Adhesion force measurement system for micro-objects in a scanning electron microscope

An in situ measurement system for the adhesion forces acting on micrometer-sized objects in a scanning electron microscope has been developed. This system is used to measure the adhesion forces at the object–probe (needle) or the object–substrate interface, while a micro-object which is deposited on the substrate is manipulated with a single probe. The measurement of forces ranging from 50 to 3000 nN with a resolution of about 1 nN has become possible by the combination of a V-shaped double cantilever system with a stiffness of 0.1–0.3 N/m and a heterodyne laser interferometer with a resolution of 10 nm. A numerical analysis showed that the V-shaped double cantilever system is compliant only for normal displacements and is rigid toward other movements. Therefore, the reliable measurement of separation forces without applying unwanted stresses to the contact interfaces has become possible. The value of the stiffness was experimentally determined from the change in the resonant frequency when known masses were added to the tip of the cantilever system. The measured values of controlled electrostatic adhesion forces showed fairly good agreement with the calculated results. It was found that the adhesion forces between a 25-μ m solder sphere and a metal probe tip under SEM observation were on the order of 100 nN.