IMPROVED CATHODE ARC SOURCE

Abstract

A cathode arc source comprises: a cathode target; a first magnetic field source located above the target; a second magnetic field source located below the target; and a third magnetic field source located between the first and second magnetic field sources and having an opposite polarity to the first magnetic field source; wherein the resultant magnetic field from the first, second and third magnetic field sources has zero field strength in a direction substantially normal to the target at a position above the target. The invention also provides methods of striking a cathode target and methods of depositing coatings which can be carried out using the cathode arc source described herein.

Claims

1. A cathode arc source comprising: a station for a cathode target; a first magnetic field source located above the target station; a second magnetic field source located below the target station; and a third magnetic field source located between the first and second magnetic field sources and having an opposite polarity to the first magnetic field source; characterised in that the resultant magnetic field from the first, second and third magnetic field sources has zero field strength in a direction substantially normal to the target station at a position of up to 10 cm above the target.

2. A cathode arc source according to claim 1 wherein the resultant magnetic field from the first, second and third magnetic field sources has zero field strength in a direction substantially normal to the target station at a position of up to 8 cm above the target.

3. A cathode arc source according to claim 1 wherein the second magnetic field source has an opposite polarity to the first magnetic field source.

4. A cathode arc source according to claim 1 wherein the first, second and/or third magnetic field sources are magnetic field generating coils.

5. A cathode arc source according to claim 1 wherein the strength of at least one of the first, second and third magnetic field sources are adjustable.

6. A cathode arc source according to claim 5 wherein the strengths of at least two of the first, second and third magnetic field sources are adjustable.

7. A cathode arc source according to claim 1 wherein the strength of the first, second and third magnetic field sources are all adjustable.

8. A cathode arc source according to claim 1 wherein the first and third magnetic field sources are magnetic field generating coils and the second magnetic field source is a permanent magnet.

9. A cathode arc source according to claim 1 wherein the distances of at least one of the first, second and third magnetic field sources either above or below the target are adjustable.

10. A cathode arc source according to claim 9 wherein the distances of at least two of the first, second and third magnetic field sources either above or below the target are adjustable.

11. A cathode arc source according to claim 1 wherein the distances of the first, second and third magnetic field sources above or below the target are all adjustable.

12. A cathode arc source according to claim 1, comprising a carbon target.

13. A cathode arc source according to claim 1, comprising a metal target or an alloy target.

14. A method of depositing a coating on a substrate, comprising generating positive ions from a target in a cathode vacuum arc source according to claim 1, and depositing the ions onto the substrate, wherein the target is a metal other than aluminum, chromium or titanium.

15. A method according to claim 14, wherein the target comprises copper or nickel.

16. A method according to claim 15, wherein the coating is deposited using a cathode arc source according to claim 1.

17. A substrate coated with a metallic coating, wherein the coating is deposited by FCVA using a cathode arc source according to claim 1.

18. A coated substrate according to claim 17, comprising a FCVA-deposited coating comprising copper.

19. A coated substrate according to claim 17, comprising a FCVA-deposited coating comprising nickel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0082] The invention is now described in the following specific examples, with reference to the accompanying drawings, which are not to be construed as limiting the scope of the invention, in which:

[0083] FIG. 1 shows a side, cut-away schematic view of a conventional cathode arc source;

[0084] FIG. 2A shows a similar view of a cathode arc source according to a first embodiment of the invention;

[0085] FIG. 2B shows a view of a cathode arc source according to a second embodiment of the invention;

[0086] FIGS. 3A and 3B are schematic diagrams showing the resultant magnetic field lines in a conventional cathode arc source (FIG. 3A) and a cathode arc source of the invention (FIG. 3B);

[0087] FIG. 4A shows the simulated magnetic field strength as a function of the distance above the target in an apparatus comprising only filter and anode coils (i.e. not comprising the third, auxiliary coil of the invention);

[0088] FIG. 4B shows the simulated magnetic field strength as a function of the distance above the target in an apparatus of the invention (i.e. an apparatus comprising filter, anode and auxiliary coils);

[0089] FIG. 5A shows the simulated magnetic field strength as a function of the radial distance from the target centre in an apparatus comprising only filter and anode coils (i.e. not comprising the third, auxiliary coil of the invention); and

[0090] FIG. 5B shows the simulated magnetic field strength as a function of the radial distance from the target centre in an apparatus of the invention (i.e. an apparatus comprising filter, anode and auxiliary coils).

[0091] FIG. 6 shows polymer sample strips coated with copper using an apparatus and method of the invention.

[0092] FIGS. 7A to 7E show samples of aluminium alloy hard disk drive platters coated with chromium using an apparatus and method of the invention, where the arc current was set at 85V, no bias applied.

[0093] FIGS. 8A to 8E show samples of aluminium alloy hard disk drive platters coated with chromium using an apparatus and method of the invention, where the arc current was set at 160V, no bias applied.

[0094] FIG. 1 shows a conventional cathode arc source (10), as described in further detail in WO 98/03988.

[0095] The source (10) comprises a cathode (12) shrouded by a non-insulating shroud (13) and an anode (14) that is formed by the inside wall of the vacuum chamber (11). A target (16) is in electrical contact with the cathode (12). An insulating shroud (17) surrounds the target to prevent arcing between sides of the target (16) and the anode (14). The cathode (12) and the anode (14) are connected to an arc power supply (not shown).

[0096] Cooling of the cathode is achieved via supply of cooling water via water inlet (20) and water outlet (22). Cooling of the anode is likewise achieved by supply of cooling water via a water inlet and water outlet (not shown) of the anode cooling jacket (27).

[0097] A rotatable striker (28) is mounted on the wall of the vacuum chamber and is adapted to rotate towards and contact the target (16) to achieve ignition of the cathode arc.

[0098] A view port (30) including a swagelock fitting for gas input (31) is mounted on the side of the source for visible inspection of the arc during operation.

[0099] Above the target (16) there is a filter coil (32) which acts as a first magnetic field source and mounted above the target (16) and around the cylindrical wall of the chamber is a anode coil (34) which acts as a second magnetic field source.

[0100] FIG. 2A shows a cathode arc source according to one embodiment of the invention. The cathode arc sources comprises a cathode (12), non-insulating shroud (13), anode (14), vacuum chamber (11), target (16), insulating shroud (17), water inlet (20), water outlet (22), anode cooling jacket (27), striker (28), view port (30), gas input (31) and first and second magnetic coils (32, 34), referred to as the filter coil and the anode coil respectively, as in the conventional cathode arc source shown in FIG. 1 and as described above.

[0101] In addition, the cathode arc source shown in FIG. 2A comprises an auxiliary coil (36) which acts as a third magnetic field source and surrounds the vacuum chamber (11) at a position between the filter (32) and anode (34) coils. Due to the position of the striker (28), the auxiliary coil (36) can only be seen on the left-hand side of the cathode arc source shown in FIG. 2A.

[0102] Alternatively, the anode coil (34) can be replaced with a cylindrical permanent magnet (34B), as shown in FIG. 2B. It will be understood that in the description of the operation of the apparatus below, the anode coil (34) can be replaced with this permanent magnet (34B) without substantially affecting the working of the invention.

[0103] The magnet (34B) is has a strength of 500mT.

[0104] Magnet (34B) is attached to rod 40 which can be used to move the magnet up and down in a direction normal to the target (16) at distances from 4 cm to 9 cm beneath the target surface. The magnet may also be surrounded by a wall (42) to segregate the magnet (34B) from the water cooling chamber (supplied by inlet (20)) to ensure that the magnet remains dry.

[0105] In operation of the cathode arc source (10) magnetic fields are generated by the respective coils (32, 34, 36) and a resultant magnetic field is produced within the vacuum chamber (11) such that, at a region above the target, the magnetic field strength is zero (or minimal) in a direction substantially normal to the target (16). The region of zero field strength, or “null region”, is within the vacuum chamber (11) and a short distance above the target (16). Variation of the currents in the respective coils (32, 34) will vary the distance between the surface of the target (16) and the null point.

[0106] In use of this cathode arc source, the currents in the respective first, second and third coils (32, 34, 36) are varied such that the null region, i.e. the region at which the magnetic field in a direction substantially normal to the target has zero strength, is between 0.5 cm and about 5 cm away from the target (16).

[0107] The filter (32) and anode (34) coils are of opposite polarity and hence cancel each other out in a direction normal to the target (16) such that there is an area above the target in which the resultant magnetic field in a direction normal to the target is zero. However, the magnetic fields from the filter (32) and anode (34) coils reinforce each other at positions radial to the target (16) and hence (with the auxiliary coil (36)) the magnetic field strength radial to the target (16) is large. The auxiliary coil (36) (located between the first and second coils) has an opposite polarity to the filter coil (32). The magnetic field generated by the auxiliary coil (36) reduces the radial magnetic field strength. This is shown in schematic FIGS. 3A and 3B which show the magnetic field lines of the resultant magnetic field in a conventional cathode arc source (FIG. 3A) and in a cathode arc source of the invention (FIG. 3B). The reduced radial field strength in the cathode arc source of the invention can be seen in FIG. 3B.

[0108] In addition, the auxiliary coil (36) increases the size of the area of low magnetic field strength above the target (see FIGS. 4A, 4B, 5A and 5B). FIGS. 4A, 4B, 5A and 5B are simulated magnetic field strength plots. FIGS. 4A and 5A are representative of conventional cathode arc sources (i.e. those containing only two separate magnetic field sources), whilst FIGS. 4B and 5B are representative of cathode arc sources of the invention.

[0109] For each of the pairs of plots, it can be seen that for the cathode arc sources of the invention both the region of lower field strength above the target is larger in size and the field strength at positions radial to the target (i.e. at regions between the first (32) and third (36) coils) is reduced.

Example 1—Chopping Current and Plasma Output with Varying Anode/Auxiliary Coil Currents

[0110] In order to determine arc stability at lower currents, the apparatus of FIG. 2A was used and the current through the anode coil (34) and the auxiliary coil (36) were varied along with the arc current used. The filter coil (32) current was kept constant at 12 A. The target was a 99.95% pure copper target having a diameter of 9 cm.

[0111] The chopping current (i.e. the highest arc current at which chopping of the arc is observed) was measured and recorded for different coil currents for the anode and auxiliary current, and are shown in Tables 1 A and 1B below. In addition, the plasma output was measured and recorded for each combination of auxiliary and anode coil currents when the arc current was 85 A and these are shown in Tables 2 A and 2B.

TABLE-US-00001 TABLE 1A Chopping Current Anode Coil (A) (A) 2 3 4 5 6 7 Auxiliary 0 69 67 68 63 63 73 Coil (A) 1 68 64 67 69 74 82 2 60 67 72 78 80 81 3 65 64 65 74 98 90 4 67 67 73 78 99 85 5 64 73 72 85 82 82

TABLE-US-00002 TABLE 1B Anode Coil (A) Chopping Current (A) 1.2 1.5 1.8 2 3 Auxiliary 0 68 71 73 73 77 Coil (A) 1 68 70 71 73 70 2 74 71 67 67 70 3 70 73 68 67 70 4 70 70 75 77 70 5 70 70 67 73 76

TABLE-US-00003 TABLE 2A Anode Coil (A) Plasma Output (V) 2 3 4 5 6 7 Auxiliary 0 0.00 0.00 0.13 0.19 0.07 0.19 Coil (A) 1 0.00 0.10 0.20 0.20 0.18 0.18 2 0.10 0.19 0.22 0.20 0.20 0.16 3 0.29 0.29 0.15 0.12 0.12 0.10 4 0.20 0.11 0.06 0.04 0.07 0.09 5 0.10 0.05 0.07 0.08 0.06 0.09

TABLE-US-00004 TABLE 2B Plasma Output Anode Coil (A) (V) 1.2 1.5 1.8 2 3 Auxiliary 0 0.00 0.00 0.00 0.00 0.00 Coil (A) 1 0.00 0.00 0.00 0.00 0.10 2 0.00 0.00 0.10 0.10 0.20 3 0.20 0.20 0.29 0.21 0.20 4 0.20 0.20 0.20 0.11 0.09 5 0.09 0.10 0.02 0.03 0.05

[0112] The inventors have thus found that using a cathode arc source having three separate magnetic field source gives an increased area above the target where the magnetic field strength is low and also reduces the strength of the magnetic field radial to the target. This means stable arcs can be produced using lower currents and thus allows for cathode arc sources to be used to deposit a wider range of metallic coatings on substrates.

Example 2—Magnetic Field Strength Simulation Studies

[0113] In addition, simulation studies were carried out to assess the effect the addition of the auxiliary coil has on the magnetic field strength at the target.

[0114] FIG. 4A shows the simulated normal magnetic field strength (T) from 0.05m below the target to a height of 0.4m above the target in an apparatus in which no auxiliary coil is present (comparative example). FIG. 4B shows the simulated normal magnetic field strength (T) from 0.05m below the target to a height of 0.4m above the target in an apparatus of the invention comprising three coils; a filter coil, an anode coil and an auxiliary coil.

[0115] It can be seen that the addition of the third, auxiliary coil results in a greater region where the normal magnetic field strength is zero (from approx. 0.05m below the target to 0.05m above the target in FIG. 4B, compared to approx. 0.03m in FIG. 4A).

[0116] In addition, the radial magnetic field strength was simulated at radial distances from the centre of the target for up to 0.15m. FIG. 5A shows the simulated radial magnetic field strength (T) in an apparatus in which no auxiliary coil is present (comparative example). FIG. 5B shows the simulated radial magnetic field strength (T) in an apparatus of the invention comprising three coils; a filter coil, an anode coil and an auxiliary coil.

[0117] In contrast to FIG. 5A, in FIG. 5B it can be seen that the radial magnetic field strength at regions from 0.05 to 0.15m from the centre of the target is significantly reduced. This is attributed to the addition of a third, auxiliary coil which reduce the resultant radial field strength as described herein.

Example 3—Example Coatings

[0118] Using a FCVA source of the invention and a copper target, thin films of copper (c. 200 nm) were deposited onto polymer strips. Samples are shown in FIG. 6. Conductivity of the copper films were tested; conductivity was found in all cases to be close to that of, and in some cases comparable to that of, bulk copper. Different appearance of the strips reflects underlying surface morphology prior to FCVA copper deposition.

Example 4—Coating Quality

[0119] Two sets of five aluminium alloy hard disk drive platters were coated with chromium using the three-coil apparatus of the invention using common operating parameters (anode coil current of 1.2 A, auxiliary coil current of 4 A and filter coil current of 12 A), targets and substrates, with only the arc current being changed between Set 1 and Set 2. The coated disks were then examined for surface particle content.

[0120] The results are shown in FIGS. 7 and 8. FIGS. 7A to 7E show ×3000 magnification optical microscope analysis of the five disks coated using arc current of 85 A (Set 1) and FIGS. 8A to 8E show ×3000 magnification optical microscope analysis of the five disks coated using arc current of 160 A (Set 2).

[0121] These results showed there were more visible particles in the coatings made using an arc current of 160 A and the particles created in the 160 A arc current were visibly larger.

[0122] The roughness of samples of Set 1 and Set 2 were analysed at 2 positions each for R.sub.a and R.sub.Z values, indicators respectively of overall roughness (neutralizing outlying points) and roughness based on highest peak to lowest valley across the coating. The results are set out in the table below:

TABLE-US-00005 Set 1 Set 2 (85A) (160A) Arc Current #1 #2 #1 #2 Thickness (nm) 227 229 230 234 R.sub.a (nm) 3.2 3.6 3.0 3.0 R.sub.z (nm) 39.1 29.9 42.1 33.0

[0123] The thickness of each measured coating sample was similar. The coating made at arc current 85 A had similar R.sub.a to that made at arc current 160 A, while having generally lower R.sub.Z.

Example 5—Nickel Coatings

[0124] Using a FCVA source of the invention and a nickel target (surrounded by a magnetic ring mounted in the chamber and encircling the nickel target) thin films of nickel (c. 200 nm thickness) were deposited onto polymer strips. These coatings were found to be magnetic, thus exhibiting this property of bulk nickel.

Example 6—Etchable Nickel and Copper Coatings

[0125] Using a FCVA source of the invention and a nickel target (surrounded by a magnetic ring mounted in the chamber and encircling the nickel target) thin films of nickel (c. 30 nm) were deposited onto polymer strips as seed layers and then on top were deposited thin upper layers of copper (c. 200 nm), using a copper target. These coated substrates are suitable for etching into electronic components, e.g. as part of circuit boards.

[0126] The invention thus provides an improved cathode arc source, especially for use with metallic and alloy targets.