Simulation of processing Influence of secondary electron statistics

1. More Moore SP3WP6.4 Simulation of processingInfluence of secondary electron statistics

2. Simulations of processing • Rough aerial image in resist represented with white noise • PEB acid diffusion represented by ‘blurring’ edge outward • Subsequent etch represented by ‘blurring’ edge inward DPS 2004, Leunissen et al.

3. Simulations of processing • High frequency components mitigated by acid diffusion Animation of acid diffusion 0 to 10 nm

4. Simulations of processing • Decrease of high frequency components reduces total spectral power Animation of acid diffusion 0 to 30 nm

5. Power Spectrum y ~ x-1.46 litho(30nm) white noise edge 1 10 100 1000 Simulations of processing • Simulation matches shape familiar from typical experimental results

6. Simulations of processing • Not so much influence on spectral power since high frequency components are already ‘blurred away’ Animation of etch 0 to 30 nm

7. Simulations of processing • LER decreases during etch, but it depends on amount of LER that is already ‘blurred away’ during acid diffusion

8. hn < 20 eV hn > 20 eV Statistics of secondary electrons • DUV lithography: pure photochemistry • EUV lithography: secondary electron generation • Secondary electron blur • Super-Poissonian noise

9. "single photon noise" MC simulation Poisson distribution mAE=3.2 0 5 10 15 # chemical excitation events Statistics of secondary electrons • Model predicting SE blur from excitations, ionizations, plasmon loss and elastic scattering (MNE 2004) • Mean number of chemical activation events: mAE 3 • (S. Tagawa: 1~3 e.g. MNE 2004)

10. Statistics of secondary electrons • Resist sensitivity according to the ITRS Litho RoadmapEUV: 2 – 15 mJ/cm2 1.4 – 10 g/nm2 • Shot noise induced dose variation can be reduced using higher dose • Statistics in chemical activation events leads to “effective dose variations”:For mAE=2, effective dose variations have to be compensated with 50% higher dose

11. Determination of dose induced LER • Need high contrast and good dose control: preferably MET vary dose / line width

12. Experimental artifacts • Environmental vibrations • Source uniformity (temporal) • Source uniformity (spatial) • Optics / mask errors • CD measurement • Resist contrast repeat exposures with different illumination time; source characteristics repeat with different masks repeat CD measurements repeat exposures with different resist contrast

13. Procedure to correct for artifacts • Line edge Yi,j = Ai + Bj + Ei,j • i is index of photo • j is index of line within a photo • A is measure for variation due to SEM imaging • B is measure for variation due to mask error, source uniformity • E is measurement error and shot noise • E = dose dependent noise + residual noise • This elaborate procedure proves necessary at the desired extreme sensitivities, to discriminate true shot noise from experimental artifacts

14. redundancy mask errors multiple illumination CD wafer / PEB variations Experimental setup • Multiple CDs on mask • Multiple gratings • Multiple wafer positions • Multiple illuminations • Multiple photon energies (for SE blur measurement) • Multiple CD SEM imaging

15. Summary • Transfer of LER during etch better understood • Additional effective “dose variation” due to statistics in chemical activation  possible point of concern • Determination of dose induced high frequency LER could be seriously hampered by experimental artifacts