JP2002311209A - Antireflection film, optical element and aligner mounting the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antireflection film having a wide antireflective band in which changes in the refractive index in an inhomogeneous refractive index material layer are suppressed and to provide an antireflection film having uniform optical characteristics in a lens plane. SOLUTION: In the antireflection multilayered film formed on a substrate which is transparent in the wavelength range from 150 nm to 400 nm, the optical film thickness of at least one layer in the layer of substances having inhomogeneous property of the refractive index in the film thickness direction is controlled to <=0.25λ0 with respect to the designed main wavelength λ0 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antireflection film formed on an optical element.

[0002]

2. Description of the Related Art In recent years, in order to increase the degree of integration of semiconductor devices, there is an increasing demand for high resolution reduction projection exposure apparatuses (steppers). One method of increasing the resolution of photolithography using this stepper is to shorten the wavelength of the light source. Recently, a stepper using a high-output excimer laser as a light source that can oscillate light in a shorter wavelength range than a mercury lamp has begun to be put into practical use. In the optical system of this stepper, it is necessary to form an anti-reflection film in order to reduce a light amount loss, a flare, and a ghost due to surface reflection of an optical element such as a lens.

Here, one of the performances required for an antireflection film on an optical element used in a stepper is that the exposure wavelength is as close to 0% reflection as possible. The reason is that the optical system of the stepper has dozens of planes only in the image forming system, and if the residual reflectance is large, the light amount reaching the wafer becomes small, so that the exposure efficiency deteriorates. Because. For example,
If the residual reflectance per surface is 0.3% and the number of optical components is 50 (100 surfaces), (1− (1−0.003) ^ 100 = 26
%) Near light cannot pass through the optical component.

As a conventional film structure, an antireflection film having a three-layer structure as shown in FIG. 5 is known. This is because an intermediate refractive index material layer 32, a high refractive index material layer 33, a low refractive index material layer 34
Are sequentially laminated. A substance having a lower refractive index than the substrate is a low refractive index substance, a substance having a higher refractive index than the substrate is a high refractive index substance, and a substance having a refractive index between the low refractive index substance and the high refractive index substance is intermediately refracted. Rate substance.
Here, the design center wavelength λ ₀ is an exposure wavelength of 248.4 nm, the substrate 31 is synthetic quartz glass (n = 1.51), the intermediate refractive index material layer 32 is Al ₂ O ₃ (n = 1.71), and the high refractive index material is Layer 33 is made of HfO ₂ (n
FIG. 6 shows the spectral reflectance characteristics when the low refractive index material layer 34 is made of MgF ₂ (n = 1.41).

As can be seen from FIG. 6, the wavelength bands having a reflectance of 0.1% or less are 220 to 235 nm and 290 nm to 3 nm.
The wavelength band of 25 nm is divided into two and narrowed. This is shown in the spectral reflectance characteristic diagram of FIG.
The wavelength band is divided into two portions because the reflectance rises near the center of the antireflection band. The inventor has considered that the cause is a physical property of the HfO ₂ used in the high refractive index material layer 33, “caused by the phenomenon that the refractive index decreases as the film thickness increases”. This phenomenon is called inhomogeneity, and tends to appear significantly as the film thickness increases.

Accordingly, when an optical element having the optical characteristics shown in FIG. 6 is mounted on a stepper, a sufficient antireflection effect cannot be obtained at the exposure wavelength. In addition, when an antireflection film is formed on a convex lens by a vacuum evaporation method, since the deposited particles are incident on the substrate at a high incident angle at the periphery of the lens, the refractive index easily changes in the film thickness direction. . In particular, a substance having a refractive index inhomogeneity in the film thickness direction has a large change in the refractive index.

FIG. 7 is a diagram showing an optical element having a three-layer structure in a conventional film structure. In FIG. 7, from the substrate side,
The first and third layers are made of a uniform refractive index material, and the second layer is made of a heterogeneous refractive index material. The design center wavelength λ ₁ of the antireflection film is 193.4 nm, which is the ArF exposure wavelength, and the substrate 41
Is synthetic quartz glass (n = 1.56), and the inhomogeneous refractive index material 42 is La
F ₃ (n = 1.71), the uniform refractive index material layer 43 is MgF ₂ (n = 1.43), and the thickness of each layer is 0.11λ ₁ , 0.31
λ ₁ , 0.25λ ₁ .

FIG. 8 is a diagram showing the spectral reflectance of the lens center portion and the peripheral portion when the antireflection film having the film configuration shown in FIG. 7 is formed on a lens having a radius of curvature of 160 mm and an effective diameter of 235 mm. is there. As can be seen from FIG. 8, the optical characteristics of the central portion and the peripheral portion of the lens are different.

When an optical element having the optical characteristics shown in FIG. 8 is mounted on a stepper, a difference in transmittance between a light beam passing through the center of the lens and a light beam passing through the periphery of the lens is large, so that the imaging performance is deteriorated. . As a result of the sharp research, the applicants concluded that the thickness of the inhomogeneous refractive index material layer is related to the refractive index of the lens. It was found that the difference in optical properties between the part and the peripheral part became smaller.

[0010]

In the conventional antireflection film for ultraviolet light, since the refractive index changes in the heterogeneous refractive index material layer, it is difficult to widen the antireflection band.
In addition, the optical characteristics in the lens surface become non-uniform. In an exposure apparatus in which such a conventional optical element is mounted, a reduction in the amount of transmitted light, a flare, a ghost, and the like are caused, and the exposure efficiency and the exposure accuracy are reduced.

An object of the present invention is to provide an antireflection film having a wide antireflection band and a uniform optical characteristic in the lens surface by suppressing a change in the refractive index in the heterogeneous refractive index material layer. And Another object of the present invention is to provide an exposure apparatus including an optical element on which the antireflection film is formed.

[0012]

According to the present invention, there is provided an antireflection multilayer film formed on a transparent substrate in a wavelength range of 150 nm to 400 nm. optical thickness of the at least one layer of the layer of material having inhomogeneities rate is, the design dominant wavelength lambda _0, and the structure is 0.25 [lambda ₀ or less.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, an optical element according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of an optical element according to the present invention. Intermediate refractive index material layer 12, high refractive index material layer on substrate 11
13, a five-layer structure in which an intermediate refractive index material layer 14, a high refractive index material layer 15, and a low refractive index material layer 16 are sequentially laminated. A substance having a lower refractive index than the substrate is a low refractive index substance, a substance having a higher refractive index than the substrate is a high refractive index substance, and a substance having a refractive index between the low refractive index substance and the high refractive index substance is intermediately refracted. Rate substance.

In this embodiment, the design center wavelength λ₀Is KrF exci
The oscillation wavelength of the laser is 248.4 nm.
It is synthetic quartz glass (n = 1.51). Also, a low refractive index material layer
Is MgF _Two(N = 1.41), the intermediate refractive index material layer is Al_TwoO_Three(N = 1.7
1) High refractive index material layer is HfO_Two(N = 2.28). Each
The optical layer thickness of the first layer is 0.27λ from the substrate side.₀,No. 2
0.19λ for layer and 4th layer₀, The third layer is 0.06λ₀, The fifth layer is 0.27
λ₀It is.

In this embodiment, since the heterogeneous substance is HfO ₂ , the second and fourth layers are heterogeneous substance layers. In the film configuration shown in this embodiment, the second high refractive index material layer in the conventional film configuration of FIG. 5 is divided by an extremely thin layer of Al ₂ O ₃ as an intermediate refractive index material layer. This is the configuration. That is, the thickness of each layer of the high refractive index material HfO ₂ having inhomogeneity is reduced.

The intermediate refractive index material is Al ₂ O ₃ , LaF ₃ , N
dF ₃ , GdF ₃ , DyF ₃ , PbF ₂ , YF ₃ or a material selected from a mixture thereof, and the low refractive index material is MgF ₂ , SiO ₂ ,
AlF ₃ , NaF, LiF, CaF ₂ , BaF ₂ , SrF ₂ , Na ₃ AlF ₆ , Na ₅ Al ₃ F
₁₄ or a mixture thereof, and the substance having heterogeneity may be HfO ₂ or ZrO ₂ .

FIG. 2 is a diagram showing the spectral reflectance characteristics of the optical element obtained in this embodiment. As can be seen from FIG. 2, the wavelength band having a reflectance of 0.1% or less is 235 to 310 nm. Therefore, the antireflection band of the optical element of the present invention,
In addition, the transmittance at λ ₀ = 248.4 nm of the optical element provided with the antireflection film on both surfaces was 99.8% or more, and the absorption loss was very small as compared with the related art.

Further, 1 J / cm ² , 10 ⁶ with a KrF excimer laser
Although pulse irradiation was performed, there was no damage and there was no problem in laser durability. As described above, it has been found that the optical element of the present invention has no practical problem. (Second Embodiment) An optical element according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a diagram illustrating a film configuration of the optical element of the present embodiment. The antireflection film according to the present invention,
It has a four-layer structure in which a heterogeneous material layer 42 and a uniform refractive index material layer 43 are alternately and sequentially laminated on a substrate 41. In this embodiment, the design center wavelength λ ₁ is the oscillation wavelength of the ArF excimer laser.
3.4 nm, and the substrate is synthetic quartz glass (n = 1.53). The uniform refractive index material layer is MgF ₂ (n = 1.43), and the heterogeneous refractive index material layer is LaF ₃ (n = 1.71). The optical film thickness is 0.05λ ₁ for the first layer and 0.49 for the second layer, respectively, in order from the substrate side.
λ ₁ , the third layer is 0.24λ ₁ , and the fourth layer is 0.24λ ₁ .

FIG. 4 is a diagram showing the spectral reflectance of the center portion and the peripheral portion of the lens when the antireflection film having the film configuration shown in FIG. 3 is formed on a lens having a radius of curvature of 160 mm and an effective diameter of 235 mm. is there. As can be seen from FIG. 4, it can be seen that substantially the same spectral reflection characteristics are obtained in the central portion and the peripheral portion of the lens.

Therefore, the optical characteristics in the optical element could be made uniform. (Application to Product) Next, an example of the exposure apparatus of the present invention will be described. FIG. 9 shows a basic structure of an exposure apparatus using the optical element according to the present invention. The projection exposure apparatus, which is called a stepper, projects an image of a reticle pattern on a wafer coated with a photoresist. Especially applied.

As shown in FIG. 9, the exposure apparatus of the present invention comprises at least a wafer stage 301 on which a substrate W coated with a photosensitive agent placed on a surface 301a can be placed, and ultraviolet light having a wavelength prepared as exposure light. And an illumination optical system 101 for transferring a mask pattern (reticle R) prepared on the substrate W, a light source 100 for supplying exposure light to the illumination optical system 101, and a mask R on the substrate W. A projection optical system 50 placed between a first surface P1 (object plane) on which a mask R for projecting an image of a pattern is arranged and a second surface (image plane) matched with the surface of the substrate W
0. The illumination optical system 101 also includes an alignment optical system 110 for adjusting a relative position between the mask R and the wafer W, and the mask R is a reticle that can move parallel to the surface of the wafer stage 301. It is arranged on the stage 201. Reticle exchange system 200
Replaces and transports the reticle (mask R) set on the reticle stage 201. Reticle exchange system 200
Includes a stage driver for moving the reticle stage 201 parallel to the surface 301a of the wafer stage 301. The projection optical system 500 has an alignment optical system applied to a scan type exposure apparatus.

An exposure apparatus according to the present invention uses the optical element according to the present invention. Specifically, the exposure apparatus of the present invention shown in FIG. 9 can include the optical lens according to the present invention as the optical lens 90 of the illumination optical system 101 and / or the optical lens 100 of the projection optical system 500. .

[0023]

As described above, according to the present invention, since the thickness of the heterogeneous material layer is reduced, a low reflectance close to 0% can be obtained at the exposure wavelength, and a very wide wavelength range can be obtained. A low reflectance can be obtained, and the optical characteristics in the lens surface can be made uniform.

An exposure apparatus equipped with the optical element of the present invention has a reduced transmitted light amount and improved flare and ghost.
Exposure efficiency and exposure accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an antireflection film according to the present invention.

FIG. 2 is a diagram illustrating spectral reflectance characteristics of an antireflection film according to the present invention.

FIG. 3 is a diagram illustrating an antireflection film according to the present invention.

FIG. 4 is a diagram illustrating spectral reflectance characteristics of an antireflection film according to the present invention.

FIG. 5 is a view showing a conventional antireflection film.

FIG. 6 is a diagram illustrating spectral reflectance characteristics of a conventional antireflection film.

FIG. 7 is a view showing a conventional antireflection film.

FIG. 8 is a diagram showing a spectral reflectance characteristic of a conventional antireflection film.

FIG. 9 is a diagram showing a basic structure of an exposure apparatus using an optical element according to the present invention.

[Explanation of symbols]

 11, 31, 41 ・ ・ ・ Substrate 12, 14, 32 ・ ・ ・ Intermediate refractive index material layer 13, 15, 33 ・ ・ ・ High refractive index material layer 16, 34 ・ ・ ・ Low refractive index material layer 42 ・ ・ ・Inhomogeneous refractive index material layer 43 ・ ・ ・ Uniform refractive index material layer

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) H01L 21/027 H01L 21/30 515D F-term (Reference) 2H097 AA03 AB09 BA10 CA13 EA01 GB00 LA10 2K009 AA06 AA07 AA08 AA10 BB02 CC03 CC06 4F100 AA17B AA27B AG00A AT00A BA03 BA04 BA05 BA07 BA10A BA10B BA26 GB90 JN01A JN06B JN18B 4G059 AA11 AC04 EA01 EA05 EA09 GA02 GA04 GA12 5F046 CB12

Claims (7)

[Claims] 1. An antireflection multilayer film formed on a substrate transparent to a wavelength range of 150 nm to 400 nm, wherein at least one of layers of a substance having a refractive index inhomogeneity in a film thickness direction. The optical thickness of the layer is 0.25λ _{0 with} respect to the design dominant wavelength λ ₀ .
An antireflection film characterized by the following. 2. The substance having heterogeneity is HfO ₂ , ZrO ₂ ,
2. The anti-reflection film according to claim 1, wherein the anti-reflection film is any one of LaF ₃ and LaF ₃ . 3. A low-refractive-index layer made of a material having a refractive index smaller than the refractive index of the substrate on a substrate transparent to a wavelength range of 150 nm to 400 nm, and a material having a refractive index larger than the refractive index of the substrate. In an antireflection film formed by laminating a high refractive index layer composed of: and an intermediate refractive index layer having a refractive index between the low refractive index layer and the high refractive index layer, the optical thickness of each layer is mainly designed. sequentially from the substrate side with respect to the wavelength lambda _0, 0.25 [lambda ₀ is greater than the intermediate refractive index layer, 0.25 [lambda ₀ following the high refractive index layer, 0.1 [lambda] ₀ or less of the intermediate refractive index layer, 0. 25λ ₀
Following the high refractive index layer, an antireflection film, which is a 0.25 [lambda ₀ is greater than the low refractive index layer. 4. The intermediate refractive index material is Al ₂ O ₃ , LaF ₃ , NdF
₃ , GdF ₃ , DyF ₃ , PbF ₂ , YF ₃ or a material selected from a mixture thereof, wherein the low refractive index material is MgF ₂ , SiO ₂ ,
AlF ₃ , NaF, LiF, CaF ₂ , BaF ₂ , SrF ₂ , Na ₃ AlF ₆ , Na ₅ Al ₃ F
_The anti-reflection coating according to claim 3, wherein the anti-reflection coating is a substance selected from the group consisting of _{14 and} a mixture thereof. 5. An optical element on which the antireflection film according to claim 1 is formed. 6. An apparatus for projecting and exposing a pattern image of a mask onto a substrate using a projection optical system, comprising: an illumination optical system for illuminating the mask with ultraviolet light as exposure light; and an optical element according to claim 5; And a projection optical system for forming a pattern image of the mask on a substrate. 7. An illumination optical system for projecting and exposing a pattern image of a mask onto a substrate using a projection optical system, the illumination optical system including the optical element according to claim 5 and illuminating the mask with ultraviolet rays as exposure light. And a projection optical system for forming a pattern image of the mask on a substrate.