Inductively Coupled Plasmas: The GEC cell at NASA-Ames, which has been designed to study inductively coupled plasmas, is currently equipped with various diagnostics - (1) Mass Spectrometer, (2) Langmuir Probe, (3) Fourier Transform Infrared (FTIR) spectroscopy, (4) Ultraviolet (UV) absorption, (5) Optical Emission Spectroscopy (OES), and (6) Plasma Impedance Monitoring (PIM). An additional diagnostic "Microwave Interferometry" is under construction.
The primary objective of this research is to develop a database for improving the fundamental understanding of the physical and chemical phenomena occurring in the plasma processing. Low-pressure fluorocarbon gas plasmas such as CF4, CHF3, C4F8, etc. mixed with oxygen or hydrogen or argon or a combination of them have been routinely employed in etching of silicon dioxide (SiO2) over silicon (Si) and other materials for the fabrication of Ultra-Large-Scale Integrated circuits (ULSI). However, many plasma-based processes suffer from stability and reliability problems leading to a compromise in performance and a potentially increased cost for the semiconductor manufacturing industry. Such a lack of understanding has hindered the development of process models that can aid in the scaling and improvement of plasma etch and deposition systems. With the present state-of-art capabilities in our laboratory the much needed fundamental parameters, such as species concentrations, electron and ion kinetics, and the reactions due to electron-impact, gas-phase ion-molecule collisions, and plasma surface interactions, can be measured. In the present studies, the fluxes and energy distributions of ions and neutrals are measured by using Mass Spectrometry, FTIR, UV and OES, and the electron energy distribution function, electron number density, electron temperature, and plasma potential by Langmuir Probe technique.
Electron-Atom/Molecule Collision Studies: The aim of this research program is to measure collision cross-sections for electron attachment, total ionization, direct and dissociative ionization, and kinetic energy distributions of ions by electron impact on molecules of interest to plasma processing gases by using crossed electron beam-molecular beam apparatus. The present apparatus was designed and fabricated at the NASA-Ames Research Center. It consists of a trochoidal electron monochromater, a Faraday Cup, a capillary array for producing molecular beam, a pair of ion extraction grids, a set of ion transporting lenses, and a mass spectrometer for ion selection depending on their mass to charge ratio (M/q). These components are housed in a vacuum chamber. This research project is a complementary to our efforts to advance plasma chemistry for materials processing as discussed above. The most daunting current problem in modeling of low temperature plasmas is the lack of cross-section data for many fundamental collisional processes. A comprehensive knowledge of cross-sections for electron-molecule collisions of interest in plasma processing can significantly improve the predictive capability of computational models.
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