A metrological large range atomic force microscope with improved performance

Abstract

A metrological large range atomic force microscope (Met. LR-AFM) has been set up and improved over the past years at Physikalisch-Technische Bundesanstalt (PTB). Being designed as a scanning sample type instrument, the sample is moved in three dimensions by a mechanical ball bearing stage in combination with a compact z-piezostage. Its topography is detected by a position-stationary AFM head. The sample displacement is measured by three embedded miniature homodyne interferometers in the x, y, and z directions. The AFM head is aligned in such a way that its cantilever tip is positioned on the sample surface at the intersection point of the three interferometer measurement beams for satisfying the Abbe measurement principle. In this paper, further improvements of the Met. LR-AFM are reported. A new AFM head using the beam deflection principle has been developed to reduce the influence of parasitic optical interference phenomena. Furthermore, an off-line Heydemann correction method has been applied to reduce the inherent interferometer nonlinearities to less than 0.3 nm (p-v). Versatile scanning functions, for example, radial scanning or local AFM measurement functions, have been implemented to optimize the measurement process. The measurement software is also improved and allows comfortable operations of the instrument via graphical user interface or script-based command sets. The improved Met. LR-AFM is capable of measuring, for instance, the step height, lateral pitch, line width, nanoroughness, and other geometrical parameters of nanostructures. Calibration results of a one-dimensional grating and a set of film thickness standards are demonstrated, showing the excellent metrological performance of the instrument.

Six-axis interferometric coordinates measurement system for nanometrology

“…Monitoring/measuring of the stage position in the simplest configuration should include two axes in the horizontal plane; measurement in the vertical axis realizes 3D control [20]. Guidance errors resulting in tilting the stage may introduce cosine errors into the path measured by the interferometers and distortion of the scanned surface on a scale that can be considered not negligible.…”

New developments at PTB in 3D-AFM with tapping and torsion AFM mode and vector approach probing strategy

“…The nano positioning stage is a flexure hinge stage driven by piezo actuators with its positions and angles measured and servo controlled based on high resolution capacitive sensors. The geometrical scaling factors of the 3D-AFM are calibrated to the PTB metrological large range AFM [7] via a sets of step height and lateral standards. The measurement range of the 3D-AFM is 15 μm × 45 μm × 45 μm (x, y, z).…”

Challenges in nanometrology: high precision measurement of position and size

“…Among them also is a large range metrological scanning probe microscope (LR-SPM) on the basis of a nanopositioning machine of company SIOS [29]. For traceable CD metrology on larger substrates such as photomasks or wafers, we are using a Nanostation 300 as the basic positioning machine, a scanning head based on a 6-axis flexure stage and a self-developed operation mode for probing the surface under test, the so-called vector approach probing [30].…”