액적/액주의 레이저 유기 절연 파괴를 이용한 신개념 세정 공정 개발

Abstract

Removal of nanoscale contaminant particles from a solid surface is a critical and challenging task with numerous applications such as integrated circuit, nano technology and NEMS devices. The laser based method is one of the promising techniques, among the various cleaning methods. Among the cleaning process based on high power pulsed laser, it has been shown that the laser shock cleaning (LSC) method is effective for eliminating submicron-scale particulates from solid surfaces. In the LSC process, a high-power laser pulse induces optical breakdown of the ambient gas close to the solid surface to be cleaned and the subsequently created shock followed by a high-speed flow stream detaches the particles. However, removal of nanoscale particles is not efficient for contaminant particles less than 100 nm in size. In this work, laser cleaning techniques based on laser-induced breakdown are developed for removal of nanoscale contaminant particles. First, confinement of laser-induced plasma (LIP) techniques is developed to amplify the shock wave intensity in the laser shock cleaning process. The cleaning process using the LIP under geometrical confinement is analyzed experimentally. Secondly, a method of amplifying a LIP-generated shock wave by breakdown of a liquid column/droplet is developed. In normal LSC, the impinging shock wave is generated by LIB of the ambient gas. When the laser beam is focused on a microscale liquid droplet/column, the velocity and pressure of the shock wave increase significantly compared with air breakdown. These increases amplify the cleaning force

therefore, the distance between the LIP core and the substrate can be increased, thus reducing exposure of the substrate to radiation from the LIP. The peak of the laser-induced shock wave was ~2 times greater than that of air breakdown at the same laser pulse energy. Finally, a cleaning method using high-speed micro liquid jet is developed. During the breakdown of liquid column/droplet, LIP generates high-speed micro liquid jet with a velocity ~ 1000 m/s. This high-speed micro liquid jet can remove nanoscale particular contaminates from the solid surface. Experiments demonstrate that the proposed method can remove particles as small as 30 nm.