Angle-resolved spectral reflectometry with a digital light processing projector

Bridging Nanomanufacturing and Artificial Intelligence-A Comprehensive Review

Nanomanufacturing and digital manufacturing (DM) are defining the forefront of the fourth industrial revolution-Industry 4.0-as enabling technologies for the processing of materials spanning several length scales. This review delineates the evolution of nanomaterials and nanomanufacturing in the digital age for applications in medicine, robotics, sensory technology, semiconductors, and consumer electronics. The incorporation of artificial intelligence (AI) tools to explore nanomaterial synthesis, optimize nanomanufacturing processes, and aid high-fidelity nanoscale characterization is discussed. This paper elaborates on different machine-learning and deep-learning algorithms for analyzing nanoscale images, designing nanomaterials, and nano quality assurance. The challenges associated with the application of machine- and deep-learning models to achieve robust and accurate predictions are outlined. The prospects of incorporating sophisticated AI algorithms such as reinforced learning, explainable artificial intelligence (XAI), big data analytics for material synthesis, manufacturing process innovation, and nanosystem integration are discussed.

Angle-resolving spectral ellipsometry using structured light for direct measurement of ellipsometric parameters

We propose a compact angle-resolving spectral ellipsometry. Using the structured light generated from a digital micro-mirror device (DMD), what we believe to be a novel pattern is illuminated to the back focal plane of the high numerical aperture (NA) objective lens. As a result, ellipsometric parameters with fine resolution of both the wavelength and incidence angle domain can be directly measured. The incidence angle can be resolved by resolution under 1° ranging from 35° to 59° by the radius of the projected images. A spectrometer as a detector enables acquisition by the resolution of 0.7 nm from 410 to 700 nm, and the fiber reduces measurement spot size to a single micrometer. Additionally, the measurement process does not require any rotating optical components or moving parts, needing only digital modification of the projected image. This simplifies the sequences and reduces the measurement time. The 2D (angle of incidence and spectral domain) ellipsometric parameter plane measured by the proposed method was used to measure the thickness of various samples. The measurement result was verified in comparison with a commercial ellipsometer. The accuracy and precision of the result show that the proposed method is capable of precise measurement of thin films.

Polarized angle-resolved spectral reflectometry for real-time ultra-thin film measurement

We propose a polarized, angle-resolved spectral (PARS) reflectometry for simultaneous thickness and refractive-index measurement of ultra-thin films in real time. This technology acquires a two-dimensional, angle-resolved spectrum through a dual-angle analyzer in a single shot by radially filtering the back-focal-plane image of a high-NA objective for dispersion analysis. Thus, film parameters, including thickness and refractive indices, are precisely fitted from the hyper-spectrum in angular and wavelength domains. Through a high-accuracy spectral calibration, a primary PARS system was built. Its accuracy was carefully verified by testing a set of SiO₂ thin films of thicknesses within two µm grown on monocrystalline-Si substrates against a commercial spectroscopic ellipsometer. Results show that the single-shot PARS reflectometry results in a root-mean-square absolute accuracy error of ∼1 nm in film thickness measurement without knowing its refractive indices.

Single-sequence stable spectroscopic reflectometry using simultaneous measurement of incident light and reflected light

We proposed a new scheme of spectroscopic reflectometry (SR) that improves the stability with respect to the intensity variations of the incident light and simplifies the measurement procedure. The proposed method enables this by simultaneously measuring the incident light and the reflected light. Using the multi-order retarder, we modulate the incident light intensity into a high-frequency signal at the spectral domain. Even though the spectrometer measures the sum of reflected light and modulated incident light, each signal can be separately obtained using the Fourier transform. The proposed method is verified through the measurement of SiO₂ thin film on the Si substrate with various incident light intensities.

Robust incident angle calibration of angle-resolved ellipsometry for thin film measurement

Angle-resolved ellipsometry with back focal plane imaging has been found to be of increasing importance in recent industrial sensing by virtue of its rich information provided at various incident and azimuthal angles. To achieve high sensing accuracy, the incident angles of a back focal plane must be accurately calibrated. For this purpose, a simple and robust incident angle calibration method based on full-field Brewster angle fitting is proposed, without expensive tools or complex operations. With this method, a back focal plane image is first captured from boundary reflectance through a high-numerical-aperture objective. By extracting annular data from the image, radius-dependent ellipsometric parameters $ (\psi,{\Delta)}$ are calculated. At the end, the radii of the back focal plane are mapped to the angle of incidence by using a fitted Brewster angle as the reference. The method is validated by simulation and experiments using a homemade angle-resolved ellipsometer and a commercial spectroscopic ellipsometer. The results show that the proposed method provides a 75% error reduction approximately from generally used methods.