Depth-modulated slanted gratings using gray-tone lithography and slant etch
An apparatus with a grating structure and a method for forming the same are disclosed. The grating structure includes forming a wedge-shaped structure in a grating layer using a grayscale resist and photo lithography. A plurality of channels is formed in the grating layer to define slanted grating structures therein. The wedge-shaped structure and the slanted grating structures are formed using a selective etch process.
1. A waveguide structure, comprising:
a substrate having a grating layer thereon;
a wedge-shaped structure formed in the grating layer; and
a plurality of channels formed in the grating layer, each channel partially defining a plurality of grating structures, wherein the plurality of channels are formed by a process comprising:
forming a wedge-shaped structure in the grating layer;
disposing a hardmask over the grating layer and a photoresist over the hardmask, the photoresist having an optical planarization layer (OPL) disposed thereunder;
forming grating lines, the forming of grating lines comprising:
performing a lithography process to pattern the photoresist to expose OPL portions of the OPL; and
removing the OPL portions exposed by the photoresist to form grating lines of the photoresist and OPL, wherein adjacent grating lines expose portions of the hardmask;
etching the portions of the hardmask to expose the wedge-shaped structure in the grating layer; and
etching exposed grating layer portions of the wedge-shaped structure to form the plurality of channels in the grating layer.
2. The structure of claim 1 , wherein a depth of the wedge-shaped structure changes linearly in a first direction and a second direction.
3. The structure of claim 1 , wherein a depth of the wedge-shaped structure changes non-linearly in a first direction and a second direction.
4. The structure of claim 1 , wherein each grating structure of the plurality of grating structures has a depth in a range of about 5 nm to about 700 nm.
5. The structure of claim 1 , wherein each grating structure of the plurality of grating structures is slanted at an angle in a range of about 0 degrees to about 70 degrees relative to a plane that is normal to a surface of an etch stop layer.
6. The structure of claim 1 , wherein the grating layer is formed from an optically transparent material having a refractive index of about 1.3 or higher.
7. The structure of claim 1 , wherein the wedge-shaped structure has a saddle-point shape.
8. The structure of claim 1 , wherein the wedge-shaped structure has an elliptic paraboloid shape with positive curvature.
9. A method of forming a waveguide structure comprising:
forming a wedge-shaped structure in a resist layer using grayscale lithography, the resist layer disposed over a grating layer;
performing a transfer etch process to form the wedge-shaped structure in the grating layer;
disposing a hardmask over the grating layer and a photoresist over the hardmask, the photoresist having an optical planarization layer (OPL) disposed thereunder, the OPL having a planar top surface;
forming grating lines, the forming of grating lines comprising:
performing a lithography process to pattern the photoresist to expose OPL portions of the OPL; and
removing the OPL portions exposed by the photoresist to form grating lines of the photoresist and OPL, wherein adjacent grating lines expose portions of the hardmask;
etching the portions of the hardmask to expose the wedge-shaped structure in the grating layer; and
etching exposed grating layer portions of the wedge-shaped structure to form a plurality of grating structures in the grating layer.
10. The method of claim 9 , wherein the wedge-shaped structure changes in depth along:
a first direction, a depth at peripheral regions of the wedge-shaped structure greater than a depth at a central region of the wedge-shaped structure; and
a second direction, a depth at the peripheral regions of the wedge-shaped structure is greater than a depth at the central region of the wedge-shaped structure, wherein the first direction is perpendicular to the second direction.
11. The method of claim 10 , wherein the depth of the wedge-shaped structure changes linearly in the first direction and the second direction.
12. The method of claim 10 , wherein the depth of the wedge-shaped structure changes non-linearly in the first direction and the second direction.
13. A method of forming a waveguide structure comprising:
forming a wedge-shaped structure in a resist layer using grayscale lithography, the resist layer disposed over a grating layer;
performing a transfer etch process to form the wedge-shaped structure in the grating layer;
disposing a hardmask over the grating layer and a photoresist over the hardmask, the photoresist having an optical planarization layer (OPL) disposed thereunder, the OPL having a planar top surface;
forming grating lines, the forming of grating lines comprising:
performing a lithography process to pattern the photoresist to expose OPL portions of the OPL; and
removing the OPL portions exposed by the photoresist to form grating lines of the photoresist and OPL, wherein adjacent grating lines expose portions of the hardmask;
etching the portions of the hardmask to expose the wedge-shaped structure in the grating layer; and
etching exposed grating layer portions of the wedge-shaped structure with a slant etch process to form a plurality of grating structures in the grating layer.
14. A method of forming a waveguide structure comprising:
forming a wedge-shaped structure in a grating layer;
disposing a hardmask over the grating layer and a photoresist over the hardmask, the photoresist having an optical planarization layer (OPL) disposed thereunder;
forming grating lines, the forming of grating lines comprising:
performing a lithography process to pattern the photoresist to expose OPL portions of the OPL; and
removing the OPL portions exposed by the photoresist to form grating lines of the photoresist and OPL, wherein adjacent grating lines expose portions of the hardmask;
etching the portions of the hardmask to expose the wedge-shaped structure in the grating layer; and
etching exposed grating layer portions of the wedge-shaped structure to form a plurality of grating structures in the grating layer.
15. The method of claim 14 , wherein the wedge-shaped structure changes in depth along:
a first direction, a depth at peripheral regions of the wedge-shaped structure greater than a depth at a central region of the wedge-shaped structure; and
a second direction, a depth at the peripheral regions of the wedge-shaped structure is greater than a depth at the central region of the wedge-shaped structure, wherein the first direction is perpendicular to the second direction.
16. The method of claim 14 , wherein a depth of the wedge-shaped structure changes linearly in a first direction and a second direction.
17. The method of claim 14 , wherein a depth of the wedge-shaped structure changes non-linearly in a first direction and a second direction.