Method of fabricating tridimensional micro- and nanostructures as well as optical element assembly having a tridimensional convex structure obtained by the method

1. Method for forming three-dimensional micro- and nanostructures, based on the structuring of a body of material by means of a mould having an impression area which reproduces the three-dimensional structures in negative form, comprising the operations of:

providing a mould comprising a substrate of a material which can undergo isotropic chemical etching, in which the impression area is to be formed;

defining an etching pattern on (in) the substrate comprising a plurality of etching areas having zero-, uni- or bidimensional extension, which can be reached by an etching agent; and

carrying out a process of isotropic chemical etching of the substrate from the etching areas for a corresponding predetermined time, so as to produce cavities which in combination make up the impression area.

2. Method according to claim 1 , wherein successive etching steps take place from new etching areas and enlarged etching areas obtained by at least one preceding etching step carried out from pre-existing etching areas.

3. Method according to claim 1 , wherein the etching areas are defined by selective masking of the surface of the substrate in a pattern corresponding to the geometry of the desired etching areas.

4. Method according to claim 3 , wherein the selective masking includes the operations of:

applying a protective layer to an extended area of the surface of the substrate; and

selectively removing areas of the protective layer and exposing etching areas of the substrate.

5. Method according to claim 4 , wherein the selective removal of the protective layer is carried out by physical etching methods by means of focused ion beams.

6. Method according to claim 3 , wherein the selective removal of the protective layer is carried out by lithography and includes the operations of:

applying an upper layer of resist to the protective layer;

selectively exposing the resist;

developing and selectively removing the exposed resist;

etching the protective layer by chemical etching in areas of removal of the resist, and exposing the etching areas of the substrate.

7. Method according to claim 3 , wherein the selective masking changes over time and forms a primary pattern corresponding to the geometry of first etching areas and at least one secondary pattern comprising second etching areas.

8. Method according to claim 7 , wherein the secondary pattern additionally comprises enlarged etching areas obtained by a preceding etching step carried out from the first etching areas.

9. Method according to claim 1 , wherein the etching areas are defined by physical etching methods which can produce a cut into the substrate.

10. Method according to claim 9 , wherein the physical etching methods comprise milling etching by focused ion beams.

11. Method according to claim 9 , wherein the physical etching methods comprise a step of defining a surface pattern corresponding to the geometry of the desired etching areas by optical, electron or X-ray lithography and a subsequent step of plasma etching of the substrate.

12. Method according to claim 11 , wherein the unidimensional or bidimensional etching areas have variable depths of cut.

13. Method according to claim 9 , wherein the etching areas have different depths of cut.

14. Method according to claim 1 , wherein the material of the substrate is a non-crystalline material which is isotropic with respect to the properties of response to etching by any chemical agent.

15. Method according to claim 1 , wherein the material of the substrate is a crystalline material which is isotropic with respect to the properties of response to etching by predetermined etching chemical agents.

16. Method according to claim 1 , wherein the operation of structuring the material by moulding is a process of imprint lithography applied to plastics or cross-linkable polymers.

17. Method according to claim 1 , wherein the operation of structuring the material by moulding is an injection moulding method.

18. Method according to claim 1 , wherein the operation of structuring the material by moulding is a step and flash lithography process.

19. Method according to claim 1 , wherein the substrate of the mould is quartz, glass or other silicon oxide.

20. Method according to claim 1 , wherein the material is a thermoplastic or cross-linkable polymer.

21. Method according to claim 1 , wherein the etching agent contains hydrofluoric acid.

22. Method according to claim 1 , wherein the three-dimensional structures comprise adjacent, intersecting and/or overlapping convex formations which form refractive optical elements.

23. Method according to claim 1 , comprising a further step of micro- or nanoprocessing for producing cuts or perforations in the structured material, forming diffraction apertures.

24. Method according to claim 1 , comprising a further step of electrolytic growth of metallic elements within the impression area of the mould or on the moulded three-dimensional structures, for forming a transfer substrate which reproduces the three-dimensional structures, intended for use as a mould for reproducing the three-dimensional structures in negative form.

25. Assembly of microlenses with a convex three-dimensional structure, of the refractive or hybrid refractive/diffractive type, including a plurality of adjacent, intersecting and/or overlapping lenses for forming images on different focal planes, obtained by the method specified in claim 1 .