Novel hybrid interference and atomic force microscopy

Gaoliang Dai¹*, Ziyang Jiao¹, Xingyu Rao¹, Helmut Wolff¹, Rainer Tutsch²

¹ Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany

² Institute for Production Measurement Technology, Technical University of Braunschweig, Schleinitzstraße 20, 38106 Braunschweig, Germany

* Corresponding author: Gaoliang.Dai@ptb.de

Abstract:

Interference microscopes (IM), such as phase shifting interference (PSI) and white light interference (WLI) microscopes, are widely applied owing to their advantages of high vertical resolution, fast and noncontact measurements. However, they have limited lateral resolution and often suffer from measurement errors, particularly, when surfaces and structures with large slope angles, complex geometries, diffusely reflecting surfaces are measured. On the other hand, atomic force microscopes (AFM) are capable of high-resolution and accurate measurements but often limited by their slow measurement speed. Thus, it is very desirable to apply both IM and AFM techniques as an ensemble in one instrument, to maximize their advantages while compensating for their shortcomings.  

This presentation introduces a novel hybrid microscope for realising the purpose mentioned above. The base structure of the hybrid microscope is an IM, where an additional mechanism is added on so that an AFM cantilever can be switched in or out of the beam path of the IM. When the AFM cantilever is switched out of the beam path, the hybrid microscope works in the IM mode for non-contact and fast optical measurements. While the AFM probe is switched into the beam path of the IM, the AFM tip interacts with the sample surface, and the deformation of the AFM cantilever introduced by the tip-sample interaction force can be detected from the interference fringes measured from the backside of the AFM cantilever by the IM.

The design concept of the hybrid microscope offers several advantages. It combines the AFM and IM measurement techniques at a high synergic level. For instance, no AFM sensing mechanism, such as an optical lever for conventional AFMs, is needed for detecting the AFM signal. It thus greatly simplifies the design of the AFM system and reduces the instrumentation costs. The design avoids the needs of cantilever alignment and signal adjustment, offering great convenience in applications. In addition, this novel AFM detection technique is also extendable for detecting multiple AFM probes in a single field of view (FOV), thus is very helpful for realising parallel AFMs.

The hybrid design may offer two significant applications: (i) the limited resolution capacity of the IM mode can be complemented by the high-resolution AFM; (ii)AFM measurements are capable of offering measurement results with higher topography fidelity than interference microscopic measurements, thus for providing in-situ reference areal surface metrology.

In addition, this presentation will also highlight some recent research achievements and demonstrate some selected applications of surface and nanodimensional metrology at the PTB.