Pulse reverse electrodeposition for metallization and planarization of semiconductor substrates
View Patent ↗A smooth layer of a metal is electroplated onto a microrough electrically conducting substrate by immersing the substrate and a counterelectrode in an electroplating bath of the metal to be electroplated and passing a modulated reversing electric current between the electrodes. The current contains pulses that are cathodic with respect to said substrate and pulses that are anodic with respect to said substrate. The cathodic pulses have a duty cycle less than about 50% and said anodic pulses have a duty cycle greater than about 50%, the charge transfer ratio of the cathodic pulses to the anodic pulses is greater than one, and the frequency of said pulses ranges from about 10 Hertz to about 12000 Hertz. The plating bath is substantially devoid of levelers and may be devoid of brighteners.
1. A method for depositing a smooth layer of a metal onto a microrough substrate comprising
immersing, as an electrode, an electrically conductive substrate having a microrough surface in an electroplating bath containing ions of a metal to be deposited onto said surface, said plating bath being substantially devoid of levelers,
immersing a counter electrode in said plating bath
passing an electric current between said electrodes,
wherein
said electric current is a modulated reversing electric current comprising pulses that are cathodic with respect to said substrate and pulses that are anodic with respect to said substrate,
said cathodic pulses have a duty cycle less than about 50% and said anodic pulses have a duty cycle greater than about 50%,
the charge transfer ratio of said cathodic pulses to said anodic pulses is greater than one, and
the frequency of said pulses ranges from about 10 Hertz to about 5000 Hertz.
2. The method of claim 1 wherein an interval of no electric current flow is interposed between said cathodic pulses and succeeding anodic pulses.
3. The method of claim 1 wherein an interval of no electric current flow is interposed between said anodic pulses and succeeding cathodic pulses.
4. The method of claim 1 wherein an interval of no electric current flow is interposed between said cathodic pulses and succeeding anodic pulses and between said anodic pulses and succeeding cathodic pulses.
5. The method of claim 1 wherein said cathodic pulses and said anodic pulses succeed each other without intervening intervals of no electric current flow.
6. The method of claim 1 wherein said cathodic pulses and said anodic pulses form a pulse train having a frequency between about 50 Hertz and about 12000 Hertz.
7. The method of claim 1 wherein said cathodic pulses and said anodic pulses form a pulse train having a frequency between about 500 Hertz and about 10000 Hertz.
8. The method of claim 1 wherein said cathodic pulses and said anodic pulses form a pulse train having a frequency between about 4000 Hertz and about 10000 Hertz.
9. The method of claim 1 wherein said cathodic pulses have a duty cycle of from about 30% to about 1%.
10. The method of claim 1 wherein said cathodic pulses have a duty cycle of from about 30% to about 15%.
11. The method of claim 1 wherein said cathodic pulses have a duty cycle of from about 30% to about 20%.
12. The method of claim 1 wherein said anodic pulses have a duty cycle of from about 60% to about 99%.
13. The method of claim 1 wherein said anodic pulses have a duty cycle of from about 70% to about 85%.
14. The method of claim 1 wherein said cathodic pulses have a duty cycle of from about 70% to about 80%.
15. The method of claim 1 wherein said metal is selected from the group consisting of copper, silver, gold, zinc, chromium, nickel, bronze, brass, and alloys thereof.
16. The method of claim 1 wherein said plating bath is substantially devoid of brighteners.
17. The method of claim 1 wherein said metal is copper and said plating bath contains a suppressor.
18. The method of claim 17 wherein said suppressor is present in an amount of from about 100 parts per million to about 5% by weight of said plating bath.
19. The method of claim 17 wherein said suppressor is present in an amount of from about 200 parts per million to about 800 parts per million by weight of said plating bath.
20. The method of claim 17 wherein said suppressor is present in an amount of about 300 parts per million of said plating bath.
21. The method of claim 17 wherein said suppressor is an organic polyhydroxy compound.
22. The method of claim wherein said suppressor is poly(ethylene glycol).
23. The method of claim 22 wherein said poly(ethylene glycol) has a molecular weight in the range of from about 1000 to about 12000.
24. The method of claim 22 wherein said poly(ethylene glycol) has a molecular weight in the range of from about 2500 to about 5000.