JPH10279378A - Production of crystal and apparatus for production therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a crystal having excellent refractive index homogeneity and optical characteristics without distortion and an apparatus for production therefor. SOLUTION: The longitudinal length of the soaking walls of the crystal growth apparatus having a crucible 102, a crucible pulling down rod 103 which is included at the base of the crucible, heaters 104 which are arranged at the flanks of the crucible and are provided with spacings from the crucible and the soaking walls 107 which form spacings between the crucible and the heaters and are arranged in these spacings is longer than the longitudinal length of the crucible. The soaking walls longer in the longitudinal direction than the crucible are disposed between the heaters and the crucible and the crystallized part is moved in the space enclosed by the soaking walls even after the crystallization of a melt in the crucible descending method of melting the raw material in the crucible by heating the crucible with the heaters, then gradually lowering the crucible to the outside of the heater and crystallizing the melt from the lower part of the crucible near to the bottom ends of the heaters.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing a fluoride crystal suitable for various optical elements, lenses, window materials, prisms and the like used in a wide wavelength range from the vacuum ultraviolet region to the far infrared region. Things. In particular, large-diameter lenses for excimer lasers (diameter of 250 mm or more)
The present invention relates to a manufacturing apparatus and a manufacturing method of a fluoride crystal used for an optical component such as the above.

[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 be applied in the electronics, chemical, and energy industries.

[0003] Specifically, it is used for processing and chemical reaction of metals, resins, glass, ceramics, semiconductors and the like.

An apparatus for generating an excimer laser beam is known as an excimer laser oscillation apparatus. A laser gas, such as Ar, Kr, Xe, F ₂ , Cl _2, or the like, filled in the chamber is brought into an excited state by electron beam irradiation, discharge, or the like. Then, the excited atoms combine with 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 oscillation device is a device 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.

[0005] Among excimer laser beams, KrF laser and ArF laser each have a wavelength of 248 nm.
Or light in a wavelength range called a vacuum ultraviolet range such as 193 nm, and an optical system having a high transmittance of light in such a wavelength range must be used. Known glass materials suitable for such an optical system include fluorides such as calcium fluoride, magnesium fluoride, barium fluoride, neodymium fluoride, lithium fluoride, and lanthanum fluoride. In particular, calcium fluoride crystals known as fluorite are preferable as such optical glass materials.

The properties of these crystals differ depending on the application. For example, when the crystals are used for an optical system lens of a stepper for the purpose of fine processing of a quarter micron, the uniformity of the refractive index is high. It is said that it is necessary to set the birefringence to 1 × 10 ⁻⁶ or less and the birefringence to 10 nm / cm or less.

Therefore, the present inventors have studied crystal growth under various conditions using a crystal growth apparatus of the crucible descent method shown in FIG. 5 in order to grow a crystal having such characteristics.

In FIG. 5A, reference numeral 501 denotes a growth apparatus chamber, which is usually connected to an evacuation apparatus so that the inside can be evacuated. 502 is a crucible,
The raw material in the crucible is set in a space surrounded by the heater 504 and melted. Reference numeral 503 denotes a crucible lowering rod for lowering the crucible out of the heater. Reference numeral 505 denotes a heater support member, and reference numeral 506 denotes a heat insulating material.

The procedure of crystal growth is as follows. That is, first, after the crucible 502 containing the raw material is installed, an electric current is applied to the heater 504 to heat the crucible and melt the raw material. Next, the crucible is gradually lowered by the pull-down bar 503 and pulled out of the heater 504 to solidify the melt from the lower end of the crucible and grow crystals. After that, the current of the heater is gradually decreased to cool to room temperature (Bridgman:
Proc. Amer. Acad. Arts. Sci., 60, (1925) 305).

The apparatus shown in FIG. 5 (b) is an improvement of the apparatus shown in FIG. 5 (a), and has a cylindrical shape having a heater height between the crucible and the heater for the purpose of uniforming the crystal characteristics. Wall 507
(USP. No. 2,149,076).

However, the present inventors have examined various conditions of crystal growth used for a stepper optical system by the above method, and found that a large diameter (250 mm or more in diameter) was obtained using the conventional method.
Even if a crystal is to be obtained, it has been extremely difficult to stably produce a crystal having an extremely small refractive index distribution and birefringence in the crystal plane.

Therefore, the crystal growth conditions were examined including the configuration of the crystal growth apparatus and the arrangement of each member. The homogeneity of the refractive index in the crystal plane and the birefringence showed that the melt was crystallized. After that, it was discovered that the heat distribution received by the crystal until it finally cooled to room temperature had a significant effect. The present invention has been completed based on such findings.

Further, in the crystal manufacturing method using the above-mentioned conventional manufacturing apparatus, the power consumption is extremely large, and it is indispensable to reduce the power consumption in order to reduce the entire crystal manufacturing cost.

[0014]

SUMMARY OF THE INVENTION An object of the present invention has been made in view of the above-mentioned unsolved problems of the prior art, and is directed to a crystal having excellent refractive index homogeneity and excellent optical characteristics without distortion. It is an object to provide a manufacturing method and a manufacturing apparatus.

It is another object of the present invention to provide a method and an apparatus for manufacturing 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 a method and apparatus for manufacturing a crystal with reduced power consumption during crystal growth.

[0017]

According to the method for producing a crystal of the present invention, a crucible is heated by a heater to melt the raw material in the crucible, and then the crucible is gradually lowered to the outside of the heater. In the crucible descent method for crystallizing the melt, a wall for soaking is provided between the heater and the crucible, the longitudinal direction of which is longer than the crucible, and the crystallized portion is formed even after the melt is crystallized. The method is characterized in that a space surrounded by the heat equalizing wall is moved.

On the other hand, the crystal manufacturing apparatus of the present invention comprises a crucible, a crucible pull-down bar provided on the bottom of the crucible, a heater arranged on the side surface of the crucible with an interval from the crucible, and the crucible and the crucible. In a crystal growth apparatus in which a heater is provided with an interval and a soaking wall is arranged at the interval, the length of the soaking wall in the longitudinal direction is longer than the length of the crucible in the longitudinal direction.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) In the first embodiment, the longitudinal direction of the heat equalizing wall extends beyond the lower end of the heater and extends to the lowest point where the crucible descends.

FIG. 1 shows a crystal manufacturing apparatus of the present invention.

In FIG. 1, reference numeral 101 denotes a chamber of a growth furnace, the inside of which is evacuated by an exhaust device (not shown). A crucible 102 is made of carbon. 103 is a crucible pull-down bar. Reference numeral 104 denotes a heater, for example, carbon having slits. 105 is a support member for the heater 104. Heater 1
A heat insulating material 106 is provided between the chamber 04 and the chamber 101. Here, between the heater 104 and the crucible 102, the heat equalizing wall 10 is located at a position where the distance from the crucible outer periphery is substantially equal.
7 is provided, the longitudinal direction of the heat equalizing wall is protruded from the lower end of the heater, and extends to the lowest point where the crucible 102 descends.

By adopting such a configuration, the uniformity of the refractive index of the produced crystal is improved, the distortion can be reduced, and the birefringence can be suppressed.

In the conventional example as shown in FIG. 5, immediately after the crystallization, any of the components is affected by other components and the like, so that the uniformity of the heat received by the crystal in the outer peripheral direction cannot be maintained. The heat history at each part in the crucible outer peripheral direction is different. As a result, it is considered that impurity distribution and distortion which cannot be removed by the annealing treatment performed after the crystal growth step occur, and a refractive index distribution and birefringence appear in the crystal plane.

On the other hand, in the present embodiment, even in the step of cooling to room temperature after crystallization, by uniformly applying heat to the outer periphery of the crystal, the impurity distribution and the impurity which cannot be removed only by the post-annealing treatment are removed. Generation of distortion or the like can be prevented.

As described above, in order to improve the homogeneity of the refractive index in the crystal plane and reduce the birefringence, uniform heat is applied to the crystal after crystallization until the crystal is sufficiently cooled. Is preferred.

Although it is not always necessary to provide the heat equalizing wall over the entire moving distance of the crucible, it is preferable to provide it in the entire space where the crucible moves as shown in FIG.

In the present invention, carbon, molybdenum, or the like is used for the heat equalizing wall.
(Emissivity can be measured using a well-known radiation thermometer and a temperature sensor such as a thermocouple) and a thermal conductivity of 5 to 300 Kcal / m · h.
-It is preferable to use one at ° C. By using these, the homogenization of heat at the outer periphery of the crucible is further improved, the in-plane uniformity of the birefringence of the finally obtained crystal is improved, and the distortion can be reduced. Further, heat can be effectively used, and power consumption can be reduced.

(Second Embodiment) The second embodiment is almost the same as the first embodiment, except that a bottom surface is provided at the bottom of the heat equalizing wall as shown in FIG. The only difference is that.

As a result, the thermal uniformity of the outer periphery of the crucible can be further improved, and the heat convection can be suppressed, so that the power consumption can be further suppressed and the crystal manufacturing cost can be reduced.

Further, a structure (not shown) in which the upper part of the heat equalizing wall is covered with a similar heat equalizing material may be employed. This allows
The uniformity of the refractive index, the reduction of birefringence, and the reduction of power consumption can be further achieved.

As described above, the crucible of the present invention is preferably a carbon crucible, but is not limited to this, and the planar shape is not limited to a circle, but may be a desired crystal such as an ellipse or a square. A combined crucible can be used.
According to the present invention, since the heat equalizing wall is formed in a crucible shape and the outer periphery of the crucible is equidistant from the heat equalizing wall, it is possible to obtain a crystal having no distortion even in crystal growth.

(Third Embodiment) In a third embodiment, a multi-stage crucible is applied to the crucible of the first or second embodiment. By using this, for example, a scavenger reaction product and other impurities can be efficiently removed, and a crystal having a high transmittance in a vacuum ultraviolet region can be obtained.

In FIG. 3, reference numeral 300 denotes a crucible body, 30
1 is a lid provided to prevent evaporation of the raw material,
302 is a connection hole for each stage crucible, 303 is a vent hole,
Reference numeral 304 denotes an overlapping portion of each crucible. The number of crucible stages is three in the example of FIG. 3, but may be one, two, or four as required.

In the present invention, the inner height of the crucible in each step is set so that the height of the crystal block to be manufactured is 10 mm or more and 50 mm or more.
It is preferably determined according to the form of the raw material so as to be not more than mm. In particular, in the structure in which the connection holes 302 are provided between the crucibles at each stage as shown in FIGS. 3B and 3C, the height of the crystal block becomes the internal height of the crucible. It is preferable that the thickness be 10 mm or more and 50 mm or less. 5
By setting the thickness to 0 mm or less, impurities such as scavenger metal elements and oxygen which are likely to remain at the bottom of the crystal are efficiently discharged to the outside, and the concentration of these impurities in the crystal can be further reduced. On the other hand, by making it 10 mm or more,
A crystal having a lower defect density can be obtained. That is, according to the defect evaluation based on the etch pit density of the cleavage plane, it is remarkable in the vicinity of the crystal bottom, and it is preferable that the thickness be 10 mm or more in order to reduce the influence.

If the internal height of the crucible is adjusted to the thickness of the optical component to be manufactured, the subsequent cutting step can be omitted, and the productivity is improved. Note that the crucible internal height of each stage does not need to be the same, and crucibles having different internal heights may be stacked.

The crucible shown in FIG. 3B has a connection hole 302 at the center of the bottom of each stage. When the material is melted through this hole, the melt falls into the lower crucible, and each stage is continuous. The size of the connection hole 303 is preferably 1 to 5 mm so that the melt can overcome the surface tension and fall down.

Crystallization proceeds from the lowermost stage. At this time, the crystals in the connection holes 302 serve as seeds, and crystal growth in the upper stage occurs in order, thereby obtaining crystals having excellent crystallinity.

The gas inside the crucible escapes to the outside from the overlapping portion 304 of each stage. By selecting a material that does not wet the melt, such as carbon, for example, the material of the crucible, the melt does not leak from the overlapped portion. However, as the number of stages increases, the pressure increases in the lower stage, which may cause leakage. Therefore, it is preferable to provide a step in the overlapping portion as shown in the figure.

In the structure shown in FIG. 3C, a gas vent hole 303 is further provided on the periphery of the bottom surface. By providing the gas vent holes, the impurity gas can be easily discharged, and a crystal with higher purity can be obtained. The size of the gas vent hole 303 is preferably smaller than the diameter of the connection hole 302, and is preferably provided at a symmetrical position.

The first, second, and third embodiments are similar to the first embodiment.
Each of them can be applied in combination with one or both of a purification step and a crystal growth step described later.

An example of the method for producing a crystal of the present invention is shown in FIG.
Will be described.

(Synthesis of Raw Materials) In order to mix a fluoride raw material and a scavenger, first, a fluoride raw material is prepared.
For that, prepare calcium carbonate and hydrogen fluoride,
The calcium carbonate and hydrogen fluoride are reacted to synthesize powdery calcium fluoride.

Calcium fluoride is produced by the following reaction.

CaCO ₃ + 2HF → CaF ₂ + H ₂ O + CO _{2 In} this synthesis, it is preferable to dry CaF ₂ generated by the above reaction and then calcine it to remove water.

The calcium fluoride raw material thus obtained is vacuum-packed so as to minimize exposure to the atmosphere.

Then, the calcium fluoride and the scavenger are mixed. At this time, the calcium fluoride and the scavenger are preferably placed in a container and the container is rotated to mix. As a scavenger, a material that is easier to bond with oxygen than a fluoride to be grown, such as zinc fluoride, bismuth fluoride, sodium fluoride, and lithium fluoride, is desirable.

Desirable are substances which react with oxides mixed in the synthetic fluoride raw material and are easily removed, and do not deteriorate optical properties even if a trace amount remains, and zinc fluoride is particularly desirable.

For example, a zinc fluoride scavenger changes calcium oxide generated by the presence of water into calcium fluoride.

CaF ₂ + H ₂ O → CaO + 2HF (300 ° C.) CaO + ZnF ₂ → CaF ₂ + ZnO The addition ratio of the scavenger is 0.05 mol% or more and 5.0.
0 mol% or less, more preferably 0.1 to 1.0
mol%.

(Purification step) The mixture of the calcium fluoride powder and the scavenger thus obtained is put into a crucible of a purification furnace. Thereafter, the heater is energized to melt the mixture. Subsequently, the crucible is lowered to cause crystal growth of the molten calcium fluoride.

This step does not require as much temperature control as the crystal growth step described later. Therefore, a grain boundary of the obtained crystal may exist. A preferred temperature range is 1390-1450 ° C.

For the temperature measurement, a thermocouple (not shown) made of platinum was used. The thermocouple measures the temperature of the crucible from the vicinity of the outer wall of the crucible. As a result of detailed studies by the present inventors, it has been found that the measured temperature is preferably in the range of 1380 to 1450 ° C.

That is, at 1380 ° C. or lower, the actual temperature of the fluoride raw material in the crucible is low, and when the temperature is close to the melting point, it takes a long time until the raw material is completely melted, thus improving the productivity. I can't do it. Also, 145
At 0 ° C. or higher, the fluoride raw material is vaporized so strongly that a reduction in productivity due to loss of the raw material cannot be avoided.

The upper part of the crystal thus obtained, that is, the part which crystallized last with time, is removed. Since impurities are likely to be concentrated in this portion, impurities that adversely affect the characteristics are removed by this removing step.

The crystal is put into a crucible again, and a series of steps of melting, crystallization and removal of the upper portion are repeated a plurality of times.

(Crystal Growth Step) Using the apparatus shown in FIG. 1 or FIG.
The crucible is heated to about 450 ° C. and melted, and then gradually cooled. In addition, in this slow cooling, 0.1 hour per hour.
It is preferable that the crucible is lowered at a speed of 1 to 5.0 mm to perform slow cooling.

(Annealing Step) The grown fluoride crystal is heat-treated in an annealing furnace. In this step, the crucible is heated to 900 to 1300C. The heating time is 20 hours or more, more preferably 20 to 30 hours.

The fluoride crystal thus obtained can have an oxygen content of 25 ppm or less and undesired impurities such as water, iron (Fe), nickel (Ni), and chromium (Cr) at 10 ppm or less.

(Processing) Thereafter, the optical article is shaped into a required shape (convex lens, concave lens, disk shape, plate shape, etc.). Further, if necessary, an anti-reflection film may be provided on the surface of the fluoride crystal optical article. As the antireflection film, magnesium fluoride, aluminum oxide, or tantalum oxide is preferably used, and these can be formed by vapor deposition by resistance heating, electron beam vapor deposition, sputtering, or the like. Since the optical article obtained by the present invention hardly contains water, the adhesion of the antireflection film is excellent.

An optical system suitable for an excimer laser, in particular, an ArF excimer laser can be constructed by variously combining the lenses thus obtained. An exposure apparatus can be configured by combining an excimer laser light source, an optical system having a lens made of calcium fluoride, and a stage capable of moving a substrate.

By using this exposure apparatus to irradiate a photosensitizing resist on a substrate with an excimer laser beam via a reticle pattern, a latent image corresponding to the pattern to be formed can be formed.

[0062]

The present invention will be described below in more detail with reference to examples.

Example 1 Calcium carbonate and hydrofluoric acid were reacted to obtain powdered calcium fluoride.

This and ZnF ₂ were added in an amount of 0.7% by weight based on calcium fluoride, and the two were mixed.

Next, this mixture was placed in a crucible of a refining furnace and heated to 1360 ° C., and then cooled to obtain molten calcium fluoride.

Next, the block was placed in a crucible of a crystal growth furnace. As a scavenger, ZnF ₂ was added to the crucible in an amount of 0.1% by weight of calcium fluoride.

In the crystal growth furnace, as shown in FIG. 1 (a), a wall for soaking carbon was arranged over the entire space between the crucible and the heater.

For comparison, a growth furnace in which nothing exists between the crucible and the heater shown in FIG. 5A (Comparative Example 1), and a heater portion between the crucible and the heater shown in FIG. 5B Crystal growth was performed in the same manner also in the growth furnace provided with only the soaking wall (Comparative Example 2).

The inside of the furnace was set at a degree of vacuum of 6 × 10 ⁻⁴ Torr.
Then, the temperature was raised from room temperature to 1360 ° C., and the degree of vacuum was 2 × 1
The temperature was maintained at 0 ^-6 Torr and a temperature of 1360 ° C. for 11 hours.

Next, the crucible was lowered at a speed of 2 mm / h. The rate of temperature decrease at this time corresponds to about 100 ° C./h. It reached the lowest point in 200 hours.

After the crucible reached the lowest point, the power supply to the heater was reduced at a rate of 60 ° C./h and cooled to room temperature.

Next, the calcium fluoride crystal grown in the crucible of the annealing furnace and the calcium fluoride in a 0.1 mm
1% by weight of ZnF ₂ was added. The furnace was evacuated to raise the temperature of the crucible from room temperature to 900 ° C. at a rate of 100 ° C./h, and then maintained at 900 ° C. for 20 hours. And 6 ° C / h
And cooled to room temperature.

The thus obtained fluoride crystal (300 m
(m diameter, 20mm thickness) homogeneity of refractive index, distortion 10mm
The thickness was measured after cutting and polishing. In addition, the crucible temperature is set to 1
The power consumption of the electric furnace for raising the temperature to 360 ° C. was also measured. Table 1 shows the results.

The homogeneity of the refractive index is represented by the difference between the maximum value and the minimum value of the refractive index in the crystal plane, and the distortion is represented by the magnitude of the birefringence, and is determined by the light of the orthogonal polarization plane. Expressed as the difference in optical distance. The power consumption of Comparative Example 1 was set to 1.

[0075]

[Table 1]

As shown in Table 1, as compared with Comparative Examples 1 and 2, the crystal of this example exhibited extremely excellent characteristics, with a refractive index distribution of 1 × 10 ⁻⁶ or less and a strain of 10 nm / cm or less. Has been found to be applicable to stepper optics. It was also found that the power consumption could be reduced.

Example 2 Calcium carbonate and hydrofluoric acid were reacted to obtain powdered calcium fluoride. This and ZnF ₂ were added at 0.7% by weight with respect to calcium fluoride, and the two were mixed.

Next, this mixture was placed in a crucible of a refining furnace and heated to 1360 ° C., and then cooled to obtain molten calcium fluoride.

Next, the block was placed in a crucible of a crystal growth furnace. As a scavenger, ZnF ₂ was added to the crucible in an amount of 0.1% by weight of calcium fluoride.

As a crystal growth furnace, a growth furnace having a structure shown in FIG. 2 was used. A carbon soaking material is provided at the lower end of the soaking wall.

The inside of the furnace was set at a degree of vacuum of 6 × 10 ⁻⁴ Torr.
Then, the temperature was raised from room temperature to 1360 ° C., and the degree of vacuum was 2 × 1
The temperature was maintained at 0 ^-6 Torr and a temperature of 1360 ° C. for 11 hours.

Next, the crucible was lowered at a speed of 2 mm / h. The rate of temperature decrease at this time corresponds to about 100 ° C./h.

Next, the calcium fluoride crystal grown in the crucible of the annealing furnace and the calcium fluoride were added to the crucible in a crucible.
1% by weight of ZnF ₂ was added. The furnace was evacuated to raise the temperature of the crucible from room temperature to 900 ° C. at a rate of 100 ° C./h, and then maintained at 900 ° C. for 20 hours. And 6 ° C / h
And cooled to room temperature.

The uniformity of the refractive index, distortion and power consumption of the thus obtained fluoride crystal were examined in the same manner as in Example 1. Table 2 shows the results.

[0085]

[Table 2]

As shown in Table 2, the provision of the soaking material on the bottom surface of the soaking wall further improved the distortion and the power consumption.

Example 3 As a crucible for a growth furnace, FIG.
Crystal growth was carried out in the same manner as in Example 1 using the multi-stage crucible shown in (b). In addition, the crucible used was a three-stage crucible in which the internal height of each stage of the crucible was 50 mm.

The internal transmittance of the obtained fluorite at 135 nm is 70%, which is higher than that of the fluorite of Example 1 (60%). It can be seen that impurities are efficiently discharged, and a crystal having a high transmittance can be obtained.

The homogeneity and distortion of the refractive index were not different from those of the fluorite of Example 1.

[0090]

According to the present invention, since the heat equalizing wall is disposed between the heater and the crucible with the longitudinal direction protruding from the lower end of the heater, the uniformity of the refractive index is high and the distortion is small. Crystals can be provided.

Further, since the power consumption can be reduced, the production cost fluorite can be provided.

Further, optical parts for excimer laser,
An optical component of a stepper for an excimer laser can be provided.

[0093] Fluorite that can be a highly reliable optical article can be provided.

It is possible to provide an optical component for an excimer laser whose optical characteristics are not degraded even when light of short wavelength and high output is repeatedly irradiated for a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a downgrowth reactor of the present invention.

FIG. 2 is a schematic sectional view showing another example of the downgrowth reactor of the present invention.

FIG. 3 is a schematic sectional view showing a crucible of the downgrowth reactor of the present invention.

FIG. 4 is a flowchart for explaining an example of a manufacturing process of optical fluorite.

FIG. 5 is a schematic sectional view showing a conventional downgrowth reactor.

[Explanation of symbols]

 101 growth furnace chamber, 102 crucible, 103 crucible lowering rod, 104 heater, 105 heater support member, 106 heat insulating material, 107 heat equalizing wall, 108 heat equalizing material bottom surface, 300 crucible body, 301 crucible lid, 302 each Step crucible connection hole, 303 degassing hole, 304 overlapping part of each stage crucible, 501 growth equipment chamber, 502 crucible, 503 crucible pull down rod, 504 heater, 505 heater support member, 506 heat insulating material, 507 cylindrical shape Wall of.

Claims (13)

[Claims] 1. A crucible, a crucible pull-down bar provided on a bottom surface of the crucible, a heater arranged on the side surface of the crucible with an interval from the crucible, and an interval between the crucible and the heater and an interval between the crucible and the heater A crystal growth apparatus having a heat equalizing wall disposed in the above, wherein the longitudinal length of the heat equalizing wall is longer than the longitudinal length of the crucible. 2. The crystal manufacturing apparatus according to claim 1, wherein a length of the heat equalizing wall in a longitudinal direction extends to a lowest point at which the crucible is pulled down by the crucible pull-down bar. 3. The crystal manufacturing apparatus according to claim 2, wherein a bottom surface made of a heat equalizing member is provided at a lowermost portion of the heat equalizing wall. 4. The crystal manufacturing apparatus according to claim 1, wherein the crucible is a block type crucible. 5. The apparatus according to claim 1, wherein the crucible is a multi-stage crucible. 6. The crystal manufacturing apparatus according to claim 5, wherein the multi-stage crucible has small holes on the bottom surface of each stage. 7. The crystal manufacturing apparatus according to claim 6, wherein the small holes are connection holes at the center of the bottom surface of each step. 8. The crystal manufacturing apparatus according to claim 6, wherein the small holes are at least two or more gas vent holes symmetrically with respect to the center of the bottom surface. 9. A crucible descent method in which a crucible is heated by a heater to melt the raw material in the crucible, and then the crucible is gradually lowered out of the heater, and the melt is crystallized from the lower portion of the crucible to near the lower end of the heater. Between the heater and the crucible, a heat equalizing wall having a longer longitudinal direction than the crucible is provided, and after the melt is crystallized, the crystallized portion is moved in a space surrounded by the heat equalizing wall. A method for producing a crystal, comprising: 10. The method according to claim 9, wherein the raw material is calcium fluoride. 11. The crucible according to claim 9, wherein after the melt is completely crystallized, heating by a heater is gradually suppressed, and a crucible is placed in a space surrounded by a soaking wall until cooled. Crystal manufacturing method. 12. The method according to claim 9, wherein the crucible is of a block type. 13. The method according to claim 9, wherein the crucible is of a multi-stage type.