JP2003014905A - Optical element and projection exposing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element with excellent optical characteristics by solving a problem of generation of surface distortion, film release, cracks, etc., caused by large internal stress and reducing internal stress, with respect to the optical element consisting of a substrate and an optical thin film made by laminating substances with refractive indexes different from that of the substrate. SOLUTION: Regarding the optical element comprising the laminated optical thin film, the optical element with the excellent optical characteristics is provided by making the sum total of thickness of all the layers constituting the optical thin film <=2,200 Å and the sum total of thickness of layers with refractive indexes lower than that of the substrate <=1,800 Å and the internal stress of the optical thin film <=800 MPa.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical element including a substrate and an optical thin film.

[0002]

2. Description of the Related Art In order to cope with an increase in the degree of integration of semiconductor elements, projection exposure apparatuses have been shortened in wavelength. This is because the resolution improves as the wavelength of the light source decreases.
Recently, a projection exposure apparatus using an ArF excimer laser (wavelength 193 nm) as a light source has been put into practical use. Light in the wavelength range of 200 nm or less like this ArF excimer laser is called vacuum ultraviolet light.

Various optical elements are used in these optical devices. An essential element for forming an optical system as an optical element is an antireflection film. By preventing the reflection of light on the surface of each optical element, the light amount loss in the optical system is reduced, and flare and ghost are suppressed.
The substance that can be used for this antireflection film is mainly fluoride. This is because some fluorides have a high transmittance for vacuum ultraviolet light. Substances other than fluoride have low transmittance for vacuum ultraviolet light and are not practical.

The antireflection film is generally formed by alternately laminating a substance whose refractive index is lower than that of the substance forming the substrate and a substance whose refractive index is higher than that of the substrate. At this time, the greater the difference in refractive index between the low refractive index material and the high refractive index material, the better the antireflection property. Among the fluorides used in this film, MgF ₂ is a substance having a low refractive index, which exhibits particularly excellent properties. Since MgF ₂ has a high transmittance for vacuum ultraviolet light, it is a very effective substance for forming a thin film.

Usually, a vacuum vapor deposition method is used for film formation using a fluoride. The film formed by this method exhibits excellent optical characteristics. However, it is known that problems such as surface change of the substrate, film peeling, and cracks are likely to occur when the vacuum deposition method is used. This is because the vacuum deposition process is a process of repeatedly raising and lowering the temperature, and internal stress remains inside the thin film due to the difference in the coefficient of thermal expansion of the substances forming the substrate and the thin film. When this internal stress is large, phenomena such as a surface change that bends the substrate, film peeling that peels the thin film from the substrate, and cracks that crack the thin film occur. These problems significantly affect optical performance. The surface change has an effect that the characteristics of the optical element (focal length, aberration, etc.) change, and thus the configuration of the optical system is distorted. Also, film peeling and cracks
Since the deterioration of the antireflection characteristic and the light absorption of the film increase, there is an influence that the light amount loss increases. Many fluorides have a large coefficient of thermal expansion, and this problem of internal stress is likely to occur. Since MgF ₂ has a particularly large coefficient of thermal expansion, the internal stress generated is also large, and the above-mentioned problems are likely to occur.

[0006]

Fluoride, especially MgF ₂ , is a very effective substance for an antireflection film because it has excellent optical characteristics in vacuum ultraviolet light. However, there is a problem that the coefficient of thermal expansion is very large, the internal stress is increased, and surface changes, film peeling, cracks and the like are likely to occur.

The present invention solves these problems and forms a film that does not cause surface changes, film peeling, cracks, etc. even when a fluoride is used, so that good optical characteristics and reduced light amount loss are achieved. An object is to provide an optical element.

[0008]

According to a first aspect of the present invention, in an optical element comprising a substrate and an optical thin film in which a substance having a refractive index different from that of the substrate is laminated, the optical thin film has a total thickness of all layers. Is 2200Å or less, the total thickness of layers of the substance having a refractive index lower than that of the substrate is 1800Å or less, and the internal stress of the optical thin film is 800 MPa or less.

With this configuration, it is possible to provide an optical element in which a film free from surface changes, film peeling, cracks and the like is formed, and which has good optical characteristics and reduced light amount loss. According to a second aspect of the invention, in the optical element according to the first aspect,
The first layer counted from the substrate is a substance having a lower refractive index than the substrate and has a thickness of 200 Å or less.

With this structure, it is possible to provide an optical element in which a film free from surface changes, film peeling, cracks and the like is formed, and which has good optical characteristics and reduced light amount loss. According to a third aspect of the invention, in the optical element according to the first aspect,
The substance forming the optical thin film is a fluoride. With this configuration, surface changes, film peeling,
Form a film that does not cause cracks, etc., and have excellent optical characteristics,
It is possible to provide an optical element with reduced light amount loss. According to a fourth aspect of the present invention, in the optical element according to the third aspect, the fluoride is MgF ₂ .

With this structure, it is possible to provide an optical element in which a film free from surface changes, film peeling, cracks and the like is formed, and which has good optical characteristics and reduced light amount loss. According to a fifth aspect of the invention, in the optical element according to the first aspect,
The substance forming the substrate of the optical element is characterized by being a substance that transmits light having a wavelength of 300 nm or less.

With this configuration, it is possible to provide an optical element in which a film free from surface changes, film peeling, cracks, etc. is formed, and which has good optical characteristics and reduced light amount loss. According to a sixth aspect of the invention, in the optical element according to the fifth aspect,
The substance that transmits light having a wavelength of 300 nm or less is quartz or fluorine-doped quartz. With this configuration, it is possible to provide an optical element in which a film that does not cause surface changes, film peeling, cracks, or the like is formed, and which has good optical characteristics and reduced light amount loss. The invention of claim 7 is
A projection exposure apparatus using vacuum ultraviolet light as a light source uses the optical element according to claim 1.

With this structure, it is possible to provide a projection exposure apparatus having an optical system having good optical characteristics and reduced light amount loss by forming a film that does not cause surface changes, film peeling, cracks, or the like. .

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing the structure of an antireflection film according to the present invention. On the optical substrate 11, the low refractive index layer 12, the high refractive index layer 13, the low refractive index layer 14, the high refractive index layer 15, and the low refractive index layer 16 are laminated in this order from the substrate side. The material of the optical substrate is quartz. The substance used for the low refractive index layer is MgF ₂ , and the substance used for the high refractive index layer is LaF ₃ . The thickness of each film is 120 for the low refractive index layer 12 (MgF ₂ ), which is the first layer counted from the substrate side.
Å, the next high refractive index layer 13 (LaF ₃ ) is 590 Å, the next low refractive index layer 14 (MgF ₂ ) is 590 Å, the next high refractive index layer 15 (La
F ₃ ) is 250 Å, and the next low refractive index layer 16 (MgF ₂ ) is 370 Å. This structure is as shown in the film structure of the present invention in FIG. The total thickness of all films in this example is 18
It is 20Å and less than 2200Å. The total film thickness of the low refractive index layer in this example is 1080Å, which is 1800Å or less. Furthermore, the thickness of the first low refractive index layer counted from the substrate is 120Å, which is less than 200Å. This structure is an example of the antireflection film when quartz is used as the substrate and the wavelength used is 200 nm.

FIG. 2 shows the structure of the antireflection film in the conventional example.
FIG. The anti-reflective film with the conventional film structure
I formed it as a substrate. The thickness of each film is the substrate
From the low refractive index layer 22 (MgF₂) Is
740Å, high refractive index layer 23 (LaF ₃) Is 85Å, low refractive index layer 2
4 (MgF₂) Is 760Å, and the high refractive index layer 25 (LaF₃) Is 270Å,
Low refractive index layer 26 (MgF₂) Is 360Å. Structure of this membrane
Is as shown in the film structure of the conventional example of FIG. this
The total thickness of all membranes of the composition is 2215Å, 2200Å
It exceeds Å. The total thickness of the low refractive index layer is 18
It is 60Å and exceeds 1800Å.

Using a quartz substrate having a diameter of 76 mm and a thickness of 0.525 mm as a substrate, the antireflection film having the thin film structure of the above-described example and the antireflection film having the thin film structure of the conventional example were formed by vacuum deposition. After the film formation was completed, it was cooled to room temperature. The internal stress due to the film formation of this element was measured from the amount of deformation of the substrate. As the measuring device, a membrane stress measuring device manufactured by KLA Tencor Co. of the United States was used.

The internal stress of the thin film structure of FIG. 5 (a), which is an example of the present invention, was measured and found to be 450 MPa. Therefore,
This film structure has an internal stress of 800 MPa or less. On the other hand, when the internal stress of the thin film structure of FIG. 5 (b) was measured as a conventional example, it was 1000 MPa. In this film structure, the internal stress exceeds 800 MPa.

FIG. 3A is a schematic view of an optical element which is an embodiment of the present invention. The substrate in this figure is made of quartz. Then, as shown in FIG.
The optical thin films having the structure shown in (a) were laminated. The internal stress of the thin film of this example is 800 MPa or less as described above. The state of this optical element is very little surface change,
It is a range that does not affect the optical characteristics. Further, neither film peeling nor cracking was observed. As shown in this example, the internal stress of the thin film formed in the optical element is 800 MPa.
In the case of the following, phenomena such as surface change, film peeling and cracking do not occur. That is, the optical characteristics of the thin film of the optical element are not deteriorated by the internal stress.

In the configuration of FIG. 5 (b) given as a conventional example,
As shown in FIG. 3B, the substrate is bent. Also, FIG.
As shown in (c), the thin film may peel off,
As shown in (d), the thin film is cracked. As described above, the internal stress of the thin film of this conventional example is 800
It exceeds MPa. As described above, the bending of the substrate and the destruction of the thin film (film peeling, cracks, etc.) may occur when the internal stress exceeds 800 MPa.

As described above, by suppressing the internal stress remaining in the optical thin film to 800 MPa or less, the destruction of the thin film is reduced. Therefore, even if a fluoride is used as the material forming the thin film, it is possible to suppress deterioration of optical characteristics and increase of optical loss. For the substrate of the optical element, a substance that transmits ultraviolet light of 300 nm or less, such as fluorine-doped quartz obtained by doping quartz glass with fluorine, may be used. Fluorine-doped quartz allows more vacuum ultraviolet light to pass therethrough. Therefore, when an antireflection film is formed using these as the substrate, an optical element having high transmittance can be obtained.

FIG. 4 is a conceptual diagram showing a projection exposure apparatus according to the present invention. The projection exposure apparatus of the present invention irradiates at least a wafer stage 301, on which a wafer W coated with a photosensitizer placed on the surface 301a can be placed, with vacuum ultraviolet light having a wavelength prepared as exposure light, and onto the wafer W. An illumination optical system 101 for transferring the pattern of the prepared mask R, a light source 100 for supplying exposure light to the illumination optical system 101, and a mask R for projecting an image of the pattern of the mask R on the wafer W are provided. First surface P1 arranged
It includes a projection optical system 500 placed between the (object plane) and a second surface (image plane) matched with the surface of the wafer W.
The illumination optical system 101 also includes an alignment optical system 110 for adjusting the relative position between the mask R and the wafer W. 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. The reticle exchange system 200 exchanges and carries the mask R set on the reticle stage 201. The reticle exchange system 200 is the surface 3 of the wafer stage 301.
01a includes a stage driver for moving the reticle stage 201 in parallel with 01a. Projection optical system 5
Reference numeral 00 has an alignment optical system applied to a scan type projection exposure apparatus. The illumination optical system 10
1. The antireflection film according to the present invention is formed on the optical element used in the projection optical system 500. As a result, the image forming performance was improved by the optical system using the optical element having good optical characteristics.

[0022]

[0023]

As described above, according to the present invention, it is possible to reduce the internal stress when a fluoride is used as a substance forming a thin film. Therefore, it is possible to reduce surface changes, film peeling, cracks and the like due to large internal stress. Therefore, it is possible to provide an optical element having good optical characteristics.

Further, by using such an optical element having good optical characteristics, it is possible to provide a projection exposure apparatus having improved optical characteristics.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram illustrating the configuration of a conventional antireflection film.

FIG. 3 is a conceptual diagram illustrating a state of a substrate and an optical thin film due to internal stress.

FIG. 4 is a configuration diagram schematically showing an embodiment of a projection exposure apparatus according to the present invention.

FIG. 5 is a conceptual diagram showing film configurations of the present invention and a conventional example.

[Explanation of symbols]

11, 21 Optical substrate 12, 14, 16, 22, 24, 26 Low refractive index layer 13, 15, 23, 25 High refractive index layer 100 Ultraviolet laser 101 Illumination optical system 500 Projection optical system R Reticle W Wafer

Claims (7)

[Claims] 1. An optical element comprising a substrate and an optical thin film in which a substance having a refractive index different from that of the substrate is laminated, wherein the optical thin film has a total thickness of 2200 Å or less, and the refractive index is The total thickness of layers of material lower than the substrate is 18
An optical element, wherein the optical stress is 00 Å or less and the internal stress of the optical thin film is 800 MPa or less. 2. The optical element according to claim 1, wherein the first layer counted from the substrate is a substance having the refractive index lower than that of the substrate and has a thickness of 200 Å or less. Optical element to do. 3. The optical element according to claim 1, wherein the substance forming the optical thin film is a fluoride. 4. The optical element according to claim 3, wherein the fluoride is MgF ₂ . 5. The optical element according to claim 1, wherein the substance forming the substrate of the optical element is a substance that transmits light having a wavelength of 300 nm or less. 6. The optical element according to claim 5, wherein:
An optical element characterized in that the substance that transmits light having a wavelength of 300 nm or less is quartz or fluorine-doped quartz. 7. A projection exposure apparatus using vacuum ultraviolet light as a light source, wherein the optical element according to claim 1 is used.