JPH11260686A - Exposure method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce variations of a resist film thickness dependente on a light quantity absorbed in a resist. SOLUTION: In this method, a photomask cutting an LSI pattern is illuminated with an exposing light and the lights transmitting the photomask are exposed, so as to transfer a pattern to a resist film 6 formed in a processed substrate 3 in a projection optical system. In this case, a gap between a projection optical system 2 and the processed substrate 3 is filled up with monobromnaphthalene, having a refractive index greater than that of a member constituting a face closest to the processed substrate of the projection optical system 2 and smaller than that of the resist film 6 to transfer patterns.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method for transferring a pattern on a mask onto a substrate to be processed.
The present invention relates to an exposure method suitable for a photolithography process for manufacturing SI.

[0002]

2. Description of the Related Art Optical lithography in a semiconductor manufacturing process is used for device production because of its advantages such as simplicity of the process and low cost. In optical lithography, technological innovation is always continuing and its development is remarkable,
In recent years, miniaturization of elements of 0.25 μm or less has been achieved by using, for example, KrF light by shortening the wavelength of a light source. As for the projection exposure apparatus, it has become possible to use a projection optical system with a larger diameter than ever before, as the development of scan type exposure equipment progresses, and it is possible to form finer patterns on wafers. Is becoming possible. For further miniaturization in the future, formation of a finer resist pattern and an accompanying exposure technology are required.

FIG. 7 is a view for explaining a conventional exposure method, and shows a schematic configuration of an exposure apparatus used in a conventional photolithography process. A conventional exposure method will be described with reference to FIG. The exposure apparatus shown in FIG. 7 is roughly composed of a photomask 1, a projection optical system 2, and a substrate 3 to be processed.

The photomask 1 has an LSI pattern to be transferred by a light-shielding film 5 made of, for example, Cr, on a quartz substrate 4 having a light-transmitting property with respect to exposure light. The photomask 1 is illuminated with exposure light, and the transmitted light is reduced and transferred onto the substrate 3 via the projection optical system 2. On the substrate 3 to be processed, a resist 6 for transferring the mask pattern of the photomask 1, an antireflection film 7 for reducing multiple reflection at the interface between the surface of the resist 6 and the substrate, and a film 8 to be processed are arranged on the Si wafer 9 in order from the top. Is formed.

FIG. 8 is a diagram showing details of the path of exposure light in the vicinity of the substrate 3 shown in FIG. FIG. 8 shows only components of light rays obliquely incident on the substrate 3 from the upper left in FIG. Other components of the light ray behave in the same manner as described below. Exposure light that travels through the projection optical system 2 and obliquely enters the interface between the surface of the projection lens closest to the substrate 3 to be processed 3 (hereinafter referred to as the final lens surface) and the air 10 at an angle of incidence ψ ₁ , some reflectance R _1, reflected by the reflection angle [psi _1, the remaining proceeds to refracted and air at a refraction angle [psi _2.

A part of the exposure light that reaches the resist 6 at an incident angle ψ ₂ is reflected at an interface between the resist 6 and the air 10 at a reflection angle ψ ₂ , and the remaining exposure light is refracted at a refraction angle ψ ₃ and Go through 6. Resist exposure light incident at an incident angle [psi ₃ in 6, the reflection is reduced for most anti-reflection film 7, a portion is reflected by the reflection preventing film 7 surface.
This reflected light is further reflected on the surface of the resist 6,
As a result, multiple reflection occurs between the interface between the resist 6 and the air 10. Thus, the total reflectance of the exposure light reflected on the interface between the resist 6 and the air 10 and the exposure light reflected on the antireflection film 7 is R ₂ .

The above-described projection optical system 2 and air 10
During, because the relationship of the refractive index and angle of incidence between the air 10 and the resist 6 is governed by the Snell's law, sinψ ₁ / si
nψ ₂ = n ₂ / n ₁ , sinψ ₂ / sinψ ₃ = n ₃ /
n ₂ holds.

As described above, due to the multiple reflections occurring on the substrate 3 to be processed, the dependency of the amount of light absorbed in the resist on the resist film thickness (swing curve) occurs as shown in FIG. The horizontal axis in FIG. 5 shows the resist film thickness, and the vertical axis shows the amount of absorbed light in the resist per unit film thickness of the resist, and the solid line in the figure shows the resist film thickness dependency in the conventional exposure method. In FIG. 5, the exposure wavelength is 248 nm, the refractive index n ₃ of the resist 6 in the exposure light is 1.78, the absorption coefficient is 0.02, the refractive index of the antireflection film 7 is 1.78, and the absorption coefficient is 0.24. The film to be processed is made of Al and has a refractive index of 0.08.
9, the case where the absorption coefficient is 2.35. The space between the final lens surface of the projection optical system and the resist 6 is air (refractive index n ₂ =
1) is satisfied. The refractive index of the last lens in the lens group constituting the projection optical system 2 is n ₁ = 1.5.

With the dependence of the absorbed light amount on the resist film thickness, the exposure amount (appropriate exposure amount) required for the resist pattern after development to have an appropriate size also varies. Conventionally, the amplitude of the swing curve was large in this way, so the resist film thickness was applied with high precision so as to correspond to the peaks or valleys of this swing curve. Therefore, it is necessary to reduce the dependency of the proper exposure amount on the resist film thickness.

[0010] [psi ₁ dependency of Figures 3 and 4, respectively R _1, shows a [psi ₂ dependence of R _2. In each figure,
The horizontal axis represents the reflection angles ψ ₁ and ψ ₂ , and the vertical axis represents the reflectances R ₁ and R ₂ . The solid line in the figure shows the case of the conventional example. From this figure, it can be confirmed that in the related art, R ₁ and R ₂ , which are the loss components other than the components absorbed and exposed to the resist, showed extremely large values.

[0011]

As described above, in the conventional exposure method, a part of the exposure light incident on the resist is reflected by the antireflection film formed on the lower surface of the resist, and the resist is exposed to the air. This causes multiple reflections at the interface and the reflectance R ₂ on the resist surface is substantially increased. The greater the value of the reflectance R ₂ , the more the variation in the amount of light absorbed in the resist depends on the resist film. As a result, in order to perform high-precision exposure, it is necessary to ensure uniformity of the exposure amount with respect to the resist film, and therefore, the thickness of the resist film must be uniformed with high precision.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an exposure method for reducing variations in the resist film thickness dependence of the amount of light absorbed in a resist. Is to do.

[0013]

According to an exposure method of the present invention, a photomask is illuminated with exposure light, and light transmitted through the photomask is patterned on a resist film formed on a substrate to be processed by a projection optical system. In the exposing method for transferring, between the surface of the projection optical system closest to the substrate to be processed and the substrate to be processed, a refractive index larger than the refractive index of air and smaller than the refractive index of the resist film. It is characterized in that pattern transfer is performed by filling the medium with the medium.

Preferred embodiments of the present invention are as follows. (1) The refractive index between the surface of the projection optical system closest to the substrate to be processed and the substrate to be processed is larger than the refractive index of the member constituting the surface closest to the substrate to be processed and smaller than the refractive index of the resist film. Fill with a medium having a refractive index. (2) The space between the surface of the projection optical system closest to the substrate to be processed and the substrate to be processed is filled with a medium having a refractive index substantially equal to the refractive index of the resist film. (3) As a medium filling the space between the substrate to be processed and the surface of the projection optical system closest to the substrate to be processed, a base resin constituting a resist in the substrate to be processed is used. (4) An alicyclic resist is used as a resist, and an alicyclic polymer is used as a medium filling a space between a substrate to be processed and a surface of the projection optical system closest to the substrate to be processed. (5) An antireflection film is formed between the resist and the substrate to be processed. (6) The space between the surface of the projection optical system closest to the processing substrate and the substrate to be processed is filled with water. (Operation) In the present invention, the refractive index between the surface of the projection optical system closest to the substrate to be processed (hereinafter, referred to as a final lens surface) and the surface of the substrate to be processed is adjusted. That is, by filling with a medium having a refractive index intermediate between the refractive index of air and the refractive index of the resist, the difference in the refractive index between the final lens surface and the medium, and the difference in the refractive index between the medium and the substrate to be processed cause the medium to be filled. If it is not satisfied, the size is smaller than that of the related art, and the reflection at the interface between the final lens surface and the medium is reduced, and the reflection at the interface between the resist and the medium is also reduced. Therefore, the substantial sensitivity of the resist is improved. Further, since the reflection at the interface between the resist and the medium is reduced, the multiple reflection in the resist between the resist and the base is reduced, and the dependency of the amount of absorbed light in the resist on the resist film thickness (swing curve) is reduced. The amplitude decreases. Thereby, the controllability required for the resist film thickness is relaxed.

Further, by filling the space between the final lens surface of the projection optical system and the wafer with a medium having substantially the same refractive index as the resist, reflection at the interface between the resist and the medium is eliminated, and the substantial sensitivity of the resist is reduced. improves. In addition, since reflection at the interface between the resist and the medium is reduced, multiple reflection in the resist between the resist and the base is eliminated,
The amplitude of the dependency of the amount of light absorbed in the resist on the resist film thickness (swing curve) is eliminated. Thereby, the controllability required for the resist film thickness is relaxed.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a view showing the overall configuration of an exposure apparatus used in an exposure method according to a first embodiment of the present invention, and FIG. 2 is a view of the exposure apparatus shown in FIG. It is a figure which shows the course of exposure light in detail.

As shown in FIG. 1, the present exposure apparatus mainly comprises a photomask 1, a projection optical system 2, and a substrate 3 to be processed. In the photomask 1, an LSI pattern to be transferred by a light-shielding film 5 made of, for example, Cr and having a light-shielding property is formed on a quartz substrate 4 having a light-transmitting property with respect to exposure light. The photomask 1 is illuminated with exposure light, and the transmitted light is reduced and transferred onto the substrate 3 by a projection optical system. A resist 6 for transferring a mask pattern of the photomask 1, an antireflection film 7 for reducing multiple reflection at the interface between the surface of the resist 6 and the substrate, and a film 8 to be processed are formed on the substrate 3.
It is formed on the wafer 9 in order from the top.

As shown in FIG. 2, the resist 6 has a refractive index n ₃ of 1.78, an absorption coefficient of 0.02, an antireflection film 7 of 1.78 and an absorption coefficient of 0.02. 24, the film 8 to be processed is Al, the refractive index is 0.089, and the absorption coefficient is 2.
35. The refractive index of the last lens in the lens group constituting the projection optical system 2 is n ₁ = 1.5. In the present embodiment, the space between the final lens surface of the projection optical system 2 and the resist is an intermediate between the refractive index n _{1 of} quartz which is the material of the final lens of the projection optical system and the refractive index n ₃ of the resist 6. This is different from the conventional example in that the medium is filled with a medium called monobromonaphthalene 11 having a refractive index n _{2 of} 1.658. Therefore, the relationship between the refractive indices of the respective parts is n ₁ <n ₂ <n ₃ .

The operation of the above embodiment will be described. As shown in FIG. 1, exposure light emitted from an illumination optical system (not shown) transmits through a photomask 1, forms an optical image having a desired mask pattern, and is incident on a projection optical system. This optical image is reduced and projected by the projection optical system 2 and is incident on the substrate 3 through the monobromonaphthalene 11.

Next, the course of the exposure light near the substrate 3 shown in FIG. 1 will be described in detail with reference to FIG. FIG. 2 shows only the components of the light beam obliquely incident on the substrate 3 from the upper left in FIG. The components of the exposure light having other angles of incidence behave similarly to the contents shown in FIG.

Exposure light that travels through the projection optical system 2 and enters the interface between the final lens surface of the projection optical system 2 and the monobromonaphthalene 11 at an incident angle ψ ₁ is partially reflected by the reflectance R ₁ . It is reflected by the corner ψ _1. The remainder of the exposure light, Sinpusai by Snell's law _{1 / sinψ 2 = n 2 /} n mono bromonaphthalene 11 is refracted relationship refraction angle [psi ₂ satisfying ₁
Enter inside.

A part of the exposure light that reaches the resist 6 at an incident angle ψ ₂ is reflected at an interface between the resist 6 and the monobromonaphthalene 11 at a reflection angle ψ ₂ , and the rest is sinψ ₂ / sinψ _3.
= Is refracted at refraction angle [psi ₃ satisfying n ₃ / n ₂ resist 6
Incident on. Most of the exposure light traveling through the resist 6 is reduced in reflection by the anti-reflection film 7, but a part of the light is reflected on the surface of the anti-reflection film 7 and multiplexed between the resist 6 and the interface between the monobromonaphthalene 11. Cause a reflection,
The reflectance R ₂ as a whole.

Next, FIGS. 3 and 4 show the relationship between the angles of incidence ψ ₁ , ψ _{2 on the} monobromonaphthalene 11 and the resist 6 and the reflectances R ₁ , R ₂ . In each figure, the horizontal axis represents the reflection angles ψ ₁ and ψ ₂ , and the vertical axis represents the reflectances R ₁ and R ₂ .
A broken line in the drawing indicates a case according to the present embodiment. As can be seen from FIGS. 3 and 4, the difference in the refractive index between the final lens surface and the monobromonaphthalene 11 and the difference in the refractive index between the monobromonaphthalene 11 and the resist 6 are determined by the projection optical system 2.
Is smaller than that in the conventional case where nothing is filled between the final lens surface and the resist 6, so that the incident angles ψ ₁ and ψ ₂
Regardless of the conventional case, the reflectances R ₁ and R ₂ are more uniform than in the conventional case.
Has been greatly reduced.

Next, the dependency of the amount of light absorbed in the resist on the resist film thickness (swing curve) is shown in FIG. The horizontal axis in FIG. 5 shows the resist film thickness, and the vertical axis shows the amount of absorbed light in the resist per unit resist film thickness, and the broken line in the figure shows the case of this embodiment. Exposure light having an exposure wavelength of 248 nm was used. According to the dependency of the absorbed light amount on the resist film thickness, the exposure amount (appropriate exposure amount) for the developed resist pattern to have an appropriate size also changes, but as shown in FIG. 4, the reflectance R ₂ is greatly reduced. As a result, the swing curve amplitude is significantly reduced as compared with the conventional case shown by the solid line.

Therefore, it is possible to reduce the dependence of the exposure light absorption on the variation of the resist film thickness and the dependence of the appropriate exposure on the variation of the resist film thickness. As described above, according to the present embodiment, the space between the final lens surface of the projection optical system 2 and the surface of the resist 6 is filled with the monobromonaphthalene 11 which is a medium having an intermediate refractive index between the two. Since the difference in the refractive index between the final lens surface and the monobromonaphthalene 11 and the difference in the refractive index between the monobromonaphthalene 11 and the resist 6 are smaller than in the conventional case where the monobromonaphthalene 11 is not filled, the reflectance R ₁ and R ₂ are greatly reduced, and the substantial sensitivity of the resist is improved. Further, variation in resist film thickness dependence of the amount of light absorbed in the resist decreases as a result of the reflectance R ₂ is reduced. Therefore, the accuracy of the thickness required for the thickness of the resist is reduced.

In this embodiment, monobromonaphthalene 11 is used as a suitable medium. However, the present embodiment is not limited to this, and the air between the final lens surface of the projection optical system 2 and the resist 6 is air. And a medium having a refractive index intermediate between the refractive index of the resist 6 and the refractive index n ₃ of the resist 6. Also, n ₁ and n ₃ are not limited to the values described above.

(Second Embodiment) FIG. 1 is a sectional view showing the entire configuration of an exposure apparatus used in an exposure method according to a second embodiment of the present invention. FIG. 6 is a sectional view of the exposure apparatus shown in FIG. FIG. 3 is a diagram illustrating in detail a path of exposure light near a substrate. FIG. 1 is also a diagram for explaining the first embodiment,
By replacing the monobromonaphthalene 11 with another medium, it corresponds to the present embodiment, and the other configuration is not different at all, so the description of FIG. 1 is omitted.

As shown in FIG. 6, the exposure method according to the present embodiment is characterized in that the space between the final lens surface of the projection optical system 2 and the resist 6 is filled with a medium having the same refractive index as that of the resist 6.
This is a different point from the embodiment. Note that, as a medium having the same refractive index as the resist 6, a base resin 61 constituting the resist 6 was specifically used.

Also, the refractive index n of the resist 36 with the exposure light
₃ is 1.78, the absorption coefficient is 0.02, the refractive index of the antireflection film 7 is 1.78, the absorption coefficient is 0.24, and the film 8 is A
At 1, the refractive index is 0.089 and the absorption coefficient is 2.35.
Further, n ₂ = 1.78 Since the refractive index n2 of the base resin 61 as described above is the same as the refractive index n ₃ of the resist 6
And the relationship of n ₁ <n ₂ = n ₃ holds. In this case, the absorption coefficient of the base resin 61 is 0.

The operation of the above embodiment will be described. The operation in FIG. 1 is the same as that in the first embodiment, and therefore will be omitted. The path of the exposure light near the substrate 3 in FIG. 1 will be described in detail with reference to FIG. FIG. 6 shows only the components of the light beam incident on the substrate 3 obliquely from the upper left in FIG. 1, but the components of the light beams incident at other angles also behave in the same manner as described below.

As shown in FIG. 6, travels through the middle projection optical system 2, the exposure light incident at an incident angle [psi ₁ at the interface between the last lens surface and the base resin 61 of the projection optical system 2, a part reflectance R _1, is reflected at a reflection angle [psi _1. The remaining exposure light is sin { ₁ / sin} according to Snell's law.
₂ = refracted by n ₂ / n refraction angle [psi ₂ satisfying the relation of ₁ enters into the base resin 61.

Exposure light reaching the resist 6 at an incident angle ψ ₂ is almost reflected at the interface between the resist 6 and the base resin 61 because the refractive index n ₂ and n ₃ of the resist 6 and the base resin 61 are the same. The light does not refract and goes straight into the resist 6 as it is (strictly, because the absorption coefficients of the base resin 61 and the resist 6 are slightly different, the light is slightly reflected at the interface between the two). Most of the exposure light that has entered the resist 6 is reduced in reflection by the antireflection film 7, but part of the light is reflected on the surface of the antireflection film 7. The reflected light further reaches the interface between the base resin 61 and the resist 6, but also at this interface, due to the relationship of n ₂ = n ₃ , goes straight to the base resin 61 with almost no multiple reflection. Therefore, the reflectivity R ₂ shows a value without considering the influence of multiple reflection.

Next, the relationship between the angles of incidence ψ ₁ , ψ _{2 on} the base resin 61 and the resist 6 and the reflectances R ₁ , R ₂ is shown in FIGS.
Shown in In each figure, the horizontal axis represents the reflection angles ψ ₁ and ψ, respectively.
₂ , and the vertical axis indicates the reflectances R ₁ and R ₂ . Further, a dotted line in the drawing indicates a case according to the present embodiment. Figures 3 and 4
As can be seen from the figure, the difference in the refractive index between the final lens surface and the base resin 61 is different, and the difference in the refractive index between the base resin 61 and the resist 6 is between the final lens surface of the projection optical system 2 and the resist 6. , The reflectivities R ₁ and R ₂ are greatly reduced more uniformly than in the conventional case regardless of the incident angles ψ ₁ and ψ ₂ .

FIG. 5 shows the dependency of the amount of light absorbed in the resist on the resist film thickness (swing curve). The horizontal axis in FIG. 5 shows the resist film thickness, and the vertical axis shows the amount of absorbed light in the resist per unit resist film thickness, and the dotted line in the figure shows the case of the present embodiment. Exposure light having an exposure wavelength of 248 nm was used. According to the dependency of the absorbed light amount on the resist film thickness, the exposure amount (appropriate exposure amount) for the resist pattern after development to have an appropriate size also varies, but the reflectances R ₁ and R ₂ as shown in FIGS. As a result, the amplitude of the swing curve was significantly reduced as compared with the conventional case shown by the solid line.

As described above, according to this embodiment,
By filling the space between the final lens surface of the projection optical system 2 and the surface of the resist 6 with monobromonaphthalene 11, which is a medium having an intermediate refractive index between the two, the reflectances R ₁ and R _{2 are obtained.}
Is greatly reduced, and as a result, there is almost no variation in the dependency of the absorbed light amount of the resist on the resist film thickness. Therefore, there is no need to control the thickness of the resist film with high precision, and it is possible to efficiently develop an LSI manufacturing process.

In this embodiment, the base resin 61 of the resist 6 used is used as a suitable medium.
This embodiment is not limited, and it is sufficient that the space between the final lens surface of the projection optical system 2 and the resist 6 is filled with a medium having the same refractive index as the resist 6. For example, in the case where an alicyclic resist is used as the resist 6, if an alicyclic polymer is used as the base resin 61, the transmittance at the above-described exposure wavelength can be almost 100%. Further, the type of the photomask is not limited to COG, but may be any type such as a Levenson type or a halftone type mask.

By filling the space between the final lens surface of the projection optical system 2 and the substrate 3 to be processed with water,
An effect similar to that of the embodiment can be obtained, and the effect that the substrate cleaning step after exposure is significantly simplified as compared with the case where many media are used.

[0038]

As described above, according to the exposure method of the present invention, the refractive index between the projection optical system and the resist is set to be larger than that of air and smaller than that of the resist. Since the difference in refractive index between the surface of the projection optical system closest to the substrate to be processed and the resist is smaller than in the conventional case where the medium is not filled, reflection at the interface between the resist and the medium is reduced, and Multiple reflections in the resist between the base and the base are reduced. Therefore, the dependence of the amount of light absorbed in the resist on the resist film thickness is reduced,
The film thickness accuracy required for the resist film thickness is relaxed.

Further, since the refractive index between the resist and the surface of the projection optical system closest to the substrate to be processed has the same refractive index as that of the resist, the reflection on the resist surface is eliminated, and the resist between the resist and the underlayer is removed. The multiple reflections at
The dependence of the amount of light absorbed in the resist on the resist film is reduced, and the required film thickness accuracy of the resist film is reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an exposure apparatus used in an exposure method according to a first embodiment of the present invention.

FIG. 2 is a diagram showing in detail a path of exposure light near a substrate to be processed in the embodiment.

FIG. 3 shows the incident angle [psi ₁ dependence of the reflectance R _1.

FIG. 4 is a diagram showing the dependency of the reflectance R _{2 on} the angle of incidence ψ ₂ .

FIG. 5 is a diagram showing the dependence of the amount of light absorbed in the resist on the resist film thickness.

FIG. 6 is a diagram showing in detail a path of exposure light near a substrate to be processed according to a second embodiment of the present invention.

FIG. 7 is a diagram showing an overall configuration of an exposure apparatus used in a conventional exposure method.

FIG. 8 is a view showing in detail a path of exposure light in the vicinity of a substrate to be processed in FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photomask 2 Projection optical system 3 Substrate to be processed 4 Quartz substrate 5 Light shielding film 6 Resist 7 Antireflection film 8 Film to be processed 9 Wafer 11 Monobromonaphthalene 61 Base resin

Claims (3)

[Claims] An exposure method for illuminating a photomask with exposure light and transferring the light transmitted through the photomask to a resist film formed on a substrate to be processed by a projection optical system. The pattern transfer is performed by filling a space between the surface closest to the processing substrate and the processing substrate with a medium having a refractive index larger than the refractive index of air and smaller than the refractive index of the resist film. Exposure method. 2. An exposure method for illuminating a photomask with exposure light and transferring the light transmitted through the photomask to a resist film formed on a substrate to be processed by a projection optical system. Between the surface closest to the processing substrate and the processing substrate, the refractive index of the member constituting the surface of the projection optical system closest to the processing substrate is larger than the refractive index of the resist film, and An exposure method characterized by performing pattern transfer by filling with a medium having a small refractive index. 3. An exposure method in which a photomask is illuminated with exposure light, and the light transmitted through the photomask is pattern-transferred to a resist film formed on a substrate to be processed by a projection optical system. An exposure method, wherein a pattern transfer is performed by filling a space between a surface closest to a substrate to be processed and the substrate to be processed with a medium having a refractive index substantially equal to the refractive index of the resist film.