Study On Diagnosis Of Probe-assisted Pulsed Laser Induced Photo-detachment Technique For Capacitively Coupled Electronegative Plasma

Investigation of electronegative plasma is becoming more and more attractive due to its applications in semiconductor and photovoltaic industry. In this thesis, we have stressed the techniques of langmuir probe and probe-assisted pulsed laser induced photo-detachment for investagating capactively coupled electronegative plasma driven by 40.68 MHz. In the first part of this thesis, we applied Langmuir electrostatic probe to measure the capacitively coupled Ar plasma driven by 40.68 MHz with adding electronegative gases, such as O2, Cl2 and SF6 into Ar. The electron energy probability function(EEPF),electron density, electron temperature, ion density and electronegativity of plasma with different flow ratio of electronegative gases were compared. Experimental results indicate that the EEPF has a transition from typically bi-Maxwell distribution in Ar plasma to a structure of low-high bienegy peak in electronegative plasma. The electron density decreases and temperature increases due to the loss of low and medium enegy electrons. Meanwhile, the electronegativity of plasma increases obviously with increasing electronagetive gas flow rate in Ar.In the second part of this thesis, we applied high energy pulsed laser beam with wavelength of 532 nm in assistance of langmuir probe to iradiate the capacitively coupled O2 plasma driven by 40.68 MHz. Spatial potential of the plasma and electronegativity were diagnosed by exerting a certain positve bias on the probe with probe axis aligned with laser beam at the center. The experimental results show that a transition of signal wave shape on the probe occurs from V-shaped to invert U-shaped as increasing positive bias. We have given an empirical method to obtain the spatial potential of negative plasma by using LIPD technique. Additionally, plasma electronegativity keeps a constant basically as increasing positve bias beyond the plasma spatial potential. The experiments still show a trend of decrease in electronegativity of O2 plasma with increasing input power.