Gratings with variable depths for waveguide displays

Abstract

A manufacturing system for fabricating self-aligned grating elements with a variable refractive index includes a patterning system, a deposition system, and an etching system. The manufacturing system performs a lithographic patterning of one or more photoresists to create a stack over a substrate. The manufacturing system performs a conformal deposition of a protective coating on the stack. The manufacturing system performs a deposition of a first photoresist of a first refractive index on the protective coating. The manufacturing system performs a removal of the first photoresist to achieve a threshold value of first thickness. The manufacturing system performs a deposition of a second photoresist of a second refractive index on the first photoresist. The second refractive index is greater than the first refractive index. The manufacturing system performs a removal of the second photoresist to achieve a threshold value of second thickness to form a portion of an optical grating.

What is claimed is: 
     
         1 . A manufacturing system comprising:
 a first patterning system configured to perform a first lithographic patterning of a first photoresist deposited over a substrate;   a second patterning system configured to perform a second lithographic patterning of a second photoresist deposited on the patterned first photoresist, the second lithographic patterning creating a modified second photoresist with a plurality of heights relative to the substrate; and   an etching system configured to perform a partial removal of the substrate based on a plurality of heights in the modified second photoresist, the partial removal forming a nanoimprint mold comprising a plurality of different etch depths and one or more duty cycles.   
     
     
         2 . The manufacturing system of  claim 1 , wherein the patterning system is configured to:
 perform a transfer of a pattern in the nanoimprint mold onto an optical waveguide, the transfer of the pattern in the nanoimprint mold forming an optical grating comprising the plurality of different etch depths and the one or more duty cycles.   
     
     
         3 . The manufacturing system of  claim 1 , wherein the second photoresist is a gray-scale photoresist lithographically patterned using a gray-scale mask. 
     
     
         4 . The manufacturing system of  claim 3 , further comprising:
 a deposition system configured to perform a deposition of a metal layer over a second substrate; and   wherein the etching system adjusts a thickness of the deposited metal layer based on an erosion process performed by a 1D ion beam scanning the metal layer, and the adjusted thickness of the deposited metal layer forms a portion of the gray-scale mask.   
     
     
         5 . The manufacturing system of  claim 3 , further comprising:
 a deposition system configured to perform a deposition of a third photoresist over a second substrate; and wherein   the patterning system is configured to perform a lithographic patterning of the third photoresist using a binary photomask,   the deposition system is configured to perform a deposition of the second material configured to block ultra-violet radiation through the gray-scale mask, and   the etching system is configured to perform a removal of the lithographically patterned third photoresist to form a portion of the second material on the second substrate, the removal of the lithographically patterned third photoresist forms a portion of the gray-scale mask with a threshold number of layers of the second material.   
     
     
         6 . The manufacturing system of  claim 3 , further comprising:
 a first deposition system configured to perform a deposition of the second material configured to block ultra-violet radiation through the gray-scale mask;   a second deposition system configured to perform a deposition of a third photoresist over a second substrate; and wherein   the patterning system is configured to perform a lithographic patterning of the third photoresist using a binary photomask, and   the etching system is configured to perform a partial removal of the second material deposited on the second substrate, the partially removed second material forming a portion of the gray-scale mask with a threshold number of layers of the second material.   
     
     
         7 . The manufacturing system of  claim 1 , further comprising:
 a deposition system configured to perform a deposition of a hard mask over the first photoresist; and wherein   the patterning system is configured to perform a lithographic patterning of the first photoresist and the hard mask.