The laser stealth dicing system is a unique wafer processing system to enable high-throughput and debris-free wafer dicing. In the laser stealth dicing system, a focused pulsed laser forms a modification layer and cracks inside a silicon wafer. During pulsed laser radiation and wafer scanning, cracks formed in the previous shot interfere with a focusing laser pulse on a defocus plane. As a result, a part of interacted laser beam scatters, generating back-side splash defects on the device layer. An asymmetric beam shaping of defocused spot becomes necessary to minimize the splash defects. At the same time, the focused spot should maintain sufficiently small focused spot size to generate a modified layer inside the silicon wafer. This paper presents a concept of an innovative focusing spot shaping with an asymmetrical pupil phase filter which is individually optimized for both defocused and focused spots. We optimized the phase filter to generate a threedimensionally- asymmetrical focused spot which deforms defocused spot with a near diffraction-limited focal spot size. The through-focus spot shaping technique is enable to minimize splash defects and improve the yield of the laser wafer dicing process.
We propose an optical method for uroflowmetry, exploiting the laser speckle contrast imaging (LSCI) technique onto an intermediate tubing apparatus having an elastic wall that can sensitively respond to flow-induced shedding vortices. Based on the method, we devised and fabricated an elastic-walled U-shaped tubing apparatus (EWUSTA), using the three-dimensional printing technique. We utilized the spatiotemporal contrast scheme for the LSCI as a fast and reliable computational algorithm. We investigated three different materials of flex-vinyl, ninja-flex, and natural rubber latex for the elastic wall of the EWUSTA in steady flow conditions, and verified that their optimal operational ranges could extend up to 7, 15, and 25 ml/s, respectively. We characterized the natural-rubber-latex-based EWUSTA in dynamic flow conditions in comparison with a commercial reservoir-weight-transducer-based gravimetric flowmeter, and verified its feasibility. We stress that the proposed method can offer precise and accurate information on flow dynamics. In addition, we found that the upper limit of the optimal operational range of the proposed apparatus had strong correlation with the tensile strength of the elastic-wall material. We reckon that the proposed and demonstrated method has great potential not only for uroflowmetry but also for other flow-related medical and industrial applications.
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