Reducing Line Edge Roughness in Si and SiN through plasma etch chemistry optimization for photonic waveguide applications

The LER and LWR of subtractively patterned Si and SiN waveguides was calculated after each step in the process. It was found for Si waveguides that adjusting the ratio of CF4: CHF3 during the hard mask open step produced reductions in LER of 26 and 43% from the initial lithography for isolated waveguides patterned with partial and full etches, respectively. However for final LER values of 3.0 and 2.5 nm on fully etched Si waveguides, the corresponding optical loss measurements were indistinguishable. For SiN waveguides, introduction of C4H9F to the conventional CF4/CHF3 measurement was able to reduce the mask height budget by a factor of 5, while reducing LER from the initial lithography by 26%.