Height-modulated diffractive master plate and method of manufacturing thereof
The invention relates to a method of fabricating a master plate for producing diffractive structures and a master plate obtainable therewith. The method comprises providing a substrate having a periodic surface profile, filling the surface profile uniformly at least partly with filling material, and partially removing the filling material in order to produce a master plate having a periodic height-modulated surface profile formed by said substrate and said filling material. The invention allows for producing master plates capable of further producing gratings with variable diffraction efficiency.
1. A method of fabricating a master plate for producing diffractive structures, the method comprising:
providing a substrate having a periodic initial surface profile,
filling the initial surface profile uniformly at least partly with filling material, and
partially removing the filling material in order to produce a master plate having a periodic height-modulated surface profile formed by said substrate and said filling material, wherein
the initial surface profile comprises fill factor modulation, which is persisted in the height-modulated surface profile, and
wherein said removing of the filling material partially comprises:
applying a physical mask layer having an uneven height profile on the filling material, and
removing at each location said mask layer and an underlying filling material, so as to replicate the height profile of the mask layer to corresponding sections of the filling material in order to produce said height-modulated surface profile.
2. The method according to claim 1 , wherein said removing of the filling material partially comprises using grayscale lithographic removal of said filling material in order to produce said height-modulated surface profile.
3. The method according to claim 1 , wherein said height-modulated surface profile comprises at least two distinct segments having different profile heights.
4. The method according to claim 1 , wherein said height-modulated surface profile comprises a lateral height gradient profile, such as linear profile.
5. The method according to claim 1 , wherein the height modulation of said height-modulated surface profile takes place at least in a periodic dimension of the surface profile.
6. The method according to claim 1 , wherein the initial surface profile is entirely filled with said filling material in order to planarize the substrate before said removal.
7. The method according to claim 1 , further comprising providing said periodic initial surface profile to the substrate by providing a substrate plate and removing material from the substrate plate, for example by electron beam lithography, or adding material to the plate, for example by nanoimprinting.
8. The method according to claim 1 , wherein the initial surface profile is a binary profile.
9. The method according to claim 1 , wherein the initial surface profile is a non-binary profile, such as a triangular profile or slanted profile.
10. The method according to claim 1 , wherein said filling material is removed different amounts within different lateral segments in one dimensions only so as to produce a one-dimensionally height-modulated surface profile.
11. The method according to claim 1 , wherein said filling material is removed different amounts within different lateral segments in two lateral dimensions so as to produce a two-dimensionally height-modulated surface profile.
12. The method according to claim 1 , wherein the initial surface profile is periodic in one dimension or in two dimensions.