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Section 7.2: Spatially Resolved Spectroscopic Analysis of the Plasma
Published in Mark A. Prelas, Galina Popovici, Louis K. Bigelow, Handbook of Industrial Diamonds and Diamond Films, 2018
A. Gicquel, M. Chenevier, M. Lefebvre
A comparison of the gas temperatures found in microwave plasma reactors with those reported in hot filament reactors is interesting since the pressure conditions are similar for both reactors. Also the growth rate and diamond film quality are comparable. In hot filament reactors, typical filaments temperatures ranging from 2000 K to 2800 K according to the power supplied to the filaments (0.5 kW to 2.7 kW)22,29, are reported. However, measurements by CARS29 very close to the filament showed that the gas temperature is lower by 200 K than the filament temperature. The gas temperature decreases slightly from this initial value until that of the substrate temperature (diffusional transport). The typical gas temperatures obtained in hot filament reactors are then similar to those measured in microwave reactors, although slightly lower. However one of the main difference between these reactors is the temperature gradient at the diamond substrate. In plasmas reactors, much higher temperature gradients at the diamond substrate are found, owing to plasma processes which maintain high temperatures closer to the surface. In reactors such as arc-jet or plasma torch, higher temperatures ranging from 3000 K to 5000 K are reported48,95.
Fundamentals of Vacuum and Plasma Technology
Published in Andrew Sarangan, Nanofabrication, 2016
Some of the problems with the hot filament ion gauges can be addressed with cold cathode ion gauges. Instead of emitting electrons from a hot filament by thermionic emission, electrons in cold cathode gauges are emitted by high electric fields. This is also known as field emission. However, this also results in a smaller number of free electrons being emitted and can lead to a smaller ion current. To increase the ionization rate, strategically placed magnets are introduced to make the electrons travel in a tight spiraling path. This greatly increases the collision rate of electrons within a volume, but the ultimate sensitivity of the gauge is still considered to be somewhat inferior to hot filament gauges. The primary advantage of cold cathode gauges is that they do not have filaments. Sudden changes in pressure are not a serious concern as they are with hot filament gauges. They also have less gas desorption issues due to the absence of a hot filament.
In-Situ Metrology
Published in Robert Doering, Yoshio Nishi, Handbook of Semiconductor Manufacturing Technology, 2017
Gas ionization is usually achieved using an electron-impact type process. Electrons are emitted from a hot filament (2200°C) using an electric current. Few metals have a low enough work function to supply currents in the milliampere range at such temperatures. Filaments are usually coated with materials with better thermo-emission properties. Typical coatings are thoria and yttria and typical base metals are tungsten, iridium, and rhenium. Electrons are then accelerated to acquire an energy in the 30–70 eV range, which corresponds to the highest ionization cross-sections for several gases. The ionization occurs in an enclosed area called the ion source. There are many types of sources, but the major distinction is between open and closed sources. The higher the pressure in the source, the greater is the sensitivity to minor constituents. The sensitivity is the minimum detectable pressure relative to the maximum number of ions produced in the source. A closed ion source has small apertures to introduce the sample gas from the process environment, to allow the electrons to enter the source, and to extract the ions into the mass filter. With the use of an auxiliary pump, the filaments and the mass filter and the detector are kept at a much lower pressure than the source. In addition to greater sensitivity, the advantages associated with closed sources are: (1) prolonging the filament lifetime in the presence of corrosive gases and (2) enabling electron multipliers to be used as ion detectors. However, the high complexity and cost associated with the aperture’s precision alignment and the required high vacuum pump make closed-source-type instruments very expensive.
Comparative electrical performance and failure analysis of air-annealed ruthenium Schottky contacts on 6H-SiC and 4H-SiC
Published in Journal of the Chinese Advanced Materials Society, 2018
The Ru thin films were deposited on the polished side of both 4H-SiC and 6H-SiC by an electron-beam deposition technique. The e-beam deposition system chamber was evacuated to a pressure of <10−6 mbar before the start of the deposition process. In the e-beam system, a hot filament emits electrons which are then focussed on the target material by magnetic and electric fields. In this investigation, the target material was Ru in a carbon crucible. The impact of the electrons on the Ru sample made it evaporate and get deposited on the sample substrate (4H-SiC or 6H-SiC) placed above the carbon crucible.