Transcript Microwave plasma CVD systems

Diamond films
prepared by Chemical Vapor Deposition
Victor Ralchenko
General Physics Institute of Russian Academy of Sciences,
Moscow, Russia
Tallinn University of Technology, Nov. 19-20, 2013
Outline
1. Chemical Vapor Deposition (CVD) of diamond films:
principles and methods
2. Growth processes for nano/micro/mono-crystalline films
in microwave plasma
3. Properties of diamond films
4. Diamond films processing
5. Applications
General Physics Institute of Russian Academy of Sciences (GPI)
Founded in 1983 by Prof. Alexander Prokhorov,
Winner of Nobel Prize in 1964 for discovery of the
principle of «laser».
The GPI is a multi-discipline research body oriented
at general and applied physics in different fields:
● laser physics and optics
● solid state physics
● crystal growth
● nanomaterials
● fiber optics
● plasma physics
● physics of magnetic phenomena
● laser medicine and ecology
The staff (total): ca. 1000 persons.
Scientific staff: ca. 500 persons.
GPI activity in CVD diamond technology:
● Laser processing of diamond films (pattering, polishing…)
● DC plasma CVD reactor built
● Nanocrystalline diamond in DC (Ar-CH4-H2) plasma
● Microwave plasma CVD reactor (from Astex)
● DC arc-jet system
● CO2 laser plasmatron
● Microwave plasma CVD system DF100
● Ultrananocrystalline diamond (UNCD) by MPCVD
● Epitaxial diamond films
Applications
● UV, X-ray, particle detectors
● Microwave transistors (MESFET)
● Raman shifters (Raman laser)
● Heat spreaders for transistors
● Electrochemistry on conductive (doped) UNCD films
● IR optical windows
● Field electron emitters
1988
1990
1995
1995
1996
1998
2001
2005
2007
Atomic structure of diamond
● atomic density 1.76х1023 сm-3 (record high)
● cubic lattice parameter а=3.56 А
● interatomic distance 1.54 А
Remarkable properties of diamond are result of
- light atom (Z=6)
- short and strong covalent bonding
(3D vs 2D for graphite).
Debye temperature ТD = 1860 K
→ Т=300 K is low temperature for diamond.
Displacement energy of atom from lattice ≈43 eV
→ radiation hardness.
Properties of diamond
Property
Band gap, eV
Carrier mobility, cm2/Vs
Resistivity, Ohm*cm
Thermal conductivity, W/mK
Dielectric constant
Loss tangent @170 GHz
Optical transmission range
Hardness, GPa
Acoustic wave velocity, km/s
Value
5.4
1600 h
2200 e
1013-1015
2000-2400
Application
High-temperature electronics
Radiation-hard detectors
Optoelectronic switches
Optical (electron) switches
Heat spreaders
5.7
0.3·10-6
225 nm – RF
81±18
Windows for gyrotrons, klystrons
Optics for lasers (mostly IR)
Tools, surgery blades
18.4 along <111>
Surface acoustic wave devices
Thermal expansion coefficient, 10-6 K-1
0.8 @293 K
Stable-dimension components
Corrosion resistance
Stable in HF
Electrochemistry (doped diamond)
Low or negative electron affinity
Field electron emitters
Biocompatibility
Coatings on implants
Natural and synthetic diamonds
Natural crystals
● Small size
● Defects and impurities
● High cost
HPHT synthetic
single crystals
● Small size, few mm.
● Catalyst impurity.
CVD polycrystalline films
and single crystals
● Very large lateral size.
● Can be highly pure.
● Reduced cost.
Why diamond ?
CVD Diamond for Electronics
Diamond samples grown by Chemical Vapor Deposition (CVD) with CH4 + H2
Polycrystalline diamond on 2-4 inch Silicon wafers (PCD)
Single Crystal Plates on HPHT (high pressure high temperature) substrate (SCD)
SCD
PCD
element six ltd
Diamond Materials
Ascot, Berkshire, UK
Fraunhofer Institute IAF in Freiburg, Germany
Delaware Diamond Knives, DDK Inc.
Ulm University, Germany
Wilgminton, USA
General Physics Institute RAS
Moscow (Russia)
Phase diagram of carbon. Diamond synthesis at high pressures.
● Diamond is unstable with respect to graphite at temperatures below 1300ºC and pressures
below 40 kbar.
● Synthesis of diamond at HPHT in mid of 1950s in General Electric Co.
P-T regions (hatched) of high-pressure phase
transformations achievable in practice
[Bundy F.P. Proc. ХI AIRAPT Int. Conf., Kiev,
1989. Vol. 1, p. 326]:
(1) graphite lonsdaleite martensitic
transformation under static compression
(2) graphite lonsdaleite diamond martensitic
transformations under shock compression
(3) commercial diamond synthesis in metal–
carbon systems
(4) direct high-temperature graphite diamond
transformation.
HPHT synthesis, 5-6 GPa
CVD, <1 atm
Synthetic single crystal diamonds
produced by HPHT technique
Production of “Adamas”, BSU, Minsk
● small size – typically less than 6 mm.
● difficult to avoid catalyst impurities.
Yellow color due to nitrogen atom
impurity in substitutional position.
Toroid- type HPHT apparatus,
maximum pressures up to 8 GPa
(Inst. High Pressure Physics, Troitsk)
Largest diamond crystal ~ 25 carats (5 g)
has been grown in “Belt” press
R.S. Burns et al. DRM. 8 (1999) 1433.
Chemical Vapor Deposition of Diamond
Parallel processes:
● Etching (sp2, sp3)
● Co-deposition (sp2, sp3)
Etch rate of diamond by atomic hydrogen is
higher than that of graphite.
►Dominating product - diamond
Methods of gas activation
● Hot filament
● DC arc jet*
● DC plasma*
● Laser plasma*
● Oxygen-acetylene flame
● Microwave plasma*
*realized at GPI
Any physical process creating atomic hydrogen and CHx radicals
potentially is able to produce diamond.
CVD systems for diamond growth
developed at GPI since 1990
DC plasma system
СО2 laser plasmatron
DC arc-jet system, 14 kW
ECR microwave plasma
Microwave plasma jet
Growth mechanism (Harris & Goodwin 1993)
Atomic H and CH3 radical are of most important species
Creation of active sites
The most of diamond surface is
covered by adsorbed hydrogen.
k1
Cd  H  H 
Cd *  H2
H desorption leave free C bond –
active site.
k2
Cd *  H 
Cd  H
Adsorption of CH3 radical and dehydrogenation
Cd  CH
*
k3

3 
k4
Cd  CH 3
k5
Cd  CH3  H 
Cd  CH 2*  H2
k6
Cd  CH 2*  H 
Cd  Cd  H  H 2
Growth rate
G(100 )
n
 k3 s
nd
The chain of reactions to add one
new C-C bond and continue
diamond building.
 k1  CH 3 s H s


 k1  k2  k4  H s
k5
Extended model includes 28 species, 130 reactions: G. Lombardi et al. J. Appl. Phys. (2005)
History
Early attempts to grow diamond on diamond seed at low pressures used CO
or CH4 only, without H2 ► very low growth rate ~0.01 nm/h
W.G. Eversole, Patent 1962; B.V. Deryaguin, Usp. Khimii, 1970
Only when importance of hydrogen has been recognized, high growth rates, ~ 1 µm/h
were obtained: B.V. Spitsyn et al. J. Cryst. Growth, 52 (1981) 219.
With pioneers in CVD diamond
Second Chinese-Russian Seminar on CVD diamond, GPI, Moscow, 2012
Hot filament CVD
● Introduced by group of S. Matsumoto (NIRIM)
[Jpn. J. Appl. Phys. 21(1982) L183].
Earlier work (1972) at Inst. Physical Chemistry,
Moscow (unpublished).
● Typical growth rate 1 μm/hour.
● Large deposition area can be achieved, ~1 m2
(array of filaments).
Drawbacks:
●Filament deformation and embritlment due to
carburization;
● diamond contamination with filament material,
~0.1%W [E. Gheerhaert, DRM 1 (1992) 504].
Diamond deposition from oxygen-acetylene flame
Introduced by Y. Matsui, Jpn. J. Appl. Phys., 29 (1990) 1552.
● Typical ratio O2:C2H2 = 0.9 – 1.1.
● Possibility to deposition in air environment
● High growth rate ~100 μm/h, but …
- inhomogeneity in deposition zone
- small area (<1 cm across).
Improvements
● flat flame at reduced pressure ~ 40 Torr
[A.Lowe, Combust. Flame, 188 (1999) 37].
► large deposition area ~ Ø4 cm
►
Problems
● Stability: flame tip–substrate distance must
be maintained strictly constant ~ 1 mm.
● High gas consumption ~ 5 l/min
● Diamond quality – moderate.
● flame scanning
35  30 cm2 area;
[M. Okada, Diamond Relat. Mater., 11 (2002), 1479].
● multiple flame systems
DC plasma CVD
● High CH4 concentrations (~10%)
acceptable due to hot (almost thermal
plasma).
● High growth rate >10 μm/h.
DC plasma system with interferometric control of
film thickness and growth rate (GPI, Moscow).
Cathode - glassy carbon or TaC rod.
[A. Smolin, Appl. Phys. Lett. 62, (1993) 3449].
Optical quality diamond can be grown.
Laser reflectivity at 633 nm wavelength.
One oscillation period corresponds to film
thickness of 131 nm.
Damping due to increasing scattering on
roughened surface.
DC plasma CVD systems
Advantages:
● low gas consumption.
● Multicathode systems to increase the substrate diameter.
Example:
- substrate diameter of 100 mm,
- discharge power of 2.4 kW per cathode in a seven-cathode system,
- deposition rate of 10 μm/h,
- diamond wafers of 800 μm thickness,
- possibility to further scale-up by increasing the number of cathodes.
K.Y. Eun et al., Proc. ADC/FCT'99, Tsukuba, 1999, p. 175
The growing film may be contaminated with electrode sputtering products.
Non-electronic grade material.
DC arc-jet for diamond growth
First publication by K. Kurihara et al. APL(1988).
- Jet diameter extension by an extra discharge
downstream of the nozzle exit, between a ring
electrode (anode) and the jet itself (cathode).
- The plasma core expands several fold.
- Pressure 70 Torr.
- Deposition rate of 40 μm/h at deposition
area of 12 cm2 with power as low as 10 kW.
-Economically viable process (16 mg/(h W).
V. Pereverzev, Diamond Relat. Mater. (2000)
● high-velocity jet with a core temperature of up
to 40,000ºC → effective gas decomposition;
● growth rates over 900 μm/h, and
8% conversion of methane carbon to diamond
(deposition area of several mm2 only)
[N. Ohtake, J. Electrochem.Soc., 137 (1990) 717].
● high gas consumption (Ar-CH4-H2)~10-30 l/min
gas recirculation is required.
● In the 1990s, Norton Co. (US) launched
commercial production of diamond wafers up to
175 mm in diameter, thermal grade.
[K.J. Gray, Diamond Relat. Mater., 8 (1999) 903].
100 kW arc-jet system at USTB, Beijing
Gas recirculation for economical process.
Growth rate ~10 μm/h for optical quality films,
~20 μm/h for thermal grade.
Control of N2 impurity.
F.X. Lu, Diamond Relat. Mater., 7 (1998) 737.
60 mm optical windows
Ordinary torch operating at
blow down mode,
substrate diameter 30mm
100kW high power torch operating
with arc roots rotation in magntec field,
substrate diamerter 110mm.
Non-vacuum laser plasma CVD system operated at 1 atm pressure
first version built at GPI
● CW CO2 laser (λ=10.6 μm) sustains stationary hot plasma, plasma position is
stabilized in gas stream.
● Xe gas is added in reaction mixture to reduce laser power necessary to maintain
plasma down to ~2 kW.
V.I. Konov et al. Appl. Phys. A, 66, (1998) 575 .
Diamond deposition conditions of laser CVD technique
CW CO2 laser power: 2.3 kW
Beam divergence : 4 mRad
Focal length: 7 – 12 cm
Substrate temperature: 650 - 1200С
Gas mixture: Xe(Ar):H2:CH4, Xe(Ar): H2:(CH4+CO2)
Flow rate: 2 - 5 l/min
Substrate material : W, Mo
Expensive Xe gas is added to reduce power threshold
to maintaine cw laser plasma.
Later Xe has been replaced by Ar at 6 kW laser system.
Scheme of the atmospheric-pressure laser plasmatron for
CVD of diamond
Ability to scan the substrate to cover large area
A.P. Bolshakov et al. Quantum Electronics (Moscow), 35 (2005) 385
Advantages of CW laser plasma for diamond growth
● High plasma temperature 15 000 – 20 000 K
(effective decomposition of H2 and CH4).
● High pressure (up to 4 atm is realized).
► High deposition rate, 120 µm/hour.
S. Metev et al. Diamond Relat. Mater. 11, 472 (2002).
► No need in vacuum chamber.
► Plasma scanning to enlarge the area coated.
A.P. Bolshakov et al. Quantum Electronics (Moscow), 35 (2005) 385
Polycrystalline diamond films and isolated crystals
Substrates W, Mo
Microwave plasma CVD: NIRIM reactor, Japan
First version: M. Kamo, et al., J. Cryst. Growth, 62 (1983), 642.
side view
NIRIM - National Institute for Research in Inorganic
Materials, Tsukuba, Japan.
● A quartz tube inserted in a rectangular waveguide.
Wave mode TE10;
Microwave source – magnetron, frequency 2.45 GHz;
● The process gas: methane + hydrogen;
Pressure below 50 Torr;
Microwave power < 1.5 kW,
Typical deposition rate ~ 0.5 μm/h.
Advantages: simple design, low cost.
Drawbacks:
● small substrate size (several cm2);
● etching of the quartz walls by the nearby plasma →
film contamination;
● carbon deposition on quartz → microwave absorption
on window.
top view
Microwave plasma CVD systems
2.45 GHz and 915 MHz
The most popular method for CVD diamond production owing to:
● the availability of standard 2.45 GHz components to build the CVD reactor;
● wide experience in microwave plasma surface processing, especially in
microelectronics;
● Large deposition area with MW plasma at 915 MHz (plasma size scales with
MW wavelength: λ=12 cm for 2.45 GHz and λ=32 cm for 915 MHz)
● microwave plasma is “sterile”, no electrode sputtering;
→ low contamination of the growing diamond with the reactor material;
→ possibility to produce optical grade and electronic-grade diamond.
High quality diamond wafers by MPCVD
●Reliable 5-6 kW magnetrons (2.45 GHz) available,
working time >5000 hours.
● 915 MHz magnetrons of 70-100 kW.
●High pressure (up 300 Torr) deposition regimes,
large area, high productivity.
● Wafers of 100 mm in diameter and larger (E6,
Aixtron, SEKI)
● Single crystal CVD diamond
SEKI AX6600 CVD reactor
Frequency 915 MHz,
Power 70-100 kW,
Max diameter 300 mm
Growth rate 15 μm/h
Diamond wafers produced with
AIXTRON reactor C. Wild, SMSA 2008
CVD diamond system with gyrotron microwave source
high frequencies 20-200 GHz (millimeter waves)
6
5
3
8
1
1
2
2
4
8
7
The gyrotron CVD system developed
at IAP (Nizhny Novgorod, Russia).
Features
● Very high power sources (up to 1 MW
power in CW mode) available;
● flat plasma
● large substrate area (Ø100 mm at 20 kW)
● high growth rate (>10 μm/h)
Remaining issues: How durable the system?
Needs many ours to work continuously.
The pilot CVD reactor with 28 GHz gyrotron, 15 kW
Institute of Applied Physics RAS, Nizhny Novgorod, Russia
Deposition of diamond films on substrates up to 100 mm diameter,
growth rate of 10-15 μm/hour.
A.L. Vikharev, et al. Diamond and Related Materials, 17 (2008) 1055