Ag, Ta) the first step, which can already occur at -150, a dissociation of the precursor molecules on the surface (Scheme I). An electron transfer from a metal substrate to the single occupied M which has an anti-bonding character with respect to copper d xy and oxygen p orbitals weakens the u- bonds and facilitates their fission. VD 9
Scheme I F 3 F 3 u F 3 F 3 F 3 F 3 F 3 e F 3-150 o u + 2 (g) 2 (ads) >100 o F 3 F 3 >250 o + F 3 u o F 3 VD 10
SEM of u film, coarse grain, high resistivity VD 11
Growth rate of u films deposited from u(hfacac) 2 with 10 torr of 2 VD 12
u(i) precursors Disproportionation to u(0) and u(ii) 2 u(diketonate)l n u + u(diketonate) 2 + n L u u L L L L: PMe 3, PEt 3,, N t Bu, SiMe 3 VD 13
Diamond films activating gas-phase carbon-containing precursor molecules: thermal (e.g. hot filament) plasma (D..,.F., or microwave) combustion flame (oxyacetylene or plasma torches) VD 14
Experimental conditions: temperature 1000-1400 K the precursor gas diluted in an excess of hydrogen (typical 4 mixing ratio ~1-2vol%) Deposited films are polycrystalline Film quality: the ratio of sp 3 (diamond) to sp 2 -bonded (graphite) carbon the composition (e.g. - versus - bond content) the crystallinity ombustion methods: high rates (100-1000 µm/hr), small, localised areas, poor quality films. ot filament and plasma methods: slower growth rates (0.1-10 µm/hr), high quality films. VD 15
ydrogen atoms generated by activation (thermally or via electron bombardment) -atoms play a number of crucial roles in the VD process: abstraction reactions with hydrocarbons, highly reactive radicals: 3 (stable hydrocarbon molecules do not react to cause diamond growth) radicals diffuse to the substrate surface and form - bonds to propagate the diamond lattice. -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 VD 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. VD 16
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 VD 17
Substrates: metals, alloys, and pure elements: Little or no Solubility or eaction: u, Sn, Pb, Ag, and Au, Ge, sapphire, diamond, graphite Diffusion: Pt, Pd, h, Fe, Ni, and Ti the substrate acts as a carbon sink, deposited carbon dissolves into the metal surface, large amounts of transported into the bulk, a temporary decrease in the surface concentration, delaying the onset of nucleation arbide Formation: Ti, Zr, f, V, Nb, Ta, r, Mo, W, Fe, o, Ni, Y, B, Si, Si 2, quartz, Si 3 N 4 also form carbide layers. Si, W, and Ti VD 18
Applications of diamond films: Thermal management - a heat sink for laser diodes, microwave integrated circuits active devices mounted on diamond can be packed more tightly without overheating utting tools - an abrasive, a coating on cutting tool inserts VD diamond-coated tools have a longer life, cut faster and provide a better finish than conventional W tool bits Wear esistant oatings -protect mechanical parts, reduce lubrication gearboxes, engines, and transmissions VD 19
ptics - protective coatings for infrared optics in harsh environments, ZnS, ZnSe, Ge: excellent I transmission but brittle the flatness of the surface, roughness causes attenuation and scattering of the I signal Electronic devices - doping, an insulator into a semiconductor p-doping: B 2 6 incorporates B into the lattice doping with atoms larger than very difficult, n-dopants such as P or As, cannot be used for diamond, alternative dopants, such as Li VD 20
VD 21
Laser-enhaced VD ArF laser Substrate eater eated source Vacuum Pump Vacuum chamber Si( 2 3 ) 4 Si 2 + 2 ( 3 ) 2 VD 22