JP2009040630A - Method for producing metal fluoride single crystal using metal fluoride single crystal pulling apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for reducing intake or remnant of a metal component constituting a solid scavenger into or in a crystal, that is one factor deteriorating the internal transmittance of a metal fluoride single crystal used in an optical member or the like. <P>SOLUTION: A scavenging reaction, and melting and crystallization of a raw material are performed so that a solid scavenger or its melt are not brought into contact with a raw material metal fluoride 19 or its melt 23. For example, a double-structure crucible is used, and the solid scavenger is accommodated in a member 22 having a recessed part, which is provided below an opening part shielding member 15 attached to the outer wall of an inner crucible 2. Thereby, the scavenger is not directly brought into contact with the raw material metal fluoride 19 accommodated in an outer crucible 1 and a semi-closed space formed by the outer crucible 1, the inner crucible 2 and the opening part shielding member 15 is filled with the gasified scavenger and the gasified scavenger stays in the space for a long period of time. Accordingly, the efficiency of the scavenging reaction is not lowered. Further, the scavenger is not brought into contact with the melt 23 of the raw material metal fluoride 19 even in melting and crystallization processes. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a metal fluoride single crystal using a pulling apparatus used for producing a metal fluoride single crystal used for an optical material or the like.

Single crystal of metal fluoride such as calcium fluoride and barium fluoride has high transmittance over a wide wavelength band, low dispersion and excellent chemical stability. Demand is expanding as optical materials such as various devices using lasers, lenses for cameras, CVD devices, and window materials. In particular, a calcium fluoride single crystal is a light source window material, a light source lens, an ArF laser (193 nm) or an F ₂ laser (157 nm), which is being developed as a next-generation short wavelength light source in the photolithography technology. Expectation is expected as a projection system lens.

  Conventionally, such a single crystal of a metal fluoride is generally produced by the Bridgeman method (crucible descent method) or the Czochralski method (single crystal pulling method). Here, the Bridgman method is a method of growing a single crystal in a crucible by cooling the molten liquid of the single crystal production raw material in the crucible while gradually lowering the whole crucible. On the other hand, the Czochralski method is a method in which a seed crystal made of a target single crystal is brought into contact with the melt surface of the single crystal production raw material in the crucible, and then the seed crystal is gradually pulled up from the heating region of the crucible. In this method, a single crystal is grown under the seed crystal by cooling.

  In the Czochralski method, the produced single crystal can be grown (grown) without contacting the crucible wall, so there is a low possibility that it will be polycrystallized, and a large single crystal with little strain is efficiently produced. It is an excellent method that can be manufactured (for example, see Patent Documents 1 and 2).

  By the way, when oxygen is present as an impurity in the metal fluoride single crystal, absorption occurs on the short wavelength side. In particular, when used in the vacuum ultraviolet region, there is a problem that not only the transmittance is lowered, but also the transmittance itself is gradually lowered (inferior in laser resistance) by laser light irradiation.

Therefore, an oxygen scavenger called a scavenger is usually used. As this scavenger, a gas scavenger made of fluorinated hydrocarbon such as CF ₄ (gas scavenger at room temperature), or a solid scavenger such as PbF ₂ or ZnF ₂ (solid scavenger at room temperature) is used (for example, (See Patent Documents 1 to 9).

  When using a solid scavenger, mix well with the raw metal fluoride and place it in a crucible, raise the temperature to the point where the scavenge reaction takes place (lower than the melting point of the metal fluoride), and then deoxygenate. The raw material metal fluoride is melted by heating, followed by single crystallization.

  In this case, in order to remove the product generated by the scavenge reaction, the system is usually evacuated intermittently from the start of temperature rise to the start of single crystallization. Furthermore, when a single crystal is manufactured by the Bridgman method, it is often performed under high vacuum exhaust during crystal growth.

  On the other hand, when a metal fluoride single crystal is produced by the Czochralski method, there is a high possibility that various problems occur when crystal growth is performed under a high vacuum. This is performed under reduced pressure (see, for example, Patent Document 8).

JP 2004-182588 A JP 2005-029455 A Japanese Patent Laid-Open No. 2003-221297 Japanese Patent Laid-Open No. 11-157982 JP 2004-315255 A Japanese Patent Laid-Open No. 2001-19586 JP 2006-199577 A JP 2006-347792 A JP 2007-106662 A

  As described above, scavengers are used to remove oxygen impurities. However, even if the metal elements constituting the scavengers are incorporated into the produced metal fluoride, they may still cause various absorptions. It becomes a factor to deteriorate the transmittance and laser resistance. As a method for preventing such uptake, it is conceivable to reduce the amount of scavenger used, but the amount of oxygen impurities contained in the raw metal fluoride is usually not constant, There is also a problem of contamination of outside air due to moisture and oxygen components adhering to the member and leakage. Therefore, the current situation is that a large amount of scavenger must be used.

  In metal fluoride single crystal production by the Bridgman method, it is easy to make a high vacuum even during crystal growth, so that moisture and oxygen components due to adhesion and leakage of members do not enter the raw material due to diffusion, and Because of this high vacuum holding, excess solid scavengers and reaction products are easily removed, so that the above problem is unlikely to occur even when a large amount of solid scavenger is used. However, in the Czochralski method, where crystal growth under high vacuum is difficult, it is necessary to use a large amount of scavenger in order to cope with diffusion and mixing of moisture and oxygen components due to adhesion and leakage of members. Since it is difficult to remove the solid scavenger and the reaction product, a problem of incorporation of the metal element constituting the solid scavenger into the single crystal often occurs.

  On the other hand, when a scavenger having no metal element, that is, a gas scavenger made of fluorinated hydrocarbon is used, such a problem of incorporation of the metal element does not occur. However, since fluorinated hydrocarbons decompose at high temperatures to produce carbon polymers, the Czochralski method in which single crystal growth is performed from above the raw material melt causes the carbon polymer to adhere (float) to the melt. The problem of inhibiting single crystal growth is likely to occur. In the case of producing a single crystal by the Bridgman method, since the single crystal is grown from below the crucible, there is substantially no problem even if a carbon polymer is formed.

  Therefore, in the present invention, particularly when producing a metal fluoride single crystal by the Czochralski method, oxygen is sufficiently removed, and a metal element derived from a solid scavenger is also difficult to be taken into the single crystal. It is an object of the present invention to provide a production method capable of stably producing a single crystal with small absorption at the surface and small damage by laser irradiation.

  The present inventors have conducted intensive studies in view of the above problems. The above problem is that when a part of the solid scavenger in contact with the metal fluoride raw material does not completely volatilize in the scavenging process, and then the temperature is further raised to melt the raw metal fluoride, As a result of further investigation, the scavenger is taken into the molten raw material metal fluoride, which makes it more difficult to volatilize and remains in the finally obtained crystal. Completed the invention.

That is, the present invention includes a step of storing a solid scavenger and a metal fluoride in a hot zone of a heating furnace and then heating the hot zone to melt the raw metal fluoride, and then crystallizing the molten metal fluoride. A method for producing a metal fluoride crystal having a step of forming a crystal,
The storage position of the solid scavenger in the hot zone is a position where the solid scavenger and its molten liquid are not in contact with the raw metal fluoride and its molten liquid until the end of the crystallization step. This is a method for producing metal halide crystals.

  When a single crystal is produced using the method for producing a metal fluoride crystal of the present invention, the metal element derived from a solid scavenger incorporated into the crystal is greatly reduced, and oxygen can be sufficiently removed. The internal transmittance of the resulting metal fluoride crystal can be improved.

The production method of the present invention can be applied to any known metal fluoride capable of removing oxygen by a solid scavenger. Specifically, calcium fluoride, magnesium fluoride, strontium fluoride, barium fluoride, lithium fluoride, aluminum fluoride, cerium fluoride, lanthanum fluoride, BaLiF ₃ , KMgF ₃ , LiCaAlF ₆ , LiSrAlF _6, etc. And metal fluorides containing two or more kinds of cationic elements. Of these, the effects are most prominent particularly in alkaline earth metal fluorides, especially calcium fluoride and barium fluoride, and the industrial value of the object is also high.

The solid scavenger used in the present invention (that is, a scavenger that is solid at room temperature) may be appropriately selected from known solid scavengers according to the metal fluoride to be produced. For example, when the metal fluoride is calcium fluoride or magnesium fluoride, the solid scavenger includes zinc fluoride (PbF ₂ ), lead fluoride (ZnF ₂ ), silver fluoride (AgF), copper fluoride ( CuF ₂ ) and the like. Of these, lead fluoride or zinc fluoride is preferable from the viewpoint of oxygen removal ability and handling properties, and zinc fluoride is particularly preferable. In the present invention, two or more solid scavengers can be used in combination.

  In the present invention, the raw metal fluoride is melted in the presence of the solid scavenger as described above, and then crystallized. In this process, the scavenging reaction as described above occurs, and oxygen impurities are removed from the metal fluoride. In the production of metal fluoride crystals, there are a raw material refining step and a single crystallization step as the steps of melting and crystallization, and the present invention may be applied to any step. It is preferable to apply it to the single crystallization step in that it was difficult to remove. In addition, as a single crystallization method involving melting and crystallization of raw materials, there are the Czochralski method, the Bridgeman method, etc., but as described above, it is more difficult to remove the components derived from the solid scavenger by the conventional technology. In this respect, it is preferable to apply the production method of the present invention to the Czochralski method.

  Hereinafter, the case where the present invention is applied to the Czochralski method will be described as an example with reference to the drawings. In the present invention, the term “solid scavenger” or “raw metal fluoride” simply refers to a solid state that is not melted or gasified.

  FIG. 1 is a schematic cross-sectional view showing a furnace (heating furnace) for producing a single crystal by the Czochralski method (showing a state during crystal pulling). In the furnace shown in FIG. 1, the crucible for melting the raw material metal fluoride is a double structure crucible comprising an outer crucible (1) and an inner crucible (2), and the wall portion (bottom wall and / or / (Or the side wall) is provided with a through hole (3) through which the raw metal fluoride metal melt can flow in the inner crucible and the outer crucible through the wall portion. When the crystal is pulled up, the raw material melt in the crucible is reduced by the amount corresponding to the amount of crystal pulled up, that is, the raw material melt level in the crucible is lowered. In the illustrated embodiment, the inner crucible is fixed at a predetermined position (height), and the outer crucible is raised by an amount corresponding to the relative lowering of the raw material melt surface. As a result, the raw material melt in the inner crucible can be kept constant, and the position of the raw material melt surface (= crystal growth interface) can be prevented from changing.

  The outer crucible is raised by an outer crucible support shaft (4) capable of moving up and down (the mechanism enabling the up and down movement and rotation is not shown). In FIG. 1, the outer crucible (1) is installed on a cradle (5), and the outer crucible support shaft (4) directly moves and rotates the cradle (5).

  The crucible is heated by a heater (6). Usually, a heat insulating wall (8) is arranged between the chamber (7) of the crystal pulling furnace and the heater (6) so as to surround the heater (6). It is also provided below the crucible, and a ceiling plate is provided above.

  In the pulling device of FIG. 1, an isolation wall (9) is provided between the outer wall surface of the outer crucible (1) and the heater (6) for the purpose of uniformizing the radiant heat from the heater. In order to prevent the heat of the heater (6) from escaping upward, the upper end of the isolation wall (9) is made higher than the upper end of the heater (6), and the upper end and the heat insulating wall (8) The lid member (10) that closes the gap between the isolation wall (9) and the heat insulating material wall (8) is horizontally placed between the two and the gap.

  On the center axis of the crucible, a seed crystal holder (12) for holding the seed crystal (11) and a crystal pulling shaft (13) for supporting the holder so as to move up and down and rotate are arranged. In the Czochralski method, the seed crystal (11) held in the holder (12) is usually brought into contact with a sufficiently melted raw material in the crucible, and then gradually pulled up while rotating to obtain a single crystal (14 ) Grow.

  In the case of producing a metal fluoride single crystal by the Czochralski method as described above, first, a raw material metal fluoride is charged and placed in a crucible, and the raw material metal fluoride is heated by a heater (6). In order to remove oxygen impurities, a solid scavenger is also charged into the furnace in addition to the raw metal fluoride.

  Conventionally, when a solid scavenger (20) is used, it has been used by mixing with a raw material metal fluoride (19) (FIG. 2). Even when not mixed, it was placed on the bottom of the crucible so that the volatilized scavenger gas could easily come into contact with the raw metal fluoride (FIG. 3). When placed at the bottom of the crucible, if the solid scavenger has not completely volatilized (normally in a molten state) when the temperature is raised to the temperature at which the raw metal fluoride melts, the molten raw material fluoride flows into the bottom. As a result, the remaining solid scavenger (the melt thereof) comes into contact.

  Thus, in the conventional method of using a solid scavenger, the solid scavenger or its molten liquid is used in a state where the raw material metal fluoride or its molten liquid is in contact with each other. It is easy to cause a problem that the metal element constituting the solid scavenger is taken in.

  On the other hand, in the present invention, the above-mentioned problem does not occur because the solid scavenger or its melt and the raw material metal fluoride or its melt are not in contact with each other, and thus it is easy to obtain a high-quality metal fluoride crystal. It becomes.

  Although the method for making the above "not in contact" is not particularly limited, typically, a crucible provided with a recess or a member having a recess above the crucible as shown in Figs. A method of producing a metal fluoride by containing a solid scavenger in the recess is mentioned.

  FIG. 4 is a schematic view showing an example in which a recess (21) is provided at the upper end of the outer crucible. In FIG. 4, the right side shows a state where the solid scavenger is accommodated in the recess, and the left side shows the state where the solid scavenger is not accommodated. By storing the solid scavenger (20) in such a recess (21), the scavenger component is volatilized by heating, and the gas comes into contact with the raw material metal fluoride (19) in the crucible (1) to generate oxygen. A removal reaction (scavenge reaction) occurs. When the temperature is further raised, the raw metal fluoride (19) is melted, but the scavenger is accommodated in the recess at the upper end of the crucible, so that the molten raw metal fluoride and the solid scavenger do not come into contact with each other. Normally, the solid scavenger (20) is also melted at the temperature at which the raw metal fluoride is melted. Therefore, when providing a recessed part, it is necessary to make it the structure which the melt of a solid scavenger flows out and does not contact with a raw material metal fluoride.

  FIG. 5 is a view showing an example in which a hole (or groove) is formed above the inner wall of the outer crucible so as to form a recess (21), and FIG. 6 is a member having a recess on the upper inner side of the outer crucible. It is a figure which shows the example which provided (22) (all do not show the solid scavenger). In the case of such an embodiment, the opening of the concave portion needs to be provided above the crucible, more specifically, above the highest position where the molten raw material metal fluoride reaches.

  4 to 6, the concave portion (21) or the member (22) having the concave portion is provided above the outer crucible in the double structure crucible, but may be provided above the inner crucible. However, when the opening shielding member described later is provided, the gasified solid scavenger and the raw material metal fluoride are easily brought into contact with each other, and a recess or a recess is formed above the outer crucible in that the scavenging reaction is easily performed. It is preferable to provide a member having Moreover, even when providing in an outer crucible, it is preferable to provide in an upper end or an inner wall side rather than an outer side wall side.

  In the case of a dual structure crucible, it is preferable to provide an opening shielding member (15) on the outer wall of the inner crucible and / or the inner wall of the outer crucible in order to close the opening between the outer crucible and the inner crucible. The opening shielding member is described in detail in Japanese Unexamined Patent Application Publication No. 2007-106662. Specifically, the volatilization of the metal fluoride during crystal pulling is suppressed and the influence of falling objects is reduced. Further, the opening shielding member (15) is a scavenger gas in a conventional method of mixing a solid scavenger and a raw metal fluoride (FIG. 2) or a method of housing a solid scavenger in the crucible bottom (FIG. 3). In the present invention, the same effect can be obtained by appropriately setting the housing position of the solid scavenger.

  That is, for example, as shown in the state before melting in FIG. 5 or FIG. 6, a recess (21) or a member (22) having a recess (hereinafter, simply referred to as “a recess or the like”) that accommodates the solid scavenger is A semi-enclosed space formed by the inner wall of the outer crucible, the outer wall of the inner crucible, and the opening shielding member (which also contains the raw material metal fluoride). An opening such as a recess is present inside. As a result, the scavenger gas that has volatilized from the opening such as the concave portion stays in the semi-enclosed space for a long time, so that the contact with the raw material metal fluoride can be made efficient.

  In addition, as shown in FIG. 4, even when the recess is provided at the upper end of the crucible with the opening facing upward, it is preferable that the position of the opening shielding member is higher than the recess until the metal fluoride is melted.

  When providing the member which has a recessed part for accommodating a solid scavenger above a crucible, it is preferable to make this member the member which can be easily attached or detached from a crucible. By making it an easily removable member, it becomes possible to charge and install the solid scavenger in the concave portion of the member in advance, and then place the solid member in a predetermined position (recessed portion) in the furnace. The operation of housing the scavenger is significantly facilitated. In particular, as shown in FIG. 7, it is particularly advantageous in terms of improving workability that the upper end of the crucible is a detachable member (also in FIG. 7, the solid scavenger accommodated in the recess is not shown). .

  As described above, in order to make the reaction between the metal fluoride metal and the scavenger gas efficient, when the opening shielding member is provided, the opening of the recess for housing the solid scavenger is more than the opening shielding member. Is preferably provided so as to have a lower portion. Even when the relative position of the outer crucible and the inner crucible is changed, the lower surface of the opening shielding member and the opening shielding member can be always lower than the opening shielding member. It is preferable to provide a recess or the like on the side wall of the crucible on the side below the lower surface and provided with the opening shielding member.

  FIG. 8 and FIG. 9 illustrate this aspect. In the embodiment shown in FIG. 8, a member (22) having a recess for accommodating the solid scavenger is provided on the lower surface of the opening shielding member (15) provided on the outer wall of the inner crucible (2). The member (22) which has a recessed part in the position below the lower surface of the opening part shielding member (15) which is an inner wall of a crucible (2) is provided. In FIGS. 8 and 9, the member for housing the solid scavenger is a separate member from the crucible body. However, as shown in FIG. 5, holes and grooves may be provided in the crucible body. As shown in FIG. 6, when a member having a recess is provided in a state protruding from the crucible opposite to the crucible to which the opening shielding member is attached, the recess is provided when the outer crucible is moved up and down. Although it is necessary to design and move up and down in consideration of interference between the member and the opening shielding member, as shown in FIGS. 8 and 9, when providing a recess or the like on the side where the opening shielding member is provided, There is no need to consider this interference (of course, it is necessary to consider the height of the melt surface of the metal fluoride raw material). Therefore, in this aspect, rather than opening a hole or the like in the crucible body and providing a recess, providing a member having a recess makes the crucible durable, easy to repair, and easy to accommodate a solid scavenger. Is preferable.

  In order for the gasified scavenger to remove oxygen on the surface of the raw material metal fluoride, it is preferable to dispose the solid scavenger as close to the raw material as possible. Therefore, in any of the above embodiments, the position of the recess is as low as possible (however, the raw material It is preferably provided above the highest position where the molten metal fluoride reaches, and the opening of the recess is preferably wide.

  Moreover, not only the method of providing a concave part etc. in a crucible as mentioned above but what kind of method may be employ | adopted. However, since the solid scavenger volatilizes at a high temperature and the generated gas causes a scavenge reaction, the solid scavenger needs to be accommodated in a hot zone in the furnace. Here, the hot zone in the present invention refers to the temperature configuration in the furnace at the time of starting the crystallization in the crystallization of the molten metal fluoride [the crystallization temperature (melting point) of the metal fluoride] 500] A space having a temperature higher than ° C. Preferably, in the hot zone, the solid scavenger is housed in a place where the temperature is higher than [crystallization temperature (melting point) -200] ° C. of the metal fluoride in the furnace temperature configuration at the start of crystallization. To do.

  The members constituting the Czochralski method single crystal production furnace as described above may be appropriately selected from known materials used in the production of metal fluoride. Specifically, the selection may be made in consideration of durability against fluorine-based gas, heat resistance, possibility of impurities being mixed into the metal fluoride, and the like. Examples of such materials include carbon-based materials such as graphite and diamond, and refractory metals such as platinum, platinum-rhodium alloys, and iridium. In particular, it is preferable that the furnace is mainly composed of a graphite-based material because of its low cost.

  As a method for producing a metal fluoride single crystal using the Czochralski method single crystal pulling apparatus (furnace) as in the above example, a known method may be applied except for the position where the solid scavenger is accommodated. The typical manufacturing method will be briefly described below.

  In the production of a single crystal, a raw material metal fluoride and a solid scavenger are charged in the furnace. Prior to this, it is preferable to clean the furnace by empty baking at a high temperature under high vacuum. This baking may be performed in the presence of a solid or gaseous scavenger.

  The raw material metal fluoride is preferably one having as few impurities as possible, and it is desirable to remove most of impurities such as oxides and moisture by heating and melting in the presence of various scavengers.

  Such a raw material metal fluoride and a solid scavenger are accommodated in the furnace in the positional relationship as described above. The amount of the solid scavenger to be used is usually about 0.01 to 1 part by mass with respect to 100 parts by mass of the raw metal fluoride.

  The raw material metal fluoride is heated in the crucible after it is contained. In this temperature raising process, it is preferable to keep the inside of the furnace under reduced pressure. This removes the surface of the raw metal fluoride or adsorbed water in the furnace up to the temperature at which the scavenge reaction takes place, and above the temperature at which the scavenge reaction takes place, the gasified scavenger reacts with the residual moisture. Reaction products and the like can be discharged out of the apparatus.

  A seed crystal is brought into contact with the molten liquid surface of the molten raw material metal fluoride, and gradually pulled up to grow a single crystal. The atmosphere during crystal pulling is preferably an inert gas such as argon. Single crystal pulling can be performed under normal pressure to reduced pressure.

  The seed crystal and the growing crystal are preferably rotated about the pulling axis, and the rotation speed is preferably 5 to 30 times / minute. In addition to the rotation of the seed crystal, the crucible may be rotated in the opposite direction at the same rotation speed. A suitable crystal pulling speed is 1 to 10 mm / hour.

After the completion of the crystal pulling, the cooling until the single crystal is taken out from the furnace is usually performed at a temperature lowering rate of 10 ° C./min or less. However, when the obtained as-grown single crystal is processed, cracking or chipping occurs. It is preferable to cool at a temperature lowering rate of 0.5 ° C./min or less, preferably about 0.1 to 0.3 ° C./min. Moreover, it is more preferable to carry out under vacuum evacuation in which the furnace pressure is about 10 ⁻³ to 10 ⁻⁵ Pa during the temperature drop because it is easy to suppress the generation of fine voids.

  The seed crystal used for pulling the single crystal is preferably a single crystal of the same material as the growing metal fluoride. The growth surface of the seed crystal can be arbitrarily selected, but when using a calcium fluoride seed crystal, the {111} plane, the {100} plane, the {110} plane, and their equivalent planes are preferably used. be able to.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not limited to these Examples.

Example 1
A calcium fluoride single crystal was manufactured using a pulling apparatus for manufacturing a single crystal of a double structure crucible as shown in FIG.

  In the double structure crucible (6), the outer crucible (4) has a depth of 30 cm and an inner diameter of 50 cm, the inner crucible (5) has a depth of 150 cm and an inner diameter of 36 cm, and the crucible bottom is inclined at an inner angle of 120 ° toward the center. V-shaped (mortar shape). A donut plate-shaped opening shielding member having a thickness of 6 mm and a gap of 1.5 mm from the inner wall of the outer crucible is attached to the outer wall of the inner crucible at a position 2 cm from the upper end. The inner crucible is formed with a cylindrical communication hole (14) with one piece at the lower end and eight pieces above the circumference at a height of 25 mm at equal intervals and a diameter of 4 mm.

The heat insulating wall (6) is a pitch-based graphite molded heat insulating material and has a heat dissipation capability in the thickness direction of 9 W / m ² · K, while the ceiling plate (14) is made of graphite and has a thickness of The heat dissipation capability in the direction was 5000 W / m ² · K.

  The outer crucible position is lowered, 70 kg of calcium fluoride raw material is placed in the outer crucible, and 70 g of zinc fluoride (solid scavenger) is set in the graphite container attached to the lower surface of the donut-shaped opening shielding member as shown in FIG. The position of the outer crucible was raised to the position where the opening of the gap space was closed by the opening shielding member.

The chamber was evacuated, and when the pressure reached 5 × 10 ⁻³ Pa or less, the heater was energized while starting the evacuation, and the heating of the raw material was started. The temperature was raised at about 50 ° C./Hr until the temperature at the bottom of the crucible reached 250 ° C., and this temperature was maintained for 24 hours. The degree of vacuum in the chamber at that time was 5 × 10 ⁻⁴ Pa. Thereafter, the temperature was raised again at about 50 ° C./Hr, and after reaching 600 ° C., the temperature was further maintained for 12 hours. Thereafter, the vacuum exhaust line was shut off, and high-purity argon was supplied into the chamber. The gas was not introduced until the internal pressure was reduced to 50 kPa (abs) and the pulling was completed and the temperature was lowered to around room temperature.

  After returning to 50 kPa, the temperature was raised to around 1500 ° C. and held for 3 hours to melt the raw material. In this state, the position of the outer crucible is raised so that a part of the melt flows into the inner space of the inner crucible, and the calcium fluoride raw material melt (7) enters the outer crucible (4) and the inner crucible (5). Was in a housed state.

  The temperature of the melt was lowered to a state where it could be grown, the seed crystal was brought into contact with the surface of the melt, and the seed rod (13) was pulled up at 4 mm / Hr for growth. A single crystal body having a diameter of 250 mm and a length of 150 mm of the straight body portion was grown, the crystal was separated from the melt, and the temperature was lowered to room temperature.

  From a single crystal produced under the above conditions, a columnar test piece having a diameter of 20 mm and a thickness of 30 mm was cut out, both ends were polished, and the internal transmittance at a wavelength of 193 nm was measured. As a result, it was very good at 99.9% / cm. there were.

Further, when 10 ⁵ shots of 30 mJ / cm ² ArF laser (wavelength 193 nm) were irradiated on this test piece and the transmittance in the visible / ultraviolet wavelength region (190 to 800 nm) before and after the irradiation was compared, it was slightly near 270 nm. Although a decrease in transmittance was observed, there was almost no change in transmittance in other regions.

As described above, the calcium fluoride crystal having a small decrease in transmittance in the visible / ultraviolet wavelength region before and after irradiation with a relatively high intensity ArF laser of about 30 mJ / cm ² uses a relatively low intensity ArF laser many times ( 10 about ⁹ shots) has confirmed that the decrease of the transmittance at the wavelength of 193nm after irradiation is very small, i.e., single crystal produced in this example can be evaluated to be excellent in laser resistance.

Example 2
As shown in FIG. 4, 70 g of scavenger was filled in the recess at the upper end of the crucible, and the rise of the outer crucible was stopped at a position where the opening shielding member and the upper end of the outer crucible were not closed. The operating conditions were exactly the same as in Example 1.

  From a single crystal produced under the above conditions, a columnar test piece having a diameter of 20 mm and a thickness of 30 mm was cut out, both ends were polished, and the internal transmittance at a wavelength of 193 nm was measured. As a result, it was very good at 99.8% / cm. there were.

Further, when 10 ⁵ shots of 30 mJ / cm ArF laser (wavelength 193 nm) were irradiated on this test piece and the transmittance in the visible / ultraviolet wavelength region (190 to 800 nm) before and after irradiation was compared, it was slightly transmitted at around 270 nm. A decrease in the rate was observed, but the transmittance in the other regions was almost unchanged.

Comparative Example 1
A scavenger 70g was set at the center bottom of the outer crucible, and the rising of the outer crucible was stopped at a position where the opening shielding member and the upper end of the outer crucible were not closed. The operating conditions were exactly the same as in Example 1.

  A columnar test piece having a diameter of 20 mm and a thickness of 30 mm was cut out from the single crystal produced under the above conditions, both ends were polished, and the internal transmittance at a wavelength of 193 nm was measured to be 99.6% / cm.

Further, when 10 ⁵ shots of 30 mJ / cm ArF laser (wavelength 193 nm) were irradiated on this test piece, and the transmittance in the visible / ultraviolet wavelength region (190 to 800 nm) before and after irradiation was compared, the transmittance was around 270 nm. In other areas, a slight decrease in transmittance was observed.

Comparative Example 2
A scavenger 70g was set at the center bottom of the outer crucible, and the rising of the outer crucible was stopped at a position where the opening shielding member and the upper end of the outer crucible were not closed. The operating conditions were exactly the same as in Example 1 except that the temperature at 600 ° C. was maintained at 800 ° C., the temperature at which zinc fluoride was sufficiently sublimated.

  A columnar test piece having a diameter of 20 mm and a thickness of 30 mm was cut out from the single crystal produced under the above conditions, both ends were polished, and the internal transmittance at a wavelength of 193 nm was measured to be 99.7% / cm.

Further, when 10 ⁵ shots of 30 mJ / cm ArF laser (wavelength 193 nm) were irradiated on this test piece and the transmittance in the visible / ultraviolet wavelength region (190 to 800 nm) before and after irradiation was compared, in most wavelength regions A decrease in transmittance was observed.

It is a schematic diagram which shows the typical aspect of the pulling apparatus used for the manufacturing method of the fluoride single crystal of this invention. It is a schematic diagram which shows the example of the usage method of the conventional typical solid scavenger. It is a schematic diagram which shows the other example of the usage method of the conventional solid scavenger. It is a schematic diagram which shows an example at the time of providing the recessed part which accommodates a solid scavenger in the outer crucible upper end part of a double structure crucible. It is a schematic diagram which shows an example at the time of providing the recessed part which accommodates a solid scavenger in the inner wall part above the outer crucible of a double structure crucible. It is a schematic diagram which shows an example at the time of providing the member which has a recessed part which accommodates a solid scavenger in the inner wall part above the outer crucible of a double structure crucible. It is a schematic diagram which shows an example at the time of providing the member which has a recessed part which accommodates a solid scavenger in the outer crucible upper end part of a double structure crucible, and making this member removable. It is a schematic diagram which shows an example at the time of providing the member which has a recessed part which accommodates a solid scavenger in the lower surface of the opening part shielding member provided in the inner crucible outer side wall of a double structure crucible. It is a schematic diagram which shows an example at the time of providing the member which has a recessed part which accommodates a solid scavenger in the position below the lower surface of the opening part shielding member of an inner crucible outer wall.

Explanation of symbols

1. Outer crucible2. 2. Inner crucible Through hole 4. 4. Outer crucible support shaft 5. cradle 6. Heater Chamber 8. 8. Insulation wall Isolation wall 10. Lid material11. Seed crystal 12. Seed crystal holder 13. Crystal pulling shaft 14. Single crystal 15. Opening shielding member 16. Buttocks 17. Inner crucible hanging rod 18. Connecting member 19. Raw metal fluoride 20. Solid scavenger 21. Concave part 22 provided in the crucible. Member having a recess 23. Raw material fluoride metal melt

Claims (5)

After the raw metal fluoride and the solid scavenger are accommodated in the hot zone in the furnace, the hot zone is heated to melt the raw metal fluoride, and then the molten metal fluoride is crystallized. A method for producing a metal fluoride crystal having:
The storage position of the solid scavenger in the hot zone is a position where the solid scavenger and its molten liquid are not in contact with the raw metal fluoride and its molten liquid until the end of the crystallization step. A method for producing metal halide crystals.   A crucible for containing a metal fluoride used in the manufacturing method according to claim 1, wherein a recess and / or a member having a recess for receiving a solid scavenger is provided above the crucible. A crucible characterized by.   A Czochralski method single crystal pulling apparatus used in the manufacturing method according to claim 1, wherein the Czochralski method single crystal pulling apparatus is a double unit comprising an inner crucible having a through hole in a wall portion and an outer crucible. A Czochralski method single crystal comprising a structural crucible and provided with a recess and / or a member having a recess in which a solid scavenger is accommodated above the inner crucible and / or the outer crucible Lifting device.   4. The Czochralski method single crystal pulling apparatus according to claim 3, wherein a member having a recess above the crucible is detachable from the crucible body. A Czochralski method single crystal pulling apparatus for producing a metal fluoride single crystal comprising a double structure crucible comprising an outer crucible and an inner crucible having a through hole in a wall portion, which is used in the production method according to claim 1. There,
An opening shielding member for closing the opening between the outer crucible and the inner crucible is provided on the outer wall of the inner crucible and / or the inner wall of the outer crucible, and the lower surface of the opening shielding member and / or Alternatively, the Czochralski method single crystal pulling apparatus, wherein a solid scavenger housing member is installed on the side wall of the crucible on the side below the lower surface and provided with the opening shielding member.

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