Low energy etch process for nitrogen-containing dielectric layer
A stack that includes, from bottom to top, a nitrogen-containing dielectric layer, an interconnect level dielectric material layer, and a hard mask layer is formed on a substrate. The hard mask layer and the interconnect level dielectric material layer are patterned by an etch. Employing the patterned hard mask layer as an etch mask, the nitrogen-containing dielectric layer is patterned by a break-through anisotropic etch, which employs a fluorohydrocarbon-containing plasma to break through the nitrogen-containing dielectric layer. Fluorohydrocarbon gases used to generate the fluorohydrocarbon-containing plasma generate a carbon-rich polymer residue, which interact with the nitrogen-containing dielectric layer to form volatile compounds. Plasma energy can be decreased below 100 eV to reduce damage to physically exposed surfaces of the interconnect level dielectric material layer.
1. A method of forming a metal interconnect structure comprising:
forming a stack comprising, from bottom to top, a substrate, a nitrogen-containing dielectric layer composed of a dielectric metal oxynitride selected from the group consisting of HfO x N y , ZrO x N y , La 2 O x N y , TiO x N y , SrTiO x N y , LaAlO x N y , Y 2 O x N y , and an alloy thereof, an interconnect level dielectric material layer, and a hard mask layer;
forming an opening within said hard mask layer and said interconnect level dielectric material layer; and
anisotropically etching a physically exposed portion of said nitrogen-containing dielectric layer underneath said opening employing a fluorohydrocarbon-containing plasma, wherein said fluorohydrocarbon-containing plasma includes ions of a hydrofluorocarbon gas having a formula of C x H y F z and selected from alkane hydrofluorocarbon gases and alkene hydrofluorocarbon gases, wherein x is an integer selected from 4, 5, and 6, y and z are positive integers, and y is greater than z, wherein a volatile compound is formed on, and evaporates from, a surface of said nitrogen-containing dielectric layer, wherein said volatile compound comprises nitrogen derived from said nitrogen-containing dielectric layer and a carbon-rich polymer plasma including carbon and fluorine and having a ratio of carbon to fluorine that is greater than 1.
2. The method of claim 1 , wherein said fluorohydrocarbon-containing plasma includes ions having an average kinetic energy in a range from 10 eV to 100 eV.
3. The method of claim 1 , wherein said carbon-rich polymer is additionally formed on a top surface of said hard mask layer during said anisotropic etching.
4. The method of claim 3 , wherein said carbon-rich polymer has a refractive index in a range from 1.8 to 2.2.
5. The method of claim 3 , wherein said carbon-rich polymer has a density in a range from 1.5 g/cm 3 to 1.7 g/cm 3 .
6. The method of claim 1 , wherein said carbon-rich polymer includes hydrogen at an atomic concentration that is at least one half of said atomic concentration of carbon in said carbon-rich polymer.
7. The method of claim 6 , wherein an atomic ratio of hydrogen to carbon in said carbon-rich polymer is between 0.5 and 3.0.
8. The method of claim 1 , wherein said carbon-rich polymer has a composition that includes carbon at an atomic concentration between 30% and 40%, hydrogen at an atomic concentration between 40% and 50%, fluorine at an atomic concentration between 5.0% and 10%, and oxygen at an atomic concentration less than 5%.
9. The method of claim 1 , wherein said nitrogen-containing dielectric layer comprises silicon nitride.
10. The method of claim 1 , wherein said nitrogen-containing dielectric layer comprises a dielectric material having a dielectric constant less than 3.9 and including nitrogen.
11. The method of claim 10 , wherein said nitrogen-containing dielectric layer comprises Si, C, O, H, and N.
12. The method of claim 1 , wherein said hard mask layer comprises a metallic material.
13. The method of claim 12 , further comprising forming another hard mask layer having a dielectric constant of at least 3.9 between said interconnect level dielectric material layer and said hard mask layer.
14. The method of claim 1 , wherein physically exposed surfaces of said interconnect level dielectric material layer is structurally damaged by said hydrofluorocarbons-containing plasma, and fluorine is incorporated into said interconnect level dielectric material layer during said anisotropic etching.
15. The method of claim 1 , further comprising forming a conductive metal interconnect structure extending through an opening in said nitrogen-containing dielectric layer and through said opening within said hard mask layer and said interconnect level dielectric material layer.