A Silicon-Containing Positive Photoresist Developable with Aqueous

Chapter 18

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 20, 2017 | http://pubs.acs.org Publication Date: August 26, 1987 | doi: 10.1021/bk-1987-0346.ch018

A Silicon-Containing Positive Photoresist Developable with Aqueous Alkaline Solution N. Hayashi, T. Ueno, H. Shiraishi, T. Nishida, M. Toriumi, and S. Nonogaki Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo 185, Japan Mixtures of silicon compounds and a commercially available positive photoresist (OFPR-800, Tokyo Ohka Kogyo Co.) have been evaluated as a top imaging layer for a two-layer photolithographic system. We have found that a low-molecular-weight polypheny1silsesquioxane (PSQ) is compatible with OFPR-800 and that cis-(1,3,5,7-tetrahydroxy)- 1,3,5,7- tetraphenyl cyclotetrasiloxane (phenyl-T4(OH)4) is soluble in an aqueous alkaline solution. Taking advantage of these properties, we have been able to come up with a photoresist (ASTRO) formulated from PSQ, phenyl-T4(OH) and OFPR-800 which is developable with an alkaline solution and resistant to O2-RIE. Good quality patterns of 1um line and space have been obtained as a result of a sequence starting with exposure (at 436 nm) followed by development of the top imaging layer with an aqueous alkaline solution and transferring the image by means of O2-RIE to the bottom organic polymer layer. 4

Multi-level systemsO) allow the planarization of substrate topography formation of high aspect ratio patterns, and better resolution than single level resists. There is a drawback to such systems, however, and that is additional process complexity. To reduce this complexity, two-level resist systems have been reported(2). The top imaging layer in two-level resist systems must exibit Op-RIE resistance as well as desirable lithographic characteristics. We previously reported that iodine containing compounds are resistant to oxygen plasma etching, and proposed two-level resist systems utilizing a mixture of iodine compounds and a commercially available positive photoresist(3). However, this resist has low resistance to O^-RIE. Silicon compounds are well known as O^-RIE resistant materials. 0097-6156/87/0346-0211$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

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This property has been w i d e l y utilized, and many k i n d s of s i l i c o n - c o n t a i n i n g r e s i s t s have been r e p o r t e d as a r e s u l t . Most o f the new r e s i s t s developed use s i l i c o n c o n t a i n i n g n o v o l a c r e s i n s w i t h a sensitizer(4)(5). We have developed a s i l i c o n containing positive photoresist i n t h e same manner t h a t we developed an iodine containing r e s i s t previously. I n o t h e r words, s i l i c o n compounds a r e blended i n t o a conventional p o s i t i v e photoresist.

Experimental Materials As a p o s i t i v e w o r k i n g p h o t o r e s i s t , novolac-naphthoquinonediazide type resist, OFPR-800(Tokyo Ohka Kogyo Co.) was used. P o l y p h e n y l s i l s e s q u i o x a n e (PSQ) was o b t a i n e d under t h e name o f G l a s s Resin GR-950 from Owens-Illinois Co. Cis-(1,3,5,7tetrahydroxy)-1 3,5,7-tetraphenyl cyclotetrasiloxane (phenylΤ^(ΟΗΚ) was prepared by t h e f o l l o w i n g p r o c e d u r e r e p o r t e d by Brown(S): A c o l d mixture o f p h e n y l t r i c h l o r o s i l a n e (196 g) and acetone (360 ml) was added s l o w l y t o an i c e - w a t e r s l u r r y (7100 g) with vigorous s t i r r i n g . A f t e r the e v o l u t i o n o f hydrogen c h l o r i d e d e c r e a s e d , t h e s o l u t i o n was k e p t a t 0°C f o r 2 days. A mixture of crystalline solid and r e s i n o u s m a t t e r which p r e c i p i t a t e d i n t h e s o l u t i o n was f i l t e r e d and a i r - d r i e d t o g i v e 95 g o f s o l i d s . These s o l i d s were s t i r r e d w i t h 200 ml o f carbon d i s u l f i d e i n o r d e r t o d i s s o l v e resinous m a t e r i a l s , cooled t o 0°C, filtered, and washed w i t h c o l d carbon d i s u l f i d e t o g i v e 70 g o f phenyl-T.(OH)^. Trimethylsililated phenols were prepared by lithiation of bromophenols w i t h n - b u t y l lithium f o l l o w e d by reaction with trimethylchlorosilane. Trimethylsilyl-substituted polyvinylphenol was prepared by the same p r o c e d u r e s as d e s c r i b e d above a f t e r bromination of polyvinylphenol. The other silicon compounds d e s c r i b e d i n T a b l e 1 were o b t a i n e d from S h i n - e t s u C h e m i c a l Co. and Toray S i l i c o n e Co.. C o n t e n t s o f s i l i c o n compounds i n new r e s i s t s were p r e s e n t e d by the w e i g h t r a t i o o f a d d i t i v e s as opposed t o d r y polymer w e i g h t c a l c u l a t e d from t h e s o l i d c o n t e n t s o f OFPR-800. f

Characterization of materials I n f r a r e d s p e c t r a o f polymer f i l m s were o b t a i n e d on a H i t a c h i 260-10 Spectrometer. The f i l m s were formed from polymer s o l u t i o n s on NaCl discs. Molecular weight d i s t r i b u t i o n s were measured by gel permeation chromatography (GPC) u s i n g a H i t a c h i 635 Liquid Chromatograph equipped w i t h Shodex A-804, A-802 and A-801 GPC columns. T e t r a h y d r o f u r a n e was used as the m o b i l e phase. Sensitivity To measure the s e n s i t i v i t y , t h e r e s i s t s o l u t i o n was s p i n - c o a t e d onto a hard-baked ( a t 200°C) OFPR-800 r e s i s t l a y e r or a baked ( a t 2 0 0 C ) p o l y i m i d e f i l m (PIQ, H i t a c h i C h e m i c a l Co.). I r r a d i a t i o n was c a r r i e d out u s i n g a h i g h p r e s s u r e mercury-xenon source (600W, Hanovia). C

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

18.

A Silicon-Containing

HAYASHI ET AL.

Positive

Photoresist

213

A f t e r exposure, the r e s i s t f i l m was d i p p e d i n a NMD-3 d e v e l o p e r (tetramethylammonium h y d r o x i d e s o l u t i o n , Tokyo Ohka K o g y o C o . ) , which was d i l u t e d w i t h water t o an a p p r o p r i a t e c o n c e n t r a t i o n . Exposure c h a r a c t e r i s t i c s were o b t a i n e d by p l o t t i n g n o r m a l i z e d f i l m t h i c k n e s s r e m a i n i n g vs exposure t i m e under c o n s t a n t l i g h t i n t e n s i t y . F i l m t h i c k n e s s was measured by A l p h a Step 200. 0 -RIE


2

The Op-RIE r e s i s t a n c e o f each m a t e r i a l was determined u s i n g an I n c . model ΑΜΕ 8181 o r a m o d i f i e d NEVA FP-67A.

R e s u l t s and

ATM

discussion

The new s i l i c o n c o n t a i n i n g p o s i t i v e p h o t o r e s i s t s which c o n s i s t o f s i l i c o n compounds and a commercially a v a i l a b l e p o s i t i v e r e s i s t , OFPR-800, were e v a l u a t e d as t h e t o p imaging l a y e r i n a t w o - l e v e l resist system. We sought s i l i c o n compounds s p e c i f i e d by the following restrictions. 1. M i s c i b l e w i t h OFPR-800 w i t h o u t phase s e p a r a t i o n . 2. D e v e l o p a b l e under t h e same c o n d i t i o n s as t h o s e f o r OFPR-800. 3. W e l l r e s i s t a n t t o 0 - R I E . Many k i n d s o f s i l i c o n compounds and s i l i c o n e polymers were examined as m a t e r i a l s t o be used under t h e s e r e s t r i c t i o n s . The r e s u l t s a r e shown i n T a b l e 1. As seen i n t h e t a b l e , low m o l e c u l a r weight s i l i c o n compounds have good c o m p a t i b i l i t y w i t h OFPR-800. W i t h i n c r e a s i n g t h e m o l e c u l a r w e i g h t , t h e w e i g h t r a t i o o f compound blended w i t h o u t phase s e p a r a t i o n was decreased. However, low m o l e c u l a r weight compounds have poor r e s i s t a n c e t o Op-RIE. We assume t h a t t h i s i s a r e s u l t o f low m o l e c u l a r w e i g h t silicon compounds b e i n g v a p o r i z e d by the heat generated i n the e t c h i n g process. Most o f t h e s i l i c o n e polymers i n Table 1 had good r e s i s t a n c e t o 0 - R I E , but i n c u r r e d phase s e p a r a t i o n a f t e r t h e y blended t o OFPR-800. We found t h a t p o l y s i l s e s q u i o x a n e o l i g o m e r GR-950 was t h e o n l y a v a i l a b l e m a t e r i a l f o r t h e s e p u r p o s e s . We have f u r t h e r examined PSQ and OFPR-800 r e s i s t s w i t h r e s p e c t t o t h e i r compatibility, solubility in aqueous alkaline solution and resistance to 0 -RIE. 2

2

2

Compatibility GR-950 i s a b l e t o mix w i t h OFPR-800 i n an a r b i t r a r y r a t i o . It is a l a d d e r t y p e PSQ o l i g o m e r and i t s s t r u c t u r e i s shown i n F i g . 1 . Another s i l i c o n e r e s i n , L P - 1 0 3 ( S h i n - E t s u Chemical C o . ) , has the same s t r u c t u r e and h i g h e r m o l e c u l a r w e i g h t than GR-950 but i s not m i s c i b l e w i t h OFPR-800. I n o r d e r t o c e r t i f y the f a c t o r s a f f e c t i n g c o m p a t i b i l i t y , IR s p e c t r a were measured. S p e c t r a o f GR-950 and LP-103 a r e shown i n F i g . 2 and F i g . 3 r e s p e c t i v e l y . As can be seen i n F i g . 2 , s t r o n g hydroxy1 bands from s i l a n o l group(Si-OH) a r e observed a t 3350 and 900 cm" . The IR spectrum o f LP-103 i n F i g . 3 , however, has no apparent hydroxy1 band. LP-103 has h i g h e r m o l e c u l a r w e i g h t than GR-950, and t h e r e f o r e t h e hydroxy1 groups i t c o n t a i n e s compared t o o t h e r f u n c t i o n a l groups i n t h e m o l e c u l e i s s m a l l e r t h a n t h a t o f GR-950. The possibility o f whether m o l e c u l a r w e i g h t affected



Compd.

octaphenylcyclotetrasiloxane

hexamethylcyclotrisiloxane

diphenylsilanediol

2,H-bis(trimethylsilyDphenol

m-trimethylsilylphenol

3-(o-hydroxyphenoxyp r o p y l ) t r i m e t h y l s i lane

o-hydroxyphenoxytrimethylsilane

Silicon

Table

1

of S i l i c o n

Compounds.

3

3

3

2

3

Ph

Ph

CH

2

Ph Si(OHy

3

3

(CHî-^-OH Si(CH^)

3

Si(CH )

3

^0(CH2> Si(CH )

3

OSi(CH )

Structure

and

good

good

good

good

good

poor

poor

poor

poor

poor

poor

Resistance to 02-plasma 02-RIE etching

resistance

25 no c o m p a t i b i l i t y in r e s i s t solution

25

25

50

50

50

50

Compatibility ( w e i g h t % per OFPR-800)

Compatibilility in positive photoresist t o 0 2 - p l a s m a e t c h i n g and 0 2 - R I E

Characteristics



trimethylsililatedpolyvinylphenol

(LP-103)

phenylsilsesquioxane (Glass resin GR-950)

methylsilsesquioxane (Glass resin GR-650)

ethylsilicateoligomer

polydimethylsiloxane (Toray-silicone Co. SH-6018)

tetraacetoxysilane

tris-(2-methoxyethoxy) vinylsilane

tet.raethoxysilane

2

3

3

A

n

2

2

n

ψ * Si ( C H ^ OH

4CH -CH-)-

H0fSi-04-H Ph

0

HO Si-0

n

HO^Si-O^H CHo

3

ÇH HO-fSi-OfH 0

OEt

OEt

CH

3

Si(0COCH )

2

A

3

CH =CHSi (OCH CH OCH )

2

Si(OCH CH )

3

separation

separation

insoluble i n alkaline soin.

insoluble i n resist solution

200

50, phase

8, phase

poor

poor

separation

gelation

*»8, phase

50,

50

50



216


Ι 1 Λ

Pfr

Q

Ph

Ph

Ph

0

0

Ph

Ph

I

\

Ph

0

ι

Ph

Fig.1 S t r u c t u r e of polyphenylsilsesquioxane(PSQ).

F i g . 2 IR spectrum o f G l a s s R e s i n GR-950.



18.

HAYASHI ET AL.


Positive

217

Photoresist

c o m p a t i b i l i t y w i t h the p h o t o r e s i s t was examined by e l i m i n a t i n g s i l a n o l groups from GR-950. T e r m i n a l s i l a n o l groups were changed t o trimethylsilyl ether groups through a reaction with t r i m e t h y l c h l o r o s i l a n e and p y r i d i n e (Scheme 1 ) . The IR spectrum o f t r i m e t h y l s i l y l a t e d GR-950 i s shown i n Fj^g.4. As can be seen i n F i g . 4 , h y d r o x y l bands a t 3350 and 900 cm" d i s a p p e a r c o m p l e t e l y by trimethylsilylation. GPC a n a l y s i s shows t h a t m o l e c u l a r weight o f t h i s s i l y l a t e d GR-950 does not change from t h e original. T r i m e t h y l s i l y l a t e d GR-950 was m i s c i b l e w i t h OFPR-800, but phase s e p a r a t i o n o c c u r r e d when the r e s i s t f i l m was formed on a w a f e r . From t h e s e r e s u l t s , i t i s c l e a r t h a t s i l a n o l groups o f PSQ p l a y an i m p o r t a n t r o l e i n e n s u r i n g t h a t PSQ i s miscible with a positive r e s i s t and makes a c l e a r f i l m w i t h o u t phase s e p a r a t i o n . S o l u b i l i t y i n aqueous a l k a l i n e

solution

GR-950 i s not s o l u b l e a l o n e i n t h e aqueous a l k a l i n e s o l u t i o n which i s used as the d e v e l o p e r o f a p o s i t i v e p h o t o r e s i s t . F u r t h e r , we found a d i f f e r e n c e i n t h e d e v e l o p i n g t i m e o f a r e s i s t f i l m when u s i n g the same weight but a d i f f e r e n t l o t o f GR-950. Molecular weight d i s t r i b u t i o n o f t h e s e l o t s a r e shown i n F i g . 5 . The IR spectrum o f t h e s e samples were t h e same. Though l o t A i n F i g . 5 has a h i g h e r average m o l e c u l a r w e i g h t , i t s d e v e l o p i n g time w i t h a l k a l i n e s o l u t i o n i s s h o r t e r than t h e case u s i n g l o t B. Compared w i t h t h e two m o l e c u l a r weight d i s t r i b u t i o n c u r v e s i n F i g . 5 , c u r v e A shows a d i s c e r n i b l e s h o u l d e r a t a m o l e c u l a r weight o f about 500. I t can be presumed t h a t this shoulder is due to the e x i s t e n c e of p h e n y l - T ^ O H ) ^ , t h e s t r u c t u r e o f which i s shown i n F i g . 6 . However, t h i s can not be c o n s i d e r e d c o n c l u s i v e i n d e t e r m i n i n g t h e a c c u r a c y o f GPC a n a l y s i s f o r m o l e c u l a r w e i g h t determination. We t h e r e f o r e p r e p a r e d p h e n y l - T ^ O H ) ^ as a u n i t s t r u c t u r e o f PSQ and c a r r i e d out further examinations. Molecular weight distributions of p h e n y l - T ^ O H ) ^ and GR-950 were shown i n F i g . 7 . As can be seen t h e f i g u r e , t h e s h o u l d e r o f GR-950 d i s t r i b u t i o n c u r v e near m o l e c u l a r weight 500 c o r r e s p o n d s to phenyl-TÔH)^. Furthermore, we have found t h a t p h e n y l - T ^ i O H ) ^ is s o l u b l e i n an aqueous a l k a l i n e solution. The p o s s i b i l i t y o f whether m o l e c u l a r w e i g h t a f f e c t e d t h e s o l u b i l i t y i n the aqueous a l k a l i n e s o l u t i o n was examined through p r e p a r i n g p h e n y l - T ^ ( 0 H ) ( 7 ) . Two p h e n y l groups were s u b s t i t u t e d f o r the two h y d r o x y l groups o f phenyl-T^COH)^. Phenyl-T (OH> was i n s o l u b l e i n an a l k a l i n e s o l u t i o n . I t appears t h a t phenyl-T.(OH), has a d e s i r a b l e p r o p o r t i o n among s i l i c o n , p h e n y l group and h y a r o x y l group i n terms o f s o l u b i l i t y in alkaline solution. From t h e m o l e c u l a r weight d i s t r i b u t i o n o f GR-950 i n F i g . 5 , p h e n y l - T ^ O H ) ^ i s e v a l u a t e d t o comprise about 5 % GR-950. We assume t h a t t h e d i f f e r e n t b e h a v i o r s i n development among some l o t s o f GR-950 a r e caused by the d i f f e r n t r a t i o s o f phenyl-T.(OH), they c o n t a i n among them. The r a t i o o f phenyl-T.(OH)^ c o n t a i n e d i s s i g n i f i c a n t f a c t o r i n t h e s o l u b i l i t y i n aqueous a l k a l i n e s o l u t i o n . 2

2|

2

0 -RIE behavior 2

The e t c h i n g r a t e s as a f u n c t i o n o f m i x i n g r a t i o w i t h GR-950 t o OFPR-800 exposed t o an oxygen RF d i s c h a r g e are examined. Curves o b t a i n e d by p l o t t i n g f i l m t h i c k n e s s o f r e l i e f image as a f u n c t i o n o f




4000

3000

2000 1500 WAVENUMBERtcm" )

1000

1

F i g . 3 IR spectrum o f S i l i c o n e R e s i n LP-103

ι

ι

0 (-0-Si-ÔH

+ ClSiMe

0

pyridine

(-O-Si-fcO-SiMeI η J

3

Ph

Ph Scheme I .

4000

3000

2000 1500 WAVE NUMBER (cnr )

1000

1

F i g . 4 IR spectrum o f t r i m e t h y l s i l i l a t e d GR-950.


18.


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Positive

219

Photoresist


Lot No.

MOLECULAR WEIGHT F i g . 5 G e l permeation chromatogram A(#52509-0) and B(#52538)

Ph

o f GR-950.

U

Si /

0 \

Difference of l o t :

Ph *>0H Si \

0 /

\ ' 's>OH Ph

HO * Ph

Fig.6 Structure of cis-(1,3,5,7-tetrahydroxy)cyclotetrasiloxane. (Phenyl-T (0H) ). J |

Α. Λ

1,3,5,7-tetraphenyl

2 i

—

GR 950

—

Phenyl-T (0H) A

A

if V

i I

\

In

\

It

\

11

1

1 1 J1 1 killl^.J.-jSÎ l ill 2

10

3

A

10 10 MOLECULAR WEIGHT

1 __L 1 1 1 1 1 1 K) !

F i g . 7 G e l permeation chromatograph o f GR-950 and p h e n y l - T . ( O H )



220

the e t c h i n g time a r e shown i n F i g . 8 . I n t h i s c a s e , 0 - R I E was performed by a m o d i f i e d NEVA FP-67A. RIE c o n d i t i o n s were as follows: Oxygen p r e s s u r e was 2 m t o r r and RF s u p p l y was 100 W. Curves o b t a i n e d by p l o t t i n g t h e decrease o f f i l m t h i c k n e s s a f t e r 40 min exposure t o O^-RIE as a f u n c t i o n o f w e i g h t r a t i o o f GR-950 blended OFPR-800 a r e shown i n F i g . 9 . The oxygen e t c h i n g r a t e s o f the r e s i s t f i l m a r e markedly dependent upon t h e r a t i o o f GR-950 i t contain. With i n c r e a s i n g GR-950, f i l m thickness loss rate decreased. The a d d i t i o n o f phenyl-T^COH)^ makes no d i f f e r e n c e t o the case i n which GR-950 i s added. As seen i n F i g . 8 , t h e r e s i s t f i l m i n which OFPR-800 and GR-950 a r e mixed i n a r a t i o o f 2 t o 1 (GR-950, 33 %) i s 7 t i m e s as r e s i s t a n t t o 0 - R I E as t h e p a r e n t hard-baked OFPR-800 f i l m under t h e same c o n d i t i o n s . C o n s i d e r i n g t h e p r o c e s s c o n d i t i o n s f o r 0 - R I E , t h e r a t i o o f OFPR-800 t o PSQ f o r a p o s i t i v e r e s i s t should be l e s s than 2 t o 1.


2

2

2

S e n s i t i v i t y c h a r a c t e r i s t i c s and 0 - R I E t r a n s f e r o f p a t t e r n 2

The p h o t o r e s i s t which c o n t a i n e s PSQ and a c o n v e n t i o n a l p o s i t i v e p h o t o r e s i s t i s named ASTRO ( A l k a l i n e d e v e l o p a b l e S i l i c o n c o n t a i n i n g Top R e s i s t w i t h Oxygen RIE r e s i s t a n c e ) . As d e s c r i b e d b e f o r e , t h e use o f GR-950 a l o n e c o u l d n o t be developed under t h e same c o n d i t i o n s f o r the parent p o s i t i v e p h o t o r e s i s t . U s i n g phenyl-T.(OH)^ i n p l a c e o f GR-950, development o f t h e exposed area c o u l d be done very e a s i l y . P h e n y l - T ^ i O H ) ^ i s very s o l u b l e i n an a l k a l i n e s o l u t i o n , b u t the f i l m t h i c k n e s s o f t h e unexposed area becomes t h i n n e r a f t e r development. We examined t h e p o s s i b i l i t y o f u s i n g GR-950 and phenyl-T.(OH), t o g e t h e r . I n these examinations, we found t h a t t h e ASTRO which c o n s i s t e d o f OFPR-800, 45 % GR-950, and 30 % p h e n y l - T ^ O H ) . by w e i g h t , as opposed t o t h e s o l i d c o n t e n t s o f OFPR-800, had s i m i l a r s e n s i t i v i t y c h a r a c t e r i s t i c s t o t h o s e o f OFPR-800. This composition i s c a l l e d ASTRO-7530. Sensitivity c h a r a c t e r i s t i c s o f ASTRO-7530 and OFPR-800 a r e shown i n F i g . 1 0 . Development c o n d i t i o n s f o r OFPR-800 were 24 sec d i p p i n g i n a 2.38 % s o l u t i o n o f NMD-3 and 27 s e c d i p p i n g i n a 2.5 % s o l u t i o n o f NMD-3 f o r ASTRO-7530. As shown i n F i g . 1 0 , c o n t r a s t and r e m a i n i n g f i l m t h i c k n e s s o f t h e unexposed a r e a o f ASTRO-7530 were s l i g h t l y i n f e r i o r t o those o f OFPR-800. I n p r a c t i c e , however, o n l y ASTRO-7530 c a n be used t h e same way as a c o n v e n t i o n a l p o s i t i v e p h o t o r e s i s t . A p r e f e r r e d b i - l a y e r p r o c e s s employing RIE t r a n s f e r o f a p a t t e r n i n ASTRO-7530 as a t o p l a y e r used 200°C-baked PIQ as t h e planarizing layer. R o u t i n e exposure and development o f t h e t o p l a y e r , f o l l o w e d by Op-RIE, t r a n s f e r r e d t h e p a t t e r n t o t h e s u b s t r a t e . Figure 11 shows t n e r e s u l t i n g nominal 1 pm l i n e s and spaces obtained. I t i s c l e a r t h a t ASTRO-7530 can a c t as an e t c h i n g mask and t h a t f i n e p a t t e r n s t r a n s f e r t o t h e bottom PIQ l a y e r . In this c a s e , exposure was c a r r i e d o u t by a r e d u c t i o n a l i g n e r H i t a c h i RA-101L(at 436 nm). 0 - R I E was performed by a m o d i f i e d s p u t t e r i n g machine NEVA FP-67A and RIE c o n d i t i o n s were oxygen p r e s s u r e o f 2 m t o r r , RF s u p p l y o f 300 W and e t c h i n g t i m e o f 12 min. 2

Conclusion Mixtures o f ladder type s i l i c o n

compounds

PSQ and a

commercially



18.

HAYASHI ET A L .


O2-RIE

time

Positive

Photoresist

221

(min)

Fig.8 Plot of the f i l m thickness loss vs O--RIE time. 6ΟΟ1

Containing

r a t i o of G R - 9 5 0 in

OFPR-800

Fig.9 Plot of the f i l m thickness loss after 40 min O^-RIE vs containing r a t i o of GR-950 i n OFPR-800(by weight).




222

EXPOSURE TIME(s) F i g . 1 0 S e n s i t i v i t y c h a r a c t e r i s t i c s o f ASTRO-7530 and OFPR-800.

Fig.11 SEM m i c r o g r a p h o f 1 pm l i n e s and spaces i n ASTRO-7530 as a top i m a g i n g l a y e r a f t e r 0 -RIE pattern t r a n s f e r i n t o the PIQ bottom l a y e r . 2



18. HAYASHI ET AL. A Silicon-Containing Positive Photoresist 223 available positive photoresist (OFPR-800) have been evaluated as the top imaging layer for a bi-layer photolithographic system. The results are as follows. 1 The silicon compound, polyphenylsilsesquioxane (PSQ) oligomer, is compatible with commercially available positive photoresist without phase separation. Terminal hydroxyl groups of PSQ are necessary to ensure that PSQ is miscible with positive photoresist and makes a clear film without phase separation. 2 Ci s-(1,3,5,7-tetrahydroxy)-1,3,5,7-tetrapheny1 cyclotetrasiloxane (phenyl-TÔH).) which can be looked upon as unit structure of PSQ, has been found to be soluble in an aqueous alkaline solution. The addition of phenyl-TÔH)^ and PSQ oligomer to commercially available positive photoresists has resulted in improved developability with alkaline solution. 3 A mixture called ASTRO-7530, which consists of OFPR-800, 45 % PSQ oligomer (obtained as GR-950 from Owens-Illinois Co.) and 30 % phenyl-TÔH)^, as opposed to the solid contents of OFPR-800, shows the same sensitivity characteristics as that of OFPR-800. The mixture is applied as the top imaging layer for a bi-layer photolithographic system. Good quality patterns of 1 pm lines and spaces have been obtained as a result of a sequence starting with exposure followed by development of the top imaging layer and transferring the image by means of O^-RIE to the bottom organic polymer layer. f

Acknowledgments The authors would like to thank Dr. Kazuya Kadota for his helpful discussion. They also thank Dr. Hiroshi Yanazawa for his assistance in the exposure experiment using a reduction aligner. References 1 J.M.Moran and D.Maydan, J.Vac.Sci.Tech., 1979, 16, 1620. 2 J.M.Shaw, M.Hatzakis, J.Paraszczak, J.Liutkus, and E.Babich, Polymer Eng.Sci., 1983, 23, 1054. 3 T.Ueno, H.Shiraishi, T.Iwayanagi, and S.Nonogaki, J.Electrochem.Soc. 1985, 132, 1168. 4 Y.Saotome, H.Gokan, K.Saigo, M.Suzuki, and Y.Ohnishi, J.Electrochem.Soc., 1985, 132, 909. 5 C.W.Wilkins,Jr., E.Reichmanis, T.M.Wolf, and B.C.Smith, J.Vac.Sci.Tech., 1985, B3, 306. 6 J.F.Brown,Jr., J.Amer.Chem.Soc., 1965, 87, 4317. 7 K.A.Andrianov, V.N.Emel'yanov, and A.M.Muzafarav, Dokl.Akad. Nauk.SSSR. 1976, 226, 827; Chem.Abstr., 1976, 85, 5744k. RECEIVED May 5, 1987


A Silicon-Containing Positive Photoresist Developable with Aqueous

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