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Interferometric measurement system for cost effective e-beam writer
Řeřucha, Šimon ; Šarbort, Martin ; Lazar, Josef ; Číp, Ondřej
The reliability of nanometer track writing in the large scale chip manufacturing process depends mainly on a precise positioning of the e-beam writer moving stage. The laser interferometers are usually employed to control this positioning, but their complicated optical scheme leads to an expensive instrument which increases the e-beam writer’s manufacturing costs. We present a new design of an interferometric system useful in a currently developed cost effective e-beam writers. Our approach simplifies the optical scheme of known industrial interferometers and shifts the interference phase detection complexity from optical domain to the digital signal processing part. Besides the effective cost, the low number of optical components minimizes the total uncertainty of this measuring instrument. The scheme consists of a single wavelength DFB laser working at 1550 nm, one beam splitter, measuring and reference reflectors and one photo-detector at the interferometer output. The DFB laser is frequency modulated by slight changes of injection current while the interference intensity signal is processed synchronously. Our algorithm quantifies the phase as two sinusoidal waveforms with a phase offset equal to the quarter of the DFB laser wavelength. Besides the computation of these quadrature signals, the scale linearization techniques are used for an additional suppression of optical setup imperfections, noise and the residual amplitude modulation caused by the laser modulation. The stage position is calculated on basis of the DFB laser wavelength and the processed interference phase. To validate the precision and accuracy we have carried out a pilot experimental comparison with a reference interferometer over the 100 mm measurement range. The first tests promise only 2 nm deviation between simplified and the reference interferometer.
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Deflection Measurement by Position Detection of the Laser Beam
Šarbort, Martin ; Řeřucha, Šimon ; Jedlička, Petr ; Lazar, Josef
We present a high precision angular deflection measurement system based on a triangulation method which provides resolution below 1 microradian within a range of several degrees. It is based on a triangulation method and a numerical position detection of the laser beam spot on a CCD/CMOS sensor. The experimental results indicate that the assembled instrument achieves a measurement error of 0.12 microrad in the range ± 0.6 degrees over the period of one hour.
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Adaptive optics for control of the laser welding process
Mrňa, Libor ; Šarbort, Martin ; Řeřucha, Šimon ; Jedlička, Petr
The laser head with f xed focus optics is commonly used for the deep penetration laser welding. In such case the geometry and position of the beam waist are def ned by the focusing lens. If the laser beam incident on the focusing lens is not well collimated but divergent and its divergence can be varied by proper adaptive optical elements, then also the geometry and position of the focus will be changeable. In this way it is possible to affect the energy coupling from the laser beam to the keyhole walls and thus to control the geometry and quality of the weld. In this paper we present a theoretical and numerical study of the beam shaping by adaptive optics and its inf uence on the weld quality. For the CO2 laser welding machine the adaptive optics was realized by a deformable mirror and its effect was tested also experimentally. For the solid-state laser welding machine we designed a laser head with changeable distance between the optical f ber and the collimating lens and we simulated its performance.
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