JPH11248903A - Reflection preventive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the reflection preventive film which shows reflection preventive effect (excellent angle of incidence characteristic) over a wide light-beam incidence angle and has small variation in polarized light reflection factor with the angle of incidence of a light beam (small separation of polarized light components) for specific wavelength within a wavelength range of 160 to 300 nm. SOLUTION: On a substrate 1 wherein light of arbitrary design reference wavelength λ0 within a wavelength range of at least 160 to 300 nm is transmitted, a low-refractive-index layer 2 of 0.525 to 0.575 λ in optical film thickness, a high-refractive-index layer 3 of 0.2625 to 0.2875 λ in optical film thickness, and a low-refractive-index layer 4 of 0.2625 to 0.2875 λ in optical film thickness are stacked in order.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an antireflection effect at a specific wavelength in the ultraviolet region at a wide incident angle of light (has good incident angle characteristics), and a change in polarization reflectance with respect to a change in the incident angle of light. (The polarization component separation is small).

[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 a high-resolution reduction projection exposure apparatus (stepper) for semiconductor manufacturing. As one method to increase the resolution of photolithography by this stepper,
Shortening of the light source wavelength can be mentioned. 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 started to be put into practical use. In the optical system of this stepper, it is necessary to form an antireflection film in order to reduce a light amount loss, a flare, a ghost, and the like due to surface reflection of an optical element such as a lens. Excimer lasers as light sources include a KrF excimer laser (λ = 248.4 nm) and an ArF excimer laser (λ = 193.4 nm). When an optical thin film is composed of a low-temperature film material, light loss due to absorption,
Changes in the substrate surface and film destruction due to absorption heat are likely to occur. For this reason, it is desirable that the film material used has low absorption and high laser resistance. Film materials that can be used at the wavelength of the excimer laser are mainly fluorine compounds such as magnesium fluoride (MgF ₂ ) and some oxides, but the types are limited. Similarly, substrates used are also limited to fluorine compound crystals such as fluorite or quartz glass.

As an example of a conventional antireflection film, a high refractive index layer made of lanthanum fluoride having an optical film thickness of λ / 4 on a substrate,
There is known a two-layer structure in which low refractive index layers made of magnesium fluoride having an optical thickness of λ / 4 are sequentially laminated. FIG.
FIG. 3 is an incident angle characteristic diagram of the conventional antireflection film at λ ₀ = 248 nm.

In the range of an incident angle of 0 to about 30 °, the average reflectance is 0.5% or less, and in the range of an incident angle of 0 to about 41 °, the average reflectance is 1% or less. In addition, it can be seen that, with respect to a change in the incident angle, a characteristic that the polarization component of the reflectance is largely separated is exhibited. Further, as a second conventional anti-reflection film, MgF ₂ having an optical film thickness of λ / 2 is formed on the substrate.
A three-layer structure is known in which a low refractive index layer made of NdF ₃ having an optical thickness of λ / 4 and a low refractive index layer made of MgF ₂ having an optical thickness of λ / 4 are sequentially laminated. Have been.

FIG. 6 shows the conventional antireflection film having λ ₀ = 2.
It is an incident-angle characteristic figure in 48 nm. 0 to about 38 °
Shows an average reflectance of 0.5% or less in the range of the incident angle, and shows a reflectance of 1% or less in the range of the incident angle of 0 to about 44 °. In addition, it can be seen that, with respect to a change in the incident angle, a characteristic that the polarization component of the reflectance is largely separated is exhibited.

[0006]

However, in the projection optical system in the stepper, the light illuminated on the mask by the illumination optical system and transmitted therethrough everywhere on the entire surface of the lens (whether at the center or at the periphery). Light at any angle in the range of 0 ° to about 50 ° is incident and imaged on the wafer.

Therefore, in the conventional antireflection film, when the incident angle is larger than about 40 °, the antireflection effect is sharply reduced and the separation of the polarized light component is increased. The incidence of light in the range of ゜ 50 ° has caused a problem that the imaging unevenness becomes large as a whole. In general, a film can be formed almost uniformly on a flat substrate, but the thickness of both the convex lens and the concave lens gradually decreases from the center to the periphery thereof. Since a lens having a smaller radius is more remarkable, an antireflection film for concave and convex lenses is required to have a wide antireflection band in order to reduce this effect. In the evaporation method, a substantially uniform film can be formed by, for example, providing a predetermined correction plate between the evaporation source and the substrate.

[0008] Accordingly, the present invention provides a method for controlling the wavelength from 160 nm to 30 nm.
At a specific wavelength within the wavelength range of 0 nm, it exhibits an antireflection effect at a wide light incident angle (good incident angle characteristics), and has a small change in polarization reflectance with respect to a change in the light incident angle (a small separation of polarization components). The object is to provide an antireflection film.

[0009]

Means for Solving the Problems The inventors of the present invention have made intensive studies and have made the present invention. The present invention firstly provides "at least an optical film thickness of about 0.525 λ from the substrate side on a substrate that transmits light of the wavelength with respect to any design reference wavelength λ ₀ within a wavelength range of 160 to 300 nm. ~ 0.57
5λ low refractive index layer, optical film thickness 0.2625λ-0.
High refractive index layer of 2875λ, optical film thickness of 0.2625λ
The present invention provides an antireflection film (Claim 1) in which low-refractive-index layers having a thickness of 0.2875λ are sequentially laminated.

Further, the present invention is as a material of the second "high refractive index layer, neodymium fluoride (NdF _3), lanthanum fluoride (LaF _3), gadolinium fluoride (GdF _3), dysprosium fluoride (DyF ₃ ), one or more components selected from the group consisting of aluminum oxide (Al ₂ O ₃ ), lead fluoride (PbF ₂ ), hafnium oxide (HfO ₂ ), and mixtures or compounds thereof, and has a low refractive index Examples of the material of the rate layer include magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), sodium fluoride (NaF), lithium fluoride (LiF), and calcium fluoride (CaF).
F ₂ ), barium fluoride (BaF ₂ ), strontium fluoride (SrF ₂ ), silicon oxide (SiO ₂ ), cryolite (Na ₃ AlF ₆ ), thiolite (Na ₅ Al)
₃ F ₁₄ ) 1 selected from the group of these mixtures or compounds
The antireflection film according to claim 1, which is one or more components (claim 2).

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an antireflection film according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view of the antireflection film of the first embodiment. The anti-reflection film of the first embodiment is formed from magnesium fluoride (n = 1.41) having an optical thickness of 0.55λ on a precision-polished synthetic quartz glass substrate (n = 1.51) 1. Low refractive index layer 2, an aluminum oxide having an optical film thickness of 0.275λ (n =
1.72), the high refractive index layer 3 having an optical thickness of O.D. 2
This is a configuration in which low refractive index layers 4 made of 75? Magnesium fluoride (n = 1.41) are sequentially laminated.

FIG. 2 shows the λ = value of the antireflection film of the first embodiment.
It is an incident-angle characteristic figure in 248.4 nm. The antireflection film according to the second embodiment will be described with reference to FIG. 1. Magnesium fluoride (0.55λ) having an optical thickness of 0.55λ is formed on a precision-polished fluorite substrate (n = 1.47). n = 1.4
1) low refractive index layer 2 having an optical thickness of 0.275λ
A high refractive index layer 3 made of neodymium fluoride (n = 1.68) and a low refractive index layer 4 made of magnesium fluoride (n = 1.41) having an optical thickness of 0.275λ. It is.

FIG. 3 shows the λ = value of the antireflection film of the second embodiment.
It is an incident-angle characteristic figure in 248.4 nm. The antireflection film according to the third embodiment is described with reference to FIG. 1. Magnesium fluoride (0.56λ) having an optical thickness of 0.56λ is formed on a polished fluorite substrate (n = 1.47) 1. n = 1.4
1), a high refractive index layer 3 made of lanthanum fluoride (n = 1.65) having an optical thickness of 0.28λ, and magnesium fluoride (0.275λ) having an optical thickness of 0.275λ. n = 1.41).

FIG. 4 shows the λ = value of the antireflection film of the third embodiment.
It is an incident-angle characteristic figure in 248.4 nm. Figure 2
4, at an incident angle θ = 0 to 45 °, the average reflectance is 0.5% or less, and θ = 0 to about 50 °
It can be seen that an antireflection effect of an average reflectance of 1% or less is obtained at a wide incident angle, and that the polarization component of the reflectance has a small characteristic with respect to a change in the incident angle.

The substrate is transparent in the ultraviolet region,
A material having a refractive index of about 1.4 to 1.6 can be used.
For example, quartz glass, fluorite, magnesium fluoride substrate
Can be Material of high refractive index layer of antireflection film according to the present invention
Has a refractive index higher than that of the substrate and indicates about 1.6 or more.
Neodymium fluoride (NdF_Three), Lanthanum fluoride (La
F_Three), Gadolinium fluoride (GdF_Three), Fluoride fluoride
Prosium (DyF_Three), Aluminum oxide (Al
_TwoO_Three), Lead fluoride (PbF_Two), Hafnium oxide (Hf
O_Two) And mixtures or compounds thereof.
One or more components are used as low refractive index layer material
Has a lower refractive index than the substrate and has a refractive index of less than about 1.6.
Magnesium iodide (MgF_Two), Aluminum fluoride
(AlF_Three), Sodium fluoride (NaF),
Titanium (LiF), calcium fluoride (CaF _Two),
Barium nitride (BaF_Two), Strontium fluoride (S
rF_Two), Silicon oxide (SiO_Two), Cryolite
(Na_ThreeAlF₆), Thiolite (Na_FiveAl _ThreeF₁₄)this
One or more components selected from the group of mixtures or compounds thereof
Is used.

The film of each layer is formed on the substrate by vacuum evaporation such as resistance heating evaporation, ion beam evaporation, and sputtering.

[0017]

As described above, the antireflection film according to the present invention is effective against laser light oscillating in the ultraviolet region.
Has an anti-reflection effect at a wide incident angle (good incident angle characteristics), and has a small variation in polarization reflectance with respect to a change in the incident angle of a light beam (small separation of polarization components)
It has the characteristic.

Therefore, when the lens on which the antireflection film according to the present invention is formed is mounted on the optical system of the stepper, there is no problem of causing uneven image formation and no problem of lowering the exposure efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an antireflection film according to first to third embodiments.

FIG. 2 shows λ = 248.4 of the antireflection film of the first embodiment.
FIG. 9 is an incident angle characteristic diagram in nm.

FIG. 3 shows λ = 248.4 of the antireflection film of the second embodiment.
FIG. 9 is an incident angle characteristic diagram in nm.

FIG. 4 shows λ = 248.4 of the antireflection film of the third embodiment.
FIG. 9 is an incident angle characteristic diagram in nm.

FIG. 5: λ = 248.4 nm of the first conventional antireflection film
FIG. 4 is an incident angle characteristic diagram at the time of the measurement.

FIG. 6: λ = 248.4 nm of the second conventional antireflection film
FIG. 4 is an incident angle characteristic diagram at the time of the measurement.

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Low refractive index layer 3 ... High refractive index layer 4 ... Low refractive index layer

Claims (2)

[Claims] 1. An optical film having an optical thickness of about 0.5 from a substrate side on a substrate that transmits light of at least an arbitrary design reference wavelength λ ₀ within a wavelength range of 160 to 300 nm.
A low refractive index layer having a wavelength of 25λ to 0.575λ and an optical film thickness of 0.2.
An antireflection film formed by sequentially stacking a high refractive index layer having a thickness of 2625λ to 0.2875λ and a low refractive index layer having an optical thickness of 0.2625λ to 0.2875λ. 2. The material of the high refractive index layer includes neodymium fluoride (NdF ₃ ), lanthanum fluoride (LaF ₃ ), gadolinium fluoride (GdF ₃ ), dysprosium fluoride (DyF ₃ ), and aluminum oxide. (Al ₂ O ₃ ), lead fluoride (PbF ₂ ), hafnium oxide (HfO ₂ ), and one or more components selected from the group consisting of a mixture or a compound thereof. magnesium fluoride (MgF _2), aluminum fluoride (AlF _3), sodium fluoride (NaF), lithium fluoride (LiF), calcium fluoride (CaF _2), barium fluoride (Ba
F ₂ ), strontium fluoride (SrF ₂ ), silicon oxide (SiO ₂ ), cryolite (Na ₃ AlF ₆ ), thiolite (Na ₅ Al ₃ F ₁₄ ), or a mixture or compound selected from the group consisting of these compounds 2. The anti-reflection coating according to claim 1, wherein said anti-reflection coating is a component.