Radical Density Measurements Research Articles

Measurement of absolute radical densities in a plasma using modulated-beam line-of-sight threshold ionization mass spectrometry

Using modulated beam line-of-sight threshold ionization mass spectrometry (LOS-TIMS) we measured absolute O, O2, and Ar densities, and the average neutral-gas temperature in an O2/Ar electrical discharge as a function of pressure in the plasma chamber and the mole fraction of Ar in O2; the pressure and mole fraction range was 25–200 mTorr and 0–0.90, respectively. Although LOS-TIMS is a versatile tool for measuring absolute radical densities, it requires careful vacuum design and calibration to account for various sources of error such as the contribution to the quadrupole mass spectrometer (QMS) ion current from the background gases, the ion mass-to-charge ratio dependent sensitivity of the various QMS components, and space-charge limitations in the QMS ionizer. In addition, collisions within the molecular beam extracted from the discharge must be taken into account particularly for higher plasma chamber pressures (>75 mTorr). In our measurements, these effects are carefully considered and the consequences of ignoring them are discussed. The O atom density increases with pressure and O2 mole fraction in the feed gas and is in the range of 2.1×1018–2.6×1019 m−3. At low pressures, our measurements show that the O2 translational temperature is higher than that for Ar.

Oxygen Radical Density Measurement in O2-N2 Mixture Gas Plasma by means of a Platinum Thin Wire

Oxygen Radical Density Measurement in O2-N2 Mixture Gas Plasma by means of a Platinum Thin Wire

Radical Density Measurement at Low-Pressure Discharge Denitrification by Appearance Mass Spectrometry

In discharge denitrification, radical production by electron collision with combustion gas is a key process which determines the denitrification process and its performance. In this study N, O, OH and H radical densities have been measured by appearance mass spectrometry in a low-pressure discharge field with parallel electrodes (2 cm gap) under simulated combustion gas flow. Also, electric field, electron number density and electron temperature at the radical sampling position have been measured by the Langmuir probe method. Under constant discharge pressure the radical density (cm-3) was about 1011–1012 cm-3, and the density increased with increasing the discharge current. Under constant discharge current, both the radical concentration [-] and electron temperature increased with decreasing pressure. The radical concentration in the cathode fall region was greater than that for the outer region. Additionally, we measured the concentration change of NO mixed in the simulated combustion gas and observed a little change of the NO concentration.

Radical density measurements in an atmospheric pressure oxyacetylene torch

We used highly sensitive absorption spectroscopy to quantify molecular radicals in the gas phase of an oxyacetylene torch diamond growth system. We measured column densities of , CH, CN and OH as a function of position in the flame for several different flame mixtures. We derived the flame gas kinetic temperature from the Swan band spectra. We searched for , singlet , and and established upper limits on the column densities of these radicals. The results were qualitatively correlated with diamond growth as judged by Raman spectra and scanning electron microscopy. The column densities of and CH correlate best with the growth of diamond.

Application of Non-Linear Optical Methods to Plasma Diagnostics

The application of non-linear optical methods nowadays allows the measurement of an increasing number of specific plasma quantities which were previously not amenable to diagnostics. Among those are state resolved measurements of molecular density distributions, sensitive measurement of light atomic radical densities, electric field measurements, and determination of quenching rates. In this paper an overview of the available techniques and trends is given. Some selected topics are discussed in more detail.

Radical density measurements in an oxyacetylene torch diamond growth flame

The column densities of several molecular radicals are measured in an oxyacetylene torch flame during the growth of diamond films. The column densities of CH, C2, CN, and OH radicals are determined by highly sensitive absorption spectroscopy. The radical densities are measured as a function of position in the flame for different fuel/oxidant ratios. The growth of diamond is confirmed by scanning electron microscopy and Raman spectroscopy. Of the four radicals measured, the C2 and CH densities are the most correlated with diamond growth. The measured densities are compared with numerical flame models.

CH 3 detection in a low-density supersonic arcjet plasma during diamond synthesis

We report on the measurement of methyl radical (CH3) densities in a low-density supersonic arcjet plasma used in the synthesis of diamond films. Single-pass, high-sensitivity ultraviolet (UV) absorption spectroscopy has been employed to study the X(2A2″)→B(2A1′) transition of the methyl radical near 216 nm. The minimum detectable CH3 density is found to be ∼4×1013 cm−3, which corresponds to a fractional absorption of 2×10−3 at a gas temperature of 1200 K. The dependence of the measured methyl column density on pressure and CH4/H2 flow ratio has been studied. The results are used to revise our previous estimates of the reactive “sticking” coefficient for CH3, and we now find that it is of order 10−2 under conditions where we have previously documented the growth of high quality diamond films.

Fluorocarbon radicals and surface reactions in fluorocarbon high density etching plasma. I. O2 addition to electron cyclotron resonance plasma employing CHF3

Gas phase reactions of CFx (x=1−3) radicals and F atoms in an electron cyclotron resonance (ECR) downstream plasma were investigated at 300 W and a CHF3 pressure of 0.4 Pa by adding O2 to CHF3 using infrared diode laser absorption spectroscopy and actinometry, respectively. By adding a small amount of O2 to CHF3, the CF and CF2 radical densities rapidly decreased, while the CF3 radical density rapidly increased but then decreased with further addition of O2 to CHF3. These reaction mechanisms in the plasma were evaluated on the basis of measurement results of CFx (x=1−3) radical and F atom densities. Under the same conditions as the measurements of radical densities, the etching rates of Si and SiO2 were measured. Furthermore, the etched Si surfaces were also analyzed with x-ray photoelectron spectroscopy. The etching mechanisms for Si and SiO2 in the CHF3/O2 ECR plasma were investigated by connecting these etching characteristics on Si and SiO2 with the behaviors of CFx (x=1−3) radical and F atom densities. The Si etching rate was affected primarily by the concentrations of the CF and CF2 radicals and F atoms in the plasma.

Fluorocarbon radicals and surface reactions in fluorocarbon high density etching plasma. II. H2 addition to electron cyclotron resonance plasma employing CHF3

Gas phase reactions of CFx (x=1–3) radicals and F atoms in an electron cyclotron resonance (ECR) downstream plasma have been investigated at 300 W and a CHF3 pressure of 0.4 Pa by adding H2 to CHF3. The behaviors of CFx radical densities were measured using infrared diode laser absorption spectroscopy, while F atom density was estimated with actinometry. Furthermore, the composition of fluorocarbon films deposited on the chamber walls in the CHF3/H2 ECR plasma has been investigated with x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. On the basis of measurement results, the correlation between the characteristics of fluorocarbon films and the behaviors of radicals in the plasma has been investigated. The CF radical density was found to be changed by the variation of the composition, in particular F/C ratio, of the films deposited on the chamber walls. Under the same conditions as the measurements of radical densities, the deposition rates of fluorocarbon films formed on the substrate set in the downstream plasma region were measured. The behavior of CF radical density followed the deposition rates, which suggested that the CF radical played an important role for the formation of carbon-rich fluorocarbon films in the CHF3/H2 ECR plasma.

SiO2 Etching Employing Inductively Coupled Plasma with Hot Inner Wall

The selective etching of SiO2 on Si employing C4F8/H2 inductively coupled plasma (ICP) was studied based on measurements of radical and ion densities, flow rate and wall temperature. Since polymer films were not deposited when the reacter wall was heated to temperatures above 200° C, CF1 radical density at 200° C was one order higher than that at the wall temperature of 30° C. Thus both Si and SiO2 etch rates decreased rapidly with increasing H2 concentration in C4F8, and Si etching stopped at 15% H2. The etch stop was attributed to insufficient removal of polymer with a reduced amount of ions and was suppressed considerably by increasing the RF power to generate a large amount of ions. The use of poly-Si masks reduced the microloading effect in comparison to resist masks and a contact hole feature with 0.2 µ m size and aspect ratio of 6 was successfully obtained.

Measurement and Calculation of SiH2 Radical Density in SiH4 and Si2H6 Plasma for the Deposition of Hydrogenated Amorphous Silicon Thin Films

SiH2 radical density in SiH4 and Si2H6 plasmas diluted with He, Ar and Xe has been measured using intracavity laser absorption spectroscopy, and analyzed by a gas-phase reaction simulation. The density of SiH2 increases with dilution due to increase in dissociation rate of parent-gas molecules. The increase in the dissociation rate for He and Xe dilution originates in the increase of electron energy and density, respectively, and both of these contribute for Ar dilution.

CH3 and CH Densities in a Diamond Growth DC Discharge

AbstractA highly sensitive multi‐element optical absorption technique is used to measure the absolute column density of both CH3 and CH radicals in a dc hollow cathode plasma‐assisted chemical vapor deposition (CVD) system with CH4 and H2 used as the input gases. The plasma gas temperature is determined at different spatial points using the H2 emission spectrum near 460 nm. The spatial maps of the temperature and the radical densities provide information on the chemical processes taking place in the discharge. The CH3 and CH radical density measurements made in the dc discharge system are compared with similar measurements made in a hot filament CVD system. The [H]/[H2] ratio is derived from the CH3 and CH densities using an analysis based on partial thermodynamic equilibrium of the single carbon hydrocarbon abstraction reactions.

Calculated Three Dimensional Spatial Distribution of CH3 Radical Density in the RF Discharge CH4 Plasma with Parallel-Plate Electrodes

The three-dimensional spatial distribution of the CH3 radical density has been calculated in the model of an RF discharge CH4 plasma-enhanced chemical vapor deposition (P-CVD) chamber with parallel-plate electrodes in both cases with and without the White-type multiple reflection arrangement for absorption spectroscopy. The result showed that the CH3 radical density decreased sharply and was negligible outside the plasma region irrespective of the geometry of the White-type multiple reflection of the glass tube. The deposition of carbon thin film was also measured. The result showed a tendency similar to that of the calculated distribution of the CH3 radical. Therefore, it is concluded that the absorption path length of the laser beam can be defined as the length of the beam which passes through the plasma region in the case of CH3 radical density measurement using infrared laser absorption spectroscopy.

CF3, CF2 and CF Radical Measurements in RF CHF3 Etching Plasma Using Infrared Diode Laser Absorption Spectroscopy

We have measured the characteristics of CF3, CF2 and CF radical densities in RF CHF3 etching plasma under the same condition using infrared diode laser absorption spectroscopy, for the first time. The CFx radical density measurements have been performed as a function of input RF power, CHF3 gas pressure and distance from the RF electrode. On the basis of these systematic measurements, the generation and loss processes of CFx radicals in RF CHF3 plasma were discussed.

Absolute radical density measurements in a CH 4[sbnd]H 2 d.c. discharge

A highly sensitive multi-element optical absorption technique is used to measure the absolute column density of both CH 3 and CH radicals in a d.c. hollow cathode plasma-assisted chemical vapor deposition (CVD) system with CH 4 and H 2 used as the input gases. The plasma gas temperature is determined at different spatial points using the H 2 emission spectrum. The temperature and radical density spatial maps provide clues to the chemical processes taking place in the discharge. CH 3 and CH radical density measurements made in a hot-filament CVD system are compared with those made in the d.c. discharge CVD system.