Method of making a superconducting nanowire single photon detector using a sidewall image transfer process

1 . A method of manufacturing a superconducting nanowire, comprising:

forming a multilayer thin film stack comprising a superconducting layer;

forming a mandrel over the multilayer thin film stack;

forming an etch mask comprising a first mask portion on a first side of the mandrel and a second mask portion on a second side of the mandrel;

removing the mandrel; and

etching the multilayer thin film stack using the etch mask to thereby form the superconducting nanowire.

2 . The method of claim 1 , wherein forming the multilayer thin film stack further comprises:

depositing a layer of SiN over a substrate;

depositing a layer of AlN over the layer of SiN;

depositing the superconducting layer of NbN over the layer of AlN; and

depositing a layer of amorphous silicon over the layer of NbN.

3 . The method of claim 1 , further comprising depositing a first hard mask layer, a second hard mask layer, and a third hard mask layer over the multilayer thin film stack.

4 . The method of claim 3 , wherein the first hard mask layer comprises silicon oxide, the second hard mask layer comprises silicon nitride, and the third hard mask layer comprises titanium nitride.

5 . The method of claim 3 , further comprising:

depositing a mandrel layer over the third hard mask layer; and

etching the mandrel layer to thereby form the mandrel as an unetched portion of the mandrel layer.

6 . The method of claim 3 , further comprising:

forming a photoresist layer over the third hard mask layer; and

patterning the photoresist layer to form the mandrel.

7 . The method of claim 1 , wherein forming the etch mask further comprises:

depositing a spacer layer over the mandrel; and

anisotropically etching the spacer layer to form sidewall spacers comprising the first mask portion on the first side of the mandrel and the second mask portion on the second side of the mandrel.

8 . The method of claim 7 , wherein the spacer layer comprises one or more of silicon dioxide, silicon nitride, silicon oxynitride, hafnium oxide, hafnium silicon oxide, hafnium tantalum oxide, hafnium titanium oxide, hafnium zirconium oxide, zirconium oxide, titanium oxide, aluminum oxide, and hafnium aluminum oxide.

9 . The method of claim 7 , further comprising forming at least one hard mask layer over the multilayer thin film stack, wherein the mandrel is formed over the at least one hard mask layer.

10 . The method of claim 9 , wherein the step of forming the etch mask further comprises:

etching the at least one hard mask layer using the first and second mask portions to form third and fourth mask portions;

removing the first and second mask portions; and

removing the third mask portion without removing the fourth mask portion.

11 . The method of claim 10 , wherein the step of etching the multilayer thin film stack using the etch mask comprises etching the multilayer thin film stack using the fourth mask portion as a mask.

12 . The method of claim 1 , wherein the superconducting nanowire comprises a portion of a superconducting nanowire single photon detector.

13 . The method of claim 12 , further comprising

forming a waveguide over a substrate; and

forming a cladding layer surrounding the waveguide, wherein the multilayer thin film stack is formed over the cladding layer.

14 . The method of claim 13 , wherein the step of etching the multilayer thin film stack forms plurality of nanowires each having a width of less than 90 nm.

15 . The method of claim 13 , wherein the step of etching the multilayer thin film stack further forms a first electrical connector portion in contact with a first end of the superconducting nanowire and a second electrical connector portion in contact with a second end of the superconducting nanowire.

16 . The method of claim 15 , wherein the superconducting nanowire is narrower than the first electrical connector portion and the second electrical connector portion.

17 . The method of claim 15 , wherein the first electrical connector portion comprises one or more passive electrical components.

18 . The method of claim 17 , wherein the one or more passive electrical components comprise one or more inductors.

19 . The method of claim 15 , further comprising forming an encapsulation layer over the superconducting nanowire, the first electrical connector portion and the second electrical connector portion.

20 . The method of claim 19 , wherein the encapsulating layer comprises silicon nitride.