U.S. patent application number 12/857710 was filed with the patent office on 2011-02-17 for pattern forming method and method of manufacturing semiconductor device.
This patent application is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Shinichi ITO, Daisuke Kawamura, Kentaro Matsunaga, Yasunobu Onishi.
Application Number | 20110039214 12/857710 |
Document ID | / |
Family ID | 37389843 |
Filed Date | 2011-02-17 |
United States Patent
Application |
20110039214 |
Kind Code |
A1 |
ITO; Shinichi ; et
al. |
February 17, 2011 |
Pattern Forming Method and Method of Manufacturing Semiconductor
Device
Abstract
A pattern forming method includes forming a photo resist film on
a film to be processed, forming a protective film for protecting
the photo resist film from an immersion liquid on the photo resist
film by coating method, performing immersion exposure selectively
to a region of part of the photo resist film via the immersion
liquid, the immersion liquid being supplied onto the photo resist
film, removing a residual substance including an affinitive part
for the immersion liquid from the protective film after the forming
the protective film and before the performing immersion exposure
selectively to the region of part of the photo resist film,
removing the protective film, and forming a pattern comprising the
photo resist film by selectively removing an exposed region or a
non-exposed region of the photo resist film.
Inventors: |
ITO; Shinichi;
(Yokohama-shi, JP) ; Matsunaga; Kentaro;
(Yokohama-shi, JP) ; Kawamura; Daisuke;
(Yokohama-shi, JP) ; Onishi; Yasunobu;
(Yokohama-shi, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
Kabushiki Kaisha Toshiba
|
Family ID: |
37389843 |
Appl. No.: |
12/857710 |
Filed: |
August 17, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11431823 |
May 11, 2006 |
7794922 |
|
|
12857710 |
|
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Current U.S.
Class: |
430/326 ;
257/E21.231; 438/694 |
Current CPC
Class: |
G03F 7/2041 20130101;
Y10S 430/162 20130101; G03F 7/11 20130101 |
Class at
Publication: |
430/326 ;
438/694; 257/E21.231 |
International
Class: |
G03F 7/20 20060101
G03F007/20; H01L 21/308 20060101 H01L021/308 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 2005 |
JP |
2005-141193 |
Claims
1-4. (canceled)
5. A pattern forming method comprising: forming a photo resist film
on a film to be processed; performing immersion exposure
selectively to a region of part of the photo resist film via an
immersion liquid, the immersion liquid being supplied onto the
photo resist film; removing a residual substance including an
affinitive part for the immersion liquid from the photo resist film
after the forming the protective film and before the performing
immersion exposure selectively to the region of part of the photo
resist film; and forming a pattern comprising the photo resist film
by selectively removing an exposed region or a non-exposed region
of the photo resist film.
6. The pattern forming method according to claim 5, wherein the
removing the residual substance is baking for the photo resist
film, the baking is carried out after applying a first solvent
whose boiling point is lower than that of a second solvent which is
remained on the photo resist film, or baking for the photo resist
film, the baking is carried during applying the first solvent whose
boiling point is lower than that of the second solvent.
7. The pattern forming method according to claim 6, wherein the
applying the first solvent is applying a first atmosphere which is
prepared by adding a solvent whose boiling point is lower than that
of the second solvent into a second atmosphere having no affinity
with the immersion liquid has.
8. The pattern forming method according to claim 6, wherein the
baking is carried out at a higher temperature than the boiling
point of the first solvent.
9-17. (canceled)
18. A method of manufacturing a semiconductor device, comprising:
forming a resist pattern on a substrate including a semiconductor
substrate, the resist pattern being formed by pattern forming
method of claim 5; and forming a pattern by etching the substrate
using the resist pattern as a mask.
19-20. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2005-141193,
filed May 13, 2005, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a pattern forming method in
the field of semiconductor and a method of manufacturing a
semiconductor device.
[0004] 2. Description of the Related Art
[0005] In recent years, with a downsized element and a highly
integrated LSI, there has been a request for resolution equal to or
smaller than a wavelength an ultraviolet ray. For this reason,
exposure process latitudes such as exposure latitude and focus
latitude have been insufficient.
[0006] Thus, a liquid immersion exposure technique has been
proposed as a technique of improving a resolution by using a
conventional exposure light source. The liquid immersion exposure
technique, as disclosed in Japanese Patent No. 2753930, is provided
as a technique for separating an optical element opposed to a
surface of substrate of a projection optical system from a
projection optical system main body and using the optical element
as a flat shaped element having two surfaces parallel to each
other; providing means comprising a container that configures a
closed space for filling a liquid between the flat shaped element
and the substrate opposed thereto; and carrying out exposure while
relatively moving the means and an exposure region on the
substrate.
[0007] In the liquid immersion exposure technique, there has been
studied that a protective film is formed on a resist film in order
to prevent entry of an immersion liquid into the resist film or
elusion from the resist film into the immersion liquid.
[0008] A typical example of a protective film to be formed on a
resist film before exposure is, for example, a film which is formed
by applying fluorine-based process gas on a surface of a resist
film as disclosed in Jpn. Pat. Appln. KOKAI Publication No.
2001-319862.
[0009] In contrast, as disclosed in Keita Ishizuka et al., New
Cover material Development Status for Immersion Lithography, Web
publication of International symposium on immersion and 157 nm
lithography, a protective film used in immersion exposure is a film
formed as a coating film on a resist film, apart from the resist
film.
[0010] However, the protective film formed by the method of this
type cannot achieve the purpose described previously. For example,
Daisuke Kawamura et al., Influence of the watermark in immersion
lithography process (SPIE2005) discloses that, as shown in FIG. 1,
depending on the shape of an immersion liquid 93 that remains on a
protective film 92, the immersion liquid as the droplet 93
penetrates the protective film 92 and reaches a resist film, and a
water stain (watermark) 94 occurs on an interface between the
protective film 92 and the resist film 91. The immersion liquid 93
shown in FIG. 1 shows a water droplet having a diameter of 0.1
mm.
[0011] A behavior of a photosensitizing agent or the like eluting
from a film into an immersion liquid is studied with respect to the
resist film as well. For example, in Karen Petrillo et. al.,
(SPIE2005 5753-9), there is disclosed that, even in the case of
forming a resist film including the same solid component, an eluted
amount of a photosensitive substance differs depending on the type
of a solvent included in a photosensitizing agent solution, as
shown in Table 1 (refer to FIG. 2 for a molecular structure of the
solvent). In an example of Table 1, the eluted amount increases in
the case where ethyl lactate having alcoholic property OH is
included.
TABLE-US-00001 TABLE 1 Contact angle Eluted amount Solvent system
(.degree.) (ppb) PGMEA + EL + GBL 68.5 73 PGMEA + EL 67 55 PGMEA +
GBL 65 25 PGMEA + Cycrohexanon 65 25
[0012] The elusion of a photosensitizing agent or a dissolution
inhibitor agent from a resist film into an immersion liquid
degrades a resist performance. In addition, an optical system of an
exposure apparatus is contaminated with the eluted liquid. The
contamination of the optical system degrades an image forming
property.
[0013] A resist film or a protective film is formed by a rotating
coating method. In this technique, baking is carried out after
forming a coat film in order to remove a solvent.
[0014] The baking is carried out in a humidity-controlled
atmosphere. The baking may be carried out in an atmosphere
containing a dry air, oxygen, or nitrogen, etc., as disclosed in
Jpn. Pat. Appln. KOKAI Publication No. 10-335203. Jpn. Pat. Appln.
KOKAI Publication No. 10-335203 discloses selecting a gas which is
preferable to an atmosphere at the time of baking and a device for
supplying the gas. There is also disclosed that atmosphere
switching means can be applied to a cool plate or a device for
continuously carrying out a plurality of substrate processings.
[0015] After the baking, the substrate is cooled. For example, Jpn.
Pat. Appln. KOKAI Publication No. 2001-76984 discloses a technique
for substituting a current atmosphere with an inert gas or a
purified air atmosphere after carrying out a substrate heating
process, and then, cooling the substrate, in order to reduce a
cooling time and to make uniform in-plane temperature distributions
of a substrate to be processed.
[0016] Further, Jpn. Pat. Appln. KOKAI Publication No. 2005-19969
discloses a technique for, with respect to a resist pattern after
developed, applying a solvent steam which dissolves the developed
resist pattern, thereby smoothening a surface of the resist
pattern.
BRIEF SUMMARY OF THE INVENTION
[0017] According to an aspect of the present invention, there is
provided a pattern forming method comprising forming a photo resist
film on a film to be processed; forming a protective film for
protecting the photo resist film from an immersion liquid on the
photo resist film by coating method; performing immersion exposure
selectively to a region of part of the photo resist film via the
immersion liquid, the immersion liquid being supplied onto the
photo resist film; removing a residual substance including an
affinitive part for the immersion liquid from the protective film
after the forming the protective film and before the performing
immersion exposure selectively to the region of part of the photo
resist film; removing the protective film; and forming a pattern
comprising the photo resist film by selectively removing, an
exposed region or a non-exposed region of the photo resist
film.
[0018] According to another aspect of the present invention, there
is provided a pattern forming method comprising forming a photo
resist film on a film to be processed; performing immersion
exposure selectively to a region of part of the photo resist film
via an immersion liquid, the immersion liquid being supplied onto
the photo resist film; removing a residual substance including an
affinitive part for the immersion liquid from the photo resist film
after the forming the protective film and before the performing
immersion exposure-selectively to the region of part of the photo
resist film; and forming a pattern comprising the photo resist film
by selectively removing an exposed region or a non-exposed region
of the photo resist film.
[0019] According to another aspect of the present invention, there
is provided a pattern forming method comprising forming a photo
resist film on a film to be processed; forming a protective film
for protecting the photo resist film from an immersion liquid on
the photo resist film by coating method; performing immersion
exposure selectively to a region of part of the photo resist film
via the immersion liquid, the immersion liquid being supplied onto
the photo resist film; smoothening a surface of the protective film
after the forming the protective film and before the performing
immersion exposure selectively to the region of part of the photo
resist film; removing the protective film; and forming a pattern
comprising the photo resist film by selectively removing an exposed
region or a non-exposed region of the photo resist film.
[0020] According to another aspect of the present invention, there
is provided a pattern forming method comprising forming a photo
resist film on a film to be processed; performing immersion
exposure selectively to a region of part of the photo resist film
via an immersion liquid, the immersion liquid being supplied onto
the photo resist film; smoothening a surface of the photo resist
film after the forming the photo resist film and before the
performing immersion exposure selectively to the region of part of
the photo resist film; forming a pattern comprising the photo
resist film by selectively removing an exposed region or a
non-exposed region of the photo resist film.
[0021] According to another aspect of the present invention, there
is provided a pattern forming method comprising forming a photo
resist film on a film to be processed; forming a protective film
for protecting the photo resist film from an immersion liquid on
the photo resist film by coating method; performing immersion
exposure selectively to a region of part of the photo resist film
via the immersion liquid, the immersion liquid being supplied onto
the photo resist film; removing the protective film by using a
first developing solution having an alkali concentration at which a
dissolution rate of the protective film is faster than that of the
photo resist film; and forming a pattern comprising the photo
resist film by selectively removing an exposed region or a
non-exposed region of the photo resist film using a second
developing solution whose an alkali concentration is higher than
that of the first developing solution.
[0022] According to an aspect of the present invention, there is
provided a method of manufacturing a semiconductor device
comprising forming a resist pattern on a substrate including a
semiconductor substrate, the resist pattern being formed by pattern
forming method according to an aspect of the present invention; and
forming a pattern by etching the substrate using the resist pattern
as a mask.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0023] FIG. 1 is a drawing for explaining a problem of prior
art;
[0024] FIG. 2 shows a molecular structure of a solvent;
[0025] FIG. 3 is a process flow showing a method of forming a
resist pattern of a second embodiment according to the present
invention;
[0026] FIG. 4 is a process flow showing a conventional method of
forming a resist pattern;
[0027] FIGS. 5A and 5B are drawings for explaining a reason why a
watermark occurs in the prior art;
[0028] FIGS. 6A to 6C are drawings for explaining a reason why an
occurrence of a watermark can be prevented in the embodiment;
[0029] FIG. 7 is a process flow showing a method of forming a
resist pattern of a third embodiment according to the present
invention;
[0030] FIGS. 8A to 8C are drawings showing an internal state of a
protective film in the case where a substrate is cooled in an
atmosphere containing a substance which has affinity with an
immersion liquid;
[0031] FIGS. 9A to 9C are drawings showing an internal state of a
protective film in the case where a substrate has been cooled in an
atmosphere containing a substance which has no affinity with an
immersion liquid;
[0032] FIGS. 10A and 10B are drawings showing an internal state of
a protective film in the case where a substance which has no
affinity with an immersion liquid is applied on a surface of the
protective film;
[0033] FIG. 11 is a process flow showing a method of forming a
resist pattern of a fourth embodiment according to the present
invention;
[0034] FIG. 12 is a process flow showing a method of forming a
resist pattern of a fifth embodiment according to the present
invention; and
[0035] FIG. 13 is a process flow showing a method of forming a
resist pattern of a sixth embodiment according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0036] Now, embodiments of the present invention will be described
below with reference to the accompanying drawings.
First Embodiment
[0037] Brief descriptions of a pattern forming method and a method
of manufacturing a semiconductor device in an embodiment according
to the present invention will be given below.
[0038] (1) A pattern forming method includes:
[0039] a first film forming step of forming a photo resist film
(first film) containing a first film material on a film to be
processed;
[0040] a second film forming step of coating a solution containing
a second film material on the photo resist film (by coating
method), thereby forming a second film (protective film to protect
the photo resist film);
[0041] an immersion exposure step of performing immersion exposure
to the photo resist film with the second film formed thereon
selectively via an immersion liquid;
[0042] a step of removing the second film; and
[0043] a developing step of removing an exposed region or a
non-exposed region of the photo resist film selectively, the method
further including:
[0044] a step of removing a residual substance including an
affinitive part for the immersion liquid used in the immersion
exposure step from the second film, prior to the immersion exposure
step from the second film forming step.
[0045] In the present embodiment and following other embodiments,
photo resist film includes photosensitive resin film or film that
includes resin and photo acid generator.
[0046] (2) In the (1) above,
[0047] the step of removing the residual substance is a step of
baking the second film which is carried out after applying a first
solvent whose boiling point is lower than that of a second solvent
which is remained on the second film, or a step of baking the
second film, which is carried during applying the first solvent
whose boiling point is lower than that of the second solvent.
[0048] (3) In the (2),
[0049] the first solvent is made by adding a solvent whose boiling
point is lower than that of the second solvent into an atmosphere
which is has no affinity with the immersion liquid.
[0050] (4) In the (2),
[0051] the baking step is carried out at a higher temperature than
the boiling point of the first solvent.
[0052] (5) In the (2),
[0053] a surface of the second film is exposed in the atmosphere
after baking the second film material, thereafter, the second film
is cooled.
[0054] (6) In the (1),
[0055] the step of removing a residual substance is a process for
increasing a receding contact angle relevant to an immersion liquid
of the second film, as compared with the step prior to the step of
removing the residual substance.
[0056] (7) In the (3) or (5),
[0057] the atmosphere is any one of a dry air, dry nitrogen, and
dry helium.
[0058] (8) In any one of the (1) to (4),
[0059] a light beam used in the immersion exposure step is an ArF
laser light beam (wavelength 193 nm) or a KrF laser light beam
(wavelength 248 nm), the immersion liquid is water, and the first
solvent and the second solvent have an alcoholic OH group.
[0060] (9) In the (7),
[0061] the first solvent is 1-butanol or an alcohol having 5 or
more carbons.
[0062] (10) In the (7),
[0063] the second solvent is methanol, ethanol, or 2-propanol.
[0064] (11) In the (1),
[0065] a light beam used in the immersion exposure step is an ArF
laser light beam (wavelength 193 nm), a KrF laser light beam
(wavelength 248 nm) or a fluorine laser light beam (wavelength 157
nm), and the immersion liquid is an organic substance.
[0066] (12) A pattern forming method includes:
[0067] a film forming step of a photo resist film by coating a
solvent containing a photo resist film material on a film to be
processed (by coating method);
[0068] an immersion exposure step of selectively performing
immersion exposing to the photo resist film via an immersion
liquid; and
[0069] a developing step of selectively removing an exposed region
or a non-exposed region of the photo resist film, the method
further including:
[0070] a step of removing a residual solvent having a portion that
is affinitive with an immersion liquid used in the immersion
exposure step from the photo resist film, after the first film
forming step and before the immersion exposure step.
[0071] (13) In the (12),
[0072] the step of removing the residual solvent is a step of
baking which is carried out after applying a second solvent whose
boiling point is lower than that of the first solvent that remains
on the photo resist film, or a step of baking which is carried out
while the second solvent whose boiling point is lower than that of
the first solvent is applying to the photo resist film.
[0073] (14) In the (13),
[0074] the second solvent is made by adding the second solvent into
an atmosphere which has no affinity with the immersion liquid.
[0075] (15) In the (13),
[0076] the baking step is carried out at a temperature higher than
the boiling point of the second solvent.
[0077] (16) In the (13),
[0078] a surface of the second film is exposed in the atmosphere
after baking the second film material, thereafter, the second film
is cooled.
[0079] (17) In the (12),
[0080] the step of removing a residual substance is a process for
increasing a receding contact angle relevant to an immersion liquid
of the second film, as compared with the step prior to the step of
removing the residual substance.
[0081] (18) In the (14) or (16),
[0082] the atmosphere is any one of a dry air, dry nitrogen, and
dry helium.
[0083] (19) In any one of the (12) to (15),
[0084] a light beam used in the immersion exposure step is an ArF
laser light beam (wavelength 193 nm) or a KrF laser light beam
(wavelength 248 nm), the immersion liquid is water, and the first
solvent and the second solvent have an alcoholic OH group.
[0085] (20) In the (18),
[0086] the first solvent is 1-butanol, ethyl lactate, or an alcohol
having 5 or more carbons.
[0087] (21) In the (18),
[0088] the second solvent is methanol, ethanol, or 2-propanol.
[0089] (22) In the (12),
[0090] a light beam used in the immersion exposure step is an ArF
laser light beam (wavelength 193 nm), a KrF laser light beam
(wavelength nm) or a fluorine laser light beam (wavelength 157 nm),
and the immersion liquid is an organic substance.
[0091] (23) A pattern forming method includes:
[0092] a first film forming step of forming a photo resist film
(first film) on a film to be processed;
[0093] a second film forming step of forming a second film
(protective film to protect the photo resist film) by coating a
second film material on the photo resist film (by coating
method);
[0094] an immersion exposure step of performing immersion exposure
to the photo resist film selectively via an immersion liquid in a
state that the second film is formed;
[0095] a step of removing the second film; and
[0096] a developing step of selectively removing an exposed region
or a non-exposed region of the photo resist film, the method
further including:
[0097] a step of smoothening a surface of the second film after the
second film forming step and before the immersion exposure
step.
[0098] (24) In the (23),
[0099] the smoothening step is carried out by exposing the second
film in an atmosphere containing a solvent which dissolves the
second film.
[0100] (25) In the (23),
[0101] the smoothening step is carried out while heating the second
film.
[0102] (26) In the (24),
[0103] the solvent in which the second film dissolves is a solvent
material contained in the second film material.
[0104] (27) In the (25),
[0105] The solvent in which the second film dissolves is acetone,
propylene glycol monomethyl ether acetate, N-methyl
2-pyrrolidinone, or alcohol.
[0106] (28) In the (29),
[0107] the atmosphere is mainly made of a dry air, dry nitrogen, or
dry helium.
[0108] (29) In the (23),
[0109] a light beam used in the immersion exposure step is an ArF
laser light beam (wavelength 193 nm), a KrF laser light beam
(wavelength 248 nm), or an F.sub.2 laser light beam (wavelength 157
nm).
[0110] (30) A pattern forming method includes:
[0111] a film forming step of forming a photo resist film on a film
to be processed;
[0112] an immersion exposure step of performing immersion exposure
to the photo resist film selectively via an immersion liquid;
[0113] a developing step of selectively removing an exposed region
or a non-exposed region of the photo resist film, the method
further including:
[0114] a step of smoothing a surface of the photo resist film after
the film forming step and before the immersion exposure.
[0115] (31) In the (30),
[0116] the smoothening step is carried out by exposing a surface of
the photo resist film in an atmosphere containing a solvent which
dissolves the photo resist film.
[0117] (32) In the (30),
[0118] the smoothening step is carried out while heating the photo
resist film.
[0119] (33) In the (30),
[0120] the solvent in which the photo resist film dissolves is a
solvent material contained in the photo resist film.
[0121] (34) In the (30),
[0122] the solvent in which the photo resist film dissolves is
acetone, propylene glycol monomethyl ether acetate, N-methyl
2-pyrrolidinone, or alcohol.
[0123] (35) In the (30),
[0124] the atmosphere is mainly made of a dry air, dry nitrogen, or
dry helium.
[0125] (36) In the (30),
[0126] a light beam for use in the immersion exposure step is an
ArF laser light beam (wavelength 193 nm), a KrF laser light beam
(wavelength 248 nm), or an F.sub.2 laser light beam (wavelength 157
nm).
[0127] (37) A pattern forming method includes:
[0128] a first film forming step of forming a photo resist film
(first film) on a film to be processed;
[0129] a second film forming step of forming a second film
(protective film to protect the photo resist film) by coating a
second film material on the photo resist film (by coating
method);
[0130] an immersion exposure step of performing immersion exposure
to the photo resist film selectively via an immersion liquid in a
state that the second film is formed;
[0131] a step of removing the second film; and
[0132] a developing step of selectively removing an exposed region
or a non-exposed region of the photo resist film,
[0133] wherein the second film is a film soluble in a developer
used in the developing step, and
[0134] the developing step includes: a first developing step of
selectively carrying out dissolution of the second film by using a
first developer having a concentration at which a dissolution rate
of the second film is faster than that of the photo resist film;
and a second developing step of carrying out development of the
photo resist film by using a developer whose concentration is
higher than that of the first developer.
[0135] (38) In the (37),
[0136] further including: a step of removing a dissolved substance
of the second film eluted in the first developing step between the
first developing step and the second developing step.
[0137] (39) A method of manufacturing a semiconductor device,
includes:
[0138] a step of forming a resist pattern on a substrate including
a semiconductor substrate by the pattern forming method of any one
of the (1) to (37); and
[0139] a step of forming a pattern by etching the substrate using
the resist pattern as a mask.
[0140] Now, the pattern forming method and the method of
manufacturing a semiconductor device will be described below in
detail by way of second to sixth embodiments.
Second Embodiment
[0141] FIG. 3 is a process flow showing a method of forming a
resist pattern in a second embodiment according to the present
invention. The present embodiment describes a method of forming a
resist pattern when an ArF excimer laser (wavelength 193 nm) is
used as a light source and when pure water is used as an immersion
liquid. For the sake of comparison, a process flow of a
conventional method of forming a resist pattern is shown in FIG.
4.
[0142] First, a film to be processed is prepared (step S1). The
film includes an oxide film (first film to be processed) and an
antireflection film (second film to be processed) formed on the
oxide film. The film to be processed (oxide film, antireflection
film) is formed on a semiconductor substrate (wafer).
[0143] The step of forming the antireflection film includes a step
of forming a film having an antireflection effect with respect to
an exposure light beam (wavelength 193 nm) on the oxide film by
spin coating method; and a step of baking the film.
[0144] Next, a photo resist film (first film) is formed on the film
to be processed (step S2). The step of forming the photo resist
film (step S2) includes a step (coating of photo resist film step
(step S2a)) of coating a photo resist material having
photosensitivity with respect to an exposure light beam (wavelength
193 nm) on a film (antireflection film) obtained by cooling the
baked film to be adjusted at a desired temperature; a step (baking
of photo resist film step (step S2b)) of baking for curing the
photo resist film at 110.degree. C.; and a step (step S2c) of
cooling the cured photo resist film (heated resist film) by the
baking.
[0145] The coating of photo resist film step (step S2a) includes a
step of dropping a photo resist solution on the film to be
processed on the main surface of the semiconductor substrate; and a
step of approximately removing a solvent of the photo resist
solution while rotating the semiconductor substrate.
[0146] Next, a protective film (second film) for preventing an
immersion liquid from being absorbed into the photo resist film or
a substance contained in the photo resist film from being eluted in
the immersion liquid is formed on the photo resist film (first
film) (step S3).
[0147] The step of forming a protective film (step S3) includes a
step (step of coating protective film (step S3a)) of coating a
solution (protective film solution) containing a material for the
protective film on the resist film; a step (step of baking
protective film (step S3b)) of baking for curing the protective
film solution; and a step (step S3c) of cooling the cured
protective solution film (heated protective film) by the
baking.
[0148] 1-hexanol (having affinitive group of alcoholic OH relevant
to an immersion liquid (water) and boiling point of 158.degree. C.)
is contained in a solvent of the protective film solution. It was
verified that a very small amount of 1-hexanol remained even in the
protective film after baked (step S3c).
[0149] The above steps (steps S1 to S3) are identical in comparison
between the embodiment and a prior art. After step S3, in the case
where the substrate including the protective film and the film to
be processed was exposed to the immersion liquid (water)
immediately, and then, immersion exposure was carried out, several
hundreds of watermarks per wafer were detected on the photo resist
film.
[0150] A reason why the watermarks have occurred will be described
with reference to FIGS. 5A and 5B.
[0151] In FIGS. 5A and 5B, reference numeral 1 denotes a photo
resist film; 2 denotes a protective film; 3 denotes a polymer
(aggregate) contained in a protective film; 4 denotes a remained
solvent having affinity with an immersion liquid; 5 denotes an
immersion liquid; 6 denotes a passage through which an immersion
liquid is guided. FIG. 5A shows an internal state of the protective
film 2 after heating (step S3b), and FIG. 5B shows an internal
state of the protective film after immersion exposure (step
S6).
[0152] In the protective film 2, there exist a number of exits of
the solvent that has occurred at the time of substrate rotation and
baking. These exits are trajectories produced when a certain degree
of solvent aggregates and evaporates from the film, and thus, a
very small amount of solvent 4 exists in the vicinity of the exits.
In the case where the solvent 4 has affinity with the immersion
liquid 5, it is considered that the immersion liquid 5 is
introduced into the protective film 2 at the time of immersion
exposure, and, for example, the immersion liquid 5 arrives at the
surface of the resist film 1 by way of the passage 6.
[0153] Therefore, in the present embodiment, after forming a
protective film and before immersion exposure, a solvent (residual
affinitive substance) is removed from the immersion liquid
contained in the protective film (step S4).
[0154] A reason why an occurrence of a watermark can be prevented
will be described with reference to FIGS. 6A to 6C. FIG. 6A shows
an internal state of the protective film 2 after heating (step
S3b), FIG. 6B shows an internal state of the protective film 2
after removing the residual affinitive substance (step S4), and
FIG. 6C shows an internal state of the protective film at the time
of immersion exposure (step S6).
[0155] In the present embodiment, the protective film 2 is formed,
and then, an isopropyl alcohol having affinity with the solvent 4
and having a lower boiling point than the solvent 4 is applied to
the solvent 7 in order to remove the solvent 4 (alcohol) that
remains in the vicinity of the exit of the solvent, thereby, the
solvent 4 is evaporated together with the isopropyl alcohol.
[0156] That is, the isopropyl alcohol is bulled with dry nitrogen,
thereby producing a dry nitrogen atmosphere which contains the
isopropyl alcohol, and then, supplying this atmosphere to the
surface of the protective film 2. Since a boiling point of the
isopropyl alcohol is 82.4.degree. C., an environment has been
established such that a substance applied to the protective film 2
by heating 95.degree. C. easily evaporates. In accordance with this
process, the solvent 4 that remains in the protective film 2 is
removed. As a result, affinity of the exit (passage 6) of the
solvent with the immersion liquid 5 is greatly lowered.
[0157] Prior to the step (step S4) of removing the substance having
affinity with the immersion liquid from the protective film, a
receding contact angle relevant to the surface of the protective
film was measured as 65.degree. by expansion and contraction
technique.
[0158] On the other hand, a receding contact angle of the
protective film having removed therefrom the substance having
affinity after step S4 was 80.degree., and it was verified that,
the receding contact angle significantly increased.
[0159] When exposure was carried out while a liquid film was
maintained in a local region including an exposed region at the
time of immersion exposure, the residual liquid droplets occurred
on the substrate in an exposure operation at the time of immersion
exposure in the case where the receding contact angle was
65.degree.. In the case of the receding contact angle after step S4
was 80.degree., the residual liquid droplets were not observed.
Although the residual liquid droplets can cause a watermark defect,
the risk was greatly reduced by this process (step S4).
[0160] When the residual liquid droplets were evaluated with
respect to a variety of films, the residual liquid droplets were
not observed when the receding contact angle was equal to or
greater than 75.degree.. From this fact, it is preferable to
control a concentration of isopropyl alcohol contained in an
atmosphere, a flow rate of the atmosphere, a pressure, a substrate
temperature, and a processing time such that the receding contact
angle is equal to or greater than 75.degree..
[0161] In addition, apart from the isopropyl alcohol, the receding
contact angle was successfully set to equal to or greater than
75.degree. by means of treatment with methanol (boiling point of
64.7.degree. C. and proper baking temperature of 85.degree. C. or
higher) and ethanol (boiling point of 78.3.degree. C. and proper
baking temperature of 80.degree. C. or higher).
[0162] Immersion exposure is carried out by using a substrate
having the thus processed protective film (step S6), and then, a
resist pattern is formed through well known steps, namely, a
post-exposure baking (PEE) step (step S7), a protective film
removing step (step S8), and a photo resist film developing step
(step S9).
[0163] When the thus formed resist pattern in the present
embodiment was inspected, it was verified that the number of
watermarks having occurred in a conventional process was reduced to
several watermarks per wafer.
[0164] When, with the resist pattern of the present embodiment
using as a mask, a trench pattern formed by sequentially etching
the antireflection film (second film to be processed) and the oxide
film (first film to be processed) was inspected, the number of
defects was merely produced as several defects per wafer, and a
good result was obtained. A device produced by filling the inside
of the trench pattern with a wiring material, and by further
performing a post-processing showed good reliability.
[0165] The present embodiment relates to a 1-hexanol solvent
contained in a protective film solvent, however it is not limited
thereto. The target solvent includes a substance having an
alcoholic OH group whose boiling point under normal pressure is
approximately 100.degree. C. or higher.
[0166] For example, substances having one alcohol OH group showed
an effect of removing the residual substance from the inside of the
protective film in the case where they have 4 carbons and having a
OH group at position 1 such as 1-butanol, 1-pentanol, 2-pentanol,
3-pentanol, 2-hexanol, 3-hexanol, 1-heptanol, 2-heptanol,
3-heptanol, 4-heptanol, 1-octanol, 1-octanoil, 2-octanol,
2-octanbol, 3-octanol and 4-octanol and in the case where they have
OH at the other position and having 5 carbons.
[0167] Further, an effect of removing the residual substance was
verified in an alcohol having an ester structure (for example,
ethyl lactate: boiling point of 154.degree. C.).
[0168] Also in substances having two or more alcoholic OH groups, a
removing effect was observed although it was less significant than
these alcohols.
[0169] In the present embodiment, an isopropyl alcohol was used in
order to remove the affinitive substance with the immersion liquid
caused by a solvent contained in the protective film, however it is
not limited thereto. The target substances are those having an
alcoholic OH group whose boiling point under normal pressure is
approximately less than 100.degree. C. Dehydrated and amine-removed
methanol and ethanol may be supplied to the surface of the
protective film after they are contained in a dry air, dry helium,
or dry nitrogen.
[0170] A reason why a dehydrating process and an amine-removing
process are carried out for an atmosphere and substances contained
in the atmosphere is that, if exposure is carried out while these
substances are contained, these substances are prevent from being
reversibly adsorbed by the exit of the solvent, and these
substances are prevented from being inductive substances of the
immersion liquid and from being sources of producing
watermarks.
[0171] From the heating using an isopropyl alcohol to the ending of
film cooling, it is preferable that an atmosphere in which the
surface of the protective film is exposed is controlled so as not
to contain a substance having affinity with an immersion liquid
(substance chemically and physically adsorbed with moisture or
alcohol and amine or water in the case where the immersion liquid
is water or analogous organic substance in the case where the
immersion liquid is an organic substance).
[0172] Desirably, exposure may be carried out in an atmosphere
containing a dry air, dry helium, or dry nitrogen. More desirably,
chemical reaction or physical adsorption may be carried out at the
time of exposure to an atmosphere having no affinity with an
immersion liquid (atmosphere containing a fluorine-based substance
in the case where the immersion liquid is water and silazane
compounds (hexamethyl silazane or tetramethyl silazane, etc.) or an
atmosphere containing alcohol in the case where the immersion
liquid is an organic substance).
[0173] In the case where affinity with an immersion liquid is
caused by carrying out chemical reaction, affinitive substances may
be removed again by applying the alcohol having a low boiling point
as shown in the present embodiment after the processing or may be
removed after the chemical reaction is carried out.
[0174] In the case where the surface of the protective film before
immersion exposure is contaminated with fine particles, the surface
of the protective film may be washed prior to immersion exposure
(processing of protective film before exposure (step S5)).
[0175] In addition, in the case where exposure is carried out while
a liquid film is maintained in a local region including an exposed
region at the time of immersion exposure, a reforming process may
be carried out with respect to the surface of the protective film
so as not to cause the liquid film to splash out of the local
region (processing of protective film before exposure (step
S5)).
[0176] In the case where a liquid droplet has occurred on the
protective film at the time of immersion exposure, such a liquid
droplet may be removed immediately prior to carrying out
post-exposure balking (step S8) in order to prevent an occurrence
of a watermark or a pattern dimension/shape failure (processing of
protective film after exposure (step S7)).
[0177] The present embodiment describes a case of using an exposure
light beam having a wavelength 193 nm. Even in the case of using an
exposure light beam having a wavelength 248 nm and even in the case
of using water or an organic substance for an immersion liquid, an
effect capable of reducing a watermark defect in accordance with a
similar process was verified.
[0178] Further, even when an exposure light beam having a
wavelength 157 nm was used and a fluorine-based organic substance
was used for an immersion liquid, an effect capable of reducing a
watermark defect by a similar process was verified.
[0179] The baking temperatures for the photo resist film and
protective film are not limited to the values according to the
present embodiment, and may be temperatures capable of attaining
protecting characteristics depending on materials. It is desirable
that the baking temperature for the protective film is lower than
that for the photo resist film so as not to cause a substance in
the photo resist film to move into the protective film.
[0180] The underlying layer processing step according to the
present embodiment relates to the step of forming a trench on the
oxide film, however it is not limited thereto. For example, this
step can be applied to lithography step for all the device
manufacturing steps such as contact hole formation, gate formation,
active area formation, and ion implantation.
Third Embodiment
[0181] FIG. 7 is a process flow showing a method of forming a
resist pattern in a third embodiment according to the present
invention.
[0182] First, a film to be processed is prepared (Step S21). The
film to be processed includes an oxide film (first film to be
processed) and an antireflection film (second film to be processed)
formed on the oxide film. The film to be processed (oxide film,
antireflection film) is formed on a semiconductor substrate
(wafer).
[0183] The step of forming the antireflection film includes a step
of forming a film having an antireflection effect with respect to
an exposure light beam (wavelength 193 nm) on the oxide film by
spin coating method; and a step of baking the film.
[0184] Next, a photo resist film (first film) is formed on the film
to be processed (step S22). The step of forming the photo resist
film (step S22) includes a step (coating of photo resist film step
(step S22a)) of coating a photo resist material having
photosensitivity with respect to an exposure light beam (wavelength
193 nm) on a film (antireflection film) obtained by cooling the
baked film to be adjusted at a desired temperature; a step (baking
of photo resist film step (step S22b)) of baking for curing the
photo resist film; and a step (step S22c) of cooling the cured
photo resist film (heated resist film) by the baking.
[0185] The coating of photo resist film step (step S22a) includes a
step of dropping a photo resist solution on the film to be
processed on the main surface of the semiconductor substrate; and a
step of approximately removing a solvent of the photo resist
solution while rotating the semiconductor substrate.
[0186] Next, a protective film (second film) for preventing an
immersion liquid from being absorbed into the photo resist film or
a substance contained in the resist film from being eluted in the
immersion liquid is formed on the photo resist film (first film)
(step S23).
[0187] The step of forming a protective film (step S23) includes a
step (step of coating protective film (step S23a)) of coating a
solution (protective film solution) containing a material for the
protective film on the photo resist film; a step (step of baking
protective film (step S23b)) of baking for curing the protective
film solution; and a step (step S23c) of cooling the cured
protective solution film (heated protective film) by the
baking.
[0188] 2-hexanol is included in a solvent of the protective film
solution. A very small amount of 2-hexanol was observed on a
protective film prepared by baking it in an atmosphere having
humidity of 40%.
[0189] Therefore, in the present embodiment, the step of forming a
protective film (step S23) was carried out as follows.
[0190] The step of coating protective film (step S23a) includes a
step of dropping the protective film solution on the photo resist
film on the main surface of the semiconductor substrate; and a step
of appropriately removing a solvent of the protective film solution
while rotating the semiconductor substrate.
[0191] The step of baking protective film (step S23b) is the step
of baking the protective film while removing a substance having a
portion that is affinitive with an immersion liquid from the
protective film, and includes a step of introducing an atmosphere
that contains ethanol anhydride having a lower boiling point than
2-hexanol in a dry air into a bake chamber; and a step of heating
the substrate in the atmosphere at 110.degree. C.
[0192] By heating the substrate in the atmosphere, 2-hexanol that
remains in the protective film after rotational coating (having
alcoholic OH at a portion, that is weakly affinitive with an
immersion liquid) was applied to the ethanol anhydride while in
baking process so as to be easily discharged from the film. When
the protective film subjected to the baking process in this
atmosphere was inspected, it was verified that an alcohol caused by
the solvent could be approximately removed.
[0193] In the case where the substrate was cooled in an atmosphere
in which ethanol anhydride (substance having affinity with an
immersion liquid) in a dry air, a dropwise condensation of the
ethanol anhydride made in the protective film was detected, and it
was found that the thus the dropwise condensation of the ethanol
anhydride induced the immersion liquid into the protective
film.
[0194] FIGS. 8A to 8C each show an internal state of the protective
film between the step of cooling the substrate in the atmosphere
containing a substance having affinity with the immersion liquid
and the step of carrying out immersion exposure to the photo resist
film. In FIGS. 8A to 8C, reference numeral 10 denotes a substance
having affinity with the immersion liquid. References 1 to 6 shown
in FIGS. 8A to 8C denote like elements shown in FIGS. 5A and
5B.
[0195] FIG. 8A shows the protective film 2 with the residual
substance after baked (step S23b) in the present embodiment is
removed therefrom. FIG. 8B shows a step of cooling a substance in
an atmosphere containing the substance 10 having affinity with the
immersion liquid. In this cooling step, the substance 10 having
affinity with the immersion liquid enters a region (exit of a
solvent) of the protective film 2 from which the residual substance
is removed. FIG. 8C shows a step of immersion exposing for the
photo resist film 1. In the immersion exposure step, the immersion
liquid enters the protective film 2 by means of the substance 10
having affinity with the immersion liquid, and further, the
immersion liquid 5 arrives at the surface of the photo resist film
1 by way of the passage 6.
[0196] Based on the above finding, the protective film after heated
is cooled in an atmosphere (dry air) which contains no substance
having affinity with the immersion liquid in the present
embodiment, in order to restrict entry of an immersion liquid
inductive substance into the protective film (step S23c).
[0197] FIGS. 9A to 9C each show an internal state of the protective
film from the step of cooling the substance in the atmosphere
containing the substance having no affinity with the immersion
liquid to the step of immersion exposing for the photo resist film.
In FIGS. 9A to 9C, reference numeral 11 denotes a substance having
no affinity with the immersion liquid 5 or a substance showing
resistance against the immersion liquid 5. Reference numerals 1 to
6 shown in FIGS. 9A to 9C denotes like elements shown in FIGS. 5A
and 5B.
[0198] FIG. 9A shows the protective film 2 with the residual
substance after baked (step S23b) is removed therefrom. FIG. 9B
shows a step of cooling the substance in an atmosphere containing
the substance 11 having no affinity with the immersion liquid. In
this cooling step, the substance 11 having no affinity with the
immersion liquid enters a region (exit of a solvent) of the
protective film 2 from which the residual substance is removed.
FIG. 9C shows a step of immersion exposing for the photo resist
film 1. In this immersion exposure step, the substance having
affinity with the immersion liquid 5 does not exist in the
protective, film 2, and thus, the immersion liquid 5 does not enter
the protective film 2.
[0199] In step S23b, the receding contact angle relevant to the
surface of the protective film obtained by heating at 110.degree.
C. in the atmosphere that contains ethanol anhydride having a lower
boiling point than the substance 11 having no affinity with the
immersion liquid in the dry air was measured as 61.degree. by
expansion and contraction technique.
[0200] In contrast, a receding contact angle of the protective film
obtained by heating in the atmosphere that contains ethanol
anhydride having the lower boiling point in a dry air was
85.degree., and it was verified that the receding contact angle
significantly increased.
[0201] When exposure was carried out while a liquid film was
maintained in a local region including an exposed region at the
time of immersion exposure, the residual liquid droplets occurred
on the substrate in an exposure operation at the time of immersion
exposure in the case where the receding contact angle was
61.degree.. However, in the case where the receding contact angle
after step S23c was 85.degree., the residual liquid droplets were
not observed. Although the residual liquid droplets can cause the
watermark defect, the risk was greatly reduced by this process
(steps S23b and S23c).
[0202] When the residual liquid droplets were evaluated with
respect to a variety of films, the residual liquid droplets were
not observed when the receding contact angle was equal to or
greater than 75.degree.. Thus, it is preferable to control a
concentration of an alcohol anhydride having a low boiling point
contained in an atmosphere, a flow rate of the atmosphere, a
pressure, a substrate temperature, and a processing time such that
the receding contact angle is equal to or greater than
75.degree..
[0203] Immersion exposure is carried out by using a substrate
having the thus processed protective, film (step S26), and then, a
resist pattern is formed through well known steps, namely, a
post-exposure baking (PEE) step (step S28), a protective film
removing step (step S29), and a photo resist film developing step
(step S30).
[0204] When the thus formed resist pattern in the present
embodiment was inspected, it was verified that the number of
watermarks having occurred in a conventional process was reduced to
several watermarks per wafer.
[0205] When, the resist pattern of the present embodiment is used
as a mask, a hole pattern formed by sequentially etching the
antireflection film (second film to be processed) and the oxide
film (first film to be processed) was inspected, the number of
defects was merely produced as several defects per wafer, and a
good result was obtained. A device produced by filling the hole
pattern with an inter-wire joining material, and by further
performing a post-processing showed good reliability.
[0206] In the present embodiment, ethanol anhydride having a low
boiling point was used in order to remove a substance that is
affinitive with the immersion liquid caused by a solvent contained
in the protective film in the baking atmosphere, however it is not
limited thereto. By virtue of the same reason as that described in
the first embodiment, while dehydrated and amine-removed methanol
or isopropyl alcohol is contained in a dry air, dry helium, dry
nitrogen or the like, the contained substance may be supplied to
the surface of the protective film. In addition, the solvent
contained in the protective film also includes like solvent
according to the first embodiment.
[0207] After the step (protective film cooling step) shown in FIG.
9B and before the step (immersion exposure step) shown in FIG. 9 in
the above-described process, affinity with the immersion liquid 5
was successfully lowered more remarkably and the receding contact
angle was successfully improved by, as shown in FIGS. 10A and 10B,
applying the substance having no affinity with the immersion liquid
or the substance 12 showing resistance against the immersion
liquid, for example, a chlorofluorocarbon compound to act
(physically adsorb) to the surface and the inside of the protective
film 2.
[0208] Similarly, after the step (step of baking protective film)
shown in FIG. 6B and before the step (immersion exposure step)
shown in FIG. 6C in the first embodiment, affinity with the
immersion liquid was successfully lowered more remarkably, and the
receding contact angle was successfully improved by applying
(physically adsorbing) the substance having no affinity with the
immersion liquid, to the surface of the protective film.
[0209] In the case where the surface of the protective film before
immersion exposure is contaminated with fine particles, the surface
of the protective film may be washed prior to immersion exposure
(processing of protective film before exposure (step S25)).
[0210] In the case where exposure is carried out while a liquid
film is maintained in a local region including an exposed region at
the time of immersion exposure, a reforming process may be carried
out for the surface of the protective film such that the liquid
film does not splash out of the local region (processing of
protective film before exposure (step S25)).
[0211] In addition, in the case where a liquid droplet has occurred
on the protective film at the time of immersion exposure, such a
liquid droplet may be removed immediately before carrying out
post-exposure baking (step S28) in order to prevent an occurrence
of, a watermark or pattern dimension/shape failure (processing of
protective film after exposure (step S27)).
[0212] While the present embodiment describes a case of using an
exposure light beam having a wavelength 193 nm, it was verified
that a watermark defect could be reduced in accordance with similar
processing even when an exposure light beam having a wavelength 248
nm was used and water or an organic substance was used for an
immersion liquid.
[0213] Moreover, even when an exposure light beam having a
wavelength 157 nm was used and a fluorine-based organic substance
was used for an immersion liquid, an effect capable of reducing a
watermark defect in accordance with similar processing was
verified.
[0214] Baking temperatures for the photo resist film and protective
film are not limited to the values according to the present
embodiment, and may be temperatures capable of attaining protecting
characteristics depending on materials. It is desirable that the
baking temperature of the protective film is lower than that of the
photo resist film so as not to cause a substance in the photo
resist film to move into the protective film.
[0215] The underlying layer processing step according to the
present embodiment relates to the step of forming the hole of the
oxide film, however it is not limited thereto. For example, this
step can be applied to lithography step for all the device
manufacturing steps such as wire formation, gate formation, active
area formation, and ion implantation.
Fourth Embodiment
[0216] FIG. 11 is a process flow showing a method of forming a
resist pattern in a fourth embodiment according to the present
invention. The present embodiment describes a method of forming a
resist pattern when a KrF excimer laser (wavelength 248 nm) is used
as a light source and pure water is used as an immersion
liquid.
[0217] First, a film to be processed is prepared (step S41). The
film to be processed includes an oxide film (first film to be
processed) and an antireflection film (second film to be processed)
formed on the oxide film. The film to be processed (oxide film,
antireflection film) is formed on a semiconductor substrate
(wafer).
[0218] The step of forming the antireflection film includes a step
of forming a film having an antireflection effect with respect to
an exposure light beam (wavelength 248 nm) on the oxide film by
spin coating method; and a step of baking the film.
[0219] Next, a photo resist film (first film) is formed on the film
to be processed (step S42). The step of forming the photo resist
film (step S42) includes a step (step S42a) of coating a photo
resist material having photosensitivity with respect to an exposure
light beam (wavelength 248 nm) on a film (antireflection film)
obtained by cooling the baked film to be adjusted at a desired
temperature; a step (step S42b) of baking for curing the photo
resist film; and a step (step S42c) of cooling the cured photo
resist film (heated photo resist film) by the baking.
[0220] The coating of photo resist film step (step S42a) includes:
a step of dropping a photo resist solution on the film to be
processed on the main surface of the semiconductor substrate; and a
step of approximately removing a solvent of the photo resist
solution while rotating the semiconductor substrate.
[0221] While this photo resist film was weak in permeability of an
immersion liquid, slight entry was observed. Thus, a solvent having
a portion which is affinitive with the immersion liquid (water)
that remains in the resist film was removed without using a
protective film (step S43).
[0222] Here, the solvent that remains in the photo resist film was
ethyl lactate. Thus, while an atmosphere in which an isopropyl
alcohol having a low boiling point is contained in a dry air
applied to the photo resist film, the dry air was evaporated
together with the isopropyl alcohol. The atmosphere (substance
having no affinity with immersion liquid) was applied to the photo
resist film after supplied to the surface of the photo resist
film.
[0223] Here, since the boiling point of the isopropyl alcohol was
82, 4.degree. C., an environment was established such that the
substance applied to the photo resist film by heating the photo
resist film to 95.degree. C. easily evaporated.
[0224] In accordance with the processing (step S43), the ethyl
lactate that remains in the photo resist film was successfully
removed, and affinity with the immersion liquid in an exit of a
solvent was greatly lowered. In addition, with the isopropyl
alcohol steam, the surface of the photo resist film slightly
dissolved, and a smoother surface was successfully obtained. The
photo resist film was cooled in an atmosphere containing only a dry
air (step S42c).
[0225] Prior to the step (step S43) of removing a substance having
affinity with an immersion liquid from the photo resist film, a
receding contact angle relevant to the surface of the photo resist
film was measured as 55.degree. in an expansion and contraction
technique.
[0226] In contrast, with respect of the protective film having
removed therefrom a substance having ethyl lactate after step S43,
affinity with water was lowered, and the surface became smoother,
whereby the receding contact angle significantly increased as
83.degree..
[0227] When exposure is carried out while a liquid film is
maintained in a local including an exposed region at the time of
immersion exposure, the number of the residual liquid droplets
occurred on the substrate in an exposure operation at the time of
immersion exposure in the case where the receding contact angle was
55.degree.. In the case where the receding contact angle was
83.degree. after step S43, however, the residual liquid droplets
were not observed. Although the residual liquid droplets can cause
a watermark defect, the risk was greatly reduced in accordance with
this processing (step S43).
[0228] When the residual liquid droplets were evaluated with
respect to a variety of films, the residual liquid droplets were
not observed when the receding contact angle was equal to or
greater than 75.degree.. Thus, it is preferable to control a
concentration of an isopropyl alcohol contained in an atmosphere, a
flow rate of the atmosphere, a pressure, a substrate temperature,
and a processing time such that the receding contact angle is equal
to or greater than 75.degree..
[0229] In addition, apart from the isopropyl alcohol, the receding
contact angle was successfully set to equal to or greater than
75.degree. by means of treatment with methanol (boiling point of
64.7.degree. C. and proper baking temperature of 65.degree. C. or
higher) and ethanol (boiling point of 78.3.degree. C. and proper
baking temperature of 80.degree. C. or higher).
[0230] Immersion exposure is carried out by using a substrate
having the thus processed protective film (step S46), and then, a
resist pattern is formed through well, known steps, namely, a
post-exposure baking (PEB) step (step S48) and a photo resist film
developing step (step S49).
[0231] When the thus formed photo resist pattern in the present
embodiment was inspected, it was verified that the number of
watermarks having occurred in a conventional process was reduced to
several watermarks per wafer.
[0232] When, with the resist pattern of the present embodiment
using as a mask, a trench pattern formed by sequentially etching
the antireflection film (second film to be processed) and the oxide
film (first film to be processed) was inspected, the number of
defects was merely produced as several defects per wafer and a good
result was obtained. A device produced by filling the inside of the
trench pattern with a wiring material, and by further performing a
post-processing showed good reliability.
[0233] The present embodiment relates to an ethyl lactate solvent
contained in a resist solvent. The target solvent is not limited
thereto. The removing effect was verified also in an alcohol having
another ester structure (for example, ethyl lactate: boiling point
of 154.degree. C.), and the like.
[0234] The target solvent will be a substance having an alcoholic
OH group whose boiling point under normal pressure is approximately
100.degree. C. or higher.
[0235] For example, substances having one alcohol OH group showed
an effect of removing the residual substance from the inside of the
protective film in the case where they have 4 carbons and having a
OH group at position 1 such as 1-butanol, 1-pentanol, 2-pentanol,
3-pentanol, 2-hexanol, 3-hexanol, 1-heptanol, 2-heptanol,
3-heptanol, 4-heptanol, 1-octanol, 1-octanoil, 2-octanol,
2-octanbol, 3-octanol and 4-octanol and in the case where they have
OH at the other position and having 5 carbons.
[0236] In addition, in substances having two or more alcoholic OH
groups as well, a removing effect was observed, although it was
less significant than these alcohols.
[0237] In the present embodiment, an isopropyl alcohol was used in
order to remove the substance that is affinitive with the immersion
liquid caused by a solvent contained in the photo resist film,
however it is not limited thereto. The target substances are those
having an alcoholic OH group whose boiling point under normal
pressure is approximately less than 100.degree. C. Dehydrated and
amine-removed methanol and ethanol may be supplied to the surface
of the protective film after they are contained in a dry air, dry
helium, dry nitrogen or the like.
[0238] A reason why a dehydrating process and an amine-removing
process are carried out with respect to an atmosphere and
substances contained in the atmosphere is that, if exposure is
carried out while these substances are contained, these substances
are prevent from being reversibly adsorbed by an exit of a solvent,
and these substances are prevented from being inductive substances
of the immersion liquid and from being sources of producing
watermarks.
[0239] It is preferable that an atmosphere in which the surface of
the photo resist film is exposed from the heating using isopropyl
alcohol to the ending film cooling is controlled so as not to
contain a substance having affinity with an immersion liquid
(substance chemically and physically adsorbed with moisture or
alcohol and amine or water in the case where an immersion liquid is
water or analogous organic substance in the case where an immersion
liquid is an organic substance) (step S44). Desirably, exposure may
be carried out in an atmosphere containing a dry air, dry helium,
or dry nitrogen.
[0240] More desirably, More desirably, chemical reaction or
physical adsorption may be carried out at the time of exposure to
an atmosphere having no affinity with an immersion liquid
(atmosphere containing a fluorine-based substance in the case where
the immersion liquid is water and silazane compounds (hexamethyl
silazane or tetramethyl silazane, etc.) or an atmosphere containing
alcohol in the case where the immersion liquid is an organic
substance).
[0241] In the case where affinity with an immersion liquid is
caused by carrying out chemical reaction, affinitive substances may
be removed again by applying the alcohol having a low boiling point
as shown in the present embodiment after the processing or may be
removed after the chemical reaction is carried out.
[0242] In the case where the surface of the photo resist film
before immersion exposure is contaminated with fine particles, the
surface of the resist film may be washed prior to immersion
exposure (processing of resist film before exposure (step
S45)).
[0243] In the case where exposure is carried out while a liquid
film is maintained in a local region including an exposed region at
the time of immersion exposure, a reforming process may be carried
out for the surface of the photo resist film so as not to cause the
liquid film to splash out of the local region (processing of photo
resist film before exposure (step S45)).
[0244] In addition, in the case where a liquid droplet has occurred
on the photo resist film at the time of immersion exposure, such a
liquid droplet may be removed immediately prior to carrying out
post-exposure balking (step S48) in order to prevent an occurrence
of a watermark or a pattern dimension/shape failure (processing of
photo resist film after exposure (step S47)).
[0245] The present embodiment describes a case of using the
exposure light beam having a wavelength 193 nm. Even when an
exposure light beam having a wavelength 248 nm was used and water
or an organic substance was used for an immersion liquid, an effect
capable of reducing a watermark defect in accordance with a similar
process was verified.
[0246] Further, even when an exposure light beam having a
wavelength 157 nm was used and a fluorine-based organic substance
was used for an immersion liquid, an effect capable of reducing a
watermark defect by a similar process was verified.
[0247] Baking temperature of the photo resist film is not limited
to the value according to the present embodiment, and may be
temperature capable of attaining characteristics of photo resist
depending on materials.
[0248] The underlying layer processing step according to the
present embodiment relates to the step of forming the trench of the
oxide film, however it is not limited thereto. For example, this
step can be applied to lithography step for all the device
manufacturing steps such as contact hole formation, gate formation,
active area formation, and ion implantation.
Fifth Embodiment
[0249] FIG. 12 is a process flow showing a method of forming a
resist pattern in a fourth embodiment according to the present
invention. The present embodiment describes a method of forming a
resist pattern when a KrF excimer laser (wavelength 193 nm) is used
as a light source and pure water is used as an immersion
liquid.
[0250] First, a film to be processed is prepared (step S51). The
film to be processed includes an oxide film (first film to be
processed) and an antireflection film (second film to be processed)
formed on the oxide film. The film to be processed (oxide film,
antireflection film) is formed on a semiconductor substrate
(wafer).
[0251] The step of forming the antireflection film includes a step
of forming a film having an antireflection effect with respect to
an exposure light beam (wavelength 193 nm) on the oxide film by
spin coating method; and a step of baking the film.
[0252] Next, a photo resist film (first film) is formed on the film
to be processed (step S52). The step of forming the photo resist
film (step S52) includes a step (step S52a) of coating a resist
material having photosensitivity with respect to an exposure light
beam (wavelength 193 nm) on a film (antireflection film) obtained
by cooling the baked film to be adjusted at a desired temperature;
a step (step S52b) of baking for curing the photo resist film at
110.degree. C.; and a step (step S52c) of cooling the cured photo
resist film (heated photo resist film) by the baking.
[0253] The step of coating the photo resist (step S52a) includes a
step of dropping a photo resist solution on the film to be
processed on the main surface of the semiconductor substrate; and a
step of approximately removing a solvent of the resist solution
while rotating the semiconductor substrate.
[0254] Next, a protective film (second film) for preventing an
immersion liquid from being absorbed into the photo resist film and
a substance contained in the resist film from being eluted in the
immersion liquid is formed on the photo resist film (first film)
(step S53).
[0255] The step of forming the protective film (step S53) includes
a step (step S53a) of coating a solution (protective film solution)
containing a material for the protective film on the photo resist
film; and a step (step S53b) of baking for curing the protective
film solution (step S53c). If required (depending on the
situation), the cured protective solution film (heated protective
film) by the baking is cooled (step S53c).
[0256] The step of coating the protective film solution (step S53a)
includes a step of dropping the protective film solution on the
film to be processed on the main surface of the semiconductor
substrate; and a step of approximately removing a solvent of the
protective film solution while rotating the semiconductor
substrate.
[0257] The step (step S53b) of baking for curing the protective
film solution is carried out at 110.degree. C. At this time, the
solvent is removed from the protective film. With removal of the
solvent, irregularities (fine irregularities) of about .+-.1 nm
occurred on the surface of the protective film. When immersion
exposure is carried out with the fine irregularities having
occurred on the surface of the protective film, the immersion
liquid is adsorbed to a recess portion, and the liquid is prone to
remain at the time of step exposure. It was verified that a number
of liquid droplets existed on the substrate after immersion
exposure. In the case where the irregularities on the surface of
the protective film were as large as .+-.2 nm, the immersion liquid
splashed out of the substrate at the time of stepwise immersion
exposure.
[0258] Therefore, in the present embodiment, smoothening of the
surface of the protective film is carried out after the baking
process (step S53b) for removing the solvent from the protective
film (step S54).
[0259] The smoothening of the surface of the protective film was
carried out after N-methyl 2-pyrolinodine steam was applied to the
surface of the protective film while the substrate temperature was
maintained at 110.degree. C. After smoothing the surface of the
protective film, the supply of the steam was stopped. Subsequently,
N-methyl 2-pyrolinodine that remains on the surface of the
protective film was removed by heat treatment, and then, the
substrate was cooled.
[0260] The irregularities on the surface of the protective film
obtained by these processes were .+-.0.2 nm. When immersion
exposure was carried out for the protective film having the surface
flattened, the residual liquid droplets or liquid splash at the
time of step exposure was not observed, and no liquid droplets were
observed on the substrate after exposure. According to this
technique, an exit of a solvent produced as a result of removing
the solvent from the protective film in the step of baking
protective film (step S53b) is sealed so that the entry of the
immersion liquid into the protective film is restricted.
[0261] In the case where the smoothening on the surface of the
protective film was not carried out, the receding contact angle of
the immersion liquid relevant to the surface of the protective film
was measured as 65.degree. by expansion and contraction technique.
On the other hand, in the case where smoothening was carried out,
the angle was properly obtained as 85.degree..
[0262] Immersion exposure is carried out by using a substrate
having the thus processed protective film (step S56), and then, a
resist pattern is formed through well known steps, namely, a
post-exposure baking (PEE) step (step S58), a protective film
removing step (step S59), and a photo resist film developing step
(step S60).
[0263] When the thus formed resist pattern of the present
embodiment was inspected, none of the watermarks having occurred in
a conventional process was observed.
[0264] When, with the resist pattern of the present embodiment
using as a mask, a trench pattern formed by sequentially etching
the antireflection film (second film to be processed) and the oxide
film (first film to be processed) was inspected, the number of
defects was merely produced as several defects per wafer, and a
good result was obtained. A device produced by filling the inside
of the trench pattern with a wiring material, and by further
performing a post-processing showed good reliability.
[0265] In the present embodiment, N-methyl 2-pyrolidinone steam was
used to smoothen the protective film, however it is not limited
thereto. When an effect was inspected with respect to a variety of
protective films, a smoothening effect of almost of the protective
films was successfully verified with respect to acetone steam,
propylene glycol monomethyl ether acetate (pGMEA) steam, and
N-methyl 2-pyrolidinone (NMP) steam.
[0266] In addition, a smoothening effect was successfully verified
also in the case where the solvent contained in that solution was
applied to a variety of protective films.
[0267] Moreover, substances having one alcohol OH group showed an
effect of removing the residual substance from the inside of the
protective film in the case where they have 4 carbons and having a
OH group at position 1 such as 1-butanol, 1-pentanol, 2-pentanol,
3-pentanol, 2-hexanol, 3-hexanol, 1-heptanol, 2-heptanol,
3-heptanol, 4-heptanol, 1-octanol, 1-octanoil, 2-octanol,
2-octanbol, 3-octanol and 4-octanol and in the case where they have
OH at the other position and having 5 carbons.
[0268] Although these substances can be applied as they are, a
crater or dome-shaped film thickness variation occurs unpreferably
when an excessive amount of these substances is supplied. In such a
case, these substances may be diluted, and the diluted substances
may be applied while it is contained in a dry air, dry helium, dry
nitrogen or the like.
[0269] In the case where the surface of the protective film before
immersion exposure is contaminated with fine particles, the surface
of the protective film may be washed prior to immersion exposure
(processing of protective film before exposure (step S55)).
[0270] In the case where liquid droplets have occurred on the
protective film at the time of immersion exposure, the liquid
droplets may be removed immediately prior carrying out
post-exposure baking (step S58) in order to prevent an occurrence
of a watermark or pattern dimension/shape failure (processing of
protective film after exposure (step S57)).
[0271] The present embodiment describes a case of using an exposure
light beam having a wavelength 193 nm. Even when an exposure light
beam having a wavelength 248 nm was used and water or an organic
substance was used for an immersion liquid, an effect capable of
reducing a watermark defect was successfully verified in accordance
with a similar processing.
[0272] In addition, even when an exposure light beam having a
wavelength 157 nm was used and a fluorine-based organic substance
was used for an immersion liquid, an effect capable of eliminating
the residual light droplets and reducing a watermark defect was
verified by a similar processing.
[0273] Baking temperatures for the photo resist film and protective
film are not limited to the values according to the present
embodiment, and may be temperatures capable of attaining protecting
characteristics depending on materials. It is desirable that the
baking temperature for the protective film is lower than that for
the photo resist film so as not to cause a substance in the photo
resist film to move into the protective film.
[0274] The underlying layer processing step according the present
embodiment relates to a step of forming a trench of an oxide film,
however it is not limited thereto. For example, this step can be
applied to lithography step for all the device manufacturing steps
such as contact hole formation, gate formation, active area
formation, and ion implantation.
Sixth Embodiment
[0275] FIG. 13 is a process flow showing a method of forming a
resist pattern in a sixth embodiment according to the present
invention. The present embodiment describes a method of forming a
resist pattern when a KrF excimer laser (wavelength 193 nm) is used
as a light source and pure water is used as an immersion
liquid.
[0276] First, a film to be processed is prepared. The film to be
processed includes an oxide film (first film to be processed) and
an antireflection film (second film to be processed) formed on the
oxide film. The film to be processed (oxide film, antireflection
film) is formed on a semiconductor substrate (wafer).
[0277] The step of forming the antireflection film includes a step
of forming a film having an antireflection effect with respect to
an exposure light beam (wavelength 193 nm) on the oxide film by
spin coating method; and a step of baking the film.
[0278] Next, a photo resist film (first film) is formed on the film
to be processed. The step of forming the photo resist film includes
a step of coating a photo resist material having photosensitivity
with respect to an exposure light beam (wavelength 193 nm) on a
film (antireflection film) obtained by cooling the baked film to be
adjusted at a desired temperature; a step of baking for curing the
photo resist film at 110.degree. C.; and a step of cooling the
cured photo resist film (heated resist film) by the baking.
[0279] The step of coating the photo resist includes a step of
dropping a resist solution on the film to be processed on the main
surface of the semiconductor substrate; and a step of approximately
removing a solvent of the photo resist solution while rotating the
semiconductor substrate.
[0280] Next, a protective film (second film) for preventing an
immersion liquid from being absorbed into the photo resist film and
a substance contained in the resist film from being eluted in the
immersion liquid is formed on the photo resist film (first film).
The protective film is soluble in alkali.
[0281] The step of forming the protective film includes a step of
coating a solution (protective film solution) containing a material
for the protective film on the photo resist film; and a step of
baking for curing the protective film solution. If required
(depending on the situation), the cured protective solution film
(heated protective film) by the baking is cooled.
[0282] The step of coating a protective film solution includes a
step of dropping a protective film solution on the film to be
processed on the main surface of the semiconductor substrate; and a
step of approximately removing a solvent of the protective film
solution while rotating the semiconductor substrate.
[0283] The step of baking for curing the protective film solution
is carried out at 110.degree. C. At this time, the solvent is
removed from the protective film.
[0284] The smoothening of the surface of the protective film was
carried out after N-methyl 2-pyrolinodine steam was applied to the
surface of the protective film while the substrate temperature was
maintained at 110.degree. C. After smoothing the surface of the
protective film, the supply of the steam was stopped.
Subsequently, N-methyl 2-pyrolinodine that remains on the surface
of the protective film was removed by heat treatment, and then, the
substrate was cooled. The irregularities on the surface of the
protective film obtained by these processes were .+-.0.2 nm.
[0285] Next, immersion exposure is carried out by using a substrate
having the thus processed protective film, and then, a
post-exposure baking (PEB) step (step S71) is carried out.
[0286] In the prior art, with respect to an alkali soluble
protective film, the protective film and resist film have been
developed altogether by using a developer having the same
concentration as that used for developing the photo resist
film.
[0287] However, since the protective film and photo resist film are
eluted, there has been a problem that a defect occurs due to
interaction of these films.
[0288] In addition, in the case where a dissolution rate of the
protective film of the photo resist film is slow, there has been a
problem that the uniformity of dimensions of the resist pattern is
impaired and no pattern is resolved as an image.
[0289] Therefore, the following process is carried out in the
present embodiment.
[0290] The protective film is removed while rotating the substrate
by using a first developer (aqueous solution of tetra methyl
ammonium oxide) obtained by diluting the developer when pH=12.5
(step S72).
[0291] At this time, in order to carry out the removing of the
protective film within a short period of time, the first developer
is used while a liquid supply nozzle is moved in a radial direction
on the substrate.
[0292] At a stage at which the protective film has dissolved and
the photo resist film has been exposed, the supply of the first
developer is stopped. While pure water is supplied from the same
liquid supply nozzle and nozzle movement in the radial direction
and substrate rotation are carried out, an eluted substance of the
protective film is removed from the substrate (step S73).
[0293] Next, rotational drying is carried out at 1800 rpm at which
the air flow on the substrate does not become a turbulent flow on
the outer circumference of the substrate (step S74).
[0294] Next, a second developer of pH 13.8 is continuously supplied
in the same unit as that used for removal of the protective film
(step S75), and an eluted substance of the photo resist film is
removed (step S76).
[0295] Thereafter, a drying process is carried out (step S77), and
a resist pattern is completed.
[0296] When, with the thus formed resist pattern of the present
embodiment using as a mask, a trench pattern formed by sequentially
etching the antireflection film (second film to be processed) and
the oxide film (first film to be processed) was inspected, the
number of defects was merely produced as several defects per wafer,
and a good result was obtained. A device produced by filling the
inside of the trench pattern with a wiring material and by further
performing a post-processing showed good reliability.
[0297] In the present embodiment, the protective film was removed
by supplying the first developer having a comparatively low
concentration and dissolving the protective film, and thereafter, a
resist pattern is formed by drying the substrate and supplying the
second developer onto the substrate (photo resist film), however it
is not limited thereto. The resist pattern may be formed by
supplying the second developer immediately after the protective
film has dissolved.
[0298] In addition, the concentration of the first developer is not
limited thereto, and any alkaline solution may be used as long as
it has a concentration (alkali concentration) at which the
protective film dissolves and the photo resist film hardly
dissolves. In addition, any concentration of the second developer
may be used as long as it is a concentration (alkali concentration)
at which the photo resist film is developed and which is higher
than that of the first developer.
[0299] Further, in the case where a liquid droplet has occurred on
the protective film at the time of immersion exposure, such a
liquid droplet may be removed immediately prior to carrying out
post-exposure baking in order to prevent a watermark or pattern
dimension/shape failure (processing of protective film after
exposure).
[0300] When the dissolution compound that is produced during the
first development process dose not affect to second development
process, the step S73 and step S74 can be skipped.
[0301] The underlying layer processing step according to the
present embodiment relates to a step of forming a trench of an
oxide film without being limited thereto. For example, this step
can be applied to lithography step for all the device manufacturing
steps such as contact hole formation, gate formation, active area
formation, and ion implantation.
[0302] In addition, a semiconductor device is manufactured by
forming a resist pattern on a substrate including a semiconductor
substrate by the method of any of the above mentioned embodiments,
then, etching the substrate using the resist pattern as a mask. The
semiconductor substrate is, for instance, a silicon substrate or an
SOI substrate.
[0303] Here, in the case where an underlying layer of the resist
pattern (i.e. uppermost layer of the substrate) is a
polycrystalline silicon film or a metal film, a fine electrode
pattern or wiring pattern or the like is formed. In the case where
the underlying layer of the resist pattern (i.e. uppermost layer of
the substrate) is an insulating film, a fine contact hole pattern
or a gate insulating film or the like is formed. In the case where
the underlying layer of the resist pattern is the above-mentioned
semiconductor substrate, a fine isolation trench (STI: shallow
trench isolation) is formed.
[0304] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *