METHOD OF MANUFACTURING A GAS ELECTRON MULTIPLIER

• US 20110089042A1
• Filed: 04/14/2008
• Published: 04/21/2011
• Est. Priority Date: 04/14/2008
• Status: Active Grant

• Current Assignee: CERN-European Organization For Nuclear Research
• Original Assignee: CERN-European Organization For Nuclear Research
• Inventors: De Oliveira, Rui, Duarte Pinto, Serge
• Granted Patent: US 8,597,490 B2
• Time in Patent Office: Days
• US Class Current: 205/223
• CPC Class Codes: H01J 47/02 Ionisation chambers

Abstract

Methods for manufacturing a gas electron multiplier. One method comprises a step of preparing a blank sheet comprised of an insulating sheet with first and second metal layers on its surface, a first metal layer hole forming step in which the first metal layer is patterned by means of photolithography, such as to form holes through the first metal layer, an insulating sheet hole forming step, in which the holes formed in the first metal layer are extended through the insulating layer by etching from the first surface side only, and a second metal layer hole forming step, in which the holes are extended through the second metal layer. Alternatively, the second metal layer hole forming step is performed by electrochemical etching, such that the first metal layer remains unaffected during etching of the second metal layer. In another embodiment, in the second metal layer hole forming step, the first and second metal layers are etched from the outside, thereby reducing the initial thicknesses of the first and second metal layers and the second metal layer is simultaneously etched through the holes in the first metal layer and the insulating sheet, said etching being maintained until the holes extend through the second metal layer, wherein said initial average thickness of the first and second metal layers is between 6.5 μm and 25 μm, preferably between 7.5 μm and 12 μm.

Claims

1. A method for manufacturing a gas electron multiplier (GEM), said GEM comprising an insulating sheet having first and second surfaces, first and second metal layers provided on top of said first and second surfaces, respectively, and a plurality of throughholes extending through said insulating sheet and said first and second metal layers, said method comprising:

preparing a blank sheet comprised of an insulating sheet provided with first and second metal layers on its first and second surfaces, respectively, said first and second metal layers having an initial thickness;

a first metal layer hole forming step in which the first metal layer is patterned by means of photolithography, such as to form holes through said first metal layer, an insulating sheet hole forming step, in which the holes formed in the first metal layer are extended through the insulating layer by etching from the first surface side; and

a second metal layer hole forming step, in which the first and second metal layers are etched from the outside, thereby reducing the initial thicknesses of the first and second metal layers and in which simultaneously the second metal layer is etched through the holes in the first metal layer and the insulating sheet, said etching being maintained until the holes extend through the second metal layer,

wherein said initial average thickness of the first and second metal layers is between 6.5 μ

m and 25 μ

m, preferably between 7.5 μ

m and 12 μ

m.

2. The method of claim 1, wherein the initial average thicknesses of the first and second metal layers are chosen such that after the second metal layer hole forming step, a ring-like area surrounding the holes, at which the insulating sheet is exposed from the first metal layer, has a width of 15 μ

m or less, preferably 10 μ

m or less.

3. The method of claim 1, wherein in the second metal layer forming step, the blank sheet is etched in a bath containing ammonium persulfate.

4. The method of claim 3, wherein said bath is kept at a temperature of 20°

C. to 30°

C., preferably 23°

C. to 27°

C.

16. A method as in claim 1 or 5, wherein the first and second metal layers are made from copper.

17. A method as in claim 1 or 5, wherein the insulating sheet is made from a polymer material, preferably from polyimide.

18. A method as in claim 16 or 17, wherein a chromium layer is provided between the copper layers and the insulating sheet.

19. A method as in claim 1 or 5, wherein the photolithographic first metal layer hole forming step comprises the following steps:

providing a photoresist on both metal layers;

placing a mask on top of the first metal layer defining the location of the holes to be formed;

exposing and developing the photoresist on both sides of the blank such that the whole second metal layer is covered by the photoresist and the first metal layer is covered by the photoresist except for the places where the holes are to be formed; and

etching the holes in the first metal layer.

20. A method as in claim 1 or 5, wherein the first metal layer is etched using iron perchloride at 30°

C. to 35°

C.

21. A method as in claim 1 or 5, wherein the insulating sheet hole forming step is performed such that the diameter of the hole within the insulating sheet at the end adjacent to the first metal layer differs from the diameter of said hole at the end adjacent to the second metal layer by less than 20%, preferably less than 15%.

22. A method as in claim 1 or 5, wherein the insulating sheet hole forming step comprises dipping the blank sheet in a bath comprising 55% to 65% diamine ethylene and 35% to 45% water, and in addition 5 to 10 g/l KOH.

23. The method of claim 22, wherein the insulating sheet hole forming step is performed at a temperature of 60°

C. to 80°

C., preferably 65°

C. to 75°

C.

24. A method as in claim 1 or 5, wherein in the insulating sheet hole forming process, the etchant is stirred by generating bubbles therein, in particular nitrogen bubbles.

25. A method as in claim 1 or 5, further comprising a step of forming electrodes by means of photolithography for connecting the first and second metal layers to a voltage source.

26. A method as in claim 1 or 5, further comprising, after said second metal layer hole forming step, a step of cleaning the GEM, said cleaning step being adapted to not remove any exposed chromium layers.

27. A method as in claim 1 or 5, wherein the holes are simultaneously formed in an area larger than 0.1 m², and in particular larger than 0.5 m².

28. A method as in claim 1 or 5, wherein the holes have a diameter of 20 μ

m to 100 μ

m, preferably 50 to 70 μ

m, and a pitch of 50 to 300 μ

m, preferably 100 μ

m to 200 μ

m.

5. A method of manufacturing a gas electron multiplier (GEM), said GEM comprising an insulating sheet having first and second surfaces, first and second metal layers provided on top of said first and second surface, respectively, and a plurality of throughholes extending through said insulating sheet and said first and second metal layers, said method comprising the following steps:

preparing a blank sheet comprising an insulating sheet provided with first and second metal layers on its first and second surfaces, respectively, said first and second metal layers having an initial thickness;

a first metal layer hole forming step in which the first metal layer is patterned by means of photolithography such as to form holes through said first metal layer, an insulating sheet hole forming step, in which the holes formed in the first metal layer are extended through the insulating layer by etching from the first surface side; and

a second metal layer hole forming step, in which the holes formed in the first metal layer and the insulating sheet are extended through the second metal layer,

said second metal layer hole forming step comprising an electrochemical etching process in which a voltage is applied between the second metal layer and an electrode immersed in the etchant, said voltage being chosen such that the second metal layer is etched.

6. The method of claim 5, wherein the potential between the electrode and the second metal layer is such that the second metal layer forms an anode and the electrode immersed in the etchant forms a cathode.

7. The method of claim 5, in which the etchant used in the electrochemical etching comprises sulfuric acid, hydrochloric acid and copper sulfate.

8. The method of claim 5, wherein during at least a portion of said second metal layer hole forming step, the electrode is provided on the first metal layer side of the blank sheet, such as to etch the second metal layer through the holes formed in the first metal layer and the insulating sheet.

9. The method of claim 5, wherein during a portion of said second metal layer hole forming step the electrode is provided on the second metal layer side of the blank sheet, such as to etch the second metal layer from the outside.

10. The method of claim 9, wherein the step of electrochemical etching of the second metal layer with the electrode provided on the second metal layer side of the blank sheet is maintained at least until the holes extend through said second metal layer.

11. The method of claim 9, wherein the electrochemical etching through the holes formed in the first metal layer and the insulating sheet is maintained until said holes are extended into said second metal layer to an average depth that is at least 2 μ

m deeper than the final thickness of the second metal layer.

12. The method of claim 5, wherein the initial thickness of the second metal layer exceeds the initial thickness of the first metal layer by 5 to 15 μ

m, preferably 8 to 12 μ

m.

13. The method of claim 5, wherein the final thicknesses of the first and second metal layers differ by less than 2 μ

m.

14. The method of claim 5, wherein the average final thicknesses of the first and second metal layers are between 4 μ

m and 7 μ

m.

15. The method of claim 5, wherein said step of preparing a blank sheet comprises a step of adding to the thickness of the second metal layer by an electrolytic process.