| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2005: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Research Abstract |
We propose and demonstrate a fabrication process of Si photonic wire waveguides by selective oxidation of Si. In the proposed method, an optical waveguide pattern is delineated using a Si_3N_4 film on a SOI wafer, and the SOI wafer is thermally oxidized. The Si under the Si_3N_4 film is not oxidized and works as a core, and the Si without the Si_3N_4 film is oxidized and works as a clad. The roughness at the core/clad interface is smoothed while the oxidation process because of isotropic nature of thermal oxidation, and then the propagation loss is reduced.
When a 40 nm-thick Si_3N_4 film is used, the Si_3N_4 film is converted to SiO_2 and a portion of the Si layer is also oxidized after 7 hours wet oxidation at 1100℃. Although the Si is slightly oxidized, the thickness of the remaining Si layer is sufficient to fabricate Si photonic wire waveguides, and then the Si_3N_4 film can be used as an oxidation-resistant film.
A Si photonic wire waveguide is fabricated by using a 3 μm-wide Si_3N_4 film. Selective oxidation is clearly observed from the cross-sectional microscope image and the scanning microscope image. The propagation loss and the coupling loss of the fabricated waveguide are 6.3 dB/cm and 29.8 dB, respectively. As compared to the Si photonic wire waveguide fabricated by dry etching process, the propagation loss is decreased by 4 dB and the coupling loss is increased by 3 dB, and therefore the proposed method is useful to reduce propagation loss of the Si photonic wire waveguide. The increase of the coupling loss is attributed to reduced thickness of the Si layer during the oxidation process.
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