JP3542444B2 - Crystal manufacturing apparatus and method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a crystal manufacturing apparatus and a crystal manufacturing method for manufacturing crystal materials (glass materials) such as quartz and fluorite used for optical members such as lenses.
[0002]
[Prior art]
The optical member is used for a telescope, a camera, an exposure apparatus for manufacturing a semiconductor integrated circuit, 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, as semiconductor integrated circuits have become more highly integrated, there has been an increasing demand for the formation of ultrafine 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 diameter) of the projection lens by using exposure light having a short wavelength.
[0003]
The wavelength of exposure light has been shortened to g-line (wavelength 436 nm) and i-line (wavelength 365 nm). In the future, KrF excimer laser light (wavelength 248 nm) and ArF excimer laser light ( The use of a wavelength of 193 nm) is 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 the 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 that there are two or more glass materials having different refractive indexes.
[0004]
Further, each lens constituting the stepper-projection lens is polished with the ultimate surface accuracy. However, since the polishing speed is different depending on the crystal orientation in the case of polycrystal, it is difficult to secure the surface accuracy of the lens. Become. Further, in the case of a polycrystal, impurities are easily segregated at the crystal interface, which impairs the uniformity of the refractive index and emits fluorescence by laser irradiation.
[0005]
For these reasons, a large diameter single crystal fluorite is desired for a projection lens of an excimer laser exposure apparatus.
[0006]
For example, fluorite is conventionally manufactured by a crucible descent method (Bridgeman method), and the manufacturing apparatus thereof has a one-chamber type shown in FIG. 5 and a two-chamber type shown in FIG. 6 (see US Pat. No. 2,214,976). ).
[0007]
FIG. 5 is a sectional view schematically showing one example of a conventional one-chamber type fluorite manufacturing apparatus. This apparatus mainly includes a furnace main body 4 forming a furnace chamber 4a and a graphite side heater-3 disposed in the furnace chamber. The upper part of the crucible support rod 2 reaches the furnace chamber 4a through the bottom of the furnace body 4, and the crucible 1 is attached to the upper end of the support rod 2. The raw material is put in 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, and is melted. 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.
[0008]
The two-chamber type shown in FIG. 6 has been developed to make it possible to adjust the temperature distribution in the furnace. The graphs on the left side of both sides of FIGS. 5 and 6 show 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 has one peak as shown on the left side of FIG. In contrast to the two-chamber type, the two-chamber type has two mountain shapes as shown on the left side of FIG.
[0009]
In order to produce a high-quality single crystal, there are several points to consider, such as slowing down the crystallization speed, smoothing the inner surface of the crucible, and setting the crystal starting point at one point at the lowermost end of the crucible. According to the findings of the present inventors, it is important to keep the isotherm as horizontal as possible in the temperature distribution of the crystal melt.
In the apparatus as shown in FIG. 5 or FIG. 6, a temperature difference occurs 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 (see JP-A-4-349198 and JP-A-4-349199). 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), pp550-553).
[0010]
In FIG. 7, the crucible is composed of five crucibles (11 to 15) and is connected by screw portions (16 to 19). The bottom surfaces 12a to 15a of the crucibles 12 to 15 are partition plates for upper and lower crucibles, and small holes 12b to 15b are opened in the center. Reference numeral 20 denotes a support bar.
[0011]
[Problems to be solved by the invention]
However, as a result of a detailed study by the present inventor, even in the conventional example shown in FIG. 7, when a crystal having a large diameter (for example, a diameter of 250 mm or more) as recently required is formed, the crystal from the crucible side wall in the region for cooling the crucible is cooled. It was found that the temperature difference in the radial direction due to heat radiation could not be ignored, and it was difficult to obtain high-quality large-diameter crystalline fluorite.
[0012]
An object of the present invention is to provide an apparatus and a method for producing a crystal having a simple structure and capable of producing a high-quality large-diameter crystal.
[0013]
[Means for Solving the Problems]
In order to solve the above problems and achieve the above-described object, the present invention relates to a crystal manufacturing apparatus that crystallizes a crystalline substance melted in a cylindrical crucible by cooling the raw material. A crystal production apparatus and a crystal growth method, comprising: a partition plate provided above and below a region for accommodating the raw material; and a heat insulating means provided on a side surface of the cylinder.
[0014]
(Action)
According to the present invention, by providing the heat insulating means on the inner cylindrical surface of the crucible, heat radiation from the side of the crucible in the region for cooling the crucible is cut off, the temperature difference in the radial direction is suppressed, and good quality large The production of a crystal having a diameter becomes possible.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
(First embodiment)
FIG. 1 is a schematic sectional view of a crucible of a crystal manufacturing apparatus according to a first embodiment of the present invention. The first embodiment is an embodiment 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 crystalline material and melting and crystallizing. The disk-shaped crucibles 11 to 15 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 between upper and lower regions, and small holes 12b to 15b are formed in the center of the partition. 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.
[0016]
In the configuration of FIG. 1, the crystallization process can be described as follows.
[0017]
Raw materials are put into each of the crucibles 11 to 15 and melted. When the crucible is lowered, crystallization starts at the bottom of the crucible 11 at the lowermost end. Crystallization proceeds as the crucible descends, and the small holes 12b crystallize soon. Next, the crystals in the small holes 12b serve as starting points, 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 hole 13b, it becomes a crystallization starting point, and the inside of the crucible is crystallized. In this manner, the crystallization is sequentially performed between the uppermost crucibles 15. Usually, the crystal in the crucible 11 at the lowermost end is crushed, and the crystal in the crucible above the crucible 12 is 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, the bottom surface 13a acts as a high-temperature surface with a substantially uniform temperature due to the thermal conductivity of the crucible material, and 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 of the crystal melt in the crucible 12 in the radial direction is suppressed, and the isotherm is maintained in a substantially horizontal temperature distribution. You. Therefore, it is possible to produce a high-quality large-diameter fluorite single crystal.
[0018]
The materials of the heat insulating materials 21 to 25 have low thermal conductivity to the crucibles 11 to 15, for example, MgO, ceramic, metal mesh, heat-resistant refractory brick, porous carbon, Mo and MgO, Mo. And ceramic, and a material selected from each combination of Mo and metal mesh, which may be arbitrarily selected in consideration of the radius of the furnace and the thickness of the furnace in the longitudinal direction.
[0019]
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 isotherm appears 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. I can explain it.
[0020]
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. .
[0021]
(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 a mode in which a space is provided 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 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. Raw materials are stored in the regions 41 to 45.
[0022]
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. By making the thickness of the space layers 31a to 35a thicker than the wall thickness of the inner cylindrical wall portions 31 to 35, the high thermal conductivity of the wall is lost, and at the same time, the large thermal insulation due to the very low thermal conductivity of the space The effect can be expected. Further, the inner cylindrical wall portions 31 to 35 can be processed as an integral body with the crucible.
[0023]
(Third embodiment)
FIG. 3 is a schematic 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 composed of five disk-shaped regions 41 to 45, 21 to 25 are heat insulators arranged on the inner cylindrical wall surfaces of the disk-shaped regions 41 to 45, and 51 to 56 are formed on the disk-shaped regions 41 to 45. It is a heat transfer member that forms the lower surfaces 51a to 56a and the outer cylindrical surface.
[0024]
In the configuration of FIG. 3, since each of the heat transfer members 51 to 56 is divided, the upper and lower heat conduction between the heat transfer members 51 to 56 is shut off. Therefore, for example, when the disc-shaped region 42 enters the cooling zone, the surface 52a has a uniform temperature at a 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. Due to this and the effect of the heat insulating material 22 on the side surface, the latent heat during crystal growth can be reliably and uniformly released downward, and the crystal melt in the disk-shaped region 42 has a horizontal temperature distribution with isotherms. Maintained, it is possible to produce high-quality large-diameter fluorite single crystals.
[0025]
(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. In FIG. 4, the crucible is the same as the apparatus of FIG. 3, and is composed of five disk-shaped regions 41 to 45. Heat transfer members that form the upper and lower surfaces 51a to 56a and the outer peripheral cylindrical surface of the regions 41 to 45. Reference numeral 26 denotes a heat insulator supporting the entire crucible and fixed to the base 50 of the apparatus. Reference numerals 61 to 66 denote independent heaters for heating the heat transfer members 51 to 56, respectively.
[0026]
In the configuration shown in FIG. 4, first, a current is supplied from a power source (not shown) to each of the heaters 61 to 66 to generate heat and maintain each crucible at a high temperature, thereby melting the raw materials. Next, the temperature of the surface 51a is lowered by stopping the energization of the lowermost heater 61 or reducing the current to reduce the temperature of the heater 61, and the crystallization is performed from the lower portion of the disk-shaped region 41. Let it. Similarly, by successively lowering the temperature between heaters 62 to 66, crystallization is performed sequentially between disk-shaped regions 42 to 45.
[0027]
The fourth embodiment shown in FIG. 4 differs from the embodiments of FIGS. 1, 2, 3, 5, and 6 in that the crucible is not moved in the course of crystallization, so that vibration that adversely affects crystal growth can be eliminated. In addition, the size of the apparatus can be reduced. Further, since the heaters 61 to 66 can independently control the temperature, in the process of crystallizing the disk-shaped regions 41 to 45, the surfaces 51a to 56a can be set as the low-temperature surface or the high-temperature surface, so that more precise temperature control can be performed. There is an advantage.
[0028]
【The invention's effect】
As described above, according to the present invention, in a simple method of providing heat insulation means on the side of the crucible, when cooling the crucible, suppress heat radiation from the side of the crucible, suppress the temperature difference in the radial direction, High quality large diameter crystals such as fluorite can be produced.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a crucible of a crystal manufacturing apparatus 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 device 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 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 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 chamber 3c Low-temperature heater
4 Furnace body 4a Furnace chamber 4b High-temperature furnace chamber 4c Low-temperature furnace chamber 11-15 Disc-shaped crucible 12a-15a Bottom surface 12b-15b Small hole 16-19 Screw part 20 Support rod 21-26 Insulation material 31-35 Inner cylindrical part 31a-35a Space layers 41-45 Disk-shaped area 50 Bases 51-56 Heat transfer members 51a-56a Upper and lower surfaces 61-66 Heaters

Claims (13)

In a crystal manufacturing apparatus for crystallizing by cooling a raw material of a crystalline substance melted in a cylindrical crucible, the crucible has partition plates provided above and below a region for accommodating the raw material, and a cylindrical side surface. A crystal manufacturing apparatus, comprising: a heat insulating means provided. The crystal manufacturing apparatus according to claim 1, wherein the heat insulating means is a heat insulating member. 2. The crystal manufacturing apparatus according to claim 1, wherein the heat insulating means has a crucible inner wall having a multi-layer structure and a space formed by the inner wall. The crystal manufacturing apparatus according to claim 2, wherein the heat insulating member is a cylindrical member made of a material having a lower thermal conductivity than the partition plate. 3. The crystal manufacturing apparatus according to claim 2, wherein the heat insulating member is made of a material selected from MgO, ceramic, metal mesh, heat-resistant refractory brick, and porous carbon. The crystal manufacturing apparatus according to claim 2, wherein the heat insulating means is made of a material selected from a combination of Mo and MgO, Mo and ceramic, and Mo and metal mesh. The crystal manufacturing apparatus according to claim 1, wherein a bottom surface of the region is substantially flat. The crystal manufacturing apparatus according to claim 1, wherein the crucible has only one of the regions. The crystal manufacturing apparatus according to claim 1, wherein the crucible has three or more partition plates and has a plurality of the regions. 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 through the hole. The crystal manufacturing apparatus according to claim 1, further comprising a heater for heating the partition plate. In a crystal production method for crystallizing by cooling a raw material of a crystalline substance melted in the cylindrical crucible, a partition plate is provided on the upper and lower sides, and the crucible provided with heat insulating means on the side of the cylinder is moved downward. A crystallization of the raw material by gradually cooling the raw material. The method for producing a crystal according to claim 12, wherein the crystalline substance is fluorite.

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