Atomic force microscopy with carbon nanotube tip for critical dimension measurement

Abstract

Since the carbon nanotube (CNT) tip was first reported in 1996, its application to CD metrology has been an interest because of its unique properties. It is needle-like, which is the ideal shape as the scanning probe. In addition it elastically buckles, and therefore is robust and does not produce damage to the surface. It is also hydrophobic. The conventional AFM tip has the pyramidal or conical shape, so that either the steep side wall or high aspect ratio pattern like deep and narrow trench is difficult to measure, although the obtained image tends to be more stable than with the other kinds of tips. Recently, FIB(focused ion beam) tip or HDC(high dense carbon) tip with high aspect ratio structure became commercially available, improving the measurement capability of AFM. They are, however, weaker compared with the conventional tip, and still subject to the wear and contamination. In spite of the theoretical advantages, more researches seem to be needed either to make the CNT tip practicable for the precision CD measurement or even to examine its usefulness as a routine metrology tool. At KRISS, the geometry of the CNT tip is being improved by using the 3D manipulator in SEM for better performance, while commercial CNT tips are already available. Two kinds of patterns, groove and dot, have been measured with the three kinds of tips(conventional, HDC, and CNT as home-made). The AFM measurement results are compared, and the characteristics of CNT tips at the current stage, are discussed from the practical point of view.