Mid-UV Photosensitization of Diazoquinone Positive Photoresists

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 16, 2016 | http://pubs.acs.org Publication Date: March 15, 1984 | doi: 10.1021/bk-1984-0242.ch004

4 M i d - U V Photosensitization of Diazoquinone Positive Photoresists W. T. BABIE, M-F. CHOW, and W. M. MOREAU East Fishkill GTD, IBM Corporation, Rt. 52, Hopewell Junction, NY 12533 Higher resolution projection printing requires uti lization of shorter exposure wavelengths than 365-435nm. The spectral sensitivity, however, of diazonaphthoquinones (DQ) is lower at 313nm than at 365 and 405nm. At 313nm, the actinic absorption of diazoquinones is lower than the actinic peaks at 365 and 405nm. The enhancement of the spectral absorption and sensitivity can be achieved by the addition of pyrene photosensitizers. Pyrene (P) acts as a singlet energy transfer sensitizer via intermolecular resonance interaction. The photomechanism and application of sensitized PDQ to the mid-UV region will be discussed. In order to enhance the resolution of 1:1 projection photolithography, shorter exposure wavelengths (240 to 330nm) than the currently employed wavelengths of 360 to 400nm are required.(1) In the 300-330nm region, however, commercial diazoquinone-novolak resists suffer from a lower sensitizer absorption and interference by a tailing novolak resin. Because of the undesirable absorption characteristics of the novolak photoresists and the lower output of mercury lamps in this region, we investigated the enhancement of the actinic sensitivity of diazoquinone-novolak resists for the mid-UV region. The enhancement of spectral absorptivity at 313nm was accomplished by the addition of singlet photosensitizers to ester derivatives of diazonaphthoquinone (DQ). These photosensitizers absorb incident photons and transfer the energy to the DQ derivative which is then converted to the alkaline soluble product without the interference of the sensitizer. Theoretical ly, the mechanism of energy transfer in the solid phase involves dipole-dipole interaction because of the insignificant extent of 0097-6156/ 84/ 0242-0041 $06.00/ 0 © 1984 American Chemical Society Davidson; Polymers in Electronics ACS Symposium Series; American Chemical Society: Washington, DC, 1984.


42

P O L Y M E R S IN E L E C T R O N I C S

d i f f u s i o n o f t h e s e n s i t i z e r and a c c e p t o r . I n o r d e r t o be e f f e c t i v e , t h e s e n s i t i z e r must meet, t h e f o l l o w i n g r e q u i r e m e n t s : (1) Have a h i g h ε ( c a . 10 M~ cm" a t 313nm), (2) s u s t a i n a l o n g s i n g l e t s t a t e l i f e t i m e τ (3) be i n s e n s i t i v e t o o x y g e n ; and (4) possess a h i g h e r energy^of e x c i t e d s i n g l e t s t a t e than t h a t of the DQ ( c a . 58 k c a l m o l " ) . I t i s w e l l known t h a t p y r e n e and methyl pyrene are s u i t a b l e s e n s i t i z e r s f o r £ h i s purpose.(2) The e, τ , and j n e r g y o f p y r e n e a r e 1 χ 10 M cm , 3 0 0 n s , and 75 k c a l m o l respectively. The P e r k i n E l m e r p r o j e c t i o n p r i n t e r i s t h e t o o l most c u r r e n t l y used i n p h o t o l i t h o g r a p h y m a n u f a c t u r i n g . Because of the i n t e r f e r e n c e o f p h o t o n s a t t h e r e s i s t - s u b s t r a t e i n t e r f a c e and t h e a b s o r p t i o n o f t h e r e s i s t , i t i s a l w a y s more d i f f i c u l t t o d e v e l o p t h e b o t t o m o f t h e r e s i s t image t o s i z e t h a n t o o b t a i n a s u r f a c e image. A d o u b l e l a y e r t e c h n i q u e h a s been d e v e l o p e d t o r e s o l v e t h i s problem. The t o p image l a y e r i s s e n s i t i z e d DQ and t h e b o t t o m l a y e r i s composed o f a DQ d e r i v a t i v e . Experimental Material. The r e s i s t m a t e r i a l p h o t o a c t i v e compound (PAC), a d i a z o n a p h t h o q u i n o n e d e r i v a t i v e i n a n o v o l a k r e s i n m a t r i x , was u s e d as a c o n t r o l and a l s o r e f o r m u l a t e d t o o b t a i n P A C / p y r e n e . P y r e n e was o b t a i n e d f r o m A l d r i c h and was added t o t h e PAC i n t h i s s t u d y i n t h e q u a n t i t y o f 2.5% o f t h e t o t a l s o l i d s c o n t e n t o f t h e resist. The r e s i s t s were m i x e d on a r o l l e r o v e r n i g h t and t h e n f i l t e r e d t h r o u g h a 0.8pm s i l v e r membrane f i l t e r . DQ D i s a p p e a r a n c e . To s t u d y t h e e f f e c t o f p y r e n e on DQ d i s a p p e a r a n c e , n - p r o p a n o l s o l u t i o n s i n a q u a r t z t u b e w i t h I . D . o f 4mm were i r r a d i a t e d w i t h a 450W medium p r e s s u r e Hg lamp t h r o u g h a 313nm interference f i l t e r . T y p i c a l l y , t h e o p t i c a l d e n s i t i e s a t 313nm f o r DQ s o l u t i o n s w i t h and w i t h o u t p y r e n e a r e 0 . 8 and 0 . 4 r e s p e c tively. The d i s a p p e a r a n c e o f DQ was m o n i t o r e d a t 405nm i n a s o l u t i o n of s u l f o n y l c h l o r i d e diazonaphthoquinone. To o b s e r v e t h e e f f e c t o f p y r e n e on t h e d i s a p p e a r a n c e o f t h e DQ d e r i v a t i v e i n t h e s o l i d f i l m , s a m p l e s were s p i n c o a t e d on q u a r t z p l a t e s , p r e b a k e d a t 8 5 ° c f o r 30 m i n u t e s , and t h e n i r r a d i a t e d w i t h a 250W Hg lamp w i t h a 313nm i n t e r f e r e n c e f i l t e r u n d e r air. The d i s a p p e a r a n c e o f t h e DQ d e r i v a t i v e was a g a i n m o n i t o r e d a t 405nm by UV s p e c t r o s c o p y . L i f e t i m e of P y r e n e . The l i f e t i m e o f s i n g l e t p y r e n e was measured i n n - p r o p a n o l w i t h and w i t h o u t t h e a d d i t i o n o f DQ. The p y r e n e was e x c i t e d by a n a n o s e c o n d d e u t e r i u m l a m p . The e m i s s i o n o f s i n g l e t p y r e n e was m o n i t o r e d a t 420nm w i t h a s i n g l e photon counter. The l i f e t i m e was c a l c u l a t e d by e m p l o y i n g t h e method o f l e a s t - s q u a r e f i t t i n g to the d a t a .

Davidson; Polymers in Electronics ACS Symposium Series; American Chemical Society: Washington, DC, 1984.


4.

BABIE ETA L .

Diazoquinone

Positive

43

Photoresists

Lithographie Studies. S i l i c o n w a f e r s w i t h c a . 0.5ym SiO« were c o a t e d w i t h t h e r e s i s t m a t e r i a l s t o a t h i c k n e s s o f l . l u m aria t h e n p r e b a k e d a t 85°C f o r 30 m i n u t e s . A P e r k i n - E l m e r UV-3 exposure tool equipped with a UBK-7 filter was employed in this lithographic study. The o u t p u t o f t h e t o o l shows m a j o r e m i s s i o n p e a k s a t 2 9 5 , 3 1 3 , and 334nm w i t h 313nm b e i n g t h e d o m i n a n t wavelength. The s a m p l e s were e x p o s e d f o r 9 s e c o n d s u s i n g a 1mm s l i t w i d t h , a p e r t u r e 1, and a s c a n s p e e d o f 7 2 0 . The w a f e r s were d e v e l o p e d w i t h AZ2401(3) d e v e l o p e r d i l u t e d w i t h d e i o n i z e d w a t e r to a composition of 1:3.5 AZ2401/H O at 24.0°C. SEM m i c r o g r a p h s were o b t a i n e d o f the developed images and l i n e measurement d a t a was t a k e n . A t w o - l a y e r s y s t e m was a l s o s t u d i e d e m p l o y i n g a l a y e r o f t h e u n s e n s i t i z e d PAC as t h e b o t t o m l a y e r and t h e s e n s i t i z e d PAC on top. The b o t t o m l a y e r was s p i n c o a t e d a t 4000 rpm f o r 30 s e c o n d s and p r e b a k e d a t 85°C f o r 30 m i n u t e s . T h i s m a t e r i a l was t h e n b l a n k e t e x p o s e d w i t h c a . 60mJ a t 313nm. T h i s l a y e r was t h e n c o v e r e d w i t h t h e s e n s i t i z e d PAC a t a s p i n s p e e d o f 4300 rpm and t h e n a g a i n p r e b a k e d a t 85°C f o r 30 m i n u t e s . The w a f e r s were t h e n imaged on a U V - 3 e x p o s u r e t o o l t h r o u g h a UBK-7 f i l t e r e m p l o y i n g a 1mm s l i t w i d t h , a p e r t u r e 1 and a s c a n s p e e d o f 7 2 0 . These w a f e r s were s u b s e q u e n t l y d e v e l o p e d u s i n g t h e same d e v e l o p e r and c o n ditions described previously. For the topology study, i d e n t i c a l exposure and d e v e l o p m e n t conditions were employed w i t h the e x c e p t i o n o f a s c a n s p e e d o f 600 i n p l a c e o f 7 2 0 . 2

R e s u l t s and D i s c u s s i o n s Photochemical Studies. The scheme b e l o w o u t l i n e s t h e mechanism o f e n e r g y t r a n s f e r f r o m p y r e n e (P) t o t h e d i a z o n a p h t h o q u i n o n e d e r i v a t i v e (DQ) and i t s s u b s e q u e n t c o n v e r s i o n t o t h e a l k a l i n e soluble product.

COOH

S0 R 3

Where R i s an a r y l

substituent



44


E l e c t r o n i c e n e r g y t r a n s f e r c a n t a k e p l a c e by two m e c h a n i s m s : exchange i n t e r a c t i o n and d i p o l e - d i p o l e interaction. Exchange i n t e r a c t i o n r e q u i r e s a c o l l i s i o n between a d o n o r (D) and a c c e p t o r (A) and d i m i n i s h e s as an e x p o n e n t i a l f u n c t i o n o f t h e d i s t a n c e b e t w e e n D and A . D i p o l e - d i p o l e i n t e r a c t i o n can operate over a g r e a t e r d i s t a n c e and d e c r e a s e s as a r e c i p r o c a l f u n c t i o n o f t h e distance. Because of the d i f f e r e n t f u n c t i o n s of the d i s t a n c e between D and A , e l e c t r o n i c e n e r g y t r a n s f e r c a n be e x p e c t e d t o be conducted m a i n l y v i a d i p o l e - d i p o l e i n t e r a c t i o n i n a d i f f u s i o n r e s t r i c t e d medium, s o l i d p h a s e . A q u a l i t a t i v e e x p r e s s i o n f o r the rate constant (k) of dipole-dipole i n t e r a c t i o n i s shown i n E q u a t i o n 1: k

Œ

Φ ε D A η

Α

(1)

where Φ and a r e t h e quantum y i e l d o f d o n o r e m i s s i o n and t h e e x t i n c t i o n c o e f f i c i e n t o f t h e a c c e p t o r i n t h e r e g i o n where the donor e m i t s . Because of the h i g h ε of pyrene i n the mid-UV r e g i o n , a s m a l l q u a n t i t y of pyrene can absorb s u f f i c i e n t energy in this region. The e n e r g y transfer from pyrene to the d i a z o n a p h t h o q u i n o n e i s f e a s i b l e i n the s o l i d phase because o f the s i g n i f i c a n t o v e r l a p between t h e e m i s s i o n s p e c t r a o f p y r e n e and the diazonaphthoquinone d e r i v a t i v e a b s o r p t i o n . The UV s p e c t r a o f t h e d i a z o n a p h t h o q u i n o n e d e r i v a t i v e (DQ) and t h e p y r e n e s e n s i t i z e d DQ d e r i v a t i v e (PDQ) a r e shown i n F i g u r e 1. G e n e r a l l y , t h e d i a z o n a p h t h o q u i n o n e d e r i v a t i v e c o n s i s t s o f DQ and o t h e r a r o m a t i c p o r t i o n s w h i c h a r e c o n n e c t e d by s u l f o n y l e s t e r linkages. In order to avoid the i n t e r f e r e n c e of the aromatic p o r t i o n on t h e e n e r g y t r a n s f e r f r o m p y r e n e t o DQ i n l i q u i d s o l u t i o n s , a s u l f o n y l c h l o r i d e d i a z o n a p h t h o q u i n o n e was u s e d i n the study i n n - p r o p a n o l . I n t h e a b s e n c e o f s u l f o n y l c h l o r i d e DQ, t h e l i f e t i m e o f p y r e n e i n n - p r o p a n o ^ was measured^ t o be 280 ns.(4) In the presence of 6x10 M and 3x10 M s u l f o n y l c h l o r i d e DQ, t h e l i f e t i m e s o f p y r e n e w e r e 155ns and 107ns r e s p e c tively. The t o t a l q u e n c h i n g r a t e c o n s t a n t o f ^ u ^ f o i r y l c h l o r i d e DQ _was calculated to be ca. 3 x l 0 ~ M~ s " . When 3x10 s u l f o n y l c h l o r i d e DQ i n p r o p a n o l was i r r a d i a t e d at 313nm, t h e d i s a p p e a r a n c e o f s u l f o n y l c h l o r i d e DQ was 42% and 57% i n t h e a b s e n c e and p r e s e n c e of 2x10 M p y r e n e respectively. From t h e d i s a p p e a r a n c e o f s u l f o n y l c h l o r i d e DQ, t h e r a t e ^ g o n ç t a n t of energy t r a n s f e r was estimated to be ca. 2x10 M s O v e r a l l , t h e e f f i c i e n c y o f e n e r g y t r a n s f e r i s a p p r o x i m a t e l y 70% o f t^ig t o t a j . q u e n c h i n g p r o c e s s w i t h a q u e n c h i n g r a t e c o n s t a n t o f 3x10 M~ s~ . The d a t a i s s u m m a r i z e d i n T a b l e I . P A C - p y r e n e was u s e d f o r t h e s t u d y o f t h e e f f e c t o f p y r e n e on t h e c o n v e r s i o n o f DQ. When t h e f i l m was i r r a d i a t e d a t w a v e l e n g t h s where t h e p y r e n e does n o t a b s o r b (>360nm), t h e d i s a p p e a r ance o f DQ was n o t a f f e c t e d by p y r e n e . T h i s o b s e r v a t i o n demon-



4.

BABIE ET A L .

Diazoquinone

Positive

45

Photoresists

Figure 1 A b s o r b a n c e s p e c t r a o f DQ and PDQ. DQ i s r e p r e s e n t e d by d a s h e d l i n e s , PDQ by s o l i d Wavelength (nm)

line.


46


s t r a t e s t h a t p y r e n e does n o t a l t e r t h e p h o t o r e a c t i o n o f DQ. When t h e f i l m was i r r a d i a t e d a t 313nm, p y r e n e i n c r e a s e s t h e c o n v e r s i o n o f DQ by 21% and 31% i n f i l m s w i t h t h i c k n e s s e s o f 1.3um and 0.9ym respectively. The d a t a i s summarized i n T a b l e I I . I n summary, the a d d i t i o n of pyrene' i n c r e a s e s t h e c o n v e r s i o n o f DQ and improvement o f p h o t o l i t h o g r a p h i c p e r f o r m a n c e c a n be e x p e c t e d .


Table I .

C o n v e r s i o n s o f s u l f o n y l c h l o r i d e DQ as a f u n c t i o n o f pyrene i n n - p r o p a n o l . The s o l u t i o n was i r r a d i a t e d w i t h 313nm. O p t i c a l p a t h l e n g t h was c a . 3 mm.

S u l f o n y l C h l o r i d e DQ t=o

[ P y r e n e ]1

42%

0

3xlO" M 4

Conversion of S u l f o n y l C h l o r i d e DQ

2xlO" M

57%

0

56%

4

lxlO~ M

64%

7xlO" M

4

5

Table I I .

C o n v e r s i o n s o f DQ as a F u n c t i o n o f P y r e n e i n P A C - p y r e n e I r r a d i a t e d a t 313nm

C o n v e r s i o n o f PAC Relative Sensitivity

PAC

PAC PYRENE

PAC

PAC PYRENE

28%

34%

32%

42%

1

1.23

1

1.33

0.45

0.80

0.30

0.50

313nm D t=o Thickness

1.3ym

0 . 9ym


4.

BABIE ET A L .

Diazoquinone

47

Positive Photoresists


Lithographie Studies. W a f e r s c o a t e d w i t h PAC and P A C - p y r e n e were d e v e l o p e d i n 1 : 3 . 5 AZ2401 d e v e l o p e r a t 2 4 . 0 ° C a f t e r e x p o s u r e o n the P e r k i n - E l m e r UV-3 t o o l . T h e s e r e s u l t s a r e summarized i n Table I I I . P A C - p y r e n e c a n p r o v i d e a s i d e w a l l a n g l e o f 6 5 ° and a n e x p o s e d / u n e x p o s e d d i s s o l u t i o n r a t e r a t i o ( R / R o ) o f 10 w i t h 1.5um line/space geometries. I n comparison, PAC p r o v i d e s sidewall a n g l e s o f 4 6 ° and R / R o = 2 a t t h e same g e o m e t r i e s . SEM m i c r o g r a p h s a r e shown i n F i g u r e 2 .

Table I I I .

Summary o f L i t h o g r a p h i c

Results

Deve lop Time

Δ ThickSideness a t wall 1.5mm L / S A n g l e (R/Ro)

Dose o f Bottom Coating

Expose Time

Scan Speed

Aper ture

PAC

10"

720

1

130"

50% ( 2 )

46°

-

PACPyrene

10"

720

1

580"

10% ( 1 0 )

65°

-

PACPyrene

10"

720

1

240"

7% ( 1 5 )

70°

50mJ

Resist

PAC

B e c a u s e o f t h e p h o t o n d i f f r a c t i o n s t a n d i n g waves i n p r o j e c t i o n p r i n t i n g and t h e i n h e r e n t a b s o r p t i o n o f t h e p h o t o r e s i s t , t h e a v a i l a b l e energy i s n o t homogeneously d i s t r i b u t e d i n t h e r e s i s t . A q u a l i t a t i v e p i c t u r e o f a lpm t h i c k r e s i s t w i t h an o p t i c a l d e n s i t y (OD) o f 0 . 5 i s i l l u s t r a t e d i n F i g u r e 3 a - d . From t h i s f i g u r e , i t i s shown t h a t t h e r e i s j u s t 32% o f t h e i n c i d e n t d o s e a v a i l a b l e f o r a b s o r p t i o n a t the bottom o f the r e s i s t l a y e r . From t h i s , i t c a n be s e e n t h a t a s u r f a c e image i s e a s i e r t o o b t a i n than t o achieve a completely developed one. I n order t o develop t h e d e s i r e d i m a g e , t h e s i d e w a l l a n g l e and t h e c o n t r a s t w i l l be d e c r e a s e d s i g n i f i c a n t l y a s shown i n F i g u r e 3 c . F o r e x a m p l e , l e t u s assume t h a t b e f o r e t h e image i s d e v e l oped t o t h e s o l i d l i n e i n F i g u r e 3 c , s u d d e n l y t h e d i s s o l u t i o n rate increases a n i s o t r o p i c a l l y normal t o t h e surface plane. I n s t e a d o f t h e shape o b t a i n e d b y t h e d o t t e d l i n e i n F i g u r e 3 c , t h e image c a n be d e v e l o p e d t o t h e shape shown b y t h e d o t t e d l i n e i n F i g u r e 3 d . O v e r a l l , i t i s p r e d i c t e d that by i n c r e a s i n g t h e d i s s o l u t i o n r a t e i n t h e v e r t i c a l d i r e c t i o n , t h e c o n t r a s t and s i d e w a l l a n g l e o f t h e image c a n be i n c r e a s e d s i g n i f i c a n t l y .

American Chemical Society Library 1155 16th St. N. W. Davidson; Polymers Washington, 0. C.in Electronics 20036

ACS Symposium Series; American Chemical Society: Washington, DC, 1984.


48


Figure 2 L i t h o g r a p h i c S t u d y C o n t r o l s o f 1.5ym L i n e / 1 . 5 y m Space

0.00 μΠΙ 0.25

μΠΊ

Depth 0.50

μΠΙ

0.75 μπν 1.00

μΠΊ—

(b) Sample showing absorbed dose at various depths in the film.

(a) Sample during irradiation

3

0.75

η

μητι-

1.00 μνη—ί (c) Actual dimensions of developed image

(d) Desired dimensions of developed image

Figure 3 S i n g l e l.Oym C o a t i n g o f PAC D i s p l a y i n g A v a i l a b l e Dose as a F u n c t i o n o f D e p t h i n t o t h e F i l m



4.

BABIE ET A L .

Diazoquinone

Positive

Photoresists

49

To a c c o m p l i s h t h i s sudden change i n d i s s o l u t i o n r a t e d u r i n g d e v e l o p m e n t o f t h e i m a g e , a two l a y e r s y s t e m was e m p l o y e d , t h e top r e s i s t l a y e r h a v i n g a slower d i s s o l u t i o n r a t e than the bottom layer. From T a b l e I I I , i t i s shown t h a t t h e PAC h a s a f a s t e r d i s s o l u t i o n r a t e t h a n i t s s e n s i t i z e d c o u n t e r p a r t and t h a t b o t h r e s i s t s a r e s o l u b l e i n t h e same d e v e l o p e r . To t e s t o u r h y p o t h e s i s , we employed t h e s e n s i t i z e d PAC as t h e t o p l a y e r and t h e u n s e n s i t i z e d PAC as t h e b o t t o m o n e . N a t u r a l l y , when t h e s e n s i t i z e d PAC i s s p i n c o a t e d on t o p o f t h e e x i s t i n g P A C , t h e r e w i l l n o t be a s h a r p s e p a r a t i o n between t h e two l a y e r s . In f a c t , there i s a c o n c e n t r a t i o n g r a d i e n t o f p y r e n e w i t h t h e h i g h e s t and l o w e s t c o n c e n t r a t i o n b e i n g i n t h e t o p and b o t t o m l a y e r s r e s p e c t i v e l y . A l s o , the d i s s o l u t i o n r a t e of the double coated system w i l l i n c r e a s e g r a d u a l l y as t h e c o n c e n t r a t i o n o f t h e p y r e n e d e c r e a s e s as the d e v e l o p e r p e n e t r a t e s deeper i n t o the f i l m . In order to h a v e t h e d i s s o l u t i o n r a t e change d r a m a t i c a l l y , t h e b o t t o m c o a t i n g was p r e - e x p o s e d b e f o r e t h e s e n s i t i z e d m a t e r i a l was c o a t e d over the top of the e x i s t i n g m a t e r i a l . W a f e r s c o a t e d w i t h t h e s e n s i t i z e d PAC o v e r t h e u n s e n s i t i z e d PAC were e x p o s e d on a U V - 3 t o o l e m p l o y i n g a U B K - 7 f i l t e r . These r e s u l t s a r e s u m m a r i z e d i n T a b l e I I I and F i g u r e s 4 a - c . These r e s u l t s a r e c o m p l e t e l y c o n s i s t e n t w i t h o u r p r e d i c t i o n s ; compared w i t h s i n g l e c o a t i n g , t h e d e v e l o p m e n t t i m e i s r e d u c e d by a p p r o x i m a t e l y 50%. A l s o , s i d e w a l l a n g l e i s i n c r e a s e d f r o m 65° t o 70° and t h e d i s s o l u t i o n r a t e r a t i o R / R o i s i n c r e a s e d f r o m 10 t o 1 5 . Furthermore, the b l a n k e t pre-exposure of the bottom u n s e n s i t i z e d l a y e r c a n be o m i t t e d by i r r a d i a t i o n o f t h i s m a t e r i a l i n s o l u t i o n b e f o r e c o a t i n g o r by p r e b a k i n g a t a h i g h e r t e m p e r a t u r e t o i n crease t h e d i s s o l u t i o n r a t e by thermal degradation of the p h o t o a c t i v e compound. The l a t t e r p r o c e s s may a c t u a l l y i m p r o v e a d h e s i o n o f t h e u n s e n s i t i z e d DQ t o t h e s u b s t r a t e . ( 5 ) When a d o u b l e l a y e r s y s t e m i s e m p l o y e d , t h e u n i f o r m i t y o f t h e f i l m s may be i n q u e s t i o n . To t e s t t h e u n i f o r m i t y o f t h i s s y s t e m , t h e l i n e w i d t h t o l e r a n c e o f t h e image was m e a s u r e d . This t o l e r a n c e d a t a i s s u m m a r i z e d i n T a b l e I V . The d a t a r e p r e s e n t s 15 s e t s o f images f r o m t h r e e w a f e r s d e v e l o p e d s i m u l t a n e o u s l y . This i n c l u d e s f i v e s e t s from each wafer w i t h each s e t c o n s i s t i n g of f o u r g e o m e t r i e s , 2 . 0 u m , 1.75ym, 1.50pm and 1.25ym. A l l of the t o l e r a n c e s e x c l u d i n g t h o s e o f t h e 1.25pm image a r e w i t h i n t h e e r r o r of the d i m e n s i o n a l measurements. This tolerance test demonstrates t h a t the double c o a t i n g can p r o v i d e satisfactory f i l m u n i f o r m i t y i n terms of l i t h o g r a p h i c p e r f o r m a n c e . A l s o , the a v e r a g e u n i f o r m i t y o f t h e f i l m t h i c k n e s s was b e t t e r f o r the double l a y e r system than f o r the u n i f o r m i t y of the s i n g l e s e n s i t i z e d o r u n s e n s i t i z e d DQ l a y e r as m e a s u r e d o n a f i l m t h i c k n e s s a n a l y z e r ( F T A ) . R e s u l t s a r e shown i n T a b l e V .



P O L Y M E R S IN ELECTRONICS

Figure 4 D o u b l e C o a t i n g E m p l o y i n g PAC/Pyrene Over a L a y e r o f PAC. 1.5ym L i n e / S p a c e A r r a y s


4.

BABIE E T A L .

Table I V .

Diazoquinone

T o l e r a n c e of

Mask Geometry

Positive

Geometries

M e a s u r e d w a f e r g e o m e t r y (The d a t a p r e s e n t s 15 s e t s o f g e o m e t r i e s f r o m 3 w a f e r s d e v e l o p e d s i m u l t a n e o u s l y . Measurement was done by SEM.) Double Coating PAC/Pyrene-PAC

Single Coating PAC/Pyrene Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 16, 2016 | http://pubs.acs.org Publication Date: March 15, 1984 | doi: 10.1021/bk-1984-0242.ch004

51

Photoresists

Line

Space

Line

Space

Line

Space

1.43 1.63 1.94 2.19

0.9010.03 1.14±0.04 1.38±0.04 1.63±0.05

1.5±0.2 1.6210.06 1.9410.07 2.210.1

1.2±0.2 1.4510.09 1.7010.07 1.910.1

1.410.1 1.7010.07 1.9410.06 2.2110.05

l.HO.l 1.3610.07 1.6210.06 1.8810.03

Table V.

U n i f o r m i t y of F i l m T h i c k n e s s Percentage of Wafer 1

PAC Pyrene

Variation

Wafer 2

Wafer 3

Average

12.3%

12.4%

9.9%

PAC

5.1%

Single Coating

12%

3.2%

12.2%

9.1%

Double Coating

7.8%

9.9%

4.6%

7.4%

Another concern i s the problem of l i t h o g r a p h i c r e s o l u t i o n over topology. I t i s r e q u i r e d t h a t t h e l i n e and s p a c e w i d t h d i m e n s i o n s be c o n s t a n t when c o a t i n g a r e s i s t m a t e r i a l over topologies. The d o u b l e c o a t i n g s y s t e m employed was s p i n c o a t e d on a 0.5pm d e p t h t o p o l o g y w a f e r t o y i e l d a f i n a l t h i c k n e s s o f 1.2pm. S c a n n i n g e l e c t r o n m i c r o g r a p h s o f t h e 2.0pm l i n e / 1 . 5 p m s p a c e and 1.5pm l i n e / 1 . 0 p m s p a c e g e o m e t r i e s a r e shown i n F i g u r e s 5a-d. The l i n e w i d t h o v e r t h e t o p o l o g y r e m a i n e d c o n s t a n t i n t h e 2.0pm and 1.5pm g e o m e t r i e s . These r e s u l t s demonstrate t h a t t h e r e



52


Figure 5 D o u b l e L a y e r PAC/Pyrene Over PAC C o a t i n g s , S p i n C o a t e d Over 0.5ym T o p o l o g y


4. BABIE ET AL. Diazoquinone Positive Photoresists

53

is no problem of lithographic resolution over a 0.5pm depth of topology.


Conclusions PAC-pyrene has shown a significant lithographic improvement over PAC. Further formulation and process study is required to optimize the lithographic performance of this system. This system also demonstrates that the concept of energy transfer can enhance lithographic sensitivity significantly. Energy transfer is not limited by the particular donor (pyrene) and acceptor. The active energy acceptor can be as general as α-diazoketone, and pyrene can enhance the sensitivity of any photoresist in which an α-diazoketone is used as a photoactive compound, such as AZ resists.(3) Also, pyrene is but one example of a singlet sensitizer. Compounds which exhibit photophysical properties similar to pyrene can also be potential candidates for energy transfer in photoresists. Acknowle dgment s The authors would like to thank F. P. Hood and J. M. Yang of IBM East Fishkill for their critical review and comments. We would also like to thank Karen J. Kline, Angela M. Marcano and Debra J. Perez for their patience in helping prepare this manuscript. Literature Cited 1. King, M. C., IEEE Trans. Elect. Devices 1979, 26, 711. 2. Murov, S., "Handbook of Photochemistry"; Marcel Dekker, New York, 1973. 3. Trademark of American Hoechst, Summit, NJ. 4. The lifetime of singlet pyrene was measured by single photon counting. 5. Horst, R.; Kaplan, L . ; Merritt, D., U.S. Patent 3 873 813, 1977. RECEIVED September

15, 1983


Mid-UV Photosensitization of Diazoquinone Positive Photoresists

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