Catalytic and autocatalytic mechanisms of acid amplifiers for use in EUV photoresists

Article abstract of DOI:10.1021/cm101867g

Twelve fluorinated acid amplifiers (AAs) were synthesized and studied for use in photoresists exposed to 13.5 nm, extreme ultraviolet (EUV) light. Acid amplifiers are compounds that decompose in the presence of acid to generate more acid via catalytic or autocatalytic mechanisms. These AAs are composed of a body, trigger, and an acid precursor. Thermal decomposition rates of solutions of the AAs in C₆D₆/m-ethylphenol (50/50 wt %) at 100 °C were monitored by ¹⁹F NMR with and without 1.2 equiv. of 2,4,6-tri-t-butylpyridine. All of the AAs in the presence of base decompose according to first-order kinetics with rate constants k_Base. The rate constants, k_Base, at various temperatures yielded the activation parameters ΔH^?, ΔS^?, and ΔG^?. The enthalpy of activation, ΔH, ^?, was in a narrow range of 16.6-19.1 (kcal/mol), whereas the entropy of activation, ΔS^?, spanned from 0 to -12 (cal/(mol K)). When acid is allowed to build up in solution (in the absence of base), six of the AAs with tertiary triggers (Body-3) decompose autocatalytically, but the six with secondary triggers (Body-2) are unaffected. Although Body-2 AAs do not decompose autocatalytically, nonaflate acid does catalyze their decomposition. Lithographic evaluation showed that some AAs are capable of simultaneously improving the resolution, line-edge-roughness, and sensitivity of a control EUV photoresist. This simultaneous improvement was quantified using the Z-Parameter. The AAs investigated here were found to improve the Z-Parameter by as much as a factor of 3.

Full text of DOI:10.1021/cm101867g

Chem. Mater. 2010, 22, 5609–5616 5609
DOI:10.1021/cm101867g
Catalytic and Autocatalytic Mechanisms of Acid Amplifiers for
Use in EUV Photoresists
Seth A. Kruger,† Craig Higgins,† Brian Cardineau,† Todd R. Younkin,‡ and
Robert L. Brainard*,†
†College of Nanoscale Science and Engineering, University at Albany, Albany, New York 12203, and
‡Intel Corporation, Hillsboro, Oregon 97124
Received July 5, 2010
Twelve fluorinated acid amplifiers (AAs) were synthesized and studied for use in photoresists
exposed to 13.5 nm, extreme ultraviolet (EUV) light. Acid amplifiers are compounds that decompose
in the presence of acid to generate more acid via catalytic or autocatalytic mechanisms. These AAs are
composed of a body, trigger, and an acid precursor. Thermal decomposition rates of solutions of the
AAs in C6D6/m-ethylphenol (50/50 wt %) at 100 °C were monitored by 19F NMR with and without
1.2 equiv. of 2,4,6-tri-t-butylpyridine. All of the AAs in the presence of base decompose according to
first-order kinetics with rate constants kBase. The rate constants, kBase, at various temperatures
yielded the activation parameters ΔH‡, ΔS‡, and ΔG‡. The enthalpy of activation, ΔH,‡, was in a
narrow range of 16.6-19.1 (kcal/mol), whereas the entropy of activation, ΔS‡, spanned from 0 to
-12 (cal/(mol K)). When acid is allowed to build up in solution (in the absence of base), six of the AAs
with tertiary triggers (Body-3) decompose autocatalytically, but the six with secondary triggers
(Body-2) are unaffected. Although Body-2 AAs do not decompose autocatalytically, nonaflate acid
does catalyze their decomposition. Lithographic evaluation showed that some AAs are capable of
simultaneously improving the resolution, line-edge-roughness, and sensitivity of a control EUV
photoresist. This simultaneous improvement was quantified using the Z-Parameter. The AAs
investigated here were found to improve the Z-Parameter by as much as a factor of 3.
Introduction
have proposed that the best way to simultaneously im-
prove these three properties in an EUV resist is to increase
the number of strong acids generated during exposure,4
and we assert that acid amplifiers may be one of the best
ways to achieve this goal. Acid amplifiers (AAs) are
compounds that decompose via acid-catalyzed mechan-
isms to produce more acid.5 When the product acid is
strong enough to catalyze the decomposition of the AA,
the decomposition occurs autocatalytically (Scheme 1).6
Previous work shows that to improve the imaging in a
modern photoresist, AAs must meet the following require-
ments.7,8 First, AAs must be thermally stable in the absence
of acid, at least within the process conditions of photoli-
thography. Second, AAs must rapidly decompose autoca-
talytically in the presence of catalytic acid. Third, AAs must
generate strong (fluorine-containing sulfonic) acids capa-
ble of participating in the photoresist chemistry. Prior to
our first communication on this topic,9 there were 26 acid
High-resolution, positive chemically amplified photore-
sists1 are central to the manufacture of today’s integrated
circuits. These thin film resists are composed primarily of
organic polymers and photoacid generators (PAGs). During
exposure to 193 or 13.5 nm light, the PAGs produce strong
acids. During a subsequent bake step, these strong acids
typically catalyze reactions of the organic polymer. For posi-
tive resists, these acid-catalyzed reactions transform the resist
from a material that is insoluble in aqueous alkaline deve-
loper into a material that is now soluble in this developer.
Development reveals patterns of photoresist features in
which the exposed regions have been removed and the
unexposed regions remain behind.
The development of chemically amplified photoresists
for use with extreme ultraviolet (EUV, 13.5 nm) light is
critical to meet the future photolithographic require-
ments of the microelectronics industry. These resists must
simultaneously exhibit three properties: high resolution,
low line edge roughness (LER),2 and high sensitivity.3 We
(4) Brainard, R. L.; Trefonas, P.; Lammers, J. H.; Cutler, C. A.;
Mackevich, J. F.; Trefonas, A.; Robertson, S. A. Proc. SPIE
2004, 5374(Pt. 1), 74–85.
(5) Ichimura, K. Chem. Rec. 2002, 2, 46–55.
*Corresponding author. E-mail: rbrainard@uamail.albany.edu.
(1) Ito, H.; Breyta, G.; Hofer, D.; Sooriyakumaran, R.; Petrillo, K.;
Seeger, D. J. Photopolym. Sci. Technol. 1994, 7, 433–47.
(2) Shumway, M. D.; Naulleau, P.; Goldberg, K. A.; Bokor, J. J. Vac.
Sci. Technol., B 2005, 23, 2844–2847.
(3) Gallatin, G. M.; Naulleau, P.; Niakoula, D.; Brainard, R. L.;
Hassanein, E.; Matyi, R.; Thackeray, J.; Spear, K.; Dean, K. Proc.
SPIE 2008, 6921, 69211E/1–69211E/11.
(6) Gerdts, C. J.; Sharoyan, D. E.; Ismagilov, R. F. J. Am. Chem. Soc.
2004, 126, 6327–31.
(7) Ichimura, K.; Arimitsu, K.; Kudo, K. Chem. Lett. 1995, 551–552.
(8) Arimitsu, K.; Kudo, K.; Ichimura, K. J. Am. Chem. Soc. 1998, 120,
37–45.
(9) Kruger, S. A.; Revure, S.; Higgins, C.; Gibbons, S.; Freedman,
D. A.; Wang, Y.; Younkin, T.; Brainard, R. L. J. Am. Chem. Soc.
2009, 131(29), 9862–9863.
r
2010 American Chemical Society
Published on Web 09/20/2010
pubs.acs.org/cm

5610 Chem. Mater., Vol. 22, No. 19, 2010
Kruger et al.
than the starting AA, yielding a second double bond and a
sulfonic acid. Surprisingly, we found that the AA’s with ter-
tiary triggers react with these product acids to undergo auto-
catalytic reaction kinetics, whereas the AAs with secondary
triggers do not generate acids that are strong enough to
catalyze their own decomposition. Instead, we found that the
decomposition of AAs with secondary triggers can be cata-
lyzed by an added super acid.
Additionally, the performance of these twelve acid ampli-
fiers was also evaluated for their performance in EUV
photoresists using a global performance constant called the
Z-Parameter.19-22 We found that AAs with both secondary
and tertiary triggers can enhance the lithographic perfor-
mance of EUV resists. The best AA can improve the
Z-Parameter of our control resist by a factor of 3.
Figure 1. Acid amplifiers described here consist of three parts: a trigger,
an acid precursor, and a body. Six AAs have bodies resulting in tertiary
triggers (R1 = CH3) and six AAs have bodies resulting in secondary
triggers (R1 = H).
Scheme 1. Our Proposed Reaction Mechanism for the
Acid-Catalyzed and Uncatalyzed Decomposition of
Tertiary Acid Amplifiers
Experimental Section
General Procedures. All nuclear magnetic resonance spectra
were recorded on Bruker 400 spectrometer and the chemical
shifts are reported in parts per million. 1H NMR data are
referenced to CDCl3 (7.24 ppm) and 19F data are referenced to
C6F6 (-164.9 ppm). All reagents were purchased from commer-
cial suppliers and used without further purification. Kinetic
experiments were run in flame-sealed NMR tubes and the
solvent system was a 50/50 wt % mixture of C6D6 and m-ethyl
phenol with a trace amount of C6F6 as a fluorine reference. The
samples were heated by submerging the tubes in a hot oil bath at
the desired temperature.23 Elemental analyses were performed
by Midwest Microlab LLC.
amplifiers in the literature. The AAs previously reported
consist of acetoacetate derivatives,7 cyclohexane-1,2-diol
monosulfonates,10,11 a trioxane derivative,12 ketal sulfo-
nates,13 pinane-1,2 diol monosulfonates,14,15 cyclohexane-
1,4-disulfonates,16 and benzyl sulfonates.17 Only two of the
AA’s described in the literature produce fluorinated acids.16
In addition, only five of the AAs were evaluated for their
additive effects on photoresist imaging. Nonfluorinated AAs
were incorporated into acrylate based ArF resists11,15 and
phenolic KrF resists.18 The results of these experiments show
that AAs designed for lithographic applications must gen-
erate strong acids and be thermally stable. Our efforts focus
on designing thermally stable AAs that produce fluorinated
sulfonic acids for use in phenolic EUV resists.
In this work, we report on the synthesis, thermal decom-
position kinetics, and lithographic performance of 12 acid
amplifiers. We systematically vary the chemical structures
to give a range of reactivities. These acid amplifiers consist
of three parts (Figure 1), a body, an acid-sensitive trigger
(T, either hydroxyl or methoxy), and a fluorinated sulfonic
acid precursor (A). During autocatalysis, the trigger under-
goes acidolysis8 yielding an allylic sulfonic ester (E1 or E2)
(Scheme 1). This allows the sulfonic ester to thermally
decompose via an E1 or E2 elimination reaction more rapidly
3-Hydroxy-3-methylbutyl 4-(trifluoromethyl)benzenesulfonate
(3HA). To a solution of 3-methyl-1,3-butane diol (1.9 g, 18.2 mmol)
in pyridine (15 mL) was added p-(trifluorormethyl)- benzenesulfo-
nyl chloride (3.67 g, 15 mmol). The solution was stirred at 0 °C for
2 h. The reaction mixture was diluted with ethyl acetate (40 mL) and
washed with 1 M HCl (3 ꢀ 50 mL), saturated aqueous NaHCO3 (50
mL) and saturated aqueous NaCl (50 mL). The organics were dried
over Na2SO4 and concentrated to give a white, low-melting-point
solid (3.33 g, 71%). 1H NMR (400 MHz CDCl3) δ8.04 (d, 2 H, J=
8.0 Hz), 7.81 (d, 2 H, J = 8.0 Hz), 4.72 (t, 2 H, J = 7.0 Hz), 1.87 (t,
2 H, J = 7.0 Hz), 1.21 (s, 6 H). Anal. Calcd for C12H15F3O4S: C,
46.15; H 4.84. Found: C, 46.14; H, 4.90.
3-Hydroxy-3-methylbutyl 2-(trifluoromethyl)benzenesulfonate
(3HB). To a solution of 3-methyl-1,3-butane diol (2.5 g, 21 mmol)
and TEA (1.63 g, 16 mmol) in CH2Cl2 (15 mL) was added
o-(trifluorormethyl)benzenesulfonyl chloride (2.03 g, 8.3 mmol)
dissolved in CH2Cl2 (20 mL). The solution was stirred at room
temperature (RT) for 7 h. The reaction mixture was diluted with
CH2Cl2 (75 mL) and washed with 1 M HCl (2 ꢀ 25 mL), saturated
aqueous NaHCO3 (25 mL), and saturated aqueous NaCl (25 mL).
The organics were dried over Na2SO4 and concentrated to give a
(10) Noguchi, S.; Arimitsu, K.; Ichimura, K.; Kudo, K. J. Photopolym.
Sci. Technol. 1997, 10, 315–316.
(11) Ohfuji, T.; Takahashi, Ml; Sasago, M.; Noguchi, S.; Ichimura, K.
J. Photopolym. Sci Technol. 1997, 10, 551–558.
(12) Arimitsu, K.; Ichimura, K. Chem. Lett. 1998, 823–824.
(13) Kudo, K.; Arimitsu, K.; Ohmori; Ito, H; Ichimura, K. Chem.
Mater. 1999, 11, 2119–2125.
(19) Wallow, T.; Higgins, C.; Brainard, R. L.; Petrillo, K.; Montgom-
ery, W.; Koay, C. S.; Denbeaux, G.; Wood, O.; Wei, Y. Proc. SPIE
2008, 6921, 1–11.
(20) Higgins, C.; Antohe, A.; Denbeaux, G.; Kruger, S. A.; Georger, J.;
Brainard, R. L. Proc. SPIE 2009, 7271, 47.
(21) The Z-Parameter can be calculated from a single SEM as Z =
CD3 ꢀ LER2 ꢀ Esize, where a smaller value is better.
(22) Gallatin, G. M.; Naulleau, P.; Brainard., R. L.; Niakoula, D.;
Dean, K. Presented at the EUVL Symposium; Sapporo, Japan, Oct
29-31, 2007; Extreme UltraViolet Lithography System Development
Association : Kawasaki, Japan, 2007.
(23) Brainard, R.; Kruger, S.; Higgins, C.; Revuru, S.; Gibbons, S.;
Freedman, D.; Wang, Y.; Younkin, T. J. Photopolym. Sci. Technol.
2009, 22, 43–50.
(14) Park, S.-W.; Arimitsu, K.; Ichimura, K.; Ohfuji, T. J. Photopolym.
Sci. Technol. 1999, 12, 293–296.
(15) Naito, T.; Ohfuji, T.; Endo, M.; Morimoto, H.; Arimitsu, K.;
Ichimura, K. J. Photopolym. Sci. Technol. 1999, 12, 509–514.
(16) Lee, S.; Arimitsu, K.; Park, S.-W.; Ichimura, K. J. Photopolym. Sci.
Technol. 2000, 13, 215–216.
(17) Ito, H.; Ichimura, K. Macromol. Chem. Phys. 2000, 201, 132–138.
(18) Huang, W.-S.; Kwong, R.; Moreau, W. Proc. SPIE 2000, 3999,
591–597.

Article
Chem. Mater., Vol. 22, No. 19, 2010 5611
crude mixture. Silica gel chromatography with ethyl acetate in
hexanes yielded the desired product (1.73 g, 66%). 1H NMR (400
MHz CDCl3) δ8.23(m, 1H), 7.91(m, 1H), 7.75(m, 2H), 4.32(t, 2
H, J = 7.0 Hz), 1.91 (t, 2 H, J = 7.0 Hz) 1.22 (s, 6 H). Anal. Calcd
for C12H15F3O4S: C, 46.15; H 4.84. Found: C, 45.73; H, 4.88.
3-Hydroxy-3-methylbutyl 2,3,4,5,6-pentafluororbenzenesulfo-
nate (3HC). To a solution of 3-methyl-1,3-butane diol (0.79 g,
7.5 mmol) and TEA (0.37 g, 3.6 mmol) in CH2Cl2 (7 mL) at 0 °C
was added pentafluororbenzenesulfonyl chloride (0.80 g, 3.0
mmol). The solution was stirred at 0 °C for 1.5 h. Saturated
aqueous NaHCO3 (10 mL) was added to the solution and the
mixture was stirred at RT for 15 min. The organics were
extracted with CH2Cl2 and washed with 0.5 M HCl (20 mL)
and saturated aqueous NaCl (20 mL). The organics were dried
over Na2SO4 and concentrated to give a crude mixture. Silica gel
chromatography with 30% ethyl acetate in hexanes yielded the
desired product as a white, crystalline, low-melting-point solid
(0.69 g, 66%). 1H NMR (400 MHz CDCl3) δ 4.49 (t, 2 H, J = 7.0
Hz), 1.97 (t, 2 H, J = 7.0 Hz) 1.27 (s, 6 H). Anal. Calcd for
C11H11F5O4S: C, 39.53; H 3.32. Found: C, 39.54; H, 3.22.
3-Methoxy-3-methylbutyl 4-(trifluoromethyl)benzenesulfonate
(3MA). To a solution of 3-methoxy-3-methylbutane-1-ol (0.58 g,
4.9 mmol) in pyridine (5 mL) was added p-(trifluorormethyl)-
benzenesulfonyl chloride (0.98 g, 4 mmol). The solution was stirred
at RT for 3.5 h. The reaction mixture was diluted with ethyl acetate
(25 mL) and washed with 1 M HCl (6 ꢀ 25 mL), saturated aqueous
NaHCO3 (25 mL) and saturated aqueous NaCl (25 mL). The
organics were dried over Na2SO4 and concentrated to give an oil
(0.53 g, 40%). 1H NMR (400 MHz CDCl3) δ 8.03(d, 2 H, J = 8.0
Hz), 7.81 (d, 2 H, J = 8.0 Hz), 4.19 (t, 2 H, J = 7.3 Hz), 3.09 (s, 3
H), 1.88 (t, 2 H, J = 7.3 Hz), 1.12 (s, 6 H). Anal. Calcd for
C13H17F3O4S: C, 47.85; H 5.25. Found: C, 47.72; H, 5.05.
3-Methoxy-3-methylbutyl 2-(trifluoromethyl)benzenesulfonate
(3MB). To a solution of 3-methoxy-3-methylbutane-1-ol (2.8 g,
24 mmol) and TEA (1.6 g, 16 mmol) in CH2Cl2 (15 mL) was added
o-(trifluorormethyl)benzenesulfonyl chloride (1.9 g, 8 mmol) dis-
solved in CH2Cl2 (20 mL). The solution was stirred at RT for 4 h.
Saturated aqueous NaHCO3 (15 mL) was added to the solution
and mixture was stirred at RT for 30 min. The organics were ex-
tracted with CH2Cl2 (75 mL) and washed with 1 M HCl (2 ꢀ 25
mL), saturated aqueous NaHCO3 (25 mL), and saturated aqueous
NaCl (25 mL). The organics were dried over Na2SO4 and con-
centrated to give a crude mixture. Silica gel chromatography with
ethyl acetate in hexanes yielded the desired product (2.1 g, 81%).
1H NMR (400 MHz CDCl3) δ 8.23 (m, 1 H), 7.91 (m, 1 H), 7.74
(m, 2H), 4.25(t, 2H, J=7.5Hz), 3.10(s, 1H), 1.92(t, 2H, J=7.5
Hz) 1.13 (s, 6 H). Anal. Calcd. For C13H17F3O4S: C, 47.85; H 5.25.
Found: C, 47.95; H, 5.11.
3-Hydroxybutyl 4-(trifluoromethyl)benzenesulfonate (2HA).
To a solution of 1,3-butane diol (4.34 g, 48 mmol) and TEA
(3.19 g, 31.5 mmol) in CH2Cl2 (20 mL) at 0 °C was added
p-(trifluorormethyl)benzenesulfonyl chloride (3.97 g, 16.2
mmol) dissolved in CH2Cl2 (20 mL). The solution was stirred
at 0 °C for 2 h. Saturated aqueous NaHCO3 (15 mL) was added
to the solution and mixture was stirred at RT for 40 min. The
organics were extracted with CH2Cl2 (50 mL) and washed with
1 M HCl (3 ꢀ 25 mL) and saturated aqueous NaCl (25 mL). The
organics were dried over Na2SO4 and concentrated to give the
1
desired product (3.28 g, 65%). H NMR (400 MHz CDCl3) δ
8.02 (d, 2 H, J = 8.2 Hz), 7.80 (d, 2 H, J = 8.3), 4.29 (m, 1 H),
4.17 (m, 1 H), 3.91 (m, 1 H), 1.83 (m, 1 H), 1.70 (m, 1 H), 1.17 (d,
3 H, J = 6.2 Hz). Anal. Calcd for C11H13F3O4S: C, 44.29; H
4.39. Found: C, 44.16; H, 4.17.
3-Hydroxybutyl 2-(trifluoromethyl)benzenesulfonate (2HB).
To a solution of 1,3-butane diol (2.18 g, 24 mmol) and TEA
(1.64 g, 16 mmol) in CH2Cl2 (15 mL) at 0 °C was added
o-(trifluorormethyl)benzenesulfonyl chloride (2 g, 8 mmol) dis-
solved in CH2Cl2 (20 mL). The solution was stirred at 0 °C for
2 h. Saturated aqueous NaHCO3 (15 mL) was added to the
solution and mixture was stirred at RT for 45 min. The organics
were extracted with CH2Cl2 (150 mL) and washed with 0.5 M
HCl (2 ꢀ 80 mL) and saturated aqueous NaCl (50 mL). The
organics were dried over Na2SO4 and concentrated to give a
crude mixture. Silica gel chromatography (50% ethyl acetate in
hexanes) yielded the desired product (2 g, 84%). 1H NMR (400
MHz CDCl3) δ 8.23 (m, 1 H), 7.92 (m, 1 H), 7.74 (m, 2 H), 4.34
(m, 1 H), 4.24 (m, 1 H), 3.95 (m, 1 H), 1.89 (m, 1 H), 1.73 (m, 1
H), 1.20 (d, 3 H, J = 6.3 Hz). Anal. Calcd for C11H13F3O4S: C,
44.29; H 4.39. Found: C, 44.29; H, 4.28.
3-Hydroxybutyl 2,3,4,5,6-pentafluororbenzenesulfonate (2HC).
Toa solutionof1,3-butanediol (0.9 g, 10 mmol) andTEA (0.61 g,
6 mmol) in CH2Cl2 (4 mL) at 0 °C was added pentafluororben-
zenesulfonyl chloride (0.53 g, 2 mmol) dissolved in CH2Cl2
(4 mL). The solution was stirred for 6 h, during which time the
solution slowly warmed to RT. Saturated aqueous NaHCO3
(25 mL) was added to the solution and the mixture was stirred
at RT for 30 min. The organics were extracted with CH2Cl2
(50 mL) and washed with 0.5 M HCl (3 ꢀ 20 mL), saturated
aqueous NaHCO3 (20 mL), and saturated aqueous NaCl (20
mL). The organics were dried over Na2SO4 and concentrated to
givea crudemixture. Silica gelchromatography withethylacetate
in hexanes yielded the desired product (0.26 g, 40%). 1H NMR
(400 MHz CDCl3) δ 4.62 (m, 2 H), 4.13 (m, 1 H), 2.11 (m, 1 H),
1.94 (m, 1 H), 1.40 (d, 3 H, J = 6.2 Hz). Anal. Calcd for
C10H9F5O4S: C, 37.51; H 2.83. Found: C, 37.70; H, 2.93.
3-Methoxybutyl 4-(trifluoromethyl)benzenesulfonate (2MA).
To a solution of 3-methoxybutane-1-ol (0.58 g, 4.9 mmol) in
pyridine (5 mL) was added p-(trifluorormethyl)benzenesulfonyl
chloride (0.98 g, 4 mmol). The solution was stirred at RT for 3.5 h.
The reaction mixture was diluted with ethyl acetate (25 mL) and
washed with 1 M HCl (6 ꢀ 25 mL), saturated aqueous NaHCO3
(25 mL), and saturated aqueous NaCl (25 mL). The organics were
dried over Na2SO4 and concentrated to give an oil (0.53 g, 40%).
1H NMR (400 MHz CDCl3) δ 8.03 (d, 2 H, J = 8.1 Hz), 7.81 (d,
2 H, J = 8.3 Hz), 4.19 (m, 2 H), 3.35 (m, 1 H), 3.18 (s, 3 H), 1.78
(m, 2 H), 1.09 (d, 3 H, J = 6.0 Hz). Anal. Calcd for C12H15F3O4S:
C, 46.15; H 4.84. Found: C, 45.99; H, 4.64.
3-Methoxy-3-methylbutyl 2,3,4,5,6-pentafluororbenzenesulfo-
nate (3MC). To a solution of 3-methoxy-3-methylbutane-1-ol
(1.07 g, 9 mmol) and TEA (0.61 g, 6 mmol) in CH2Cl2 (12 mL)
was added pentafluororbenzenesulfonyl chloride (0.99 g,
3.7 mmol). The solution was stirred at RT for 2 h. Saturated
aqueous NaHCO3 (12 mL) was added to the solution and the
mixture was stirred at RT for 30 min. The organics were
extracted with CH2Cl2 (50 mL) and washed with 0.5 M HCl
(3 ꢀ 40 mL), saturated aqueous NaHCO3 (40 mL), and
saturated aqueous NaCl (40 mL). The organics were dried
over Na2SO4 and concentrated to give a crude mixture. Silica
gel chromatography with ethyl acetate in hexanes yielded the
desired product (0.68 g, 51%). 1H NMR (400 MHz CDCl3) δ
4.42 (t, 2 H, J = 7.3 Hz), 3.13 (s, 3 H), 1.97 (t, 2 H, J = 7.4 Hz),
1.17 (s, 6 H). Anal. Calcd for C12H13F5O4S: C, 41.38; H 3.76.
Found: C, 41.37; H, 3.77.
3-Methoxybutyl 2-(trifluoromethyl)benzenesulfonate (2MB).
To a solution of 3-methoxybutane-1-ol (0.63 g, 6.0 mmol) and
TEA (0.42 g, 4.1 mmol), in CH2Cl2 (5 mL) was added o-(trifluo-
rormethyl)benzenesulfonyl chloride (0.50 g, 2.0 mmol). The
solution was stirred at RT for 2 h. The reaction mixture was

5612 Chem. Mater., Vol. 22, No. 19, 2010
Kruger et al.
Scheme 2. Twelve AAs Were synthesized by Reacting Primary
Alcohols with Sulfonyl Chlorides in the Presence of Base
Table 1. Unique Names for Twelve AAs Synthesized for This Study Based
on Their Body, Trigger, and Acid Precursor Combinationa
compd
R1
R2
R3
3HA
3HB
3HC
3MA
3MB
3MC
2HA
2HB
2HC
2MA
2MB
2MC
Me
Me
Me
Me
Me
Me
H
H
H
H
H
H
H
H
Me
Me
Me
H
H
H
p-CF3C6H4
o-CF3C6H4
C6F5
p-CF3C6H4
o-CF3C6H4
C6F5
p-CF3C6H4
o-CF3C6H4
C6F5
p-CF3C6H4
o-CF3C6H4
C6H5
diluted with CH2Cl2 (15 mL) and washed with 1 M HCl (3 ꢀ 15
mL), saturated aqueous NaHCO3 (15 mL), and saturated aqu-
eous NaCl (15 mL). The organics were dried over Na2SO4 and
concentrated to give a crude mixture. Silica gel chromatography
with ethyl acetate in hexanes yielded the desired product (0.34 g,
Me
Me
Me
1
50%). H NMR (400 MHz CDCl3) δ 8.23 (m, 1 H), 7.91 (m,
H
1 H), 7.75 (m, 2 H), 4.24 (m, 2 H), 3.40 (m, 1 H), 3.21 (s, 3 H), 1.80
(m, 2 H), 1.10 (d, 3 H, J = 6.2 Hz). Anal. Calcd for C12H15F3-
O4S: C, 46.15; H 4.84. Found: C, 46.30; H, 4.88.
a The Names of AAs start with either a 3 or a 2 indicating bodies with
tertiary or secondary triggers, respectively.
3-Methoxybutyl 2,3,4,5,6-pentafluororbenzenesulfonate (2MC).
To a solution of 3-methoxybutane-1-ol (0.78 g, 7.5 mmol) and
TEA (0.388 g, 3.8 mmol), in CH2Cl2 (15 mL) was added penta-
fluororbenzenesulfonyl chloride (0.79 g, 3.0 mmol). The solution
was stirred at RT for 4 h. Saturated aqueous NaHCO3 (10mL) was
added to the solution and the mixture was stirred at RT for 30 min.
The organics were extracted with CH2Cl2 (30 mL) and washed
with 0.5 M HCl (2 ꢀ 20 mL) and saturated aqueous NaCl (20 mL).
The organics were dried over Na2SO4 and concentrated to give a
crude mixture. Silica gel chromatography (15% ethyl acetate in
hexanes) yielded the desired product (0.39 g, 36%). 1H NMR (400
MHz CDCl3) δ4.40 (m, 2 H), 3.45 (m, 1 H), 3.26 (s, 3 H), 1.87 (m, 2
H), 1.15 (d, 3 H, J = 6.1 Hz). Anal. Calcd for C11H11F5O4S: C,
39.53; H 3.32. Found: C, 39.83; H, 3.45.
(in sealed NMR tubes) were measured using 19F NMR.
Solutions of AAs (70 mM) in 50/50 wt % C6D6/m-ethylphe-
nol (to simulate the environment of a phenolic polymer
matrix) in the presence and absence of 1.2 eq of added
2,4,6-tri-t-butylpyridine (TBP) were monitored. The steri-
cally hindered base was added to consume acid as it formed,
so that the uncatalyzed reactions could be studied indepen-
dently.9 All rate constants24 at 100 °C and kinetic parameters
are reported in Table 2. We chose to compare rate constants
at 100 °C because they can be measured accurately at this
temperature for all 12 compounds in the presence and
absence of added base. Additional rate constants were
measured at temperatures chosen on the basis of the boiling
points of readily available, nonflammable solvents that are
used to heat an oil bath at a constant temperature.23
Uncatalyzed Thermal Decomposition of Acid Amplifiers
in the Presence of Base. All decomposition reactions con-
ducted in the presence of excess base showed first-order reac-
tion kinetics. As expected, the decomposition rate increases as
the number of fluorine atoms increase or when they are lo-
cated closer to the sulfonate ester, because increasing the
electronegativity of sulfonates increases their leaving ability.
In particular, the AAs having perfluorobenzenesulfonate
(PFBS) esters decompose at 100 °C in the presence of base
11-27 times faster than do the AAs prepared with either of
the p- or o-trifluoromethyl benzenesulfonate (TMBS) esters.
The trigger also has a significant effect on the first-order
rate of decomposition. Comparisons of decomposition rates
inthepresenceofbasemadebetweenAAswiththesamebody
and acid precursors show that AAs prepared with methoxy
triggers decompose faster than AAs prepared with hydroxyl
triggers (Body-3, 3-4ꢀ faster; Body-2, 1.1-1.3ꢀ faster).
Uncatalyzed first-order reaction rates (kBase) were mea-
sured at three temperatures in the presence of excess base.
Eyring plots of these rate constants yielded ΔH‡, ΔS‡, and
ΔG‡ for each reaction (Table 2). Interestingly, the enthalpy of
activation (ΔH‡) values are constrained within a fairly narrow
range of values (16.6-19.1 kcal/mol), whereas the entropy of
activation (ΔS‡) seems to give the largest range of values (0 to
Lithographic Evaluation. We evaluated acid amplifiers by
adding equal molar concentrations of the AAs (70 mM except
where noted) to a control ESCAP resist formulation composed
of: 7.5 wt % of solids of Di(4-tert-butylphenyl) iodonium
perfluoro-1-butane-sulfonate (DTBI-PFBS) PAG, 1.0 wt % of
tetrabutylammonium hydroxide base (TBAH), 4-hydroxystyr-
ene/styrene/t-butyl acrylate (65/15/20) polymer and a 50/50
mixture solvent of ethyl lactate and propylene glycol methyl
ether acetate. Formulations were prepared at 5 wt % solids (vs
solvent), spin coated to a film thickness of 125 nm and soft-
baked (90 °C, 60 s). Exposures were performed using dense line/
space patterns (annular illumination on Berkeley EUV MET),
followed by postexposure bake (PEB, 90 °C, 90 s), and 45 s
development in 0.26 N Me4NþOH- (TMAH).
Results and Discussion
Synthesis of Twelve Fluorinated Acid Amplifiers. Twelve
acid amplifiers were synthesized to give a range of reactivities
by reacting primary alcohols with sulfonyl chlorides in the
presence of pyridine or triethylamine (TEA). Pyridine and
TEA give similar yields when p-(CF3)C6H4SO2Cl or o-(CF3)-
C6H4SO2Cl are reacted with a 1,3-diol. Most of the other
reactions give better yields when TEA is used, especially reac-
tions with perfluorobenzenesulfonyl chloride. The acid sensi-
tive triggers are secondary (2°) or tertiary (3°) hydroxyl or
methoxy groups and the acids generated upon AA decom-
position are p-(CF3)C6H4SO3H, o-(CF3)C6H4SO3H or
C6F5SO3H. Scheme 2 shows the general synthetic strategy
and Table 1 lists the 12 AAs that were synthesized using this
method.
(24) Second-order catalyzed reaction kinetics was evaluated by fitting
data to Capellos, C.; Bielski, B. Kinetic Systems: Mathematical
Description of Chemical Kinetics in Solution; Wiley-Interscience:
New York, 1972.
Decomposition Kinetics of Acid Amplifiers in Solution.
The thermal decomposition kinetics of the AAs in solution

Article
Chem. Mater., Vol. 22, No. 19, 2010 5613
Table 2. Rate Constants and Activation Parameters for the Thermal Decomposition of Acid Amplifiers Vary with Chemical Structure
compd
kBase ꢀ 105 (s-1 a
)
kNoBase ꢀ 105 (M s)-1a
ΔH‡ (kcal/mol)
ΔS‡ (cal/(mol K))
ΔG‡ (kcal/mol)a
3HA
3HB
3HC
3MA
3MB
3MC
2HA
2HB
2HC
2MA
2MB
2MC
3.6 ( 0.1
5.1 ( 0.1
73 ( 2
4400 ( 800
7100 ( 1300
22 000 ( 3000
3700 ( 200
5700 ( 300
20 000 ( 2000
1.1 ( 0.1
18.0 ( 0.4
17.3 ( 0.1
18.6 ( 0.9
19.1 ( 1.0
18.6 ( 0.8
17.6 ( 1.3
17.2 ( 1.5
17.7 ( 0.3
16.8 ( 1.5
18.7 ( 1.6
18.9 ( 0.3
16.6 ( 0.1
-7.7 ( 0.9
-8.9 ( 0.3
-0.1 ( 2.5
-2.1 ( 2.7
-2.7 ( 2.2
-0.3 ( 3.8
-12.0 ( 3.7
-9.8 ( 0.6
-6.9 ( 4.1
-7.3 ( 4.0
-6.1 ( 0.7
-6.9 ( 0.2
20.9 ( 0.4
20.6 ( 0.1
18.6 ( 0.9
19.9 ( 1.0
19.6 ( 0.8
17.7 ( 1.3
21.6 ( 1.5
21.4 ( 0.3
19.4 ( 1.5
21.4 ( 1.6
21.2 ( 0.3
19.2 ( 0.1
16 ( 1
21 ( 1
240 ( 10
1.2 ( 0.1
1.7 ( 0.1
33 ( 3
1.7 ( 0.1
27 ( 3
1.6 ( 0.1
2.4 ( 0.1
37 ( 1
1.7 ( 0.1
2.6 ( 0.1
42 ( 2
a Temperature = 100 °C. The AAs were decomposed in 50/50 wt % d6-benzene/m-ethylphenol in sealed NMR tubes. The activation parameters were
calculated using Erying plots.
-12 cal/(mol K)). Not surprisingly, therefore, the entropy of
activation seems to be the strongest predictor of rate and ΔG‡,
with the most negative values of ΔS‡ giving the slowest first-
order rate constants and the highest values of ΔG‡.
The most significant pattern that emerges from these
kinetic parameters is the differences between the ΔS‡ values
of AAs prepared with hydroxyl vs methoxy triggers. A pair-
wise comparison of the eight AAs prepared with either p- or
o-TMBS esters, shows that the AAs with hydroxyl triggers
have considerably lower ΔS‡ values. This pattern does not
exist for the AAs prepared with the PFBS esters, presumably
because of a change in mechanism of the first-order decom-
position for these highly fluorinated compounds.
Thermal Decomposition of Acid Amplifiers without
Added Base. In order for a resist containing an AA to pro-
perly distinguish between exposed and unexposed regions,
the acid-catalyzed decomposition rate of the AA must be
significantly faster than the uncatalyzed decomposition rate.
To study the interactions between acid amplifiers and the acid
generated by them during their decomposition, we studied
the thermal decomposition kinetics of the 12 AAs without
any added base at 100 °C. The six acid amplifiers with tertiary
triggers (Body-3) decompose according to the autocatalytic
mechanism illustrated in Scheme 1. For example, in the pre-
Figure 2. (A) Decomposition rate of b 3HA with base is first-order and
sence of added base, AA-3HA decomposes according to first-
O 3HA without base is autocatalytic. (B) Decomposition rates of b 2HA
order kinetics so that the plot of ln [3HA] vs time is linear
with base and O 2HA without base are both first order, regardless of the
build up of acid generated by AA decomposition.
(R2 = 0.998, Figure 2A). Without base, the plot of ln [3HA]
vs time is initially first-order, but once a small amount of acid
is generated, the reaction proceeds autocatalytically, giving
the observed curvature. Conversely, the six acid amplifiers
with secondary triggers (Body-2) give first-order kinetics
independent of the presence or absence of added base as
illustrated by AA-2HA (Figure 2B), indicating that the build-
up of the sulfonic acid product has no effect on reaction rate.
One important criterion we use for evaluating the per-
formance of an acid amplifier is the ratio of rate constants
evaluated in the absence and presence of added base
(kNoBase/kBase). Table 3 shows the ratios of all compounds
at 100 °C. Body-3 AAs have rate ratios in the range of
80-1400. Unexpectedly, all six Body-2 AAs with secon-
dary triggers have rate ratios of 1.0. This means that the
decomposition rates of Body-2 AAs are independent of
the presence or absence of the buildup of sulfonic acid
generated during their decomposition. Yet, as described
below, Body-2 AAs show reasonably good lithographic
performance and improved resist sensitivity, indicating
that acids are being generated. These observations led us
to study the rate of decomposition of AA-2HA in the
presence of added nonaflate acid. This acid, C4F9SO3H, is
produced during photodecomposition of the photoacid
generator (PAG) in the polymeric resist film during
imaging. Nonaflate acid is stronger than any of the acids
generated by the 12 AAs studied here. We measured the
decomposition rate of 2HA at 100 °C in the presence of 0,
0.25, 0.5, and 0.75 equiv. of nonaflate acid. Figure 3
shows that the rate increases linearly with increasing
nonaflate acid concentration. This means that although
2HA does not decompose autocatalytically, the decom-
position is catalyzed by nonaflate acid (Figure 3). Figure 4
compares the reaction energy profiles for Body-3 and

5614 Chem. Mater., Vol. 22, No. 19, 2010
Kruger et al.
Body-2 AAs. The trigger-pull (T) reaction for Body-3
AAs is catalyzed by the acid generated from the AA
decomposition resulting in a lower energy pathway than
the uncatalyzed decomposition (U). On the other hand,
these acids do not catalyze the trigger-pull for Body-2
AAs (solid curve) but nonaflate acid does (dashed curve).
Lithographic Evaluation of Acid Amplifiers. To assess
the impact of our AAs on improving EUV patterning per-
formance, we calculated the Z-Parameter of the control resist
(no AA) along with resists containing 70 mM AA. We com-
pare the Z-Parameter at 50 nm equal lines and spaces because
most of the resists resolved these features. A smaller Z-Para-
meter reflects overall improvement in lithographic perfor-
mance.21 Figure 5 shows lithographic results for the control
resist without AA and 12 resists with 70 mM AA. For the
most part, resist performance was evaluated by printing
50 nm equal lines and spaces. The sizing dose, LER and
Z-Parameter are reported for each resist. All resists prepared
with 70 mM concentration of AAs show sensitivity improve-
ments (except 2HB). The best overall resists contain AA
3MA, 3MB, 3HF, or 2MA. The Z-Parameter of resists that
contain 70 mM of either of these AAs improves by factors
of two or three relative to the control resist (control Z-Para-
meter =13). Addition of AA 3HA, 2HA, or 2HC improves
the Z-Parameter from 13 (control) to 7. The AAs 2MB and
2HB do not improve Z-Parameter of the control resist.
Figure 6 shows representative scanning electron micrographs
Figure 3. Decomposition rate constant of 2HA at 100 °C increases
linearly with respect to the concentration of added nonaflate acid, the
acid generated photochemically in the resist formulations.
Table 3. We Compare Lithographic Properties at 50 nm Resolution (unless noted) and rate ratiso at 100 °C for Hydroxyl and Methoxy Trigger AAs
Esize
(mJ/cm2)
LER
(nm)
Z ꢀ 107
Esize
(mJ/cm2)
LER
(nm)
Z ꢀ 107
R1
R3
name
kNoBase/kBase
(mJ nm3)c
name
kNoBase/kBase
(mJ nm3)c
Me
Me
Me
H
H
H
p-CF3C6H4
o-CF3C6H4
C6F5
p-CF3C6H4
o-CF3C6H4
C6F5
3HA
3HB
3HCa
2HA
2HB
2HC
1210
1390
300
1
1
1
16.7
16.1
6.9
18.4
23.1
9.3
5.9 ( 0.3
4.8 ( 0.2
7.7 ( 0.4
5.6 ( 0.3
10.4 ( 0.3
7.5 ( 0.3
7
5
9
7
31
7
3MA
3MB
3MCb
2MA
2MB
2MCb
230
270
80
1
1
1
15.4
18.6
7.0
19.2
19.3
9.8
4.6 ( 0.2
4.6 ( 0.2
7.0 ( 0.4
5.0 ( 0.1
7.3 ( 0.2
7.0 ( 0.2
4
5
18
6
13
25
a Lithographic data are reported for 60 nm lines and spaces. b Lithographic data are reported for 80 nm lines and spaces. c Z = Z-Parameter.
Figure 4. Acids generated by these AAs are strong enough to catalyze the trigger pull reaction of Body-3 AAs but not Body-2 AAs. However, nonaflate
acid is strong enough to catalyze the trigger pull reaction of Body-2 AAs.

Article
Chem. Mater., Vol. 22, No. 19, 2010 5615
Figure 5. We exposed one control resist without AA and 12 resist with 70 mM AA to EUV light. The sensitivity (Esize), LER, and Z-Parameter of these
resists are reported for 50 nm equal lines and spaces (L/S) or at best resolution.
For the most part, resists prepared with perfluoroben-
zenesulfonate esters (3HC, 3MC, or 2MC) gave poor
lithographic performance versus the control, so they were
only evaluated lithographically using 60-80 nm dense
lines and space patterns. 19F NMR kinetics showed that
these three AAs gave the fastest thermal decomposition
rates, so their poor lithographic performance may have
been due to poor thermal stability in the resist. Interest-
ingly, the only AA with a perfluorobenzenesulfonate ester
that gave good lithographic performance is 2HC, which
has a secondary hydroxyl trigger. This AA resulted in the
greatest improvement in resist sensitivity with only a
modest degradation in LER.
In general, we found that the AAs that are the most
stable toward uncatalyzed thermal decomposition give
the best lithographic improvements. We think that AAs
Figure 6. Scanning electron micrographs showing 50 nm dense lines of
the control resist (no AA) and resists with 70 mM of added 2HA, 2MA,
3HA, or 3MA.
improve the sensitivity of EUV resists by generating acid
during acid catalyzed decomposition. However, the re-
lative diffusion rates of the acids generated by PAGs and
AAs are certainly important factors in determining litho-
graphic performance. We suspect that the acids generated
by AAs in our experiments tend to diffuse further than the
nonaflate acid generated by the PAG. Increasing acid
diffusion rates generally results in sensitivity improve-
ments, however, more diffusion can also degrade resolu-
tion and LER.25 Therefore, the interpretation of imaging
results is complicated by a trade-off between higher
of 50 nm lines and spaces for the control resist (no AA) and
resists with 70 mM of added tertiary AAs (3HA or 3MA) and
secondary AAs (2HA, 2MA). All four AAs improve both
sensitivity and LER. Our working hypothesis is that the
performance of the resist is improved because more acid is
generated in the exposed regions of the resist resulting in
more efficient catalytic transformation of the polymer, re-
sulting in better sensitivity, and the higher concentrations of
acid allow the domain of each acid to be smaller, resulting in
better LER. Both secondary and tertiary AAs are capable of
yielding lithographic improvements.
(25) Mack, C. Fundamental Principles of Optical Lithography; Wiley:
London, 2007.

5616 Chem. Mater., Vol. 22, No. 19, 2010
Kruger et al.
sensitivity arising from more total acid being generated in
the exposed regions vs the detrimental effects of increased
overall acid diffusion.
Figure 3. This is important for photoresist applications
because nonaflate acid or similar super acids are pro-
duced in modern resist formulations. In a resist, Body-2
AAs are catalytically decomposed by the photo acid.
Indeed, five of the six AAs with secondary triggers gave
photoresists with improved sensitivity.
Conclusions
We systematically varied the chemical structure of 12
acid amplifiers and studied their reaction kinetics. We
found that decomposition rates of AAs in the presence of
base follow first-order kinetics regardless of body, trigger
or acid precursor type. Entropy of activation (ΔS‡)
appears to be the primary criteria for determining decom-
position rate at 100 °C. Acid amplifiers with methoxy
triggers all have higher entropies of activation than their
corresponding hydroxyl analogues. In the absence of
base, AAs with tertiary triggers decompose according to
second-order autocatalytic kinetics, but AAs with sec-
ondary triggers decompose by first-order kinetics. We
find that tertiary AAs have no-base/base rate ratios at 100
°C between 80 and 1400, whereas secondary AAs all have
no-base/base rate ratios of 1.0. Although secondary AAs
do not decompose autocatalytically, their decomposition
can be catalyzed by nonaflate acid as shown by 2HA in
We used the Z-Parameter to compare the lithographic
performance of EUV resists prepared with and without
70 mM concentration of acid amplifier. Resists that
contain AAs that generate perfluorobenzensulfonic acid
have the best sensitivity but poorest resolution. Seven of
the AAs were capable of showing improved lithographic
performance (lower Z-Parameter) versus the control resist.
The Z-Parameter improved 3-fold with the addition of
3MA, the best improvement for the 12 AAs presented
here. We speculate that 3MA gives the best lithographic
improvement on the basis of the combination of the
three attributes; it decomposes autocatalytically, generates
the slowest diffusing acid, and releases methanol as a
byproduct.
Acknowledgment. This work was supported by Intel
Corporation. We also thank DuPont for supplying polymers.