| Since the atomic force microscope (AFM) was invented, its applications have been explored extensively. Because of its ability to scan surfaces nondestructively with nanometer lateral resolution and sub-nanometer vertical resolution, it has potential as a metrology tool at these scales. From the metrological point of view, it is important to calibrate an AFM to improve the accuracy of the resulting measurements. Although the commercial AFM manufactures provide their own calibration artifacts and procedures for calibrating their instruments, these are not traceable to any national standard at present. Therefore, the National Institute of Standards and Technology (NIST) has developed a specially designed AFM, called the C-AFM, that will be used to calibrate artifacts. These, in turn, can be used to calibrate commercial AFMs. Because of the decreasing feature dimensions used in the semiconductor industry, accurate metrology at nanometer and sub-nanometer scales is becoming more important. Due to the limitations of present fabrication technology, there is no height artifact at the sub-nanometer scale commercially available. A potential AFM calibration standard at this scale is a silicon surface with single atomic steps. Such surfaces can have steps ranging in height from 0.14 nm to 0.31 nm depending upon which crystal plane is used. The development and performance of the C-AFM are described in this work. The qualitative and quantitative results from the study of different atomic step surfaces, prepared in ultra high vacuum (UHV) system, characterized by UHV scanning tunneling microscopy (UHV-STM), and measured by the C-AFM under ambient condition are also presented and discussed. The measurement results agree with the theoretical value of Si(111) single step height within 0.021 nm (2{dollar}sigma{dollar}). These results indicate the Si(111) stepped surface has considerable potential as an AFM calibration standard. |
