New atomic force microscope method for critical dimension metrology with carbon nanotube

The atomic force microscope (AFM) is expected as an evaluation method for semiconductor processes. The AFM can take a three dimensional image without cracking a wafer. As the design rule of the semiconductor device becomes smaller, higher aspect ratio probes will be needed. The conventional AFM methods, however, have difficulty in using a high aspect ratio probe because the probe scanning is carried out keeping in touch with a surface of a sample and therefore lateral force acts on the probe especially at an edge of a steep wall. A high aspect probe is bent easily or broken in the worst case. We developed a new AFM method that we call the STEP-IN mode AFM. The measurement of the Si gratings is demonstrated by the STEP-IN mode with the FIB probe and the CNT probe. It is clear that the STEP-IN mode can take symmetric profiles and utilize CNT probes. The STEP-IN mode with the CNT probe has capability for CD metrology in semiconductor process evaluation.