Ultraviolet and vacuum ultraviolet antireflection substrate

Details Ultraviolet and vacuum ultraviolet antireflection substrate Ultraviolet and vacuum ultraviolet antireflection substrate

2002-05-06

2003-09-30

Sikder, Mohammad (Department: 2872)

Optical: systems and elements

Having significant infrared or ultraviolet property

Multilayer filter or multilayer reflector

C359S360000, C359S361000, C359S356000

Reexamination Certificate

active

06628456

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an ultraviolet and vacuum ultraviolet antireflection substrate. In particular, it relates to an antireflection substrate suitable for various low-reflection lenses, substrates of low-reflection photomasks and substrates of low-reflection pellicles (pellicle membranes) used in exposure to light in the ultraviolet and vacuum ultraviolet regions in manufacture of semiconductor integrated circuits.
BACKGROUND ART
In recent years, the resolution of exposure systems for fabrication of semiconductor integrated circuits is increasing in order to improve the integration of semiconductor circuits. Exposure light having shorter wavelengths is increasingly used to improve the resolution of exposure systems, and exposure light has changed from g-line (wavelength: 435 nm) to i-line (wavelength: 365 nm) and then to KrF excimer laser beams (wavelength: 248 nm) in current use. Even ArF excimer laser beams (wavelength: 193 nm) and F
2
laser beams (wavelength: 157 nm) in the vacuum ultraviolet region are being put into practical use.
These exposure systems use optical materials such as lenses, photomasks and pellicles, which serve as dust covers for photomasks. A familiar material for lenses and photomasks is synthetic quartz glass, while synthetic quartz glass and transparent fluoroplastics are known as materials for pellicle membranes.
However, the refractive indices of such materials as synthetic quartz glass and transparent fluoroplastics increase as the wavelength of the exposure light becomes shorter, and therefore, if nothing is done, the light loss resulting from surface reflection and the development of flare ghosts are prominent. There is another problem that the high light transmission, for example, of at least 95%, required in the ultraviolet region and the vacuum ultraviolet region is not secured.
Therefore, the first object of the present invention is to provide an antireflection substrate which suppresses light loss resulting from surface reflection and development of flare ghosts in the ultraviolet region and the vacuum ultraviolet region.
The second object of the present invention is to provide an antireflection substrate having high light transmission.
DISCLOSURE OF THE INVENTION
The present invention provides an ultraviolet and vacuum ultraviolet antireflection substrate (hereinafter referred to as “the first substrate”) comprising a substrate which is transparent to ultraviolet and vacuum ultraviolet rays in the wavelength region from 155 nm to 200 nm and a monolayer antireflection film formed on at least one side of the substrate, wherein the center wavelength &lgr;
0
of the wavelength region of ultraviolet or vacuum ultraviolet light which needs antireflection, the refractive index n
s
of the substrate at the wavelength of &lgr;
0
, the refractive index n
1
of the antireflection film at the wavelength of &lgr;
0
and the physical thickness d
1
of the antireflection film satisfy the conditions that n
1
<n
s
, and that n
1
d
1
is almost (1/4+m/2)&lgr;
0
(wherein m is an integer of at least 0).
In the present invention, n
1
d
1
being almost (1/4+m/2)&lgr;
0
(m is an integer of at least 0) means that (0.187+m/2)&lgr;
0
≦n
1
d
1
≦(0.327+m/2)&lgr;
0
.
The present invention also provides an ultraviolet and vacuum ultraviolet antireflection substrate (hereinafter referred to as “the second substrate”) comprising a substrate which is transparent to ultraviolet and vacuum ultraviolet rays in the wavelength region from 155 nm to 200 nm and a bilayer antireflection film comprising a second layer and a first layer formed on at least one side of the substrate in this order from the substrate side, wherein the center wavelength &lgr;
0
of the wavelength region of ultraviolet or vacuum ultraviolet light which needs antireflection, the refractive index n
s
of the substrate at the wavelength of &lgr;
0
, the refractive index n
2
of the second layer at the wavelength of &lgr;
0
, the physical thickness d
2
of the second layer, the refractive index n
1
of the first layer at the wavelength of &lgr;
0
, and the physical thickness d
1
of the first layer satisfy the conditions that n
1
<n
s
<n
2
, that n
1
d
1
is almost (1/4+m/2)&lgr;
0
(wherein m is an integer of at least 0), and that 0.05&lgr;
0
≦n
2
d
2
≦0.50&lgr;
0
.
The present invention further provides an ultraviolet and vacuum ultraviolet antireflection substrate (hereinafter referred to as “the third substrate”) comprising a substrate which is transparent to ultraviolet and vacuum ultraviolet rays in the wavelength region from 155 nm to 200 nm and a trilayer antireflection film comprising a third layer, a second layer and a first layer formed on at least one side of the substrate in this order from the substrate side, wherein the center wavelength &lgr;
0
of the wavelength region of ultraviolet or vacuum ultraviolet light which needs antireflection, the refractive index n
s
of the substrate at the wavelength of &lgr;
0
, the refractive index n
3
of the third layer at the wavelength of &lgr;
0
, the physical thickness d
3
of the third layer, the refractive index n
2
of the second layer at the wavelength of &lgr;
0
, the physical thickness d
2
of the second layer, the refractive index n
1
of the first layer at the wavelength of &lgr;
0
, and the physical thickness d
1
of the first layer satisfy the following conditions (1) to (4):
n
1
, n
3
<n
s
and n
1
, n
3
<n
2
,  (1)
 0
<n
1
d
1
≦0.47&lgr;
0
,  (2)
0.14&lgr;
0
≦n
3
d
3
≦0.33&lgr;
0
,  (3)
and
0.16&lgr;
0
≦n
2
d
2
≦0.38&lgr;
0
,  (4)
0.64&lgr;
0
≦n
2
d
2
≦0.86&lgr;
0
,
or
1.13&lgr;
0
≦n
2
d
2
≦1.35&lgr;
0
.


REFERENCES:
patent: 5963365 (1999-10-01), Shirai
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patent: 63-113501 (1988-05-01), None
patent: 63-142302 (1988-06-01), None
patent: 5-188203 (1993-07-01), None
patent: WO 01/35125 (2001-05-01), None
H.A. Macleod,Thin-Film Optical Filters, McGraw-Hill Publishing Co., pp. 72-74.
Alfred Thelen,Design of Optical Intereference Coatings, Mc-Graw-Hill Publishing Co., pp. 86-88, 1989.

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