CA1210824A - Apparatus and method for evaporation arc stabilization - Google Patents

Abstract

Improved Apparatus And Method For Evaporation Arc Stabilization Abstract Apparatus and method for evaporation arc stabili-zation including a target having a surface of material to be evaporated; circuitry for establishing an arc on the target surface for evaporating the target material, the arc being characterized by the presence of charged particles and a cathode spot which randomly migrates over the target surface; and a confinement ring contacting and surrounding the target surface, the ring being com-posed of a material such as boron nitride having (a) a secondary emission ratio less than one at the mean energies of the charged particles of the arc and (b) a surface energy less than that of the evaporated target material to thereby confine the cathode spot to the target surface. Further, the secondary emission ratio of the confinement ring is preferably less than that of the target.
If the target is permeable, a permeable ring may also surround the target for effecting substantially uniform evaporation from the target.
The confinement ring may also be employed as a cover for a permeable ring to prevent migration of the cathode spot onto the permeable ring during initial clean-up of the target.

Description

Improved Apparatus ~nd Method Por Evaporation Arc Stabil _ ation Back~round of the Invention This inventlon relates to arc stabili~ation pro-cesses and devices which may be employed, for example,in arc coating systems. Such coating systems are dis-closed in UOS. Patent Nos. 3,625,848 and 3,836,451 to Alvin A. Snaper and U.S. Patent Nos. 3,783,231 and 3,793,179 to L. Sablev, et al. These systems are char-acterized by high deposition rates and other advanta-~eous features. HowevQr~ these advantages can be some-what offset due to insta~ility of the arc. That is, the arc involves currents of about 60 amperes, or more, concentrated into a cathode spot so small that current densities are 103 to 106 amperes per square inch. The voltages are 15 to 45 volts. Thus, power densities at the ~ny cathode spot are in the order o megawatts/
inch2. Accoraingly~ local vioIence is an understatemen~.
The target surface under the cathode spot flash evaporates from the intense heat. ~t is this evaporated target material which deposits as the coating on a substrate.
The cathode spot migrates about the target surface in a random, jerky motion with reported velocities of many meters per second. Because of this random movement, damage to the device and contamination of the coating can occur if the spot moves of the target surface.
Different solutions to the arc instability problem have been proposed. Thus, in Sablev, et al., Patent No.
; 3,793,17~/ a shield is placed close to the edge of the target. In particularj it is placed at a distance from the target which represents less than a mean frea path of the gas present. In an arc discharge, gas and plasma are generated at the cathode spot with sufficient violence that local mean-free-paths may occasionally .

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be reduced to a few thousands of an inch. When such a blast of local high pressure is blow:n under the shield, which is spaced at several millimeters (:~ 80 thousandths of an inch), there is finite possibility the arc ~an migrate under the shield. When this happens, there will be arc damage to the cathode, contamination of the evaporant, or the arc will extinguish.
Sablev, et al., Patent No. 3,783,231 apparently addresses the foregoing problem by providing a feedback mechanism of some complexity that emphasizes the frustra-tions caused by the problem. The ~eedback in~ol~es the utilization of a ma~netic field to retain the cathode spot on the target surface. U.S~ Patent No. 2,972,6g5 to ~. Wroe also suggests the utilization of a magnetic field for cathode spot retention.
It is an object of the present invention to provide, in an arc coating device, stabilization o the arc in such a manner as to avoid the inadequacies ancl complexities of the prior art approaches.
Generally, this is effected by surrounding a pre-determined area of the eYaporation surace of the target with a confinement ring which contacts the target and directs the arc back to the evaporation surface whenever it wanders onto the confinement ring surface even i the ring is coated with concluctive material evaporated ~rom the target. As will be described in further detail hereinafter, materials from which the confinement ring may be fabricated are such that the ring is char~
acterized by ~a) a low absolute value of seco.ndar~ electron emmission ratio where preferably the ratio of the target is greater than that of the ring and (b) a low surface energy of the confinement ring relative to that of the evaporant.

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Although the theory of operation is not completely understood, i~ is thought the above characteristics function in the following manner to effect the advantageous results of the present invention. Due to the con~inement ring's low secondary electron emission ratio, the arc will return to the target whenever the arc wanders onto the ring surface. During the coating process, some of the target material evaporant may deposit on the ring. This could proYide a bridge for the arc over the ring in spite of its low secondary emission ratio. How-ever, due to the low surface energy relative to that of the evaporant, there is no wetting of the ring by the evaporant. Thus, the deposit~is instankeously evaporated by the arc so that the arc again contacts the conin~-ment ring sur~ace whereby it is returned to the targe~.
One material which possesses the abov~ charac~eris-tics is boron nitride (BN~ This material has been used as a wiper and insulator in high curre~t switches. It has also been used as a nozzle on arc spray devices. In such devices, the reusal of BN to permit arcing against its surface is involv~d. However, in neithPr case is the BN heavily coated by target material in its operation as discussed above. Insta~ces where BN has been employed for other purposes are disclosed in U.S. Patent Nos.
3~202,862; 3,555,238; and 3,945,240.
In summary, a primary purpose of this invention is to provide an improved apparatus and method of arc stabilization which provides long term stability in a straightforward manner for both permeable ~nd non-per-meable t~rgets and which may be used in such applications as arc coating and which may be used during the initial clean-up of the target.

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Other objects and advantag~s of this in~ention will be apparent from a reading of the following specification and claims taken with the drawing.

Brief Description of Drawings Figures lA and lB are diagrammatic illustrations of first and second embodiments wher~e confinement rings in accordance with the invention are respectively em-ployed with clamped targets.
Figures 2A and 2B are diagrammatic illustrations of further embodiments where the t æ get is bonded to the cathode.
Figure 3 is a schematic diagram in cross-section which illustrates the uniform erosion pattern which results when a non-permeable target is confined by a N-ring.

Figure 4 is a schematic diagram in cross~section illustrating the erosion pattern which results when a permeable target is confined by an N-ring.
Figure 5 is a schematic diagram in cross-secticn of an illustrative embodiment of an arc stabilization ap-paratus for a permeable target in accordance with the present invention.
Figures 6(a), 6(b~, 7(a~, and 7(b) are schematic "iron filings" diagrams in cross-section which illustrate various conditions of permeable and non-permeable targets.
Figure 8 is a schematic diagram in cross-section of an illustrative embodiment of an arc stabilization apparatus for use during initial clean-up of a target.

Detailed Description of Preferred Embodiments Reference should be made to the dr~wing where like reference numerals refer to like parts. Further, each of the figures of the drawing illus-trate one-half of a figure of revolution where the axis of symmetry of each figure is indicated at 10. Thus, with respect to Figures lA and lB, the le~t half of a complete embodiment is shown in Figure lA while the right half of a complete embodiment is shown in Figure lB.
In Figure lA, an arc coating system for a substrate 12 comprises an anode 14 where, if desired, the anode and substrate may be the same member/ a target 16 of conductive or insulative material, a cathode 18 where, if desired, the target and cathode may be the same member, lS a clamp ring 20, a bolt 22, a confinement ring 24, and a power source 26, which is DC if the target is conductive and RF if it is in~ulative. In accordance with the in-venkion, the confinement ring is composed of boron nitride or a similar material as discussed in more detail herein-after.
In opera ion, source 26 is energized across the anodeand cathode to strike an arc between the anode and target in a well known mahner. Arc initiating means ~not shown) may be employed to initiate the arc. Target material is then flash evaporated from the cathode spot formed at the root of the arc on the target surface and deposited on the substrate as a coating. Confinement ring 24 contacts taxget 16 and surrounds an exposed area constituting an evaporation surface of the target to thereby confine the cathode spot to the evaporation surface in such a manner that continuous, stable operation is effected for the entire lifetime of the target even though the ring may be overlayed with evaporated target material many mils thick.

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Briefly, the confinement ring is made of a material such that the ring is characteri~ed by (a) a low absolute value of secondary emission ratio where preferably the ratio of the target is greater than that of the ring and (b) a low surface energy of the ring relative to that of the eYaporant.
The secondary emission ratio ~ is defined as the number of secondary electrons produced by a primary electron~ or other charged particle, incident upon a0 target. Thus, number of electrons_emitted by material per primary charged partlcle The number of electrons emitted by the target is dependent not only on the particulax target material but also on the energy of the primary charged particle. In accordance with one aspect oE the present invention, the secondary emission ratlo of the confinement ring, ~
tconfinement ring), should be less than one at the mean energies of the charged primary particles typically found in arc coating processes such as disclosed in the aforementioned Snaper and Sablev patents where these mean particle energies are about 20-100 eV, and, preferably, 40-60 eV. Moreover7 the secondary emission ratio of the target, ~ ~target) is preferably greater than ~ (confinement ring).
One class of materials which, generally speaking, has a ~ < 1 is the nitrides and boron nitride, in particular. The nitrides differ with respect to the oxide ceramics in that the oxides enhance secondary electron emission while the nitrides decrease it relative to the metals where the electron emission ratios for the different metals are approximately equal.
This is consistent with the ~ for alumina ~A1203), which is about 15-20. This apparently accounts for the unstable arcing observed against alumina shields.

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Boron nitride has been observed to be effective with metal targetsO It also can be used wi~h insulative targets, many vf which have a high secondary electron emission ratio due to a substantial oxide content. Titanium nitride 7 even though ~uite conductive electrically, also restricts arc paths.
Another significant difference between the oxide ceramics and boron nitride and similar materials is that metallic coatings do not wet the latter materials, ~ence, it appears e~aporation of a conductive coating at the edge of a RN confinement rin~ readily o~curs when an arc moves against it. The arc inst~ntly e~apora-tes the loose flap of ~oa-ting for the coating is not thermally supported by bonding to the BN. This exposes a freshly cleaned in-sulatiny surface for at least a small distance at the edgeof the confinement ring, making motion of the arc in a different direction away from the ring a most probable alternative. Further, once the poorly bonded coating at the edge of the ring ls evaporated away, there will be ~ery poor electrical contact between the conductive coating remaining on the ring and the target. This further reduces the chance of the arc proceeding onto the coating since 60 or more amperes requires rather a significant connection~ Low current resistance measurements often show no electrical contact between target and coatings on the ring.
In general, a further aspect of the invention for effecting arc confinement is the low surface energy ~) of the confinement ring relative to that of the evaporant -that is, y (ring~ < y ~evaporant~. -In this regard, BN
(surface energy of 600-700 ergs/cm.2) is not wet by most metals at the temperatures encountered in the arc coating processes described in the aforementioned Snaper .

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and SableY patents. Only the oxides o~ lead, bismuth~
copper and antimony will wet and attack BN, the surface energies of these oxides ranging from lQ0-300 ergs/cm.2.
However, BN and materials similar thereto are suitable for the practical applications encountered in arc coa~ing pro-cesses.
In summary, confinement ring 24 should ~e formed from or coated with materials having the foregoing charac-teristics. The nitride compounds are particularly suitable and, in particular, the nitrides of boron and titanium~ In this regard, it should be noted if the nitride compound constitutes less than 100% of the confine-ment ring composition, the ring will nevertheless function in the desired manner as along as entire composition has the above-discussed characteristics. Hereinaftax, a ring of the above type will be termed an "N-ring".
Other con~igurations of confinement ring 24 are illustrated in Figures lB, 2~ and 2B where Figure lB
illustrates another embodiment where ~he target is clamped to the cathode by ring 20 and bolts 22 (not shown in Figure lB) while the embodimen~s of Figures 2A and 2B illustrate bonding of the target 16 to the cathode 18 by appropriate means at the interface surface 28.
There is relatively little dependance on the con-finement ring configuration and those of Figures lA,lB, 2A, and 2B are equally suitable with respect to the arc (cathode spot) containment function. Further/ as illustrated in Figure lC the ring 24 may comprise a coating on a support me~ber 30 where the coatin~is inten-tionally enlarged in thickness for purposes of illustra-tion~ If the ring is not ormed by coating, it may be attached by bolts or o~her known expedients. If bolted, the heads of the bolts may be covered with the ring material.

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Furthermore, the arc stabilization of the present invention permits non-cylindrical symmetry, for example, linear, rectangular cathodes and cylindrical arc sources, ~here magnetic confinement techniques such as those disclosed in the abo~e-mentioned Patent Nos. 3,7B3,231 and 2,q72,6g5 cannot produce the necessary uniform fields for confinement. Moreover, the present invention operates over all pressure ranges Cparticularl~ high pressures~
where the technique disclosed in the above-mentioned Patent NoO 3r793/179 is limited in this respect~
Although the preferred embodiments of the invention have been described in connection with an arc coating system, it is to be understood, it is also applicable to other syst~ms where material is flash evaporated lS ~rom a target by an arc which must be confined ko a precletermined area of the target surface.
As can be seen in Figure 3, as long as the target 16 i5 non-permeable, the erosion pattern 17 obtained with the confinement ring of Figs. lA, lB, lC and lD
is quite uniform. However, if a permeable target 16 is employed, the erosion pattern 17 is not unifrom, as can be seen in Figure 4. Examination of the target of Figure 2 leads to the conclusion that the arc is in-fluenced to move toward the edge of the permeable taryet~ for there is no reason to e~pect it to move specifically toward the N-ring 24 otherwise.
The assignee of the present application has con ducted experiments, one of which involved placing an N-ring on a large sheet of permeable material such that the plane of the ring was parallel to that of the sheet, the ring being in the approximate center of the sheet. An arc was struc~ within the ring and the resulting erosion pattern was normal -- that is, it corresponde~ to that of Figure 3.

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The above principles are incorporated in the Figure 5 embodiment of the present inventioll where a permeable target 16 is surrounded by a flat ring 19 made 9f a per-meable material such as soft iron or Permalloy or the target material itself. In fact, any material considered to be permeable may be used, such materials including bllt not limited to iron; nickel; cobal~; and alloys thereo with small amounts of optional additives; ~errites; steel;
etc. Fuxther, the ring 19 may comprise an integral ex-tension of the target itself. Hereinaftex ring 19, whetheri~ be a separate member, as shown in Figure 5 or an inte gral extension of the target will ~e termed a "P-ring".
N-ring 24 is disposed around the periphery o~ target 16 and contributes to the conEinement of the arc on the target sur~ace. The N-ring also retains ring 19 and target 16 in place via a bolt 21 which is threaded into cathode body 18.
Although there is no intent to be limited to a parti-cular theory of operation, the following considerations apparently are applicable to P-rings of the present inven-tion. It has been observed a vacuum arc struck on a non-permeable target wanders randomly a~out, most often leaving the target for other areas of the cathode within a second or so. A permeable target looses the arc to other cathode axeas in milliseconds. Obviously, for uncontaminated coatings, the arc must remain only on the target.
The early literature of magnetic flelds applied to the vacuum arc indicates the arc moves most readily in the direction of greatest magnetic field density. Assuming this is the mechanism for forcing the arc to the edge of the target in Figure 4 r it appears the arc moves away from the permeable naterial that reduces field density.

, ~ ., , . , , Another insight relating to the containment mech-anism is obtained from the work of Naoe and Yamanaka C''Vacuum-Arc Evaporations o Ferrites and Compositions of their Deposits" Japanese Journal of Applied Physics, Vol. 10, No. 6, June 1971, copy submitted herewith~, who arc-e~apora-ted ferri~e composites from a cup-shaped ferrite target. They were attaining a melted portion of the target, and the oxide materials behaved very clifferently from the metals. They repor~ed a very stable arc tha~
moved in a Yery slow circular motion at the approximate center of the cup. They made no reference to this as unusual behavior,-but gave considerahle detail of the axc motion as observed visually. Implications relative to general arc containment were lacking.
To ~etter understand this phenomenon the assignee of the present invention has used a DC current th~ough a wire to generate a cylindrical magnetic field of the type that the arc appears to produce close ~o the target.
This wire has been brought into the proximity of various geometries of permeable tar~ets and "iron filings diagrams"
produced to give insights to the magnetic influence of these per~eable materials on the magnetic field.
It should be noted th.i~ is somewhat diFferent from the application of a magne~ic field to interact with the arc field as applied in aforementioned U.S. Patent Nos.

2,972,695 and 3,783,231, for no ex~ernal field is applied.
When current is passed through the wire, magnetic flux is generated symmetrically around the wire. When two wires are placed in parallel with current in the same direction through them, the wires are pulled toward each other. The field senerated between the wires is cancelled, for the flux direction is different on the right versus the left of the wire.

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In actuality, an arc is quite unique, and modeling it ~s a wire with current flowing is not a true indicator o what an arc will do. If sufficient current is permitted to flow in the arc, it will divide itself into two simul-taneous arc spots moving independ~lt:Ly about the cathodesurface. This i5 quite the re~erse o the wires which move together as current flows. Simple e~planation of this differerlce between the arc and the wire is sometimes given in terms of the electrons being free to move sideways in space in the arc, but being confined within the wire. They try to move sidPways in the wire, creating equal and oppo-site forces on the wires. Thus the wire moves opposite to the direction the arc moves where the magnitude o the force moving an arc toward the edge of a permeable target lS is significant relative to the random motion ~orces that typically move the arc about a non-permeable target.
Figures 6(a), 6(b), 7(a), and 7~b) show the nature of the filing diagrams from thP various conditions of permeable and non-permeable targets. In Figure 6 less and less flùx density 23 is seen as the iron plate 32 is approached for these lines ~of which only the cross sec-tions ar~ seen) are drawn into the iron, for they travel more easily there. In the case of the aluminum target 34, the ~lux remains very constant as the pl~ate is approached, as can be seen in Figure 6(b). Moving to the target edge, as in Figure 7(b~j makes no change in the case of the aluminum target. However, as shown in Fi~gure 7(a~
mo~ement to the edga o~ the iron target produces a reasonably strong flux outboard of the target, and virtually none inboard. With the foree on the arc thus outward, it is quite understandable that the arc xaaes for the outside edge. The forces will be nil when the arc is perfectly in the targe~ eenter, ~ut normal random migration from v~ .
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:'''' ~ ' ' ~13-the arc action will qulckly push it off center. As it gets closer to an edge, the force toward the edge multiplies.
It is thus quite logical that erosion would occur as shown in Figure 4, for the arc i5 trapped between the induced electromagnetic force outward, and the "N"-ring which pre~ents the arc from moving further outwardO There is relative freedom of motion only into the plane of Figure 4. Thus the arc moves around the target perpendi~-cularly to the ~rap. The at~empt here is not to fully define the arc motion, but only to show certain aspects of it can be influenced significan~ly or purposes of control.
Furthermore ! it follows that the presence of P-ring 19 of Figure 5/ the lines of forae travel as easily through ring l9 as they do through target 16 disposed within the inner periphery of the ring. Hence, the flux density within the ring i5 substantially equal to khat outside the ringls inner perphery. Thus, there :is no outward force on the arc as is the case in Pigure 4 deviceO Accordingly r the arc randomly migrates over the entirety of -the permeable target sur~ace in,the same manner it migrates over the non-permeable target of Figure 3 to thereby effect uniform erosion of the permeable target.
Reference should now be made to Figure 8, whlch illustrates a further application of the invention. Due to work performed by the assignee of the subject application, it has been established a P-ring surrounding a non-per-meable target is very effective in containing an arc on such a target once the target is ultra-clean. As will now be described, the Figure 8 configuration enables the taxget to be ultra-cleaned by ~n arc so that the P-ring can then ba employed to effect its arc re-tention function where, in Figure 8, N-ring 24 may be ~a) a separ~ble cover on or (b~ a coat painted, sputtered, evaporated~ or otherwise applied to P~ring 19.

The literature repeatedly stresses the need for ultra-clean conditions for the target assembly, but gives little description of the ~ehavior of arl unclean target contaminated with oxides and the like. It is indicated the oxides are evaporated (or exploded) from the surface by an arc before meaningful metal evaporation can start.
Most of th~ removal of these contaminants occurs during the initial cleaning phase of the target with the sub-strate in some instances, ramoved from the system. During thi5 time, so-called type-one cathode spots are formed which do not effectively evaporate the target. Only after the contaminants have been effectively removed, are the type-one spots replaced by so-called type-two spots which are e~ective to evaporate the target. At this time, the substrate may be placed in the system preparat.ory to coating thereof if not already in place.
The N-ring appears to restrain the arc tc) the tar~et during the initial cleaning phase even when the target is assemhled in a dirty stateO The P-ring i5 not that absolute a repellant, so that the arc may run upon the target and the P-ring for the first few starts of the arc during the initial cleaning phase. Once the target is sufficiently clean to evaporate target material, it coa~s the portion of the ring immediately adjacent the target, and the control of the arc bec~mes quite absolute.
Elowever, during the initial cleaning phase, the arc can move onto the back and sides of the cathode body 13 where it may damage the structure, or evaporate contaminating metals into the chamber.
In cartain applications, the N-ring tends to ~a) be somewhat fragile, ~b~ have a rAthex limited life time ~c) ~e expensive and ~dl lose target material deposited therein due to its lo~ ~ettability. Hence, it is desirable . .

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to take advantage of the N-ring's arc retention capability during the initial clean-up (that is, the ~-ring appears to hold type-one arcs for many taxget materials, perhaps all, at least all that have been tesl~ed by the assignee to date) and then utilize a P-ring once the target h~s been arc-cleaned.
In general, two items are of major concern. First, it is necessary to protect non-target areas of the cathode from eroding, especially, near the insulators. Thus, the arc cleaning activity must be kept on the target and clamp assembly. Secondly, the arc extinction frequency must be reduced, such that a few strikes will lead to a clean surface. With present methods, over a hundred strikes may be needed on a large aluminum cathode with light P-ring containment.
The severity o~ the arc-cleaning problem is a funtion o the target material. For example, aluminum is very bad, zirconium is ~ery good. The observation of the assignee is that type-one arcs have a hierarchy of functions.
First, they sear~h out and attack oxided areas. This is reasonable, for such compounds as the metal oxides tend to be ready electron emitters. It appears only this oxide search mode can easily jump the P-ring. When the violent flashes from the obvious oxide areas are gone, progress is made through many more strikings of the arc, usually with longer and longer periods of operation before ex-tinction. During most of this period there is almos-t no evaporated metal coming from the discharge - even though it may last for many seconds. It appears to still be operating as a type~one arc which has only a tiny ~vaporation output. This is probably the explosion of sharp points and ridges which can give vast numbers of electrons at quite low arc vo~ages.

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In the oxide phase of clean-up, the arc easily trans-gresses the P-ring, onto the non-target parts of the cathode. In the point and ridge phase, the P-ring holds the discharge, but the discharge extinguishes very often. Only when the type-one arc has eliminated all ready sources o elect~ons does it change into a type-two arc and proceed with flash eYaporation of the target surace.
Because, as stated aho~e, the N--ring will hold the oxide phase discharge, the embodiment of Figure 8 may be employed to optimize the respecti~e advantages of N~ring 24 and P-ring 19. When the N-ring is employed as a separable cover, it would be in place during the initial arc, clean-up phase until the type-two arc i5 established on the target. The covex would then be remo~ed from the target to uncover it. There would then ~e a second arc clean-up phase conducted which remove the oxide areas, etc., covered by the N-ring 24 during the first clean-up phase~
There are les~ than before, however, and the total clean-up time is less than that which would be required in thea~sence of the N-ring cover. Moreover~ SinGe this cover would be removed after thQ clean-up ~to thereafter allow the P-ring to effect the arc retention funetion, as discussed above), the life time of the cover would be substantially increased~ Furthermore, the loss of target material deposited thereon would not be a problem.
~ hen the N-ring cover 24 is applied as a thin film coating, this should be done for each new target. Although this may be inconvenient in certain situations, there are certain advantages e.specially when the coating is made from TiN or a similar material. The BN paints ~o not adhere very well. Rad~o frequency sputtering o BN onto the ring 19 is better. The most acceptable approach is the use of ~ ....

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titanium nitride - the very material that many arc systems are designed to produce. An extra iron ring 19 can be coated along with a batch of tools, for example. This xing can then serve with the ne~t target, which may be titanium.
The TiN bonds very tightly to the iron ring. Even though this coating is electrically conductive, it does reject the arc for the reasons discussed hereinbefore. It is only necessary for this nitride coating to be exposed during the oxide pha~e of the target clean-up, 50 this method can be very practical. Furthermore, the TiN coating does not result in flaking.
I~ is to be understood that the above detailed description of ~he various embodiments of the invention is provided by way of example only. Various details of design and construction may be modified without departing from the true spirit and scope of the invention as set forth in the appended claims.

Claims (22)

1. Apparatus for evaporation arc stabilization comprising a target having a surface of material to be evaporated;
means for establishing an arc on the target surface for evaporating the target material, the arc being characterized by the presence of charged particles and a cathode spot which randomly migrates over said tar-get surface; and a first confinement ring contacting the target and surrounding the target surface, the ring being com-posed of a material having (a) a secondary emission ratio less than one at the mean energies of the charged parti-cles of the arc and (b) a surface energy less than that of the evaporated target material to thereby confine the cathode spot to the target surface.

2. Apparatus as in Claim 1, where said target has a surface of permeable material and said apparatus includes a permeable ring surrounding the target for effecting substantially uniform evaporation of the target material from the target surface.

3. Apparatus as in Claim 1 including a permeable ring surrounding said target for retaining the cathode spot on the target surface, said confinement ring covering said permeable ring so that, at least during the initial clean-up of contaminants from the target, the cathode spot will not move onto the permeable ring.

4. Apparatus as in Claim 3 where said confinement ring is separable from said permeable ring so that it may be removed from the permeable ring after said initial clean-up of contaminants from the target.

5. Apparatus as in Claim 4 where said confinement ring is coated onto said permeable ring.

6. Apparatus as in Claim 5 where said confinement ring comprises titanium nitride.

7. Apparatus as in Claim 2 where said permeable ring and said target constitute separate members.

8. Apparatus as in Claim 2 where permeable ring and said target are integrally connected to another.

9. Apparatus as in Claim 7 or 8 where said permeable ring is made of the same material as said target.

10. Apparatus as in Claims 7 or 8 where said permeable ring is made of iron or Permalloy.

11. Apparatus as in Claims 1, 2 or 3 where the secondary emission ratio of the confinement ring is less than that of the target.

12. Apparatus as in Claims l, 2 or 3 where the mean charged particle energies of said arc are about 20-100eV.

13. Apparatus as in claims 1, 2 or 3 where the mean charged particle energies of said arc are 40-60eV.

14. Apparatus as in claims 1, 2 or 3 where the confinement ring comprises a nitride compound.

15. Apparatus as in claims 1, where the confinement ring comprises a nitride compound selected from the group consisting of boron nitride and titanium nitride.

16. Apparatus as in claims 15 where the nitride compound is boron nitride.

17. Apparatus as in claims 1, 2 or 3, including a substrate upon which the evaporated target material is deposited as a coating.

18. Apparatus as in claims 1, 2 or 3, including a substrate upon which the evaporated target material is deposited as a coating and where the anode and substrate are the same material.

19. Apparatus as in claims 1, 2 or 3 where the means for establishing the arc on the target surface includes a cathode and an anode.

20. Apparatus as in claims 1, 2 or 3 where said target is mounted on said cathode.

21. Apparatus as in claims 1, 2 or 3 where said target and cathode are the same member.

22. Apparatus as in claim 3 where said target comprises a non-permeable material.