9/28/2023 0 Comments Rf generatorThe aim of the present study is to develop a compact, automatic, and fast-controlled rf system for future applications of the rf plasma source to the terrestrial plasma processing tools in “Minimal Fab” and the space propulsion device called a helicon thruster. ![]() ![]() Since the primary parameter deciding the plasma characteristics in terms of the rf system would be the net power given by the forward power minus the reflected power, it would be favorable to maintain the constant net power during plasma production rather than the forward power when the perfect impedance matching is difficult. The traditional impedance matching technique can perform nearly perfect impedance matching by adjusting two capacitors, while it would be difficult to obtain the zero power reflection for the frequency tuning since only one control parameter (frequency) is adjustable. These experiments have been performed with the linear rf amplifier classified as class AB, while class D or class E switching amplifiers have also been used for the frequency-tunable matching. One of the authors has used an amplifier operational for the broader range of the frequency to match the impedance for the industrial plasma source, where the frequency was manually adjusted for the initial laboratory test. has used the frequency-variable power generator operated at around 13.56 ± 0.678 MHz with the fixed small ceramic capacitors for impedance tuning. To overcome this issue, a frequency-variable tuning has been tested in several laboratory experiments. Furthermore, the precise control of the pulsed plasma would also be required for some plasma processing methods, e.g., plasma etching by Bosch process, where gas species are alternatively switched for etching and passivation.Īs described above, the available space for the rf system is strictly limited in the applications hence, the development of the compact rf system for the plasma source is a significantly important technology. ![]() Therefore, all of the components required for each tool, e.g., a plasma reactor, a pumping system, an rf generator, the wafer transfer mechanics, and the programmable logic controller, and so on, have to be contained within the compact frame. The frame and wafer transfer structures are strictly standardized to connect the processing tools. Since the wafer is transferred between the processing tools in a localized clean wafer transfer system, no clean room is required for the device production the facility and production costs can be reduced for the high-mix and low-volume products. On the other hand, Minimal Fab consists of various manufacturing tools in processing a half-inch wafer. In the traditional semiconductor manufacturing system, the diameter of the silicon wafer has been increased to yield sufficient economic benefit by low-mix high-volume production in the large-scale manufacturing system (called “Mega Fab”). The compact, automatically controlled, and fast-controlled rf plasma system is also useful for terrestrial industrial plasma devices such as plasma sputtering and etching reactors in a recently developed new concept of the semiconductor manufacturing system, being called “Minimal Fab”. Therefore, automatic and fast control of the impedance tuning is useful for further development of the rf plasma thruster. Further addressing space propulsion, the time lag of the communication between the spacecraft and the ground control station would be a serious problem for the impedance matching. Since the weight and size of the rf system mountable on the spacecraft is very limited, development of the compact rf system is required for the rf plasma thruster. The impedance matching is generally performed by inserting two variable capacitors and an inductor (if necessary), where the capacitances are adjusted by mechanical motion.įundamental studies on and development of space propulsion devices utilizing the rf plasma sources have vigorously progressed in recent years. To transfer the rf power to a load, the load impedance has to be matched to the output impedance of the generator and the characteristic impedance of a power transmission line, being typically 50 Ω. Radiofrequency (rf) plasma source operated in the frequency of 1–100 MHz has been widely used for various applications such as industrial plasmas, space propulsion devices, and fusion plasmas.
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