Design Analysis And Fabrication Of Subwavelength Antireflective Gratings

This paper mainly discusses the design consideration of antireflective subwavelength grating and the technology of fabrication.I use rigorous coupled wave analysis (RCWA) and effective media theory (EMT) to analyze the effects of parameters of subwavelength grating and the grating's material on the diffraction character of grating. Through the analysis, it is shown that: 1, while fabricating the grating, the principle of selecting the parameters is: the period should be as large as possible, the etching depth should be small and filling factor should approach to 0.25. 2, if selecting the parameter combine the selecting principle and the requirement of concrete application, the space of selecting the parameter should be larger than before. 3, while the period TO.4A,, the surface profile has no effect on the reflectivity. 4, if applying the relation between refractive index and critical point, the failure of fabricating grating because the first order diffractive wave appears as we select the excessive large period, can be avoid.In the section of fabricating technology, I first discuss the ion beam technology. Through the analysis of the effects of each parameter on the surface smoothness, profile fidelity and linewidth resolution in the process of ion etching, the suitable angle of incident ion beam, ion energy, density of ion beam and time of etching are selected combining the actual status of the mask. The submicron ring, laser beam shaper and Fresnel lens is fabricated by ion etching according to the selected parameter. According to the measurement of the elements, it is shown that the surface smoothness, profile fidelity and steep sidewall are very well.Then, the square-pillar grating is fabricated by plasma-assisted etching. The testing results shows that the grating has a very well antireflective characteristic, and the values of testing parameters approximately equals to the designed parameters'. It indicates that the plasma-assisted etching method is very valid to fabricate deep grating. The experimental results are analyzed and discussed. The difference between the experimental results and theoretic calculation also is analyzed. Through the analysis, it is shown that the critical periodic point as a function of refractive index is very important to fabricate the antireflective subwavelength grating.