Phenolic Resin-Based Negative Electron-Beam Resists

Chapter 7 Phenolic Resin-Based Negative Electron-Beam Resists

Downloaded by FUDAN UNIV on January 16, 2017 | http://pubs.acs.org Publication Date: August 26, 1987 | doi: 10.1021/bk-1987-0346.ch007

H. Shiraishi, N. Hayashi, T. Ueno, O. Suga, F. Murai, and S. Nonogaki Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo 185, Japan

Phenolic resin-based negative resists such as MRS (deep UV negative resist) do not swell aqueous alkaline developers. An attempt has been made to clarify the non-swelling dissolution mechanism of the resist containing poly-p-vinylphenol as a matrix following exposure to electron beam irradiation. The following results have been obtained: (1) electron beam exposure causes an increase in molecular weight of the poly-p-vinylphenol matrix, (2) the dissolution rate of poly-p-vinylphenol in the developer decreases with increasing molecular weight, and (3) there is no fractional dissolution during the development of the resist. It is concluded that non-swelling development, non-fractional dissolution in the proceeds by an etching-type mechanism rather than the fractional dissolution mechanism that occurs with most organic-laser developers. Many reports have been published on negative electron-beam resists. Most of these resists utilize radiation-induced gel-formation as the insolubilzation reaction. However, a major problem with these resists, is that their resolution is limited by swelling which is induced by the developer during development. Novolac- or phenolic resin-based resists usually show no pattern deformation induced by swelling during development in aqueous alkaline solution. Examples of such resists are naphthoquinonediazide/novolac positive photoresists, novolac-based positive electron-beam resist (NPR) (1), and azide/phenolic negative deep-UV resist (MRS) (2). Iwayanagi et al.(2) reported that the development of MRS proceeds in the same manner as the etching process. This resist, consisting of a deep-UV sensitive azide and phenolic resis matrix, is also sensitive to electron-beams. This paper deals with the development mechanism of non-swelling MRS and its electron-beam exposure characteristics.

0097-6156/87/0346-0077$06.00/0 © 1987 American Chemical Society

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

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

78 Experimental

Materials. The r e s i s t used i n t h i s study c o n s i s t e d of poly(pv i n y l p h e n o l ) as t h e p h e n o l i c r e s i n m a t r i x and 3 , 3 - d i a z i d o d i p h e n y l sulfone as t h e s e n s i t i z e r . T h e c o m p o s i t i o n was e s s e n t i a l l y the same a s t h a t o f R D - 2 0 0 0 N ( t r a d e name o f H i t a c h i C h e m i c a l C o . s MRS). Two k i n d s o f p o l y ( p - v i n y l p h e n o l ) were u s e d . One was c o m m e r c i a l l y a v a i l a b l e f r o m M a r u z e n O i l C o . , u n d e r t h e name o f R E S I N M , a n d t h e o t h e r was s y n t h e s i z e d i n o u r l a b o r a t o r y . The l a t t e r p o l y m e r , m o s t l y w i t h h i g h m o l e c u l a r w e i g h t , was p r e p a r e d b y h y d r o l y z i n g poly(p-acetoxystyrene) with a hydrazine(3). The poly(p-acetoxys t l y r e n e ) was o b t a i n e d b y p o l y m e r i z a t i o n o f t h e monomer u s i n g 2 , 2 ' azobisisobutyronitrile a s an i n i t i a t o r . The a l k a l i n e d e v e l o p e r s u s e d were aqueous tetramethylammoniumhydroxide (TMA) solutions. Isoamylacetate was u s e d as t h e o r g a n i c s o l v e n t developer. 1


1

Characteristics. E l e c t r o n - b e a m exposure e x p e r i m e n t s were c a r r i e d o u t by u s i n g a p r o t o t l y p e H L - 6 0 0 H i t a c h i E l e c t r o n - B e a m L i t h o g r a p h y System which i s a vector scanning type variable-shaped electronbeam m a c h i n e . T h e a c c e l e r a t i o n v o l t a g e was 30 k V . Resist films w e r e f o r m e d on s i l i c o n w a f e r s b y s p i n - c o a t i n g a n d p r e b a k e d a t 80 C f o r 20 m i n b e f o r e e x p o s u r e . The molecular weight distributions were measured by gel p e r m e a t i o n c h r o m a t o g r a p h y (GPC) w i t h a H i t a c h i 635 l i q u i d c h r o m a t o graphy slystem equipped w i t h Gelpack A150, A140, a n d A120 GPC columns ( H i t a c h i Chemical C o . ) . T h e GPC s o l v e n t was tetrahydrofuran. F i l m t h i c k n e s s was d e t e r m i n e d w i t h a n A l p h a S t e p 200 ( T e n c o r ) profilometer. The d i s s o l u t i o n r a t e o f t h e s a m p l e f i l m s d u r i n g development was m e a s u r e d b y l a s e r - i n t e r f e r o m e t r y ( 4 ) . A 5 mW H e - N e l a s e r was used as the monitering light source and a s i l i c o n photodiode c o n n e c t e d t o a c h a r t r e c o r d e r was u s e d a s t h e s i g n a l detector. Results

and D i s c u s s i o n

I n t h e r e s i s t s c o n t a i n i n g p h e n o l i c r e s i n and b i s a z i d e , electronbeam e x p o s u r e r e s u l t e d i n t h e p r o d u c t i o n o f p r i m a r l y a m i n e s and increased the m o l e c u l a r weight of the phenolic resin (5). A t y p i c a l e x a m p l e i s shown i n F i g . 1. I n t h i s f i g u r e , peaks 1 and 2 are bisazide and t h e poly(p-vinylphenol) matrix, respectively. Peak 3 is a primary amine p r o d u c e d from the decomposition of bisazide. The p r i m a r y a m i n e d o e s n o t a f f e c t t h e s o l u b i l i t y o f t h e resist (6). Since high-molecular-weight p h e n o l i c r e s i n s are less a l k a l i n e - s o l u b l e than low-molecular-weight resins (7), it follows t h a t t h e r e d u c e d s o l u b i l i t y must be due t o t h e i n c r e a s e i n m o l e c u lar weight. The change i n molecular weight distribution of p h e n o l i c r e s i n c o n t a i n e d i n MRS f o l l o w i n g e l e c t r o n - b e a m e x p o s u r e is shown i n F i g . 2 . T h e m o l e c u l a r w e i g h t o f t h e r e s i n i n c r e a s e d as exposure proceeded. I n a p r e v i o u s p a p e r ( 8 ) , we c o n c l u d e d t h a t t h e p h o t o - i n d u c e d decomposition of azide i n the p h e n o l i c r e s i n m a t r i x c a u s e s a n i n c r e a s e i n t h e r e s i n ' s m o l e c u l a r w e i g h t due t o crosslinking. This scheme is the same m e c h a n i s m as that in the i n s o l u b i l i z a t i o n of c r o s s - l i n k i n g n e g a t i v e r e s i s t . T h e r e f o r e , as



7.

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F i g . 1. M o l e c u l a r w e i g h t d i s t r i b u t i o n s o f MRS b e f o r e a n d a f t e r electron-beam exposure. Dose: 50 u C / c m . P e a k s 1, 2 , 3 a r e a z i d e , p o l y ( p - v i n y l p h e n o l ) , and p r i m a r y a m i n e , r e s p e c t i v e l y . 2

10" MOLECULAR

10

3

WEIGHT

F i g . 2. M o l e c u l a r weight d i s t r i b u t i o n s of poly(p-vinylphenol) m a t r i x i n e l e c t r o n - b e a m - e x p o s e d MRS f i l m s as a f u n c t i o n o f e l e c t r o n dose.



80

p r e d i c t e d i n s u c h c a s e s , h i g h s e n s i t i v i t y c a n be e x p e c t e d when h i g h e r m o l e c u l a r w e i g h t p h e n o l i c r e s i n i s u s e d as t h e m a t r i x .

a

F i g u r e 3 shows t h e e l e c t o n - b e a m exposure characteristics of two MRS s a m p l e s using high molecular weight poly(p-vinylphenol) (Mw=7 .4X1Ο * ) and standard molecular weight poly( p-vinylphenol) ( M w = 6 . 7 x l 0 ^ ) as m a t r i c e s . Azide content i n e a c h r e s i s t was 1 6 . 7 % by weight. The d e v e l o p e r s were aqueous a l k a l i n e s o l u t i o n s . The development of each resist was stopped immediately after the u n e x p o s e d a r e a s were d e s s o l v e d by the d e v e l o p e r . The i n c r e a s e i n sensitivity shown i n F i g . 3 i s s m a l l e r t h a n e x p e c t e d given the assumption that the sensitivity is proportional to the weight average m o l e c u l a r weight of the r e s i s t . Some p a t t e r n deformation d u e t o s w e l l i n g was s e e n i n t h e c a s e o f h i g h m o l e c u l a r w e i g h t M R S . In c o n v i e n t i o n a l n e g a t i v e electron-beam r e s i s t s , the g e l - p o i n t dose is inversely p r o p o r t i o n a l to the weight average m o l e c u l a r weight (9). In order to determine the g e l - p o i n t s o f t h e s e MRS s a m p l e s , t h e r e s i s t f i l m s were d e v e l o p e d w i t h o r g a n i c s o l v e n t . The e x p o s u r e c h a r a c t e r i s t i c s t h u s o b t a i n e d a r e shown i n F i g . 4 . G e l - p o i n t s were 2.3 yC/cm f o r t h e h i g h m o l e c u l a r w e i g h t M R S , a n d 70 y C / c m f o r t h e s t a n d a r d m o l e c u l a r w e i g h t MRS.


1

2

2

A s shown i n F i g . 3 a n d 4 , t h e e x p o s u r e c h a r a c t e r i s t i c s o f h i g h m o l e c u l a r w e i g h t MRS a r e s i m i l a r when d e v e l o p e d i n d i f f e r e n t devel opers. I n a d d i t i o n , p a t t e r n s i n h i g h m o l e c u l a r w e i g h t MRS d e v e l o p ed w i t h o r g a n i c s o l v e n t a r e d e f o r m e d as a r e s u l t o f s w e l l i n g . To elucidate this phenomenon, the r e l a t i o n s h i p between d i s s o l u t i o n r a t e i n a l k a l i n e d e v e l o p e r and t h e m o l e c u l a r w e i g h t o f t h e p o l y m e r was i n v e s t i g a t e d over a wide range of m o l e c u l a r w e i g h t . The r e s u l t s are summarized i n F i g . 5. The d i s s o l u t i o n r a t e o f p o l y ( p vinylphenol) in the alkaline solution decreased rapidly with i n c r e a s i n g m o l e c u l a r w e i g h t up t o 10 * . However, the decrease tend ed t o s a t u r a t e a f t e r the m o l e c u l a r weight exceeded 10 . This is t h e r e a s o n t h e h i g h m o l e c u l a r w e i g h t MRS was n o t as s e n s i t i v e as e x p e c t e d when d e v e l o p e d i n a l k a l i n e d e v e l o p e r . 1

4

On t h e c o n t r a r y , t h e s t a n d a r d m o l e c u l a r w e i g h t MRS e x h i b i t s a large difference i n e x p o s u r e c h a r a c t e r i s t i c s between F i g . 3 and 4 . In order to i n v e s t i g a t e this difference, the m o l e c u l a r weight of poly(p-vinylphenol) i n t h e e x p o s e d MRS f i l m was m e a s u r e d a s a f u n c t i o n of electron-beam dose. T h e r e s u l t s a r e shown i n F i g . 6 . The m o l e c u l a r weight of the m a t r i x - r e s i n i n c r e a s e d a f t e r the electronbeam d o s e e x c e e d e d 5 μ C / c m . W i t h i n t h e d o s e r a n g e o f 5 t o 20 yC/cm , the m o l e c u l a r weight ranged f r o m 7 x 1 0 ^ t o 1χ1θ{ . This m o l e c u l a r weight range corresponds to the r a p i d l y changing range of t h e d i s s o l u t i o n r a t e i n F i g . 5. T h i s d i s s o l u t i o n r a t e change gave t h e s t a n d a r d m o l e c u l a r w e i g h t MRS much h i g h e r s e n s i t i v i t y i n a l k a l i n e d e v e l o p e r comared w i t h the g e l - p o i n t dose. 2

2

Figure 7 shows SEM p h o t o g r a p h s of the s t a n d a r d MRS fine p a t t e r n s d e l i n e a t e d by e l e c t r o n - b e a m s . A s shown i n t h e f i g u r e , no s w e l l i n g occured d u r i n g the development o f MRS h a v i n g a s t a n d a r d molecular weight matrix, because the d i s s o l u t i o n process is an e t c h i n g - l i k e p r o c e s s , i . e , the r e s i s t f i l m d i s s o l v e s from the s u r f a c e g r a d u a l l y w i t h o u t any f r a c t i o n a l d i s s o l u t i o n . We h a v e p r e v i o u s l y r e p o r t e d a s i m i l a r n o n - f r a c t i o n a l development process (10). In order to confirm the non-fractional dissolution, molecular w e i g h t d i s t r i b u t i o n s were measured for electron-beam-exposed MRS


SHIRAISHI ET AL.

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F i g . 3 . E x p o s u r e c h a r a c t e r i s t i c s o f MRS o b t a i n e d b y a q u e o u s a l k a l i n e development. o m o l e c u l a r w e i g h t MRS ( M w = 7 A x l O ) . · : s t a n d a r d m o l e c u l a r w e i g h t MRS ( M w = 6 . 7 x l 0 ) . k

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F i g . 4 . E x p o s u r e c h a r a c t e r i s t i c s o f MRS o b t a i n e d b y o r g a n i c solvent development. ο : h i g h m o l e c u l a r we i g h t MRS ( M w = 7 . 4 x l O ) . · : s t a n d a r d m o l e c u l a r w e i g h t MRS ( M w ^ o , 7 x l 0 ) . l +

3



82


F i g . 5. D i s s o l u t i o n r a t e o f p o l y ( p - v i n y l p h e n o l ) as a f u n c t i o n molecular weight. 0 : 1.0% t e t r a m e t h y l a m m o n i u m h y d r o x i d e ( T M A ) aqueous s o l u t i o n , α : 1.2% TMA a q u e o u s s o l u t i o n .

F i g . 6. M o l e c u l a r weight of p o l y ( p - v i n y l phenol) a function of electron-beam dose.

of

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Resists


7.

F i g . 7. SEM p h o t o g r a p h s o f MRS p a t t e r n s d u r i n g a l k a l i n e development. Patterns: 0 . 4 pm l i n e a n d s p a c e . D o s e : 40 y C / c m . D e v e l o p e r : 0 . 7 2 w t . % TMA s o l u t i o n . 2



84

f i l m s b e f o r e and a f t e r development. T h e r e s u l t s a r e shown i n F i g . 8. T h e e x p o s u r e d o s e was 15 u C / c m , a n d d e v e l o p m e n t was s t o p p e d s o a s t o l e a v e 50% o f t h e i n i t i a l f i l m thickness remaining i n the exposed areas. T h e m o l e c u l a r w e i g h t d i s t r i b u t i o n o f MRS b e f o r e d e v e l o p m e n t was a l m o s t t h e same a s t h a t a f t e r h a l f - d e v e l o p m e n t . It i s c o n c l u d e d t h a t t h e r e i s no e v i d e n c e o f f r a c t i o n a l d i s s o l u t i o n i n which lower molecular weight components are dissolved preferen tially. 2


Conclusion Electron-beam exposure characteristics of the negative deep-UV resist (MRS) w e r e investigated when t h e r e s i s t was u s e d a s a p h e n o l i c r e s i n - b a s e d n e g a t i v e e l e c t r o n beam r e s i s t . In p a r t i c u l a r , the development p r o c e s s was s t u d i e d i n a n a q u e o u s a l k a l i n e s o l u t i o n by measuring t h e d i s s o l u t i o n r a t e o f p h e n o l i c r e s i n and t h e m o l e c u lar weight distributions of electron-beam-exposed resist films. The m o l e c u l a r w e i g h t o f t h e r e s i n m a t r i x i n c r e a s e d c o n t i n o u s l y as exposure proceeded. The d i s s o l u t i o n r a t e of the resin matrix decreased r a p i d l y with increasing molecular weight i n the molecu l a r w e i g h t r a n g e b e l o w ϊΦ , a n d t h e d e c r e a s e t e n d e d t o s a t u r a t e when m o l e c u l a r w e i g h t e x c e e d e d 10 * . When a s t a n d a r d molecular w e i g h t p h e n o l i c r e s i n m a t r i x and a l k a l i n e d e v e l o p e r were u s e d , no f r a c t i o n a l d i s s o l u t i o n was s e e n t o o c c u r d u r i n g t h e d e v e l o p m e n t o f the r e s i s t . T h i s development process corresponded t o an e t c h i n g l i k e development of the r e s i s t . 1

(a)

POLYSTYRENE EQUIVALENT MOLECULAR WEIGHT Fig. 8. Molecular weight d i s t r i b u t i o n s of electron-beam-exposed MRS r e s i s t . D o s e : 15 y C / c m . (a) b e f o r e development, (b) a f t e r h a l f d e v e l o p m e n t (50% r e m a i n i n g ) . 2


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REFERENCES (1)

M. J. Bowden, L. F. Thompson, S. R. Fahrenholtz, and Ε. M. Doerries, J. Electrochem. Soc., 128, 1304-1313 (1981).

(2)

T. Iwayanagi, T. Kohashi, S. Nonogaki, T. Matsuzawa, K. Douta, and H. Yanazawa, IEEE trans. Electron Devices, ED-28, 1306-1310 (1981).

(3)

R. Arshady, G. W. Kenner, and A. Ledwith, J. Polymer Sci.: Polymer Chem. Ed., 12, 2017-2025 (1974).

(4)

C. G. Willson, ACS Symp. Series 219 "Introduction to Micro lithography", Ed. by L. G. Thompson, C. G. Willson, and M. J. Bowden, Chapt. 3, (1983).

(5)

H. Shiraishi, T. Ueno, O. Suga, and S. Nonogaki, ACS Symp. Series 266 "Materials for Microlithography", Ed. by L. F. Thompson, C. G. Willson, and J. M. Frecht, 423-434 (1984).

(6)

T. Iwayanagi, M. Hashimoto, S. Nonogaki, S. Koibuchi, and D. Makino, Polymer Eng. Sci., 23, 935-940 (1983).

(7)

S. Nonogaki, M. Hashimoto, T. Iwayanagi, and H. Shiraishi, Proc. SPIE 539, Advances in Resist Technology and Processing II, 189-193 (1985).

(8)

M. Hashimoto, T. Iwayanagi, H. Shiraishi, and S. Nonogaki, Technical Papers, SPE Regional Technical Conference "Photopolymers: Principles, Processes and Materials", pp. 11-33, Ellenville, New York, Oct. 28-30 (1985).

(9)

H. Y. Ku and L. C. Scala, J. Electrochem. Soc., 116, 980-985, (1969).

(10) Y. Hatano, H. Shiraishi, Y. Taniguchi, S. Horigome, S. Nonogaki, and K. Naraoka, Proc. Symp. Electron and Ion Beam Sci. Technol. 8th Int. Conf., 332-340 (1978). RECEIVED May 5, 1987


Phenolic Resin-Based Negative Electron-Beam Resists

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