Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/0021—Reactive sputtering or evaporation
  • C23C14/0036—Reactive sputtering
  • C23C14/0047—Activation or excitation of reactive gases outside the coating chamber
  • C23C14/0052—Bombardment of substrates by reactive ion beams
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/0021—Reactive sputtering or evaporation
  • C23C14/0036—Reactive sputtering
  • C23C14/0063—Reactive sputtering characterised by means for introducing or removing gases
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
  • H01J2237/06—Sources
  • H01J2237/08—Ion sources

Definitions

• the present invention relates to extremely low pressure reactive magnetron sputtering apparatus and method for fabricating dielectric optical coatings on substrates.
• the invention in this application deals with the specialized field of optical interference filters suitable for
• IBS Ion Beam Sputtering
• IAD Ion Assisted Deposition
• a high energy ion beam in the energy range of 500 eV to 1500 eV is directed at a target (source) composed of desired coating materials.
• the effect of the ion bombardment is to
• the chamber is desired to be maintained at a very low level to prevent gas-phase collisions of
• IBS provides over other coating techniques such as evaporation and other methods of sputtering.
• Fig. 1 which is a reproduction of Fig. 1 of Wei et al, shows an ion gun
• the films produced by the foregoing techniques can have total losses well less than 100 ppm.
• references to "low loss" films or coatings means films or coatings having less than 500 ppm loss.
• DC or magnetron sputtering has also been used to produce dielectric coatings for many low tolerance or low film quality applications.
• these methods involve filling a chamber with inert gas which is then ionized to form a low energy plasma. A target is then
• DC sputtering is used to sputter metals.
• RF sputtering utilizes oscillating target voltage with a net zero DC current
• parts are shuttled on a high speed drum between a deposition zone maintained
• target material is sputtered through an orifice or aperture onto a rotating drum.
• Inert working gas is bled into the target chamber, and a reactive gas is bled into the rest of the chamber.
• the aperture limits the amount of reactive gas to the target.
• Dielectrics also discloses a sputtering through an orifice and produces an alternating current field (AC) component to the DC drive voltage to prevent arcing.
• AC field is said in
• Scherer et al patent to have the added effect of increasing deposition rate due to an increase in collisions between oscillating electrons and the working gas.
• the field is said to have the further effect of allowing a reduction in the coating pressure to as low as 0.5 Torr
• Thin Layers to a Substrate also discloses the use of an aperture between the cathode and the substrate and adds a positive voltage near the substrate over which the reactive gas flows.
• the reactive gas becomes ionized by the anode which has the effect of improving film
• the source to substrate distance is short. In Scobey et al, the distance is approximately 10 cm; in Maniv et al, the distance is 10 cm; in Scherer et
• Pond 1033 developed a magnetron sputtering process using 8 inch magnetrons to coat moderate size substrates of 8 inches or less in diameter
• the Pond system was characterized by low coating rates of typically 0 5 to 1 5 A/sec These low coating rates can in general be attributed to poisoning of the target, arcing, poor film reaction and low applied power levels
• the total pressure is maintained at conventional sputtering pressures of approximately 3 x 10 '3 Torr between the substrate and target, except for the Scherer et al patent and the Pond et al report
• the method and apparatus which accomplishes this object includes a conventional magnetron sputtering system in a vacuum tank outfitted with an unusually high pumping
• a gas manifold around the magnetron and target material confines the inert working gas (argon) in the vicinity of the magnetron As the gas diffuses and expands from the area of the magnetron, the unusually high pumping speed vacuum removes the expanding gas from the chamber at a high speed. The pressure in the chamber is then a
• Reactive gas enters the chamber through an ion gun which ionizes the gas and directs it toward the substrate This has the effect of reducing the amount of gas required
• This invention distinguishes sha ⁇ ly from the known prior magnetron sputtering
• the reactive gas pressure such as O 2 , N 2 , NO, etc. (measured at the substrate surface being coated) is preferably in the range of 2.0 x 10 s to 1.5 x 10" 4 Torr, more preferably 3 x 10 '5 to 9 x 10 "5 Torr. This advantageously reduces or eliminates arcing at the magnetron and "poisoning" of the source by the reactive gas.
• the inert gas such as argon, krypton, xenon, etc., is in preferred embodiments introduced primarily at the
• a sha ⁇ pressure drop is established for the inert gas, preferably having a pressure (measured at the substrate surface being coated) in the range of 5.0 x 10 '5 Torr to 2.0 x 10 "4 Torr, more preferably 5 x 10 "5 Torr to 1.5 x lO ⁇ Torr.
• gas pressures provide long mean free path, (MFP) and correspondingly allow advantageously long throw distances without undue collisions between the chamber gasses and the sputtered material.
• Advantageously good coating uniformity is achieved via long throw distance, preferably greater than 12", more preferably 20" or longer.
• IBS which, for example, operates in
• This novel system based on magnetron sputtering substantially improves the coating speed
• Fig. 1 is a reproduction of Fig. 1 of Wei et al, as mentioned in the Background of the
• Fig. 2 is a reproduction of Fig. 2 of Scott et al, as mentioned in the Background of the Invention;
• Fig. 3 is a cross-sectional schematic illustration of the apparatus of this invention.
• Fig. 4 is a schematic representation in cross-section of a magnetron sputtering apparatus of this invention.
• Fig. 5 is a cross-sectional schematic illustration of the apparatus of this invention.
• Fig. 6 is a graph showing the relationship between chamber pressure and chamber pumping speed assuming the magnetron pressure of 0.7 microns and a magnetron assembly conductance (C M ) of 3000 1/sec;
• Fig. 7 is a graph showing the relationship between chamber pressure and chamber pumping speed assuming a magnetron pressure of 0.4 microns and a magnetron assembly
• Figs 1 and 2 show IBS systems capable of producing high
• Total losses for a high reflector laser mirror made in accordance with preferred embodiments of the method disclosed here, for example, are well less than 0.01% or 100 ppm.
• Figs. 3 and 4 show the method and apparatus of preferred embodiments of the method
• the housing 10 forms a vacuum chamber 1 1 containing a low pressure magnetron assembly 12 and a planetary substrate holder 13 with a plurality of rotatable planets 14. Each planet 14 holds a substrate facing the magnetron assembly 12. In this embodiment, the distance between the top of the magnetron assembly 12 and the planets is 16".
• the magnetron assembly 12 is connected to a source of working gas 16 by conduit 17.
• the housing 10 is shown spherical with a radius of 48", but other
• the housing 10 has a lower sleeve 18 which opens into the vacuum chamber 11 and
• the vacuum pump is of course used to lower and maintain the pressure
• Typical high speed vacuum pumps useful in the embodiments disclosed here include turbopumps, cryopumps and diffusion pumps.
• 16" turbopump or 16" diffusion pump or, more preferably, in this invention are 16" cryopumps or 16" diffusion pumps. Pumping speeds with these pumps are on the order of
• the magnetron assembly 12 is in vertical alignment with the axis of rotation (main center line 22) of the planetary substrate holder 13 and with a holder for monitoring witness chip 23.
• the planets are 15" and the substrates are 15" or any size less than 15" in diameter, and the center line of each planet is 14" from the center line 22 to
• An ion gun 26 whose output, represented by dashed lines 27, is directed obliquely
• the ion gun is positioned such that its output of ions and gas mixture cover the entire substrate holder 13 and in this embodiment the top of the ion gun is
• the principal function of the ion gun is twofold. The first is to modify
• the second function may be more important, which is to serve to maintain low reactive gas background pressure.
• reactive gas is ionized and directed toward the substrat ⁇ ).
• the momentum of the reactive gas then, carries it only toward the substrate(s)
• Typical reactive gas pressures are in the range of 2 x 10 "$ Torr to 1.5 x 10" 4 Torr, preferably, 3 x 10 5 Torr to 8 x 10 "5 Torr
• a suitable hot cathode pressure gauge 31 is also connected to the vacuum chamber 11 to measure the pressure within the vacuum chamber. Also, vacuum chamber is provided with a shutter 32 oscillatible about a stem 33 blocking the output of the magnetron assembly
• the stem 33 is connected in any suitable manner to a platform 35 and to a means for oscillating the stem (not shown)
• the shutter is used to pre- sputter the source(s) to remove contaminates from the target which may have condensed, etc., onto the surface of the target while the apparatus was idle between layers being
• the magnetron assembly 12 comprises a target holder 36 having
• holder also is water cooled A manifold 44, spaced slightly from the holder 36, and sealed
• conduit 17 (Fig. 3) which
• the manifold 44 has an opening 45 substantially the size of the metallic target material so that sputtered target material and working gas is emitted as represented by the
• the magnetron is available from Material Sciences of Boulder, Colorado and is typically 6" to 8" in diameter with high strength magnets.
• this invention has the capability of producing extremely high quality film coatings by magnetron sputtering without the constraints of IBS or other known techniques, it will also be realized that this invention is a major advance over the prior art
• the throughput of this invention is 20 to 120 times
• the method of this invention scales easily to larger apparatus dimensions All of the dimensions above can be easily increased at least by a factor of two to allow coating of optical substrates of 30" diameter or even large with laser low loss coatings having good uniformity Scaling is a simple linear issue A larger system uses larger magnetrons and more
• process gas e.g , argon
• the vacuum pumps need to be correspondingly increased to accommodate the larger chamber and the increase in process gas flow
• this invention is capable of producing, for example, laser quality mirrors which are many times greater in diameter than those known to be made by current IBS systems
• the long throw of 16" and more and low chamber pressures of preferred embodiments of this invention allow two or more materials to be concurrently deposited to form high optical films composed of mixtures of materials
• Fig 5 shows two sources, magnetron
• a layer of selected refra ⁇ ive index can be formed as a mixture of two or more materials The mixture can be homogenous throughout the layer to form a film of selected
• the pumping speed must be roughly increased by a factor of two for two concurrent deposition sources, or a factor of N forN sources. Given the benefit of the disclosure, adding pumping speed will be a simple
• the rate from the sources is additive, and hence the sources can be sized to smaller levels which use less gas.
• Another device which may be used in this invention is an arc reducing electronic device sold by Advanced Energy of Boulder, Colorado under the trademark SPARC-LE.
• the SPARC-LE 46 is shown connected to the magnetron assemblies 12 by an electrical conductor 47 with its own DC power supply 48.
• the SPARC-LE is connected similarly to the two magnetron assemblies 12 and 12a as shown in Fig 4.
• Such a device helps in reducing arcing but it is not necessary in the method and apparatus of this invention.
• the chamber pressure of the inert gas will be a function of the magnetron pressure.
• p chamber is the pressure in the chamber
• C P is the conductance of the high vacuum pump (chamber pumping speed)
• p Magnetron is the pressure in the magnetron
• C M is the conductance due to gas confinement at the magnetron (confinement
• chamber pressures can be determined approximately for
• any new chamber with known pumping speed as shown in Figs 6 and 7
• any suitable desired pressure can be achieved by increasing the pumping speed of the chamber. If the operating inert gas pressure in the magnetron is
• C M magnetron assembly conductance

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physical Vapour Deposition (AREA)

Priority Applications (4)

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Cited By (3)

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Citations (4)

• 1996
  • 1996-06-10 CA CA002254354A patent/CA2254354A1/en not_active Abandoned
  • 1996-06-10 EP EP96918398A patent/EP0956375A1/de not_active Withdrawn
  • 1996-06-10 JP JP10501529A patent/JP2001502754A/ja not_active Ceased
  • 1996-06-10 WO PCT/US1996/009742 patent/WO1997047781A1/en not_active Application Discontinuation

Patent Citations (4)

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