Study on micro-machining using a small particle controlled by optical radiation pressure

This paper presents a new micro-machining using a small particle controlled by optical radiation pressure induced by focused laser light, which is based on laser trapping technology. It is known that the particle of several micrometer can be trapped and moved in liquid by optical radiation pressure force, which is as small as pN to nN. It is so called laser trapping technology. In this paper, the new micro-machining are proposed, that is using small dielectric particle like a diamond grain or a silica sphere, controlled by optical radiation pressure as a machining tool. In order to verify the feasibility of new micro-machining, at first, computer simulation of trapping force are performed. The simulation results suggest that the objective with larger numerical aperture and the particles with larger refractive index are suitable for this micro-machining. Second, fundamental experiments are carried out based on the simulation results. The laser trapped diamond grain is moved at the constant path in hundreds of times on the silicon wafer surface in the machining fluid. After that, the surface to be machined is observed by using AFM. From the AFM image, it is found that the diamond grain removes the silicon wafer surface with the depth of several nanometer, even if the pressure force is as small as 0.1nN. Furthermore, it is suggested that rotating diamond grain is more efficient for micro-machining than the non-rotating diamond grain, and that even a silica sphere with smaller refractive index will be able to perform micro-machining for the surface with low mechanical strength.