Manufacture of surface relief structures
A method and apparatus for the etching of variable depth features in a substrate is described. Movement of the substrate relative to an etchant (e.g. into or out of the etchant) during the etching process is utilised to provide a varying etch time, and hence depth, across the substrate, and in various examples this is enabled without requiring a varying mask.
1. A method of etching a blazed surface relief structure in a substrate, the method comprising:
moving the substrate between a first position and a second position in an etching system, wherein in the first position only a first part of the area to be etched is exposed to an etchant, wherein the etchant is an anisotropic etchant, and in the second position the area to be etched is exposed to the etchant such that the first part of the area to be etched is exposed to the etchant for a longer period of time than at least one other part of the area to be etched, and wherein the movement is defined according to an etching profile, both the movement of the substrate and an orientation of the substrate are relative to a surface of the etchant defined according to the etching profile; and
removing the substrate from the etchant when etching is complete;
wherein the surface relief structure comprises a variable depth etching profile.
2. The method according to claim 1 , wherein moving the substrate between the first position and the second position in the etching system comprises either moving the substrate from the first position to the second position or moving the substrate from the second position to the first position.
3. The method according to claim 1 , wherein the etchant includes a fluid.
4. The method according to claim 1 , wherein prior to moving the substrate between the first position and the second position, the method comprises: preparing the substrate with an etch-resist mask.
5. The method according to claim 4 , wherein after removing the substrate from the etchant, the method comprises: removing any remaining etch-resist mask from the substrate.
6. The method according to claim 1 , wherein the movement between the first position and the second position is along an axis substantially perpendicular to a surface of the etchant.
7. The method according to claim 1 , wherein the etching profile is a non-linear profile.
8. The method according to claim 1 , wherein the movement between the first position and the second position comprises a series of discrete steps.
9. The method according to claim 8 , wherein the time between each step is variable.
10. The method according to claim 1 , wherein the movement between the first position and the second position comprises a continuous movement.
11. The method according to claim 1 , wherein the surface relief structure is an optical grating.
12. The method according to claim 11 , wherein an axis of movement between the first position and the second position is aligned with an axis of the grating.
13. The method according to claim 1 , wherein the surface relief structure is an array of facets.
14. The method according to claim 1 , wherein a resulting structure with the surface relief structure is an optical master.
15. The method according to claim 1 , wherein the substrate is a substrate formed of a crystalline material.
16. The method according to claim 1 , wherein the substrate is an off-axis silicon wafer.
17. The method according to claim 1 , wherein moving the substrate between the first position and the second position in the etching system is the first time the substrate is etched, such that the substrate is un-etched immediately prior to moving the substrate between a first position and a second position in the etching system.
18. A method of etching a nanostructure-based surface relief structure in a substrate, the method comprising:
moving the substrate between a first position and a second position in an etching system, wherein in the first position only a first part of the area to be etched is exposed to an anisotropic etch process, and in the second position at least one other part of the area to be etched is exposed to the anisotropic etch process such that the first part of the area to be etched is etched for a longer period of time than the at least one other part of the area to be etched, and wherein the movement is defined according to an etching profile, both the movement of the substrate and an orientation of the substrate are relative to a surface of the etchant defined according to the etching profile; and
in response to the anisotropic etch process being complete, removing the substrate from the anisotropic etch process;
wherein the surface relief structure comprises a variable depth etching profile;
wherein moving the substrate between the first position and the second position in the etching system comprises either moving the substrate from the first position to the second position or moving the substrate from the second position to the first position.