X-Rays, Electrons and Lithography: Fundamental Processes in Molecular Radiation Chemistry

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1 X-Rays, Electrons and Lithography: Fundamental Processes in Molecular Radiation Chemistry D. Frank Ogletree Molecular Foundry, Berkeley Lab Berkeley CA USA

2 Our Berkeley Lab Team EUV Lithography and Pattern Transfer Deirdre Olynick Foundry Patrick Naulleau CXRO Resist Chemistry Paul Ashby, Yi Liu Foundry Greg Wallraff, IBM Bill Hinsberg, Col. Hill Tech. Consult Spectroscopy and Chemical Physics Bo Xu Oleg Kostko, Musa Ahmed ALS Chemical Dynamics Dan Slaughter Chemical Sciences Frank Ogletree Foundry Theory Kristina Closser, David Prendergast Foundry 2

3 The Problem Molecular Fragmentation e-, E=? Auger e-, E=? D. Frank Ogletree LBNL LBNL 2017

4 Bulk vs Gas Phase

5 EUV Standard Model Photoionization M + hν M + + e - γ M + e - 92 ev x-ray in ionization energy ~ 10 ev ~80 ev secondary electron out Stable parent ion left behind The electron does the work! 5

6 EBL Standard Model Secondary e - Impact Ionization M + e - M + + 2e - M + Primary e - Fast primary electron in ionization energy ~ 10 ev ~10-30 ev secondary electron out ev energy transfer Stable parent ion left behind The SE does the work! 6

7 EUV Atomic Cross Sections A molecule has many cross sections, one for each orbital Orbitals closer to the photon energy have higher EUV cross sections Photoemission from deeper levels leaves significant residual energy in the ionized molecule Cross section data cxro.lbl.gov 7

8 Excitation and Relaxation Step 1 Photoionization M + hν M + + e - γ M + e - e - Step 3 Atomic Relaxation Fragmentation? M + R R 2 R 1 + R 2 Step 2 Electronic Relaxation Auger process? M + M ++ + e - D. F. Ogletree, Molecular Excitation and Relaxation of Extreme Ultraviolet Lithography Photoresists. In Frontiers of Nanoscience: Materials and Processes for Next Generation Lithography, Eds. A. P. G. Robinson and R. A. Lawson, Elsivier 2016 M ++ 8

9 Gas Phase Chemical Dynamics x-ray e - e - Count electrons, energy distribution Count ions and ionized fragments Branching ratios for different processes Cross sections Photon energy dependence 9

10 Experiment Concept Camera x-rays All electrons pushed into imaging detector (4π collection) Radial position depends on emission energy and angle Positive ions detected with reversed field (Time of Flight) Electric Field 10

11 Gas Phase Instrumentation Channel Plate & Phosphor Screen Photo-electron energy-momentum imaging Counts Electron Energy Counts Time-of-flight mass spectroscopy Fragment Mass

12 Methylphenol Model Compounds Relative EUV Cross-Section Cross section data cxro.lbl.gov

13 Cloud or molecular beam of gas What is density and distribution? How to Quantify? X-ray beam What is flux and overlap with target? All the molecules have 7 carbon atoms Scan the photon energy through the carbon 1s edge (XAS) and measure the ion yield The edge jump ~ 50 ev above threshold is proportional to the gas pressure All the photoemission spectra are normalized to the same number of phenol molecules 13

14 Carbon 1s Ion-Yield NEXAFS 14

15 Methyl Phenol Photoemission O 2p 13.6 XPS at EUV Energy electron KE = BE Cl 3s 24.5 O 2s 28.7 Br 3d

16 Kinetic Energy Plot 16

17 Effects of Fluorine 3x F 2p 17.4 F 2s 37.2 Auger Relaxation? 17

18 Effects of Iodine 8x I 4d 57.5 Auger Relaxation!! 18

19 Variable Photon Energy Auger peaks constant energy Photoemission peaks shift with photon energy Kinetic Energy [ev] 19

20 Per-Molecule Electron Yield 20

21 Yield and Cross Section Cross Section Electrons 21

22 Summary: Electrons Electron yield per molecule can be significantly increased by incorporating high cross-section atoms Iodo-methyl Phenol ~ 10x Fluro-methyl Phenol ~ 1.5 x Photoemission can create more than 2 electrons per molecule through Auger relaxation Energy distribution is changed, can be two ~ 35 ev electrons instead of one ~ 80 ev electron Is this better or worse for pattern transfer?? Better photon statistics Can lower energy SEs reduce electron blur? Can multiple electrons drive multi spur chemistry?? Can resist chemistries be tailored to exploit EUV photoemission? 22

23 VMI Mass Spec C 6 H 5 + C 7 H 7 O + C 7 H 7 OCl + C 4 H 3 + H 2 O + N 2 + C 3 H 4 + C 5 H 4 + C 7 H 5 + H Chloro-Methyl Phenol Fragmentation by EUV photons m/z 23

24 EUV Fragmentation Patterns 24

25 Electron Impact Ionization 25

26 Relative Ion Yield 26

27 Summary: Ions EUV photoabsorption fragments molecules Parent ion generation less than ~ 10% Radicals, excited-state ions and small molecules are generated Auger relaxation will always fragment molecules Can Secondary Ions be exploited to drive pattern formation? H + can be directly generated in the primary event Should with think about XAG, x-ray acid generators? Is there a way to provide solvating anions for acid catalysis? Can the simultaneous, localized generation of electrons and ions be exploited? 27

28 Gas vs Solid Experiments? Gas Phase Molecules Condensed Films Quantitative photoemission and absorption cross sections for each molecular component Electron yield and energy spectrum, Auger relaxation Molecular structure and bonding almost unchanged Photoemission lines broadened, dielectric film reduces energies ~ 5 ev Ion yield and mass spectrum, fragmentation patterns Variable photon energy photoemission at the synchrotron Electron-molecule interactions, dissociative electron attachment Film photoemission mixed with inelastic losses, all molecules contribute, only near-surface region detected Reaction cascade, transient electrons/ions/radicals decay or react in fs to ns to us, very hard to detect Some reaction products stable (latent image) 28

29 Outlook: Beyond Small Molecules Nanoparticle Beam Nanoparticles: uniform Aerodynamic lens for larger particles Nebulizer or Electrospray Ionization for smaller particles and large molecules core-shell nm polymer resist particle Continuous change from small molecule to condensed phase, add complexity Damage free characterization with molecular or aerodynamic beam 29

30 This work was supported by the LBNL Laboratory Directed Research and Development Program. Portions of this work were carried out at the Molecular Foundry and at the Advanced Light Source under U.S. Department of Energy contract No. DE-AC02-05CH