2009 International Workshop on EUV Lithography

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2 Contents Introduction Absorber Stack Optimization Non-flatness Correction Blank Defect and Its Mitigation Wafer Printing Inspection Actinic Metrology Cleaning and Repair Status Remaining Issues in EUV Mask & Infra 1

3 Introduction Samsung s DRAM Roadmap Half Pitch (nm) Minimum Half Pitch Roadmap ArF DPT EUVL 1 st G ( NA = 0.32 ) EUVL 2 nd G EUV PPT 1 st EUV Production 2 nd EUVL Prod

4 Introduction Key Focus Areas in EUVL (2008 EUVL Symposium) Key Focus Areas Ranking Long-term source operation with 100W at IF and 5MJ/day 1 Defect free masks through lifecycle & inspection/review infrastructure 2 Resist resolution, sensitivity & LER met simultaneously 3 Reticle protection during storage, handling and use 4 Projection/illuminator optics and mask lifetime 5 3

5 Issues in EUV Mask Shadowing Effect Non-flatness 6 Imaging Performance Optical Density Carbon Contamination Etch & Cleaning Damage Pit Multilayer Defects Substrate Defects Bump Multilayer Defect Substrate Defect Hardness Defect 4

6 EUV Mask Infra IBD Sputter(SEC) EUV Reflectometer(SEC) Ultra Flat(SEC) CSM(Hyogo Univ.) EUV MET(LBNL/SMT) AIT(LBNL/SMT) M7360(SMT) EUV ADT(IMEC/SMT) Ref. Naulleau etal.spie 2005 Ref. Goldberg etal.spie

7 Absorber Stack Optimization TaN-Absorber/Si-capping Layer/ML/Qz Substrate Exposed by LBNL MET ( σ = 0.55/0.35 ) H-V Bias Out-of-Phase Condition 0.8 LWR DOF 1st/Oth ratio TaN Thickness (nm) Best Imaging Performance at Out-of-phase thickness 6

8 Non-flatness Correction Chucking effect of EUV mask with non-flat profile Flatness history Substrate Stress effect ML, Absorber Substrate x F,y F,z F x B,y B,z B Chucking effect ES chuck Substrate Effective flatness: Thickness variation (Frontside flatness) (Backside flatness) x F,y F,z F x B,y B,z B Overlay effect Concave profile of backside Overlay of inward direction U#822 Regi. Overlay (w.r.t U#822) U#884 EUV mask 최진 7

9 Non-flatness Correction IPE OPE (due to Non-flatness) Non-compensated Step0 Flatness check Step1 Chucking regi Step2 Chucking overlay calculation Overlay 3σ ~ 20 nm Step3 Nonflatness regi IPE IPD (due to chucking) Compensated Step4 Sum of Regis Step5 E-beam format Step6 E-beam Grid Correction Overlay 3σ~ 3nm To determine relaxed spec., additional experiments are required. 8

10 Blank Defect and Its Mitigation Defect Density in Currently Available Blanks LTEM (> 70nm) LTEM (> 80nm) Substrate Defect ML Defect 250 Qz (> 70nm) Defects (ea.) Qz (> 80nm) / / / / /07 Phase Defect Pareto ~ ~ * ~100X improvement needed * (Defect = (Defect * (Size/25)^

11 Substrate Pit Defect in EUV Mask ArF Mask 2π/λ*(n-1)*h=π (out-of phase) h=λ=193 nm EUV Mask 2π/λ*2*h=π (out-of phase) h=λ/4=3.38 nm h n ~ 1.5 h Transmission Air to Quartz (n=1 vs. n=1.5) Reflection (x2) Vacuum to Vacuum (n=1 vs. n=1) Out-of phase depth in EUV ~ 1/57 of ArF 10

12 Pit Defect Smoothing by ML Deposition Programmed Pit Defect Mask 160nm 50nm 110nm 100nm 170nm 40nm 120nm 90nm 180nm 30nm 130nm 80nm 190nm 20nm 140nm 70nm 200nm 10nm 150nm 60nm No pits (?) Smoothing effect due to ML deposition Before ML depo Width = 67.3 nm, Depth = 24.8 nm After ML depo Width = 59.8 nm, Depth = 8.5 nm 11

13 Pit Defect Smoothing by ML Deposition Depo. Angle Effect Depo. angle = 55 (SAMSUNG) - Best uniformity & Lower deposition rate Depo. angle = 26 (SEMATECH) - Lowest Defect Density 12

14 Pit Defect Smoothing by ML Deposition AIT Image of PDM after ML Deposition Depo. Angle = 55 Depo. Angle = 26 Not printed Printed 60nm-pit was patterned but not observed by AIT. Possibility of pit smoothing by multilayer deposition 13

15 Pattern Placement Defect Mitigation Pattern Placement Fiducial Marking Transform Algorithm Defect-free Fiducial Marking Process Blank Inspection Defect map generation (GDSII) Rotation Defect map matching on mask layout Extraction mask layout around each defect Scanning within marginal area for defect displacement Shift Find effective zero defect yes Standardization of Fiducial Mark, SEMATECH Alignment Accuracy < writer > No Next Blank End 14

16 Pattern Placement Defect Mitigation Fiducial Mark Depth 488 nm wavelength 100 nm depth Fiducial mark signal is maximum at λ/4 depth but E- beam alignment signal has to be considered. Contrast =0.7 (NA0.7/s0.83) 15

17 Pattern Placement Defect Mitigation Requirement for Inspection Infra Actinic Inspection Tool by MIRAI-Selete (SPIE2009) Energy flow rate through ML CCD pixel: 1000 x 1000 (13 um cell size) SC mag. = 26X (13 um cell size 500 nm cell on the mask) Beam size at mask= 0.8 mm diameter (< 0.5 mm CCD size) CCD 1 frame scan area = 0.5 x 0.5 mm 2 Defect location measurement needs additional review tool!! 16

18 Wafer Printing Inspection vs Mask Pattern Inspection Design Wafer Printing Inspection 160nm 140nm 120nm 100nm 80nm 60nm 50nm Mask SEM Mask Inspection Wafer(ADT) Inspection Mask Inspection ~ 15nm(1X) Wafer Printing Inspection ~ 33nm(1X) 17

19 Wafer Printing Image of Defect Extrusion Bridge Big Bridge Wafer SEM (ADT) Mask SEM All real defects captured by WPI are repairable!! 18

20 Coherent Scattering Microscope Aerial Image Emulation by Diffracted Beam Distribution EUV Mask Diffracted Beam Aerial Image EUV Coherent Scattering Microscopy High NA (>0.59 for 4X) Aerial Image Analysis without Aberrations 19

21 Coherent Scattering Microscope PSM Condition HV Bias NILS CD Uniformity Pattern Damage Inspection 20

22 Cleaning Status Cleaning Chemical Damage Δt of Si & Ru-capping Layer ΔR vs Cleaning Cycle Δt (nm) ΔR(%) Position Ru-capping layer shows much better chemical endurance than Si except O 3 water. ΔR ~ 0.04% after 24 cleaning cycle. 21

23 Repair Status Process Development of E-beam Repair Before Now SEM Image AFM Image Collapsed Undercut Wafer Image Repaired Pattern 22

24 Remaining Issues in EUV Mask & Infrastructure 100x improvement of blank defect density 5x improvement of actinic inspection tool throughput and its commercialization Inexpensive defect review tool for defect location measurement with ~10nm-stage accuracy EUV aerial image defect review tool (EUV-AIMS) Pattern inspection tool for 22nm-HP Proved reticle protection and handling technique 23

25 Thank You 24