| The plasma is fourth state of the material and widely exists in the universe and human daily life. In recent years, low temperature plasma has a wide appli-cation in the physics, chemistry, microelectronics, material science, energy, and national defense security. Low temperature plasma is produced in a number of of ways including capacitive coupled plasma, glow discharge plasma, dielectric bar-rier discharge plasma and so on. Compared with the others, inductively coupled plasma (ICP) has some desirable characteristics, such as a relatively high plasma density, reduced ion damage, and independently controllable ion energy. There-fore, ICP is widely used in chemical deposition, material surface modification, crystal growth, etching semiconductor and display processes. Industrial plasma need to be controlled and stable, however there exists many problems in the pro-duction mechanism and physical environment in the ICP. Based on this subject, the dissertation carried out the work on the inductively coupled plasma.The inductively coupled plasma is operating in two distinct modes on in-creasing radio frequency (RF) power injected into the discharge. At low RF power or current, the discharge is primarily sustained by an axial electrostatic field produced by a potential difference across the induction coil. This capacitive discharge of ICP is customarily referred to as an E mode discharge. When the input power reaches a certain critical value, there is a sudden jump in the electron density and light emission. Usually it is assumed that the discharge is primarily maintained by the annular induced electrical field by Faraday’s effect. There-fore, this inductive discharge is often called as the H mode. If the RF power is decreased, the discharge mode will return back to E mode. However, the second transition threshold power (H'E) is lower than the first one (E'H) and the hysteresis behavior is displayed. The E←'H mode transition and hysteresis are mainly caused by the nonlinearity of power absorption and power dissipation.We designed a cylindrical interlaid vacuum chamber and generated the in-ductively coupled plasma. The plasma electron density was measured by mi-crowave interferometry. The E←'H mode transition was clearly observed in our experiment, we investigated the effects of the pressure on E'H, H->E mode transition points (transition density and transition power). The key results are as follows:(1).The E'H transition density increases with pressure at high pressure (v/w>>1). While at low pressure(v/w<<1), it hardly changes with pres-sure. Meanwhile, there exists a minimum value in E'H transition power at4Pa(v=w) for argon.(2).The H'E transition density increases with pressure at high pressure, while it hardly changes at low pressure. The result is the same with the E'H mode transition. However, the H'E transition power almost decreases with the pressure, expect of a slight increase towards the higher pressure(≥50Pa). Furthermore, the hysteresis is not observed at low pressure. Only at sufficient-ly high pressure (≥8Pa) the hysteresis loop is clearly manifested. Moreover,the width of hysteresis loop increases with the pressure.In addition, we also investigated the effects of coil antenna on the mode tran-sition points. The experimental result showed that both transition density and power were lower in the discharge by internal antenna. The theoretical model was made to explain this:when the discharge is maintained by external anten-na, the larger antenna enlarges the area of stochastic heating the capacitively transferred power. The higher electron density and higher input power are need-ed for the inductively transferred power exceeding the capacitively transferred power to achieve E'H mode transition. The theoretical and experimental result demonstrated the importance of stochastic heating on mode transition. Our s-tudy is useful for the understanding about E←'H mode transition, especially the controlling of transition points in real plasma processing.When the RF power is injected into the plasma reactor, the bulk plasma exists in the area of coil and diffuses to the whole chamber. The electron density is high in the area of coil, and decreases in the faraway place from the coil. However, the industrial plasma is need to be large-area and high-density. This is a difficult problem and depends on the coil design and arrangement. We designed three kinds of coil antenna including cylindrical external antenna, re-entrant internal antenna and re-entrant six-coils antenna. The plasma distribution was investigated at various pressures (1-200Pa). The result showed the plasma distribution in the discharge by external antenna is almost the same with that by internal antenna. The electron density was high at the bottom of chamber and decreased along the axial position. The electron density (3x1010cm-3) at the top of chamber failed by one order of magnitude. While the electron density at the top of chamber was higher (1011cm-3) in the discharge by re-entrant six-coils antenna. This was attributed to the closed electrodes in the the discharge by re-entrant six-coils antenna, which decreased the energy dissipation and increased the energy coupling efficiency. This study is of fundamental importance to the industrial applications of ICP.The inductively coupled plasma is also widely used in the national defense besides the industry, because of that the plasma could absorb the incident electro-magnetic wave (EMW) through collision and refraction and finally reduce radar cross section (RCS) of air vehicle. By controlling the electron density in the dis-charge by re-entrant six-coils antenna, we studied the influence of the top plasma in the interlaid chamber on the microwave attenuation in the frequency region5.0-6.0GHz and9.0-12.0GHz. The result shows that the plasma can greatly attenuate the energy of incident EMW and the attenuation enhances with the electron density. In the frequency region5.0-6.0GHz, at the argon pressure of25Pa and input power1600W, the attenuation value is about15dB. The plasma at the power1500W can attenuate the microwave of5.26GHz to about31dB. Be-sides, in the frequency region9.0-12.0GHz, the attenuation value is about lOdB at wide band (9.0-10.0GHz). Then the plasma at the power1700W can attenuate the microwave of9.8GHz to about32dB. Therefore, the top plasma can greatly attenuate the energy of incident C band and X band microwave. In addition, we observed the attenuation absorption peak would shift with the electron density and pressure because of the nonlinearity of attenuation coefficient. This work provides a solid experimental basis for the application in national defense. |
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