Nanofabrication using thermal probes

Transcription

1 cqom, February 2013 Nanofabrication using thermal probes Urs Duerig, IBM Research Zurich Thermo-Mechanical Patterning: Microfabrication: Directed Assembly: Polymer Synthesis: Armin Knoll, Felix Holzner, Philip Paul, Urs Duerig Ute Drechsler, Michel Despont Cyrill Kuemin, Heiko Wolf Jim Hedrick (IBM Almaden) Urs Duerig,

2 Agenda IBM Research - Zurich State of the art direct write lithography e-beam lithography AFM methods Thermal Scanning Probe Lithography Resolution and throughput In-situ metrology 3D nanofabrication Applications Directed particle assembly High resolution patterning of Si 2

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11 IBM Research - Zurich 1956 in Adliswil 1963 in Rueschlikon Since 2011 Binnig-Rohrer Nanotechnology Center Private-public partnership with ETHZ 11 Urs Duerig, drg@zurich.ibm.com

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14 Direct Write Lithography Using Thermal Probes Writing relief structures into polymer films using hot Si tips Si tip at 900 o C 14 Urs Duerig, drg@zurich.ibm.com

15 E-Beam Lithography Challenge: High energy of incident e - : Monte Carlo simulation of electron scattering in resist on a silicon substrate at a) 10 kv and b) 20 kv. D. F. Kyser and N. S. Viswanathan, J. Vac. Sci. Technol. 12, 1305 (1975). Proximity effect 20 kv electron beam, positive resist 15 Courtesy of Leica Lithography Systems Ltd. SPIE Handbook of Microlithography, Micromachining and Microfabrication Volume 1: Microlithography

16 Scanning Probe Lithography (SPL) STM (Tunneling Microscope) Local Anodic Oxidation Field-induced Deposition IBM Research Almaden, Don Eigler, 1990 Dagata 1990 A. Fuhrer et al., Nature 2001, 413, 822. Garcia et al., Nano Lett. 2007, 7, Nano-Scratching Dong et al., small, 2010 Dip-Pen Nanolithography Mirkin et al., Science 1999, 283, p661 Main issues of SPL: - only specific applications - slow - contact method IBM

17 Nano/Micro Fabrication Landscape: Throughput Resolution Scaling - Single lever throughput competitive to e-beam - Massive parallelism required for mask/volume production High throughput mask lithography Chemically amplified resists VSB optical EUV? (NIL?) parallelization?? Low throughput mask-less lithography electron beam (E-beam) probe based Adapted from: C. Marrian, D. Tennant, J. Vac. Sci. Technol., A, 2003, 21, S207 S.V. Sreenivasan, MRS Bulletin, Sept. 2008; Mask production: cm 2 /s 1 mask in 8h Wafer scale litho: 1 20 cm 2 /s wph 3 µ m 17 5ˣ10 4 µm 2 /h

18 Thermal probes for patterning IBM s probe storage project: - Density: 15 nm feature size - Rate: 1 µs per probe - Tip endurance: bits corresponding to 1 km of travel - Scalable using probe arrays ( 64 x 64 probe array fabricated) Physical nano-indentation (volume preserving) No chemical modification Probe patterning by local evaporation: - direct write - creates relief in polymeric resist - pattern can be used as etch mask - in-situ inspection Need high temperatures to overcome activation barriers on a 1 µs time scale 18 excess ΔT ~ o C for an acceleration by 10 8

19 Thermal probe technology for µs time scale patterning and imaging 10 µm write resistor read resistor hinge capacitive platform tip Current design: Stiffness ~ N/m Resonance frequency ~ khz Thermal time constant ~ 5 µs Apex radius of tip ~ 5 nm Tip height ~ 500 nm Thermo-mechanical writing: Efficient electrostatic actuation: up to 1 µn Resistive tip heating: up to 700 C no feedback => fast Thermo-resistive reading: Read resistor heated to ~ 200C Sensitivity ~ khz BW Measures height and not lever deflection in contact no feedback => fast hot heater low current cold heater high current 19

20 Early attempts using a Diels-Alder polymer resist Reversible chemical cross-links: High tip temperatures and long contact times needed Thermal decomposition DA activation energy 2.8 ev 100 nm B. Gotsmann et al, Adv. Funct. Mater 16, 1499 (2006). Diels Alder chemistry: chemical bonds polymer indentation (PMMA, SU8) 20

21 Material Strategy Molecular glass Unzip polymer Direct removal of organic material Versatile HO OH H 3 C OH n Compatible to CMOS In-situ inspection HO CH 3 HO CH 3 OH 700 C, 2-15 µs n Polyphthalaldehyde (PPA) Efficient thermally activated process Thermal process active at ~ 150 C M w = 715 g/mol physical intermolecular bonds complete molecules are removed thermodynamically unstable backbone synthesis at -78 C unzips into monomers upon bond breakage Stability Imaging and etching 21 H-bonds: Tg 126 C A. De Silva; J. Lee, X. André, N. Felix, H. Cao, H. Deng & C. Ober Chem. Mater., 20, 1606 (2008) Tg = Tunzip 150 C H. Ito, C. G. Willson, Technical Papers of SPE Regional Technical Conference on Photopolymers, 1982, 331

22 Thermo-Mechanical Direct Write Patterning Principle Local thermo-mechanical removal of organic resist using a heated tip (nano-chisel) Pattern defined as Bitmap Heated tip is pulled into contact by electrostatic force at each pixel Organic resist material is locally decomposed and evaporated µs pulses Temperature ( C) pixel depth (nm) Force (nn) patterning regime mechanical indentation Evaporation Patterning Embossing Data storage Materials challenge: - low evaporation temperature - chemically inert fragments - efficient depolymerization Urs Duerig, drg@zurich.ibm.com

23 Molecular Glass: Patterning Results High resolution patterning 2 nm -10 nm 15 nm half pitch line pattern 6 nm deep lines no proximity effects large area patterning uniform patterning depth 10 µs per pixel writing time 1µm Pitch 29 nm 8 nm depth Material contained in box Tip after patterning several fields: same scale: 100nm Parameters: # Pixels: Heater temperature: 300 C Load force: 80nN Pulse duration: 5.5µs µm 3 SEM of the tip after written pixels

24 Self Amplified Depolymerization Polymer Phthalaldehyde ( unzip ) polymer Mw = 36 kda n ~ 200 Tdec~ 150 C ROH + H (n+1) O O H T h = 700 C; 2-14 us IMes THF/-78 C O RO O n O OH NEt 3 RT (thermodynamically unstable backbone) Self amplified depolymerization O Cl final polymer stabilized by end groups O RO O n O O Polymer synthesis by J. Hedrick, ARC O H. Ito, IBM - thermally activated breaking of one single bond in the backbone spontaneous unzipping of the entire polymer chain n x amplification of the effect of the thermal stimulus H. Ito, C. G. Willson, Technical Papers of SPE Regional Technical Conference 24 on Photopolymers, 1982, 331 Urs Duerig, drg@zurich.ibm.com

25 Extremely efficient 3-D patterning temperature ( C) Adv. Mater. 22, (2010) τpulse = 5.5 μs F Patterning depth T s,h ~ 580 C force ( nn) 4 5 depth / nm T H ΔF / nn Tip endurance: t = 700º C = 14 μs written pixels = 40 µm 3 controlled by cantilever deflection and not by polymer compliance Black line: Static lever deflection (k=0.1 N/m) 2 µm 500'000 pixels, 143 s writing time, lateral scale: 1 : 2'000'000'000'000 vertical scale: 1 : 125'000'000'000 (8 nm / 1000 m) Comparison: V(tip cone) 0.13 µm 3 no contamination Urs Duerig, drg@zurich.ibm.com

26 3-D patterning: Image gallery 300 x 600 pixels Patterning depth ~ 50 nm Appr 40 patterning time Urs Duerig, drg@zurich.ibm.com

27 Nanotechnology (2011) High speed writing Large and small scale fidelity and uniformity 15 nm pixel size 500 khz, 7.5 mm/s ca. 5 nm deep 880X880 pixels Read: 10x slower reveals distortions / no time constant compensation ~1 Mpixels <12s write time No errors <1min overall turnaround Urs Duerig, drg@zurich.ibm.com

28 Application: Particle Placement Collaboration w. H. Wolf, C Kuemin, IBM-Zurich Process flow: - Write shape matching structures T 350 C tip substrate 90 nm Design: - V-shaped profiles => centering of particles - Arms designed to hold 3 rods - Arms written at different width to study confinement effects 28 F. Holzner, et al, Nano Lett. 11, 3957 (2011).

29 Application: Particle Placement Process flow: T 350 C tip Phase images substrate - Capillary assembly of Au nanorods (25 x 80 nm) - Evaporate template T = 215 C evap Experiment: 20 fields with 30 micron distance Capillary assembly: Moving suspension droplet across the written fields Evaporation => increasing concentration => high yield assembly Topography Red: SEM outline after PPA decomposition 29 F. Holzner, et al, Nano Lett. 11, 3957 (2011).

30 Application: Particle Placement SEM and analysis of assembled particles Result: T 350 C tip Accurate (σ=10 nm) substrate and directed (entire angular range, σ = 24 ) Generic process: - placement on substrate of choice - in registry with underlying features T = 215 C evap 500nm α 100 nm d # Au nanorods ~ 10 nm accuracy α ( ) d (nm) F. Holzner, et al, Nano Lett. 11, 3957 (2011).

31 Application: High Performance Optical Micro-Cavities Simulation: >10 x improvement Gaussian structures by tspl: A B 1 µ m C D d (nm) x ( μm) Final structure: - Two DBR mirrors for high Q cavity - Light confining envelope written by tspl for minimal mode volume V - Quantum rod positioned and aligned h top DBR spacer with curved surface profile nano-object bottom DBR In collaboration with Fei Ding, Lijian Mai, Thilo Stoeffele and Rainer Mahrt, IBM IBM

32 High resolution patterning of Si SiO 2 hard mask transfer process 4 nm sputtered SiO 2 hard mask layer 20 nm PPA 6-8 nm patterning depth Poly-phthalaldehyde resist for thermal patterning n 50 nm HM8006 Si etch mask most critical step 1 O N 2 RIE thinning of PPA 3-4 nm PPA as etch mask low etch rate is crucial Mw~40k, n~300, synthesized by ARC Thermal probe patterning: Raster scanning at a pixel and line pitch of 9.2 nm Write pulse 5µs per pixel Scan speed ~1 mm/s Tip temperature 630 o C CHF 3 RIE transfer of pattern into SiO 2 hard mask 1:2 PPA-SiO 2 etch contrast Details of the RIE sequence O 2 RIE transfer of hard mask pattern into HM8006 resist

33 Transfer result AFM image of patterned PPA: depth of structures is 6-8 nm (black corresponding to -8nm) line width in pixels nested L, half pitch 27 nm 36 nm 46 nm 27 nm 36 nm 46 nm inverted nested L SEM image after transfer into 50 nm thick HM8006 Si etch mask thin free standing lines collapsed because of under-etching nested L, half pitch 27 nm 36 nm 46 nm 27 nm 36 nm 46 nm inverted nested L

34 Final Patterns in Silicon 45o ~ 60 nm 95 nm 55 nm 72 nm top view 45o inverse lines 55 nm 45o ~ 15 nm 55 nm 55 nm 34

35 Line edge roughness Deviation from straight line Correlated deviation Uncorrelated deviation = + Due to position error of the mechanical scan system used for thermal patterning Genuine line edge roughness. Roughness is extremely sensitive to contamination in the first O 2 RIE step upper edge lower edge nm rms roughness after transfer SEM image of transferred pattern

36 Why important ITRS 2011 mask-less lithography requirements: half pitch (nm) σ CD control (nm) Potential for acceleration of mask less lithography road map Oct Y Y 200 nm requires optimization of polymer resist and transfer layer within reach with process fine tuning and PPA+PPA-acid resist 10 nm half pitch pattern in PPA resist depth (nm) y-position ( µ m) 27 nm half pitch patterns successfully transferred into 50 nm HM8006 resist nm rms line edge roughness

37 Thermal robe patterning is becoming a competitive tool Mechanics: Fast scanning > 10 mm/s Position accuracy better 10 nm Large fields ~50 µm x 50 µm Imaging: Integrated fast imaging In-situ inspection (accelerates overall turn around time) Patterning: Fast and ultra-reliable write ~µs / pixel Competitive with e-beam for writing No development required (enables in-situ inspection) Rapid turnaround time (minutes not hours) Flexibility of patterns (no proximity effects) Seamless stitching of scan fields Unique 3-d patterning capability Huge opportunity for novel materials and applications 37 Urs Duerig, drg@zurich.ibm.com

38 Acknowledgements Nano-Patterning at IBM Research Zurich: Felix Holzner, Armin Knoll, Michel Despont, Philip Paul, Urs Duerig References D. Pires et al., Science, 238, 732, (2010) A. Knoll et al., Advanced Materials, 22, 31, (2010) P. Paul et al., Nanotechnology, 22, 275, (2011) F. Holzner et al., Appl. Phys. Lett., 99, , (2011) F. Holzner et al., Nanoletters, 11, 3957 (2011) Thank You! 38 Synthesis of PPA at IBM Research Almaden: James L. Hedrick, Mellany Ramaekers Capillary Assembly at IBM Research Zurich: Cyrill Kuemin, Heiko Wolf ToF-SIMS at Empa, Zurich: Peggy Rossbach Collaboration ETH Zurich: Nicholas Spencer Microfabrication at IBM Research Zurich: Ute Drechsler Optical Microcavities at IBM Research Zurich: Fei Ding, Lijian Mai, Thilo Stoeffele, Rainer Mahrt Various at IBM Research Zurich: Abu Sebastian, Evangelos Eleftheriou, Walter Riess Funding: Schweizer National Fonds (SNF)