Volume 92, Issue 8, 15 October 2002
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
Measurements of and CH concentrations and temperatures in a dc arc jet using cavity ring-down spectroscopy92(2002); http://dx.doi.org/10.1063/1.1505675View Description Hide Description
Cavity ring-down spectroscopy has been used to measure the absorbances, concentrations and temperatures of and radicals in a ⩽10 kW dc arc jet used for chemical vapor deposition(CVD) of polycrystallinediamondfilms and operated with gas mixtures. Gas temperatures derived from the intensities and widths of rotationally resolved spectral lines are in the free plume, rising to ∼4800 K close to the substrate on which the diamondfilm is grown. For an input power of ∼6 kW, a 3.3% ratio with excess Ar and a pressure of 50 Torr, the conditions typically employed for diamondfilmCVD, concentrations of are between and in the free plume at distances >5 mm from the substrate. These values are derived assuming a 1 cm column length as implied by spatially resolved studies of optical emission; the spread reflects the decline in performance of the arc jet torch heads over time. The concentration of in the free plume is under similar operating conditions. Within 5 mm of the substrate, the measured absorption by both radicals rises steeply. The concentrations of and increase with added at fixed powers of 5.5 and 5.8 kW, but for mixing ratios in excess of 5% the concentrations of both radicals become invariant. Measured absorbance also increases with power input to the arc jet, but the CH absorbance is independent of this operating parameter.
92(2002); http://dx.doi.org/10.1063/1.1505683View Description Hide Description
The neutral gas temperature in a planar inductive discharge was measured with space and time resolution using laser-induced fluorescence of the CF radical with analysis of the rotationally resolved excitation spectra. Strong temperature gradients are observed and temperatures as high as 900 K are reached at the reactor center at 50 mTorr with a power density of The temperature at the reactor center increases with both gas pressure and power, but is independent of the gas flow rate. A simple model based on the global thermal energy balance is proposed to explain these results. The fraction of the injected rf power consumed in gas heating varies from 4.4% to 42% under our conditions (5–50 mTorr, 250 W rf power). Axial temperature profiles were measured in the steady state and in the time afterglow. The typical temperature relaxation times are several hundreds of microseconds. A numerical two-dimensional, time-dependent thermal model is in good agreement with the results.
92(2002); http://dx.doi.org/10.1063/1.1505682View Description Hide Description
A linear stability analysis of the low-current gliding arc discharge in the transitional regime is performed. It is shown that the gliding arc remains stable during the evolution and gradually transforms into a more nonequilibrium one. The low-current arc discharge can propagate with the effect of “overshooting” at which the gliding arc extinguishes long after its maximum power has been achieved. Analytical and numerical solutions explain the general behavior of the low-current gliding arc and are in a good agreement with our experiment.
92(2002); http://dx.doi.org/10.1063/1.1506421View Description Hide Description
We investigated the gas phase reaction mechanisms in the -deposition plasma using zirconium tert-butoxide (ZTB) as a metalorganic precursor, Ar as a carrier of the ZTB vapor, and as an oxidant using quadrupole mass spectrometry (QMS). Zirconium containing ions including and were clearly observed in the plasma, and ions of higher zirconiumoxidation states become progressively favored at higher -to-ZTB carrying Ar flow rate ratio increased chamber pressure, and decreased microwave power. The average oxidation state calculated from the partition of varied from 0.5 to 2.1 in the process range covering of 0 to 4, pressure of 5 to 40 mTorr, and power of 150 to 700 W. Based on the QMS analyses, we proposed two main opposing reaction paths responsible for the complex gas phase reactions, i.e., serial dissociations and serial oxidations. The increase in the electron temperature and density resulted in the shift of to lower oxidation states by enhancing the dissociation of Zr–O bond and by depleting oxygen through gas phase reactions. The repartitioning of the species was also contributed by their different Zr–O dissociation energies. To ascertain the effect of various process variables, we monitored the time evolutions of and intensities as we abruptly change a process variable: the chemical effect led to gradual changes in their intensities, whereas physical effects (pressure and power) caused an abrupt step change in accordance with an instant response of the plasma electrons.
92(2002); http://dx.doi.org/10.1063/1.1486056View Description Hide Description
In this work, the anode–cathode distance in a direct currentglow discharge is reduced manually to values smaller than the Child–Langmuir extent, while the discharge current, the discharge voltage and the Langmuir probe current are monitored continuously. The discharge current is observed to develop a large peak as soon as the sheath edge contacts with the anode, then decays to negligible values for a certain time interval, after which, this cycle starts repeating itself periodically. A model is described to interpret the behavior of all three quantities self-consistently. The experiment is performed with different anode–cathode distances and the implications of the observations regarding ion implantation processes are discussed.