Electron-beam lithography process adapted for a sample comprising at least one fragile nanostructure
Disclosed is a lithography process on a sample including at least one structure and covered by at least a lower layer of resist and a upper layer of resist the process including: using an optical device to image or determine, in reference to the optical device, a position of the selected structure and positions of markers integral with the sample; using an electron-beam device, imaging or determining the position of each marker in reference to the electron-beam device; deducing the position of the selected structure in reference to the electron-beam device; exposing to an electron beam the upper layer of resist above the position of the selected structure to remove all the thickness of the upper layer of resist above the position of the selected structure but none or only part of the thickness of the lower layer of resist above the position of the selected structure.
1. A lithography process on a sample ( 2 ) comprising at least one structure ( 1 ), said process comprising:
putting above the sample ( 2 ) at least two layers ( 3 , 4 ) of resist comprising a lower layer ( 3 ) of resist in contact with the sample ( 2 ) and an upper layer ( 4 ) of resist above the lower layer of resist ( 3 ),
using an optical device ( 8 ), receiving a radiation ( 14 ) from a selected structure ( 1 ) and imaging or determining, with reference to the optical device ( 8 ), a position of the selected structure ( 1 ) and positions of markers ( 21 ) integral with the sample ( 2 ),
using an electron-beam device, imaging or determining the position of each marker ( 21 ) with reference to the electron-beam device,
using:
the position of each marker ( 21 ) with reference to the electron-beam device, and
the position of the selected structure ( 1 ) and the positions of the markers ( 21 ) with reference to the optical device ( 8 ),
deducing the position of the selected structure ( 1 ) with reference to the electron-beam device, and
using the electron-beam device, exposing to an electron beam the upper layer ( 4 ) of resist above the position of the selected structure ( 1 ) in order to remove all the thickness of the upper layer ( 4 ) of resist above the position of the selected structure ( 1 ) but no part or only an incomplete part of the thickness of the lower layer ( 3 ) of resist above the position of the selected structure ( 1 ).
2. The process according to claim 1 , further comprising, after removing all the thickness of the upper layer ( 4 ) of resist above the position of the selected structure ( 1 ), another removing step comprising removing at least a part of the remaining thickness of the lower layer ( 3 ) of resist above the position of the selected structure ( 1 ).
3. The process according to claim 2 , wherein imaging or determining the position of the selected structure ( 1 ) with reference to the optical device ( 8 ) comprises a step of acquiring an image imaging the markers ( 21 ) and a fluorescence radiation ( 14 ) from the selected structure ( 1 ).
4. The process according to claim 2 , wherein the markers ( 21 ) are made by optical lithography.
5. The process according to claim 2 , wherein the lower layer ( 3 ) has a thickness of at least 50 nm.
6. The process according to claim 1 , wherein imaging or determining the position of the selected structure ( 1 ) with reference to the optical device ( 8 ) comprises a step of acquiring an image imaging the markers ( 21 ) and a fluorescence radiation ( 14 ) from the selected structure ( 1 ).
7. The process according to claim 6 , wherein the markers ( 21 ) are made by optical lithography.
8. The process according to claim 1 , wherein the markers ( 21 ) are made by optical lithography.
9. The process according to claim 8 , wherein the markers ( 21 ) are made by a laser with the same optical device ( 8 ).
10. The process according to claim 1 , wherein the markers are made at least on the upper layer of resist ( 4 ).
11. The process according to claim 1 , wherein the lower layer ( 3 ) has a thickness of at least 50 nm.
12. The process according to claim 1 , wherein the upper layer ( 4 ) has a thickness of less than 5 μm.
13. The process according to claim 1 , further comprising, before the steps of exposing to an electron beam the upper layer ( 4 ) of resist and removing all the thickness of the upper layer ( 4 ) of resist above the position of the selected structure ( 1 ), a step of selecting the selected structure ( 1 ) based on the radiation ( 14 ) from the selected structure ( 1 ).
14. The process according to claim 13 , wherein the step of selecting the selected structure ( 1 ) is based:
on a wavelength, and/or
on a polarization, and/or
on an intensity, and/or
on bunched or antibunched emission characteristics of the radiation ( 14 ) from the selected structure ( 1 ) and/or an estimated lifetime of the selected structure ( 1 ).
15. The process according to claim 1 , further comprising a step of deposing a metallic layer ( 11 ) above the position of the selected structure ( 1 ), where all the thickness of the upper ( 4 ) layer of resist have been removed.
16. The process according to claim 1 , wherein the at least one structure ( 1 ) is comprised in the sample inside a structure layer ( 7 a , 7 b ).
17. The process according to claim 16 , wherein the at least one structure ( 1 ) is comprised in the sample between two layers ( 7 a , 7 b ) of the same dielectric material forming the structure layer.
18. The process according to claim 16 , wherein:
one first side of the structure layer ( 7 a , 7 b ) is in contact with one ( 3 ) of the at least two layers ( 3 , 4 ) of resist, and
one second side of the structure layer ( 7 a , 7 b ) is in contact with a metallic layer ( 6 ) or a Bragg mirror.
19. The process according to claim 1 , wherein each structure ( 1 ) is quantum dot, a nitrogen vacancy center in a nanodiamond, or a fluorescent molecule.
20. The process according to claim 1 , wherein the markers are made on the lower layer of resist ( 3 ) and on the upper layer of resist ( 4 ).