Adhesive forces acting on micro-objects in manipulation under SEM

In this paper, a system for measuring adhesive forces acting on micro objects under SEM and the obtained experimental results are discussed. In order to manipulate micro objects as small as 0.1 to 100 micrometers under scanning electron microscope (SEM) reliably, it is necessary to examine microadhesive forces acting on the objects by direct measurement. This is because adhesive forces acting on micro objects such as electrostatic force, surface tension force and van der Waals force are affected by various factors not considered in idealized theories. We have constructed an in situ micro force measurement system under SEM with a resolution of 1nN. The system is attached to the micro object handling system under SEM developed by the authors. The forces are obtained by measuring the displacement of a V-shaped parallel leaf cantilever with the laser interferometer. A worktable is attached to the cantilever is calculated from the change of its natural frequency, which is caused when a known mass is added at the tip. Utilizing this system, we have measured adhesive forces acting on micro solder spheres of 25 micrometers in diameter in situ while manipulating them and found the magnitude of the force is several 100nN. Besides, we proved the effectiveness of the micro object handling skills modifying facing area proposed by the authors.