Adhesion force measurement system for micro-objects in a scanning electronmicroscope

An in situ measurement system for the adhesion forces acting on micrometer- sized objects in a scanning electron microscope has been developed. This sy stem 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 force s ranging from 50 to 3000 nN with a resolution of about 1 nN has become pos sible by the combination of a V-shaped double cantilever system with a stif fness of 0.1-0.3 N/m and a heterodyne laser interferometer with a resolutio n of 10 nm. A numerical analysis showed that the V-shaped double cantilever system is compliant only for normal displacements and is rigid toward othe r movements. Therefore, the reliable measurement of separation forces witho ut 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 ca ntilever system. The measured values of controlled electrostatic adhesion f orces showed fairly good agreement with the calculated results. It was foun d that the adhesion forces between a 25-mu m solder sphere and a metal prob e tip under SEM observation were on the order of 100 nN. (C) 2000 American Institute of Physics. [S0034-6748(00)04308-2].