Calibration of height in atomic force microscope images with subnanometer scale silicon dioxide steps

Patterned SiO2 surfaces formed on silicon wafer were observed by the atomic force microscope (AFM). The samples which have fine steps were prepared by wet etching with newly developed buffered hydrogen fluoride (BHF) which has an extremely low etching rate of around 1 Å/min level. The height data in the AFM images were successfully calibrated with etching depth measured by the ellipsometry. We recommend this method to calibrate the z-axis in the scanning probe microscope images at sub-nanometer scale.