Optical emission from plasma

Optical emission from the plasma center was studied in Ref. [231]. The plasma was generated by a NIRlM-type reactor using CH4/H2 as the reaction gas. The substrate temperature was measured by a thermocouple on the backside of the 

In Ref [224], optical emission was studied for the plasma generated by an ASTeX reactor under conditions of ( =2%CH4/H2, P = 20Torr, rs = 750-800 °C, and Fp=-170 V. The substrate was a 3-inch Si wafer. For the purpose of actino-metric measurements, 10% Ar was added to the source gas. It should however be noted [235] that this Ar concentration might be too high, and could disturb the distribution of plasma species and other conditions. The bias current was higher if 

In Ref. [235], a plasma emission study was undertaken for CH4-H2-Ar plasma in an ASTeX reactor to investigate the effects of c, and P on (656 nm), Hp (486 nm), and C2 (516nm) emission lines. The typical plasma conditions were P=30Torr, / , = 800W, Ts hOO C, and Kb —300V. The source gas was CH4/H2/Ar = 8/392/11 seem, and the substrate was tungsten (W) of 50 mm in diameter and 6 mm in thickness, which had been mechanically abraded with 8-pm diamond powder. An Ar line at 696 nm was used as a calibration line. The observed 

For a detailed study of plasma emission under conditions that HOD films could be grown, see Ref. [236]. For studies of plasma emission spectroscopy without bias voltage, the readers can refer to Refs. [237-240]. 

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As can most clearly be seen in Figure 46d, the a-y transition occurs at a pressure of about 0.3 mbar for these experimental conditions. The impedance of the plasma, as well as the optical emission from the plasma, changes on going through the transition. The depletion of SiHq during deposition was already shown and... 

Figure 21. Experimental arrangement for monitoring optical emission from an r.f plasma. The photomultiplier tube (PMT) and picoammeter detection electronics are frequently replaced with photodiode arrays and photographic film in many spectroscopic studies.

Figure 10.21. Optical emission from the center of the plasma. The plasma conditions are listed in Table 10.1 [231].

Time-gated detectors that allow the optical emission from the laser plasma to be recorded at some time delay after the laser pulse are required to accurately capture the emission spectra. For the first few microseconds after the ignition of the laser spark, the plasma emits a strong white light continuum (also called bremsstrahlung), which decays as the plasma cools the characteristic atomic and ionic emission lines only appear as the plasma cools. A detector delay on the order of several microseconds after the laser pulse is used to eliminate interference from the continuum radiation. The principle is demonstrated in Figure 7.52. 

Analyses of alloys or ores for hafnium by plasma emission atomic absorption spectroscopy, optical emission spectroscopy (qv), mass spectrometry (qv), x-ray spectroscopy (see X-ray technology), and neutron activation are possible without prior separation of hafnium (19). Alternatively, the combined hafnium and zirconium content can be separated from the sample by fusing the sample with sodium hydroxide, separating silica if present, and precipitating with mandelic acid from a dilute hydrochloric acid solution (20). The precipitate is ignited to oxide which is analy2ed by x-ray or emission spectroscopy to determine the relative proportion of each oxide. 

In Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), a gaseous, solid (as fine particles), or liquid (as an aerosol) sample is directed into the center of a gaseous plasma. The sample is vaporized, atomized, and partially ionized in the plasma. Atoms and ions are excited and emit light at characteristic wavelengths in the ultraviolet or visible region of the spectrum. The emission line intensities are proportional to the concentration of each element in the sample. A grating spectrometer is used for either simultaneous or sequential multielement analysis. The concentration of each element is determined from measured intensities via calibration with standards. 

For intermediate temperatures from 400-1000°C (Fig. 11), the volatilization of carbon atoms by energetic plasma ions becomes important. As seen in the upper curve of Fig. 11, helium does not have a chemical erosion component of its sputter yield. In currently operating machines the two major contributors to chemical erosion are the ions of hydrogen and oxygen. The typical chemical species which evolve from the surface, as measured by residual gas analysis [37] and optical emission [38], are hydrocarbons, carbon monoxide, and carbon dioxide. 

Plasma analysis is essential in order to compare plasma parameters with simulated or calculated parameters. From the optical emission of the plasma one may infer pathways of chemical reactions in the plasma. Electrical measurements with electrostatic probes are able to verify the electrical properties of the plasma. Further, mass spectrometry on neutrals, radicals, and ions, either present in or coming out of the plasma, will elucidate even more of the chemistry involved, and will shed at least some light on the relation between plasma and material properties. Together with ellipsometry experiments, all these plasma analysis techniques provide a basis for the model of deposition. 

Knowledge on the plasma species can be obtained by the use of plasma diagnostics techniques, such as optical emission spectroscopy (OES) and mass spectroscopy (MS). Both techniques are able to probe atomic and molecular, neutral or ionized species present in plasmas. OES is based on measuring the light emission spectrum that arises from the relaxation of plasma species in excited energy states. MS, on the other hand, is generally based on the measurement of mass spectra of ground state species. 

Berndt et al. [740] have shown that traces of bismuth, cadmium, copper, cobalt, indium, nickel, lead, thallium, and zinc could be separated from samples of seawater, mineral water, and drinking water by complexation with the ammonium salt of pyrrolidine- 1-dithiocarboxylic acid, followed by filtration through a filter covered with a layer of active carbon. Sample volumes could range from 100 ml to 10 litres. The elements were dissolved in nitric acid and then determined by atomic absorption or inductively coupled plasma optical emission spectrometry. 

The basic instrumentation used for spectrometric measurements has already been described in the previous chapter (p. 277). Methods of excitation, monochromators and detectors used in atomic emission and absorption techniques are included in Table 8.1. Sources of radiation physically separated from the sample are required for atomic absorption, atomic fluorescence and X-ray fluorescence spectrometry (cf. molecular absorption spectrometry), whereas in flame photometry, arc/spark and plasma emission techniques, the sample is excited directly by thermal means. Diffraction gratings or prism monochromators are used for dispersion in all the techniques including X-ray fluorescence where a single crystal of appropriate lattice dimensions acts as a grating. Atomic fluorescence spectra are sufficiently simple to allow the use of an interference filter in many instances. Photomultiplier detectors are used in every technique except X-ray fluorescence where proportional counting or scintillation devices are employed. Photographic recording of a complete spectrum facilitates qualitative analysis by optical emission spectrometry, but is now rarely used. 

C.2. Mass Spectrometry. Like optical emission spectroscopy, mass spectrometry offers the ability to fingerprint and identify individual species in a plasma discharge or products in the effluent from a plasma reactor. Its most common application is the latter, and a diagram for effluent monitoring by... 

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