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A vertical stack including a dielectric hard mask layer and a titanium nitride layer is formed over an interconnect-level dielectric material layer such as an organosilicate glass layer. The titanium nitride layer may be partially or fully converted into a titanium oxynitride layer, which is subsequ

A vertical stack including a dielectric hard mask layer and a titanium nitride layer is formed over an interconnect-level dielectric material layer such as an organosilicate glass layer. The titanium nitride layer may be partially or fully converted into a titanium oxynitride layer, which is subsequently patterned with a first pattern. Alternately, the titanium nitride layer, with or without a titanium oxynitride layer thereupon, may be patterned with a line pattern, and physically exposed surface portions of the titanium nitride layer may be converted into titanium oxynitride. Titanium oxynitride provides etch resistance during transfer of a combined first and second pattern, but can be readily removed by a wet etch without causing surface damages to copper surfaces. A chamfer may be formed in the interconnect-level dielectric material layer by an anisotropic etch that employs any remnant portion of titanium nitride as an etch mask.

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1. A method of forming a patterned structure comprising: forming a vertical stack including an interconnect-level dielectric material layer, a dielectric hard mask layer, and a patterned titanium oxynitride layer defining a first pattern over a substrate, wherein said patterned titanium oxynitride l

1. A method of forming a patterned structure comprising: forming a vertical stack including an interconnect-level dielectric material layer, a dielectric hard mask layer, and a patterned titanium oxynitride layer defining a first pattern over a substrate, wherein said patterned titanium oxynitride layer is formed by: forming a blanket titanium nitride (TiN) layer on said dielectric hard mask layer;converting an upper portion of said blanket TiN layer into a blanket titanium oxynitride layer; andpatterning said blanket titanium oxynitride layer with said first pattern;forming a patterned lithographic material stack including at least a patterned photoresist layer over said titanium oxynitride layer, said patterned photoresist layer defining a second pattern; andetching said interconnect-level dielectric material layer employing a combination of said patterned lithographic material stack and said patterned titanium oxynitride layer to form a cavity embedded within said interconnect-level dielectric material layer. 2. The method of claim 1, further comprising: forming a dielectric oxide layer over said blanket titanium oxynitride layer;forming a first photoresist layer including said first pattern over said dielectric oxide layer; andetching said dielectric oxide layer, said blanket titanium oxynitride layer, and said blanket TiN layer employing said first photoresist layer as an etch mask to form a stack of a patterned TiN layer, said patterned titanium oxynitride layer, and a patterned dielectric oxide layer. 3. The method of claim 1, further comprising oxidizing sidewalls of said patterned TiN layer, wherein oxidized portions of said patterned TiN layer is merged into said patterned titanium oxynitride layer. 4. The method of claim 3, wherein a sidewall of said cavity is vertically coincident with an outer sidewall of said patterned titanium oxynitride layer upon said etching of said interconnect-level dielectric material layer. 5. The method of claim 4, further comprising removing said patterned titanium oxynitride layer selective to said remnant TiN layer after said etching of said interconnect-level dielectric material layer. 6. The method of claim 1, wherein said converting said upper portion of said blanket TiN layer into said blanket titanium oxynitride layer comprises a plasma treatment utilizing a plasma of an oxygen-containing gas. 7. The method of claim 6, wherein said plasma treatment is performed at a pressure in a range from 5 mTorr to 2000 mTorr, a radio frequency (13.56 MHz RF) power level in a range from 200 W to 1 kW at a frequency from 1 MHz to 100 MHz, an O2 gas flow in a range from 50 sccm to 2 slm, and a processing temperature in a range from 20 degree Celsius to 300 degree Celsius. 8. The method of claim 6, wherein said plasma treatment is performed at a pressure in a range from 5 mTorr to 200 mTorr, a radio frequency (RF) power level in a range from 200 W to 1 kW at a frequency from 1 MHz to 100 MHz, a CO2 gas flow in a range from 50 sccm to 2 slm, and a processing temperature in a range from 20 degree Celsius to 300 degree Celsius. 9. The method of claim 1, wherein said converting said upper portion of said blanket TiN layer into said blanket titanium oxynitride layer comprises an electrochemical oxidation process. 10. The method of claim 9, wherein said electrochemical oxidation process is used in conjunction with dehydration. 11. The method of claim 1, wherein said blanket titanium oxynitride layer has a composition of TiOxNy wherein x is in a range from 0.1 to 1.9 and y is in a range from 0.05 to 0.95, and (1−x)+2Y is in a range from 0.9 to 2.4. 12. The method of claim 1, wherein said first pattern includes a first opening, said second pattern includes a second opening, and an area of said first opening and an area of said second opening overlap. 13. The method of claim 1, wherein said dielectric hard mask layer comprises a material selected from silicon oxide, silicon oxynitride, silicon nitride, and nitrogen-doped organosilicate glass. 14. The method of claim 1, wherein said patterned lithographic material stack includes: an organic planarizing layer (OPL) located on said patterned titanium oxynitride layer;an antireflective coating (ARC) layer located over said OPL; andsaid patterned photoresist layer. 15. The method of claim 1, wherein said forming said blanket titanium nitride (TiN) layer comprises a physical vapor deposition process, and said blanket titanium nitride (TiN) layer that is formed has a uniform thickness throughout an entirety thereof. 16. The method of claim 15, wherein said blanket layer of titanium nitride has a ratio of titanium atoms to nitrogen atoms that is equal to 1.0.