Experimental Investigation Of Dual Frequency Capacitively Coupled Plasma Using Phase Resolved Optical Emission Spectroscopy At Low Pressures

In this article we use phase resolved optical emission spectroscopy to study space-time distributation in plasma sheath of dual frequency capacitively coupled plasma in Ar, O2and Ar-O2discharge at low pressures. And we also discuss the influence of different discharge conditions on the corresponding excitation rate of the excited states. The main results presented in the dissertation have been summarized as follows:It was found two emission patterns in sheath region of RF coupled powered electrode in pure argon and mixtures of argon and oxygen discharge. An emission pattern is related to electron impact excitation because of the sheath expansion. An emission pattern is caused by electron impact excitation of secondary electrons. The excitation profiles of two emission patterns are also highly modulated with the low frequency cycle. In oxygen plasma we mainly observed the emission pattern caused by sheath expansion in front of the powered electrode.Phase resolved optical emission spectroscopy was used to study the spatially and temporally resolved emission of the atomic argon at750.4nm in dual frequency capacitively coupled argon discharge at low pressures. The results show that both of the discharge power and gas pressure have a significant impact on the electron impact excitation caused by sheath expansion and secondary electrons. But the power absorption may occur in the electrode when the power of the low frequency source is too high. The excitation profiles caused by secondary electrons are nearly changed at the higher power of low frequency source. The two excitation profiles were becoming weaker at the higher discharge pressure or the increase the oxygen content of the gas discharge and electrode distance.The axial resolution was investigated in dual frequency capacitively coupled argon plasma. The results show that the axial resolution curve shows a single peak-like structure before powered electrode. And the peak had been approximate to be the thickness of the plasma sheath. The increases of the power of the high frequency source and adding a small amount of oxygen can significantly enhance the strength of the spectral lines. The low-frequency power has little effect on the spectral line intensity. The increases of discharge plate spacing, higher discharge pressure and the addition the content oxygen had reduced the axial uniformity. A preliminary experimental study of spatiotemporal distributions was investigated by atomic oxygen at777.4nm and844.6nm in pure oxygen discharge. The changes of high-frequency power, low-frequency power and discharge pressure had a significant effect on the electron impact excitation rate of plasma sheath. Additionally, two excitation profiles will shift to the first half low frequency cycle when adding the power of high frequency source. The electron impact excitation intensity is enhanced within a certain discharge pressure range. But the electron impact excitation intensity will be weakened at higher pressure. The excitation profile caused by secondary electron will gradually decrease as adding discharge pressure.