No abstract

Ion-induced secondary electron emission at a target surface is an essential mechanism for laboratory plasmas, i.e. magnetron sputtering discharges. Electron emission, however, is strongly affected by the target condition itself such as oxidation. Data of oxidized targets, however, are very sparse and prone to significant systematic errors, because they were often determined by modeling the complex behavior of the plasma. Thus, it is difficult to isolate the process of ion-induced electron emission from all other plasma-surface-interactions. By utilizing ion beams, the complex plasma environment is avoided and electron yields are determined with a higher accuracy. In this study, ion-induced secondary electron emission coefficients (SEEC) of clean, untreated (air-exposed), and intentionally oxidized copper and nickel surfaces were investigated in such a particle beam experiment. Pristine and oxidized metal foils were exposed to beams of singly charged argon ions with energies of 200 eV - 10 keV. After the ion beam treatment, the surface conditions were analyzed by ex-situ XPS measurements. Further, a model for the electron emission of a partly oxidized surface is presented, which is in agreement with the experimental data. It was found, that oxidized and untreated/air-exposed surfaces do not show the same SEEC: for intentionally oxidized targets, the electron yields were smaller by a factor of 2 than for untreated/air-exposed surfaces. SEECs of oxides were found to be between the values for clean and for untreated metal surfaces. Further, the SEEC was at maximum for untreated/air-exposed surfaces and at minimum for clean surfaces; the electron yields of untreated/air-exposed and clean surfaces were in agreement with values reported in literature.

Due to the increasing number of applications for ceramic components in reactive etching processes, the interest in the specific erosion behavior of highly etchresistant materials like yttrium oxide (Y 2 O 3 ) has increased in the past years.Despite the large number of investigations already existing in this field, a more general understanding of the erosion mechanisms still lacks due to the limited comparability of these investigations. The huge difference in the kind of etching setups, processing parameters (bias voltage and plasma gas composition), and sample microstructures prevented consistent conclusions so far. To achieve a more general understanding, this study investigates the erosion behavior Y 2 O 3 under a broad spectrum of plasma etching parameters. Therefore, the bias voltage is increased from 50 to 300 V and the plasma gas composition is gradually changed from Ar-rich to CF 4 -rich compositions. This systematic approach allows to directly correlate the morphology changes caused by plasma erosion with the related plasma etching parameters and enables to better understand their influence on the depth of physical and chemical interactions, surface damage, and etching rate. We discovered three distinct erosion regimes, which exhibit specific erosion characteristics. Using these observations, a schematic processing map for Y 2 O 3 was developed, which could help to estimate the severity of the erosion attack dependent on the processing parameters.

The evolution of SiO2 microstructures, deposited from hexamethyldisiloxane (HMDSO) and oxygen gas mixtures by two different low pressure plasma sources, namely an inductively coupled plasma (ICP process) at 3 Pa and a microwave plasma (MW process) at 100 Pa, is evaluated and compared. The microstructure is monitored using ellipsometric porosimetry (EP) applying three different solvent molecules (water, ethanol, and toluene) to probe the different adsorption and absorption mechanisms as well as the pore sizes. Both plasma processes are adjusted so that an equivalent oxygen atom contribution to the growth flux is established and that an equivalent specific energy per molecule is dissipated in the process. The major difference is the partial pressure of the HMDSO precursor molecules, which is 0.04 Pa in the ICP process and 1 Pa in the MW process. The porosimetry analysis indicates that the SiO2 films originating from the MW process are more porous than those from the ICP process. The pore sizes are typically in the range of 0.3 nm for films deposited from both plasma processes. This is explained by assuming that the gas phase polymerization in the MW process is much stronger due to the higher HMDSO partial pressure and, therefore, the SiO2 films are deposited from larger HMDSO fragments in the MW process compared with smaller HMDSO fragments in the ICP process. This difference in the main growth species becomes visible in the different microstructures. Consequently, a plasma process using smaller precursor partial pressures seems to be optimal.

Ion-induced secondary electron emission of surfaces occurs in all gas
discharges which have contact to surfaces such as electrodes or chamber walls. These
secondary electrons (SE) play an important role, for instance, in the performance of
DC discharges, RF discharges and magnetron sputtering discharges. SE generation can
be separated into potential electron emission due to the neutralization of the incident
ion upon impact and kinetic electron emission due to the electronic stopping of the
penetrating ion in the solid. SE due to neutralization is usually described by Auger
processes and the density of states of the electrons in the solid, whereas kinetic electron
emission scales with the electronic stopping of the ion in the solid, as being calculated
by ion collision simulations. The measurement of the energy distribution of the SEs of
three metals (Al, Ti, Cu) and their oxides reveals the occurrence of Auger peaks, which
are not reflected by standard models such as the Hagstrum model. Instead, in this
paper, a model is proposed describing these Auger peaks by Auger neutralization of
holes created by the collision cascade of the incident ion. This shows decent agreement.
The contribution of Auger peaks in the metals Al and Ti is very significant, whereas
it is negligible in the case of Cu. The implication of these energy distributions to the
performance of magnetron sputtering discharges is discussed.