This study develops a parametric system transfer function (STF) model using scalar diffraction theory and Fourier optics to address the loss of precision in image-based positioning caused by the diffraction limit on marker scale. By fitting the model to observed STFs and employing deconvolution and a deep convolutional neural network, the method enhances image quality, overcoming traditional deconvolution limitations. Applied to critical dimension measurements, it improved radius accuracy for vias and pillars by 54.8% and reduced displacement measurement bias by 36.4%. The development particularly benefits automatic optical inspection (AOI) for quality control in semiconductor manufacturing.
A new non-integral optical scatterometry technique has been introduced to circumvent issues with traditional methods in the critical dimension (CD) characterization of micro and nano-structures in semiconductor inspections. This method uses the high spatial coherence of the laser source, and an adjustable numerical aperture (NA) for effective beam shaping, enabling precise measurement of high-aspect-ratio structures. It incorporates a model-based approach with a virtual optical system and the Finite- Difference Time-Domain (FDTD) method for multiple CD characterizations, improving measurement precision. Early tests indicate a minimal average bias of 1.74% from calibrated references and standard deviations within 7 nm.
A neural network-assisted spectral scatterometry method is presented to measure multi-dimensional critical dimensions (CDs) on high aspect ratio (HAR) structures with micron or submicron scales. With the rise of 3D integrated circuit packaging, there is a need for accurate characterization of HAR sub-micron structures. This method uses DUV scatterometry and a broadband light source from DUV to visible light to gather multi-channel reflection data. The inverse modeling method and artificial neural network model enable accurate measurement of multiple CDs of test structures. The results showed accurate measurement of deep trench critical dimensions with a nominal line width of 0.6 μm and aspect ratio up to 5:1, with accuracy within a few nanometers comparable to SEM results using the same sample.
The article presents a novel optical metrology method for accurate critical dimension (CD) measurement of sub-micrometer structures with high spatial resolution and light efficiency. The proposed method takes advantage of the spatially coherent nature of the supercontinuum laser to detect submicron-scale structures with high aspect ratios. By using the method, CD measurement of individual microstructures such as vias and redistribution layers (RDL) becomes achievable when a high magnification optical configuration is incorporated. Proved by a test run on measuring submicron structures with linewidths as small as 0.7 μm and an aspect ratio over 4, the measurement precision of the depth can be kept within a few nanometers.
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