Study On Key Technologies Of 3D Microfabrication By Overlapped Increment Scanning Manner Of Electron Beam

System microminiaturization is one important development direction of up-to-date science and technology all along. Micro electro mechanical system (MEMS) developed on this trend is a new domain involving many subjects and has broad application foreground. Micromachining technology is the key of MEMS. With in-depth study and rapid development of MEMS, new technologies are required to produce complex curved surfaces and various shapes of three-dimensional (3D) microstructures. Now the 3D micromachining technologies are mainly silicon bulk micromachining, LIGA (Lithographie, Galvanoformung and Abformung) and IH (Integrated Harden Polymer Stereo Lithography), etc. Silicon bulk micromachining and LIGA can produce steep microstrucrure with high-precision and high-aspect-ratio, but it is difficult to fabricate various microdevices with curved surfaces and more complex structures. IH can theoretically fabricate complex structures with arbitrary curved-surfaces and high-aspect-ratio, but its scans in x and y directions are completed by the movement of X-Y workstations mechanically, the machining precision is little lower and only submicron resolution can be achieved. To satisfy rapid development of MEMS, new 3D micromachining methods should be developed.Electron beam lithography (EBL) is admittedly the best technology to produce patterns with high resolution and is mainly used to fabricate two-dimensional precise masks of integrated circuit (IC) at present. The diameter of beam spot can be focused to several A theoretically and is easy to control. Its important applications in VLSI IC masks fabrication are not replaced by others methods so far. Under the lab conditions, the diameter of beam spot has been focused to less than 2nm and EBL has been used to fabricate the nanopatterns.The resist patterns with different depths can be obtained by adjusting exposure doses. EBL traditionally fabricates 3D microstructures by changing doses. For the universal EBL systems, exposure doses can not be changed in the processing, so it is difficult for them to fabricate 3D microstructures directly. Considering the symmetric structures of some microelements (e.g. Diffractive Optical Elements), a new method of overlapped increment scanning exposure is proposed by our lab based on new pattern generator which is developed by ourselves and controlled by DSP. This method keeps single exposure dose constant and changes total exposure dose by changing scanning times. It raises exposure efficiency and supplies a gap of not changing doses of universal EBL systems, which provides a new method of producing 3D microstructures for universal EBL systems. New method can directly produce high-precision 3D microstructures on the films such as vertical, curvilinear and micro tip arrays, so it belongs to electron beam direct writing (EBDW) technology. When this new method is proposed, its feasibility needs to be studied firstly. Next, to meet the demands of higher precision of microsystems and fabrications of complex devices, many aspects are needed to be studied thoroughly, such as selection of exposure parameters, design and data processing of exposure patterns, applications of new methods etc. In this paper, some key questions are mainly studied, such as exposure mechanism of overlapped increment scanning manner of EB, influence of energy and dose to etching depth of EB, data processing of exposure patterns and application foreground of new method. The main research works and achievements are summed up as follows:1. Based on the macromolecular radiation chemistry, the practical reaction mechanism of overlapped increment scanning method of EB acting to positive resist PMMA is studied thoroughly. According to Charlesby-Pinner theory, the relationships of radiation dose to radiation degradation degree and average molecular weight of polymer after degradation are educed. The conclusions are made that greater is radiation dose, more is radiation degrading degree, smaller is average molecular weight of degrading yields, then greater is the solubility of polymer. These conclusions are correct proved by the results of exposure experiments. The overlapped increment scanning exposure method can be used in 3D micromachining by the theoretical and experimental confirmations.2. The relationship between EB energy and etching depth is studied thoroughly by two ways, Monte Carlo simulation and Grun formula. The conclusions are summarized as:(1) Etching depth in resists increases with EB incident energy increasing.(2) With the increase of EB incident energy, lateral effect range of electrons becomes larger, but the distribution curve of absorbing energy density becomes sharper. So increasing EB incident energy can weaken proximity effect and is favorable to the improvement of exposure resolution. Referring to theoretical analysis results, exposure experiments are made with PMMA resist on SDS-II. And the experimental results are consistent with analytical results primarily, which proves theoretical analysis methods correct and can provide the important directions for the selection of accelerating voltage of EB micro 3D exposure experiments.3. The relationship between EB exposure dose and etching depth is studied thoroughly by Monte Carlo simulation and analytic method. The conclusions are summarized that etching depth increases with exposure dose increasing. The experiments are made with PMMA and TMPTA on SDS-II. And the experimental results are consistent with theoretical ones primarily, which proves those conclusions correct. The analytical results of liquid resist TMPTA show that the above conclusions are also fit for EB liquid lithography. By Monte Carlo simulation results, lateral scattering range of EB expands with exposure dose increasing, which will result in the interaction of exposure patterns, intensify proximity effect and affect line-width resolution of exposure patterns. So in the exposure experiments of overlapped increment scanning, exposure doses can be chosen reasonably to satisfy the size and precision of exposure patterns with the direction of dose-depth theoretical analysis results.4. A new way to determinate the relationship between EB exposure dose and etching depth accurately is proposed by experiential formula of contrast and the contrast is calculated by absorbing energy density gained by Monte Carlo simulation, which get over the complexity of experimental ways. With the calculated results made curve fitting, the relationship curve of depth-dose is obtained and the calculated results keeps consistent with experimental ones primarily which proves this way feasible. With the depths of exposure patterns known, exposure dose can be chosen by this relationship, which can save experiment time and raise efficiency.5. The microchannel structure of micro-flow PCR chip is made optimized design by microfluid mechanical theory. The cross sections of the microchannel studied in fore references and obtained by current machining methods are rectangular mostly. When the liquid is flowing in the circular microchannels, the resistances caused by the friction and surface tension of the circular microchannels are smaller than the rectangular ones with the same cross-section area. To overcome those resistances, driving powers needed by the circular microchannels are smaller than the rectangular ones.6. A new way of fabricating the circular microchannel of PCR chip is proposed on overlapped increment scanning exposure method which can fabricate the curved surfaces. Exposure experiments are made on JSM-35CF with round-beam vector scanning manner. After the development, the microchannels are obtained with smooth brims.7. A new way of fabricating micro three-dimensional master of soft lithography by overlapped increment scanning exposure method is studied experimentally. The elastic stamp is the key of soft lithography. So the master is required in fabricating the elastic stamp. This way is proved to fabricate micro 3D master by studying many aspects, such as calculations of exposure dose, discussions of fabricating process and results of exposure experiment, etc.8. A new way combining overlapped increment scanning exposure method with soft lithography is studied to fabricate 3D microdevices, which may become a simple, efficient and cheap way of 3D micromachining to satisfy the development of MEMS in future.