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We have investigated a process for fabricating three-dimensional (3D) structures using electron beam lithography (EBL), in which such a structure is fabricated from a negative tone resist of hydrogen silsesquioxane (HSQ). The HSQ film for this purpose is coated on a Si wafer and is about 250 nm thick. In electron beam (EB) exposure, the depth of HSQ resist is controlled by the strength of the EB acceleration voltage. After exposing the resist according to a carefully planned scheme, followed by a developing process, a free standing and 3D HSQ structure is fabricated. This structure is a mesh saved in midair, and a line in the structure is 200 nm wide, 100 nm thick, and 1.8 mm long. These samples consisting of a periodic structure are then used as 3D photonic crystals. Fabrication of 3D photonic crystals is a complicated process, but our current work simplifies the task to a great extent.

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