Abstract:
System and method for high vacuum sputtering combining magnetron sputtering and pulsed laser plasma deposition are described wherein simultaneous or sequential magnetron sputtering and pulsed laser deposition operations in a single ultra-high vacuum system provides high deposition rates with precise control of film morphology, stoichiometry, microstructure, composition gradient, and uniformity, in the deposition of high performance coatings of various metal, ceramic and diamond-like carbon materials.

Description:
RIGHTS OF THE GOVERNMENT 
     The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to systems and methods for high vacuum sputtering, and more particularly to a system and method combining magnetron sputtering with pulsed laser plasma sputtering which provides precise control of film composition, microstructure and uniformity. 
     In magnetron sputtering, the film is grown by bombardment of a target of film material with ions of inert gas. The bombarding atoms are ionized and accelerated toward the target by intersecting magnetic and electric fields. A chemically reactive gas may be added to grow films of nitrides, carbides or oxides in conjunction with appropriate transition metal targets. This technique provides rapid deposition rates of both metal and ceramic materials with large-area coating uniformity, but the required presence of sputtering or reactive gas limits attainable film composition, microstructure, uniformity, adhesion and purity. Because direct control of the energy of sputtered atoms is not practical, electrical bias applied to the growing film is required for control of film microstructure. 
     In the pulsed laser deposition technique, a pulsed laser beam is focused onto a target of the film material. Laser-target interactions result in material ablation and an energetic gas plume which condenses on the substrate as a film. This method may be applied in ultra-high vacuum and does not require the presence of a gas to generate the plasma. Direct control of the kinetic energy of ablated species is obtained by varying laser power and focus parameters allowing control of film microstructure, but the method is limited by low deposition rates. 
     The invention solves or substantially reduces in critical importance problems with prior art sputtering systems and methods as just described by providing system and method for high vacuum sputtering of films combining in a single system both magnetron sputtering and pulsed laser plasma sputtering, which, in combination with suitable substrate position control, allows attainment of high deposition rates with precise control of film morphology, stoichiometry, microstructure, composition gradient, and uniformity not achievable with prior art systems. In the practice of the invention, the magnetron sputtering provides high deposition rates, while plasma laser deposition allows control of film structure, microcrystallinity and stoichiometry. Deposition of a variety of metal, ceramic and diamond-like carbon materials having optimum composition, microstructure, thickness and stress state for any selected application may be accomplished. 
     The invention is especially useful for the deposition of composite and layered coatings with low friction, low wear rates, and high load support capability and substantially improved wear life for such applications as precision turbine engine components. 
     It is therefore a principle object of the invention to provide improved system and method for high vacuum sputtering of film materials. 
     It is another object of the invention to provide an improved high vacuum sputtering system and method combining magnetron sputtering and pulsed laser plasma sputtering. 
     It is yet another object of the invention to provide improved system and method for vacuum sputtering of films with precise control of film composition, microstructure and uniformity. 
     It is yet another object of the invention to provide improved system and method for vacuum sputtering of high performance wear resistant coatings. 
     These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds. 
     SUMMARY OF THE INVENTION 
     In accordance with the foregoing principles and objects of the invention, system and method for high vacuum sputtering combining magnetron sputtering and pulsed laser plasma deposition are described wherein simultaneous or sequential magnetron sputtering and pulsed laser deposition operations in a single ultra-high vacuum system provides high deposition rates with precise control of film morphology, stoichiometry, microstructure, composition gradient, and uniformity, in the deposition of high performance coatings of various metal, ceramic and diamond-like carbon materials. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention will be more clearly understood from the following detailed description of representative embodiments thereof read in conjunction with the accompanying drawing which is schematic showing the essential components of a system representative of the invention and useful in the practice of the method thereof. 
    
    
     DETAILED DESCRIPTION 
     Referring now to the accompanying drawing, shown therein is schematic diagram of the essential components of a system  10  representative of the invention and useful in the practice of the method thereof. An ultra-high vacuum chamber  11 , grounded as at  12 , was operatively connected to vacuum system  13  capable of evacuating chamber  11  to about 10 −9  to 10 −10  torr. Rotatable substrate table  15  was disposed within chamber  11  and driven by suitable motor means  16  operatively connected thereto. Gas inlet  18  defined in a wall of chamber  11  and communicating with source  19  of inert gas and with source  20  of reactive gas provided means for selective insertion of a controlled inert gas atmosphere and/or a reactive gas atmosphere in the operation of system  10  described below. Inert gases suitable for use in the practice of the invention include argon, krypton, xenon, or selected mixtures thereof, and reactive gases suitable for use include oxygen, nitrogen, acetylene, methane, hydrogen sulfide or hydrogen or selected mixtures thereof, or others as would occur to the skilled artisan practicing the invention guided by these teachings. Magnetron sputtering source  21  was disposed in a wall of chamber  11  in suitable position as suggested in the drawing for performing sputtering onto a substrate disposed on table  15 . In a unit built and operated in demonstration of the invention, source  21  was a Mini-Mac manufactured by US, Inc. Magnetron power supply  22  (model MDX-1, mfg by Advanced Energy) was operatively connected to source  21 . Materials which may generally be sputtered using source  21  include silicon, titanium, chromium, molybdenum, tungsten, niobium, copper, aluminum, hafnium, zirconium, graphite and composite type materials such as Si 3 N 4 , TiC, B 4 C, BN, TiN, Cr-nitride, Cr-carbide, HfC, HfN, WC, Al 2 O 3  and AIN, and others as would occur to the skilled artisan practicing the invention. Pulsed laser generator  24  (model 110I, mfg by Lambda Physik in the demonstration system) was disposed externally of chamber  11  as suggested in the drawing, and programmable mirror  25 , focusing lens  26 , and an entrance window  27  in a wall of chamber  11  provided representative optical means for directing a pulsed laser beam onto rotatable target  28  disposed within chamber  11 . The laser beam ablates the target  28  material for deposit as a thin film onto the substrate. Materials comprising target  28  which may generally be sputtered using laser generator  24  include graphite, transition metals (including Ti, Cr, Ni, Mo, W, V, Hf, Zr and Ta, and the carbides, oxides, nitrides and dichalcogens of elements including MoS 2 , MoSe 2 , MoTe 2 , WS 2 , WSe 2 , WTe 2 , NbS 2 , NbSe 2 , NbTe 2 , TaS 2 , TaSe 2 , TaTe 2 , TiC, TiN, TCN, CN, CrC, CrN, WC, HfC, TaC, and TiB 2 , and polymers of the polycarbonate, polyamide, polyimide, or polytetrafluoroethylene type (such as LEXANTM) and other materials as would occur to the skilled artisan. Externally disposed motor means  29  was operatively connected to target  28  for selectively rotating target  28 . 
     In the deposition of films according to the teachings of the invention, system  10  may be operated in three different modes, namely, sequential deposition wherein magnetron sputtering and pulsed laser deposition are performed in sequence in either order to produce a film deposit, simultaneous deposition wherein magnetron sputtering and pulsed laser deposition operations are performed simultaneously, and a mode comprising laser film processing during film growth. 
     In the sequential deposition mode of operation, chamber  11  is first evacuated to vacuum of about 10 −9  to 10 −10  torr, an inert gas is introduced as at inlet  18  to a pressure of about 10 −3  torr and power is applied to magnetron source  21  to start sputtering. The sputtered material is deposited as a film (usually about 0.01 to 5 μm) onto a substrate disposed on table  15 . A reactive gas may be added to chamber  11  in order to synthesize a film comprised of a compound such as carbide, nitride and/or oxide. After a desired film thickness is achieved, magnetron source  21  is switched off, the reactive gas feed is closed and chamber  11  again evacuated. Pulsed laser deposition is initiated by energizing laser generator  24  and focusing a laser beam  31  onto target  28  utilizing mirror  25  and lens  26 . Ablated material from target  28  is deposited on the substrate (to an additional thickness of about 0.01 to 5 μm) disposed on table  15 . Suitable control of motor  16  allows substrate table  15  to be positioned in confronting relationship to target  28  as shown by solid lines in the drawing or to magnetron sputtering source  21  as shown by dashed lines. Multilayer coatings of various compositions and thicknesses can be deposited utilizing this mode. Since the same material deposited using these two techniques can have considerable differences in mechanical properties, stress relief in the films can be achieved by multilayering of the same compound with alternate layers grown by different sources which allows growth of thicker films (viz., about 0.1 to 10 μm). 
     The simultaneous deposition mode is analogous to the sequential deposition mode except that magnetron source  21  and pulsed laser generator  24  are operated simultaneously at chamber  11  pressures corresponding to that required for magnetron sputtering. During such depositions, table  15  may be either continuously rotated or fixed at selected incidence angles with respect to target  28  and magnetron source  21 . In this mode, composite films comprising sputtering and laser ablated target materials and reactive gas may be deposited. The heat within the plume generated by laser  31  impingement on target  28  beneficially affects the microstructure, morphology, crystallinity and stress state of the deposited films independently of the magnetron sputtering parameters. In addition, high energy species produced by the laser deposition provide nucleation sites for magnetron produced species. Crystal structure and orientation is determined by the nucleation sites, and the growth rate is determined by the high density magnetron generated plasma. 
     The laser film processing during film growth mode is analogous to the other modes except that all or part of laser beam  31  is delivered to the surface of the film as it is deposited in order to directly control film microstructure as well as other important physical and crystallographic properties of the deposit. Additionally, laser processing of the magnetron target may be employed to initiate plasma from high refractory materials and promote plasma ionization to a desired level, which maintains constant target texture allowing optimum control over film stoichiometry, while sputtering sintered and/or composite target materials. Any of the aforementioned modes may be used in combination. 
     The invention therefore provides an improved system and method combining magnetron sputtering with plasma sputtering characterized by substantial control of film composition, structure and uniformity. It is understood that modifications to the invention may be made as might occur to one skilled in the field of the invention within the scope of the appended claims. All embodiments contemplated hereunder which achieve the objects of the invention have therefore not been shown in complete detail. Other embodiments may be developed without departing from the spirit of the invention or from the scope of the appended claims.