JP3257245B2 - Method of forming fine pattern - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a fine pattern, and more particularly, to a method for forming a transparent film on a highly reflective substrate and forming a resist film on the transparent film. The present invention relates to a method capable of preventing line width fluctuation of a pattern in a wafer surface when forming a fine pattern by performing photolithography processing of a film.

[0002]

2. Description of the Related Art When forming a fine pattern in optical lithography, a variation in line width is a serious problem. recent years,
Line width variations tend to increase with the reduction in design rules. Factors of the line width variation include a step of the underlying substrate and the density of the pattern. With the reduction in design rules, the exposure wavelength in photolithography is g-line (436 nm) → i-line (365 nm) → Kr
The wavelength has been shortened to F excimer laser (248 nm).

With the shortening of the exposure wavelength, as shown in FIG. 7, incident light incident on the resist 2 and reflected light from the interface between the resist 2 and the base substrate 4 due to the incident light are:
The so-called standing wave effect that causes interference in the resist becomes a significant problem. The cause of the standing wave effect becoming remarkable when the exposure wavelength is shortened is that the period of the multiple interference is reduced and the reflectance of the substrate is increased. FIG.
As shown in (1), as the exposure wavelength becomes shorter from the g-line to the KrF excimer, the variation in the line width due to the change in the resist film thickness increases. This is because the influence of multiple interference (standing wave effect) increases. Therefore, if a step or the like is formed on the base substrate, the thickness of the resist film changes, and there is a possibility that the line width varies.

As a method of suppressing line width fluctuation of a pattern,
An anti-reflection technique as shown in FIGS. 9 and 10 is known.
In the technique shown in FIG. 9, a transparent organic film 6 is formed on a resist film 2 formed on a base substrate 4 so that the film thickness of the resist film 2 changes due to a phase canceling action. However, the amount of light absorbed inside the resist film 2 is kept constant, and the fluctuation of the line width is suppressed. In the technique shown in FIG. 10, the thickness of the resist film 2 is changed by the light absorbing function and the phase canceling function by interposing the absorptive antireflection film 8 between the base substrate 4 and the resist film 2. Even in such a case, the amount of light absorbed inside the resist film 2 is kept constant, and the fluctuation of the line width is suppressed.

In the case of a highly reflective base substrate, FIG.
In the case where the anti-reflection film 8 is provided as shown in FIG. 11B, the step 10 in the step 10 has a greater effect than when the anti-reflection film is not provided on the base substrate 4 as shown in FIG.
The amount of reflected light reflected in various directions is reduced, which is advantageous in terms of preventing line width fluctuation and preventing halation. That is, from the viewpoint of preventing line width fluctuation and preventing halation, it is preferable to interpose an antireflection film between the underlying substrate and the resist film.

When a transparent film is formed on a highly reflective base substrate and the upper resist film is patterned, there are two methods as shown in FIGS. 12 (A) and 12 (B). is there. In the method shown in FIG. 12A, an antireflection film 8 is provided on a transparent film 12 formed on a base substrate 4, and a resist film 2 is formed thereon. In the method shown in FIG. 12B, an antireflection film 8 is provided on a base substrate 4, a transparent film 12 is formed thereon, and a resist film 2 is formed thereon.

In terms of optical phase cancellation,
When the anti-reflection film 8 is formed between the transparent film 12 and the base substrate 4, the line width variation in the wafer surface due to the variation in the thickness of the transparent film and the like is reduced.

[0008]

However, when the anti-reflection film 8 is formed between the transparent film 12 and the base substrate 4, it is difficult to form the transparent film 12 on the anti-reflection film 8. Depending on the temperature or atmospheric conditions, the antireflection film may be deteriorated. Therefore, it is difficult to form an organic film or a film having a possibility of deterioration as a film having an antireflection function.

When the anti-reflection film 8 is formed between the resist film 2 and the transparent film 12, the influence of variations in the thickness of the transparent film 12, etc. becomes large, and the line width of the pattern becomes large. Table 1 below shows the resist against the variation in the thickness of the transparent film between the case where the antireflection film was formed between the resist film and the transparent film and the case where it was formed between the transparent film and the base substrate. The variation in the amount of light absorbed by the film is shown.
The variation in the amount of light absorbed by the resist film corresponds to the variation in the line width of the pattern.

[0010]

[Table 1]

As shown in Table 1, when an antireflection film is formed between the base substrate and the transparent film, the dispersion of the transparent film is ± 6.
%, The variation of the absorption amount is ± 2.7%. However, when an antireflection film is formed on the transparent film, even if the dispersion of the transparent film is ± 3.8%, the dispersion of the absorption amount is ± 4.1%. That is, from the viewpoint of reducing the variation in the absorption amount, it is preferable to form an antireflection film between the base substrate and the transparent film.

However, as described above, when an anti-reflection film is formed between a transparent film and an underlying substrate, the temperature or the atmosphere conditions at the time of forming the transparent film on the anti-reflection film depends on the conditions. The antireflection film may be deteriorated. As a result, an effective antireflection effect may not be obtained.

The present invention has been made in view of such circumstances, and a method of forming a fine pattern capable of minimizing a line width variation of a pattern irrespective of variations in a transparent film formed on the surface of a highly reflective base substrate. The purpose is to provide.

[0014]

In order to achieve the above object, a method for forming a fine pattern according to the present invention comprises forming a transparent film on a highly reflective substrate, and forming a resist film on the transparent film. In the method of forming a film, performing a photolithography process on the resist film, and forming a fine pattern, a high-absorbing film having high optical absorption is disposed between the substrate and the transparent film, and the lower layer of the resist film is formed. Alternatively, an antireflection film is provided as an upper layer, and exposure is performed.

Examples of the highly reflective substrate include a single crystal silicon substrate on which a tungsten silicide film, a tungsten film, an aluminum film, an aluminum alloy film, a polysilicon film, or the like is formed. The transparent film is not particularly limited, and examples thereof include a silicon oxide film and a silicon nitride film. The method for forming the film is not particularly limited, and includes a low pressure CVD method, a SOG method,
An S-CVD method or the like can be exemplified. Note that the transparent film only needs to be substantially transparent, and in the present invention, the concept includes a semi-transparent film.

As the above high absorption film, k × d = 0 to 600
It is preferable to use an [nm] absorbing film. Where k
Is the extinction coefficient, and d is the film thickness. SiO _x N _y film was formed by a plasma CVD _{method: H, SiC, Si x N} y: H film becomes the candidate. If k × d is large, it is not economical and k
When xd is small, the function as an absorbing film is reduced.

As an anti-reflection film located between the resist film and the transparent film, SiO _x N _y : H, Si whose optical constant and film thickness are selected so as to maximize the anti-reflection effect.
_{C, Si x N y: H} , can be used any one of amorphous carbon. The thickness and the optical constant of the antireflection film are selected so that the antireflection effect is optimized. As a method for optimizing the anti-reflection effect, a method for minimizing the standing wave effect proposed by the present applicant in Japanese Patent Application No. 5-350386 or the like can be adopted. . In particular, the SiO _x N _y : H film is preferable because the optical constant can be changed widely by changing the film forming conditions, and it is easy to obtain an anti-reflection film having an optimum anti-reflection effect.

As the anti-reflection film located between the resist film and the transparent film, either TiON or TiN whose film thickness is selected so as to optimize the anti-reflection effect can be used. The thickness of the antireflection film is selected so that the antireflection effect is optimized.

As the antireflection film, an organic antireflection film can be used. Either SiO ₂ or SiN can be used as the transparent film.

[0020]

In the method for forming a fine pattern according to the present invention, a high optically absorbing high absorption film is disposed between the substrate and the transparent film. By forming the high absorption film, reflection from the high reflection substrate can be reduced. The optical conditions of this high absorption film vary depending on the temperature or atmospheric conditions at the time of formation of the transparent film. However, by providing an antireflection film on the transparent film and selecting its thickness and / or optical constant. , High absorption membrane,
The total antireflection effect of the three layers of the transparent film and the antireflection film can be optimized. As a result, even if the thickness of the transparent film varies, the standing wave effect in the resist film can be suppressed, and the line width variation of the fine pattern can be suppressed.

[0021]

EXAMPLES Hereinafter, the method for forming a fine pattern according to the present invention will be described based on examples, but the present invention is not limited to these examples. Example 1 In this example, as shown in FIG. 1, a high absorption film 22 having high optical absorption was formed on a highly reflective base substrate 20. In the present embodiment, as the highly reflective base substrate 20,
Bulk tungsten silicide was used. The optical constants of tungsten silicide are n = 1.93 ± 0.2 and k = 2.73 ± 0.
It was 2.

As the high absorption film 22, SiO _x N _y : H
A (hydrogen-containing silicon oxynitride) film was used. This SiO _x N
_{The y} : H film was formed by plasma CVD. The thickness d was 80.7 ± 2.0 nm. Further, the optical constant is n = 2.
1 ± 0.2 and k = 0.52 ± 0.05.

Next, on this high absorption film 22, the transparent film 2
4 was formed. As the transparent film 24, a 0.17 μm-thick silicon oxide film formed by a low pressure CVD method was used. The optical constant of the transparent film 24 is n = 1.52 ± 0.
2, k = 0.0 ± 0.05.

Depending on the temperature and the atmospheric conditions at the time of forming the transparent film 24, the high-absorption film 22 having a chemical non-stoichiometric composition located thereunder is altered, and its optical constant is n = 1.
65 ± 0.2, k = 0.66 ± 0.05. Next, in this embodiment, the antireflection film 26 is formed on the transparent film 24.
Was formed. In this embodiment, an SiO _x N _y : H film whose optical constant can be controlled by a chemical non-stoichiometric composition is used as the antireflection film 26. This SiO
_{The xNy} : H film was formed by plasma CVD. At the time of film formation, the film thickness and optical constants of the transparent film 24 and the high absorption film 22 are taken into consideration so as to minimize the standing wave effect in the resist film formed thereon. , The optical constant and the film thickness of the antireflection film 26, n = 2.10 ± 0.2
k = 0.56 ± 0.05, film thickness d = 12.8 nm ± 2n
m. The optimization conditions at that time are shown in Table 2 below.

[0025]

[Table 2]

When a resist film 28 was formed on the antireflection film 26 and the variation in the thickness of the transparent film 24 was changed by ± 5%, the variation in the amount of light absorbed by the resist film was determined. The results are shown in FIG. As shown in FIG. 2, even when the variation of the transparent film 24 made of SiO ₂ is ± 5%, the variation in the amount of light absorbed by the resist film when the thickness of the resist film is changed is ± 3. 23%. Therefore, the line width variation in the wafer plane is reduced.

COMPARATIVE EXAMPLE 1 As shown in FIG.
a without providing an anti-reflection film on
a was formed. In Comparative Example 1, as shown in FIG. 3A, an antireflection film 22a is formed on a highly reflective base substrate 20a.
As a SiO _x N _y : H film. In this embodiment, bulk tungsten silicide is used as the highly reflective base substrate 20a. The optical constant of tungsten silicide is such that n = 248 nm for light having a wavelength of 248 nm.
BR> 1.93 ± 0.2, k = 2.73 ± 0.2.

The SiO _x N _y : H film was formed by plasma CVD. The thickness d was 29.0 ± 2.0 nm. In addition, the optical constants are n = 2.1 ± 0.2 and k = 0.52 ± 2 for light of wavelength λ = 248 nm.
It was 0.05. Next, a transparent film 24a was formed on the antireflection film 22a. As the transparent film 24a,
A 0.17 μm-thick silicon oxide film formed by a low pressure CVD method was used. The temperature at which the transparent film 24 was formed (7
(00 ° C. or higher)) and the atmospheric conditions, the antireflection film 22 a of a lower layer, which has a chemical non-stoichiometric composition, is altered, and its optical constants are n = 1.65 ± 0.2 and k = 0.
66 ± 0.05. Therefore, as in Comparative Example 1 shown in FIG.
When provided between a and the base substrate 20, a good antireflection effect cannot be obtained.

Comparative Example 2 In Comparative Example 2, as shown in FIG. 3B, a transparent film 24a was formed on a highly reflective base substrate 20a, and an antireflection film 22a and a resist film 28a were formed thereon. Was provided.

In this embodiment, bulk tungsten silicide is used as the highly reflective base substrate 20a.
The optical constant of tungsten silicide is λ = 248 nm
, N = 1.93 ± 0.2, k = 2.
73 ± 0.2. As the transparent film 24a, a reduced pressure C
A 0.17 μm-thick silicon oxide film formed by the VD method was used.

The anti-reflection film 22a is made of SiO
_{An xNy} : H film was used. The SiO _x N _y : H film was formed by plasma CVD. At the time of film formation, the film thickness and optical constants of the transparent film 24a and the substrate 20 are taken into consideration so as to minimize the standing wave effect in the resist film 28a formed thereon, The optical constant and the film thickness of the antireflection film 22a are set as n = 2.09 ± 0.2 and k = 0.68 ±
0.05 and the thickness d = 0.023 μm ± 0.002 μm.

A resist film 28a is formed on the antireflection film 22a.
Was formed, and when the variation in the thickness of the transparent film 24a was changed by ± 5%, the variation in the amount of light absorbed by the resist film 28a was obtained. FIG. 4 shows the results. As shown in FIG. 4, the dispersion of the transparent film 24a made of SiO ₂ is ± 5%.
In the case of (1), the variation in the amount of light absorbed by the resist film when the thickness of the resist film was changed was ± 5.74%.

Comparing the second comparative example with the first embodiment, the first embodiment shows that the variation in the amount of absorbed light is ± 3.
It was confirmed that it could be reduced to 23%. Therefore, in Example 1, the line width variation in the wafer surface is smaller than in Comparative Example 2. Example 2 Except that the antireflection film shown in FIG. 1 was formed by the following method,
An antireflection treatment was performed in the same manner as in Example 1 to form a fine pattern.

[0034] In this embodiment, as a deposition method for changing the optical constant with the film of chemical non-stoichiometric composition as an antireflection film, a SiO ₂ as a _{target, NH 3, N 2, N} 2
A method of forming a film by a reactive sputtering method using O gas,
Alternatively, a reactive sputtering method using SiN as a target and using O ₂ gas was used.

Example 3 The film thickness and optical constants of the high absorption film 22 and the antireflection film 26 shown in FIG. 1 are shown in Table 3 below to optimize the antireflection effect. Similarly, a fine pattern was formed.

[0036]

[Table 3]

The antireflection film 26 is made of SiH ₄ , N ₂ , N ₂
A film was formed by plasma CVD using an O gas system. A resist film 28 is formed on the antireflection film 26, and the transparent film 24 is formed.
When the variation in film thickness was changed by ± 5%, the variation in the amount of light absorbed by the resist film was determined. FIG. 5 shows the results. As shown in FIG. 5, the transparent film 24 made of SiO ₂
Even when the variation of the resist film was ± 5%, the variation in the amount of light absorbed by the resist film when the thickness of the resist film was changed was ± 1.85%. Therefore, the line width variation in the wafer plane is reduced.

Example 4 Except that the antireflection film shown in FIG. 1 was formed by the following method,
An antireflection treatment was performed in the same manner as in Example 3 to form a fine pattern. In this embodiment, as the film formation method of changing the optical constant with the film of chemical non-stoichiometric composition as an antireflection film, a SiO ₂ as a target, NH _3, N _2, N
_A method of forming a film by a reactive sputtering method using ₂ O gas or a reactive sputtering method using O ₂ gas with SiN as a target was used.

EXAMPLE 5 An organic film was used as the antireflection film 26 shown in FIG. 1, and the film thickness and optical constants of the high absorption film 22 and the antireflection film 26 were set as shown in Table 4 below. The antireflection effect was optimized, and a fine pattern was formed in the same manner as in Example 1.

[0040]

[Table 4]

When a resist film 28 was formed on the antireflection film 26 and the variation in the thickness of the transparent film 24 was changed by ± 5%, the variation in the amount of light absorbed by the resist film was determined. FIG. 6 shows the results. As shown in FIG. 6, even if the variation of the transparent film 24 made of SiO ₂ is ± 5%, the variation in the amount of light absorbed by the resist film when the thickness of the resist film is changed is ± 2. 04%. Therefore, the line width variation in the wafer plane is reduced.

Embodiment 6 As the high absorption film 22 shown in FIG. 1, n = 3.1 ± 0.3,
SiC film with k = 0.24 ± 0.05, or n = 2.4
± 0.3, k = a 0.56 ± 0.05 Si _x N _y: H film was formed by plasma CVD or sputtering.
SiC is SiH ₄ , C ₂ H ₂ -based gas and Si _x
N _y : H was formed using SiH ₄ and N ₂ -based gas.
As the transparent film 24 formed thereon, SiO ₂ or SiN was used. The heat at the time of forming the transparent film modified the high absorption film and changed its optical constant. Transparent film 24
SiH ₄ ,
NH ₃ , SiO _x N _y is deposited by plasma CVD using N _2, N ₂ O gas: H film, Ar, amorphous carbon film formed by plasma CVD using a C ₂ H ₂ based gas, SiH ₄ Plasma CVD using N ₂ based gas
Either a Si _x N _y film formed by sputtering or a film formed by reactive sputtering was used. An organic film can also be used as an antireflection film.

One of these films is formed on a transparent film under the conditions of a film thickness or an optical constant so that the antireflection effect is optimized, and a resist film 28 is formed thereon. A fine pattern was formed in the same manner as in Example 1.

[0044]

As described above, according to the present invention, even if the thickness of the transparent film varies, the standing wave effect in the resist film is suppressed, and the line width variation of the fine pattern is reduced. Can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an antireflection technique according to an embodiment of the present invention.

FIG. 2 is a graph showing an antireflection effect according to the first embodiment of the present invention.

FIGS. 3A and 3B are cross-sectional views of main parts of an antireflection technique according to a comparative example of the present invention.

FIG. 4 is a graph showing an antireflection effect according to a comparative example of the present invention.

FIG. 5 is a graph showing an anti-reflection effect according to another embodiment of the present invention.

FIG. 6 is a graph showing an anti-reflection effect according to another embodiment of the present invention.

FIG. 7 is a schematic diagram showing multiple interference inside a resist.

FIG. 8 is a graph showing an increase in fluctuation of a pattern line width with a decrease in wavelength.

FIG. 9 is a sectional view of an essential part when an anti-reflection film is provided on a resist film.

FIG. 10 is a sectional view of a main part when an antireflection film is provided below a resist.

FIGS. 11A and 11B are cross-sectional views of a main part showing a state of reflected light at a step portion.

FIGS. 12A and 12B are cross-sectional views of a main part of an antireflection technique according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 20 ... Substrate 22 ... High absorption film 24 ... Transparent film 26 ... Antireflection film 28 ... Resist film

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-234109 (JP, A) JP-A-5-114559 (JP, A) JP-A-5-299338 (JP, A) JP-A-4-234 188730 (JP, A) JP-A-63-202915 (JP, A) JP-A-5-343314 (JP, A) JP-A-6-84848 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/027

Claims (8)

(57) [Claims] 1. A method for forming a fine pattern by forming a transparent film on a highly reflective substrate, forming a resist film on the transparent film, performing photolithography on the resist film, and forming a fine pattern. A highly optically absorbing high absorption film is disposed between the resist film and the transparent film, and an antireflection film is provided below or above the resist film, and exposure is performed. 2. The extinction coefficient k and the thickness d [n of the high absorption film
m], and a film satisfying 0 to 600 in a product with [m] is used.
3. The method for forming a fine pattern according to 1. 3. The high-absorbing film is made of SiO _x N _y : H, Si
C, Si _x N _y: method of forming a fine pattern according to claim 1 is either H. 4. A film that satisfies 0 to 100 as a product of an extinction coefficient k and a film thickness d [nm] as an antireflection film located between the resist film and the transparent film. The method for forming a fine pattern according to claim 1. 5. A method according to claim 1, wherein said transparent film is located between said resist film and said transparent film.
As an anti-reflection film to optimize the anti-reflection effect
SiO with selected optical constant and film thickness_xN _y: H, S
iC, Si_xN_y: Any of H and amorphous carbon
5. The method according to claim 1, wherein
Or a method for forming a fine pattern. 6. An anti-reflection film located between the resist film and the transparent film, wherein one of TiON and TiN whose film thickness is selected such that an anti-reflection effect is optimal is used. The method for forming a fine pattern according to claim 1. 7. The method for forming a fine pattern according to claim 1, wherein the antireflection film is an organic antireflection film located between the resist film and the transparent film or above the resist film. 8. The method according to claim 1, wherein the transparent film is made of one of SiO _{2 and} SiN.