| This paper is mainly divided into three different parts:In the first part, we focus on the designing and fabrication of a new kind of nano-imprint lithography (NIL) machine—"multi-functional NIL machine with UV and hot pressing solidification methods". Under the vacuum condition, we can speed up the solidification of UV resist and reduce the number of defects with nanostructures in the procedure of NIL. The pressure used in NIL originates from compressed air. One feature of our design of this NIL machine is to use positive pressure in the high-pressure cabin and negative pressure in vacuum chamber to control the "up and down" of imprint platform, in order to reduce the impulse force to the quartz datum plane and soften the interaction between them. Through the design for pressure-guided system (including high-pressure welded bellows cabin), high-pressure air can be used to buffer, uniform, adjust and control the interaction force in large contact area, so that high precision and high resolution patterning may be obtained, and the service life of mold may be raised. In the equipment, a original automatic parallel-adjustment system is used to parallel two planes of the sample and the quartz datum plane, which consists of the following three parts:welded bellows cabin structure, semi-sphere copper ring regulation structure and ring-shape steel ball regulation structure. With these considerations, it can increase the range of parallel-adjustment and the stability, and enhance the regulation flexibility and precision. The plane of high quality quartz, with double-surface polishing and super-smooth and high degree of planarity, is selected as the datum plane. Combining with the quartz window, datum plane quartz plate and exposure shutter, high voltage mercury arc lamp accomplish UV exposure solidification for imprint resist; and a functional assembly is used for hot pressing solidification of resist which contains temperature-controlled armored heating wire and plate with cooling water conduit. The implement of all functions for NIL about this machine has three modes:manual operation mode, manual safeguard and repair mode and automatic operation mode, in which the core unit of the automatic control system is PLC(programmable logic controller) with a touch screen performing the functions of displaying processing parameters and flow chart,and inputing operation command. This developed NIL machine has all necessary functions with rational structures. It is easy to operate, its performance is stable and reliable, and it is also of high degree of process automation.In the second part, we have prepared Au free-standing transmission gratings based on the NIL technology combined with RIE (reactive ion etching), microelectroplating, photolithography and wet etching. We have successfully realized pattern transfer with gratings of period200nm, line-space ratio1:1and trench height100nm. To pattern high aspect ratio gratings, the double layer resist system was used to amplify low aspect ratio patterns formed in the top film into high aspect ratio patterns in the sub-layer through a selective etching process. The sub-layer is PMMA and the top-layer is UV-resist for pattern transfer. In the processing, the residual layer of the top layer was stripped by CHF3and O2, and the sub-layer was etched by O2. Because of their different etching rate by O2RIE, we can obtain about350nm height polymer grating pattern. The pattern was served as a mold during the following micro-electroplating process. Thorough optimizing the prescription of electroplating solution and process parameters, a200nm period,300nm trench height Au grating was successfully fabricated. The meshes support the nanostructure with periods2μm and150μm, respectively, and height1.5μm, which was fabricated by UV contact lithography and gold electroplating. After the support structure patterning, the center region of the backside of the wafer was removed by selecting proper etchant. Finally, the plating base was etched by Argon plasma, and then Au free-standing transmission gratings were obtained with period200nm, line-space ratio1:1, trench height300nm in large area of5mm x8mm.This work provides a high throughout and low-cost method for the fabrication of metal free-standing transmission gratings. Also we have researched the grating’s microstructure and characterized the diffraction efficiency of the gratings using SEM method and synchronous radiation X-ray diffraction, respectively.In the third part, we have systematically studied, theoretically and experimentally, the physical properties of surface electromagnetical waves (SEWs) which are excited and coupled in the one dimensional photonic crystal (1DPC)-metal thin film structures by visuable light. The surface waves excited in finite period1DPC are a new kind of SEWs, different from surface plasmons (SPs) excited in the surface of metals. The surface wave can be not only TM modes, but also TE modes, and its modes may exist at any frequency in any bandgap of1DPC depending on the materials and the structures. In this system, the surface field enhancement effect originated from the localized surface modes is even stronger, thus results stronger the coupling intensity with incident light, than surface plasmon polariton.1DPC-metal film structure provides a new principle, new method and new structure for exciting and coupling SEWs. The observation of extraordinary transmission within the bandgap of1DPC from1DPC-metal film structures could obviously verify the existence of exciting radiative SEWs. The frequency of the transmission peak, corresponding to the surface mode frequency, is mainly determined by the bandgap and conditions of the outmost surface material. And the intensity of the peak, corresponding to the intensity of coupling between surface mode and incident light, is decided by the period number of1DPC and the thickness of metal film. To achieve a high transmission peak, we must manipulate the two evanescent waves in1DPC and metal film to reach the interface in order to make surface field enhancement effect strong enough. According to the dispersion curves of the surface modes, we found out that TE surface modes with different frequency may be excited by the incident light at any incident angle, but TM surface modes may be excited only at incident angles smaller than Brewster’s angle. We discovered two extraordinary phenomena from the reflection and transmission spectrum:the first one is that TM surface modes may be excited at angles greater than Brewster’s angle, and the second is that there exists extraordinary transmission for TM surface modes which intensity rises with the incident angle increasing, quite different from TE surface modes. In near future, we may study the propagating properties of both the surface waves along the interface from both their reflection and transmission spectrum. We also propose that the Goos-Hass shift may exist for the surface waves from1DPC surface, which may be used to research some new physical effects of the surface electromagnetic waves. |
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