Laser interference lithography (LIL) is a maskless lithography technique with many advantages such as simple optical design, low cost, maskless, infinite depth of focus, and large area patterning with single exposure. Compare to the tradition optical lithography, LIL is very suitable for applications which need periodic nanostructure, such as grating, light-emitting diode (LED), photonic crystals, etc. However, due to the principle of LIL, the exposure result is very sensitive to the light source and the environment vibration. Defects which perpendicular or parallel to the grating occurs when the LIL system is effect by the environment vibration. The reason that cause this defect is Moiré fringe. When the periodic structure is fabricated in an environment with vibration source, the grating structure will have a small angle rotational vibration and the Moiré fringe defect is formed. In order to eliminate the Moiré fringe defect, this paper developed a new LIL system with chopper and accelerometer. The accelerometer can measure the vibration frequency. And by setting the chopper frequency equal to the vibration frequency, the Moiré fringe defects can be eliminate. In this paper, we use a piezo stage to generate a stable vibration source with tunable frequency. In this way, we can produce a repeatable Moiré fringe defect. By setting the chopper frequency equal to the stage vibration frequency, the Moiré fringe defect can be eliminate. And we successfully fabricated large area periodic structure without any vibration defects. The periodic structure is 360nm pitch and the area is 2x3 cm2 .
This paper has developed the multi-beam laser interference lithography (LIL) system for nano/micro pattern sapphire substrate process (PSS/NPSS). However, the multi-beam LIL system is very sensitive to the light source and the vibration. When there is a vibration source in the exposure environment, the standing wave distribution on the substrate will be affected by the vibration and move in a certain angle. As a result, Moiré fringe defects occur on the exposure result. In order to eliminate the effect of the vibration, we use the software ANSYS to analyze the resonant frequencies of our multi-beam LIL system. Therefore, we need to design new multi-beam LIL system to raise the value of resonant frequencies. The new design of the multi-beam LIL system has higher resonant frequencies and successfully eliminates the bending and rotating effect of the resonant frequencies. As a result, the new multi-beam LIL system can fabricate large area and defects free period structures.
Laser interference lithography (LIL) is a great way to produce micro and nano scale periodic structures. The principle of LIL is that two or more coherent laser beams overlap with each other and form a standing wave in the space which can be recorded by the photoresist. However, due to the principle of LIL, exposure result is very sensitive to the light source, especially in large area exposure. Regular defects occurs in large area exposure result when the laser source has multiple longitudinal mode or mode hopping. Therefore, this paper design and build up an advanced achromatic interference lithography system to solve this problem. Due to the principle of achromatic interference lithography, the exposure result is no longer relative to the wavelength of the laser source, and the pitch of the periodic structures is half of the grating pitch. As a result, achromatic interference lithography is able to eliminate the regular defects caused by the unstable laser source. But traditional achromatic interference lithography system is not very efficient due to transmission lost and only first order light is used. This paper build up an advanced achromatic interference lithography system with two reflective blazed gratings. Because of the principle of the reflective blazed grating, we can improve the efficiency of our achromatic interference lithography system. In this paper, 20 mm2 of large area periodic structures with 420nm pitch and 130 nm linewidth have been successfully fabricated without any defects.
Laser interference lithography (LIL) is a maskless lithography technique with many advantages such as simple optical design, inexpensive, infinite depth of focus, and large area patterning with single exposure. However, the intensity of normal laser beam is Gaussian distribution. In order to obtain large area uniform structure, we have to expand the laser beam much bigger than the wafer and use only the center part of the beam. Resulting in wasting lots of energy and the production capacity decrease. In this study, we designed a beam shaping device which consists of two parallel fused silicon optical window with different coating on both side. Two optical window form an air thin film. When the expanded laser beam pass through the device, the beam will experience many refraction and reflection between two optical window and interference with each other. The transmittance of laser beam will depend on the incident angle. The output intensity distribution will change from Gaussian distribution to a flat top distribution. In our experiment, we combined the beam shaping device with a Lloyd’s mirror LIL system. Experiment results indicated that the LIL system with beam shaping device can obtain large area uniform pattern. And compare with the traditional Lloyd’s mirror LIL system, the exposure time is shorten up to 4.5 times. In conclusion, this study design a beam flattening device for LIL system. The flat top beam can improve the large area uniformity and the production capacity of LIL. Making LIL more suitable for industry application.