Atomic Force Microscopy in nanometrology: modeling and enhancement of the instrument

This Ph.D. project is aimed at developing and validating techniques for successful use of Atomic Force Microscopy in nanometrology. In particular modeling of the instrument behavior, appropriate calibration, correction of distortions and enhancement of AFMs performances are addressed. Typical AFM error sources are described, mainly arising from the scanning system, the probe, the environment and from data processing subsequent to measurement. Scaling and crosstalk, creep and hysteresis, noise, drift, tip convolution and software are some of the error sources discussed. Different contributions are eventually unified into a single mathematical model, which in principle completely describes AFM scanning. The issue of AFM calibration is addressed. A new concept of calibration standards is introduced, based on optical fiber technology. It is shown how fiber micro-cylinders can be applied for accurate calibration of horizontal and vertical AFM axes, in the whole scan range. Crosstalk error evaluation and correction are also discussed. The work continues with a section discussing the possibility of compensating or avoiding typical AFM distortions. Three-dimensional topography reconstruction achieved through surface coupling is proposed for elimination of vertical drift artifacts. Application of an auto-correlation function is then proposed for alignment of profiles and lateral drift distortion removal. A method for modeling distortions due to tip wear rate in contact mode AFM is eventually proposed, based on lateral force monitoring. The last part addresses instrument enhancement, proposing a solution to three typical AFM problems. 1) Difficult tip access to steep slopes is overcome through matching and coupling of two or more surface topographies, scanned with different installation slopes. 2) A matching automatic routine is also implemented for mosaicking operations: stitching of three-dimensional topography data sets allows the maximum measurable range limitations to be overcome. 3) The problem of scan time reduction is discussed in the last section, where a feature oriented measurement approach is investigated for overcoming raster scan limitations. With the new method, the probe is driven along free-form paths, scanning with high resolution only discrete features of interest and collecting only relevant data.