Sputtering cathode structure for sputtering apparatuses, method of controlling magnetic flux generated by said sputtering cathode struct

Claims

We claim:

1. A cathode structure for planar magnetron sputtering apparatuses comprising:

a target plate made of a material to be sputtered and having first and second main surfaces, said first main surface of said target plate facing a main surface of a sample substrate with a predetermined spacing therebetween, said material being deposited on said main surface of said sample substrate,

magnetic flux generating means provided on the side of said second main surface of said target plate for generating magnetic flux having a certain flux density and a certain distribution in an empty space between said sample substrate and said first main surface of said target plate, said magnetic flux generating means including main magnetic flux generating means and magnetic flux distribution control means in such a manner that said main magnetic flux generating means and said magnetic flux distribution control means form a united magnetic flux source, said main magnetic flux generating means including one or a plurality of first pole portions and one or a plurality of first magnetic flux path means, said magnetic flux distribution control means including a plurality of second pole portions and a plurality of second magnetic flux path means, one end of said one or a plurality of first pole portions lying in close vicinity to or being kept in contact with said second main surface of the target plate with a predetermined magnetic polarity, the other end of the one or a plurality of first pole portions being kept in contact with and magnetically connected to said first magnetic flux path means, one end of each of said second pole portions lying in close vicinity to or being kept in contact with said second main surface of the target plate, the other end of each second pole portion being kept in contact with and magnetically connected to said second magnetic flux path means, said first magnetic flux path means and said second magnetic flux path means being magnetically connected to each other, thereby said magnetic flux density and said magnetic flux distribution formed in said empty space by said magnetic flux generating means being controlled by said magnetic flux control means; and electric field applying means having first and second electrodes and a power source for establishing an electric field in said empty space, said first electrode being provided on the side of said second main surface of the target plate in such a manner that said first electrode lies in close vicinity to or is kept in contact with said second main surface, said second electrode being provided in said empty space and spaced apart from said first electrode, said power source supplying electric power to said first and second electrodes.

2. A cathode structure according to claim 1, wherein a main part of said first and second pole portions has a cylinder form having a thick wall, and said first and second magnetic flux path means are formed of a common disc-shaped member which is made of a high permeability magnetic material and whose main portion has the form of a disc.

3. A cathode structure according to claim 2, wherein part of the plurality of second pole portions for forming said magnetic flux distribution control means is arranged in an outer peripheral region of said main magnetic flux generating means.

4. A cathode structure according to claim 2, wherein part of the plurality of second pole portions for forming said magnetic flux distribution control means is arranged inside said main magnetic flux generating means.

5. A cathode structure according to claim 2, wherein part of the plurality of second pole portions for forming said magnetic flux distribution control means is arranged in an outer peripheral region of said main magnetic flux generating means, and all or part of the remaining second pole portions is arranged inside said main magnetic flux generating means.

6. A cathode structure according to any one of claims 3 through 5, wherein part of the plurality of second pole portions for forming said magnetic flux distribution control means is arranged within a region in which the plurality of first pole portions for forming said main magnetic flux generating means are arranged.

7. A cathode structure according to any one of claims 1 through 5, wherein said one or a plurality of first pole portions for forming said main magnetic flux generating means are each formed of a permanent magnet.

8. A cathode structure according to any one of claims 1 through 5, wherein said one or a plurality of first pole portions for forming said main magnetic flux generating means are each formed of a united structure of a pole piece made of a high permeability magnetic material and an exciting coil disposed in the proximity of said pole piece.

9. A cathode structure according to any one of claims 1 through 5, wherein part of the plurality of first pole portions for forming said main magnetic flux generating means is formed of a permanent magnet, and the remaining first pole portion is formed of a united structure of a pole piece made of a high permeability magnetic material and an exciting coil disposed in the proximity of said pole piece.

10. A cathode structure according to any one of claims 1 through 5, wherein the plurality of first pole portions for forming said main magnetic flux generating means are divided into three groups, a first one of which is formed of a permanent magnet, a second one of which is formed of a united structure of a pole piece made of a high permeability magnetic material and an exciting coil disposed in the proximity of said pole piece, and a third one of which is formed of a pole piece made of a high permeability magnetic material.

11. A cathode structure according to any one of claims 1 through 5, wherein each of a plurality of second pole portions for forming said magnetic flux distribution control means is formed of a permanent magnet.

12. A cathode structure according to any one of claims 1 through 5, wherein each of the plurality of second pole portions for forming said magnetic flux distribution control means is formed of a united structure of a pole piece made of a high permeability magnetic material and an exciting coil disposed in the proximity of said pole piece.

13. A cathode structure according to any one of claims 1 through 5, wherein part of the plurality of second pole portions for forming said magnetic flux distribution control means is formed of a permanent magnet, and the remaining second pole portion is formed of a united structure of a pole piece made of a high permeability magnetic material and an exciting coil disposed in the proximity of said pole piece.

14. A cathode structure according to any one of claims 1 through 5, wherein part of the plurality of second pole portions for forming said magnetic flux distribution control means is formed of a united structure of a pole piece made of a high permeability magnetic material and an exciting coil disposed in the proximity of said pole piece, and the remaining second pole portion is formed of a pole piece made of a high permeability magnetic material.

15. A cathode structure according to any one of claims 1 through 5, wherein the plurality of second pole portions for forming said magnetic flux distribution control means are divided into three groups, a first one of which is formed of a permanent magnet, a second one of which is formed of a united structure of a pole piece made of a high permability magnetic material and an exciting coil disposed in the proximity of said pole piece, and a third one of which is formed of a pole piece made of a high permeability magnetic material.

16. A method of controlling magnetic flux in a cathode structure for planar magnetron sputtering apparatuses, said cathode structure including: a target plate made of a material to be sputtered and having first and second main surfaces, said first main surface of said target plate facing a main surface of a sample substrate with a certain spacing therebetween, said material to be sputtered being deposited on said main surface of said sample substrate; and magnetic flux generating means provided on the side of said second main surface of said target plane for generating magnetic flux having a certain flux density and a certain distribution in an empty space between said sample substrate and said first main surface of said target plate, said magnetic flux generating means including main magnetic flux generating means and magnetic flux distribution control means in such a manner that said main magnetic flux generating means and said magnetic flux distribution control means form a united magnetic flux source, said main magnetic flux generating means including one or a plurality of first pole portions and one or a plurality of first magnetic flux path means, said magnetic flux distribution control means including a plurality of second pole portions and a plurality of second magnetic flux path means including an exciting coil which forms a united structure together with a pole piece provided in the proximity of said exciting coil and made of a high permeability magnetic material, one end of said one or a plurality of first pole portions lying in close vicinity to or being kept in contact with said second main surface of the target plate, the other end of the one or a plurality of first pole portions being magnetically connected to said first magnetic flux path means including a high permeability magnetic material, one end of said second pole portions lying in close vicinity to or being kept in contact with said second main surface of the target plate, the other end of the second pole portions being magnetically connected to said second magnetic flux path means made of a high permeability magnetic material, said first magnetic flux path means and said second magnetic flux path means being magnetically connected to each other, thereby a magnetic flux distribution formed in said empty space by said main magnetic flux generating means being controlled by said magnetic flux distribution control means, said method of controlling magnetic flux comprising a step of causing a magnetic flux control current to flow through said exciting coil.

17. A method of controlling magnetic flux according to claim 16, wherein a magnetic flux distribution formed in said empty space on the side of said first main surface of the target plate is controlled by a static, magnetic flux control current flowing through said exciting coil so that a plasma region formed dependently on said magnetic flux distribution by the ionization of a gas is statically extended in a planar form and covers said main surface of said sample substrate.

18. A method of controlling magnetic flux according to claim 16, wherein a magnetic flux distribution formed in said empty space on the side of said first main surface of the target plate is controlled by a dynamic, magnetic flux control current flowing through said exciting coil so that a plasma region formed dependently on said magnetic flux distribution by the ionization of a gas moves with time above said main surface of said sample substrate and periodically covers said main surface of said sample substrate.

19. A method of controlling magnetic flux according to claim 18, wherein said dynamic, magnetic flux control current flowing through said exciting coil is a current of a periodic function type having a predetermined amplitude and a predetermined period.

20. A method of controlling magnetic flux according to claim 19, wherein said current of a periodic function type having a predetermined amplitude and a predetermined period is a current having the waveform of a sinusoidal function.

21. A method of controlling magnetic flux according to claim 19, wherein said current of a periodic function type having a predetermined amplitude and a predetermined period is a current having the waveform of a composite function made up of a plurality of sinusoidal functions.

22. A method of controlling magnetic flux according to claim 19 or 21, wherein said current of a periodic function type having a predetermined amplitude and a predetermined period is a current having a sawtooth waveform, namely, a triangular waveform.

23. A method of controlling magnetic flux according to claim 19 or 21, wherein said current of a periodic function type having a predetermined amplitude and a predetermined period is a current having a square waveform, that is, having the waveform of a rectangular pulse train.

24. A method of forming a film in a planar magnetron sputtering apparatus provided with a cathode structure having a united magnetic flux source including at least three pole pieces and at least two magnetic field generating means, at least one of which is an electromagnet, said three pole pieces and said at least two magnetic field generating means being magnetically coupled to generate a concentric field distribution, said method comprising a step of causing a current having a predetermined period to flow through said electromagnet to move a ring-shaped plasma region at least one cycle in said predetermined period, whereby deposited layers corresponding to a plurality of positions of said ring-shaped plasma region form a film.

25. A method of forming a film according to claim 24, wherein when said ring-shaped plasma region is moved to vary the size of said ring-shaped plasma region to be at least large and small, a time during which said ring-shaped plasma region is large is longer than a time during which said ring-shaped plasma region is small.

26. A method of forming a film in a planar magnetron sputtering apparatus provided with a cathode structure provided with a united magnetic flux source incuding at least three pole pieces, at least two magnetic field generating means, at least one of which is an electromagnet, and means for supplying a current to said electromagnet, said three pole pieces and said two magnetic field generating means being magnetically coupled to generate a controllable magnetic flux distribution, said method comprising a step of supplying a current having a predetermined period from said current supplying means to said electromagnet to move a plasma region to a plurality of positions at least one cycle at said predetermined period, whereby deposited layers corresponding to the plurality of positions of said plasma region form a film.

27. A method of forming a film according to claim 26, wherein said electromagnet is arranged outside the other magnetic field generating means.

28. A method of forming a film according to claim 26 or 27, wherein said current supplying means supplies a square wave current in which a time said current takes a high level is longer than a time said current takes a low level.

29. A method of forming a film according to claim 26, wherein said cathode structure includes, as said magnetic field generating means, at least two electromagnets arranged concentrically.

30. A method of forming a film in a planar magnetron sputtering apparatus provided with a cathode structure having sputtering power source and having a united magnetic flux including at least three pole pieces and at least two magnetic field generating means, at least one of which is an electromagnet, the three pole pieces and the two magnetic field generating means being magnetically coupled to generate a concentric magnetic flux distribution, said method comprising a step of causing a current having a predetermined period to flow through said electromagnet, and simultaneously varying a sputtering power in synchronism with said current to vary the amount of a material sputtered while moving a ring-shaped plasma region to a plurality of positions at least one cycle in said predetermined period, whereby deposited layers corresponding to a plurality of positions of said annular plasma region form a film.

31. A method of forming a film in a planar magnetron sputtering apparatus provided with a cathode structure including a target plate, at least three pole pieces, at least two magnetic field generating means, at least one of which is an electromagnet, means for supplying a current having a predetermined period to said electromagnet, and means for controlling a sputtering power supplied to said target plate, said three pole pieces and said two magnetic field generating means being magnetically coupled to form a united magnetic flux source, said method comprising a step of varying said sputtering power supplied from said control means in synchronism with said current to vary the amount of a material sputtered from said target plate while moving a plasma region to a plurality of positions at least one cycle in said predetermined period, whereby deposited layers corresponding to a plurality of positions of said plasma region form a film.

32. A sputtering cathode structure adapted for use in a planar magnetron sputtering apparatus comprising:

at least two magnet means for generating magnetic flux, including at least one electromagnet coil to be energized by a controlled current source;

means for magnetically coupling said at least two magnet means to form an integrated magnetic flux source together with said at least two magnet means, including a magnetic member bridging said at least two magnet means and formed of a soft magnetic material, and said at least two magnet means being disposed on one side of the magnetic coupling means;

means for supplying a controlled current to said at least one electromagnet coil for generating controlled magnetic flux, thereby controlling the distribution of magnetic flux at least in the neighborhood of said integrated magnetic flux source.

33. A sputtering cathode structure according to claim 32, wherein said soft magnetic material has a magnetic permeability greater than about 100.

34. A sputtering cathode structure according to claim 32, wherein said magnetic coupling means includes a magnetic enclosure magnetically coupled with said magnetic member and surrounding said at least two magnet means.

35. A sputtering cathode structure according to claim 34, wherein a first one of said at least two magnet means surrounds a second one of said at least two magnet means.

36. A sputtering cathode structure according to claim 35, wherein said first one of said at least two magnet means comprises said at least one electromagnet coil.

37. A sputtering cathode structure according to claim 36, wherein said first one of said at least two magnet means comprises an intermediate magnetic member formed of a soft magnetic material and surrounding said second one of said at least two magnet means and said at least one electromagnet coil wound around said intermediate magnetic member, inside said magnetic enclosure.

38. A sputtering cathode structure according to claim 35, wherein said second one of said at least two magnet means comprises said at least one electromagnet coil.

39. A sputtering cathode structure according to claim 38, wherein said second one of said at least two magnet means comprises a central magnetic member formed of a soft magnetic material and said at least one electromagnet coil wound around said central magnetic member.

40. A sputtering cathode structure according to any one of claims 34 to 37, further comprising;

a cathode body formed of a non-magnetic material and disposed in the vicinity of said magnetic coupling means on the other side of said magnetic coupling member.

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention relates to a sputtering cathode structure for sputtering apparatuses of the planar magnetron type which can increase the life of a planar target plate for sputtering a film material and can control the thickness distribution of a film deposited on a substrate. Further, the present invention relates to a method of controlling magnetic flux generated in the target structure, and to a method of forming films by the use of the target structure.

2. DESCRIPTION OF THE PRIOR ART

In the sputtering technique, a low-pressure gas, e.g. argon, in a space is ionized by glow discharge to form a plasma, and ions in the plasma are accelerated by an electric field generated by a voltage applied between a cathode and an anode to bombard a planar target plate placed on the cathode. Atoms or particles sputtered from the target plate by the bombardment of ions are successively deposited on a substrate place in the vicinity of the anode to form a thin film of a target material.

In this case, in order to assure good qualities for the film deposited on the substrate, to improve the rate of deposition, and to lower the damage to the substrate by electrons, it is important to confine ions and electrons generated by glow discharge in a limited space to a high density, and to effectively transfer the ions in the limited space to the planar target plate.

Therefore, various magnetic field configurations have been studied which can confine the ions in a limited space above the planar target plate to obtain high ion and electron densities.

In recent years, a planar magnetron sputtering apparatus has attained nearly equal deposition rate to that of a conventional resistance heating type vacuum evaporation apparatus, and therefore is widely used in a film forming process for mass production of this films for use in thin film integrated circuits and semi-conductor devices. A recent technical trend of planar magnetron sputtering apparatuses is described in, for example, an article by Waits entitled "Planar magnetron sputtering", J. Vac. Soc. Technol. 15 (2), March/April, 1978, pp. 179 to 187.

FIG. 1 is a cross sectional view for explaining an outline of a structure including a planar target material plate and its peripheral members, namely, a sputtering cathode structure of a well-known conventional planar magnetron sputtering apparatus. In this conventional sputtering apparatus, a ring-shaped magnetic pole portion 2 and a columnar magnet 3 placed at a central part of the magnetic pole ring 2 are magnetically coupled by a yoke 6 on the back side of a planar target material plate 1 (hereinafter referred to as "planar target plate") to form a magnetic circuit. A distribution of lines of magnetic force is established, by the magnetic poles at the pole portions 2 and 3, in a space on the surface side of the planar target plate 1 (in FIG. 1 on the lower side of the plate 1). In more detail, there is established a magnetic field distribution which has such a form as obtained by bisecting a torus by a plane perpendicular to the axis of the torus and by placing the bisecting plane parallel to the surface of the plate 1. In other words, a so-called tunnel-shaped magnetic field distribution 11 is generated. Electrons (not shown) generated by glow discharge are confined in the tunnel-shaped magnetic field distribution 11 so that a high ion density is obtained. The ions are accelerated by an electric field which is approximately perpendicular to the surface of the planar target plate 1 and is generated by a voltage applied between a ring-shaped anode 10 and a disc-like cathode 7, to bombard the surface of the target plate 1. The anode 10 may be directly connected to a directly grounded shield 9 or may be slightly positively biased. As a result, atoms or particles of the target material are successively sputtered from the surface of the target plate 1. Thus, an erosion region 12 is formed in the surface of the plate 1. Incidentally, the cathode body 7 is disposed on the back side of the planar target plate 1 and is electrically connected to a negative high voltage source, and the anode 9 is fixed to the cathode 7 through an insulating spacer 8. Further, reference numeral 5 designates a water cooling mechanism.

As can be seen from the above-mentioned explanation, erosion proceeds with the elapse of time in a sputtering process, and thus the erosion region 12 is formed. In the sputtering cathode structure shown in FIG. 1, the above-mentioned erosion proceeds only in a specified region of the planar target plate, and therefore only a portion of the planar target plate corresponding to the erosion region is used to form a deposited film.

Owing to the erosion region formation mechanism, although a film having a uniform thickness can be obtained in an initial stage, the amount of atoms sputtered from the planar target plate and the direction in which the target material is sputtered, vary with the elapse of time, and therefore the thickness of a film deposited on a substrate (not shown) is not uniform when the erosive action has proceeded. That is, a film which is deposited on the substrate when the erosive action has proceeded, has a thickness distribution having a cross-sectional form of an upwardly convex curve with a central part being downwardly convex, i.e. saddle-like shape as explained later. Accordingly, it is not possible to obtain a deposited film having a desired thickness distribution, e.g. uniform distribution.

In the case where a film having a large thickness is required, or in the case where it is required to perform a long-time sputtering operation which is important from the practical point of view, the planar target plate of the conventional planar magnetron sputtering apparatus cannot be employed due to the above-mentioned localized erosion in the planar target plate and a nonuniform distribution of thickness of a deposited film. That is, the conventional sputtering process is restricted in operating time. In order to eliminate the above-mentioned drawbacks, it has been proposed to vary the magnetic field distribution 11 so that the erosion region 12 is formed in a large surface portion of the planar target plate 1 (refer to U.S. Pat. No. 3,956,093).

The theoretical background or technical thought of this proposal, as is described in column 1, lines 53 to 57 to U.S. Pat. No. 3,956,093, resides in that maximum target erosion is generated at a region substantially aligned with and underlying the point or region over which magnetic flux lines are parallel to the target plate. In more detail, an apparatus is claimed in claim 3 of the above-referred patent which comprises anode means spaced from a planar sputtering source for establishing an electrostatic field therebetween, first magnet means for providing flux lines exiting the source and returning thereto along a curved path thereby defining an erosion region on the source in a closed loop configuration, second magnet means adapted to produce an auxiliary, variable magnetic field in a direction substantially normal to the source in the presence of the flux lines such that upon variation of the variable magnetic field, the location at which resultant flux lines are generally parallel to the source is continuously translated across the erosion region whereby the source is eroded to a generally uniform depth substantially throughout the erosion region. Further, an embodiment in which an electromagnet serving as the second magnet means is arranged separately, is disclosed in the above patent. Besides, a Japanese Patent Application Laid-open Specification (No. 7586/1978) discloses a technique in which magnet means itself is moved mechanically.

The present inventors have restudied the technical thought and technical means disclosed in the patent and laid-open specification with reference to experimental facts which were obtained by the present inventors. As a result thereof, a sputtering cathode structure and a method of controlling magnetic flux generated in the sputtering cathode structure have been obtained which can enhance the effect obtained by the technical means disclosed in the patent and laid-open specification. Further, a technique has been obtained which can freely control the thickness distribution of a deposited thin film.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a sputtering cathode structure for planar magnetron sputtering apparatuses which eliminates the above-mentioned drawbacks of the prior arts and increases the life of a planar target plate, which enables a continuous sputtering process, a long-time sputtering process and an automatic sputtering process.

Another object of the present invention is to provide a sputtering cathode structure for planar magnetron sputtering apparatuses which eliminates the above-mentioned drawbacks of the prior arts, increases the life of a planar target plate, and furthermore can control the thickness distribution of a deposited thin film.

A further object of the present invention is to provide a method of controlling magnetic flux which can control a plasma region formed in a space above a planar target plate during a sputtering process, to eliminate the above-mentioned drawbacks of the prior art, to increase the life of the planar target plate, and to control the thickness distribution of a deposited thin film.

Still another object of the present invention is to provide a method of forming a film through the planar magnetron sputtering technique which eliminates the above-mentioned drawbacks of the prior arts, can make uniform the thickness of a deposited film, and can facilitate the practical use.

According to an aspect of the present invention, there is provided a sputtering cathode structure adapted for use in a planar magnetron sputtering comprising:

at least two magnet means for generating magnetic flux, including at least one electromagnet coil to be energized by a controlled current;

means for magnetically coupling said at least two magnet means to form an integrated magnetic flux source together with said at least two magnet means, including a magnetic member bridging said at least two magnet means and formed of a soft magnetic material; and

means for supplying a controlled current to said at least one electromagnet coil for generating controlled magnetic flux, thereby controlling the distribution of magnetic flux at least in the neighborhood of said integrated magnetic flux source.

For example, the integrated magnetic flux source is preferably provided with a magnetic enclosure which surrounds the magnet means and works to limit the maximum envelope of the substantial flux distribution. It can be considered that, in the integrated magnetic flux source, the location and distribution of generation and sinking of magnetic flux lines can be widely varied by changing the polarity and the magnitude of the exciting current for the electromagnet.

Another aspect of the present invention is to provide a sputtering cathode structure for planar magnetron sputtering apparatuses in which, in view of the facts that lines of magnetic flux generated by a single flux source don't cross or link each other and respective positions of the lines of magnetic flux can be moved by the action of the Maxwell stress, namely, attraction or repulsion between the lines of magnetic flux, a flux source having at least three pole pieces is provided, and the amount of magnetic flux starting from a portion of the pole pieces is controlled to vary the density of magnetic flux existing at the remaining pole pieces and the place where magnetic flux is distributed, thereby moving a region where a plasma is present.

Namely, when another magnetic flux source is introduced into an existing field, the distribution of the magnetic flux all over the fields is changed into a new one. The change of the flux distribution is enhanced by the integral structure of the flux source. The new flux source is not limited to be one and may be more than one or may be distributed.

Further aspect of the present invention is to provide a method of controlling magnetic flux generated in a sputtering cathode structure for planar magnetron sputtering apparatuses, in which method a flux source having at least three pole pieces is provided in a sputtering cathode structure, and a controlled direct current or a periodically varying current is caused to flow through exciting means attached to at least one of the pole pieces during a sputtering process, to move a plasma region with time, thereby forming or controlling a flux distribution so that the life of a planar target plate is increased and the thickness distribution of a deposited film can be controlled.

Another aspect of the present invention is to provide a sputtering method using a planar magnetron sputtering apparatus which is based on the facts that lines of magnetic flux generated by a single flux source don't link each other and respective positions of the lines of magnetic flux can be moved by the action of the Maxwell stress, namely, attraction or repulsion between the lines of magnetic flux, and which is provided with a flux source having at least three pole pieces. The amount of magnetic flux existing at a portion of the pole pieces is controlled to vary the amount of magnetic flux starting from the remaining pole pieces and the place where magnetic flux is distributed, thereby moving a region where a plasma is present. In this sputtering method, a current which varies in magnitude at a predetermined period is caused to flow through an electromagnet coil provided for at least one of the pole pieces during a sputtering period, to move a ring-shaped plasma region at least once within the predetermined period. Thus, different layers are deposited from two positions of the target below the plasma generating region, and these deposited layers are synthesized to compose a single film.

Another aspect of the present invention is to provide a planar magnetron sputtering apparatus in which, in view of the facts that lines of magnetic flux generated by a single flux source don't link each other and respective positions of the lines of magnetic flux can be moved by the action of the Maxwell stress, namely, attraction or repulsion between the lines of magnetic flux, at least three pole pieces are integrated to constitute a flux source and the amount of magnetic flux existing at a portion of the pole pieces is controlled to vary the amount of magnetic flux associated the remaining pole pieces and the place where magnetic flux is distributed, thereby moving a region where a plasma is present, readily and widely. In this planar magnetron sputtering apparatus, a varying current having a predetermined period is caused to flow through an electromagnet provided for at least one of the pole pieces during a sputtering process, and an electric power for performing a sputtering operation is simultaneously increased or decreased in synchronism with the above-mentioned current to increase or decrease the amount of sputtered material while moving a ring-shaped plasma generating region at least once at the predetermined period. Thus, different layers are deposited from two positions of the ring-shaped plasma generating region, and these layers constitute a single film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view for showing an outline of a sputtering cathode structure in a conventional planar magnetron sputtering apparatus.

FIG. 2 is a cross sectional view for showing an outline of an embodiment of a sputtering cathode structure according to the present invention which is suitable for use in planar magnetron sputtering apparatuses.

FIGS. 3 and 4 are cross sectional views for explaining the operation of the embodiment shown in FIG. 1.

FIG. 5 is a sectional view for showing an outline of another embodiment of a target structure according to the present invention which is suitable for use in planar magnetron sputtering apparatuses.

FIGS. 6 and 7 are sectional views for explaining the operation of the embodiment shown in FIG. 5.

FIG. 8 is a graph showing relations between a time during which a planar target plate has been used in sputtering process and variations of the maximum fluctuation of film thickness distribution within a substrate with the eplase of time, for the case where a conventional target structure is employed and the case where a sputtering cathode structure according to the present invention is employed.

FIG. 9a is a partly cutaway view in perspective of a first actual embodiment of a target structure according to the present invention which is suitable for use in planar magnetron sputtering apparatuses.

FIG. 9b is a transverse sectional view of the embodiment shown in FIG. 9a.

FIG. 10 is a transverse sectional view showing a second embodiment of a target structure according to the present invention in which a permanent magnet is used as a center pole portion.

FIG. 11 is a transverse sectional view showing a third embodiment of a target structure according to the present invention in which a permanent magnet is used as an outer pole portion.

FIG. 12 is a block diagram showing a circuit arrangement of a driving device for driving electromagnets used in each of the embodiments shown in FIGS. 9a, 9b, 10 and 11.

FIG. 13 is a block diagram showing a circuit arrangement of a driving device for driving electromagnets used in each of the embodiments shown in FIGS. 9a, 9b, 10 and 11 and a power source for sputtering.