Bubble nucleation and pressure generation during laser cleaning of surfaces

Abstract

Abstract. Bubble nucleation and growth dynamics, on a nanosecond time scale, induced by pulsed laser heating of a liquid-solid interface are studied experimentally. A surface-plasmon probe is implemented as a novel, highly sensitive method for the study of submicroscopic bubbles, providing accurate information on the nucleation thresholds, growth velocities, and transient pressure generation by rapid bubble growth. Owing to the higher sensitivity of the surface plasmon probe to small bubbles, it is demonstrated that bubble nucleation sets in at a lower liquid superheating than previously determined with the use of optical reflectance or piezoelectric transducer measurements. A comparison of experimentally determined bubble growth velocities with computational results confirms that bubble growth is governed by the heat transfer from the solid surface into the liquid. Reconstructed surface plasmon resonance curves from transient signals are used to estimate the fractional volume and number density of bubbles in the superheated liquid layer. Further, a surface plasmon probe is utilized for the absolute measurement of bubble-growthinduced pressure amplitudes on a nanosecond time scale. The measurements yield peak pressure amplitudes in the range of ∼ 1-5 MPa with a pressure pulse width of ∼ 40 ns. Additionally, the phase of an acoustic pulse is observed to change upon reflection at the liquid-solid interface if bubbles are present, providing a direct proof for laser-induced bubbles.

Near field induced defects and influence of the liquid layer thickness in Steam Laser Cleaning of silicon wafers

“…If the peak pressure increases only weakly with laser fluence, as in the models mentioned above, this dependence should also be noticeable in the cleaning threshold. In contrast, the observed universal values imply that the rise of the pressure amplitude as a function of laser fluence is much steeper, which is also suggested by measurements conducted on metal films [1].…”

“…Laser induced bubble nucleation and growth in bulk liquids have been studied in a variety of experiments [1,17,18] in the past, but in order to draw conclusions about the cleaning mechanisms in SLC, measurements have to be conducted under equivalent conditions to the cleaning experiments. Therefore, the laser induced explosive evaporation of water droplets on an uncontaminated wafer was studied with the same setup used for the determination of the cleaning threshold.…”

“…Then, a laser pulse heats the liquid either by direct absorption or by absorption in the sample and subsequent heat conduction into the liquid. If the laser fluence is high enough, part of the liquid is driven to a superheated metastable state, resulting in bubble growth and the generation of a pressure wave [1]. When this wave hits the particles, they experience an acceleration force away from the surface which can overcome the adhesion forces.…”

A microscopic steam engine implemented in an optical tweezer

“…Experiments that have used current pulses to heat thin films and filaments immersed in water have reported temperatures T cav at p 0 around 302°C (refs 7,8), which correspond to pressure rises of 8.7 MPa (at the binodal). However, in general, reported values of T cav are scattered in a wide range of temperatures [9][10][11][12][13] showing that the results are very sensitive to the heating rate, surface properties of the heater and contaminants in the liquid. In this experiment T cav is not measured, but the relevant parameters about the explosion are derived from the maximum bubble size.…”

Mécanismes d'éjection de particules par laser impulsionnel

“…Le processus qui, à ce jour, semble le plus probable est l'évaporation explosive de l'humidité résiduelle piégée entre la particule et le substrat [12,18]. Les causes de l'éjection seraient alors très similaires à ce qui est observée lors du nettoyage par procédé humide (SLC) qui consiste à enlever par irradiation laser un film liquide qui entraîne avec lui les particules [19,20]. Comme le montre la figure 11, l'interaction se produit à l'interface liquide-substrat et le film est éjecté sans être détruit.…”