What constitutes a good diamond film?

13.04.2010

Thin film technologyTapani Alasaarela, Oskari Elomaa, Marianne Leinikka,

Henri Nykänen, Ville Vähänissi

What constitutes a good diamond film?

It is what the customer wants!

Why diamond?

• Extreme mechanical hardness• Highest thermal conductivity• Broad optical transparency• Excellent electrical insulator• Very resistant to chemicals

Why diamond film?

Extreme Diamond Properties - Thin Film Usability

Why diamond film?Growth• Substrate

– Virtually any material (limitations from growth temperature and adhesion)

• Techniques– High-pressure high-temperature

growth (old method)– Different CVD processes

(microwave plasma CVD most common)

– PVD

• Polishing required

• Film properties depend on crystal orientation

Paul W. May, Diamond thin films: a 21st-century material, Phil. Trans. R. Soc. Lond. A (2000)

R. F. Davis, Diamond Films and Coatings, William Andrew Publishing/Noyes (1993)

Why diamond film? Optics• Very low absorption

– From UV to IR

– Depends on deposition method

– Very high laser damage threshold

• High refractive index – n ≈ 2.4 for bulk diamond

• Roughness leads to scattering losses

Optical testing:

• Spectroscopic ellipsometry (for n and k)

• Spectroscopy (UV-VIS-NIR, FTIR, Raman)

• Luminescence (PL, CL, EL)

• Laser damage threshold

Paul W. May, Diamond thin films: a 21st-century material, Phil. Trans. R. Soc. Lond. A (2000)

R. F. Davis, Diamond Films and Coatings, William Andrew Publishing/Noyes (1993)

Why diamond film? Optical applications• Durable optical coatings

– E.g. antireflective coating on silicon at IR wavelengths

• High laser power coatings– Small thermal distortion, easy to cool

• X-ray, UV, Visible, IR windows

• X-ray detector windows and x-ray lithography mask membranes

• Emitter for field-emission display

Paul W. May, Diamond thin films: a 21st-century material, Phil. Trans. R. Soc. Lond. A (2000)

R. F. Davis, Diamond Films and Coatings, William Andrew Publishing/Noyes (1993)

Why diamond film?Electronics• Bulk properties

– Thermal conductivity > 100Wcm-1K-1 (even up to >400 at 100K temp) 2)

– Resistivity ~1016Ωcm (room temp) 4)

– Band gap 5,47eV (1,12eV for Si) 1)

• Thin film– Thermal conductivity > 10Wcm-1K-1 (60μm film) 2)

– Grain size Single crystal (>50μm thick) 3)

• Doping (for ex, Nitrogen, Boron, Sulfur, Phosphorous)– Resistivity: <12 Ωcm (with B/S-codoping, p-type)– Dopant density example: >1017 cm-3 (p-type) 3)

• Diamond based semiconductor main benefits: Operation in high voltages (>10kV), high power levels, high temperatures (>400C), extreme radiation conditions,

• (Still no practical n-type doping available)

Electrical testing:• I-V, Hall, DLTS (Deep-level transient spectroscopy), XRD,

• Any test which determines electrical properties of a material...

1) Measurements of Defect Density Inside CVD Diamond Films Through Nuclear Particle Penetration, Potenza and Tuvé, Springer 100/2006

2) Thermal conductivity of CVD diamond films, H.B. Chae et al., Int. Journal of t.phys. 17(3) 19963) Free-standing Diamond Single Crystal Film for Electronics Applications,

Yang et al, MRS 20094) http://www.chm.bris.ac.uk/pt/diamond/end.htm

Why diamond film?Electronic applications• Substrates for Integrated Circuits

– High heat conduction, good insulator, ...• Solar Cells

– Radiation resistance (space), high temp operation, potential efficiency 50% (silicon 10-15%)

• Probe tips– Wear resistant, hard, ...

• Thermal actuators– Low heat capacity, High heat conduction

• Heat sinks for electronics• Piezoelectric effect devices• Radiation detectors• FET• Electron emitter (in flat panel displays)

Why diamond film?Mechanical• High strength

– up to 2200 MPa fracture strength

• High hardness– up to 100 GPa

• High elastic modulus– up to 1000 GPa

• Low wear coefficient– due to the above

• Low friction coefficient– less than 0,1– due to passive nature of sliding surface (no dangling bonds)

Mechanical testing: ball-on-disk tribometer, indentation, adhesion test etc.

Paul W. May, Diamond thin films: a 21st-century material, Phil. Trans. R. Soc. Lond. A (2000) Mark Antonio Prelas,Galina Popovici,Louis K. Bigelow, Handbook of industrial diamonds and diamond filmsKazuhisa Miyoshi, Masao Murakawa, Shuichi Watanabe, Sadao Takeuchi, Shojiro Miyake and Richard L.C. Wu, CVD diamond, DLC, and c‐BN coatings for solid film lubrication, Tribology Letters, Volume 5, Numbers 2-3 / September, 1998 Tao LIU, Dierk RAABE, Wei-Min MAO, A review of crystallographic textures in chemical vapor-deposited diamond films, Front. Mater. Sci. China 2010, 4(1): 1–16

Why diamond film?Mechanical applications• Hard coatings + solid lubricant

– machine-tooling (cutters, saws, drills, mills)• for machining non-ferrous metals, plastics, chip-board and composite

materials etc.

– bearings– seals– gears

• Protective coatings

• Decorative coatings

CVD-diamond films for cutting tools

Paul W. May, Diamond thin films: a 21st-century material, Phil. Trans. R. Soc. Lond. A (2000)Center of Super-Diamond and Advanced Films, City University of Hong KongTao LIU, Dierk RAABE, Wei-Min MAO, A review of crystallographic textures in chemical vapor-deposited diamond films, Front. Mater. Sci. China 2010, 4(1): 1–16

Why diamond film?Chemical• Resistant to chemical corrosion and extremely stable chemically:

– Under 1000°C : sodium nitrate and presence of atomic oxygen– Over 1000 °C or under high pressure: – Dissolves in iron, cobolt, manganese, nickel, chromium and platinum-group

metals– Reacts with strong carbide forming metals (tungsten, tantalum, zirconium and

titanium)

• Grain size of individual diamond should be adjusted to be less than 30nm – prevents the KOH-like corrosive liquids to attack the substrate

• Extremely hydrophobic• Biocompatible (improved hemocompatibility)• Adhesion

– Good with carbide formers (e.g. silicon)– Delamination with non-carbide forming materials (e.g. copper)– Poor with materials which do not tend to nucleate diamond (stainless steel)

Why diamond film?ChemicalChemical testing:

Rotational abrading method and the practical drawing wire test (adhesion)

different etching tests (e.g. concentrated saline solution, sulphuric acid)

SIMS (elemental depth profiles for dopants and impurities

Raman and FTIR spectroscopy

Why diamond film?Chemical applications• Un-sticky coatings

– Protection of ship hulls– Improved machine-tooling ability (e.g. paper industry, aluminium related processes)

• Oxidation resistant products– Turbine engine coating

• Biomedical applications– Orthopedics and prosthesis (especially hip joint coatings with ta-C)– Improved hemocompatibility in vascular stents and artificial heart valves– Surgical tools for microsurgical procedures (diminished tissue damage)– Electrodes in biosensors

THANK YOU!