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Sidewall roughness-caused optical loss of waveguides is one of the critical limitations to the proliferation of the silicon photonic integrated circuits in fiber-optic communications and optical interconnects in computers, so it is imperative to investigate the distribution characteristics of sidewall roughness and its impact upon the optical losses. In this article, we investigated the distribution properties of waveguide sidewall roughness (SWR) with the analysis for the three-dimensional (3-D) SWR of dielectric waveguides, and, then the accurate SWR measurements for silicon-on-insulator (SOI) waveguide were carried out with confocal laser scanning microscopy (CLSM). Further, we composed a theoretical/experimental combinative model of the SWR-caused optical propagation loss. Consequently, with the systematic simulations for the characteristics of optical propagation loss of SOI waveguides, the two critical points were found: (i) the sidewall roughness-caused optical loss was synchronously dependent on the correlation length and the waveguide width in addition to the SWR and (ii) the theoretical upper limit of the correlation length was the bottleneck to compressing the roughness-induced optical loss. The simulation results for the optical loss characteristics, including the differences between the TE and TM modes, were in accord with the experimental data published in the literature. The above research outcomes are very sustainable to the selection of coatings before/after the SOI waveguide fabrication.

This article reports on the limitation analyses for the sidewall angle (SWA) measurements of microstructures with a confocal laser scanning microscope (CLSM). Under the resolutions of three-dimensional imaging process of CLSM and its spatial frequency spectrum distribution, the optical phase signal of an object is studied to model the signal-noise-ratio (SNR) performance of measurements and the point spread function theory is applied to discuss the limitation to the measurement accuracy of SWA. Then, the characteristics of both the relative SNR performance and the measurement accuracy are numerically simulated with these two theoretical models. As a result, two important characteristics of CLSM measurements for SWA are found as that the relative SNR is quickly decreasing with SWA; the intrinsic measurement error linearly decreases with SWA. Furthermore, for a fabricated device sample having the waveguide dimension of 6  ×  10 µm2, with a scanning section of 10nm and a detector aperture of PH  =  0.3 Airy Unit, a CLSM image of 300  ×  300 µm2 is acquired and reconstructed, in which 10 waveguide channels is covered. For a selected channel, based on ten measurements the averaged values of the left and right SWAs are 85.68°  ±  0.32° and 86.59°  ±  0.24°, respectively, after being compensated with the intrinsic measurement errors. Finally, the distribution and uniformity of SWA values among the ten waveguide channels in the image are analyzed.

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For a multilayered configuration of SiO2 film created by plasma enhanced chemical vapor deposition (PECVD), the thermal stress and growth-caused stress are two intrinsic stresses. In this work, based on the interactions of all the layers of film, a nonlinearly distributed structural stress over a large substrate is found. The numerical simulations for the nonlinear distribution of the structural stress and the uniform distributions of the two intrinsic stresses are carried out. As a result, the tensile structural stress decreases by ∼4x105MPa from center to edge of a 6” silicon wafer and the compressive growth-caused stress increases by ∼5x105MPa corresponding to the growth-rate increase of 40nm/s, which matches a ∼120MPa distribution of residual compressive stress obtained with in-situ measurements of film samples. In simulations, it is also discovered that the initial curvature of substrate has an impressive influence on the later grown film.