JPH1087391A - Crystallizer and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a crystallizer of simple structure capable of producing a high-quality and large-diameter crystal in the crystal producing device for cooling a cryatallizable raw material melted in a cylindrical crucible to crystallize it by providing a heat insulating means on the inner cylindrical face of the crucible to interupt the heat radiated from the side face of the crucible in the crucible cooling region and suppressing the temp. difference in the radial direction. SOLUTION: A crystallizable raw material is melted in a cylindrical crucible, cooled and crystallized in the crystollizer. The crucible consists of the five discoid crucibles 11 to 15 each having a cylindrical side wall connected through threaded parts 16 to 19 and has a partition plate above and below the regions 41 to 45 contg. the crystallizable raw material and in which the material is melted and crystallized and the heat insulating means 21 to 26 provided with the cylindrical side face. Heat insulating members 21 to 26 are preferably used as the heat insulating means 21 to 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a crystal manufacturing apparatus and a crystal manufacturing method for manufacturing a crystal material (glass material) such as quartz or fluorite used for an optical member such as a lens.

[0002]

2. Description of the Related Art Optical members are used in telescopes, cameras, exposure apparatuses for manufacturing semiconductor integrated circuits, and the like. In particular, a high quality optical member is desired for an exposure apparatus. 2. Description of the Related Art In recent years, with the increase in the degree of integration of semiconductor integrated circuits, there has been an increasing demand for forming ultra-fine patterns. As an apparatus for transferring a fine pattern onto a wafer, a step-and-repeat type reduced projection small exposure apparatus (stepper) is frequently used. For high integration, it is necessary to increase the resolution of the stepper-projection lens. In order to increase the resolving power of the projection lens, it is necessary to increase the numerical aperture (increase the aperture) of the projection lens by using exposure light having a short wavelength.

[0003] In addition, shortening the wavelength of exposure light is achieved by using g-line (wavelength 43 nm).
6 nm) and i-line (wavelength 365 nm)
In the future, KrF excimer laser light (wavelength 248 n
m), the use of ArF excimer laser light (wavelength 193 nm) is considered promising. In the wavelength range up to the i-line, it was possible to use a conventional optical lens in the optical system, but in the wavelength range of KrF and ArF excimer laser light, the transmittance was low, and conventional optical glass was used. It is impossible to use. For this reason, it is common to use quartz glass or fluorite, which has a high transmittance for short-wavelength light, in the optical system of the excimer laser exposure apparatus. In order to correct the chromatic aberration of the optical system, it is desirable to have two or more glass materials having different refractive indexes.

Further, each lens constituting a stepper-projection lens is polished with an extreme surface precision. However, if the crystal is polycrystalline, the polishing speed differs depending on the crystal orientation. Becomes difficult. Further, in the case of polycrystal, impurities are easily segregated at the crystal interface, which impairs the uniformity of the refractive index and emits fluorescence by laser irradiation.

For these reasons, a large diameter single crystal fluorite is desired for a projection lens of an excimer laser exposure apparatus.

For example, fluorite is conventionally manufactured by a crucible descent method (Bridgeman method), and its manufacturing apparatus includes a one-chamber type shown in FIG. 5 and a two-chamber type shown in FIG.
214, 976).

FIG. 5 is a sectional view schematically showing one example of a conventional one-chamber type fluorite manufacturing apparatus. This apparatus is mainly composed of a furnace main body 4 forming a furnace chamber 4a and a graphite side heater-3 arranged in the furnace chamber. The upper part of the crucible support rod 2 reaches the furnace chamber 4a through the bottom of the furnace main body 4, and the crucible 1 is attached to the upper end of the support rod 2.
The raw material is put into the crucible 1, the inside of the furnace is evacuated, and the furnace temperature is raised to the melting point of fluorite or more, usually to 1390 to 1450 degrees Celsius,
Melt. When growing a crystal, the crucible 1 is lowered at a speed of about 0.1 to 5 mm / hour and crystallized from the lower part.

The two-chamber type shown in FIG. 6 has been developed to make it possible to adjust the temperature distribution in the furnace. FIG.
6 The left graph on both sides shows the temperature along the vertical direction at the center of the furnace. In the case of the one-chamber type, the temperature distribution along the center of the furnace becomes one mountain shape as shown on the left side of FIG. On the other hand, the two-chamber type has two mountain shapes as shown on the left side of FIG.

In order to produce a high quality single crystal, there are several points to be taken into consideration, such as reducing the crystal rate, smoothing the inner surface of the crucible, and setting the starting point of the crystal at one point at the lowermost end of the crucible. According to the findings of the present inventors, the temperature distribution of the crystal melt,
It is important to keep the isotherm as horizontal as possible. FIG.
In addition, in the apparatus as shown in FIG. 6, a temperature difference is generated between the vicinity of the furnace wall of the crystal melt and the central portion due to the large diameter, and it becomes difficult to control the temperature distribution. As a countermeasure, a device has been proposed in which a heater is added to the upper or lower part of the furnace liquid to control the temperature (JP-A-4-349198, JP-A-4-349199).
reference). However, such devices have a complicated structure. Therefore, as a simple method, a device as shown in FIG. 7 is used in which the structure of the crucible is devised to improve the temperature distribution of the crystal melt (Cheredov V.N., Nieorgany-Cesky Material, No. 3, vol.
28, (1992), pp 550-553).

In FIG. 7, the crucible has five crucibles (11 to 11).
15) and are connected by screw portions (16 to 19). The bottom surfaces 12a to 15a of the crucibles 12 to 15 serve as partition plates for upper and lower crucibles.
2b to 15b are open. Reference numeral 20 denotes a support bar.

[0011]

However, as a result of a detailed study by the present inventor, the conventional example shown in FIG. 7 has a large diameter (for example, a diameter of 250 mm or more) recently required.
In the region where the crucible is cooled, the temperature difference in the radial direction due to heat radiation from the side wall of the crucible cannot be ignored,
It has been found that high quality large diameter fluorite is difficult to obtain.

An object of the present invention is to provide an apparatus and a method for producing a crystal having a simple structure capable of producing a high-quality large-diameter crystal.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems and to achieve the above-mentioned object, the present invention provides a method of crystallization by cooling a raw material of a crystalline substance melted in a cylindrical crucible. A crucible having a partition plate provided above and below a region for accommodating the raw materials, and heat insulating means provided on a cylindrical side surface, and a crystal growing method. I will provide a.

(Operation) According to the present invention, the heat insulation from the side surface of the crucible in the region for cooling the crucible is blocked by providing the heat insulating means on the inner cylindrical surface of the crucible, and the temperature difference in the radial direction is suppressed. As a result, it is possible to produce high-quality large-diameter crystals.

[0015]

(First Embodiment) FIG. 1 is a schematic cross-sectional view of a crucible of a crystal manufacturing apparatus according to a first embodiment of the present invention.
The first embodiment is a mode in which a heat insulating material is provided on the crucible cylindrical surface. In FIG. 1, the crucible is composed of disk-shaped crucibles 11 to 15 having five cylindrical side walls, and forms regions 41 to 45 for accommodating a crystal material and melting and crystallizing. And each disk-shaped crucible 11-15,
They are connected by screw portions 16 to 19. The bottom surfaces 12a to 15a below each of the disk-shaped crucibles 12 to 15 are composed of a partition plate between upper and lower regions, and small holes 12b to 15b are formed in the center of the partition plate. Reference numeral 20 denotes a support rod for supporting the entire crucible, and reference numerals 21 to 25 denote heat insulating means provided inside the cylindrical side surfaces of the regions 11 to 15.

In the structure shown in FIG. 1, the crystallization process can be explained as follows.

The raw materials are put into each of the crucibles 11 to 15 and melted.
When the crucible is lowered, crystallization starts first from the lower part of the crucible 11 at the lowermost end. As the crucible descends, crystallization proceeds,
Eventually, the small holes 12b crystallize. Next, this small hole 12b
The inside of the crucible 12 becomes a starting point, and the inside of the crucible 12 is crystallized.
At this time, due to the thermal conductivity of the crucible material itself, the bottom surface 12a acts as a low-temperature surface with a substantially uniform temperature, and the bottom surface 13a acts as a high-temperature surface with a substantially uniform temperature. Temperature distribution is maintained. When the crystallization reaches the small holes 13b, it becomes the starting point of crystallization, and the inside of the crucible is crystallized. In this manner, crystallization is sequentially performed between the crucibles 15 at the uppermost end. Normally, the crystal in the crucible 11 at the lowermost end is made to be dummy, and the crystal in the crucible above the crucible 12 is made to be a product.
Therefore, for example, when the crucible enters the cooling zone, the bottom surface 12a acts as a low-temperature surface with a substantially uniform temperature and the bottom surface 13a acts as a high-temperature surface with a substantially uniform temperature due to the thermal conductivity of the crucible material.
In addition, since the heat radiation from the side surface is blocked by the effect of the heat insulating material 22, even if the diameter of the crystal melt becomes large, the temperature difference in the radial direction of the crystal melt in the crucible 12 is suppressed, and the isotherm has a substantially horizontal temperature distribution. Will be maintained. Therefore, it is possible to produce a high-quality large-diameter fluorite single crystal.

The material of the heat insulators 21 to 25 is the crucible 1
1 to 15 having a low thermal conductivity, for example, Mg
O, ceramic, metal mesh, heat-resistant refractory brick, porous carbon, and a combination of Mo and MgO, Mo and ceramic, and Mo and metal mesh. May be arbitrarily selected in consideration of the thickness in the vertical direction.

In the case where there is no heat insulating means, an isotherm indicating the temperature of the melt appears in a form of drawing an upwardly projecting circular arc isotropically around the partition plate. As a result, the atomic arrangement was largely disturbed in the crystal, and it was difficult to obtain a high-performance large-diameter crystal. The phenomenon in which the isotherms appear convex upward is that heat is released from the inner wall of the furnace, and as a result, a temperature difference occurs between the vicinity of the inner wall of the furnace and the center of the partition plate. Can be explained.

As a result of detailed studies by the present inventors, a preferred method of solving this problem is to maintain an isotherm indicating the melt temperature parallel to the partition. That is, by reducing the heat released from the inner wall of the furnace and releasing the heat mainly from the lower partition plate, it is possible to control the isotherm of the melt to have anisotropy along the partition plate. .

(Second Embodiment) FIG. 2 is a schematic cross-sectional view of a crucible of a crystal manufacturing apparatus according to a second embodiment of the present invention. The second embodiment is an embodiment having a space on the cylindrical side surface of the crucible. 2, the crucible is composed of five disk-shaped crucibles 11 to 15 as in the apparatus of FIG. 1, and 31 to 35 are inner cylindrical wall portions provided inside the outer peripheral cylindrical wall of each disk-shaped crucible 11 to 15, 31a to 35a are cylindrical spaces formed between the outer cylindrical wall and the inner cylindrical wall. The raw materials are stored in the regions 41 to 45.

In the second embodiment, a heat insulating effect is achieved by using a double cylindrical structure 31 to 35 as heat insulating means instead of the heat insulating materials 21 to 25 used in the first embodiment. Space layer 3 from the wall thickness of the inner cylindrical wall portions 31 to 35
By increasing the thickness of 1a to 35a, the high thermal conductivity of the wall is lost, and at the same time, a large heat insulating effect can be expected due to the very low thermal conductivity of the space. Further, the inner cylindrical wall portions 31 to 35 can be processed as an integral body with the crucible.

(Third Embodiment) FIG. 3 is a schematic cross-sectional view of a crucible of a crystal manufacturing apparatus according to a third embodiment of the present invention. In the third embodiment, a heat insulating material is provided on the crucible cylindrical surface, and the heat transfer members above and below the region for accommodating the raw materials are separated. In FIG. 3, the crucible is 5
The disk-shaped regions 41 to 45 are composed of two heat-insulating materials disposed on the inner cylindrical wall surface of the disk-shaped regions 41 to 45, and the upper and lower surfaces 51a to 56a and the outer peripheral cylinder of the disk-shaped regions 41 to 45 are provided. A heat transfer member that forms a surface.

In the configuration of FIG. 3, each of the heat transfer members 51-5
6 is cut off, so that the upper and lower heat conduction between the heat transfer members 51 to 56 is shut off. Therefore, for example, when the disk-shaped region 42 enters the cooling zone, the surface 52a has a uniform low temperature surface due to the thermal conductivity of the heat transfer member 52, and the surface 53a has one surface due to the thermal conductivity of the heat transfer member 53. Although it acts as a high-temperature surface of similar temperature, heat conduction between the heat transfer members 52 and 53 is cut off, so that the surface 52 more reliably functions as a uniform low-temperature surface. By this and the effect of the heat insulating material 22 on the side surface, the latent heat at the time of crystal growth can be surely and uniformly released downward,
The crystal melt in the disk-shaped region 42 is maintained at a temperature distribution in which the isotherm is horizontal, and a high-quality large-diameter fluorite single crystal can be manufactured.

(Fourth Embodiment) FIG. 4 is a schematic sectional view of a crucible and a heater of a crystal manufacturing apparatus according to a fourth embodiment of the present invention. In the fourth embodiment, the heat transfer members in the third embodiment are provided with independent heaters.
Is provided. In FIG. 4, the crucible consists of five disk-shaped regions 41 to 45 as in the apparatus of FIG.
1 to 25 are heat insulating materials forming the inner cylindrical surface of the disc-shaped areas 41 to 45, and 51 to 56 are disc-shaped areas 41 to 45.
Is a heat transfer member that forms the upper and lower surfaces 51a to 56a and the outer peripheral cylindrical surface. 26 supports the entire crucible and supports the base 50 of the apparatus.
The heat insulators 61 to 66 are fixed to the heat transfer members 51, respectively.
An independent heater for heating ~ 56.

In the configuration shown in FIG. 4, first, each heater 6
An electric current is supplied from a power supply (not shown) to 1 to 66, and the crucibles are maintained at a high temperature by energizing and generating heat to melt the raw materials. Next, by stopping the current supply to the lowermost heater 61 or reducing the current to lower the temperature of the heater 61, the temperature of the surface 51a is lowered, and the crystallization starts from the lower part of the disk-shaped region 41. Let it. Similarly, by sequentially lowering the temperature between heaters 62 to 66, crystallization is sequentially performed between disk-shaped regions 42 to 45.

The fourth embodiment shown in FIG.
Unlike the second, third, fifth, and sixth embodiments, the crucible is not moved during the crystallization process, so that vibration that adversely affects crystal growth can be eliminated, and the apparatus can be downsized. Also, since the heaters 61 to 66 can be independently temperature controlled,
In the process of crystallizing each of the disk-shaped regions 41 to 45, the surface 5
There is an advantage that finer temperature control can be performed by setting 1a to 56a as a low temperature surface or a high temperature surface.

[0028]

As described above, according to the present invention,
A simple method of providing heat insulation means on the side of the crucible, which suppresses heat radiation from the side of the crucible when cooling the crucible, suppresses the temperature difference in the radial direction, and produces high-quality large-diameter fluorite crystals. it can.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a crucible of a crystal manufacturing device according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of a crucible of a crystal manufacturing apparatus according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view of a crucible of a crystal manufacturing apparatus according to a third embodiment of the present invention.

FIG. 4 is a schematic sectional view of a crucible and a heater of a crystal manufacturing apparatus according to a fourth embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view of a conventional one-chamber type crystal manufacturing apparatus.

FIG. 6 is a schematic sectional view of a conventional two-chamber type crystal manufacturing apparatus.

FIG. 7 is a schematic cross-sectional view of a crucible of another type of conventional crystal manufacturing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crucible 2 Support rod 3 Heater 3b High-temperature furnace room 3c Low-temperature heater 4 Furnace main body 4a Furnace room 4b High-temperature furnace room 4c Low-temperature furnace room 11-15 Disk-shaped crucible 12a-15a Bottom surface 12b- 15b Small hole 16-19 Screw part 20 Support rod 21-26 Heat insulating material 31-35 Inner cylindrical part 31a-35a Space layer 41-45 Disk-shaped area 50 Base 51-56 Heat transfer member 51a-56a Upper and lower surfaces 61-66 Heater

Claims (13)

[Claims] 1. A crystal manufacturing apparatus for crystallizing a crystalline material melted in a cylindrical crucible by cooling the material, wherein the crucible includes partition plates provided above and below a region for accommodating the material. And a heat insulating means provided on a side surface of the cylinder. 2. The crystal manufacturing apparatus according to claim 1, wherein said heat insulating means is a heat insulating member. 3. The heat insulating means has an inner wall of a crucible having a multi-layer structure and a space formed by the inner wall.
The crystal manufacturing apparatus according to the above. 4. The crystal manufacturing apparatus according to claim 2, wherein said heat insulating member is a cylindrical member made of a material having a lower thermal conductivity than said partition plate. 5. The heat insulating member is made of MgO, ceramic,
3. The crystal manufacturing apparatus according to claim 2, comprising a material selected from a metal mesh, a heat-resistant refractory brick, and a porous carbon. 6. The crystal manufacturing apparatus according to claim 2, wherein said heat insulating means is made of a material selected from a combination of Mo and MgO, Mo and ceramic, and Mo and metal mesh. 7. The crystal manufacturing apparatus according to claim 1, wherein a bottom surface of the region is substantially flat. 8. The crystal manufacturing apparatus according to claim 1, wherein the crucible has only one of the regions. 9. The crystal manufacturing apparatus according to claim 1, wherein the crucible has three or more partition plates and has a plurality of the regions. 10. The crystal manufacturing apparatus according to claim 9, wherein at least one of the partition plates has a hole in the center, and the upper and lower regions communicate with each other via the hole. 11. The crystal production apparatus according to claim 1, further comprising a heater for heating said partition plate. 12. A method for producing a crystal, wherein a raw material of a crystalline substance melted in a cylindrical crucible is cooled to be crystallized, wherein upper and lower partition plates are provided, and heat insulating means is provided on a side surface of the cylinder. A crystallization of the raw material by gradually cooling the crucible from below. 13. The method according to claim 1, wherein the crystalline material is fluorite.
3. The method for producing a crystal according to 2.