Low temperature plasmas are widely used in both industry and everyday life, from fluorescent lighting, water purification to important processes in semiconductor industry fabricating electronic devices.In most of these applications, the flux of various energetic species generated by low temperature plasmas are the main promoter of necessary reactions facilitating the applications, by efficiently delivering energy for chemical reactions at molecular level.For example, in the process of plasma etching for semiconductor material processing, fluxes of radicals and ions can selectively react with material on the surface of the wafer, creating surface structures on the order of 10s of nm over the surface area of 103 cm-3.In the work of this thesis, the possibility of gaining a better understanding at controlling those fluxes is explored numerically using a two-dimensional plasma equipment model.In semiconductor industry, control of ion fluxes and ion energy distribution is critical to optimizing fabrication process and pushing the limit of Moore’s law.In this thesis, a unconventional tri-frequency capacitively coupled plasma (CCP) is investigated for scaling of ion fluxes and energy over power of individual frequencies. Compared with the conventional single-frequency and state-of-the-art dual-frequency CCP, we discovered that additional control of ion energy distribution can be achieved by the power of two lower frequencies.Ion fluxes scale positively with increasing power at all frequencies, and are more sensitive to low frequency power.Vacuum-Ultra-Violet (VUV) photon fluxes are also discovered to have important effect during plasma etching, such that controlling of VUV photon fluxes could potentially benefit to process optimization.This work studied dynamics of a low pressure inductively coupled plasma (ICP), trying to develop approaches of separate controlling VUV and ion fluxes.It was discovered that the ratio of VUV and ion flux, β, can be controlled by pressure, gas mixture and even surface conditions of the reactor wall. β can also be a function of duty cycle in pulsed ICP, caused by the customized electron energy distribution facilitated by the pulse power.Pulsed ICP has been widely studied for its unique tunability of electron energy distribution.Normally operating in radio frequency, power delivery of ICP can be sensitive to the matching circuit of the system.In this thesis, the dynamics of a pulsed ICP is investigated against the matching network.Instead of considering power mismatch as limiting factor, a deliberately tuned off-match condition is used to control the plasma density of a pulsed ICP.Both experimental and computational results are reported to observe instantaneous match time changes with configuration of matching circuit.Pulsed ICP that matches at a later time exhibits delayed density rise time with a larger final density.Low temperature plasma source are also investigated as a device for chemical analysis.A microwave excited microplasma, operated at several watts, is generated in dielectric cavities of hundreds of microns as ionization source for a novel concept of mass spectrometer.VUV photon fluxes produced from such microplasma source are then used to ionize samples for spectrometry.Result shows that the power efficiency of VUV emission is less than 1% and saturates as power increases.The VUV spectra can be individually tuned by adding Penning gas in the mixtures.
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Controlling Photon and Ion Fluxes in Low Pressure Low Temperature Plasmas
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