Cathode sputtering apparatus

Abstract

Cathode sputtering apparatus for operation within an evacuable enclosure for coating a substrate which is also contained within the enclosure. The apparatus includes a cathode which carries a face of material to be sputtered. Magnetic means is placed adjacent to the cathode at a side thereof opposite from the face, and the magnetic means includes a pair of magnetic poles, between which there are developed magnetic lines of force. At least some of these lines of force enter and leave the face at spaced-apart intersections therewith and include segments which extend between the intersections and are spaced from the face whereby to form a boundary, along with the face, of a closed area in the plane of the respective lines of force. An anode is placed in proximity to the cathode. Connector means is provided to connect the cathode and anode to a source of electrical potential. Preferably, at least one of the magnetic poles is elongated and generally aligned with the face so as to generate a magnetic field wherein closed areas are continuously and contiguously formed over a substantial distance along the face whereby to form a tunnel-like path within which charged particles tend to be retained, and along which they tend to move. Preferably, this tunnel-like path is closed upon itself to form a continuous path without beginning or end.

Description

This invention relates to apparatus for use in cathode sputtering. Cathodic sputtering is widely known and extensively used, especially for the application of thin films of material onto substrates. The process involves the transport of a material from a cathode to a substrate via the vapor phase. The ejection of the material into the vapor phase is accomplished by bombarding the cathode (sometimes called a "target") with ions of sufficient energy to accomplish this. The target surface disintegrates primarily as a result of momentum transfer between the incident ions and the cathode face. The ejected particles traverse the evacuable enclosure and subsequently condense onto a substrate to form a thin film.

The process of sputtering is ably described in U.S. Pat. No. 2,146,025, issued to Penning on Feb. 7, 1939, and in U.S. Pat. No. 3,282,816, issued to Kay on Nov. 1, 1966. In addition, two relatively more recent patents are of general interest, U.S. Pat. Nos. 3,616,450 and 3,711,398, issued to Clarke on Oct. 26, 1971, and Jan. 16, 1973, respectively. Because the physics of sputtering techniques are generally well-understood and are ably described in the Penning and Kay patents, a full description of the basic theory and operation of sputtering apparatus is unnecessary to an understanding of this invention.

While devices for sputtering have been intensively developed, still it is found that the purity and cohesiveness of films are subject to improvement, as is the production rate of deposition. This invention enables cathode sputtering to take place at substantially increased production rates and at convenient pressure levels, while producing films of greater purity and adhesiveness to the substrate. The device operates economically, is rugged in construction, and is simple to service and to maintain.

A persistent problem in prior art sputtering devices is that charged particles have been able to escape from the cathode region. When that occurs, efficiency drops, and so does the quality of the coating. If charged particles are used efficiently, then lower chamber pressures and fewer ions are needed for the sputtering process. Under these circumstances, fewer stray particles are in the chamber where they might contaminate the product. Concomitantly, a reduced voltage can be used along with a reduced pressure (ordinarily an incompatible situation), and power consumption is greatly reduced. Reduction of power consumption reduces the need for coolants, and also exposes the substrate being coated to less radiant heat which may tend to curl or otherwise adversely affect the substrate.

It is an object of this invention to provide cathode sputtering apparatus which is efficient in its utilization of charged particles, tending to retain them at the cathode region, thereby attaining the foregoing advantages.

Another persistent problem in the prior art has been the tendency of stray magnetic fields to cause glowing and sputtering at incorrect places. This can damage the equipment and contaminate the product. It is an object of this invention to provide a magnetic structure which concentrates the magnetic field where it is intended to be used, and which inherently inhibits the formation of stray magnetic fields in the magnetic structure.

A further improvement of function is secured by this invention in many of its embodiments. It is a considerable advantage to utilize as much as possible of the light from the glow which is present during the sputtering process, for causing electron emission. Most electron emission is caused by photoexcitation, and in many of the embodiments of this invention, a cathode structure is utilized wherein the light from the glow at one region is received by another region and utilized there for emission of electrons.

Still another improvement is attainable with many of the embodiments of this invention. Because the vaporized particles can move in all directions, including away from the substrate, it is an advantage to generate them in such a manner that their initial paths are directed as much as possible toward the substrate to be coated. In many of the emodiments of this invention, the cathode face opens (or faces) in a direction toward the substrate to be coated, and is excluded from initial paths in the opposite direction, thereby substantially increasing the yield and production rate. This is a particularly important advantage when the material being sputtered is expensive, for example, gold.

Cathode sputtering apparatus according to this invention is intended to be utilized in an evacuable enclosure for coating a substrate which is also contained within the enclosure. This apparatus comprises a cathode which carries a face of material to be sputtered. Magnetic means is provided adjacent to the cathode and to the side thereof opposite from the face. The magnetic means includes a pair of magnetic poles, between which there are developed magnetic lines of force, at least some of which enter and leave the face at spaced-apart intersections therewith, and which include arched segments which are spaced from the face and which extend between the intersections, thereby to form a boundary, along with the face, of a closed area in the plane of each respective line of force. An anode is placed in proximity to the cathode, and connector means is provided for the cathode and anode so that they may be connected to a source of electrical potential.

According to a preferred but optional feature of the invention, at least one of the magnetic poles is elongated and generally aligned with the face, whereby to generate a magnetic field in which a tunnel-like path is formed within which charged particles tend to be retained, and along which they tend to move.

According to still another preferred but optional feature of the invention, the cathode is held by a cathode support in surface-to-surface abutment therewith, and cooling means is provided for the cathode support to cool both it and the cathode.

According to yet another preferred but optional feature of the invention, the magnetic means includes a pair of pole pieces which embrace the cathode support and which is abut said of the cathode.

FIG. 1 is an axial cross-section of the presently preferred embodiment of the invention;

FIG. 2 is a cross-section taken at line 2--2 of FIG. 1;

FIG. 3 is an axial cross-section of a modification of FIG. 1;

FIG. 4 is an axial cross-section of yet another modification of FIG. 1;

FIG. 5 is a lateral cross-section of another embodiment of the invention taken at line 5--5 of FIGS. 6 and 8;

FIG. 6 is a top view taken at line 6--6 of FIG. 5;

FIG. 7 is a lateral cross-section of still another embodiment of the invention taken at line 7--7 of FIG. 9;

FIG. 8 is a top plan view of another embodiment of the invention whose lateral cross-section, like that of the embodiment of FIG. 6 is shown in FIG. 5;

FIG. 9 is a top plan view of the embodiment of FIG. 7;

FIG. 10 is a fragementary cross-section of a modification of the cathode suitable for use with this invention;

FIG. 11 is a fragmentary cross-section showing another type of magnetic means usable with this invention;

FIG. 12 is an axial cross-section of another suitable cathode construction;

FIGS. 13 and 14 are perspective views of the embodiments of FIGS. 9 and 16, respectively, showing their magnetic fields in greater detail;

FIG. 15 is a fragmentary cross-section showing yet another usuable cathode shape;

FIG. 16 is a cross-section taken at line 16--16 in FIG. 14;

FIG. 17 is a fragmentary cross-section of another modification of FIG. 1;

FIG. 18 is a perspective view of yet another embodiment of the invention; the device of FIG. 9; and

FIG. 20 is a cross-section showing another suitable form of magnetic means.

In FIG. 1 there is shown cathode sputtering apparatus 20 enclosed within an evacuable enclosure 21. The encloure has a top section 22 and a bottom section 23 which are schematically shown joined together at a hermetic seal 24.

An opening 25 in top section 22 is provided for receiving a closure plate 26, which both closes opening 25 and supports the cathod sputtering apparatus. Plate 26 may, if desired, be made of insulating material. A substrate support 27 supports a substrate 28 whose upper surface 29 is to be coated by the use of this invention. A vacuum pump 30 is provided to evacuate the enclosure to the desired pressure. Should it be desired to inject gases into the enclosure, it may be done through conduit 31 which is controlled by valve 32.

Closure plate 26 acts as a suport for the sputtering apparatus and is itself sealed to the inside surface 35 of the enclosure by sealing ring 36. Plate 26 is fastened in place by fasteners 37. A metal anode 38 is supported by plate 26. A sealing ring 39 surrounds a conductive support stem 40 which supports the anode. The stem constitutes connector means for connecting the anode to a source of electrical potential. As shown, anode potential will be that of the enclosure. Alternatively, the stem may be insulated from the closure plate where it passes through it by means such as an insulating grommet, and anode potential applied to the stem which is different from that of the enclosure.

A metal conduit 42 is provided for supplying coolant fluid. It also constitutes conductor means for connecting the cathode to a source of electrical potential. This conduit passes twice through closure plate 26 for the entry and exit of coolant fluid. It is brazed and sealed by brazing at joint 44 to a first plug 45. A second plug 46 is opposed thereto, and these plugs are drawn toward one another by fasteners 47. An insulating spacer 48 is fitted under second plug 46, and a sealing plate 49 is placed between the first plug and the closure. Sealing plate 49 carries a pair of sealing rings 50, 51. Accordingly, the plugs, spacer and sealing plate form a hermetically sealed pass-through for metal conduit 42.

A cathode 55, having a face 56 of material to be sputtered, is formed in this embodiment as a right circular cylinder having a central axis 57. It has a cylindrical face 56 and a cylinderical outer wall 58. The cylindrical face is concave curved surface.

A cathode support 59 surrounds the cathode and has an inner wall 60 which is in contiguous, surface-to-surface contact with the outer wall 58 of the cathode. In its outer wall 61, the support has a groove 62 in which conduit 42 is seated in heat-transfer relationship to the cathode support. Coolant fluid passing through conduit 42 cools the cathode support and through it cools the cathode. It also is in intimate electrically conductive contact therewith so as to apply cathode potential to the cathode support and through the conductive cathode support to the cathode itself.

A magnetic means 65 surrounds the cathode and also surrounds the cathode support. In the embodiment shown in FIG. 1, this means comprises a plurality of permanent magnets 66, each of which has a pair of inherent magnetic poles 67 and 68 (north and south). Because all of the magnets are alike, only one will be described. All of the upper poles in FIG. 1 will have the same polarity, and all of the lower poles therein will have the opposite polarity. The magnets are grouped substantially continuously around the cathode so as to form a magnetic field inside the cathode. Because in this invention it is desired to particularly place and shape the mamgnetic field, pole pieces 69, 70 are provided which act as the poles of the magnetic means. They are rings of magnetizable material, and are attached to the top and the bottom of the magnets and are held together by supports 71 which also hold the cathode assembly spaced from the cover plate 26. Accordingly, pole pieces 69 and 70 comprise extensions of the magnets and are referred to as poles of the magnetic means. Each has a different polarity from the other. They embrace the cathode support. At least one, and in this embodiment. both, of the pole pieces are elongated and aligned with the said face in the sense that they extend along it, adjacent to the side 72 of the cathod, i.e., its cylindrical outer wall 58, which is on the opposite side of the cathode from face 56.

It will be seen that the magent, the pole pieces, the cathode support and the cathode are all in a compressive fit with one another, whereby to be electrically conductively connected with one another and also so as to be in a good heat-transfer relationship with one another. When the cathode becomes heated, and the support is cooled, the cathode expands into a tighter fit therewith.

It is a feature of this magnetic means which enter and leave the said face at intersections 76, 77, which are spaced apart by a portion of the face. Each line of force includes a continuously arched segment 78 which is spaced from the face. With the face, each segment forms the boundary of a closed area 79. It will be understood that there is an infinite numer of lines of force through any axial plane, and that their curvatures, and therefore the closed areas which they define, will differ. What is intended to be defined is a region contiguous to the face, closed and bounded by the face and by the curved lines of force. Because at least one of the poles is elongated, there is formed a tunnel-like path within which charged particles tend to be retained, and along which they tend to move. In this embodiment, the tunnel-like path is closed on itself to form a continuous path without beginning or end. Geometrically speaking, this path is a volume of revolutions with the closed area as a generator moved around the central axis 57.

The use of the pole pieces concentrates the intersections at peripheral band-shaped regions which are axially aligned with the pole pieces. Because the magnetic field is substantially continuous around its periphery, an infinite number of said closed areas is formed contiguous to and continuous with one another, whereby a ring-shaped, tunnel-like region of magnetic force is provided which tends to trap charged particles and prevent their escape. Instead, it causes them to whirl around the inside of the ring adjacent to the face, whereby to increase the efficiency of sputtering. This overcomes the objections found in much of the prior art, especially in the Clarke patents, wherein it is possible for charged particles to escape from the magentic region, and those devices therefore operate at considerably lesser efficiency.

FIG. 1 shows a construction wherein the cathode sputtering apparatus is entirely contained within the evacuable enclosure, and the cover plate is substantially flush with the enclosure. FIG. 3 shows a construction wherein cathode sputtering apparatus 85, which is generally similar to that shown in FIG. 1, is supported on the outside of an evacuable enclosure 86 and above a substrate 87 to be coated. The cathode structure bears numbers used in FIG. 1 for similar parts. It is sandwiched between two sealing plates 88, 89 which are provided with appropriate sealing rings 90, 91, 92, 93 and are pressed together in a pile by a closure plate 94 and fasteners 95.

Anode 38 passes through end plate 94 as it passes through closure plate 26 in FIG. 1. Apart from this difference in details of construction, and the fact that the cathode support itself forms part of the hermetic enclosure, the devices of FIGS. 1 and 3 are basically identical. Again, plate 94 can be made of insulating material, or the anode stem insulated from the plate, if anode potential is to be different from that of the enclosure.

FIG. 4 shows a construction which differs from FIG. 1 in certain details, wherein and anode 100 is at the same potential as that of the evacuable enclosure 101 and is more rigidly attached thereto. The means attaching the anode to the enclosure is the connector means for it. In this case, and adapter plate 102 is utilized to mount both the anode and the cathode construction which bear indentical numerals to those used in FIG. 1. An insulating spacer 103 spaces the cathode from anode potential.

The cathode in this embodiment is made in two parts. One is a central sleeve 104 having a face 104a of material to be sputtered, and the other is a ring 105 which closely fits inside the cathode support, and in which the sleeves fits. A flange 106 on the ring is located adjacent to the magnetic means when the ring is in place. A magnetizable ring 107 is shrunk onto flange 106, and holds ring 105 in place because it is attracted by the magnets. The cathode can therefore readily be removed and replaced in the support, and a new sleeve can readily be fitted into ring 105. The fit is close enough that heat conductivity and electrical condutivity are assured, even when cold. When the cathode is heated in operation, it expands to make a tighter fits in the cathode support.

A ring-shaped shield 108 is placed just below the lower end of the cathode to form a physical shield that protects the cathode from stray charged particles. This protects the end of the cathode from erosion. This shield may be maintained at anode potential by a conductive connection 108a, and is supported in place by means not shown.

The foregoing sputtering devices are ring-shaped, and the faces of the cathodes are concave surfaces, for example, right circular cylinders, although it will be understood that tapered surfaces and the like may also be used. In FIG. 12, a frustoconical cathod 109 is shown which can be used with an appropriately shaped cathode support. An economy of use of the light generated in this construction is accomplished when concave surfaces are used, because all portions of the face are exposed to the light from other portions of the face, and this light is utilized in the photoemission of electrons.

FIGS. 5-9, 13, 14, 18 and 19 illustrate that the construction of the apparatus need not be circular, by may be linear or curvilinear instead.

FIGS. 5 and 6 show a linear (straight-line) cathode sputtering apparatus 110. It is intended that this device be contained in an evacuable enclosure during sputtering operation. It has as its objective to coat a substrate 111 suitably supported in the enclosure. The device may be operated in any position. As shown, it is arranged so its ejected material cannot move downwardly, but principally upwardly, in order to coat lower surface 112 of the substrate. An anode 113 is provided in the form of a plate-like strip running parallel to the sturcture, and conductive means 114 provides for applying an electrical potential to it. As in the other embodiments of the invention, a metal conduit 115 for conducting coolant fluid also operates as conductive means 116 to apply electrical potential to the cathode.

The structure includes a metal cathode 117, having a face 118 of material to be sputtered. The cathode has a side 119 opposite from the face in contiguity with a cathode support 120. The cathode support is embraced by a pair of magnetic pole pieces 121, 122 which also embrace a permanent magnet 123. The pole pieces extend longitudinally for substantially the full lenth of the structure, as will the magnet itself. Therefore, the pole pieces are of opposite magnetic polarity.

Side frame members 124, 125 clamp the aforesaid members together and include lips 127, 128 which form channels into which the cathode may be slid or snapped. The cathode when installed is preferably a bent plane, of which the example shown is the axial fragment of a cylinder. The cathode extends parallel to a linear axis 129. Similarly, the magnetic means extends axially behind the cathode and generates magnetic lines of force 130 which enter and leave the said face at intersections 131, 132 and include continuously arched segments 133, all as heretofore described. A closed area 134 is formed at every section line similar to FIG. 5--5 along the length of the device.

In the devices of FIGS. 5-9, 13, 14, 18, and 19, the face of the cathode opens in a direction generally opposite side 119, i.e., the side of the cathode which abuts the cathode support. This is to say that they do not make a complete circle, and parts of the magnetic structure and parts of the face do not face in the same direction. Instead, the fact is directed in a principal direction (upwardly in FIG. 5), and there is no possibility that sputtered material will be projected downwardly. This contrasts with FIGS. 1-4 wherein the cathode opens in a direction wherein the face faces toward itself, and the ejected material can migrate both upwardly and downwardly. Parenthetically, it is noted here that ejected material which simply files from one part of the face in FIG. 1 to another part of the face represents a lesser efficiency of operation. Such a condition can occur in FIG. 5 only in a very narrow range of angles.

FIGS. 7, 8, 9 and 14 utilize the principles of FIG. 6, except that the tunnel-like path formed by the magnetic lines of force closes on itself, and has no beginning or end. In FIG. 6, the path has a beginning and an end, and an accompanying disadvantage which will later be discussed.

FIGS. 7, 9 and 13 illustrate a cathode sputtering apparatus 134 generally similar to that of FIG. 5 wherein two sets of closed areas 152, 153 are provided. In this arrangement, the cathode 135 is held by side plates 136, 137 against three pole pieces 138, 139, 140 and two cathode supports 141, 142. An anode 143, similar to anode 113 (of FIG. 5), is similarly provided and conductive metal conduit 144 passes through both of the cathode supports to apply electrical potential and to cool the cathode.

The permanent magnets 145, 146 are oppositely magnetically oriented so that the outer two pole pieces are of the same polarity, and the central pole piece is of opposite polarity. Two sets of magnetic lines of force 147, 148 are provided, each of which intersects the face 149 at spaced-apart intersections forming continuously arched segments 150, 151 and two sets of closed areas 152, 153 which contiguously and continuously extend in the form of a tunnel-like path for the full length of the linear device. With this arrangement, the charged particles in each of the sets of segments will travel in opposite direction. It is noted here that, if the construction of FIG. 7 is used to form only a linear path as is done in FIG. 6, then the arrangement of polarity of the magnets may instead be made so that they are similarly directed. In this event, the polarity of the outer pole pieces will be different from one another, and the direction of travel of charged particles will be the same.

The embodiment of FIG. 6 has the disadvantage that its path has a beginning and an end, and that charged particles will be ejected from the end. Also, since there is a beginning, sputtering will not occur for an intial length of the path, and part of the device is not functional for generation of sputtered material.

The devices of FIGS. 7, 8, 9, 13, 14, 18 and 19 overcome this deficiency. FIG. 8 shows a "racetrack" shaped cathode sputtering apparatus 155, a lateral cross-section taken anywhere normal to the path being substantially indentical to that of FIG. 5. It is simply the straight device of FIG. 5 wrapped into the shape shown so that the tunnel-like path (dotted line 156 shows the orientation of the path) is closed on itself so that it has neither beginning nor end.

Now to return to the embodiment of FIGS. 7 and 9. Because the direction of travel of charged particles through areas 152 and 153 are opposite from one another, by interconnecting their ends, a continuous ovular path can be established. This can readily be accomplished by providing end pieces 157, 158 which comprise semi-circular pieces that include a continuation of the magnets, the outer side plates, and outer poles pieces, but not the inside pole piece 139. The effect is to create a dish-shaped cathode support and cathode with side plates 136 and 137, pole pieces 138 and 140, and cathode supports 141, 142 joined as part of a continuation ovular structure supports 141, 142 joined as part of a continuous ovular structure around pole piece 139 as a center. The path 159 of charged particles is then as shown in FIGS. 9 and 13. The outer pole piece in FIGS. 13 and 14 is sometimes called a "peripheral" pole piece.

The dish-shaped cathode may be provided as a central straight section with a semi-circular section adjacent to each end, or it may be made as a single piece, and the side plate made in two pieces held together by removable fasteners 159a, 159b, as shown in FIG. 7, to permit removal and replacement of the cathode by lifting off the top part.

FIG. 10 illustrates that, while the preferred embodiment of cathode is that of a concave surface in order to make maximum use of the light from the glow, a planar surface will also function, although with less efficiency as to the use of the glow. In this embodiment, a cathode sputtering apparatus 165 is shown with side plates 166, 167 embracing a pair of pole pieces 168, 169, a permanent magnet 170, and a cathode support 171. The effect of this arrangement is to generate magnetic lines of force 172 as aforesaid to create a closed area 173 with the face 174 of the electrode, and this construction may be utilized in a ring or ovular shape as shown in the other embodiments, suitably modified to support a flat surface.

FIG. 11 illustrates the substitution in cathode sputtering apparatus 175 of an electromagnetic 176 in place of a permanent magnet. FIG. 11 may be considered a lateral cross section taken in FIG. 1, or in any of the other embodiments, with the direct substitution of an electromagnet for the permanent magent disclosed in those embodiments. In order to generate magnetic lines of force 177 with best shape for this device, the electromagnet should be spaced from the cathode far enough that the irregularties in the field caused by the windings 178 will not affect the field shape inside the cathode.

FIG. 12 shows a frustoconical cathode face 109 which can be utilized with obvious modification of supporting structure. This shape provides an improved downward concentration of sputtered material, compared to the devices of FIGS. 1-4.

FIG. 15 is a modification generally similar to that of FIG. 10 showing the use in a cathode sputtering apparatus 180 of a cathode 181 with a convex face 182, in which lines of force 183 are generated to form a tunnel-like path. The comments pertinent to FIG. 10 as to the non-concavity of the cathode face and the utility of the modification are pertinent here.

FIGS. 14 and 16 show a circular cathode sputtering apparatus 210. It includes a central magnetic pole piece 211 formed as a post, a peripheral pole piece 212 formed as a cylinder, and a ring-shaped magnet 213 between them, magnetized with a pole adjacent to each pole piece. A ring-shaped cathode support 214 lies between the pole pieces and includes a conductive metallic coolant conduit 215 for cooling and providing cathode potential. A cathode 216 is held in the groove 217 in a side plate 218 which surrounds the structure. Magnetic lines of force 219 are generated and from a circular path 220 all as heretofore described, with intersections 221, 222, with the cathode, and continuously arched segments 223. A ring-shaped anode 224 (shown only in FIG. 16) is placed adjacent to the cathode, and has connector means (not shown) for providing anode potential.

In the devices of FIGS. 1-12, 15 and 16, the material to be sputtered will ordinarily be metallic and non-magnetic, such as copper or gold. It is also possible with this invention to sputter insulating materials, and also magnetic materials. A modification which makes sputtering of magnetic material feasible is shown in FIG. 17. An electromagnet 190 and a cathode support 191 are embraced by a pair of magentic pole pieces 192, 193. A pair of anode shields 194, 195 extend parallel to the pole pieces, and overlap the edges of cathode 196, whose face 197 faces away from side 198 where the magnetic means is placed. The anode shields are conductively interconnected by a lead 199. Instead of abutting the cathode, the pole pieces are spaced from it to leave air gaps 200, 201. When the cathode is made of a magentic material, the edges will become polarized, and lines of force 202 will be provided as in the other embodiments, and the field can be made strong enough that the cathode will have become magnetically saturated.

When insulating material is to be sputtered, radio-frequencies on the order of about 13.5 megacycles are utilized for the anode-cathode potential, rather than d.c. voltages as in the other applications already discussed. The structures, except for the gap portion will be otherwise indentical.

FIG. 13 is a perspective view of the device of FIG. 9, which shows the trough-like cathode face overlaid by the tunnel-like path formed by the face and the magnetic lines of force.

FIG. 14 is intended to show in perspective the tunnel-like path of the device of FIG. 16.

FIG. 18 shows a modification wherein the tunnel-like path 205 lies on a curved plane 206, rather than on a plane as in FIG. 10. This arrangement can provide something of a focusing action for the sputtered material Plane 206 can, of course, be convex instead of concave, at the sacrifice of some of the advantages of concavity.

FIG. 19 illustrates an advantageous modification adaptable to the embodiments of FIGS. 1-18. An examination of these embodiments will show that, while they provide magnetic poles adjacent to the cathode, they also provide them adjacent to the other ends of the pole pieces. While this does not adversely affect the sputtering operation, it does provide in a vacuum system a useless field which might be the source of mischief. This is avoided by providing the outer pole pieces in such form that they form part of a single piece with a U-shaped lateral cross-section.

FIG. 19 is a lateral cross-section of the device of FIG. 7, bearing like reference numbers. However, pole pieces 138 and 140 are formed integrally with a bight section 225. The bight section prevents a magentic field from being formed at its end of the magnetic structure. This scheme can be applied to any of the embodiments of the invention (other than FIG. 20 which inherently has it).

FIG. 20 shows a permanent magnet 230 whose legs 231, 232 are oppositely polarized, adjacent to a cathode 233, forming magnetic lines of force 234 as in the other embodiments. This type of magnetic construction can be substituted for the multiple piece constructions heretofore discussed.

FIG. 20 illustrates that the term "pole pieces" is not limited to parts which are separable from a magnet, although they may be, but instead is intended to define structure which directs magnetic flux to locations adjacent to the cathode where the desired magnetic field will be developed.

The pole pieces will, of course, be made of magnetizable material. Also, all of the devices described herein will have anode means in close enough proximity to generate the necessary electrical field, and the anode and cathode will have connector means for the application of the necessary potential for this function.

The dimensions for the various embodiments are readily determinable by persons skilled in the art of sputtering. Many of the dimensions will be selected as a consequence of a desired production rate or bulk of the device. The device of FIG. 1 is drawn substantially to scale, with the diameter of face 56 equal to about three inches. A magnetic field of about 1,000 gauss, and a d.c. electrical potential of about 600 volts, are utilized in the illustrated device. A pressure of about 5 to 10 microns is used in the evacuable enclosure.

An advantage of this invention is that the pole pieces provide an exact definition of location of the field and the area of erosion, and magnetic components of other sputtering apparatus which may be located in the same chamber, or of other parts of the same system, cannot substantially interfere to cause stray erosion. This has been a problem in known devices. The field lines in this device which are utilized in sputtering are not appreciably affected to stray fields.

It will be noted that in this construction, charged particles cannot escape from the field in the direction of the substrate. They are trapped in the tunnel-like paths by a barrier between them and the substrate. Substantially all charged particles are retained by the magnetic field and cannot bombard or contaminate the article being coated. The particles which neutral escape past the visible glow region are netural and are in the sputtered material. The substrate can be located anywhere in the chamber, which constitutes a great advantage in design and operation. When the devices wherein the cathode faces open on one side are used, there is a considerable potential saving of expensive material obtained from the directional effect, because there is a major sector toward which the material will not migrate.

Accordingly, it will be particularly noted that there exists a magnetic field between the cathode and the substrate which acts as a barrier to the passage of charged particles. Further, because these constructions have closed magnetic fields, it is unimportant where the anode is located. It merely needs to be sensibly close to the cathode, but the ability to locate it in any desired location gives considerable versatility to where the substrate may be located for coating.

When curved concave structure is utilized, the light generated in the operation of the system is effectively utilized for electron emission by photoexcitation. The use of a flat or convex surface would be a less efficient use of this glow, but such shapes may have advantages in other design "trade-offs."

Still another advantage will be noted in every embodiment where a concave cathode is used, because when the concave cathode plate is heated, its material will expand to press against the cooled cathode support which acts as a heat sink. The hotter the cathode gets, the tighter it fits against the sink to be cooled, thereby increasing the efficiency of thermal transfer and also of electrical potential.

In the operation of the device of FIG. 1, a ring-shaped glow will be noted around the entire periphery of the inside of the cathode, and erosion will be substantially uniform throughout its entire periphery. The same is true of the operations in the other embodiments wherein the path is closed on itself, because there is a continuous path for the electrons without beginning or end. However, in the device of FIG. 6, which is a purely linear device, it will be found that near one end there will be substantially no erosion, and the erosion area grows toward the other end. Should it be desired to stop the beam, insulated dielectric material may be placed in its path for this purpose. In the closed-path devices, the glow extends along the entire length of the path.

The operation of the devices will be readily understood by persons skilled in the art and requires no further detailed description, other than to observe that by causing the magnetic lines of force to intersect the wall of the cathode in two spaced-apart locations connected by a continuous and continuously arched segment of the magnetic lines of force, there are defined closed areas within which the charged particles tend to be retained and along which they travel, whereby they are most efficiently utilized in this device.

This invention is not to be limited by the embodiments shown in the drawings and described in the description, which are given by way of example and not of limitation, but only in accordance with the scope of the appended claims.

Claims

I claim:

1. Cathode sputtering apparatus for operation within an evacuable enclosure, for coating a substrate which is also contained within said enclosure, said apparatus comprising: a cathode having a face of material to be sputtered; magnetic means adjacent to the cathode and at a side thereof opposite from the face, said magnetic means including a pair of magentic poles, at least one of which is elongated, and between which there are developed magnetic lines of force, at least some of said lines of force entering and leaving said face at spaced-apart intersections therewith, and including continuously arched segments extending between said intersections which are spaced from the face, said face together with said lines of force forming a boundary of a closed area in the plane of each of the respective lines of force, a tunnel-like path within which charged particles tend to be retained, and along which they tend to move; an anode in proximity to the cathode; and connector means whereby said cathode and said anode can be connected to a source of electrical potential.

2. Cathode sputtering apparatus according to claim 1 in which the tunnel-like path is closed on itself, whereby to form a continuous path without beginning or end.

3. Cathode sputtering apparatus according to claim 2 in which the face opens in a direction generally opposite from said side.

4. Cathode sputtering apparatus according to claim 3 in which the path is a closed loop.

5. Cathode sputtering apparatus to claim 4 in which the path includes straight and curved portions.

6. Cathode sputtering apparatus according to claim 4 in which the path is circular.

7. Cathode sputtering apparatus according to claim 4 in which the path lies on a plane.

8. Cathode sputtering apparatus according to claim 4 in which the path lies on a curved surface.

9. Cathode sputtering apparatus according to claim 2 in which the magnetic means is formed as a closed loop.

10. Cathode sputtering apparatus according to claim 9 in which the magnetic means includes a central pole piece, a peripheral pole piece, and a magnet extending between them, the cathode lying adjacent to the pole pieces whereby to form said closed path.

11. Cathode sputtering apparatus according to claim 10 in which the peripheral pole piece is closed by a bight section to suppress a magnetic field except at the cathode.

12. Cathode sputtering apparatus according to claim 2 in which the face comprises a curved surface with a central axis which it and the magnetic means surround.

13. Cathode sputtering apparatus according to claim 1 in which the magnetic means comprises a permanent magnet.

14. Cathode sputtering apparatus according to claim 13 in which the magnetic means includes a pair of magnetizable pole pieces placed adjacent to the magnet and forming said magnetic poles, and disposed adjacent to the said side of the cathode, whereby the said magnetic lines of forces are principally directed through the said cathode.

15. Cathode sputtering apparatus according to claim 14 in which a cathode is disposed between and is embraced by said pole pieces, and which supports said cathode in surface-to-surface contiguous contact therewith.

16. Cathode sputtering apparatus according to claim 15 in which cooling means is provided to cool said cathode support.

17. Cathode sputtering apparatus according to claim 14 in which the magnetizable pole pieces abut said side of the cathode.

18. Cathode sputtering apparatus according to claim 14 in which the magnetic pole pieces are continuously joined to one another at their sides on the opposite side of the magnet from the cathode.

19. Cathode sputtering apparatus according to claim 14 in which the magnetizable pole pieces are spaced from said side of the cathode whereby to leave an air gap therebetween.

20. Cathode sputtering apparatus according to claim 1 in which the magnetic means comprises an electromagnet adapted to be energized to generate said magnetic lines of force.

21. Cathode sputtering apparatus according to claim 20 in which the magnetic means includes a pair of magnetizable pole pieces placed adjacent to the magnet and forming said magnetic poles, and disposed adjacent to the said side of the cathode, whereby the said magnetic lines of force are principally directed through the said cathode.

22. Cathode sputtering apparatus according to claim 21 in which the magnetizable pole pieces abut said side of the cathode.

23. Cathode sputtering apparatus according to claim 21 in which the magnetizable pole pieces are spaced from said side of the cathode whereby to leave an air gap therebetween.

24. Cathode sputtering apparatus according to claim 21 in which the magnetic pole pieces are continuously joined to one another at their sides on the opposite side of the magnet from the cathode.

25. Cathode sputtering apparatus according to claim 1 wherein said face comprises a curved surface.

26. Cathode sputtering apparatus according to claim 25 in which the face has a central axis which it and the magnetic means surround.

27. Cathode sputtering apparatus according to claim 26 in which the face is a circular cylinder.

28. Cathode sputtering apparatus according to claim 25 in which the curved surface is concave.

29. Cathode sputtering apparatus according to claim 25 in which the curved surface is convex.

30. Cathode sputtering apparatus according to claim 1 in which a conductive cathode support supports said cathode in surface-to-surface contiguous contact therewith.

31. Cathode sputtering apparatus according to claim 30 in which the cathode support forms a recess, and in which the cathode closely fits in said recess, whereby when the cathode temperature increases and the cathode expands, the cathode is pressed into firm contact with the cathode support.

32. Cathode sputtering apparatus according to claim 30 in which said cathode support includes abutment means adapted to engage a pair of opposite edges of said cathode, whereby when the cathode temperature increases and the cathode expands, the cathode is pressed into firm contact with the support.

33. Cathode sputtering apparatus according to claim 1 in which the face comprises a curved surface on which one and only one straight line can be drawn through each and every point thereon, said lines being normal to the plane of the closed area, all of said lines being parallel to one another.

34. Cathode sputtering apparatus according to claim 1 in which the face opens in a direction generally opposite from the said side.

35. Cathode sputtering apparatus according to claim 1 in which the face is planar.

36. In combination: an evacuable enclosure; means for evacuating said closure; a substrate support in said enclosure; and cathode sputtering apparatus according to claim 1 in said enclosure.

37. A combination according to claim 36 in which the tunnel-like path is closed on itself, whereby to form a continuous path without beginning or end.