GB2140040A - Evaporation arc stabilization - Google Patents

Abstract

In apparatus including a target 16 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, a confinement ring 24 contacts and surrounds the target surface, the ring being composed 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. <IMAGE>

Description

SPECIFICATION Improved apparatus and method for evaporation arc stabilization Background of the Invention This invention relates to arc stabilization processes and devices which may be employed, for example, in arc coating systems. Such coating systems are disclosed in U.S. 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 characterized by high deposition rates and other advantageous features. However, these advantages can be some-what offset due to instability 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 1 5 to 45 volts.

Thus, power densities at the tiny cathode spot are in the order of megawatts/ inch2. Accordingly, local violence is an understatement. The target surface under the cathode spot flash evaporates from the intense heat. It 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 off the target surface.

Different solutions to the arc instability problem have been proposed. Thus, in Sablev, et al., Patent No. 3,793,179, a shield is placed close to the edge of the target. In particular, it is placed at a distance from the target which represents less than a mean free path of the gas present. In an arc discharge, gas and plasma are generated at the cathode spot with sufficient violence that local meanfree-paths may occasionally be reduced to a few thousands of an inch. When such a blast of local high pressure is blown under the shield, which is spaced at several millimeters (-80 thousandths of an inch), there is finite possibility the arc can 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 frustrations caused by the problem. The feedback involves the utilization of a magnetic field to retain the cathode spot on the target surface. U.S. Patent No. 2,972,695 to H. 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 of the arc in such a manner as to avoid the inadequacies and complexities of the prior art approaches.

Generally, this is effected by surrounding a predetermined area of the evaporation surface 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 if the ring is coated with conductive material evaporated from 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 characterized by (a) a low absolute value of secondary 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.

Although the theory of operation is not completely understood, it is thought the above characteristics function in the following manner to effect the advantageous results of the present invention. Due to the confinement 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 provide a bridge for the arc over the ring in spite of its low secondary emission ratio.

However, 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 instanteously evaporated by the arc so that the arc again contacts the confinement ring surface whereby it is returned to the target.

One material which possesses the above characteristics is boron nitride (BN). This material has been used as a wiper and insulator in high current switches. It has also been used as a nozzle on arc spray devices. In such devices, the refusal of BN to permit arcing against its surface is involved. However, in neither case is the BN heavily coated by target material in its operation as discussed above.

Instances 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 and non-permeable targets and which may be used in such applications as arc coating and which may be used during the initial clean-up of the target.

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 Drawings Figures 1A and 1 B are diagrammatic illus trations of first and second embodiments where confinement rings in accordance with the invention are respectively employed with clamped targets.

Figures 1 C and 1 D are diagrammatic illustrations of further embodiments where the target is bonded to the cathode.

Figure 3 is a schematic diagram in crosssection 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 crosssection illustrating the erosion pattern which results when a permeable target is confined by an N-ring.

Figure 5 is a schematic diagram in crosssection of an illustrative embodiment of an arc stabilization apparatus 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 crosssection 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 drawing where like reference numerals refer to like parts. Further, each of the figures of the drawing illustrate one-half of a figure of revolution where the axis of symmetry of each figure is indicated at 10. Thus, with respect to Figures 1 A and 1 B, the left half of a complete embodiment is shown in Figure 1 A while the right half of a complete embodiment is shown in Figure 1B.

In Figure 1A, an arc coating system for a substrate 1 2 comprises an anode 14 where, if desired, the anode and substrate may be the same member, a target 1 6 of conductive or insulative material, a cathode 18 where, if desired, the target and cathode may be the same member, 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 insulative. In accordance with the invention, the confinement ring is composed of boron nitride or a similar material as discussed in more detail hereinafter.

In operation, source 26 is energized across the anode and cathode to strike-an arc between the anode and target in a well known manner. Arc initiating means (not shown) may be employed to initiate the arc. Target ma teriai 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 target 1 6 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.

Briefly, the confinement ring is made of a material such that the ring is characterized 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 evaporant.

The secondary emission ratio ss is defined as the number of secondary electrons produced by a primary electron, or other charged particle, incident upon a target. Thus, number of electrons emitted by material = per primary charged particle The number of electrons emitted by the target is dependent not only on the particular target material but also on the energy of the primary charged particle, In accordance with one aspect of the present invention, the secondary emission ratio of the confinement ring, (confinement 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 40-60 eV.

Moreover, the secondary emission ratio of the target, 8 (target) is preferably greater than 8 (confinement ring).

One class of materials which, generally speaking, has a 6 < 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 8 for alumina (Al2O3), which is about 1 5-20. This apparently accounts for the unstable arcing observed against alumina shields.

Boron nitride has been observed to be effective with metal targets. It also can be used with insulative targets, many of which have a high secondary electron emission ratio due to a substantial oxide content. Titanium nitride, even though quite 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, Hence, it appears evaporation of a conductive coating at the edge of a BN confinement ring readily occurs when an arc moves against it. The arc instantly evaporates the loose flap of coating for the coating is not thermally supported by bonding to the BN. This exposes a freshly cleaned insulating surface for at least a small distance at the edge of 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 is evaporated away, there will be very 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 (y) 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 and Sablev patents. Only the oxides of lead, bismuth, copper and antimony will wet and attack BN, the surface energies of these oxides ranging from 100-300 ergs/cm.2. However, BN and materials similar thereto are suitable for the practical applications encountered in arc coating processes.

In summary, confinement ring 24 should be formed from or coated with materials having the foregoing characteristics. 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 confinement ring composition, the ring will nevertheless function in the desired manner as along as entire composition has the abovediscussed characteristics. Hereinafter, a ring of the above type will be termed an "Nring".

Other configurations of confinement ririg 24 are illustrated in Figures 1B, 1C and 1D where Figure 1 B illustrates another embodiment where the target is clamped to the cathode by ring 20 and bolts 22 (not shown in Figure 1 B) while the embodiments of Figures 1 C and 1 D illustrate bonding of the target 1 6 to the cathode 1 8 by appropriate means at the interface surface 28.

There is relatively little dependance on the confinement ring configuration and those of Figures IA, 1 B, 1 C, and 1 D are equally suitable with respect to the arc (cathode spot) containment function. Further, as illustrated in Figure 1 C the ring 24 may comprise a coating on a support member 30 where the coating is intentionally enlarged in thickness for purposes of illustration. If the ring is not formed by coating, it may be attached by bolts or other known expedients. If bolted, the heads of the bolts may be covered with the ring material.

Furthermore, the arc stabilization of the present invention permits non-cylindrical symmetry, for example, linear, rectangular cathodes and cylindrical arc sources, where magnetic confinement techniques such as those disclosed in the above-mentioned Patent Nos. 3,783,231 and 2,972,695 cannot produce the necessary uniform fields for confinement. Moreover, the present invention operates over all pressure ranges (particularly high pressures) where the technique disclosed in the above-mentioned Patent No. 3,793,179 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 systems where material is flash evaporated from a target by an arc which must be confined to a predetermined area of the target surface.

As can be seen in Figure 3, as long as the target 1 6 is non-permeable, the erosion pattern 1 7 obtained with the confinement ring of Figs. 1A, 1B, 1C and 1D is quite uniform.

However, if a permeable target 1 6 is employed, the erosion pattern 1 7 is not uniform, as can be seen in Figure 4. Examination of the target of Figure 2 leads to the conclusion that the arc is influenced to move toward the edge of the permeable target, for there is no reason to expect it to move specifically toward the N-ring 24 otherwise.

The assignee of the present application has conducted 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 struck within the ring and the resulting erosion pattern was normal -- that is, it corresponded to that of Figure 3.

The above principles are incorporated in the Figure 5 embodiment of the present invention where a permeable target 16 is surrounded by a flat ring 1 9 made of a permeable 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 but not limited to iron; nickel; cobalt; and alloys thereof with small amounts of optional additives; ferrites; steel; etc. Further, the ring 1 9 may comprise an integral extension of the target itself. Hereinafter ring 19, whether it be a separate member, as shown in Figure 5 or an integral extension of the target will be termed a "P-ring".

N-ring 24 is disposed around the periphery of target 1 6 and contributes to the confinement of the arc on the target surface. The Nring also retains ring 1 9 and target 1 6 in place via a bolt 21 which is threaded into cathode body 1 8.

Although there is no intent to be limited to a particular theory of operation, the following considerations apparently are applicable to P rings of the present invention. It has been observed a vacuum arc struck on a nonpermeable target wanders randomly about, 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 areas in milliseconds. Obviously, for uncontaminated coatings, the arc must remain only on the target.

The early literature of magnetic fields 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, it appears the arc moves away from the permeable material that reduces field density.

Another insight relating to the containment mechanism is obtained from the work of Naoe and Yamanaka ("Vacuum-Arc Evaporations of Ferrites and Compositions of their Deposits" Japanese Journal of Applied Physics, Vol. 10, No. 6, June 1971, copy submitted herewith), who arc-evaporated ferrite composites from a cup-shaped ferrite target. They were attaining a melted portion of the target, and the oxide materials behaved very differently from the metals. They reported a very stable arc that moved in a very slow circular motion at the approximate center of the cup. They made no reference to this as unusual behavior, but gave considerable detail of the arc motion as observed visually. Implications relative to general arc containment were lacking.

To better understand this phenomenon the assignee of the present invention has used a DC current through a wire to generate a cylindrical magnetic field of the type that the arc appears to produce close to the target.

This wire has been brought into the proximity of various geometries of permeable targets and "iron filings diagrams" produced to give insights to the magnetic influence of these permeable materials on the magnetic field.

It should be noted this is somewhat different from the application of a magnetic field to interact with the arc field as applied in aforementioned U.S. Patent Nos. 2,972,695 and 3,783,231, for no external 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 generated between the wires is cancelled, for the flux direction is different on the right versus the left of the wire.

In actuality, an arc is quite unique, and modeling it as a wire with current flowing is not a true indicator of what an arc will do. If sufficient current is permitted to flow in the arc, it will divide itself into two simultaneous arc spots moving independently about the cathode surface. This is quite the reverse of the wires which move together as current flows. Simple explanation of this difference 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 sideways in the wire, creating equal and opposite forces on the wires.Thus the wire moves opposite to the direction the arc moves where the magnitude of the force moving an arc toward the edge of a permeable target is significant relative to the random motion forces that typically move the arc about a nonpermeable target.

Figures 6(a), 6(b), 7(a), and 7(b) show the nature of the filing diagrams from the various conditions of permeable and non-permeable targets. In Figure 6 less and less flux density 23 is seen as the iron plate 32 is approached for these lines (of which only the cross sections are seen) are drawn into the iron, for they travel more easily there. In the case of the aluminum target 34, the flux remains very constant as the plate is approached, as can be seen in Figure 6(b). Moving to the target edge, as in Figure 7(b), makes no change in the case of the aluminum target. However, as shown in Figure 7(a) movement to the edge of the iron target produces a reasonably strong flux outboard of the target, and virtually none inboard. With the force on the arc thus outward, it is quite understandable that the arc races for the outside edge.The forces will be nil when the arc is perfectly in the target center, but normal random migration from the arc action will quickly 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 is trapped between the induced electromagnetic force outward, and the "N' '-ring which prevents the arc from moving further outward. There is relative freedom of motion only into the plane of Figure 4. Thus the arc moves around the target perpendicularly to the trap. The attempt here is not to fully define the arc motion, but only to show certain aspects of it can be influenced significantly for purposes of control.

Furthermore, it follows that the presence of P-ring 1 9 of Figure 5, the lines of force travel as easily through ring 1 9 as they do through target 1 6 disposed within the inner periphery of the ring. Hence, the flux density within the ring is substantially equal to that outside the ring's inner periphery. Tfius, there is no outward force on the arc as is the case in Figure 4 device. Accordingly, the arc randomly migrates over the entirety of the permeable target surface 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, which 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 nonpermeable 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 target to be ultra-cleaned by an arc so that the P-ring can then be employed to effect its arc retention function where, in Figure 8, N-ring 24 may be (a) a separable cover on or (b) a coat painted, sputtered, evaporated, or otherwise applied to P-ring 1 9.

The literature repeatedly stresses the need for ultra-clean conditions for the target assembly, but gives little description of the behaviour of an 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 the removal of these contaminants occurs during the initial cleaning phase of the target with the substrate in some instances, removed from the system.

During this 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 effective to evaporate the target. At this time, the substrate may be placed in the system preparatory to coating thereof if not already in place.

The N-ring appears to restrain the arc to the target during the initial cleaning phase even when the target is assembled in a dirty state.

The P-ring is 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 coats the portion of the ring immediately adjacent the target, and the control of the arc becomes quite absolute. However, during the initial cleaning phase, the arc can move onto the back and sides of the cathode body 1 8 where it may damage the structure, or evaporate contaminating metals into the chamber.

In certain applications, the N-ring tends to (a) be somewhat fragile, (b) have a rather limited life time, (c) be expensive and (d) lose target material deposited therein due to its low wettability. Hence, it is desirable to take advantage of the N-ring's arc retention capability during the initial clean-up (that is, the Nring appears to hold type-one arcs for many target materials, perhaps all, at least all that have been tested by the assignee to date) and then utilize a P-ring once the target has 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 of the arc-cleaning problem is a function of the target material. For example, aluminum is very bad, zirconium is very good.

The observation of the assignee is that typeone arcs have a hierarchy of functions. First, they search 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 extinction. During most of this period there is almost no evaporated metal coming from the dischargeeven though it may last for many seconds. It appears to still be operating as a type-one arc which has only a tiny evaporation output.

There is probably the explosion of sharp points and ridges which can give vast numbers of electrons at quite low arc voltages.

In the oxide phase of clean-up, the arc easily transgresses the P-ring, onto the nontarget 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 of electrons does it change into a type-two arc and proceed with flash evaporation of the target surface.

Because, as stated above, the N-ring will hold the oxide phase discharge, the embodiment of Figure 8 may be employed to optimize the respective advantages of N-ring 24 and P-ring 1 9. 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 is established on the target. The cover would then be removed from the target to uncover it. There would then be 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 less than before, however, and the total cleanup time is less than that which would be required in the absence of the N-ring cover.

Moreover, since this cover would be removed after the clean-up (to thereafter allow the Pring to effect the arc retention function, 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.

When 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 especially when the coating is made from Tin or a similar material. The BN paints do not adhere very well. Radio frequency sputtering of BN onto the ring 1 9 is better. The most acceptable approach is the use of titanium nitride--the very material that many arc systems are designed to produce.

An extra iron ring 1 9 can be coated along with a batch of tools, for example. This ring can then serve with the next 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 phase of the target clean-up, so this method can be very practical. Furthermore, the TiN coating does not result in flaking.

It is to be understood that the above detailed description of the 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 (23)

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 target surface; and a first confinement ring contacting the target and surrounding the target surface, the ring being composed of a material 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.

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 cleanup 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 1, 2 or 3 where the mean charged particle energies of said arc are about 20-100eV.

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

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

15. Apparatus as in Claim 14 where the nitride compound is selected from the group consisting of boron nitride and titanium nitride.

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

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

1 8. Apparatus as in Claim 1 7 where the anode and substrate are the same member.

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 Claim 19 where said target is mounted on said cathode.

21. Apparatus as in Claim 19 where said target and cathode are the same member.

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

23. Apparatus for evaporation arc stabilization substantially as hereinbefore described with reference to the accompanying drawings.