Study On Broadband Antireflective Subwavelength Structures Process

Subwavelength structures (SWS) are defined as periodic structures that contain apattern with smaller period sizes than light wavelength. When the periods of thesubwavelength structures are much smaller than light wavelength, the structures appearas a homogeneous refractive index layer and with only the zeroth order diffractionexists. The antireflective layer can be fabricated on the optic devices by changing theperiod, height and filling factor of the structures. The transmittance and reflectivity ofthe structures are depended on those parameters. In this paper, the subwavelengthantireflective structures are introduced in detail by theory and experiment. It is focusedon the effective medium theory (EMT) and the rigorous coupled-wave analysis (RCWA)theory and focused on the design and fabrication of the dual-side subwavelengthantireflective structures (the dual-side SWS). At last, it proposes a new SWS with apolymer protective film on it.The main contents of the dissertation are as follows:(1) Introduced the analysis process of EMT on SWS. The effective indices ofzeroth-order is compared with second-order in one-dimension SWS with transverseelectric(TE) and transverse magnetic(TM）polarization. According to EMT, it studiedthe structural parameters with several Infrared optical materials which are in8mto14mband and discussed the cycle threshold of SWS.(2) Introduced the RCWA and studied the structural parameters of dual-side SWS.Matlab programming is used to calculate the best numerical results of the structure bychanging the period, height and filling factor of the structures.(3) Introduced the production process of the silicon dual-side SWS infraredwindow. Due to the high temperature when etching the photoresist will melt, siliconnitride film is used instead of the photoresist. The experimental results show that themethod is feasible and can improve the quality of the etching effect. The silicon wasetched by ICP etching, which has high aspect ratio and resolution ratio.(4) Designed a dual-side SWS window to reduce the influence of the internalreflection based on the fact of the optical path. The average infrared transmittance of the silicon infrared window reached to65%and with a peak value of73%in8mto14mband. It had10%and20%more transmittance than a single side SWS and thebare silicon.(5) The SWS will have some trouble with their own structures when work in someharsh environments. A new SWS with a polymer protective film on it was proposed. Westudied the structure and got an antireflective structure with polyethylene coat on it. Thetheoretical transmittance of the structure in8mto14mband is80%, whichprovides the practical use of the structure for theory and technical basis.