Effects and Applications of Electron Beam Irradiation and Nanoimprinting on Polymers

• Main Authors: Jem-Kun Chen, 陳建光
• Other Authors: Feng-Chin Chang
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/65386307863363264467

博士 === 國立交通大學 === 應用化學系所 === 93 === Alternative techniques to cost-intensive or limited-access fabrication methods with nanometre resolution have been under development for nearly two decades. Two clear examples are electron beam and nanoimprint lithography technologies. The main attributes of the electron beam lithography are as following: 1. It is capable of very high resolution, almost to atomic level. 2. It is a flexible technique that can work with a variety of materials and almost infinite number of patterns. Nevertheless, electron beam lithography is a technique with limited throughput, leading to high costs in device production. The contest of lithography techniques for reliable fabrication of future integrated nanometer-scaled devices is not yet settled. Nanoimprint is an emerging lithographic technology that promises high-throughput patterning of nanostructures. Based on the mechanical embossing principle, nanoimprint technique can achieve pattern resolutions beyond the limitations set by the light diffractions or beam scatterings in other conventional technique. In this thesis, we focus on the subjects which based on the materials for electron beam and nanoimprint lithography: (1)The behaviors of polymer under electron beam irradiation and the applications Structural transformation of polymers from linear to crosslinked structure by using electron beam irradiation has been defined as the zwitter-polymers. The novel sensitivity curve has been determined for the zwitter-polymer. The irradiation dose in the center can create a ring pattern due to simultaneous exhibition of the positive tone and negative tone of zwitter-polymer. The natural logarithm dependence of ring width and electron beam dose is linear in two ranges, irrespective of the dot design radius. The heating effect is identified from 600 �媴/cm2. Mathematical modeling for the prediction of ring width for zwitter-polymer is achieved by considering the electron scattering and heating effects. The results of experimental measurement and modeling on ring width show a very good correlation. Furthermore, the polymer may exhibit either linear and crosslinked behavior depending on dosage of the electron beam irradiation. The property change from the structural transformation is suitable for application of positive and negative tone resists in semiconductor field. The contrast ratio and threshold dose both increase with increasing resist thickness for both the positive and negative tones, however, the positive tone exhibits better contrast than the negative tone. The epoxy material, SU-8, has been successfully fabricated to oblique, concave, and convex structures by a new electron beam technology. We study the contrast, sensitivity, etching, and thermal properties of SU-8, PMMA, and KrF resists and evaluate their suitability for the fabrication of these structures. Among these resists, SU-8 reveals the lowest contrast ratio, highest throughout, and best thermal stability, and so it becomes the candidate material for patterning the oblique structures. The technique that we have developed involves five regional exposures of a thick SU-8 resist layer with gradual increase of electron beam dosages. Furthermore, we discuss the surface morphology, reaction mechanism, and hydrophobicity after subjecting the SU-8 resist to a series of plasma treatments. The formation of surface nano-nodules during oxygen plasma treatment explains the surface hydrophobicity. Furthermore, oxygen plasma treatment increases the surface roughness of SU-8 polymer, while minimizing the outgassing problem and stabilizing the SU-8 film. We have carefully evaluated the effects of the electron beam writing dose and the design of the exposure area with respect to the inclined angle of the fabricated structure. Convex, concave, and spiral structures are fabricated successfully by using a gradient dosing strategy. The interface between two shot sections is smoothed by the electron scattering effect. The curved profile is fabricated at various curvatures, and characterized using scanning electron microscopy and a profiler. In addition, a spiral structure is fabricated that possesses the advantageous feature of having a small chip area. We discuss a method of characterizing the spiral structure. (2) The studies of self-assembled monolayer on the silicon oxide surface and fabrication of microlens As all imprint techniques rely on contact between resist and mold, the wetting and adhesion characteristics of the polymer materials to the substrate are critical issues. The strength of adhesion between mold surface and resist is characterized by the amount of energy required to separate the two materials. In this study, trichloro(3,3,3-trifluoropropyl)silane (FPTS) and trichloro(1H, 1H, 2H, 2H- perfluorooctyl)silane (FOTS) are used for self-assembled monolayers (SAM) on mold (SiO2/Si) as releasing and anti-sticking layers for nanoimprint. Chemical reaction between the head groups of different fluorinated trichlorosilanes and the surface hydroxyl groups is investigated by FTIR. The SAM quality depends on immersion time and silanization temperature investigated through measurement of the ellipsometer and calculation of the surface energy. It has been demonstrated that less defect and lower roughness of the resist surface can be achieved by mold with SAMs of FOTS and FPTS. The mold with FOTS layer processes lower surface energy (8 mJ/m2) and smoother of the resist after imprinting. The surface energy of the SAM on mold (SiO2/Si) dictates the results in quality of better resist surface and the pattern formation. Mold fabrication for imprinting can be significantly simplified by using specialized crosslinking polymers for pattern definition on silicon wafer. The thermosetting polymer pattern can be used on silicon molds for imprint technology because of two possibilities: (1) the silicon oxide molds with thermosetting polymer pattern can be obtained by any conventional semiconductor technology; (2) thermosetting polymers have no obvious Tg because of cross-linking structure, whereas decreases the hardness as the temperature increasing over their Tg. In this work, the SU-8 resist is used as the thermosetting polymer pattern on silicon wafer for molds. Thermal properties of the thermosetting and thermoplastic polymers are tested for imprinting pattern and imprinted resist. The hill-like structure fabricated by electron beam strategy for thick film is used to increase the adhesion between pattern and silicon wafer. The resolution of the thermoplastic polymer resist pattern imprinted by thermosetting polymer pattern is investigated by SEM. The shrink factor of the feature size after separation between thermosetting polymer pattern and thermoplastic polymer resist is utilized to define the feature size after imprinting. In addition, a microlens of polydimenthyl siloxane (PDMS) has been fabricated by replication using the thermoplastic polymer resist after imprinting by the mold with microlens structure of the thermosetting polymer (SU-8).