OPTICAL PROBE MICROSCOPE FOR NONDESTRUCTIVE METROLOGY OF LARGE-SAMPLE SURFACES

We describe the design and implementation of a tip-scanning omnidirectional force-sensing probe microscope. Chemically etched optical-fiber probes are employed for nanometer resolution imaging of structures on large samples, such as lithographic masks and semiconductor wafers. The use of light-emitting optical-fiber probes has had significant implications regarding the important issues of probe shape and fine scanner nonlinearity in scanned probe metrology. The fiber probe shapes are especially suited for metrology of high-aspect-ratio features often encountered in integrated circuit fabrication. Position monitoring, to avoid fine scanner nonlinearities, can be achieved without Abbe offset errors because the optical signal used to detect the tip motion is emitted directly from the apex of the fiber probe. The force-sensing technique in this system also allows detection of lateral forces from sidewalls in addition to shear forces for tip-to-sample regulation. The optical probe microscope system has an intrinsically higher throughput capability than other types of probe microscopes because feature imaging and probe positioning are done optically so that only the line profile measurement is done with the probe. This system should also allow future acquisition of spatially resolved optical properties of the sample in addition to pure topography.