Metrology for single nanometer manufacturing. Richard Koops, Arthur van de Nes, Marijn van Veghel

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1 Metrology for single nanometer manufacturing Richard Koops, Arthur van de Nes, Marijn van Veghel International MicroNano Conference Amsterdam, 13 December 2016

2 About VSL - National Metrology Institute of the Netherlands - Appointed by the Dutch government to maintain and develop the national measurement standards - Represents the Netherlands in the international metrology infrastructure - Research institute in the field of metrology - Provides metrology services to customers P 2

3 The challenge: how to compare Everybody his own nm? Or measurements that are comparable? P 3

4 The solution: traceability to SI Definition of metre: length of the path travelled by light in vacuum during a time interval of 1/ of a second Primary realisation of metre Primary standard of time ( Dutch second ) Frequency comb Primary standard of length ( Dutch metre ) P 4 Secondary measurements Laser interferometer Traceable measurement of displacement, size etc.

5 AFM calibration Step 1: Scanner volume P 5

6 Classical AFM calibration - Expensive to fabricate and calibrate - Fixed height/pitch; multiple standards needed for full scanner volume - Limited availability small heights/pitches - Cross-talk effects - Delicate structures, susceptible to contamination and damage ISO 5436 step height standard 1D pitch standard P 6

7 Virtual height standard concept AFM probe flat surface Arbitrary waveform generator Nanometer displacement generator Calibration standard library Texture library - AFM lateral scan motion disabled - Virtual standard synchronized to scan frequency - AFM sees motion of virtual standard as topography P 7

8 Virtual standard calibration Single picometers! P 8

9 AFM calibration Step 2: Probe P 9

10 Method 1: Width vs. height - Nanoparticles with wide size distribution - Measured width = measured height + probe diameter - Probe diameter from intercept linear fit P 10

11 Method 2: Fitting individual particles (a) z-axis (b) probe z-axis z probe ρ φ w/2 φ R probe ρ w/2 R θ z probe (b) x-axis θ x-axis z-axis probe w/2 ρ R θ - Measurement of spherical nanoparticles of radius R x-axis z probe θ x-axis - Appearant width w at probe height z probe - Fitting parameters: R, ρ, θ, α P 11

12 Method 2: Fitting individual particles - For each identified particle determine the width as a function of probe height - Fit the probe model to the data for each individual particle - Determine the probe parameters from the set of individual values by taking the median P 12

13 Radius / nm Method 2: Fitting individual particles Measurement Uncertainty contribution CNT-100 (C , #1) 5 nm gold particles 60 nm Applied Microspheres particles Spherical probe of 20 nm probe radius Cylindrical probe of 5 nm probe radius Assymetry of probe 1.4 nm 0.4 nm Assymertry of particles 1.4 nm 0.4 nm Residual tilt 0.4 nm Repeatability 1.5 nm 1.5 nm Scanner calibration 0.5 nm 0.5 nm Total standard uncertainty 2.5 nm 1.7 nm - Good repeatability - Reproduces for different particle sizes - Accomodates both mono- and polydisperse particle distributions - Allows more sophisticated probe models - Statistics available for each fitted parameter - Possibility to eliminate bad particles - Uncertainty in single-nm range P 13

14 P 14 Conclusion

15 Summary - In order to sensibly compare measurements, they have to be traceable to SI, by calibration using proper standards - A calibration method for the scanner volume of an AFM using virtual standards has been presented - Sub-nm uncertainty - Flexible - Robust against damage and contamination - Two probe calibration methods using spherical nanoparticles have been presented: - Fitting width vs. particle height for a distribution of particle sizes - Fitting width vs. probe height for individual particles based on a detailed geometrical model of the probe P 15

16 SNM Benchmark Line 1 CD Position & Pitch Line mm 0.3 mm - Good calibration essential - Note: CD not necessarily identical for all samples P 16

17 Acknowledgements snm-project/ - IMEC for supplying the benchmark wafer - Nanotools for support with probes - All partners in the FP7 project SNM - All partners in the FP7 project aim4np - The EU for funding - The Ministry of Economic Affairs of the Netherlands for funding P 17

18 VSL PO Box AR Delft The Netherlands T F E I info@vsl.nl