JP2001019596A - Artificial crystal for ultraviolet light optics, and optical substrate using the same and optical lithography device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an artificial crystal from which optical lenses having practical transmittance qualities in vacuum ultraviolet light can be produced, and to produce an optical lithography device using the vacuum ultraviolet light as a light source. SOLUTION: This artificial single crystal consists mainly of a calcium fluoride crystal and has a magnesium concentration of <=3 ppm, a sodium concentration of <=0.2 ppm, an yttrium concentration of <=0.2 ppm, a chromium concentration of <=0.2 ppm, a manganese concentration of <=0.2 ppm, a representative diameter of >=2.5 cm and a 633 nm birefringence of <=5 nm/cm. An optical substrate for ultraviolet light optical systems is produced from the artificial single crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial crystal having an excellent transmission quality in an ultraviolet region, particularly in a vacuum ultraviolet region, and an optical substrate and an optical lithography apparatus using the same. In particular, the present invention relates to a calcium fluoride crystal exhibiting excellent transmission quality even in vacuum ultraviolet light of 157 nm which is the wavelength of an F ₂ laser.

[0002]

2. Description of the Related Art High integration of LSIs is progressing, and light exposure (optical lithography) is performed. In optical lithography, a method of transferring a pattern drawn on a mask onto a wafer by a lens group is mainly performed. The resolution of the transfer pattern increases in proportion to the numerical aperture of the lens and the reciprocal of the wavelength of the light to be exposed. However,
In order to increase the numerical aperture of the lens, a large-diameter lens is required, which limits the production. Therefore, in order to improve the resolution of optical lithography, it is very effective to shorten the wavelength of the light source.

As a light source used in optical lithography,
Until now, ultraviolet rays such as i-line (365 nm) of a high-pressure mercury lamp have been used. In recent years, use of a KrF excimer laser (248 nm) as a light source having a shorter wavelength has been studied. Particularly, since this KrF excimer laser has a high output and is capable of high repetition oscillation (high frequency), it has been actively researched, developed, and put into practical use as a light source suitable for optical lithography. In recent years, this KrF excimer laser has been widely used as a light source for optical lithography, and an optical lithography apparatus using this light source has also been generally put to practical use. As an optical system constituting this optical lithography apparatus, an optical element using glass having high optical transmittance of ultraviolet light as an optical base material has been used.

[0004] The ultraviolet region is a general term for a short wavelength region of about 400 nm or less. A wavelength region of 200 nm or less is called a vacuum ultraviolet region, and a longer wavelength region (200 nm to 400 nm) is distinguished from a near ultraviolet region. There is also. In recent years, in order to further improve the resolution, development of an optical lithography apparatus using light in a vacuum ultraviolet region having a shorter wavelength, that is, vacuum ultraviolet light as a light source has been expected.

[0005] Since vacuum ultraviolet light has a larger photon energy, it tends to induce light absorption in an optical element using glass as an optical base material. Even an optical element which is said to have high light transmittance and can be used in an optical system of a conventional optical lithography apparatus, if vacuum ultraviolet light such as an ArF excimer laser (193 nm) having a shorter wavelength is used as a light source, optical lithography is performed. It was not possible to maintain the practical light transmittance as a device. In an optical lithography apparatus, if the optical transmittance of an optical element is inferior, a critical disadvantage such as insufficient resolution of a transfer pattern due to an insufficient amount of light for exposing a resist occurs. Therefore, in an optical lithography apparatus using vacuum ultraviolet light as a light source, it is indispensable that the optical element used therein keeps practical light transmittance. However, the shorter wavelength F
_{With 2} lasers (157 nm), light is no longer transmitted by an optical element using a general optical glass as an optical base material.

[0006] optical substrate for the optical lithography apparatus with a light source of vacuum ultraviolet light such as F ₂ laser, in place of the conventional optical glass, and a new optical substrate material is strongly demanded. Therefore, use of a fluoride-based optical crystal material having a small absorption end (cutoff wavelength) on the short wavelength side has been studied. For example, lithium fluoride crystals (Li
F), magnesium fluoride crystals (MgF ₂ ), calcium fluoride crystals (CaF ₂ ), and the like.

[0007] However, lithium fluoride crystals are not practical as optical elements because they have a significant deliquescence. It is known that magnesium fluoride crystals exhibit a birefringence phenomenon due to optical anisotropy. Therefore, it is not suitable for an imaging optical element such as a lens. Source other hand, calcium fluoride crystal was cut-off wavelength 124 nm, significant deliquescence, no optical anisotropy, because it is believed to improve transmission of vacuum ultraviolet light, vacuum ultraviolet light such as F ₂ laser The use as an optical substrate of an optical lithography apparatus is most expected.

[0008]

Attempts have been made to manufacture an optical system of an optical lithography apparatus using such a calcium fluoride crystal as an optical base material and a light source of an F ₂ laser which is vacuum ultraviolet light. However, fatal problem resolution of the transferred pattern can not be obtained occurs, this is it difficult to realize an optical lithographic device as a light source an F ₂ laser.

[0009]

The present invention comprises calcium fluoride crystals as a main component, and has a magnesium concentration of 3 ppm or less, a sodium concentration of 0.2 ppm or less, a yttrium concentration of 0.2 ppm or less, and a chromium concentration of 0.2 ppm or less. Below, the manganese concentration is 0.2 ppm or less, the representative diameter is 2.5
The present invention solves the conventional problems by providing an artificial single crystal having a birefringence of not less than 6 cm and a 633 nm birefringence of not more than 5 nm / cm, and using this as an optical base material for an ultraviolet optical system.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to solve the problem that the resolution of a transfer pattern cannot be obtained, it is most important to first determine the cause. Factors that cause a state in which resolution cannot be obtained generally include variations in resist sensitivity, variations in mask line width, variations in wafer substrates, optical system quality, and the like. In the present invention, attention has been paid to the crystal material of the optical base material used in the optical system. That is, it was thought that the optical quality of the calcium fluoride crystal used for the optical base material was insufficient.

The optical quality of an optical substrate can be generally classified into two types, ie, reflection quality and transmission quality. Since the artificial crystal of the present invention is mainly used as a light-transmitting optical substrate, transmission quality is considered. The transmission quality of an optical substrate can be generally grasped from various optical characteristics, but it is not necessary to consider so many optical characteristics from the viewpoint of resolution of a transfer pattern. In the present invention, the transmission quality was examined from the viewpoint of the amount of exposure light, considering that the lack of the amount of exposure light might adversely affect the resolution of the transfer pattern.

Focusing on the material components present in the artificial crystal, the optical system of the optical lithography apparatus which caused a poor resolution in which no transfer pattern was obtained,
A plurality of optical substrates of calcium fluoride crystals were collected and used as samples for investigation. The substances contained in these samples were quantified. The quantification was performed by inductively coupled plasma emission spectrometry (hereinafter referred to as I
CP-AES) or neutron activation analysis (hereinafter, activation analysis). These ICP-AEs
S and activation analysis are both highly sensitive analytical methods that can quantify a plurality of substances. Of the specific substances in the calcium fluoride crystal, ICP-AES quantified magnesium and yttrium, and activation analysis quantified sodium, chromium, and manganese.

As a result, it was found that magnesium contained 3.9-9.
6 ppm, 0.23 to 1.49 ppm of sodium, 0.24 to 0.98 ppm of yttrium, and 0.4% of chromium.
23 to 0.74 ppm, manganese is 0.22 to 1.21
ppm. Here, ppm means μg / g. From these results, poor resolution is due to multiple specific substances magnesium, sodium,
It was possible to estimate that it was strongly related to yttrium, chromium, and manganese.

In order to verify this estimation, the following investigation was further performed. An optical substrate made of calcium fluoride crystal was further sampled from the optical system of the optical lithography apparatus in which a poor resolution in which a transfer pattern could not be obtained occurred. Table 1 shows the results of the survey. The table also shows the optical system number and the results of quantitative analysis using the optical substrate used in the optical system as an analysis sample. The quantification is for magnesium, sodium, yttrium, chromium, and manganese. The numbering of the optical systems, that is, the order of the optical systems in the table, was formally determined by aligning the optical systems so that the quantitative results could be easily understood.

This table shows that (1) magnesium is 3 pp
m, (2) 0.2p of sodium
(3) when yttrium is present in an amount of more than 0.1 pm.
When more than 2 ppm is present, (4) chromium is 0.2
If more than 5 ppm, (5) manganese is 0.2
The case where more than ppm is present is shown. In these cases, it is shown that a significant resolution failure occurs.

[0016]

[Table 1]

That is, magnesium is 3 ppm or less, sodium is 0.2 ppm or less, yttrium is 0.2 ppm or less.
pm or less, chromium is 0.2 ppm or less, and manganese is 0.1 ppm or less.
If an artificial crystal of 2 ppm or less is used as an optical substrate,
Does not cause gross poor resolution.

The use of a calcium fluoride crystal, which does not control a specific substance to be focused on even if the light transmittance to ultraviolet light is good, as an optical substrate of an optical lithography apparatus using a F ₂ laser as a light source. Can not. Therefore,
In the present invention, a calcium fluoride crystal having a magnesium concentration of 3 ppm or less, a sodium concentration of 0.2 ppm or less, a yttrium concentration of 0.2 ppm or less, a chromium concentration of 0.2 ppm or less, and a manganese concentration of 0.2 ppm or less is subjected to photolithography. Used as the optical substrate of the device.

The calcium fluoride crystal was formed into an optical substrate shape according to the optical design. Further, the surface was polished. An optical thin film was formed on the polished optical base material thus obtained to form an optical element, and an optical system was configured using a plurality of optical elements according to an optical design. When an optical lithography apparatus was manufactured in this manner and the resolution of the transfer pattern was examined, it was found that a transfer pattern that was impossible until now could be obtained for the first time.

From this, it was found that calcium fluoride crystals containing 3 ppm or less of magnesium, 0.2 ppm or less of sodium, 0.2 ppm or less of yttrium, 0.2 ppm or less of chromium, and 0.2 ppm or less of manganese were necessary. did. Optical substrates containing calcium fluoride as a main component include fluorite which is a natural crystal and calcium fluoride crystal which is an artificial crystal. Fluorite, a natural crystal, and artificial crystals made from it, are sometimes used as optical base materials in the visible to infrared region, such as camera lenses. It is unsuitable as a material.
That is, it is important that the optical base material used in the optical lithography apparatus using vacuum ultraviolet light as a light source is a calcium fluoride crystal produced using an artificially synthesized raw material.

For the preparation of artificial calcium fluoride crystals,
A method can be used in which an artificial synthetic raw material is once melted to form a melt and solidified from the melt. The calcium fluoride crystal thus produced is a single crystal or a polycrystal which is a collection of single crystals, and such a massive crystal is called an ingot. Since the ingot does not form a shape as an optical element, it is cut out as a material having the same shape and size as the target optical element, or as a material once larger than the target optical element.

In the present invention, such a material or a material formed and processed in accordance with the shape and size of a target optical element is referred to as an optical substrate in the present invention. In addition, not only the material is processed in this way, but also the material that has been further polished, the original material itself, and even the ingot before that, unless the material properties are different, This is a category of the optical substrate of the present invention.

Next, in the present invention, the transmission quality was examined from the viewpoint of the birefringence, considering that the sharpness reduction of the image due to the birefringence may have a bad influence on the resolution of the transfer pattern. The birefringence of the optical substrate greatly affects the transmission quality.
In particular, it is desirable that the birefringence of an optical substrate used in an optical system requiring high imaging performance such as an optical lithography apparatus be as small as possible. In particular, among optical systems of an optical lithography apparatus, an imaging optical system that performs projection is required to have a smaller birefringence than an illumination optical system.

Any optical substrate that does not exhibit birefringence or an optical substrate that exhibits almost no birefringence can be used for an imaging optical system. Of course, it can also be used for an illumination optical system. It is considered that even an optical base material that shows a slight birefringence can be used for an imaging optical system if the degree of the birefringence is sufficiently small to a level that is practical. Therefore, the transmission quality of the optical substrate is investigated by precisely measuring the birefringence. It is considered that the illumination optical system can be used as long as the degree of birefringence is sufficiently small to a practical level. Therefore, it is necessary to investigate the transmission quality of the optical base material by precisely measuring the birefringence.

If they show large birefringence, they can no longer be used for optical substrates. For accurate measurement of birefringence, the wavelength is 633n
The measurement can be performed by a high-sensitivity automatic birefringence measuring device (hereinafter, referred to as ADR) of Oak Manufacturing Co., Ltd., which can measure the birefringence of the light having a m (He-Ne laser light). Table 2 shows the results of measuring the birefringence. Sample 11-
13 had good resolution, and Samples 14 to 16 had poor resolution. Samples 11 to 13 have low birefringence and samples 14 to 16
Has a large birefringence. In all these samples, the magnesium concentration was 3 ppm or less, the sodium concentration was 0.2 ppm or less, and the yttrium concentration was 0.2 ppm or less.
ppm, the chromium concentration was 0.2 ppm or less, and the manganese concentration was 0.2 ppm or less.

[0026]

[Table 2]

From the result of the detailed measurement, 5 nm / cm
Important value was clarified. That is,
If the birefringence is 5 nm / cm or less, it can be concluded that it can be used in an optical system as an optical substrate for photolithography. A single crystal calcium fluoride crystal has a relatively small birefringence as compared with a polycrystalline calcium fluoride crystal, and thus is suitable for an optical substrate. But,
As mentioned earlier, the importance of precision measurement of birefringence was stated, even if it is a single-crystal calcium fluoride crystal that is considered to have a small birefringence, it can be used after actually performing birefringence measurement. desirable. Polycrystalline calcium fluoride crystals sometimes exhibit very large birefringence. Therefore, it is necessary to always check the quality by measuring the birefringence to determine whether or not it can be used as an optical substrate. For use as an optical substrate for photolithography, it is necessary that the birefringence is 5 nm / cm or less.

In order to stably produce a single-crystal calcium fluoride crystal which is more advantageous than polycrystal in terms of birefringence, one of the methods of solidifying from a melt is the Czochralski method (hereinafter, referred to as the “solidification”).
It is desirable to use the CZ method) or the Bridgman-Stockberger method (hereinafter referred to as the BS method). CZ
According to the method, a columnar calcium fluoride single crystal having a diameter of a straight body of about 2.5 cm to about 40 cm can be obtained. Also, B
Even in the -S method, the diameter of the straight body is about 2.5 cm to 40 cm
A columnar calcium fluoride single crystal of a degree is obtained. As described above, the CZ method and the BS method have an advantage that a single-crystal calcium fluoride crystal can be relatively easily produced, but any method in which an artificial synthetic raw material is once melted into a melt, and then solidified from the melt. For example, in the present invention, it is not necessary to limit to only these manufacturing methods.

The optical base material of the present invention is obtained by forming an optical thin film such as a metal film or a dielectric film for the purpose of anti-reflection or reflection on an optical base material processed and polished to a desired shape. Elements are also included. As can be seen from the fact that the optical substrate of the present invention has high transmission quality as an optical system of an optical lithography apparatus using vacuum ultraviolet light as a light source, it is applicable not only to the optical system of an optical lithography apparatus but also to various uses. It is possible. For example, it can be used for spherical lenses, aspherical lenses, cylindrical lenses, rod lenses, right angle prisms, corner cube lenses, dispersion prisms, laser mirrors, laser windows, beam splitters, dichroic mirrors, polarizing prisms, and achromatic lenses.

In the present invention, the representative diameter of the artificial crystal or the optical substrate is determined as follows. In other words, when virtually considering a columnar shape that includes the optical substrate without excess or shortage,
The diameter in this imaginary column shape is defined as a representative diameter. Less than,
As one example of the optical lithography apparatus according to the present invention, F ₂
An outline of an optical lithography apparatus using a laser as a light source will be described. For details of an optical lithography apparatus (projection exposure apparatus) using an F ₂ laser as a light source, see Japanese Patent Application No.
0-370143.

FIG. 2 is a view schematically showing the entire configuration of an optical lithography apparatus having a catadioptric optical system. In FIG. 2, the Z axis is parallel to the optical axis AX of the catadioptric optical system 8 constituting the projection optical system, the X axis is parallel to the plane of FIG. 2 in a plane perpendicular to the optical axis AX, and The Y axis is set vertically. The illustrated optical lithography apparatus includes an F ₂ laser (having an oscillation center wavelength of 157.6 nm) as a light source for supplying illumination light in an ultraviolet region. Light source 1
Is uniformly illuminated through the illumination optical system 2 on the mask 3 on which a predetermined pattern is formed.

In the optical path from the light source 1 to the illumination optical system 2, one or a plurality of bending mirrors for deflecting the optical path are arranged as necessary. Also, the illumination optical system 2
Is a field stop for defining the size and shape of the illumination area on the mask 3, an optical integrator comprising a fly-eye lens or an internal reflection type integrator to form a surface light source of a predetermined size and shape, this field stop And an optical system such as a field stop imaging optical system for projecting the image on the mask. Further, an optical path between the light source 1 and the illumination optical system 2 is sealed by a casing (not shown).
The space from to the optical element closest to the mask in the illumination optical system 2 is replaced with an inert gas having a low absorptance of exposure light.

The mask 3 is held on a mask stage 5 via a mask holder 4 in parallel with the XY plane. A pattern to be transferred is formed on the mask 3 and has a rectangular shape (slit shape) having a long side along the Y direction and a short side along the X direction in the entire pattern area.
Are illuminated. The mask stage 5 is two-dimensionally movable along a mask plane (that is, an XY plane), and its position coordinates are measured and controlled by an interferometer 7 using a mask moving mirror 6. ing.

Light from the pattern formed on the mask 3 forms a mask pattern image on a wafer 9 as a photosensitive substrate via a catadioptric projection optical system 8. The wafer 9 is placed on a wafer stage 11 via a wafer holder 10.
Above, it is held parallel to the XY plane. And
In order to optically correspond to a rectangular illumination area on the mask 3, the wafer 9 has a long side along the Y direction and X
A pattern image is formed in a rectangular exposure area having a short side along the direction.

The wafer stage 11 can be moved two-dimensionally along the wafer surface (ie, XY plane), and its position coordinates are measured and controlled by an interferometer 13 using a wafer moving mirror 12. Is configured.
In the illustrated projection exposure apparatus, the inside of the projection optical system 8 is configured to maintain an airtight state, and the gas inside the projection optical system 8 is replaced with an inert gas.

Further, a mask 3 and a mask stage 5 are disposed in a narrow optical path between the illumination optical system 2 and the projection optical system 8. (Not shown) is filled with an inert gas. In a narrow optical path between the projection optical system 8 and the wafer 9, the wafer 9 and the wafer stage 11 are disposed, but inside a casing (not shown) that hermetically surrounds the wafer 9 and the wafer stage 11. Is filled with an inert gas such as nitrogen or helium gas.

As described above, an atmosphere in which the exposure light is hardly absorbed is formed over the entire optical path from the light source 1 to the wafer 9. As described above, the viewing area (illumination area) on the mask 3 and the projection area (exposure area) on the wafer 9 defined by the projection optical system 8 are X
It has a rectangular shape with short sides along the direction. Therefore,
Mask 3 using drive system and interferometer (7, 13)
While controlling the position of the wafer 9, the mask stage 5 and the wafer stage 11, that is, the mask 3 and the wafer 9 are synchronously moved along the short side direction of the rectangular exposure region and the illumination region, that is, in the X direction. By performing (scanning), the mask pattern is scanned and exposed on the wafer 9 in a region having a width equal to the long side of the exposure region and having a length corresponding to the scanning amount (movement amount) of the wafer 9. You.

In FIG. 2, an optical substrate made of a calcium fluoride crystal is used for all refractive optical elements (lens components) constituting the projection optical system 8, and all or a part of the optical substrate of the present invention is used. And FIG. 3 is a diagram showing a lens configuration of the catadioptric optical system (projection optical system 8) according to FIG. The projection optical system including the catadioptric optical system shown in FIG. 3 includes a first imaging optical system K1 for forming a primary image (intermediate image) I of the pattern of the mask 3 and a mask based on light from the primary image I. A second imaging optical system K2 for forming a secondary image of the pattern on the wafer 9 as a photosensitive substrate at a reduced magnification;
It is composed of

The first imaging optical system K1 includes, in order from the mask side, a first lens group G1 having a positive refractive power, an aperture stop S, and a second lens group G2 having a positive refractive power. ing. The second imaging optical system K2 includes, in order from the mask side, a main mirror M1 having a surface reflection surface R1 with a concave surface facing the wafer side and having an opening at the center, a lens component L2,
And a secondary mirror M2 provided on the wafer-side lens surface and having a reflective surface R2 having an opening at the center. That is, according to another viewpoint, the sub-mirror M2 and the lens component L2 constitute a back surface reflection mirror, and the lens component L2 constitutes a refraction portion of the back surface reflection mirror.

All the optical elements (G1, G2, M1, M2) constituting the projection optical system are arranged along a single optical axis AX. The primary mirror M1 is arranged near the position where the primary image I is formed, and the secondary mirror M2 is arranged close to the wafer 9. Thus, the light from the pattern of the mask 3 forms the primary image (intermediate image) I of the mask pattern via the first imaging optical system K1. The light from the primary image I is
The light is reflected by the secondary mirror M2 via the central opening of the primary mirror M1 and the lens component L2, and the light reflected by the secondary mirror M2 is reflected by the primary mirror M1 via the lens component L2. The light reflected by the primary mirror M1 forms a secondary image of the mask pattern on the surface of the wafer 9 at a reduction magnification through the lens component L2 and the central opening of the secondary mirror M2.

It has been described that it is very important to use an optical element having excellent transmission quality, that is, an optical base material having excellent transmission quality in the optical system of such an optical lithography apparatus. It is as expected. The artificial crystal (calcium fluoride crystal) used as the optical substrate of the photolithography apparatus of the present invention is manufactured by a CZ method, a BS method, or the like. A sample for quantitative analysis is collected from the manufactured calcium fluoride crystal ingot. The substances contained in these samples are quantified. IC for quantification
P-AES or activation analysis is used. As a result of quantification of this specific substance, a fluorine concentration of 3 ppm or less, a sodium concentration of 0.2 ppm or less, a yttrium concentration of 0.2 ppm or less, a chromium concentration of 0.2 ppm or less, and a manganese concentration of 0.2 ppm or less are obtained. Calcium iodide crystals are used as optical substrates for photolithography.

Next, the birefringence will be examined. Since an optical substrate having a small birefringence is desirable, it is selected by measuring the birefringence of the optical substrate. That is, the measurement of birefringence is performed by ADR or the like, and if the birefringence is 5 nm / cm or less at a wavelength of 633 nm, it is used as an optical substrate in an optical system of a photolithography apparatus. Optical substrates having a birefringence greater than 5 nm / cm are not used in the optical system of the photolithographic apparatus. The shape of the optical substrate when measuring birefringence with ADR is
It is good to have two parallel surfaces. By injecting the measurement light so as to be perpendicular to the two parallel surfaces, the measurement can be easily performed without correcting the optical path shift.

Such an appropriate ingot or material is formed into an optical substrate shape according to the optical design. Further, a predetermined surface is polished. An optical thin film is formed on the optical base material thus obtained to obtain an optical element. Further, by using a plurality of such optical elements, an optical system is configured according to the optical design. The optical element that constitutes the optical system may include a single element itself, and may be up to about 50 depending on the requirements of the optical design. Therefore, in some cases, the sum of the optical path lengths may be as large as 1000 mm or more, which cannot be imagined by conventional optical equipment. For this reason, the transmission quality of the individual optical substrates is very important. The optical substrate of the present invention exhibits good transmission quality even in such a very long optical path.

As described above, according to the present invention, it is possible to realize an optical lithography apparatus using an F ₂ laser as a light source, which has not been possible conventionally, and to obtain a good resolution of a line width of 120 nm or less. As described above, according to the present invention, F ₂
Although the present invention realizes optical lithography using a laser as a light source, the present invention can also be applied to optical lithography using light having smaller photon energy than an F ₂ laser, that is, vacuum ultraviolet light having a wavelength longer than 157 nm as a light source. is there. As a light source of such an optical lithography apparatus, for example, a gas laser such as an ArF excimer laser, a solid laser, an excimer lamp light, a low-pressure mercury lamp light, or the like is used.

Therefore, of these vacuum ultraviolet light, Ar
An attempt was made to manufacture an optical lithography apparatus using an F excimer laser (193 nm) as a light source. Hereinafter, an optical lithography apparatus using an ArF excimer laser as a light source will be described. Vacuum ultraviolet light supplied from an ArF excimer laser, which is a light source, reaches a mask via an illumination optical system. Further, the pattern of the mask is projected by the imaging optical system onto the photosensitive agent applied on the wafer substrate.

First, an ingot of a calcium fluoride crystal is prepared by the CZ method or the BS method. A sample for quantitative analysis is collected from a calcium fluoride crystal such as an ingot or a material or an optical substrate. The substances contained in these samples are quantified. ICP-AES for quantification
Or activation analysis. The results of quantification of this specific substance show that the magnesium concentration is 3 ppm or less and the sodium concentration is 0.
2 ppm or less, yttrium concentration of 0.2 ppm or less,
Chromium concentration is 0.2ppm or less, manganese concentration is 0.2ppm
Only calcium fluoride crystals, such as ingots or raw materials or optical substrates, which are less than ppm, are used as optical substrates for photolithography.

The selection is made by measuring the birefringence of the material or the optical substrate. That is, the measurement of birefringence is performed by ADR or the like, and if the birefringence is 5 nm / cm or less at a wavelength of 633 nm, it is used as an optical substrate in an optical system of a photolithography apparatus. In this way, the ingot, the material, or the optical substrate is formed into an optical substrate shape according to the optical design. Further, a predetermined surface is polished. An optical thin film is formed on the optical base material thus obtained to obtain an optical element. Further, by using a plurality of such optical elements, an optical system is configured according to the optical design.

Thus, an optical lithography apparatus using an ArF excimer laser as a light source was manufactured. With this optical lithography apparatus, a sufficient resolution of the transfer pattern of 150 nm or less could be obtained. That is, ArF
An optical lithography apparatus using an excimer laser as a light source can be realized. Hereinafter, the optical lithography apparatus will be described with reference to the flowchart of FIG.

An ingot of calcium fluoride crystal is prepared by the CZ method or the BS method. From calcium fluoride crystals such as ingots, or materials, or optical substrates,
Collect a sample for quantitative analysis. The substances contained in these samples are quantified. ICP-AES or activation analysis is used for quantification. In FIG. 1, magnesium (Mg),
Sodium (Na), Yttrium (Y), Chromium (C
Although r) and manganese (Mn) are displayed in this order, it is logically clear that this order is not always necessary.

The results of quantification of these specific substances show that the magnesium concentration is 3 ppm or less and the sodium concentration is 0.2 ppm.
Hereinafter, when the yttrium concentration is 0.2 ppm or less, the chromium concentration is 0.2 ppm or less, and the manganese concentration is 0.2 ppm or less, it is determined to be suitable. As a result of quantification of these specific substances, when the magnesium concentration is higher than 3 ppm, the sodium concentration is higher than 0.2 ppm, the yttrium concentration is higher than 0.2 ppm, the chromium concentration is higher than 0.2 ppm, and the manganese concentration is 0. If it is more than 0.2 ppm, it is determined to be inappropriate.

With respect to the calcium fluoride crystal determined to be suitable as described above, the birefringence of the material or the optical substrate is further measured. In FIG. 1, the birefringence is represented by R. That is, birefringence is measured by ADR or the like, and it is determined that birefringence of 5 nm / cm or less at a wavelength of 633 nm is preferable. If the birefringence is greater than 5 nm / cm, it is determined to be inappropriate.

The calcium fluoride crystal thus selected is formed into an optical substrate shape according to the optical design,
A predetermined surface is polished to obtain an optical substrate. An optical thin film for preventing reflection is formed on this optical base material to obtain an optical element. Using a plurality of such optical elements, an optical system is configured according to the optical design.

Thus, an optical lithography apparatus using vacuum ultraviolet light such as an F ₂ laser or an ArF excimer laser as a light source was manufactured.

[0054]

EXAMPLES Example 1] Examples of optical lithography apparatus with a light source an F ₂ laser according to the present invention. Using a synthetic material of calcium fluoride, the straight body is 4 by CZ method.
A 0 cm single crystal ingot was produced.

A sample for quantitative analysis was collected from the ingot. As determined by ICP-AES, magnesium was 1.1 ppm and yttrium was 0.1 ppm.
In addition, when quantified by activation analysis, sodium was 0.1%.
11 ppm, chromium 0.1 ppm, manganese 0.0
It was 9 ppm. In other words, magnesium concentration 3ppm
Below, the sodium concentration is 0.2 ppm or less, the yttrium concentration is 0.2 ppm or less, and the chromium concentration is 0.2 ppm.
Hereinafter, it was confirmed that the manganese concentration was 0.2 ppm or less.

From the ingot, caliber 30cm, thickness 5c
m was cut out. The periphery was formed, and two parallel surfaces were subjected to simple polishing. The birefringence of this material is A
Measured by DR. 500 measurement points in the measurement area
Set to a point and measured at a wavelength of 633 nm,
The maximum value was 1.9 nm / cm. That is, it was confirmed that the birefringence of this material was 5 nm / cm or less.

This material was formed into a substrate shape according to the optical design. Further, an optical lens substrate was manufactured by performing polishing processing so as to have a predetermined surface shape. An optical element was obtained by forming an antireflection film on the optical lens substrate thus obtained. Further, an optical system was configured according to the optical design by using a plurality of such optical elements. In this way, it was possible to realize an optical lithographic device in which the F ₂ laser as a light source. This optical lithography apparatus was able to obtain a resolution of 100 nm. Embodiment 2 An example of an optical lithography apparatus using an ArF excimer laser according to the present invention as a light source will be described. Using a calcium fluoride artificial synthetic raw material, a single crystal ingot having a straight body of 40 cm was produced by the CZ method.

A sample for quantitative analysis was collected from the ingot. As determined by ICP-AES, magnesium was 1.2 ppm and yttrium was 0.1 ppm.
In addition, when quantified by activation analysis, sodium was 0.1%.
08 ppm, chromium 0.1 ppm, manganese 0.0
It was 9 ppm. In other words, magnesium concentration 3ppm
Hereafter, the sodium concentration is 0.2 ppm or less, the yttrium concentration is 0.2 ppm or less, and the chromium concentration is 0.2 ppm.
Hereinafter, it was confirmed that the manganese concentration was 0.2 ppm or less.

From ingot, caliber 30cm, thickness 5c
m was cut out. The periphery was formed, and two parallel surfaces were subjected to simple polishing. The birefringence of this material is A
Measured by DR. 500 measurement points in the measurement area
Set to a point and measured at a wavelength of 633 nm,
The maximum value was 2.9 nm / cm. That is, it was confirmed that the birefringence of this material was 5 nm / cm or less.

This material was formed into a substrate shape according to the optical design. Further, an optical lens substrate was manufactured by performing polishing processing so as to have a predetermined surface shape. An optical element was obtained by forming an antireflection film on the optical lens substrate thus obtained. Further, an optical system was configured according to the optical design by using a plurality of such optical elements. Thus, an optical lithography apparatus using an ArF excimer laser as a light source was realized. This optical lithography apparatus was able to obtain a resolution of 130 nm. [Example 3] Examples of optical lithography apparatus with a light source an F ₂ laser according to the present invention.

Using a calcium fluoride artificial synthetic raw material,
A single crystal ingot having a straight body portion of 40 cm was produced by the BS method. A sample for quantitative analysis was taken from the ingot. As determined by ICP-AES, magnesium was 0.8 ppm and yttrium was 0.1 ppm.
In addition, when quantified by activation analysis, sodium was 0.1%.
08 ppm, chromium 0.1 ppm, manganese 0.0
It was 9 ppm. In other words, magnesium concentration 3ppm
Below, the sodium concentration is 0.2 ppm or less, the yttrium concentration is 0.2 ppm or less, and the chromium concentration is 0.2 ppm.
Hereinafter, it was confirmed that the manganese concentration was 0.2 ppm or less.

From the ingot, caliber 30cm, thickness 5c
m was cut out. The periphery was formed, and two parallel surfaces were subjected to simple polishing. The birefringence of this material is A
Measured by DR. 500 measurement points in the measurement area
Set to a point and measured at a wavelength of 633 nm,
The maximum value was 3.5 nm / cm. That is, it was confirmed that the birefringence of this material was 5 nm / cm or less.

This material was formed into a substrate shape according to the optical design. Further, an optical lens substrate was manufactured by performing polishing processing so as to have a predetermined surface shape. An optical element was obtained by forming an antireflection film on the optical lens substrate thus obtained. Further, an optical system was configured according to the optical design by using a plurality of such optical elements. In this way, it was possible to realize an optical lithographic device in which the F ₂ laser as a light source. This optical lithography apparatus was able to obtain a resolution of 100 nm. Embodiment 4 An example of an optical lithography apparatus using an ArF excimer laser according to the present invention as a light source will be described. Using a calcium fluoride artificial synthetic raw material, a single crystal ingot having a straight body portion of 40 cm was produced by the BS method.

A sample for quantitative analysis was collected from the ingot. When quantified by ICP-AES, magnesium was 0.9 ppm and yttrium was 0.1 ppm.
In addition, when quantified by activation analysis, sodium was 0.1%.
09 ppm, chromium 0.1 ppm, manganese 0.0
It was 9 ppm. In other words, magnesium concentration 3ppm
Below, the sodium concentration is 0.2 ppm or less, the yttrium concentration is 0.2 ppm or less, and the chromium concentration is 0.2 ppm.
Hereinafter, it was confirmed that the manganese concentration was 0.2 ppm or less.

From the ingot, caliber 30cm, thickness 5c
m was cut out. The periphery was formed, and two parallel surfaces were subjected to simple polishing. The birefringence of this material is A
Measured by DR. 500 measurement points in the measurement area
Set to a point and measured at a wavelength of 633 nm,
The maximum value was 3.4 nm / cm. That is, it was confirmed that the birefringence of this material was 5 nm / cm or less.

This material was formed into a substrate shape according to the optical design. Further, an optical lens substrate was manufactured by performing polishing processing so as to have a predetermined surface shape. An optical element was obtained by forming an antireflection film on the optical lens substrate thus obtained. Further, an optical system was configured according to the optical design by using a plurality of such optical elements. Thus, an optical lithography apparatus using an ArF excimer laser as a light source was realized. This optical lithography apparatus was able to obtain a resolution of 130 nm.

[0067]

According to the present invention, an optical lens having practical transmission quality in vacuum ultraviolet light can be obtained, and an optical lithography apparatus using vacuum ultraviolet light as a light source can be manufactured.

[Brief description of the drawings]

FIG. 1 shows a flow chart for manufacturing an optical lithography apparatus using an artificial single crystal according to the present invention.

FIG. 2 illustrates a configuration of an optical lithography apparatus according to the first embodiment of the present invention.

FIG. 3 shows a lens configuration of an optical system of the optical lithography apparatus shown in FIG. 2;

[Explanation of symbols]

 Reference Signs List 1 laser light source 2 illumination optical system 3 mask 4 mask holder 5 mask stage 6, 12 moving mirror 7, 13 interferometer 8 projection optical system 9 wafer 10 wafer holder 11 wafer stage AX optical axis K1 first imaging optical system K2 second imaging Image optical system G1 First lens group G2 Second lens group S Aperture stop M1 Primary mirror M2 Secondary mirror I Intermediate image Li Each lens component

Claims (7)

[Claims] A calcium fluoride crystal as a main component, having a magnesium concentration of 3 ppm or less and a sodium concentration of 0.2 ppm.
ppm or less, yttrium concentration is 0.2 ppm or less, chromium concentration is 0.2 ppm, manganese concentration is 0.2 ppm
The following artificial crystals for ultraviolet optics. 2. A composition comprising a calcium fluoride crystal as a main component, a magnesium concentration of 3 ppm or less, and a sodium concentration of 0.2 ppm.
ppm or less, yttrium concentration is 0.2 ppm or less, chromium concentration is 0.2 ppm or less, manganese concentration is 0.2p
pm or less, a typical diameter is 2.5 cm or more, and a birefringence at 633 nm is 5 nm / cm or less. Czochralski method or Bridgman method.
The artificial single crystal for ultraviolet optics according to claim 1 or 2, wherein the artificial single crystal is manufactured by a stock burger method. 4. An optical substrate for ultraviolet optics using the artificial single crystal according to claim 1, 2 or 3. 5. An ultraviolet lithography apparatus comprising a plurality of optical substrates using the artificial single crystal according to claim 1, 2, or 3. 6. An optical lithography apparatus according to claim 5, wherein an F ₂ laser is used as a light source. 7. The optical lithography apparatus according to claim 5, wherein an ArF excimer laser is used as a light source.