Patent Application: US-23574705-A

Abstract:
the a cathode - arc source of metal plasma with filtration , used , in particular , for deposition of dlc , utilizes the effect of fast ions reflection from the hall stratum in a transversal arched magnetic field to filtrate vacuum arc plasma arc from contaminating macroparticles and vapor . various embodiments for producing maximal plasma flux at the source outlet , in particular , a pulse source with more the one cathode units for deposition of coating inside pipes / cavities , for deposition of coating in a stationary / quasi - stationary condition are offered . the cathode is made of a consumable material and is exposed to poles of magnets on both ends of cathode for creating a transversal magnetic field of an arched configuration in a discharge gap between the cathode and the anode . the anode geometry adequate to the mechanism of the arc current passage through a transversal magnetic field is offered . to avoid longitudinal and transverse short circuits of the current layer , an installation of non - conducting surfaces at ends or sectioned shields under a floating potential at the cathode sides is provided . the method of creating the hall stratum in said transversal magnetic field of arched configuration is offered .

Description:
the present invention characterizes to a novel source of filtered cathodic arc plasma ; in the source a transversal magnetic field of an arched form so that to develop a compact and efficient macroparticle - free plasma source with high throughput deposition . the basic embodiment of an ion source is shown in fig1 a , where vacuum chamber 1 and area 2 are illustrated schematically . the vacuum chambers for cathodic arcs are well - known in practice , therefore components and design of the chamber are not given here . the details ( workpieces ) for producing deposition ( diamond - like coating ) are arranged in area 2 and can be mounted in a holder or fastening and to move in said area for providing coating uniformity and high throughput of workpieces for coating deposition . vacuum chamber 1 is capped at one end by an cover 3 , equipped with partitions or other elements of more complicated structure to prevent macroparticles reflection in direction to area 2 . the vacuum arc discharge is sustained between cathode 4 , on which cathode spots 5 are formed and produce cathode plasma jets , and anode 6 ( fig1 c , 1d ). the vacuum arc discharge in transversal magnetic field b is characterized by occurrence of hall layer 7 on boundary of the cathode plasma of a vacuum arc and thus the plasma boundary in one direction coincides with direction of a magnetic field b , and in other projection has a cardioid - like shape . the hall layer is characterized by an electric field , which is perpendicular to magnetic field , at that the arc current transfers from cathode to anode only in hall layer on boundary of plasma by electrons drifting in crossed fields . therefore further a current - carrying hall layer term is used in the patent application . an arc discharge can exist only if anode is present on drifting path of electrons , therefore anode 6 is located within this boundary layer . ions 8 , reaching boundary layer 7 , are reflected by an electric field , whereas marcroparticles 9 pass through the boundary and thus move away from plasma , since , unlike the electrons and ions , marcroparticles 9 flying from the cathode 4 are not strongly affected by magnetic or electrostatic field in the hall layer , and they cannot make an abrupt turn required to reach area 2 . instead , of the marcroparticles collide with housing 1 or cover 3 and are thereby removed from the ion stream . the reflected ions 8 are utilized for a coating on a substrate which is placed in area 2 , where there is a straight line between it and the hall layer , but no straight line between the substrate and the cathode surface . creation of a stable hall layer and prevention of plasma &# 39 ; s leaving along a magnetic field is possible only in case of an arched form of transversal magnetic field . an arched magnetic field is formed by a constant magnet 10 with poles 11 and 12 , arranged on both sides of cathode . on the ends of magnet the plates of ceramics 13 are installed to exclude longitudinal and cross shorting of the current - carrying hall layer , since an electron current along a magnetic field can destroy electric field in the hall layer and impair stability of vacuum arc . in the process of operation the ceramics surface turned to the hall layer will be coated by a coating of cathodic material . to prevent this coating become conductive , it is advisable to use a high - porous ceramics . presence of surface enables to keep the ceramics surface non - conducting for a long time , as deposition is produced in one direction . in the event a graphite cathode is utilized , simple ceramics can be used , as a graphite coating deposited during discharge possesses diamond - like properties , i . e . low conductivity . the cathode &# 39 ; s length is chosen from 1 cm to 5 cm . arc discharge in the source is triggered by a starting ignition pulse of the trigger device 14 ( fig1 c , 2a ). during pulse of the arc discharge cathode spots 15 ( fig1 c ) make a retrograde travel along an effective surface of the cathode 4 across a magnetic field from the triggering place 14 in direction of the current outlet 16 ( fig1 c , 2a , 2 b ). an average time of retrograde motion of the cathode spots from the triggering place to the opposite end of cathode is equal to operating pulse duration . the cathode spots , due to an arched form of magnetic field , travel , mainly , in the middle band of cathode and do not transfer beyond the bounds of the cathode effective surface . screens 17 ( fig1 c ), situated under a floating potential , force the cathode spots to be only within the cathode effective surface and thereby to protect the cathode inactive surfaces against an accident penetration of the cathode spots on them . the principle of operation of vacuum arc trigger device 14 is similar to electron disruption on ceramics surface . these devices are well known in the art ( see work [ 20 ]), therefore there details are not described in the present patent application . current - carrying electrode to the trigger device is executed via a vacuum inlet 18 ( fig1 c , 1d , 2 a , 2 b ). the anode 6 has a flat inverse segment bent in direction from cathode and down , which is divided into longitudinal sections 19 ( fig1 c , 1e ). it was done to enlarge stability of discharge and to increase plasma transport efficiency . behavior of current layer near the anode 6 depends on configuration of magnetic field b a in its proximity ( see fig1 d ), which to great extent is formed by a current flowing on anode . a cross direction of magnetic fields of the anode current b a in proximity of anode coincides with direction of magnetic field b of constant magnets near the surface of cathode ( see fig1 c ). electron current of arc in the hall current layer flows in general to the end of inverse segment , and further flows back along this segment and then right on the main part of anode . owing to this fact the hall layer can be extended , and , as a result of this , the number of ions reflecting from the hall layer to deposition area 2 will be enlarged , i . e . the plasma transport efficiency will be increased . longitudinal sections in the inverse segment of anode provide uniform distribution of current in width , eliminate distortion of total magnetic field under it and loosen deformation of field with time . geometrical dimensions of the plasma source depend on value of the used magnetic field , as the cardioid &# 39 ; s radius is inversely proportional to the magnetic field value . it was also experimentally tested feasibility of stable hall layer within range of b = 0 . 005 ÷ 0 . 05 ) t , that corresponds to value limits of the cardioid &# 39 ; s radius ( 80 ÷ 8 ) mm . thus , a real value of characteristic dimensions of the described source is within ( 18 - 160 ) mm . operating voltage on vacuum arc in the arched transversal magnetic field reaches 100 v at no - load voltage of 250 v , whereas these values are equal to 20v and 60v , correspondingly , for conventional vacuum arcs without magnetic field or in a longitudinal magnetic field . therefore knowledge and skill of designing accumulated during operating conventional vacuum arcs appeared to be insufficient for the given construction . coming of cathode spots into inactive surfaces of cathode results in occurrence of a parasitic arc discharge along magnetic field and in ceasing of basic discharge . to provide the construction with a safe protection , it was undertaken a number of additional measures , which enable avoiding occurrence of parasitic arc discharges , shunting the basic discharge : in particular screens 17 , which completely cover the cathode surface , leaving open only the effective surface , are made twofold from molybdenum ; besides screens , there is also the whole magnetic system under floating potential . a power supply unit for arc discharge ( fig1 c , 3a , 3 b , 3 c ) consists of a rectifier 20 , having no - load voltage of 250 v and current of from 100 to 300 a , and a power supply unit 21 for vacuum arc ignition device ( trigger device 14 in fig1 c , 2a ). the power supply unit of arc discharge is connected to the plasma source via hermetic current outlets 16 , 18 , and 22 ( fig1 c , 1b ). embodiments of the proposed sources of filtered arc discharge plasma , including two or more cathode units , arranged symmetrically on a circle and installed in vacuum chamber 1 , closed from one end 3 and open from another end for the area 2 , where workpieces for coating deposition can be mounted , are shown in fig3 a , 3b and 3 c . the cathode unit is a set of components ( elements ) described in the basic embodiment . the cathode unit ( fig2 a , 2b ) includes cathode 4 of consumable materials ; molybdenum screens 17 , isolated one from another and from all other components and being under floating potential during discharge ; constant magnets 10 ; magnetic poles 23 and magnetic core 24 . the device for ignition arc discharge ( fig2 a ) operates as an electron disruption on ceramics surface . at feeding an ignition pulse to electrode 25 ( fig2 b ), an electron disruption on surface of the insulator 26 takes place , initiating an arc discharge . insulator 27 serves for purpose of apparatus mounting . mentioned cathode units 28 ( fig3 a ) of the considered embodiment of source are used for mounting the plasma source , shown in fig3 a , with orientation of plasma flux along the axis of chamber 1 for depositing coating on various workpieces ( parts and units ) located below the chamber . cathode units 28 1 - 28 6 are arranged symmetrically on a circle . all cathodes are connected to one current outlet 16 ( fig3 a , 3b ) of power supply unit 20 and are triggered during operation in turn from a triggering unit 21 . such design enables to have large reserve of coating material , as well as allow loosening thermal behavior of cathodes , because in each cathode the interval between operating pulses increase in six times . central anode 6 consists of sections 29 , which reproduce the boundary form of plasma ( cardioid ) at the cathode , opposite which it is located . around each section of the central anode a magnetic field is formed during a discharge current running in it . direction of magnetic field of anode coincides with the direction of constant magnets . in principle ( in some specific cases ) the cathode units can be arranged nearby and placed at an alternate angle of one to another ( fig3 d ). in embodiment sowed in fig3 a area 2 with workpieces for coating deposition can be arranged at a distance maximal close to effective surface of cathodes , this enables producing a macroparticles - free high density flux of metal or carbon plasma on the surface of workpieces . in some cases it is advisable to use an embodiment , in which area 2 containing workpieces for coating deposition is arranged at a remote distance from the plasma source . in this embodiment ( fig3 b ) the cathode units can be mounted at the angle to the chamber &# 39 ; s axis of less than 90 °. this , to some extent , facilitates the arc discharge mode and enables operating at no - load voltage of 200 v . in this embodiment electric coil 31 serves to form a plasma flux coming in direction of workpieces for coating deposition . all cathodes are connected to the same outlet 16 of power supply 20 and are triggered during operation in turn by a triggering unit 21 . central anode 6 is divided into sections 19 . around the nearest to operating cathode sections a magnetic field is formed during a discharge current running along them . direction of magnetic field of the anode &# 39 ; s sections coincides with direction of constant magnets ( as in embodiment in fig3 a ). fig3 c illustrates an embodiment of the source of filtered arc discharge plasma with two or more cathode units , arranged symmetrically on a circle , placed at a remote distance from the workpieces for coating deposition , or comparatively small aperture of plasma flux output . in this embodiment the cathode units can be arranged at the angle to the chamber &# 39 ; s axis about 45 - 30 °. this enables operating at no - load voltage of 180 v . in this embodiment a set of electric coils 31 serves to form a plasma flux coming in direction of workpieces for coating deposition . in this embodiment electromagnets 32 are used to exclude impact of magnetic field of neighboring cathode units due to close arrangement . effective voltage pulses are fed to the cathode units 28 1 ÷ 28 6 in turn . the cathodes are connected through individual current leads to one power supply 20 and triggered in turn by a set of triggers 21 . to create an arched magnetic field , electromagnets 32 ( switching in turn with operating cathodes ) are installed . electromagnets are used in this embodiment to exclude impact of magnetic field of neighboring cathode units due to close arrangement . electromagnets 32 and magnetic cores 33 are installed outside the vacuum space . electromagnets and cathodes are connected in series to a power supply . at triggering of one of cathodes the arc discharge and magnetic field near this cathode occur simultaneously . a series connection , creating a back coupling of magnetic field with current discharge , facilitates triggering of arc discharge and provides stability of vacuum arc with a hall layer during operating pulse . a variable resistor 34 is used for adjusting a back coupling . the central anode 6 has a form of thin rod . a magnetic field is formed around the rod during discharge current running in it . direction of magnetic field of the anode coincides with direction of field constant magnets . fig3 c fig . illustrates an embodiment of the source of filtered arc discharge plasma with two cathode units , arranged parallel one to another and oriented so as the plasma flux from cathodes is guided to different directions . in this embodiment the cathode units can be arranged at an angle to horizontal line of about 45 - 30 °. this enables avoiding the cathodic material coming from one cathode to another . such arrangement of cathodes can be used , when presence of traces of other cathode material during coating deposition is forbidden . for example , during deposition of dlc coating the occurrence of titanium traces , used for coating the intermediate layers , is inadmissible . the cathodes 4 are connected to one power supply 20 and triggered in turn by a set of triggers 21 . the area of workpieces &# 39 ; s location is arranged in bottom part of the chamber . in top part of the chamber the means for entrapping macroparticles can be installed . the anode 6 has a form of plates bent in the shape of a hall layer . a magnetic field is formed around the plates during discharge current running in them . direction of magnetic field of the anode coincides with direction of constant magnets . fig4 a and fig4 b illustrate an embodiment of the source of filtered plasma of vacuum arc with cylindrical cathode and barrel magnetic field . the source is installed on a flange , connected to the vacuum chamber , not shown in drawing . a cylindrical cathode 4 is arranged on axis of axial - symmetric system and is surrounded by the anode 6 in form of a squirrel cage . a barrel magnetic field is created by a constant magnet 10 , installed inside cathode , and annular magnetic poles 23 1 and 23 2 , located in both ends of cathode . the cathode is isolated from the poles by means of ceramics inserts 35 and 36 . the cathode is connected to a minus terminal of the power supply 20 via a bushing insulator 16 . in the top part of cathode a vacuum arc trigger device 14 is installed . the principle of operation of this device 14 is similar to that of electron disruption on ceramics surface . these devices are known in the art , therefore their components and design are not given here [ 20 ]. current lead to a trigger device is executed via a hermetical current lead - in 18 . after discharge initiation the cathode spots 5 perform a retrograde motion along a circle on cylinder surface ( effective surface of cathode ). the barrel magnetic field sustains the cathode spots within effective surface . the cathode unit ( cathode 4 , trigger device 14 and annular magnetic poles 23 1 and 23 2 ) is mounted on a stainless steel pipe 37 , hermetically capped from one end and being under a floating potential . the packing elements , such as textolite rings 38 and rubber gasket 39 , provide a vacuum pipe - to - flange joint without electric contact . owing to this fact magnet poles will be under a floating potential and protect inactive surfaces of cathode from penetration of cathode spots . a discharge can exist in a stationary mode . duration and periodicity of operating pulses can be chosen depending on cooling conditions and deposition technological process requirements . a cylindrical constant magnet 10 and a system of magnetic field regulation 40 are arranged inside the pipe cavity . it enables in automatic mode to achieve maximal output of ion stream to the surface of substrate 2 in area at changing form of cathode in the process of operation . current supply to the anode 6 is carried out via a hermetical current lead 22 . vanes 41 ( fig4 b ) fastened of discs 42 and 43 ( fig4 a ). shape and angle of vanes &# 39 ; turn ( fig4 b ) are selected so as the surface ( in area 2 ) of substrate lies beyond the sight from the cathode spots , and at the same time the maximal number of ion trajectories terminates on the deposited surface . macroparticles trajectories a 1 , a 2 , a 3 ( fig4 b ) terminate on the vanes &# 39 ; walls . this enables to protect a workpiece against macroparticles and vapor at minimal losses of ion stream . it should be noticed that ions , flying from a cathode spot at the angle of ( 0 ÷ 120 )° to the surface ( i . e . ⅔ of total amount of ions ), reflect repeatedly from the hall layer , slightly moving away from the hall layer , and so almost all of them pass through the vanes . the remaining ⅓ part of ions partly pass through the vanes and partly come on the vanes at small angle to the surface . the arc discharge current flows along the vanes and creates a magnetic field parallel to the vanes &# 39 ; surface . this field is sufficient for magnetizing the electrons that let the ions , traveling at small angle to the vanes &# 39 ; surface , reflect from the surface . to intensify this effect the vanes are coupled in pairs on the top and fastened to the isolator on top disc 43 . a contact with a bottom disc 42 is performed by one vane of the pair . owing to this fact the current flows in the neighboring vanes in different directions , as in a loop , and in this case a magnetic field b a of current i a of neighboring vanes has the same direction , this provides better conditions for losses - free plasma flux flowing between the vanes . dimensions of the source , determined by an external diameter of anode , can vary within 30 - 250 mm and , respectively , minimal diameter of the inner cavity for deposition should be 35 mm . a power supply unit consists of a vacuum arc source 20 , designed for operation in a quasi - stationary state at no - load voltage of 200 v and discharge current of 20 - 300 a ; and a power unit for trigger device 21 . fig5 a , 5b and 5 c illustrate embodiment of the source of filtered arc discharge plasma with a conical cathode and toroidal magnetic field , intended to operate in a stationary mode or quasi - stationary regime . the source of filtered arc discharge plasma is arranged on one flange and installed in the center of a cylindrical chamber 46 , which in its turn is connected to a vacuum system , not shown in drawing . the cathode unit includes a conical cathode 4 , vacuum arc trigger device 14 , cooled current - carrying electrode 16 , cylindrical screen 17 and a magnetic system creating toroidal magnetic field in cathode area . the magnetic system consists of an annular constant magnet 10 , conical magnet pole 44 and annular pole 45 . the pole 45 is also a screw , which fastens the cathode 4 to current - currying electrode 16 to create electric and thermal contact . ceramic washers 47 1 and 47 2 isolate the pole 44 , that enables using it as a screen for protection of inactive surfaces of cathode 4 from the cathode spots hitting them . the cathode spots 5 ( fig5 b , 5c ) make a retrograde motion 15 in a circle . a toroidal shape of magnetic field b makes the cathode spots remain on effective conical surface of cathode . the hall layer 7 in a toroidal magnetic field has more complicated configuration than that in an arched magnetic field , and reminds a cardioid in section only passing through a cathode spot and parallel to drawing of fig5 b . fig5 b shows location of plasma flux 49 in the source , averaged per one turn of cathode spots . major part of ions 8 reflects in direction of workpieces placing in the area 2 . the principle of operation of the vacuum arc trigger device 14 is similar to electron disruption on ceramics surface . it is important to notice that the device is located in the area , from which the cathode spots are easily transferred in a toroidal magnetic field to effective surface of cathode and cannot return to the place of trigger device to destroy it . current supply to a trigger device is executed via hermetical current lead - in 18 . anode 6 is made in the form of truncated cone divided into strips 19 by grooves ( fig5 c ). behavior of current layer near the anode depends on configuration of magnetic field in its vicinity , which is formed by a current flowing on anode . a cross direction of magnetic fields b a of the anode current is perpendicular to direction of magnetic field b of constant magnets near the surface of cathode . electron current of arc in the hall current layer flows , in general , to the bottom end of anode strip and further flows back along this strip . owing to this fact , the hall layer can be extended , and thus to enlarge the number of ions reflecting from the hall layer to deposition area 2 . longitudinal sections in the anode provide occurrence of more intensive magnetic field only in the plasma flux area . the embodiments described above relate to use of the present invention in a physical vapor deposition system using the cathodic arc . it is important to note that the present invention is by no means limited to deposition of materials on substrates , but rather , the macroparticle filtering at small distance from the cathode aspect of the present invention has several beneficial uses besides deposition or coating application . for example , efficient macroparticle filtering enables an arc ion source to function as a high intensity electron source for heating workpieces prior to coating . additionally , this space - saving high electron density source is able to be used for excitation and ionization of vapor produced by an auxiliary evaporation source . when operating such electron source , high intensity , and low energy electron streams are capable of being produced . this heating capability may be exploited as a means for vacuum degassing components , surface annealing or other vacuum heat treatments . besides , effective filtering of macroparticle allows this arc plasma source to function as ion source of a cathode material for further acceleration in devices of ionic implantation , ionic alloying or ionic etching . thus , the present invention is by no means limited to use as a deposition system , but rather any situation , where efficient filtering of macroparticles from ions is beneficial , can utilize the present invention . furthermore , the embodiments described below relate to all deposition systems using consumable cathode materials . a proof - of - principle demonstration hall sheath plasma source designed , constructed and tested . the test device , illustrated in fig6 a , had the following characteristics : 2 × 4 cm cathode , of either graphite or ti arched magnetic field , with a field strength in the range of 16 - 21 mt at the cathode surface interchangeable cu strip anodes with various sizes , and the ability to adjust the anode position by bending . a 5 - element probe array , located below the cathode plane , so that plasma reaching it was bent through a trajectory of ˜ 180 °. the source was excited by a pulsed power supply , capable of supplying arc current pulses of up to 200 a , with a rise time of 0 . 2 ms , with a flat - top pulse of 7 ms duration . after preliminary experiments to establish the optimum operating conditions , the following was found : the photographically observed plasma shape corresponded to that predicted in theoretical models . ( fig6 b ) the arc voltage was 75 - 100 v . the floating potential of the probe elements was negative −( 50 ÷ 70 ) v relative to the cathode potential . optimum ion current to the probe was observed with a magnetic field of 18 - 21 mt . carbon ion currents of up to 16 a , corresponding to 6 - 8 % of the arc current , were measured at the probes , which negatively biased to −( 100 ÷ 150 ) v with respect to the cathode . we have experimentally checked the influence of ceramic plates installed at the magnetic poles ( fig1 c ). we found out that with the ceramic plates , the arc discharge stability and plasma transport efficiency become better to 20 - 30 %. at the experimental arc source of carbon ions with the transverse magnetic field , the plasma transport efficiency up to 70 % was achieved , that exceeds substantially the value obtained at the other types of arc sources . the best results have been obtained with the arch magnetic field optimized by its value and shape and also with the ceramic plates on the magnet poles and with the vacuum arc glowing rather stably . on a fig6 c it is shown : voltage on the discharge gap u arc and the discharge current i arc waveforms during a discharge with magnetic field b = 17 mt . also shown is the plasma efficiency experimental results and especially measurements of the fast ion flows and pictures of the glowing inter - electrode plasma of the vacuum arc in the transverse magnetic field prove the formation of the hall current layer . these results demonstrate that the hall sheath ion reflection principle can be used to construct an efficient , compact filtered cathode arc plasma source . 1 . sanders d . m ., “ ion beam self - sputtering using a cathodic arc ion source ”, j . vac . sci . technol . a 6 ( 3 ): 1929 ( 1987 ) 2 . falabella s . et at ., “ comparison of two filtered cathodic arc sources ”, j . vac . sci ., technol . a 10 ( 2 ), march / april 1992 , 394 - 397 . 3 . anders s . et al , s - shaped magnetic macroparticle filter for cathodic arc deposition ”, ieee transactions of plasma science , vol . 25 , no . 4 , august 1997 4 . d . a . karpov , “ cathodic arc sources and macroparticle filtering ”, surface and coating technology 96 ( 1997 ) 22 - 33 . 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