Diamond films prepared by Chemical Vapor Deposition

Victor RalchenkoGeneral Physics Institute of  Russian Academy of Sciences,

Moscow, Russia

Tallinn University of Technology, Nov. 19-20, 2013

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

Outline

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 orientedat 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

General Physics Institute of  Russian Academy of Sciences (GPI)

The staff (total): ca. 1000 persons.Scientific staff: ca. 500 persons.

GPI activity in CVD diamond technology:● Laser processing of diamond films (pattering, polishing…) 1988● DC plasma CVD reactor built 1990● Nanocrystalline diamond in DC (Ar-CH4-H2) plasma 1995● Microwave plasma CVD reactor (from Astex) 1995● DC arc-jet system 1996● CO2 laser plasmatron 1998● Microwave plasma CVD system DF100 2001● Ultrananocrystalline diamond (UNCD) by MPCVD2005● Epitaxial diamond films 2007

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

● 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.

Atomic structure of diamond

Properties of diamond 

 

 

Property Value Application

Band gap, eV 5.4 High-temperature electronics

Carrier mobility, cm2/Vs 1600 h2200 e

Radiation-hard detectorsOptoelectronic switches

Resistivity, Ohm*cm 1013-1015 Optical (electron) switches

Thermal conductivity, W/mK 2000-2400 Heat spreaders

Dielectric constant 5.7  

Loss tangent @170 GHz 0.3·10-6 Windows for gyrotrons, klystrons

Optical transmission range 225 nm – RF Optics for lasers (mostly IR)

Hardness, GPa 81±18 Tools, surgery blades

Acoustic wave velocity, km/s 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 diamondsHPHT synthetic single crystalsNatural crystals

CVD polycrystalline films and single crystals

● Small size● Defects and impurities● High cost

● Small size, few mm.● Catalyst impurity.

● Very large lateral size. ● Can be highly pure. ● Reduced cost.

Diamond samples grown by Chemical Vapor Deposition (CVD) with CH4 + H2Polycrystalline diamond on 2-4 inch Silicon wafers (PCD)Single Crystal Plates on HPHT (high pressure high temperature) substrate (SCD)

CVD Diamond for Electronics

Ulm University, Germany 

Diamond MaterialsFraunhofer Institute IAF in Freiburg, Germany

Delaware Diamond Knives, DDK Inc.

Wilgminton, USA

SCD PCD

element six ltd Ascot, Berkshire, UK

General Physics Institute RAS

Moscow (Russia)

Why diamond ?

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.

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.

HPHT synthesis, 5-6 GPaCVD, <1 atm

● small size – typically less than 6 mm.● difficult to avoid catalyst impurities.

Yellow color due to nitrogen atom impurity in substitutional position.

Synthetic single crystal diamonds produced by HPHT technique

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.

Production of “Adamas”, BSU, Minsk

Chemical Vapor Deposition of 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.

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

CVD systems for diamond growthdeveloped at GPI since 1990

DC plasma system СО2 laser plasmatron ECR microwave plasma

DC arc-jet system, 14 kW Microwave plasma jet

Growth mechanism (Harris & Goodwin 1993)

33* 3

4CHCdCHCd

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53 HCHCdHCHCd k

26*

2 HHCdCdHCHCd k

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Adsorption of CH3 radical and dehydrogenation

2*1 HCdHHCd k

HCdHCd k 2*

Creation of active sites

Growth rate

Atomic H and CH3 radical are of most important species

The most of diamond surface is covered by adsorbed hydrogen.

H desorption leave free C bond –active site.

The chain of reactions to add one new C-C bond and continue diamond building.

Extended model includes 28 species, 130 reactions: G. Lombardi et al. J. Appl. Phys. (2005)

With pioneers in CVD diamondSecond Chinese-Russian Seminar on CVD diamond, GPI, Moscow, 2012

HistoryEarly 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.

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 flameIntroduced 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

● flame scanning ► 35 30 cm2 area;[M. Okada, Diamond Relat. Mater., 11 (2002), 1479].

● multiple flame systemsProblems● Stability: flame tip–substrate distance must be maintained strictly constant ~ 1 mm.● High gas consumption ~ 5 l/min● Diamond quality – moderate.

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 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].

● High CH4 concentrations (~10%) acceptable due to hot (almost thermal plasma).● High growth rate >10 μm/h.

DC plasma CVD

Optical quality diamond can be grown.

DC plasma CVD systemsAdvantages:● 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 growthFirst publication by K. Kurihara et al. APL(1988).

● high-velocity jet with a core temperature of up to 40,000ºC → effective gas decomposition;● growth rates over 900 μm/h, and8% 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/mingas 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].

- 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)

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.

100 kW arc-jet system at USTB, Beijing

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.60 mm optical windows

Non-vacuum laser plasma CVD system operated at 1 atm pressure first version built at GPI

V.I. Konov et al. Appl. Phys. A, 66, (1998) 575 .

● 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.

Diamond deposition conditions of laser CVD technique

CW CO2 laser power: 2.3 kWBeam divergence : 4 mRadFocal length: 7 – 12 cmSubstrate temperature: 650 - 1200СGas mixture: Xe(Ar):H2:CH4, Xe(Ar): H2:(CH4+CO2)Flow rate: 2 - 5 l/minSubstrate 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.

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.

side view

top view

Microwave plasma CVD systems2.45 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

Diamond wafers produced withAIXTRON reactor C. Wild, SMSA 2008

SEKI AX6600 CVD reactorFrequency 915 MHz,Power 70-100 kW,Max diameter 300 mmGrowth rate 15 μm/h

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CVD diamond system with gyrotron microwave source

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 gyrotron CVD system developed at IAP (Nizhny Novgorod, Russia).

high frequencies 20-200 GHz (millimeter waves)

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

The pilot CVD reactor with 28 GHz gyrotron, 15 kW Institute of Applied Physics RAS, Nizhny Novgorod, Russia