GB2125440A

GB2125440A - Tunnel magnetron for cathode sputtering

Info

Publication number: GB2125440A
Application number: GB08318406A
Authority: GB
Inventors: Christopher Elphick; Ali Reza Nyaiesh
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-07-13
Filing date: 1983-07-07
Publication date: 1984-03-07
Also published as: GB8318406D0

Abstract

A tunnel magnetron source includes an array of magnets arranged to provide magnetic field lines of at least one tunnel magnetic field at a surface of the source, and a pipe through which a cooling fluid can be supplied, the surface and the array of magnets being relatively movable so that said at least one tunnel magnetic field moves over said surface of the source, and one of the surface and the array of magnets having at least one planar vane on which the cooling fluid impinges so as to cause said relative movement. The magnetron is used in sputtering equipment e.g. for sputtering Pt.

Description

SPECIFICATION Improved magnetron This invention relates to magnetrons, i.e. to devices in which a gas is ionised to form a plasma which is constrained by a magnetic field and relates particularly to tunnel magnetrons in which the magnetic field lines begin and end on a plane surface to form a "tunnel" in which the ions move.

Tunnel magnetrons are described in general in a paper by L. Holland, Institute of Physics Conference Series Number 54, Chapter 6, 1980, pages 220 to 228. In Vacuum, Volume 31, 1981, pages 5 to 7, C. Elphick describes the construction of a particular type of tunnel magnetron intended for cathode sputtering and which has a planar electrode which is water cooled.

It is a disadvantage of a tunnel magnetron when used for cathode sputtering that the sputtering material is eroded only in the area coincident with the magnetic field tunnel. Thus -the material, which may be expensive, is used inefficiently and deep erosion may change the sputtering conditions so that the characteristics of the sputtered film vary with time.

To overcome this disadvantage, it has been suggested that the magnets forming the tunnel should be rotated with respect to the sputtering material so that material is removed more evenly, and a mechanical arrangement to achieve this rotation-is known.

In the present invention, an alternative arrangement for providing the relative movement is disclosed.

According to the invention, a tunnel magnetron source includes an array of magnets arranged to provide magnetic field lines of at least one tunnel magnetic field at a surface of the source, and pipe means through which a cooling fluid can be supplied, the surface and the array of magnets being relatively movable so that said at least one tunnel magnetic field moves over said surface of the source, and one of the surface and the array of magnets having at least one planar vane on which the cooling fluid impinges so as to cause said relative movement.

Preferably the array of magnets is movable and the surface is static. The source is usually a cathode.

In one arrangement the source surface supports a planar horizontal sputtering material and the array of magnets is arranged to give a circular axis tunnel magnetic field, the array of magnets being arranged for movement by rotation about a vertical axis spaced from the circular centre of the tunnel whereby the tunnel magnetic field moves over the surface of the material with planetary motion.

In another arrangement the array of magnets may be generally planar and form a series of tunnel magnetic fields spaced side by side over the array, the array being arranged for movement to and fro.

In further arrangement, the array of magnets is generally cylindrical and forms a series of tunnel magnetic fields spaced around the inside and outside of the cylinder and parallel to the cylindrical axis, movement of the array by rotation about the cylindrical axis causing the tunnel magnetic fields to sweep over an adjacent solid sputtering material inside or outside the magnet array.

The invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is an exploded view of a first embodiment of a tunnel magnetron source; Figure 2 is a section through the stator plates of the source shown in Figure 1; Figure 3 is a view of the magnetic rotor of a second embodiment of a tunnel magnetron source; Figure 4 is a part sectional view of the second embodiment source; Figure 5 is a view of the magnetic rotor of a third embodiment of a tunnel magnetron source; Figure 6 is a part sectional view of the third embodiment source; Figure 7 illustrates the electrical connections when a tunnel magnetron source according to the invention is used in a cathode sputtering apparatus; and Figure 8 is an exploded view of the magnetic array and drive arrangement of a tunnel magnetron source.

In Figure 1, a circular stator plate 10 is supplied with cooling water through a coaxial pipe 12 which also acts as a drain. The stator plate 10 supports a spacing ring 1 4 which carries a circular electrode 16, which is in this case a cathode, on the upper surface of which a sputtering plate (not illustrated in Figure 1) can be placed. The plate 10, ring 1 4 and cathode 16 are sealed by "0" rings in respective grooves 18, 20, 22.

The centre of the stator plate 10 carries a bush 23 which supports the stainless steel spindle 24 of a rotary magnet assembly, indicated generally at 26. The assembly consists of a rectangular vane 28, typically of polymethylmethacrylate, attached to the spindle 24. At one end of the vane and on the upper surface is a circular plate 30 which carries an array 32 of eight ceramic magnets and at the other end is a lead counterweight 34. The magnets are cut to form an octagonal annulus with all of the faces directed to the inside and outside of the octagonal annulus having the same poles, e.g. North poles inside, South poles outside as illustrated, so that the magnetic field lines, some of which are indicated at 36, form a tunnel having a circular axis or centre line. This shape of magnetic array for use in a tunnel magnetron is known.A plasma generated in the vicinity of the array is constrained by the field lines and the ions in the plasma more generally within a toroid.

The upper surface of the stator plate 10 is provided with three apertures 38, which are angled so that when cooling is provided through the pipe 12 and through a labyrinth channel, (not illustrated in Figure 1) within the plate 10, water is expelled through each aperture as a jet which impinges on the vane 28 at a position spaced from the spindle 24, causing the vane to rotate. A water jet from each aperture in turn strikes the vane as it rotates. The array of magnets 32 is therefore swept over the underside of the cathode 16, and the tunnel magnetic field sweeps over any sputtering plate on the cathode 16, so that the plate is more evenly eroded than with a static magnetic array. There is therefore more effective use of the sputtering material and the deposition conditions are less subject to variation with time.

Figure 2 shows the stator 10 in more detail.

The stator is in two parts, an outer, lower plate 10 which is recessed on its upper face to receive an upper plate 42 of smaller diameter, there being an annular channel 44 between the plates. The upper plate, which is usually of an acrylic material, is formed of two plates 42(at 42(b) in contact, which facilitates the formation of water channels in the slate 42.

The coaxial pipe 12 is attached to the lower plate 40 by a collet 46. The outer part of the pipe 12 is connected to a labyrinth channel 48 in the lower face of the upper plate 42, the channel being shaped to connect with each of the three apertures 38 (Figure 1). Water is supplied through the pipe 12 at sufficient pressure to emerge from the apertures as jets having sufficient velocity to cause rotation of the vane 28 and magnet assembly 32. The speed of rotation of the magnet assembly is controlled by the pressure of the water. The water also strikes the underside of the cathode plate 10 to provide cooling.

The inner part 50 of the coaxial pipe 12 is connected to a channel 52 within the upper plate 42 which is connected to a central drainage aperture 54 around the spindle bush 23. Water flows out by this route.

Figure 3 shows the magnet array 60 for a second embodiment of a tunnel magnetron source. Eight rectangular planar magnets 62 are arranged radially around a spindle 64 with their long sides parallel to the spindle and their largearea faces adjacent each other. Sixteen spaced magnets 66 are arranged, one between the outer ends of each pair of rectangular magnets, to form a series of hollow rectangular outer surfaces, the magnets 62, 66, all having their north poles directed outwards. Within each hollow rectangular surface is the south pole of one of eight further rectangular magnets 68.

In the magnet array 60, a plurality of tunnel magnetic fields is formed, the tunnels having rectangular axes or centre lines and the long sides of each rectangle being parallel.

It will be seen that if the array 60 is rotated about the spindle 64, each tunnel magnetic field in turn will be swept past an adjacent surface and at the central position, the effect will be to sweep a series of straight axis tunnel magnetic fields past the surface.

Figure 4 illustrates a magnetron source using the magnet array 60. The array 60 is supported with the spindle 64 horizontal within a rectangular chamber 70. A coaxial pipe 72 is connected to the bottom of the chamber and the outer part of the pipe 72 is connected to a groove 74 in a stator block 76 within the chamber 70.

The groove is connected to a plurality of angled apertures 78 along the floor of the chamber which are arranged so that water emerging from each aperture as a jet impinges on the large-area faces of the magnets in the array 60, causing the array to rotate on the spindle 64, i.e. the magnets themselves constitute the vanes. The jet impinges on each magnet in turn during the rotation.

The upper surface of the chamber 70 constitutes a cathode 80 on which a plane sputtering material can be placed. When the magnet array is rotated, the tunnel magnetic fields are swept over the cathode.

The coaxial pipe 72 has an inner pipe which is connected to a drainage groove 82 in the stator block.

The magnet array 90 of a third embodiment is illustrated in Figure 5. The array 90 is similar to the array 60, but contains a larger number of magnets, the array having a central aperture of considerable diameter. The inner face of the array 90 has the reverse magnetic poles to the outer face, so that a plurality of rectangular section tunnel magnetic fields is formed.

Referring now to Figure 6, the array 90 is enclosed by an outer cylinder 92 and a double walled inner cylinder 94, the cylinders being joined by watertight end caps 96.

The array is arranged with its cylindrical axis vertical. One magnet 98 is shown. The magnet array has upper and lower caps 100, 1 02 which are grooved to carry ball bearings 104 which run in upper and lower bearings 106, 108. The lower bearing is carried by an annular support plate 110.

The upper face of the lower bearing 1 08 has a deep annular channel 112 which accommodates a plurality of vanes 114 attached to the lower cap 100 and spaced around the magnet array. The lower face of the lower bearing 1 08 has a water supply channel 11 6 connected to a plurality of angled apertures 117 to the channel 112, and the supply channel 11 6 is connected to the inner pipe 120 of a coaxial pipe 11 8. The outer part of the pipe 118 is connected to the annular space of the double walled inner cylinder 94. A sputtering plate, which may be cylindrical or part cylindrical, is located within the inner cylinder 94 (and is not illustrated in Figure 6).

When cooling water is supplied through the inner pipe 120, jets of water emerge through the angles apertures 117 and strike the vanes 114, causing the magnet array rotate on the ball bearings 1 04. Water passes upwards between the magnets, as indicated by the arrows, and passes down through the annular space of the double walled inner cylinder 94 to the outer part of the coaxial pipe 120, cooling the inner cylinder 94 which constitutes a cathode. The tunnel magnet fields on the inside of the magnet array 90 sweep across the cathode surface.

Figure 8 shows an embodiment in which the tunnel fields are swept by a reciprocation of a planar array of magnets. Figure 8 shows a magnet array and cooling fluid drive constituted as a multilayer sandwich.

A water feed and return lock 201 supports a stator plate 202 and is covered by a water baffle plate 203. A rotating vane and connecting rod assembly 204 are housed in items 202 and 203.

A spacer plate 205 gives clearance for the connecting rod. A magnet array 206 provides the top layer of the sandwich.

It will be seen that cooling fluid, e.g. water, is circulated inside the elements of the sandwich so suitable seals and materials will be needed. These are well-known to those skilled in the art so only points of special care of difficulty will be identified.

Feed and return block 201 provides channels for water feed and return paths from a central connection 210. These paths, as indicated by the arrows, link with the paths in the stator plate 202.

Water from central connection 210 enters cavity 220 of plate 202. Part of the water flows through channels 211, 212 of block 201 to enter cavity 221 of plate 202. From cavities 220, 221 of plate 202 inclined bores such as 223, typically six in number, extend to a drive chamber 222. The bores 223, as shown by the arrows, produce inclined jets of water in chamber 222. A water feed baffle plate 203 closes cavities 220, 221. A rotatable vane device 241 fits into drive chamber 222 and is pivotted on axle 242 fitted in a bore 213 in block 201. The inclined jets of water in chamber 222, in operation, drive vane device 241 round.A bronze connecting rod 243 is attached eccentrically to vane device 241 at pivot 244 so that rotation of vane device 241 becomes reciprocation of connecting rod 243 and attached slide block 244. Slide block 244 is housed, for reciprocation, in slot 231 of plate 203 and recess 224 in plate 202. The stroke of the reciprocation is "S".

Two drive pins, 245, project from slide block 244 and through spacer plate 205. Plate 205 has a central slot 251 to accommodate the connecting rod 243 as it moves and also allows cooling fluid from chamber rod 243 as it moves and also allows cooling fluid from chamber 223 to pass to array 206. Plate 205 also has upper surface channels 252, 253 to provide a return cooling fluid path from the array 206 to block 201 and connection 210 through two bores formed through by the stack of elements 201,202, 203, 205, to the exit from the arrangement.

Array 206 is arranged to reciprocate over spacer plate 205 by the action of connecting rod 243 engaged by drive pins 245 in suitable bores 261 in the array 206. A housing, not shown, is provided to contain the cooling fluid and the elements 201 to 206. Array 206 is shorter than elements 201 to 205 by stroke "S" so that it can reciprocate in the housing. Conveniently the long sides of array 206 have "V" grooves 262 to receive stainless steel balls which are also received in the housing, not shown, so that array 206 can reciprocate smoothly while being supported by the balls and "V" grooves. Array 206 is constructed of galvanised iron sheet, for mechanical and magnetic reasons, and supports an array of ceramic magnets.This array is similar to that described for Figures 3 and 5, longer magnets, such as 265 and shorter magnets, such as 266, being arranged spaced apart with alternating polarity upwards as shown and the outer ring completed by link magnets 267. The joins between magnets are not shown and various detailed forms are possible. The ceramic magnets thus create the array of a plurality of tunnel magnetic fields on a plane base.

A central lengthwise slot 264 in array 206 conveys cooling fluid to the spaces between the magnets and outer lengthwise slots 262, 263, collect cooling fluid for return via channels 252, 253 as mentioned above.

A source of sputtering material, (not shown) is placed above the array to be within the plurality of reciprocating tunnel magnetic fields from the array.

It is an advantage of the latter embodiments that a sputtering plate placed on the cathode is evenly eroded during the sputtering process and that the propulsive force is supplied by the cooling water and no additional mechanical drive needs to be provided. Although the illustrated embodiments all show the magnet array moving with respect to the surface in other forms of the source the relative movement can be reversed if preferred or if more convenient.

Figure 7 illustrates, in highly schematic form, a cathode sputtering apparatus. Within a chamber 122, which can be evacuated or connected to a gas supply through a valve 124, an earthed cathode 126 supports a plate of sputtering material 128. A magnet array 130 sweeps over the underside of the cathode 126 and a tunnel magnetic field 132 sweeps over the sputtering plate 128. An anode 134 is spaced from the cathode 126 and is connected to a power source 1 36. A substrate 138 to be coated is spaced from the sputtering plate 128 and when a plasma is generated in the chamber receives a coating layer 140 of material from the sputtering plate. This general electrical arrangement is applicable to all the embodiments described above. The material sputtered will usually be metallic and nonmagnetic, e.g. platinum, but an electrically insulating material can also be sputtered.

Claims

1. A tunnel magnetron source includes an array of magnets arranged to provide magnetic field lines of at least one tunnel magnetic field at a surface of the source, and pipe means through which a cooling fluid can be supplied, the surface and the array of magnets being relativeiy movable so that said at least one tunnel magnetic field moves over said surface of the source, and one of the surface and the array of magnets having at least one planar vane on which the cooling fluid impinges so as to cause said relative movement.

2. A source according to Claim 1 in which the array of magnets is movable and the surface is static.

3. A source according to Claim 1 or Claim 2 in which the source is a cathode.

4. A source according to Claim 1 in which the source surface supports a planar horizontal sputtering material and the array of magnets is arranged to give a circula'r axis tunnel magnetic field, the array of magnets being arranged for movement by rotation about a vertical axis spaced from the circular centre of the tunnel whereby the tunnel magnetic field moves over the surface of the material with planetary motion.

5. A source according to Claim 1 in which the array of magnets is generally cylindrical and forms a series of tunnel magnetic fields spaced around the inside and outside of the cylinder and parallel to the cylindrical axis, movement of the array by rotation about the cylindrical axis causing the tunnel magnetic fields to sweep over an adjacent solid sputtering material inside or outside the magnet array.

6. A source according to Claim 1 in which the array of magnets is generally planar and forms a series of tunnel magnetic fields spaced side-byside over the array being arranged for movement to and fro to move the fields to and fro over the surface of the electrode.

7. A tunnel magnetron source movement arrangement substantially as herein described with reference to any one of Figures 1 to 6 and 8 of the accompanying drawings.

8. A tunnel magnetron sputtering apparatus including a source as claimed in any one of the preceding claims.

9. A tunnel magnetron cathode sputtering arrangement substantiaily as herein described with reference to Figure 7 of the accompanying drawings.