Polymers in Microlithography - American Chemical Society

Chapter 16

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on April 15, 2018 | https://pubs.acs.org Publication Date: October 31, 1989 | doi: 10.1021/bk-1989-0412.ch016

New Negative Deep-UV Resist for K r F Excimer Laser Lithography Masayuki Endo, Yoshiyuki Tani, Masaru Sasago, and Noboru Nomura Semiconductor Research Center, Matsushita Electric Industrial Company Ltd., 3-15, Yagumo-nakamachi, Moriguchi, Osaka 570, Japan

A photosensitive composition, consisting of an aromatic azide compound (4,4'-diazidodiphenyl methane) and a resin matrix (poly (styrene-co-maleic acid half ester)), has been developed and evaluated as a negative deep UV r e s i s t for high resolution KrF excimer laser lithography. S o l u b i l i t y of this r e s i s t in aqueous alkaline developer decreases upon exposure to KrF excimer laser i r r a d i a t i o n . The alkaline developer removes the unexposed areas of this r e s i s t . No swelling-induced pattern deformation occurs and high aspect ratio sub-halfmicron patterns in 1 micron film thickness are obtained with high s e n s i t i v i t y . 1.

Introduction

KrF excimer l a s e r l i t h o g r a p h y t h a t u t i l i z e s s h o r t e r w a v e l e n g t h h a s become o f g r e a t i n t e r e s t a s a means o f f a b r i c a t i n g 0.3-0.5 micron patterns i n semiconductors (1-3). One p r o b l e m w i t h K r F e x c i m e r l a s e r l i t h o g r a p h y i s t h e l a c k o f h i g h r e s o l u t i o n r e s i s t . Many a t t e m p t s t o o b t a i n s u i t a b l e r e s i s t f o r K r F excimer l a s e r has been r e p o r t e d . C o - a n d t e r p o l y m e r s o f PMMA w i t h i n d e n o n e ( 4 ) , o x i m i n o b u t a n o n e m e t h a c r y l a t e ( 5 ) , and m e t h a c r y l o n i t r i l e (6) h a v e been used as h i g h r e s o l u t i o n p o s i t i v e d e e p UV r e s i s t s . However, t h e i r s e n s i t i v i t y t o K r F e x c i m e r l a s e r i r r a d i a t i o n and r e s o l u t i o n are not s u f f i c i e n t f o r use i n p r a c t i c a l KrF excimer l a s e r l i t h o g r a p h y process (7). N a p h t h o q u i n o n e d i a z i d e - b a s e d p o s i t i v e r e s i s t s have h i g h o p t i c a l d e n s i t y , so t h e p r o f i l e s o f t h e i r p a t t e r n a r e degraded ( 2 , 3 , 7 ) . R e c e n t l y , W i l l s o n e t a l . have r e p o r t e d on 1 , 3 - d i a c y l - 2 - d i a z o l i n k a g e d e r i v a t i v e d i s s o l u t i o n i n h i b i t i o n system w i t h h i g h s e n s i t i v i t y as a p o s i t i v e deep UV r e s i s t . However, t h e r e s o l u t i o n a n d p a t t e r n 0097-6156/89/0412-0269$06.00/0 © 1989 American Chemical Society

Reichmanis et al.; Polymers in Microlithography ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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p r o f i l e s of the r e s i s t have not been f u l l y d e s c r i b e d (8). Orvek e t a l . have presented o r g a n o s i l i c o n p o s i t i v e photo r e s i s t f o r KrF excimer l a s e r . Half-micron p a t t e r n s were obtained u s i n g a KrF excimer l a s e r contact p r i n t i n g system, while the complicated b i l a y e r process i s r e q u i r e d f o r the use of the r e s i s t (9). As f o r negative deep UV r e s i s t , Ο'Toole e t a l . have e x h i b i t e d h a l f - m i c r o n p a t t e r n r e s o l u t i o n i n 0.5 micron f i l m t h i c k n e s s u s i n g the new r e s i s t and PIE process (10). The p a t t e r n p r o f i l e s , however, were r e - e n t r a n t , due t o the l a r g e photo a b s o r p t i o n and the a p p l i c a t i o n s t o s i n g l e - l a y e r - r e s i s t system have not been presented (11). We have developed a new negative deep UV r e s i s t f o r KrF excimer l a s e r l i t h o g r a p h y . The r e s i s t i s composed of 4,4'-diazidodiphenyl methane ((a) i n F i g u r e 1) as a p h o t o s e n s i t i v e azide compound and p o l y ( s t y r e n e - c o - m a l e i c a c i d h a l f e s t e r ) ((b) i n Figure 1) as a r e s i n matrix. A z i d e - p h e n o l i c r e s i n p h o t o r e s i s t s have been r e p o r t e d by workers at H i t a c h i . They are used f o r i - l i n e (12) or f o r deep UV l i g h t (13), and the a p p l i c a t i o n s t o KrF excimer l a s e r l i t h o g r a p h y have not been demonstrated. We have found the combination of the a z i d e compound and the styrene r e s i n i s w e l l s u i t e d f o r a c h i e v i n g h i g h r e s o l u t i o n and high aspect r a t i o p a t t e r n s u s i n g KrF excimer l a s e r stepper system, because of the absence of s w e l l i n g - i n d u c e d p a t t e r n deformation d u r i n g a l k a l i n e development and the s u i t a b l e o p t i c a l d e n s i t y a t 248 nm i n terms o f s e n s i t i v i t y . In t h i s paper, the m a t e r i a l c h a r a c t e r i s t i c s and l i t h o g r a p h i c e v a l u a t i o n of t h i s new r e s i s t are demonstrated. The r e s i s t meets the requirements f o r KrF excimer l a s e r l i t h o g r a p h y , which e x h i b i t s h i g h s e n s i t i v i t y , h i g h r e s o l u t i o n and high aspect r a t i o pattern p r o f i l e s . 2.

Experimental

2.1.

Resist preparation 1

The p h o t o s e n s i t i v e azide compound was 4 , 4 - d i a z i d o d i phenyl methane (m.p. 44.0 t ) . The p o l y (styrene-co-maleic a c i d h a l f e s t e r ) was used as a r e s i n matrix. The a z i d e compound was mixed with the styrene r e s i n i n the range of 10 t o 40 wt%, and d i s s o l v e d i n 2-methoxyethyl acetate. 2.2.

Spectroscopic c h a r a c t e r i z a t i o n

The IR s p e c t r a of t h i s new r e s i s t f i l m s on s i l i c o n s u b s t r a t e s were measured with a Shimadzu FTIR-4000 F o u r i e r transform spectrometer. The UV s p e c t r a of 4,4·d i a z i d o d i p h e n y l methane i n a quartz c e l l and the f i l m s of p o l y ( s t y r e n e - c o - m a l e i c a c i d h a l f e s t e r ) and the new r e s i s t on quartz s u b s t r a t e s were measured with a Shimadzu UV-265FS double-beam spectrometer.


16.

ENDOETAL.


2.3.

Deep-UV Resistfor KrFExcimer Laser Lithography

271

Lithographic evaluation

The new r e s i s t was spin-coated on a s i l i c o n s u b s t r a t e and baked f o r 20 min. a t 80°C i n a convection oven. A f t e r exposure, the r e s i s t f i l m was developed with a 60s immersion i n tetramethyl ammonium hydroxide (TMAH) aqueous s o l u t i o n . The f i l m t h i c k n e s s of the r e s i s t was 1.0 micron. The exposure was done with a 5X KrF excimer l a s e r stepper system (N.A 0.36) we manufactured (14). S e n s i t i v i t y i s d e f i n e d as the exposure energy necessary f o r 50% r e s i s t t h i c k n e s s remaining i n the exposed areas. Contrast values are assessed by measuring the slope o f the l i n e a r p o r t i o n of the curve obtained by p l o t t i n g the t h i c k n e s s of the r e l i e f image as a f u n c t i o n of the logarithm of the exposure energy (15). The f i l m t h i c k n e s s was measured with a Nanospec AFT f i l m t h i c k n e s s monitor (Nanometrics). The r e s i s t p a t t e r n p r o f i l e s were evaluated u s i n g a JEOL JSM-T200 scanning e l e c t r o n microscope. 3.Results 3.1.

and

Discussion

O p t i m i z a t i o n of the r e s i s t

composition

Figure 2 shows the exposure c h a r a c t e r i s t i c s f o r a z i d e - s t y r e n e r e s i n r e s i s t f i l m with an a z i d e c o n c e n t r a t i o n from 10 t o 40 wt% (based on the styrene r e s i n weight) and Figure 3 shows the c o n t r a s t of the r e s i s t f i l m s as a f u n c t i o n of the azide c o n c e n t r a t i o n . Development was done with a 60s immersion i n 0.83% TMAH s o l u t i o n . The styrene r e s i n matrix alone has been found to be a negative deep UV r e s i s t . However, r a t h e r low c o n t r a s t (1.48) and low s e n s i t i v i t y (2.5 J/cm ) are observed. The c o n t r a s t and the s e n s i t i v i t y of the styrene r e s i n i s remarkedly increased by adding the a z i d e , as shown i n F i g u r e s 2 and 3. When the c o n c e n t r a t i o n of the azide exceeds 30 wt%, s e n s i t i v i t y decreases (Figure 2) and the c o n t r a s t becomes worse (Figure 3). T h i s i s due t o the i n c r e a s e o f the o p t i c a l d e n s i t y of the r e s i s t . Large o p t i c a l d e n s i t y prevents the l i g h t from p e n e t r a t i n g i n t o the r e s i s t (3,11). A l s o , the r e s i s t t h i c k n e s s remainig a f t e r development i s maximum at the 30 wt% azide c o n c e n t r a t i o n (Figure 2). From these r e s u l t s , i t was concluded t h a t the a z i d e - s t y r e n e r e s i n r e s i s t which contains 30 wt% 4,4'-diazidodiphenyl methane based on p o l y ( s t y r e n e - c o maleic a c i d h a l f ester) would be most s u i t e d f o r KrF excimer l a s e r l i t h o g r a p h y . The c o n t r a s t (4.72) was e x c e l l e n t and the s e n s i t i v i t y (30 mJ/cm ) was i n the d e s i r e d range. T h i s r e s i s t composition was subjected t o s p e c t r o s c o p i c c h a r a c t e r i z a t i o n and l i t h o g r a p h i c evaluation. 2

2




272

b

Figure 1. Chemical s t r u c t u r e s o f (a) 4 , 4 ' - d i a z i d o d i phenyl methane and (b) p o l y ( s t y r e n e - c o - m a l e i c a c i d half ester).

Figure 2 . E f f e c t o f a z i d e c o n c e n t r a t i o n on exposure c h a r a c t e r i s t i c s f o r azide-styrene r e s i n r e s i s t of 1 . 0 micron f i l m t h i c k n e s s .


16. ENDOETAK

Deep-UV Resist for KrF Excimer Laser Lithography

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3.2. S p e c t r o s c o p i c c h a r a c t e r i s t i c s F i g u r e 4 demonstrates a FT-IR s p e c t r a o f t h i s new r e s i s t before and a f t e r 80C prebaking, and a f t e r exposure t o KrF excimer l a s e r i r r a d i a t i o n f o r 100 mJ/cm . The s t r o n g a b s o r p t i o n a t 2100 cm" due t o t h e a z i d e group s t r e t c h i n g v i b r a t i o n i n t h i s r e s i s t i s c l e a r l y present before prebaking. I t can be seen t h a t t h e c h a r a c t e r i s t i c bond a t 2100 cm-i of t h e azide decreased t o h a l f a f t e r prebaking and disappeared a f t e r exposure. No other s i g n i f i c a n t changes a r e observed. T h i s i n d i c a t e s t h a t t h e prebaking temperature h i g h e r than the m e l t i n g p o i n t o f t h e a z i d e decomposes t h e a z i d e (50%) and i t t o t a l l y decomposes upto 100 mJ/cm irradiation. I t i s p o s s i b l e t h a t subsequent r e a c t i o n s o f the n i t r e n e , generated from the a z i d e t h e r m o l y s i s and p h o t o l y s i s , with t h e styrene r e s i n c o u l d be r e s p o n s i b l e f o r s o l u b i l i t y modulation o f t h i s type r e s i s t (16). The UV s p e c t r a f o r t h e azide i n a d i e t h y l e n e g l y c o l dimethyl ether s o l u t i o n and f o r t h e styrene r e s i n f i l m with 1.0 micron t h i c k n e s s a r e shown i n F i g u r e 5. The a z i d e has an intense a b s o r p t i o n a t around 248 nm (molar e x t i n c t i o n c o e f f i c i e n t a t 248 nm = 3.0xl0 1/M*cm). The syrene r e s i n used as matrix polymer e x h i b i t s a s i g n i f i c a n t transparency a t 248 nm (70%). The UV s p e c t r a f o r t h i s r e s i s t f i l m , before and a f t e r exposure t o KrF excimer l a s e r i r r a d i a t i o n f o r 100 mJ/cm , are shown i n F i g u r e 6. The absorbance o f t h e a z i d e renders t h e r e i s t f i l m o f 1.0 micron t h i c k n e s s e s s e n t i a l l y opaque a t 248 nm. A f t e r exposure o f 100 mJ/cm , t h e absorbance bleaches from 0.5 t o 6.0% a t 248 nm. Intense a b s o r p t i o n by t h i s r e s i s t a t 248 nm c l o s e l y r e l a t e s t o the pattern p r o f i l e of the r e s i s t , which w i l l be d i s c u s s e d i n the l a s t s e c t i o n . e

2


1

2

4

2

2

3.3. D i s s o l u t i o n k i n e t i c s In order t o determine t h e a p p r o p r i a t e development c o n d i t i o n s , we examined d i s s o l u t i o n c h a r a c t e r i s t i c s f o r r e s i s t f i l m s i n t h e aqueous a l k a l i n e developers by measuring f i l m t h i c k n e s s as a f u n c t i o n o f development time. In F i g u r e 7, d i s s o l u t i o n c h a r a c t e r i s t i c s f o r t h e new r e s i s t before and a f t e r exposure t o KrF excimer l a s e r are compared with those f o r t h e styrene r e s i n matrix. The exposure energy was 100 mJ/cm and t h e a l k a l i n e c o n c e n t r a t i o n i n TMAH s o l u t i o n was 0.83%. Large d i f f e r e n c e s i n s o l u b i l i t y a r e observed between these three f i l m s . T h i s i n d i c a t e s t h a t the thermally o r photochemically decomposed a z i d e (Figure 4) i n h i b i t s t h e d i s s o l u t i o n o f the styrene r e s i n i n t o t h e a l k a l i n e developer. The i n h i b i t i o n may be due t o t h e i n c r e a s e o f t h e molecular weight o f t h e styrene r e s i n i n t h e presence o f t h e decomposed a z i d e . Hydrogen a b s t r a c t i o n from t h e polymer by n i t r e n e o f t h e decomposed a z i d e and subsequent polymer r a d i c a l recombination r e s u l t i n a i n c r e a s e i n t h e molecular weight o f t h e polymer (17). 2



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5.0 4.0 ω 3.0

Polymers in Microlithography - American Chemical Society

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