JP2012012244A - Method for producing metal fluoride single crystal body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a metal fluoride single crystal body having a small inclination of a crystal orientation azimuth on both parts in the growth direction (vertical direction) and in the horizontal direction.SOLUTION: In this method for producing a metal fluoride single crystal body, a seed crystal body is brought from the upside into contact with a raw material molten liquid surface in a crucible used in the Czochralski method or the like, and a crystal having the same crystal orientation azimuth as the seed crystal body is grown up, to thereby acquire a single crystal body having a rod-like part (a) originated in the seed crystal body, a columnar straight body part (b) having a larger diameter than the rod-like part (a), and an enlarged diameter part (c) for connecting the rod-like part (a) to the straight body part (b), wherein the enlarged diameter part (c) is formed so that the ratio h/r between a height h of the enlarged diameter part (c) and a diameter r of the straight body part (b) is ≤0.35, preferably ≤0.25.

Description

  The present invention relates to a method for producing a metal fluoride single crystal used for an optical material or the like by a melt solidification method using a seed crystal.

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, the calcium fluoride single crystal is used as a light source window material, light source system lens, and projection system lens with an ArF laser (193 nm) or an F ₂ laser (157 nm).

  Conventionally, such a single crystal of a metal fluoride has been manufactured by a melt solidification method. Among melt coagulation methods, it is common to manufacture by a method using a crucible such as the Bridgeman method or the Czochralski method. In the Bridgman method, a seed crystal is placed at the bottom of the crucible, and the raw material melt stored in the crucible is cooled by gradually lowering the crucible and moving to a low temperature region, and then stored in the crucible. This is a method for growing the raw material melt. On the other hand, in the Czochralski method, the seed crystal is brought into contact with the surface of the raw material melt in the crucible, and then the seed crystal is gradually pulled up from the heating region of the crucible and cooled, thereby lowering the seed crystal. (See, for example, Patent Documents 1 to 4).

  When producing a metal fluoride single crystal by the melt solidification method, it is usually accompanied by the generation of line defects such as edge transitions and spiral transitions. In many cases, the obtained single crystal has a number of subgrains with slightly different orientation directions. Furthermore, even if the sub-grains are not used, there are many cases where the orientation azimuth is inclined between the central portion and the peripheral portion of the grown single crystal due to the generation of the line defects.

  However, when a glass material for obtaining the optical material is obtained from such a grown single crystal, the main orientation direction is different between the center portion and the peripheral portion or between the front surface and the back surface. Optical properties may not be obtained. The same applies to the case where there are large subgrains with extremely different orientation directions.

JP-A-11-130594 JP 2006-117494 A JP 2007-106662 A JP 2004-231502 A

  Therefore, the present invention suppresses as much as possible the generation of line defects and surface defects that cause a deviation from the orientation orientation of the seed crystal used, and the main orientation orientations at the central portion and the peripheral portion, and at the upper and lower portions. An object is to provide a method for producing a metal fluoride single crystal having little difference and excellent single crystallinity.

  In view of the above problems, the present inventors have intensively studied. And, it was found that the crystal orientation orientation shift in the crystal growth direction (vertical direction) is less when the grown crystal is produced by the Czochralski method without the restraint than the Bridgman method where the grown crystal is restrained by the crucible. As a result, the shoulder part (expanded part) inevitably formed when the crystal diameter is expanded from the seed crystal part to the straight body part with respect to the deviation of the crystal orientation orientation between the central part and the peripheral part. As a result, the present invention was completed.

That is, the present invention is a method in which a seed crystal is brought into contact with the raw material melt liquid surface in a crucible from above, a crystal having the same crystal orientation as the seed crystal is grown, and a rod-like portion derived from the seed crystal, In the method for producing a metal fluoride single crystal having a columnar straight body having a diameter larger than that of the rod-shaped portion, and a single crystal having an enlarged diameter portion connecting the rod-shaped portion and the straight drum portion,
A method for producing a metal fluoride single crystal, comprising forming a diameter-expanded portion so that a ratio h / r between a height h of the shoulder portion and a diameter r of the straight body portion is 0.35 or less. It is.

  According to the present invention, there is little deviation from the orientation orientation of the seed crystal used at any position in the growth direction (upper and lower) and lateral direction (central and peripheral) of the obtained metal fluoride single crystal. Therefore, a single crystal body excellent in various optical performances can be obtained with a high yield.

  Further, when the straight body portion is grown, the deviation of the orientation direction in the lateral direction can be further reduced by setting the diameter of the straight body portion and the diameter of the raw material melt to a specific range. .

The schematic diagram which shows the shoulder (expansion part) formation process of single crystal pulling. Schematic diagram of manufactured single crystal The schematic diagram which shows the boundary of an enlarged diameter part and a straight body part. The schematic diagram which shows the structure of a Czochralski method single crystal pulling furnace. The schematic diagram which shows the measuring point of the inclination of an orientation azimuth | direction.

  In the crystal growth furnace, a seed crystal is brought into contact with the raw material melt surface from above, a crystal having the same crystal orientation as the seed crystal is grown, and a metal fluoride single crystal is obtained by a melt solidification method. The present invention can be applied to a method for producing a metal fluoride that is possible by a method for producing a body (Czochralski method, kiloporous method, etc.). Specific examples of such metal fluoride include lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride, magnesium fluoride, calcium fluoride, barium fluoride, strontium fluoride, aluminum fluoride, and fluoride. Barium lithium, potassium potassium fluoride, lithium aluminum fluoride, calcium strontium fluoride, magnesium magnesium fluoride, lithium strontium fluoride, cesium calcium fluoride, lithium calcium calcium fluoride, lithium strontium aluminum fluoride, and lanthanoid fluorides Etc.

  When these metal fluoride single crystals are obtained by bringing the seed crystal into contact with the raw material melt surface from above and growing the single crystal under the seed crystal, the crystal growth is larger than the diameter of the seed crystal. In general, the diameter of the single crystal body (straight body portion) obtained is large. For this reason, a portion that expands from the seed crystal body to the straight body portion is generated. The present invention is characterized in that the diameter-expanded portion is not more than the specific value.

  More specifically, referring to the drawings, as shown in FIG. 1, the seed crystal (116) is lowered from above, and is brought into contact with the metal fluoride raw material melt (104) (in some cases, immersed). (FIG. 1A). Thereafter, the seed crystal is pulled up, and gradually expanded until the final desired diameter is reached (FIG. 1B). After reaching the desired diameter by the diameter expansion, the pulling is further continued to maintain the diameter (FIG. 1C).

  As shown in FIG. 2, the single crystal produced in this way has a rod-shaped portion (a) derived from the seed crystal, a cylindrical straight body portion (b) having a diameter larger than that of the rod-shaped portion, and the It has an enlarged diameter part (c) which connects a rod-shaped part and a straight body part. Furthermore, normally, it has a convex part which reduces in diameter at the lower part of the straight body part.

  In the present invention, when manufacturing such a single crystal body, the ratio (h / r) of the height h of the enlarged diameter portion and the diameter r of the straight body portion is 0.35 or less. The difference in crystal orientation between the central part and the peripheral part of the straight body part can be made extremely small by forming the diameter-expanded part in the above (this ratio may be referred to as “the diameter-expanding ratio” hereinafter) ). As the diameter expansion ratio increases, the difference in crystal orientation between the central portion and the peripheral portion tends to increase. In order to make the difference equal to or less than a value satisfactory for an optical member for a lithography apparatus using ArF laser light, for example, the diameter expansion ratio is preferably 0.25 or less, more preferably 0.20 or less.

  The lower limit is not particularly defined, but it is extremely difficult to make it 0 in terms of manufacturing technology. From the viewpoint of easy formation of the expanded diameter portion, the expanded diameter ratio is preferably 0.02 or more, and more preferably 0.05 or more.

  The shape (expansion ratio) control method for forming the expanded portion is well known in the manufacturing method of silicon single crystals and oxide single crystals by the Czochralski method, and a new special means is also used in the present invention. It is not necessary. Specifically, for example, while monitoring the increase in the weight of the single crystal of the expanded diameter portion grown by a load cell or the like, the pulling speed may be adjusted to obtain a desired expanded diameter ratio.

  Also, the method of controlling the diameter of the straight body is well known in the production methods of various single crystals by the Czochralski method, and these known methods may be adopted as appropriate. Specifically, it is only necessary to adjust the pulling speed and the heater output (furnace temperature) to a desired diameter while monitoring the increase in the weight of the single crystal grown by, for example, a load cell.

  In addition, the diameter control of the straight body part by the Czochralski method or the like, especially in the case of a metal fluoride single crystal, the straight body part of the growing single crystal rarely becomes a cylinder with a uniform diameter. However, the diameter increases or decreases over time due to various factors, and the diameter actually measured by the measurement site is often different from the target control diameter.

  For this reason, the diameter r of the straight body portion in the present invention is a target control diameter at the time of manufacture, but the actually obtained single crystal body includes a portion larger or smaller than the r. In the present invention, the cylindrical straight body portion refers to a portion within a range of ± 5% with respect to r (except for the enlarged diameter portion).

  For the same reason, the transition part from the enlarged diameter part to the straight body part hardly has a clear corner as shown in FIGS. 1 and 2 and is rounded. Is normal. In the present invention, the grown single crystal has a diameter of 95% or more of the target controlled diameter (diameter r of the straight body portion), and the inclination with respect to the growth axis direction (vertical direction) is 5 °. With the following portion as a boundary, the diameter-upward part is above the part and the straight body part is below (FIG. 3). Note that the inclination in this case is an inclination of a tangent line when the shape of the portion of the single crystal has a curved line. Further, it is necessary that the inclination of all the peripheral portions is 5 ° or less.

  The manufacturing method of the present invention is not particularly different from a conventionally known method, except that the above-mentioned diameter expansion ratio is not more than a specific value, and a manufacturing apparatus to be used may be appropriately selected and adopted. .

  Hereinafter, the production method of the present invention will be described in more detail using the Czochralski method as a representative example.

  FIG. 4 is an example (schematic diagram) of a manufacturing apparatus used in the manufacturing method of the present invention. In the apparatus shown in FIG. 4, the crucible for melting the raw material metal fluoride is a double structure crucible composed of an outer crucible 101 and an inner crucible 102, and the wall (bottom wall and / or side wall) of the inner crucible 102 is provided. Is provided with a through-hole 103 through which the raw material metal fluoride melt 104 can flow in the inner crucible and the outer crucible through the wall. When the crystal is pulled up, the raw material melt in the crucible is reduced by an amount corresponding to the pulled crystal amount, 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.

  These crucibles, particularly the inner crucible, are particularly preferably circular in cross section in the horizontal (lateral) direction from the viewpoint of stably growing crystals.

  The outer crucible is raised and rotated by an outer crucible support shaft 105 that can move up and down and rotate.

  The crucible is heated by the heater 109. A heat insulating wall 110 is disposed between the crystal pulling furnace chamber 108 and the heater 109 so as to surround the heater 109, and more usually, the heat insulating wall is also provided below the crucible. By disposing the heat insulating wall 110, the chamber 108 is protected from the radiant heat of the heater 109, the heat is prevented from being dissipated to the outside, and the temperature around the crucible is easily maintained.

  In the illustrated embodiment, the opening at the top of the heat insulating wall 110 is covered with a ceiling plate 119 disposed so as to be in contact with the upper end of the heat insulating wall. By installing the ceiling plate 119, (1) heat dissipation in the upper direction is suppressed, the heat retention of the single crystal pulling chamber surrounded by the heat insulating wall 110 and the ceiling plate 119 is improved, and the single crystal pulling chamber is (2) Prevents radiant heat from the melt and the single crystal being pulled directly from reaching the chamber 108, and (3) Dust falls from above to the melt. Mixing can be prevented. On the other hand, in order to prevent material fluoride metal and scavenger volatilized from condensing on the bottom surface of the ceiling plate and falling into the melt during crystal growth, It is also a preferable aspect to provide a slight gap therebetween.

  The ceiling plate 119 has an insertion hole 120 through which the single crystal pulling rod 115 is inserted. Further, if necessary, a window hole 122 for observing the state of the single crystal being pulled up or the state of the melt in the crucible may be drilled. Further, the ceiling plate may be doubled for the purpose of controlling heat dissipation.

  On the central axis of the crucible, a seed crystal holder 117 that holds the seed crystal body 116 and a crystal pulling shaft 115 that supports the holder so as to move up and down and rotate are arranged.

  The metal fluoride used as a raw material is usually one obtained by removing metal impurities, oxygen (oxide) and the like as much as possible using various scavengers, and charging this purified raw material into a crucible. The refined raw material is heated to obtain a raw material melt, and it is preferable to further remove adsorbed moisture by subjecting it to a heat treatment under reduced pressure to evacuation prior to melting. More generally, the heating / melting is carried out in the presence of a scavenger to further reduce impurities such as oxygen.

As a scavenger to be used, either a solid scavenger or a gas scavenger may be used, or a plurality of types may be used in combination. Examples of solid scavengers include metal fluorides such as zinc fluoride, lead fluoride, silver fluoride, copper fluoride, and poly (perfluoroethylene). Examples of gas scavengers include CF ₄ , COF ₂ , HF, Examples include F ₂ , NF ₃ , C ₂ F _{6 and the} like. Zinc fluoride and / or CF ₄ gas is particularly preferable in consideration of handling properties, availability of high-purity products, efficiency as a scavenger, and the like.

  During the heating and melting, it is preferable to charge the raw material into the outer crucible. In this case, the outer crucible 101 is preferably pulled down and heated and melted in a semi-enclosed space formed by the outer wall of the inner crucible 002 and the closing member 107.

  After the raw material is sufficiently melted, the outer crucible 101 is raised, and the raw material melt 104 is caused to flow from the through hole 103 into the inner crucible 102. Thereafter, the seed crystal mounted on the seed crystal holder 117 at the tip of the crystal pulling shaft 115 is brought into contact with the raw material melt surface, and then gradually pulled to grow a single crystal body 118.

  In the illustrated embodiment, there is only one through hole 103 at the lower end of the inner crucible, but, for example, a large number of small holes may be drilled in the entire inner crucible like a shower head.

  The temperature at which the single crystal is pulled is determined in accordance with the target metal fluoride. For example, at the measurement temperature at the bottom of the outer crucible, in the case of calcium fluoride, 1440 ° C. or higher, preferably 1440-1520 ° C. In the case of barium fluoride, it is preferably carried out at a temperature of 1300 to 1400 ° C. Moreover, it is preferable that the temperature increase rate to this temperature is 10-500 degreeC / hour.

  The seed crystal 116 used in the pulling method is a single crystal of metal fluoride, and the growth surface of the seed crystal is the [111] plane, the [100] plane, etc., depending on the main crystal growth plane of the as-grown single crystal to be produced. A contact surface with the raw material melt may be used. The seed crystal generally has a rod-shaped portion (for example, a cylinder, a quadrangular column, etc.) to be brought into contact with the raw material melt surface, and an enlarged portion and / or a constricted portion for holding it with a holder above it. .

  After bringing the seed crystal into contact with the raw material melt surface, forming a diameter-enlarged portion by controlling the pulling speed and the like so as to achieve the diameter expansion ratio defined in the present invention, Pulling up is performed so as to maintain the crystal diameter.

  The size of the expanded diameter is determined depending on the size of the single crystal to be manufactured, but the effect of the present invention is more remarkable as the diameter of the straight body portion is larger. The production method of the present invention is effective when applied to a straight body diameter of 100 mm or more, more effective when the diameter is 150 mm or more, and particularly effective when the diameter is 200 mm or more. On the other hand, since a larger crystal tends to have various defects other than the crystal orientation, even if the manufacturing method of the present invention is applied to a crystal having a straight body diameter exceeding 500 mm, other defects cause. It is difficult to obtain a practical single crystal. Even more realistically, the diameter of the straight body portion is 300 mm or less.

  The pulling up can usually be performed at a speed of 0.1 to 20 mm / h. As described above, the raw material melt in the inner crucible 102 is consumed as the single crystal body 118 grows. By raising the outer crucible 101, the amount of the raw material melt that reaches the reduced amount is penetrated. By gradually supplying into the inner crucible through the hole 103, the position of the melt surface, that is, the crystal growth surface can be made constant.

  During the growth of the single crystal, the seed crystal 116 is preferably rotated about the pulling shaft 115, and the rotation speed is preferably 5 to 30 times / minute. In addition to the rotation of the seed crystal, the outer crucible may be rotated at the same rotational speed in the opposite direction or the same direction as the rotation direction of the seed crystal.

  The furnace pressure during the pulling of the single crystal may be any of increased pressure, normal pressure, and reduced pressure, but is preferably performed under reduced pressure. When crystal growth is performed under reduced pressure, the furnace pressure is preferably 0.5 to 70 kPa, and more preferably 5 to 50 kPa. The atmosphere may be an inert gas such as Ar or the gas scavenger atmosphere. Further, the inside of the furnace may be sealed, or Ar or a gas scavenger may be supplied little by little (while supplying into the furnace and exhausting).

  In the present invention, during the growth of the straight body portion, when the diameter of the raw material melt surface is R, r / R is in the range of 0.2 to 0.6. This is preferable in that the deviation in orientation can be further reduced. More preferably, it is 0.3-0.5. Here, the diameter of the raw material melt surface is the diameter of the uppermost surface of the raw metal fluoride in the crucible having a circular cross-sectional shape. Moreover, when using a multiple crucible as shown in FIG. 4, it is the diameter of the raw material melt surface divided by the innermost crucible (side closer to the straight body).

  As described above, if a double structure crucible as shown in FIG. 4 is employed, the position of the surface of the melt during crystal growth can be kept constant. Therefore, the inner diameter of the inner crucible 102 used and the raw material hook used. If the amount of the metal halide is set within an appropriate range, it is very easy to set the relationship with the straight body diameter r to the above range of 0.2 to 0.6.

  In this way, after pulling up the single crystal body 118 having a desired length and a straight body diameter, the temperature is lowered to a temperature at which it can be taken out from the furnace. The rate of temperature reduction is preferably 0.01 to 3 ° C./min. The faster the temperature drop rate, the shorter the time required to occupy the crystal growth furnace, and the growth productivity can be improved. However, if the rate is too high, the residual strain increases and machining may become difficult.

  After pulling up the single crystal in this manner, polishing / grinding or heat treatment can be performed as necessary to obtain final products such as lens blanks, lenses, window materials, and the like.

  Hereinafter, the present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples.

  In the following experiments, the inclination of the orientation direction of the straight body portion of the as-grown single crystal was measured by the following methods.

<Measurement of orientation orientation tilt>
About the straight body part of the as-grown single crystal body, a 6.5 cm thick cylindrical body was obtained by cutting from the upper part and the lower part. Next, the cylindrical grinding of the side surface and the grinding / polishing of the cut surface were performed to obtain a disk-like columnar body.

  The obtained disk-shaped cylindrical body was measured for the tilt angle [unit: degree (°)] from the main orientation direction using an X-ray direction measuring device. In addition, as shown in FIG. 5, the central part (measurement point 1) and the outer peripheral part (position of 90% of the diameter) of the disk-shaped cylindrical body are 6 points every 60 degrees (measurement points 2 to 7) as shown in FIG. The difference between the measurement points 2 to 7 and the measurement point 1 was defined as the inclination from the orientation direction in the disk-shaped cylindrical surface (1-2, 1-3, 1-4, 1-5, 1-6, 1-7 6 points).

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 this single crystal production pulling apparatus, the high-purity graphite outer crucible installed in the chamber had an inner diameter of 50 cm (outer diameter of 52 cm) and a height of 24 cm. The inner crucible accommodated in the outer crucible while being fixed to the lid material 113 by the lifting tool 114 has an inner diameter of 44 cm (outer diameter of 45.2 cm) and a height of 25 cm, and the angle of the inclined wall 102 with respect to the horizontal plane is It was 30 degrees.

  The inner crucible has one cylindrical through-hole 103 with a diameter of 6 mm at the center, and is equally spaced circumferentially at positions 18.4 cm and 20.4 cm away from the center along the inclined wall surface. In each case, 60 cylindrical through holes each having a diameter of 0.8 mm were formed.

The heat insulating material wall is a pitch-based graphite molded heat insulating material, and the heat dissipation capacity in the thickness direction is 9 W / m ² · K, while the ceiling plate is made of graphite, and the heat dissipation capacity in the thickness direction is 500 W / m. ^{It was 2} · K.

After the furnace is fully baked in the presence of zinc fluoride, 70 kg of raw material calcium fluoride mass and 10 g of zinc fluoride as a scavenger are formed in the space formed by the outer wall of the inner crucible, the inner wall of the outer crucible and the shielding member. And evacuation was started. When the internal pressure reached 5 × 10 ⁻³ Pa or less, the heater was energized while evacuation was continued to start heating the raw material. 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 30 kPa (abs) and the pulling was completed and the temperature was lowered to around room temperature.

  After returning to 30 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 and a part of the molten liquid is caused to flow into the inner space of the inner crucible through the through-hole 103, and the molten liquid of the calcium fluoride raw material is also stored in the inner crucible. did. At this time, the diameter R of the raw material melt in the inner crucible was adjusted to 44 cm.

  After the temperature of the melt is lowered until the temperature of the raw material melt becomes substantially equal to the melt temperature of calcium fluoride, the seed crystal rotated at a speed of 7 rpm is brought into contact with the melt surface, and the shoulder is 2 mm / H, the straight body part was grown at a pulling rate of 4 mm / Hr. At this time, the shoulder length h was adjusted to 5.1 cm, and the diameter r of the straight body portion was adjusted to 22.5 cm (h / r = 0.23, r / R = 0.5). During the above pulling, the outer crucible support shaft 105 was continuously raised so that the depth of the melt in the inner crucible was maintained at 10 cm. After the completion of the pulling, the crystal was separated from the melt and cooled to room temperature.

  As a result of the above operation, an as-grown single crystal of calcium fluoride having a diameter r of the straight body portion of 22.5 cm and a length of the straight body portion of 25 cm (a volume of the straight body portion of 10380 cm 3 and a weight of the straight body portion of 32.9 kg) is obtained. It was. The shape of the bottom was a symmetric shape with a downward projection.

  With respect to this single crystal, a disk-shaped cylinder having a thickness of 6.5 cm was obtained from the top and bottom of the straight body portion, and the inclination [°] from the orientation direction on the surface of the disk-shaped cylinder was measured. The results are shown in Table 1 below.

Examples 2 and 3
In the pulling apparatus for producing a single crystal used in Example 1, the calcium fluoride single crystal was pulled twice further under the same conditions as in Example 1 to obtain a single crystal.

  With respect to this single crystal, a disk-shaped cylinder having a thickness of 6.5 cm was obtained from the top and bottom of the straight body portion, and the inclination [°] from the orientation direction on the surface of the disk-shaped cylinder was measured. The results are shown in Table 2 below.

Example 4
Example 1 is the same as Example 1 except that the diameter-increased part is formed so that the shoulder length h is 3.7 cm (h / r = 0.16) using the single crystal production pulling apparatus used in Example 1. Similarly, the calcium fluoride single crystal was pulled up to obtain a single crystal.

  With respect to this single crystal, a disk-shaped cylinder having a thickness of 6.5 cm was obtained from the top and bottom of the straight body portion, and the inclination [°] from the orientation direction on the surface of the disk-shaped cylinder was measured. The results are shown in Table 3 below.

Examples 5, 6, and 7
Using the single crystal production pulling apparatus used in Example 1, the calcium fluoride single crystal was pulled three times in the same manner as in Example 1 to obtain a single crystal. However, the inner crucible having an inner diameter of 32 cm (outer diameter of 33.2 cm) and a height of 13 cm is used.
Thus, the crystal growth was performed by adjusting the melt surface height so that the diameter R of the raw material melt surface in the inner crucible was maintained at 32 cm (r / R = 0.7).

  With respect to this single crystal, a disk-shaped cylinder having a thickness of 6.5 cm was obtained from the top and bottom of the straight body portion, and the inclination [°] from the orientation direction on the surface of the disk-shaped cylinder was measured. The results are shown in Table 4 below.

Example 8
In the single crystal manufacturing pulling apparatus used in Example 1, the shoulder length h is 4.1 cm, and the diameter r of the straight body portion is 12.5 cm (h / r = 0.33, r / R = 0.3). ) Except that the calcium fluoride single crystal was pulled up in the same manner as in Example 1 to obtain a single crystal.
With respect to this single crystal, a disk-shaped cylinder having a thickness of 6.5 cm was obtained from the top and bottom of the straight body portion, and the inclination [°] from the orientation direction on the surface of the disk-shaped cylinder was measured. The results are shown in Table 5 below.

Comparative Examples 1 and 2
In the pulling apparatus for producing a single crystal used in Example 1, an enlarged diameter portion is formed so that the shoulder length h is 10.2 cm, and the diameter of the straight body portion is 22.5 cm. Raising was performed (h / r = 0.45). However, as in Examples 5 to 7, the inner crucible had an inner diameter of 32 cm (outer diameter of 33.2 cm) and a height of 13 cm.
Thus, crystal growth was performed by adjusting the melt surface height so that the diameter R of the raw material melt surface in the inner crucible was maintained at 32 cm (r / R = 0.7).

  With respect to the obtained single crystal, a disk-like cylinder having a thickness of 6.5 cm was obtained from the top and bottom of the straight body part, and the inclination [°] from the orientation direction on the disk-like cylinder surface was measured. The results are shown in the table below.

DESCRIPTION OF SYMBOLS 101: Outer crucible 102: Inner crucible 103: Through-hole of inner crucible wall 104: Raw material melt 105: Outer crucible support shaft 106: Receptacle 107: Opening block member 108: Chamber 109: Melting heater 110: Insulating wall 111: Isolation Wall 112: Lid material 113: Connecting member 114: Inner crucible hanging rod 115: Crystal pulling shaft 116: Seed crystal 117: Seed crystal holder 118: Single crystal 119: Ceiling plate 120: Crystal pulling shaft insertion hole 121: Peep Window 122: Window hole

Claims (2)

A seed crystal is brought into contact with the raw material melt surface in the crucible from above, and a crystal having the same crystal orientation as the seed crystal is grown, so that the diameter of the rod-shaped portion derived from the seed crystal is larger than that of the rod-shaped portion. In a method for producing a metal fluoride single crystal having a large cylindrical straight body portion and a single crystal body having a rod-shaped portion and a diameter-expanding portion connecting the straight body portion,
A diameter-expanded portion is formed so that a ratio h / r of a height h of the diameter-expanded portion and a diameter r of the straight body portion is 0.35 or less. Method.   When the cross-sectional shape of the crucible is circular and the diameter of the raw material melt surface in the crucible is R, r / R is in the range of 0.2 to 0.6 during the formation of the straight body part. The manufacturing method of the metal fluoride single crystal of Claim 1 which forms a straight body part.

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