| Radio frequency inductively coupled plasma (RF ICP) is widely used in plasma etching of microelectronic chip, deposition of semiconductor thin film, broad high-current ion source, plasma immersion ion implantation, chemical synthesis and crystal growth due to the advantage of the high plasma density at low gas pressure, simplified device and more precise control over spatial uniformity. In the research of RF ICP, anomalous skin effect, E-H mode transition and pulse modulation discharge have intrigued researchers. The improvement of RF magnetic probe and Langmuir probe, which are important tools of RF ICP, has important significance.For the concerned subjects, the following works are done in this thesis:I. Improvement of tunable RF magnetic probe and Langmuir probe1. The rotary capacitor tunable RF magnetic probe has been improved by adding the compensating capacitor, which remedies the asymmetry of the probe for the propagation of common mode(CM) signal. The effect of compensating capacitor on suppressing CM signal was tested. The propagation model of CM signal was built and the CM signal sensitivity of the magnetic probe was calculated. The results show that:compared with conventional magnetic probe, the improved magnetic probe increases the output of differential mode (DM) signal and suppresses the output of CM signal. The signal-to-noise ratio (SNR) of the rotary capacitor tunable RF magnetic probe was improved.2. In practical measurement on RF ICP source, it was found that the effect of compensating capacitor on suppressing CM signal is closely related to the magnitude of RF CM signal (RF plasma potential). For the RF CM signal being not constant in the ICP, the electrical asymmetry of the rotary capacitor is difficult to be compensated completely. To solve this problem, the resonant RF magnetic probe tuned by series-connected coaxial cable, which has better electrical symmetry, was proposed. The electrical symmetry of primary winding of center-trapped transformer (CTT) was also improved by twisted wires to further suppress the CM signal. The magnitude and relative phase of the series-connected cable tunable RF magnetic probe was calibrated. The output voltage as a function of the temperature of the pickup coil was also studied. The measurement result show that the CM noise with different magnitudes is well suppressed by the series-connected cable tunable RF magnetic probe, and it can be used to the measurements on the RF ICP source.3. When the Langmuir probe is used to measure the parameters of RF plasma by Ⅰ-Ⅴ characteristic, passive compensation is a simple and effective method to reduce the RF potential interference. The high impedance RF filter is designed near the tip of the probe. This kind of probe needs to be cool and is easy to be destroyed by the high temperature, so that the range of RF discharge power of plasma is limited. We adopted a wide-band high impedance filter installed out of the discharge chamber to solve the problem, and a compensation electrode with large capacitance was used to further reduce the RF interference. In this paper, the manufacturing process of compensation probe is described in detail, and the advantages of the Langmuir probe with high impedance filter out of the chamber is discussed. The improved Langmuir probe can be used to the measurement in the plasma with different frequency and high RF discharge power.II. Studies on the anomalous skin effect in cylindrical RF ICP.The radial distribution of magnetic field in cylindrical RF (13.56MHz) ICP was measured by the series-connected cable tunable RF magnetic probe. The radial distribution of RF current density was calculated using the experimental result. The effects of absorbed power of plasma, gas pressure, local and different coupling of antenna, on anomalous skin were studied. The results suggest that the anomalous skin effect exists in the condition of low gas pressure and high discharge power. Compared with the measured results in other ICP, the distance between the position of the anomalous skin effect in cylindrical RF (13.56MHz) ICP and antenna is smaller. With the increasing RF power of ICP, the magnetic field and current density demonstrates anomalous behavior:the magnetic field has local minima and anomalous increases; two rings of current (the outer and the inner rings of current are off-phase and in-phase with the current of antenna respectively) are formed in plasma. The relative phase between the two rings of current increases with the increasing RF power of ICP. At lower gas pressure, the anomalous behavior of magnetic and current density becomes more significant with the increasing gas pressure, however, at higher gas pressure, the anomalous behavior disappears gradually with the increasing gas pressure. The experimental results for effects of local and different coupling of the antenna are shown. The results shown that anomalous skin effect is closely related to the local plasma density. According to the physical principles, the characteristics of anomalous skin effect in cylindrical RF (13.56MHz) ICP are discussed and explained, combined with the coil geometry characteristics of cylindrical RF ICP.III. Studies on temporal evolution in pulsed RF ICP 1. The current of antenna was found not equal in different feedback region with same voltage (discharge power) of antenna, when it was measured by current probe. The difference of the current measured by current probe is caused by the interference of the current through the matching network. The interference was effectively reduced by shielding the matching network.2. For explaining the complex temporal evolution behavior in pulsed RF ICP, the current and voltage of the antenna was measured with different discharge mode, different feedback region, different antenna and different discharge power in continuous discharge, and the Smith chart was also given. The difference of feedback region and Smith chart with different antenna is explained by the calculation of the system impedance.3. The waveforms of antenna current and voltage were measured with different feedback region, different antenna, different discharge power and different off-time in pulsed RF ICP. With the measured results in continuous wave discharge, the effects of feedback region, antenna, discharge power and temperature for the temporal evolution are analyzed. The results show that the complex temporal evolution behavior is closely related to the E-H mode transition in different feedback region and the temperature rise of the gas. Compared with that in the positive feedback region, the waveform in the negative feedback region evolves gently. When the whole pulse is in E mode discharge, the waveform is relatively simple that only influenced by breakdown processes at the initial stage of the pulse. When the discharge power approach the E-H mode transition region, the temperature rise of the gas will promote the appearance of transition, and the antenna current and voltage fluctuate during the pulse. When the discharge power is relatively higher, the E-H mode transition is completed in the breakdown process. The initial stage of the pulse is influenced by both E-H mode transition and the breakdown process. |
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