A Design for an efficient cylindrical magnetron cathode with rotating magnets and optical emission incorporated

Transcription

1 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.

2 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

3 Sputtering Process: * Effective creation of Argon ions by secondary electron bombardment

4 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.

5 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.

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7 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)

8 Simple Cylindrical magnetron: * Electromagnets requires high current which results in enhanced heating.

9 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.

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11 3 Vacuum coating technologies, Fairfield

12 US 5,047,131 US

13 * 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.

14 Present Invention: Optical fiber port High torque Motor Power connection Cooling water port Magnet arrangement 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.

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17 Thickness variation along the cylindrical axis: % thickness variation from average value ± 3 % Distance from one end of CM (cm) * A strip 12.0 cm 2.5 cm of glass plate is used as substrate. * Surface profilometry is used for thickness measurements. 10 Surface at the step Target Utilization: U t = t t w w ( initial ) ( final ) 100 % In the present design; U t 90%

18 Process control by plasma emission monitoring: Plasma Emission spectra Argon (first ionization) nm Tantalum (atomic) nm Nitrogen (exited) nm

19 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

20 Important references: 1. Design advances and applications of the rotatable cylindrical magnetron by Michael Wright and Terry Beardow JVST A 4 (1986) Homogeneous coatings inside cylinders by F. Loffler and C. Siewert Surf. Coat. Technol (2004) 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) 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.