The paper presents a dual-beam interference lithography technology for fabrication of diffraction gratings for surface encoders by using cost-effective 405 nm blu-ray laser diodes. In this system, an amplitude division interferometer system is employed. A laser beam raying from a blu-ray laser diode is collimated and then divided into two beams by a beam splitter. These two beams are changed their propagation directions and interfere with each other. Generated interference fringes are exposed on the photoresist coated substrate. Grating line spacing d can be adjusted by changing the incident angle between these two beams. Grating width Wc that determines the measurement of the surface encoder is decided by the coherence length Lc of the laser diode and the grating line spacing d. Calculation and simulation were carried out to decide the grating width. Lc was experimentally obtained. A fabrication system was constructed to verify the feasibility of this technology. Diffraction gratings with a 2.5 micron line spacing and a 2.5 mm width was obtained.
A low-cost lithography technology is presented in this paper for fabrication of sub-micron order one-dimensional diffraction gratings. A Lloyd’s mirror interferometer which can generate stable interference fringes is used as fabrication tool. The Lloyd’s mirror interferometer is composed of a mirror and a substrate coated by photoresist, which are placed by nighty degrees. A plane wave is projected onto the Lloyd’s mirror and divided into two halves, one of which is directly projected onto the substrate and the other one reaches the substrate after being reflected by the mirror. These two beam interfere with each other and generate interference fringes, which are exposed onto the photoresist. After being developed, the exposed photoresist shows a one-dimensional surface-relief grating structures. In conventional lithography system based on the principle mentioned above, gas lasers, such as He-Cd laser are widely employed. The cost and footprint of such laser sources, however, are always high and bulky. A low-cost system by using cost-efficient 405 nm laser diodes is then proposed for solving these problems. A key parameter, coherence length that determines one-dimensional grating width is systematically studied. A fabrication system based on the interference lithography principle and 405 nm laser diodes is constructed for evaluation of the feasibility of using laser didoes as laser source. Gratings with 570 nm pitch are fabricated and evaluated by an atomic force microscope. Experiments results show that low-cost 405 nm laser diode is an effective laser source for one-dimensional grating fabrication.
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