GB2051877A - Magnetically Enhanced Sputtering Device and Method - Google Patents

Abstract

Magnetically enhanced sputtering device including first and second magnets disposed adjacent opposite sides of the target where one of the magnets projects a field over the target surface and through the magnet on the other side, the magnets preferably comprising contacting layers of oriented ferrite impregnated tape. Included is magnetic structure for establishing a magnetic bridge circuit for sputtering magnetically permeable targets. Also included is magnetic structure where a third magnet is disposed beneath the cathode and the fields generated by the first and second magnets pass through the third magnet to enhance the parallelism of the field with respect to the target.

Description

SPECIFICATION Magnetically Enhanced Sputtering Device and Method Background of the Invention This invention relates to magnetically enhanced sputtering devices and, in particular, to improved means for implementing the magnetic enhancement of such devices.

Generally, crossed magnetic and electric fields are established in such devices. The electric field extends between an anode (which may be the chamber wall) and a target, which is typically at cathode potential and in circuit with the anode, whereby electrons are removed from the target.

The removed electrons ionize gas particles to thereby produce a plasma. The ions are accelerated to the target to dislodge atoms of the target material. The dislodged target material then typically deposits as a coating film on an object to be coated. In order to improve the sputtering rate at low gas pressures, the crossed magnetic field is provided to lengthen the path travelled by the removed electrons and thus enhance the ionizing efficiency of the electrons. In order to further improve the ionizing efficiency of the electrons, a closed plasma loop is preferably established so that a Hall effect current circulates around the loop.

The ionizing electrons tend to concentrate in the regions where the magnetic lines of force are parallel to the target surface. In prior art devices which employ a closed plasma loop, the region over which the magnetic lines of force are parallel to the target surface tends to be rather small thus promoting non-uniformity of target erosion and inhibiting the realization of higher sputter rates.

Figures 1A and 1 B illustrate one technique which was attempted (but not published) by applicant to provide a uniform, parallel magnetic field with respect to the target surface. In these Figures, the target 10 has a configuration of an endless belt and may be provided on a cooling system 12 having a rectangular, ring-like configuration as indicated in Figure 1 B. Magnets 14 are provided inside the belt-like target 10, all of which are polarized in the direction indicated in Figure 1 A. Pole plates 1 6 are connected to opposite ends of the magnets where one of the plates 1 6 is shown in disassembled relation in Figure 1 B.

The resulting plasma is trapped such that it circulates in the oval, belt-like pattern, sputtering from the top, bottom, and ends of the target. The magnetic field seems to emanate from the steel pole plates as if the magnets were adjacent the target. The erosion pattern is deepest in the center, and falls to zero at the edges. This is at least partially a function of electrostatic effects and parallel magnetic field intensity. The steel pole plates are able to radiate lines of force into space such that as one moves perpendicular to the pole plates and parallel to the target, the flux is strongly a function of distance from the pole plates. Thus, the field is non-uniform in this respect.

It is thus one primary object of this invention to provide a solution to the above problem and, in particular, an improved magnetically enhanced sputtering device and methods employing a uniform magnetic field which is parallel with respect to a large portion of the target surface.

It is another primary object of this invention to provide an improved magnetically enhanced sputtering device and method for sputtering magnetically permeable targets which may be relatively thick.

Other objects include the provision of (a) very high percentage target utilization while maintaining high sputter rates; (b) very high power densities for very high rates; and (c) smaller target areas than previously practical for minimizing target inventory of expensive materials.

Other objects and advantages of this invention will be apparent from a reading of the following specification and claims taken with the drawing.

Brief Description of the Drawing Figures 1 A and 1 B are perspective and crosssectional views of an earlier, non-published embodiment designed by applicant for producing a uniform, parallel magnetic field with respect to a target surface.

Figures 2 and 3 are perspective and crosssectional views of an illustrative embodiment of the invention where magnetic blocks are employed to produce a uniform magnetic field parallel to a target surface.

Figures 4A and 4B are cross-sectional and perspective views of a further illustrative embodiment of the invention where magnetic loops or rings are employed.

Figure 5 is a further illustrative embodiment of the invention for sputtering small targets.

Figures 6 and 6A are further illustrative embodiments of the invention where the orientation of the flux within the field establishing magnets is different from that in Figure 3.

Figure 7 is a diagram illustrating the difficulty associated with establishing an appropriate crossed electric-magnetic field over a magnetically permeable target.

Figure 8A is a further illustrative embodiment of the invention for sputtering magnetically permeable materials.

Figure SB is an illustration of electrical analog of the embodiment of Figure 8A.

Figures 8C-8G are illustrative embodiments of magnetic bridges for use in the present invention.

Figures 9A and 9B are plan and cross-sectional views of a further illustrative embodiment of the invention where the magnetic structure is generally disposed within the cathode.

Figure 10 is a cross-sectional view of a further illustrative embodiment of the invention where a non-sputtering plasma return path is provided over the target surface.

Figures 1 1A and 11 B are plan and crosssectional views of a further illustrative embodiment of the invention where coplanar loops are employed.

Figure 12 is a cross-sectional view of a further illustrative embodiment of the invention where auxiliary magnets are used to strengthen the field.

Figure 1 3 is a further illustrative embodiment of the invention.

Detailed Description of the Preferred Embodiments of the Invention Reference should be made to the drawing where like reference numerals refer to like parts.

In Figures 2 and 3 a magnetic field is generated by block magnets 20 and 22, each of which may comprise a plurality or stack of overlapping strips 24 where each strip preferably comprises oriented ferrite impregnated plastic or rubber tapes such as those manufactured and designated as PL-1 .4H by the Minnesota Mining and Manufacturing Co. There is preferably no magnetic connection between the outboard ends 28 and 30 of the magnets. The field between the faces 34 and 36 of the block magnets is stronger than if a steel "U" 32 (shown dotted were connected between the outboard ends. The field is also unique in that it is almost perfectly constant from the center of face 34 perpendicularly through space to the center of face 36.

In Figure 3 it can be seen the lines of force that connect faces 34 and 36 are very nearly parallel and are substantially, totally encased between the portions of the field that are returning to the opposite ends of the respective block magnets.

Thus there is essentially a fixed number of lines of force per unit area in substantially all of the center space. The result is an extremely uniform field there. Once this band of flux is trapped, it is possible to increase or decrease the distance between magnets 20 and 22 without changing the flux density (within limits). The magnets can even be tipped or bent so the center pattern arches up or down and the flux does not change significantly. It appears the protective return flux loops may make this phenomenon possible.

Separate auxiliary magnets may also be employed, as will be discussed in more detail hereinafter with respect to Figure 12, making more of the central magnet flux available to the parallel beam. The trapped band of magnetic flux thus permits the realization of unique behavior.

A unidirectional plasma stream may be established across the surface of target 37. Thus, the central target area of limited erosion, which tends to occur in the prior art as discussed with respect to Figures 1-3 in the aforementioned co-pending U.S. Applications, is eliminated. Also it is possible to eliminate corners which fail to erode due to the curving plasma stream not being directable into a corner. Very near 50% target utilization is typically realized without the parallel uniform field provision of the present invention.

With this provision, the utilization becomes strongly dependent upon the target hold-down method, etc., and has practical values as high as 90%. Target 37 can be fed up into the parallel beam region and all but the clamped part is used.

The clamp can provide cooling, etc.

Instead of block magnets 20 and 22, loop magnets 38 and 40 can be used as shown in Figures 4A and 4B. This permits the magnets 38, 40 to be slipped over cooled target 42 or the target to be slipped through the magnets. As target 42 is eroded to the limit, it may be relatively slipped through the magnet to expose fresh target as indicated in Figure 4A. This permits very near 100% target untilization.

Further, target may be provided on the bottom of cooling plate 44. The loops 38 and 40 would then provide both top and bottom sputtering for higher production rates and efficiency. The power efficiency would then be typically 2 to 4 times that of a conventional magnetron cathode. In embodiments where target is provided both at 42 and on the bottom of cooling plate 44, the cooling plate, for purposes of the following claims, may also be considered part of the cathode.

If only the top face is sputtered as in Figures 4A and 4B, conventional power efficiency can still be attained. Sputtering of magnet loops 38 and 40 is prevented by shields 48, which are maintained at anode potential. Confinement of electrons within the plasma is assisted by shield 54, which is maintained at cathode potential where the orientation of the magnetic lines of force with respect to the surface of shield 54 is preferably 900 or more. Sputtering of the upper inside faces 56 and 58 of magnets and of shield 54 is substantially avoided due to the perpendicular orientation of the lines of force with respect to these surfaces.Anode 60 establishes the requisite electric field at the return portion of the plasma loop while the chamber wall (not shown) or some other anode means above target 42 may be employed to establish the requisite electrical field above target 42, where anode 60 may be a rod as shown in Figure 4A.

Generally speaking, reference has been made above to the division of the cathode structure into sputtering and non-sputtering sections. It can be defined to a resonable degree the situations where sputtering does not occur to meaningful extent even in the presence of an intense plasma discharge. First, in the absence of momentum and centrifical effects, sputtering will not usually extend beyond the areas where lines of force form an angle of about 900 or more with the target surface.

The foregoing is discussed in the aforementioned co-pending applications where, for example, the use of such angles permits the maintenance of intense discharges without sputtering an angled element. Properly shaped target clamp rings are an example of such elements.

Second, physical separation between the plasma and the target surface can provide very delicate separation between sputtering and non sputtering plasmas. Such a separation is not usually achieved in magnetron technology such as that shown in Figures 1-3 of the aforementioned co-pending applications, in that the trapping magnetic field extends up from the target surface, the field becoming ever stronger as one moves closer to the target surface. When that relationship with the surface is avoided and a magnetic field parallel to the target surface is provided in accordance with the present invention so that its maximum intensity appropriately separates from the target surface, it is possible to approach non-sputtering conditions. The plasma tends to center in the intense field region.If the mean free path of ions from the plasma that are accelerated toward the target is short compared with the distance to the target, only rather low energy ions will reach the target surface. The ions will have lost most of their voltage caused energy through repeated collisions. When the energy of these ions is below the sputter threshold value, no sputtering can occur. To sputter, individual bombarding ions must possess sufficient energy to knock individual target atoms out of the target structure. When they fall below this energy, they provide only a heating action and possibly an increase in the electron emission.

In an intentionally non-sputtering area, an attempt should be made to (a) keep all cathode potential items at 900 or more with respect to the lines of force such as illustrated at shield 54 of Figure 4A and (b) provide a large separation relative to the mean free ion path of items not at these angles with respect to the lines of force.

Providing higher gas pressures in these areas also makes the distances less critical. In tunnel systems, such as that of Figure 4A where the plasma passes over the top and under the bottom of the target, this can be achieved by introducing the sputter gas via the tunnel as illustrated in Figure 4A where gas source 61 is connected to the tunnel 63 by line 65, the gas being removed by pump 67 which is connected to the space over target 42. As is conventional, source 61 and pump 67 are located outside the vacuum chamber containing the structure of Figure 4A.

The introduction of sputter gas into the tunnel gives high tunnel pressure while permitting much lower pressures at the sputter areas of target 42.

Further, this further inhibits contamination of the plasma with non-target ions during its passage through the tunnel as it returns to the target surface.

In accordance with a further aspect of the invention, it is possible to narrow the target area as in Figure 5 such that small inventories of expensive target materials may be maintained.

Thus, a small volume target 62 may be clamped as shown in Figure 5 by a cooling member 64 to effect sputtering thereof, the magnetic lines of force being substantially parallel over the entire surface of the small target and cathode potential surfaces 69 and 71 being provided to assist in plasma confinement.

Magnet orientation can be changed 900 adjacent target 70 so that the field projects out of one end of magnet 66 and thence over the target to magnet 68, as shown in Figure 6. The orientation of the magnets may also be changed to angles between those shown in Figures 5 and 6. Even tipping outboard (where the separation between the upper portions of loop magnets 66 and 68 is less than that between the lower portions thereof) can provide some effective field projection. In fact, any of the field projection methods of Figures 2-6 can be employed without concern about center void problems of the type hereinbefore discussed with respect to Figures 1-3 of the above mentioned co-pending applications. Thus, by changing the direction of the rotational axis, this concern has been eliminated. It is also possible to remain uniplanar with an intentional center void area.

Further, as can be seen in Figure 6A, the loop magnets 66 and 68 of Figure 6 can be bent 900, for example, as indicated at 71 and 73 whereby target 70 can be moved under the control of moving means 75 through the sputtering plasma indicated at 77. The return plasma indicated at 79 is removed from the path traversed by the target and hence does not sputter the target. This is in contradistinction to the embodiment of Figure 6 where the target should not extend below the loops 66 and 68 into the return plasma less the target be sputtered both by the sputtering portion of the plasma above the loops 66 and 68 and by the return plasma.

Reference should now be made to Figure 7 regarding magnetically enhanced sputtering of magnetically permeable materials in accordance with a very important further aspect of the invention. When a permeable target is placed over the conventional magnetic structures, the preferential flux flow is via the target, it not being projected through and above the target to provide the required flux pattern above it. Limited sputter rates have been obtained by using very thin target material and/or placing this in only the "race track" area of the target, which is not an adequate solution to the problem.

If it is assumed the structure in Figure 6 is fitted with a permeable target 72, the field picture shown in Figure 7 results. The high permeability of target 72 causes the flux that previously arched over the target area to be drawn into the target.

The parallel field at the critical height of 1/8 3/4" above the target surface is almost zero rather than the 80-100 gauss level typically needed for support of a plasma. Thus the embodiments illustrated thus far are not directly applicable to the sputtering at high power levels of high permeability materials.

The permeability of target 72 may be seen as conductance for magnetic lines of force. Flux only goes where it wants to go or is forced to go. The question thus arises as to how the environs of high permeability target 42 can be changed such that the flux that must be above it cannot enter the target. The classical terminology of magnetics is less familar than that of electricity. Hence, there is illustrated in Figure 8B an electrical analog of a magnetic solution to the problem shown in Figure 8A. If it were an electrical field that target 72 were to be inserted into without substantially disturbing it, the potential of the target would have to be adjusted to be the same as that of the field at the position the target was to occupy.It is therefore necessary to place the target at a "magnetic potential" the same as that midway between the north pole magnet 66 and the south pole of magnet 68. This is effected by magnets 74 and 76 which stop the flux flow through the "meter" (that is, target 72) in the bridge circuit where the magnets are preferably connected by pole plates 75 and 77. A flux field is thus established above permeable target 72 that is almost totally oblivious to the target's presence just as balanced bridge 78 of Figure 8B is oblivious to the presence of meter 80.

This above may be also viewed as removing the flux paths from point A of magnet 66 to point B of magnet 74 and from point C of magnet 68 to point D of magnet 76, just as creating equal electrical potentials at E and F in bridge 80 prevents current flow through meter 80. There is some small difference in "magnetic potential" over the width of target 72 so that the field shape is not quite perfect over the target, but the improvement brought about by this magnetic bridge is such that sputtering of magnectially permeable materials becomes practicable.

There are many possible magnet configurations for the bridge of Figure 8A. It is only necessary that the tendency for flux to flow through the target be substantially reduced. It should also be noted lower magnets 74 and 76 can provide the return plasma path rather than be part of the figure of rotation and extension shown in Figure 8A. Configuration of various bracket-like combinations as shown in Figures 8C-8G can serve this double function or be extended and rotated as in Figure 8A-or involve tunnel returns, etc. Note that the pole piece of such embodiments as that of Figure 8C may be eliminated whereby the facing south poles of magnets 66 and 74 would be held in close proximity to one another or in contacting relationship.Also note the return portion of the plasma need not extend fully around the target to form a tunnel return. Rather, it can be bent to curve to the side and optionally return close to the sputter surface, the bending of the magnetics being generally indicated hereinbefore with respect to Figure 6A. This permits targets to be long and move quite independently of the magnetics.

The double function bracket system types at first appear to be very simple-yet they make possible the sputtering of high permeability materials. It should also be noted that the target need not be permeable in the above embodiments of Figures 8A-8G.

Generally speaking, the principles discussed hereinbefore for establishing a magnetic bridge circuit within which a permeable target is disposed are applicable to most, if not all, magnetically enhanced sputtering devices regardless of the location of (a) the primary magnetic structure employed to establish the magnetic field in the sputtering portion of the plasma with respect to (b) the target surface.

Further, the lines of force produced by the auxiliary magnetic structure to complete the magnetic bridge circuit behind the target surface may pass through the permeable target as indicated in Figure 8A.

In the embodiment of Figures 2-8, the target is relatively located within the magnet system.

However, in the embodiment of Figures 9A and 9B, the magnet loops 38 and 40 are relatively located within endless belt-like target 82. An anode 84 is placed within the magnet loop to establish the voltage relationships needed for crossed field plasma trapping. This system sputters inward. Shields (not shown) at cathode potential should be disposed against the inner magnet faces. These will not sputter because of the perpendicular lines of force. If target 82 were to be removed, but not the shields, the remaining structure is generally similar to the magnetron vacuum gauge. This device is a very effective plasma trap.

It is possible to emp!oy only the bottom segment 86 of the target. A sputter-up system results with its plasma return through the open space over the target as shown in Figure 10. The loops 38 and 40 can be tipped or bent to give a larger opening at top 88 such that the flow of sputtered material is not impeded. A cathode with single direction plasma flow across the target results but no plasma tunnel under the target is required. Further, the target support system and cathode structure is significantly simplified. Also the embodiment of Figure 10 markedly decreases the chance of plasma contamination. Further, the return portion 38, 40 may be bent under target 90 or adjacent it, the bending of the magnetics being generally indicated hereinbefore with respect to Figure 6A. It may also have auxiliary lower magnets for use with high permeability targets as indicated at 92 and 94.Anode 84 should be crossed at its ends. Optional pole plates 96 and 98 may also be included. Further, cooling plate 100 may also be employed to clamp target 90 in place.

The loops formed by the magnetic structure may also be such that they are substantially coplanar as indicated by magnets 102 and 104 in Figures 11 A and 11 B. Target 106 thus takes the form of a planar ring or rectangular tube, etc. This type of system also has practical applications. The target can be fed up through the space between the magnet rings 102 and 104.

There are also many obvious combinations and permutations of the above embodiments that are advantageous. Combinations of magnets as shown in Figure 12 appear to be effective where additional ring magnet 108 under gap 110 causes the flux value in the gap to be higher than available with the two loops 38 and 40 alone. If ring 108 is not employed, additional inner rings 112 can be employed for magnetic targets.

Referring to Figure 13, there is shown a further illustrative embodiment of the invention where the magnets 114 and 11 6 are disposed adjacent the sides of target 120 as in other embodiments of the invention discussed herein before. However, the lines of force projected by magnets 114 and 11 6 are in general opposition to one another and pass through the target to a magnet 11 8 located below the target, the flux in magnet 11 8 being generally perpendicular to the target surface.

Hence, the embodiment of Figure 1 3 tends to combine features of the embodiments of Figures 1-12 of the present invention with those described in the aforementioned, co-pending U.S.

applications whereby the parallelism of a field which passes through the target is enhanced by magnets adjacent the sides of the target.

The desired strength uniformity and parallelism of the magnetic field is preferably obtained with the ferrite magnets described hereinbefore where the rubber or plastic tapes impregnated with oriented ferrite particles are paticularly advantageous. The presence of these particles, which are capable of producing a very strong magnetic field, in a low permeability binder such as rubber or plastic, is apparently effective in generating fields having the requisite characteristics. Further, the oriented ferrite impregnated plastics make practical multi-part magnet systems in which there is no need for interconnecting high permeability connections. In fact, such items as steel interconnecting plates ofter detract from the flux levels obtained.

Many of the embodiments of this invention may use ferrite magnets in whole or in part such as those ferrite magnets made by Arnold Magnetics, Inc. or Crucible Iron and Steel Co.

Also, many of the embodiments described herein may use more conventional magnets such as alnico ferromagnetic magnets in whole or in part but seldom with the convenience and practicality of the preferred materials. Electromagnets may also be employed, but they also are subject to the same objection. In any event, the above magnet means such as permanent magnets or electromagnets are preferably used in the subject application although magnetic means such as pole plates may also be used in conjunction with the magnet means discussed hereinbefore with respect to Figures 1A and 1 B and other figures of the drawing.

The magnetic structures of the present invention may be employed with planar cathodes which are circular or oblong. Oblong cathodes may be rectangular, elliptical or oval. Also, the planar cathode may be annular as in Figure 11 A.

Further, the planar cathode may include nonlinear portions such as the concave portions shown in the cathodes of Figures 5 and 7 of U.S.

Patent 3,878,085. In addition to planar cathodes cylindrical, conical, endless belt, etc. cathodes may also be employed. Also, as the cathode is sputtered, there may be a tendency for it to erode unevenly. Nevertherless, the cathode may still be considered planar, cylindrical or whatever its original shape was. Further, contoured surfaces may be imparted to the cathode so that it is thicker in areas of greatest expected erosion whereby the target will sputter relatively uniformly. Again, such a cathode is to be considered planar, cylindrical, etc. depending upon its general configuration prior to sputtering thereof.

The target material to be sputtered may or may not be the cathode of the device. If not, it may be clamped to the cathode by a clamp similar to those illustrated for various embodiments of the invention where the clamp may also be employed to secure the cathode within the sputtering device.

Regarding the anode referred to hereinbefore, it is usually so-called because sputtering systems are typically self-rectifying when an AC potential is applied. Hence, although the term anode is employed in the following claims, it is to be understood that it may be any other equivalent electrode in the system. Further, the anode can be the container wall of the sputtering device. DC, low frequency AC (60 Hz, for example) or industrial radio frequencies, such as 13.56 MHz or 27.12 MHz, may be applied across the anode and cathode:To effect RF isolation, the anode is almost always the container wall when these high frequencies are employed although it is quite often employed as the anode when DC is employed.

As to the gas employed in the system, it may be either active or inert depending upon the type of sputtered layer desired.

It should be further noted that the principles of the present invention can be applied to sputter etching.

Claims (51)

Claims

1. A magnetically enhanced sputtering device comprising a cathode, at least a portion of which is provided with a sputtering surface; anode means spaced from said cathode for establishing an electric field therebetween; first and second magnet means for establishing a first magnetic field crossed with respect to said electric field so that at least a portion of a closed plasma loop is established adjacent said sputtering surface, at least a portion of said first and second magnet means being so disposed above or to the side of said sputtering surface that some of the lines of force of said first magnetic field are projected over said sputtering surface from said first magnet means through said second magnet means, the strength of said field being approximately uniform over a substantial portion of the distance between said first and second magnet means.

2. A sputtering device as in claim 1 where at least a portion of said first magnet means is disposed adjacent one side of said sputtering surface and at least a portion of said second magnet means is disposed adjacent a side of said sputtering surface opposite said one side.

3. A sputtering device as in Claims 1 or 2 where said first and second magnet means are each ferrite magnets.

4. A sputtering device as in Claim 3 where said ferrite magnets each include a plurality of layers of oriented ferrite impregnated tape where at least one of the layers at least partially overlaps one of the layers adjacent thereto.

5. A sputtering device as in Claims 1 or 2 where the magnetic flux in said first and second magnet means is disposed at an angle with respect to a plane containing at least a porrion of said sputtering surface so that said lines of force arch over said sputtering surface.

6. A sputtering device as in Claim 5 where said flux in the first and second magnet means is substantially perpendicular to said plane.

7. A sputtering device as in Claim 1 or 2 where the magnetic flux in said first and second magnet means is approximately parallel to said sputtering surface so that said lines of force are projected parallel to said sputtering surface.

8. A sputtering device as in Claims 1 or 2 where said first and second magnet means are each annular and are substantially disposed in different planes.

9. A sputtering device as in Claim 8 where at least one of said first and second annular magnet means are bent so that said one annular magnet means includes a first portion disposed in one plane and a second portion disposed in another plane inclined with respect to said one plane.

10. A sputtering device as in Claim 8 where said planes are substantially parallel to one another.

11. A sputtering device as in Claim 8 where said sputtering surface is substantially disposed between said first and second annular magnet means.

12. A sputtering device as in Claim 11 including means for relatively moving said sputtering surface between said first and second magnet means in a third plane disposed between the planes containing said first and second annular magnet means.

13. A sputtering device as in Claim 8 where said sputtering surface is disposed in the open spaces of said first and second annular magnet means so that a first portion of said plasma loop sputters said sputtering surface and a return portion of the plasma loop extends below the side of said cathode opposite said sputtering surface to return the plasma to said first portion.

14. A sputtering device as in Claim 1 3 where said return portion of the plasma loop is sufficiently removed from the side of said cathode opposite said sputtering surface that said opposite side is not sputtered.

1 5. A sputtering device as in Claim 1 3 including means for introducing an ionizable sputter gas into said device where the return portion of the plasma loop extends below said opposite side of the cathode.

1 6. A sputtering device as in Claim 1 3 where the side of said cathode opposite said sputtering surface is also provided with a second sputtering surface over at least a portion thereof, said second sputtering surface being sputtered by said return portion of the closed plasma loop.

17. A sputtering device as in Claim 13 including cooling means for cooling and supporting the cathode.

1 8. A sputtering device as in Claim 1 3 including auxiliary magnet means disposed on the side of said cathode opposite said sputtering surface, said auxiliary magnet means strengthening the magnetic field between said first and second magnet means.

1 9. A sputtering device as in Claim 13 including means for relatively moving said sputtering surface with respect to said open spaces.

20. A sputtering device as in Claim 8 where said first and second annular magnet means are both disposed above said sputtering surface so that a first portion of said closed plasma loop sputters said sputtering surface and a return portion of said plasma loop is also disposed above said sputtering surface, the return portion of the plasma loop returning the plasma to said first portion.

21. A sputtering device as in Claim 20 where the portions of said first and second magnet means closest to said sputtering surface are closer to one another than the opposite portions thereof to thereby facilitate the transfer of sputtered material away from said sputtering surface.

22. A sputtering device as in Claim 8 where said cathode is annular and said sputtering surface extends around at least a portion of the interior surface of the cathode and where said first and second magnet means are disposed in the proximity of the opposite open ends of the annular cathode so that said closed plasma loop extends at least partially around said sputtering surface.

23. A sputtering device as in Claims 1 or 2 where said first and second magnet means are each annular and concentrically co-planar.

24. A sputtering device as in Claim 23 where said cathode is annular.

25. A sputtering device as in Claim 24 including means for relatively moving said annular sputtering surface between said first and second magnet means.

26. A sputtering device as in Claims 1 or 2 where said sputtering surface comprises a magnetically permeable material and where said device includes further magnet means for establishing a second magnetic field so disposed with respect to said first magnetic field and said sputtering surface that the tendency for said first magnetic field to pass through said magnetically permeable sputtering surface is substantially reduced.

27. A sputtering device as in Claim 26 where said first and second magnetic fields are disposed on opposite sides of said sputtering surface.

28. A sputtering device as in Claim 27 where the lines of force of said first and second magnetic fields are substantially parallel with respect to one another.

29. A magnetically enhanced sputtering device comprising a cathode, at least a portion of which is provided with a sputtering surface; anode means spaced from said cathode for establishing an electric field therebetween; primary magnet means for establishing a first magnetic field crossed with respect to said electric field so that a plasma is established adjacent said sputtering surface, said magnet means projecting some of the lines of force of said magnetic field over said sputtering surface: and further magnet means for establishing a second magnetic field so disposed with respect to said first magnetic field and said sputtering surface that the tendency for said first magnetic field to pass through said sputtering surface is substantially reduced.

30. A sputtering device as in Claim 29 where said sputtering surface comprises a magnetically permeable material.

31. A sputtering device as in Claims 29 or 30 where said first and second magnetic fields are respectively disposed on opposite sides of said sputtering surface.

32. A sputtering device as in Claim 31 where said lines of force are generally in the same direction.

33. A sputtering device as in Claim 32 where the lines of force of said first and second magnetic fields are substantially parallel with respect to one another.

34. A sputtering device as in Claims 29 or 30 where said primary magnet means includes first and second magnet means, at least a portion of said first and second magnet means being so disposed above said sputtering surface that some of the lines of force of said first magnetic field are projected over said sputtering surface from said first magnet means through said second magnet means.

35. A sputtering device as in Claim 34 where said first and second magnet means and said anode means include means for establishing at least a portion of a closed plasma loop adjacent said sputtering surface.

36. A sputtering device as in Claim 35 where said first and second magnet means are annular and where said further magnet means includes third and fourth annular magnet means disposed within said first and second annular magnet means respectively so that some of the lines of force of said second magnetic field are projected behind said sputtering surface.

37. A sputtering device as in Claim 29 or 30 including first and second annular magnet loops, which together with said anode means, establish a closed plasma loop adjacent said sputtering surface, said primary magnet means comprising a first portion of each of said annular magnet loops where some of the lines of force of said first magnetic field are projected over said sputtering surface from one of said first portions through the other of said first portions of said first and second annular loops.

38. A sputtering device as in Claim 37 where said further magnet means comprises a second portion of each of said annular magnet loops where some of the lines of force of said second magnetic field are projected behind said sputtering surface.

39. A magnetically enhanced sputtering device comprising a cathode, at least a portion of which is provided with a sputtering surface; anode means spaced from said cathode for establishing an electric field therebetween; first and second magnet means for establishing a first magnetic field crossed with respect to said electric field so that a plasma is established adjacent said sputtering surface, at least a portion of said magnet means being so disposed above said sputtering surface that some of the lines of force of said first magnetic field are projected over said sputtering surface from said first magnet means through said second magnet means, the strength of said field being approximately uniform over a substantial portion of the distance between said first and second magnet means, said first and second magnet means each comprising a plurality of layers of oriented ferrite impregnated tape where at least one of the layers at least partially overlaps one of the layers adjacent thereto.

40. A magnetically enhanced sputtering device comprising a cathode, at least a portion of which is provided with a sputtering surface; anode means spaced from said cathode for establishing an electric field therebetween; first and second magnet means for respectively establishing first and second magnetic fields crossed with respect to said electric field so that a plasma is established adjacent said sputtering surface; third magnet means disposed on the side of said cathode opposite said sputtering surface; and at least a portion of said first and second magnet means being so disposed above said sputtering surface that some of the lines of force of said first and second magnetic fields are projected over said sputtering surface from said first and second magnet means through said cathode and said magnet means.

41. A method of providing magnetic enhancement in a device for sputtering target material, said method comprising establishing a magnetic bridge circuit around said target material to reduce the tendency for magnetic lines of force to pass through said target material.

42. A method as in Claim 41 where said target material is magnetically permeable.

43. A method as in Claims 41 or 42 where said magnetic bridge circuit includes first and second magnetic fields so disposed with respect to said target material that the tendency for said first field to pass through said target is substantially reduced.

44. A method as in Claim 43 where said first and second magnetic fields are disposed on opposite sides of said target material.

45. A method as in Claim 44 where the lines of force of said first and second magnetic fields are substantially in the same direction.

46. A method as in Claim 45 where the lines of force of said first and second magnetic fields are substantially parallel to one another.

47. A method of providing magnetic enhancement in a device for sputtering target material, said method comprising directing a first magnetic field over a sputtering surface of said target material; and directing a second magnetic field with respect to the side of said target opposite said sputtering surface where the direction and strength of said second magnetic field is such as to reduce any tendency for said first magnetic field to pass through said target material.

48. A method as in Claim 47 where said target material is magnetically permeable.

49. A method as in Claims 47 or 48 where said first and second magnetic field are disposed on opposite sides of said target material.

50. A method as in Claim 49 where the lines of force of said first and second magnetic fields are substantially in the same direction.

51. A method as in Claim 50 where the lines of force of said first and second magnetic fields are substantially parallel to one another.