A process that would include a combination of dry and wet chemical etching has been proposed for making facets for low-loss mirrors on silicon-on-insulator (SOI) optical waveguides. Heretofore, such facets have been made by a process that includes dicing and polishing. This process is time-consuming and thus not suitable for mass production; moreover, the optical quality of the facets is limited by the size of the powder grains used in polishing. (Although it is possible to make nearly optically perfect facets by cleaving, the yield achieved in practice is too low for mass production.)
The etching techniques in the proposed process are already used for mass production in the semiconductor and integrated-circuit industries, and are expected to yield facets with optical quality superior to that achievable by polishing. There are two versions of the proposed process. The main steps of the first version (see figure) are the following:
- Deposit an etching mask on top of the silicon active layer.
- Do a reactive-ion etch through the thickness of the silicon layer.
- Do either a dry etch or a wet chemical etch through the thickness of the SiO2 layer.
- Optionally, etch a shallow groove into the silicon substrate.
- Cleave the silicon substrate. A high yield can be obtained if one cleaves via an etched groove.
6. Remove the etching mask.
The main steps of the second version of the proposed process are nearly identical, except that one would turn the wafer upside-down and etch through the substrate first. The advantage of the second approach is that one would generate the facets by cleaving the silicon active layer; the quality of the facets would therefore be better than that achievable (by etching) in the first version.
This work was done by Chi Wu of Caltech for NASA's Jet Propulsion Laboratory.
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Refer to NPO-20757.