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0.1-Micrometer scaling by 1:1 synchrotron radiation lithography
Microelectronic Engineering 18 (1992) 333-340 Elsevier
333
O.1-Micrometer scaling by 1:1 synchrotron radiation lithography K. Mochiji, T. Ogawa, H. Oizumil and T. Soga Central Research Laboratory, Hitachi Ltd., Kokubunfi, Tokyo 185, Japan
Received November 15, 1991 Accepted June 26, 1992 Abstract. The dimensional accuracy of an X-ray mask and resolution capability of 1 : 1 SR
(synchrotron radiation) lithography for 0.1-~m scaling are studied. The mask-to-mask overlay error is minimized below the measurement accuracy (0.04 p.m, 3tr) by controlling the stress of the SiN membrane and the W absorber. 1 : 1 SR proximity printing is capable of 0.1-1~m resolution by adjusting the exposing SR wavelength just over the Si-K edge and reducing the mask-wafer gap to 10 I~m. Keywords. X-ray lithography; Synchrotron radiation; X-ray mask; Stress; 1:1 Proximity printing; Secondary electron; X-ray diffraction
1. Introduction
X-ray lithography has only been studied for the last two decades. S o m e V L S I manufacturers are moving toward producing 0.3-0.5-1xm scaling LSIs by using X-ray lithography [1]. On the other hand, optical lithography has b e e n evolving rapidly in recent years [2], and it will be used to m a k e 64- or 256-Mbit m e m o r i e s . We think that the main goal of X-ray lithography is high-volume p r o d u c t i o n of 1-Gbit or 4-Gbit m e m o r y and that these advanced m e m o r i e s will require 0.1-1~m scaling. A m o n g m a n y technical problems, the dimensional accuracy of X-ray masks and the resolution for 1 : 1 proximity printing has to be greatly improved. This p a p e r reports on the dimensional stability of X-ray masks, with special attention to mask materials. T h e physical factors that affect the resolution of 1:1 proximity printing using synchrotron radiation (SR) are also presented. Correspondence to: Dr. K. Mochiji, Central Research Laboratory, Hitachi Ltd., Kokubunji, Tokyo 185, Japan.
0167-9317/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved
334
K. Mochiji et al. / 0.1-Micrometer scaling
2. X-ray mask materials Silicon nitride (SIN) film p r e p a r e d by chemical v a p o r d e p o s i t i o n ( C V D ) has b e e n widely used as a m a s k m e m b r a n e , mainly because it is well c h a r a c t e r i z e d a n d its high optical t r a n s p a r e n c y facilitates m a s k - w a f e r a l i g n m e n t . S y n c h r o t r o n r a d i a t i o n has b e e n r e p o r t e d to d a m a g e SiN m e m b r a n e s [3], a n d we h a v e p r e v i o u s l y investigated the relationship b e t w e e n r a d i a t i o n durability a n d the c h e m i c a l c o m p o s i t i o n of SiN m e m b r a n e s [4]. In the w o r k r e p o r t e d here, SiN films were d e p o s i t e d by low-pressure C V D
Kozo Mochiji received his BS and MS degrees in chemistry from Tohoku University in 1973 and 1975, respectively. After joining the Central Research Laboratory, Hitachi Ltd. in 1978, he worked on the research and development of lithographic technologies for semiconductor devices. He is now engaged in X-ray lithography research. His main interest is in photo- and radiation-chemistry of the materials used in lithography. He received a Doctor's degree from Osaka University in 1986. Dr. Mochiji is a member of the Japan Society of Applied Physics. !-r:....
Taro Ogawa received his BS and MS degrees in metallurgical engineering from Tokyo Institute of Technology in 1982 and 1984, respectively. After joining the Central Research Laboratory, Hitachi Ltd. in 1984, he has been engaged in the research of SR-application for ULSI processes, mainly X-ray lithography. Mr. Ogawa is a member of the Japan Society of Applied Physics, and the Physical Society of Japan.
Hiroaki Oizumi received his BS and MS degrees in applied chemistry from Yokohama National University in 1984 and 1986, respectively. He joined the Central Research Laboratory, Hitachi Ltd. in 1986, and now he is engaged in the research of SR-application of the ULSI processes, mainly X-ray lithography. Mr. Oizumi is a member of the Physical Society of Japan, the Japan Society of Applied Physics, and the Chemical Society of Japan.
Takashi Soga graduated from the electrical engineering course of Niigata Technical High-school in 1981. After joining the Central Research Laboratory, Hitachi Ltd. in 1981, he has been engaged in the research of X-ray Lithography, mainly mask technology. Mr. Soga is a member of the Japan Society of Applied Physics.
K. Mochiji et al. / 0.1-Micrometer scaling
335
Table 1 Atomic composition and distortion of SiN membranes after SR exposure Sample No.
Relative composition Si N O
Distortion after SR exposure (3or)
1 2 3 4 5
1.0 1.0 1.0 1.0 1.0
0.07 ~m 0.06 ~m 0.6 I~m 2.7 ~m broken
0.69 0.73 0.68 0.58 0.48
<0.01 <0.01 0.04 0.13 0.26
at 880°C using SiH2CI 2 and NH 3 as raw material gases. Oxygen remaining in the SiN membrane was found to cause X-ray induced distortion by breaking the S i - O bonds, but SiN membranes with an oxygen concentration below 1% were stable under SR irradiation at 5 kJ/cm 2 (Table 1). The distortion of the X-ray mask was estimated by measuring the displacement of a mask pattem before and after SR irradiation. The dimensional accuracy of an X-ray mask strongly depends on the stress in the absorber and the membrane [5]. The tensile stress of SiN films was reduced to less than 5 x 107 N / m E by optimizing the flow of the raw material gas. The film stress was estimated from the bowing of the Si substrate by the film deposition. The displacement shift induced by this film's stress during removal of the Si substrate (525 ixm thick) was less than 0.02 ~m (Fig. 1). displacement shift
before etching
[=,~ . . ~ i = j ~ , , ~ ¢ . ~ = = ~ l ~ i~
/SiN
I:~:'~-'-':-'~t '~. Ir~ ~-<°~-"~'-'"-"-'~'~'~I
1-
20ram
rl
0.30 E0.25 == '~ 0.20
A
s0 ~'o
30 .20 ° ~ t 10
0.15 E ~0.10
==
¢0 (9
"o 0.0~
0.0(
40
;
0
5
10
15
20
SiN film's stress ( xl07 N/m2 )
Fig. 1. Displacement error induced by SiN film stress during Si substrate removal.
o
~'-10 E 8
.
0
.
.
.
.
.
.
.
.
2 4 6 8 15 2 Ar* Dose ( x 10 atoms/cm )
10
Fig. 2. Dependence of W film stress on A r + ion dosage.
336
K. Mochiji et al. / O.1-Micrometer scaling
CVD-prepared W is a promising material for use as an absorber because its chemical stability is high. A W film was deposited to a thickness of 0.6 Ixm by u s i n g W F 6 and H 2. To reduce the tensile stress of these films, Ar ÷ ions were implanted with an acceleration voltage of 150 kV. The tensile stress in these films decreased toward the compressive direction when the Ar ÷ ion dose was increased, and the stress could be precisely controlled below 1 x 10 7 N / m 2 (Fig. 2). The well-packed structure of the CVD-prepared W film was not changed by ion implantation and the controlled stress was stable during the mask fabrication process.
3. Dimensional accuracy of the X-ray mask
The W absorbers and SiN membranes were used to fabricate X-ray masks with LSI patterns (Fig. 3). The X-ray masks had two kinds of patterns delineated by different lithographic techniques: LSI patterns corresponding to a 64-Mbit D R A M were delineated by e-beam writing, and 121 (11 x 11) marks for dimensional evaluation were fabricated in one shot across the LSI pattern area by using an i-line stepper. Because optical distortion, such as lens aberration during i-line exposure, is nearly the same for different masks, the shift of the overlay between the different masks is attributable only to the membrane and absorber stresses and to their drifts during the mask fabrication process. The overlay accuracy between the metal layer (absorber coverage of 50%) and the LOCOS layer (absorber coverage of 34%) is shown in Fig. 4. The mask-to-mask overlay was less than 0.04 ~m (3o-), which is very nearly the
//••21
marksdelineated y I-lineexposure
E~ ( ~ ; ~ : : : : ' r n field E ~ delineatedbyEB
7-= LSIpatterns ~ _ markdellneated m m m • r - 0,I-line exposure
J~- 20mm =J Fig. 3. Structure of fabricated X-ray masks.
K. Mochifi et al. / O.1-Micrometer scaling lOmm
337
t
___.__
0
¢,_1!
3~x=0.033 pm 3 ~ y = 0 . 0 3 6 I-tm
-o.1 gm
Fig. 4, Overlay accuracy between the metal layer (absorber coverage of 50%) and the LOCOS layer (absorber coverage of 34%). limit of measurement accuracy (Nikon 3I). The in-plane distortion induced by the W absorber stress of 1 x 107 N/m-" was estimated to be less than 0.01 Ixm by finite element simulation [6]. Consequently, the mask-to-mask overlay in this work was caused mainly by the SiN film stress during Si substrate etching, which was less than 0.02 Ixm as shown in Fig. 1.
4. Resolution for 1:1 proximity printing The most important factors affecting the resolution of 1:1 proximity printing are secondary electrons and X-ray diffraction, so we investigated these factors by using SR at the National Laboratory for High Energy Physics. The SR beam was filtered with Be films and reflected from a platinum-coated mirror (Fig. 5). The wavelength range of the exposing light was 0.5-0.8 nm.
SR
Be filter : 501.tm t
Be w i n d o w : 50gm t
X-ray mask
Fig. 5. Schematic diagram of set-up used for SR lithography.
338
K. Mochifi et al. / O.1-Micrometer scaling
Tile replicated resist (PMMA) patterns on Si and polymer substrates are shown in Fig. 6. The resist pattern was degraded by the secondary electrons from the Si surface. Analyzing the yield and kinetic energy of the secondary electrons revealed and the resolution was degraded tile most by Si-KLL Auger electrons from the substrate. Simulation results indicated that the wavelength used here (0.5-0.8nm) is not optimal for lithography and using an SR wavelength just above the Si-K absorption edge (0.67nm) would almost eliminate this secondary electron effect (Fig. 7). More quantitative consideration of electrons with energies less than 1 keV will be needed for complete analysis. To minimize the influence of X-ray diffraction, the mask-wafer gap should be reduced as much as possible. The results of using a Fresnel approximation to sinmlate the X-ray intensity profile through mask patterns are shown in Fig. 8. A gap of about 101xm is needed for 0.1-1xm resolution. A mask pattern replication experiment using a 10-1xm gap successfully delineated a pattern with 0.1-1xm lines 0.2 ~m apart (Fig. 9).
(}im)
(a)
0.4
0
l
i \I
/,
~ ,
I
1
-0.4 -0.2 0 +0.2 +0.4(J~m] (Jam)
(b)
0'4 ~ i e e J t 0.2 0
18osee' ,
I
-0,4 -0.2
Fig. 6. Rcplicatcd resist (PMMA) pattern oil (a) Si and (b) polymer substratcs (SR exposure dosage: 2 J/cm2).
I
I
t
0 +0.2 +O,4(llm)
Fig. 7. Sinmlated resist pattern produced by wavelengths of (a) 0.67nm and (b) 0.70nm (patterns labeled with development time).
339
K. Mochiji et al. I O.I-Micrometer scaling
\
O.15-p.m p a t t e r n
i
i O. l O - ~ m p a t t e r n I
II :& I o ..-4
I I I I
t
E
I O ¢-.I
I I
Fig. 8. Simulated X-ray intensity prolile through mask patterns (SR wavelength: 0.7 nm).
!
:~.-_,~,~_%~_ ~_~~~r,
.~,~,.~
Fig. 9. Replicated resist (PMIV1A) pattern using a 10-1J.m proximity gap.
5. Conclusion
The dimensional error of an X-ray mask caused by mask material can be minimized to within the measurement error (0.04 ~m). In order to achieve the total overlay (~<0.03 ~m) for 0.1-bin1 scaling, the accuracy of the electron-beam writer for mask making and the alignment capability of an X-ray stepper have to be greatly improved. 1:1 proximity printing is optically capable of 0.1-i.zm resolution if the SR wavelength is adjusted to just above the Si-K absorption edge and the mask-wafer gap is reduced to 10 bern. Attaining this resolution, however, will require investigation of the effect of lower-energy secondary electrons and micro-gap controllability.
340
K. Mochiji et al. / O.1-Micrometer scaling
6. Acknowledgements We thank Dr. Kenichi K o d a m a and Dr. Hisao Izawa of Nikon Co. for m e a s u r e m e n t of the mask pattern placement. This work was partially perf o r m e d u n d e r the approval of the National Laboratory for High E n e r g y Physics (Acceptance No. 91-005).
References [1] J. Warlaumont, J. Vac. Sci. Technol. B 7(6) (1989) 1634. [2] Y. Ozaki, Y. Kawai and A. Yoshikawa, Proc~ b~t. MicroProcess Conf., Chiba, 1990, p. 3. [3] M. Hori, I. Mori, S. Nadahara, Y. Kikuchi, H. Komano and K. Tanaka, Proc. 1st Microprocess Conf. Tokyo, 1988, p. 78. [4] H. Oizumi, S. Iijima and K. Mochiji, Jpn, J. Appl. Phys. 29(21) (1990) 2199. [5] A.W. Yanof, D.J. Resnick, C.A. Jankoski and W.A. Johnson, Proc. SPIE 632 (1986) 118. [6] A. Kishimoto, S. Kuniyoshi, N. Saito, K. Mochiji and T. Kimura, Jpn. J. Appl. Phys. 29(10) (1990) 2203.
333
O.1-Micrometer scaling by 1:1 synchrotron radiation lithography K. Mochiji, T. Ogawa, H. Oizumil and T. Soga Central Research Laboratory, Hitachi Ltd., Kokubunfi, Tokyo 185, Japan
Received November 15, 1991 Accepted June 26, 1992 Abstract. The dimensional accuracy of an X-ray mask and resolution capability of 1 : 1 SR
(synchrotron radiation) lithography for 0.1-~m scaling are studied. The mask-to-mask overlay error is minimized below the measurement accuracy (0.04 p.m, 3tr) by controlling the stress of the SiN membrane and the W absorber. 1 : 1 SR proximity printing is capable of 0.1-1~m resolution by adjusting the exposing SR wavelength just over the Si-K edge and reducing the mask-wafer gap to 10 I~m. Keywords. X-ray lithography; Synchrotron radiation; X-ray mask; Stress; 1:1 Proximity printing; Secondary electron; X-ray diffraction
1. Introduction
X-ray lithography has only been studied for the last two decades. S o m e V L S I manufacturers are moving toward producing 0.3-0.5-1xm scaling LSIs by using X-ray lithography [1]. On the other hand, optical lithography has b e e n evolving rapidly in recent years [2], and it will be used to m a k e 64- or 256-Mbit m e m o r i e s . We think that the main goal of X-ray lithography is high-volume p r o d u c t i o n of 1-Gbit or 4-Gbit m e m o r y and that these advanced m e m o r i e s will require 0.1-1~m scaling. A m o n g m a n y technical problems, the dimensional accuracy of X-ray masks and the resolution for 1 : 1 proximity printing has to be greatly improved. This p a p e r reports on the dimensional stability of X-ray masks, with special attention to mask materials. T h e physical factors that affect the resolution of 1:1 proximity printing using synchrotron radiation (SR) are also presented. Correspondence to: Dr. K. Mochiji, Central Research Laboratory, Hitachi Ltd., Kokubunji, Tokyo 185, Japan.
0167-9317/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved
334
K. Mochiji et al. / 0.1-Micrometer scaling
2. X-ray mask materials Silicon nitride (SIN) film p r e p a r e d by chemical v a p o r d e p o s i t i o n ( C V D ) has b e e n widely used as a m a s k m e m b r a n e , mainly because it is well c h a r a c t e r i z e d a n d its high optical t r a n s p a r e n c y facilitates m a s k - w a f e r a l i g n m e n t . S y n c h r o t r o n r a d i a t i o n has b e e n r e p o r t e d to d a m a g e SiN m e m b r a n e s [3], a n d we h a v e p r e v i o u s l y investigated the relationship b e t w e e n r a d i a t i o n durability a n d the c h e m i c a l c o m p o s i t i o n of SiN m e m b r a n e s [4]. In the w o r k r e p o r t e d here, SiN films were d e p o s i t e d by low-pressure C V D
Kozo Mochiji received his BS and MS degrees in chemistry from Tohoku University in 1973 and 1975, respectively. After joining the Central Research Laboratory, Hitachi Ltd. in 1978, he worked on the research and development of lithographic technologies for semiconductor devices. He is now engaged in X-ray lithography research. His main interest is in photo- and radiation-chemistry of the materials used in lithography. He received a Doctor's degree from Osaka University in 1986. Dr. Mochiji is a member of the Japan Society of Applied Physics. !-r:....
Taro Ogawa received his BS and MS degrees in metallurgical engineering from Tokyo Institute of Technology in 1982 and 1984, respectively. After joining the Central Research Laboratory, Hitachi Ltd. in 1984, he has been engaged in the research of SR-application for ULSI processes, mainly X-ray lithography. Mr. Ogawa is a member of the Japan Society of Applied Physics, and the Physical Society of Japan.
Hiroaki Oizumi received his BS and MS degrees in applied chemistry from Yokohama National University in 1984 and 1986, respectively. He joined the Central Research Laboratory, Hitachi Ltd. in 1986, and now he is engaged in the research of SR-application of the ULSI processes, mainly X-ray lithography. Mr. Oizumi is a member of the Physical Society of Japan, the Japan Society of Applied Physics, and the Chemical Society of Japan.
Takashi Soga graduated from the electrical engineering course of Niigata Technical High-school in 1981. After joining the Central Research Laboratory, Hitachi Ltd. in 1981, he has been engaged in the research of X-ray Lithography, mainly mask technology. Mr. Soga is a member of the Japan Society of Applied Physics.
K. Mochiji et al. / 0.1-Micrometer scaling
335
Table 1 Atomic composition and distortion of SiN membranes after SR exposure Sample No.
Relative composition Si N O
Distortion after SR exposure (3or)
1 2 3 4 5
1.0 1.0 1.0 1.0 1.0
0.07 ~m 0.06 ~m 0.6 I~m 2.7 ~m broken
0.69 0.73 0.68 0.58 0.48
<0.01 <0.01 0.04 0.13 0.26
at 880°C using SiH2CI 2 and NH 3 as raw material gases. Oxygen remaining in the SiN membrane was found to cause X-ray induced distortion by breaking the S i - O bonds, but SiN membranes with an oxygen concentration below 1% were stable under SR irradiation at 5 kJ/cm 2 (Table 1). The distortion of the X-ray mask was estimated by measuring the displacement of a mask pattem before and after SR irradiation. The dimensional accuracy of an X-ray mask strongly depends on the stress in the absorber and the membrane [5]. The tensile stress of SiN films was reduced to less than 5 x 107 N / m E by optimizing the flow of the raw material gas. The film stress was estimated from the bowing of the Si substrate by the film deposition. The displacement shift induced by this film's stress during removal of the Si substrate (525 ixm thick) was less than 0.02 ~m (Fig. 1). displacement shift
before etching
[=,~ . . ~ i = j ~ , , ~ ¢ . ~ = = ~ l ~ i~
/SiN
I:~:'~-'-':-'~t '~. Ir~ ~-<°~-"~'-'"-"-'~'~'~I
1-
20ram
rl
0.30 E0.25 == '~ 0.20
A
s0 ~'o
30 .20 ° ~ t 10
0.15 E ~0.10
==
¢0 (9
"o 0.0~
0.0(
40
;
0
5
10
15
20
SiN film's stress ( xl07 N/m2 )
Fig. 1. Displacement error induced by SiN film stress during Si substrate removal.
o
~'-10 E 8
.
0
.
.
.
.
.
.
.
.
2 4 6 8 15 2 Ar* Dose ( x 10 atoms/cm )
10
Fig. 2. Dependence of W film stress on A r + ion dosage.
336
K. Mochiji et al. / O.1-Micrometer scaling
CVD-prepared W is a promising material for use as an absorber because its chemical stability is high. A W film was deposited to a thickness of 0.6 Ixm by u s i n g W F 6 and H 2. To reduce the tensile stress of these films, Ar ÷ ions were implanted with an acceleration voltage of 150 kV. The tensile stress in these films decreased toward the compressive direction when the Ar ÷ ion dose was increased, and the stress could be precisely controlled below 1 x 10 7 N / m 2 (Fig. 2). The well-packed structure of the CVD-prepared W film was not changed by ion implantation and the controlled stress was stable during the mask fabrication process.
3. Dimensional accuracy of the X-ray mask
The W absorbers and SiN membranes were used to fabricate X-ray masks with LSI patterns (Fig. 3). The X-ray masks had two kinds of patterns delineated by different lithographic techniques: LSI patterns corresponding to a 64-Mbit D R A M were delineated by e-beam writing, and 121 (11 x 11) marks for dimensional evaluation were fabricated in one shot across the LSI pattern area by using an i-line stepper. Because optical distortion, such as lens aberration during i-line exposure, is nearly the same for different masks, the shift of the overlay between the different masks is attributable only to the membrane and absorber stresses and to their drifts during the mask fabrication process. The overlay accuracy between the metal layer (absorber coverage of 50%) and the LOCOS layer (absorber coverage of 34%) is shown in Fig. 4. The mask-to-mask overlay was less than 0.04 ~m (3o-), which is very nearly the
//••21
marksdelineated y I-lineexposure
E~ ( ~ ; ~ : : : : ' r n field E ~ delineatedbyEB
7-= LSIpatterns ~ _ markdellneated m m m • r - 0,I-line exposure
J~- 20mm =J Fig. 3. Structure of fabricated X-ray masks.
K. Mochifi et al. / O.1-Micrometer scaling lOmm
337
t
___.__
0
¢,_1!
3~x=0.033 pm 3 ~ y = 0 . 0 3 6 I-tm
-o.1 gm
Fig. 4, Overlay accuracy between the metal layer (absorber coverage of 50%) and the LOCOS layer (absorber coverage of 34%). limit of measurement accuracy (Nikon 3I). The in-plane distortion induced by the W absorber stress of 1 x 107 N/m-" was estimated to be less than 0.01 Ixm by finite element simulation [6]. Consequently, the mask-to-mask overlay in this work was caused mainly by the SiN film stress during Si substrate etching, which was less than 0.02 Ixm as shown in Fig. 1.
4. Resolution for 1:1 proximity printing The most important factors affecting the resolution of 1:1 proximity printing are secondary electrons and X-ray diffraction, so we investigated these factors by using SR at the National Laboratory for High Energy Physics. The SR beam was filtered with Be films and reflected from a platinum-coated mirror (Fig. 5). The wavelength range of the exposing light was 0.5-0.8 nm.
SR
Be filter : 501.tm t
Be w i n d o w : 50gm t
X-ray mask
Fig. 5. Schematic diagram of set-up used for SR lithography.
338
K. Mochifi et al. / O.1-Micrometer scaling
Tile replicated resist (PMMA) patterns on Si and polymer substrates are shown in Fig. 6. The resist pattern was degraded by the secondary electrons from the Si surface. Analyzing the yield and kinetic energy of the secondary electrons revealed and the resolution was degraded tile most by Si-KLL Auger electrons from the substrate. Simulation results indicated that the wavelength used here (0.5-0.8nm) is not optimal for lithography and using an SR wavelength just above the Si-K absorption edge (0.67nm) would almost eliminate this secondary electron effect (Fig. 7). More quantitative consideration of electrons with energies less than 1 keV will be needed for complete analysis. To minimize the influence of X-ray diffraction, the mask-wafer gap should be reduced as much as possible. The results of using a Fresnel approximation to sinmlate the X-ray intensity profile through mask patterns are shown in Fig. 8. A gap of about 101xm is needed for 0.1-1xm resolution. A mask pattern replication experiment using a 10-1xm gap successfully delineated a pattern with 0.1-1xm lines 0.2 ~m apart (Fig. 9).
(}im)
(a)
0.4
0
l
i \I
/,
~ ,
I
1
-0.4 -0.2 0 +0.2 +0.4(J~m] (Jam)
(b)
0'4 ~ i e e J t 0.2 0
18osee' ,
I
-0,4 -0.2
Fig. 6. Rcplicatcd resist (PMMA) pattern oil (a) Si and (b) polymer substratcs (SR exposure dosage: 2 J/cm2).
I
I
t
0 +0.2 +O,4(llm)
Fig. 7. Sinmlated resist pattern produced by wavelengths of (a) 0.67nm and (b) 0.70nm (patterns labeled with development time).
339
K. Mochiji et al. I O.I-Micrometer scaling
\
O.15-p.m p a t t e r n
i
i O. l O - ~ m p a t t e r n I
II :& I o ..-4
I I I I
t
E
I O ¢-.I
I I
Fig. 8. Simulated X-ray intensity prolile through mask patterns (SR wavelength: 0.7 nm).
!
:~.-_,~,~_%~_ ~_~~~r,
.~,~,.~
Fig. 9. Replicated resist (PMIV1A) pattern using a 10-1J.m proximity gap.
5. Conclusion
The dimensional error of an X-ray mask caused by mask material can be minimized to within the measurement error (0.04 ~m). In order to achieve the total overlay (~<0.03 ~m) for 0.1-bin1 scaling, the accuracy of the electron-beam writer for mask making and the alignment capability of an X-ray stepper have to be greatly improved. 1:1 proximity printing is optically capable of 0.1-i.zm resolution if the SR wavelength is adjusted to just above the Si-K absorption edge and the mask-wafer gap is reduced to 10 bern. Attaining this resolution, however, will require investigation of the effect of lower-energy secondary electrons and micro-gap controllability.
340
K. Mochiji et al. / O.1-Micrometer scaling
6. Acknowledgements We thank Dr. Kenichi K o d a m a and Dr. Hisao Izawa of Nikon Co. for m e a s u r e m e n t of the mask pattern placement. This work was partially perf o r m e d u n d e r the approval of the National Laboratory for High E n e r g y Physics (Acceptance No. 91-005).
References [1] J. Warlaumont, J. Vac. Sci. Technol. B 7(6) (1989) 1634. [2] Y. Ozaki, Y. Kawai and A. Yoshikawa, Proc~ b~t. MicroProcess Conf., Chiba, 1990, p. 3. [3] M. Hori, I. Mori, S. Nadahara, Y. Kikuchi, H. Komano and K. Tanaka, Proc. 1st Microprocess Conf. Tokyo, 1988, p. 78. [4] H. Oizumi, S. Iijima and K. Mochiji, Jpn, J. Appl. Phys. 29(21) (1990) 2199. [5] A.W. Yanof, D.J. Resnick, C.A. Jankoski and W.A. Johnson, Proc. SPIE 632 (1986) 118. [6] A. Kishimoto, S. Kuniyoshi, N. Saito, K. Mochiji and T. Kimura, Jpn. J. Appl. Phys. 29(10) (1990) 2203.