TRUE 3D METROLOGY OF NANOSTRUCTURES
This research task aims to develop reference 3D nanometrology, particularly the measurement of feature width, edge profile, sidewall angle, corner rounding, footing, contour, line edge/width roughness etc.
Our research activities in this task consist of:
- advanced instrumentation of 3D/CD AFMs;
- development of novel 3D-AFM probes;
- new measurement and new 3D probing strategy;
- new traceable route;
- sub-nm accurate tip characterisation;
- modelling of tip-sample interaction in 3D;
- calibration services with the highest level of accuracy;
A representative metrology tool applied for this task is the 3D/CD-AFM developed at PTB. In this device, an air bearing stage with a motion range of 500 mm x 300 mm developed by the former surface imaging systems company (S.I.S.) is applied for positing very large samples such as photomasks.
- 3D/CD-AFM for true 3D metrology of nanostructures
- Novel “Vector Approaching Probing (VAP)” technique applied in the design for better 3D probing sensitivity and reduced tip wear;
- Outstanding metrology performance in 3D measurement, with point-wise measurement repeatability reaches about 0.12 nm;
- Air bearing stage with motion range of 500 mm x 300 mm (x, y) offers measurement capability on very large samples, e.g., photomasks;
- Scanning range of the AFM module: 45 µm x 12 µm x 45 µm (x, y, z);
- AFM measurements using flared tips, allowing measurements of vertical or even under cut surface;
- AFM tip width accurately and traceably calibrated to the nature silicon lattice constant, offering accurate calibration of feature width and sidewall profiles;
- Excellent extend ability of the tool for satisfying special metrology demands;
- Metrology performance confirmed by the international comparison Nano6 and the PTB-NIST bilateral comparison.
Fig.1 (a) Photo of the base instrument Nanostation 300 developed by the former surface imaging systems company (S.I.S.);
(b) Photo of the 3D/CD-AFM module developed at PTB. The module is mounted to the measurement frame of the Nanostation 300 for the measurement of large samples.
Fig.2 Typical measurement performance of the 3D/CD-AFM shown as a profile measured on an IVPS-100 sample, where four profiles repeatedly measured are plotted, showing excellent measurement repeatability below 1 nm. Insets show the details of the feature at the marked areas.
For more details of this research task, please refer to some selected publications listed below:
- Gaoliang Dai et al. New developments at Physikalisch Technische Bundesanstalt in three-dimensional atomic force microscopy with tapping and torsion atomic force microscopy mode and vector approach probing strategy, J. Micro/Nanolith. MEMS MOEMS 11(1), (2012 ) 011004
- Gaoliang Dai et al. Measurements of CD and sidewall profile of EUV photomask structures using CD-AFM and tilting-AFM, Meas. Sci. Technol. 25 (2014) 044002
- Patent of a new 3D-AFM probe