JP3006147B2 - Large diameter fluorite single crystal manufacturing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a "crucible descent" manufacturing apparatus capable of manufacturing a large-diameter fluorite single crystal. The fluorite single crystal produced by the production apparatus of the present invention is an optical system of an excimer laser stepper,
For example, it is useful for components used in optical systems such as a laser oscillation device, a laser CVD device, and a laser fusion device, such as a lens, a window material, and a prism.

[0002]

BACKGROUND OF THE INVENTION The present invention relates to an apparatus for producing a fluorite single crystal for an optical system of an excimer laser stepper, among the above-mentioned fields of application. In recent years, lithography technology for drawing an integrated circuit pattern on a wafer has been rapidly developing. The demand for higher integration of integrated circuits is only increasing, and to achieve this, it is necessary to increase the resolution of the stepper projection lens. The resolution of the projection lens depends on the wavelength of light used and the NA (numerical aperture) of the projection lens.
In order to increase the resolving power, the wavelength of the light to be used may be made shorter, and the NA of the projection lens may be made larger (larger diameter).

[0003] First of all, to shorten the wavelength of light, the wavelengths used for steppers have already been advanced to g-line (wavelength 436 nm) and i-line (wavelength 365 nm), and currently the i-line stepper is at its peak. Up to this wavelength range, it was possible to use optical glass for the optical system, but a shorter wavelength KrF excimer laser light (wavelength 248 nm), A
In the case of rF excimer laser light (wavelength 193 nm) or the like, it is no longer possible to use optical glass for the optical system because of its transmittance.

For this reason, the optical system of the excimer laser stepper includes quartz glass or fluorite (calcium fluoride Ca).
To use an F ₂ crystals) has become common. Next, regarding the enlargement of the diameter, it is desirable that the crystal is not only a large diameter but also a single crystal. The reason will be described below. In order to increase the resolution of the stepper projection lens, each lens constituting the projection lens is polished with the ultimate surface accuracy, but if it is polycrystalline, the polishing speed differs depending on the crystal orientation, so the lens surface accuracy is secured It will be difficult to do. Further, in the case of polycrystal, impurities are segregated at the crystal interface, which emits fluorescence by laser irradiation. In severe cases, heat is generated at the crystal interface, and the lens may even be broken. For this reason, single crystal fluorite is desirable for the projection lens of an excimer laser stepper. Conventionally, a fluorite single crystal that has been stably manufactured has a size of 120 mm or less. However, recently, φ150mm
Fluorite single crystals having a large diameter of about 250 mm have been required.

Conventionally, fluorite has been manufactured by the "crucible descent method (called Bridgman method or Stockberger method)", and the manufacturing apparatus (furnace) is called a "crucible descent method" manufacturing apparatus. This apparatus has a one-chamber type shown in FIG. 4 and a two-chamber type shown in FIG.
976).

FIG. 4 is a schematic vertical sectional view showing an example of a one-chamber type fluorite manufacturing apparatus. This apparatus (furnace) mainly comprises a furnace body (7) forming a furnace chamber (7a) and a graphite side heater (5) arranged in the furnace chamber. The furnace body (7) generally comprises a water-cooled stainless steel can. The can has a double cylindrical shape, and has a structure in which water can circulate inside. Through the bottom of the furnace body (7), the upper part of the crucible support bar (3) is present in the furnace chamber (7a). A “crucible (1)” is attached to the upper end of the support bar (3).

In the case of fluorite used in the ultraviolet or vacuum ultraviolet region, natural fluorite is rarely used as a raw material as it is, and a high-purity raw material produced by chemical synthesis is generally used. The raw material may be used in the form of powder, but cullet is generally used because the loss upon melting is severe due to the bulk specific gravity. The cullet is obtained by pulverizing a lump obtained by melting the high-purity raw material powder once.
A “crucible (1)” filled with raw materials (adding a trace amount of a fluorinating agent such as PbF ₂ ) in a furnace is placed in the furnace, and the inside of the furnace is heated for 10 minutes.
A vacuum of about ^-5 to 10 ^-6 Torr is maintained. Next, the furnace temperature is raised to the melting point of fluorite or higher, usually 1390-1450 ° C., and the raw materials are melted. In order to prevent fluctuations in the furnace temperature as much as possible, the output control of the heater (5) should be constant power control or highly accurate PI
Change to D control. At this time, the temperature distribution along the center line of the furnace has a gentle mountain shape as shown on the left side of FIG. When growing the crystal, lower the “crucible (1)” at a speed of about 0.1 to 5 mm / H (in some cases, lower it while rotating), and crystallize from the lower part of the “crucible (1)”. Let me do it. When the crystal is crystallized to the uppermost end of the melt, the crystal growth is completed, and simple slow cooling is performed in the furnace without breaking the crystal (called an ingot). When the furnace temperature falls to room temperature, the ingot is taken out of the furnace. However, since the residual strain is large as it is, annealing is performed to remove the strain. The obtained fluorite is then processed into a suitable size for each target product. In order to adjust the temperature distribution in the furnace, a two-chamber type shown in FIG. 5 was developed. In the one-chamber type, the temperature distribution along the center line of the furnace is a single mountain shape shown on the left side of FIG. On the other hand, in the case of the two-chamber type, the temperature distribution is a two-ridge type shown on the left side of FIG.

[0008]

SUMMARY OF THE INVENTION The present inventor has proposed a large-diameter (φ150 mm to φ250 mm) which has recently been required.
Fluorite single crystal was manufactured by a conventional fluorite "crucible descent method" manufacturing apparatus. However, the conventional apparatus has a problem that a large-diameter fluorite single crystal cannot be obtained.

An object of the present invention is to provide a "crucible descent method" manufacturing apparatus (furnace) capable of manufacturing a large-diameter fluorite single crystal.

[0010]

Therefore, the present invention firstly provides an apparatus for manufacturing a fluorite "crucible lowering method" comprising a furnace main body forming a furnace chamber and a side heater disposed in the furnace chamber. An apparatus for manufacturing a fluorite single crystal, wherein a top heater is added to the upper part of the furnace chamber (the invention of claim 1).
I will provide a.

Second, a furnace main body forming a furnace chamber, a heat insulating plate for vertically separating the furnace chamber into a high-temperature furnace chamber and a low-temperature furnace chamber, and disposed in the high-temperature furnace chamber In the fluorite "crucible descent method" manufacturing apparatus, comprising a first side heater and a second side heater disposed in the low temperature furnace chamber, a top end heater is provided above the high temperature furnace chamber. A fluorite single crystal manufacturing apparatus characterized by the addition (invention of claim 2) is provided.

[0012]

[Function] In order to make a single crystal, in addition to slowing down the crystal growth rate, the starting point of the crystal is set at one point at the bottom of the "crucible"
There are some points to consider, such as smoothing the inner surface of the crucible and sharpening the lowermost end of the crucible (a cylindrical hole may be provided at the lowermost end and a seed crystal may be placed there). Most important, however, is to create a slightly upwardly convex temperature distribution in the crystal melt as shown in FIG. Since the crystal grows perpendicular to the isotherm (isothermal surface), a single crystallization is made possible by growing the crystal outward from the center of the melt by creating an upwardly convex temperature distribution. You do it. On the contrary, if a downwardly convex temperature distribution is created, the crystal grows from the outside toward the center and becomes a polycrystal without fail.

In FIG. 6, considering the heat transfer state of the crystal melt (4) in the "crucible", the melt (4) is mainly conducted from the crucible (1) by conduction, and the "crucible"
Receives heat by radiation from the lid (2). The crucible (1) and the lid (2) are heated by radiation from the side heater (5). In addition, the crucible (1)
Heat is taken away in the direction of the crucible support rod (3). Eventually, the temperature distribution in the crystal melt (4) includes the heat transfer rate Q1 from the heater (5) to the "crucible (1)", the heat transfer rate Q2 from the heater (5) to the lid (2), and Crucible support rod (3)
Determined by the overall balance of heat transfer Q3 due to conduction in the direction. Whether the temperature distribution in the melt is upwardly convex or downwardly convex depends on the temperature of the melt around the melt (the temperature of the portion in contact with the crucible (1)). Since the problem is whether the temperature at the center becomes low or high, the lid (2)
From the surface of the melt (4) is very important (from the theory of radiation heat transfer, the heat transfer from the facing surface is dominant).

For example, as shown in FIG. 7, when Q3 is small (a material having small thermal conductivity and a thin "crucible" is used) and Q1 is much larger than Q2, Since the temperature around the melt is too high as compared with the temperature of, the convection of the melt falls at the center of the melt and rises around the melt as shown in FIG. 7, and it is not possible to stably produce an upwardly convex temperature distribution. .

On the other hand, as shown in FIG. 8, Q3 is large (a material having high thermal conductivity and a thick "crucible").
If Q2 is much larger than Q1, the temperature at the center of the melt is too high compared to the temperature around the melt. As a result, rising convection occurs, and it is impossible to stably produce an upwardly convex temperature distribution. The viscosity of the calcium fluoride melt is less than 0.01 poise in the molten state, and convection is very sensitive to temperature distribution. However, FIGS. 4 and 5
In the conventional manufacturing equipment as shown in Fig. 1, although Q3 can be varied to some extent by changing the material and thickness of the crucible, the balance between Q1 and Q2 is determined uniquely once the equipment is determined and cannot be adjusted. It is. It is clear from the theory of radiative heat transfer that the larger the diameter, the higher the contribution of Q2 to the determination of the temperature distribution of the melt.
It is virtually impossible to produce a large diameter fluorite single crystal with a conventional production apparatus in which the balance of Q2 and Q2 cannot be adjusted.

On the other hand, by providing a top heater according to the present invention, the balance between Q1 and Q2 can be adjusted, and a large-diameter fluorite single crystal can be manufactured. Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.

[0017]

FIG. 1 is a schematic vertical sectional view of a manufacturing apparatus (one-chamber type) according to the present embodiment. This apparatus mainly comprises a furnace body (7) forming a furnace chamber (7a) and a graphite side heater (5) arranged in the furnace chamber as in FIG. The furnace body (7) generally comprises a water-cooled stainless steel can. The can body has a double cylindrical shape, and has a structure in which water can circulate. Through the bottom of the furnace body (7), the upper part of the crucible support bar (3) is present in the furnace chamber (7a). A “crucible (1)” is attached to the upper end of the support bar (3). A heat shield plate (6), for example, a polished molybdenum plate, is disposed inside the furnace body (7) to reduce heat loss and protect the furnace body (7) from high heat.

In this apparatus, the top heater (9), which is a feature of the present invention, is mounted on the upper part of the furnace chamber (7a). The top heater (9) is, of course, controlled independently of the side heater (5).

[0019]

Second Embodiment FIG. 2 is a schematic vertical sectional view of a manufacturing apparatus (two-chamber type) according to the present embodiment. This apparatus mainly separates a furnace body (7) forming a furnace chamber into two chambers in a vertical direction into a high-temperature furnace chamber (7b) and a low-temperature furnace chamber (7c) as in FIG. It comprises a heat insulating plate (10), a first side heater (5b) arranged in the high temperature furnace chamber, and a second side heater (5c) arranged in the low temperature furnace chamber. The furnace body (7) generally comprises a water-cooled stainless steel can.
The can body has a double cylindrical shape, and has a structure in which water can circulate. Through the bottom of the furnace body (7), the upper part of the crucible support bar (3) is present in the furnace chamber (7a). A “crucible (1)” is attached to the upper end of the support bar (3). The insulation plate (10) is generally made of graphite,
Optionally, a polished molybdenum plate is also used as a heat insulating plate.

In this apparatus, the top heater (9), which is a feature of the present invention, is attached to the upper part of the high-temperature furnace chamber (7b). Top end heater (9), first side heater (5
b) and the second side heater (5c) are, of course, independently controlled.

[0021]

Third Embodiment FIG. 3 is a schematic longitudinal sectional view of a manufacturing apparatus (two-chamber type) according to the present embodiment. This apparatus is the same as that of the second embodiment (FIG. 2), except that a bottom heater (11) and a thermocouple (8b) below the bottom heater (11b) are attached to the lower part of the low-temperature furnace chamber (7c). Different.

The first side heater (5b), the second side heater (5c), the top heater (9) and the bottom heater (11) are, of course, independently controlled. The "crucible (1)" filled with the raw materials is first set in the high-temperature furnace chamber (7b), and all the heaters are energized to melt the raw materials in a vacuum. The melting point of pure calcium fluoride is 1373 ° C., and a thermocouple (8
The indicated temperature of c) is slightly lower than 1350 to 136.
The high temperature furnace chamber (7b) and the low temperature furnace chamber (7
Adjust the temperature of c). The reason for bringing the melting point of 1373 ° C. into the high temperature furnace chamber is that the melting point of 1
This is because the isotherm at 373 ° C. (isothermal surface), that is, the shape of the interface between the crystal and the melt becomes convex downward. Normally, the temperature of the high-temperature furnace chamber (7b) (the indicated value of the thermocouple 8d) is set to about 50 ° C. higher than the melting point, and the temperature of the low-temperature furnace chamber (7c) (the indicated value of the thermocouple 8e) is 50 to 50 ° C. Adjust so that it is lower by about 100 ° C. At this time, in the high temperature furnace chamber (7b), the output balance between the first side heater (5b) and the top heater (9) is optimized (actually, the balance is set by setting the temperature of the thermocouples (8f, 8a)). By performing the above optimization, a slightly upwardly convex temperature distribution can be formed in the crystal melt (4) in the crucible (1).

After the raw material is melted and held for a certain period of time, the supporting rod (3) is lowered in a furnace having such a temperature distribution to lower the crucible (1) (in some cases, while rotating). By performing crystal growth, it is possible to produce a large-diameter fluorite single crystal as an object. Now, in the present embodiment, the presence of the top heater (9) allows the following applications to be further applied.

In crystal production, the heater output is generally controlled by constant power control or high-precision PID control in order to minimize fluctuations in furnace temperature. However, in the conventional manufacturing apparatus shown in FIGS. 4 and 5, as the “crucible (1)” descends as the crystal grows, the temperature distribution in the furnace slightly changes. Especially the side heater (5),
The radiation heat transfer speed Q2 from (5b) to the lid (2) increases as the crucible (1) descends. For this reason, with the crystal growth, a downwardly convex temperature distribution gradually becomes easier to be formed in the melt (4), and in the past, the upper part of the ingot had a strong tendency to become polycrystalline. In this case, if processing (removal) is performed so as not to include the crystal interface, a single crystal can be taken out, but this single crystal has a small diameter.

However, when the top heater (9) is provided according to the present invention, the output of the heater (9) is reduced by program control as the crucible (1) is lowered (actually, the thermocouple (8a) Can be lowered by a program), and the crystal growth can be completed without forming a downwardly convex temperature distribution in the melt (4). As a result, all ingots become single crystals.
Therefore, it has a large diameter and a high yield.
This is the same in the first and second embodiments.

[0026]

According to the present invention, the provision of the top heater makes it possible to stably form an upwardly convex temperature distribution in the melt (4) during crystal growth, and to provide a large-diameter heater. Fluorite single crystals can be produced. Until now, diameter φ1
Although it was difficult even to obtain a fluorite single crystal of 50 mm, the present invention makes it possible to stably produce a large-diameter fluorite single crystal of φ200 mm class. As described above, the larger the diameter, the more the advantages of the manufacturing apparatus of the present invention can be utilized.

Therefore, the fluorite single crystal produced by the apparatus of the present invention is extremely useful as a material constituting an optical system of an excimer laser stepper.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view of a manufacturing apparatus according to a first embodiment of the present invention. The furnace chamber temperature distribution along the vertical center line of the apparatus (furnace) is added to the left side.

FIG. 2 is a schematic vertical sectional view of a manufacturing apparatus according to a second embodiment of the present invention. The furnace chamber temperature distribution along the vertical center line of the apparatus (furnace) is added to the left side.

FIG. 3 is a schematic vertical sectional view of a manufacturing apparatus according to a third embodiment of the present invention. The furnace chamber temperature distribution along the vertical center line of the apparatus (furnace) is added to the left side.

FIG. 4 is a schematic vertical sectional view of a conventional one-chamber type manufacturing apparatus. The furnace chamber temperature distribution along the vertical center line of the apparatus (furnace) is added to the left side.

FIG. 5 is a schematic vertical sectional view of a conventional two-chamber type manufacturing apparatus. The furnace chamber temperature distribution along the vertical center line of the apparatus (furnace) is added to the left side.

FIG. 6 is a conceptual diagram showing a schematic vertical cross section of a “crucible” and a temperature distribution of a melt (in which raw materials are melted).

FIG. 7 is a conceptual diagram showing a schematic vertical cross section of a “crucible” and a temperature distribution of a melt (a material in which a raw material is melted).

FIG. 8 is a conceptual diagram showing a schematic vertical cross section of a “crucible” and a temperature distribution of a melt (where the raw material is melted).

[Explanation of Signs of Main Parts]

3 Crucible support rod 1 Crucible 5 Side heater 2 Crucible lid 5b First side heater 4 Material melt 5c 2nd side heater 6 ··· thermal insulation plate 7 ··· furnace main body 7a ··· furnace room 7b ··· high temperature side furnace room 7c ··· low temperature side furnace room 8, 8a to 8h ···・ Thermocouple (part of thermometer) 9 ・ ・ ・ ・ Top heater 10 ・ ・ ・ Insulation plate 11 ・ ・ ・ Bottom heater

Claims (2)

(57) [Claims] 1. A fluorite "crucible descent method" manufacturing apparatus comprising a furnace main body forming a furnace chamber and a side heater disposed in the furnace chamber, wherein a top heater is added to an upper portion of the furnace chamber. Characteristic fluorite single crystal manufacturing equipment. 2. A furnace main body forming a furnace chamber, a heat insulating plate for vertically separating the furnace chamber into a high-temperature furnace chamber and a low-temperature furnace chamber, and a first heat treatment chamber disposed in the high-temperature furnace chamber. Side heater,
And a fluorite "crucible descent method" manufacturing apparatus comprising a second side heater disposed in the low temperature furnace chamber, wherein a top heater is added to an upper portion of the high temperature furnace chamber. Stone single crystal manufacturing equipment.