EUV Resists Considered as Materials for Optics Tom Wallow - - PowerPoint PPT Presentation

EUV Resists Considered as Materials for Optics

Tom Wallow GLOBALFOUNDRIES Strategic Lithography Technology

IEUVI Resist TWG 2/27/2011

EUV Photoresists as Optical Materials

This analysis emerges from fundamental optical physics merged with models of EUV photon energy cascades in resist materials Ultimately, there are fundamental limits here (RLS triangle) However, the RLS response surface is currently responsive to materials and process refinement

IEUVI Resist TWG 2/27/2011

EUV Resists as Materials for Optics

Confinement effects on physical properties Component segregation Reaction-Diffusion Confinement effects on Reaction-Diffusion Interfacial gelation Swelling Modulus, etc.

IEUVI Resist TWG There are fundamental limits here too. However, these limits are softer:

• Materials are too complex for a priori theoretical descriptions
• Impact and severity may be more gradual

How does this Recipe work at all?

1) In a metal-ion free container, combine:

• 1 or more complex copolymers, Rg ~ 3nm
• n additives
• PAG(s)
• Quencher(s)
• Dissolution modifiers
• Leveling agents
• etc.
• Solvent(s)

Mix until dissolved, then filter really well. 2) Coat to 20 Rg thickness with ~1 Rg uniformity over ~1016 Rg

2 wafer area.

3) Lightly dust with modulated ionizing radiation. Hold flat. Don’t tilt or wiggle. 4) Bake immediately. Use same temp. and time everywhere on the wafer, every time. 5) Soak in caustic, then rinse and spin dry. Very carefully. Yields: ~1012 patterns with ~7 Rg width, height of ~ 15 Rg, <~ 1 Rg LWR 3s. Serve (in a particle-free container) to etch chamber for destruction.

• The Way to Cook, ITRS, 2014-2015

1) In a metal-ion free container, combine:

• 1 or more complex copolymers, Rg ~ 3nm
• n additives
• PAG(s)
• Quencher(s)
• Dissolution modifiers
• Leveling agents
• etc.
• Solvent(s)

Mix until dissolved, then filter really well. 2) Coat to 20 Rg thickness with ~1 Rg uniformity over ~1016 Rg

2 wafer area.

3) Lightly dust with modulated ionizing radiation. Hold flat. Don’t tilt or wiggle. 4) Bake immediately. Use same temp. and time everywhere on the wafer, every time. 5) Soak in caustic, then rinse and spin dry. Very carefully. Yields: ~1012 patterns with ~7 Rg width, height of ~ 15 Rg, <~ 1 Rg LWR 3s. Serve (in a particle-free container) to etch chamber for destruction.

• The Way to Cook, ITRS, 2014-2015

IEUVI Resist TWG 2/27/2011

Interfacial Gradients from Resist Components

Normalized F intensity

Triflate PAG Nonaflate PAG

Normalized F intensity

• Sundaramoorthi et al., Proc. SPIE 2009

EUV Resist, 2009 193 nm Resist, 1999

• Narayan et al., J. Photopolym. Sci. Technol. 1999

IEUVI Resist TWG 2/27/2011

• Pham, J. Q., in Materials Science and Engineering
• Univ. of Texas Press, 2004

Confinement Effects at the Substrate Interface

PMMA/SiO2

• Rittigstein et al., Nat. Mater. 2007

p(2VP)/SiO2 At 50 nm FT and below, interfacial properties become dominant

‘Protected’ Resist ‘Deprotected’ Resist

• Soles et al., Proc. SPIE 2006
• Soles et al., JVST B 2001
• Soles et al., Proc. SPIE 2006

IEUVI Resist TWG 2/27/2011

Confinement Effects at the Free Interface

Relatively uncomplicated for simple copolymers-

• Tg depression, local mechanical property changes

For resists, PAG segregation effects need to be considered

IEUVI Resist TWG 2/27/2011

Blur and the Deprotection Gradient

• Hinsberg et al., 2002-2004

Photoacid reaction-diffusion is enhanced in high acid concentration areas This behavior can be viewed as the origin of local interfaces

IEUVI Resist TWG 2/27/2011

The Deprotection Gradient (continued)

• Lavery et al., Proc. SPIE 2006
• Prabhu et al., Macromolecules 2007
• Rao et al., Langmuir 2006

Deprotection confinement produced by reaction-diffusion results in discrete domains

IEUVI Resist TWG 2/27/2011

Interfacial Gelation and Swelling

Deprotection

Modern quartz crystal microbalances can distinguish dissolution and swelling Interfacial gelation is always (?) present at some level Case II diffusion is typical for resists- interfacial gel mediates transport

Deprotection

• Wallow et al., Proc. SPIE 2002

IEUVI Resist TWG 2/27/2011

Developer Impact on Interfacial Gelation

• A. Sawano, T. Kumagai, TOK

IEUVI Resist TWG 2/27/2011

Deformation of Resist Beams

W δmax φ ΔP θ sY = yield stress E = Young’s modulus a = geometric parameter

• Yoshimoto et al. J. Appl. Phys. 2004

Multiple scaling issues for pattern collapse:

• Young’s modulus
• Yield stress
• Interfacial gelation

IEUVI Resist TWG 2/27/2011

Materials Properties Scaling

Weakening arises from local modulus fluctuations Scaling may be compounded by other effects such as swelling, etc. Recent Henderson group experimental match is excellent

• Van Workum and de Pablo, Phys. Rev. Lett. 2003

IEUVI Resist TWG 2/27/2011

Critical Aspect Ratio for Collapse

• Yoshimoto et al., SPIE 2011 Resist Session 5, Tuesday 11:20 AM

IEUVI Resist TWG 2/27/2011

Interfaces and LER

• Patsis, Microelect. Eng. 2004

Yes, but… What about the interfaces?

IEUVI Resist TWG 2/27/2011

Film Thickness Effects at EUV ca. 2006

Top-loss and roughness become worse as thickness decreases Confinement effects are the likely root cause, but which ones??? What does ‘LER’ actually mean at these film thicknesses? What solutions should we pursue?

40L80P, 10.8mJ/cm2 LER=7.1±1.1

FT = 40 nm

40L80P, 10.8mJ/cm2 LER=4.2±0.9

FT = 60 nm

40L80P, 11.3mJ/cm2 LER=3.7±0.7

FT = 80 nm

• Wallow et al., EUVL Symposium 2006

IEUVI Resist TWG 2/27/2011

• Foucher et al. SPIE 2005
• Goldfarb et al. JVSTB 2004

Sidewall LER Studies and Observations

Isotropic sidewall roughness is observed for large resist structures Sidewall roughness in ultrathin resists is much more complex

IEUVI Resist TWG 2/27/2011

Anisotropic Sidewall LER in EUV Resists

• George et al., SPIE 2010
• Std. Develop: LER 5.7 nm
• Surf. Rinse: LER 4.4 nm

IEUVI Resist TWG 2/27/2011

Underlayer Effects on LER

• Koh et al., SPIE 2010
• George et al., SPIE 2010

POR processes for many current EUV integration studies Linkage between underlayer smoothing, LER anisotropy, and interfacial confinement can be inferred, but definitive studies are needed

IEUVI Resist TWG 2/27/2011

Process Mitigation of Collapse and LER

• Petrillo et al., EUVL Symposium 2010

IEUVI Resist TWG 2/27/2011

Summary

• Ultrathin polymeric resists (<100 nm thickness) are better viewed as a

collection of dissimilar interfaces than as a bulk material

• This materials model underlies at least part of the currently still responsive

RLS surface for EUV resists

• Numerous process enhancements can mitigate aspects of materials

performance limits. Initial implementations have largely moved from research to development

• Simulation and experiment indicate that maintaining patterning performance

will continue to become more challenging as resist films become thinner. This is probably a manifestation of the onset of ‘soft’ materials limits.

• As an overly broad statement of historical inevitability, there will be a limit

for polymeric chemically amplified resists.

• “Why?,” “when?,” and “what then?” are very interesting questions.

IEUVI Resist TWG 2/27/2011

Extras

Resist Copolymers

Polymeric systems are inevitably statistical mixtures

• chain microarchitecture
• molecular weight distribution

… … … … Functional Monomers Typical MW ~ 5000-10000 (~25-75 monomers/chain) Typical radius of gyration ~ 3 nm

IEUVI Resist TWG 2/27/2011

Film Heterogeneity from Chain-Chain Interactions

• Chan and Dunstan, J. Phys. Chem. B 2010

Interchain behavior in copolymers is highly cooperative Cooperative behavior is observed at multi-Rg length scales The behavior of even simple statistical random copolymers is very challenging to describe

IEUVI Resist TWG 2/27/2011

Free-standing Film Moduli- Surface Softening at Small Dimensions

Softened exterior grows both in absolute and relative thickness below ~40 nm CD XRR: similar observations

s (MD segment size; s ~1.5 nm)

• Yoshimoto et al. J. Chem. Phys. 2005

Glassy core; softened exterior Molecular Dynamics simulations IEUVI Resist TWG 2/27/2011