Elisabeth Camerotto

Study of ultrasound-assisted radio-frequency plasma discharges in n-dodecane

This paper investigates the generation of a stable plasma phase in a liquid hydrocarbon (n-dodecane) by means of ultrasound (US) and radio-frequency (RF) or electromagnetic radiation. It is demonstrated for the first time that ultrasonic aided RF plasma discharges can be generated in a liquid. Plasma discharges are obtained for different gas mixtures at a pressure of 12?kPa and at low ignition powers (100?W for RF and 2.4?W?cm?2 for US). Direct carbon deposition from the liquid precursor on Cu, Ni, SiO2 and Si substrates has been obtained and no apparent compositional or structural difference among the substrate materials was observed. Characterization of the deposited solid phase revealed an amorphous structure. In addition, structural changes in the liquid precursor after plasma treatment have been analysed. Optical emission spectroscopy (OES) allowed the estimation of several plasma characteristic temperatures. The plasma excitation temperature was estimated to be about 2.3?2.4?eV. The rotational and vibrational temperatures of the discharge in n-dodecane with Ar as a feed gas were 1400?K and 6500?K, respectively. In Ar/O2 plasma, an increased rotational (1630?K) and vibrational temperature (7200?K) were obtained.

Influence of surface tension on cavitation noise spectra and particle removal efficiency in high frequency ultrasound fields

Physical cleaning methods are applied in the semiconductor industry and have become increasingly challenging due to the continued scaling of semiconductors device elements. Cavitation and acoustic phenomena are known to play a fundamental role in megasonic cleaning. Hence, a better understanding of cavitation phenomena in multi-bubble systems is crucial. Here, a study on the effects of lower bulk surface tension and different O2 concentrations on the bubble activity in the megahertz range is presented. A lower bulk surface tension (45 mN/m) with respect to ultra pure water (72 mN/m) is obtained by adding a non-ionic surface-active agent (Triton X-100). After a thorough surfactant characterization, a Triton X-100-containing cleaning solution is investigated under pulsed and continuous acoustic fields, for different acoustic amplitudes and gas concentrations. It is demonstrated that cavitation activity, measured by means of ultraharmonic cavitation noise, is enhanced in presence of a lower surface tension, ...

Physical forces exerted by microbubbles on a surface in a traveling wave field.

The effect of a wave with a varying traveling component on the bubble activity as well as the physical force generated by microbubbles on a surface has been studied. The acoustic emission from a collection of bubbles is measured in a 928 kHz sound field. Particle removal tests on a surface, which actually measures the applied physical force by the bubbles on that surface, indicate a very strong dependence on the angle of incidence. In other words, when the traveling wave component is maximized, the average physical force applied by microbubbles reaches a maximum. Almost complete particle removal for 78 nm silica particles was obtained for a traveling wave, while particle removal efficiency was reduced to only a few percent when a standing wave was applied. This increase in particle removal for a traveling wave is probably caused by a decrease in bubble trapping at nodes and antinodes in a standing wave field.

Impact of Acoustical Reflections on Megasonic Cleaning Performance

Electrical measurements have shown a direct impact of reflection of acoustic waves back into a transducer. Impedance measurements illustrate in specific cases the existence of multiple resonance peaks when reflected acoustic waves are present. Current and voltage measurements have confirmed this result. From these results, one can already conclude that acoustic reflections have a large impact on the operation of a transducer. Furthermore, it is shown that for megasonic cleaning tools with a face-to-face configuration of transducer and wafer, a precise control over the distance (control over the reflections) between the transducer and wafer is very important. Particle Removal Efficiency (PRE) measurements immediately show a major dependence on the position of the wafer. The PRE dependence is directly linked to the forward power consumed by the transducer, which is largely influenced by the position of the wafer or, in other words, by the reflection of acoustic waves.