U.S. patent application number 09/736805 was filed with the patent office on 2001-06-28 for blank for halftone phase shift photomask and halftone phase shift photomask.
Invention is credited to Fujikawa, Junji, Kinase, Yoshinori, Mohri, Hiroshi, Motonaga, Toshiaki, Nakagawa, Hiro-o, Ohtsuki, Masashi, Okamura, Takafumi, Sumida, Shigeki, Yokoyama, Toshifumi, Yusa, Satoshi.
Application Number | 20010005564 09/736805 |
Document ID | / |
Family ID | 26580275 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010005564 |
Kind Code |
A1 |
Motonaga, Toshiaki ; et
al. |
June 28, 2001 |
Blank for halftone phase shift photomask and halftone phase shift
photomask
Abstract
A blank for a halftone phase shift photomask in the present
invention comprises a transparent substrate and a halftone phase
shift film provided thereon, and said halftone phase shift film has
a multilayer construction in which at least a first layer capable
of being etched with a chlorinated gas and a second layer capable
of being etched with a fluorinated gas are disposed in this order
from the side near said transparent substrate. A film made of
tantalum silicides is suitable to use as the second layer of the
halftone phase shift film. When such a blank is first etched with a
fluorinated gas and then etched with chlorinated gas, because an
etching selective ratio to a transparent substrate made of
synthetic quartz and the like can be taken sufficiently while
maintaining the applicability to the exposure light with a short
wavelength that is characteristic of silicide materials in addition
to good chemical stability and good processing properties that are
characteristic of tantalum materials, patterning in high precision
will be made possible. As a result, it is possible to obtain an
ideal halftone phase shift photomask excellent in stability after
mask processing and in the applicability to the short
wavelength.
Inventors: |
Motonaga, Toshiaki;
(Tokyo-to, JP) ; Yokoyama, Toshifumi; (Tokyo-to,
JP) ; Okamura, Takafumi; (Tokyo-to, JP) ;
Kinase, Yoshinori; (Tokyo-to, JP) ; Mohri,
Hiroshi; (Tokyo-to, JP) ; Fujikawa, Junji;
(Tokyo-to, JP) ; Nakagawa, Hiro-o; (Tokyo-to,
JP) ; Sumida, Shigeki; (Tokyo-to, JP) ; Yusa,
Satoshi; (Tokyo-to, JP) ; Ohtsuki, Masashi;
(Tokyo-to, JP) |
Correspondence
Address: |
Timothy J. Keefer
c/o Wildman, Harrold, Allen & Dixon
225 W. Wacker Drive
Chicago
IL
60606
US
|
Family ID: |
26580275 |
Appl. No.: |
09/736805 |
Filed: |
December 14, 2000 |
Current U.S.
Class: |
430/5 ; 428/432;
428/433 |
Current CPC
Class: |
B32B 17/06 20130101;
G03F 1/32 20130101 |
Class at
Publication: |
430/5 ; 428/432;
428/433 |
International
Class: |
G03F 009/00; B32B
015/00; B32B 017/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 1999 |
JP |
P11-355522 |
May 25, 2000 |
JP |
P2000-154687 |
Claims
What is claimed is:
1. A blank for a halftone phase shift photomask comprising a
transparent substrate and a halftone phase shift film provided on
said transparent substrate, wherein said halftone phase shift film
has a multilayer construction in which at least a first layer
capable of being etched with a chlorinated gas and a second layer
capable of being etched with a fluorinated gas are disposed in this
order from the side near to said transparent substrate.
2. A blank for a half tone phase shift photomask according to claim
1, wherein said second layer has an element composition comprising
tantalum, silicon and oxygen as essential elements.
3. A blank for a halftone phase shift photomask according to claim
1, wherein said first layer has an element composition comprising
tantalum as an essential element and said second layer has an
element composition comprising tantalum, silicon and oxygen as
essential elements.
4. A blank for a halftone phase shift photomask according to claim
3, wherein said first layer has an element composition further
containing oxygen and/or nitrogen as essential elements.
5. A blank for a halftone phase shift photomask according to claim
1, wherein said first layer has an element composition comprising
chromium as an essential element and said second layer has an
element composition comprising tantalum, silicon and oxygen as
essential elements.
6. A blank for a halftone phase shift photomask according to claim
5, wherein said first layer has an element composition further
containing oxygen, fluorine and/or nitrogen as essential
elements.
7. A blank for a halftone phase shift photomask according to claim
5, wherein said first layer has an element composition further
containing silicon as an essential element.
8. A blank for a halftone phase shift photomask according to claim
7, wherein said first layer has an element composition further
containing oxygen, fluorine and/or nitrogen as essential
elements.
9. A blank for a halftone phase shift photomask according to claim
5, wherein said first layer has an element composition further
containing tantalum as an essential element.
10. A blank for a halftone phase shift photomask according to claim
9, wherein said first layer has an element composition further
containing oxygen, fluorine and/or nitrogen as essential
elements.
11. A blank for a halftone phase shift photomask according to claim
9, wherein said first layer has an element composition further
containing silicon as an essential element.
12. A blank for a halftone phase shift photomask according to claim
11, wherein said first layer has an element composition further
containing oxygen, fluorine and/or nitrogen as essential
elements.
13. A blank for a halftone phase shift photomask according to claim
1, wherein a halftone phase shift film is formed on a transparent
substrate so as to have a phase difference .phi. within the range
of n.pi..+-..pi./3 radian (n is an odd number) according to the
following expression: 4 = k = 1 m - 1 k , k + 1 + k = 2 m - 1 2 ( u
k - 1 ) d k / wherein, .phi. is a phase change caused to light
vertically transmitting through the blank for a photomask in which
a multilayer film with (m-2) layers is disposed on said transparent
substrate, .chi..sup.k,k+1 is a phase change occurring in the
interface between a k.sup.th layer and a (k+1)th layer, u.sub.k and
d.sub.k are the refractive index and film thickness of a material
forming the k.sup.th layer, respectively, and .lambda. is the
wavelength of exposure light, providing that the layer of k=1 is
said transparent substrate and the layer of k=m is air.
14. A blank for a halftone phase shift photomask according to claim
1, wherein a halftone phase shift film is formed on said
transparent substrate so as to have a film thickness with the
transmittance of exposure light within the range of 1 to 50% when
the transmittance of exposure light of the transparent substrate is
defined as 100%.
15. A blank for a halftone phase shift photomask according to claim
1, wherein the absolute reflectance of the surface on which a
halftone phase shift film is formed is from 0 to 30% with respect
to exposure light.
16. A blank for a halftone phase shift photomask according to claim
1, wherein a light shielding film having an element composition
comprising chromium as an essential element is formed on the
halftone phase shift film in succession.
17. A blank for a halftone phase shift photomask according to claim
1, wherein a light shielding film having an element composition
comprising chromium as an essential element is formed under the
halftone phase shift film in succession.
18. A halftone phase shift photomask comprising a transparent
substrate and a halftone phase shift film provided on said
transparent substrate, wherein said halftone phase shift film has a
multilayer construction in which at least a first layer capable of
being etched with a chlorinated gas and a second layer capable of
being etched with a fluorinated gas are disposed in this order from
the side near said transparent substrate, and said halftone phase
shift film also comprises apertures made by removing part of said
halftone phase shift film in a prescribed pattern.
19. A Halftone phase shift photomask according to claim 18, wherein
said second layer has an element composition comprising tantalum,
silicon and oxygen as essential elements.
20. A halftone phase shift photomask according to claim 18, wherein
said first layer has an element composition comprising tantalum as
an essential element and said second layer has an element
composition comprising tantalum, silicon and oxygen as essential
elements.
21. A halftone phase shift photomask according to claim 20, wherein
said first layer has an element composition further containing
oxygen and/or nitrogen as essential elements.
22. A halftone phase shift photomask according to claim 18, wherein
said first layer has an element composition comprising chromium as
an essential element and said second layer has an element
composition comprising tantalum, silicon and oxygen as essential
elements.
23. A halftone phase shift photomask according to claim 22, wherein
said first layer has an element composition further containing
oxygen, fluorine and/or nitrogen as essential elements.
24. A halftone phase shift photomask according to claim 22, wherein
said first layer has an element composition further containing
silicon as an essential element.
25. A halftone phase shift photomask according to claim 24, wherein
said first layer has an element composition further containing
oxygen, fluorine and/or nitrogen as essential elements.
26. A halftone phase shift photomask according to claim 22, wherein
said first layer has an element composition further containing
tantalum as an essential element.
27. A halftone phase shift photomask according to claim 26, wherein
said first layer has an element composition further containing
oxygen, fluorine and/or nitrogen as essential elements.
28. A halftone phase shift photomask according to claim 26, wherein
said first layer has an element composition further containing
silicon as an essential element.
29. A halftone phase shift photomask according to claim 28, wherein
said first layer has an element composition further containing
oxygen, fluorine and/or nitrogen as essential elements.
30. A halftone phase shift photomask according to claim 18, wherein
a halftone phase shift film is formed on a transparent substrate so
as to have a phase difference .phi. within the range of
n.pi..+-..pi./3 radian (n is an odd number) according to the
following expression: 5 = k = 1 m - 1 k , k + 1 + k = 2 m - 1 2 ( u
k - 1 ) d k / wherein, .phi. is a phase change caused to light
vertically transmitting through the photomask in which a multilayer
film with (m-2) layers is disposed on said transparent substrate,
.chi..sup.k,k+1 is a phase change occurring in the interface
between a k.sup.th layer and a (k+1)th layer, u.sub.k and d.sub.k
are the refractive index and film thickness of a material forming
the k.sup.th layer, respectively, and .lambda. is the wavelength of
exposure light, providing that the layer of k=1 is said transparent
substrate and the layer of k=m is air.
31. A halftone phase shift photomask according to claim 18, wherein
a halftone phase shift film has a transmittance of exposure light
within the range of 1 to 50% when the transmittance of exposure
light of the transparent substrate is defined as 100%.
32. A halftone phase shift photomask according to claim 18, wherein
the absolute reflectance of the surface on which a halftone phase
shift film is formed is from 0 to 30% with respect to exposure
light.
33. A halftone phase shift photomask according to claim 18, wherein
a light shielding film having an element composition comprising
chromium as an essential element is formed on a halftone phase
shift film in the same pattern.
34. A halftone phase shift photomask according to claim 18, wherein
a light shielding film having an element composition comprising
chromium as an essential element is formed under a halftone phase
shift film in the same pattern.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a photomask that is used
for producing high density integrated circuits like LSI and VLSI or
for forming other microscopic patterns, and to a blank for
producing the such a photomask, especially relates to a halftone
phase shift photomask by which projection image in fine dimension
can be obtained and to a blank for producing the halftone phase
shift photomask.
[0003] 2. Description of the Related Art
[0004] Semiconductor integrated circuits, including IC, LSI and
VLSI, are produced by repeating the lithography process of using a
photomask, especially in case of forming fine circuit patterns, it
is studied to use phase shift photomasks disclosed in, for example,
Japanese Patent Application Laid-Open No. 58-173744, Japanese
Patent Application Publication No. 62-59296 and others.
[0005] Although phase shift photomasks with various types of
constitution are proposed, among them, for example, halftone phase
shift photomasks disclosed in Japanese Patent Application Laid-Open
No. 4-136854, U.S. Pat. No. 4,890,309 and others attract attentions
from the viewpoint of possibility of being put to practical use in
early time.
[0006] As for halftone phase shift photomasks, in literatures,
including, for example, Japanese Patent Application Laid-Open Nos.
5-2259 and 5-127361, the improvement of yield rates by reducing the
number of production processes, the constitution with possibility
of reducing the cost, preferable materials and others have been
proposed.
[0007] In the following, a common halftone phase shift method and a
common halftone phase shift photomask will be briefly explained
with reference to the accompanying drawings.
[0008] FIG. 14(a) to FIG. 14(d) are views showing the principle of
a halftone phase shift method (a halftone phase shift photo
lithography), and FIG. 15(a) to FIG. 15(d) are views showing the
principle of a photomasking method using a photomask except a phase
shift photomask. FIG. 14(a) and FIG. 15(a) are sectional views of a
photomask, FIG. 14(b) and FIG. 15(b) show the amplitude of light on
a photomask, FIG. 14(c) and FIG. 15(c) show the amplitude of light
on a wafer, and FIG. 14(d) and FIG. 15(d) show the strength of
light on a wafer. Reference numerals 911 and 921 denote substrates,
912 denotes a halftone phase shift film in which the phase of
incident light is substantially shifted by 180 degree and the
transmittance of transmitted light is within the range of 1 to 50%,
922 denotes a 100% light shielding film, and 913 and 923 denote
incident light.
[0009] In a conventional photomasking method, as shown in FIG.
15(a), the 100% light shielding film 922 made of chromium or the
like is formed on the substrate 921 consisting of quartz glass to
form a light transmission part (an aperture) in a desired pattern.
In this case, the distribution of light strength on a wafer is
broadened toward the end as shown in FIG. 15(d), resulting in
inferior resolution.
[0010] On the other hand, in a halftone phase shift method, because
the phase of light transmitted through the halftone phase shift
film 912 is substantially inverted to that of light transmitted
through the aperture, light strength on boundary parts of patterns
on a wafer becomes zero as shown in FIG. 14(d), which can prevent
light from broadening toward the end. In this case, therefore,
resolution can be improved.
[0011] Here, it should be noted that, in phase shift photo
lithography that belongs in types except a halftone phase shift
method, because a light shielding film and a phase shifter film are
formed in different patterns with different materials, the plate
making process is needed to be repeated at least 2 times, while
because it is enough to form only one pattern in the halftone phase
shift photo lithography, it is essentially needed to carry out the
plate making process only once and this is a big advantage in
halftone phase shift lithography.
[0012] In the halftone phase shift film 912 of a halftone phase
shift photomask, two functions, that is, phase inversion and
permeability control are needed. Out of them, as for the phase
inversion function, it is sufficient that phase will be
substantially inverted between exposure light transmitting through
the halftone phase shift film 912 and exposure light transmitting
through the aperture. Here, if the halftone phase shift film 912 is
considered as an absorption film that is shown, for example, in
pages 628 to 632 of "Principles of Optics" written by M. Born and
E. Wolf, since multiplex interference can be ignored, phase change
oof vertically transmitted light will be calculated using the
following expression. And when the value of .phi. is within the
range of n.pi..+-..pi./3 (n is an odd number), the above-mentioned
phase shift effect will be obtained. 1 = k = 1 m - 1 k , k + 1 + k
= 2 m - 1 2 ( u k - 1 ) d k / Expression (1)
[0013] Further, in expression (1), .phi. is a phase change caused
to light vertically transmitting through a photomask in which a
multilayer film of (m-2) layers is formed on the substrate,
.chi..sup.k,k+1 is a phase change occurring in the interface
between a k.sup.th layer and a (k+1).sup.th layer, u.sub.k and
d.sub.k are the refractive index and film thickness of the k.sup.th
layer, respectively and .lambda. is the wavelength of exposure
light, providing that the layer of k=1 is the above mentioned
transparent substrate and the layer of k=m is air.
[0014] On the other hand, the transmittance of exposure light
transmitted through the halftone phase shift film 912 for obtaining
a halftone phase shift effect is determined by the dimension, area,
arrangement, shape and the like of a transcription pattern, and
differs depending on patterns.
[0015] In order to substantially obtain the above-mentioned effect,
the transmittance of exposure light transmitted through the
halftone phase shift film 912 should be within the range of the
optimum transmittance i some percents, where the center value is
the optimum transmittance determined by the pattern.
[0016] Generally, this optimum transmittance greatly varies within
the wide range of 1 to 50% depending on transcription patterns when
the transmittance in the aperture of the halftone phase shift film
is set to 100%. That is, in order to adapt to all patterns,
halftone phase shift photomasks having various transmittances are
needed.
[0017] In a practical situation, the phase inversion function and
the transmittance control function are determined by a complex
refractive index (a refractive index and an extinction coefficient)
and film thickness of a material forming the halftone phase shift
film. In case of a multilayer structure, the phase inversion
function and the transmittance control function are determined
depending on a complex refractive index and a film thickness of
each layer. In other words, it is possible to use a material
adjustable its film thickness so as to control phase difference
calculated by the above mentioned expression (1) within the range
of n.pi..+-..pi./3 (n is an odd number) as a halftone phase shift
film of a halftone phase shift photomask.
[0018] As thin film materials for photomask patterns, tantalum
based materials are commonly known as shown in, for example,
Japanese Patent Application Laid-Open No. 57-64739, Japanese Patent
Application Publication Nos. 62-51460 and 62-51461. Because
tantalum based materials are extremely excellent in processing
properties, chemical stability after being processed, and others,
they have been vigorously studied and tried to apply them in
halftone phase shift films by oxidizing or nitriding tantalum as
disclosed in, for example, Japanese Patent Application Laid-Open
Nos. 5-257264, 7-134396 and 7-281414. Furthermore, with the
advancement of shortening the wavelength of exposure light in
connection with the minuteness of LSI patterns, studies have also
been carried out to use materials of tantalum silicides that are
able be applied to exposure light of shorter wavelength as shown
in, for example, Japanese Patent Application Laid-Open No.
6-83027.
[0019] However, generally, dry etching of tantalum silicides is
carried out using an etching gas of fluorinated compounds,
including CF.sub.4, CHF.sub.3, SF.sub.6, C.sub.2F.sub.6, NF.sub.3,
CF.sub.4+H.sub.2 and CBrF.sub.3, but there was such a problem that
in this case, the fluorinated-etching gas also etches a transparent
substrate of synthetic quartz and the like, and therefore, dry
etching with high precision can not be carried out. Generally,
concerning the production of a halftone phase shift photomask, the
high precision control of the phase angle is indispensable, but if
a quartz substrate is also etched when etching a halftone phase
shift film as mentioned above, errors will be induced in phase
difference by etching depth. Furthermore, because etching of a
halftone phase shift film has an important role in controlling
pattern dimensions, it is desired to set conditions so that the
uniformity and reproducibility of pattern dimensions can be
obtained as good as possible, but there may be such a problem that
a margin in the range for setting conditions becomes narrow due to
the addition of a new parameter of an etching selective ratio to
quartz. This problem will be induced because the optimum etching
process for attaching much importance to dimension control does not
always accord with that for attaching much importance to phase
difference control. That is, materials of tantalum silicides for a
halftone phase shift film in themselves show excellent processing
properties and chemical stability after being processed, but when
phase difference control in high degree is further taken into
consideration, the patterning with high precision will be
difficult.
SUMMARY OF THE INVENTION
[0020] An object of the present invention is to provide a halftone
phase shift photomask capable of providing an improved etching
selective ratio to substrate materials such as a quartz substrate,
as well as maintaining desirable properties of tantalum silicides
including applicability to exposure light with the short
wavelength, excellent processing properties, and chemical stability
after processing.
[0021] Another object of the present invention is to provide blanks
for a halftone phase shift photomask that permit to form halftone
phase shift photomasks with such excellent properties.
[0022] Another object of the present invention is to provide a
halftone phase shift photomask capable of providing an etching
selective ratio to substrate materials such as a quartz substrate
whether a material of tantalum silicides is used or not.
[0023] A halftone phase shift photomask to be provided in the
present invention comprises a transparent substrate and a halftone
phase shift film provided on said transparent substrate,
characterized in that said halftone phase shift film has a
multilayer construction in which at least a first layer capable of
being etched with a chlorinated gas and a second layer capable of
being etched with a fluorinated gas are disposed in this order from
the side near said transparent substrate, and that said halftone
phase shift film also comprises apertures made by removing part of
said halftone phase shift film in a prescribed pattern.
[0024] The present invention also provides a blank enabling to
produce such a halftone phase shift photomask. The blank for a
halftone phase shift photomask comprises a transparent substrate
and a halftone phase shift film provided on said transparent
substrate, characterized in that said halftone phase shift film has
a multilayer construction in which at least a first layer capable
of being etched with a chlorinated gas and a second layer capable
of being etched with a fluorinated gas are disposed in this order
from the side near to said transparent substrate.
[0025] When the blank having the halftone phase shift film with
such a multilayer construction is first etched with a fluorinated
gas, the second layer of the halftone phase shift film is patterned
in a prescribed shape. Next, the halftone phase shift film of the
blank is etched with a chlorinated gas in the pattern coincident
with that etched with the fluorinated gas, and thus the first layer
of the halftone phase shift film is patterned coincidentally with
the second layer, but the transparent substrate is not
substantially etched. As a result, only the halftone phase shift
film can be precisely etched. And it is also possible to control
freely the phase angle and transmittance by forming 2 or more
layers constituting a halftone phase shift film with respective
different materials and by controlling the thickness of each
layer.
[0026] Because the phase angle and transmittance of a halftone
phase shift photomask can be controlled in high precision as well
as improving an etching selective ratio to the transparent
substrate, it becomes possible to obtain a projection image with
precise minute dimensions by using the halftone phase shift
photomask.
[0027] As a method of improving the etching selective ratio to the
substrate, it is known to provide an etching stopper layer between
the substrate and the halftone phase shift film. By this known
method, however, the etching stopper layer will remain in the
aperture of the accomplished halftone phase shift photomask to
affect the phase angle and light transmittance in the aperture. To
the contrary, any no etching stopper layer remains at the aperture
in the present invention.
[0028] The first layer of the halftone phase shift film is disposed
at a portion near the transparent substrate, and it is formed of a
material capable of being etched with a chlorinated gas. For
example, the material capable of being etched with a chlorinated
gas may be selected from among tantalum based materials and
chromium based materials, and the first layer can be formed of the
thus selected material.
[0029] The second layer of the halftone phase shift film is
disposed at a portion distant from the transparent substrate in
comparison with the first layer. It is preferable that the second
layer is formed of tantalum silicide based material. Though the
tantalum silicide based material does not have so large etching
selective ratio to the transparent substrate, it is excellent in
processing properties, chemical stability and applicability to a
light exposure with a short wavelength. Accordingly, when a
halftone phase shift layer made of the tantalum silicide based
material (namely, the second layer) is formed on the transparent
substrate via the other halftone phase shift layer having a large
etching selective ratio to the transparent substrate (namely, the
first layer), it is possible to use the layer made of the tantalum
silicide based material with a large etching selective ratio.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a view schematically showing a section of an
example (a first example) of a blank for a halftone phase shift
photomask in the present invention.
[0031] FIG. 2 is a view schematically showing a section of an
example (a second example) of the a blank for a halftone phase
shift photomask in the present invention.
[0032] FIG. 3 is a view schematically showing a section of an
example (a first example) of a halftone phase shift photomask in
the present invention.
[0033] FIG. 4 is a view schematically showing a section of an
example (a second example) of the halftone phase shift photomask in
the present invention.
[0034] FIG. 5(a) to FIG. 5(e) are views explaining the process of
producing the first example of the photomask shown in FIG. 3 with
the use of the first example of the blank shown in FIG. 1.
[0035] FIG. 6(a) to FIG. 6(d) are views explaining the process of
producing the second example of the photomask shown in FIG. 4 with
the use of the second example of the blank shown in FIG. 2. In
particular, FIG. 6(a) and FIG. 6(b) show the etching process of a
light shielding layer, and FIG. 6(c) and FIG. 6(d) schematically
show sections of etching forms.
[0036] FIG. 7(a) and FIG. 7(b) are views schematically showing the
production process of a blank for a halftone phase shift photomask
and the section of the obtained blank in example 1. In particular,
FIG. 7(a) shows the section of the blank and FIG. 7(b) shows the
section of a test piece obtained by a lift off method.
[0037] FIG. 8 is a graph showing the spectra of transmittance and
reflectance of the blank for a halftone phase shift photomask
obtained in example 1.
[0038] FIG. 9(a) to FIG. 9(c) are views schematically showing the
production process of a blank for a halftone phase shift photomask
and the section of the obtained blank in example 2.
[0039] FIG. 10(a) and FIG. 10(b) are views schematically showing
the production process of a blank for a halftone phase shift
photomask and the section of the obtained blank in example 3. In
particular, FIG. 10(a) shows the section of the blank and FIG.
10(b) shows the section of a test piece obtained by a lift off
method.
[0040] FIG. 11 is a graph showing the spectra of transmittance and
reflectance of the blank for a halftone phase shift photomask
obtained in example 3.
[0041] FIG. 12 shows the section of a test piece obtained by a lift
off method in examples 4, 5 and 6.
[0042] FIG. 13 is a graph showing the transmission spectrum of the
blank obtained in example 6.
[0043] FIG. 14(a) to FIG. 14(d) are views explaining the principle
of a halftone phase shift photo lithography.
[0044] FIG. 15(a) to FIG. 15(d) are views explaining the principle
of a conventional photomasking method.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] A halftone phase shift photomask to be provided in the
present invention comprises a transparent substrate and a halftone
phase shift film provided on the transparent substrate, the
halftone phase shift film is characterized in that it has a
multilayer construction in which at least a first layer that can be
etched with a chlorinated gas and a second layer that can be etched
with a fluorinated gas are disposed in this order from the side
near the transparent substrate, and it also comprises an aperture
made by removing part of the halftone phase shift film in a
prescribed pattern.
[0046] Furthermore, the present invention will provide a blank for
a halftone phase shift photomask, with which a halftone phase shift
photomask like this can be made. The Blank for a halftone phase
shift photomask to be provided by the present invention comprises a
transparent substrate and a halftone phase shift film provided on
the transparent substrate, the halftone phase shift film is
characterized in that it has a multilayer construction in which at
least the first layer that can be etched with a chlorinated gas and
the second layer that can be etched with a fluorinated gas are
disposed in this order from the side near the transparent
substrate. The transparent substrate is formed with a transparent
material, for example, synthetic quartz that can be etched with a
fluorinated gas but not etched with a chlorinated gas.
[0047] The present invention has succeeded in developing a halftone
phase shift photomask in which the pattern processing is possible
in high precision and a blank therefor by making a halftone phase
shift film to be a multilayer construction and by forming one layer
of the multilayer with a material that can take a sufficiently high
etching selective ratio to a transparent substrate.
[0048] In the present invention, on a transparent substrate of the
blank for a halftone phase shift photomask, a halftone phase shift
film having a multilayer of 2 or more plies is formed. Individual
layer constituting a halftone phase shift film is formed with a
halftone phase shift material different from that of forming
adjacent layers. In the plural layers constituting a halftone phase
shift film, the first layer, which is the nearest layer to the
transparent substrate, is formed with a material that can be etched
with a chlorinated dry etching gas and is preferably provided just
on the transparent substrate. As a chlorinated dry etching gas, it
is possible to use a gas containing Cl.sub.2, CH.sub.2Cl.sub.2 and
the like, or a gas in which O.sub.2 is further added in such a gas,
but such a chlorinated gas substantially can not etch a transparent
substrate made of synthetic quartz and the like. Moreover, the
second layer to be laminated adjacent to the first layer on the
etched surface side of the above-mentioned first layer is formed
with a material that is possible to be etched with a fluorinated
dry etching gas.
[0049] When the blank having a halftone phase shift film with a
multilayer construction like this are first etched in a prescribed
pattern with a fluorinated dry etching gas, the second layer of the
halftone phase shift film is etched. Then, when the halftone phase
shift film of this blank is next etched in the same pattern state
with a chlorinated dry etching gas, the first layer of the halftone
phase shift film is etched but the transparent substrate is not
substantially etched. As a result, it is possible to etch only the
halftone phase shift film precisely. And it is also possible to
control freely the phase angle and transmittance by forming 2 or
more layers constituting a halftone phase shift film with
respective different materials and by controlling the thickness of
each layer.
[0050] Because the phase angle and transmittance of a halftone
phase shift photomask can be controlled in high precision, it
becomes possible to obtain a projection image with precise minute
dimensions by using the halftone phase shift photomask.
[0051] As a method of improving the etching selective ratio to a
substrate, it is known to provide an etching stopper layer between
the substrate and the halftone phase shift film. By this known
method, however, the etching stopper layer will be remained in the
aperture of the accomplished halftone phase shift photomask to
affect the phase angle and light transmittance in the aperture. To
the contrary, since no etching stopper layer is remained in the
aperture in the present invention, it is possible to control in
high precision the phase difference and light transmittance
difference between the aperture and pattern part of the halftone
phase shift film.
[0052] In the present invention, as the second layer (that is, a
layer outer than the first layer) of the halftone phase shift film,
a layer of a halftone phase shift material having an element
composition comprising tantalum, silicon and oxygen as essential
elements is preferably used. A layer of a halftone phase shift
material having an element composition comprising tantalum, silicon
and oxygen as essential elements is a layer containing at least one
of TaSix, TaOx, SiOx and TaSixOy as a main component.
[0053] In cases where the second layer is formed with a material of
such tantalum silicides, it is possible to maintain excellent
processing properties and chemical stability after processing that
are characteristic of tantalum based materials, and the
applicability to exposure light of the short wavelength that is
characteristic of silicide based materials. A material of tantalum
silicides can be used as a halftone phase shift film because they
have an enough light transmission property to fluorinated krypton
excimer laser lithography (wavelength of exposure light is 248 nm)
and fluorinated argon excimer laser lithography (wavelength of
exposure light is 193 nm).
[0054] Furthermore, because the first layer of the halftone phase
shift film can be etched without substantially invading a
transparent substrate made of synthetic quartz and the like by
making the halftone phase shift film to be multilayer and by
preparing the first layer, which can be etched with a chlorinated
gas, between the second layer having an element composition
comprising tantalum, silicon and oxygen as essential elements and
the transparent substrate, it is possible to take an etching
selective ratio to the transparent substrate sufficiently high.
[0055] Therefore, it is possible to realize high precision
patterning by the use of a layer having an element composition
comprising tantalum, silicon and oxygen as essential elements as
the second layer, because an etching selective ratio to a
transparent substrate made of synthetic quartz and the like can be
taken sufficiently while maintaining the applicability to the short
wavelength that is characteristic of silicide materials in addition
to good chemical stability and good processing properties that are
characteristic of tantalum materials. As a result, it is possible
to obtain an ideal mask member that is excellent in stability after
mask processing and in the applicability of short wavelength.
Moreover, a halftone phase shift photomask with high precision can
be produced in a high yield and low cost.
[0056] The first layer of a halftone phase shift film is prepared
near a transparent substrate and is a layer that can be dry etched
with a chlorinated gas. This first layer can be formed with a
material having an element composition comprising tantalum or
chromium as an essential element.
[0057] As a material that has an element composition comprising
tantalum as an essential element and can be form the first layer, a
material having an element composition in which tantalum is an
essential element and silicon is not contained substantially can be
used. FIG. 8 shows the typical optical characteristic spectra of a
blank for a halftone phase shift photomask that can be obtained by
laminating the first layer formed of such a tantalum based material
and the second layer having an element composition comprising
tantalum, silicon and oxygen as essential elements. Generally,
these optical characteristic spectra are considered to be
sufficiently applicable in practical use, but there are some cases
where reflectance on the film surface is somewhat high. That is,
the reflectance of exposure light on the film surface is required
to be 30% or less (from 0 to 30%), preferably 20% or less in some
cases. In case of such a requirement, the third layer may be
prepared between the halftone phase shift film and the transparent
substrate to change the reflectance spectra. Even if the etching
selective ratio of the third layer to the transparent substrate is
low, sufficiently thin thickness of the third layer will not cause
large errors in phase difference. As an example, it is possible to
form a film having an element composition comprising tantalum,
silicon and oxygen as essential elements in thickness of several
tens to 100 angstroms (.ANG.) between the first layer in which
tantalum is an essential element and silicon is substantially not
contained and the transparent substrate. In this case, it becomes
possible to change freely the reflectance spectrum by changing the
thickness of the third thin film within the above-mentioned range,
which does not have large influence to the phase difference of the
mask even if the etching selective ratio is worse, because of thin
film thickness.
[0058] Furthermore, as another method, it is possible to control
the reflectance spectrum by adding a very small amount of oxygen
and/or nitrogen to a material in which tantalum is an essential
element and silicon is substantially not contained. Therefore, the
first layer of the halftone phase shift film can be formed with a
material having an element composition comprising further oxygen
and/or nitrogen, along with tantalum as essential components. A
layer of a material having an element composition comprising oxygen
and/or nitrogen, along with tantalum as essential components is a
layer that contains at least one of TaNx, TaOx and TaNxOy, along
with Ta as main components.
[0059] As a material that has an element composition comprising
chromium as an essential element and can form the first layer, a
material having an element composition comprising oxygen, fluorine
and/nitrogen, along with chromium as essential elements can be
used. This material contains one or more components of metal
chromium (Cr), CrOx, CrFx, CrNx, CrFxOy, CrNxOy, CrFxNy and
CrFxNyOz.
[0060] As another material that has an element composition
comprising chromium as an essential element and can form the first
layer, a material having an element composition comprising silicon,
along with chromium as an essential element can be used. This
material contains metal chromium (Cr) and/or CrSix.
[0061] A further material that has an element composition
comprising chromium as an essential element and can form the first
layer, a material having an element composition comprising
tantalum, along with chromium as an essential element can be used.
This material contains metal chromium (Cr) and/or a
chromium-tantalum alloy (CrTax).
[0062] In addition, it is possible to use a material having an
element composition comprising one or more of the above-mentioned
oxygen, fluorine, nitrogen, silicon, tantalum and others, along
with chromium as essential elements. For example, in cases where
tantalum and silicon, along with chromium are essential elements,
the material contains at least one of CrSix, TaSix and CrTaxSiy as
a main components, along with one or both of metal chromium (Cr)
and a chromium-tantalum alloy (CrTax).
[0063] Furthermore, in cases where tantalum, oxygen, fluorine and
nitrogen, along with chromium are essential elements, the material
contains at least one of CrOx, CrFx, CrNx, CrFxOy, CrNxOy, CrFxNy,
CrFxNyOz, TaOx, TaFx, TaNx, TaFxOy, TaNxOy, TaFxNy, TaFxNyOz,
CrTaxOy, CrTaxFy, CrTaxNy, CrTaxFyOz, CrTaxNyOz, CrTaxFyNz and
CrTawFxNyOz, along with one or both of metal chromium (Cr) and a
chromium-tantalum alloy (CrTax) as main components.
[0064] A halftone phase shift film with multilayer construction
having at least the first layer and the second layer is preferable
to be formed on a transparent substrate so that the phase
difference .phi. obtained from the following expression (1) is
within the range of n.pi..+-..pi./3 radian (here, n is an odd
number): 2 = k = 1 m - 1 k , k + 1 + k = 2 m - 1 2 ( u k - 1 ) d k
/ Expression (1)
[0065] wherein, .phi. is a phase change caused to light vertically
transmitting through a photomask or a blank for a photomask in
which a halftone phase shift film consisting of (m-2) layers is
formed on the transparent substrate, .chi..sup.k,k+1 is a phase
change occurring in the interface between a k.sup.th layer and a
(k+1).sup.th layer, u.sub.k and d.sub.k are the refractive index
and film thickness of the k.sup.th layer, respectively, and
.lambda. is the wavelength of exposure light, providing that the
layer of k=1 is the transparent substrate and the layer of k=m is
air.
[0066] Moreover, it is preferable that a halftone phase shift film
is formed in such a film thickness as the halftone phase shift film
has the transmittance of exposure light within the range of 1 to
50% provided that a transparent substrate has a transmittance of
exposure light as 100%, in order to control transmittance to be
optimum corresponding to any pattern.
[0067] In a halftone phase shift photomask or a blank therefor of
the present invention, a light shielding film may be formed in
succession just on or under a halftone phase shift film. It is
possible to prevent the solarization of the resist due to the
overlap of adjoining shots in the process of a halftone phase shift
photo lithography by preparing a light shielding layer. Further, it
is possible to control the transcription properties of a
transcribing and forming pattern with this light shielding
film.
[0068] For the reason that a light shielding film is required to be
excellent in plate making properties, durability and others, a
light shielding film is preferable to be formed using a material
having an element composition comprising chromium as an essential
element. In case of preparing a light shielding film of chromium
materials, plate making of a light shielding film may be carried
out using a wet etchant of cerium nitrates after a pattern in a
halftone phase shift film is formed by a gas dry etching as
described later.
[0069] In the present invention, there are some cases where a film
comprising chromium and/or a chromium tantalum alloy as main
components is formed as the first layer of the halftone phase shift
film. In this case, it is feared that the first layer of the
halftone phase shift film is invaded by a wet etchant of cerium
nitrates to cause some problems in pattern formation.
[0070] However, corrosive resistant of the first layer comprising
chromium and/or a chromium tantalum alloy as main components to wet
etchants can be improved by adding oxygen, fluorine and/or nitrogen
as mentioned above, or by making an alloy through the addition of
an other metal like silicon, tantalum or the like.
[0071] Furthermore, because as mentioned later, the film thickness
of the first layer comprising chromium and/or a chromium tantalum
alloy as main components is often thin, the layer has inherently
low possibility of being invaded by wet etchants, and if the layer
is invaded, the invasion is often stopped at the degree
substantially not to adversely affect the transcription
property.
[0072] The production method of a blank for a halftone phase shift
photomask and the method of producing a halftone phase shift
photomask by carrying out the halftone phase shift photo
lithography using the blank in the present invention will be
explained in the following.
[0073] FIG. 1 is a schematically sectional view showing a first
example of a blank for a halftone phase shift photomask in the
present invention. In FIG. 1, a reference numeral 110 denotes a
transparent substrate, 120 denotes a halftone phase shift film with
multilayer construction, 121 denotes a first layer having an
element composition comprising chromium as an essential element,
and 122 denotes a second layer having an element composition
comprising tantalum, silicon and oxygen as essential elements.
[0074] The Blank for a halftone phase shift photomask in the first
example have the halftone phase shift film 120 having a multilayer
construction composed of the second layer 122 having an element
composition comprising tantalum, silicon and oxygen as essential
elements and the first layer 121 having an element composition
comprising chromium as an essential element, and the first layer
121 and the second layer 122 are laminated and formed in this order
on the transparent substrate 110.
[0075] And, the second layer 122 has processing properties and
chemical stability, which are characteristic of tantalum based
materials, and can be etched with a fluorinated gas. The first
layer 121 can be etched with a chlorinated gas after etching the
second layer 122 with a fluorinated gas. At this time, since the
transparent substrate 110 made of synthetic quartz and the like is
not substantially etched with a chlorinated gas, it is possible to
take a sufficiently high etching selective ratio of the first layer
121 to the transparent substrate 110. As a result, high precision
patterning can be achieved when a photomask is formed.
[0076] In the first example, since the second layer 122 formed of a
tantalum silicide material is prepared as one layer of the halftone
phase shift film 120, a photomask produced using this blank is
applicable to exposure light of the short wavelength, including
fluorinated krypton excimer laser (wavelength is 248 nm) and
fluorinated argon excimer laser (wavelength is 193 nm).
[0077] In the first example, for the purpose of obtaining some good
phase shift effects when a halftone phase shift photomask is
produced, the halftone phase shift film 120 is formed on the
transparent substrate 110 so that the phase difference .phi. that
is obtained from the following expression when m=4, is within the
range of n.pi..+-..pi./3 radian (here, n is an odd number): 3 = k =
1 3 k , k + 1 + k = 2 3 2 ( u k - 1 ) d k /
[0078] wherein, .phi. is a phase change caused to light vertically
transmitting through a blank for a photomask in which the halftone
phase shift film 120 with 2 layer construction is formed on the
transparent substrate 110, .chi..sup.k,k+1 is a phase change
occurring in the interface between a k.sup.th layer and a (k+1)th
layer, u.sub.k and d.sub.k are the refractive index and film
thickness of the k.sup.th layer (the first layer 121 of a chromium
material and the second layer 122 of a tantalum silicide material)
respectively, and .lambda. is the wavelength of exposure light,
providing that the layer of k=1 is the transparent substrate 110
and the layer of k=m is air.
[0079] Moreover, in order to obtain a substantial phase shift
effect when a halftone phase shift photomask is produced, the
halftone phase shift film 120 is formed in such a film thickness as
the halftone phase shift film 120 has a transmittance of exposure
light within the range of 1 to 50% provided that the transparent
substrate 110 has a transmittance of exposure light as 100%.
[0080] As the first layer 121 having an element composition
comprising chromium as an essential element, it is possible to form
a chromium metal layer, a chromium oxide layer, a chromium nitride
layer, a chromium oxide nitride layer or others, all of which can
be etched with a chlorinated gas. This first layer 121 made of a
chromium material can be easily formed by the sputtering method
that has been conventionally applied for forming thin films for
photomasks. If metal chromium is used as a target and a mixed gas
in which oxygen and/or nitrogen are mixed with a sputtering gas of
argon is used, the chromium oxide layer, the chromium nitride layer
or the chromium oxide nitride layer can be obtained. It is possible
to conduct the adjustment and control of a refractive index by
changing sputtering pressure or sputtering current, as well as
changing the mixing ratio of gases. It is possible to form such a
thin film made of a material of chromium compounds by applying
technologies, including the vacuum deposition, the CVD method, the
ion plating method and the ion beam sputtering method, as well as
the sputtering method.
[0081] The second layer 122 made of a material having an element
composition comprising tantalum, silicon and oxygen as essential
elements can be easily formed by the sputtering method that has
been conventionally applied for forming thin films for photomasks.
For example, a tantalum silicide oxide film can be obtained by
using tantalum silicide as a target and by using a mixed gas in
which oxygen is mixed with a sputtering gas of argon. It is
possible to conduct the adjustment and control of the refractive
index of a tantalum silicide oxide film by changing sputtering
pressure or sputtering current, as well as changing the mixing
ratio of gases. It is possible to form such a thin film made of
tantalum silicides by applying technologies, including the vacuum
deposition, the CVD method, the ion plating method and the ion beam
sputtering method, as well as the sputtering method.
[0082] Synthetic quartz as the transparent substrate 110 is
transparent to exposure light of the short wavelength, including
fluorinated krypton excimer laser (wavelength is 248 nm) and
fluorinated argon excimer laser (wavelength is 193 nm) and further
can take a high etching selective ratio of the first layer 121 to
the transparent substrate 110 in cases where the first layer 121 of
a chromium compounds based-thin film is subjected to etching
processing with a chlorinated gas when producing a photomask.
[0083] Next, another example of a blank for a halftone phase shift
photomask in the present invention will be explained. FIG. 2 is a
schematically sectional view showing a second example of the blank
for a halftone phase shift photomask in the present invention. In
FIG. 2, a reference numeral 110 denotes a transparent substrate,
120 denotes a halftone phase shift film with multilayer
construction, 121 denotes a first layer having an element
composition comprising chromium as an essential element, 122
denotes a second layer having an element composition comprising
tantalum, silicon and oxygen as essential elements, 125 denotes a
halftone pattern area (a shift layer pattern area), and 130 denotes
a light shielding layer (also referred to as a substantial light
shielding film). The Blans for a halftone phase shift photomask in
the second example has the constitution in which the light
shielding layer 130 is provided on the halftone phase shift film of
that in the first example.
[0084] The light shielding layer 130 should be finally removed from
the halftone pattern area (shift layer pattern area) 125 to be
remained only in peripheral parts of the halftone pattern area 125,
and is needed to substantially have a light shielding property so
as to prevent undesirable solarization caused by the multiplex
exposure of adjoining shots in wafer exposure process and to form
an alignment mark and others. Specifically, transmittanse of the
light shielding layer is usually made not more than 1% with respect
to the exposure light.
[0085] A layer of chromium-based metals such as metal chromium,
chromium oxide, chromium nitride, chromium oxide nitride and the
like is generally used as the light shielding layer 130, but it is
not limited to these materials. These films made of chromium
compounds can be formed by applying technologies, including the
sputtering method, the vacuum deposition, the CVD method, the ion
plating method and the ion beam sputtering method.
[0086] Further, in a case where the light shielding layer made of
chromium compounds in the blank is etched with the use of a wet
etchant to produce a halftone phase shift photomask, it is
preferable to previously improve the corrosion resistance of the
first layer made of chromium compounds by the method of forming the
layer using a material of chromium compounds in which oxygen,
fluorine and/or nitrogen are added, or using a material of chromium
alloys made with other metals, including silicon and tantalum, and
by other methods, as mentioned above.
[0087] As variations of blanks in the first and second examples,
there may be exemplified one in which the first layer 121 made of
chromium compounds is altered to a layer made of another material
capable of being etched with a chlorinated gas, for example, a
chromium tantalum alloy as a main component. Furthermore, as other
materials that can be etched with a chlorinated gas, materials that
have an element composition comprising tantalum as an essential
element and further containing oxygen and/or nitrogen as needed can
be used as mentioned above, and the first layer may be formed with
such a material. A layer containing a chromium tantalum alloy as a
main component and a layer made of a material that has an element
composition comprising tantalum as an essential element and further
containing oxygen and/or nitrogen as needed can also be formed in
film similarly to a film made of chromium compounds by applying
technologies, including the sputtering method, the vacuum
deposition, the CVD method, the ion plating method and the ion beam
sputtering method.
[0088] Next, examples of a halftone phase shift photomask in the
present invention will be explained. FIG. 3 is a schematically
sectional view showing a first example of a halftone phase shift
photomask in the present invention. This photomask is produced
using the above-mentioned first example (FIG. 1) of blank, in which
the halftone phase shift film 120 is patterned in the prescribed
shape and an aperture is formed, where the surface of the
transparent substrate 110 is exposed. Explanation about each layer
and optical properties of a photomask in the first example will be
omitted because they are the same as those of the blank in the
above-mentioned first example.
[0089] FIG. 4 is a schematically sectional view showing a second
example of a halftone phase shift photomask in the present
invention. This photomask is produced using the above-mentioned
second example (FIG. 2) of blank, in which the halftone phase shift
film 120 is patterned in the prescribed shape and an aperture is
formed, where the surface of the transparent substrate 110 is
exposed. Furthermore, in this second example of photomask, the
halftone pattern area (shift layer pattern area) 125 for obtaining
phase shift effects and the light shielding pattern area 135 for
obtaining substantial light shielding effects are prepared.
Explanation about each layer and optical properties of a photomask
in the second example will be omitted because they are the same as
those of the blank in the above-mentioned second example.
[0090] As variations of photomasks in the first and second
examples, the same variations as those of blanks can be
illustrated. That is, it is possible to illustrate such variations
as the first layer 121 made of chromium compounds is altered to a
layer having another material capable of being etched with a
chlorinated gas, for example, a chromium tantalum alloy as a main
component or a layer made of a material that has an element
composition comprising tantalum as an essential element and further
containing oxygen and/or nitrogen as needed.
[0091] Next, the production method of a halftone phase shift
photomask in the present invention will be explained with reference
to the accompanying drawings. In FIG. 5, one example of the method
of producing a halftone phase shift photomask in the first example
is shown. In the production method, first, the blank for a halftone
phase shift photomask of the first example (FIG. 1) is provided as
shown in FIG. 5(a), and then a resist material is applied on the
halftone phase shift film 120 and dried to form the resist layer
140 as shown in FIG. 5(b).
[0092] After the resist layer 140 is formed, only a prescribed area
of the resist layer 140 is solarized using an electron beam writer
as shown in FIG. 5(c), and the resist layer is developed and
patterned in conformity with a pattern shape required in the
halftone phase shift film 120. An aperture 140A in the resist layer
140 is also formed by the patterning. A resist material is
preferable to have easily handling property, prescribed resolution
and high dry etching resistance, but not especially limited.
[0093] After the resist layer 140 is patterned, the resist layer
140 is used as an etching resistance mask as shown in FIG. 5(d),
and the second layer that is a film made of tantalum silicides, and
the first layer that is a film made of chromium compounds, of the
halftone phase shift film 120 are etched in succession using a
fluorinated gas and a chlorinated gas in the order. Then, the
pattern of the halftone phase shift film as shown in FIG. 5(e) is
obtained by peeling the resist layer 140 off.
[0094] Next, one example of a method of producing a halftone phase
shift photomask in the second example is shown in FIG. 6. In the
production method, patterning processing is carried out similarly
to the production method for the first example in the previous step
shown in the figure. That is, first, the blank for a halftone phase
shift photomask in the second example (FIG. 2) is provided, and a
resist material is applied on the light shielding film 130 and
dried to form the resist layer 140. Then, only a prescribed area of
the resist layer 140 is solarized using an electron beam writer,
and the resist layer is developed and patterned in conformity with
a pattern shape required in the halftone phase shift film 120.
After the resist layer 140 is patterned, the resist layer 140 is
used as an etching resistance mask, and the light shielding film
130, a film made of tantalum silicides that is the second layer of
the halftone phase shift film 120 and a film made of chromium
compounds that is the first layer of the halftone phase shift film
120 are etched in succession using a fluorinated gas and a
chlorinated gas in the order. Then, the pattern of the halftone
phase shift film is obtained by peeling the resist layer 140
off.
[0095] Processes to this step are the same as those in the
production method in the first example. After that, a resist layer
145 is newly formed on the light shielding layer 130 and is
patterned by exposing and developing as shown in FIG. 6(a). This
new resist layer 145 is formed only on a light shielding pattern
area 135 that is desired to finally obtain substantial light
shielding effects and is patterned in a shape having an aperture
145A. Said aperture 145A is in accord with the halftone pattern
area (shift layer pattern area) 125 which should obtain phase shift
effects. After that, this resist layer 145 is used as an etching
resistance mask as shown in FIG. 6(b), and the light shielding
layer of aperture 145A is removed by conducting wet etching with a
wet etchant of cerium nitrates. After that, when the resist layer
145 is peeled off, a halftone phase shift photomask in the second
example is obtained.
[0096] FIG. 6(c) and FIG. 6(d) are enlarged views of D1 part of
FIG. 6(a) and D2 part of FIG. 6(b), respectively. At the time of
wet etching, it is feared that the first layer 121, which is a film
made of chromium compounds, is etched and becomes to be as shown in
enlarged FIG. 6(d) to cause some problems in pattern. However, the
first layer 121, which is a film made of chromium compounds, has
generally low possibility of being invaded as shown in FIG. 6(d)
because its film thickness is thin. And, even if the layer is
invaded, the invasion is considered to stop in the degree
substantially not to adversely affect its transcription
properties.
[0097] Furthermore, corrosion resistance of the first layer of the
film made of chromium compounds to wet etchants can be improved by
adding fluorine and/or nitrogen to the first layer or by making an
alloy through the addition of an other metal like silicon, tantalum
or the like. As a result, the part of WO shown in FIG. 6(d) can be
extremely small, so adverse effects to the transcription properties
can be certainly prevented.
[0098] A halftone phase shift photomask in the above-mentioned
variation examples can be produced fundamentally by the same
procedure as the production method of the first and second
examples.
EXAMPLES
(Example 1)
[0099] An example of a blank for a halftone phase shift photomask
applicable to KrF exposure in the present invention will be
explained with reference to FIG. 7. In this example, too, a
halftone phase shift film 120 will be constituted of 2 layers.
[0100] As shown in FIG. 7(a), a first layer 121 of a halftone phase
shift film was formed on a substrate 110 of optically polished and
sufficiently washed high purity synthetic quartz with 6 inches
square and 0.25 inch in thickness under conditions as shown in the
following. The thickness of the first layer 121 was made to be
about 25 nm.
[0101] <Film forming conditions>
[0102] Film forming device: Planer type DC magnetron sputtering
device
[0103] Target: Tantalum metal
[0104] Gas and its flow rate: Argon gas, 50 sccm
[0105] Sputtering pressure: 0.3 Pa
[0106] Sputtering current: 3.0 A
[0107] Next, a second layer 122 of a halftone phase shift film was
formed on the first layer under conditions as shown in the
following. The thickness of the second layer 122 was made to be
about 140 nm.
[0108] <Film forming conditions>
[0109] Film forming device: Planer type DC magnetron sputtering
device
[0110] Target: Tantalum: Silicon=1:3 (atomic ratio)
[0111] Gas and its flow rate: Argon gas, 50 sccm+Oxygen gas, 50
sccm
[0112] Sputtering pressure: 0.3 Pa
[0113] Sputtering current: 3.5 A
[0114] Thus, the blank 1 for a halftone phase shift photomask,
which are applicable to KrF excimer laser exposure and have the
transmittance of 6%, were obtained. Optical properties of the blank
are shown in FIG. 8.
[0115] Moreover, as shown in FIG. 7(b), the first layer and second
layer of a halftone phase shift film were formed under the same
conditions as mentioned above on the synthetic quartz substrate
that had been masked with a tape in advance, and test piece 2 was
obtained. Using this test piece 2, phase difference and
transmittance to light of 248 nm in wavelength were measured with a
commercially available phase difference measuring device (MPM248,
produced by Laser Tech. Co. Ltd.). Measured values were
182.62.degree. and 5.37%, respectively.
[0116] Next, concerning this test piece 2, its resistance to
chemical solutions like washing liquids, etching liquids and others
used in the production process of photomasks was investigated. The
results are shown in the following TABLE 1.
[0117] Chemical solution (a): Sulfuric acid: nitric acid=10:1
(volume ratio), 80.degree. C. of the temperature
[0118] Chemical solution (b): 10% aqueous ammonia, room
temperature
[0119] Chemical solution (c): Commercially available Chromium
etchant (MR-ES, produced by Ink Tech. Co. Ltd.), room
temperature
1 TABLE 1 Chemical Dipping Change in Change in solution duration
phase difference transmittance (a) 2 hours -0.11.degree. +0.01% (b)
2 hours -0.05.degree. +0.00% (c) 2 hours -0.03.degree. +0.02%
(Example 2)
[0120] An example of a halftone phase shift photomask in the
present invention will be explained with reference to FIG. 9. In
this example, too, a halftone phase shift film 120 will be
constituted of 2 layers.
[0121] As shown in FIG. 9(a), a resist material was applied on the
blank 1 obtained in example 1 and then the usual method of electron
beam lithography or photo lithography was carried out to form a
resist layer 140 containing organic compounds as main components
and having a prescribed pattern.
[0122] Next, as shown in FIG. 9(b), second layer 122 and first
layer 121 on a halftone phase shift film having exposed portions at
an aperture of the resist layer 140 were selectively dry etched
successively by exposing to high density plasma and the halftone
phase shift film 120 was patterned in the prescribed shape by means
of a commercially available dry etcher for photomasks (VLR700,
produced by PTI Co. Ltd.). The dry etcher used in this example has
2 etching treatment chambers, and following conditions 1 and 2 were
carried out in separate treatment chambers.
[0123] <Condition 1>
[0124] Etching gas: CF.sub.4 gas
[0125] Pressure: 10 mTorr
[0126] ICP power (high density plasma generation): 950 W
[0127] Bias power (drawing power): 50 W
[0128] Time: 360 sec
[0129] <Condition 2>
[0130] Etching gas: Cl.sub.2 gas
[0131] Pressure: 3 mTorr
[0132] ICP power (high density plasma generation): 500 W
[0133] Bias power (drawing power): 25 W
[0134] Time: 200 sec
[0135] Next, the remaining resist layer 140 was peeled off in the
usual manner to make a halftone phase shift photomask 3 as shown in
FIG. 9(c). The transmittance of the halftone phase shift part in
this photomask 3 to light of 248 nm in wavelength was 6%. It was
noticeable that synthetic quartz is hardly etched in the etching
process of the condition 2 and phase difference can be controlled
in extremely high precision.
[0136] Furthermore, it was possible to put this halftone phase
shift photomask 3 to practical use in every respect of the
dimensional accuracy, the sectional shape, the film thickness
distribution, the transmittance distribution and the film adhesion
to the substrate.
(Example 3)
[0137] Concerning blanks for a halftone phase shift photomask
applicable to KrF exposure in the present invention, the example of
blank in which the film surface reflectance at 248 nm wavelength
was lowered as compared to the blank in example 1 will be explained
with reference to FIG. 10. In this example, lowered reflectance was
realized by adding a minute amount of oxygen to the first layer
substantially not containing silicon out of 2 layers constituting a
halftone phase shift film 120.
[0138] As shown in FIG. 10(a), a first layer 121 of a halftone
phase shift film was formed on a substrate 110 of optically
polished and sufficiently washed high purity synthetic quartz of 6
inches square and 0.25 inch in thickness under conditions as shown
in the following. The thickness of the first layer 121 was made to
be about 40 nm.
[0139] <Film forming conditions>
[0140] Film forming device: Planer type DC magnetron sputtering
device
[0141] Target: Tantalum metal
[0142] Gas and its flow rate: Argon gas, 40 sccm+Oxygen gas, 5
sccm
[0143] Sputtering pressure: 0.3 Pa
[0144] Sputtering current: 2.0 A
[0145] Next, a second layer 122 of a halftone phase shift film was
formed on the first layer under conditions as shown in the
following. The thickness of the second layer 122 was made to be
about 90 nm.
[0146] <Film forming conditions>
[0147] Film forming device: Planer type DC magnetron sputtering
device
[0148] Target: Tantalum: Silicon=1:3 (atomic ratio)
[0149] Gas and its flow rate: Argon gas, 50 sccm+Oxygen gas, 50
sccm
[0150] Sputtering pressure: 0.3 Pa
[0151] Sputtering current: 3.5 A
[0152] Thus, the blank 4 for a halftone phase shift photomask,
which are applicable to KrF excimer laser exposure and which have
the transmittance of 6 %,was obtained. Optical properties of the
blank are shown in FIG. 11. The film surface reflectance of the
blank in example 1 at 248 nm wavelength was about 43% as shown in
FIG. 8, while in this example, the film surface reflectance could
be lowered to the degree of 2%, resulting in the realization of
lowered reflectance.
[0153] Moreover, as shown in FIG. 10(b), the first layer and second
layer of a halftone phase shift film were formed under the same
conditions as mentioned above on the synthetic quartz substrate
that had been masked with a tape in advance, and test piece 5 was
obtained. Using this test piece 5, phase difference and
transmittance to light of 248 nm in wavelength were measured by
means of a commercially available phase difference measuring device
(MPM248, produced by Laser Tech. Co. Ltd.). Measured values were
186.59.degree. and 6.07%, respectively.
(Example 4)
[0154] Example 4 is an example in which a halftone phase shift
photomask in the first example shown in FIG. 3 was produced by the
production method shown in FIG. 5 using the blank for a halftone
phase shift photomask in the first example shown in FIG. 1. In this
example, a halftone phase shift photomask applicable to KrF
exposure was produced.
[0155] A first layer 121 of a halftone phase shift film was formed
on a transparent substrate 110 of optically polished and
sufficiently washed high purity synthetic quartz of 6 inches square
and 0.25 inch in thickness under conditions as shown in the
following. The first layer 121 was made of chromium compounds and
its thickness was made to be about 10 nm.
[0156] <Film forming conditions>
[0157] Film forming device: Planer type DC magnetron sputtering
device
[0158] Target: Chromium metal
[0159] Gas and its flow rate: Argon gas, 70 sccm
[0160] Sputtering pressure: 0.35 Pa
[0161] Sputtering current: 5.0 A
[0162] Next, a second layer 122 of a halftone phase shift film was
formed on the first layer under conditions as shown in the
following. The second layer 122 was made of tantalum silicides with
an element composition comprising tantalum, silicon and oxygen as
essential elements. The thickness of the second layer 122 was made
to be about 140 nm.
[0163] <Film forming conditions>
[0164] Film forming device: Planer type DC magnetron sputtering
device
[0165] Target: Tantalum: Silicon=1:3 (atomic ratio)
[0166] Gas and its flow rate: Argon gas, 50 sccm+Oxygen gas, 50
sccm
[0167] Sputtering pressure: 0.3 Pa
[0168] Sputtering current: 3.5 A
[0169] Thus, the blank for a halftone phase shift photomask, which
are applicable to KrF excimer laser exposure and which have the
transmittance of 6%, was obtained.
[0170] Further, the lift-off method was also carried out to make a
test piece as shown in FIG. 12. That is, after the first layer and
second layer of a halftone phase shift film were formed under the
same conditions as mentioned above on the synthetic quartz
substrate that had been masked with a tape in advance, the masked
tape was peeled off to make a test piece by means of difference in
level. Using this test piece, phase difference and transmittance to
light of 248 nm in wavelength were measured with a commercially
available phase difference measuring device (MPM248, produced by
Laser Tech. Co. Ltd.). Measured values were 179.22.degree. and
5.88%, respectively.
[0171] Next, a halftone phase shift photomask in the first example
as shown in FIG. 3 was produced with the use of the obtained blank.
First, as shown in FIG. 5(a), the blank for a halftone phase shift
photomask was provided, and then resist material "ZEP7000"
containing organic compounds as main components (produced by Nippon
Zeon Co. Ltd.) was applied on the halftone phase shift film 120 of
this blank and dried to form a resist layer 140 as shown in FIG.
5(b). Next, as shown in FIG. 5(c), the resist layer 140 was
patterned in the prescribed shape by exposing only the prescribed
area of the resist layer by means of an electron beam writer and
then developing.
[0172] Next, as shown in FIG. 5(d), the second layer 122 and the
first layer 121 of a halftone phase shift film at an aperture of
the resist layer 140 where the halftone phase shift film was
exposed were selectively dry etched successively by exposing to
high density plasma and the halftone phase shift film 120 was
patterned in the prescribed shape by means of a commercially
available dry etcher for photomasks (VLR700, produced by PTI Co.
Ltd.). The dry etcher used in this example has 2 etching treatment
chambers, and following condition 1 and 2 were carried out in
separate treatment chambers.
[0173] <Condition 1>
[0174] Etching gas: CF.sub.4 gas
[0175] Pressure: 10 mTorr
[0176] ICP power (high density plasma generation): 950 W
[0177] Bias power (drawing power): 50 W
[0178] Time: 360 sec
[0179] <Condition 2>
[0180] Etching gas: Cl.sub.2 gas+O.sub.2 gas (2:3)
[0181] Pressure: 100 mTorr
[0182] ICP power (high density plasma generation): 500 W
[0183] Bias power (drawing power): 25 W
[0184] Time: 200 sec
[0185] Next, the remaining resist layer 140 was peeled off in the
usual manner to make a halftone phase shift photomask as shown in
FIG. 5(e). The transmittance of the halftone phase shift part in
this photomask to light of 248 nm in wavelength was 6%. It was
noticeable that the transparent substrate 110 of synthetic quartz
is hardly etched in the etching process of the condition 2 and
phase difference can be controlled in extremely high precision.
[0186] Furthermore, it was possible to put this halftone phase
shift photomask to practical use in every respect of the
dimensional accuracy, the sectional shape, the film thickness
distribution, the transmittance distribution and the film adhesion
to a substrate.
(Example 5)
[0187] Example 5 is an example in which a halftone phase shift
photomask in the second example shown in FIG. 4 was produced by a
series of production methods shown in FIG. 5 and FIG. 6 using a
blank for a halftone phase shift photomask in the second example
shown in FIG. 2. In this example, a halftone phase shift photomask
for KrF exposure was produced. And, in consideration of wetly
etching a light shielding film made of chromium in this example,
corrosion resistance of the first layer made of chromium compounds
was improved by adding tantalum.
[0188] First, a first layer 121 of a halftone phase shift film was
formed on a transparent substrate 110 of optically polished and
sufficiently washed high purity synthetic quartz of 6 inches square
and 0.25 inch in thickness under conditions as shown in the
following. The first layer 121 was made of tantalum chromium alloys
and its thickness was made to be about 10 nm.
[0189] <Film forming conditions>
[0190] Film forming device: Planer type DC magnetron sputtering
device
[0191] Target: Tantalum chromium alloy (Tantalum: Chromium=1:9)
[0192] Gas and its flow rate: Argon gas, 70 sccm
[0193] Sputtering pressure: 0.35 Pa
[0194] Sputtering current: 5.0 A
[0195] Next, a second layer 122 of a halftone phase shift film was
formed on the first layer under conditions as shown in the
following. The second layer 122 was made of tantalum silicides with
an element composition comprising tantalum, silicon and oxygen as
essential elements. The thickness of the second layer 122 was made
to be about 90 nm.
[0196] <Film forming conditions>
[0197] Film forming device: Planer type DC magnetron sputtering
device
[0198] Target: Tantalum: Silicon=1:3 (atomic ratio)
[0199] Gas and its flow rate: Argon gas, 50 sccm+Oxygen gas, 50
sccm
[0200] Sputtering pressure: 0.3 Pa
[0201] Sputtering current: 3.5 A
[0202] Next, a light shielding film 130 was formed on the halftone
phase shift film 120 by the sputtering method. The light shielding
film 130 was made of chromium metal, and its thickness was made to
be 1000 angstroms (.ANG.).
[0203] <Sputtering conditions of a light shielding film>
[0204] Film forming device: Planer type DC magnetron sputtering
device
[0205] Target: Chromium metal
[0206] Gas and its flow rate: Argon gas, 50 sccm
[0207] Sputtering pressure: 0.3 Pa
[0208] Sputtering current: 3.5 A
[0209] Thus, a blank for a halftone phase shift photomask that are
applicable to KrF excimer laser exposure and which have the
transmittance of 6%, was obtained.
[0210] Further, the lift-off method was also carried out to make a
test piece as shown in FIG. 12. That is, after the first layer and
second layer of a halftone phase shift film were formed under the
same conditions as mentioned above on the synthetic quartz
substrate that had been masked with a tape in advance, the masked
tape was peeled off to make a test piece with difference in level.
Using this test piece, phase difference and transmittance to light
of 248 nm in wavelength were measured by means of a commercially
available phase difference measuring device (MPM248, produced by
Laser Tech. Co. Ltd.). Measured values were 180.12.degree. and
6.33%, respectively.
[0211] After this test piece with difference in level was immersed
in a commercially available chromium etchant (MR-ES produced by Ink
Tech. Co. Ltd.) at room temperature for 240 seconds, the section of
the pattern portion was observed by means of the SEM (scanning
electron microscope), and thus no corrosion as shown in FIG. 6(d)
was found.
[0212] For comparison with this test piece, after the test pieces
with difference in level produced in example 4 were also immersed
in a commercially available chromium etchant (MR-ES produced by Ink
Tech. Co. Ltd.) at room temperature for 180 seconds and 240
seconds, respectively, the section of the pattern portion of each
test piece was observed by means of the SEM. As a result, no
corrosion was found in the test piece immersed for 180 seconds, but
some corrosion as shown in FIG. 6(d) was observed in the test piece
immersed for 240 seconds. By this comparison, it was confirmed that
the corrosion resistance of the first layer in example 5 had been
improved in comparison with the first layer in example 4.
[0213] Next, a halftone phase shift photomask in the second example
as shown in FIG. 4 was produced with the use of the obtained blank.
First, resist material "ZEP7000" containing organic compounds as
main components (produced by Nippon Zeon Co. Ltd.) was applied on
the light shielding layer 130 and dried to form a resist layer 140.
Next, the resist layer 140 was patterned in the prescribed shape by
exposing only the prescribed area of the resist layer by means of
an electron beam writer and then developing.
[0214] Next, the light shielding layer 130 at a portion exposing
through an aperture of the resist layer 140 and the halftone phase
shift film 120 just under the exposed portion were selectively dry
etched successively by exposing to high density plasma to pattern
the light shielding layer 130 and the halftone phase shift film 120
in the prescribed shapes by means of a commercially available dry
etcher for photomasks (VLR700, produced by PTI Co. Ltd.). In this
example, etching conditions 1, 2 and 3 were carried out in this
order, that is, etching of light shielding layer 130 by etching
condition 1, the second layer by etching condition 2 and the first
layer by etching condition 3 (the same as condition 1) was carried
out in succession. The dry etcher used in this example has 2
etching treatment chambers, and following conditions 1 and 3 were
carried out in the same treatment chamber, and condition 2 was
carried out in the different treatment chamber.
[0215] <Condition 1: Etching of the light shielding
layer>
[0216] Etching gas: Cl.sub.2 gas+O.sub.2 gas (2:3)
[0217] Pressure: 100 mTorr
[0218] ICP power (high density plasma generation): 500 W
[0219] Bias power (drawing power): 25 W
[0220] Time: 200 sec
[0221] <Condition 2: Etching of the second layer>
[0222] Etching gas: CF.sub.4
[0223] Pressure: 10 mTorr
[0224] ICP power (high density plasma generation): 950 W
[0225] Bias power (drawing power): 50 W
[0226] Time: 360 sec
[0227] <Condition 3: Etching of the first layer>
[0228] Etching gas: Cl.sub.2 gas+O.sub.2 gas (2:3)
[0229] Pressure: 100 mTorr
[0230] ICP power (high density plasma generation): 500 W
[0231] Bias power (drawing power): 25 W
[0232] Time: 200 sec
[0233] Next, resist material "IP3500" (produced by Tokyo Ohka Kogyo
Co. Ltd.) was applied again on this layer and dried, and then photo
lithography was carried out to form a resist layer 145 having
apertures only in areas desired to expose the halftone phase shift
film as shown in FIG. 6(a). After that, wet etching was carried out
under the following condition to selectively remove the exposed
light shielding layer 130 at an aperture 145A of the resist layer
as shown in FIG. 6(b). And the remaining resist layer 145 was
peeled off in the usual manner to make a halftone phase shift
photomask.
[0234] The transmittance of the halftone phase shift part in this
photomask to light of 248 nm in wavelength was 6%. Furthermore, in
the halftone phase shift film in this photomask, no problem due to
corrosion as shown in FIG. 6(d) was found in the first layer 121
made of chromium compounds. In this example, too, the transparent
substrate 110 was not etched under etching condition 3 similarly to
example 4 and phase difference could be controlled in extremely
high precision.
[0235] Furthermore, it was possible to put this halftone phase
shift photomask to practical use in every respect of the
dimensional accuracy, the sectional shape, the film thickness
distribution, the transmittance distribution and the film adhesion
to a substrate.
(Example 6)
[0236] Also in the example 6, a halftone phase shift photomask in
the second example shown in FIG. 4 was produced by a series of
production methods shown in FIG. 5 and FIG. 6 using the blank for a
halftone phase shift photomask in the second example shown in FIG.
2. In this example, the film forming condition of the first layer
and the etching condition of the first layer (corresponding to
etching condition 3 in example 5) were set as the following. Other
conditions were the same as those in example 5. The optical
characteristic spectrum (transmittance spectrum) of the thus
obtained blank is shown in FIG. 13.
[0237] <The film forming condition of the first layer>
[0238] Film forming device: Planer type DC magnetron sputtering
device
[0239] Target: Tantalum chromium alloy (Tantalum Chromium=97:3)
[0240] Gas and its flow rate: Argon gas, 95 sccm
[0241] Sputtering pressure: 1.0 Pa
[0242] Sputtering current: 1.0 A
[0243] <The etching condition of the first layer>
[0244] Etching gas: Cl.sub.2 gas
[0245] Pressure: 3 mTorr
[0246] ICP power (high density plasma generation): 250 W
[0247] Bias power (drawing power): 25 W
[0248] Time: 250 sec
* * * * *