Materials and methods for forming nano-structures on substrates
Materials and methods useful in forming nano-scale features on substrates, and articles such as optical films incorporating such nano-scale patterned substrates.
1. A method of forming an etched nano-scale pattern on a substrate, the method comprising:
(i) providing a multi-layer material stack comprising
(a) a first substrate having a patterned surface, the patterned surface of the first substrate including one or more recessed features, each recessed feature adjoining at least one plateau feature extending away from the recessed feature;
(b) a masking layer overlaying at least a portion of the patterned surface of the first substrate;
(c) a first etch resist comprising a first etch resistant material overlaying the masking layer;
(d) a pattern transfer layer overlaying at least a portion of the first etch resist;
(e) a second etch resist comprising a second etch resistant material overlaying the pattern transfer layer; and
(f) a second substrate overlaying the second etch resist;
(ii) removing the patterned surface of the first substrate from the masking layer and the first etch resist to create a patterned surface of the masking layer on the first etch resist, wherein the patterned surface of the masking layer comprises plateau features corresponding to the recessed features of the patterned surface of the first substrate surrounded by recessed areas corresponding to the plateau features of the patterned surface of the first substrate;
(iii) performing a first etching step to the patterned surface of the masking layer to remove the masking layer and the first etch resistant material in the recessed areas of the masking layer to expose the underlying pattern transfer layer without removing the first etch resistant material covered by the masking layer forming the plateau features of the masking layer, thereby forming a first etched nanoscale pattern on the pattern transfer layer, wherein the first etched nano-scale pattern comprises a plurality of first nano-scale features; and
(iv) performing a second selective etching step to remove the pattern transfer layer in the recessed areas exposing the second etch resist layer and to remove the masking layer in the plateau regions to expose the first etch resist layer thereby forming a second etched nanoscale pattern on the second substrate, wherein the second etched nano-scale pattern comprises a plurality of second nano-scale features;
wherein each second nano-scale feature exhibits at least one dimension from 1 nm to 900 nm; and
wherein the second substrate is not etched.
2. The method of claim 1 , wherein the first etching step is carried out using reactive ion etching, high density RF inductive plasma etching, high density linear ion plasma etching, microwave plasma etching, linear microwave plasma etching, helicon wave plasma etching, ion-beam milling, pulsed ion beam etching, pulsed reactive ion etching, or a combination thereof.
3. The method of claim 1 , wherein the first etching step is a reactive ion etch in a fluorine-containing environment and the second selective etching step is a reactive ion etch in an oxygen-containing environment.
4. The method of claim 3 further comprising back-filling the second etched nano-scale pattern with a high refractive index layer comprising a material having a refractive index of at least 1.7.
5. The method of claim 4 , wherein the high refractive index layer is deposited by chemical vapor deposition, atomic layer deposition, liquid coating, or a combination thereof.
6. The method of claim 3 , wherein an aspect ratio of the second etched pattern is at least 2.5:1.
7. The method of claim 1 , wherein providing the multi-layer material stack comprises coating the masking layer onto the patterned surface of the first substrate, then laminating masking layer to the first etch resist layer, then solidifying the masking layer.
8. The method of claim 1 , wherein at least one of the first substrate and the second substrate is a flexible substrate.
9. The method of claim 1 , wherein providing the multi-layer material stack comprises modifying the surface of the first etch resist to increase adhesion to the masking layer.
10. The method of claim 1 , wherein providing the multi-layer material stack comprises applying a coating to modify a surface composition of one or more of: the patterned surface, the first etch layer, the pattern transfer layer, the second etch layer or the second substrate to modify the surface.
11. The method of claim 1 , wherein the method is carried out on a roll of the multi-layer material stack, (iii) performing a first etching step is performed using a substantially continuous roll-to-roll processes, and (iv) performing the second selective etching step is performed using a substantially continuous roll-to-roll process.