Superconductive interconnect structure
A method for forming a superconducting interconnect structure, comprising: providing a substrate, forming a superconductive layer, forming a layer of a first dielectric material, removing parts of the layer of the first dielectric material and of the superconductive layer so as to form a pattern comprising a first set of line structures comprising: a first set of superconductive line structures, and a first set of line structures made of the first dielectric material, forming a second dielectric material between the line structures of the first set, forming a layer formed of a third dielectric material, providing a patterned mask, transferring the pattern into the first dielectric material and into the layer formed of the third dielectric material, so as to form the at least one via hole, removing the patterned mask, and forming a superconductive material layer so as to form at least one via.
1. A method for forming a superconducting interconnect structure of an integrated circuit, comprising:
a. forming a first entity on a substrate by:
a1. providing a substrate,
a2. forming a first superconductive layer of a first superconductive material having a first critical temperature on the substrate,
a3. forming a layer of a first dielectric material over the first superconductive layer,
a4. removing parts of the layer of the first dielectric material and of the first superconductive layer, said parts extending from a bottom surface of the first superconductive layer to a top surface of the first dielectric material, so as to form a pattern comprising a first set of line structures having a top surface, comprising:
a first set of superconductive line structures, and
a first set of line structures made of the first dielectric material, aligned with and overlying the first set of superconductive line structures, and comprising the top surface,
a5. forming a second dielectric material, different from the first dielectric material, over and between the line structures of the first set,
a6. planarizing the second dielectric material so that a top surface of the second dielectric material is coplanar with the top surface of the first set of line structures, and thereafter
a7. forming a layer formed of a third dielectric material over the first set of line structures and the second dielectric material,
thereby forming the first entity,
b. providing a patterned mask over the first entity, the pattern comprising at least one opening overlapping with an underlying superconductive line structure of the first set of superconductive line structures for forming at least one via hole in the first dielectric material and the layer formed of the third dielectric material,
c. transferring the pattern of the patterned mask into the first dielectric material and into the layer formed of the third dielectric material, so as to form the at least one via hole extending through the first dielectric material and the layer formed of the third dielectric material, thereby exposing part of the underlying superconductive line structure,
d. removing the patterned mask, thereby exposing a perforated surface, and
e. forming a superconductive unit made of one or more superconductive materials, each having a critical temperature within 1K of the first critical temperature, over the perforated surface thereby also forming at least one via by filling the at least one via hole, the at least one via extending through the first dielectric material and the layer formed of the third dielectric material, such that the formed superconductive unit physically contacts the underlying first set of superconductive line structures.
2. The method according to claim 1 , further comprising, after step a7., and before step b.:
a7′.: forming a hard mask layer over the first set of line structures, the second dielectric material, and the third dielectric material,
wherein, in step b., the patterned mask is provided over the hard mask layer,
wherein, in a step b1., after step b. and before step c., the pattern of the patterned mask is transferred into the hard mask layer,
wherein, in step c., transferring the pattern of the patterned mask into the first dielectric material and into the layer formed of the third dielectric material, comprises transferring said pattern from the patterned hard mask layer into the layer formed of the third dielectric material and into the first dielectric material, and
wherein step d. further comprises removing the patterned hard mask layer.
3. The method according to claim 1 , comprising providing, after step e., a second entity over the superconductive unit, comprising the steps of:
f. forming a layer of a fourth dielectric material over the superconductive unit,
g. removing parts of the layer of the fourth dielectric material and of the superconductive unit so as to form a pattern comprising a second set of line structures, comprising:
a second set of superconductive line structures, and
a second set of line structures made of the fourth dielectric material, aligned with and overlying the second set of superconductive line structures, thereby providing the second entity over the first entity.
4. The method according to claim 3 , wherein step e. consists of depositing a second superconductive layer made of a single second superconductive material having a critical temperature within 1K of the first critical temperature over the perforated surface so as to fill the at least one via hole extending through the first dielectric material and the layer formed of the third dielectric material and such that the deposited second superconductive layer physically contacts the underlying first set of superconductive line structures, and wherein step f. is performed directly after step e.
5. The method according to claim 1 , wherein step e. comprises:
e1. Forming a first part of the superconductive unit by depositing a second superconductive layer, made of a single superconductive material having a critical temperature within 1K of the first critical temperature, over the perforated surface so as to form at least one via by filling the at least one via hole, the at least one via extending through the first dielectric material, and extending through the layer formed of the third dielectric material, such that the formed second superconductive layer physically contacts the underlying first set of superconductive line structures,
e2. planarizing the deposited second superconductive layer so as to remove a top portion of the second superconductive layer without removing the at least one via, and
e3. Forming a second part of the superconductive unit by depositing a third superconductive layer, made of a single third superconductive material having a critical temperature within 1K of the first critical temperature, on the planarized second superconductive layer.
6. The method according to claim 5 , wherein step e2. comprises using chemical mechanical polishing and/or etching.
7. The method according to claim 1 , wherein the materials forming the first set of superconductive line structures and the superconductive unit are independently selected from MoN, Nb 3 Sn, NbTi, Nb, NbTiN and NbN.
8. The method according to claim 1 , wherein the at least one via hole in the first dielectric material and in the layer formed of the third dielectric material, has an aspect ratio of at most 0.5.
9. The method according to claim 1 , comprising the following steps after step a. and before step b., or after step e. and before step f., when present:
h. providing a third patterned mask over the first entity, the pattern comprising at least one further opening overlapping with an underlying superconductive line structure of the first set of superconductive line structures for forming at least one further via hole in the first dielectric material and the layer formed of the third dielectric material,
i. transferring the pattern of the third patterned mask into the first dielectric material and the layer formed of the third dielectric material, so as to form at least one further via hole extending through the first dielectric material and the layer formed of the third dielectric material exposing part of the underlying superconductive line structure,
j. removing the third patterned mask so as to expose a second perforated surface, and
k. depositing a resistive material, the resistive material having a resistivity of at least 100 μΩ·cm at a temperature of 1K, over the second perforated surface so as to fill the at least one further via hole extending through the first dielectric material and the layer formed of the third dielectric material and such that the deposited resistive material contacts physically the underlying superconductive line structure.
10. The method according to claim 9 , wherein said resistive material consists of the same chemical elements as the superconductive line structures, wherein a chemical composition of the resistive material is different from a chemical composition of the first superconductive material.
11. The method according to claim 1 , wherein the first dielectric material is silicon nitride and wherein the second dielectric material is silicon oxide.
12. The method according to claim 1 , wherein step e. comprises a step of depositing the superconductive material layer by physical vapor deposition.
13. The method according to claim 12 , wherein step a2. is performed by physical vapor deposition.
14. A superconducting interconnect structure formable by the method according to claim 1 , the interconnect structure comprising a first entity comprising:
i. a first set of line structures having a top surface, comprising:
a first set of superconductive line structures,
a first set of lines structures made of a first dielectric material, aligned with and overlying the first set of superconductive line structures, and comprising the top surface, and
ii. a second dielectric material, different from the first dielectric material, between the line structures of the first set having a top surface coplanar with the top surface of the first set of line structures, and
iii. a third dielectric material overlying the first set of line structures and the second dielectric material,
and wherein a via extends through the first dielectric material and the layer formed of the third dielectric material, wherein the via comprises a superconducting material physically contacting the underlying superconductive line structure.
15. The superconducting interconnect structure according to claim 14 , wherein the at least one via in the first dielectric material and in the layer formed of the third dielectric material, has an aspect ratio of at most 0.5.