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Implementation in France of a traceability chain for dimensional measurements at nanometer scale 19 ÈME CONGRÈS INTERNATIONAL DE MÉTROLOGIE, PARIS

Authors:
  • C2N - Centre de Nanosciences et de Nanotechnologies

Abstract

The presentation will focus on the recent commissioning of the first French metrological atomic force microscope (mAFM), the keystone of a new traceability chain implemented by the French national metrology institute (LNE) for dimensional measurements performed at the nanometre scale.
Implementation in France of a traceability chain for dimensional
measurements at nanometer scale
19ÈME CONGRÈS INTERNATIONAL DE MÉTROLOGIE, PARIS
S. Ducourtieux, A. Delvallée, C. Ulysse, A. Dervillé Cottini, G. Bernard and J. Foucher
INTRODUCTION
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Layer thickness Dimensions of a component Size of nanoparticles Roughness Depth
AFM
- If you perform some dimensional measurements at nanometer scale (AFM, SPM, SEM, profilometer, ...)
-If you need to improve the trueness of your measurements
- And if you need for a better comparability of your measurements
Then you certainly need to calibrate your instruments
Distance between patterns Size of nanoparticles Angular properties Layer thickness
SEM Height
HOW TO CALIBRATE YOUR INSTRUMENTS
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- You need to find a standard whose dimensional properties are traceable to SI meter.
- Until the end of 2018, it was very difficult to find calibration service in France for such applications but since the beginning of 2019
LNE has established a new traceability chain.
Step height Pitch
- You need to find a National Metrology Institute that possesses a reference instrument and offers calibration service.
Certificate of calibration
Issued to : ……………………
Designation :…………………
Manufacturer :……………….
Type :…………………………
Pitch = 1800 +/- 10 nm
Step height = 40 +/- 3,5 nm
Traceable to SI
2D grating standard
Metrological AFM
Interferometer
HOW IS THE TRACEABILITY CHAIN NOW ESTABLISHED IN FRANCE ?
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[1] S. Ducourtieux and B. Poyet, Meas. Sci. Technol. 22 (2011) 094010
LNE’S METROLOGICAL OPERATING PRINCIPLE
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Cloud of 3D points
Each point has three coordinates (x,y,z)
measured by the instrument interferometers
Laser
diode Quad cell
photodiode
- The metrological AFM uses the same operating principle as commercial AFM
[1] S. Ducourtieux and B. Poyet, Meas. Sci. Technol. 22 (2011) 094010
mAFM DESIGN
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- The metrological AFM uses the same operating principle as commercial AFM
- It is specifically design for dimensional metrology applications with:
- the use of 4 interferometers,
- a metrology loop made of low thermal expansion material (Zerodur),
- a high thermal inertia (500 kg of aluminium) to reduce thermal drift,
- a closed loop scanner with real-time feedback from interferometers,
- a low noise position control (0,15 nm for XY, 0,05 nm for Z),
- a low drift in position < 1nm / hour,
- a specific AFM head,
- a minimization of Abbe errors (low parasitic rotations and low Abbe offsets),
- measurements traceable to meter definition with a controlled and known
measurement uncertainty.
[1] S. Ducourtieux and B. Poyet, Meas. Sci. Technol. 22 (2011) 094010
A dedicated AFM head
7 2019/09/26
[1] : Y. Boukellal and al., Meas. Sci. Technol., 26 (2014), 015201
[2] : Y. Boukellal and al., Meas. Sci. Technol., 26 (2015), 095403
[3] : Younes Boukellal, PhD thesis, July 2015 (ENS Cachan)
- No heat source for better stability,
- Equipped with a fibred superluminescente diode to measure cantilever
deflections with no interference,
- The quad cell photodiode has been replaced by a bundle of 40000
optic fibers to remove the heat sources linked to signal amplification.
mAFM METROLOGY LOOP
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- Deeper look inside the instrument
AFM head
Metrology loop
XYZ PZT scanner
Structural frame
[1] S. Ducourtieux and B. Poyet, Meas. Sci. Technol. 22 (2011) 094010
mAFM METROLOGY LOOP
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- Deeper look inside the instrument
- 4 differential interferometers from Renishaw
- two prisms made of Zerodur
x
y
z
[1] S. Ducourtieux and B. Poyet, Meas. Sci. Technol. 22 (2011) 094010
mAFM METROLOGY LOOP
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- Deeper look inside the instrument
- a static prism is linked to AFM head,
- a moving prism is linked to the scanning stage,
- the differential position measurement occurs
between the two prisms.
Static prism
Moving prism
Sample
[1] S. Ducourtieux and B. Poyet, Meas. Sci. Technol. 22 (2011) 094010
AFM tip
Static prism
Sample
Beam aligned
with tip apex
- the AFM tip is directly linked to the static prism,
- the sample is clamped on the moving prism,
- the beams of the moving prism are aligned with
respect to the AFM tip apex to minimize Abbe
error.
Substrate
Silicon dioxide on silicon
Die size: 10 x 5 mm²
Die thickness: 1 mm
Surface roughness (Sq): typically 1 nm or below
Finding structures: 60 nm depth arrows
Grating
Type : 2D
Size of grating : 250 x 250 µm²
Pitch
Nominal mean pitch value: 900 nm (X and Y)
Typical expanded uncertainty for mean pitch: ± 2 nm (k=2)
Height
Nominal mean height value: 60 nm
Typical expanded uncertainty for mean height: ± 1 nm (k=2)
Calibration and
traceability
Traceable to SI units through a calibration performed upon request by the French
Institute of Metrology LNE using a metrological AFM*
DEVELOPMENT OF THE FIRST FRENCH STANDARD - in collaboration with
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Centre for Nanoscience and Nanotechnology
Christian Ulysse (christian.ulysse@c2n.upsaclay.fr)
2D grating standard P900H60
HOW THE MEASUREMENT UNCERTAINTY IS EVALUATED ?
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- A model has been developed under Matlab to simulate the
instrument behaviour. It integrates :
- the metrology loop (about 150 parameters),
- the standard under measurement,
- the tip shape and tip convolution,
-
- Experimental data collected during the instrument
characterization are the inputs into the model.
- Measurement uncertainty is established by propagation of
distribution by using Monte Carlo method.
- Take into account the software used.
Flatness and
roughness of the
mirrors
Prisms geometry
Laser beam profile
Parasitic rotations
Thermal stability of the
instrument
Model
[2] P. Ceria, PhD thesis, July 2017 (Université Toulouse 3 Paul Sabatier)
[3] P. Ceria et al., Meas. Sci. Technol. 28 (2017), 034007
EVALUATION OF THE SOFTWARE USED FOR DATA PROCESSING
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Platyplus from
- The model is used to generate mAFM images of virtual standards with known values for pitch and step height.
- Images are then batch processed by the software to evaluate its capabilities to determine the good values.
MountainsLab from
Measurement #
Pitch (nm)
Measurement #
Step height (nm)
LONG TERM MEASUREMENTS
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- Measurement on the same sample during 3 years
- Sample measured 246 times
- During this period, the instruments has undergone changes
(software, laser beam alignment, mechanical modifications …)
- After all, the stated expanded uncertainty (k=2) includes every
measurements without exception.
2D grating standard P900H60
COMPARISON BETWEEN LNE AND PTB
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LNE’s mAFM
PTB’s Met. LR-SPM
2D grating standard P900H60
Pitch (nm)
Measurement #
Measurement #
Step height (nm)
Gaoliang Dai
Pitch (nm)
Step height (nm)
LNE
899,1 ± 2,0
57,2 ± 1,0
PTB
899,63 ± 0,06
56,7 ± 1,3
LNE/PTB deviation
-0,53 nm
0,5
CONCLUSION
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-A traceability chain is now available in France for dimensional
measurement at nanometer scale thanks to :
- the implementation of a metrological AFM,
- the development of standards,
- the implementation of a calibration service.
NEXT STEPS
- Cofrac accreditation is under preparation for 2020.
- New standards are under development : P140H20, Step Height.
- Reduction of the uncertainties linked to Abbe errors that represent 75 % of the overall uncertainty by improving the laser beam
alignment with respect to AFM tip.
- We would like to participate to an international key comparison and claim for CMC (Calibration and Measurement Capabilities).
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Thank you for your attention
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