Research On Fabrication Processes And The Application Of High Aspect Ratio Nanooptics

With the development of nanometer science and technology, we have been living in the society with the hot topic of nanometer. Nanometer science and technology includes a number of areas, such as nano-material, nano-electronics, nano-optics (nano-photonics), nanotechnology, nanometer machinery and nanofabrication technologies. Nano-optics is a hotspot in recent years, which includes nanometer level limitation of materials, nanometer restrictions of the radiation, nano-processing technology and nano-devices. Nanofabrication technology is an important approach to carry out the development of nanometer science and technology. Since the discovery of X-ray, technologies related to X-ray have become one of the important tools for the study and research. In the1970, Smith of MIT developed X-ray lithography, which broke the resolution limitation of the traditional optical lithography. In this paper, fabrication processes of nano-optical devices with high aspect ratio were studied. Based on the fabrication processes, high aspect ratio polymer photonic crystal laser was fabricated.Based on X-ray lithography and soft X-ray lithography station of National Synchrotron Radiation Laboratory (NSRL), the main contents of this thesis are summarized as follows:1. A method of gap control for X-ray lithography has been proposed based on the principle of equal thickness interference. Experimental research has also been applied to verify it in the soft X-ray lithography station of NSRL.Principle and component of X-ray lithography has been introduced. Application of X-ray lithography need three parts, which are X-ray source, high precision X-ray mask and high resolution X-ray resist. Based on the technique parameters of soft X-ray lithography of NSRL, a method of controlling the gap between the mask and the sample has been proposed in this paper. This method can be divided in two steps. Firstly, an accessorial structure with the height of the gap is fabricated on the mask support to achieve a small gap. Then the principle of equal-thickness interference is applied to adjust the parallelism to ensure a uniform gap between the mask and the wafer. A detection light path was also established in the paper. It not only can be used to just the parallelism between the mask and the sample, but also can be used to detect stress of the mask caused by the heat during the lithography. This method is not only simple and low cost, but also can control a small and uniform gap accurately, so that the quality of pattern replication during X-ray lithography can be improved and the mask can also be protected. Based on this method, a small and uniform gap is realized and high aspect ratio nanostructures (HARNS) are fabricated.2. In order to solve the problem of deformation or collapse during the drying of high aspect ratio nanostructures, the method named auxiliary drying has been proposed. Theoretical analysis and experimental research has been carried out in the paper to explain and verify this method.This part of the paper focused on theoretical analysis and experimental research on the deformation or collapse of high aspect ratio nanostructures. Theoretical analysis was carried out to achieve the reason of the deformation or collapse during the drying high aspect ratio nanostructures. Parameters related to nanostructures which influenced the deformation or pattern collapse have been also discussed. Then, based on the model of beam sway and ANSYS, deformations of high aspect ratio nanostructures caused by surface tension were calculated in condition of patterns with different high aspect ratios and pitches. A method of auxiliary drying is presented to prevent pattern collapse in high aspect ratio nanostructures by adding an auxiliary substrate as a reinforcing rib to restrict deformation and to balance the capillary force. The principle of the method is presented based on the analysis of pattern collapse. A finite element method is then applied to analyze the deformation of the resist beams caused by the surface tension using the ANSYS software, and the effect of the nanostructure’s length to width ratio simulated and analyzed. Finally, the possible range of applications based on the proposed method is discussed. Our results show that the aspect ratio may be increased2.6times without pattern collapse. Nanostructures with line width of150nm and aspect ratio of16.7were fabricated after fully studying the theory of pattern collapse or deformation. The experiment validated the feasibility of auxiliary drying method, which reduces the pattern deformation and increases the aspect ratio of nanostructures. In addition, the method of auxiliary drying was enlarged to be suitable for closed structures. Auxiliary structure was also optimized. Deformation of closed structures is calculated under the condition of using auxiliary drying by finite element method.3. Based on the plane wave expansion method, two dimensional polymer photonic crystal laser was designed. Theoretical methods and applications of photonic crystal were introduced. Polymer photonic crystal has been paid much attention because it has merits such as ease fabrication and a wide range of the lasing wavelength. Rhodamine6G is the most commonly used gain material. Its properties and fluorescence spectrum have been experimentally studied. Band gap cannot be formed due to small refractive index difference. Principle of group velocity anomalies was used to explain how polymer photonic crystal devices work. Energy bands of the triangle lattice, the honeycomb lattice and the square lattice were calculated by using the plane wave expansion method. Compared with the other energy bands, energy band of the triangle lattice is relatively simple. Types of lattices and refractive index difference are the main factors which influence energy band of photonic crystal structures. Therefore, they were carefully studied.4. Fabrication and preliminary test of two dimensional polymer high aspect ratio photonic crystal laser. Based on results of test and analyze the spectrum of photonic crystal laser, polymer photonic crystal laser was optimized by redesigning the structure parameters.Firstly, electron beam lithography combined with X-ray lithography was applied to fabricate two dimensional polymer high aspect ratio photonic crystal laser. The method has utilized high resolution of electron beam lithography and X-ray lithography with high efficiency and the merit of fabricating high aspect ratio structures. Processes of electron beam lithography, proximity effect and pattern stitching of electron beam lithography have been introduced. Correction technology of proximity effect was also studied in this paper to achieve patterns with high quality.X-ray photonic crystal mask with the period of800nm and filling rate of0.25was fabricated by electron beam lithography combined with gold plating. After high resolution masks were fabricated, X-ray lithography was applied to achieve high aspect ratio photonic crystal structures. Rhodamine6G was used as the gain material in the polymer photonic crystal laser. Rhodamine6G is activated by the laser. The spectrum of rhodamine6G is modulated by photonic crystal structures. The platform was established to test the performance of two dimensional high aspect ratio polymer photonic crystal laser. Different baking temperatures for PMMA doped with rhodamine6G were studied, which influenced the fluorescence spectrum of rhodamine6G. After testing the spectrum of two dimensional polymer photonic crystal laser with different lattices, it found that the property is consistent with the design. Because the emission points in the design are complicated, the emission is not clear. Therefore, photonic crystals with the period of400nm and filling rate of0.25were redesigned. High aspect ratio photonic crystal structures were also fabricated by X-ray lithography.