In the field of laser photolithography, automatic focusing is a key technology. The focusing degree of the writing light on the sample surface determines the quality of photolithography. In addition to the mask manufacturing in semiconductor industry, autofocus is also widely used in optical imaging and optical information reading. With the increasing demand of semiconductor market, it is necessary to reduce the cost of autofocus as much as possible on the premise of ensuring the accuracy. Dual-quadrant detector(DQD) is a kind of detector combining two photodetectors, in which the common edge of two photodetectors is usually a straight line. In this work, a defocusing detection method using a dual-quadrant detector is proposed, the expression of focusing error signal(FES) is defined. The relationship between defocus amount and FES is analyzed and simulated, accordingly. A focusing error detection system is established to demonstrate the theoretical analysis. The tracking range is up to 20μm, and the tracking accuracy is approximately 50. The theoretical and experimental results indicate that the defocusing detection method with a dual-quadrant detector takes into account the tracking range and tracking accuracy, and has good results. This technology is expected to be used in maskless laser direct writing lithography and optical imaging.
The available information which is sharply increased requires a long time-period and high-capacity preservation method. In this paper, we proposed a method to preserve miniature image in stack structure. A large number of information images with a minimum pixel size of 200 nm were transferred to an AIST thin film using a laser directly writing system. After clearness, the information region was retained and the non-information region was removed. The single-layer information region samples with a thickness of 0.15 mm have high contrast and high transmittance. After being stacked and packaged into a 52-layer structure, each layer information image can be read out directly by an optical microscopy. The tolerance of the material to acid, alkali, and temperature is tested, and the results show that this method has excellent information preservation performance. This work provides a promising solution for future information preservation.
Laser heat-mode lithography is very useful for the fabrication of micro/nanostructure-based optical elements. In laser heat-mode lithography, the pattern structures need to be transferred to the substrates by wet-etching or dry-etching method. In this work, a lift-off method for the pattern transfer in laser heat-mode lithography was proposed and studied. A desirable undercut profile was obtained by manipulating the thermal field profile of laser heat-mode exposure, and a lift-off of Cr layer with a thickness of 80 nm on a quartz glass substrate was achieved. The results indicated that laser heat-mode lithography with lift-off process is an effective method to transfer the pattern structures to Cr layer and generate a Cr-based hard mask, which is useful for the fabrication of micro/nanostructure-based optical elements.
The GeSbTe (GST) thin films are usually used as optical and electronic data recording materials. In this work, the GST thin films were used as both negative and positive resists, and the positive and negative tone pattern structures were fabricated on the GST thin films, accordingly. The GST films were first deposited on the substrate, then the laser exposures were conducted through a focused laser beam spot. For negative resist, a Tetramethyl ammonium hydroxide (TMAH) was used as developing solution. For positive resist, (NH4)2S was used as developing solution. The structure heights of positive and negative resists are 53 nm and 180 nm were obtained, respectively. This work provides an effective method for fabricating the micro/nanostructures of optical and electronic elements.
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