Stochastic modeling of EUV resists: simulation of the effects of absorption,
quantum yield and photoelectric blur on 18 nm contact hole performance
John J. Biafore, Alessandro Vaglio Pret, Mark D. Smith, David A. Blankenship, Trey S. Graves
IEUVI TWG Resist, Hiroshima, 10.2016
2 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Stochastic resist effects = local, random variability in the after-develop image
Examples: patterns printed in chemically-amplified photoresist with EUV [1]
[1] P. De Bisschop, J. Biafore, A.V. Pret, ‘Stochastic effects in EUV Lithography,’ ICPST, 2016
• Observed as variability in printed image or failure in electronic devices (LER, LWR, LCDU, etc.)
• Two components:
• Optical: Photon Shot Noise (PSN)
• Uncertainty in the amount of energy incident upon the resist
• Produces well-known dose dependence of variability
• Physical-Chemical: Effects specific to photoresists
• Uncertainty (noise) in the amount of energy absorbed by the resist
• Spatial blurring of absorbed energy by the photoelectric effect
• Noise in the number and positions of released acids
• Diffusional blurring during bake (but well-controlled in modern systems)
• Poor dissolution contrast (but well-controlled in modern systems)
3 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
0 20 40 60 80 100 120
LCDU, 34 nm holes, 56 nm pitch, 0.25NA, 0.51/0.81 45° quasar, 60 nm FTLCDU, 34 nm holes, 56 nm pitch, 0.33NA, 0.42/0.62 45° quasar, 60 nm FT
Neisser, EUVL Symposium 2013
Stochastic effects are reproduced well by PROLITH stochastic simulation
1𝜎
𝐿𝐶
𝐷𝑈
,𝑛𝑚
𝑠𝑖𝑧𝑖𝑛𝑔 𝑑𝑜𝑠𝑒, 𝑚𝐽/𝑐𝑚2
PROLITH EUV stochastic simulation of 170 virtual resists
Hole LCDU 1-sigma vs. Incident Dose
Measurements of many actual EUV resists
LWR 3-sigma vs. Incident Dose
𝑠𝑖𝑧𝑖𝑛𝑔 𝑑𝑜𝑠𝑒, 𝑚𝐽/𝑐𝑚2
L𝑊
𝑅,n
m
De Bisschop, JPS 2016
Smith, Biafore, SPIE2013
• Optical and physical-chemical effects conspire to produce feature variability
• Effects are modeled well by PROLITH stochastic simulation
• Optical effects: Well-known 1/ 𝑑𝑜𝑠𝑒 dependence is a consequence of PSN
• Physical-Chemical effects: Much variability observed among samples at fixed dose
4 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Simulated effect of dose on hole LCDU 4 virtual resists, 24 nm holes, 48 nm mask pitch, EUV, 0.33 NA, 0.81/0.51 quasar
Hole diameter, nm Hole diameter, nm Hole diameter, nm Hole diameter, nm
2
2
Virtual EUV resist 1
16 /
1.7 1
1.57 acids/photon
D 0.047 / sec
0.0071
6.61/
quencher =
size
Acid
E mJ cm
LCDU nm
nm
k
m
PDB
2
2
Virtual EUV resist 2
24.5 /
1.4 1
1.77 acids/photon
D 0.056 / sec
0.0056
5.21/
quencher =
size
Acid
E mJ cm
LCDU nm
nm
k
m
PDB
2
2
Virtual EUV resist 3
44.5 /
0.9 1
1.72acids/photon
D 0.0185 / sec
0.0061
5.67 /
quencher =
size
Acid
E mJ cm
LCDU nm
nm
k
m
PDB
2
2
Virtual EUV resist 4
81 /
0.7 1
1.44acids/photon
D 0.136 / sec
0.0052
4.84 /
quencher = conventional
size
Acid
E mJ cm
LCDU nm
nm
k
m
𝑬𝒔𝒊𝒛𝒆 = 𝟏𝟔 𝒎𝑱/𝒄𝒎𝟐 𝑬𝒔𝒊𝒛𝒆 = 𝟐𝟒. 𝟓 𝒎𝑱/𝒄𝒎𝟐 𝑬𝒔𝒊𝒛𝒆 = 𝟒𝟒. 𝟓 𝒎𝑱/𝒄𝒎𝟐 𝑬𝒔𝒊𝒛𝒆 = 𝟖𝟏 𝒎𝑱/𝒄𝒎𝟐
𝑳𝑪𝑫𝑼 = 𝟏. 𝟕 𝒏𝒎 𝟏𝝈 𝑳𝑪𝑫𝑼 = 𝟏. 𝟒 𝒏𝒎 𝟏𝝈 𝑳𝑪𝑫𝑼 = 𝟎. 𝟗 𝒏𝒎 𝟏𝝈 𝑳𝑪𝑫𝑼 = 𝟎. 𝟕 𝒏𝒎 𝟏𝝈
• Reduction in variability can be achieved by ‘simply’ increasing dose, but very painful
5 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Status of IMEC Low-Dose EUV CAR Resist Project, as of 10.5.16
IMEC conclusions:
• Resolution-roughness-sensitivity targets for the project are difficult to meet
• More than 300 exposures with 5 different suppliers performed over 7 months
• Few resists have shown acceptable printability
• All suppliers are able to formulate low-dose resists
• LWR target the most difficult to achieve
• All resists are in the LWR range of 5-6nm vs. target of < 3.2nm (20% of CD!)
16 nm dense line
6 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Only way to repair PSN in resist (without raising dose) is to increase absorption
𝜶 = 6.5/um
𝜶 = 18.6/um
𝑭𝑻 = 30 nm
𝑭𝑻 = 50 nm
• Low EUV absorbance by organic resists increases PSN effects and wastes incident energy
• But very difficult to increase EUV absorption in organic resists
• Reducing organic resist thickness is also problematic
• Optical density of a CAR is about 0.20 at 30 nm FT (0.80 of photons pass through)
• Target optical density is closer to 0.45-0.50
𝑃𝑆𝑁 =1
𝑛 𝑎𝑏𝑠=
1
𝜶 𝑬𝒊𝒏𝒄 𝑽𝝀
ℎ𝑐
7 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
1. Direct photolysis: 1 absorbed photon releases at most 1 acid
Photon absorption by the generating molecule produces an electronically-excited state
favorable for conversion. [2] A. Reiser, ‘Photoreactive Polymers,’ Wiley, 1989
[3] N. Turro, ‘Modern Molecular Photochemistry,’ University Science Press, 1991
2. Electronic excitation: 1 scattering electron may release > 1 acid
Absorption of an EUV photon results in ionization and a cascade of secondary electrons.
Scattering electrons induce time-dependent electric fields whose individual Fourier
components may be treated using the method of virtual quanta. If a resonating system is
located within the field, it may interact with the passing charge. [4] E. Fermi, 1924
[5] Weizsacker, Williams, 1934
[6] J. D. Jackson, ‘Classical Electrodynamics’, Wiley, pp. 724-729, 1975
[7] A. Reiser, ‘Photoreactive Polymers,’ Wiley, 1989
[8] G. Han, F. Cerrina, ‘Energy transfer between electrons and photoresist,’ JVST B18(6), 3297, 2000
[9] (as applied to EUV resists) Mack, Thackeray, Biafore, Smith, ‘Stochastic Exposure Kinetics of EUV Photoresists: A Simulation
Study,’ SPIE 2011
3. Dissociative electron attachment: 1 scattering electron may release at most 1 acid
• Absorption of an EUV photon results in ionization and a cascade of secondary electrons.
The dissociative‐attachment peak cross section is a function of peak resonance energy [8]. [10] Christophorou, Stockdale, ‘Dissociative Electron Attachment to Molecules,’ JCP, 48-5, 1967
[11] (as applied to EUV resists) Kozawa et al, J. Vac. Sci. Technology. B22, 2004 3489
Supported EUV exposure mechanisms
• Simulation of these exposure mechanisms is supported by PROLITH
8 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Electrons
PROLITH ™
Acids
PROLITH ™
Visualization of the photoelectric exposure blur in PROLITH X6
Discrete Acid PSF in XY plane
Discrete Electron PSF in XY plane
ℎ𝜈
ℎ𝜈
e
ℎ𝜈
𝑃𝑆𝑁 = 𝜎𝑛
𝑛=
0
1= 0
~60 𝑛𝑚
• Absorb 1 EUV photon at the center of a cube of resist
• Perform simulation of stochastic exposure within cube
• Record the number and positions of acids released
• Record the number and positions of electrons at 10 eV
• Re-initialize cubic domain
• Repeat for a specified number of randomized trials
• PSN component is zero – why?
• In each trial, we absorb 1 photon with probability = 100%
• Standard deviation of n absorbed photons is therefore 0
• PSN vanishes and the approach models a pure resist effect
9 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Simulation of material-specific electron scattering properties in PROLITH X6
Resist electronic response characterization via dielectric function measurement [12-15]
• The dielectric (or loss) function ε(ω,0) is calculated by measuring the
extinction coefficient κ(ω) and the real refractive index n(ω).
• To cover a large enough range of energies, 3 techniques are used:
• CXRO website for n(E), κ(E) in the 1nm < λ < 41nm range[11]
• Spectroscopic ellipsometry for n(E), κ(E) in the 150nm < λ < 750nm range
• XAS, for n(E), κ(E) in the 4.5nm < λ < 450nm range (@ Elettra synchrotron)[12]
• Electron mean free path, CDSA energy loss and screening parameter can
be modeled from ε(ω,0)
• Scattering data can be loaded in PROLITH X6 to simulate the resist’s
electronic response to absorption of high energy photons [13-22].
• XAS can be also used to estimate other material properties such as Total
and Secondary Electron Yield (TEY, SEY), and used in PROLITH X6 [12] J. Biafore et al. “Pattern prediction in EUV resists”, Proc. SPIE 7520 (2009)
[13] A. Vaglio Pret et al. “Characterization and modeling electrical response to light for metal based EUV photoresists, Proc. SPIE 9779-5 (2015)
[14] P. De Schepper et al. XAS Photoresists Electron/Quantum yields study with synchrotron Light, Proc. SPIE 9425-6 (2015)
[15] CXRO website: http://www.cxro.lbl.gov/
[16] A. Giglia et al. “FEL multilayer optics damaged by multiple laser shots: experimental results and discussion”, Nucl. Instr. Meth. Phys. Res. A. 635,
530 (2011).
[17] J. C. Ashley et al. “Interaction of low-energy electrons with condensed matter stopping powers and inelastic mean free paths from optical data”, J.
Elec. Spectr. 46 (1988)
[18] M. Dapor et al. “Monte Carlo modeling in the low energy domain of the secondary electron emission of PMMA for CD-SEM”, JM3 9, (2010)
[19] D. R. Penn. “Electron mean-free-path calculations using a model dielectric function”, Phys. Rev. B, 35, (1987)
[20] V. P. Singh, et al. “Determination of Effective Atomic Numbers Using Different Methods for Some Low-Z Materials”, J. Nuc. Chem. (2014)
[21] H. Bethe, “Zur Theorie des Durchgangs schneller Korpuskularstrahlen durch Materie”, Annalen der Physik, 397(3), 325-400, (1930).
[22] M. Born, "Quantenmechanik der Stossvorgänge". Zeitschrift für Physik 38(11-12), 803-827, (1926).
[23] T. Schnattinger, “An Introduction to the Passage of Energetic Particles through Matter”, Taylor & Francis Group, LLC, CRC Press, Boca Raton,
(2007).
10 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Details of the following stochastic simulation experiment
• PROLITH X6, EUV, 0.33 NA, 0.862 / 0.60 30° quasar, no aberrations, 3.5% flare, 3D mask model
• 18 nm contact holes, 36 nm mask pitch, 22.36 nm mask opening
• Build 8 virtual resists based on a state-of-the-art calibrated resist model
• Each virtual sample has different properties
• Simulate 10,000 contact holes using each sample
• Dose = 35 mJ/cm2 for all samples, unless noted
• Quencher loading is modified to adjust sizing of each virtual resist
• Absorbance coefficient ~ 5/um, unless noted
• Resist thickness = 30 nm
• All other parameters are identical for all samples and describe high-performance EUV CARs:
• Low PEB acid diffusion length ~ 2.5 nm
• Steep dissolution contrast with low Rmin 0.005 nm/s and high Rmax 120 nm/s
• Moderate-low amplification reaction rate constant 0.42 nm3/s
• High quenching rate constant 4 nm3/s, conventional quencher
Collect simulation output:
• 3σ hole CD
• Failure rate, number closed holes / 10,000
• Acid quantum yield, electron quantum yield
• Displacement of acids from the absorption site
• Displacement of electrons <= 10 eV from the absorption site
11 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
3𝜎 𝐶𝐷 = 6.3 𝑛𝑚
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 0.0061
Acids
PROLITH ™
Electrons
PROLITH ™
Φ = 2.9 𝑎𝑐𝑖𝑑𝑠/ℎ𝜈
𝑟 = 3.8 𝑛𝑚
Φ = 3.8 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠/ℎ𝜈
𝑟 = 4.4 𝑛𝑚
𝐴𝑐𝑖𝑑 𝑃𝑆𝐹
𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛 𝑃𝑆𝐹 𝑎𝑡 10𝑒𝑉
𝑟𝑚𝑎𝑥 = 12.3 𝑛𝑚
𝑟𝑚𝑎𝑥 = 42.5 𝑛𝑚
Sample 1: Control, based on calibrated model of a modern state-of-the-art CAR
• Distribution of CD is non-normal likely due to nonlinearity of underexposure latitude
Emulation of SEM image
12 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Electrons
PROLITH ™
Acids
PROLITH ™
Electrons
PROLITH ™
𝑆𝑎𝑚𝑝𝑙𝑒 2 3𝜎 𝐶𝐷 = 𝟗. 𝟑 𝒏𝒎
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 𝟎. 𝟏𝟑𝟏
𝚽 = 𝟏𝟏. 𝟑 𝐚𝐜𝐢𝐝𝐬/𝐡𝛎
𝑟 = 3. 0 𝑛𝑚
Φ = 3.5 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠/ℎ𝜈
𝑟 = 3.6 𝑛𝑚
𝐴𝑐𝑖𝑑 𝑃𝑆𝐹
𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛 𝑃𝑆𝐹 𝑎𝑡 10𝑒𝑉
𝑟𝑚𝑎𝑥 = 16 𝑛𝑚
𝑟𝑚𝑎𝑥 = 35.9 𝑛𝑚
Sample 2: Extreme quantum yield using direct excitation mechanism only
• No benefit is observed for very high quantum yield, even if it were possible
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 3𝜎 𝐶𝐷 = 6.3 𝑛𝑚
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 0.0061
2.9
3.8 𝑛𝑚
12.3 𝑛𝑚
3.8
4.4 𝑛𝑚
42.5 𝑛𝑚
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 Emulation of SEM image Acids
PROLITH ™
13 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Electrons
PROLITH ™
Acids
PROLITH ™
Electrons
PROLITH ™
Φ = 2.3 𝑎𝑐𝑖𝑑𝑠/ℎ𝜈
𝑟 = 1.9 𝑛𝑚
Φ = 2.5 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠/ℎ𝜈
𝑟 = 2.3 𝑛𝑚
𝐴𝑐𝑖𝑑 𝑃𝑆𝐹
𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛 𝑃𝑆𝐹 𝑎𝑡 10𝑒𝑉
𝑟𝑚𝑎𝑥 = 4.8 𝑛𝑚
𝑟𝑚𝑎𝑥 = 34.8 𝑛𝑚
𝑆𝑎𝑚𝑝𝑙𝑒 3 3𝜎 𝐶𝐷 = 𝟔. 𝟎 𝒏𝒎
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 𝟎. 𝟎𝟎𝟑𝟔
Sample 3: Controlled exposure blur and moderate quantum yield
• Reduction of acid exposure blur produces better CDU and 1/2 the
failure rate of the control. Acid yield less than control.
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 3𝜎 𝐶𝐷 = 6.3 𝑛𝑚
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 0.0061
Emulation of SEM image
2.9
3.8 𝑛𝑚
12.3 𝑛𝑚
3.8
4.4 𝑛𝑚
42.5 𝑛𝑚
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 Acids
PROLITH ™
14 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Electrons
PROLITH ™𝑆𝑎𝑚𝑝𝑙𝑒 4
3𝜎 𝐶𝐷 = 𝟓. 𝟏 𝒏𝒎
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 𝟎. 𝟎𝟎𝟎𝟑
𝜶 ≈ 𝟏𝟎/𝝁𝒎
Acids
PROLITH ™
Electrons
PROLITH ™
Φ = 2.3 𝑎𝑐𝑖𝑑𝑠/ℎ𝜈
𝑟 = 1.9 𝑛𝑚
Φ = 2.5 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠/ℎ𝜈
𝑟 = 2.2 𝑛𝑚
𝐴𝑐𝑖𝑑 𝑃𝑆𝐹
𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛 𝑃𝑆𝐹 𝑎𝑡 10𝑒𝑉
𝑟𝑚𝑎𝑥 = 5.0 𝑛𝑚
𝑟𝑚𝑎𝑥 = 25.6 𝑛𝑚
• Reduction of acid exposure blur & higher absorption produces better
CDU and 20x less failures versus control.
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 3𝜎 𝐶𝐷 = 6.3 𝑛𝑚
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 0.0061
𝛼 ≈ 5/𝜇𝑚
Emulation of SEM image
2.9
3.8 𝑛𝑚
12.3 𝑛𝑚
3.8
4.35 𝑛𝑚
42.5 𝑛𝑚
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 Acids
PROLITH ™
Sample 4: Controlled exposure blur, moderate quantum yield and higher absorption
15 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Electrons
PROLITH ™
𝑆𝑎𝑚𝑝𝑙𝑒 5 𝟑𝝈 𝑪𝑫 = 𝟑. 𝟗 𝒏𝒎
𝒇𝒂𝒊𝒍 𝒓𝒂𝒕𝒆 = 𝟏/𝟏𝟖𝟎𝑲
𝒅𝒐𝒔𝒆 = 𝟕𝟎 𝒎𝑱/𝒄𝒎𝟐
𝜶 ≈ 𝟏𝟎 /𝝁𝒎
Acids
PROLITH ™
Electrons
PROLITH ™
Φ = 2.3 𝑎𝑐𝑖𝑑𝑠/ℎ𝜈
𝑟 = 1.8 𝑛𝑚
Φ = 2.4/ℎ𝜈
𝑟 = 2.2 𝑛𝑚
𝐴𝑐𝑖𝑑 𝑃𝑆𝐹
𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛 𝑃𝑆𝐹 𝑎𝑡 10𝑒𝑉
𝑟𝑚𝑎𝑥 = 3.8 𝑛𝑚
𝑟𝑚𝑎𝑥 = 32 𝑛𝑚
𝐶 = 0.044 𝑐𝑚2
𝑚𝐽
• Reduction of acid blur, increased absorbance, 70 mJ/cm2 dose and
modest yield gives low CDU and failure rate of 0 over 30000 trials.
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 3𝜎 𝐶𝐷 = 6.3 𝑛𝑚
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 0.0061
𝑑𝑜𝑠𝑒 = 35 𝑚𝐽/𝑐𝑚2
𝛼 ≈ 5/𝜇𝑚
Emulation of SEM image
2.9
3.8 𝑛𝑚
12.3 𝑛𝑚
3.8
4.4 𝑛𝑚
42.5 𝑛𝑚
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 Acids
PROLITH ™
Sample 4: Controlled exposure blur, moderate yield, higher absorption, higher dose
16 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Intermediate summary
Acids
PROLITH ™
1. CONTROL
6. CONTROL + HIGH [F] POLYMER
3. LOWER EXP. BLUR
8. CONTROL & METAL OX. ABSORPTION & e SCATTERING
4. LOWER EXP. BLUR
HIGHER ABSORPTION
5. LOWER EXP. BLUR
HIGHER ABSORPTION
HIGHER DOSE
1. CONTROL
Acids
PROLITH ™
𝑨𝒗𝒆𝒓𝒂𝒈𝒆 𝒂𝒄𝒊𝒅 𝒆𝒙𝒑𝒐𝒔𝒖𝒓𝒆 𝒃𝒍𝒖𝒓 𝒓𝒂𝒅𝒊𝒖𝒔, 𝒏𝒎
𝑯𝑶𝑳𝑬 𝑭𝑨𝑰𝑳 𝑹𝑨𝑻𝑬
4. LOWER EXP. BLUR
HIGHER ABSORPTION
𝑟 = 3.8 𝑛𝑚
𝑟 = 1.9 𝑛𝑚
• Feature failure rate complements CDU and its reduction is obviously of utmost concern
• So far, failure rate improves with:
• Higher absorption (maximize absorbed photons to minimize PSN effects)
• Smaller photoelectric acid blur (avoid degradation of the image)
• Modest acid yield (information transfer is via photons and noise associated with
stochastic acid generation mechanism only makes image worse)
0.000006
17 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Electrons
PROLITH ™
Electrons
PROLITH ™
Acids
PROLITH ™
𝑆𝑎𝑚𝑝𝑙𝑒 6
3𝜎 𝐶𝐷 = 𝟗. 𝟐 𝒏𝒎
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 𝟎. 𝟏𝟓𝟓
𝜶 ≈ 𝟐. 𝟒 /𝝁𝒎
𝚽 = 𝟏. 𝟏 𝐚𝐜𝐢𝐝𝐬/𝐡𝛎
𝑟 = 2.3 𝑛𝑚
𝚽 = 𝟏. 𝟔/𝐡𝛎
𝑟 = 2.0 𝑛𝑚
𝐴𝑐𝑖𝑑 𝑃𝑆𝐹
𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛 𝑃𝑆𝐹 𝑎𝑡 10𝑒𝑉
𝑟𝑚𝑎𝑥 = 5.1 𝑛𝑚
𝑟𝑚𝑎𝑥 = 10.6 𝑛𝑚
Sample 6: Control with PHS polymer
Using PHS-specific electron scattering model
• Low absorption polymer = high PSN effects and catastrophic failure
Φ = 1.5 measured
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 3𝜎 𝐶𝐷 = 6.3 𝑛𝑚
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 0.0061
𝛼 ≈ 5/𝜇𝑚
Emulation of SEM image
2.9
3.8 𝑛𝑚
12.3 𝑛𝑚
3.8
4.35 𝑛𝑚
42.5 𝑛𝑚
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 Acids
PROLITH ™
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Electrons
PROLITH ™
Electrons
PROLITH ™
Acids
PROLITH ™
𝑆𝑎𝑚𝑝𝑙𝑒 7 3𝜎 𝐶𝐷 = 𝟓. 𝟔 𝒏𝒎
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 𝟎. 𝟎𝟎𝟓𝟏
𝜶 ≈ 𝟓 +/𝝁𝒎
Φ = 2.4 𝑎𝑐𝑖𝑑𝑠/ℎ𝜈
𝑟 = 2.3 𝑛𝑚
Φ = 3.4/ℎ𝜈
𝑟 = 1.9 𝑛𝑚
𝐴𝑐𝑖𝑑 𝑃𝑆𝐹
𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛 𝑃𝑆𝐹 𝑎𝑡 10𝑒𝑉
𝑟𝑚𝑎𝑥 = 5.5 𝑛𝑚
𝑟𝑚𝑎𝑥 = 10.3 𝑛𝑚
• Higher absorption vs. PHS, better control of acid exposure blur vs.
control, better CDU and 20% less failures vs. control
Sample 7: Control with highly fluorinated polymer
Using high [F] polymer electron scattering model
Φ = 4.2 measured
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 3𝜎 𝐶𝐷 = 6.3 𝑛𝑚
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 0.0061
Emulation of SEM image
2.9
3.8 𝑛𝑚
12.3 𝑛𝑚
3.8
4.35 𝑛𝑚
42.5 𝑛𝑚
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 Acids
PROLITH ™
19 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Electrons
PROLITH ™
Electrons
PROLITH ™
Acids
PROLITH ™
𝑆𝑎𝑚𝑝𝑙𝑒 8 3𝜎 𝐶𝐷 = 𝟓. 𝟎 𝒏𝒎
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 𝟎. 𝟎𝟎𝟐𝟔
𝜶 ≈ 𝟏𝟗 /𝝁𝒎
Φ = 2 acids/hν
𝑟 = 1.8 𝑛𝑚
Φ = 2.4/hν
𝑟 = 1. 1𝑛𝑚
𝐴𝑐𝑖𝑑 𝑃𝑆𝐹
𝐸𝑙𝑒𝑐𝑡𝑟𝑜𝑛 𝑃𝑆𝐹 𝑎𝑡 10𝑒𝑉
𝑟𝑚𝑎𝑥 = 4.1 𝑛𝑚
𝑟𝑚𝑎𝑥 = 5.4 𝑛𝑚
Sample 8: Control with metal-containing additives
Using metal-oxide specific electron scattering model
Φ = 2.3 measured
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 3𝜎 𝐶𝐷 = 6.3 𝑛𝑚
𝑓𝑎𝑖𝑙 𝑟𝑎𝑡𝑒 = 0.0061
𝛼 ≈ 5/𝜇𝑚
• Electron scattering and acid blur are well-controlled. Very high
absorption. Better CDU and 42% less failures vs. control
Emulation of SEM image
2.9
3.8 𝑛𝑚
12.3 𝑛𝑚
3.8
4.35 𝑛𝑚
42.5 𝑛𝑚
𝐶𝑜𝑛𝑡𝑟𝑜𝑙 Acids
PROLITH ™
20 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Summary
Acids
PROLITH ™
1. CONTROL
7. CONTROL + HIGH [F] POLYMER
3. LOWER EXP. BLUR
8. CONTROL & METAL OX. ABSORPTION & e SCATTERING
4. LOWER EXP. BLUR
HIGHER ABSORPTION
5. LOWER EXP. BLUR
HIGHER ABSORPTION
HIGHER DOSE
1. CONTROL
Acids
PROLITH ™
𝑨𝒗𝒆𝒓𝒂𝒈𝒆 𝒂𝒄𝒊𝒅 𝒆𝒙𝒑𝒐𝒔𝒖𝒓𝒆 𝒃𝒍𝒖𝒓 𝒓𝒂𝒅𝒊𝒖𝒔, 𝒏𝒎
𝑯𝑶𝑳𝑬 𝑭𝑨𝑰𝑳 𝑹𝑨𝑻𝑬
4. LOWER EXP. BLUR
HIGHER ABSORPTION
𝑟 = 3.8 𝑛𝑚
𝑟 = 1.9 𝑛𝑚
• Clear by now that reduction of stochastics is a difficult challenge for EUV lithography
• Minimization of feature failure rate is of utmost concern
• Failure rate improves with:
• Higher absorption (minimize PSN effects)
• Smaller acid exposure blur (avoid image degradation upon exposure)
• Modest yield (less noise associated with stochastic acid generation mechanism)
• Low PEB blur, steep dissolution contrast are known requirements
0.000006
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CNR/Elettra
Angelo Giglia
IAP
Marco Ornigotti
IMEC
Kurt Ronse, Geert Vandenberghe, Peter De Bisschop
Inpria
Peter De Schepper, Mike Kocsis, Jason Stowers
JSR
Kenji Hoshiko, Hori Masafumi, Dei Satoshi
KLA-Tencor
Antonio Mani, Roel Gronheid
NIMS
Shigeo Tanuma
NIST
Cedric J. Powell
Acknowledgements
Copyright © 2010 KLA-Tencor Corporation www.kla-tencor.com
23 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Two measurements of acid quantum yield vs. PAG loading at EUV in CARs
• Quantum yield, Φ, is the number of acids produced per absorbed photon
• Two different experiments yet qualitatively similar results
• For the majority of the acid produced, the yield saturates with PAG loading
Kozawa et al ICPST, 6.2011 Higgins et al 2011
24 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Simulated yield using a simplified electronic excitation mechanism in PROLITH
Kozawa, Tagawa, ICPST, 6.2011
Potentially high yield
No saturation
• Energy loss process is uniform along the electron trajectory and is described by the loss function.
• The passing charge induces a time-dependent electric field upon the system (PAG) whose Fourier
components represent ‘virtual photons’ [3,4]
• Electron is not trapped by the PAG
• One electron may convert multiple PAGs and simulated yields can be very large (unphysical)
• Trend is roughly linear with PAG loading and no saturation is observed
• Excitation mechanism alone doesn’t fully explain data
25 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Simulated yield using a simplified electron trapping mechanism in PROLITH
Yield limited
Saturation
Kozawa, Tagawa, ICPST, 6.2011
• Electron may be trapped by the struck system
• The dissociative‐attachment peak cross section is a function of peak resonance energy [7]
• One electron may convert at most one PAG
• Yields is limited by the number of electrons
• Trend is nonlinear with PAG loading
• Saturation observed in model but max yield less than data; doesn’t fully explain data
26 KLA-Tencor Confidential. Copyright KLA-Tencor Corporation. All rights reserved.
Modeling quantum yield vs. loading for different PAGs
Higgins 2011 [9]
• Calibration of exposure simulation parameters
using both the direct excitation and electron trapping
mechanisms produces a good match to data for
each PAG tested by Higgins
[ ]( )PAG mM
Biafore, Smith, 2012 [10]
[9] C. Higgins, ‘EUV Photoresists: Film Quantum Yield and LER …,’ Dissertation, Univ. Albany, NY, CNSE, 2011
[10] Biafore, Smith, ‘Application of stochastic simulation to resist optimization,’ SPIE 8325-17, 2012
Lines = PROLITH
Points = Data
Φ
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