o achieve the positioning and multi-degree-of-freedom machining of rotary micro-feature structures on the five- axis motion table in the focused ion beam micro-nano machining system, a high-precision sample rotator based on worm gear drive in vacuum environment is designed. The finite element method is used to simulate and optimize the key components. After loading, the maximum deformation of the component is less than 0.2μm, and the natural frequency is more than 10000Hz, which meet the requirements of the working accuracy and strength of the component. The focused ion beam machining experiment of high aspect ratio microstructure of metal material was carried out by using this sample rotator, and the surface roughness of metal material after machining was better than 5nm. The developed sample rotator expands the processing range of focused ion beam processing system.
KEYWORDS: Ion beams, Optical components, Ions, Chemical species, Thermal effects, Optical surfaces, Monte Carlo methods, Glasses, Sputter deposition, Optical simulations
Ion beam has the advantages of high accuracy and little damage to components, which has been widely used in the figuring of optical components. However, in figuring, the collision between the ions with high-speed collides and the surface of the optical component will cause the temperature of the optical component to rise quickly. In order to investigate the thermal effect of the ion beam figuring, the thermal deposition model is established based on the Sigmund theory of sputtering, and the thermal power density function of the surface heat source is obtained. On this basis, taking BK7 glass as the research object, Monte Carlo method was used to obtain the total power of thermal deposition under the different incidence angle of ion beam. Then the finite element method was used to simulate the thermal effect of the ion beam figuring. The result shows that the deposition energy, maximum temperature and the maximum stress decrease with the increase of incidence angle, and the maximum stress appeared in the clamping position of fixture. The corresponding simulation result shows that comparing with the fixing fixture, the maximum stress in the optical component could be reduced more than 70% by using elastic fixture.
In order to the dwell time function can be solved quickly and accurately, the sampling step length of the dwell point in the solution process of ion beam polishing dwell time has been optimized. Taking the PV value for per unit of uniform material removal and dwell time as the analysis object, the fluctuation caused of uniform removal and the total dwell time under different dwell time sampling step length are analyzed. The optimal dwell time sampling step length of ion beam polishing is 1.5σ。Using the determined sampling step length, the optical element with a diameter of 50mm is simulated polishing, and the surface PV value of the element decreases from 110.81nm to 20.06 nm. The optical element was polished by ion beam according to the simulation results, the PV value of the element surface decreased from 110.81nm to 46.46nm. The experimental results verify the effectiveness of the simulation results. Using the determined dwell point sampling step length, the dwell time can be solved quickly, and the PV value of the optical elements converges well.
In the ion beam figuring(IBF) process, a stable removal function is the premise of ion beam figuring, and the information of removal function is generally obtained by experimental methods. Based on the study of removal function model, the stability of the removal function is analyzed by line scan method. A line scan experiment was performed on a 50mm diameter optical component, within 1h, the removal function's peak removal rate varies in 0.74%, full width at half maximum (FWHM) varies in 0.41%, and volume removal rate varies in 2.62%. The removal function is stable and can be used for actual ion beam figuring. Using this method, the stability of the removal function can be verified to ensure that it satisfies the figuring requirements.
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