Bis(diaryliodonium) perfluorosulfonimide zwitterions as potential photo acid generators

Article abstract of DOI:10.1016/j.jfluchem.2014.01.004

Three examples of bis(diaryliodonium) perfluorosulfonimide (BDI-PFSI) zwitterions have been prepared as a potential new class of ionic photo-acid generators for chemically amplified photoresist formulations.

Full text of DOI:10.1016/j.jfluchem.2014.01.004

Accepted Manuscript
Title: Bis(Diaryliodonium) Perfluorosulfonimide Zwitterions
as Potential Photo Acid Generators
Author: Hua Mei Darryl D. DesMarteau
PII:
S0022-1139(14)00014-1
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jfluchem.2014.01.004
FLUOR 8251
To appear in:
FLUOR
Received date:
Revised date:
Accepted date:
30-9-2013
6-1-2014
7-1-2014
Please cite this article as: H. Mei, D.D. DesMarteau, Bis(Diaryliodonium)
Perfluorosulfonimide Zwitterions as Potential Photo Acid Generators, Journal of
Fluorine Chemistry (2014), http://dx.doi.org/10.1016/j.jfluchem.2014.01.004
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Bis(Diaryliodonium) Perfluorosulfonimide Zwitterions as Potential Photo Acid Generators
Hua Meia* and Darryl D DesMarteaub
aDepartment of Chemistry, East Tennessee State University, Johnson City, TN 37604
bDepartment of Chemistry, Clemson University, Clemson, SC 29631
Abstract
Three examples of bis(diaryliodonium) perfluorosulfonimide (BDI-PFSI) zwitterions
have been prepared as a potential new class of ionic photo-acid generators for chemically
amplified photoresist formulations.
Keywords: Iodonium, photo-acid generators, acid diffusion, zwitterions
* Corresponding author. Tel.: +1-423-439-4452
Fax: +1-423-439-5835
Email address: meih01@etsu.edu
1. Introduction
Potential Photo Acid Generators (PAGs) will produce an acid by the following simplified
reaction mechanism upon irradiation with UV light 1. Onium salt PAGs have played an enabling
role in the development of high photosensitivity resists for microlithography. Both
diaryliodonium and triarylsulfonium salts have been extensively utilized 2. Expectations are that
onium PAGs will continue to be important in the application of deep ultraviolet (DUV) and
extreme ultraviolet (EUV) technologies for decreasing feature size in semiconductor devices as
well as other applications 3, 4. EUV lithography (EUVL) is a rapid advancing lithography
technology, which uses an EUV wavelength, currently expected to be 13.5 nm.5 DUV refers to a
range of light on the violet side of the color spectrum, far beyond what the human eye can see.
Often, 248nm (KrF) and 193nm (ArF) excimer lasers are used6. The design and selection of a
PAG depends on many factors as expertly summarized by Crivello and Ito 2-4
.
Perfluoroalkylsulfonimide (PFSI) onium salts have been shown to have excellent
properties as PAGs 7, 8. The very acidic bis((perfluoroalkyl)sulfonyl)imides produced are as
effective as perfluoroalkyl sulfonic acids from PFSA based onium salts. In addition the larger
moleculear size of the PFSIs can have a favorable effect on acid diffusion as minimum feature
size decreases.
Herein we describe a series of novel zwitterionic bis(diaryliodonium) -
perfluoroalkylsulfonimides (BDI-PFSI) as potential PAGs (Figure 1). These difunctional
materials may offer advantages in lower PAG concentration and solubility in resist formulations.
Page 1 of 11

I
Ph
Ph
I
SO2NSO2(RF)SO2NSO2
Figure 1. BDI-PFSI (6a-c) Zwitterions
This research evolved from earlier work with iodinanes stabilized by
bis((trifluoromethyl)sulfonyl)imides anions and iodonium zwitterions based on sulfonamide
anions 9, 10
.
2. Results and Discussion
2.1 Preparation of BDI-PFSI zwitterions
The syntheses of the BDI-PFSI zwitterions are outlined in Scheme 1. 4-iodo-
benzenesulfonamide 1 and perfluororalkyl disulfonyl fluorides 4a-c are coupled, and the
products 5a-c are isolated as the Cesium salts. The Cs salts are then oxidized with persulfate in
sulfuric acid in the presence of benzene to form the BDI-PFSI zwitterionic compounds 6a-c.
I
I
I
1) DIEA, Dry CH3CN
2) 36.5%HCl
2
+ FSO2(RF)SO2F
3) Cs2CO3
SO2NSO2(RF)SO2NSO2
SO2NH2
Cs
Cs
1
4a-c
5a-c
I
I
Ph
I
I
Ph
H2SO4/K2S2O8
C6H6
SO N
SO2(RF)SO2NSO2
2
SO2NSO2(RF)SO2NSO2
Cs
Cs
5a-c
6a-c
Scheme 1. Synthesis of Symmetric BDI-PFSI Zwitterions 6a-c (RF = (CF2)4, a; (CF2)6, b;
(CF2CF2OCF2CF2) c.
Page 2 of 11

The starting perfluororalkyl disulfonyl fluorides (4a-4c) are prepared in three steps
(Scheme 2) from commercially available α, ω-diiodoperfluoroalkyl compounds I(CF2)nI. The
reaction chemistry is an extension and refinement of earlier work in China 11 and in our
laboratory 12.
Na2S2O4 / NaHCO3
NaSO2RFSO2Na
Cl2
KF
ClSO2RFSO2Cl
FSO2RFSO2F
IRFI
CH3CN, H2O
CH3CN/H2O, r.t
CH3CN
4a-c
3a-c
2a-c
Scheme 2. Synthesis of Perfluororalkyl Disulfonyl Fluorides 4a-c
The sodium-sulfinate salts 2a-c are not isolated and are converted to the sulfonyl
chlorides 3a-c. The chlorination is carried out by the reverse dropwise addition of the dilute
aqueous solution of 2a-c to chlorine saturated water. In this way the I-(aq) from the
deiodosulfination is rapidly converted to ICl3 and the intermediate I2 and ICl do not react with
2a-c to form the unstable -CF2SO2I which form -CF2I groups on decomposition. If chlorine is
not present in large excess as in the addition of Cl2(g) to the aqueous 2a-c, then substantial
amounts of the -CF2SO2Na functions are converted back to –CF2I and separation of the mixtures
is difficult. Finally, conversion of 3 to 4 is a high yield reaction and the progress is easily
monitored by 19F NMR.
The coupling reaction of 1 with 4 proceeds well with very dry acetonitrile and DIPEA
catalyst. The presence of water leads to hydrolysis of the sulfonyl fluoride. The isolation of 5 as
the cesium salts is greatly facilitated by the low solubility of 5-Cs in water. This low solubility is
as
counter intuitive. Conversion of 5 to 6 is carried out using Beringer’s methodology [10] 13and
applied to the earlier synthesis of DI-PFSI zwitterions (Figure 2) 10.
I
R
SO2NSO2RF
Figure 2. DI-PFSI Zwitterions (R=H; or R=F)
2.2 Properties of BDI-PFSI Zwitterions
The new zwitterionic compounds 4a-c are similar in many ways to the previously
isolated DI-PFSI zwitterions. They have high thermal stability with decomposition onset for 4a-
b beginning near 240o C. In comparison, the two DI-PFSI zwitterions (R=H; or R=F) (Figure 2)
decompose at 305 and 294o C, respectively 14. The difference in polarity of the DI – vs - BDI
zwitterions is apparent by the low solubility of the latter in CH3CN. Both types of zwitterions
have good solubility in DMSO.
Page 3 of 11

Table 1 (molar absorptivity) values for 6 a-b are given and a value for a DI-PFI for
comparison. The BDI zwitterions are clearly somewhat more absorbing at a given wavelength
and all have large values at193 nm.
Table 1 ε values for DI-PFSI and BDI-PFSIs
(cm-1 M)
Compound
193 nm
254 nm
PhI+PhSO2N-SO2CF3
1.17x 105
3.21x 105
2.17x 105
16.86 x 103
42.56 x 103
35.85 x 103
(PhI+PhSO2N-SO2C2F4)2 6a
(PhI+PhSO2N-SO2C3F6)2 6b
3. Conclusions
Three novel bis(diaryliodonium) perfluoroalkylsulfonimide BDI-PFSI zwitterions of the
type (Figure 1) were prepared in good yield. They are very unusual examples of zwitterionic
structures. The compounds have high thermal stability, are soluble in polar organic solvents and
strongly absorb UV light. Based on known PAGs used in photoresists, these new compounds
have potential for utilization as PAGs.
4. Experimental
4.1 General considerations
1H and 1 F NMR spectroscopic studies were carried on a Bruker AC 200 ( 1H
200.33MHz and 19F 188.13 MHz) or JEOL ECX-300 ( 1H 300.53 MHz and 19F 282.78 MHz).
All chemical shifts are quoted in ppm using the high-frequency position convention. NMR
spectra were measured using solutions of 1–2 mmol/L (unless otherwise stated) in an
1
appropriate deuterated solvent. H NMR spectra were referenced to external TMS, and 19F
chemical shifts were referenced to internal CFCl3. The infrared spectra were recorded on
Perkin-Elmer 1600 and 2000 series FTIR spectrometers. Liquids were run as a film between
two KCl plates. Unless indicated otherwise, samples were a minimum of 99.5% pure by 19F
NMR spectroscopy. Thermogravimetric analyses were obtained under nitrogen on a Perkin-
Elmer TGA7 with heating rates of 20 °C/min. The sample size for the TGA was normally 10–20
mg. The UV-Vis absorptions were measured on a Shimadzu UV-3101PC spectrophotometer
with CH3CN solution. Extinction coefficients of samples at 193 and 248 nm were calculated
based on absorption at these two wavelengths and have estimated error limits of +/-10%. Sample
concentration was adjusted so that the absorbance at the wavelength of interest was close to 2.5
in order to minimize effects of possible PAG photodecomposition on the measured ε values.
Each sample was run in triplicate and the ε values reported are averages.
The starting materials perfluoroalkyl disulfonyl fluorides 4a-c were prepared by
published methods 11, 12. All other starting materials were from commercial sources and were
used as received except where noted.
4.2 Preparation of p-IPhSO2NH2 1
Page 4 of 11

p-iodobenzenesulfonyl chloride (9.08 g, 0.03 mol), 10 mL acetonitrile and 30 mL water
were added into a 100-mL round-bottomed flask. Then around 15 mL of NH3 gas was bubbled
into the mixture. The solution was refluxed for 8 hours at 100 oC, and the volatile material was
removed using a rotary evaporator. The solid crude product was then recrystallized from a water
solution and filtered. The pure product 7.64 g of p-iodobenzenesulfonyl amide 1 was obtained
with a yield of 90% after drying under high vacuum for 2 hours.
Alternatively, in a 250-mL three-necked round bottom flask, p-iodobenzenesulfonyl
chloride (9.08 g, 0.03 mol) was added. Then ca. 30 mL of ammonia was condensed into the
flask at -60 oC and the flask was allowed to slowly warm to room temperature over 8 hours. The
crude product was washed with 40 mL water and dried under the vacuum to give 8.07 g purified
amide 1 with a yield of 95%.
I
SO2NH2
c
Ha
Hb
1
1H NMR (CD3CN, ppm): (ab, δa 7.89 (2H, d), δb 7.60 (2H, d), Jab= 10 Hz, δc 5.70 (2H, s)
(note: The 1H for this and related compounds represents an aa′bb′ spin system but it appears as
a deceptively simple ab system with J/ near 0.5. The a,b for all compounds are taken as the
midpoint of the second order doublets as an approximation as if it is a classic ab spin system.
The Ja,b is assigned as that of a classic ab spin system. No effort was made to analyze the spectra
further.)
4.3 Preparation of NaSO2RfSO2Na 2a-c
In a typical procedure (IC2F4)2 (45.40 g, 0.1 mol) was dissolved in 100 mL of acetonitrile
and 200 mL of water in a 500-mL round-bottomed flask. The solution was made basic with
NaHCO3 (30.00 g, 0.36 mol) and then fresh Na2S2O4 (50.00 g 0.28 mmol, the ratio is 1:2.8) was
slowly added with good stirring at 22o C. After 20 h, fluorine-19 NMR spectroscopy indicated
the reaction was complete by disappearance of the –CF2I signal. The solution (NaSO2C2F4)2 and
other byproducts are light yellow.
a
b
2a (NaSO2CF2aCF2b)2 19F NMR (CD3CN, ppm): δa –121.6(4F, m) , δb –129.6(4F, m).
c
2b (NaSO2CF2 CF2 CF2 )2 19F NMR (CD3CN, ppm): δa –121.3(4F, m), δb –121.7(4F, m), δc –
129.8(4F, m).
a
b
2c (NaSO2CF2 CF2 )2O 19F NMR (CD3CN, ppm): δa –81.9(4F, m), δb –132.6(4F, m).
4.4 Preparation of ClSO2RfSO2Cl 3a-c
In a typical procedure, 100-mL of water was added to the (NaSO2C2F4)2 solution above.
At 0 ˚C, chlorine was bubbled into another 100 mL of ice water in a 1000-mL flask. While
continuously bubbling Cl2 gas, the (NaSO2C2F4)2 solution was slowly added from a dropping
funnel. Each drop instantly gave a red-brown color in the solution, and then quickly turned back
to light yellow. After the reaction was complete, the white solid was filtered out and redissolved
in CH2Cl2. Then, the resulting solution was washed with water and dried over anhydrous Na2SO4
for at least 48 hours. Finally 31.90 g of white product (ClSO2C2F4)2 was obtained after removing
Page 5 of 11

the Na2SO4 crystals by filtration, followed by removal of CH2Cl2 under vacuum. The yield was
80% for the two reactions.
a
b
3a (ClSO2CF2aCF2b)2 19F NMR (CDCl3, ppm): δa –103.9 (4F, m) , δb –118.1 (4F, m).
c
3b (ClSO2CF2 CF2 CF2 )2 (yield, 88%).
19F NMR (CDCl3, ppm): δa –104.7(4F, m), δb –119.6(4F, m), δc –121.6(4F, m).
a
b
3c (ClSO2CF2 CF2 )2O (yield, 84%).
19F NMR (CDCl3, ppm): δa –78.8(4F, m), δb –108.5(4F, m).
4.5 Preparation of FSO2RfSO2F 4a-c
In a typical reaction, 3a (31.00 g, 77.69 mmol) and dry KF (15.00 g, 0.259 mol, 1: 3.33)
were added into a 250-mL round-bottomed flask in the dry box. The flask was evacuated and dry
CH3CN (50 mL) was vacuum transferred into the flask. The mixture was stirred at 22 oC for 24
h. 19F NMR spectroscopy was used to monitor the reaction process. After reaction was complete,
the crude product and CH3CN were transferred to a trap at high vacuum. Water (30 mL) was
then added to the CH3CN mixture. The lower layer was separated and distilled over P4O10.
Purified product 21.34 g of (FSO2C2F4)2 4a (yield 75%) was collected in the flask.
b
c
4a (FaSO2CF2 CF2 )2 19F NMR (CD3CN, ppm): δa 47.5 (2F, s) , δb –106.9 (4F, m), δc –119.0 (4F,
m). bp (750 torr) 120o C.
b
c
d
4b (FaSO2CF2 CF2 CF2 )2 (yield, 79%).
19F NMR (CD3CN, ppm): δa 47.2 (2F, s), δb –106.8 (4F, m), δc–119.1 (4F, m), δd –120.3 (4F, m).
bp (750 torr) 140o C.
b
c
4c (FaSO2CF2 CF2 )2O (yield, 73%).
19F NMR (CD3CN, ppm): δa 46.6 (2F, s), δb –80.9 (4F, m), δc–111.2 (4F, m).
bp (750 torr) 120o C.
4.6 Preparation of p-IPhSO2N(Cs)SO2RfSO2N(Cs)SO2PhI-p 5a-c
In a typical reaction, dry p-iodobenzenesulfonyl amide 1 (5.66 g, 0.02 mol) and
(FSO2C2F4)2 1a (3.66 g, 0.01 mol) (2:1) were put into a gas tight vessel with 10 mL of dry
diisopropyl ethyl amine (DIEA) and 20 mL of dry CH3CN. The solution was refluxed with good
stirring at 80 oC for 2 days. 19F NMR spectroscopy indicated the reaction was complete by the
disappearance of the –SO2F signal. All the volatile compounds were then removed under vacuum
leaving the crude product R3NH+ salt and the inorganic impurities. The mixture was redissolved
in 5 mL of acetone and then acidified with 20 mL of 15% dilute hydrochloric acid to pH= 2.5.
The crude product was obtained after precipitation with 20 mL of aqueous Cs2CO3 solution
(0.025 mol). The final product was filtered out and dried under vacuum for 24 hours. The yield
was 10.85 g, 80%.
Cs
A
B
I
SO2NSO2CF2 CF2
5a
Ha
Hb
2
Page 6 of 11

19F NMR (CD3CN, ppm): AB δA –112.2 (4F, t), δB -119.3 (4F, t);
1H NMR (CD3CN, ppm): ab 1H NMR δa 7.83(4H, d), δb 7.60(4H, d), Jab= 10 Hz;
IR (cm-1) (KBr pellet, acetone) 2924(vs), 2855(vs), 1650(w), 1572(m), 1460(s), 1385(m),
1325(vs), 1294(s), 1270(m)1314(s), 1196(vs), 1142(vs), 1093(s), 1007(m), 818(m), 761 (m),
719(w).
Cs
SO2NSO2CF2 CF2 CF2
5b
A
B
C
I
Ha
Hb
2
Yield, 87%; 19F NMR (CD3CN, ppm): ABC δA –112.4 (4F, t), δB -119.7 (4F, m), δC–121.1 (4F,
t);
1H NMR (CD3CN, ppm): ab, δa 7.86 (4H, d), δb 7.51(4H, d), Jab= 10 Hz;
IR (cm-1) (KBr pellet, acetone) 2926 (vs), 2855(vs), 1650(w), 1569(m), 1460(s), 1377(s),
1314(s), 1201(m), 1147(s), 1097(m), 1002(m), 767(m), 722 (m).
Cs
5c
A
B
I
SO2NSO2CF2 CF2
O
Ha
Hb
2
Yield, 84%; 19F NMR (CD3CN, ppm): AB, δA –80.5(4F, t), δB –115.3(4F, m);
1H NMR (CD3CN, ppm): ab, δa 7.83 (4H, d), δb 7.60 (4H, d), Jab= 10 Hz;
IR (cm-1) (KBr pellet, acetone): 2926(vs), 2855(vs), 1650(m), 1572(m), 1460(s), 1383(s),
1326(s), 1226(s), 1142(vs), 1090(s), 1059(m), 1008(m), 986(m), 819(m), 765(s), 721(m).
4.7 Preparation of BDI-PFSI zwitterions 6a-c
In a typical reaction, (I-PhSO2N(Cs)SO2CF2CF2)2 5a (2.33 g, 2.0 mmol) was mixed with
30 mL of conc. sulfuric acid in a 50-mL round-bottomed flask, cooled to -30 ˚C. Potassium
persulfate (1.39 g, 8.0 mmol) was added in one portion and the reaction mixture was slowly
warmed to -20 ˚C in an 50% ice-isopropanol bath with good stirring. To the resulting suspension,
benzene (0.37 mL, 4.2 mmol, the ratio is 1.4:2.1) was added. The reaction mixture became a
dark yellow solution and was warmed to 20˚C over 8 h. The mixture was then poured into the ice
to quench the reaction. The resulting suspension was filtered and the solid was washed with 30
mL of water. The 1.62 g of dried solid 5a (the yield is 65%) was obtained with the purity of
95%. The impurity was tentatively identified as the hydrolysis product from 5a, PhI+PhSO2N-
-
SO2CF2CF2CF2CF2SO3H (or SO3 ). We were unsuccessful in separating it from 5a or 6a.
Presumably more rigorous anhydrous conditions would eliminate this impurity.
Page 7 of 11

6a
A
B
He
I
SO2NSO2CF2 CF2
Hd
Hc
Ha
Hb
2
19F NMR (DMSO, ppm): δA –112.3(4F, t), δB -119.6(4F, t);
1H NMR (DMSO, ppm): ab, δa 8.32(4H, d), δb 8.23(4H, d), Jab = 8 Hz; (cc'dd'e) δc 7.83(4H, d), δe
7.66(2H, t), δd 7.52(4H, t), Jcd  8 Hz, Jde  7 Hz;
13C NMR (DMSO, ppm): δ 207.1, 148.9, 135.8, 135.8, 132.7, 132.4, 129.7, 128.7, 119.5, 117.2
IR (cm-1) (KBr pellet, acetone) 2927(vs), 2855(vs), 1564(m), 1461(s), 1377(s), 1317(m),
1140(m), 1085(m), 987(m), 725 (m);
Td=242 ˚C.
6b
A
B
C
He
I
SO2NSO2CF2 CF2 CF2
Hd
Hc
Ha
Hb
2
Yield, 68%, purity 98%; 19F NMR (DMSO, ppm): δA –112.3(4F, t), δB -119.7(4F, m), δC
–121.1(4F, t);
1H NMR(DMSO, ppm): ab, δa 8.33(4H, d), δb 8.25(4H, d), Jab=8 Hz; (cc'dd'e)
(cc'dd'e) δc 7.84(4H, d), δe 7.66(2H, t), δd 7.53(4H, t), Jcd 8 Hz, Jde 7 Hz;
13C NMR (DMSO, ppm): δ 207.1, 148.7, 137.8, 135.8, 132.7, 132.4, 129.7, 128.6, 119.5, 119.4,
117.1;
IR (cm-1) (KBr pellet, acetone) 2919(vs), 2855(vs), 1565(m), 1461(s), 1377(s), 1326(s),
1272(m), 1210(m), 1149(s), 1086(m), 987(m), 821(m), 767 (m), 740(m);
Td=243 ˚C.
6c
A
B
He
I
SO2NSO2CF2 CF2
O
Hd
Hc
Ha
Hb
2
Yield, 60%, purity, 94%; 19F NMR (CD3CN, ppm): δA –115.4 (4F, t), δB -80.3 (4F, t);
1H NMR (CD3CN, ppm): ab, δa 8.32 (4H, d), δb 8.23 (4H, d), Jab = 8 Hz; (cc'dd'e) δc 7.85 (4H, d),
δe 7.67(2H, t), δd 7.50 (4H, t), Jcd  8 Hz, Jde  7 Hz;
IR (cm-1) (KBr pellet, acetone) 2927(vs), 2856(vs), 1565(m), 1461(s), 1378(s), 1318(s), 1194(s),
1157(s), 1114(m), 1086(m), 987(m), 822(m), 782(m), 735(m).
Page 8 of 11

Graphical Abstract – Synopsis
Three examples of bis(diaryliodonium) perfluorosulfonimide (BDI-PFSI) zwitterions
have been prepared as a potential new class of ionic photo-acid generators for chemically
amplified photoresist formulations.
Page 9 of 11

I
Ph
Ph
I
SO2NSO2(RF)SO2NSO2
Figure 1. Bis(Diaryliodonium) Perfluorosulfonimide Zwitterions
Graphical Abstract
Page 10 of 11

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