Materials for Microlithography - American Chemical Society

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Novel Synthesis and Photochemical Reaction of the Polymers with Pendant Photosensitive and Photosensitizer Groups T. NISHIKUBO, T. IIZAWA and E. TAKAHASHI Department of Applied Chemistry Faculty of Engineering Kanagawa University Rokkakubashi, Kanagawa-ku Yokohama-shi, 221 Japan Polymers with pendant cinnamoyl groups are well known as photosensitive polymers (1) and have been used as photoresists in the fabrication of printed circuits, integrated circuits or printing plates. Their excellent thermal stability, resolving power, high tensile strength, good resistance to solvents, and photosensitivity are all properties that have led to their acceptance. The use of cinnamic acid as a starting material for the syntheses of polymers is advantageous because of its commercial availability. Polymers derived from cinnamic acid are frequently used with suitable, low molecular weight photosensitizers, because the polymers alone lack satisfactory photosensitivity. However, some of the photosensitizers used have vaporized from the polymer film during use of the photosensitive polymer. This phenomenon is sometimes responsible for the lack of reproducibility of the photosensitivity and resolving power, and corrosion of the working environment. Polymers with other pendant photosensitive moieties such as βfurylacrylic ester (2) or β-styrylacrylic ester (3) are highly photosensitive and have even higher photosensitivity after the addition of photosensitizers. However, the thermal stability of these polymers is inferior to that of the polymer with pendant cinnamic esters (4). Polymers with pendant benzalacetophenone (5), styrylpyridinium (6), α-cyanocinnamic ester (7) or aphenylmaleimide (8) have high photosensitivity but they can not be sensitized. In addition, the photosensitive moieties that are used in the syntheses of these polymers are not commercially available, in contrast to cinnamic acid. Accordingly, the synthesis of novel cinnamate polymers with high functionality and performance is very important from the viewpoint of both polymer chemistry and practical use. Recently, we have reported the synthesis of polymers with pendant photosensitive moieties such as cinnamic ester and suitable photosensitizer groups by radical copolymerizations of 2(cinnamoyloxy) ethyl methacrylate with photosensitizer monomers (9), by copolymerizations of chloromethylated styrene with the photosensitizer monomers followed by the reactions of the copolymers with salts of 0097-6156/ 84/0266-0225S06.00/0 © 1984 American Chemical Society

Thompson et al.; Materials for Microlithography ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

226

MATERIALS FOR MICROLITHOGRAPHY

photosensitive compounds (70), and by substitution reactions of poly(chloromethylstyrene) with salts of photosensitizer compounds (77). This article reports on the synthesis of photosensitive polymers with pendant cinnamic ester moieties and suitable photosensitizer groups by cationic copolymerizations of 2-(cinnamoyloxy)ethyl vinyl ether (CEVE) (72) with other vinyl ethers containing photosensitizer groups, and by cationic polymerization of 2-chloroethyl vinyl ether (CVE) followed by substitution reactions of the resulting poly (2-chloroethyl vinyl ether) (PCVE) with salts of photosensitizer compounds and potassium cinnamate using a phase transfer catalyst in an aprotic polar solvent. The photochemical reactivity of the obtained polymers was also investigated. Experimental Materials. C E V E and 4-nitrophenyl vinyl ether (VNP) were synthesized and purified as reported earlier (72,75), respectively. 2-(4-Nitrophenoxy)ethyl vinyl ether (NPVE) (m.p. 72-73 °C) was prepared by reacting of potassium 4nitrophenoxide (PNP) (142 g; 0.8 mol) and C V E (842 g; 7.9 mol) using tetran-butylammonium bromide (TBAB) (4.0 g; 12 mmol) as a phase transfer catalyst at the boiling temperature of C V E for 12 h. The potassium chloride produced was filtered off, the filtrate washed with water, excess C V E evaporated, and then the crude product was recrystallized twice from n-hexane. (Yield: 61.7%. IR (KBr): 1630 (C=C), 1520 ( - N 0 ) , and 1340 c m " (-N0 ).) Elemental analysis on the product provided the following data: Calculated for C H N O : C., 57.40%, H , 5.30%, N , 6.69%. Found: C., 57.49%, H , 5.3%, N , 6.72%. 2-(4-Nitro-l-napthoxy)ethyl vinyl ether ( N N V E ) (m.p. 79-80 °C) was obtained by the reaction of C V E with potassium 4-nitro-l-naphthoxide ( P N N ) under the similar conditions as the synthesis of N P V E , and then it was recrystallized twice from methanol. (Yield: 72.0%. IR (KBr): 1620 (C=C), 1500 ( - N 0 ) , and 1320" (-N0 ).) Elemental analysis on the product provided the following data: Calculated for C H N 0 : C., 64.85%, H , 5.05%, N , 5.40%. Found: C., 64.64%, H , 4.97%, N , 5.29%. 2-[2-(4-Nitrophenoxy)ethoxy]ethyl vinyl ether ( N P E V E ) (m.p. 4950 °C) was synthesized with 30% yield by the reaction of C V E (86.3 g; 0.80 mol) with 2-(4-nitrophenoxy)ethanol (16.3 g; 0.09 mol) and potassium hydroxide (9.3 g; 0.14 mol) using T B A B (2.9 g; 0.01 mol) at the boiling temperature of C V E for 8 h and treated in the similar way for N P V E . (IR (KBr): 1630 (C=C), 1520 ( - N 0 ) , and 1340 c m " (-N0 ).) Elemental analysis on the product provided the following data: Calculated for C H N 0 : 1

2

2

1 0

n

4

1

2

2

1 4

1 3

4

1

2

2

1 6

1 7

5

P C V E (reduced viscosity: 0.33, measured at 0.5 g/dl in D M F at 30°C) was prepared quantitatively by cationic polymerization of C V E using trifluoroboron ether complex (TFB) in toluene at — 65 °C for 3 h. Typical Procedure for Cationic Copolymerization of CEVE with Photosensitizer Monomer. C E V E (9.81 g; 45 mmol) and 0.86 g (5 mmol) of N P V E were dissolved in 50 ml of toluene and the solution cooled with dry ice/methanol. Next 0.13 ml (1 mmol) of T F B was dissolved in 5 ml of toluene


10.

Pendant Photosensitive and Photosensitizer Groups 227

NISHIKUBO ET AL.

and added to the solution, and then polymerization was carried out at - 6 5 °C for 3 h in a stream of dry nitrogen. The polymerization was terminated by the addition of a small amount of 2-aminoethanol, then the solution was poured into methanol. The obtained copolymer was reprecipitated from T H F into methanol, and dried in vacuum at 50 °C. The yield of polymer was 96.8%. The amount of photosensitizer unit was 9.2 mol-% (determined by elemental analysis). The reduced viscosity was: 0.32 (0.5 g/dl in D M F at 30°C). (IR (film): 1710 (C=0), 1640 (C=C), 1520 ( - N 0 ) , and 1340 c m " ( - N 0 ) . H N M R (100 M H z , in CDC1 ): δ - 1.8 ( C - C H - C ) , 3.7 and 4.3 ( C - C H O - C and 0 - C H - C H - 0 ) , 6.4 and 7.6 ( - C H = C H - doublet), and 6.8-8.0 (aromatic proton).) 1

l

2

3

2

2

2

2

Typical Synthesis of Polymeric Photosensitizer. P C V E (1.07 g; 10 mmol) was dissolved in 10 ml of D M F , and then 0.18 g (1 mmol) of P N P and 0.32 g (1 mmol) of T B A B were added to the polymer solution. The reaction mixture was stirred at 80 °C for 24 h and then poured into methanol. The resulting polymer was reprecipitated twice from T H F into water and then from T H F into methanol, and dried in vacuum at 50 °C. The yield of polymer was 1.02 g. The conversion of chlorine in P C V E was 10.1 mol-% (calculated from the halogen analysis) (14). (Reduced viscosity: 0.38 (0.5 g/dl in D M F at 30°C). IR (film): 1520 ( - N 0 ) and 1340 c m " (-N0 ).) 1

2

2

Typical Reaction of Polymeric Photosensitizer with Potassium Cinnamate. The polymeric photosensitizer containing 90 mol-% of pendant 2-chloroethoxy group and 10 mol-% of the 2-(4-nitrophenoxy)ethoxy group (0.59 g; 4.5 mmol of chlorine in the polymer) was dissolved in 10 ml of D M F , and then 1.01 g (5.4 mmol) of potassium cinnamate and 0.15 g (0.45 mmol) of T B A B were added to the polymer solution. The reaction mixture was stirred at 100°C for 24 h and then poured into methanol. The resultant polymer was reprecipitated twice from T H F into water and then from T H F into methanol, and dried in vacuum at 50 °C. The yield of polymer was 1.01 g. The conversion of chlorine was 100 mol-% (calculated from the halogen analysis). (Reduced viscosity: 0.33 (0.5 g/dl in D M F at 30°C). IR (film): 1710 (C=0), 1640 (C=C), 1520 ( - N 0 ) , and 1340 c m " ( - N 0 ) . H N M R (100 M H z , in CDC1 ): δ = 1.8 ( C - C H - C ) , 3.7 and 4.3 ( C - C H O - C and 0 - C H - C H - 0 ) , 6.4 and 7.6 ( - C H = C H - doublet), and 6.8-8.0 aromatic proton).) 1

2

l

2

2

3

2

2

Measurement of Photochemical Reactivity. The polymer solution in T H F was cast on a K R S plate and dried. The film obtained on the plate was irradiated by a high-pressure mercury lamp (Ushio Electric Co: USH-250D) without a filter at a distance of 30 cm in air. The rate of disappearance of the C = C bonds at 1640 c m " was measured by IR spectrometry ( J A S C O A-202 model). 1

Measurement of Practical Photosensitivity. The photosensitivity of the polymer was measured by a gray-scale method (75) as follows. The polymer solution (10%) in cyclohexanone was cast on a copper plate by using a rotary applicator and dried. The Kodak step tablet No. 2 (Eastman Kodak Co.) was placed upon the polymer film cast on the plate, exposed on a chemical lamp (15w x 7) from 3 cm for 1 min., and then the exposed film was developed by the solvent for 2 min.


228

MATERIALS FOR

MICROLITHOGRAPHY

Measurement of Glass Transition Temperature (T ). The T values of the obtained polymers were measured by D S C analysis (Du Pont Inc., 910 model) at a heating rate of 20°C/min. g

g

Results and Discussion Syntheses of Self-Sensitized Polymers by Cationic Copolymerizations. The cationic polymerizations of several vinyl ethers containing pendant ester groups such as cinnamic ester (12), methacrylic ester (16), acrylic ester (17), and crotonic ester (18) have been reported. Based on these reports, cationic copolymerizations of C E V E with photosensitizer monomers such as N P V E , N N V E , V N P and N P E V E were carried out using T F B as a catalyst in toluene at — 65 °C. Each copolymer was obtained with high yield except in the case of copolymerization of C E V E with V N P as summarized in Table I. The cationic copolymerizations of C E V E (M ) with N P V E (M ) and N N V E (M ) gave the copolymers with the photosensitizer monomer in proportion to the photosensitizer monomers in the charge when the molar content of M was lower than 30 mol-%. However, copolymers with equal amounts of photosensitizer units were not obtained by the copolymerization of 60 or 70 mol-% of C E V E with 40 mol-% of N P V E and 30 mol-% of N N V E in toluene, because a portion of the photosensitizer monomer in each case was precipitated during the copolymerization under similar reaction conditions. It was reported (19) that a low T value is required from the viewpoint of the photochemical reactivity of pendant cinnamic ester in the polymer film. As summarized in Table I, the T of all the copolymers of P C E V E - N P V E and P C E V E - N N V E were in the vicinity of room temperature as expected from the flexible ethoxy chain in the polymer structure. ( -j j x

2

2

2

g

g

CH =CH

+

2

C H = CH

0 CH CH

—("CH -CH^—(-CH -CH^

2

TFB AT-65°C

0 CH

2

CH

2

Ο

2

IN TOLUENE

2

O-R

CH

0 2

2

Ο

(CEVE)

-CH

0

CH

2

2

CH CH

2

2

O-R

(PCEVE-NPVE, PCEVE-NNVE, OR P C E V E - N P E V E )

2

-CH

2

-O - @ ^ N 0

2

(NPEVE)


10.

Table I. Reaction Conditions and Results of Cationic Copolymerizations of C E V E with Photosensitizer Monomers

No. 1 2 3

Molar ratio of monomer (Af /M ) l

2

Yield (%)

M in copolymer (mol-%)

T (°C) Sensitivity g

77

B SP/C

(9.5/0.5)

e

98.1

4.4

0.38

29

4

(9.0/1.0)

e

96.5

9.2

0.37

24

6

(.5/1.5)

e

80.2

15.3

0.68

—

9

97.4

19.2

0.35

27

5

4

(8.0/2.0)

5

(7.0/3.0)

e

94.9

28.1

0.25

27

—

(6.0/4.0)

e

83.8

28.4

0.22

—

—

(9.5/0.5)

e

93.6

5.4

0.33

33

8

(9.0/1.0)

e

96.9

9.7

0.28

30

9

9

(8.5/1.5)

e

96.6

14.3

0.51

—

12

10

(8.0/2.0)

e

92.9

20.0

0.17

32

12

(7.0/3.0)

e

89.8

17.8

0.23

—

8

80.7

0

0.33

—

3

99.2

10.2

0.49

—

8

98.7

0

0.80

7 8

11 12

(9..0/1.0)

13

(9.0/1.0)

14

(10.0)

h

g

f

a

2

e

6

229

Pendant Photosensitive and Photosensitizer Groups

NISHIKUBO ET A L .

4

0

d

d

a

Copolymerization was carried out with 50 mmol of monomer in 50 ml of toluene using 1 mmol of T F B as a cationic catalyst at — 65 °C for 3 h.

b

Measured at 0.5 g/dl in D M F at 30 °C.

0

Exposed with a chemical lamp (15w x 7) for 1 min., and then developed in toluene for 2 min. The numbers correspond to the step number from the Kodak step table number 2.

d

Exposed for 3 min.

e

CEVE/NNVE

f

CEVE/VNP

g

CEVE/NPEVE

h

CEVE

P C E V E - N P E V E with 10 mol-% of pendant photosensitizer unit was also prepared by the cationic copolymerization of 90 mol-% of C E V E with 10 mol-% of N P E V E under similar reaction conditions used for the copolymerization of C E V E with N P V E . In contrast, a copolymer with pendant photosensitizer group could be obtained from the cationic copolymerization of C E V E with


230

MATERIALS FOB MICROLITHOGRAPHY

V N P , and only homopolymer of polyL2- (cinnamoyloxy) ethyl vinyl ether] (PCEVE) was obtained. It seems that the cationic reactivity of the vinyl ether group in V N P was decreased because of the electron attracting nitro group attached at the 4-position on the phenoxide. Syntheses of Polymeric Photosensitizers and Self-sensitized Polymers by the Reactions of PCVE. Photosensitizer monomers such as N P V E , N N V E and N P E V E were synthesized by the reaction of excess C V E with potassium salts of the corresponding photosensitizing compounds using T B A B as a phase transfer catalyst as described in the experimental part. Substitution reactions of chloroethyl groups in P C V E with P N P and P N N were also carried out using T B A B as a phase transfer catalyst in D M F at 80 °C for 24 h. The reactions of P C V E with P N P are quantitative under these reaction conditions, and polymeric photosensitizers such as poly[2-chloro-ethyl vinyl ether-co-2-(4-nitrophenoxy) ethyl vinyl ether] ( P C V E - N P V E ) containing about 4, 10, 19, 28, 37, and 46 mol-% of pendant 4-nitrophenoxy (NP) groups were prepared (Table II). Although the reactions of P C V E with P N N were carried Table II. Reaction Condition and Results of the Syntheses of Polymeric Photosensitizers a

Photosensitizer compound (mmol)

Yield (g)

Degree of substitution (mol-%)

No.

PCVE (mmol)

15

10

P N P (0.5)

0.93

4.4

0.64

16

10

P N P (1.0)

1.02

10.1

0.38

17

10

P N P (2.0)

0.96

19.0

0.42

18

10

P N P (3.0)

1.03

28,2

0.42

19

10

P N P (4.0)

1.36

37.0

0.35

20

10

P N P (5.0)

1.46

46.0

0.36

21

10

P N N (0.5)

1.04

3.5

0.39

22

10

P N N (1.0)

1.08

7.9

0.56

23

10

P N N (1.5)

1.16

12.8

0.49

24

10

P N N (2.0)

1.21

15.8

0.49

25

10

P N N (3.0)

1.42

24.1

0.40

26

10

P N N (5.0)

1.45

27.0

0.48

27

10

P N N (5.0)

1.49

30.7

0.34

D

^sp/c

The reaction was carried out using 1.0 mmol of T B A B in 10 ml of D M F at 80°C for 24 h. Measured at 0.5 g/dl in D M F at 30 °C.


10.

NISHIKUBO ET AL.

Pendant Photosensitive and Photosensitizer Groups 231

out under the similar reaction conditions which were used for the reactions of PNP, the resulting poly [2-chloroethyl vinyl ether-co-2-(4-nitro-lnaphthoxy) ethyl vinyl ether] ( P C V E - N N V E ) containing pendant 4-nitro-lnaphthoxy ( N N ) groups did not contain the expected amounts of the N N groups when more than 20 mol-% of P N N were charged in the reaction system. The degree of substitution of chlorine measured by halogen analysis (14) agrees with the contents of the photosensitizer groups in the polymer determined by the U V absorptions. From these results, it can be concluded that no side reactions occur during the substitution reactions of P C V E with P N P and P N N using a phase transfer catalyst. The IR spectrum of P C V E N P V E showed absorptions at 1530 and 1340 c m " due to the - N 0 stretching of the photosensitizer units. The IR spectrum of P C V E - N N V E also showed the corresponding characteristic absorptions. (2) 1

2

- K H

2

- C H - ^ 0 1 CH

—fCH -CH) 2

R-OK/TBAB

2

I CHo-Cl

0 I CH

^

AT 8 0 ° C IN D M F "

f C H

? i

C

2

H

2

(PCVE-NPVE

P C V E - N P V E

2

I , CH -CI

2 I O - R

(PCVE)

- C H ^ -

0 I CH

I

ά

2

OR P C V E - N N V E )

/ Q V C H =C H - C O O K / T B A B

OR

(3) ^

P C V E - N N V E

A T 1 0 0 ° C IN

DM F

-CH

NOs

2

-

CH^ 0 I CH J CH

? r

(CH -CH^ 2

m

0

2

2

I

1

O-R

CH j CH

2

2

I

1

0 0 = C - C H = CH

(PCEVE-NPVE

OR P C E V E - N N V E )

Substitution reactions of the remaining pendant chloroethyl groups in P C V E - N P V E with 20 mol-% excess of potassium cinnamate were carried out using T B A B as a phase transfer catalyst in D M F at 100°C for 24 h. The reaction conditions and results are summarized in Table III. It should be noted that 100 mole % substitution occurred in all cases.


232


The reactions of P C V E - N P V E and P C V E - N N V E with excess potassium cinnamate proceeded quantitatively under these reaction conditions leading to P C E V E - N P V E and P C E V E - N N V E containing cinnamic ester as the photosensitive moiety, suitable photosensitizer groups such as N P and N N groups and no unreacted chloroethyl groups. The IR and *H N M R spectra of P C E V E - N P V E and P C E V E - N N V E obtained from the reaction of the polymeric photosensitizers with potassium cinnamate are the same as the spectra of the corresponding copolymers prepared from the cationic copolymerizations of C E V E with N P V E or N N V E . Table III. Reaction Conditions and Results of the Reactions of Polymeric Photosensitizers with Potassium Cinnamate

Mole % photo sensitizer

a

mmole chlorine

Potassium cinnamate (mmol)

TBAB (mmol)

Yield (g)

b ^sp/c

No.

Mole % ester

28

95.6

4.4

4.8

5.7

0.48

1.01

0.41

29

89.9

10.1

4.5

5.4

0.45

1.01

0.33

30

81.0

19.0

4.0

4.8

0.40

1.02

0.33

31

72.8

28.0

3.5

4.2

0.35

0.94

0.35

32

63.0

37.0

3.0

3.6

0.30

1.00

0.32

33

54.0

46.0

2.5

3.0

0.25

1.02

0.32

34

96.5

3.5

4.8

5.7

0.48

1.03

0.34

35

92.1

7.9

4.5

5.4

0.45

1.03

0.39

36

87.2

12.8

4.3

5.1

0.43

1.04

0.33

37

84.5

15.5

4.0

4.8

0.40

1.00

0.39

38

75.9

24.1

3.5

4.2

0.35

1.05

0.34

39

73.0

27.0

3.0

3.6

0.30

1.15

0.39

40

69.3

30.7

2.5

3.0

0.25

1.00

0.34

a

The reaction was carried out in 10 ml of D M F at 100°C for 24 h.

b

Measured at 0.5 g/dl in D M F at 30 °C.


10.

NISHIKUBO ET A L .


These results suggest that the reaction conditions for the syntheses of P C E V E - N P V E and P C E V E - N N V E can be accomplished by the reactions of P C V E with any ratio of potassium cinnamate and P N P or P N N in one pot using a phase transfer catalyst. In addition, it is to be expected that P C E V E N P V E and P C E V E - N N V E prepared from the reactions of P C V E have the same degree of polymerization if no side reactions occur during the substitution reactions. It is also expected that these copolymers are more random compared to the copolymers prepared from the cationic copolymerizations of the monomers, because the former is not affected by the monomer reactivity ratios. Therefore, we believe that P C E V E - N P V E and P C E V E - N N V E prepared from the reactions of P C V E are better model polymers for the determination of the relationship between the photochemical reactivity and the contents of the photosensitizer units in the copolymers than the copolymers prepared by copolymerization. On the other hand, P C E V E - N P V E and P C E V E - N N V E prepared from the cationic copolymerization seem to be more photosensitive than P C E V E - N P V E and P C E V E - N N V E polymers prepared from the reactions of P C V E and have better properties practical applications since the former copolymers have higher purity than the latter copolymers. Photochemical Reaction of PCEVE-NPVE and PCEVE-NNVE. Photo chemical reactions of polymer films (3 μηι thick) containing the cinnamic ester moiety and suitable photosensitizer groups were carried out by irradiation with a high-pressure mercury lamp on a K R S plate under identical reaction condition. As shown in Figure 1, the rates of disappearance of the C = C bonds in P C E V E - N P V E , P C E V E - N N V E , and P C E V E - N P E V E , which were prepared by the cationic copolymerizations of C E V E with the corresponding photosensitizer monomers, containing about 10 mol-% of pendant photosensitizer groups and 90 mol-% of the cinnamic ester moieties are much higher than that of P C E V E , which has only pendant cinnamic ester moieties. In addition, it was found that the photochemical reactivity of this P C E V E N N V E was about two times higher than those of P C E V E - N P V E , P C E V E N P E V E , and P C E V E with 4-nitroanisole as the corresponding low molecular weight photosensitizer, however, the photochemical reactivity of P C E V E - N N V E was slightly lower than that of P C E V E with the corresponding low molecular weight photosensitizer such as l-methoxy-4-nitronaphthalene. As shown in Figure 2, P C E V E - N P V E and P C E V E - N N V E containing about 10 mol-% of pendant sensitizer groups prepared from the reactions of P C V E with potassium cinnamate and P N P or P N N have photochemical reactivity equal to P C E V E - N P V E and P C E V E - N N V E prepared from the cationic copolymerizations, however, their photochemical reactivities were changed by the contents of photosensitizer units in the copolymers. The relationship between the content of the photosensitizer unit in P C E V E - N P V E and the conversions of the C = C bonds after 10 min. irradiation is shown in Figure 3. The photochemical reactivities of P C E V E - N P V E prepared from the cationic copolymerizations were higher than those of P C E V E - N P V E prepared from the reactions of P C V E at photosensitizer contents lower than 15 mol-%. On the other hand, P C E V E - N P V E prepared from the reactions of P C V E has its highest rate of disappearance of the C = C


233


234 ι

1

Γ

IRRADIATION TIME (min) Figure 1. The rate of disappearance of the C=C group in cinnamic ester in the polymer (A) PCEVE-NNVE containing 9.7 mol-% of pendant NN group; (O) PCEVE-NPVE containing 9.2 mol-%* of pendant NP group; (Ώ) PCEVENPEVE containing 10.2 mol-% of pendant NP group (*); (A) PCEVE + 9.7 mol-% of 4-nitro-l-methoxynaphthalene; Ο PCEVE + 9.2 mol-% of 4nitroanisole. bond at about 30 mol-% of pendant 4-nitrophenoxy (NP) groups. Furthermore, the photochemical reactivity of P C E V E with 4-nitroanisole gave linear plots from 5 to 45 mol-% of photosensitizer content, because they are highly compatible and the photosensitizers are relatively mobile in the polymer film. It seems that P C E V E - N P V E prepared from the reactions of P C V E have a random distribution of substituents, and the maximum in the photochemical reactivity of these copolymers results from the balance of the positive effect of


10.

N I S H I K U B O ET A L .


235

60 h

IRRADIATION TIME (min) Figure 2. The rate of disappearance of the C=C group in cinnamic ester in the polymer prepared by the reaction of PCVE (A) PVEVE-NNVE containing 7.9 mol-% of pendant Ν Ν group; (A) PCEVE-NNVE containing 12.8 mol-% of the NN group (A) PCEVE-NNVE containing 27.0 mol-Ψο of the NN group; (O) PCEVE-NPVE containing 4.4 mol-% of the NP group; C) PCEVENPVE containing 10.1 mol-% of the NP group; (OJ PCEVE-NPVE containing 19.0 mol-% of the NP group.

pendant photosensitizer groups and the negative effect such as screening of the sensitizer on the surface of polymer film and steric interference of the sensitizer groups with the reaction of pendant photosensitive moieties (77). The relationship between the content of the photosensitizer unit in P C E V E - N N V E and the conversions of the C = C bonds after 10 min. irradiation is shown in Figure 4. PCEVE-NNVE prepared from cationic


236

\


/ Ο II

Ο

/ \ ϋ_ Ο

CO

(Τ

ο ο 10

20

30

40

50

PHOTOSENSITIZER GROUP IN COPOLYMER ( m o l % ) Figure 3. The relationship between the conversion of the C=C group in cinnamic ester in the polymer by 10 min. of irradiation and the photosensitizer content in PCEVE-NPVE: (O) PCEVE-NPVE prepared from the cationic copolymerization; (+) PCEVE-NPVE prepared from the reaction of PCVE; (O) PCEVE with 4-nitroanisole. copolymerizations have higher photochemical reactivities than P C E V E - N N V E polymers prepared from the reactions of P C V E at the low photosensitizer contents. The former copolymer has its highest rate of disappearance of the C=C bonds when 10 mol-% of pendant N N groups are incorporated. On the other hand, P C E V E - N N V E prepared from the reactions of P C V E has its highest rate at about 15 mol-% of pendant N N groups. P C E V E with 4methoxy-l-nitronaphthalene has its highest rate with 10 mol-% of the low molecular weight photosensitizer present. However, the rate decreased rapidly with increasing content of the sensitizer, because they do not have good compatibility and the photosensitizer separates and forms the clusters in the polymer film. The relationship between the thickness of polymer films containing about 10 mol-% of pendant photosensitizer groups and the conversions of the C = C bonds after 10 min. irradiation is shown in Figure 5. The photochemical reactivity of P C E V E - N N V E decreased slightly with increasing thickness of the film. Interestingly, the reactivity of P C E V E - N P V E was not influenced by the thickness of the film in contrast to the self-sensitized polymers previously


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NISHIKUBO ET AL.

01 0

I 10

I 20

I 30

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PHOTOSENSITIZER GROUP IN COPOLYMER ( m o l % )

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237

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Figure 4. The relationship between the conversion of the C=C group in cinnamic ester in the polymer by 10 min. of irradiation and the photosensitizer content in PCEVE-NNVE: (A) PCEVE-NNVE prepared from the cationic copolymerization; (A) PCEVE-NNVE prepared from the reaction of PCVE; (A) PCEVE with 4-nitro-I-methoxynaphthalene. reported (20). In addition, these copolymers have the T near room temperature as summarized in Table I. These results raise the possibility of P C E V E - N P V E and P C E V E - N N V E use as the polymer for the preparation of dry film resists (21) containing cinnamic ester as a photosensitive moiety. Practical photosensitivities, which were measured by a gray-scale method (75) of P C E V E - N P V E , P C E V E - N N V E and P C E V E - N P E V E prepared from the cationic copolymerization are summarized in Table I. The photosensitivities of P C E V E - N P V E , P C E V E - N N V E and P C E V E - N P E V E were much higher than that of P C E V E . In addition, it was found that P C E V E - N N V E containing pendant N N groups ( X : 360 nm) as a photosensitizer has a relatively higher photosensitivity than P C E V E - N P V E containing pendant N P groups ( X : g

max

max


238


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THICKNESS OF FILM (μΠ))

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Figure 5. The relationship between the conversion of the C=C group in cinnamic ester in the polymer by 10 min. of irradiation and the thickness of the polymer film: (A) PCEVE-NNVE containing 9.7 mol-% of pendant NN group; (O) PCEVE-NPVE containing 9.2 mol-% of pendant NP group. 305 nm) as a photosensitizer. The rate of disappearance of the C = C bonds in the polymer indicates that photochemical reactivity of the system includes intra-molecular photo-dimerization reaction of pendant cinnamic ester in a polymer chain. However, the photosensitivity of the polymer depends on the rate of gelation of the polymer based on the inter-molecular photo-dimerization of pendant cinnamic ester in two polymer chains. In addition, the practical photosensitivity of the polymer is strongly affected by the contents of the photosensitizer in the polymer and by the degree of polymerization of the photosensitive polymer (22). Accordingly, as shown in Figure 6, the practical photosensitivities of P C E V E - N P V E and P C E V E - N N V E prepared from the reactions of P C V E , which have the same degree of polymerization, were measured. The


10.


N I S H I K U B O ET A L .

239

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ι 10

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PHOTOSENSITIZER GROUP IN COPOLYMER ( mol %) Figure 6. The relationship between the practical photosensitivity and the photosensitizer content: (A) PCEVE-NNVE; (O) PCEVE-NPVE. development of the irradiated polymer film was carried out using ethyl methyl ketone, because polymers containing larger amounts of the photosensitizer groups were insoluble in toluene. P C E V E - N P V E and P C E V E - N N V E have their highest photosensitivity at the contents of about 30 mol-% of pendant N P groups and 15 mol-% of pendant N N groups, respectively. These maximum values agree with the maximum values of the rates of disappearance of the C=C bonds in these copolymers. Furthermore, P C E V E - N N V E has higher photosensitivity than P C E V E - N P V E at the contents of the photosensitizers from 25 to 5 mol-%. This result suggests that the pendant N N group is more effective photosensitizer than the pendant N P group in the self-sensitized photosensitive polymer in practice. Conclusions From all these results, it was concluded that polymers have high photochemical reactivity and high practical photosensitivity when synthesized by the cationic copolymerizations of C E V E with N N V E or N P V E , or by the reactions of P C V E with potassium cinnamate and P N N or P N P using phase transfer catalyst in D M F .


240


The photochemical reactivity and the practical photosensitivity of the resulting polymers were measured by IR spectroscopy and by the gray-scale method, respectively. Poly[2- (cinnamoyloxy) ethyl vinyl ether-co-2- (4-nitrophenoxy)ethyl vinyl ether] (PCEVE-NPVE) and polyt 2-(cinnamoyloxy) ethyl vinyl ether-co-2-(4-nitro-l-naphthoxy) ethyl vinyl ether] (PCEVE-NNVE) have their highest photochemical reactivity and highest practical photosensitivity at the contents of about 30 and 15 mol-% of pendant photosensitizer groups, respectively. In addition, it was found that PCEVE-NNVE has higher photochemical reactivity and higher practical photosensitivity than PCEVENPVE at the contents of the photosensitizers from 25 to 5 mol-%. Literature Cited 1. Nagamatsu, G.; Inui, H. "Photosensitive Polymers", Kodansha, Tokyo, 1977. 2. Tsuda, M. J. Polym. Sci. A-1, 1969, 7, 259. 3. Tanaka, H.; Tsuda, M.; Nakanishi, H. J. Polym. Sci. A-1, 1972, 10, 1729. 4. Tanaka, H.; Sato, Y. J. Polym. Sci. A-1, 1972, 10, 3279. 5. Unruh, C.C.;Smith, Jr., A. C. J. Appl. Polym. Sci. 1960, 3, 310. 6. Borden, D. G.; Williams, J. L. R. Makromol. Chem. 1977, 178, 3035. 7. Nishikubo, T.; Ichijyo, T.; Takaoka, T. J. Appl. Polym. Sci. 1974, 218, 2009. 8. Ichimura, K.; Watanabe, S.; Ochi, H. J. Polym.Sci.,Polym. Lett. Ed. 1976, 14, 207. 9. Nishikubo, T.; Iizawa, T.; Yamada, M.; Tsuchiya, K. J. Polym. Sci., Polym. Chem. Ed. 1983, 21, 2025. 10. Iizawa, T.; Nishikubo, T.; Uemura, S.; Kakuta, K. Takahashi, E.; Hasegawa, M. Kobunshi Ronbunshu 1983, 40, 425. 11. Iizawa, T.; Nishikubo, T.; Takahashi, E.; Hasegawa, M. Makromol. Chem. 1983, 184, 2297. 12. Kato, M.; Ichijyo, T.; Ishii, K.; Hasegawa, M. J. Polym. Sci. A-1, 1971, 9, 2109. 13. Montanari, F. Bull. Sci. Fac. Chem. Ind. Balogan 1956, 14, 55; Che Abstr. 1957, 51, 5723d. 14. Nara, A. "Micro Quantitative Analysis", Nankodo, Tokyo, 1968, p. 283. 15. Minsk, L. M.; Smith, J. G.; Van Deusen, W. P.; Wright, J. F.J.Appl. Polym. Sci. 1959, 2, 302. 16. Haas, H.C.;Simon, M. S. J. Polym. Sci. 1955,17,421. 17. Nishikubo, T.; Kishida, M.; Ichijyo, T.; Takaoka, T. Makromol. Chem. 1974, 175, 3357. 18. Nishikubo, T.; Kishida, M.; Ichijyo, T.; Takaoka, T. Nippon Kagaku Kaishi 1974, 1581; Chem. Abstr. 1974, 83, 4370q. 19. Nishikubo, T.; Ichijyo, T.; Takaoka, T. Nippon Kagaku Kaishi 1973, 35; Chem. Abstr. 1973, 78, 150375q. 20. Nishikubo, T.; Takahashi, E.; Iizawa, T.; Hasegawa, M. Nippon Kagaku Kaishi 1984, (2), 306. 21. Celeste, J. R. U.S. Patent No. 3, 526, 504, 1970; Chem. Abstr. 1970, 73, 104324g. RECEIVED October 3, 1984 Thompson et al.; Materials for Microlithography ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

Materials for Microlithography - American Chemical Society

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