Download “A Design for an efficient cylindrical ma with rotating magnets and

Patent on,
“A Design for an efficient cylindrical magnetron cathode
with rotating magnets and optical emission incorporated”
Inventors
A. Subrahmanyam, Krishna Valleti
IIT Madras, Chennai, INDIA.
Shrikanth V Joshi, G.Sundararajan
ARCI, Hyderabad, INDIA.
Out look of the presentation:
◙ Brief introduction to sputtering mechanism
◙ Different sputtering techniques – focused on planar & cylindrical
◙ About & limitations of planar magnetrons (circular, rectangular)
◙ Description of existing cylindrical magnetrons
◙ Drawbacks
◙ Present invention design and evaluation
◙ Important references related to present invention
Sputtering Process: * Effective creation of Argon ions by secondary electron bombardment
Effective creation of Argon ions by secondary electron bombardment Sputtering Diode Sputtering Magnetron Sputtering R electron = 3.37 x E 1/2 (eV) / B (Gauss) R ion = 911 x E 1/2 (eV) / B (Gauss) ♦ Planar magnetron sputtering ♦ Cylindrical magnetron sputtering * The magnetic field confines the glow discharge plasma and increases the length of the path of electrons moving under the influence of the electric field. length of the path of electrons moving under the influence of the electric field.
Planar magnetron sputtering * The cathode includes an array of permanent magnets arranged in a closed loop and mounted in a fixed position in relation to the flat target plate. * The magnetic confinement of the plasma results in a high rate of erosion of the target along the narrow "race track". Limitations * Only a relatively small portion of the total target material is used. * Limited heat transfer and arcing at the edges and the center of the target. * The spitting of debris is very high. * Only planar objects can be coated uniformly.
Only planar objects can be coated uniformly. Scope of present invention:
◙ Batch of Industrial tool coating cost
effectively (more number in a single run).
◙ For large area glass coatings in the
architectural, automotive and display industry.
◙ Defense equipment protection form wear
and corrosion loss (mainly Gun barrels)
Simple Cylindrical magnetron:
* Electromagnets requires high current which results in enhanced heating.
Existing Cylindrical magnetron designs:
1
Magnet
Non magnetic
Spacer
U.S.Army Armament Research,
Development and Engineering Center
* A cathode target assembly in the form of an elongated, cylindrical tube
carries a layer of material applied to its outer surface that is to be sputtered.
U.S.Army Armament Research, Development and Engineering Center
Design reference: US 4,179,351 patent issued on Dec. 18, 1979 to Hawton, Jr. et al.
2
3
Vacuum coating technologies, Fairfield
US ­ 6375815
US ­ 5,047,131 * The target tube is rotated about its longitudinal axis. A magnetic structure is arranged inside
the tube but does not rotate with it.
* The rotation of the target surface through the stationary plasma sputters the top layer of
material from entire surface as that surface is rotated through the magnetic field.
* Any dielectric that is deposited on the target surface is apparently removed by sputtering
when it rotates in the region of the magnetic field thereby reducing arcing ("self-cleaning" ).
* The non uniformity in the deposited films is around 12%.
* Rotating seals are included in this support structure for isolating the electrical contacts and
cooling fluid from the vacuum chamber.
* Rotation of the target (not magnetic arrangement) results in local gas fluctuations.
* Sputtering in rotating target geometry will not allow oblique deposition (which results in
improved depositing film properties).
* Permanent magnets were damaged with time because of coolant water circulation (over
the magnets) and the magnetic field strength decreases slowly.
Present Invention:
Optical fiber port
High torque Motor
Power connection
Magnet arrangement
Cooling water port
Cylindrical cathode
Plasma profile
* Electron Confining efficiency;
I = K V n , n = 6.8 ( in the present geometry)
K – function of working pressure and magnetic field strength.
Thickness variation along the cylindrical axis: * A strip 12.0 cm × 2.5 cm of glass plate
is used as substrate.
% thickness variation from average value 100 80 ± 3%
60 * Surface profilometry is used for
thickness measurements.
40 20 0 0 2 4 6 8 10
Surface at the step
­20 Distance from one end of CM (cm)
­40 ­60 ­80 ­100 Target Utilization: t w (initial ) U t = ´ 100 % t w ( final ) In the present design; U t ≈ 90%
Process control by plasma emission monitoring:
Plasma Emission spectra
Tantalum (atomic) – 696.6 nm
Argon (first ionization) – 750.4 nm
Nitrogen (exited) – 738.5 nm
Over all achievements in the design:
◙ Maximum uniformity in thickness along the length of the cylindrical
magnetron is achieved
◙ Maximum target utilization is achieved
◙ Complicated rotation seal mechanism is eliminated
◙ Permanent magnetic material property degradation by corrosion is eliminated
◙ Ease of target loading is achieved
◙ Difficulties in monitoring gas distribution uniformity by gas showers is
eliminated
Important references:
1. “Design
Design advances and applications of the rotatable cylindrical magnetron”
magnetron by
Michael Wright and Terry Beardow – JVST A 4 (1986) 388.
2. “Homogeneous coatings inside cylinders” by F. Loffler and C. Siewert – Surf. Coat.
Technol. 177-178 (2004) 355.
3. “Characterization and Comparison of Magnetron Sputtered and Electroplated Gun
Bore Coatings” by Christopher P. Mulligan, Stephen B. Smith and Gregory N. Vigilante –
Transactions of the ASME 128 (2006) 240.
4. “Advanced generation of rotatable magnetron technology for high performance
reactive sputtering” by S.J. Nadel, P. Greene, J. Rietzel, M. Perata, L. Malaszewski, and R. Hill
– Thin solid films 502 (2006) 15.