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:
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…) 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 MPCVD 2005 ● 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 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 ≈43eV • → radiation hardness.
CVD polycrystalline films and single crystals HPHT synthetic single crystals Natural crystals Natural and synthetic diamonds ●Small size ● Defects and impurities ● High cost ●Small size, few mm. ● Catalyst impurity. ● Very large lateral size. ● Can be highly pure. ● Reduced cost.
SCD PCD element six ltd Ascot, Berkshire, UK Diamond MaterialsFraunhofer Institute IAF in Freiburg, Germany Delaware Diamond Knives, DDK Inc. Wilgminton, USA General Physics Institute RAS Moscow (Russia) Ulm University, Germany 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)
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 lonsdaleitemartensitic 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. 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” 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 СО2laser plasmatron ECR microwave plasma DC arc-jet system, 14 kW 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. 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 dehydrogenation Growth rate 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 embritlmentdue 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 ● flame scanning ► 35 30 cm2 area; [M. Okada, Diamond Relat. Mater., 11 (2002), 1479]. ● multiple flame systems Problems ● Stability: flame tip–substrate distance must be maintained strictly constant ~ 1 mm. ● High gas consumption ~ 5 l/min ● Diamond quality – moderate.
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.
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). ● 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]. • - 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)
100 kW arc-jet system at USTB, Beijing Ordinary torch operating at blow down mode, substrate diameter 30mm 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. 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 ● CW CO2 laser (λ=10.6 μm) sustains stationary hot plasma, plasma position is stabilized in gas stream. ● Xegas 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 - 1200С 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 maintainecw 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 reactorC. Wild, SMSA 2008
CVD diamond system with gyrotron microwave source high frequencies 20-200 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).
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