| Summary: | 碩士 === 國立東華大學 === 電機工程學系 === 91 ===
There are some semiconductor manufacturing technology bottlenecks existing in the recently development for the device dimension shrinking. Photolithography is the one of those key challenges. Nowadays, photolithography uses ArF 193 nm wavelength laser source for 0.13um~90nm technology node, but it seems to be emergent to search a new light source for the next generation according to technical roadmap (eg. 45nm and beyond). EUV technology is the one of potential candidates for the next generation photolithography light source. In this research, we mainly focus on the generation of high order harmonics (Extreme Ultraviolet; EUV) from incident laser beam based on the interaction between electromagnetic wave and plasma.
In this study, we simulate the electromagnetic wave propagation in non-uniform plasmas and calculate harmonic generation by using double pulses laser structure. Analyzing the harmonics influence with the pre-pulse and main pulse laser beam time difference, intensity of pre-pulse and environment pressure. These analyses showing the reasons why the structure of single pulse laser plasma could not efficiently produce the harmonics. Furthermore we proposed an efficient criterion in harmonic generation in double pulse laser plasma model.
Our results show that thickness of critical sheath is a very important factor to harmonic generation while the electromagnetic wave propagates in the plasma. It must choose the proper thickness of critical sheath (1.5-5.5λ0) to generate harmonics efficiently. If the thickness of the critical sheath is too thin (0.5-1.5λ0), the electromagnetic wave will not efficiently interact with plasma. However, the energy of electromagnetic wave will dissipate in the critical sheath area when the thickness of critical sheath is too thick (5.5-15λ0). The intensity of pre-pulse is also an important factor for harmonic generation. Weak pre-pulse field (4x1012w/cm2) can enhance the generation of harmonics. Besides, the influence of collision frequency between electron-ion to electromagnetic wave is also a main subject in this study. In a high pressure environment with a higher electron-ion collision frequency, more energy of electromagnetic wave is dissipated in environment, therefore larger harmonic electric field generated in low pressure.
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