JP2660951B2 - Sputtering equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sputtering apparatus, and more particularly to a sputtering apparatus having a uniform thickness and uniform thickness on a surface of a substrate having a relatively large area while effectively consuming the entire target surface. The present invention relates to a sputtering apparatus provided with a magnetron cathode electrode capable of forming a thin film.

[0002]

2. Description of the Related Art In a conventional sputtering apparatus, various types of cathode electrode structures have been proposed. Among them, the magnetron type cathode electrode structure is most often used industrially. The reason is that the film formation speed is high. There are various types of conventional magnetron type electrodes. These types are, for example, “Thin F
ilm Process "(Academic Press Publishing, 1978
Year, edited by JLVossen and W. Kern), pp. 75-173
Pages or "Thin Film Handbook" (published in 1983, edited by the 131st committee of the Japan Society for the Promotion of Science), pages 186-1
It is described on page 89. At present, among the magnetron type cathode electrodes, a Planar Magnetron cathode electrode provided with a target having a planar shape is industrially most useful.

Conventionally, in a sputtering apparatus using a flat magnetron cathode electrode having a rectangular planar shape,
When a thin film is formed on a large-area substrate, the following problems (1) to (4) are raised. (1) Enlargement of equipment (2) Economical cost due to non-uniform consumption of target (3) Sputtered film on substrate due to non-uniform ion bombardment on target surface and non-uniformity of plasma spatial density distribution (4) Generation of particles due to non-uniform ion bombardment on the target surface The above problems (1) to (4) will be described below.

(1) Problem of enlargement of apparatus Regarding the relative positional relationship between a substrate and a target in a sputtering apparatus, see, for example, "Dry Process Application Technology" (Haruhiro Kobayashi, Takashi Okada, Naoyoshi Hosokawa, Nikkan) Kogyo Shimbun Shuppan, 1984), pp. 63 and 64. Usually, when forming a thin film on a large area substrate,
A substrate translation method is employed. In this substrate translation method, sputtering is performed while transporting a substrate along a plane parallel to the surface of the rectangular target in a sputtering apparatus having a rectangular target disposed therein, and a thin film is formed on the surface of the substrate. It is a method. For example, Japanese Patent Publication No. 63-65754 (Japanese Patent Application Laid-Open No. 60-86272) discloses a configuration example of a substrate-parallel type sputtering apparatus incorporating a rectangular magnetron cathode electrode. In the substrate translation type sputtering apparatus, the direction of transport of the substrate is selected to be parallel to the short side of the rectangular target in order to obtain a thin film having a uniform thickness.

In general, when the size of the substrate is larger than the length of the short side of the target, in order to form a thin film having a uniform thickness on the substrate, the substrate to be transported while being formed is required. It is required that the transfer distance of the substrate be sufficiently large. Based on this demand and the demand for improving productivity, the size of a substrate translation type sputtering apparatus for a large substrate tends to be large at present.

[0006] For example, a height of 7
In a sputtering apparatus (ANELVA 3960S) for forming a thin film having a uniform thickness within ± 10% on a glass substrate having a width of 00 mm and a width of 680 mm, a short side length of 250 mm is used.
mm, a magnetron cathode electrode having a flat target with a long side of 864 mm, a height of 950 mm and a width of 83
Film formation is performed using a 0 mm tray.

Further, a load lock mechanism for carrying an unprocessed substrate from the atmosphere side and carrying out a film-processed substrate to the atmosphere side while maintaining and managing the sputtering chamber in a vacuum state, and a load lock mechanism for transporting an unprocessed substrate to the atmosphere side. Heating zone to heat,
Due to the necessity of a buffer space for transporting the tray almost continuously, the length of the entire apparatus reaches 10 m to 20 m.

(2) Problems of uneconomicity due to non-uniform consumption of the target As described in the above-mentioned documents, the target surface of the magnetron cathode electrode is subjected to non-uniform ion bombardment. Therefore, it is consumed unevenly. This uneven wear is
This is caused by utilizing an inhomogeneous magnetic field generated near the target surface in the magnetron cathode electrode.

Conventionally, in order to improve the uneconomicity and film thickness distribution due to non-uniform consumption of the target, for example, a cylindrical coaxial magnetron cathode electrode or a circular flat magnetron cathode electrode is used.
In the case of the cathode electrode, a configuration was provided in which the position of the magnet assembly provided in the cathode electrode was changed with time (Japanese Patent Publication No. Sho 5).
5-27627, JP-A-3-6372, etc.). This configuration is a technique suitable for an electrode having a rotationally symmetric structure. According to this configuration, in the circular flat magnetron cathode electrode, the consumption of the target can be made uniform by rotating the magnet assembly around a certain rotation axis. On the other hand, such a configuration is not an effective technique as a means for uniformly consuming a rectangular flat target.

(3) The problem of non-uniformity of the sputtered film on the substrate The non-uniformity of the ion bombardment on the target surface of the magnetron cathode electrode affects the homogeneity of the film formed on the substrate. This effect is described in the above-mentioned JP-B-63-65.
This will be described below with reference to the configuration described in Japanese Patent Application Publication No. 754 (JP-A-60-86272). In this configuration, a thin film is formed by a combination of a rectangular magnetron cathode electrode and a substrate translation type sputtering apparatus.

When a voltage is applied between a cathode electrode and the wall of a vacuum vessel to perform a discharge in a vacuum and form a film by sputtering, the film is formed on the surface of a flat target of a rectangular magnetron cathode electrode. The electron drifts along a closed tunnel-like path created by the lines of magnetic force and draws a loop-like trajectory. Drift electrons collide with gas molecules and ionize them, so that a high-density plasma is formed along the locus drawn by the drift electrons. The target surface immediately below the trajectory drawn by the drift electrons receives a strong ion bombardment and is sputtered. Actually, since the drift electrons are extremely large, the trajectory becomes a band shape having a certain width. Therefore, the plasma formed along this band also has a band shape. The region to be sputtered on the target surface is also a band-shaped loop region.

The substrate placed on the transferred tray passes through the space in front of the target for film formation. As it passes, a particular location on the substrate passes across the space above the two sputtering strip regions parallel to the long sides of the rectangular target. This upper space is a space having a high plasma density. As is well known, sputtered atoms are emitted not only in a direction perpendicular to the target surface but also in various other directions. Therefore, sputtered particles begin to deposit at a specific location on the substrate before reaching the space above the sputtering zone. Then, the deposition rate increases as the specific location on the substrate approaches the space above the first sputtering zone region. This deposition rate is maximum just above the sputtering zone area. With further transfer of the tray, the deposition rate at a particular location on the substrate once decreases. As a particular location on the substrate approaches the second sputtering zone region, the deposition rate increases again, and at a position directly above the sputtering zone region, the deposition rate again becomes maximum. The deposition rate is maximized for the second time. In subsequent tray transfers, the deposition rate at a particular location on the substrate monotonically decreases as the substrate moves away from the space in front of the target.

As described above, when paying attention to a specific portion on the substrate, the film forming speed changes with time. Further, the incident angle of the sputtered particles deposited on the substrate surface and the plasma density in the space where the substrate surface is in contact each vary greatly with time. As a result, in the final thin film formed on the substrate, when attention is paid to a specific portion on the substrate, a portion having different physical characteristics in the thickness direction of the film is formed.

Further, for the purpose of forming a film on a large substrate, in order to improve the uniformity of the film forming rate and the uniformity of the film quality,
Consider a magnet assembly in which four magnet units having the same magnetic pole arrangement are arranged. In this case, the film thickness distribution is reduced on the substrate surface facing the magnet portion of the magnet unit. In the case of the above-mentioned quadruple magnet, in addition to the problem of the film thickness distribution, the magnetic fields of a plurality of magnet units interfere with each other, and the magnetic field intensity "unevenness" occurs at a magnetic field intensity parallel to the target surface. In accordance with the intensity distribution due to the interference of the magnetic field, "unevenness" occurs in the ion current density, that is, the amount of sputtering on the target surface. Therefore, non-uniformity of the film thickness distribution and the film quality distribution occurs. This has already been mentioned in Japanese Patent Application No. 3-194298 filed by the present applicant. In this prior application, a structure in which a plurality of two kinds of magnet units having different magnetic pole arrangements are alternately arranged to solve the magnetic field intensity “unevenness” was proposed. Although this structure is useful, the strength of the magnetic field tends to be weak due to the cancellation of adjacent opposite poles. Therefore, in order to obtain a strong magnetic field strength, it is necessary to increase the size of the magnet, and there is a problem that the cost for this is high.

(4) Problem of Particle Generation The non-uniformity of ion bombardment on the target surface of the magnetron cathode electrode causes particles to be generated during film formation. As mentioned above, the rectangular magnetron cathode
On the target surface on the gate electrode, one closed band-like region having a width smaller than the width of the target is sputter-etched by ion bombardment. Other regions on the target surface are not sputter-etched, and sputtered atoms that scatter out of the target, scattered by colliding with gas molecules many times in space and depositing thereon. When the sputtering is continued for a long time, a sputtered film is formed on the surface other than the strip-like region to be sputtered on the target surface. The sputtered film deposited on the target is
As it gets thicker, it peels off naturally due to its internal stress,
It becomes a particle. When processing fine patterns on a thin film on a substrate to produce electronic components, particles are regarded as one of the biggest factors in lowering the yield of non-defective products. -The development of a gate electrode is desired.

[0016]

As described above,
Various problems can be pointed out in the sputtering apparatus using the rectangular plate magnetron cathode. An object of the present invention is to solve the problem that ions bombard a target non-uniformly, to provide a cathode electrode structure capable of forming a good thin film while a relatively large rectangular substrate is stationary, and ,
An object of the present invention is to provide a sputtering apparatus capable of reducing the size of the entire apparatus. Another object of the present invention is to provide a cathode electrode structure which solves the problems of uneconomical consumption due to uneven consumption of a rectangular target, inhomogeneity of a thin film deposited on a substrate, and generation of particles. And a sputtering apparatus having the same.

[0017]

The first aspect of the present invention provides
A vacuum container provided with an exhaust system for evacuating the inside, a substrate holding member that is disposed inside the vacuum container and mounts a substrate on which a film is to be formed, and is disposed in a positional relationship facing the substrate; At least one magnetron cathode electrode provided with a rectangular planar target to be formed on the substrate, a gas control system for flowing gas inside the vacuum vessel to appropriately maintain an internal pressure, and supplying power to the magnetron cathode electrode. The present invention relates to a sputtering apparatus including a power supply system for supplying the following, and has the following features. (A) The magnetron cathode electrode includes a plurality of magnet units on the back surface of one rectangular planar target. (B) The magnet unit has a rectangular cross section parallel to the target surface, and a plurality of magnet units are arranged such that a long side is adjacent to a long side of an adjacent magnet unit. (C) The dimensions and magnetic pole arrangement of the magnet units are the same in all magnet units included in the same magnetron cathode electrode. (D) The magnet unit is configured to generate an annular electron drift motion trajectory on the surface of the target. (E) The back of one of the rectangular planar targets
A magnetic shield wall is disposed between adjacent magnet units.

That is, according to the present invention, a plurality of magnet units are arranged on the back of one target.
Thus, a plurality of annular trajectories due to drift electrons are formed on the surface of one target. The dimensions and magnetic pole arrangement of each magnet unit are made equal to each other. If the magnetic poles of a plurality of magnet units are arranged to be equal to each other and arranged side by side, there is no cancellation between adjacent different poles, and the magnet strength does not need to be increased more than necessary. However, if the same magnet units are arranged in a row, as described in the section of the related art, the magnetic field intensity "unevenness" is likely to occur. In other words, when a plurality of equivalent magnet units having a slight difference in the magnetic field distribution are arranged side by side, the difference in the magnetic field distribution is emphasized as a result of the mutual interference of the magnetic fields, and the magnetic field distribution having a strong irregularity as a whole is obtained. This is a major factor that adversely affects the discharge characteristics and film thickness distribution characteristics of the magnetron cathode. In order to solve this, in the present invention, a magnetic shield wall made of a ferromagnetic material is arranged between the magnet units. The magnetic shield wall has a function of preventing mutual interference between the magnet units.

Here, the above-mentioned prior literature of Japanese Patent Publication No.
The difference between the electrode structure disclosed in No. 65754 and the electrode structure according to the present invention will be described. In the electrode disclosed in the prior art, one cathode electrode includes one magnet unit, and only one circular locus is formed by drift electrons. By providing a plurality of such cathode electrodes, the movement directions of the annular trajectory are made equal between adjacent cathode electrodes. The cathode electrode of this sputtering apparatus is effective when forming a thin film while moving the substrate. On the other hand, in the present invention, a plurality of magnet units are provided in one cathode electrode, and those having the same magnetic pole arrangement are arranged in parallel, and the drift electron To form a plurality of annular trajectories. In the ring trajectory of the neighbors, the movement direction of the electrons is the same.

According to a second aspect of the present invention, the magnet unit according to the first aspect of the present invention is capable of reciprocating in a short side direction of the rectangle. When the rectangular magnet unit is moved in the short side direction, the annular trajectory caused by the drift electrons moves perpendicularly to the longitudinal direction, and a target portion that has not been sputtered is sputtered. Thereby, the film thickness distribution on the substrate is improved, and the use efficiency of the target is dramatically improved. For example, by making the amplitude of the reciprocating motion equal to the length of one magnet unit in the short side direction, it is possible to uniform the region of the target to be etched.

According to a third aspect, in the first or second aspect, the magnetic field of the magnet unit is equalized. That is, the magnetic field uniformity within ± 5% is provided within a single magnet unit, and the magnetic field uniformity within ± 5% is provided between the magnet units. This eliminates uneven distribution and instability of the discharge and improves the film thickness distribution on the substrate.

Here, regarding the magnetic field uniformity in a single magnet unit and the magnetic field uniformity between the magnet units,
The definition is described below. In FIG. 20A,
Consider the strength of the magnetic field generated by the magnet unit 80 on the target surface 82 above the magnet unit 80. On the target surface 82, the point immediately above the center of the magnet unit 80 is set as the point O, which is the origin of the coordinate axis. Magnet unit 80
X-axis in the short side direction, Y-axis in the long side direction, target surface 8
The direction perpendicular to 2 is the Z axis. Now, target surface 8
The intensity of the magnetic field at an arbitrary point on 2 is represented by magnetic flux density B. The magnetic flux density B is a vector, and the component in the X-axis direction is BX, the component in the Y-axis direction is BY, and the component in the Z-axis direction is BZ. The projection component of the magnetic flux density B on the XY plane is represented by BXY. This BXY is equal to the combined vector of BX and BY. It is the strength of the magnetic field on the target surface that determines the amount of sputtering of the target.
The component orthogonal to the electric field, that is, the absolute value of BXY has the most influence on the sputtering amount. Therefore, as an index indicating the strength of the magnetic field of the magnet unit, the absolute value of the component BXY parallel to the target surface out of the magnetic flux density on the target surface (hereinafter referred to as the effective magnetic field intensity).
Is most appropriate.

To evaluate the magnetic field uniformity of the magnet unit, the above-mentioned effective magnetic field strength is used. When the effective magnetic field strength is measured at each point on the target surface and the points where the large strength is obtained are connected, an annular trajectory 84 is obtained. This annular trajectory 84 matches the position of the target erosion area. If the effective magnetic field strength measured along this annular trajectory 84 is uniform at any point, the target will be sputtered uniformly along the erosion region. In the present invention, the degree of distribution of the effective magnetic field intensity measured along the above-described annular locus 84 is defined as the magnetic field uniformity, and the magnet unit 80 is manufactured so that this is within ± 5%. However, in order to obtain the magnetic field uniformity, a region near the short side of the magnet unit is excluded. 20B, the horizontal axis represents the distance along the annular trajectory 84, and the vertical axis represents the effective magnetic field strength (B
7 is a graph showing the magnetic field uniformity when taking the absolute value of XY). The effective magnetic field strength is large at the points D and F where the annular trajectory 84 is closest to the short side of the magnet unit 80, but the effective magnetic field strength is large in the long side direction (Y-axis direction) of the magnet unit 80. Is almost constant. Assuming that the length of the long side of the magnet unit 80 is LA, it is desirable to make the magnetic field uniformity within ± 5% at least within a range of 80% of LA. Therefore, the term "magnetic field uniformity" in the present invention means that the degree of distribution of the effective magnetic field intensity measured along the above-mentioned annular locus 84 is measured in an area within 80% of the long side direction of the magnet unit. Can be.

Next, the uniformity of the magnetic field between the magnet units will be described. In FIG. 20B, the average value BAV of the magnetic field uniformity is obtained for one magnet unit. This value can be determined for each magnet unit. Then, the average value BAV is compared between the magnet units, and the degree of the distribution is defined as the magnetic field uniformity between the magnet units. According to the present invention, the magnetic field uniformity between the magnet units is ± 5.
%, The variation of the film thickness distribution due to the variation of the strength of the magnetic field between the magnet units is prevented.

As described above, the magnetic field uniformity of the magnet unit alone and the magnetic field uniformity between the magnet units are ± 1.
The reason for limiting to within 5% is as follows. Since the magnetic field strength distribution is directly reflected on the film thickness distribution of a thin film formed by sputtering, a uniform distribution is desired. The extent to which the uniformity of the film thickness distribution within the substrate must be kept depends on the application field. However, in many electronic device manufacturing processes, the currently desired maximum allowable deviation of the film thickness distribution of a thin film is often ± 5%. Considering this point, in order to obtain a film thickness distribution with good uniformity, it is necessary to suppress the magnetic field intensity distribution of the magnet unit to at most ± 5%. Also, if the magnetic field uniformity of the magnet units and the magnetic field uniformity between the magnet units are good, a plurality of rectangular annular electron drift trajectories can be efficiently and uniformly generated on the target surface as a whole magnet assembly. Thereby, the discharge on the target surface can be stably maintained without uneven distribution. For the above reasons, the magnetic field uniformity of the magnet units and the magnetic field uniformity between the magnet units are each set to within ± 5%. Of course, as the maximum allowable deviation of the film thickness distribution in the substrate becomes smaller, the uniformity of the magnetic field intensity distribution in the magnet unit and between the magnet units must be limited to a narrower range. However, as the homogeneity of the magnetic field is limited to a narrower range, it is technically difficult to consider the magnet design and manufacturing for realizing it. Therefore, from the viewpoint of cost effectiveness, the uniformity of the magnetic field intensity distribution is limited to about ± 5%.

The degree of variation in the magnetic field intensity distribution of the magnet unit largely depends on the processing dimensional accuracy of the pole piece. For example, when the processing dimensional accuracy is ± 0.2 mm, the worst
mm differences may occur. In that case, a magnetic field intensity difference of about 7% occurs at a point 32 mm above the pole surface (corresponding to the target surface). When the processing dimensional accuracy is improved to ± 0.05 mm, the above-mentioned difference in the magnetic field strength becomes about 2%. In this description, it is assumed that the residual magnetic flux density of the magnetic pole constituting material is uniform in all regions of the magnetic pole.
In practice, non-uniformity of material properties cannot be ignored. Therefore, in order to keep the magnetic field uniformity of the magnet unit within ± 5%, it is necessary to consider both the processing dimensional accuracy and the material homogeneity. As an example of the means for achieving the predetermined magnetic field uniformity, the material and shape of each magnetic pole piece constituting the magnet unit are examined, and the residual magnetic flux density of each magnetic pole piece is set to 12000 G ± 500 G or less. did. The machining accuracy of the pole piece was set to ± 0.05 mm or less, and attention was paid to the assembly accuracy. This allows
Improved the magnetic field uniformity in the magnet unit.

The fourth invention embodies a magnet structure for producing an annular electron drift motion trajectory on the surface of a target. That is, the magnet unit according to the first invention comprises a yoke, a center magnet fixed on the yoke, and peripheral magnets fixed on the yoke and surrounding the center magnet. The center magnet and the peripheral magnet
Magnetic pole surfaces exist on the surface fixed to the yoke and the target-side surface, and the target-side magnetic pole of the center magnet and the target-side magnetic pole of the peripheral magnet have opposite polarities.

According to a fifth aspect, in the first aspect, a magnetic shield wall is arranged around the entirety of a plurality of magnet units included in the same magnetron cathode.
That is, in addition to disposing the magnetic shield wall between the magnet units, the magnetic shield wall is also disposed around the entire magnet assembly.

[0029]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a front sectional view showing a basic configuration of a sputtering apparatus according to a first embodiment of the present invention. The sputtering apparatus includes a substrate tray insertion chamber 1, a sputtering chamber 2 for forming a thin film on a surface of a substrate mounted on the tray, and a substrate tray unloading chamber 3. The substrate tray insertion chamber 1, the sputtering chamber 2, and the substrate tray unloading chamber 3 are connected in series. These chambers are formed by vacuum vessels having a configuration that can be independently evacuated and maintained and managed in a vacuum state. A gate valve 4 is provided between the substrate tray insertion chamber 1 and the sputtering chamber 2, and a gate valve 5 is provided between the sputtering chamber 2 and the substrate tray removal chamber 3.

The sputtering chamber 2 is usually maintained and managed in a vacuum state. The substrate tray insertion chamber 1 can be opened to the atmosphere by using a leak valve 6, and the substrate tray unloading chamber 3 can be opened to the atmosphere by using a leak valve 7. In the substrate tray insertion chamber 1, the air is exhausted in the direction of arrow 10 by an exhaust pump (not shown) via an exhaust pipe 8. In the substrate tray unloading chamber 3, the air is exhausted in the direction of arrow 11 by an exhaust pump (not shown) via an exhaust pipe 9. The left end of the substrate tray insertion chamber 1 in FIG. 1 is an entrance door 12, and the right end of the substrate tray unloading chamber 3 in FIG. 1 is an exit door 13.

The tray 14 on which the substrates are mounted is carried into the substrate tray insertion chamber 1 from the entrance door 12. The tray 14 is a device for holding a substrate. This substrate is a relatively large substrate. After the tray 14 is carried in, with the entrance door 12 and the gate valve 4 closed,
Exhaust is performed using an exhaust system. When the internal pressure of the substrate tray insertion chamber 1 is sufficiently reduced, the gate valve 4 is opened, and the tray 14 is guided by a rail (not shown) and transported in the direction of arrow 15 to the sputtering chamber 2. Sent in.

In the sputtering chamber 2, a thin film is formed by a sputtering method on the surface of the substrate mounted on the tray 14 by a thin film forming mechanism described later. In this embodiment, when a thin film is deposited on a substrate, the tray 14
Is at rest. After the thin film is formed on the substrate, the tray 14 is sent into the substrate tray unloading chamber 3 via the gate valve 5. After the tray 14 has been sent to the substrate tray unloading chamber 3, the gate valve 5 is closed, and the
The valve 7 is opened. Thus, the substrate mounted on the tray 14 is placed in an atmospheric pressure environment. Thereafter, the take-out door 13 is opened, and the tray 14 is taken out.

In the sputtering chamber 2, a gas is introduced from a cylinder (not shown) through a gas introduction pipe 16 in the direction of arrow 18a. In the sputtering chamber 2, the gas is exhausted by an exhaust pump (not shown) through the exhaust port 17 in the direction of arrow 18 b. As a result, in a state where the flow rate of the introduced gas and the flow rate of the exhaust gas are balanced, the sputtering chamber 2 is maintained in a discharge state, and 10-3 suitable for performing sputtering.
It is maintained at a constant pressure within a pressure range of -10 to Torr.

Gate valve 4 in sputtering chamber 2
A substrate heating lamp 19 is disposed at a location near (the front side). The substrate heating lamp 19 is provided as needed. By the heat ray radiation of the substrate heating lamp 19, the temperature of the substrate can be increased before the thin film is formed.
A magnetron cathode electrode 20 (hereinafter, referred to as a cathode electrode 20) having a large target in the form of a rectangular plane is disposed on the rear side of the sputtering chamber 2 via an insulator 21. A target assembly 22 is mounted on the cathode electrode 20. The upper surface of the target assembly 22 of FIG. 1 is the target surface. The cathode electrode 20 has a power supply 24 and a power supply line 25 between the cathode electrode and the power supply.
Power supply system 23 comprising a power supply and a connection 26 between the power supply and the earth.
Is connected. The power supply system 23 controls the cathode electrode 20.
Is supplied with power.

In the sputtering chamber 2, the tray 14
Is stationary with respect to the cathode electrode 20. In this stationary state, the substrate on the tray 14 faces the target surface of the target assembly 22. Sputtering particles flying from the target assembly 22 are deposited on the opposite surface of the substrate,
A thin film is formed on the substrate. In the example of FIG. 1, a combination of one tray 14 and one cathode electrode 20 is shown, but an arbitrary number of cathode electrodes 20 can be provided in the sputtering chamber 2. . The wall of the sputtering chamber 2 is grounded.

FIG. 2 is a front sectional view of the cathode electrode 20, and the structure of the cathode electrode 20 will be described in detail with reference to FIG. The cathode electrode 20 is connected to the electrode housing 31.
And the magnet assembly 3 disposed inside the electrode housing 31
2 and a target assembly 22. Caso
The gate electrode 20 is attached via an insulator 21 to an opening 34 formed in a wall 33 of a vacuum vessel forming the sputtering chamber 2. The cathode electrode 20 is attached to the opening 34 so that the target surface of the target assembly 22 is exposed to the vacuum chamber. Illustrations of a fixture for attachment, a clamp mechanism, and the like are omitted.

The target assembly 22 includes the target plate 3
5 and a target holding jig 36 and a target back plate 37, which are fixed to the electrode housing 31 by a coupling (not shown).

The magnet assembly 32 is provided in a concave space 38 formed inside the electrode housing 31. Specifically, in the concave space 38, the magnet unit 4 including the center magnet 41, the peripheral magnet 42, and the yoke 43
4 are provided. The five magnet units 44
The dimensions, materials and magnetic pole arrangement are all the same. Details of the magnet unit will be described later. Magnet unit 4
A magnetic shield 49 made of a ferromagnetic material is arranged between the four and outside the whole of the five magnet units 44.
The magnet unit 44 and the magnetic shield 49 are connected to the magnet fixing base 4.
It is fixed to 8. As described above, the magnet assembly 32 includes the five magnet units 44, the magnetic shield 49, and the magnet fixing base 48.

Although not shown, the concave space 38
, Cooling water is introduced from outside the electrode housing 31. The cooling water contacts the target back plate 37 to cool it. When the discharge is performed, the heat generated on the target surface of the target assembly 22 is released to the outside using the cooling water as a medium.

The electrode housing 31 and the target back plate 37
An O-ring 39 is provided between them to maintain airtightness. The airtightness between the electrode housing 31 and the insulator 21 is maintained by the O-ring 40, and the airtightness between the insulator 21 and the wall 33 of the vacuum vessel is maintained by the O-ring 30.

It is not desirable that the surface of the target assembly 22 exposed to the vacuum side other than the surface to be sputtered be subjected to ion bombardment. Therefore, a target shield member 47 is provided around the opening 34 on the inner surface of the wall 33 in order to prevent the surface not to be sputtered from being bombarded with ions.

FIG. 3 is a plan view of the magnet assembly 32. 5
Between the four magnet units 44 and the five magnet units 4
A magnetic shield 49 is provided outside the entirety of 4.
The magnetic shield 49 is made of a material having a high magnetic permeability, such as soft iron. Between the magnet units 44, there is a magnetic shield 49a slightly longer than the long side of the magnet unit 44, and this is connected to the surrounding magnetic shield 49b. The magnet unit 44 and the magnetic shield 49 are fixed on a ferromagnetic magnet fixing base 48 (see FIG. 2), and the lower part is also magnetically shielded. , Magnet unit 4
4 are absorbed by the magnetic shield 49,
Mutual interference of magnetic fields is prevented. Thereby, the magnetic field distribution of the entire magnet assembly can be maintained in a well-balanced manner. If the magnet fixing base 48 and the magnetic shield 49 are not provided, a magnetic field distribution is biased in a diagonal direction of the magnet assembly 32 due to mutual interference of the magnetic fields, and a thin film having a uniform thickness cannot be produced.

The magnetic shield 49b outside the short side of the magnet unit 44 can be omitted. However, when the magnetic field near the short side of the magnet unit 44 is stronger than the magnetic field at the center in the long side direction of the magnet unit, it is preferable to attach the magnetic shield 49b also outside the short side.

Next, the structure of the magnet unit 44 will be described. 4A is a cross-sectional view of the magnet unit cut along a plane parallel to the short side, FIG. 4B is a plan view of the magnet unit,
(C) is a perspective view thereof. The magnet unit 44 is composed of a yoke 43 having a substantially rectangular planar shape, a long plate-shaped central magnet 41, and a rectangular ring-shaped peripheral magnet 42 disposed around the central magnet 41. In this embodiment, the length LA of the long side of the magnet unit 44 is 630 mm, and the length of the short side is 110 mm. The magnetic pole on the yoke 43 side of the center magnet 41 is an N pole, and the opposite side is an S pole.
The magnetic pole on the yoke 43 side is an S pole, and the opposite side is an N pole. Due to this magnetic pole arrangement, lines of magnetic force 45 from the peripheral magnet 42 to the center magnet 41 are formed on the target side. Accordingly, the lines of magnetic force exit from the surface of the target above the peripheral magnet 42, and enter the surface of the target above the center magnet 41. The lines of magnetic force form an annularly closed tunnel path. The magnetic field uniformity of the single magnet unit 44 is within ± 5%, and the magnetic field uniformity between the magnet units is also within ± 5%.

When a high negative potential is applied to the cathode electrode 20 in a state where the magnetic field lines 45 are generated as described above, the
An electric field perpendicular to the get surface is generated. The electrons drift along the tunnel path on the target surface based on the combination of the electric field perpendicular to the target surface and the magnetic field forming the tunnel path. The electron drift motion describes an annular trajectory. As a result, a discharge of a low voltage and a large current is generated, and this discharge enables a sputtered film to be formed on a substrate at a high speed.

FIG. 5A is a plan view showing the trajectory of the drift motion of electrons on the target surface, and FIG. 5B is a sectional view of the magnet assembly 32 corresponding thereto. The electron
A drift motion is performed along the annular trajectory 46 in the direction indicated by the arrow. The annular trajectory 46 is shown as a closed thin line in the drawing, but is actually a band shape having a certain width. Ions are generated by electrons drifting and colliding with gas molecules. Therefore, the distribution of the ion current density can be regarded as a projection of the spatial density of the drift electrons passing on the target surface 28 onto the target surface. The trajectory of the drift electrons is not a single thin line but a wide space having a probability distribution. In addition, ions bombard the target and sputter it,
The broad ion current density distribution corresponds to the sputtering depth distribution of the target. In each annular trajectory 46,
The two parallel long sides 46a and 46b adjacent to each other are
The drift directions are opposite to each other.

FIG. 6 is a sectional view showing the lines of magnetic force of the magnet assembly 32, which is cut along a section parallel to the short side of the magnet unit. This drawing relates to a magnet assembly composed of four magnet units and shows only the right side from the center line. It can be clearly seen that the lines of magnetic force 45 of each magnet unit are absorbed by the magnetic shield 49, and as a result, the mutual interference of the magnetic fields is suppressed.

In the above embodiment, the cathode electrode 20
The surface of the target has a relatively large rectangular area. On the target surface, a portion to be sputtered is specified as a band-like portion of an annular trajectory formed by lines of magnetic force of the magnet unit 44. By forming a plurality of annular erosion regions on one target, it is possible to form an erosion region over as large an area as possible. Thereby, the utilization efficiency of the target having a relatively large area (the ratio of the annular locus area to the total area of the target) can be improved.

As described above, the interaction between the electric field and the magnetic field formed by the central magnet and the peripheral magnet causes the
An annular locus of drift electrons is formed on the get surface. The required magnetic field is, for example, on the order of 200 to 500 Gauss as a magnetic field component parallel to the target surface.

FIG. 7 is a front sectional view of a cathode electrode according to a second embodiment of the present invention. In this cathode electrode, the electrode housing, the target assembly, the wall of the sputtering chamber and its opening, and a plurality of Os for maintaining airtightness.
The configuration and relative positional relationship of the ring, the target shield member, and the like are the same as those of the cathode electrode of the embodiment shown in FIG. Therefore, the same components are denoted by the same reference numerals, and description thereof will be omitted. The feature of this embodiment is that the magnet assembly is made movable. Hereinafter, the configuration of the magnet assembly will be described.

The magnet assembly 51 includes four magnet units 4
4, a magnetic shield 49 is provided between the magnet units, and a magnet fixing base 48 is provided below the magnet units.
In the magnet assembly 51 of the present embodiment, the magnet unit 44
, The concave space 3 inside the electrode housing 31.
8, a space 52 having the same width as the width of one magnet unit remains. Therefore, in the concave space 38 in the electrode housing 31, the magnet assembly 51 is
Or, it is possible to reciprocate in the direction of 54.
The amplitude of the reciprocation of the magnet assembly 51 is substantially equal to the width of one magnet unit. In the magnet assembly 51 of the present embodiment,
A moving mechanism for moving this is provided.

The above moving mechanism will be described with reference to FIGS. FIG. 8 is a sectional view taken along line VIII-VIII of FIG.
In FIG. 7, the magnet assembly 51 is supported by a support 55. The magnet assembly 51 is supported by a support 55 using screws (not shown) or the like.
Fixed to Further, the support table 55 is fixed to the driving plate 56. As shown in FIG. 8, a rectangular guide hole 57 is formed in the center of the drive plate 56, and a circular cam 58 that is in contact with a part of the inner wall is arranged in the guide hole 57.
The cam 58 is rotated by a cam shaft 59.

Four slide bearings 60 are fixed to the bottom of the driving plate 56. Two guide bars 61 are disposed in the longitudinal direction near the bottom of the concave space 38, and the slide bearing 60 is inserted through the guide bar 61. Both ends of each guide bar 61 are fixed by receiving cylinders 62 provided on the inner wall surface of the concave space 38 of the electrode housing 31. With such a configuration, the driving plate 56 is guided by the guide bar 61 and is movable in the direction of the arrow 53 or 54. When the camshaft 59 rotates, the driving plate 56 reciprocates in the concave space 38 according to the contact relationship between the cam 58 and the guide hole 57. Since the circular cam 58 is directly connected to the camshaft 59 in an eccentric state from the center thereof, when the rotational speed of the camshaft 59 is constant, the speed of the reciprocating motion of the driving plate 56 is slow at both ends, and the center portion is And it becomes a simple vibration motion.

The shape of the above-described guide hole 57 is not limited to a rectangle, but may be an elliptical shape or an arbitrary shape similar thereto as long as the driving plate 56 can reciprocate by rotating the cam 58. can do.

In FIG. 7, a cam shaft 59 is connected to an output shaft of a motor 63 and is rotated by the motor 63. The motor 63 is arranged outside the electrode housing 31, and is fixed to the electrode housing 31 by the support frame 64 and the support 65. The camshaft 59 is a radial bearing 6 that supports the camshaft while rotating it smoothly.
6 and an oil seal 67 for sealing the cooling water in the electrode housing while rotating. With the above configuration, the motor 63
When the camshaft 59 rotates in a certain direction by the rotation of the magnet assembly 51, the magnet assembly 51 is moved to the concave space 3 of the electrode housing 31.
8 reciprocate inside.

FIG. 9A is a plan view showing an erosion region formed on the target surface, and FIG. 9B is a sectional view thereof. This erosion region 69 corresponds to the electron drift motion trajectory 46 as shown in FIG. The amount of sputter etching in the erosion region is indicated by the hatched portion S in FIG. In this embodiment, since the four magnet units move in the short side direction, the erosion area 69 also reciprocates in the direction of the arrow 53 or 54. as a result,
The hatched portion S in (B) reciprocates, and as a whole, a dashed line 7
The uniform sputter etching as indicated by 0 is performed. As a result, the utilization efficiency of the target 35 is improved.

In particular, by making the amplitude of the reciprocating motion of the entire magnet assembly equal to the width of the magnet unit, the thickness distribution in the substrate and the target use efficiency are almost the same as when a single magnet unit is reciprocated. , The average film forming rate can be increased, and the uniformity of the film quality in the substrate can be improved.

FIGS. 10 to 12 are plan views showing modified examples of the magnetic shield means in the magnet assembly. In each case,
It is an example of a magnet assembly including four magnet units. FIG.
In the example of No. 0, a ferromagnetic block 71 made of iron, nickel or the like is inserted between the short side of the magnet unit 44 and the magnetic shield 49b outside the short side. Magnet unit 44
When the magnetic field near the short side of is strong, it is preferable to adopt such a configuration. Thereby, the magnetic field distribution and the thickness distribution of the thin film can be adjusted. In the example of FIG.
A ferromagnetic block 72 is inserted into a gap between the magnet unit 44 and the magnetic shield 49a. In the example of FIG. 12, a ferromagnetic plate 73 is attached to the surface of the magnet assembly 32 to block the magnetic field. The ferromagnetic plate 73 is attached only near the short side of the magnet unit. This example
It is effective for a wide range of magnetic field adjustment and film thickness adjustment.

FIG. 13 is a front sectional view of a cathode portion according to a third embodiment of the present invention. In this cathode electrode, the configurations and relative positional relationships of an electrode housing, a target assembly, a wall of a sputtering chamber and its opening, a plurality of O-rings for maintaining airtightness, a target shield member, and the like are shown in FIG. This is the same as the case of the cathode electrode of the embodiment. Therefore, the same components are denoted by the same reference numerals, and description thereof will be omitted. The feature of this embodiment resides in the magnet assembly, and the configuration of this magnet assembly will be described below.

This magnet assembly includes five magnet units, of which two magnet units 74A on both sides are provided.
And the three inner magnet units 74B have different configurations. The basic configuration of the magnet units 74A on both sides is the same as the magnet unit 44 of the embodiment shown in FIG. On the other hand, in the inner magnet unit 74B, a spacer 75 is inserted between the yoke 43 and the magnet fixing base 48. The height of the magnet portion is smaller than that of the magnet unit 74A. The height positions of the magnetic pole surfaces of the magnet units are all equal among the five magnet units. A magnetic shield 49 is arranged between the magnet units. Then, within a single magnet unit, the magnetic field uniformity is within ± 5%, and between the two magnet units 74A on both sides, the magnetic field uniformity is within ± 5%,
Magnetic field uniformity of ± 5% between inner magnet units 74B
Within.

Next, the operation of this embodiment will be described. FIG.
FIG. 4A shows a state in which four identical magnet units are arranged in parallel. In this case, four magnetic field distributions corresponding to the magnet units are formed on the surface of the target 35,
The strengths of these magnetic field distributions are substantially equal to each other. FIG.
(B) is an example in which the height (hence the volume) of the magnet part is different as in this embodiment. That is, the height of the magnet part of the magnet unit 74A on both sides is larger than the height of the magnet part of the inner magnet unit. In addition,
This drawing shows an example including four magnet units. In this case, the strength of the magnetic field on the surface of the target 35 is strong on both sides and weak on the inside. In the drawing, a strong magnetic field is indicated by H, and a weak magnetic field is indicated by L. In H, the magnetic field intensity is large, the ion current density is large, and the sputter etching amount is large. Conversely, in the case of L, the sputter etching amount is small.

FIG. 14C shows another means for increasing the magnetic field on both sides. In this example, the magnet units themselves are all the same, but the magnet units 76 on both sides are identical.
Insert a spacer 77 between A and the magnet fixing base 48,
Only the magnet units 76A on both sides are close to the target 35. Therefore, there is a step between the magnetic pole surfaces of the magnet units 76A on both sides and the magnetic pole surfaces of the inner magnet unit 76B. By such means, the strength of the magnetic field on the surface of the target 35 can be increased on both sides and reduced on the inside. For example, when the step is 3 mm, the magnetic field strength of L (effective magnetic field strength described above) is 200 G
(Gauss), the magnetic field strength of H becomes 225G.

FIG. 15 is a graph showing contour lines of a film thickness distribution when a film is formed on a substrate using the magnet assembly shown in FIG. The conditions were as follows: the distance between the target and the substrate was 135 mm; the pressure of Ar gas was 5 mTorr;
Copper was used as a get material. Both the magnet assembly and the substrate are stationary. The film thickness of the substrate 14 was measured within a rectangular measurement range 78. The dimension of the target effective area 79 is such that the direction parallel to the short side of the magnet unit, that is, the X direction is LX =
LY = 450 mm in the direction parallel to the long side of the magnet unit, that is, in the Y direction, is 360 mm. The uniformity of the film thickness distribution within the effective area 79 was ± 14.3%. The figures of the contour lines in the figure show the film thickness in percentage when the maximum film thickness is 100%. What can be seen from this graph is that the film thickness distribution at both ends in the X-axis direction is particularly undesirable.

On the other hand, FIG. 16 is a graph of the film thickness distribution when the magnet assembly shown in FIG. 14C is used. The film forming conditions are the same as in FIG. The step between the magnet units on both sides and the inner magnet unit is 5 mm. In this case, an effective area 7 of 360 mm × 450 mm
Within the range of 9, the uniformity of the film thickness distribution was greatly improved to ± 8.1%. FIG. 17 shows a case where the step is 3 mm.
6 is a graph similar to FIG. 6, and the uniformity of the film thickness distribution in the effective region 79 was ± 11.1% Thus, by increasing the strength of the magnetic field on both sides in the X-axis direction, the uniformity of the film thickness distribution was greatly improved.

In order to increase the strength of the magnetic field on both sides in the X-axis direction, in addition to the above-described means, the dimensions of the center magnet and the peripheral magnet in the horizontal section and the material of the magnet are changed. The same effect can be obtained by these means. The space in FIG.
The support 75 may or may not be used depending on the film forming conditions.
If it is used, it becomes the same as FIG. 14B, and if it is not used, the effect of the step as shown in FIG. 14C is added.

FIG. 18 is a front sectional view of a cathode electrode according to a fourth embodiment of the present invention. This cathode electrode is obtained by combining the magnet assembly of the cathode electrode shown in FIG. 13 with the moving mechanism shown in FIGS. The structure of the moving mechanism is the same as that shown in FIGS. Therefore, the same components are denoted by the same reference numerals, and description thereof will be omitted.

Also in this embodiment, similar to the embodiment shown in FIGS. 7 and 8 described above, the annular trajectory of a plurality of drift electrons periodically moves on the target surface.
The target is uniformly consumed except at both ends in the moving direction, thereby improving the use efficiency of the target. Moreover, in this embodiment, the magnetic fields near both ends in the moving direction are stronger than the inside in the same manner as in the embodiment of FIG. 13, so that the target portions at both ends in the moving direction are hardly uniformly consumed by such a moving mechanism. Is more actively sputtered, and the utilization efficiency is further improved.

FIGS. 19A and 19B show another type of magnet unit having a different structure from the magnet unit used in all of the embodiments described above. FIG. 19A is a perspective view of the magnet unit, and FIG. () Is a front sectional view of a magnet assembly including the magnet unit. In this magnet unit 85,
There is no central magnet, only a rectangular and annular magnet portion 86 is present, the inner wall surface of which is an S pole and the outer wall surface of which is an N pole. That is, when the magnet unit 85 is arranged in the electrode housing, the magnetic pole surface is perpendicular to the target surface. This magnet unit 85 corresponds to FIG.
It can be used as a magnet unit in the eighth embodiment. For example, as shown in FIG. 19B, by combining the magnet units 85A and 85B, the magnetic field generated by the outer magnet unit 85A on the target surface is made larger than the magnetic field generated by the inner magnet unit 85B. The inner magnet unit 85A is placed on the spacer 87 to reduce the height of the magnet part. With this type of magnet assembly, there is no need to place a magnetic shield between the magnet units to suppress mutual interference between adjacent magnetic poles.
Therefore, the size of the magnet assembly can be further reduced.

The present invention is not limited to the above-described embodiment, but can be modified as follows. (1) The dimensions, materials, numbers, and the like of the magnet assemblies and the magnet units included therein in each of the above-described embodiments are not limited thereto, and can be arbitrarily changed without departing from the scope of the present invention. It is. (2) Although the moving mechanism of the magnet assembly in the above-described second and fourth embodiments uses a combination of the eccentric cam and the guide hole, other moving mechanisms may be employed. . (3) In each of the above embodiments, the magnetic pole arrangement of the magnet unit is such that the magnetic pole surface of the center magnet on the target side is the S pole and the magnetic pole surface of the peripheral magnet on the target side is the N pole. However, the opposite magnetic pole arrangement may be adopted. That is, the magnetic pole arrangement of all the magnet units can be such that the magnetic pole surface on the target side of the center magnet is the N pole and the magnetic pole surface on the target side of the peripheral magnet is the S pole.

[0070]

According to the first aspect of the present invention, a plurality of magnet units having the same magnetic pole arrangement are arranged side by side, and a magnetic shield is arranged between the magnet units, so that the mutual cancellation of the magnetic fields of the magnet units is eliminated. In addition, uneven distribution of the magnetic field due to mutual interference of the magnetic fields is prevented. Claims
According to the second aspect of the present invention , since the magnet assembly including a plurality of magnet units is reciprocated, the film thickness distribution can be further improved, the use efficiency of the target can be improved, and the target can be further improved. Particles generated due to the deposited film on the surface can be suppressed.

[Brief description of the drawings]

FIG. 1 is a front sectional view of the overall configuration of a sputtering apparatus according to a first embodiment of the present invention.

FIG. 2 is a front sectional view of the cathode electrode of the first embodiment.

FIG. 3 is a plan view of the magnet assembly of the first embodiment.

FIG. 4 is a sectional view, a plan view, and a perspective view of the magnet unit of the first embodiment.

FIG. 5 is a plan view showing a movement trajectory of drift electrons and a cross-sectional view of a corresponding magnet assembly.

FIG. 6 is a cross-sectional view showing lines of magnetic force generated by the magnet assembly.

FIG. 7 is a front sectional view of a cathode electrode according to a second embodiment of the present invention.

8 is a sectional view taken along line VIII-VIII in FIG.

FIG. 9 is a plan view and a cross-sectional view showing an erosion region on a target.

FIG. 10 is a plan view showing a modification of the magnetic shield of the magnet assembly.

FIG. 11 is a plan view showing another modification of the magnetic shield of the magnet assembly.

FIG. 12 is a plan view showing still another modification of the magnetic shield of the magnet assembly.

FIG. 13 is a front sectional view of a cathode electrode according to a third embodiment of the present invention.

FIG. 14 is a cross-sectional view showing three arrangement examples of the magnet unit.

FIG. 15 is a graph showing a film thickness distribution of a thin film manufactured using the arrangement of FIG.

FIG. 16 is a graph showing a film thickness distribution of a thin film manufactured with a step of 5 mm in the arrangement of FIG. 14C.

FIG. 17 is a graph showing a film thickness distribution of a thin film manufactured with a step of 3 mm in the arrangement of FIG. 14C.

FIG. 18 is a front sectional view of a cathode electrode according to a fourth embodiment of the present invention.

FIG. 19 is a perspective view of another type of magnet unit and a sectional view of a magnet assembly using the same.

FIG. 20 is a diagram for explaining the magnetic field uniformity of the magnet unit.

DESCRIPTION OF SYMBOLS 20 ... Cathode 22 ... Target assembly 23 ... Power supply system 32 ... Magnet assembly 35 ... Target plate 41 ... Center magnet 42 ... Peripheral magnet 43 ... Yoke 44 ... Magnet unit 48 ... Magnet fixing base 49 ... Magnetic shield

Claims (5)

(57) [Claims] 1. A vacuum vessel provided with an exhaust system for evacuating the inside, a substrate holding member disposed inside the vacuum vessel for mounting a substrate on which a film is to be formed, and a position facing the substrate. At least one magnetron cathode electrode provided with a rectangular planar target that is disposed in relation to the substrate, a gas control system that circulates gas inside the vacuum vessel and appropriately maintains an internal pressure, A sputtering apparatus comprising: a power supply system for supplying power to a magnetron cathode electrode; (A) The magnetron cathode electrode includes a plurality of magnet units on the back surface of one rectangular planar target. (B) The magnet unit has a rectangular cross section parallel to the target surface, and a plurality of magnet units are arranged such that a long side is adjacent to a long side of an adjacent magnet unit. (C) The dimensions and magnetic pole arrangement of the magnet units are the same in all magnet units included in the same magnetron cathode electrode. (D) The magnet unit is configured to generate an annular electron drift motion trajectory on the surface of the target. (E) The back of one of the rectangular planar targets
A magnetic shield wall is disposed between adjacent magnet units. 2. The sputtering apparatus according to claim 1, wherein the magnet unit is capable of reciprocating in a short side direction of the rectangle. 3. The sputtering apparatus according to claim 1, wherein the plurality of magnet units have a magnetic field uniformity within ± 5% within a single magnet unit, and within ± 5% between magnet units. A sputtering apparatus having magnetic field uniformity. 4. The sputtering apparatus according to claim 1, wherein the magnet unit includes a yoke, a center magnet fixed on the yoke, and a peripheral magnet fixed on the yoke and surrounding the center magnet. The center magnet and the peripheral magnet have magnetic pole surfaces on the surface fixed to the yoke and the target-side surface, and the target-side magnetic pole of the center magnet and the target-side magnetic pole of the peripheral magnet have opposite polarities. A sputtering apparatus characterized by the above-mentioned. 5. The sputtering apparatus according to claim 1, wherein a magnetic shield wall is arranged around the whole of the plurality of magnet units included in the same magnetron cathode.