The modeling of excimer laser particle removal from hydrophilic silicon surfaces

Abstract

We summarize experimental results on the successful removal of submicron-sized polystyrene latex, carboxylate-modified latex, SiO 2 , and Al 2 O 3 particles from hydrophilic silicon surfaces by excimer laser, using both dry and steam cleaning; the cleaning and damage thresholds have also been determined for these particles. Adhesion and removal models for an ideal sphere particle, that include van der Waals forces, hydrogen bonding, and thermoelastic effects, theoretically explain the laser cleaning results. Two models of the removal force due to the explosive evaporation of liquid film have been calculated and compared. The effects of both asperities on the particle surface and particle aggregation have also been considered. The results of the calculations show that even those surface asperities which are small compared with the particle dimension can cause a large reduction in both adhesion and thermoelastic removal forces. The theoretical predictions are consistent with the experimental observations.

Steam Laser Cleaning of Silicon Surfaces: Laser-Induced Gas Bubble Nucleation and Efficiency Measurements

“…In contrast on smooth silicon wafers we measured superheating of about 150 K! Moreover, from these superheating temperatures it was possible to show that the heat does not flow freely from the substrate to the liquid, but is inhibited by the solid-liquid heat resistance described in the case of a silicon-water interface by a heat transfer coefficient of 3 ·10 7 W/m 2 K. These two results -high superheating temperatures on smooth silicon wafers and the existence of a finite temperature jump between substrate and liquid -severely question the predictions of the existing SLC models (Lu, 1999;Wu, 2000). Both models strongly rely on several assumptions whose validity must be challenged against the experimental findings.…”

“…However, none of the published computations of temperature profiles in laser cleaning (Lu, 1999;Wu, 2000) incorporates this fact. Probably one reason is that although the phenomenon is well investigated for low temperatures below 50 K (Kapitza resistance, see Swartz, 1989) and for technical applications at room temperature, for long time scales (several seconds) and macroscopic dimensions (Nusselt-number, see Cerbe, 1999), there are no data at ns time scales and nm length scales, which would be needed for the interpretation of laser cleaning results.…”

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

“…In contrast, early simplistic models of the SLC process [12,13] predicted an increase of the cleaning threshold for smaller particle diameters.…”

A high-sensitivity in situ optical diagnostic technique for laser cleaning of transparent substrates

“…The strong adhesion of these contaminants to the surface makes conventional processes inefficient, this problem being of major importance, among others, in the field of microelectronics. Two different procedures for laser cleaning have been described in the literature: dry laser cleaning (DLC) [1][2][3][4][5] and steam laser cleaning (SLC) [1,[6][7][8][9][10]. DLC is based on the interaction between the incident laser light and the substrate to be cleaned.…”

“…Laser cleaning [1][2][3][4][5][6][7][8][9][10] appears as one of the most promising techniques for the removal of sub-micron-sized particles from surfaces. The strong adhesion of these contaminants to the surface makes conventional processes inefficient, this problem being of major importance, among others, in the field of microelectronics.…”