| Silicon nitride micro-pyramid structured films have wide band antireflection effect.Traditional preparation methods based on MEMS can only obtain micro-pyramid structures with right angle of bottom surface.In this paper,the advantages of single-point diamond cutting to prepare micro-pyramid structure are brought into play.By adjusting the cutting direction,the angle of the bottom surface of the micro-pyramid structure array is controlled from 0 to 90 degrees.Through the simulation analysis and experimental research on the near-fidd light field modulation characteristics of silicon nitride micro-pyramid structured thin film with variable bottom angle,it is proved that the thin film optical micro-pyramid structured thin film can modulate the beam propagation direction and energy distribution,change the bottom angle of the micro-pyramid structure,and allow light waves to propagate according to the design of the bottom angle.This phenomenon provides a wider degree of freedom for the optical path design of the photoelectric system.The near-field optical field modulation characteristics of silicon nitride micro-pyramid structured films are simulated and analyzed.By finite difference time domain method,the phase modulation results of visible light wave band and different wavelength thin film optical micro pyramid structure array on different wavelength light wave are simulated and calculated.The law of phase distribution of incident electromagnetic wave modulated by microstructure is revealed.The simulation results show that in visible light band,with the increase of wavelength,the amplitude of phase change becomes larger,resulting in the transmission of electromagnetic waves with different wavelengths from microstructure showing a regular distribution of wavelengths from large to small.Based on the ray tracing method and the finite element numerical calculation theory,the modulation results of pyramid structure on ray propagation direction are analyzed.The simulation results show that light waves are modulated into four light waves to propagate in different directions through the pyramid microstructure array,and each light wave carries the wavefront phase characteristic information of its own microstructure array.Based on the simulation results,this paper combines the single-point diamond cutting technology with the traditional micro-electromechanical system preparation technology to give full play to the advantages of single-point diamond cutting to prepare micro-pyramid structures.By adjusting the cutting direction,the bottom surface angle of silicon nitride micro-pyramid structured films is controlled at 0?90 degrees.Silicon nitride thin films with a thickness of 4?m were prepared by PECVD technology.Under the experimental conditions of SiH4:40 sccm,N2:103 sccm,deposition temperature:250?,working pressure:67Pa,and RF power:240W,the thin films have the minimum stress under the condition of 4?m thickness.The method for preparing the thin film micro-pyramid structure by utilizing the nano-thermal imprinting technology with the characteristic of three-dimensional molding is simple to operate,low in cost and high in resolution.The experimental results show that the microstructure prepared by nano-imprint technology can keep the integrity of pyramid microstructure and achieve a pattern transfer close to 1:1.The etching ratio of silicon nitride film and epoxy resin was verified by ICP etching technology.The experimental results show that when the optimal parameters are SF6:45 sccm,ICP power:430w,RF power:12w,pressure:12 mTorr,the etching rate of silicon nitride film is 16.98nm/s,the etching rate of epoxy resin imprint glue is 23.55nm/s,and the etching rate ratio of silicon oxide film and imprint glue is 1:1.39.The transmittance and transmission light field distribution of the prepared thin film micro-pyramid structures with different bottom angles are detected.In the wavelength band of 1000-2500nm,the average transmittance of Si substrate is 55%,and the transmittance of SiNx film oscillates sinusoidally between 55%and 70%.The transmittance of microstructure eliminates the oscillation effect of film,and the micropyramid structure with a bottom angle of 45 has the highest transmittance.The location of near infrared transmittance enhancement is affected by the aspect ratio of the thin film micro-pyramid structure.The distribution of transmitted light field is consistent with the bottom surface angle of microstructure,which is consistent with the simulation results.The intensity and direction of scattered light can be controlled by designing the size of microstructure and the angle of bottom surface. |
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