Method of fabricating a polymer waveguide
A method of fabricating a waveguide device is disclosed. The method includes providing a substrate having an elector-interconnection region and a waveguide region and forming a patterned dielectric layer and a patterned redistribution layer (RDL) over the substrate in the electro-interconnection region. The method also includes bonding the patterned RDL to a vertical-cavity surface-emitting laser (VCSEL) through a bonding stack. A reflecting-mirror trench is formed in the substrate in the waveguide region, and a reflecting layer is formed over a reflecting-mirror region inside the waveguide region. The method further includes forming and patterning a bottom cladding layer in a wave-tunnel region inside the waveguide region and forming and patterning a core layer and a top cladding layer in the waveguide region.
1. A method of fabricating a polymer waveguide device, the method comprising:
providing a substrate having an electro-interconnection region and a waveguide region;
forming a patterned dielectric layer, a patterned redistribution layer (RDL), and a patterned passivation layer over the substrate in the electro-interconnection region;
bonding the patterned RDL to a vertical-cavity surface-emitting laser (VCSEL) through a bonding stack;
forming a reflecting-mirror trench in the substrate in the waveguide region, wherein the waveguide region has a reflecting-mirror region and a wave-tunnel region;
forming a reflecting layer over the patterned passivation layer, the patterned RDL, the reflecting-mirror region, and the wave-tunnel region;
forming a patterned bottom cladding layer over the reflecting layer in the wave-tunnel region; and
forming a patterned core layer and a patterned top cladding layer over the reflecting layer in the reflecting-mirror region and over the bottom cladding layer in the wave-tunnel region.
2. The method of claim 1 , wherein the substrate includes Si with a (100) crystal orientation.
3. The method of claim 1 , wherein the reflecting-mirror trench is formed with a 45° inclined slope sidewall profile in the Si (100) substrate.
4. The method of claim 3 , wherein the 45° inclined slope sidewall reflecting-mirror trench is formed with a larger than 30 um depth by a wet etch process including etchants from the group consisting of ethylene diamine pyrocatechol (EDP), potassium hydroxide (KOH), and tetramethyl ammonium hydroxide (TMAH).
5. The method of claim 1 , wherein the bottom and top cladding layers and the core layer each include a photo-sensitive polymer.
6. The method of claim 1 , wherein the core layer is configured to have a thickness of half or larger than the depth of the reflecting-mirror trench and have a refractive index 0.025 or more larger than the refractive index of the bottom/top cladding layers.
7. The method of claim 1 , wherein the bottom and top cladding layers and the core layer are selected to be transparent to a wavelength from 600 nm to 1600 nm.
8. The method of claim 1 , wherein the bottom and top cladding layers and the core layer are selected to have a less than 2% volume and thickness variation during the bonding process.
9. The method of claim 1 , wherein the bottom and top cladding layers and the core layer are deposited by a spin-on coating technique.
10. The method of claim 1 , wherein the bottom and top cladding layers and the core layer are patterned by a photolithography technique, wherein the bottom cladding layer is patterned to be formed at the wave-tunnel region only, and the core layer and the top cladding layer are patterned to be formed at the reflecting-mirror region and the wave-tunnel region.
11. The method of claim 1 , wherein the bonding of the patterned RDL to the VCSEL through the bonding stack includes coupling the bonding stack to the patterned RDL through the reflecting layer.
12. A method of fabricating a polymer waveguide device, the method comprising:
providing a substrate having an electro-interconnection region and a waveguide region;
forming a patterned dielectric layer, a patterned redistribution layer (RDL), and a patterned passivation layer over the substrate in the electro-interconnection region;
bonding the patterned RDL to a vertical-cavity surface-emitting laser (VCSEL) through a bonding stack;
forming a 45° inclined sidewall reflecting-mirror trench in the substrate in the waveguide region, wherein the waveguide region having a reflecting-mirror region and a wave-tunnel region;
forming a reflecting layer over the patterned passivation layer, the patterned RDL, the reflecting-mirror region, and the wave-tunnel region;
performing spin-on coating and lithography patterning techniques to form a patterned bottom cladding layer over the reflecting layer in the wave-tunnel region; and
performing spin-on coating and lithography patterning processes to form a patterned core layer and a patterned top cladding layer in the waveguide region.
13. The method of claim 12 , wherein a vacancy space is formed above the reflecting layer in the reflecting-mirror region.
14. The method of claim 13 , wherein a functional element is built in the vacancy space.
15. The method of claim 12 , wherein the bonding of the patterned RDL to the VCSEL through the bonding stack uses the reflecting layer as a wetting layer.
16. A polymer waveguide device comprising:
a substrate having an electro-interconnection region and a waveguide region;
a patterned dielectric layer disposed over the substrate in the electro-interconnection region;
a patterned redistribution metal layer (RDL) disposed over the dielectric layer;
a patterned passivation layer disposed over the patterned RDL;
a bond stack over the patterned RDL, through which a wave source connects to the patterned RDL;
a reflecting-mirror trench in the substrate, with a 45° inclined sidewall in a reflecting-mirror region and a flat bottom in a wave-tunnel region;
a reflecting layer disposed over the patterned passivation layer, the patterned RDL, the reflecting-mirror region, and the wave-tunnel region;
a patterned bottom cladding layer disposed over the reflecting layer in the wave-tunnel region by spin-on coating and photolithography techniques; and
a patterned core layer and a patterned top cladding layer disposed over the reflecting-mirror region and the wave-tunnel region by spin-on coating and photolithography techniques.
17. The polymer waveguide device of claim 16 , wherein the patterned core layer has a refractive index of about 0.025 larger than a refractive index of the patterned bottom and top cladding layers.
18. The polymer waveguide device of claim 16 , wherein the patterned bottom and top cladding layers and the patterned core layer are transparent to a wavelength from 600 nm to 1600 nm.
19. The polymer waveguide device of claim 16 , configured such that a light beam from the wave source passes through the patterned top cladding layer and the patterned core layer, reflect 90° on a surface of the reflecting-mirror region, and passes within the patterned core layer in the wave-tunnel region.
20. The polymer waveguide device of claim 16 , wherein the bond stack is coupled to the patterned RDL through the reflecting layer.