Shigeaki Goto

An ultra-precision scanning tunneling microscope Z-scanner for surface profile measurement of large amplitude micro-structures

This paper presents an ultra-precision STM Z-scanner for surface profile measurement of micro-structures with large amplitudes on the order of several tens of micrometers. The Z-scanner consists of an STM probe, a long stroke PZT actuator with a full stroke of 70 µm, and a linear encoder. The linear encoder is employed to accurately measure a Z-directional displacement of a STM probe tracking a sample surface. The linear encoder yields a least significant bit resolution of 0.5 nm over the full stroke of the actuator. The peak-to-valley value of the Z-scanner nonlinearity is smaller than 10 nm over an effective measurement range of 50 µm. Experiments of surface profile measurement of samples with micro-structures were carried out by combining the Z-scanner and an X-directional PZT scanning stage, on which the sample is mounted. The feasibility of the developed ultra-precision Z-scanner has been confirmed from the measurement results.

Drift reduction in a scanning electrostatic force microscope for surface profile measurement

The influence of drifts on the measurement results of an electrostatic force microscope (EFM) based on a dual-height method for surface profile measurement is analyzed. Two types of drifts and their influence on the EFM measurement are discussed by computer simulation. It is figured out that the mechanical drift has a larger impact compared to the resonance frequency drift for the specific EFM with the conventional round-trip scan mode. It is also verified that the profile reconstruction algorithm of the dual-height method for separating the electric property distribution and the surface profile of the surface has an effect of magnifying the drift error in the result of surface profile measurement, which is a much more significant measurement of uncertainty sources for the developed EFM compared with an ordinary scanning probe microscope (SPM). A new vertical reciprocating scan (VRS) mode is then employed to reduce the influences of the drifts. The feasibility of the VRS mode is demonstrated by computer simulation and measurement experiments with a diffraction grating.

Modeling and analysis of a scanning electrostatic force microscope for surface profile measurement

This paper presents the analysis of a prototype scanning electrostatic force microscope (SEFM) system developed for noncontact surface profile measurement. In the SEFM system, with a dual height method, the distance between the probe tip and the sample surface can be accurately obtained through removing the influence of the electric field distribution on the sample surface. Since the electrostatic force is greatly influenced by the capacitance between the probe tip and the sample surface, a new approach for modeling and analysis of the distribution of capacitance between the probe tip with an arbitrary shape and the sample surface with a random topography by using the finite difference method (FDM) is proposed. The electrostatic forces calculated by the FDM method and the conventional sphere-plane model are compared to verify the validity of the FDM method. The frequency shift values measured by experiment are also compared with the simulation results computed by the FDM method. It has been demonstrated that the electrostatic force between arbitrary shapes of the probe tip and the sample surface can be well calculated by the finite difference method.