| Summary: | 碩士 === 國立清華大學 === 原子科學系 === 89 === There are two major parts in this thesis. One is establishing the anti-reflective coatings technique for using in deep ultraviolet photomask. The other is to investigate the behavior of DUV photoresists for applying in electron beam direct writing system.
In the development of the anti-reflective coating techniques for photomask applications, we demonstrated a novel anti-reflective coating structure for deep ultraviolet binary mask, which is based on three-layer Fabry-Perot structure. The anti-reflective coating structure is composed of the chrome / oxide / chrome stack. By adding different optimized structures, reflectance of less than 2 % at both 248 nm and 193 nm has been achieved. The results are also agreed well with simulated ones. At the three-layer Fabry-Perot structure, the thickness of bottom chrome layer should be larger than 100 nm to provide suitable absorption. By controlling the thickness of the intermediate oxide layer, we can tune the minimum reflection regime for the desired exposure wavelength of interest. The thickness of top chrome layer should be well controlled in order to optimize transmission light into Fabry-Perot structures. In general, the mask layer should have good electrical conductivity for e-beam writing in order to prevent writing errors due to charging effects. In the Fabry-Perot structure, the top metal layer can also prevent charge accumulation during e-beam writing.
As to the investigation of the properties of a positive tone deep ultraviolet chemically amplified resist, UV86 (DUV CARs, Shipley®), has been evaluated for electron beam direct writing. Including the characteristics in electron beam lithography, etching process and thermal flow phenomena after hard baking. UV86 with its contrast higher than 16 is highly sensitive to electron beam exposure. The optimization condition for the electron beam lithography is SB 130℃/60 sec, PEB 135℃/90 sec with sensitivities of 11~13.5μC/cm2 at 40 kV. It could give contact holes critical dimension (CD) from 200 nm to 25 nm with almost perfect profiles by various hard baking temperatures. Moreover, the flow amount would decrease on hard baking temperature process by increasing the temperature of SB. In addition, the etching selectivity to thermal oxide, poly-Si and Cr has been examined by using the gas CHF3 / CF4, Cl2 / O2, and Cl2 / O2, respectively.
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