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Nanotechnology and Nanoelectronics - Materials, Devices, Measurement Techniques Part 2

Tham khảo tài liệu 'nanotechnology and nanoelectronics - materials, devices, measurement techniques part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 2.4 Preliminary Considerations for Lithography 9 Fig. 2.4 Development of the Si band gap A wafer is covered with a photoresist and a mask containing black transparent structures is laid on top of it. If the mask is radiated with UV light the light will be absorbed in the black areas and transmitted in the other positions. The UV light subsequently hardens the photoresist under the transparent areas so that it cannot be attacked by a chemical solution the developer . Thus a window is opened in the photoresist at a position in the wafer where for instance ion implantation will be performed. The hardened photoresist acts as a mask which protects those areas that are not intended for implantation. 10 2 Quantum Mechanical Aspects Confinement Fig. 2.5 Energy gaps V5. confinement. The different symbols refer to different computer programs which were used in the simulation. Fig. 2.6 Measured band gaps for silicon clusters Up to now a geometrical light path has been tacitly assumed i.e. an exact reproduction of the illuminated areas. However wave optics teaches us that this not true 11 . The main problem is with the reproduction of the edges. From geometrical optics we expect a sharp rise in intensity from 0 shaded area to 100 the irradiated area . The real transition is shown in Fig. 2.9. 2.4 Preliminary Considerations for Lithography 11 Fig. 2.8 Optical lithography It turns out that the resolution of an image produced cannot be better than approximately one wavelength of the light used. In this context light means anything that can be described by a wavelength. This includes x-rays synchrotron radiation electrons and ions. As an example the wavelength of an incident electron is given by h 1 . h 2.1 ự2q V .