Anti-reflective structures
An anti-reflective structure is formed on a surface to transmit incident light with minimal losses. The anti-reflective surface has a plurality of protrusions having a feature size smaller than the wavelength of incident light. The protrusions increase in height in either a sloped linear manner or in a curvilinear manner, and the protrusions repeat across the surface in at least one dimension to transmit the incident light. Gray scale lithography may be used to produce these patterns of protrusions in photoresist layers. High fidelity transfer of the protrusion patterns into the surfaces is accomplished by utilizing, for example, an electron cyclotron resonance plasma. Transmission values at such patterned surfaces maybe as high as 99.3%.
1. A method to manufacture an anti-reflective structure, which comprises:
providing a curved substrate;
forming a layer of photoresist over the curved substrate;
drawing a cone pattern in the photoresist; and
etching the photoresist, wherein the structure has a plurality of
protrusions having a feature size that is smaller than a wavelength of incident light and the protrusions are smoothly increasing In height in either a sloped linear manner or a curvilinear manner, wherein the curved substrate comprises a microlens fabricated using gray-scale lithography and an etching processes, and wherein the conical pattern has a pitch of approximately 2 μm and wherein the microlens is designed to operate in the long wavelength infrared (LWIR) and medium wavelength infrared (MWIR) frequencies.
2. The method of claim 1 , wherein drawing the cone pattern in the resist is performed using a gray scale mask.
3. The method of claim 1 , wherein the etching the photoresist is performed using reactive ion etching or electron cyclotron etching.
4. The method of claim 1 , wherein the protrusions have a sinusoidal cross-section or a triangular cross section.
5. The method of claim 1 , wherein the structure comprises at least one material selected from the group consisting of CdTe, CdZnTe, Cd 0.97 Zn 0.00 Te, Si, ZnSe and CdTe/Si.
6. The method of claim 1 , wherein the etching the photoresist is a two-step etching process.
7. The method of claim 6 , wherein the two-step etching process comprises a first etch having a lower DC bias input power and a second etch having a higher DC bias input power.
8. The method of claim 1 , wherein the etching the photoresist is performed using electron cyclotron resonance.
9. The method of claim 1 , wherein the protrusions repeat across a surface of the structure in at least one dimension to transmit the incident light.
10. The method of claim 1 , wherein the protrusions periodically repeat across a surface of the structure in two dimension.
11. The method of claim 1 , wherein the protrusions do not periodically repeat across a surface of the structure in two dimensions.
12. The method of claim 1 , wherein the microlens and conical pattern are applied to the photoresist simultaneously using gray-scale lithography.
13. A method of manufacturing an anti-reflective structure for at least one light wavelength, which comprises:
developing a conical pattern in a photoresist, where the photoresist has been deposited on a curved substrate; and
etching the photoresist, wherein the etching forms a conical pattern in the substrate made up of individual conical elements, the conical pattern in the substrate forming the anti-reflective structure in the curved substrate, where the conical elements have features sizes smaller than the wavelength, wherein the curved substrate comprises a microlens fabricated using gray-scale lithography, and wherein the conical pattern has a pitch of approximately 2 μm and wherein the microlens is designed to operate in the long wavelength infrared (LWIR) and medium wavelength infrared (MWIR) frequencies.
14. The method of claim 13 , wherein the etching of the photoresist is substantially complete.
15. The method of claim 13 , wherein the microlens and conical pattern are applied to the photoresist simultaneously using gray-scale lithography.
16. A method of manufacturing a microlens with an anti-reflective structure comprising:
fabricating a curved microlens using gray-scale lithography and an etching processes;
developing a conical pattern in a photoresist, where the photoresist has been deposited on the microlens; and
etching the photoresist, wherein the etching forms a conical pattern in the microlens made up of individual conical elements, the conical pattern in the microlens forming the anti-reflective structure in the curved substrate, wherein the conical pattern has a pitch of approximately 2 μm and an etch depth of ≧2 μm.
17. The method of claim 16 , wherein the microlens has a lens diameter of approximately 60 μm and a lens etch depth of approximately 5 μm.
18. The method of claim 17 , wherein the microlens has a hemispherical shape.
19. The method of claim 16 , wherein the microlens is designed to operate in the long wavelength infrared (LWIR) and medium wavelength infrared (MWIR) frequencies.
20. The method of claim 19 , wherein the microlens has a lens diameter of approximately 60 μm and a lens etch depth of approximately 5 μm.
21. The method of claim 16 , wherein the microlens and conical pattern are applled to the photoresist simultaneously using gray-scale lithography.