Polymers for High Technology - American Chemical Society

Chapter 41 Preparation of Polyimide Mono- and Multilayer Films 1

3

1

2

Masa-aki Kakimoto , Masa-aki Suzuki , Yoshio Imai , Mitsumasa Iwamoto , and Taro H i n o

3

1

Downloaded by FUDAN UNIV on December 7, 2016 | http://pubs.acs.org Publication Date: August 26, 1987 | doi: 10.1021/bk-1987-0346.ch041

2

Department of Textile and Polymeric Materials, Tokyo Institute of Technology, Meguro-ku, Tokyo 152, Japan Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, Meguro-ku, Tokyo 152, Japan Department of Physical Electronics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152, Japan 3

Mono- and m u l t i l a y e r f i l m s o f p o l y i m i d e s were s u c c e s s fully prepared using Langmuir-Blodgett technique. Monolayer f i l m s o f p o l y a m i c a c i d l o n g a l k y l a m i n e salts were p r e p a r e d a t the a i r - w a t e r interface. The monolayer films were d e p o s i t e d on a p p r o p r i a t e plates to produce m u l t i l a y e r f i l m s o f the p r e c u r s o r t o p o l y i m i d e films. Finaly, the polyimide multilayer films were obtained by t r e a t m e n t o f the m u l t i l a y e r f i l m s of the polyamic acid amine salts w i t h acetic anhydride and pyridine. The p o l y i m i d e m u l t i l a y e r f i l m s had e x c e l l e n t coating ability g i v i n g a v e r y smooth s u r f a c e . They a l s o exhibited insulating c h a r a c t e r i s t i c s as reliable as polyimide thick f i l m s .

Wholly aromatic polyimides are h i g h l y thermally stable engineering plastics, and have been w i d e l y used as the r e l i a b l e i n s u l a t i n g materials in microelectronics. Recent developments i n t h i s f i e l d toward higher i n t e g r a t i o n of devices r e q u i r e d u l t r a t h i n f i l m s of p o l y i m i d e s . Minimum t h i c k n e s s o f p o l y i m i d e f i l m s c a s t by s p i n c o a t i n g was about 0.1 um. Since polyimides 5 a r e e s s e n t i a l l y i n f u s i b l e and i n s o l u b l e in organic solvents, they a r e p r o c e s s e d i n t o f i l m s a t the s t a g e o f p o l y amic acids _3 which a r e r e a d i l y s y n t h e s i z e d from t e t r a c a r b o x y l i c dia n h y d r i d e s 1 and d i a m i n e s 2. Thermal t r e a t m e n t o f p o l y a m i c a c i d f i l m s t o 300 °C a f f o r d s p o l y i m i d e f i l m s t h r o u g h c y c l o d e h y d r a t i o n (Scheme 1 ) . Alternatively, chemical treatment of polyamic a c i d f i l m s with a mixture o f a c e t i c a n h y d r i d e and p y r i d i n e i s a l s o e f f e c t i v e i n obtaining polyimide f i l m s . ( 1 ) Langmuir-Blodgett technique (LB t e c h n i q u e ) i s one o f the most p r o m i s i n g methods f o r the p r e p a r a t i o n o f u l t r a t h i n o r d e r e d m u l t i l a y e r films with uniform t h i c k n e s s . ( 2 ) T y p i c a l monomeric m u l t i l a y e r films of amphiphilic substances such as l o n g a l k y l c a r b o x y l i c acids are thermally and m e c h a n i c a l l y u n s t a b l e . Improvements i n the stability have been a c h i e v e d u s i n g p o l y m e r i c m u l t i l a y e r f i l m s which have been 0097-6156/87/0346-0484$06.00/0 © 1987 A m e r i c a n C h e m i c a l Society

Bowden and Turner; Polymers for High Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

41.

K A K I M O T O ET A L .

Preparation

of Polyimide

Mono-

and Multilayer

Films

485


prepared by polymerization of a m p h i p h i l i c m u l t i l a y e r f i l m s having polymerizable functions such as diacetylenes,(3) o l e f i n s , ( 4 ) and aminoacid e s t e r s . ( 5 ) A few examples o f d i r e c t p r e p a r a t i o n o f multi l a y e r f i l m s o f p r e f o r m e d polymers have a l s o been reported, including long alkyl p o l y a c r y l a t e s , ( 6 ) a l t e r n a t e copolymers o f p o l y m a l e i c an hydride^?) and c e l l u l o s e e s t e r s with long alkyl acids.(8) These polymeric m u l t i l a y e r f i l m s s t i l l possess thermally unstable long a l k y l chains. In t h i s a r t i c l e , we d e s c r i b e the f i r s t s u c c e s s f u l p r e p a r a t i o n o f polyimide mono- and m u l t i l a y e r f i l m s w i t h o u t any pendant long alkyl c h a i n s u s i n g LB t e c h n i q u e .

R E S U L T S AND D I S C U S S I O N The p r e s e n t method c o n s i s t s o f t h r e e s t e p s as i l l u s t r a t e d i n Scheme 1. In the f i r s t s t e p , monolayer f i l m s o f p o l y a m i c a c i d l o n g c h a i n a l k y l amine s a l t s A a t the a i r - w a t e r i n t e r f a c e a r e p r e p a r e d . ( 9 ) Unexpected ly, the polyamic a c i d 3 i t s e l f , which p o s s e s s h y d r o p h i l i c c a r b o x y l functions i n the polymer backbone, d i d not a f f o r d a s t a b l e monolayer at the a i r - w a t e r i n t e r f a c e . I n t r o d u c t i o n of a hydrophobic long a l k y l chain i n t o _3 was performed by m i x i n g p o l y a m i c acids and longchain alkylamines. Polyamic a c i d s a l t s 4, thus o b t a i n e d , afforded very stable monolayer f i l m s a t the a i r - w a t e r i n t e r f a c e . In the second step,(10) the polyamic a c i d s a l t monolayer f i l m s are s u c c e s s f u l l y deposited on a p p r o p r i a t e p l a t e s such as glass, quartz, or silicon wafer. Finally p o l y i m i d e m u l t i l a y e r f i l m s a r e o b t a i n e d by t r e a t m e n t of p o l y a m i c a c i d s a l t m u l t i l a y e r f i l m s on the p l a t e s w i t h a m i x t u r e o f a c e t i c a n h y d r i d e and p y r i d i n e . Preparation o f Monolayer F i l m s o f P o l y a m i c A c i d A l k y l a m i n e Air-water Interface; a

r

Salts

e

at

The s t r u c t u r e and the code o f v a r i o u s p o l y a m i c a c i d s 3^ shown i n T a b l e 1. A s o l u t i o n o f 3 i n a m i x t u r e o f Ν,Ν-dimethylacetamide (DMAc) and benzene (1:1) p r e p a r e d t o a c o n c e n t r a t i o n o f 1 mmol/L and a s o l u t i o n o f d i m e t h y l h e x a d e c y l a m i n e (DMC16) i n the same mixed s o l v e n t with the same c o n c e n t r a t i o n were combined t o produce a s o l u t i o n o f p o l y a m i c acid salts 4. The s o l u t i o n s were then s p r e a d on deionized water. The measurement o f s u r f a c e p r e s s u r e - a r e a r e l a t i o n s h i p s (π-Α isotherms) was carried out a t about 1.8 cm/min compression speed a t 20 °C u s i n g Wilhelmy type f i l m b a l a n c e (Kyowa Kaimenkagaku Co., Japan). Figure 1 shows π-Α c u r v e s o f p o l y a m i c a c i d s a l t s 4a where the molar ratio of p o l y a m i c a c i d 3a °MC16 was v a r i e d . Each curve r o s e s t e e p l y and the collapsed pressures fell by i n c r e a s i n g the r a t i o o f 3a to DMC16. P o l y a m i c a c i d 3a c o u l d not be s p r e a d i n t o a s t a b l e f i l m as i l l u s t r a t e d on curve A. When the r a t i o o f 3a t o DMC16 was 1:2 ( c u r v e D), the c o l l a p s e p o i n t r e a c h e d 40 dyne/cm. In t h i s c a s e , an e q u i m o l a r amount of c a r b o x y l i c f u n c t i o n and amine f u n c t i o n was present. Figure 2 i l l u s t r a t e s the m o l e c u l a r model o f the r e p e a t i n g u n i t o f p o l y a m i c a c i d 3a i n which the a r o m a t i c r i n g coming from the p y r o m e l l i t i c a c i d lies flat on the water s u r f a c e . Ttje a r e a o f t h e square l i n e around the model was c a l c u l a t e d as 3,· 28 nm , which was i n good agreement w i t h a surface a r e a o f 1.38 nm o b t a i n e d by e x t r a p o l a t i o n o f the s t e e p rise t

o


486

POLYMERS FOR HIGH T E C H N O L O G Y

0

/

0 π

V

0

C

ii

\ V ΑΓ

C

ii

ii

0

0

\ /Ο +

. 2 H2N—ΑΓ-ΝΗ2

N

COH 0

HOC 0

1

^C-NH—Ar-INH-

Ar Jn

3

2

ÇH3

il-KH2-%CH3


H 3 C

9

- C ^ϊ-ΝΗ—Ar-NH-4N

DMC16

Ar

I

(ÇH2) CH3

15

C

-+N

0

9

\

1

/

Jn

C

\

Λ

2

I

Ar N-Ar-f-

V

II

»

Η 0 H3C-N-CH3

/

Y

H3C-N-CH3 (ÇH2) CH3

Scheme 1.

AREA PER UNIT (nm2) Figure 1 7T-A C u r v e s o f p o l y a m i c a c i d s a l t s 4a v a r y i n g t h e r a t i o o f N,N-dimethylhexadecylamine (DMC16) t o p o l y a m i c a c i d 3a. A; p o l y a m i c a c i d 3a, B; 3a:DMC16=2:1, C; 3a:DMC16=1:1, D; 3 a ' E; 3a :DMC16=1:4. :

D

M

C

1

6

=

1

:

2

1.6 nm

Figure 2

^

M o l e c u l a r model o f p o l y a m i c a c i d 3a.


41.


Table

Preparation

of Polyimide

Mono-

and Multilayer

Films

1. E x t r a p o l a t e d S u r f a c e Area o f V a r i o u s Polyamic A c i d s S a l t s

Polyamic

Surface Area (nm /unit )

Acid

2


--HNONHHO-OHQ--

1.38

H O C ^ C O H

.

Γ ~

0

9 H

N

Jn

0

C

fi 9 0 0 ™

/=\

n

y=\~L ^^"~

r

1.65


487


488

POLYMERS FOR HIGH T E C H N O L O G Y

of curve D to zero pressure. T h i s f a c t s t r o n g l y supports that the spread f i l m a t the a i r - w a t e r i n t e r f a c e has the monolayer structure. When an e x c e s s o f DMC16 was employed ( c u r v e Ε i n F i g u r e 1 ) , the e x t r a polated s u r f a c e a r e a d i d not i n c r e a s e markedly compared w i t h the case o f c u r v e D. A v a r i e t y o f p o l y a m i c a c i d s 3b~3f were used f o r the preparation of monolayers t o examine the b e h a v i o r o f monolayers a t the air-water interface i n more d e t a i l . Two e q u i v a l e n t o f a l k y l a m i n e DMC16 were used t o produce p o l y a m i c a c i d s a l t s 4b-4f, which were s p r e a d o n t o the pure water under the same c o n d i t i o n s d e s c r i b e d above. In a l l c a s e s , steeply r i s i n g π-Α c u r v e s were o b t a i n e d . The v a l u e s o f each extra polated s u r f a c e a r e a a r e summarized i n T a b l e 1. The d i f f e r e n c e be tween the a r e a o f 4a and 4b was a l m o s t e q u i v a l e n t t o the difference between 4c and 4d, c o r r e s p o n d i n g t o the s u r f a c e a r e a o f b e n z o y l f u n c t i o n which was c a l c u l a t e d t o be about 0.20 nm by the use o f a molecu l a r model. S i m i l a r l y , the o b s e r v e d a r e a o f the phenoxy group from t h e d i f f e r e n c e between 4a and 410 1.85 >200

Si0

o

1 5

io

1 2

io -io

1 8

2.76X10

3.9

2.7

3.5

3.3 1 4

c)

5a and O t h e r

2.77

0.4

io -io

Cd-LB

case.(12)

6

>10"

1.78

1.51

500

100

a) M u l t i l a y e r F i l m s o f 5 a . b) P o l y i m i d e f i l m c) Cadmium a r a c h i d a t e LB f i l m .

1 3

1 4

io -io

1 6

10 1.46

(25 ym t h i c k n e s s ) ,

It was o b s e r v e d t h a t the l i q u i d c r y s t a l l i n e s u b s t a n c e s incorporated on t h e p o l y i m i d e f i l m s which were o n l y 0.8 nm (2 l a y e r s ) thick were s u c c e s s f u l l y o r i e n t e d t o the t r a n s f e r d i r e c t i o n w i t h o u t a s u r f a c e rubbing treatment o f the p o l y i m i d e f i l m . This observation can be explained by o r i e n t a t i o n o f the polymer m o l e c u l e t o the f i l m t r a n s f e r d i r e c t i o n as o b s e r v e d by p o l a r i z e d UV and IR s p e c t r o s c o p y . To our knowledge, the p r e s e n t p o l y i m i d e monolayer f i l m s possess the minimum t h i c k n e s s e v e r p r o d u c e d . We b e l i e v e t h a t t h i s s i m p l e and e f f i c i e n t method f o r the p r e p a r a t i o n o f p o l y i m i d e mono- and m u l t i l a y e r f i l m s w i l l b r i n g about new t e c h n o l o g y e s p e c i a l l y i n m i c r o e l e c t r o n i c s .

REFERENCES 1) Sroog, C. E. In Macromolecular Synthesis; Moore, J. Α., Ed., John Wiley & sons: New York, 1977; Coll. Vol. 1, Ρ 295.


41.


Preparation

of Polyimide Mono-

and Multilayer

Films


2)

495

For special issue of Langmuir-Blodgett films: Thin Solid Films 1980, 68, 1983, 99, and 1985, 132, 133, and 134. 3) Akimoto, Α., Dorn, K., Gros, L., Ringsdorf, H., and Schupp, H., Angew. Chem. Int. Ed. Engl. 1981, 20, 90. 4) Fukuda, K., and Shiozawa, T., Thin Solid Films 1980, 68, 55. 5) Fukuda, K., Shibasaki, Y., and Nakahara, H., J. Macromol. Sci., Chem. 1981, A15, 999. 6) Mumby, S. J . , Swalen, J. D., and Rabolt, J. F., Macromolecules 1986, 19, 1054. 7) Tredgold, R. H., Vickers, A. J . , Hoorfar, Α., Hodge, P., and Khoshdel, E., J. Phys. D: Appl. Phys. 1985, 18, 1139. 8) Kawaguchi, T., Nakahara, H., and Fukuda, K., J. Colloid Interface Sci. 1985, 104, 290. 9) Suzuki, M., Kakimoto, M., Konishi, T., Imai, Y., Iwamoto, Μ., and Hino, T., Chem. Lett. 1986, 395. 10) Kakimoto, M. Suzuki, Μ., Konishi, T., Imai, Y., Iwamoto, M., and Hino, T., Chem. Lett. 1986, 823. 11) Nakahara, H., and Fukuda, K., J. Colloid Interface Sci. 1979, 69, 24. 12) Yoneyama, M., Sugi, M., Saito, M., Ikegami, K., Kuroda, S., and Iijima, S., Jpn. J. Appl. Phys. 1986, 25, 961. RECEIVED May 11, 1987


Polymers for High Technology - American Chemical Society

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