Nanophotonic structure formation by dry e-beam etching of the resist: resolution limitation origins

Abstract

A wide range of structures for nanophotonics and optoelectronics can be formed by dry e-beam etching of the resist (DEBER). High resist sensitivity due to chain depolymerization reaction provides efficient etching with high throughput of the method. The structures obtained by the DEBER in this research are well-rounded diffraction gratings, binary gratings and staircase profiles. The major disadvantage of DEBER is poor lateral resolution, which may be caused by different physical mechanisms. Four groups of possible mechanisms leading to the resolution limitation are determined and the influence of some mechanisms is estimated Keywords: DEBER, e-beam etching, nanophotonics, diffractive optical elements, diffractive optics, three-dimensional lithography, three-dimensional fabrication, microlithography, optical design and fabrication.Citation: Rogozhin A, Bruk M, Zhikharev E, Sidorov F. Nanophotonic structure formation by dry e-beam etching of the resist: resolution limitation origins. Computer Optics 2016; 41(4): 499-503. DOI: 10.18287/2412DOI: 10.18287/ -6179-2017.Acknowledgments: This study was partially supported by the President of the Russian Federation's grant No. MK-3327.2017.9. IntroductionDry electron beam etching of resist (DEBER) proposed by Bruk et. al. [1,2] could be used for formation of wide range of optoelectronic and photonic structures. The method is based on the chain depolymerization reaction, which takes place in the polymer resists during e-beam exposure at the glass-transition or higher temperatures. The volatile reaction products (monomers) are pumped out during exposure. The method provides quite simple way for formation of well-rounded or 3D structures. In some cases, it could be much more flexible than usual methods, in others it could be more productive or convenient. Similar phenomena were observed in PMMA during ion beam irradiation [3] and UV radiation [4].PMMA sensitivity to e-beam in the DEBER method is about 100 times higher than that in the standard "wet" e-beam lithography process. Because of high vertical resolution (about 1 nm) the method could be used for high-precision 3D structuring. On the other hand, DEBER lateral resolution (about 200 nm) and contrast (0.7 -1.5) are rather low. It is difficult to use DEBER method for nanophotonic structure fabrication due to low lateral resolution. For nanophotonic applications the lateral resolution of the formation method should be lower than 100 nm [5,6].It is not clear which physical mechanism leads to the lateral resolution limitation. It seems that most of the possible mechanisms are the same for DEBER and ordinary e-beam lithography [7,8,9] but their contribution to the lateral resolution lowering should be reconsidered.In this paper structures of diffraction or binary gratings, some diffractive optical elements (DOE), 3D structures or planar photonic crystals obtained by DEBER method are presented. Also in the paper, different mechanisms that could lead to the broadening of the trenches