Method and apparatus for eliminating defects and improving uniformity in electrochemically processed conductive layers
View Patent ↗A method of removing material from a conductive surface of a workpiece while the conductive surface and an electrode are wetted by a process solution. The method comprises the steps of applying power between the conductive surface and the electrode, rendering the conductive surface anodic. The method includes the step of allowing a passivation layer to build up on the conductive surface/The method includes the step of applying an external influence to the conductive surface to periodically reduce the passivation layer thickness. Advantages of the invention include an efficient technique for electropolishing a workpiece.
1. A method of removing material from a conductive surface of a workpiece while the conductive surface and an electrode are wetted by a process solution, the method comprising:
applying power between the conductive surface and the electrode, rendering the conductive surface anodic;
forming a passivation layer to a first thickness on the conductive surface by transforming a portion of the conductive surface while applying power; and
applying an external influence to the conductive surface to periodically reduce the thickness of the passivation layer, wherein periodically reducing comprises reducing the thickness of the passivation layer from the first thickness to a second thickness after allowing the passivation layer to increase in thickness substantially to the first thickness, wherein the external influence does not contact the conductive surface while allowing the passivation layer to increase in thickness, and wherein the thickness is reduced more than once.
2. The method of claim 1 , wherein the applying an external influence step includes physically sweeping the conductive surface.
3. The method of claim 1 , wherein the applying an external influence step includes establishing a relative motion between the conductive surface and the solution.
4. The method of claim 3 , wherein the relative motion during the applying an external influence step is higher than during the forming a passivation layer step.
5. The method of claim 1 , wherein the applying an external influence step includes physically sweeping the conductive surface with a structure sufficiently large to reduce the local current density applied to a local region of the conductive surface under the structure.
6. The method of claim 1 , wherein the applying power step includes varying the power between a maximum level and a minimum level.
7. The method of claim 6 , wherein the applying an external influence step is performed when the power is in minimum level.
8. The method of claim 6 , wherein the step of varying the power between a maximum level and a minimum level includes pulsing the power.
9. The method of claim 6 , wherein the minimum power level comprises approximately zero voltage.
10. The method of claim 6 , wherein the minimum power level comprises a negative voltage.
11. The method of claim 2 , wherein the applying power step includes varying the power between a maximum level and a minimum level.
12. The method of claim 11 , wherein the applying an external influence step is performed when the power is in minimum level.
13. The method of claim 1 , wherein the applying an external influence step includes increasing local temperature of the process solution over the conductive surface.
14. The method of claim 1 , wherein the applying an external influence step includes increasing the flow rate of the process solution.
15. The method of claim 1 , wherein the thickness of the passivation layer is allowed to increase in thickness for a period of 3-10 seconds.
16. The method of claim 1 , wherein the thickness of the passivation layer is reduced from a period of 2-5 seconds.
17. The method of claim 1 , wherein the passivation layer increases in thickness during electropolishing.
18. The method of claim 17 , further comprising stopping electropolishing before reducing the thickness of the passivation layer.
19. A method of removing material from a conductive surface of a workpiece while the conductive surface and an electrode are wetted by a process solution, the method comprising:
forming a layer on the conductive surface by applying a first power between the conductive surface and the electrode, wherein forming comprises transforming a portion of the conductive surface; and
removing the layer on the conductive surface while applying a second power, wherein the first and second powers have a same polarity.
20. The method of claim 19 , wherein the step of removing comprises applying an external influence onto the conductive surface.
21. The method of claim 20 , wherein applying an external influence comprises establishing a relative motion between the conductive surface and the process solution.
22. The method of claim 21 , wherein the conductive surface is spun in the process solution.
23. The method of claim 20 , wherein the step of applying an external influence includes reducing a local current density at a local region of the layer on the conductive surface.
24. The method of claim 23 , wherein the step of reducing a local current density includes physically sweeping the layer on the conductive surface to reduce the local current density.
25. The method of claim 19 , wherein the first power is applied for a predetermined time.
26. The method of claim 19 , wherein the second power is applied for a predetermined time.
27. The method of claim 19 , wherein the first power comprises an electropolishing voltage.
28. The method of claim 19 , wherein the second power comprises zero voltage.
29. The method of claim 19 , wherein the second power comprises negative voltage.
30. The method of claim 19 , wherein the first power and the second power comprise a pulsed wave form.
31. The method of claim 19 , wherein the applying an external influence step includes increasing local temperature of the process solution over the conductive surface.
32. The method of claim 19 , wherein the applying an external influence step includes increasing the flow rate of the process solution.
33. A method of removing material from a conductive surface of a workpiece in a process solution, the method comprising:
forming a layer on the conductive surface by applying a first power between the conductive surface and an electrode while the conductive surface and the electrode are wetted by the process solution, wherein forming comprises transforming a portion of the conductive surface; and
removing the layer on the conductive surface while applying zero voltage and applying an external influence onto the conductive surface, wherein applying the external influence is performed by spinning the conductive surface outside the process solution.