JP3006148B2 - Fluorite production equipment with excellent excimer resistance - 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 method" manufacturing apparatus capable of manufacturing fluorite excellent in excimer resistance. Fluorite manufactured by the manufacturing apparatus of the present invention is, outside the optical system of the excimer laser stepper, for example, a laser oscillation device, a laser CVD device,
It is useful for components used in optical systems such as laser fusion devices, for example, lenses, window materials, prisms, and the like.

[0002]

BACKGROUND OF THE INVENTION The present invention relates to an apparatus for producing fluorite for an optical system of an excimer laser stepper. 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 is governed by the wavelength of the light used and the NA (numerical aperture) of the projection lens. To increase the resolution, the wavelength of the light used is made shorter and the NA of the projection lens is made larger. (Large diameter)
Do it.

[0003] Wavelengths used for steppers have already progressed to g-line (wavelength 436 nm) and i-line (wavelength 365 nm), and are currently the prime of i-line steppers. Up to this wavelength range, it was possible to use optical glass for the optical system. However, when the wavelength becomes shorter, such as KrF excimer laser light (wavelength 248 nm) or ArF excimer laser light (wavelength 193 nm), the optical system becomes The use of optical glass is no longer possible due to 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. However, when fluorite is irradiated with light with high photon energy such as excimer laser for a long time, its transmittance decreases, and the temperature of the lens itself rises due to heat absorption. The resolution decreases. This is because electrons ejected by the laser irradiation are captured in lattice defects in the crystal, mainly in a positively charged portion lacking fluorine ions, and form a coloring center.
The property that does not lead to such a result is called “excimer resistance”. In recent years, this “excimer resistance” has been strongly required for fluorite.

Conventionally, fluorite has been manufactured by the "crucible descent method (called the Bridgman method or Stockberger method)", and the manufacturing apparatus (furnace) is called a "crucible descent method" manufacturing apparatus. This device has a one-chamber type shown in FIG. 4 and a two-chamber type shown in FIG.
76).

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]

The conventional crucible descent method manufacturing apparatus has a problem that the manufactured fluorite is not sufficient in excimer resistance. An object of the present invention is to provide a "crucible descent method" manufacturing apparatus (furnace) capable of manufacturing fluorite excellent in excimer resistance.

[0009]

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 (invention of claim 1) is provided, wherein a bottom heater is added to a lower part of the furnace chamber.

Second, a furnace 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 bottom heater is added to a lower part of the high temperature furnace chamber. An apparatus (the invention of claim 2) characterized by the following is provided.

[0011]

[Action] The excimer resistance can be improved by increasing the crystal integrity.
improves. In order to increase the integrity, that is, to reduce the lattice defects, it is necessary to first reduce the crystal growth rate, and the crucible descending speed is reduced to 1/2 to 1 of the normal descending speed.
/ 3. In addition, it is necessary to increase the temperature gradient in the normal direction of the interface between the crystal formed from the melt and the melt to make the interface clear. In the manufacturing apparatus (one-chamber type) shown in FIG. 4, the temperature gradient is uniquely determined. However, as in the manufacturing apparatus in FIG. 5, the high-temperature furnace chamber and the low-temperature furnace chamber are vertically sandwiched by an insulating plate. In a manufacturing apparatus (two-chamber type) in which two chambers are placed adjacent to each other in the direction, the temperature gradient can be set to some extent freely. However, in both the manufacturing apparatus shown in FIG. 4 and the manufacturing apparatus shown in FIG. 5, since there is no heater in the lower part of the furnace chamber, during the crystal growth, a large amount of heat is dissipated from the crystal ingot to the lower part of the furnace. Causes a large temperature gradient and generates stress. For this reason, in the ingot, many dislocations are generated in an attempt to relieve the generated stress, and as a result, the number of lattice defects is increased and the crystal integrity is reduced. Conventionally, the ingot has to be annealed and then secondarily annealed, but this is only for the purpose of macroscopic stress release, or so-called strain relief, and microscopically reduces the crystal integrity. There were limits to improving.

On the other hand, in the present invention, since the bottom heater is provided in the lower part of the furnace chamber, a large temperature gradient does not occur in the ingot during crystal growth, so that no stress is generated inside. For this reason, crystal defects are reduced in the crystal, and the excimer resistance is improved. Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.

[0013]

FIG. 1 is a schematic longitudinal 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 bottom heater (11), which is a feature of the present invention, is attached to the lower part of the furnace chamber (7a). The bottom heater (11) is, of course, controlled independently of the side heater (5).

[0015]

Second Embodiment FIG. 2 is a schematic longitudinal 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 (7b). 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 bottom heater (11), which is a feature of the present invention, is attached to the lower part of the low temperature furnace chamber (7c) . The bottom heater (11), the first side heater (5b) and the second side heater (5c) are, of course, independently controlled.

[0017]

FIG. 3 is a schematic longitudinal sectional view of a manufacturing apparatus (two-chamber type) according to a third embodiment. This apparatus is the same as that of Example 2 (FIG. 2) except that a top heater (9) and a thermocouple (8a) are mounted on the top heater (9) above the high-temperature furnace chamber (7b). Are 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 the raw materials are melted in a vacuum by energizing all the heaters. 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).
With this temperature distribution, single crystallization of fluorite can be more reliably achieved.

In the low-temperature furnace chamber (7c),
The output balance between the second side heater (5c) and the bottom heater (11) is optimized (actually, thermocouple 8g,
By optimizing the balance by setting the temperature at 8b), a uniform temperature gradient in the vertical direction as shown on the left side of FIG. 3 can be created. After the raw material is melted and held for a certain period of time, the support rod (3) is placed in a furnace having such a temperature distribution.
By lowering the temperature, the crucible (1) is lowered (in some cases, lowered while rotating) to grow crystals.

In the apparatus of this embodiment, the bottom heater (1
1), the low-temperature furnace chamber (7b) can be kept at a uniform temperature. As a result, the stress generated in the ingot during crystal growth can be reduced, and the crystal integrity can be improved. Which is excellent in excimer resistance. Now, in the present embodiment, the presence of the top heater (9) and the bottom heater (11) enables the following applications.

The annealing is usually performed at a temperature of about 1000 ° C.
It is common to carry out in a fluorine atmosphere or vacuum in a stainless steel container. However, in order to further improve the integrity of the crystal for the purpose of improving the excimer resistance, it is preferable to thermally anneal to a higher temperature of about 1200 to 1300 ° C. for annealing. In this temperature range, in the stainless steel container, due to the heat resistance of the stainless steel itself,
Annealing is not possible. After the crystal growth is completed, when the ingot is taken out of the crystal manufacturing apparatus, oxygen is adsorbed on the surface of the ingot or metal impurities are attached from the moment, resulting in a smear in the next annealing process. Or colored.

For this reason, after completion of the crystal growth, it is preferable to directly shift to an annealing step at 1200 to 1300 ° C. in the crystal manufacturing apparatus. However, in the conventional manufacturing apparatus as shown in FIGS. 4 and 5, it is impossible to make the temperature distribution in the furnace chamber uniform. However, Embodiment 3 of the present invention (FIG. 3)
Like the top heater (9) and the bottom heater (1
In the case of a manufacturing apparatus to which 1) is added, after completion of crystal growth,
The first side heater (5b) and the second side heater (5b)
c) By optimizing the output balance between the top heater (9) and the bottom heater (11), annealing can be performed at a high temperature of 1200 to 1300 ° C in a furnace chamber having a uniform temperature distribution. As a result of the addition of the high-temperature annealing, the excimer resistance of the fluorite was further improved.

[0023]

According to the present invention, by providing the bottom heater, the lower half of the furnace chamber can be maintained at a uniform temperature in the one-chamber type apparatus, and the low-temperature side furnace chamber can be maintained in the two-chamber type apparatus. As a result, the stress generated in the ingot during crystal growth can be reduced. As a result, it has become possible to produce fluorite with sufficiently high excimer resistance.

Therefore, the fluorite 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.

[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 bottom heater is added to a lower portion of the furnace chamber. And 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,
A fluorite "crucible descent method" manufacturing apparatus comprising a second side heater disposed in the low temperature furnace chamber, wherein a bottom heater is added to a lower portion of the low temperature furnace chamber.