Laser light scattering (LLS) to observe plasma impact on the adhesion of micrometer-sized particles to a surface

Abstract

Laser Light Scattering (LLS) method, combined with a long-distance microscope was utilized to detect micrometer-sized particles on a smooth substrate. LLS was capable to detect individual particle release, shrink, or fragmentation during exposure to a plasma or a gas jet. In-situ monitoring of hundreds of particles was carried out to investigate the effect of hydrogen plasma exposure on particle adhesion, morphology, and composition. LLS was calibrated with monodisperse melamine resin spheres with known sizes of 2.14 μm, 2.94 μm, and 5.26 μm in diameter. The lowest achievable noise level of approximately 3% was demonstrated for counting 5.26 µm spherical melamine particles. The accuracy for melamine particle size measurements ranged from 50% for 2.14 μm particles to 10% for 5.26 μm particles. This scatter was taken as the imprecision of the method. Size distribution for polydisperse particles with known refractive index was obtained by interpolating to an effective scattering cross-section of a sphere using Mie theory. While the Abbe diffraction limit was about 2 μm in our system, the detection limit for Si particles in LLS according to Mie approximation was assessed to about 3 μm, given the limitations of the laser flux, microscope resolution, camera noise, and particle composition. Additionally, the gradual changes in forward scattering cross-sections for Si particles during the exposure to the hydrogen plasma were consistent with Si etching reported in the literature.

Particle mobilization by EUV-induced plasma and fast electrons

“…Also, it is well known that the diffusion of hydrogen radicals into metals may be very high, and may be further promoted by ion energies exceeding the surface absorption barrier, to lead to possible supersaturation of the metal. Thus, radicals and ions may penetrate underneath the surface of particles, and form pressurized bubbles of molecular hydrogen, as has been observed in materials like silicon (Si), lead (Pb) and tin (Sn) 24 . When these pressurized bubbles exceed the internal ultimate tensile strength (UTS) of the particle, these bubbles will result in ruptures and generation of multiple smaller particles 25 , as illustrated in Fig.…”

Investigation of an electrode-driven hydrogen plasma method for in situ cleaning of tin-based contamination

“…The pressure was set to 50 Pa, and the average and at 1-20 W were substituted into the initial values of the equation. According to the literature, the recombination coefficient of hydrogen atoms on the surface of stainless steel is 0.07 [19,20], and the recombination coefficient of hydrogen ions is 0.9 [21]. The plasma is electrically neutral by default.…”