Formation of OVD Using Laser Interference Lithography
Keywords:optically variable devices (OVDs), laser interference lithography (LIL), submicron period diffraction gratings, diffraction efficiency.
In the present research we have fabricated and investigated optically variable devices (OVDs) (a system of submicron
period surface relief diffraction gratings). For this purpose we have recorded interference pattern of two HeCd laser
beams through a set of masks, forming contours of the image, in the photoresist (holographic technique). Changing the
angles between the interfering beams we have achieved 0.7, 0.8, 0.9 and 1.2 μm period diffraction gratings. The
microrelief of diffraction gratings from the resist was transferred to the metallic stamp using vacuum deposition (of Ag,
Ni, Cu) and electrochemical nickel deposition. Diffraction efficiency of the diffraction gratings was measured
experimentally and linear dimensions of diffraction gratings were defined by scanning electron microscopy (SEM) and
atomic force microscopy (AFM). The main experimental results were compared with the computer simulations where
the standard software (“PCGrate”) was employed to calculate diffraction efficiency of the different depth of diffraction
gratings for two wavelengths of the visible light. Influence of different sublayers used during the electrochemical
deposition on the parameters (period, depth and shape) of the submicron structures was defined
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