Techniques for manufacturing slanted structures
A surface-relief grating comprises a plurality of grating ridges including a first material, and a layer of a second material conformally deposited on surfaces of the plurality of grating ridges. A first region of the surface-relief grating is characterized by a first grating depth and a first duty cycle greater than a first threshold value. A second region of the surface-relief grating is characterized by a second grating depth and a second duty cycle lower than a second threshold value that is lower than the first threshold value. A difference between the first grating depth and the second grating depth is less than 20% of the second grating depth.
1. A surface-relief grating comprising:
a plurality of grating ridges including a first material; and
a layer of a second material conformally deposited on surfaces of the plurality of grating ridges,
wherein:
the surface-relief grating is a contiguous grating in a contiguous area of a substrate;
a first region of the surface-relief grating is characterized by a first grating depth and a first duty cycle greater than a first threshold value;
a second region of the surface-relief grating is characterized by a second grating depth and a second duty cycle lower than a second threshold value that is lower than the first threshold value; and
a difference between the first grating depth and the second grating depth is less than 20% of the second grating depth.
2. The surface-relief grating of claim 1 , wherein the first threshold value is greater than 0.7.
3. The surface-relief grating of claim 2 , wherein the first threshold value is greater than 0.8.
4. The surface-relief grating of claim 1 , wherein the second threshold value is lower than 0.5.
5. The surface-relief grating of claim 4 , wherein the second threshold value is lower than 0.4.
6. The surface-relief grating of claim 1 , wherein the first threshold value is greater than 0.8 and the second threshold value is lower than 0.4.
7. The surface-relief grating of claim 1 , wherein a thickness of the layer of the second material is less than 20% of a period of the surface-relief grating.
8. The surface-relief grating of claim 1 , wherein the first region of the surface-relief grating is characterized by a slant angle greater than 30°.
9. The surface-relief grating of claim 1 , wherein the second grating depth is greater than 100 nm.
10. The surface-relief grating of claim 1 , wherein the first material includes at least one of metal alloy, silicon, amorphous silicon, SiO 2 , Si 3 N 4 , titanium oxide, alumina, TaO x , HfO x , SiC, SiO x N y , spin-on carbon (SOC), amorphous carbon, diamond-like carbon (DLC), or an organic material.
11. The surface-relief grating of claim 1 , wherein the second material includes at least one of SiO 2 , Al 2 O 3 , TiO 2 , HfO 2 , ZrO, ZnO 2 , or Si 3 N 4 .
12. The surface-relief grating of claim 1 , wherein the second material has a higher refractive index than the first material.
13. The surface-relief grating of claim 1 , wherein the layer of the second material is characterized by a variation in thickness less than 10% of an average thickness of the layer of the second material.
14. The surface-relief grating of claim 1 , wherein the layer of the second material is conformally deposited on the surfaces of the plurality of grating ridges by atomic layer deposition or plasma enhanced chemical vapor deposition (PECVD).
15. The surface-relief grating of claim 1 , wherein the first region of the surface-relief grating is characterized by a grating period less than 200 nm.