U.S. patent application number 10/212113 was filed with the patent office on 2003-02-06 for phase shift mask blank, phase shift mask, and method of manufacture.
Invention is credited to Inazuki, Yukio, Kaneko, Hideo, Nakatsu, Masayuki, Numanami, Tsuneo, Okazaki, Satoshi, Tajika, Atsushi.
Application Number | 20030025216 10/212113 |
Document ID | / |
Family ID | 19068710 |
Filed Date | 2003-02-06 |
United States Patent
Application |
20030025216 |
Kind Code |
A1 |
Inazuki, Yukio ; et
al. |
February 6, 2003 |
Phase shift mask blank, phase shift mask, and method of
manufacture
Abstract
In a phase shift mask blank comprising a transparent substrate
and a phase shift film thereon, after the phase shift film is
formed on the substrate, it is surface treated with ozone water
having an ozone concentration of at least 1 ppm. The resulting
phase shift film is of quality in that it experiences minimized
changes of phase difference and transmittance upon immersion in
chemical liquid during subsequent mask cleaning step or the
like.
Inventors: |
Inazuki, Yukio;
(Niigata-ken, JP) ; Nakatsu, Masayuki;
(Niigata-ken, JP) ; Numanami, Tsuneo;
(Niigata-ken, JP) ; Tajika, Atsushi; (Niigata-ken,
JP) ; Kaneko, Hideo; (Niigata-ken, JP) ;
Okazaki, Satoshi; (Niigata-ken, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
19068710 |
Appl. No.: |
10/212113 |
Filed: |
August 6, 2002 |
Current U.S.
Class: |
257/797 ;
438/401; 438/462; 438/975 |
Current CPC
Class: |
G03F 1/32 20130101; G03F
1/26 20130101 |
Class at
Publication: |
257/797 ;
438/401; 438/462; 438/975 |
International
Class: |
H01L 021/76; H01L
023/544 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 6, 2001 |
JP |
2001-237670 |
Claims
1. A phase shift mask blank comprising a transparent substrate and
at least one layer of phase shift film thereon, wherein said phase
shift film has been surface treated with ozone water having at
least 1 ppm of ozone dissolved therein.
2. A phase shift mask blank comprising a transparent substrate and
at least one layer of phase shift film thereon, wherein said phase
shift film is formed of a metal silicide oxide, metal silicide
nitride or metal silicide oxynitride and then surface treated with
ozone water having at least 1 ppm of ozone dissolved therein.
3. A phase shift mask blank comprising a transparent substrate and
at least one layer of phase shift film thereon, wherein said phase
shift film is formed of molybdenum silicide oxide, molybdenum
silicide nitride or molybdenum silicide oxynitride and then surface
treated with ozone water having at least 1 ppm of ozone dissolved
therein.
4. The phase shift mask blank of claim 2 wherein said phase shift
film has an oxygen content and a silicon content at its surface,
and a molar ratio of the oxygen content to the silicon content is
at least 1.
5. The phase shift mask blank of claim 1 wherein said phase shift
film changes the phase of exposure light passing therethrough by
180.+-.5 degrees and has a transmittance of 3 to 40%.
6. A phase shift mask obtained by patterning the phase shift film
in the phase shift mask blank of claim 1.
7. A method of manufacturing a phase shift mask blank comprising a
transparent substrate and at least one layer of phase shift film
thereon, said method comprising the steps of forming the phase
shift film on the substrate and surface treating the phase shift
film with ozone water having at least 1 ppm of ozone dissolved
therein.
8. A method of manufacturing a phase shift mask blank comprising a
transparent substrate and at least one layer of phase shift film
thereon, said method comprising the steps of forming the phase
shift film of a metal silicide oxide, metal silicide nitride or
metal silicide oxynitride on the substrate and surface treating the
phase shift film with ozone water having at least 1 ppm of ozone
dissolved therein.
9. A method of manufacturing a phase shift mask blank comprising a
transparent substrate and at least one layer of phase shift film
thereon, said method comprising the steps of forming the phase
shift film of molybdenum silicide oxide, molybdenum silicide
nitride or molybdenum silicide oxynitride on the substrate and
surface treating the phase shift film with ozone water having at
least 1 ppm of ozone dissolved therein.
10. The method of manufacturing a phase shift mask blank of claim 7
wherein said phase shift film changes the phase of exposure light
passing therethrough by 180.+-.5 degrees and has a transmittance of
3 to 40%.
11. A method of manufacturing a phase shift mask, comprising the
steps of forming by photolithography a patterned resist film on the
phase shift film in the phase shift mask blank obtained by the
method of claim 7, etching away the portions of the phase shift
mask which are uncovered with the resist film, and thereafter,
removing the resist film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to phase shift mask blanks and
phase shift masks suitable for use in the microfabrication of
electronic products such as semiconductor integrated circuits. It
relates also to methods of manufacturing such phase shift mask
blanks and phase shift masks. More particularly, it relates to
halftone phase shift mask blanks and phase shift masks which can
attenuate the intensity of exposure wavelength light with a phase
shift film, and to methods of manufacturing such phase shift mask
blanks and phase shift masks.
[0003] 2. Prior Art
[0004] Photomasks are used in a broad range of applications,
including the manufacture of semiconductor integrated circuit (IC),
large-scale integration (LSI) and VLSI chips. They are basically
constructed by starting with a photomask blank comprising a
transparent substrate and a light-shielding film made primarily of
chromium thereon and processing the light-shielding film by
photolithography using UV radiation or electron beams for thereby
forming a desired pattern in the film. The market demand for ever
higher levels of integration in semiconductor integrated circuits
has led to a rapid reduction in the minimum feature size of
photomask patterns. Such miniaturization has been achieved in part
by the use of shorter wavelength exposure light.
[0005] Although exposure using shorter wavelength light does
improve resolution, it has undesirable effects, such as reducing
the focal depth, lowering process stability and adversely impacting
product yield.
[0006] One pattern transfer technique that has been effective for
resolving such problems is phase shifting. This involves the use of
a phase shift mask as the mask for transferring microscopic circuit
patterns.
[0007] As shown in accompanying FIGS. 7A and 7B, a phase shift mask
(typically, halftone phase shift mask) is generally composed of a
substrate 1 on which a phase shift film 2 has been patterned. The
mask has both exposed substrate areas (first light-transmitting
areas) 1a on which there is no phase shift film, and phase shifters
(second light-transmitting areas) 2a that form a pattern region on
the mask. The phase shift mask improves the contrast of a
transferred image by providing, as shown in FIG. 7B, a phase
difference of 180 degrees between light passing through the pattern
region and light passing through the non-pattern region, and
utilizing the destructive interference of light at the boundary
regions of the pattern to set the light intensity in the areas of
interference to zero. The use of phase shifting also makes it
possible to increase the focal depth at the necessary resolution.
Hence, compared with a conventional mask having an ordinary
light-shielding pattern such as chromium film, the phase shift mask
can improve resolution and increase the margin of the exposure
process.
[0008] For practical purposes, such phase shift masks can be
broadly categorized, according to the light-transmitting
characteristics of the phase shifter, as either completely
transmitting phase shift masks or halftone phase shift masks.
Completely transmitting phase shift masks are masks in which the
phase shifter has the same light transmittance as the substrate,
and which are thus transparent to light at the exposure wavelength.
In halftone phase shift masks, the phase shifter has a light
transmittance that ranges from about several percent to several
tens of percent the transmittance of exposed substrate areas.
[0009] Accompanying FIG. 1 shows the basic structure of a halftone
phase shift mask blank, and FIG. 2 shows the basic structure of a
halftone phase shift mask. The halftone phase shift mask blank
shown in FIG. 1 includes a transparent substrate 1 and a halftone
phase shift film 2 formed over the substantially entire surface of
the substrate 1. The halftone phase shift mask shown in FIG. 2 is
arrived at by patterning the phase shift film 2 of the blank and
includes phase shifters 2a which form the pattern regions of the
mask and exposed substrate areas 1a on which there is no phase
shift film. Exposure light that has passed through the phase
shifter 2a is phase-shifted relative to exposure light that has
passed through the exposed substrate area 1a (see FIGS. 7A and 7B).
The transmittance of the phase shifter 2a is selected such that
exposure light which has passed through the phase shifter 2a has
too low an intensity to sensitize the resist on the substrate to
which the pattern is being transferred. Accordingly, the phase
shifter 2a functions to substantially shield out the exposure
light.
[0010] Halftone phase shift masks of the above type encompass
halftone phase shift masks of the single-layer type which are
simple in structure and easy to manufacture. Single-layer halftone
phase shift masks known to the art include those described in JP-A
7-140635 which have a phase shifting film composed of a molybdenum
silicide material such as MoSiO or MoSiON.
[0011] One important feature for these phase shift masks and phase
shift mask blanks is resistance to acids, for example, chemical
liquids such as sulfuric acid and aqueous persulfuric acid (mixture
of sulfuric acid and aqueous hydrogen peroxide) used in the resist
removing and cleaning steps of the mask manufacture process, and
chromium etchants having a high oxidizing power used in removal of
chromium film.
[0012] Prior art phase shift films are less resistant to chemical
liquids and raise a problem that the cleaning or chromium etching
step results in deviations of phase difference and transmittance
from the preset values.
SUMMARY OF THE INVENTION
[0013] It is therefore an object of the invention to provide phase
shift mask blanks and phase shift masks of quality which experience
little changes of phase difference and transmittance under the
action of chemical liquids used for cleaning. Another object of the
invention is to provide methods of manufacturing such phase shift
mask blanks and phase shift masks.
[0014] The invention addresses a phase shift mask blank comprising
a substrate which is transparent to exposure wavelength and at
least one layer of phase shift film thereon. It has been found that
once the phase shift film is formed, it is surface treated with
ozone water having at least 1 ppm of ozone dissolved therein
whereby the surface of the phase shift film is modified such that
the phase shift film will experience little changes of phase
difference and transmittance when later treated with chemical
liquids in cleaning and chromium etching steps. The resulting phase
shift mask blank is of high quality in this sense, and a phase
shift mask obtained therefrom is as well.
[0015] In a first aspect, the present invention provides a phase
shift mask blank comprising a transparent substrate and at least
one layer of phase shift film thereon. In a first embodiment, the
phase shift film has been surface treated with ozone water having
at least 1 ppm of ozone dissolved therein. In a second embodiment,
the phase shift film is formed of a metal silicide oxide, metal
silicide nitride or metal silicide oxynitride and then surface
treated with ozone water having at least 1 ppm of ozone dissolved
therein. In a third embodiment, the phase shift film is formed of
molybdenum silicide oxide, molybdenum silicide nitride or
molybdenum silicide oxynitride and then surface treated with ozone
water having at least 1 ppm of ozone dissolved therein.
[0016] Preferably, the phase shift film has an oxygen content and a
silicon content at its surface, and a molar ratio of the oxygen
content to the silicon content is at least 1. Also preferably, the
phase shift film changes the phase of exposure light passing
therethrough by 180.+-.5 degrees and has a transmittance of 3 to
40%.
[0017] In a second aspect, the present invention provides a phase
shift mask obtained by patterning the phase shift film in the
inventive phase shift mask blank.
[0018] In a third aspect, the present invention provides a method
of manufacturing a phase shift mask blank comprising a transparent
substrate and at least one layer of phase shift film thereon. In a
first embodiment, the method includes the steps of forming the
phase shift film on the substrate and surface treating the phase
shift film with ozone water having at least 1 ppm of ozone
dissolved therein. In a second embodiment, the method includes the
steps of forming the phase shift film of a metal silicide oxide,
metal silicide nitride or metal silicide oxynitride on the
substrate and surface treating the phase shift film with ozone
water having at least 1 ppm of ozone dissolved therein. In a third
embodiment, the method includes the steps of forming the phase
shift film of molybdenum silicide oxide, molybdenum silicide
nitride or molybdenum silicide oxynitride on the substrate and
surface treating the phase shift film with ozone water having at
least 1 ppm of ozone dissolved therein.
[0019] In a fourth aspect, the present invention provides a method
of manufacturing a phase shift mask, comprising the steps of
forming by photolithography a patterned resist film on the phase
shift film in the phase shift mask blank obtained by the above
method, etching away the portions of the phase shift mask which are
uncovered with the resist film, and thereafter, removing the resist
film.
[0020] According to the invention, once the phase shift film is
formed, it is surface treated with ozone water having at least 1
ppm of ozone dissolved therein whereby the outermost surface of the
film is uniformly oxidized such that the phase shift film will
experience little changes of phase difference and transmittance
when later treated with chemical liquids such as aqueous
persulfuric acid in the mask manufacturing process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The objects, features and advantages of the invention will
become more apparent from the following detailed description, taken
in conjunction with the accompanying drawings.
[0022] FIG. 1 is a sectional view of a phase shift mask blank
according to one embodiment of the invention.
[0023] FIG. 2 is a sectional view of a phase shift mask made from
the same blank.
[0024] FIG. 3 is a sectional view of a phase shift mask blank
having a Cr base light-shielding film according to another
embodiment of the invention.
[0025] FIG. 4 is a sectional view of a phase shift mask blank
having a Cr base light-shielding film and a Cr base antireflection
film according to a further embodiment of the invention.
[0026] FIG. 5 is a sectional view of a phase shift mask blank
according to a still further embodiment of the invention.
[0027] FIGS. 6A to 6D are sectional views illustrating the method
of manufacturing a phase shift mask from a phase shift mask blank
according to the invention. FIG. 6A shows a mask blank on which a
resist film has been formed, FIG. 6B shows the structure after the
resist film has been patterned, FIG. 6C shows the structure after
etching has been carried out, and FIG. 6D shows the completed mask
after the resist film has been removed.
[0028] FIGS. 7A and 7B illustrate the operating principle of a
halftone phase shift mask. FIG. 7B is an enlarged view of region X
in FIG. 7A.
[0029] FIG. 8 is a diagram showing the composition in depth
direction of a phase shift film as analyzed by ESCA.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Referring to FIG. 1, a phase shift mask blank according to
the invention includes a substrate 1 of quartz, CaF.sub.2 or the
like which is transparent to exposure light and at least one layer
of phase shift film 2. After the phase shift film 2 is formed on
the substrate 1, it is surface treated with ozone water having at
least 1 ppm of ozone dissolved therein. The phase shift mask of the
invention is obtained by patterning the phase shift film 2 of the
phase shift mask blank shown in FIG. 1. The mask has patterned
phase shifters 2 as shown in FIG. 2, wherein first
light-transmitting areas (exposed substrate areas) 1a are defined
between the patterned phase shifters and second light-transmitting
areas 2a are provided by the patterned phase shifters.
[0031] The phase shift film is preferably formed of a metal
silicide oxide, metal silicide nitride or metal silicide
oxynitride, and more preferably molybdenum silicide oxide (MoSiO),
molybdenum silicide nitride (MoSiN) or molybdenum silicide
oxynitride (MoSiON).
[0032] For depositing the phase shift film, a reactive sputtering
technique is preferred. When a metal silicide oxide, metal silicide
nitride or metal silicide oxynitride is to be deposited, the target
used in sputtering is a metal silicide target containing that
metal. When molybdenum silicide oxide, molybdenum silicide nitride
or molybdenum silicide oxynitride is to be deposited, a molybdenum
silicide target is used. To maintain a constant film composition, a
metal silicide having either one or both of oxygen and nitrogen
added thereto may be used.
[0033] The sputtering process may employ a direct-current power
supply (DC sputtering) or a high-frequency power supply (RF
sputtering). Either a magnetron sputtering system or a conventional
sputtering system may be used. The film-forming system may be
either a continuous, in-line system or a single-wafer processing
system.
[0034] The sputtering gas may contain an inert gas such as argon or
xenon, nitrogen gas, oxygen gas and various nitrogen oxide gases,
which are suitably combined so that the phase shift film deposited
therefrom may have a desired composition.
[0035] Where it is desired to increase the transmittance of a phase
shift film to be deposited, it is recommended that the amounts of
oxygen and nitrogen-containing gases in the sputtering gas be
increased so that more oxygen and nitrogen are taken into the film,
or a metal silicide having more oxygen and nitrogen previously
added thereto be used as the sputtering target.
[0036] In the phase shift mask blank of the invention, the phase
shift film may include a plurality of layers.
[0037] According to the invention, after the phase shift film is
formed on the substrate, it is surface treated with ozone water.
The ozone water used herein should preferably have an ozone
concentration of at least 1 ppm, more preferably at least 5 ppm.
The upper limit of the ozone concentration is not critical and may
be the ozone saturation level. Specifically, the ozone
concentration is often up to 50 ppm, and especially up to 20 ppm.
The ozone treatment may be carried out by immersing the phase shift
mask blank in a tank full of ozone water, or by flowing ozone water
over the phase shift mask blank while spinning the blank. The
treatment temperature may be in the range of 0 to 60.degree. C.,
especially 0 to 30.degree. C. although room temperature is most
often used. The treatment time may be suitably determined and is
preferably about 1 to 10 minutes, especially about 2 to 5
minutes.
[0038] preferably, the phase shift film has an oxygen content and a
silicon content at its surface, and a molar ratio of the oxygen
content to the silicon content is at least 1 and more preferably
between 1 and 2.
[0039] By the action of ozone water, the outermost surface of the
phase shift film is oxidized and stabilized so that it will
experience little changes of phase difference and transmittance
when later contacted with chemical liquids such as sulfuric
acid.
[0040] In summary, the phase shift mask blank of the invention
includes a transparent substrate and at least one layer of phase
shift film which is deposited thereon, preferably by a reactive
sputtering technique using a sputtering gas containing oxygen
and/or nitrogen and then treated with ozone water containing at
least 1 ppm of ozone, which ensures that the phase shift film has a
transmittance of several percent to several tens of percent,
especially 3 to 40% to exposure light and the resulting phase shift
mask provides a phase difference of 180.degree..+-.5.degree.
between light transmitted by the phase shifter and light
transmitted by the transparent substrate.
[0041] In another embodiment, the phase shift mask blank of the
invention may include a chromium-base light-shielding film 3 which
is formed on the phase shift film 2 (which has been surface treated
with ozone water) as shown in FIG. 3. In a further embodiment, as
shown in FIG. 4, a chromium-base antireflection film 4 may be
formed on the chromium-base light-shielding film 3 for reducing
reflection from the chromium-base light-shielding film 3. In a
still further embodiment, as shown in FIG. 5, a phase shift film 2,
a first Cr base antireflection film 4, a Cr base light-shielding
film 3, and a second Cr base antireflection film 4' are formed on
the substrate 1 in order.
[0042] By patterning the phase shift film of the phase shift mask
blank according to the invention, a phase shift mask as shown in
FIG. 2 is manufactured. A typical process is shown in FIG. 6. After
a phase shift film 12 is formed on a transparent substrate 11 and
surface treated with ozone water containing at least 1 ppm of
ozone, a resist film 13 is formed on the phase shift film 12 (FIG.
6A). Next, the resist film 13 is lithographically patterned (FIG.
6B), after which the phase shift film 12 is etched (FIG. 6C). The
resist film 13 is subsequently stripped (FIG. 6D). In this process,
application of the resist film, patterning (exposure and
development), etching and resist film removal may be carried out by
known techniques.
EXAMPLE
[0043] Examples and comparative examples are given below by way of
illustration, and are not intended to limit the scope of the
invention.
Example 1
[0044] A molybdenum silicide oxynitride (MoSiON) film of 120 nm
thick was deposited on a quartz substrate of 6 inches square by a
DC sputtering technique using molybdenum silicide as the sputtering
target and a gas mixture of argon, nitrogen and oxygen in a flow
ratio of 1:15:1 as the sputtering gas at a discharge power of 200
W, and a deposition temperature of 200.degree. C. The phase shift
film as deposited had a phase difference of 185.4.degree. and a
transmittance of 5.62%.
[0045] Using a spin washer, the sample was treated for 5 minutes
with ozone water having an ozone concentration of 18 ppm at room
temperature and then spin dried. The ozone-treated phase shift film
had a phase difference of 184.6.degree. and a transmittance of
5.82%.
[0046] The sample was immersed in a chemical liquid which was a 1:4
mixture of sulfuric acid and aqueous hydrogen peroxide at
80.degree. C. for 2 hours. The sample was measured for phase
difference and transmittance again, and its chemical resistance was
evaluated from changes of phase difference and transmittance before
and after the chemical immersion.
[0047] The sample after 2 hours of immersion in chemical liquid had
a phase difference of 182.1.degree. and a transmittance of 6.50%.
By the chemical immersion, the phase difference changed
-2.5.degree. and the transmittance changed +0.68%. The results are
shown in Table 1.
[0048] It is noted that the phase difference and transmittance were
measured by MPM-248 by Laser Tec Co. at a wavelength of 248 nm.
[0049] The composition of the sample after ozone water treatment
was analyzed in a depth direction by ESCA. The results are shown in
FIG. 8, which indicates that the oxygen content within the film has
a molar ratio of about 0.3 to the silicon content whereas the
oxygen content at the outermost surface has a molar ratio of 1.2 to
the silicon content.
Comparative Example 1
[0050] A molybdenum silicide oxynitride (MoSiON) film of 118 nm
thick was deposited as in Example 1. The phase shift film as
deposited had a phase difference of 178.8.degree. and a
transmittance of 6.09%.
[0051] The sample was tested for chemical resistance as in Example
1. The sample after 2 hours of immersion in chemical liquid had a
phase difference of 173.9.degree. and a transmittance of 7.61%. By
the chemical immersion, the phase difference changed -4.9.degree.
and the transmittance changed +1.52%. The results are also shown in
Table 1.
[0052] It is noted that the measurement of phase difference and
transmittance is the same as in Example 1.
1 TABLE 1 Chemical resistance Before After immersion immersion
Change Example 1 Phase difference 184.6.degree. 182.1.degree.
-2.5.degree. Transmittance 5.82% 6.50% +0.68% Comparative Phase
difference 178.8.degree. 173.9.degree. -4.9.degree. Example 1
Transmittance 6.09% 7.61% +1.52%
[0053] It is evident that the ozone water treatment of the phase
shift film after its formation improves the acid resistance of the
film so that the resulting phase shift mask blank (and phase shift
mask thereof) is of quality in that it experiences minimized
changes of phase difference and transmittance upon contact with
chemical liquid during subsequent cleaning step.
[0054] Although ozone water having an ozone concentration of 18 ppm
was used in Example, the invention is not limited thereto.
Treatment with ozone water is effective to the purpose of the
invention as long as ozone is contained even in a minute amount,
specifically at least 1 ppm.
[0055] Although a molybdenum silicide oxynitride film was used in
Example, the invention is not limited thereto. Equivalent results
are obtainable on use of molybdenum silicide oxide or molybdenum
silicide nitride. This is also true to phase shift mask blanks and
phase shift masks using silicide oxides, silicide nitrides or
silicide oxynitrides of metals other than molybdenum as the phase
shift film. Moreover, the invention is not limited to those
containing phase shift mask blanks and phase shift masks having
phase shift films of metal silicides, and equivalent results are
obtainable from phase shift mask blanks and phase shift masks
having other phase shift films.
[0056] There have been described a phase shift mask blank and a
phase shift mask thereof in which a phase shift film is formed by a
reactive sputtering technique and then treated with ozone water
whereby the resulting phase shift film is of quality in that it
will experience minimized changes of phase difference and
transmittance upon contact with chemical liquid during subsequent
mask cleaning step or the like.
[0057] Japanese Patent Application No. 2001-237670 is incorporated
herein by reference.
[0058] Although some preferred embodiments have been described,
many modifications and variations may be made thereto in light of
the above teachings. It is therefore to be understood that the
invention may be practiced otherwise than as specifically described
without departing from the scope of the appended claims.
* * * * *