Atomic Force Microscopy for High Aspect Ratio Structure Metrology

A new atomic force microscopy (AFM) imaging method called the step-in mode for high aspect ratio structures has been proposed and developed. In the step-in mode operation, probe scanning is performed only while a probe is far from the surface of a sample. Therefore. this method can remove frictional and torsional force acting on the probe caused by probe scanning. In high aspect ratio measurement, it is demonstrated that the position error caused by torsional force is smaller than 1 nm using the probe with an aspect ratio of 5 and that the probe tip is not damaged in the step-in mode measurement. As in experimental result, using the probe with an aspect ratio of 5 the image of a shallow trench isolation (STI) structure with a top width of 315 nm and a depth of 580 nm is faithfully obtained.