Tham khảo tài liệu 'biomedical engineering trends in materials science part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 382 Biomedical Engineering Trends in Materials Science kV which gives a wavelength of Ầ nm. This is also known as the de Broglie wavelength. Where photolithography is a parallel process a whole wafer can be exposed at the same time electron beam lithography is a serial technology. For example with a pixel size of 10x10 nm2 and a patterning rate of 5 million pixels per second typical values for general patterns it will take nearly 6 hours to pattern a 1x1 cm2 area with 10 pattern density. This time exclude the stage movement calibration and settle time during the exposure which easily can double the actual lithography time. To overcome this time constraint we have developed a method that dramatically reduces the exposure time Gadegaard 2003 . This will be described in more detail in the following section. The fabrication procedure is similar to photolithography where a substrate is coated with a resist sensitive to radiation. In contrast to photolithography which uses light EBL uses an electron sensitive polymer which either breaks down during exposure positive tone or cross-links negative tone . After exposure the sample is developed to reveal the exposed pattern. One major difference between the two lithographic techniques is that EBL requires a conducting sample or the surface will build charge as a result of the electron bombardment. Here either a conducting substrate is used typically silicon or a metallic film can be deposited on non-conducting substrates. A fast and flexible EBL nanopatterning model system To gain the ultimate degree of pattern control at the nanometre length scale Gadegaard has for a decade used electron beam lithography EBL . EBL is found at the heart of semiconductor production in the generation of the photolithographic masks for exactly this ultimate performance. Its nature of serial patterning means that it is generally regarded a slow technique. However over the years we have developed technologies to overcome this limitation.
