In recent years, there has been growth in the development of high-speed AFMs, which offer the possibility of video rate scanning and long-range scanning over several hundred micrometres. However, until recently these instruments have been lacking full traceable metrology. In this paper traceable metrology, using optical interferometry, has been added to an open-loop contact-mode high-speed AFM to provide traceability both for short-range video rate images and large-area scans made using a combination of a high-speed dual-axis scanner and long-range positioning system. Using optical interferometry to determine stages’ positions and cantilever displacement enables the direct formation of images, obviating the need for complex post-processing corrections to compensate for lateral stage error. The application of metrology increases the spatial accuracy and linearisation of the high-speed AFM measurements, enabling the generation of very large traceable composite images.

Nanopositioning stages are used in many areas of nanotechnology and advanced materials analysis, often being integrated into analytical devices such as scanning probe and optical microscopes and manufacturing devices (e.g. lithographic systems). We present a metrological instrument, together with software, designed for traceable evaluation of stage performance. The system capabilities and performance are illustrated by measurement of stages of different levels of accuracy, including a low cost custom built stage manufactured by 3D printing. The traceability of the system is described and main uncertainty sources are discussed. Guidelines are given for the specification of stage performance.

No abstract

Atomic force microscopy (AFM) often relies on the assumption that cantilever bending can be described by simple beam theory and that the displacement of the tip can be evaluated from the cantilever angle. Some more advanced metrological instruments use free-space or fibre interferometers for measuring the position of the cantilever apex directly, thereby simplifying the metrology traceability chain. The next logical development, covering measurements of both the cantilever apex position and its deformation due to lateral forces acting during different AFM measurement regimes, is presented in this paper. It is based on using a set of closely packed fibre interferometers that can be used to determine localised bending of the cantilever at different positions along the cantilever. This can be used for detection of cantilever deformation beyond classical beam theory, and can yield both better understanding of sources of uncertainty in individual AFM force–distance measurements and more accurate scanning in constant height mode in high-speed AFM applications.

Scanning Capacitance Microscopy (SCM) is an Atomic Force Microscopy (AFM) based technique that simultaneously records topography and local capacitance with high spatial resolution. This tool is based on the high frequency MOS capacitor theory, and is routinely used in failure analysis to discern the 2D carrier profiles and/or defects in insulator layers of semiconductor devices. An ac voltage induces a dynamic change in capacitance formed by the SCM tip and oxidized semiconductor sample surface. Because of the small contact area, sensitivity of the capacitance measurements must be lower than 10-18 F in a 1 kHz bandwidth. SCM sensors capable of such sensitivity are commonly based on the Radio Corporation of America (RCA) capacitance sensor, and rely on the detection of the frequency shift of a resonator. High operating frequency for the resonator significantly improves the measurement sensitivity. In this article, we describe a sensor for SCM with sub-zeptofarad (< 10-21 F) sensitivity based on the designs of Tran et. al., but realized using a phase – sensitive detection system. This results in improved low frequency noise in the capacitance measurement. This design has an operating frequency of 3 GHz when unloaded and a resonator Q around 110, resulting in an improvement of the system sensitivity over the conventional RCA CED sensor, and may be used in a commercial AFM system. The performance of this sensor is discussed and two-dimensional dopant profile from a semiconductor structure is presented. The limitations of bulk resonator SCM systems are discussed and the prospects for monolithic sensors are described in the context of a 0.35 µm SiGe BiCMOS process.