WO1998036107A1

WO1998036107A1 - Plating apparatus and method

Info

Publication number: WO1998036107A1
Application number: PCT/US1998/002712
Authority: WO
Inventors: Ariel Gilbert Schrodt; Nikolai Nikolaevich Issaev; Boris Grigorievich Karbassov
Original assignee: Dover Industrial Chrome, Inc.
Priority date: 1997-02-14
Filing date: 1998-02-13
Publication date: 1998-08-20
Also published as: AU6159898A

Abstract

This invention includes an apparatus and method for plating. The apparatus (10) includes a housing (11) that receives a plating solution; and a cathode disposed in the housing. A heating assembly heats the cathode and establishes a temperature gradient between the cathode and the electrolyte. A vacuum assembly (19) places the electrolyte in the housing under a vacuum to facilitate the flow of electrolyte into the housing and to remove any bubbles or entrapped air in the electrolyte. Aternatively, the apparatus and method may use an electroless solution to plate a substrate or a device.

Description

PLATING APPARATUS AND METHOD

BACKGROUND OF THE INVENTION Field Of The Invention

The present invention relates to a plating apparatus and process, and more particularly to a plating apparatus and process that place plating solution under a vacuum to remove any entrapped air or bubbles in it and/or that elevate the temperature in the area of the substrate where the plating takes place to establish a temperature gradient between the substrate and the solution.

Description Of The Prior Art

The prior art includes a wide variety of apparatus and procedures for plating structures. For example, one known process uses radiation lithography to produce a template and then fills the template by electrodeposition. Such apparatus and procedures have produced microstructures with heights of several hundred micrometers. The electrodeposition and other plating processes of the prior art, however, do not allow rapid fabrication of desired structures due to the slow movement of the plating material.

Unlike the prior art apparatus and procedures, the apparatus and method of the present invention facilitate the rapid fabrication of precision devices and microstructures of any lateral shape and aspect ratio. The present invention uses thermal gradients to increase the flow of the plating material to the substrate that receives the material. It also applies a vacuum to the plating solution to remove any entrapped air or bubbles that may disrupt this movement. SUMMARY OF THE INVENTION In accordance with one embodiment of this invention, an apparatus for electroplating includes a housing that receives electrolyte and contains cathode means that carries a negative charge. The cathode means includes a template member which shapes the electroplating material as it moves onto the cathode means. Heating means heats the cathode means and generates a temperature gradient between the cathode means and the electrolyte that surrounds it. Vacuum means reduces the pressure in the housing member to remove any entrapped air and any bubbles forming at or near the cathode means.

The method of the present invention includes placing cathode means with the template member into the housing member, placing the inside of the housing member under a vacuum and allowing electrolyte to flow into the member. It also includes charging the cathode means and heating it to a temperature that is greater than the average temperature of the electrolyte in the housing. This temperature differential creates thermal gradients that increase the movement of the electroplating material to the cathode means and the vacuum removes any bubbles or entrapped air in the electrolyte that may impede that movement.

Alternatively, the apparatus and method of the present invention may use an electroless solution to plate a substrate or a device.

BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of this invention, one should now refer to the embodiment illustrated in greater detail in the accompanying drawings and described below by way of an example of the invention. In the drawings:

FIG. 1 is a sectional view of the apparatus of the present invention;

FIG. 2 is a partial and exploded perspective view of the cathode assembly used in the apparatus; and

FIG. 3 is a sectional view of the cathode assembly.

While the following disclosure describes the invention in connection with one embodiment, one should understand that the invention is not limited to this embodiment. Furthermore, one should understand that the drawings are not to scale and that graphic symbols, diagrammatic representatives, and fragmentary views, in part, may illustrate the embodiment. In certain instances, the disclosure may not include details which are not necessary for an understanding of the present invention such as conventional details of fabrication and assembly.

DETAILED DESCRIPTION OF THE DRAWINGS Turning now to the drawings, FIG. 1 shows the apparatus of the present i vention generally at 10. The apparatus includes a housing member or tank 11 and an auxiliary tank 12 that supplies the tank 11 with electrolyte. The tank 11 defines an electrolyte inlet 13 controlled by a valve 14, electrolyte outlets 15 and 16 controlled by valve 17 , an opening 18 through which a vacuum pump 19 places the inside of the tank 11 under a vacuum, and an opening 20 through which the inside of the tank 11 vents to the atmosphere. Valves 18a and 20a control the openings 18 and 20, respectively.

The tank 11 contains partitions 21 and 22 that separate the inside 23 of the tank 11 into three portions 23a, b and c. (These two partitions are electrical conductors, and they serve as barriers for the electrolyte moving within the tank 11.) The tank 11 also contains anodes 24 and 25, a level detector 26 and an assembly 27 that includes one or more template members 28 (See FIG. 3) that help form the electroplating material.

The auxiliary tank 12 contains "dummy" anodes 29 and "dummy" cathodes 30. It receives electrolyte from the tank 11 through pipes 31, 32, 33, 34 and 35. It discharges electrolyte through a filter assembly 36 and through a pipe 37 after the electrolyte flows through filter screens 12a and 12b. The vacuum created by the pump 19 in the inside of the housing 11 induces flow through the pipe 37 and the inlet 13. As stated above, the valve 14 controls this flow.

The assembly 27 includes a column segment 38 (See FIG. 1) and a main body segment 39 that the column segment 38 suspends from a lid portion 11a of the tank 11. The main body segment 39 includes two sets of the same components on opposite sides of a centerline 40. Alternatively, the apparatus 10 may include an assembly with only one set of components or one with more than two sets. (The following text uses the same reference number for corresponding components of each set.)

The components of one set of the main body segment 39 (a first set to the left of the centerline 40) include a flat wire heater 41 comprising a wire heating element embedded in a thin plate of plastic. (One example of such a heater 41 is a Kapton Mat marketed by Cole-Parmer of Vernon Hills, Illinois.) This heater 41 heats the area that surrounds it and establishes a temperature gradient with the surrounding electrolyte.

A non-conductive wafer 42 (made out of silicon or any other suitable material) lies next to the heater 41, in face-to-face relation with it. It supports a first layer of metal 42a (e.g. , copper) on a face, opposite the face that contacts the heater 41. This layer 42a is a mass of vacuum deposited metal particles that secures a second vacuum deposited metal layer 42b (e.g. , titanium) to the wafer 42. The first metal layer 42b on the wafer 42 serves as the primary cathode after removal of the second layer in the patterned area for the first set of components of the segment 39. A ring contact 43 made out of an electrically conductive metal (e.g, gold) or any other suitable material and electrical wiring (not shown) connect the layer 42b to a DC power source P.

The template member 28 for this set of components lies secured, in face-to-face relation with the layer 42b within the ring 43. In this embodiment, the template member 28 is a plate of polymethyl- methacrylate material (PMMA) with a pattern formed through it using x-ray lithography or any other suitable procedure, e.g. micro injection molding. (A monomer for of the PMMA adheres the member 28 to the layer 42b.) The pattern extends from an exposed face 28a to the face that contacts the layer 42b. It includes one or more openings that receive the deposits from the electrolyte and help form the object or device produced by the apparatus.

The first set of components also includes a secondary cathode that comprises an electrically conductive screen 44 made out of stainless steel or any other suitable material, a ring contact 45 made out of an electrically conductive metal (e.g. , gold, gold plated copper, etc.), wiring, controls and a DC power source (wiring, controls and power source not shown) . An insulator spacer ring 46 made out of rubber or any other suitable material insulates the primary from the secondary cathode assemblies.

The controls can vary the current in the screen 44 and maintain it at a level substantially lower than the current in the primary cathode 42b. When energized, the screen 44 receives some of the electrolyte particles as they move towards the primary cathode. This feature assures that the deposition of particles in the openings of the template member is uniform and organized.

The first set of components also includes a thermocouple 47 disposed between the spacer ring 46 and the layer 42b proximate the template member 28. This thermocouple 47 takes temperature readings at that location to determine if the temperature has risen to approximately the boiling point of the electrolyte, or above that level. (At the boiling point of the electrolyte bubbles begin to form, and they obstruct the deposition.) This feature allows the controls to monitor the temperature level and thus minimize the formation of bubbles. Moreover, as stated above, the vacuum under which the apparatus 10 operates removes any inadvertent formation of bubbles.

A securing plate 48 made out of plastic or any other suitable material cooperates with bolts 49 and serves as a clamp to secure the two sets of components against another, similar plate 50. The bolts also secure the assembly 27 to the column 38. These plates 48 and 50 have openings 48a and 50a, respectively, through which the electrolyte flows to the template members 28.

By way of an example, an assembly 27 includes a 10 square centimeter heater 41 with a thickness of 1/2 millimeters. The wafer 42 is a round disc with a diameter of 10 centimeters and a thickness of 1/2 millimeters. It supports a vacuum deposited copper layer 42a of approximately 1,000 Angstroms and a vacuum deposited titanium layer 42b of approximately 100 Angstroms. The template is a disc with a diameter of approximately 5 centimeters. The contacts 43 and 45 are gold wire rings with a 1 millimeter thickness and an outside diameter of approximately 10 centimeters. The spacer ring 46 is a rubber ring with an outside diameter of approximately 10 centimeters and a thickness of approximately 3 millimeters. Finally, the screen 44 is made of stainless steel wire that defines a mesh with, for example, 1 millimeter square openings. Using nickel anodes, a nickel sulfamate electrolyte and a current density of 30-150 amperes/ft² in the cathode 42b and maintaining a cathode temperature of 55-60° Centigrade and an electrolyte temperature of 22-25° Centigrade, the apparatus 10 in this example achieved deposition rates of 50-125 microns/hour.

To operate the apparatus 10, one first places the assembly 27 in the housing 11, fills the central, cathode compartment 23b of the housing 11 with electrolyte, hermetically seals the housing, engages the power supply and energizes the heaters 41. The valve 18a opens while the other valves remain closed and the vacuum pump 19 places the inside of the housing 11 under a vacuum. Valve 14 then opens, and the vacuum induces flow of electrolyte from the auxiliary tank 12 to the tank 11. The electrolyte flows to the central cathodic compartment 23b and overflows over the partitions 21 and 22 into the anodic compartments 23a and 23c until the level of the electrolyte reaches the level detector 26. The valve 14 then closes, and the electrolyte plates the cathode, filling the openings in the templates 28. Controls (not shown) allow separate control of each of the primary and secondary cathodes, screens and heaters. The valve 20a opens and allows the inside of the housing 11 to vent to atmosphere, and then valve 17 opens so that electrolyte from in the side compartments 23a and c discharges into the auxiliary tank 12. All the valves then close and the foregoing steps repeat until a complete device or object forms in each of the templates 28.

Alternatively, the apparatus and method described above may use an electroless solution to produce a plating layer on a device or a substrate. Electroless plating requires the use of passive surfaces on the containment means for the electroless solution and the activation of the substrate surface, usually with tin or with palladium, to facilitate the onset of plating.

Electroless plating typically involves elevating the temperature of the solution to a predetermined optimum degree. However, in accordance with the plating process of the present invention the independent heating of the substrate to a higher level than the predetermined optimum degree will generate a temperature gradient between the substrate and the surrounding solution to facilitate plating.

In addition, the application of a vacuum in the electroless process further facilitates plating. As with the electroforming process described above, electroless procedures involve entrapped air, bubbles released as a result of the chemical reactions during the plating process, bubbles generated by heating, and/or bubbles formed by agitation. Application of a vacuum facilitates release and removal of the entrapped air and gas bubbles from the reactive surfaces. This vacuum would enable the electroless solution to enter high aspect ratio channels or pockets in the substrate. (As with the process described above, the electroless process may plate an unobstructed substrate surface, or it may plate a substrate surface with the guidance of a patterned template. )

The apparatus illustrated in the drawings with the following modifications may perform the electroless plating process according to the present invention. The modifications include removal of the anodes 24 and 25 and the membranes 21 and 22. They would also include removing the anodes and cathodes from the conditioning tank, as well as the filter screens 12a and 12b. Finally, the modifications would include the elimination of the wire mesh screens 44 from the wafer holder/heater assembly. While the above description and the drawings disclose and illustrate one embodiment, one should understand, of course, that the invention is not limited to this embodiment. Those skilled in the art to which the invention pertains may make other modifications and other embodiments employing the principles of this invention, particularly upon considering the foregoing teachings. For example, one heater 41 may provide the heat for the two sets of components in the assembly 27. Therefore, by the appended claims, the applicant intends to cover any modifications and other embodiments as incorporate those features which constitute the essential features of this invention.

What is claimed is:

Claims

1. Apparatus for electroforming a device, said apparatus comprising: a housing member for containing an electrolyte; cathode means disposed on the housing member for carrying a negative charge, said cathode means including template means for forming the device; heating means disposed proximate the cathode means for heating the cathode means and the area around the cathode means to generate a temperature gradient between the cathode means and the electrolyte.

2. The apparatus of claim 1, further comprising vacuum means for reducing the pressure in the housing member and removing any bubbles forming at or near the cathode means when the heating element heats the electrolyte at or near the cathode means above the boiling point.

3. The apparatus of claim 1, further comprising screen means disposed a spaced distance over the cathode means, said screen means being an electrical conductor and carrying a negative charge lower in magnitude than the magnitude of the negative charge of the cathode means.

4. The apparatus of claim 1, wherein the housing member includes an electrolyte inlet at a bottom portion and an electrolyte outlet at a top portion.

5. The apparatus of claim 2 , wherein the housing defines passageway means for the vacuum means, and the vacuum means includes a vacuum pump operably associated with the passageway means and a valve for opening and closing the passageway means.

6. The apparatus of claim 1, further comprising anode means disposed in the housing, and the housing including partition means disposed between the cathode means and the anode means, said partition means being electrically conductive.

7. The apparatus of claim 1, wherein the cathode means includes at least one layer of metal deposited on a surface of a base member.

8. The apparatus of claim 7, wherein the layer of metal is a vacuum deposited layer of copper particles.

9. The apparatus of claim 7, wherein the template means is secured to the layer of metal .

10. The apparatus of claim 1, wherein the heating means includes at least one flat, wire heater.

11. The apparatus of claim 1 further comprising an auxiliary housing operably associated with the housing to supply the housing with electrolyte.

12. A method for electroforming a device in a housing member that contains cathode means carrying a negative charge, said method comprising the steps of: pouring electrolyte into the housing member; charging the cathode means; and heating the cathode means to a temperature that is greater than the average temperature of the electrolyte in the housing.

13. The method of claim 12, wherein the step of pouring the electrolyte into the housing member includes placing the inside of the housing member under a vacuum that draws the electrolyte into the housing.

14. The method of claim 12 , further comprising the steps of placing an electrically conductive screen proximate the cathode member, charging the screen with a negative charge that is substantially lower in magnitude than the negative charge of the cathode means.

15. The method of claim 12, wherein the heating step brings the temperature of the cathode means to a level that is slightly below the boiling point of the electrolyte.

16. Apparatus for electroforming a device, said apparatus comprising: a housing member for containing an electrolyte; cathode means disposed on the housing member for carrying a negative charge, said cathode means including template means for forming the device; and vacuum means for reducing the pressure in the housing member and removing any bubbles forming at or near the cathode means.

17. The apparatus of claim 16, further comprising heating means disposed proximate the cathode means for heating the cathode means and the area around the cathode means to generate a temperature gradient between the cathode means and the electrolyte.

18. The apparatus of claim 16, further comprising screen means disposed a spaced distance over the cathode means, said screen means being an electrical conductor and carrying a negative charge lower in magnitude than the magnitude of the negative charge of the cathode means.

19. The apparatus of claim 16, wherein the housing member includes an electrolyte inlet at a bottom portion and an electrolyte outlet at a top portion.

20. The apparatus of claim 16, wherein the housing defines passageway means for the vacuum means, and the vacuum means includes a vacuum pump operably associated with the passageway means and a valve for opening and closing the passageway means.

21. The apparatus of claim 16, further comprising anode means disposed in the housing, and the housing including partition means disposed between the cathode means and the anode means , said partition means being electrically conductive.

22. The apparatus of claim 16, wherein the cathode means includes at least one layer of metal deposited on a surface of a base member.

23. The apparatus of claim 22, wherein the layer of metal is a vacuum deposited layer of copper particles.

24. The apparatus of claim 22, wherein the template means is secured to the layer of metal.

25. The apparatus of claim 17, wherein the heating means includes at least one flat, wire heater.

26. The apparatus of claim 16 further comprising an auxiliary housing operably associated with the housing to supply the housing with electrolyte.

27. A method for electroforming a device in a housing member that contains cathode means carrying a negative charge, said method comprising the steps of: pouring electrolyte into the housing member; charging the cathode means; and placing the inside of the housing member under a vacuum.

28. The method of claim 27, wherein the step of pouring electrolyte into the housing member is facilitated by the step of placing the inside of the housing member under a vacuum to draw the electrolyte into the housing member.

29. The method of claim 27, further comprising the step of heating the cathode means to a temperature that is greater than the average temperature of the electrolyte in the housing member.

30. The method of claim 27, further comprising the steps of placing an electrically conductive screen proximate the cathode member, charging the screen with a negative charge that is substantially lower in magnitude than the negative charge of the cathode means.

31. The method of claim 29, wherein the heating step brings the temperature of the cathode means to a level that is slightly below the boiling point of the electrolyte.

32. Apparatus for plating a substrate, said apparatus comprising: a housing member for containing the substrate and a plating solution; and heating means disposed proximate the substrate for heating the substrate and the area around the substrate to generate a temperature gradient between the substrate and the solution.

33. The apparatus of claim 32, further comprising vacuum means for reducing the pressure in the housing member and removing any bubbles forming at or near the substrate.

34. Apparatus for plating a substrate, said apparatus comprising: a housing member for containing the substrate and a plating solution; and vacuum means for reducing the pressure in the housing member and removing any bubbles forming at or near the substrate.

35. The apparatus of claim 34, further comprising heating means disposed proximate the substrate for heating the substrate and the area around the substrate to generate a temperature gradient between the substrate and the solution.

36. A method for plating a substrate in a housing member, said method comprising the steps of: placing the substrate in the housing member; pouring plating solution into the housing member; and heating the substrate to a temperature that is greater than the average temperature of the plating solution in the housing.

37. The method of claim 36, further comprising the step of placing the inside of the housing member under a vacuum.

38. A method for plating a substrate in a housing member, said method comprising the steps of: placing the substrate in the housing member; pouring plating solution into the housing member; and placing the inside of the housing member under a vacuum.

39. The method of claim 38, further comprising the step of heating the substrate to a temperature that is greater than the average temperature of the plating solution in the housing.