Design And Process Research Of Silicon Based Terahertz Antireflection Window

Subwavelength structure means binary the optical element whose size is smaller than the incident wavelength.When the size of multilayer subwavelength structure is much smaller than the incident wavelength,every layer of structure is similar to the antireflection coating that on the surface of traditional optical elements.Through the calculation and simulation of the periods,duty cycle and height of the structure,we can get the subwavelength structure with antireflection effect.This paper introduces the multistep subwavelength structure in two aspects: design theory and fabrication process.The theory of the traditional infrared broadband antireflection coating is combined with the equivalent medium theory of sub wavelength structure.The rigorous coupled wave theory is used to analyze the structure parameters of the three step sub wavelength structure.Finally,combining the simulation theory with the manufacturing process,the cost and difficulty of the manufacturing process are reduced by designing the appropriate structural parameters,and the optimum transmittance is obtained.The main contents of this article are as follows:(1)Introduced the equivalent medium theory,and the approximate structural parameters of multilayer structure are deduced by combining the theory with the traditional infrared broadband antireflection coating theory.And discussed the corresponding periodic threshold of subwavelength structure for zero incident diffraction of arbitrary incident light.(2)Introduced rigorous couple wave theory,and combined with the equivalent medium theory,use MATLAB tool to simulate,obtain the optimum transmittance corresponding to the structural parameters of step structure.Used the software L-Edit of mask to draw the graph and alignment mark.(3)The manufacturing process of multistep structure is introduced.The traditional multi step production is a multiple mono mask process,and the multi mask process is adopted here.The problem of poor quality of the lithography line is avoided in many single mask processes.The deposition process and etching process of the mask used are introduced.Through the measurement of the step structure after etching,it is found that the quality of the graphic lines after multi mask process etching is good.(4)A three step sub wavelength structure is designed according to the traditional multi membrane theory,which improves the maximum transmittance.The average transmittance of the terahertz enhanced window in the silicon substrate was 76% in 170?m~190?m,compared with 14% and 7% of the bare silicon and single step structure,respectively.Using the MATLAB simulation program,the simulation is carried out at 100?m~400?m band,and compared with the actual transmittance,it is concluded that the three step structure is the same as that of the three layer antireflection film,and all has three peak positions.