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.

The development of advanced lithography requires highly accurate 3D metrology methods for small line structures of both wafers and photomasks. Development of a new 3D atomic force microscopy (3D-AFM) with vertical and torsional oscillation modes is introduced in this paper. In its configuration, the AFM probe is oscillated using two piezo actuators driven at vertical and torsional resonance frequencies of the cantilever. In such a way, the AFM tip can probe the surface with a vertical and a lateral oscillation, offering high 3D probing sensitivity. In addition, a so-called vector approach probing (VAP) method has been applied. The sample is measured point-by-point using this method. At each probing point, the tip is approached towards the surface until the desired tip–sample interaction is detected and then immediately withdrawn from the surface. Compared to conventional AFMs, where the tip is kept continuously in interaction with the surface, the tip–sample interaction time using the VAP method is greatly reduced and consequently the tip wear is reduced. Preliminary experimental results show promising performance of the developed system. A measurement of a line structure of 800 nm height employing a super sharp AFM tip could be performed with a repeatability of its 3D profiles of better than 1 nm (p–v). A line structure of a Physikalisch-Technische Bundesanstalt photomask with a nominal width of 300 nm has been measured using a flared tip AFM probe. The repeatability of the middle CD values reaches 0.28 nm (1σ). A long-term stability investigation shows that the 3D-AFM has a high stability of better than 1 nm within 197 measurements taken over 30 h, which also confirms the very low tip wear.

No abstract

An atomic force microscope ͑AFM͒ probe applicable for sidewall scanning has been developed. In its configuration, a horizontal AFM cantilever is microassembled with a vertical AFM cantilever. An AFM tip located at the free end of the vertical cantilever and extending horizontally is capable of probing in a direction perpendicular to sidewalls. The bending, torsion, or deformation of the horizontal cantilever is detected when the tip is brought into contact, intermittent contact, or noncontact with sidewalls. Measurement results taken at the sidewalls of microtrenches, microgears, and line edge roughness samples are presented.

A method for direct and non-destructive sidewall scanning of nano- and micro-structures is presented. The measurements are performed with a kind of novel ‘assembled cantilever probe (ACP)’. Such ACPs consist of four parts: substrate, cantilever, extension(s) and probe tip(s). The tip(s) located at the free end of the extension may extend horizontally. As a benefit, the ACPs are capable of probing in a direction perpendicular to sidewalls. The bending, torsion or deformation of the cantilever is detected when the tip is brought into contact, intermittent contact or non-contact, with sidewalls. Investigations show that the ACPs have a low measurement noise at a subnanometre level. Measurement examples performed at the sidewalls of microtrenches, microgears and line edge roughness samples are given in this paper.