ELECTROFORMING PROCESS

Abstract

Process of electroforming a metal structure, in particular a structure with a tip protruding from adjacent outer layers. The process comprises the following steps; a first layer is deposited on a substrate followed by one or more next layers partially overlapping the first layer to form an intermediate structure having a substrate surface facing the substrate; in a next step, the intermediate structure is removed from the substrate and one or more further layers are deposited on said substrate surface of the intermediate structure.

Claims

1. A process of electroforming a metal structure, comprising steps of: depositing a first layer on a substrate and depositing one or more next layers partially overlapping the first layer to form an intermediate structure having a substrate surface facing the substrate; and subsequently removing the intermediate structure from the substrate and depositing one or more further layers on said substrate surface of the intermediate structure.

2. The process according to claim 1, further comprising forming a layer of a sacrificial material over the intermediate structure before said step of removing the intermediate structure from the substrate, and a final step of removing the layer of sacrificial material from the intermediate structure.

3. The process according to claim 2, wherein the layer of sacrificial material is removed by selective etching.

4. The process according to claim 3, wherein the sacrificial material is copper.

5. The process according to claim 1, wherein the substrate is a mandrel with a pattern of a non-conductive coating defining an outline of at least the first layer.

6. The process according to claim 5, wherein the first layer does not overgrow the non-conductive coating pattern.

7. The process according to claim 5, wherein, before forming the one or more partially overlapping layers, the non-conductive coating is at least partially removed and a new non-conductive coating pattern is applied to confine the one or more partially overlapping layers.

8. The process according to claim 1, wherein the first layer is of a different material than the one or more partially overlapping layers.

9. The process of claim 1, wherein the first layer is rhodium or a rhodium alloy.

10. The process of claim 1, wherein at least part of the one or more partially overlapping layers are of nickel or a nickel alloy.

11. The process of claim 5, wherein the non-conductive coating pattern is a photoresist.

12. The process according to claim 5, wherein the first layer does not overgrow the non-conductive coating pattern.

13. The process according to claim 6, wherein, before forming the one or more partially overlapping layers, the non-conductive coating is at least partially removed and a new non-conductive coating pattern is applied to confine the one or more partially overlapping layers.

14. The process according to claim 11, wherein, before forming the one or more partially overlapping layers, the non-conductive coating is at least partially removed and a new non-conductive coating pattern is applied to confine the one or more partially overlapping layers.

15. The process according to claim 12, wherein, before forming the one or more partially overlapping layers, the non-conductive coating is at least partially removed and a new non-conductive coating pattern is applied to confine the one or more partially overlapping layers.

16. The process according to claim 2, wherein the substrate is a mandrel with a pattern of a non-conductive coating defining an outline of at least the first layer.

17. The process according to claim 16, wherein, before forming the one or more partially overlapping layers, the non-conductive coating is at least partially removed and a new non-conductive coating pattern is applied to confine the one or more partially overlapping layers.

18. The process according to claim 16, wherein the first layer is of a different material than the one or more partially overlapping layers.

19. The process of claim 16, wherein the first layer is rhodium or a rhodium alloy.

20. The process of claim 16, wherein at least part of the one or more partially overlapping layers are of nickel or a nickel alloy.

Description

[0033] The invention is further explained with reference to the accompanying drawings, FIGS. 1A-N, showing consecutive steps of an exemplary embodiment of a process according to the invention.

[0034] FIG. 1A shows a substrate 2 partly covered by a non-conductive coating of a photoresist 3. The photoresist 3 is applied, e.g., by means of spin coating, to form a UV-sensitive coating of a uniform thickness. Parts of the photoresist 3 are removed after selective exposure to UV-light, e.g., by means of laser direct imaging. As a result, the top surface 2 of the substrate 1 has conductive bare sections 4 and non-conductive sections 3 coated with the photoresist, as shown in FIG. 1A.

[0035] The mandrel 1 is then placed in an electrolytic bath and electro-conductively connected to a cathode. By supplying rhodium cations, a rhodium layer 7 is deposited on the conductive sections 4 of the mandrel 1 (FIG. 1B). The thickness of the rhodium layer 7 does not exceed the thickness of the photoresist 3.

[0036] The mandrel 1 is then taken from the electrolytic bath and spin coated with a second photoresist layer 8, which covers the first photoresist 3 and the rhodium layer 7. Alternatively, the first photoresist may be removed and complete replaced by the fresh second photoresist. Parts of the second photoresist 8 are selectively exposed to UV for curing and the uncured parts are washed away. In FIG. 1D, the first and second photoresist layers directly adjacent the rhodium layer 7 are removed leaving part of the substrate 2 uncovered (FIG. 1D).

[0037] The mandrel 1 is then placed in a second electrolytic bath and connected to the cathode, the anode being configured to release nickel cations. A nickel layer 9 is deposited on the uncovered electro-conductive section of the mandrel's top surface 2. The nickel layer 9 has the same thickness as the rhodium layer 7 (FIG. 1E).

[0038] In a next step, the mandrel 1 is removed from the electrolytic bath and to allow removal of a part of the photoresist 8 on top of the rhodium layer 7 adjacent the nickel layer 9 (FIG. 1F). The mandrel 1 is then returned to the same electrolytic bath and a further nickel layer 10 is electroformed on top of the uncovered part of the rhodium layer 7 and the first nickel layer 9 (FIG. 1G). The resulting intermediate structure has a rhodium tip projecting from a nickel body. The rest of the photoresist is subsequently removed (FIG. 1H).

[0039] A layer 11 of a sacrificial material, in this case copper, is then applied to cover the complete mandrel 1 and the nickel and rhodium layers 7, 10 (FIG. 1I). The copper can be applied by means of electroforming or by any other suitable deposition process. The thickness of the copper layer is about the same as the thickness of the mandrel 1, but can be more if so desired. The copper, nickel and rhodium layers 7, 10, 11 are jointly removed from the mandrel 1 (FIG. 1J). The mandrel side 12 of the rhodium layer, i.e., the side facing the mandrel before its removal, is now uncovered. This side 12 is just as flat as the mandrel surface 2 and therefore a very suitable substrate for electroforming further layers, without the need of a planarization step.

[0040] A new photoresist layer 13 is applied and cured on top of the projecting part of the rhodium layer 7 (FIG. 1K). The rest of the rhodium layer 7 remains uncovered, just as the nickel layer 10.

[0041] The structure is then returned into the second electrolytic bath and again connected to the cathode. A further layer 14 of nickel is deposited on the uncovered parts of the rhodium layer 7 and the adjacent surface of the nickel part 10 (FIG. 1L).

[0042] The last photoresist 13 and the copper 11 can now be removed, e.g., by selective etching. The remaining final structure 15 comprises a nickel body 16 with one end sandwiching a projecting rhodium tip. In an alternative embodiment, the layer in line with the rhodium tip can be a different material, e.g., copper, e.g., sandwiched by layers of nickel or nickel alloys.