Research on modulation aberration numerical correction method of interference signals for high aspect ratio samples utilizing coherence scanning interferometry

Coherence scanning interferometry (CSI) is a non-destructive method for measuring the microstructure surface topography, but it fails to retrieve the bottom topography because the detection light is blocked by the sidewalls of the high aspect ratio (HAR) samples. Our team has proposed CSI technology with the detection light transparent to the sample to measure the surface topography thus ensuring the numerical aperture of the detection light with high throughput. However, a dedicated optical path to monitor the aberrations caused by the modulation from the sample is necessary and a complex optical path is added for aberration correction, which inevitably increases the design complexity and component costs of the optical system. This paper proposes a numerical correction method for sample-induced aberration of interference signals for HAR samples utilizing coherence scanning interferometry, without the need to modify the optical system. Aberration-modulated PSF is calculated for deconvolution of the interference signal affected by aberrations to solve the issues of low signal-to-noise ratio and interference fringe widening. The study integrates a rigorous numerical electromagnetic field solution to quantify the modulation aberrations of detection light by a transparent trench. A three-dimensional point spread function (3D-PSF) model based on the angular spectrum method (ASM) is employed to calculate the 3D-PSF of the system modulated by the sample, and then the impact of aberrations on the PSF is analyzed. The initial values of HAR trench width and depth are obtained from the raw interference signal collected by experiments and use the initial values to match the corresponding 3D-PSF. The HAR microstructure topography construction is completed based on the corrected interference signal. The effectiveness of our method is validated through experiments conducted on three HAR trench samples, with depths ranging from 100 µm to 300 µm and widths ranging from 10 µm to 30 µm.