Experimental Investigation Of Discharge Mode Transition And Hysteresis In Radio-Frequency Inductively Coupled Plasma

Radio frequency (rf) inductively coupled plasma (ICP) has been widely used in the semiconductor industry for etching and deposition of thin films due to their characteristics, i.e., high densities of ions, electrons, and radicals, good uniformity over large diameters and the low pressure operation enviroment. In particular, it is triggering much interest of many physicists by its different operating discharge modes, E mode (capacitive discharge) and H mode (inductive discharge). Moreover, the variation of plasma density with coil power always depends on the history of discharge and therefore a hysteresis of plasma parameter may occur with external power or coil current during the E and H mode transiton. The E-H mode transition and hysteresis can significantly affect the plasma assisted deposition and etching processes. Therefore, in order to control essential plasma parameters for the processing technology, it is crucial to study the characteristics and internal mechanisms of the E-H mode transition and hysteresis.In the thesis, a Langmuir probe, Z-Scan and an intensified charge coupled device (ICCD) camera are applied to study the discharge mode transition and hysteresis in ICP. Electron density, plasma emission intensity, input current and voltage are measured during the E-H mode transition at different pressures and different matching network sets. Besides, we also study the effects of rf bias voltage on plasma parameters in different modes.In Chapter 2, the planar coil ICP equipment and the diagnostic devices are described in detail. The working principles of the common experimental diagnostic tools, i.e., Langmuir probe, Z-Scan and ICCD are introduced. In Chapter 3, the axial and radial distributions of electron density, electron temperature, plasma potential, and the electron energy distribution function (EEDF) of Ar discharge in H mode are measured by the Langmuir probe. Furthermore, the effect of gas ratio on the electron density, electron temperature and EEDF are investigated in Ar-CF4 discharge. The results show that the electron density, electron temperature and plasma potential increase with increasing the input power. However when the pressure is increased the electron density increases, while the electron temperature and plasma potential decrease. In addition, the electron density decreases with increasing the ratio of CF4, while the electron temperature and plasma potential increase.In Chapter 4, the evolution of electron density and plasma emission intensity during the E to H mode transition are investigated by the Langmuir probe and ICCD, especially for their uncontinuous variations at the mode transition points. The results show that the electron density and emission intensity jump up discontinuously at high pressure, but they increase almost continuously at E to H mode transition at low pressureIn Chapter 5, an experimental investigation of the hysteresis during the E-H mode transitions at various matching situations in Ar discharge is carried out. The results show two hysteresis loops of the plasma density and the electrical parameters in the discharge circuit, when the series capacitance is cycled at high pressure. At low pressure only one hysteresis loop appears. In addition, the hysteresis loop of measured electron density against appled power expands with the increase of the matching capacitance. The same trend is observed in the loops based on the input current, voltage, and phase angle. In Ar-N2 and Ar-O2 discharge, the hysteresis loops shrink with the increase of the ratios of N2 or O2.In Chapter 6, an rf bias effects on the plasma properties in E and H mode are studied by the Langmuir probe and ICCD. In the E mode, a bias-induced increase in plasma emission and density is detected. The 2D profiles of the plasma emission show that the intensity significantly increases near the substrate electrode when the RF bias voltage is applied. This proves that the plasma in the region above the substrate electrode is heated by the RF bias voltage. The cooperation of two rf power sources on heating the plasma means that a synergetic discharge is formed. However, in the H mode, rf bias produces a decrease in electron density and plasma emission intensity. And the measured 2D profiles of the plasma emission are more symmetrical and the profile shape is almost unchangeable with the increase of RF bias voltage. The decreasing plasma density and emission intensity are probably caused by a high-voltage capacitive sheath which is formed between the rf biased substrate and the bulk plasma.