Influence of the rf excitation on the low energy broad ion beam characteristics

Abstract

Influence of the rf excitation in a capacitively coupled filamentless broad ion beam source with radial electrode configuration on the ion beam properties has been examined. Ion energy distribution was measured by use of a retarding field energy analyzer connected to a computer controlled data acquisition system. Influence of working conditions on the average ion energy and on the ion energy spread in the beam is described. Energy spread has typical values between 8 and 25 eV. Average ion energy can change due to variations of ion source working conditions (at constant extraction voltages) up to 60 eV. Increase of both the average ion energy and ion energy spread is observed with increasing rf power coupled to the plasma (20–100 W). This correlates to the increasing amplitude of plasma floating potential oscillation. Average ion energy decreases with increasing magnetic induction (0–75 mT) and with increasing pressure in the vacuum chamber (2×10−4–1.8×10−3 mbar) due to decreasing cathode oscillation amplitudes. Average ion energy decreases with increasing distance from the broad beam axis because of chromatical and spherical aberrations of the source extraction optics. Multiple peaks in the ion energy spectrum are observed. Their occurrence can be explained by charge exchange effects in the rf oscillating plasma sheath.

Multicusp sources for ion beam lithography applications

“…5. 1, 6 The filter offers several advantages for the multicusp ion source operation. The first screen is biased at a very negative potential ͑ϳϪ90 V͒ to repell all the incoming electrons.…”

Laser-induced fluorescence measurements for plasma processing

“…The plasma potential in the source may vary with source operating conditions which probably alter the electron temperature in the source plasma. Ion beam energies from similar sources have been measured in the past via energy analyzers [22,23] (beam width of FWHM about 23 eV) and with pulsed LIF [32] (lacking precise energy resolution, FWHM of 137 eV). In comparison, our current setup of the ion beam source and CW laser system yielded beam widths of FWHM around 29 eV via energy analyzer and as low as FWHM of 12 eV via LIF.…”

“…Transformer-coupled plasma (TCP) and reactive ion etch (RIE) sources have been studied with LIF [18,19] as have inductively coupled plasmas (ICP) [20] and microwave-driven chemical vapor deposition (CVD) sources [21]. Ion energy analyzers have been used to examine onedimensional ion distributions in the output of ion beam etching and deposition sources [22] and multidimensional energy distributions in helicon sources [23,24]. Ion distribution functions found inside ion beam etching and deposition sources have been studied with LIF [25].…”

Operation of a 0.2–1.1 keV ion source within a magnetized laboratory plasma

“…Similar offsets and energy spreads were previously reported for a capacitive rf source with similar grid structure. 7 Collisions between the beam ions and argon neutrals attenuate and scatter the beam. For our experiments, which are conducted on length scales approaching 10 m, it is important to minimize the neutral pressure in the main chamber.…”