Cathode sputtering apparatus

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CATHODE STUTTERING APPARATUS התקן התרוססות קתודה נ*

ABSTRACT A sputtering machine which has a rotary anode that isinsulated from its supporting structure and maintained ata voltage differing from that of the supporting structure.The temperature of the surface of the anode is controlledthrough circulating heat exchange liquid. 5072¾£

The field of the Invention is sputtering aid. the ^ apparatus Uhich la used In sputtering techniques. specificallythe invention Is concerned with sputtering machlnaa in Uhlah theanode is fotaiy and a flexlb&amp;amp;e substrate 1· led ever the anode andrequired to receive uftterials that are deposited thereon.

Apparatus such as described in 1.9· Patents 3.829.3721 3.884.787!tide Israeli latent 43$66)and 3.985.887 involved the use of segmentedtargets Which sere arranged to provide segmented beltf of plasma.,said targets being employed in apparatus uhloh comprises the environmentof the inventiah and indudss a pressure vessel having at least sueoatfaodin target nounted therein, a rotary anode mounted for rotation«!thin the vessel., a supply of flexible substrate such as polyester filmmounted in the vessel and a take*up mechanism for coated substratemounted also In the vessel· Suitable cdntrole are provided for operatingthe apparatus. The substrate is arranged to be led over the anodeand a spattering plasma established la the vessel, The material fromwhich the target Is made Is spattered onto the anode, bat since thesubstrate is carried on 1 he surface of the anode., the material iscoatedontothesubetratif.

Imdliary apparatus» supply means and cantrcls arefor furnishing the lonliing gas and its adsed componentsand for monitoring end cmrclllng the feed to the chamber{for ftrmlshing electrical energy to theapparatu® and monitoring

Its effects* far controlling and monitoring the a, 41 temperature, thickness of deposit, and many other param-eters; for driving the substrate in its path and moni-toring and controlling its tension; etc.

It has been found that for the deposit of certainmaterials, particularly photoconductors upon thin, flex-ible, transparent substrates, the conditions of depositioninclude, among others, the followings (a) The anode is required to rotate, (b) The power which is supplied is coupled to thecathode, anode and shielding in the vessel inan electrical circuit or network in which thecathode is at maximum negative voltage, theshielding is at ground potential and the anodeis at a potential that is also negative withrespect to ground, but to a much lesser degreethan the cathode, (c) The anode surface is required to be temperaturecontrolled to prevent excessive loss of heatduring sputtering,

Certain other requirements of the apparatus renderthe achievement of the above conditions very difficultto effect and these include: (d) Maintaining all of the supporting structureof the apparatus including the chamber walls,at ground potential for practicality andsafety, -3-

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(e) Maintaining the ends of the drum shielded tox prevent excessive deposit thereon, . י . . . . * % 4 :(f ) Moving the substrateicarrying portion or transportof the apparatus into and out of the chandler whensputtering Is coapleted« ..:·;··־·״· -׳ ; ί:־ :׳ ׳·::־־-;׳·״ ·׳·׳־׳7״ .The.:l^et^nentionod reqplr^aent is for the moat partunderstood to be necessary In th| case of a sputtering apparatustihiefr is to'produce quantities' «puttered substrate aml uhichof necessity־ is large and gjmbersome. One proposed solution tosuch problem la to motmjfc&gt;׳^he et$strate*canying portion on theapparatus od a carriage along with such . Of the controlandmeaeuring' equipment^, and to fix-the chamber and all of Its .attdJtiary apparatus to a support !fetch Is stationary· In and1case the targets: are secured within the Chamber :and .the high. tlth the chanfear,, along vith voltage connections are J..... the controls and instrumentation ^reforf hotranirert thiaan?engefasnt dose not take into .cjcmsideietion that theanode suetat a veltage.dlfferent from ground· ״־ :i · t

Ih UiS» patent 3,884*787 the.sifljstrate felons a.tortuous path about the anode and betroen the plural targets;and the anode.

The present ixcrantion ,provides a «puttering apparatue:.«heroin.a sputtering plasma condition in established ami maintained: betveen target means and [a retaxy anode mounted within &amp;amp; preaeurechamber defined within an electrically earthed motel vessel and adoaure therefor« flexible atrip substrate being transported • U · % over said rotary anode interior of the chamber throughthe sputtering condition, earthed shielding meanssurrounding at least the target means and leaving asputtering opening facing the anode and a high voltagesource coupled to said anode and target means and meansmaintaining the anode at a voltage which differs fromthat at the shielding means and the target means.

Referring now to the accompanying drawings:

Figure 1 is a side elevational view of the sput-tering apparatus of the invention in a closed condition,certain of the connections to exterior apparatus beingillustrated fragmentarily, indicating that such exte-rior apparatus is associated with the sputtering appa-ratus;

Figure 2 is a view similar to that of Figure 1 butin' which the sputtering apparatus is in an open condi-tion;

Figure 3 is a diagrammatic view taken generallyfrom the plane 3-3 of Figure 2 and looking in the direc-tion indicated to illustrate the path of movement of thesubstrate on the transport arrangement;

Figure 4 is a more or less diagrammatic perspec-tive view of the transport arrangement;

Figure 5 is a fragmentary sectional view taken gen-erally through the chamber of the apparatus along theline 5-5 of Figure 2 and in the indicated direction; ל.*י

Figure 6 is a fragmentary perspective view of gen-erally the same portion of the chamber as illustratedin Figure 5;

Figure 7 is a detailed sectional view taken throughthe lower part of the drum anode of the apparatus ofFigure 1 to illustrate the manner in which contact ismade with the same;

Figure 8 is a block diagram illustrating theelectrical circuitry of the sputtering apparatus ofFigure 1; and

Figure 9 is a sectional view, more or less diagram-matic, of a modified apparatus.

Two desired practical embodiments of the inventionherein are described. One is suitable for commerciallysputtering coatings on relatively wide strips of poly-ester film. The other is suitable for low productionor experimental work and sputters coatings on narrowstrips. The sizes of the two sputtering apparatusesare considerably different and the lengths of materialcapable of being coated without opening the apparatusalso differ. In the one instance the strip is of theorder of about 50 centimeters wide and in the other itis of the order of 10 centimeters wide.

The apparatus which shall be detailed initially isthe larger of the two and the more complex, but operat-ing and constructed in accordance with principles commonto those governing the construction and operation of thesmaller apparatus. 5 10 15 20 25

The sputtering apparatus illustrated in Figures 1through 8 is designated generally by the reference char-acter 10 and comprises a stationary base or supportingframework 12 which includes tracks 14 along an upperedge thereof; a component cabinet 16 mounted on rollersor wheels 18 engaged on the tracks 14; a pressure vesselor chamber 20 supported from the framework 12 by fixedstandards 22; and various other parts and structure tobe described. The cabinet 16 has a .transport arrange-ment 24 mounted to its left hand end supported on asuitable cantilever subframe 26 which is secured to theforwardly facing wall 28 of the cabinet 16.

The wall 28 mounts a circular sealing seat 30 andthe transport arrangement 24 and the subframe 26 thereforare dimensioned and arranged to be encompassed withinthe cylinder defined by a projection of the sealing seat30. The pressure chamber or vessel 20 is closed on allsides but its right hand end where a flange.32 is pro-vided adapted to be sealingly engaged against the seat 30.In Figure 1 the apparatus is shown in its closed condi-tion, the cabinet 16 having been rolled forward (to theleft) and thereby having inserted the transport arrange-ment 24 into the chamber or vessel 20, the joint repre-sented by the flange 32 and the sealing seat 30 being ren-dered hermetic by suitable gasket and locking arrangement. ־7- *

In Figure 2 the apparatus is shown in its open condition,the cabinet 16 and the chamber or vessel 20 being sepa-rated, giving access to the transport arrangement 24 andany substrate which is carried thereon and to the inte-rior of the chamber 20.

The transport arrangement 24 as illustrated does notshow driving and controlling mechanisms which are con-tained in the cabinet 16, these mechanisms for a greatpart being mounted on the rear of the wall 28. Theexact nature thereof is subject to wide variation andsuch details are not germane to the invention althoughpresumed to be required for the operation of the appa-ratus. The cabinet also contains considerable apparatusand structure needed for the total operation of theapparatus, including speed controls, driving mechanismpumps and conduits for handling heat exchange liquid, alarge number of measuring instruments for temperatures,pressures, currents, voltages, etc. The outer wall ofthe cabinet 16 is illustrated as having many push-buttons,meters, lights, and the like but only by way of represents-tion.

The chamber or vessel 20 is shown having gas connec-tions at 34 and 36, an electrical panel at 38, pipes andconduits at 40, electrical lines at 42, push-buttons,meters, etc. Viewing windows are shown at 44. All ofthese are also representative. The apparatus 10 requires -8- considerable control and monitoring well-known to thoseskilled in this art and the nature of measurement, opera-tion and control apparatus will vary with the requirementsof the apparatus.

Basically, there are needs to operate a sputteringmachine which must be furnished, controlled, measuredand often recorded. There are phenomena which must bemeasured and observed. The parameters are manifold.

High frequency energy must be furnished to the targets,requiring matching and control circuits, conduits, andoften cooling devices. In the latter respect, since thetargets are in the chamber or vessel 20, the coolantfor the targets must be provided in the chamber, andthe coolant must be carried and circulated. Thechamber has to be pumped down, requiring vacuum pumpswith accompanying regulation, controls and measurement;gases for ionization and background have to be intro-duced requiring regulation, control, measurement andproportioning.

It is assumed that those structures necessary foraccomplishing the functions for a sputtering machine as .described will be provided, hence there is no need toillustrate them in more detail and describe them further.

The cantilever subframe 26 is illustrated only inFigure 2 but should be understood to provide the supportfor the transport arrangement 24 although not illustrated ־9־ in other figures. There is an outer plate 46 and posts 48connected therewith and in turn connected to the wall 28but within the confines of the seat 30, All of the rollersand the drum to be described are journalled for roation,either driven or idling, between the plate 46 and the wall28.

In Figures 3 and 4 the transport arrangement 24 isillustrated, but without showing the journals and mount-ings and also without showing the drive, clutch and brakemechanisms which can be used therewith, all of the latterbeing contained within the cabinet 16 as explained. Thesubstrate which is to be coated is designated .50 and isshown to be transparent. In the preferred use of theapparatus, the substrate 50 forms the base for an electro-photographic film which has inorganic coatings sputteredthereon. In such instance the substrate 50 is syntheticresin sheeting such as polyester of about .005 to .010inch thick. Several hundred meters of this material canbe readily mounted on a spool or reel and contained withinthe apparatus 10 while being sputtered along its entirelength. Such a spool or reel is shown at 52 and comprisesthe supply within the apparatus, it is mounted on a shaft54 which is preferably driven by a suitable drive motorbut controlled by a tension clutch that receives feedbackinformation from speed measurement and control apparatus,all of which is contained in the cabinet 16, -10- %

The substrate strip 50 passes over an idler roller 56which guides the reach to the drum 58 which comprises theanode of the sputtering apparatus 10» Looking for themoment at Figure 8, it can be seen that the substrate 50passes around the drum 58 which is also rotating, nor־mally idling, in close proximity to the targets 60 and62 which are . located in the bottom of the chamber orvessel 20 as will be described and then passes upwardto another idler roller 64 from which it is led arounda take-up roller 66 that is driven by suitable drivemotors from the interior of the cabinet 16. Since thediameters of the rolls of substrate on the supply reel 52and the take-up roller 66 vary inversely to one anotherduring sputtering and it is essential that the speed ofmovement of the substrate 50 relative to the targets beuniform and carefully controlled and a suitable variabledrive to effect this must be provided.

The targets 60 and 62 are shown in Figures 5, 6 and 8.The chamber or vessel 20 is in the form of a cylindricalshell 68 with an end bell 70 that couples with the con-duit 36. All of the parts of the chamber or vessel 20are formed Of stainless steel and maintained at groundpotential for safety. Fabrication of the vessel fromthis material is relatively simple compared to makingit from glass or other insulating materials. The tar-gets 60 and 62 are mounted in target assemblies 72 and 74 -11־ * respectively that comprise shields 76 of metal that aremechanically mounted to the bottom of the shell 68 bythe brackets 78 and cooled by coolant circulated throughthe walls of the shields 76. The conduits for the cool-ant are passed through the shell 68 by way of housings80 that also provide for passage of electrical coupling .elements for connecting the targets to the power supply.The positions of the targets relative to the drum 58are adjustable as the targets are consumed. Adjustablestructure whereby such adjustments can be effected may becontained in the housings 80 or can be effected by adjust-ments on the brackets 78.

Each target 62 is formed of a plurality of plates orplaques such as best shown in Figure 6 at 82 which arecemented on a suitable metal backing plate, usuallystainless steel. The target plates 82 can have theirsurfaces facing the drum 58 flat planar or arcuatelyplanar. They are arranged generally to define a cylin-drical surface that is coaxial with the drum 58 when thedrum is in position adjacent the targets and the appa-ratus 10 is closed. Each target 60 and 62 is spacedfrom its shield 76 leaving a space framing itself.Background gas is introduced into the hollow behind eachtarget by way of the pipes 84 that pass through the wallof the shell 68 and emerge from the spaces around thetargets to bathe the surfaces of the targets. -12- %

Preferably, the target plaques are formed as sinteredmembers of the material which is to be sputtered.

Between the target assemblies there is a standard86 which mounts one or an assembly of brushes or wipercontacts at 88. These connect to a part of the power sup-ply electrical circuit by electrical lines passing throughthe shell 68 as will be explained. Preferably these con-tacts are mounted with resilient supports spring pressingthem to the right as viewed in Figures 2 and 7. Theymust be insulated from the shell 68 as are the targets60 and 62.

The details of construction of the drum 58 are beingpassed for the present to explain the operation of thecircuit of the power supply that is used in the apparatus10. Reference now is made to Figure 8 for an explanationof the circuit of the power supply. The construction ofthe drum 58 is better appreciated when one understandsthe power circuit.

In Figure 8, the power or energy supply for theapparatus 10 is shown in most basic diagrammatic form.There is a high voltage power source shown at the leftas the block 90. The source 90 is coupled to the appa-ratus 10 by way of a matching network 92 that is shownhaving two lines at 94 and 96 for its output. The high-est voltage, say of the order of 3000 volts at a fre-quency of 13.56 megahertz appears at the line 94 and -13- t is applied to the targets 60 and 62, appearing as avoltage to ground. The line 96 is at ground potential.All of the shielding in the apparatus 10 (representedhere only by the drum 58, shields 76 and the drum shields)is at ground potential, but the drum itself is not.

Thus, the output from the matching network 92 is appliedto a voltage divider which comprises in this simple ex-ample two impedances Zl and Z2 connected across the lines94 and 96. In the practical example these are capacitorsand a part of the voltage divider can take into accountparasitic capacitance paths which could have some sig-nificance at this frequency. The lines can be high fre-quency plumbing, coaxial cable, shielded leads, etc.

The voltage is divided in accordance with the re-spective reactance of the two impedances Zl and Z2. Thedrum 58 is connected by way of a line 98 to the terminal100 between the impedances Zl and Z2. In order to enablethe drum 58 to rotate, the contacts 88 previously de-scribed are provided to enable the drum to remain at avoltage which is not ground. The electronic effect insputtering in apparatus 10 is that of a diode, such thatthere is an effective rectifying action. The cathodesare the targets 60 and 62 and these are maintained at avery high negative voltage, which for the example givenis -3000 volts. This is below ground which assumes themaximum positive voltage for the system, being zero volts. -14 ' r\ t

Conventionally, the anode is at ground potential andthe substrate is laid upon it. Herein, only the shield-ing is at ground potential. The anode is the drum 58and it is maintained at a voltage which is also below5 ground, but not to the same extent as the targets 60 and 62. In the practical example, the voltage of the drumwas maintained at some value about 50 volts or less belowground, that is -50 volts. This was achieved by properdesign of the voltage divider string Zl and Z2 and other10 parts of the circuit. Those skilled in designing power supplies for r.f. energized sputtering apparatus willunderstand this type of circuit and the nature thereof.

The drum 58 is required to be rotary, it is required to be made out of metal so that it can be easily fabri- 15 cated and will have the necessary strength to stand up to the requirements of the sputtering apparatus, it is required to be journalled using mechanically durable bear- ings, shafts and supports, and yet at least its outer skin is required to be at a voltage that differs from its sur- 20 roundings. Another requirement for the drum is that its outer skin must be subjected to temperature control by means of heat exchange liquids. Thus, in the practical example of the invention, it was deemed necessary to heat the outer skin of the drum by means of oil to main- 0 25 tain the same at a temperature of about 150 C. -15-

All of these requirements are achieved using the drumas shown in Figure 7. The body of the drum 58 is formedof an inner metal cylinder 102 with end flanges or rings104 welded thereto. The metal end caps or discs 106 aresecured to the -cylinder 102 by the circumferentiallyspaced screws 108. An outer coaxial metal cylinder .110forms the circumferential skin of the drum 58 and it iswelded to a telescopically arranged coaxial metal cylinder112 of smaller diameter to form a chamber 114 betweenthem. The cylinders 110 and 112 are connected by metalend rings. 116 welded in place at each and the left handmetal end is exposed as shown.

The chamber 114 carries the heat exchange liquid 118either in a bulk form which fills the entire chamber or byway of coils wrapped around the interior of the chamber(not shown). These are connected by way of suitableconduits such as shown at 120 to the hollow shaft 122 byway of which they are connected to a source of such liquid, conduits are shown at 120'. Since the liquid / will normally be oil or other insulating fluid there isno problem with providing an insulating coupling orcouplings for the conduits 120 or 120' so that the skin110 is electrically insulated from the remainder of thedrum 58, the shaft 122, etc.

The rings 116 and the discs 106 are spaced radiallyapart to provide an annular space at each end of the.יל י -16- ׳ *־" drum 58 as shown at 124. A cylinder 126 of polytetrafluoroethylene or other stable insulating material is formedas for example by machining and is positioned betweenthe cylinder 102 and the cylinder 112. it has its endsmachined to a lesser thickness than its body so that theshoulders 128 and 130 are formed. The resulting axialends 132 are made to have a thickness the same as theannular space 124 and the axial length of the cylinder 126is made to be identical to the overall length of the drum58 so that it is flush with the outer ends of the discs106 and the rings 116. There is thus provided a compos-ite cylindrical member in which the outer skin 110 isinsulated from the remainder of the drum 58. The drumis held in assembly by a plurality of screws 134 thatengage through washers 136 of the same insulating mate-rial and are spaced circumferentially around the endsof the drum. The washers 136 are set into deep recesses138 that are bored into the ends of the drum 58, eachrecess 138 having a portion thereof in each of a disc106, a ring 116 and an axial end 132. In this way, inaddition to the washers 136 and screws 134 clamping theparts together axially, the parts are locked againstrelative movement circumferentially.

The ring 116 on the left hand end of the drum 58 islocated in such a manner that when the apparatus 10 is in -17- closed condition, the contacts 88 will engage and wipethe same thereby establishing electrical contact there-with. ' .

The ends of the drum 58 are shielded as shown at140, 142, 144 to prevent material from being sputteredonto any other parts of the drum while the substrate 50is passing around the bottom of the skin 110 and beingcoated thereat. The plasma representing the sputteringis indicated at 146. Such shielding is supported fromthe wall 28 and subframe 46 as for example by connectingbrackets indicated at 147 in Figures 2, 3 and 4. Itshould be clear from Figure 7 that the shielding members140, 142 and 144 close off the ends of the drum 58 exceptto allow passage of the substrate strip 50 and to providean opening to admit contacts 88 to wipe the ring 116.Also, these shielding members are at ground potentialand nowhere touch the drum skin 110. A modified form of the invention is illustrated inFigure 9 which is especially useful for small projects.The sputtering apparatus 200 comprises a chamber 210which has a cover member 212 adapted to be engaged ontothe flange 214 of the chamber 210 and locked in place.Sealing is provided by the gasket 216 engaged betweenthe flange 214 and the flange 218.

The cover member carries a supply reel 220 and atake-up reel 222 mounted on shafts 224 and 226 -18- -יו respectively. The shafts are driven by motors 228 and 230respectively controlled from the exterior of the appa-ratus 200.

The cover 212 mounts a coupling 232 from which thedrum 236 is suspended. In this case the drum is metaland the entire drum is insulated from the chamber 210and the cover 212 by suitable insulation provided in thecoupling 232. It is mounted on a shaft 238 which passesthrough the coupling 232 driven by the motor 240 mountedon the top of the cover 212. A sprocket chain andsprocket wheels such as 242 provides the coupling to theshaft 238 without short-circuiting the drum to ground.Suitable insulation is provided for this. A ring 244 onthe shaft 238 connects to the drum 236 electrically andis isolated from all other parts of the apparatus 200.Electrical connection 246 with the contacts 248 corre-spond to the line 98 and the contacts 88 of Figure 8.

The drum is hollow and has a central hollow conduit250 providing coaxial chambers 252 and 254 which connectwith the pipe 256 that passes around the skin 258 of thedrum 236 on the interior thereof. Heat exchange liquidenters and circulates by way of the chambers 252 and 254.

At the top of the view one can see where suitable cou-plings are attached to enable rotation of the shaft 250through the use of rotary fluid couplings. These neednot be shown. ־19־ ׳&lt;

The target 260 in this apparatus 200 is a simple discof the photoconductive material mounted on a holder 262which is connected by way of the member 264 through thewall of the chamber 210 to a source of high voltage radio5 frequency 266. There is no need to show the circuitry of

Figure 8 since it is assumed to be used in connectionwith the apparatus 200.

Shielding at 268, 270 and 272 at ground potential isprovided adjacent the drum 236, the drum mounting on the10 shaft 238 and the target 260. Sputtering plasma is pro- duced in the same manner as in the case of the apparatus10 through the use of suitable high frequency energy anda suitable background gas admitted as for example by theconduit 274 in the gap 276 between the skin 258 of the15 drum 236 and the face of the target 260. -20-