Process flow for fabricating integrated photonics optical gyroscopes
Aspects of the present disclosure are directed to configurations of compact ultra-low loss integrated photonics-based waveguides for optical gyroscope applications, and the methods of fabricating those waveguides for ease of large scale manufacturing. Four main process flows are described: (1) process flow based on a repeated sequence of oxide deposition and anneal; (2) chemical-mechanical polishing (CMP)-based process flow followed by wafer bonding; (3) Damascene process flow followed by oxide deposition and anneal, or wafer bonding; and (4) CMP-based process flows followed by oxide deposition. Any combination of these process flows may be adopted to meet the end goal of fabricating optical gyroscope waveguides in one or more layers on a silicon substrate using standard silicon fabrication technologies.
1. A method of fabricating integrated photonics optical gyroscopes, comprising:
providing a silicon substrate with a first oxide layer thereon, wherein the first oxide layer acts as a lower cladding of a waveguide;
forming a patterned silicon nitride (SiN) layer on top of the first oxide layer, the patterned SiN layer acting as a core of the waveguide;
forming a second oxide layer on top of the patterned SiN layer, wherein the second oxide layer is formed by repeating the following sequence for a predetermined number of times:
depositing a first sub-layer of the second oxide for a predetermined thickness;
annealing the deposited first sub-layer of the second oxide at a predetermined temperature for a predetermined period of time to drive impurities out;
depositing a subsequent sub-layer of the second oxide for the predetermined thickness; and
after deposition of each subsequent sub-layer of the second oxide, annealing the deposited sub-layers at the predetermined temperature for the predetermined period of time to drive impurities out, wherein each sub-layer is 0.1-0.2 μm thick; and
polishing the second oxide layer down to a reduced thickness by chemical mechanical polishing (CMP).
2. The method of claim 1 , wherein a wafer is bonded on top of the second oxide layer polished down to the reduced thickness by CMP.
3. The method of claim 2 , wherein the CMP causes to achieve a desired surface roughness for wafer bonding.
4. The method of claim 2 , wherein the wafer bonded on top of the second oxide layer comprises a fused silica wafer.
5. The method of claim 2 , wherein the wafer bonded on top of the second oxide layer acts as at least a part of an upper cladding of the waveguide.
6. The method of claim 1 , wherein forming a patterned silicon nitride (SiN) layer on top of the first oxide layer comprises:
depositing SiN layer for a first thickness that is higher than a desired thickness of the waveguide core;
reducing the first thickness of the SiN layer by an additional CMP process to a second thickness, wherein the second thickness is the desired thickness of the waveguide core.
7. The method of claim 6 , wherein the second oxide layer is deposited after the additional CMP process to obtain the desired thickness.
8. The method of claim 1 , wherein the second oxide layer comprises oxide deposited using a precursor gas chosen from: TEOS, chlorinated source, or deuterated source.
9. The method of claim 8 , wherein the impurities that are driven out from the second oxide layer comprises hydrogen.
10. The method of claim 1 , wherein the predetermined temperature for annealing ranges from 1100-1300° C.
11. The method of claim 1 , wherein the predetermined period of time for annealing depends on thickness of each sub-layer.