Kurt J. Taylor

Measurement of radial neutral pressure and plasma density profiles in various plasma conditions in large-area high-density plasma sources

Hollow neutral pressure profiles, with significant on-axis reductions in neutral pressure (up to 40%), are observed across the face of an inert wafer in discharges with uniform plasma density. These results show that significant neutral depletion, which may cause the nonuniform plasma process results, can occur in large-area high-density plasma sources with a wafer present. The neutral depletion is explained by the ion pumping effect, wherein electron impact ionization of neutral particles is followed by their rapid movement from the plasma to the chamber wall by the presheath electric field. Cooling of plasma electrons via inelastic neutral collisions is also observed at elevated fill pressure, and results in a reduction of the magnitude of neutral depletion, thus demonstrating the linkage between plasma equilibrium and neutral equilibrium conditions. Initial experiments have also been performed in O2 discharges. Similar hollow neutral pressure profiles are observed, suggesting that similar effects occur...

Control of plasma parameters by using noble gas admixtures

Electron temperature and density in pure He, Ar, and Xe plasmas are estimated by zero-dimensional particle and power balance equations and measured by a Langmuir probe. Both of the modeling and experimental results show that the He (Xe) plasma has the highest (lowest) electron temperature and lowest (highest) electron density for a given fill pressure and source power. We find that the electron temperature is weakly dependent on the rf power, and thus the electron density can be controlled using the rf power. The electron temperature and density are also modeled and measured in mixtures of two noble gas species. We find that the electron temperature can be controlled by altering the composition of the noble gas mixture. Thus modulation of noble gas admixture ratios and rf power allows the electron density and temperature to be controlled independently. This independent control is shown to maintained with the addition of up to 20% partial pressure of oxygen, suggesting binary noble gas admixtures may provi...

Control of dissociation by varying oxygen pressure in noble gas admixtures for plasma processing

The electron density, electron temperature, and atomic oxygen density are measured in mixtures of oxygen and noble gas discharges as a function of the input power and the oxygen partial pressure. The atomic oxygen density is measured by both actinometry and appearance mass spectrometry and plasma density and electron temperature are monitored with Langmuir probes. The background noble gas determines the electron density and temperature as long as the partial pressure of oxygen remains small. The dissociated atomic neutral oxygen density is highest in O2∕Xe mixtures and lowest in O2∕He mixtures, increases with electron density, and decreases with electron temperature. Estimates of the dominant source and sink rates of atomic oxygen are used to explain these results using a simple zero-dimensional dissociation kinetics and transport model. The use of noble gas/oxygen mixtures allows for a larger range of atomic oxygen density and ion density than in pure oxygen plasmas, and also allows for independent contr...

Molybdenum and Carbon Cluster Angular Sputtering Distributions Under Low Energy Xenon Ion Bombardment

Molybdenum and carbon cluster (C 2 and C 3) angular sputtering distributions are measured during xenon ion bombardment from a plasma, with incident ion energy EXe ranging between 50 and 225 eV. A quadrupole mass spectrometer (QMS) is used to detect the fraction of sputtered neutrals that is ionized in the plasma, and to obtain the angular distribution by changing the angle between the target and the QMS aperture. The angular sputteri ng distribution for molybdenum presents a maximum at 60°, and this maximum becomes less pronounced as the incident ion energy increases. The dependence of the total sputtering yield on incident ion energy is in good agreement with previous experiments. The re is a large increase of about two orders of magnitude in the sputtering yield from EXe = 50 to 125 eV, and a more moderate increase for higher energies. Sputtered C 2 and C 3 clusters exhibit a similar angular sputtering distribution with a maximum at appr oximately 45 -60°; however, this maximum becomes more pronounced for higher incident energies, in contrast to the molybdenum case. The angular distribution of the sputtered clusters depends on the energy with which they are ejected. The low energy populatio n of sputtered particles has a broad maximum at 45°, while the high energy population has a sharp maximum at 60°. The cluster sputtering yield monotonically increases by less than one order of magnitude from EXe = 50 to 225 eV for all measured sputtering a ngles except for normal sputtering, which has a maximum yield at EXe� 100 eV.