US3487000A - Sputtering apparatus - Google Patents

Description

De 30, 1969 D. G. HAJZAK 3,487,000

SPUTTERING APPARATUS Filed Feb. 27, 1967 3 Sheets-Sheet 1 Dec. 30, 1969 D. G. HAJZAK 3,487,000

SPUTTERING APPARATUS Dec. 30, 1969 D. G. H AJzAK SPUTTERING APPARATUS 3 Sheets-Sheet 5 Filed Feb. 27, 1967 United States Patent O U.S. Cl. 204-298 8 Claims ABSTRACT OF THE DISCLOSURE An ion-plasma confining enclosure, disposed within a larger enclosure, is used to increase ion intensity and uniformity over an ion target. The inner or plasma confining enclosure has two spaced-apart, parallel plates for the confinement of the ion plasma into a rectangular slab or sheet over the ion target. The enclosure also includes two confining side members to prevent plasma from escaping into the larger enclosure. The confinement of the plasma is produced by maintaining a positive charge on the confining enclosure of sufficient strength to repel incident ions from the plasma. The requisite positive charge results by electrically floating the plasma confining enclosure or, alternately, by biasing the enclosure slightly positive with respect to the mean plasma potential. Double opposing cathode and anode pairs are used to establish an ion plasma and to augment the confining enclosure in improving ion intensity and uniformity over the ion target.

BACKGROUND OF THE INVENTION This invention relates to the art of sputtering and, more in particular, to a sputtering apparatus which improves ion concentration and uniformity.

It is well known that sputtering of an ion target with ions to generate atoms or molecules of material produces extremely dense and coherent films on a substrate mounted n position to receive the sputtered material. Ideally, these sputtered films are of uniform thickness and are produced at a reasonably rapid rate. The rate of film deposit is a function of the sputtering rate of the target while uniformity of film thickness is a function of the uniformity of ion bombardment of the target. A considerable amount of effort is presently being devoted to enhancing film deposition rates and thickness uniformity. It is to the enhancement of film deposition rates and uniformity of film thickness that this invention is directed.

SUMMARY OF THE INVENTION The instant invention provides an improved sputtering apparatus which presents a relatively intense and uniform concentration of ions for the bombardment of an ion target, thereby producing uniform films on an appropriately mounted substrate as well as increased sputtering rates.

In one form, the invention contemplates an ion-plasma confining enclosure which includes first and second spaced-apart and parallel inner surfaces that form two of the inner boundaries of the enclosure. Preferably, the remaining boundaries are provided by two side plates which together with the parallel inner surfaces define a rectangular, box-like inner periphery for the ion plasma. Means are provided to evacuate the confining enclosure.. The apparatus also includes means for establishing and maintaining an ionizable atmosphere within the ion-plasma confining enclosure; these means may include, l"for example, a source of gas together with a valve for selectively admitting the gas to the enclosure. Means are also provided for establishing an ion plasma within the confining enclosure, such as an anode and cathode. Means ice for mounting an ion target within the enclosure parallel to the first inner surface as well as for mounting a substrate parallel to and -facing the target to receive sputtered material are also included. The means for mounting the substrate may be, for example, the enclosure adapted with a window over which the substrate can be positioned. Alternatively, the substrate may form a part of the enclosure or be mounted on a bracket or stand. In addition, means are provided for maintaining a positive charge on the enclosure which is sufficient in magnitude to confine the ion plasma, by repulsing ions, into a sheet-like form between the enclosures inner surfaces. 'Ihe plasma confining charge may be established by electrically floating the confining enclosure. An electrically floating state is achieved when the confining enclosure is electrically isolated from charge draining structure and accepts a positive charge from the ion plasma. The magnitude of the charge will increase until an equilibrium condition exists between the enclosure and the ion plasma. In general, equilibrium is established when the plasma confining enclosure is at a potential positive with respect to the systems cathode but slightly less than anode potential. Alternately, the repelling charge may be established by positively biasing the confining enclosure with an independent, positive potential source, preferably to a potential approaching that of the anode but slightly greater than mean plasma potential. The accumulated positive charge is limited to effect substantially plasma potential on the confining enclosure to prevent electron drain from the plasma.

The ion-plasma confining enclosure, through its positive charge, produces a sheetor slab-like plasma defined approximately by the inner geometry of the enclosure. In the sense used here, the sheet-like plasma has a thickness limited by the spacing between the upper and lower confining members. As is seen from the drawings, which depict relative dimensions of two preferred embodiments, the distance between the upper and lower confining members may be relatively large with respect to the length and breadth dimensions of the confining enclosure. The plasma is vrelatively uniform and dense over the surface of an ion target disposed within the limits of the enclosure parallel to its inner surfaces; therefore, rapid and uniform sputtering rates over the entire target surface are possible.

To augment the uniformity and increased plasma density produced by the plasma confining enclosures positive charge, a preferred embodiment of the invention employs yat least two cathode-anode pairs disposed to create a double opposed discharge within the enclosure. The double opposed discharge is produced by having the first cathode-anode pair create an electron attracting field acting in one direction within the confining enclosure while the second pair produces a field which attracts electrons emitted from its cathode in a direction opposite from that produced by the first pair. The anode-cathode pairs have independent power supplies to effect these opposed fields. The ion target is then disposed in the center of the plasma developed by the double opposed discharge in order to feel its maximum effect.

Enhancement of ion uniformity over the target is produced in one embodiment of the invention by an electron deflector or shaping means which has a slit-like opening that emits electrons as a sheet into the rectangular, boxlike plasma confining enclosure. These defiectors are preferably used with the anode-cathode pairs described. The enclosures positive electric charge still confines the ion plasma but cooperates with the slit-like openings and double discharge to increase its uniformity over the target.

It has been found, however, that good sputtering rates with uniform coatings can be produced without the slitlike electron deflectors. In this instance, electrons may be admitted into the rectangular, box-like enclosure through a standard cylindrical cathode shield. In short, the confining afiect of the positive electric charge associated with the enclosure produces a sheet-like plasma with its concomitant high ion density and uniformity.

The plasma confining enclosure is ideally suited for mounting the substrate. The substrate can form a part of the enclosure or it may be structurally independent. By providing an outer gas-tight enclosure for housing the plasma confining enclosure, a window may be provided in one of the plasma confining or inner enclosures members over which a substrate can be mounted. The substrates removal and positioning from outside the outer enclosure is then readily accomplished. Removal and positioning of the substrate is preferably provided by a frame in which the substrate can be mounted. The frame is held in position by a pair of guides disposed on one of the inner enclosures plasma confining members. The frame can be slid in the guides for the positioning of the substrate over the window. Linkage connecting the frame to outside the outer enclosure provides for substrate positioning without disturbing the vacuum environment. Such a linkage may be, for example, a rotatable shaft which extends through the outer enclosure and which is connected to a crank which in turn is connected to the frame. The ion target is preferably positioned opposite and parallel to the substrate. A target mount electrically isolated from the enclosure may be used to support the target within the enclosure a small distance from its bottom member. The spacing insures the immersion of the target in the sheet-like ion plasma and reduces sputtering from behind the target which would otherwise waste power.

To avoid the sputtering of undesirable material it is preferred to shield structural components of the sputtering apparatus from the ion plasma. The plasma confining enclosure itself, through its associated positive charge, is shielded from ion bombardment. Such items as electron deflectors and feed-through collars are normally grounded and therefore should be shielded to avoid their sputtering. Once again, the plasma confining enclosure serves as a shield against the sputtering of structure outside the enclosure and within an outer enclosure because of its confining influence on the ion plasma. Cathode shields or electron deflectors, which are normally exposed to the plasma despite the plasma confining enclosure, may be lined with a ceramic material to prevent the sputtering of its metallic structure. The anodes may serve as a barrier against ion escape from the ends of the enclosure or, alternatively, a shield may be used which is allowed to electrically fioat and develop its own repulsive positive charge.

The sputtering apparatus of this invention is ideally suited for the formation of uniform sputtered films on a substrate at a relatively rapid rate. The plasma confining enclosure intensifies the plasma and renders its ion intensity more uniform over the ion target byiforming the plasma into a sheet and preventing its escape into an outer enclosure if such is used. The use of a double opposed discharge increases ion density and uniformity over the target. Uniformity is enhanced because the discharges emanating opposite directions overlap and reduce areas of low ion intensity. The use of an electron deflector with a slit-like opening in cooperation with the confining positive charge of the enclosure also increases the plasma uniformity because of its tendency to enhance the sheet-like plasma.

These and other features, aspects and advantages will become more apparent from the following description, appended claims and drawings.

which includes a side elevation of a preferred plasma confining enclosure;

FIGURE 2 is an end elevational view of the plasma confining enclosure shown in FIGURE l;

FIGURE 3 is a plan view of the plasma confining enclosure shown in FIGURES l and 2;

FIGURE 4 is an elevational schematic, partly in half section, of an alternate embodiment of the present invention; and

FIGURE 5 is a fragmentry, perspective view of one of the electron deflectors and anodes shown in FIGURE 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGURE 1 shows a preferred embodiment 10 of the sputtering apparatus of the present invention. In general, the apparatus includes an outer cylindrical enclosure 12 in the form of a vacuum chamber which contains an inner, plasma confining enclosure 14. An ion plasma is generated within ion-plasma confining enclosure 14 by two pairs of independently powered cathodes and anodes. The first cathode-anode pair consists of anode 16 and cathode 18 which are electrically coupled to a power source. The second pair includes anode 20, shown in phantom, and cathode 22 which are coupled to an independent power source. Target 24 is mounted within inner enclosure 14 on target support assembly 26. Subtrate 28 is mounted for the receipt of sputtered material from target 24 in substrate mounting assembly 30.

Plasma confining inner enclosure 14 is depicted in the first three figures. The inner enclosure is a box-like Structure which defines an interior that confines an ion plasma into a sheet or rectangular slab. Upper plate 31 and parallel bottom plate 32 form two of the confining members of inner enclosure 14. The confining portions of the enclosure are completed by the two parallel side members 34 and 36. Plate 31 has a centrally disposed rectangular aperture 38 which forms a window for the passage of sputtered material from target 24 for the formation of a film on substrate 28 (the target and substrate are shown in FIGURE 1). Bottom plate 32 also has a centrally disposed, rectangular aperture 40 for the mounting of target 24 on target support 42 above the inner surface of plate 32. Enclosure 14 is electrically insulated from outer enclosure 12 in order to maintain it in an electrically floating state. This state is achieved when the members which define enclosure 14 accept and retain a positive charge from the ion plasma. The resultant potential of these members approaches anode potential and is therefore positive with respect to the systems electron emitting sources, that is, cathodes 18 and 22. The positive charge repulses positive ions from the plasma thereby confining the plasma within enclosure 14. In the embodiment shown in FIGURE l, an electrically floating state is achieved by mounting enclosure 14 in outer enclosure 12 through insulators. Thus, bottom plate 32 is connected to insulators 44 which in turn are mounted on brackets 46. Brackets 46 are secured to the inner wall of enclosure 12 through studs 48. The support provided through insulators 44 forms the only connection of enclosure 14 to grounded outer enclosure 12, the remaining parts of the enclosure lbeing supported by bottom plate 32. Thus, brackets 50 through 53 are connected to bottom plate 32 with upper plate 31 connected to these brackets. Side plates 34 and 36 are, in turn, supported by upper plate 31.

Anodes 16 and 20 are mounted to face the axis of the ion plasma contained in inner enclosure 14. Each anode has a centrally disposed, cylindrical opening for thek passage of electrons into the ion plasma from the apparatusv electron sources. Thus, opening 54 in anode 20 provides egress for electrons emitted from cathode 18. Each anode is electrically insulated from its supporting enclosure. Anode 16 is connected to support rods 55 which pass through, but out of electrical contact with, brackets 51 and 52 for receipt by insulator mounts 56. Similarly, anode 20 is held in place by support rods 5? which extend through brackets 50 and 53 for support in insulator mounts 58. The passage of rods 57 through brackets 50 and 53 is such as to avoid electrical contact. Insulator mounts 56 and 58 are secured to their associated brackets. Braces 59 between brackets 51 and 52 and brackets 50 and 53 are provided to increase the inner enclosures strength.

Cathode 22, in the form of a wire filament, is con tained in water cooled cathode housing or shield 60. The shield has a mounting flange 61 for connection to flange 62 on outer enclosure 12. The inside of shield 60 is bounded by a ceramic liner 63. Liner 63 extends through anode 16 and partially into the volume defined between plates 31 and 32. The ceramic liner reduces the impact of ions on the inside of the metallic body of filament shield 60 thereby diminishing the emanation of contaminants. Shield 60 is capped by closing plate 64. Power is supplied to 4filament 22 through leads 65 and -66 which pass through insulating sleeves 67 and 68. Cathodic filament 18 is also mounted in a water cooled shield which is denoted by reference numeral 69. Shield 69 is mounted to enclosure 12 through mounting flanges 61a and 61b and is capped by closing piece 64a. Ceramic liner 70 is disposed within shield 69 to avoid shield sputtering. Liner 70 extends through anode 20 for electron communication with the interior of enclosure 14. Leads 71 and 72 extend through sleeves 73 and 74 to provide current for filament 18. Power is supplied to cathode 22 by variable alternating current power source 76. Transformer 77 has its primary windings coupled to power source 76. The secondary windings of transformer 77 are connected to leads 65 and 66 for the supply of current to cathode 22. Variable alternating current source 78 is coupled through transformer 79 to lament 18. The coupling is through the secondary windings of transformer 79 which are connected to leads 71 and 72. Anode 20 is coupled through lead 80 to the secondary winding of transformer 77. Lead 80 extends through mating flanges 81, on outer enclosure 12, through insulating sleeve '82. Variable anode power source 84 is connected between anode 20 and the secondary winding of transformer 77 such that anode 20 is positive with respect to cathode 22. Anode 16 is connected to lead 86 which passes through sleeve 88 for connection to variable anode power source 90. Power source 90 is connected to the secondary winding of transformer 79 to maintain anode 16 positive with respect to cathode 18. As was previously mentioned, anode 16 and cathode 18 are electrically independent from cathode 22 and anode 20. These independent cathode-anode pairs create two distinct fields of force acting in opposite directions within enclosure 14 which enhances plasma density and uniformity over target 24 and thus the rate of deposition and the uniformity of sputtered coatings on substrate 28. Target support 42 is electrically coupled through target power supply 92 to the positive terminal of anode power supply l84 by lead 93. Lead 93 extends through mating flanges 94 on outer enclosure 12 for its connection to target support 42. Target power supply 92 is coupled in circuit such that target support 42 is negative with respect to the ion plasma in enclosure 14 for the attraction of its ions.

Target support assembly 26 comprises target support 42 which is mounted through insulators l96 to recessed bracket 98. Bracket 98 in turn is connected to plate 32. Insulators 96 maintain the electrically floating condition of inner enclosure 14 and the proper bias on target support 42. Bracket 98 has a centrally disposed aperture 100 which receives cooling lines 106 and 108 that continue as a coil in target support 42 for the latters cooling. Electrical lead 93 may be connected directly to the cooling lines as opposed to the direct connection to target support 42 illustrated. Because lines 106 and 108 are at target potential, they are insulated from remaining portions of the sputtering apparatus by insulator 104.

Plasma confining member 31 has a window 38 over which substrate 28 is mounted. Substrate 28 faces and is parallel to target 24 in order to achieve uniform film thickness. As seen in FIGURES 2 and 3, substrate 28 is mounted in substrate .mounting assembly 30 in the latters frame members 110 and 112 which together with frame members 111 and 113 constitute a slidable frame 117. Frame 117 is capable of sliding transversely on plate 31 for the positioning of substrate 28 over window 38. To this end, guides 114 and 116 slidably engage frame members 110 and 112. The substrate mounting assembly allows substrate 28 to be positioned from outside enclosure 12. This is shown in FIGURE 1 and is accomplished through control arm assembly 118 which consists of a crank 120 and a rotary shaft 122. Crank 120 has an arm 124 which is fixed to shaft 122. Arm 124 is connected through pivot pin 126 to following ar-m 128. Pivotable arm 128 is connected to the frame 117 of substrate mounting assembly 30 through insulator 130. Rotation of shaft 122, then, can be converted to translational movement of substrate 28 because of arm 128s connection to the slidable portion of the substrates mount, frame 117.

An ionizable atmosphere is supplied to enclosure 14 through gas supply line 130. Line 130 branches into two gas lines 132 and 134 which open into enclosure 14 between target 24 and anodes 16 and 20. Gas is admitted to lines 132 and 134 through valve 136. Valve 136 is connected to a source of ionizable gas such as argon (not shown). To maintain the electrically floating state of enclosure 14, lines 132 and 134 are insulated from plate 32 by insulating grommets 133 and 135.

As is usual in sputtering apparatus, means are provided for evacuating the enclosure in which an ion plasma is to be established. For this purpose, evacuation pump is conected through duct 142 to the interior of enclosure 12 and hence the interior of plasma confining enclosure 14. Pump 140 is shown schematically, for it may take the form of any of a number of prior art pumpdown systems, such as a forepump and a getter ion pump. l

Sight glass 148 is provided to allow observation of the sputtering process. Glass shield 149 is mounted in brackets 150 to protect the sight glass. Mating fianges 152 on enclosure 12 support sight glass 148 and shield 149.

FIGURES 4 and 5 depict an alternate embodiment of the present invention. This embodiment employs electron deflectors to cooperate with the plasma confining enclosure in the production of a sheet-like ion plasma within this inner enclosure. It also shows an alternate mode for maintaining an ion-plasma confining positive charge within the inner enclosure. Inner enclosure 170, rectangular and box-like in form, is contained within bell jar 172. Enclosure has an upper, horizontal, plasma confining member 174. In this embodiment, member 174 constitutes the substrate upon which a sputtered film can be deposited. Bottom plasma confining plate 176 is parallel to substrate 174 and supports target 17'8 through insulators 180. Side'plate 182, as well as a complementary side plate which is not shown, are disposed in parallel relation to each other outside of substrate 174. Thus, enclosure 170 has four sides for the confinement of an ion plasma. Standoff insulators 184 and 186, disposed at either end of the enclosure, support substrate 174 and, through brackets 188 and 190, bottom plate 176. These insulators are shielded from sputtered material by shields 192.

The outer enclosure, in the form of a bell jar 172, is mounted through seal 200 on feed-through collar 202. Feed-through collar 202 is annularly disposed on base 204. Duct 206 passes Vthrough base 204 and opens into the interior of bell jar 172 and the interior of plasma confining enclosure 170. Duct 206 is connected to a pumping system (not shown) for the proper evacuation of the enclosures. An ionizable atmosphere is established within enclosure 170 by gas supply 208 Iwhich is in commumcation with gas line 210. Valve 212 is in gas line 210 to provide control for the amount of gas admitted into the enclosures. Line 210 branches into two gas lines 214 and 216 which open into the interior of enclosure 170.

As in the previously described embodiment, the ion plasma established in the inner enclosure is produced and sustained by two independent cathode and anode pairs. Cathodic filament 220 is connected to the secondary winding of transformer 222. Transformer 222 has its primary winding connected to variable alternating current source 224. Anode power supply 226 is connected between the secondary winding of transformer 222 and anode 228. Power source 226 is provided to maintain anode 228 positive with respect to cathodic filament 20. Cathodic filament 220 is mounted in cathode housing 230 which opens into electron deflector 232. In like manner, cathodic filament 234 is coupled to a source of variable alternating current 236 through the secondary winding of transformer 238. Cathodic filament 234 is disposed in housing 239 which opens into electron deflector 241. Cathode 234s cooperating anode 240 is coupled to the cathode by connection through the secondary circuit of transformer 238. Anode power supply 242 is connected between cathode 234 and anode 240 to maintain the anode positive with respect to the cathode. Target 17-8 is biased negative with respect to an ion plasma devedoped Within enclosure 170 by connection to the negative terminal of target power supply 246. The positive terminal of target power supply 246 is connected to anode 240 to maintain the proper negative bias on the target.

The plasma confining action of enclosure 170 is provided by maintaining it at a positive potential with respect to the cathodes of the sputtering system. This potenial should approach the potential of the sputtering systems anodes. Thus, enclosure 170 is connected through variable resistor 250 to the positive terminal of anode power supply 242. Resistor 250 provides a load to reduce the potential on enclosure 170 which in this embodiment is electrically conductive.

Each of the electron defiectors illustrated in FIGURE 4 opens into enclosure 170 through a narrow slit which parallels substrate 174 and bottom plate 176. This is shown to best effect in FIGURE 5. Electron defiector 232 has a slit 252 which faces anode 240 and the interior of enclosure 170. The slit enables the electrons entering enclosure 170 to do so in a sheet-like form.

The ion-plasma confining enclosure performs its function by providing the means for maintaining a positive charge which suppresses the normal expansion of the ion plasma into :the outer enclosure. This charge can be created by maintaining the component parts of the enclosure in an electrically floating state or `by biasing them to a sufficiently positive potential with an independent potential source. Because the confining action is produced by a positive charge on the inner enclosure, the constituent parts of the inner enclosure or the enclosure itself need not be gastight. In addition, use of dielectric materials as the inner enclosures parts is also possible. Glass, for example, when exposed to the ion plasma will take on a charge and become electrically iioating resulting in the repulsion of ions which would otherwise strike the glass or escape into the outer enclosure.

The operation of sputtering apparatus will now be described with reference to FIGURE 1. Enclosures 12 and 14 are pumped down in a normal manner to a low pressure. An ionizable gas such as argon is admitted through valve 136 into ion-plasma confining enclosure 14. Cathodic filament 22 and its cooperating anode 20, as well as cathodic filament 18 and its cooperating anode 16, are energized. Target 24 is biased negative through target power supply 92. The resulting ion plasma generated within enclosure 14 will be in a sheet-like form having a relative uniform intensity over target 24 and a relatively high concentration of ions. The positive charge on side members 34 and 36 prevents the ion plasma from escaping into outer enclosure 12 while the charge on top and bottom members 31 and 32 performs a confining function and acts on the ion plasma to establish and maintain its sheet-like configuration. By providing two independently energized cathode and anode pairs, operative to draw electrons into the inner enclosure in opposite direction, the intensity of the ion plasma and the sheet-like form is enhanced. The sheet-like form is enhanced because the plasmas emanating from shields 60 and 69 diverge in a horizontal plane but overlap over target 24.

The invention has been described with reference to certain preferred embodiments. The scope and spirit of the appended claims should not, however, `be necessarily limited to the foregoing description.

What is claimed is:

1. In an apparatus for depositing thin films of material on a surface of a substrate which includes a first evacuable enclosure, means for evacuating said enclosure and providing an ionizable atmosphere therein, the improvement comprising:

a second evacuable enclosure located within and electrically insulated from said first enclosure and communicating with said means for establishing an ionizable atmosphere, said second enclosure having at least a first and a second side;

means for establishing an ion plasma within said second enclosure, said means including a first anode and cathode electrically coupled and disposed to cause an electron field in one direction through said second enclosure and a second anode and cathode electrically coupled and disposed to cause an electron field through said second enclosure in a direction opposite that caused by said first anode and cathode;

an ion target having a surface of material to be sputtered with the sputtering surface facing said ion plasma;

means for applying an ion attracting voltage to said ion target; and

means for mounting said substrate within said first enclosure with said surface of the substrate being spaced from and facing the surface of said target so that material sputtered from said target is received by said substrate.

2. A sputtering apparatus as recited in claim 1 wherein the apparatus includes:

means for establishing and maintaining a positive charge on said second enclosure of sufficient magnitude to at least confine the ion plasma therein into a sheet-like form between said target and said substrate.

3. A sputtering apparatus comprising:

(a) an enclosure adapted to confine an ion plasma, the enclosure including first and second spaced-apart members having substantially parallel inner surfaces;

(b) means for evacuating and establishing an ionizable atmosphere within the enclosure;

(c) means for establishing an ion plasma within the enclosure;

(d) means associated with the enclosure for establishing and maintaining a positive charge of sufficient magnitude to at least substantially confine the ion plasma therein and to maintain the plasma in sheet form between the first and second members inner surfaces;

(e) means for mounting a target of material to be sputtered in ion communication with and parallel to the sheet-like ion plasma;

(f) means for biasing the target to attract ions from the ion plasma; and

(g) means for mounting a substrate in position to receive sputtered material from the target such that the substrate is parallel to and facing the target.

4. The sputtering apparatus claimed in claim 3 wherein the means for maintaining a positive charge includes 'means for maintaining the ion-plasma confining enclosure in an electrically floating condition whereby the enclosure is capable of accepting and retaining a positive electric charge from the ion plasma that repulses its ions.

5. The sputtering apparatus claimed in claim 4 Wherein the means for establishing an ion plasma includes:

a irst' cathode and anode electrically coupled together and disposed to cause an electron attracting eld in one direction in the ion-plasma confining enclosure; and

a second cathode and anode electrically coupled together independently of the iirst cathode and anode and disposed to cause an electron attracting eld in the ion-plasma conning enclosure opposite that produced by the first cathode and anode;

the substrate and target mounting means being disposed to mount the substrate and target substantially at the center of the ion plasma.

6. The sputtering apparatus claimed in claim 5 Wherein the rst and second anodes are disposed across the ionplasma conning enclosure at either end thereof.

7. The sputtering apparatus claimed in claim S wherein the means for establishing an ion plasma includes an electron detlector for each cathode, each deflector having a slit-like opening extending transversely across and facing into the ion-plasma confining enclosure.

8. The sputtering apparatus claimed in claim 3 where- References Cited UNITED STATES PATENTS Maissel et al. 204--298 Anderson 204--298 Laegreid et al. 204--164 Theuerer 204-192 Vratny 204--298 Carlson 204-192- ROBERT K. MIHALEK, Primary Examiner U.S. C1. X.R.

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