Presentation on theme: "prepared by Chemical Vapor Deposition"— Presentation transcript:
1 prepared by Chemical Vapor Deposition Diamond filmsprepared by Chemical Vapor DepositionVictor RalchenkoGeneral Physics Institute of Russian Academy of Sciences,Moscow, RussiaTallinn University of Technology, Nov , 2013
2 Outline 1. Chemical Vapor Deposition (CVD) of diamond films: principles and methods2. Growth processes for nano/micro/mono-crystalline filmsin microwave plasma3. Properties of diamond films4. Diamond films processing5. Applications
3 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 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 ecologyThe staff (total): ca persons.Scientific staff: ca. 500 persons.
4 GPI activity in CVD diamond technology: ● Laser processing of diamond films (pattering, polishing…) 1988● DC plasma CVD reactor built● Nanocrystalline diamond in DC (Ar-CH4-H2) plasma 1995● Microwave plasma CVD reactor (from Astex) 1995● DC arc-jet system● CO2 laser plasmatron● Microwave plasma CVD system DF● Ultrananocrystalline diamond (UNCD) by MPCVD 2005● Epitaxial diamond filmsApplications● 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
5 Atomic structure of diamond ● atomic density 1.76х1023 сm-3 (record high)● cubic lattice parameter а=3.56 А● interatomic distance 1.54 АRemarkable 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.
6 Properties of diamond Property Value Application Band gap, eV 5.4 PropertyValueApplicationBand gap, eV5.4High-temperature electronicsCarrier mobility, cm2/Vs1600 h2200 eRadiation-hard detectorsOptoelectronic switchesResistivity, Ohm*cmOptical (electron) switchesThermal conductivity, W/mKHeat spreadersDielectric constant5.7Loss GHz0.3·10-6Windows for gyrotrons, klystronsOptical transmission range225 nm – RFOptics for lasers (mostly IR)Hardness, GPa81±18Tools, surgery bladesAcoustic wave velocity, km/s18.4 along <111>Surface acoustic wave devicesThermal expansion coefficient, 10-6 K-1KStable-dimension componentsCorrosion resistanceStable in HFElectrochemistry (doped diamond)Low or negative electron affinityField electron emittersBiocompatibilityCoatings on implants
7 Natural and synthetic diamonds HPHT syntheticsingle crystalsCVD polycrystalline films and single crystalsNatural crystals● Small size● Defects and impurities● High cost● Small size, few mm.● Catalyst impurity.● Very large lateral size.● Can be highly pure.● Reduced cost.
8 Delaware Diamond Knives, DDK Inc. General Physics Institute RAS Why diamond ?CVD Diamond for ElectronicsDiamond 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)Ulm University, Germany Diamond Materials Fraunhofer Institute IAF in Freiburg, GermanyDelaware Diamond Knives, DDK Inc.Wilgminton, USASCDPCDelement six ltd Ascot, Berkshire, UKGeneral Physics Institute RASMoscow (Russia)Natural diamond has been used up to now for detectors, only.While CVD diamond has observed very interesting results and today few producers are on the market with polycrystalline substrate up to 4” and SCD up to 5mm2, limited by HPHT substrate dimensions.8
9 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, Vol. 1, p. 326]:(1) graphite lonsdaleite martensitictransformation 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 GPaCVD, <1 atm
10 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.Toroid- type HPHT apparatus, maximum pressures up to 8 GPa(Inst. High Pressure Physics, Troitsk)Yellow color due to nitrogen atom impurity in substitutional position.Largest diamond crystal ~ 25 carats (5 g) has been grown in “Belt” pressR.S. Burns et al. DRM. 8 (1999) 1433.
11 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 - diamondMethods of gas activation● Hot filament● DC arc jet*● DC plasma*● Laser plasma*● Oxygen-acetylene flame● Microwave plasma**realized at GPIAny physical process creating atomic hydrogen and CHx radicals potentially is able to produce diamond.
12 CVD systems for diamond growth developed at GPI since 1990DC plasma systemСО2 laser plasmatronECR microwave plasmaDC arc-jet system, 14 kWMicrowave plasma jet
13 Growth mechanism (Harris & Goodwin 1993) Atomic H and CH3 radical are of most important speciesCreation of active sitesThe 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.Adsorption of CH3 radical and dehydrogenationThe model proposed by Harris and Goodwin in 1993, describes in a simple way CVD diamond growth, with only two species, H and CH3, and five reactions.Preliminary to growth, active sites are created by abstraction of the adsorbed hydrogen atoms by atoms from the gas phase.These active sites can then receive a CH3 radical, which becomes integrated into the diamond lattice, by successive abstraction reactions.From this kinetic scheme, one can derive the growth rate for (100) planes which depends on the surface concentrations on H and CH3 as shown here.Growth rateExtended model includes 28 species, 130 reactions: G. Lombardi et al. J. Appl. Phys. (2005)
14 With pioneers in CVD diamond 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/hW.G. Eversole, Patent 1962; B.V. Deryaguin, Usp. Khimii, 1970Only when importance of hydrogen has been recognized, high growth rates, ~ 1 µm/hwere obtained: B.V. Spitsyn et al. J. Cryst. Growth, 52 (1981) 219.With pioneers in CVD diamondSecond Chinese-Russian Seminar on CVD diamond, GPI, Moscow, 2012
15 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].
16 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● flame scanning ► 35 30 cm2 area;[M. Okada, Diamond Relat. Mater., 11 (2002), 1479].● multiple flame systemsProblems● Stability: flame tip–substrate distance mustbe maintained strictly constant ~ 1 mm.● High gas consumption ~ 5 l/min● Diamond quality – moderate.
17 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].Laser reflectivity at 633 nm wavelength.One oscillation period corresponds to film thickness of 131 nm.Damping due to increasing scattering on roughened surface.Optical quality diamond can be grown.
18 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. 175The growing film may be contaminated with electrode sputtering products.Non-electronic grade material.
19 DC arc-jet for diamond growth First 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)
20 100 kW arc-jet system at USTB, Beijing Ordinary torch operating at blow down mode,substrate diameter 30mmGas 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) 737.100kW high power torch operatingwith arc roots rotation in magntec field,substrate diamerter 110mm.60 mm optical windows
21 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 .
22 Diamond deposition conditions of laser CVD technique CW CO2 laser power: 2.3 kWBeam divergence : 4 mRadFocal length: 7 – 12 cmSubstrate temperature: СGas mixture: Xe(Ar):H2:CH4, Xe(Ar): H2:(CH4+CO2)Flow rate: l/minSubstrate material : W, MoExpensive 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.
23 Scheme of the atmospheric-pressure laser plasmatron for CVD of diamond Упомянуть защитные насадки коаксиального обдува подложки.Ability to scan the substrate to cover large areaA.P. Bolshakov et al. Quantum Electronics (Moscow), 35 (2005) 385
24 Advantages of CW laser plasma for diamond growth ● High plasma temperature – 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
25 Polycrystalline diamond films and isolated crystals Substrates W, Mo
26 Microwave plasma CVD: NIRIM reactor, Japan First version: M. Kamo, et al., J. Cryst. Growth, 62 (1983), 642.side viewNIRIM - 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
27 Microwave plasma CVD systems 2.45 GHz and 915 MHzThe 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 inmicroelectronics;● Large deposition area with MW plasma at 915 MHz (plasma size scales withMW 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.
28 High quality diamond wafers by MPCVD ●Reliable 5-6 kW magnetrons (2.45 GHz) available, working time >5000 hours.● 915 MHz magnetrons of 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 diamondSEKI AX6600 CVD reactorFrequency 915 MHz,Power kW,Max diameter 300 mmGrowth rate 15 μm/hDiamond wafers produced withAIXTRON reactor C. Wild, SMSA 2008
29 high frequencies 20-200 GHz (millimeter waves) CVD diamond system with gyrotron microwave sourcehigh frequencies GHz (millimeter waves)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).
30 The pilot CVD reactor with 28 GHz gyrotron, 15 kW Institute of Applied Physics RAS, Nizhny Novgorod, RussiaDeposition of diamond films on substrates up to 100 mm diameter, growth rate of μm/hour.A.L. Vikharev, et al. Diamond and Related Materials, 17 (2008) 1055