A tip characterizer for atomic force microscope (AFM) was developed to analyze the accurate tip-shape and limitation of the resolution of each tip on the cantilever [1]. Recently, many kinds of sharp tips are supplied from many vendors, and tip radius of the conventional AFM tip is typically 10nm. It is necessary to fabricate nano-structures, which are smaller than tip radius, to carry out in situ analysis of the probe apex. Additionally, the nano-structures as a tip-characterizer must be fabricated accurately and variation of the shapes should be lower than tip radius by several times to prove accuracy of measured shape of AFM probe.
A cross section of superlattices, which was made from compound semiconductor, was used to achieve accurate shape of the nano-structures. Superlattices of InGaP and GaAs were grown on the GaAs substrate. InGaP layers were controlled to be accurate thickness, which were line widths to characterize the tip. GaAs area was etched selectively from the cross section of the wafer. It is possible to fabricate fine lines and spaces which are thinner than 5nm. Line widths were measured by transmission electron microscopy and accuracy was measured from lattice images. Error of the twenty-nanometer-lines was less than 10% of the width and radius of the edge was lower than 1.5nm. Cross section of probe-tip can be measured easily from the line profile at the knife-edge of the pattern in the AFM image, and it is easy to estimate degrading of tip-shape after taking AFM images. More than three kinds of different line and space widths were fabricated to judge the quality of degraded tip shape. It is possible to estimate the deterioration of commercial tip radius in the range of 3 to 50nm, and shape of the cross section of probe-tip can be measured in the accuracy of 2nm in the range of apex radius from 3 to 30nm.
This work was partially supported by Japan Science and Technology Agency.
[1] H. Itoh, T. Fujimoto, S. Ichimura: Rev. Sci. Instrum. 77, 103704 (2006)
|