Radiation Transport in Low Pressure Plasmas: Lighting and Semiconductor Etching Plasmas
Rajaraman, Kapil
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https://hdl.handle.net/2142/35216
Description
Title
Radiation Transport in Low Pressure Plasmas: Lighting and Semiconductor Etching Plasmas
Author(s)
Rajaraman, Kapil
Issue Date
2005-10
Doctoral Committee Chair(s)
Kushner, Mark J.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Plasma Physics
Radiation Transport
Electromagnetics Module
Electron Energy Transport
Monte Carlo Radiation Transport Model
Electrodeless lamps
Language
en
Abstract
Ultra-violet (UV) radiation is emitted by many molecular and atomic species in technological plasmas. In some products like lamps, the transport of radiation is an important design consideration. In other instances, such as semiconductor materials processing, the role of UV photons in surface processes is a side product and is poorly understood. Since the basic surface reaction mechanisms in semiconductor processing are now being developed, it is an opportune time to investigate the role of UV photons.
As lamp geometries become increasingly complex, analytical methods to treat radiation transport become more difficult to implement. Design of lamps must therefore rely on numerical methods. To investigate radiative processes in lighting plasmas, a Monte Carlo Radiation Transport Model was developed and interfaced with a two-dimensional plasma equipment model (HPEM). Investigations were performed on low pressure Ar/Hg electrodeless discharges. We found that analytically computed radiation trapping factors are less accurate when there is a non-uniform density of absorbers and emitters, as may occur in low pressure lamps. In our case these non-uniformities are due primarily to cataphoresis. We found that the shape of the plasma cavity influences trapping factors, primarily due to the consequences of transport of Hg ions on the distribution of radiators.
To address the role of radiation transport in semiconductor etching plasmas, we investigated the plasma etching of SiO2 in fluorocarbon plasmas, a process dependent on polymer deposition. We first developed a surface reaction mechanism to understand the role played by the polymer film that overlays the SiO2 substrate, and is essential to facilitating an etch. This mechanism was implemented in a Surface Kinetics Model of the HPEM. We found that the dominant etch channel in C4F8 plasmas was due to the fluorine released in the polymer layer by energetic ion bombardment. For plasmas that do not lead to strongly bound films (like C2F6 plasmas), defluorination is no longer the dominant SiO2 etch process.
Finally, we combined the models above to address radiation transport in fluorocarbon/Ar etching plasmas. We found that resonance radiation from Ar produced only small increases in etch rate due to photon-induced defluorination, and this increase was well offset by the decrease in etch rate due to a lower amount of etchant fluorine in the polymer layer. At the process regimes of interest to us, the ion-induced defluorination was much more dominant than UV-induced defluorination.
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