1. 1. Paul Scherrer Institut Evaluation of EUV Resist Performance Using Interference Lithography E. Buitrago1, O. Yildirim2, C. Verspaget2, N. Tsugama2, R. Hoefnagels2, G. Rispens2 and Y. Ekinci1 1 Paul Scherrer Institute, Switzerland 2 ASML, Netherlands
2. 2. Elizabeth Buitrago Page: 2 Outline EUV interference lithography XIL-II: EUV-IL tool at PSI EUV resist challenges Evaluation of CAR resists for high volume manufacturing @ 22, 18 and 16 nm HP High performing CARs towards 11 nm HP Conclusions & Questions
3. 3. Elizabeth Buitrago Page: 3 EUV-IL XIL-II beamline at Swiss Light Source (SLS): EUV lithography: 13.5 nm wavelength Undulator source: Spatially coherent Temporal coherence: /=4% Diffractive transmission gratings written with EBL on on Si3N4 membranes (~100nm) Diffracted beams interfere Interference pattern printed in resist m g p 2sin2 p: period on wafer g: grating period on mask m: diffraction order
4. 4. Elizabeth Buitrago Page: 4 Advantages of EUV-IL Stable source: synchrotron source No depth of focus: Mask-to-wafer = 0.3-10 mm High resolution: Theoretical limit = 3.5 nm Current limit = 7 nm, modulation down to 6 nm Limited by resists and mask writing/quality Well defined image: pitch independent aerial image. Large area for cross-section analysis Low-cost for photoresist testing Powerful method for development of EUVL Enables research before tools are available.
5. 5. Elizabeth Buitrago Page: 5 Large Scale Facility with Nanotechnology Infrastructure Swiss Light Source (SLS) Laboratory for Micro and Nanotechnology (LMN) XIL-II: EUV-IL@SLS On-site clean room: Spin-coater, wet-bench, hot- plates, microscope, developer, optical thickness measurement In clean room environment with amine filters.
6. 6. Elizabeth Buitrago Page: 6 Gratings for EUV-IL: Mask Fabrication Membrane: 100 nm Si3N4 250 m Si wafer Wafer cleavage HSQ (hydrogen silsesquioxane) is spin- coated and structured with EBL SiOx 9mm PMMA photon-stop patterning by EBL, Cr/Au seed layer evaporation and lift-off Au electroplating, photon stop formation M1: HP = 50, 35, 25, 22, 18, 16 nm M2: HP = 18, 16, 14, 13, 12, 11 nm
7. 7. Elizabeth Buitrago Page: 7 EUV Chemically Amplified Resist Challenges Resolution (R, HP nm), line width roughness (LWR, 3 nm) and sensitivity (S, dose mJ/cm2) cannot be improved simultaneously RLS trade-off Higher photon density better LWR high dose (S) Small Blur better resolution (R) high dose (S) Larger Blur lower roughness (L) loss of resolution (R) EUV sources: low power high sensitivity resists required to get high throughput
8. 8. Elizabeth Buitrago Page: 8 Evaluation of CARs down to 16 nm HP Resolution CAR resist/UL combinations from different vendors are compared. Resolution down to 11 nm HP is important. High performance resist down to 16nm HP vital for high volume manufacturing needs in the near future. Z-factor used as global resist performance figure of merit, measure of the RLS trade- off-relationship. Z-factor alone cannot answer whether state-of-art EUV resist materials meet requirements for high volume manufacturing. = , 2 3 (Wallow et al. 2008) Constant Z intersecting smallest Z per HP
9. 9. Elizabeth Buitrago Page: 9 Evaluation of CARs down to 16 nm HP Resolution Patterning at high resolution, low LER, high sensitivity and wide exposure latitude (EL) are all necessary for the successful introduction of EUV lithography into HVM. Pinching, necking, bridging, and pattern collapse effectively reduce process window Most R + ULs tested show low Z-factors for all HPs down to 16 nm, yet some R10UL2 EL~12% at 16 nm HP. All resists show well resolved patterning down to 16 nm HP with EL > 10% with the exception of R7UL1 and R11UL2. Several options down to 16 nm HP (high resolution, small LER, high sensitivity, EL) M1 Name BE (mJ/cm2) EL (%) LER (nm) Z-factor R1UL1(average) 34.33 35.28 2.87 1.05E-08 R2UL1 36.3 32.52 3.73 2.07E-08 R3UL1 33.48 23.23 4.34 2.58E-08 R4UL1 38.25 27.36 3.7 2.14E-08 R5UL1 35.58 23.45 5.2 3.94E-08 R6UL1 38.35 33.33 3.23 1.64E-08 R7UL1 R8UL2 37.69 18.89 3.7 2.11E-08 R9UL2 40.96 17.09 3.37 1.91E-08 R10UL2 32.58 12.91 4.69 2.94E-08 R11UL2 HP: 16 nm
10. 10. Elizabeth Buitrago Page: 10 Several options down to 16 nm HP resolution R1UL1 in particular offers: EL > 20 % down to 16 nm HP BE ~ 35 mJ/cm2 LER ~ 2.7 nm (~ 17% of CD) down to 16 nm HP. 29.2mJ/cm2 32.1mJ/cm2 33.7mJ/cm2 35.3mJ/cm2 37.1mJ/cm2 HP = 16 nm - M1 - R1UL1 25.4mJ/cm2 28mJ/cm2 30.8mJ/cm2 32.3mJ/cm2 33.9mJ/cm2 35.5mJ/cm2 39.1mJ/cm2 43mJ/cm2 47.3mJ/cm2 26.2mJ/cm2 28.8mJ/cm2 31.7mJ/cm2 33.3mJ/cm2 34.9mJ/cm2 36.6mJ/cm2 38.4mJ/cm2 42.2mJ/cm2 46.4mJ/cm2 HP = 18 nm - M1 - R1UL1 HP = 22 nm - M1 - R1UL1 38.9mJ/cm2 40.8mJ/cm2 42.8mJ/cm2 47mJ/cm2 R1UL1 @ 16-22 nm HP
11. 11. Elizabeth Buitrago Page: 11 Evaluation with Resist R1UL1 Versatile resist down to 16 nm HP HP = 16 nm R1UL1 35 nm M1 HP = 18 nm R1UL1 35 nm M1 HP = 22 nm R1UL1 35 nm M1 HP = 35 nm R1UL1 35 nm M1 HP = 25 nm R1UL1 35 nm M1 HP = 50 nm R1UL1 35 nm M1
12. 12. Elizabeth Buitrago Page: 12 Evaluation with Resist R1 + different UL (BL) BLSEM contrast poor broadly scattered CD and LER values BE shifts towards lower values (from 37.7 to 31.3 mJ/cm2, for HP=16nm) vs. reference R1UL1. R1UL5BL1 no EL @ 16 nm HP, pattern collapse R1UL4BL1 exposure latitude improved vs. R1UL1 (from 25% to 36% 18nm HP), high LER at all HPs. . Name BE (mJ/cm2) EL (%) LER (nm) Name BE (mJ/cm2) EL (%) LER (nm) Name BE (mJ/cm2) EL (%) LER (nm) R1UL1 37.72 20.87 3.13 R1UL1 36.94 25.3 3.5 R1UL1 38.78 33.41 3.13 R1UL5BL1 32.56 26.05 5.56 R1UL5BL1 34.16 26.65 3.96 R1UL4BL1 31.31 19.79 5.52 R1UL4BL1 32.27 36.5 6.8 R1UL4BL1 35.01 34.09 8.29 HP: 16 nm HP: 18 nm HP: 22 nm HP = 18 nm R1UL1 HP = 18 nm R1UL4BL1 HP = 18 nm R1UL5BL1
13. 13. Elizabeth Buitrago Page: 13 Evaluation with Resist R14UL1, different thicknesses Use of thinner resist as pattern collapse mitigation strategy EL increases from 7% to 23 % for HP=18 nm for thin resist Can resolve patterns @ HP=16 nm yet no EL for thick resist. Comparable LER Name BE (mJ/cm2) EL (%) LER (nm) Name BE (mJ/cm2) EL (%) LER (nm) Name BE (mJ/cm2) EL (%) LER (nm) R1UL1 33.71 17.85 2.1 R1UL1 32.12 29.43 1.99 R1UL1 30.53 33.91 2.15 R14UL1thin 28.73 19.74 2.54 R14UL1thin 26.3 23.78 2.4 R14UL1thin 26.85 34.14 2.68 R14UL1thick 31.16 0 2.61 R14UL1thick 28.69 7.215058 2.26 R14UL1thick 26.76 26.18 2.43 HP: 16 nm HP: 18 nm HP: 22 nm HP = 18 nm - M1 - R14UL1 - thin (35 nm) HP = 18 nm - M1 - R14UL1 - thick (40 nm) 28.6mJ/cm2 29.2mJ/cm2 32mJ/cm2 34.4mJ/cm2 35.1mJ/cm2 37.7mJ/cm2 38.6mJ/cm2 41.4mJ/cm2 42.3mJ/cm2 30.1mJ/cm2 31.7mJ/cm2 33.1mJ/cm2 34.8mJ/cm2 36.5mJ/cm2 Negative-tone resist
14. 14. Elizabeth Buitrago Page: 14 Towards 11 nm HP with Resist R1UL1 M2 used (18 11 nm HP) R1 thickness 30 nm vs. standard 35 nm. Modulation at 11 nm HP Can resolve down to 12nm HP with some pattern collapse/bridging. HP = 14 nm well-resolved patterns without pattern collapse but pinching is evident. LER > 30% CD No exposure latitude for this HP = 14 nm. HP = 11 nm 33 mJ/cm2 HP = 12 nm 34 mJ/cm2 HP = 13 nm 35.1 mJ/cm2 HP = 14 nm 37 mJ/cm2
15. 15. Elizabeth Buitrago Page: 15 Towards 11 nm HP with R15UL1 HP 12, 13 nm is well resolved. HP 14 nm has small EL ~ 8% High EL for both HP 16 and 18 nm > 20%. Low BE < 40 mJ/cm2. Picture quality not best thin resist (25 nm), high LER values 31.4mJ/cm2 33.2mJ/cm2 34.6mJ/cm2 36.5mJ/cm2 38mJ/cm2 31.4mJ/cm2 32.6mJ/cm2 34.5mJ/cm2 35.9mJ/cm2 37.9mJ/cm2 39.4mJ/cm2 41.6mJ/cm2 43.3mJ/cm2 29.3mJ/cm2 32.2mJ/cm2 35.4mJ/cm2 38.9mJ/cm2 40.5mJ/cm2 42.8mJ/cm2 47mJ/cm2 51.7mJ/cm2 56.8mJ/cm2 HP (nm) BE (mJ/cm2) El (%) LER (nm) 18 34.96 35.85 4.51 16 36.07 24.95 4.95 14 37.43 8.84 4.87 HP = 14 nm M2 - R15UL1 - (25 nm) 30.5mJ/cm2 31.7mJ/cm2 33.5mJ/cm2 34.9mJ/cm2 36.8mJ/cm2 HP = 13 nm M2 - R15UL1 - (25 nm) HP = 16 nm M2 - R15UL1 - (25 nm) HP = 18 nm M2 - R15UL1 - (25 nm) 32.1mJ/cm2 33.9mJ/cm2 HP = 12 nm M2 - R15UL1 - (25 nm) 35.3mJ/cm2
16. 16. Elizabeth Buitrago Page: 16 Towards 11 nm HP with Resist R15UL1 Can resolve down to 11 nm HP with some pattern collapse. 12, 13 and 14 nm HP are furthermore well resolved. Small EL for 14 nm HP~ 8%. No pattern collapse mitigation strategy utilized HP = 11 nm 33.6 mJ/cm2 HP = 13 nm 36.8 mJ/cm2 HP = 14 nm 34 mJ/cm2 HP = 12 nm 33.9 mJ/cm2
17. 17. Elizabeth Buitrago Page: 17 Conclusions Demonstration of patterning down to 11 nm HP with CAR EUV photons can do it. EUV-sensitive CAR materials available Tools available Is there any CAR for the immediate future HVM down to 16 nm HP? The answer is yes! Several CARS demonstrated to be high performing with high EL 20 35 %, low BE=35mJ/cm2 and low LERs down to 2.7 nm. Is there any CAR for future HVM below 16 nm? R15UL1: HP 12 and 13 nm is well resolved. HP 14 nm has small EL ~ 8% High EL for both HP 16 and 18 nm > 20%. With decreasing HP: pattern collapse becomes the limiting factor. 2 nm improvement for same sensitivity in one year! (Ekinci et al., SPIE 2014)
18. 18. Elizabeth Buitrago Page: 18 Acknowledgments XIL-II team Members of LMN and SLS @ PSI and ASML Special thanks to: Markus Kropf Michaela Vockenhuber Simon Tschupp Daniel Fan Roberto Fallica http://www.psi.ch/lmn/nanooptics http://www.psi.ch/sls/xil We thank materials suppliers Thank you for your attention!