Seiichi Tagawa Graduate School of Engineering and The Institute of Scientific and Industrial Research Osaka University [email protected]IEUVI Resist TWG 2016 21 February 2016 Fundamental aspects of sensitivity enhancement and RLS trade-off of chemically amplified EUV resist
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Seiichi Tagawa
Graduate School of Engineering and The Institute of Scientific and Industrial Research
Critical Problems of Next Generation EUV Lithography
1. The most important critical issue of EUV lithography is the weak
intensity of EUV source.
2. The resist sensitivity and the exposure light intensity are
complimentary. Therefore high sensitization of EUV resists is required.
3. However, dramatic enhancement of resist sensitivity is widely
confirmed to be very difficult due to RLS trade-off problem.
LWR
Sensitivity
Resolution
The most difficult technical
requirement
for EUV resist is simultaneous
improvement in resolution,
LWR, and sensitivity (RLS).
There are two important points in EUV resists
(1) RLS trade off problem
(2) Change of resist reaction mechanisms
The photon energy of EUV (13.5 nm, 92.5 eV) is much higher
than ionization potential of resist materials (~10 eV).
Reaction mechanisms change from photochemistry to radiation
chemistry. (A review paper : Kozawa and Tagawa, 2010)
4
Resolution
LWR
Sensitivity
There is RLS (Resolution, Line Width Roughness , Sensitivity) Trade-off Problem (1)
1.Around 2000, the limitation of resolution was determined by acid diffusion length around 40-50 nm. EUV resists required less than 40 nm resolution. Easy method for getting high resolution is controlling acid diffusion length by high concentration quenchers.
2.So-called RLS trade-off appeared in EUV resist research at first. Many researchers on EUV chemically amplified resists (CARs) had arrived at the RLS trade-off triangle around 2003. Many experimental results:
For example, Brainard et al., Proc. SPIE (2004), Pawloski et al., Proc. SPIE (2004), Wallow et al., Proc. SPIE (2008)
3. Simulation by Gallatin clearly explained RLS trade-off. (G.M. Gallatin, Proc. SPIE 5754 (2005) 38.)
X
⑧Development ⑦Acid catalyzed image (Latent
image after PEB)
⑤Latent
acid image
③Accumulated energy profile
①Exposure
(Tool)
⑥Acid diffusion, deprotection reaction
②Interaction of EUV with resists
⑩10Other Treatments:
Vapor smoothing, Hardbake, Ectching,
Ozonation, etc.
④Acid generation
How to improve RLS trade-off relation in EUV CARs?
⑨Resist pattern formation
Problems have been improved step by step by global efforts.
But we thought the acid generation mechanisms, especially nano-space reactions
(mainly the combination of geminate recombination with dissociative electron
attachment) are important and essential for the solution of RLS trade-off problem,
because the high acid yield and the small acid space distribution are clearly the best
solutions of RLS trade-off problem.
A review paper: Kozawa and Tagawa, (2010) Acid generation
Accumulated energy profile
Interaction of EUV with resists
Acid catalyzed reaction
Comparison of products between radiolysis and photolysis of
acid generator (Triphenylsulfonium triflate)
S. Tagawa, et.al. SPIE 3999 (2000) 204.
Ph 3 S + X -
Ph 2 S Ph .
+ + H +
Ph H + X -
+ Ph 2 S +
Ionization channel
・ EUV and EB resists(Main process)
RH RH + .
+ e- RH
R . + + e- RHH+
e-
( Ph 3 S + X - )*
Ph 2 S .
Ph 2 S
Ph .
+
Ph + +
X - +
+
RH Ph 2 S PhR +
+
2 S H X - +
Homolysis
Heterolysis
RH: Solvent Exicitation channel
-PhPhSPh +
p -PhPhSPh +
m -PhPhSPh +
Ph 2 S .
+ Ph .
+ X - +
+ +
in-cage Reconbination
cage-escaped
cage-escaped
in-cage
in-cage
+ H + X -
H + X -
H +
X -
H + X -
X -
X - Ph + Ph 2 S
Ph + Ph +
o
・Photoresists (Main process)
.
.
Big Difference Between Reaction Mechanisms of
EUV (EB) Resists and Photoresists
S. Tagawa, et.al. SPIE 3999 (2000) 204.
Acid generation is
very fast and
mainly produced
in nanospace.
X -
⑧Development ⑦Acid catalyzed image (Latent
image after PEB)
⑤Latent
acid image
③Accumulated energy profile
①Exposure
(Tool)
⑥Acid diffusion, deprotection reaction
②Interaction of EUV with
resists
⑩10Other Treatments:
Vapor smoothing, Hardbake, Ectching,
Ozonation, etc.
④Acid generation
⑨Resist pattern formation
Resist Pattern Formation Processes of EUV CARs
New concept
④ Reconsideration of acid generation mechanisms
(2nd exposure) high intense UV flood exposure produces huge amount of acid
Co
nce
ntr
atio
n o
f ac
id a
nd
PS
(1st exposure)low power pattern exposure→generation of photosensitizer (PS) and acid
Co
nce
ntr
atio
n
of
acid
an
d P
S
acid PS
Co
nce
ntr
atio
n o
f ac
id
acid (A) Conventional Process
Radiation chemistry
(B) New Process Combination of radiation chemistry with photochemistry
acid PS
Photosensitized acid generation reactions at room temperature
Comparison of the new process with the conventional process
Resolution
Co
nce
ntr
atio
n
of
acid
LWR
Sensitivity
(2) Distribution and yield of latent acid image
(1) RLS trade-off
(B)
(A)
(A)
(B)
Schematic drawing of (1) RLS trade-off (2) initial distributions and yields of acid. If initial acid yield increases from (A) to (B) with the same distribution, RLS trade-off is improved from (A ) to (B).
The trade-off simulation contains two parts. (Gallatin model)
(1) The aerial image, properly normalized, is taken as the probability distribution for where a photon will be absorbed and cause an acid to be released.
(2) The acid catalyzed deprotection reactions and resist development process.
Breakthrough of RLS trade-off
The change of the first part is a key for the breakthrough of RLS trade-off.
• Fundamental aspects of a new process of high-resist sensitization by the combination lithography of EB/EUV pattern exposure with UV flood exposure of photosensitized CAR and non-CAR 22 Feb. 2016 • 4:30 - 4:50 PM
Seiichi Tagawa, Akihiro Oshima, Cong Que Dinh, Shigehiro Nishijima
• The first EUV pattern exposure produces photosensitizers.
• Resist has no absorption band of the second flood exposure light wavelength region. Therefore, no reaction of resist occurs if only the second flood exposure is carried out.
• Only photosensitizer has absorption band of the second flood exposure light wavelength region.
• New method coexisting together with most of other global efforts overcoming RLS Trade-off
Photosensitizer Generation
1st EB/EUV Pattern Exposure
•Acid Generation
2nd UV Flood Exposure
PEB Pattern Formation
Development
New Process (The combination of pattern exposure with flood exposure.)