JP2003238292A - Method of manufacturing fluorite crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide fluorite which is suitable as an optical component for excimer laser of an exposure device for photolithography. <P>SOLUTION: A method of manufacturing a fluorite crystal comprises a step for melting calcium fluoride in a crucible and then solidifying the resulting melt, and includes a step for growing the fluorite single crystal from the lower end of the melt in the crucible, and a step for subsequently depositing fluorite polycrystal from the melt. Further, in the method of manufacturing the fluorite crystal, a step for analyzing the concentration of an impurity in a part of the fluorite polycrystal and judging from the analyzed value whether the quality of the formed fluorite single crystal is good or not. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fluorite, an optical component using the same, and an exposure apparatus for photolithography.

[0002]

2. Description of the Related Art Excimer lasers are attracting attention as the only high-power lasers that oscillate in the ultraviolet region, and are expected to find applications in the electronic, chemical, and energy industries. Specifically, metal, resin, glass, ceramics,
It is used for processing semiconductors and chemical reactions.

A device for generating excimer laser light is known as an excimer laser oscillator. Ar, Kr, Xe, KrF, ArF, F filled in the manifold
A laser gas such as _{2 is} excited by electron beam irradiation, discharge, or the like. Then, the excited atoms combine with the atoms in the ground state to generate molecules that exist only in the excited state.
This molecule is called an excimer. Since the excimer is unstable, it immediately emits ultraviolet light and falls to the ground state. This is called a bond-free transition, and an excimer laser oscillator is one that multiplies the ultraviolet light obtained by this transition in an optical resonator composed of a pair of mirrors and extracts it as laser light.

Of the excimer laser lights, the KrF laser, the ArF laser, and the F ₂ laser each have a wavelength of 2
It is light in a wavelength range called vacuum ultraviolet region such as 48 nm, 193 nm, and 157 nm, and it is necessary to use an optical system having a high transmittance of light in such a wavelength range. Fluorite (calcium fluoride single crystal) is a preferable glass material for such an optical system.

Fluorite is usually manufactured by the Bridgman method (crucible descending method). As a conventional method for producing a fluorspar for the vacuum ultraviolet region, for example, JP-A-4-349199,
There is a method described in JP-A-4-349198. I will explain it briefly. First, cullet-shaped high-purity raw materials made by chemical synthesis are filled into a crucible, which is then placed in a crystal growth furnace, the furnace is evacuated to a vacuum, and the furnace temperature is set to the melting point of fluorite or higher. And melt the ingredients. In this growth furnace, the temperature is controlled so that a gentle temperature distribution can be obtained. Next, the crucible is lowered in the growth furnace and crystallized from the lower part of the crucible. The crystal growth is terminated when the uppermost end of the melt is crystallized, and the material is gradually cooled. When the furnace temperature has dropped to room temperature, the crystal ingot is taken out of the furnace and sent to the next step.

[0006]

However, although the conventional fluorite shows satisfactory performance as a base material for an optical system of visible light, it emits high-power light with a short wavelength for a long time like an excimer laser. Repeated irradiation sometimes deteriorated the optical characteristics. The present inventors, while searching for the cause, realized that it was affected by the crystal structure and the contained impurities.

The present invention has been made in view of the above-mentioned technical problems, and provides a fluorite whose transmittance characteristics are not easily deteriorated even when high-power light having a short wavelength is repeatedly irradiated for a long period of time. The main purpose is to do. Another object of the present invention is to provide a fluorite suitable for an optical component for an excimer laser, particularly an optical component for an excimer laser of an exposure apparatus for photolithography.

Still another object of the present invention is to provide an optical component for an excimer laser which does not deteriorate its optical characteristics even if it is repeatedly irradiated with light of short wavelength and high output for a long period of time.

Still another object of the present invention is to provide an exposure apparatus for photolithography, which can stably expose a fine pattern of 0.25 micron or less for a long period of time.

[0010]

The method for producing fluorite crystals according to the present invention is a method for producing fluorite crystals in which calcium fluoride is melted in a crucible and then solidified. It is characterized by including a step of growing a single crystal and a step of subsequently depositing a fluorite polycrystal body from a melt. Further, the method is characterized by including the step of analyzing the impurity concentration in the portion of the fluorite polycrystal body and determining the quality of the quality of the fluorite single crystal produced by the value.

Further, the step of growing a fluorite single crystal from the lower end of the melt in the crucible and the subsequent step of precipitating a fluorite polycrystal from the melt are performed by changing the descending speed of the crucible. Characterize.

Further, a step of growing a fluorite single crystal from the lower end of the melt in the crucible and a step of subsequently depositing a fluorite polycrystal from the melt are performed by changing the heater current. To do.

In the specification of the present invention, a single crystal refers to a crystal region grown by inheriting the orientation of a single crystal grain. In addition, a polycrystal refers to a crystal body including a plurality of regions whose crystal orientations are significantly different.

[0014]

DETAILED DESCRIPTION OF THE INVENTION

EXAMPLE 1 Example 1 will be described with reference to the flow chart of FIG.

ZnF ₂ based on calcium fluoride powder
0.7% by weight was added to mix both.

Next, this mixture was placed in a crucible of a refining furnace and heated to 1360 ° C., and then the crucible was lowered and gradually cooled to crystallize the raw material. The upper part of the crystallized calcium fluoride corresponding to the upper part of the crucible was removed with a thickness of several mm. The steps of heating, gradual cooling and removal were repeated, and a large number of calcium fluoride crystal block samples with different numbers of repeating steps were prepared. [Raw Material Purification Step] Next, the above block was placed in a crucible of a single crystal growth furnace. As a scavenger, ZnF ₂ was placed in a 0.1 wt% crucible. Then, the furnace is evacuated to heat the crucible, the degree of vacuum is 2 × 10 ⁻⁶ Torr, and the temperature is 13
The temperature was kept at 60 ° C for 11 hours. [Raw Material Melting Step] Next, the crucible is moved at a speed of 2 mm / h for 50 h for 1 hour.
It was lowered by 00 mm. The temperature drop rate at this time corresponds to about 100 ° C./h in the vicinity of the crystal growth surface (solid-liquid interface). [Single Crystal Growth Step] Next, the crucible was then lowered 100 mm at a speed of 20 mm / h for 5 hours. The temperature decrease rate at this time corresponds to about 1000 ° C./h. [Polycrystalline Growth Step] Next, the temperature inside the furnace was returned to room temperature over 12 hours. At this time, the temperature decrease rate of fluorite was about 100 ° C./h. [Slow cooling step] When the crucible in the furnace returns to room temperature, the ingot in the crucible is taken out. As shown in FIG. 3, this ingot has a total length of about 200 mm and a lower part of about 100 mm is a fluorite single crystal,
About 100 mm in the upper part is a fluorite polycrystal. This ingot was cut at the boundary between a single crystal and a polycrystal, and a part of the polycrystal was analyzed to evaluate impurities. The analysis method was performed by dissolving the sample and performing ICP mass spectrometry (ICP-MS). [Impurity Concentration Evaluation Step] Next, the above-mentioned fluorite single crystal was added to the crucible of the annealing furnace.
1 wt% ZnF ₂ was added. The furnace was evacuated, the temperature of the crucible was raised from room temperature to 900 ° C. at a rate of 100 ° C./h, and then kept at 900 ° C. for 20 hours. And 6 ° C / h
And cooled to room temperature. [Annealing Step] The fluorite crystal thus obtained exhibited good optical characteristics.
There is no coloring, the deterioration rate is 0%, and KrF, ArF, F
It was found that it can be preferably applied as an optical system for a _two- excimer laser.

Example 2 In the second example of the present invention, after the single crystal growth step was completed, the temperature inside the furnace was lowered at a rate of 100 ° C./h to form a polycrystalline portion of calcium fluoride. The other steps are the same as in the first embodiment. In this embodiment, the process time can be shortened. A time reduction of about 5 hours was achieved compared to Example 1.

[0018]

According to the present invention, the following various effects can be achieved. 1. It is possible to provide fluorite whose transmittance characteristics do not easily deteriorate even when high-power light with a short wavelength is repeatedly irradiated for a long period of time. 2. It is possible to provide a fluorite suitable for an optical component for an excimer laser, particularly for an optical component for an excimer laser of an exposure device for photolithography. 3. It is possible to provide fluorspar that can be manufactured as a highly reliable optical article and that can be manufactured at relatively low cost. 4. It is possible to provide an optical component for an excimer laser that does not deteriorate in optical characteristics even if it is repeatedly irradiated with light of short wavelength and high output for a long period of time. An exposure apparatus for photolithography that can stably expose a fine pattern of 5.0.25 microns or less for a long time can be provided.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining an example of a manufacturing process of fluorite according to the present invention.

FIG. 2 is a diagram showing a cross section of a growth furnace used in a single crystal growth step.

FIG. 3 is a schematic diagram showing a crystal structure when the crucible reaches normal temperature after crystal growth.

[Explanation of symbols]

1 chamber 2 insulation 3 heater 4 crucibles 5 Fluorite 6 Crucible lowering mechanism 7 seed crystal chamber 8 Single crystal calcium fluoride 9 Polycrystalline calcium fluoride

Claims (4)

[Claims] 1. A method for producing a fluorite crystal in which calcium fluoride is melted in a crucible and then solidified, a step of growing a fluorite single crystal from the lower end of a melt in the crucible, and subsequently, a step of growing the fluorite from the melt. And a step of precipitating a stone polycrystal, a method for producing a fluorite crystal. 2. The fluorite according to claim 1, further comprising a step of analyzing an impurity concentration in a portion of the fluorite polycrystal, and judging the quality of the fluorite single crystal produced by the value. Stone crystal manufacturing method. 3. The step of growing a fluorite single crystal from the lower end of the melt in the crucible and the subsequent step of precipitating a fluorite polycrystal from the melt are performed by changing the descending speed of the crucible. The method for producing a fluorite crystal according to claim 1, which is characterized in that. 4. A step of growing a fluorite single crystal from a lower end of a melt in a crucible and a step of subsequently depositing a fluorite polycrystal from the melt are performed by changing a heater current. The method for producing a fluorite crystal according to claim 1.