CVD 1
Basic steps in the CVD process
R ligand
metal atom
Precursor
Transport
Gas Phase Reactions
R
RR
Adsorption
R
R
R
+
Adsorption
Desorption
R
R
R
Decomposition
reactions Difusion
Nucleation
R
R
R
R +
Heated substrate
CVD 2
Chemical Vapor Deposition
Aluminum
2.27 cm, 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
Al
CH3
H
CH3
H
H
below 330 oC
-Hydride Elimination
CH3
CH3
H
H
Al
H
Al
CH3
CH3
H
H
H2
Al
CH3
H
CH3
H
H
above 330 oC
-Methyl Elimination
CH3
HH
H
Al
CH3
Al
CH3
HH
H
H2
C
CVD 3
Al deposits selectively on Al surfaces, not on SiO2
Laser-induced nucleation
248 nm only surface adsorbates pyrolysed
193 nm gas phase reactions, loss of spatial selectivity control
TMA
large carbon incorporation, Al4C3, RF plasma, laser
Al2(CH3)6 1/2 Al4C3 + 9/2 CH4 under N2
Al2(CH3)6 + 3 H2 2 Al + 6 CH4 under H2
Chemical Vapor Deposition
CVD 4
Chemical Vapor Deposition
TMAA
Al
H
H
Al
H
H
N
N
H
H
CH3
H3C
CH3
H3C
CH3
H3C
Al
H
H
N
H
CH3
CH3
H3C
Al H
H
N
H
CH3
CH3
H3C
CH3
H3C
H3C
N
(CH3)3N-AlH3 Al + (CH3)3N + 3/2 H2 below 100 °C
CVD 5
Chemical Vapor Deposition
(CH3)3N-AlH3 Al + (CH3)3N + 3/2 H2 below 100 °C
Decomposition mechanism of TMAA on Al
CVD 6
Chemical Vapor Deposition
Aluminoboranes
Al
H
H
B
H
H
N
H
H
CH3
CH3
H3C
(CH3)3N-BH3 + 3/2 H2 + Al
Al
H
H
B
H
H
H
H
H
H
B
B
H
H
H
H
DMAH
ligand redistribution
[(CH3)2AlH]3 (CH3)3Al  + AlH3 Al + H2
at 280 °C, low carbon incorporation
CVD 7
Chemical Vapor Deposition
Tungsten
5.6 cm, a high resistance to electromigration, the highest mp of
all metals 3410 °C.
2 WF6 + 3 Si  2 W + 3 SiF4
WF6 + 3 H2  W + 6 HF
WF6 + 3/2 SiH4  W + 3 H2 + 3/2 SiF4
W(CO)6  W + 6 CO
CVD 8
Chemical Vapor Deposition
Diketonate ligands O O
H3
C CH3
HH
KETO
ENOL
O O
H3
C CH3
H
H
O O
H3
C CH3
H
O O
H3
C CH3
- H+
CVD 9
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 10
Chemical Vapor Deposition
Scheme I
-150 o C
CF3
CF3F3 C
F3 C
O
O
O
Cu
O
e
O
Cu
O
F3 C CF3
+
F3 C CF3
O O
F3 C CF3
OOH
C
CO + CF 3
2 H (ads)H 2 (g)
Cu o
>250 o C
CF3C
C
O
>100 o C
CVD 11
Chemical Vapor Deposition
SEM of Cu film, coarse
grain, high resistivity
CVD 12
Chemical Vapor Deposition
Growth rate of Cu films deposited from Cu(hfacac)2 with 10 torr of H2
CVD 13
Chemical Vapor Deposition
Cu(I) precursors
Disproportionation to Cu(0) and Cu(II)
2 Cu(diketonate)Ln  Cu + Cu(diketonate)2 + n L
O
Cu
O
R R
L
O
Cu
O
R R
LL
L: PMe3, PEt3, CO, CNt
Bu,
SiMe3
CVD 14
Chemical Vapor Deposition
Diamond films
activating gas-phase carbon-containing precursor molecules:
ťhermal (e.g. hot filament)
ˇplasma (D.C., R.F., or microwave)
čombustion flame (oxyacetylene or plasma torches)
CVD 15
Chemical Vapor Deposition
Experimental conditions:
temperature 1000-1400 K
the precursor gas diluted in an excess of hydrogen (typical CH4 mixing ratio ~1-2vol%)
Deposited films are polycrystalline
Film quality:
ťhe ratio of sp3 (diamond) to sp2-bonded (graphite) carbon
ťhe composition (e.g. C-C versus C-H bond content)
ťhe crystallinity
Combustion methods: high rates (100-1000 m/hr), small, localised areas, poor quality films.
Hot filament and plasma methods: slower growth rates (0.1-10 m/hr), high quality films.
CVD 16
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 17
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 18
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, SiO2, quartz, Si3N4 also form carbide layers.
SiC, WC, and TiC
CVD 19
Chemical Vapor Deposition
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
Cutting 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
Wear Resistant Coatings -protect mechanical parts, reduce lubrication
gearboxes, engines, and transmissions
CVD 20
Chemical Vapor Deposition
Electronic devices - doping, an insulator into a semiconductor
p-doping: B2H6 incorporates B into the lattice
doping with atoms larger than C very difficult, n-dopants such as P or As, cannot be used
for diamond, alternative dopants, such as Li
Optics - 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
CVD 21
CVD 22
Laser-enhaced CVD
Si(O2CCH3)4  SiO2 + 2 O(OCCH3)2
ArF laser
Substrate
Heated source
Heater
Vacuum chamber
Vacuum
Pump