Abstract
An apparatus (1b) and method of depleting a plasma of electrons in a plasma coating apparatus is disclosed. The invention involves generating a plasma comprising ions (9), particulate material (5) and electrons (6) adjacent a target (4); forming a plasma trap (52) to constrain the plasma near to the target (4), and depleting the plasma of electrons by: providing an additional magnetic field (8b) that is superimposed over the magnetic field of the plasma trap (3, 52), which extends beyond a boundary layer (52) of the plasma trap, and which draws electrons (6) from, or near to, the boundary layer (52) of the plasma trap away from the target (4). The invention proposes applying a baseline voltage (50) to the target (4); and by applying periodic voltage pulses (13b) to the target (4). The additional magnetic field (8b) depletes the plasma of electrons, such that when a voltage pulse (13b) is applied to the target (4), ions (9) can be ejected from the plasma with reduced electron shielding. This has been shown to improve ion bombardment and reduce adverse electron bombardment effects.
Claims
1. A plasma coating apparatus comprising: a target; means for generating a plasma adjacent the target, the plasma comprising ions, particulate material and electrons; and an electron depletion device.
2. The apparatus of claim 1, wherein the means for generating a plasma adjacent the target comprises: an electric power source, which biases the target, and a magnetic arrangement, which forms a magnetic field in the vicinity of the target, the magnetic field comprising a plasma trap being a region of relatively high magnetic field strength, which confines a plasma generated by the means for generating a plasma to a region adjacent the target.
3. The apparatus of claim 2, wherein the plasma trap has an outer boundary layer where the relatively high magnetic field strength inside the boundary layer drops-off rapidly as a function of distance from the target.
4. The apparatus of claim 1, wherein the electron depletion device depletes, in use, the plasma of electrons and wherein the electron depletion device comprises a magnetic part and an electric part.
5. (canceled)
6. The apparatus of claim 4, wherein the magnetic part comprises one or more magnets configured to create a magnetic field, which is superimposed over the magnetic field of the plasma trap, the magnetic field created by the magnetic part of the electron depletion device extends beyond the boundary layer of the plasma trap, such that the part of the magnetic field created by the magnetic part of the electron depletion device that extends beyond the boundary layer of the plasma trap draws electrons from, or near to, the boundary layer of the plasma trap away from the target, and the magnetic part further comprises an electron sink.
7. (canceled)
8. (canceled)
9. The apparatus of claim 6, wherein the electron sink comprises a grounded, or positively-biased conductor, which attracts and/or absorbs the electrons drawn from, or near to, the boundary layer of the plasma trap away from the target, the magnet or magnets comprises at least one of 1) electromagnets, whose power and/or polarity is suitably adjustable and 2) permanent magnets, whose position and/or orientation is adjustable.
10. (canceled)
11. (canceled)
12. The apparatus of any of claims 5 to 11 claim 4, wherein the electric part comprises an electrical power supply selectively connectable to the target by a controller, the controller being configured to adjust the power supply so as to apply a specified voltage to the target.
13. The apparatus of claim 12, wherein the controller is configured to at least one of 1) apply a baseline negative voltage to the target, but to apply periodic positive voltage pules to the target, 2) apply a baseline positive voltage to the target, but to apply periodic negative voltage pules to the target, and 3) apply a baseline substantially zero voltage to the target, but to apply periodic positive and/or negative voltage pules to the target.
14. (canceled)
15. (canceled)
16. The apparatus of claim 13, wherein the pulse comprises at least one of 1) duration of the pulses is between about 10 ns and 2 ms, 2) frequency of between about 10 Hz and 500 kHz, 3) magnitude of between about 1 and 1.5 kV relative to the baseline potential.
17. (canceled)
18. (canceled)
19. The apparatus of claim 1, further comprising an electron filter interposed between the plasma and a substrate to be coated.
20. The apparatus of claim 1, further comprising means for retaining a substrate.
21. The apparatus of claim 20, wherein the means for retaining a substrate comprises a voltage measurement device for measuring a voltage at the substrate.
22. The apparatus of claim 21, wherein the controller is configured to adjust any one or more of the magnitude, pulse duration or frequency of the voltage pulses applied to the target in response to a measured voltage at the substrate.
23. The apparatus of claim 22, wherein the controller comprises a feedback circuit adapted, in use, to maintain the voltage measured at the substrate within specified parameters by adjusting any one or more of the magnitude, pulse duration or frequency of the pulses applied to the target.
24. The apparatus of claim 1, further comprising an electrical power supply adapted to at least one of: bias a substrate to be coated and apply a floating bias of between about +0V to +2000V to the substrate.
25. (canceled)
26. (canceled)
27. (canceled)
28. A coating apparatus comprising a plasma coating apparatus of claim 1, further comprising any one or more of: an evaporation source; a target with an inclined surface; a target comprising a cavity.
29. A method of depleting a plasma in a plasma coating apparatus of electrons, the plasma coating apparatus comprising apparatus comprising a target, the method comprising the steps of: generating a plasma comprising ions, particulate material and electrons adjacent the target using an electric power source, which biases the target, and by using a magnetic arrangement to form a magnetic field in the vicinity of the target, the magnetic field comprising a plasma trap being a region of relatively high magnetic field strength, which confines a plasma generated thereby to a region adjacent the target, the plasma trap having an outer boundary layer where the relatively high magnetic field strength inside the boundary layer drops-off rapidly as a function of distance from the target; and characterised by depleting the plasma of electrons by: providing a magnetic field that is superimposed over the magnetic field of the plasma trap and which extends beyond the boundary layer of the plasma trap, which draws electrons from, or near to, the boundary layer of the plasma trap away from the target; and by applying a baseline voltage to the target; and applying periodic voltage pules to the target.
30. The method of claim 29, wherein the pulse comprises at least one of 1) duration of the pulses is between about 10 ns and 2 ms, 2) frequency of between about 10 Hz and 500 kHz, and 3) magnitude of between about 1 and 1.5 kV relative to the baseline potential.
31. (canceled)
32. (canceled)
33. (canceled)
34. The method of claim 29, further comprising the step of monitoring a voltage at a substrate to be coated, and adjusting any one or more of the duration, frequency or magnitude of the pulses to maintain the voltage at a substrate to be coated within specified parameters.
35. A system comprising: two or more plasma coating devices, each device comprising: a target; means for generating a plasma adjacent the target, the plasma comprising ions, particulate material and electrons; and an electron depletion device; wherein at least one pair of the plasma coating devices are at least one of mirrored and opposing.
Description
[0062] The invention shall now be described, by way of example only, with reference to the accompanying drawings, in which:
[0063] FIG. 1 is a schematic representation of a known magnetron sputtering device in an unbalanced mode of operation;
[0064] FIG. 2 is a schematic representation of a known magnetron sputtering device in a balanced mode of operation;
[0065] FIGS. 3 and 4 are schematic representations of a first embodiment of the invention in different phases of operation;
[0066] FIG. 5 is a schematic representation of a second embodiment of the invention, comprising two devices as shown in FIGS. 3 and 4, with a rotating substrate stage;
[0067] FIG. 6 is a schematic representation of a fourth embodiment of the invention, fitted with an electron filter;
[0068] FIG. 7 is a schematic representation of a fifth embodiment of the invention, comprising two opposing devices as shown in FIGS. 3 and 4;
[0069] FIGS. 8, 9, 10, 12 and 16 are voltage-time graphs for an electric part of an electron depletion device in accordance with embodiments of the invention, in different modes of operation;
[0070] FIG. 11 is an oscilloscope trace corresponding to FIG. 10;
[0071] FIGS. 13, 14, 15 and 17 are graphs showing the voltage response at the substrate in response to voltage changes at the target applied by the electric part of an electron depletion device in accordance with the invention;
[0072] FIG. 18 is a schematic representation of a sixth embodiment of the invention, comprising a device as shown in FIGS. 3 and 4 in conjunction with an additional evaporation source;
[0073] FIG. 19 is a schematic representation of a seventh embodiment of the invention, comprising two opposing devices as shown in FIGS. 3 and 4, a rotating substrate stage and additional magnetic devices;
[0074] FIGS. 20 and 21 are schematic representations of an eighth and ninth embodiment of the invention, incorporated into a tubular magnetron arrangement;
[0075] FIGS. 22 and 23 are schematic representations of tenth and eleventh embodiments of the invention, having different target geometries; and
[0076] FIG. 24 is a hardness graph (force vs displacement) for coatings formed by the invention versus those formed by known deposition apparatus.
[0077] Referring to FIG. 1, a schematic representation of a known magnetron sputtering device 1 is shown. A target 4 is provided, and a magnet arrangement (not shown) is used to create a magnetic field, indicated by magnetic field lines 3 in the drawing, which trap a plasma (not shown for clarity) over the target 4.
[0078] The magnetic field is unbalanced, such that an electron flow, indicated generally by dashed arrow 6, bombards a substrate 2 located opposite the target 4. The configuration of the magnetic field is such that electrons are channelled along a path 7 defined by the magnetic field lines indicated 8a in the drawing.
[0079] Meanwhile, sputtered material, indicated by solid arrows 5 in the drawing, which is mostly neutral, will preferentially travel in the direction of the electron flow, that is to say, the direction of electron bombardment 6. In unbalanced magnetron configurations, the ion bombardment also brings electron bombardment to the substrate 2. The ions that are part of the plasma will mainly be low energy ions.
[0080] Turning now to FIG. 2 of the drawings, the known magnetron sputtering device 1 also has a magnetic field, depicted in the drawing by magnetic field lines 3, which trap plasma (not shown for clarity) over the target 4.
[0081] In this case, the magnetic field is balanced, such that the electron flow 6 is now directly outwardly, away from, and so does not reach the substrate 2.
[0082] Meanwhile, sputtered material 5, indicated by arrows 5, which is mainly neutral, does not follow the plasma, and so ions that are generated in the plasma will follow the electron flow 6, away from the substrate 2. In balanced magnetrons configurations, the substrate receives minimal ion and electron bombardment.
[0083] The difference between a “balanced” and an “unbalanced” magnetron arrangement can be seen by comparing the magnetic field lines 3 shown in FIGS. 1 and 2: those in FIG. 1 radiating generally inwardly towards the substrate 2, with the “lobes” being directed inwardly towards the midline of the arrangement; whereas those in FIG. 2 generally fanning outwardly away from the substrate 2, with the “lobes” being directed outwardly away from the midline of the arrangement.
[0084] Turning now to embodiments of the invention, which are shown in the remaining drawings, FIGS. 3 and 4 are schematic representations of a first embodiment of the invention 1b at different stages of operation: in FIG. 3, the device 1b is in a plasma-depletion phase of operation, whereas in FIG. 4, the same device 1b is in an ion bombardment mode of operation.
[0085] To avoid unnecessary repetition, identical features are indicated by identical reference signs in the drawings, thus obviating the need for detailed explanation of each embodiment.
[0086] In FIGS. 3 and 4 of the drawings, a device 1b, similar to that described previously, contains additional elements namely the magnetic part 10ab, and the electric part 50 of an electron depletion device.
[0087] As previously described, the conventional magnetic arrangement (not shown) creates a magnetic field, indicated by magnetic field lines 3, which trap a plasma (not shown) over the target 4. The target 4 is suitably biased according to the present invention, and so sputtering takes place, and sputtered material 5 is ejected from the target 4 and a flux thereof flows towards the substrate 2. By pulsing the electric field, the ions generated in the plasma trap can be impulsed (preferentially ejected from the plasma trap) towards the substrate 2, creating a flux of ions, or an ion flow indicated schematically in the drawings by arrow 9. High energy ions are in this way generated.
[0088] In FIG. 3, the electron flow 6 is separate from, or controlled independently of, the ion flow 9. This means that the substrate 2 can be made to receive a mainly positive charge that can be measured on substrate 2. The charge voltage and flow can be managed by suitable power supply means 2b.
[0089] The magnetic part 10ab of the electron depletion device comprises a set of permanent magnets, which are arranged adjacent to the magnets (not shown) that form the plasma trap 52 of the magnetron device 1b. The permanent magnets 10ab are generally cylindrical, and are rotated, as indicated schematically in the drawings, so as to form a relatively long-range magnetic field, indicated by schematically by the thick magnetic field lines 8b in the drawings. The relatively long-range magnetic field created by magnets 10ab extends beyond the boundary 52 of the magnetic field trap and so electrons within the plasma, in the vicinity of the magnetic field trap boundary 52, are attracted away from the magnetic field trap boundary 52, as indicated by chain-dash arrow 6. An electron sink (not shown) can be provided downstream of arrow 6 to absorb the attracted free electrons.
[0090] Meanwhile, a certain amount of sputtered target material (indicated schematically by solid arrows 5), and ions (indicated by arrows 9), escapes the magnetic field trap boundary 52 in the usual way, and travels towards the substrate 2. It will be appreciated that during this phase of operation, the plasma within, or near to, the magnetic field trap boundary 52 is being depleted of electrons 6, and so the electron concentration of the plasma is constantly reducing; or reaches a suppressed equilibrium concentration. A voltage 2b could be applied to the substrate, but this is not necessary.
[0091] In the next phase of operation, as shown in FIG. 4 of the drawings, the electric part 50 of the electron depletion device is activated, by switching from a negative bias state (where it attracted and retained the positive ions) to a positive state for a short duration pulse. As described above, this momentarily repels the positive ions 9, and the electrons 6, away from the target 4 and towards the substrate 2. The impetus is sufficient to overcome the magnetic field 8b produced by the magnetic part 10ab of the electron depletion device, and so at this point in time, the sputtered material 5, the ions 9 and the electrons 6 all move towards the substrate 2. However, as there are now fewer electrons present (due to the depletion in the previous phase of operation), the effect of the positive pulse applied to the target 4 by the electric part 50 of the electron depletion device is much greater, and the electron shielding effect of the electrons 6 on the ions 9 is now greatly reduced. This means that any voltage 2b applied to the substrate 2 has a greater effect, and so the ion bombardment effect is increased, whilst at the same time, the adverse effects of electron bombardment are reduced.
[0092] The apparatus 1b is then set back to the electron-depletion mode of operation, and the process repeated.
[0093] The electron depletion device enables electron flow to be channelled in different directions, namely: away from the substrate 2 as shown in FIG. 3, in which they are channelled by magnetic field lines 8b; or towards the substrate 2, as in FIG. 4, where they are channelled by magnetic field lines 8a.
[0094] As previously mentioned, the magnets 10ab can be electromagnets, which can be switched on/off at will, and/or their power/strength adjusted at will.
[0095] In FIG. 4, however, the electron flow 6 and the ion flow 9 both reach the substrate 2. By means of a suitable power supply 2a, the electron and ion current can be managed. Different power modes could be used as described, although not exclusively, as described in greater detail below.
[0096] FIG. 5 shows a schematic embodiment of the present invention in which a plurality of the devices 1b are used in order to coat or plasma treat the substrate 2.
[0097] Both devices 1b shown in contain magnetic field control elements 10ab able to change the field electron channels between configurations 8a and 8b-c for example. In The configuration 8b-c the electron flow 6 does not reach the substrate 2 while the sputtered material and the ion flow 9 do. Different power modes could be used as described, although not exclusively, as described in greater detail below.
[0098] FIG. 6 shows another schematic embodiment of the present invention, where the interaction between devices 1ca and 1cb and their relative position and angle would create magnetic fields 8b-c that would channel the electron flow 6. The material and ion flow 9 (when a suitable electric field pulse is applied) can be different from that of the electrons. The substrate position among the different flows will influence the coating properties. Substrate 2a will mainly receive positive ions. Substrates 2b and 2c will mainly receive coating material. Substrate in position between 2a and 2b or 2c will receive electron bombardment (together with coating material). The ion bombardment will be mainly influenced by low energy ions which follow the electrons. Different power modes could be used as described, although not exclusively, by FIGS. 6, 7 and 10.
[0099] FIG. 7 shows another schematic embodiment of the present invention, where two devices 1b are arranged in a relatively parallel position such as those on in-line coating systems coating on substrate 2 which would typically travel in the direction indicated by arrow 12. By magnetic means 10ab or additional magnetic means 10c, the substrate 2 can be shielded from electron flow 6, while the coating flow 5 and high energy ion flow 9 can reach the substrate 2. In addition, anodic elements 11c-d (“electron sinks”) can be added, in conjunction to magnetic shield, in such a way that the electron flow 6 is guided away from the substrate 2 in an enhanced manner. Different power modes could be used as described, as described below.
[0100] FIGS. 8, 9 and 10 show examples of three types of electric field pulses, which can be applied using the magnetic part of the electron depletion device.
[0101] FIG. 8 represents pulses 13 from a mainly cathodic voltage 13a(−) to the positive value 13b. This would typically belong to the device working in magnetron sputtering mode.
[0102] FIG. 9 represents pulses 13 from a grounded or near zero voltage level 13a(0) to a positive level 13b. This would typically belong to the device working mainly in pulsed ion source mode.
[0103] FIG. 10 represents pulses from a small positive 13a(+) to a high positive value 13b. A real oscilloscope voltage trace of this latter mode can be seen in FIG. 11 belonging to a pulsed ion source with floating output.
[0104] FIG. 12 shows an example of an adaptation of the HIPIMS pulses to the present invention. In FIG. 12 the highly negative pulses 13a(−) are followed by high positive voltage pulse 13b which themselves are followed by a non-energy delivery at 13a(0) voltage.
[0105] FIG. 13 shows an example of a HIPIMS discharge of titanium target where traces for the target voltage 13 and substrate floating potential 14 are represented. In a HIPIMS discharge, during the pulse 13a(−) of the target a negative voltage is induced on the target 14z. During the reverse in the electric field a large positive voltage peak 14a is generated on the substrate, with subsequent decay 14b due to charge interactions.
[0106] FIG. 14 shows experimental voltage traces 13 of the target and the substrate voltage trace 14. The traces correspond to experimental setup at 150 kHz DC pulsed discharge on the experiment of FIG. 6. With reference to FIG. 6, the substrate position is 2a and the target is 4. The substrate is electrically floating, isolated from ground and electrodes, except through the plasma. In FIG. 14, during the negative cycle 13a(−) on the target positive ions are being formed during the collisions and sputtering process. When reversing the polarity to a positive value, ions are ejected. As the device of FIG. 6 filters the electrons away from the substrate, then a high positive pulse 14a charged of +300V is created on the substrate due to the ion arrival. Natural decays due to interactions will bring the charge value down 14b. By selecting parameters of the discharge, it is possible to alter the values of peak voltage and discharge period.
[0107] FIG. 15 shows experimental oscilloscope measurements on the substrate of FIG. 6 (substrate 2a) in different gas discharges. FIG. 15 is a plasma discharge in Ar (C-graphite as target material). The trace 14 represents the substrate voltage charge which in the pulse 14a achieves +420 V. The current of the charge 15 on the substrate was also measured.
[0108] In FIG. 16, the gas mixture is Ar+O.sub.2. Higher positive ion bombardment is achieved due to the easier ionisation of O.sub.2 with respect to Ar. More positive ions are generated, and more positive ions would arrive at the substrate creating a higher 14a positive pulse. Also, the measured current in trace 15 is higher.
[0109] FIG. 16 shows experimental oscilloscope measurements on the substrate of FIG. 6 (substrate 2a) when the cathodes of FIG. 6 are running in dual sputtering mode where the voltage oscillates between the two cathodes as electrodes. FIG. 16 shows a theoretical trace for one of the cathodes of the dual operation mode. The target voltage oscillates between a positive 13b and a negative 13a(−). The substrate charge can be seen in FIG. 17, trace 14. There are two peaks 14a1 and 14a2 which would correspond to the positive impulse on the respective alternating cathodes. For trace 13 of FIG. 17 the period of 13a(−) voltage would generate ions that are emitted during the 13b pulse time. The peak 14a2 corresponds to the ion emission for the other cathode.
[0110] FIG. 18 shows another embodiment of the present invention, where the device 1b, described in FIGS. 3 and 4, is used in conjunction with other coating source, such as an evaporation, sublimation or effusion source, 16, which brings coating material 17 over substrate 2. The ion enhancement device 1b is able to bring ion assistance bombardment to the coating material 17, helping to achieve a denser film than those which could be possible by using the source 16 in isolation. Source 16, could be of different nature, from gas or vapour delivery (e.g. monomers, inorganic and organic molecules, MOCVD) source, or a PVD source, such as thermal evaporation, electron beam evaporation, etc. Different power modes could be used as described, although not exclusively, by FIGS. 6, 7 and 10.
[0111] FIG. 19 shows another embodiment of the present invention where a plurality of devices 1b as described in FIGS. 3 and 4, are used in conjunction with other coating sources such as magnetron sputtering sources 18a-d. In order to preserve the magnetic electron filter/channel, the overall magnetic interactions need to be considered and adequate control methods need to be implemented. The devices 1b could be used also as coating contributors, both from a target material and a gas material or could also be used as ion enhanced deposition assisting the process of elements 18a-b in their deposition. Different power modes could be used as described, although not exclusively, by FIGS. 8, 9 and 16.
[0112] FIG. 20 shows another embodiment of the present invention where the devices of the invention use cylindrical rotatable targets 19a-b with linked magnetic fields in order to create an electron shield via field lines 8d. Ion flux 9 and coating flux 5 arrive to substrate 2. Part of the sputtering zone would need additional shielding, like 8e, which can be achieved by asymmetric magnetic configurations as described in patent U.S. Pat. No. 9,028,660B2. Different power modes could be used as described, although not exclusively, by FIGS. 6, 7 and 10.
[0113] FIG. 21 shows another embodiment of the present invention where the devices of the invention use cylindrical rotatable targets 19a-b and the assistance from an anodic element 11a. The anodic element could be enhanced by magnetic means, as described by patent U.S. Pat. No. 9,028,660B2. The electron flow 6 into the anode could be controlled. The electric field in addition to the magnetic confinement of the discharge and electron exchange with the anode would affect the ability of electrons to follow the high energetic ions as they are pulled by the strong electric field towards the active anode. In this way ions 9 will also be able to produce high positive bias on the substrate 2 around the same level as the anodic element 11a. By varying the magnetic interactions on the cathodes, anode and the anodic electric field the system is able to control a variety of ion assistance levels. Different power modes could be used as described, although not exclusively, by FIGS. 8, 9 and 16.
[0114] FIGS. 22 and 23 show two schematic representations of the present invention where a different profiled target 4a or 4b could be used on the devices 1b as described in FIGS. 3 and 4. The target profiles 4a and 4b enable the control of the direction of the electric field and consequently the direction of the ion flow 9. Similar to what has been described in FIGS. 3 and 4, the electron flow 6 can be separated from the high energy ion flow 9 by magnetic means 10ab. Additional features such as magnetic or non-magnetic guided anodes can be added and form part of the present invention. Different power modes could be used as described, although not exclusively, by FIGS. 8, 9 and 16.
[0115] FIG. 24 is a graph containing data showing the improvement in hardness and elastic modulus of carbon coatings using the current invention compared with prior art systems, with indenter penetration depth plotted on the x-axis, and load plotted on the y-axis. It can be seen that carbon coatings formed using known systems produce hardnessses in the range of 15.1+/−0.7 GPa, and elastic moduli of 167.4+/−4.6 GPa; whereas carbon coatings formed using the invention can produce hardnesses es in the range of 28.4+/−0.6 GPa, and elastic moduli of 237.5+/−2.5 GPa. There is a marked improvement in the hardness and elastic modulus of coatings produced using the invention, as well as reduced variability.
