US3627663A

US3627663A - Method and apparatus for coating a substrate by utilizing the hollow cathode effect with rf sputtering

Info

Publication number: US3627663A
Application number: US715804A
Authority: US
Inventors: Pieter D Davidse; Howard L Whitaker
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1968-03-25
Filing date: 1968-03-25
Publication date: 1971-12-14
Anticipated expiration: 1988-12-14
Also published as: DE1914747A1; FR1602787A; DE1914747B2; GB1242492A

Abstract

A substrate to be coated by RF sputtering is partially or completely surrounded by a target, which has a similarly shaped cathode surrounding and supporting the target. The target and the cathode may be formed of a pair of parallel plates or a hollow member. By controlling the pressure of the gas within the partially evacuated chamber in which at least the target is disposed and/or the spacing of the cathode plates or the size and geometrical configuration of the hollow member, a single common negative glow can be produced by either having the negative glow from the two parallel cathode plates overlap or touch each other or having a single negative glow within the hollow member.

Description

United States Patent [72] Inventors Pieter D. Davldse Poughkeepsie; Howard L. Whitaker, Kingston, both of N.Y.

[211 App]. No. 715,804

[22] Filed Mar. 25, 1968 [45] Patented Dec. 14, 1971 [73] Assignee International Business Machines Corporation Armonk, N.Y.

[54] METHOD AND APPARATUS FOR COATING A SUBSTRATE BY UTILIZING THE HOLLOW CATIIODE EFFECT WITH RF SPUTTERING 19 Claims, 9 Drawing Figs.

[52] U.S. Cl 204/192,

[51] Int. Cl C23c 15/00 [50] Field otSearch 204/192,

[5 6] References Cited UNITED STATES PATENTS 1,926,336 9/1933 l-iunter,.|r. 204/192 Primary Examiner-John H. Mack Assistant ExaminerSidney S. Kanter Attorneys-Hanifin and Clark and Frank C. Leach, Jr.

ABSTRACT: A substrate to be coated by RF sputtering is par-.

tially or completely surrounded by a target, which has a similarly shaped cathode surrounding and supporting the target. The target and the cathode may be formed of a pair of parallel plates or a hollow member. By controlling the pressure of the gas within the partially evacuated chamber in which at least the target is disposed and/or the spacing of the cathode plates or the size and geometrical configuration of the hollow member, a single common negative glow can be produced by either having the negative glow from the two parallel cathode plates overlap or touch each other or having a single negative glow within the hollow member.

RF POWER SOURCE PATENTED DEC 1 4m SHEET 1 BF 3 RF POWER N SOURCE HOWARD L. WHITAKER ATTORNEY E 5 m M m D E m mr E P PATENTEUHEBWQTI 3.627.663

SHEET 2 OF 3 RF POWER SOURCE RF POWER SOURCE RE POWER SOURCE PATENIEU DEE I 41971 SHEET 3 OF 3 RF POWER SOURCE ARGON GAS R.E POWER SOURCE 53 FiIFI 'PowER SOURCE HOLLOW CATHODE EFFECT REGION OF OPERATION FIG. 8

APPLIED VOLTAGE FIG. 9

V vs.d

DISTANCE BETWEEN PARALLEL CATHODE SURFACES (d) METHOD AND APPARATUS FOR COATING A SUBSTRATE BY UTILIZING THE HOLLOW CATHODE EFFECT WITH RF SPU'ITERING Is is known that proper positioning of two parallel plates within a partially evacuated chamber in which the plates function as two parts of a cathode results in the negative glows of the two plates interacting or overlapping each other to form a single negative glow. This is accomplished by control of the pressure of the gas within the partially evacuated chamber in which the cathode plates are disposed and the spacing of the two plates from each other.

This phenomenon, which is known as the hollow cathode effect, has been utilized to produce sputtering from a target onto a substrate. U.S. Pat. No. 3,250,694 to Maissel et al. discloses the utilization of this phenomenon in which a cylindrical shaped target is surrounded by a cylindrical shaped cathode with the substrate disposed along the longitudinal axis of the cylinders. A DC voltage is applied to the cathode. The target also is surrounded by a grounded shield.

In order to utilize DC power to produce sputtering, it is necessary that the target be formed of a conductive material. Therefore, DC power cannot be utilized with dielectric materials to produce sputtering.

The present invention is an improvement of the aforesaid Maissel et al. patent in that it is particularly useful for depositing a dielectric material onto a substrate by employing the hollow cathode effect. Thus, the present invention permits a dielectric material to be deposited substantially uniformly over the various surfaces of a substrate.

Furthermore, the present invention contemplates coating substrates of various shapes, which may be nonuniform. The present invention forms the cathode and target in substantially the same geometric configuration as the substrate so that the substrate will lie within a single negative glow and not within the dark space of the cathode.

When using the apparatus of the present invention, it is not necessary to employ any type of shield to prevent leakage of current from the cathode around the target to the anode as utilized in the aforesaid Maissel et al. patent. This is prevented by making the area of the target at least as large as the cathode, and preferably larger, so that there can be no leakage around the target. When used in conjunction with the hollow cathode efi'ect wherein the glow discharge is retained within the cathode, the utilization of RF power as the source of energy eliminates the requirement for any type of shield while still producing the desired substantially uniform coating on the substrate.

The use of RF power for coating a substrate with a dielectric material has previously been suggested in 0.8. Pat. No. 3,369,99l to Davidse et al. However, the aforesaid Davidse et al. patent has required and grounded shield to suppress any glow discharge that might occur behind the target in the vicinity of the target electrode. The present invention eliminates any requirement for a shield to be utilized with the target in the vicinity of the target electrode.

In the aforesaid Davidse et al. patent, only the surface of the substrate adjacent to the target may be coated by RF sputtering. With the present invention, opposite surfaces of the substrate may be coated with the material of the target by RF sputtering.

In the copending patent application of Pieter D. Davidse et al. for Method and Apparatus for the Radio Frequency Sputtering of Dielectric Material," Serial No. 514,853, filed Dec. 20, 1965, and assigned to the same assignee as the assignee of the present application, there is shown an improvement of the aforesaid Davidse et al. patent. Thus, in the aforesaid Davidse et al. application, a blocking capacitor has been utilized to prevent any leakage of current between the anode and the cathode around the target whereby a smooth, defect-free film of the dielectric is deposited onto a substrate.

The present invention eliminates any requirement for a blocking capacitor when using RF power as the voltage source to sputter a dielectric target while still obtaining a smooth, de-

fect free film of the dielectric on the substrate. This is accomplished by making the area of the target at least as large as the area of the cathode and preferably larger.

An object of this invention is to provide a method and apparatus for coating a substrate by using the hollow cathode effect with RF power.

Another object of this invention is to provide a method and apparatus for depositing a dielectric material as a coating on a substrate in which the coating has a substantially uniform thickness and the substrate may have a nonuniform shape.

The foregoing and other objects, features, and advantages of the invention will be more apparent from the following more particular description of the preferred embodiments of the invention as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a vertical view, partly in section, of an RF sputtering apparatus for carrying out the method of the present invention.

FIG. 2 is a perspective view showing the relationship of the cathode, the target, and the substrate of FIG. 1.

FIG. 3 is a sectional view of the structure of FIG. 2 and taken along line 3-3 of FIG. 2.

FIG. 4 is a perspective view, partly in section, of another form of RF sputtering apparatus for carrying out the method of the present invention.

FIG. 5 is a sectional view of the structure of FIG. 4.

FIG. 6 is a perspective view of another form of cathode, target, and substrate.

FIG. 7 is a perspective view of still another form of cathode, target, and substrate.

FIG. 8 is a schematic sectional view of another form of cathode and target for use in coating a uniquely configured substrate by RF sputtering.

FIG. 9 is a graph illustrating the relationship of applied voltage and ion current flow in relation to the distance between the parallel cathode plates.

Referring to the drawings and particularly FIGS. 1 to 3, there is shown an RF sputtering apparatus in which the hollow cathode effect is utilized. As shown in FIG. I, the RF sputtering includes a low-pressure gas ionization chamber 10, which is formed within a bell jar 11 and a base plate 12. A gasket I4 is disposed between the jar 11 and the plate 12 to provide a vacuum seal.

A suitable inert gas such as argon, for example, is supplied to the chamber 10 from a suitable source (not shown) by a conduit 15. The gas is maintained at a desired low pressure within the chamber 10 by a vacuum pump 16, which communicates with the interior of the chamber 10, whereby a relatively high vacuum is maintained within the chamber 10.

The chamber 10 has a pair os substantially

parallel plates

17 and 18 disposed therein. The plate 18 is supported by a rod 19, which extends through the base plate 12 and is insulated therefrom. The rod 19 is connected through a lead to an RF power source 20. The plate 17 is supported by a rod 2l from the upper surface of the bell jar 11 and is connected to the RF power source 20 by a lead. Thus, both the plate 17 and the plate 18 are connected to the RF power source 20 through a common matching network or through separate matching networks.

With the base plate 12 grounded, the high-frequency alternating voltage is applied between the grounded base plate 12 and the

plates

17 and 18. The

plates

17 and 18 may be considered as the cathode while the base plate 12 functions as the anode.

It should be understood that the terms cathode and "anode" are employed merely for convenience herein. As more particularly described in the aforesaid Davidse et al. patent, the

plates

17 and 18 will function as a cathode and the base plate 12 will function as an anode only during the negative half cycles of the applied radio-frequency excitation. During the intervening positive half cycles, the polarities of the

plates

17 and 18 and the base plate 12 are reversed. However, as more particularly described in the aforesaid Davidse et al. patent, this does not produce a reversal of the sputtering operation in the present apparatus.

The plate 17 has a target 22 mounted or positioned thereon, and the plate 18 has a target 23 positioned thereon. The

targets

22 and 23 comprise the material that is to be sputtered onto a substrate. As shown in FIGS. l to 3, the substrate comprises a plurality of wires 24.

While the wires 24 could be mounted only within the bell jar 11, the wires 24 are shown extending through the wall of the bell jar ll on opposite sides thereof, Each of the wires 24 passes through air locks 25 and 2s. The air locks 25 and 26 are connected by means of vacuum lines 27 to a fast vacuum source (not shown). The fast vacuum source maintains a lower pressure in the air locks 2s and 26 than is present within the chamber 10. This seals the chamber from leakage of air from outside the chamber 10 due to the wires as passing through the wall of the bell jar l 1.

One end of each of the wires 24 is wound around a separate supply spool 28 (one shown in FIG. 1) while the other end of the wires is wound around a separate takeup spool 29 (one shown in FIG. 1). Each of the takeup spools 29 for each of the wires are may be driven by any suitable means. For example, each of the takeup spools could be connected to a motor 30. Thus, by controlling the rate of operation of the motor 30 or utilizing a gearing arrangement between the motor 30 and each of the talteup spools 29, the rate of movement of the wires 24 through the space between the

plates

17 and 18 may be controlled. The wires 24 may be moved through the chamber to either continuously or intermittently.

As shown in FIG. 2, the area of each of the

targets

22 and 23, which are plates of the same geometric configuration as the

cathode plates

17 and 18, is larger than the area of each of the

plates

17 and 18. This insures that there can be no current leakage path around the

targets

22 and 23 to the

plates

17 and 18, respectively.

The

plates

17 and 18 are positioned with respect to each other so that negative glows from the

cathode plates

17 and 18 will at least touch each other is not overlap. When this occurs, a single negative glow is produced between the

cathode plates

17 and 18. it should be understood that a dark space is adjacent each of the cathode plates 17 and H8, and the negative glow is next to the dark space. When the negative glows of the

cathode plates

17 and 13 overlap or touch each other, there is no longer any positive column or plasma in the glow discharge. Thus, the

plates

17 and 18 must be spaced a distance greater than twice the thickness of the dark space of one of the cathode plates.

The overlapping of the negative glows touching or the negative glows is known as a hollow cathode effect. Even though such a hollow cathode eifect has previously been discussed or known to be utilized with DC power, a hollow cathode effect is produced by the present invention with RF power employed.

The wires 24 are disposed so that they do not extend into the dark space. Thus, the wires 24 are disposed within the negative glow.

For a given pressure of the gas within the partially evacuated chamber it), movement of the

plates

17 and 18 toward each other would result in the overlapping or touching of the negative glows from the

plates

17 and 18 to form a single negative glow. Furthermore, as the pressure of the gas is reduced, the thickness of the dark space about each of the cathode plates 27 and i8 increases. This increase in the thickness of the dark spaces moves the negative glows toward each other until they overlap or touch. Thus, the

plates

17 and 18 may be positioned a greater distance away from each other when the pressure is lowered and still produce the desired single negative glow.

By disposing the wires 24 outside of the dark space for the

plates

17 and 18, a substantially uniform coating oi the material from the

targets

22 and 23 is deposited on the wires 2d. if the wires 25 were disposed within the dark space, the dark space would be affected in the portion of the area in which the wires 24 were disposed within the dark space. Accordingly, in such an area, there would not be a substantially uniform coating of the material of the targets 22 and 2.3 deposited on the wires 24 by RF sputtering.

The

plates

22 and 23 may be formed of any material which by itself or in combination with a gas will produce the desired coating on the wires 26. Common target materials are fused quartz and borosilicate glasses. When combined with a gas, the coating is deposited on the wires 24 by reactive sputtering of a conductive target. in the reactive sputtering arrangement, the gas is introduced into the chamber 10 through the conduit 15 along with the inert gas, which is preferably argon.

By introducing oxygen through the conduit 15 into the chamber Ml along with the argon, the coating on the wires 24 may be various oxides such as silicon dioxide, for example. If the deposited coating were silicon dioxide and oxygen were introduced in the chamber 10 along with the argon through the conduit is, the material of the

targets

22 and 23 would be silicon.

Likewise, nitrogen could be introduced into the chamber 10 through the conduit 15 along with the argon. The

targets

22 and 23 could be formed of silicon or aluminum, for example, in such an arrangement. This would result in the formation of a coating of silicon nitride or aluminum nitride.

it should be understood that the material of the target 22 may be formed of various oxides, sulfides, or nitrides including boron nitride. With this arrangement, only the inert gas is introduced into the chamber it) through the conduit 15. Thus, no reactive sputtering is needed.

it should be understood that water or other cooling fluid may be circulated in heat exchange relation with the cathode plates l7 and ill to keep the temperature of the

cathode plates

17 and 38 from rising too high while the apparatus is operating. While the RF power might be maintained sufficiently low to eliminate the need for cooling the

cathode plates

17 and 18, it should be understood that it is preferable to cool the electrode plates 17 and id.

The cooling fluid may be introduced into the chamber 10 in the same manner as shown and described in the aforesaid Davidse et a]. patent. Thus, the support rod 19 is hollow and has a hollow tubular member 3! disposed therein to permit coolant to be supplied in heat exchange relation with the cathode plate 18. A similar arrangement exists for the upper cathode plate l7. it should be understood that the RF power source 20 may be connected to the tubular members 31 rather than the

rods

19 and 21 if desired.

The following is an example of the method of the present invention for depositing a coating on a substrate in which the hollow cathode effect is utilized with RF power. The example is included merely to aid in the understanding of the invention, and variations may be made by one skilled in the art without departing from the spirit and scope of the invention.

An aluminum cathode having a hollow cylindrical shape with an inner diameter of 2 inches and a length of 4 inches was utilized. A quartz tube was mounted within the aluminum cathode widi the quartz tube being 8 inches long and having an outer diameter slightly less than 2 inches so that the quartz tube fitted snugly within the aluminum cathode. The quartz tube was cylindrical shaped.

The cathode and the tube were disposed within a chamber in which the pressure was 3 to 7 millitorr. An RF power of 400 watts was applied with a peak to peak voltage of 1050 volts.

The substrate was a silicon wafer that was mounted within the quartz tube on a slab of quartz. The hollow cathode effect was observed and the surface of the silicon wafer that was not supported on the slab of quartz was coated. Because the silicon wafer was mounted on the slab of quartz rather than being suspended within the quartz tube, the other surface was not coated.

instead of using the wires 24 as the substrate, a strip of magnetic tape, for example, could be employed as the substrate. Thus, both sides of the magnetic tape could be coated at the same time when utilizing the method of the present invention. in the same manner as described for the wires 24, the tape could either be stationary within the chamber 10 or could be moved therethrough, either continuously or intermittently, at a desired rate.

Another apparatus for coating the wires 24 is shown in FIGS. 4 and 5. In this apparatus, a hollow cylindrical target 35 is mounted in spaced relation to the wires 24. A hollow cylindrical electrode 36, which functions as the cathode in the same manner as the plates 17 and I8, surrounds the target 35 and supports the target 35. The cathode 36 is connected to an RF power source 37.

The electrode 36 is supported within a jar by a support rod 38 extending through the base plate 12 in the same manner as the rod 19. The rod 38 is conductive to permit the RF power source 37 to transmit current and voltage to the cathode 36 but is insulated from the base plate 12. It should be understood that the wires 24, the target 35, and the cathode 36 would be mounted within the chamber of FIG. 1. Thus, either the target 35 may contain the material to be deposited on the wires 24 or the chamber 10 may have a suitable gas introduced therein to form the desired oxide or nitride with the material of the target 35 by reactive sputtering. The gas flows between the target 35 and the wires 24.

The diameter of the inner surface of the cathode 36 must be selected so that only a single negative glow exists within the target 35. The negative glow is along the longitudinal axis of the hollow cylindrical cathode 36 and the hollow cylindrical target 35. It should be understood that the target 35 and the cathode 36 have the same longitudinal axis.

The diameter of the inner surface of the cathode 36 is selected in accordance with the desired operating pressure within the chamber 10. As the vacuum within the chamber 10 is increased, the diameter of the cylindrical shaped cathode 36 may be increased and still have the single negative glow therein.

Furthermore, the wires 24 must be appropriately positioned with respect to the longitudinal axis so that each is disposed with respect to the target 35 to receive a substantially uniform coating therefrom. It should be understood that the wires 24 must not extend into the dark space of the cathode 36. Accordingly, the wires 24 are disposed within the single negative glow of the cathode 36.

As with respect to the apparatus of FIGS. I to 3, the wires 24 may be either moved continuously or intermittently through the target 35. Likewise, the wires 24 could be stationary and not extend exterior of the chamber 10 in the same manner as described for the apparatus of FIGS. 1 to 3.

In the same manner as described with respect to the apparatus of FIGS. 1 to 3, the substrate could be other than the wires 24. For example, it could be a magnetic tape.

It should be understood that the diameter of the cathode 36 must be substantially greater than the width of the strip of magnetic tape if the strip is utilized with the embodiment of FIGS. 4 and 5. Therefore, the strip of magnetic tape, for example, is preferably utilized with the

parallel plates

17 and 18.

In the same manner as described for the embodiment of FIGS. 1 to 3, the target 35 preferably extends beyond each end of the cathode 36. This insures that there is no leakage current around the target 35. It should be understood that the target 35 could extend for only the same distance as the cathode 36 along the longitudinal axis. However, the target 35 must extend for at least the same distance in the longitudinal direction as the cathode 36.

It should be understood that the cathode 36 is preferably cooled by a coolant system in a manner similar to that shown in FIG. 1. However, if the RF power is kept low enough, the coolant system need not be employed.

Referring to FIG. 6, there is shown another form of the cathode. In this arrangement, a substantially rectangular shaped target 40, which is hollow, is employed for cooperation with a substantially rectangular shaped substrate 41. A substantially rectangular shaped electrode 42, which also is hollow, surrounds the target 40 and supports the target 40.

The opposite ends of the target 40 are necked down to fonn closed ends. Thus, the target 40 also functions as the chamber having the high vacuum therein so that the bell jar 10 and the related structure can be eliminated. This arrangement also could be utilized with the embodiment of FIGS. 4 and 5.

A vacuum pump would then be connected through conduit 42A to the interior of the target 40 to maintain the desired vacuum therein. Additionally, the inert gas also would have to be introduced into the interior of the target 40 by a conduit 423 in the same manner as the inert gas is introduced into the interior of the bell jar 11.

It also would be necessary to utilize some type of air locks and fast vacuum at the neck down ends of the target 40 to prevent any leakage therethrough. This could be a structure similar to the air locks 25 and 26 and the vacuum line 27, for example, of FIG. 1.

The electrode 42, which is connected to a suitable RF power source 43 and functions as a cathode in the same manner as does the plates 17 and I8, is wrapped around the target 40 and supported thereby. Co'olant could be supplied to the cathode 42; however, since it is disposed in the atmosphere this may not be necessary.

With the configuration of FIG. 6, it is preferable to provide an anode 44 within the chamber formed by the target 40. The anode 44 could be a grounded rectangular ring, for example.

If the material of the target 40 should be of a type that could not be formed into a tubular shaped and necked down so as to form an enclosed chamber therein, a glass container could be formed in the shape of the target 40 including the necked down portion and have the material, which is to be sputtered onto the substrate, disposed on the interior of the glass container. The cathode 42 would still be disposed on the exterior of the glass container.

Furthermore, the substrate 41 may be movable through the target 40, either continuously or intermittently, or may be stationary. Suitable means would have to be provided to move the substrate 41 in the same manner as the wires 24 are moved.

As shown in FIG. 6, the target 40 extends for a greater distance in the longitudinal direction beyond each end of the cathode 42. Of course, as mentioned with respect to the other embodiments, the target 40 could extend for only the same longitudinal distance as the cathode 42 but it must extend for at least this distance.

By appropriately selecting distances between opposite sides of the cathode 42, a single negative glow is formed within the target 40 along its longitudinal axis. This negative glow is so disposed that the substrate 41 does not enter into the dark space of the cathode 42. Accordingly, a substantially uniform coating of the target 40 is sputtered onto all four sides of the substantially rectangular shaped substrate 41.

Referring to FIG. 7, there is shown a triangular shaped substrate 45. The substrate 45 could be coated by fonning a target 46 and a cathode 47 of substantially the same geometric configuration as the substrate 45 with both the target and the cathode being hollow. By controlling the distance of the inner surfaces of the hollow cathode 47 from the longitudinal axis, a single negative glow is produced within the target 46. With the substrate 45 positioned within the target 46 so that its longitudinal axis is the same as the longitudinal axis of the target 46, the substrate 45 is disposed only within the negative glow.

The cathode 47 is connected to a suitable RF power source 48 in the same manner as in the embodiment of FIGS. I to 3. Furthermore, the cathode 47 is supported within the chamber 10 by suitable means in the same manner as the previously described cathodes.

If desired, the ends of the target 46 could be necked down in the same manner as the target 40. In this arrangement, the cathode 47 would be supported by the target 46. Furthermore, a grounded anode would have to be provided in the manner shown in FIG. 6.

Referring to FIG. 8, there is shown a substrate 50 having an I-shaped configuration. A target 51, which is supported by a cathode 52, is disposed in surrounding relation to the sub strate 50. The configurations of the target 51 and the cathode 52 are geometrically similar to the substrate 50. The cathode 52 has its shape selected so that the cathode 52 produces a single negative glow within the target 51. The cathode 52, which is supported within the chamber 10 by suitable means, has an RF power source 53 connected thereto as mentioned for the other embodiments.

The substrate 56 is positioned within the target 51 so that the substrate 50 is disposed in the negative glow. Thus, the substrate 50, even with its unique shape, does not penetrate into the dark space adjacent the cathode 52. As a result, a substantially uniform coating is produced on the nonuniform shaped substrate 50.

If desired, the ends of the target 51 could be necked down in the same manner as the target 40. In this arrangement, the cathode 52 would be supported by the target 51. Furthermore, a grounded anode would have to be provided in the manner shown in FIG. 6.

The general relationship of the voltage between the cathode and the anode is shown in FIG. 9 with respect to the distance between the

plates

17 and 18 of the embodiment of FIGS. l-3. Thus, as the distance between the

plates

17 and 18 decreases, a point is reached at which the voltage falls rapidly. At about the same time, the ion current flow between the

cathode plates

17 and 18 increases substantially. When these two occur, the hollow cathode efiect is produced and is the region to the left of where the two curves of voltage and current intersect each other.

While the present invention has particular utility in sputtering a dieiectric material onto a substrate by utilizing RF power, it should be understood that the invention is not limited to coating a substrate with a dielectric material. Thus, the present invention is useful in any area in which it is desired that ions of low energy be employed so as to protect a substrate that could be damaged by high energy ions. Furthermore, while the present invention utilizes a lower-energy ion than is employed in normal RF sputtering, it has a slightly higher rate of sputtering than the previously suggested RF sputtering devices because the number of ions is substantially increased.

it is preferable that the substrates not be grounded but that they be insulated. Thus, the base plate 12 or the grounded anode 44 is the only desired anode.

It should be understood that the distance between the

plates

17 and 18 or the diameter of the cathode 36, for example, is as small as possible depending on the size of the substrate. This is because a broader range of gas pressures within the chamber may be utilized with a smaller distance between the

plates

17 and 18 or a smaller diameter of the cathode 36.

An advantage of this invention is that it eliminates any requirement for a grounded shield to be utilized in conjunction with the target electrode. Another advantage of this invention is that it eliminates the leakage current from the anode to the cathode around the target without requiring a blocking capacitor or shield. A further advantage of this invention is that the energy of the ions is sufl'iciently low so as to not damage the substrate. Still another advantage of this invention is that a substantially uniform coating may be deposited on various shaped substrates having nonuniform configurations.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A method for depositing a coating of substantially uniform thickness on a substrate by RF sputtering comprising:

disposing the substrate so that it is at least partially surrounded by a target of the material to be sputtered onto the substrate;

disposing a cathode, separate from the target, in adjacent relation to the target but remote from the substrate with the cathode having substantially the same geometric configuration as the target and with the target being longer than the cathode and having a surface area greater than the surface area of the cathode so that the substrate is not exposed to the cathode and to prevent any current leakage around the target;

posiu'oning the substrate within a partially evacuated chamber having an inert gas therein and having at least the material of the target to be sputtered within the partially evacuated chamber;

applying a high-frequency alternating voltage between an anode within the chamber and the cathode in the absence of a capacitor between the high-frequency alternating voltage supply and either the anode or the cathode;

and selecting the size and geometric configuration of the cathode so that a single negative glow is formed and surrounds the portion of the substrate upon which the material is to be sputtered from the target.

2. The method according to claim 1 in which the cathode is a pair of substantially parallel plates, the target is a pair of substantially parallel plates, and the cathode and the target are completely within the chamber.

3. The method according to claim 2 in which the distance between the two parallel plates of the cathode is approximately twice the thickness of the dark space of each of the plates.

4. The method according to claim 1 in which:

the target and the cathode are hollow members with the cathode surrounding the target;

the substrate is disposed within the hollow target so as to be surrounded by the target;

and the size and geometric configuration of the hollow cathode are selected so that only a single negative glow is formed within the target with the substrate disposed within the negative glow.

5. The method according to claim 4 in which the hollow target and the hollow cathode have cylindrical shapes.

6. The method according to claim 1 in which the target is a dielectric material.

7. The method according to claim Sin which the target is a dielectric material.

8. The method according to claim 1 including advancing the substrate through the chamber.

9. The method according to claim 1 wherein the substrate being coated is at least one wire.

10. The method according to claim 1 wherein the substrate being coated is a tape.

11. The method according to claim 1 wherein said substrate is at least one semiconductor wafer.

12. An apparatus for coating a substrate comprising:

a chamber capable of holding a high vacuum and adapted to have a substrate disposed therein;

a target having at least a surface thereof disposed within said chamber and at least partially surrounding the substrate to be coated, said target comprising material to be sputtered onto the substrate;

a cathode, separate from said target, cooperating with said target and disposed adjacent said target but remote from the substrate, said cathode having substantially the same geometric configuration as said target;

said target being longer than said cathode and having a surface area greater than the surface area of said cathode to prevent any of said cathode from being exposed to the substrate and to prevent current leakage around said tar- 8 an anode disposed within said chamber; means to apply a high-frequency alternating voltage between said cathode and said anode;

and said applying means including an RF power source connected to said cathode and said anode without a capacitor between said RF power source and said cathode or between said RF power source and said anode;

said cathode having its size and geometric configuration selected to produce a single negative glow only within said target when the voltage is applied by said applying means whereby the portion of the substrate to be coated is not disposed within any dark space of said cathode and is disposed within the single negative glow.

13. The apparatus according to claim 12 including means to select the pressure within said chamber.

14. The apparatus according to claim 12 in which:

said target comprises a pair of substantially parallel plates with the substrate disposed therebetween; said cathode comprises a pair of substantially parallel plates with each of said cathode plates being in contact with one of said target plates and on the opposite side of said target plate from the substrate; and said cathode plates being spaced from each other so that the negative glows from said cathode plates are at least touching to produce a single negative glow within which the substrate is disposed. 15. The apparatus according to claim 12 in which: said target comprises a hollow member surrounding the substrate; said cathode comprises a hollow member having its inner surface in engagement with the outer surface of said hollow member of said target whereby said cathode surrounds said target and has the same longitudinal axis; and said cathode has the size of its inner surface selected so that a single negative glow is produced within said target along the longitudinal axis of said hollow member of said target and of said hollow member of said cathode. 16. The apparatus according to claim 15 in which: each of said hollow members of said target and said cathode has a substantially cylindrical shape; and said cathode has the diameter of its inner surface selected so that a single negative glow is produced within said target along the longitudinal axis of said hollow member of said target and of said hollow member of said cathode. l7. The apparatus according to claim 14 in which each of said target plates has a surface area greater than the surface area of said cathode plate adjacent said target plate so that said target plate overlies said adjacent cathode plate.

18. The apparatus according to claim 12 in which said target and said cathode are disposed within said chamber.

19. An apparatus for coating a substrate comprising: a chamber capable of holding a high vacuum and adapted to have a substrate disposed therein; a target comprising a hollow member surrounding the substrate to be coated, said target comprising material to be sputtered onto the substrate; said hollow target having its ends substantially closed to form said chamber; a cathode, separate from said target, cooperating with said target and disposed adjacent said target but remote from the substrate, said cathode having substantially the same geometric configuration as said target; said cathode comprising a hollow member having its inner surface in engagement with the outer surface of said hollow member of said target whereby said cathode surrounds said target and has the same longitudinal axis; said target being longer than said cathode and having a surface area greater than the surface area of said cathode to prevent any of said cathode from being exposed to the substrate and to prevent current leakage around said target; said hollow cathode disposed exterior of said chamber; an anode disposed within said chamber; means to apply a highfrequency alternating voltage between said cathode and said anode; and said applying means including an RF power source connected to said cathode and said anode without a capacitor between said RF power source and said cathode or between said RF power source and Said anode; said cathode having the size of its inner surface selected so that a single negative glow is produced only within said target along the longitudinal axis of said hollow member of said target and of said hollow member of said cathode when the voltage is applied by said applying means whereby the portion of the substrate to be coated is not disposed within any dark space of said cathode and is disposed within the single negative glow.

Claims

2. The method according to claim 1 in which the cathode is a pair of substantially parallel plates, the target is a pair of substantially parallel plates, and the cathode and the target are completely within the chamber.
3. The method according to claim 2 in which the distance between the two parallel plates of the cathode is approximately twice the thickness of the dark space of each of the plates.
4. The method according to claim 1 in which: the target and the cathode are hollow members with the cathode surrounding the target; the substrate is disposed within the hollow target so as to be surrounded by the target; and the size and geometric configuration of the hollow cathode are selected so that only a single negative glow is formed within the target with the substrate disposed within the negative glow.
5. The method according to claim 4 in which the hollow target and the hollow cathode have cylindrical shapes.
6. The method according to claim 1 in which the target is a dielectric material.
7. The method according to claim 5 in which the target is a dielectric material.
8. The method according to claim 1 including advancing the substrate through the chamber.
9. The method according to claim 1 wherein the substrate being coated is at least one wire.
10. The method according to claim 1 wherein the substrate being coated is a tape.
11. The method according to claim 1 wherein said substrate is at least one semiconductor wafer.
12. An apparatus for coating a substrate comprising: a chamber capable of holding a high vacuum and adapted to have a substrate disposed therein; a target having at least a surface thereof disposed within said chamber and at least partially surrounding the substrate to be coated, said target comprising material to be sputtered onto the substrate; a cathode, separate from said target, cooperating with said target and disposed adjacent said target but remote from the substrate, said cathode having substantially the same geometric configuration as said target; said target being longer than said cathode and having a surface area greater than the surface area of said cathode to prevent any of said cathode from being exposed to the substrate and to prevent current leakage around said target; an anode disposed within said chamber; means to apply a high-frequency alternating voltage between said cathode and said anode; and said applying means including an RF power source connected to said cathode and said anode without a capacitor between said RF power source and said cathode or between said RF power source and said anode; said cathode having its size and geometric configuration selected to produce a single negative glow only within said target when the voltage is applied by said applying means whereby the portion of the substrate to be coated is not disposed within any dark space of said cathode and is disposed within the single negative glow.
13. The apparatus according to claim 12 including means to select the pressure within said chamber.
14. The apparatus according to claim 12 in which: said target comprises a pair of substantially parallel plates with the substrate disposed therebetween; said cathode comprises a pair of substantially parallel plates with each of said cathode plates being in contact with one of said target plates and on the opposite side of said target plate from the substrate; and said cathode plates being spaced from each other so that the negative glows from said cathode plates are at least touching to produce a single negative glow within which the substrate is disposed.
15. The apparatus according to claim 12 in which: said target comprises a hollow member surrounding the substrate; said cathode comprises a hollow member having its inner surface in engagement with the outer surface of said hollow member of said target whereby said cathode surrounds said target and has the same longitudinal axis; and said cathode has the size of its inner surface selected so that a single negative glow is produced within said target along the longitudinal axis of said hollow member of said target and of said hollow member of said cathode.
16. The apparatus according to claim 15 in which: each of said hollow members of said target and said cathode has a substantially cylindrical shape; and said cathode has the diameter of its inner surface selected so that a single negative glow is pRoduced within said target along the longitudinal axis of said hollow member of said target and of said hollow member of said cathode.
17. The apparatus according to claim 14 in which each of said target plates has a surface area greater than the surface area of said cathode plate adjacent said target plate so that said target plate overlies said adjacent cathode plate.
18. The apparatus according to claim 12 in which said target and said cathode are disposed within said chamber.
19. An apparatus for coating a substrate comprising: a chamber capable of holding a high vacuum and adapted to have a substrate disposed therein; a target comprising a hollow member surrounding the substrate to be coated, said target comprising material to be sputtered onto the substrate; said hollow target having its ends substantially closed to form said chamber; a cathode, separate from said target, cooperating with said target and disposed adjacent said target but remote from the substrate, said cathode having substantially the same geometric configuration as said target; said cathode comprising a hollow member having its inner surface in engagement with the outer surface of said hollow member of said target whereby said cathode surrounds said target and has the same longitudinal axis; said target being longer than said cathode and having a surface area greater than the surface area of said cathode to prevent any of said cathode from being exposed to the substrate and to prevent current leakage around said target; said hollow cathode disposed exterior of said chamber; an anode disposed within said chamber; means to apply a high-frequency alternating voltage between said cathode and said anode; and said applying means including an RF power source connected to said cathode and said anode without a capacitor between said RF power source and said cathode or between said RF power source and Said anode; said cathode having the size of its inner surface selected so that a single negative glow is produced only within said target along the longitudinal axis of said hollow member of said target and of said hollow member of said cathode when the voltage is applied by said applying means whereby the portion of the substrate to be coated is not disposed within any dark space of said cathode and is disposed within the single negative glow.