Nanometrology: enabling applications of nanotechnology
C M Sotomayor Torres * , T Kehoe, N Kehagias, V Reboud, D Dudek
*ICREA Phononic and Photonic Nanostructures Group Catalan Institute of Nanotechnology (CIN2-CSIC) Barcelona SPAIN
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 1 Collaborators & Support
J Bryner, J Vollman, J Dual, C Mechanics, ETH, Zurich
S Landis, CEA, LETI , Grenoble
C Gourgon, LTM-CNRS Grenoble
S Arpiannen, J Ahopelto, VTT Espoo, Finland W Khunsin, S G Romanov, A Amann, E P O’Reilly, G Kocher
R Zentel, U Mainz S Pullteap and H C Seat, ENSEEIHT, Toulouse
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 2 Outline
1. Introduction
2. Nanometrology for Nanoimprint lithoggpyraphy:
a. Sub-wavelength diffraction b. Photoacoustic metrology
3. Nanometrology for Self-assembly
a. Opposite partners/ elements b. Rotational diffraction
4. Conclusions
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 3 Nanometrology and Nanotechnology
• Critical to enable the industrial uptake of nanotechnology • Necessary to measure: – Product characteristics , device performance, toxicology (potential public health risks), product lifetime, security • Requirements for manufacturable technology
– Standardisation, regulation – repeatable and universal
– Easy to operate
– Developpgqed in coordination with manufacturing techniques
• Integrated, in-line, real-time, advanced process control • Relevant measurands
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 4 Nanometrology Challenges
• Miniaturisation – things are getting smaller • Heterogeneous integration – things are getting more complex
–3rd Dimension increasingly used – Dimensions and material properties • Insufficient standardisation of techniques or reference sam pl es • Existing methods are slow, often destructive and not optimised for 3D
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 5 Metrology challenges for Nanofabrication
• Critical dimension measurement < 50 nm Intel SRAM Semi con duc tor lithograp hy no de 32 nm (2011) 45nm Critical dimensions and physical properties • 3D Structure Complex: Typical of heterogeneous integration, interconnects
S. Landis et al, Nanotechnology (2006) Ye et al, Langmuiir 22 7378 B.Chao, Proc SPIE 6921 (2008) (2006).3D Photonic crystal in Si • In-situ,,, inline, real-time Advanced Process Control of systematic drift and process behaviour
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 6 Metrology techniques for nanoscale – limitations
• SEM For height, slope, profile, requires destructive cross -section.
1m • AFM Difficult to access sidewalls, corners, A.E. Vladar et al, Proc SPIE 69220H reltillatively s low
• TEM Resolution ~ 0.1 nm. Destructive, slow
• X-ray Imaging Requires synchrotron x-ray B.C. Park et al, Proc. SPIE 651819 source
• Optical Scatterometry Requirement of wavelength, polarization or angle variability. Wint ech N ano-ThlTechnology Ltd
C. David et al, Proc. MNE 2008 Trends in Nanotechnology, 10th September 2010, Braga, Portugal 7 Nanoimprint Lithography (NIL)
Stamp (Si, Quartz, etc) Advantages
Resist (polymer, monomer) • Resolution (sub 10 nm) Substrate • Fast (sec/cycle) • Low cost ($0.2M vs $25M) • Simple Imprint • Flexible (UV, heat) (Pressure +heat or UV light) Applications • Semiconductors Release (cool down ) • Optics • Bio • Organic electronics RIE of residual layer • Sensors Hig h resoluti on ClComplex patterns FtilFunctional didevices
N.Kehagias, Nanotechnology 18 (2007) V.Reboud, Jpn. J. Appl. Phys., 47 (2008) Trends in Nanotechnology, 10th September 2010, Braga, Portugal 8 Sub-wavelength diffraction metrology
• Test structures of blazed gratings asymmetric diffraction pattern • Individual lines < diffraction limit. Groups of lines > diffraction limit • Sub-wavelength features in grating eg Line-width, height, defects, sidewall angle, curvature. Linewidths: 50, 100, 150, … 350nm • Defects affect relative intensity of diffraction orders in far-field • Suitable for transparent or opaque structures • Non-destructive, Fast collection of data
-2 -1 0 +1 +2 Gap 58 nm on Intensity Line 53 nm
1 m Diffracti
T. Kehoe et al, Proc. SPIE 69210F, 2008 Trends in Nanotechnology, 10th September 2010, Braga, Portugal 9 Modelling of Sub-wavelength diffraction
• Rigorous Coupled Wave Analysis Height 4.5
4.0
(()RCWA) nn 3.5 • Finite difference time domain 3.0 2.5 (FDTD) 2.0 e diffractio e ficiency
ff +first/-first vv 1.5 e 1.0 +first/+second
500nm Relati 0.5 0.0 0.07 0.08 0.09 0.10 0.11 0.12 0.13 FDTD vs. RCWA normalised to first line height/ um order 25 FDTD Width
units) 20 RCWA 6.0 +first/-first
15 5.0 +first/+second
4.0 y (arbitrary (arbitrary 10 action cc rr 3.0 5 2.0 efficien 1.0 fficiency fficiency
0 difflative EE ee
-3 -2 -1 0 1 2 3 R 0.0 Diffracted Orders 0.00 0.01 0.02 0.03 0.04 0.05 0.06 Line width increase / um
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 10 Sub-wavelength diffraction measurement system
• In-line design Laser • Sub-wavelength diffraction metrology with surface imaging by microscope optics Sample CCD A – • Enables centring of the laser spot y on the gratings diffraction z x Microscope pattern objective CCD B – image of surface
250 +1 200
itrary units 150 bb -1 100 -2 +2 50 tensity/ ar nn I 0 0 200 400 600 800 1000 1200 1400 25 m Pixels
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 11 Sub-wavelength – Detection of defects
• Defect detection 1.2 Measured (+1/-1) = 2.85 – missing 50 nm & 100 nm lines Simulated (+1/-1) = 2.68 au 1
• Agreement between simulated and 0.8 measured diffraction efficiencies 0.6 Efficiency / / Efficiency nn 1.2 No Defect (RHS/LHS) = 2.59 0.4 1 Defect (RHS/LHS) = 1.44 0.8 0.2 Diffractio 0.6 Simulated /au efficiency nn 0 0.4 -3 -2 -1 0 1 2 3 0.2 Diffractio Diffraction Order 0 -3 -2 -1 0 1 2 3 Diffraction Orders
1.2 No defect (RHS/LHS) 1 = 3.53 1 m
y / au y / Defect (RHS/LHS) = Measured cc 080.8 2112.11
0.6 0.4
0.2 Diffraction eficien 0 -3 -2 -1 0 1 2 3 Diffraction Order T. Kehoe, Microelec. Eng. 86 (2009) 100 nm 50 nm Trends in Nanotechnology, 10th September 2010, Braga, Portugal 12 Sub-wavelength – Detection of defects
• Grating stamps made with average line-width from 193 – Gap 58 nm 214 nm Line 53 st nd nm • Measured and modelled diffraction efficiencies (1 & 2 1 m order) decrease with increasing line-width, by approximately 5% per 5 nm •+1/+ 2 re la tive diffrac tion e ffic iency decreases a t approximately 4% per 5 nm
-2 Simulated ono -1 Simulated 1.1 3 +1 Simulated +1/+2 +2 Simulated Simulated -2 Measured -1 Measured +1/+2 n Efficiency Efficiency n D iffracti oo 2 +1M1 Measured y MdMeasured +2 Measured 1 fficienc d Diffracti d 1 Relative zz EE dd 0.9 195 200 205 210 215 Normali 0 rm alize Average Linewidth / nm
195 200 205 210 215 oo
Average Linewidth / nm N
T. Kehoe, NNT 08 conference, Kyoto, Japan Trends in Nanotechnology, 10th September 2010, Braga, Portugal 13 Diffraction from 3D Structures
• Polymer relaxes and partially reflows, creating rounded line profiles • Measured diffracted order intensities before and after reflowing of the lines
Comparison of measured and simulated diffraction intensities for imprinted lines and reflowed lines
T. Kehoe, NNT 2010, Copenhagen, Denmark
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 14 Key steps for NIL – Polymer physical properties
1. Stamp fabrication Imprint (Pressure +heat or UV light) 2. Imprinting process: Temp, Pressure, UV Glass transition temperature, Viscosity
3. Demoulding: Mechanical strength
Young´ s modldulus, PiPoisson ’s ra tio Release (cool down ) Adhesion / anti-sticking coating surface energy
4. Etching : Pol ym er etch r esi stan ce
RIE of residual layer At nanoscale values may change
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 15 Photoacoustic Metrology
• Thickness measurements, resolution ~10 nm • Acoustic scattering from interfaces changes surface reflectivity • Acoustic speed Physical parameters – Modulus, Poisson’s • Pump-PbLProbe Laser, 70f70 fs, = 810 nm, Time reso lu tion 0. 1 ps
Propagating Partial Reflection from acoustic waves interfaces
Pump: 70fs laser pulse Probe: Optical reflectivityyg change at surface
Laser absorppgtion / generation of thermal stress – acoustic Al Polymer Si wave
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 16 One-dimensional photoacoustic model
• Finite Element Simulation, including viscoelastic damping • Measurement R + Thickness (Ellipsometry) + Optical / Physical properties (absorption, density) Thermomechanical model
S laser power σexcit stress, T temperature, ε strain z depth attenuation F sensitivity t time ΔR reflectivity change
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 17 Photoacoustic Metrology of Nanoimprint Polymers
• Nanoimprint polymers 336 nm PMMA 13 – 586 nm thick layers • Damping in polymer not excessive • Good acoustic impedence ty change difference Strong signal ii
• Top interface: Al/polymer R Reflectiv • Bottom interface: polymer/Si • FilmThickness compared to Time / ps ellipsometry and profilometry • Physical parameters calculated using Finite Element model ess / nm cp E nn (m/s) (GPa) kg/m3) Thick mr-I PMMA 2603 3.2 0.4 1012 mr-NIL 6000 2504 2.95 0.4 1008 time of flight J. Bryner, 2007 IEEE Ultrasonics Symposium, 2007 p 1409 Time / ps Trends in Nanotechnology, 10th September 2010, Braga, Portugal 18 Nanoscale Effects
• Acoustic speed and Young’s modulus increase below 80 nm
• Acoustic speed (cp) increases by 12% • Young’s modulus (E) increases by 26% at 13 nm. • PiPrimer layer ofHMDS(f HMDS (HthldiilHexamethyldisilazane) adde d smaller increases • Increase probably due to interface effects rather than confinement Acoustic speed Young’s modulus 3500 6 3000 5 / GPa / m/s 2500 4 2000 3 1500 PMMA tic speed s Modulus ss 1000 '' 2 PMMA with PMMA 500 HMDS 1 PMMA with HMDS Acou Young 0 0 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 Thickness / nm Thickness / nm T. Kehoe, Proceedings of SPIE Vol. 6921 (2008) Trends in Nanotechnology, 10th September 2010, Braga, Portugal 19 Raised Temperature Measurements
• Investigation of physical properties 90 deg approac hing g lass t ra ns it io n te m per atur e, Tg • Acoustic speed inversely proportional to thickness
•Close to Tg increase of noise due to buckling of aluminium
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 20 Examples of self-assembled structures
Block copolymer nanophase VTT Protein crystals 10 nm separation
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 21 3D periodic structures: eg. photonic crystals
Autocloning Layer-by-layer Microassembly
S Y Lin, Sandial Lab , 1998 K. Aoki, Semicon Lab , 2003 S Kawakami, Tohoku, 1997
Holography Direct laser writing Artificial Opals
K. Aoki, Semicon Lab, 2003 M. Deubel, Karlsruhe, 2004 Tyndall/ICN-CIN2 Trends in Nanotechnology, 10th September 2010, Braga, Portugal 22 FCC colloidal crystals: Improving structural order
Equilibrium Fast crystallisation Reduce interaction with substrate Shear force to improve crystallisation -> reduce crack crystal ordering
Improved quality using acoustic noise
Acoustic vibration A .Amman et al Proc. SPIE Vol. 6603, 660321 (2007) Trends in Nanotechnology, 10th September 2010, Braga, Portugal 23 Quantifying order in self-assembly
• Define scale • MkMake approach compatibl e w ith ex itiisting me thdthods or a tlt leas t acceptable • In-line or a posteriori? • Reliable? • Suitable for a standard? 2 μm
L = 0 dB L = 20 dB L = 30 dB L = 40 dB L = 20 dB is calibrated to water displacement of 2.5 μm
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 24 Concept of “opposite beads” p(r) – probability of finding an opposite beads within a radius r, for a ggpiven tolerance parameter ε for the exact location of the spheres At sphere ‘A’ ε ABC , r()(ABABAC ) pr() ABr ()AB
1 if R y y ()R 0 else
A N A (r) p A (r) Global sum: p(r) weighted average A N A (r)
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 25 Conditions met by p(r)
• Scalar quantity (dependence on certain predefined orientation undesirable) • Integral measure of a locally observable quantity • Based on actual position of sphere (not on pixel representation of SEM image: contrast & focus dependent) • Robust against missing spheres.
Perfectly ordered system Theory 0040.04p (r ) 1100.00 Nrpr() () pr() AA A 1 Experiment 0.06 p()r 0.46 AANr()
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 26 SEM Characterisation
SEM images of size 65 μm x 40 μm (resolution: 3072 x 2304 pixels) substrate Drawing direction
Opal
Position (P)
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 27 Stochastic-resonance in photonic crystal growth
D = 368 nm r = 5.5 μm ≈ 15D, and ε = 43 nm ≈ 0.12D
P7
P10
Position (P)
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 28 3 D ordering - Experimental approach
2D analysis 3D analysis
SEM images θ – incident angle φ – azimuth angle
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 29 Transmission spectra
X (002) Bragg’s Law
(1 11) (111) U 2 (111) 2*n d (1si n () ( ) L eff hkl hkl U г W X (()020) (200) K
L' (11 1)
W.Khunsin, Adv. Funct. Mater. 18 (2008)
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 30 Rotational symmetry of T(φ)
Without Noise
X (()002)
(111) (1 11) U (111) L U г X W (020) (200) K
L' (11 1 )
Noise
W Khunsin et al, J. Nonlinear Optical. Physics & Materials 17 97 (2008) Trends in Nanotechnology, 10th September 2010, Braga, Portugal 31 Noise Susceptibility: lattice planes dependency
Without Noise
10x 5x With Noise
(311) (220) (111)
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 32 Conclusions
• New methods presented to characterise nanostructures fabricated by Nano impr in t Lithograp hy (NIL) an d se lf-assembly.
• Sub-wavelength diffraction found sensitive to defects, line-width and profile – This is potentially in-line metrology method.
• Photoacoustic metrology demonstrated suitable for dimensional and physical measurement of printed structures
• We propose a robust and generic approach to analyse quantitatively two-dimensional lattice ordering. – Opposite partners – Rotational diffraction symmetry
Trends in Nanotechnology, 10th September 2010, Braga, Portugal 33