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An etching process for selectively etching exposed metal surfaces of a substrate and forming a conductive capping layer over the metal surfaces is described. In some embodiments, the etching process involves oxidation of the exposed metal to form a metal oxide that is subsequently removed from the s

An etching process for selectively etching exposed metal surfaces of a substrate and forming a conductive capping layer over the metal surfaces is described. In some embodiments, the etching process involves oxidation of the exposed metal to form a metal oxide that is subsequently removed from the surface of the substrate. The exposed metal may be oxidized by using solutions containing oxidizing agents such as peroxides or by using oxidizing gases such as those containing oxygen or ozone. The metal oxide produced is then removed using suitable metal oxide etching agents such as glycine. The oxidation and etching may occur in the same solution. In other embodiments, the exposed metal is directly etched without forming a metal oxide. Suitable direct metal etching agents include any number of acidic solutions. The process allows for controlled oxidation and/or etching with reduced pitting. After the metal regions are etched and recessed in the substrate surface, a conductive capping layer is formed using electroless deposition over the recessed exposed metal regions.

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What is claimed is: 1. A method of depositing a metal-containing capping layer on metal portions of a substrate containing a layer of metal and dielectric, the method comprising: (a) receiving the substrate containing the layer of metal and dielectric; (b) wet etching metal from the substrate from

What is claimed is: 1. A method of depositing a metal-containing capping layer on metal portions of a substrate containing a layer of metal and dielectric, the method comprising: (a) receiving the substrate containing the layer of metal and dielectric; (b) wet etching metal from the substrate from a position above or coplanar with an upper level of dielectric to a position below the upper level of exposed dielectric in the layer by contacting the substrate with a wet etching solution, wherein the etching solution oxidizes the metal of the substrate to a metal oxide, further comprising removing the metal oxide so that the exposed metal portions attain said position below the upper level of the exposed dielectric, wherein oxidizing the metal of the substrate to a metal oxide and removing the metal oxide takes place in one etching solution; and (c) forming the capping layer on at least exposed metal portions of the substrate by electroless deposition. 2. The method of claim 1, wherein the metal of the layer is copper or a copper alloy. 3. The method of claim 1, wherein the capping layer comprises a refractory metal. 4. The method of claim 1, wherein the capping layer comprises cobalt. 5. The method of claim 1, wherein the metal of the layer is etched to a position below the level of the exposed dielectric that is approximately equal to or lower than a target thickness of the capping layer. 6. The method of claim 1, wherein the capping layer is between about 30 and 500 Angstroms thick. 7. The method of claim 1, wherein the etching solution comprises an oxidizing agent selected from the group consisting of a peroxide, a permanganate, ozone, and a persulfate. 8. The method of claim 1, wherein the etching solution further comprises a corrosion inhibitor. 9. The method of claim 1, wherein the etching solution further comprises a surfactant. 10. The method of claim 1, wherein contacting the substrate with an etching solution comprises dipping, spraying or using a thin film reactor. 11. The method of claim 1, further comprising performing a post-deposition anneal of the capping layer. 12. The method of claim 1, further comprising nitriding the capping layer. 13. The method of claim 1, wherein the substrate received in (a) comprises exposed regions of dielectric. 14. The method of claim 1, wherein the substrate received in (a) comprises metal covering the upper level of dielectric. 15. The method of claim 1, wherein removing the metal oxide comprises contacting the substrate with an oxide etchant that selectively removes the metal oxide and not the metal. 16. The method of claim 15, wherein the oxide etchant comprises glycine. 17. The method of claim 15, wherein the oxide etchant comprises a complexing agent for ions of the metal. 18. The method of claim 1, further comprising performing a post-etch treatment of the substrate prior to forming the capping layer. 19. The method of claim 18, wherein the post-etch treatment of the substrate involves cleaning the etched metal portions of the substrate prior to forming the capping layer. 20. A method of depositing a metal-containing capping layer on metal portions of a substrate containing a layer of metal and dielectric, the method comprising: (a) receiving the substrate containing the layer of metal and dielectric; (b) etching metal from the substrate from a position above or coplanar with an upper level of dielectric to a position below the upper level of exposed dielectric in the layer by contacting the substrate with an oxidizing gas that oxidizes the exposed metal to a metal oxide and further contacting the substrate with a metal oxide etching agent to remove the metal oxide; and (c) forming the capping layer on at least exposed metal portions of the substrate by electroless deposition. 21. The method of claim 20, wherein the oxidizing gas comprises oxygen. 22. The method of claim 21, wherein the oxidation occurs at a temperature between about 200 and 300 degrees Celsius and at a pressure between about 50 and 180 Torr of oxygen. 23. A method of etching metal portions of a substrate containing a layer of metal and dielectric, the method comprising: receiving the substrate containing the layer of metal and dielectric; and etching metal from the substrate to a position below an upper level of exposed dielectric by contacting the substrate with a wet etching solution comprising between about 0.05% and 15% glycine by weight and between about 0.5% and 20% peroxide by weight, at a pH in a range of between about 5 and 12, wherein the etching is accomplished by contacting at least the metal with an etching solution, wherein the contacting comprises at least one of immersing, spraying, dipping, spin on contact, and using a thin film reactor. 24. The method of claim 23, wherein the peroxide is H2O2. 25. The method of claim 23, wherein the etching solution has a pH in a range of between about 6 and 10. 26. The method of claim 23, wherein the etching solution comprises about 1% by weight glycine and about 3% by weight H2O2. 27. The method of claim 23, further comprising forming a capping layer on the etched metal portions of the substrate. 28. A method of etching metal portions of a substrate containing a layer of metal and dielectric, the method comprising: receiving the substrate containing the layer of metal and dielectric, wherein substrate comprises overburden covering dielectric field regions; and etching metal from the substrate to expose the dielectric field regions by contacting the substrate with a wet etching solution comprising between about 0.05% and 15% glycine by weight and between about 0.5% and 20% peroxide by weight, at a pH in a range of between about 5 and 12, wherein the etching is accomplished by contacting at least the metal with an etching solution, wherein the contacting comprises at least one of immersing, spraying, dipping, spin on contact, and using a thin film reactor. 29. The method of claim 28, wherein the peroxide is H2O2. 30. The method of claim 28, wherein the etching solution has a pH in a range of between about 6 and 10. 31. The method of claim 28, wherein the etching solution comprises about 1% by weight glycine and about 3% by weight H2O2. 32. The method of claim 28, comprising forming a capping layer on the etched metal portions of the substrate. 33. The method of claim 28, wherein the metal is copper. 34. The method of claim 28, further comprising, prior to the etching, planarizing the substrate surface. 35. The method of claim 34, wherein the planarization is chemical mechanical polishing. 36. The method of claim 34, wherein the planarization is an electroplanarization technique. 37. A method of etching metal portions of a substrate containing a layer of metal and dielectric, the method comprising: receiving the substrate containing the layer of metal and dielectric, wherein the substrate comprises overburden covering dielectric field regions; at least partially completing planarization of the overburden; and etching to remove the remaining overburden on the substrate by contacting the substrate with a wet etching solution at a pH in a range of between about 5 and 12 and comprising between about 0.05% and 15% glycine by weight and between about 0.5% and 20% peroxide by weight, wherein the etching is accomplished by contacting at least the metal with an etching solution, wherein the contacting comprises at least one of immersing, spraying, dipping, spin on contact, and using a thin film reactor. 38. The method of claim 37, wherein etching solution further comprises a surfactant. 39. The method of claim 37, wherein the etching solution further comprises a corrosion inhibitor. 40. The method of claim 37, wherein the peroxide is hydrogen peroxide. 41. The method of claim 37, wherein the etching solution has a pH in a range of between about 6 and 10. 42. The method of claim 37, further comprising forming a capping layer on the etched metal portions of the substrate. 43. The method of claim 37, wherein the metal is copper. 44. The method of claim 37, wherein the planarization is chemical mechanical polishing. 45. The method of claim 37, wherein the planarization is an electroplanarization technique. 46. A method of etching metal portions of a substrate containing a layer of metal and dielectric, the method comprising: receiving the substrate containing the layer of metal and dielectric, wherein substrate comprises overburden covering dielectric field regions; and etching to remove at least a portion of the overburden on the substrate by contacting the substrate with a wet etching solution at a pH in a range of between about 5 and 12 and comprising between about 0.05% and 15% glycine by weight and between about 0.5% and 20% peroxide by weight, wherein the etching is accomplished by contacting at least the metal with an etching solution, wherein the contacting comprises at least one of immersing, spraying, dipping, spin on contact, and using a thin film reactor. 47. The method of claim 46, further comprising at least partially completing removing the overburden via chemical mechanical processing. 48. The method of claim 46, further comprising forming a capping layer on the etched metal portions of the substrate. 49. The method of claim 46, wherein the metal is copper. 50. The method of claim 46, wherein etching solution further comprises a surfactant. 51. The method of claim 46, wherein the etching solution further comprises a corrosion inhibitor. 52. The method of claim 46, wherein the etching solution has a pH in a range of between about 6 and 10. 53. The method of claim 46, wherein the etching solution comprises about 1% by weight glycine and about 3% by weight H2O2. 54. A method of depositing a metal-containing capping layer on metal portions of a substrate containing a layer of metal and dielectric, the method comprising: (a) receiving the substrate containing the layer of metal and dielectric; (b) wet etching metal from the substrate from a position above or copolymer with an upper level of dielectric to a position below the upper level of exposed dielectric in the layer by contacting the substrate with a wet etching solution, wherein the etching solution oxidizes the metal of the substrate to a metal oxide, further comprising removing the metal oxide so that the exposed metal portions attain said position below the upper level of the exposed dielectric, wherein removing the metal oxide comprises contacting the substrate with an oxide etchant that selectively removes the metal oxide and not the metal, said oxide etchant comprising glycine; and (c) forming the capping layer on at least exposed metal portions of the substrate by electroless deposition.