Diagnostics and modelling of an inductively coupled RF low-pressure low-temperature plasma.
The Open University.
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This thesis is a theoretical model and experimental study of the physics of a low pressure (5-50 mtorr), low electron temperature (1-10 eV), high density (1017-1018m3 ) inductively coupled plasma. This type of plasma is similar to those much used in plasma etching, deposition, and other plasma aided materials processing of devices [I-5].
A two-dimensional, electromagnetic, finite-element model has been set up to simulate the operation of the inductively coupled plasma using the external coil configuration used in the experimental work. Given fixed external RF coil current and voltage and the measured plasma density profile, Maxwell's equations and magnetohydrodynamical (MHD) fluid equations are used to calculate the self-consistent electromagnetic field. A number of predictions are presented and compared with experiments.
A symmetric, cylindrical inductively coupled discharge system has been set up. A single turn loop magnetic probe has been used to measure electromagnetic (EM) field in the discharge chamber. A Langmuir double probe has been designed to measure the plasma density and electron temperature. An emissive probe was used to measure the time averaged plasma potential, while a capacitive probe was used to measure the RF component of the plasma potential. A retarding field energy analyser has been used to measure the total ion flux flowing to the vessel on the midplane. Experimental results show that (1) the inductively coupled plasma is well confined inside the induction coil in the pressure range of 5-50 mtorr and RF power range of 10-400 W; (2) the measured electrostatic RF field (<1.0 V/cm ) in the whole discharge chamber is negligible, compared with the large induction RF field, which is in the order of 10 V/cm; (3) the RF power is coupled into the discharge through the nonlinear electron motion and corresponding collision processes; (4) it has been shown that the induction-field-ionization, electrostatic-field-modulation and various collision processes together influence the velocity distribution function of ions at the boundary surfaces.
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