Blind Reconstruction Of AFM Tip Morphology

With the study of microelectronics, material science, precision mechanics, life sciences and biology into atomic scale, the nanoscale processing control requirements gradually increase, and the demand for nanoscale precision measurement and nanoscale standard reference structures is growing. There is an urgent need for the nanoscale/sub-nanometer precision measurement systems (including measurement equipments and calibration reference structures, etc.). Atomic force microscopy (AFM) as the true 3D nanoscale profile measurement instrument, is important and widely used. AFM measurement accuracy needs to achieve nanometer or even picometer level. The study on AFM measurement uncertainty is a focal point in nano measuring field. AFM image is a result of interaction between probe tip and sample surface. The morphology of probe tip is one of AFM measurement uncertainty factors. In order to improve the measurement accuracy of AFM and meet the needs of nanoscale traceability, it is necessary to estimate tip shape.Several kinds of tip characterizer are developed to estimate traditional AFM tip shape in this paper. The main contents include the followingFirstly, the imaging principle and working mode of AFM are introduced systematically. AFM measurement uncertainty factors are summarized and the influence of tip morphology on AFM image is analyzed.Secondly, AFM tip characterizers and reconstruction methods are introduced. The tip blind reconstruction algorithm is analyzed systematically and implemented with MATLAB.Thirdly, the porous anodic alumina (PAA) film is fabricated by two-step anodization method and detected with scanning electron microscopy (SEM) and AFM. In order to reduce the influence of image noise on tip blind estimation result and avoid tip wear, PAA film is developed as AFM tip characterizer.In addition, the gold film composed of an array of nano-rods is fabricated based on template synthesis and characterized by SEM and AFM. For characterizing tip morphology at high aspect ratio, the prepared structures are used as test sample for blind estimation of AFM probe shape.Finally, in order to avoid complex process and normalize tip sample, biaxially oriented polypropylene (BOPP) is fabricated and used to estimate AFM tip with blind reconstruction algorithm.