Developmental Research for Manipulation of Submicron Particles by Laser Beam

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Protecting the wafer of semiconductor from contamination by the particles suspended in the air, the barrier was composed of the scanning laser beam with wave length 488 nm, 438 nm visible light and 300 nm ultra-violet light in the horizontal plane. The analysis of the behavior of small particles in the laser beam and of phenomena caused by the interaction between photons, small particle and molecules of gas surrounding the small particle in the laser, and the developmental scientific research on the manipulation and the elimination of particles suspended in the air, were examined theoretically and experimentally. The consequence is that some effectual results, have not gotten in the former researches are obtained as follows.(1) It has been definitely shown by the results of experiments making-attempts trapping Particles from 1 um to 20 um in diameter consisting of polystyrene latex in the vicinity of focussing point of laser beam or manipulating particles three-dimensinonally that the' … More particles could be trapped or manipulated safely. It is clarified that polystyrene particles from 1 um to 20 um in diameter could be eliminated for the progressive direction of incident beam by the barrier scanning direct laser beam, for that purpose, it was strongly needed to preserve Gaussian intensity distribution of the laser beam steadily.(2) It is clarified that the submicron particles suspended in the air break through the barrier scanning laser beam having intensity of 1 w and wave length of 488 nm. Therefore, the effect of the resonance absorption was examined theoretically and experimentally, to improve the effect of radiation pressure eliminating particles. As the results, the effect of the resonance absorption depending on the variation of complex index number of refraction, particle size and wave length of incident laser beam has been clarified as shown in an example which the effect of resonance absorption remarkably changes from the difference of particle diameter in the point of several microns.(3) By using Mie scattering theory for the particle in the laser beam having Gaussian intensity distribution, a program software has been made to calculate the radiation pressure acting to the particle for the direction of the progression and the perpendicular to the beam. Hence, the simulation method has been built up for the radiation pressure acting to the particle at the arbitrary position in the laser beam.(4) An extraordinary phenomena which particles suddenly fly backward for the progressive direction of the incident laser beam was observed. To clear up the cause of the phenomena, the velocities of particles flying to the progressive and anti-progressive direction of incident beam, and the magnitude of the force trapping particles were measured quantitatively. The cause was conjectured as depending on the photophoresis or the emission after resonance absorption. Glarifying the cause, the experimental research on the manipulation of particles by laser beam has been continued in the vacuum chamber. Less