APPARATUS AND METHOD FOR DEPOSITING A POLY(P-XYLYLENE) FILM ON A COMPONENT

Abstract

The disclosure provides an apparatus for depositing poly(p-xylylene) onto a component (4). The apparatus comprises (i) a platen, (ii) an electrode, and (iii) a first feed means. The platen comprises an electrically conductive material, is electrically connected to an electrical power supply and is configured to support a component. The electrode is electrically insulated from the platen. The first feed means is configured to feed a poly(p-xylylene) monomer to the platen. Furthermore, the component either comprises an electrically conductive material or consists of an electrically insulating material. If the component consists of an electrically insulating material the electrical power supply is an alternating current power supply and generated an alternating electrical field which couples to the component, and is thereby able to penetrate through the component to create the plasma.

Claims

1. An apparatus for depositing poly(p-xylylene) onto a component, the apparatus comprising: a radio-frequency electrical power supply configured to operate at a frequency between 1 and 100 MHz; a platen comprising an electrically conductive material, wherein the platen is electrically connected to the electrical power supply and configured to support one of a component comprising an electrically conductive material and a component consisting of an electrically insulating material; an electrode, wherein the electrode is electrically insulated from the platen; and a first feed means configured to feed a poly(p-xylylene) monomer to the platen, wherein (i) when the platen is configured to support the component comprising an electrically conductive material, the electrical power supply is configured to apply electrical power to the electrically conductive component supported by the platen at a power of between 0.0001 Watts/cm.sup.2 and 10 Watt/cm.sup.2 to create a plasma surrounding the component; and (ii) when the component consists of an electrically insulating material, the platen comprises a plate configured to receive the component thereon and the electrical power supply is configured to apply electrical power to the platen at a power of between 0.0001 Watts/cm.sup.2 and 10 Watt/cm.sup.2 to generate an electrical field that penetrates through the component to create a plasma surrounding the component.

2. An apparatus according to claim 1, wherein the component comprises an electrically conductive material, and the platen comprises a resilient clip configured to receive a portion of the electrically conductive component.

3. An apparatus according to claim 1, wherein the component consists of an electrically insulating material and has a substantially flat surface and the platen comprises a substantially flat plate configured to receive the component thereon.

4. An apparatus according to claim 3, wherein the component consists of an electrically insulating material and has a thickness of less than 25 cm, less than 10 cm, less than 7.5 cm, less than 5 cm, less than 3 cm, less than 2 cm or less than 1 cm.

5. (canceled)

6. (canceled)

7. An apparatus according to claim 1, wherein the first feed means comprises a vacuum valve.

8. An apparatus according to claim 1, wherein the apparatus further comprises a deposition chamber, wherein the platen is disposed inside the deposition chamber and the first feed means is configured to feed a poly(p-xylylene) monomer into the deposition chamber, and the electrode is either disposed in the deposition chamber or the deposition chamber defines the electrode.

9. An apparatus according to claim 8, wherein the deposition chamber comprises an earthed conductive housing which defines the electrode.

10. An apparatus according to claim 8, wherein the apparatus further comprises: a pressure sensor disposed in the deposition chamber; a pyrolysis oven, comprising a first heating element configured to heat the pyrolysis oven to a first elevated temperature; a temperature sensor disposed in the pyrolysis oven; a vaporiser oven, comprising a second heating element configured to heat the vaporiser oven to a second elevated temperature; a second feed means comprising a conduit which extends between the vaporiser oven and the pyrolysis oven and is configured to feed a poly(p-xylylene) dimer into the pyrolysis oven; a vacuum pump configured to reduce the pressure of the deposition chamber to a pressure of less than 10 Torr; and control means configured to: activate the vacuum pump when a user initiates a first coating cycle; activate the first heating element when the pressure in the deposition chamber has fallen below a first predetermined pressure; activate the second beating element when the temperature in the pyrolysis oven has risen above a predetermined temperature; and activate the electrical power supply, after having activated the first and second heating elements and when the pressure in the deposition chamber has risen above a second predetermined pressure.

11. An apparatus according to claim 8, wherein the apparatus comprises an injection means, configured to inject a gas into the deposition chamber.

12. (canceled)

13. An apparatus according to claim 10, wherein the first elevated temperature is between 200° C. and 1500° C.

14. (canceled)

15. An apparatus according to claim 14, wherein the second elevated temperature is between 80° C. and 500° C.

16. A method for depositing poly(p-xylylene) on a component comprising an electrically conductive material or a component consisting of an electrically insulating material, the method comprising: connecting the platen to a radio-frequency electrical power supply configured to operate at a frequency between 1 and 100 MHz and electrically insulating the platen from an electrode; feeding a poly(p-xylylene) monomer to the component; activating the electrical power supply and thereby creating a plasma that surrounds the component and ionises and/or activates the poly(p-xylylene) monomer, and allowing the ionised and/or activated poly(p-xylylene) monomer to deposit on the component and polymerise, and thereby form poly(p-xylylene) on the component, wherein (i) when the component comprises an electrically conductive material, the method includes applying the electrical power of the electrical power supply to the electrically conductive component supported by the platen at a power of between 0.0001 Watts/cm.sup.2 and 10 Watt/cm.sup.2 to create the plasma surrounding the component; and (ii) when the component consists of the electrically insulating material, the method includes providing the platen with a plate configured to receive the component thereon and applying electrical power to the platen at a power of between 0.0001 Watts/cm.sup.2 and 10 Watt/cm.sup.2 to generate an electrical field to penetrate through the component to create the plasma surrounding the component.

17. A method according to claim 16, wherein the platen is disposed in a deposition chamber and feeding the poly(p-xylylene) monomer to the component comprises feeding the poly(p-xylylene) monomer into the deposition chamber, thereby causing the pressure in the deposition chamber to rise, and the method further comprises activating the electrical power supply after the pressure in the deposition chamber rises above a predetermined pressure.

18. A method according to claim 17, wherein prior to feeding the poly(p-xylylene) monomer into the deposition chamber, the method comprises reducing the pressure in the deposition chamber to less than 10 Torr.

19. A method according to claim 18, wherein the method comprises monitoring the pressure in the deposition chamber while feeding the poly(p-xylylene) monomer therein, and activating the electrical power supply after the pressure reaches a predetermined pressure.

20. A method according to claim 16, wherein the method comprises deactivating the electrical power supply a predetermined time after it has been activated or when a layer deposited on the component has reached a desired thickness.

21. A method according to claim 20, wherein the method comprises venting the deposition chamber after the electrical power supply has been deactivated.

Description

DESCRIPTION OF THE DRAWINGS

[0097] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:—

[0098] FIG. 1 is a schematic diagram of an apparatus for depositing a film of poly(p-xylylene) polymer on a component;

[0099] FIG. 2 shows a platen configured to support the component;

[0100] FIG. 3 is a scanning electron microscope (SEM) image of a film of poly(p-xylylene) polymer deposited on a substrate using a prior art method;

[0101] FIG. 4 is an SEM image of a film of poly(p-xylylene) polymer deposited on a substrate using the method in accordance with the present invention; and

[0102] FIG. 5 is a schematic diagram of an alternative apparatus for depositing a film of poly(p-xylylene) polymer on a component.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

[0103] FIG. 1 shows an apparatus 2 configured to deposit a film of poly(p-xylylene) polymer on an electrically conductive component 4. The apparatus comprises a vaporiser oven 6, a pyrolysis oven 8, a deposition chamber 10 and a vacuum pump 12. A first conduit 14 extends between the vaporiser oven 6 and the pyrolysis oven 8, a second conduit 16 extends between the pyrolysis oven 8 and the deposition chamber 10 and a third conduit 18 extends between the deposition chamber 10 and the vacuum pump 12. A vacuum valve 17 is disposed in the second conduit 16.

[0104] The vaporiser oven 6 comprises a first heating element (not shown) configured to heat the vaporiser oven 6 to a temperature between 130° C. and 200° C. and a first temperature sensor 19 configured to sense the temperature therein. Similarly, the pyrolysis oven 8 comprises a second heating element (not shown) configured to heat the pyrolysis oven 8 to a temperature between 650° C. and 800° C. and a second temperature sensor 21 configured to sense the temperature therein.

[0105] The deposition chamber 10 comprises a metallic housing 26. As shown in FIG. 1, the metallic housing 26 is earthed

[0106] As shown in FIG. 1, an electrically conductive component 4 may be disposed in the deposition chamber 10. The component 4 is disposed on a platen 20, which holds the component 4 above the base 22 of the deposition chamber 10 and electrically connects the component 4 to a radio-frequency electrical power supply 24. The radio-frequency power supply 24 used by the inventors operated at a frequency of 13.56 MHz, as this is an industrial, scientific and medical (ISM) radio band, and so will not disrupt radio communication. The component 4 is electrically insulated from the metallic housing 26 due to an insulating material 28 being disposed between the platen 20 and the housing 26.

[0107] As shown in FIG. 2, the platen 20 may comprise a metallic rod 30 with a resilient metallic clip 32 disposed thereon. The metallic clip 32 comprises spaced apart flanges 34, 36 joined by a connecting portion 38. A portion of component 4 can slot between the flanges 34, 36, and the platen 20 is thereby able to support the component 4. The metallic clip 32 is sized so as to contact as little of the component 4 as possible, and typically contacts less than 1% of the surface of the component.

[0108] To coat a component 4 with a film of poly(p-xylylene) polymer, a user first loads a poly(p-xylylene) dimer into the vaporiser oven 6. The quantity the user loads depends upon the size of the component 4 to be coated. The inventors have typically used between 1 to 20 grams, and have found that this is sufficient to coat a component 4 with complex three dimensional geometry and a maximum dimension of between about 10 and 20 cm mark, or a flat component 4 with a maximum dimension of about 50 cm. It will be appreciated that these are examples only, and the method described herein could be used to apply a poly(p-xylylene) coating to a component of any size.

[0109] The user also loads the component 4 into the deposition chamber 10 and positions it on the platen 20 to connect it electrically to the radio-frequency electrical power supply 24.

[0110] The user can also place a small amount of an adhesion promotion agent, such as A-174, in the deposition chamber 10. The adhesion promotion agent can be provided in an open container, such as a petri dish. The amount of adhesion promotion agent required would depend upon the size of the component 4, but the inventors have typically used about 3 ml. It should be noted, that the use of a plasma, as described below, enhances the reactivity of the monomers and activates the surface of the component 4. Accordingly, the adhesion of the poly(p-xylylene) polymer is stronger than was possible previously. Accordingly, the adhesion agent may not be required.

[0111] The user then hermetically seals the apparatus 2, ensures that the vacuum valve 16 is open and then activates the vacuum pump 12 to cause the pressure within the vaporiser oven 6, pyrolysis oven 8 and deposition chamber 10 to reduce to lower than 10-3 Torr. This causes the adhesion agent, if present, to evaporate and coat the inside of the deposition chamber 10 and component 4.

[0112] The user then activates the second heating element to heat the pyrolysis oven 8 to a temperature between 650° C. and 800° C. Once the vaporiser oven 8 has reached the desired temperature, the user activates the first heating element to heat the vaporiser oven 6 to a temperature between 130° C. and 200° C. As the temperature in the vaporiser oven 6 rises the poly(p-xylylene) dimer disposed therein evaporates. Due to the vacuum, the parylene dimer flows into the pyrolysis oven 8, and the high temperature therein causes the dimer to decompose into two monomer molecules. The monomer molecules continue to flow into the deposition chamber 10, raising the pressure therein.

[0113] When a pressure sensor 40 disposed in the deposition chamber 10 records that the pressure has reached 50 mTorr, the user turns-on the radio-frequency electrical power supply 24. The electrical power delivered by the radio-frequency electrical power supply 24 is typically 0.1 Watts/cm2. Due to the metallic housing 26 of the deposition chamber 10 being grounded, it acts as a virtual electrode a plasma is created around the component 4. The plasma ionises and/or activates the monomers, typically causing them to become positively charged. The plasma activates the surface of the component 4. The ionised monomers are attracted to the component 4, deposit thereon and polymerise to form a poly(p-xylylene) polymer coating.

[0114] During deposition, other gases can be added to the deposition chamber by injection. These gases could include a hydrocarbon, such as acetylene, and/or an organometallic compound, such as tetraethyl orthosilicate (TEOS), and/or titanium isopropoxide (TIPP). The additives can be present in the deposition chamber 10 throughout the deposition process so they are disposed throughout the coating to add functionality. Alternatively, they may be added at selected times to produce a multi-layer coating.

[0115] Once the desired coating thickness has been reached, as determined by a crystal film thickness monitor (not shown) disposed in the deposition chamber 10, the user can stop the process. The user can first turn-off the radio-frequency electrical power supply 24 and then turn-off both heating elements. When the vaporiser oven 6 and pyrolysis oven 8 have both cooled to a temperature below 50° C., the user stops the vacuum pump 12 and vents the deposition chamber 10 to ambient pressure. The user can then open the deposition chamber 10 and retrieve the coated component 4.

[0116] The ovens 6, 8 take a long time to cool. Accordingly, if the user would like to use the apparatus to apply a coating to a further component 4 they may not want to wait for the ovens 6, 8 to cool. In this scenario, the user can close the vacuum valve 17 to isolate the ovens 6, 8. The user then stops the vacuum pump 12 and vents the deposition chamber 10 to ambient pressure. The user can then open the deposition chamber 10 and retrieve the coated component 4, replacing it with a further component 4 to be coated.

Example 2

[0117] FIG. 5 shows an alternative apparatus 2′ configured to deposit a film of poly(p-xylylene) polymer on a component 42 comprising an electrically insulating material. As shown in the Figure, the component 42 has a thin width and is flat. The exact thickness of the component 42 will vary. For instance, it is noted that the inventors have successfully used this method to coat components thicknesses between 2 and 3 cm. It will be appreciated that thicker components could be coated if a stronger electrical field is used.

[0118] Similarly to the apparatus 2 described in example 1, the apparatus 2′ comprises a vaporiser oven 6, a pyrolysis oven 8, a deposition chamber 10 and a vacuum pump 12 interconnected by conduits 14, 16, 18, which are as described in example 1.

[0119] As shown in FIG. 5, the deposition chamber comprises a platen 44 which defines a flat platform configured to receive the component 42 thereon. The platen 44 is electrically connected to a radio-frequency electrical power supply 24, which is as defined in example 1. The platen 44 is electrically insulated from the metallic housing 26 due to an insulating material 28 being disposed between the platen 20 and the housing 26.

[0120] To coat a component 42 with a film of poly(p-xylylene) polymer, a user follows the method described in the first example.

[0121] Once the desired coating thickness has been reached, the user can close the vacuum valve 17 to isolate the ovens 6, 8. The user then stops the vacuum pump 12 and vents the deposition chamber 10 to ambient pressure. The user can then open the deposition chamber 10 and reposition the component 42, so that the uncoated underside 46 thereof is exposed. The user can then repeat the coating method described in the first aspect.

[0122] Alternatively, the apparatus 2′ may comprise rotation equipment configured to rotate the component. Accordingly, once the desired coating thickness has been reached, the rotation equipment could rotate the component without the need to break the vacuum and without any input from the user.

[0123] The user can then deactivate the apparatus 2′ or use it to coat further components, as described in the first example.

CONCLUSION

[0124] Due to the monomers being attracted to the component 4, the deposition rate for an electrically conductive component is significantly enhanced. In particular, the inventors have found that the above method can provide a uniform coating on components with complex geometries. Additionally, due to the 20 holding the component 4 above the base 22 of the deposition chamber 10, the component may be coated on all sides in one cycle.

[0125] Furthermore, the amount of monomers which deposit on the walls of the deposition chamber 10 is significantly reduced. This means that the amount the dimer required is reduced. The extent to which a reduction is observed depends upon the geometry of the component. The inventors have observed that for some geometries a tenth of the amount of the dimer is required compared to prior art processes. Furthermore, due to the lower deposition rate on the walls of the deposition chamber, the amount of cleaning required between cycles is reduced, thereby reducing down-time for the apparatus 2.

[0126] In addition, the inventors have observed that the plasma reduces the amount of dust formation in the chamber. A film of poly(p-xylylene) polymer deposited on a substrate using the method described above is shown in FIG. 4. It will be noted that due to the lack of dust formation, the poly(p-xylylene) polymer shown in FIG. 4 defines a smooth surface.

[0127] In prior art methods, dust is formed by poly(p-xylylene) monomer molecules binding to each-other prematurely in the vapour phase, as a result of collisions between molecules, instead of binding after deposition on a surface. Dust formation is typically prominent when a carrier gas is used (for example argon) for purposes of enhancing the uniformity of the poly(p-xylylene) coating. An image of a film of poly(p-xylylene) polymer deposited on a substrate using a prior art method which resulted in dust formation is shown in FIG. 3. It will be noted that due to the dust formation, the poly(p-xylylene) polymer shown in FIG. 3 defines a rough surface. It also does not adhere as well to the substrate as the poly(p-xylylene) polymer layer shown in FIG. 4.

[0128] Accordingly, the present invention allows the use of carrier gases while minimising dust.