Photolithographic patterning of polymeric materials
The invention comprises methods for the photolithographic patterning of features in a photo-curable polymer composition coated onto a plastic substrate. In one embodiment of this invention, the plastic substrate is coated with a reflective film such as a metallic barrier. In another embodiment, the plastic substrate is coated or co-extruded with a polymer barrier layer containing an additive that absorbs the photo-curing radiation. In yet another embodiment the plastic substrate contains an intrinsic additive that absorbs the photo-curing radiation. Combinations of these embodiments are also within the scope of this invention. The methods of the present invention may be advantageously applied to the fabrication of optical waveguides comprising a photo-curable polymer supported on a plastic substrate, but are applicable to the fabrication of any device or object comprising a photo-curable polymer supported on a plastic substrate.
1. A method for patterning a radiation-curable polymer supported on a plastic substrate, comprising the steps of
depositing a radiation-curable polymer onto a plastic substrate; and
imagewise exposing to curing energetic radiation, at least a portion of said radiation-curable polymer to provide a cured polymer region and an unexposed polymer region, wherein said plastic substrate is shielded from said radiation by one or more shielding means selected from the group consisting of: i) an additive designed to absorb said energetic radiation; and ii) a barrier layer opaque to said energetic radiation, wherein said barrier layer is between said radiation-curable polymer and said substrate, wherein said plastic substrate is chosen from a group consisting of: polyethylene terephthalate and a polycarbonate, wherein said radiation-curable polymer is a siloxane polymer; and
allowing the shielding means to shield the plastic substrate from the radiation to prevent gap filling between cured polymer regions or undesirable roughness at the boundary of said cured polymer regions.
2. A method according to claim 1 wherein said radiation-curable polymer layer comprises at least one monomer, oligomer or polymer bearing at least one functional group capable of undergoing addition polymerisation, and at least one photo-initiator.
3. A method according to claim 2 , wherein the at least one photo-initiator is a free radical photo-initiator.
4. A method according to claim 1 wherein the cured polymer region and the unexposed radiation-curable polymer region have a refractive index differential of at least 0.003.
5. A method according to claim 1 , further comprising the step of applying a solvent to remove said unexposed polymer region.
6. A method according to claim 1 , wherein said additive is diffused into the surface of said plastic substrate.
7. A method according to claim 2 , wherein the at least one functional group is an ethylenically unsaturated group.
8. A method according to claim 7 , wherein the ethylenically unsaturated group is selected from methacrylate, acrylate, styrene, vinyl, or vinyl ether groups.
9. A method according to claim 2 , wherein the at least one functional group is an epoxy group.
10. A method according to claim 1 , further comprising the step of depositing a lower cladding layer onto the plastic substrate prior to the deposition of the radiation-curable polymer layer.
11. A method according to claim 10 , wherein said lower cladding layer comprises a radiation-curable polymer.
12. A method according to claim 1 , further comprising a step of depositing an upper cladding layer onto the patterned radiation-cured polymer layer.
13. A method according to claim 12 , wherein said upper cladding layer comprises a radiation-curable polymer.
14. A method according to claim 1 , wherein said barrier layer comprises a metal film.
15. A method according to claim 1 , wherein said barrier layer comprise a polymer containing an additive that absorbs said energetic radiation.
16. A method according to claim 15 , wherein said barrier layer is co-extruded with said plastic substrate.
17. A method for photo-patterning a UV-curable polymer supported on a plastic substrate, comprising the steps of:
depositing a UV-curable polymer onto a plastic substrate;
imagewise exposing to UV radiation through a patterning mask, at least a portion of said UV-curable polymer to provide at least one cured polymer region and at least one unexposed UV-curable polymer region;
allowing the plastic substrate to be shielded from the radiation by adding to the substrate an additive selected to absorb UV to prevent gap filling between cured polymer regions or undesirable roughness at the boundary of said cured polymer regions; and
applying a solvent to remove unexposed UV-curable polymer from said unexposed UV-curable polymer region; wherein said plastic substrate is chosen from a group consisting of: polyethylene terephthalate and a polycarbonate, wherein said UV-curable polymer is a siloxane polymer.
18. A method for photo-patterning a UV-curable polymer supported on a plastic substrate, comprising the steps of:
depositing a UV curable polymer onto a plastic substrate;
imagewise exposing to UV radiation through a patterning mask, at least a portion of said UV-curable polymer to provide at least one cured polymer region and at least one unexposed UV-curable polymer region;
allowing the plastic substrate to be shielded from the radiation by a barrier layer opaque to said UV to prevent gap filling between cured polymer regions or undesirable roughness at the boundary of said cured polymer regions; and
applying a solvent to remove unexposed UV-curable polymer from said unexposed UV-curable polymer region; wherein said barrier layer is between said UV-curable polymer and said substrate, wherein said plastic substrate is chosen from a group consisting of: polyethylene terephthalate and a polycarbonate, wherein said UV-curable polymer is a siloxane polymer.
19. A method according to claim 18 , wherein said barrier layer comprises a metal film.
20. A method according to claim 18 , wherein said barrier layer comprises a polymer with an additive that absorbs UV radiation.
21. A method according to claim 20 , wherein said barrier layer is co-extruded with said plastic substrate.