Electron beam exciter for optical emission spectroscopy and optical excitation cross section analysis in processing systems

Abstract

Plasma processing technology is indispensable for manufacturing the very large scale integrated circuits (ICs) used by the electronics industry. 48 Generally, the precise control and characterization of the plasma processing medium becomes pivotal to develop a successful product. At present, a variety of complementary characterization techniques are providing precise and detailed information on a variety of processing plasmas. However, newer generations of plasma processing techniques are becoming far too complex and their operating conditions impose great limitations on the operability and functionality of many important diagnostics. To adapt to these new set of constraints, the present work focuses on the development of a new Electron Beam Exciter device designed to conduct quantitative optical measurements in processing systems. This newly developed Exciter prototype employs a highly controllable electron beam of controlled energy level (Ee = 1/2 mv2) and density (n e) to cause light emission from electron-impact excitation events with gas particles that are part of the chemical makeup characterizing the processing environment. As such, the current design utilizes an inductively coupled plasma (ICP) source (RF coil antenna, 29 MHz) to generate a continuous cloud of electrons that can be extracted to an excitation region where optical and electrical measurements are collected. This variable plasma source, or electron bottle, is made out of a quartz or sapphire tube and is positioned opposite to an electron extraction assembly (or accelerator assembly), so that plasma electrons are extracted from the source via controlled dc electric potentials. The electron extraction assembly is composed of three distinct electrodes, namely the nozzle extractor, an extractor plate and a Faraday cup electrode, and is protected by a Tin doped Indium Oxide (ITO) interface that allows device operability in harsh halide enriched environments. Furthermore, the ability to successfully control the electron energy distribution function (EEDF) and energy level (Ee) characterizing the extracted electron beams allows the measurement of optical excitation cross-section from several reactive plasma effluents, some of which have not been measured before. The distinctiveness of the system with such a measurement capability to real time diagnostics, and its usefulness to measure cross sections of molecular species from plasmas are discussed