JP4738966B2 - Floating zone melting device - Google Patents

Description

  In the present invention, an infrared lamp is provided at one focal point of a spheroid reflecting mirror, and a sample is heated by concentrating infrared rays reflected from the reflecting surface of the spheroid reflecting mirror on the other focal point. The present invention relates to a floating zone melting apparatus.

Infrared central heating type floating zone melting equipment
(I) The sample can be melted without using a crucible (ii) The atmosphere gas can be selected arbitrarily (iii) Single crystal growth of various compositions can be performed using the floating zone method (iv) The floating zone Being able to conduct phase equilibrium studies by slow cooling (v) Has the advantage of being able to easily obtain high temperatures with relatively little power, and is widely used for single crystal growth and phase equilibrium studies.

  In order to use the floating zone melting apparatus for single crystal growth, a high temperature is obtained in the melting part of the sample, the temperature in the circumferential direction around the rod axis of the sample is uniform, and the vertical direction (of the sample Conditions such as a steep temperature distribution (in the rod axis direction), easy local heating, and the ability to easily hold the melt on the sample rod are required. Conventionally, in order to achieve such conditions, various types of infrared central heating type floating zone melting apparatuses have been developed.

  FIG. 6A is a diagram for explaining a conventional infrared concentrated heating type floating zone melting apparatus using a single elliptical mirror furnace, in which a round bar-shaped sample bar 4 a is heated in the single elliptical mirror furnace 11. Show. In this floating zone melting apparatus, one elliptical mirror 2 is used, and an infrared lamp 3 such as a halogen lamp or a xenon lamp is installed at one of the two focal positions. Here, the elliptical mirror 2 is a metal mirror. Infrared rays from the infrared lamp 3 emitted from one focal position are reflected by the elliptical mirror 2 and collected at the other focal position. The sample bar 4a is heated at the focal position where the infrared rays are collected, and a melt is formed. By gradually moving the sample rod 4a and the infrared lamp 3 relatively in the axial direction, the grown crystal 4b is grown in a rod shape.

  In the method using the single elliptical mirror furnace 11, the light use efficiency of the infrared lamp 3 is the highest. However, in this method, the temperature of the region on the opposite side of the sample lamp 4a from the infrared lamp 3 is difficult to rise, and the temperature of the region 5 on the infrared lamp 3 side becomes relatively high, as shown in FIG. (7 represents an isotherm, 8 represents an equidistant line from the central axis of the sample rod 4a), and a temperature distribution is generated in the circumferential direction around the rod axis on the horizontal plane of the molten portion of the sample rod 4a.

  In order to improve the uneven temperature distribution, an apparatus using the double elliptical mirror furnace 21 shown in FIG. 7A has been developed. In this floating zone melting apparatus, a pair of elliptical mirrors 2 obtained by cutting a part of an ellipse are arranged in a straight line in the lateral direction so as to share one focal position with each other, and the other focal position of these elliptical mirrors 2 is arranged. The sample rod 4a is heated from both sides by a pair of infrared lamps 3 arranged in a quantity.

  In the method using the double elliptical mirror furnace 21, the sample rod 4a can be heated from both sides in the lateral direction, so that the temperature distribution in the circumferential direction is improved as compared with the single elliptical mirror furnace. However, a temperature distribution occurs in the circumferential direction of the sample bar 4a as shown in FIG. 7B, and the temperature in the vertical direction is lower than the direction in which the pair of lamps 3 are installed.

The actual temperature difference in the circumferential direction depends on the size, shape, etc. of the filament of the infrared lamp 3 to be used. In many cases, it is about 100 ° C or exceeds 100 ° C.

  An example of the temperature distribution in the circumferential direction of the melted part in the single elliptical furnace and the double elliptical furnace is shown in FIG. As shown in this example, the temperature difference between the maximum temperature portion and the minimum temperature portion reaches 10% of the maximum temperature value. It is difficult to grow a high-quality single crystal under conditions where such a temperature distribution occurs.

In order to further improve the bias of this temperature distribution, two more elliptical mirrors are added from the double elliptical mirror furnace, and four elliptical mirrors sharing one focal position with each other are arranged on the orthogonal axis. A four-elliptic mirror type device that can heat a sample rod has been developed (Patent Document 1).
JP-A-9-235171

  By using the four ellipsoidal mirrors and heating the sample rod from all sides, the temperature distribution in the circumferential direction was greatly improved. However, in the growth of single crystals, the temperature distribution in the circumferential direction is uniform, the temperature gradient in the vertical direction is steep and the maximum temperature reached is sufficiently high as described above. Although required, a conventional four-elliptic mirror type device has not been obtained that satisfies all these conditions.

  In the past, metal mirrors made by machining were used as elliptical mirrors, but the maximum temperature reached would be reduced if the temperature distribution in the circumferential direction of the sample rod and the temperature gradient in the vertical direction were considered. There was a problem that.

  The present invention has a small temperature gradient in the circumferential direction of the sample in the melting part, a steep temperature gradient in the vertical direction, and a sufficiently high maximum temperature can be obtained, so that a stable molten state can be formed. An object of the present invention is to provide an infrared concentrated heating type floating zone melting apparatus.

The floating zone melting apparatus of the present invention is provided with an infrared lamp at one focal point of four spheroid reflecting mirrors arranged opposite to each other on an orthogonal axis with the inner surface as a reflecting surface, and the infrared rays reflected from the reflecting surface are reflected on the other side. Infrared concentration heating type floating zone melting device that heats a sample by focusing it on a focal point,
The spheroid reflecting mirror has an eccentricity of 0.40 to 0.65, and a ratio of a depth of the reflecting mirror to an opening diameter is 0.38 to 0.75.

Where the above eccentricity is given by:
(A ² -b ² ) ^1/2 / a
(Here, a indicates the length of the ellipse major axis, and b indicates the length of the minor axis.)
Defined by

  Thus, by setting the ratio of the eccentricity of the ellipsoidal mirror and the depth of the reflecting mirror to the opening diameter to be within a predetermined range, the temperature gradient in the circumferential direction of the sample in the melting portion is small and the temperature gradient in the vertical direction is small. It becomes steep and a high maximum temperature is obtained.

The floating zone melting apparatus of the present invention is characterized in that the spheroidal reflecting mirror is a glass mirror.
By configuring the spheroid reflecting mirror with a glass mirror, the temperature gradient in the circumferential direction of the sample in the melting part is small, the temperature gradient in the vertical direction is steep, and a higher maximum temperature is obtained.

  In the floating zone melting apparatus of the present invention, the spheroid reflecting mirror is disposed so that a straight line from the one focus to the other focus is inclined downward, and infrared rays reflected by the reflection surface are obliquely upward. It is characterized by irradiating the sample.

By doing in this way, it is suppressed that the shape of the solid-liquid interface by the side of a crystal becomes convex. Therefore, a single crystal having a larger diameter can be grown.
The floating zone melting apparatus of the present invention includes a position adjusting mechanism that horizontally moves the spheroid reflecting mirror in a radial direction around a position where the sample is arranged.

  By providing a mechanism that can adjust the position of the ellipsoidal reflecting mirror in this way, the focal position can be easily placed at the optimum position according to the diameter of the single crystal, and the optimum according to the diameter of the single crystal. Stable growth can be performed in a simple optical arrangement.

  According to the floating zone melting apparatus of the present invention, the temperature gradient in the circumferential direction of the sample in the melting part is small, the temperature gradient in the vertical direction is steep, and a sufficiently high maximum temperature can be obtained, which is stable. A molten state can be formed.

  Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a view showing an elliptic mirror furnace of a floating zone melting apparatus according to an embodiment of the present invention, in which FIG. 1 (a) is a longitudinal sectional view and FIG. 1 (b) is a transverse sectional view. As shown in the figure, in this elliptical mirror furnace 1, four rotating ellipsoidal reflecting mirrors (elliptical mirror 2) are arranged on the orthogonal axis so as to surround the sample rod 4a. These four elliptical mirrors 2 share the focal point with each other at the center position where the sample rod 4a is located.

  The filament of the infrared lamp 3 is disposed at the focal position on the opposite side of the condensing side of each elliptical mirror 2, and the infrared rays emitted from this filament are reflected by the elliptical mirror 2 and collected at the other focal point. The sample bar 4a is heated.

  As shown in FIG. 2, the four elliptical mirrors 2 have a cross section in the major axis direction in which a part of the ellipse is cut perpendicularly from the light collecting side. It is circular. A circular opening 10 is formed at the condensing side end of the elliptical mirror 2.

  The eccentricity of the elliptical mirror 2 is 0.40 to 0.65, and the ratio L / D of the depth L of the elliptical mirror 2 to the diameter D of the opening 11 is 0.38 to 0.75. By setting the shape of the elliptical mirror 2 within this range, the temperature gradient in the vertical direction of the sample rod 4a becomes steep and a high maximum temperature can be obtained, so that a stable molten state can be formed. When the eccentricity is less than 0.40, or when L / D is less than 0.38, the maximum temperature is lowered, and when the eccentricity exceeds 0.65, or L / D is 0.1. When it exceeds 75, the temperature gradient in the vertical direction of the sample bar 4a becomes gentle, which adversely affects the growth of the single crystal and, in some cases, the molten liquid falls.

  For example, in the elliptical mirror 2a having a large eccentricity as shown in FIG. 9A, the use efficiency of the infrared rays emitted from the infrared lamp 3 can be maintained high, but the size of the focus unit 9 increases and the vertical temperature gradient is increased. Be gentle.

On the other hand, in the elliptical mirror 2b having a small eccentricity as shown in FIG. 9B, the size of the focus unit 9 can be reduced, but this overlapping portion is cut so that adjacent elliptical mirrors do not overlap each other. Since it is necessary to arrange four elliptical mirrors using this, the light utilization efficiency is lowered by the amount of cutting the ellipse, and the maximum temperature reached in the region where a stable molten state is to be formed is lowered.

  In addition, by arranging the four elliptical mirrors 2 on the orthogonal axis, the temperature deviation in the circumferential direction of the sample rod 4a is very small as shown in FIG. However, the temperature difference in the circumferential direction can be about 30 ° C. or less, for example.

  In this embodiment, glass mirrors are used for the four elliptical mirrors 2. The glass mirror has a high reflection efficiency with respect to infrared rays, and efficiently reflects infrared rays from the infrared lamp 3 such as a halogen lamp or a xenon lamp, and a high maximum temperature is obtained.

  Specifically, the elliptical mirror 2 made of a glass mirror is manufactured by covering a previously prepared ceramic mold with a glass plate softened by heating, and then cooling it and then removing the glass mirror from the mold. .

  Any glass material can be used as a material for forming the glass mirror, but Pyrex (registered trademark) glass, which is easy to process and stable in price, is usually used. It is preferable to deposit aluminum, gold or the like having excellent infrared reflectivity on the inner surface of the glass mirror, and to deposit high hardness silicon oxide or the like on the outermost surface. By depositing aluminum, gold or the like on the inner surface, infrared absorption into the glass material is reduced, and the temperature rise of the glass mirror is reduced, so that cooling is facilitated. The outer surface of the glass mirror is preferably covered with a thin aluminum plate or the like in order to improve handling and shock absorption.

  The growth of the single crystal by the elliptical mirror furnace 1 is performed as follows, for example. A sample chamber made of a quartz tube is formed in the elliptical mirror furnace 1, and the sample rod 4a is accommodated in the quartz tube. The quartz tube can be evacuated or an atmospheric gas can be circulated.

  The sample rod 4a is installed in the vertical direction in the quartz tube so as to pass through the focal position on the condensing side, and the upper end side thereof is supported by the shaft-shaped sample rod support portion. On the other hand, the lower end side of the seed crystal for growing the grown crystal is supported by the shaft-shaped grown crystal support portion. Each of these support portions can be moved in the vertical direction and rotated around the rod axis by a drive device via a drive portion attached to them. The elliptical mirror furnace 1, the support portions, the drive portions, the sample chamber, and the like are housed in the storage body, and the operator performs various operations such as moving the sample rod and adjusting the lamp voltage using a separate control panel. . A CCD camera for imaging the melting area is installed in the storage body, and an operator controls the voltage applied to the infrared lamp 3 while observing the melting area. The infrared lamp 3 and the elliptical mirror 2 are cooled by, for example, air cooling using a fan or the like.

  At the start of single crystal growth, the tip of the sample rod 4a supported by the sample rod support is opposed to the tip of the seed crystal supported by the growth crystal support, and a quartz tube is disposed, and then an infrared lamp 3 is turned on, the voltage applied to the infrared lamp 3 is gradually increased while rotating the sample rod and the seed crystal, and the tip portions thereof are melted. At the stage where both tip portions are melted, the two portions are brought close to each other and the melted portions are united. At this time, the sample bar 4a and the seed crystal are both rotated, and the voltage applied to the infrared lamp 3 is controlled to adjust the size of the melting part and form a stable melting region.

  After the stable melting zone is formed, the sample rod 4a and the seed crystal are moved downward at the same speed by the above driving device (for example, 0.1 to 100 mm / h), thereby melting the sample and growing the crystal. Continuously, rod-shaped single crystals are grown.

  The example of the method for growing a single crystal using the elliptical mirror furnace 1 and the apparatus configuration therefor have been described above. However, the present invention is not limited to this, and various modifications can be made. For example, the single crystal may be grown by moving the infrared lamp 3 and the elliptical mirror 2 relative to the sample bar 4a in the vertical direction.

  4A and 4B are diagrams showing an elliptic mirror furnace of a floating zone melting apparatus according to another embodiment of the present invention. FIG. 4A is a longitudinal sectional view, and FIG. 4B is a transverse sectional view. The floating zone melting apparatus of the present embodiment has a configuration suitable for growing a large-diameter single crystal, and each of the four elliptical mirrors 2 is disposed so as to be inclined downward.

  Thereby, the infrared rays reflected by the reflecting surface of the elliptical mirror 2 are irradiated obliquely from above to the melting portion 4c of the sample. By doing so, even when the diameter of the single crystal is large, the shape of the solid-liquid interface between the grown crystal 4b and the melted part 4c becomes stable, and a high-quality single crystal is obtained. On the other hand, as shown in FIG. 1, the four elliptical mirrors 2 are arranged so that the axis of the elliptical mirror 2 is oriented in the horizontal direction, and the infrared rays reflected by the reflecting surface of the elliptical mirror 2 are horizontally horizontal. When irradiating 4c, when the diameter of the single crystal is large, the shape of the solid-liquid interface between the grown crystal 4b and the melted part 4c may become too convex. Thus, when the shape of the solid-liquid interface becomes too convex, it becomes difficult to stably grow the single crystal.

  According to the floating zone melting apparatus of the present embodiment, a large-diameter single crystal having a diameter of 25 to 45 mm can be stably grown. In order to stably grow such a large-diameter single crystal, it is preferable to set the angle θ with respect to the horizontal direction of the straight line from one focal point of the elliptical mirror 2 to the other focal point to 25 to 35 degrees.

  Furthermore, in the present embodiment, a position adjusting mechanism 5 that horizontally moves the elliptical mirror 2 in the radial direction with the sample rod 4a as the central axis is provided. The position adjusting mechanism 5 can be composed of, for example, a moving member attached to the elliptical mirror 2 and a guide member that guides the moving member in the radial direction and can be fixed at a desired position.

  Such a position adjusting mechanism 5 adjusts the position of the elliptical mirror 2 in the radial direction and arranges the focal position at an optimum position according to the diameter of the single crystal. Thereby, stable growth can be performed in an optimal optical arrangement according to the diameter of the single crystal.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
[Example 1]
Four spheroid reflecting mirrors made of quartz glass are installed on the orthogonal axis so that one focal point position is shared with each other, and a halogen lamp is installed at the other focal point of each spheroid reflecting mirror. A mirror furnace was constructed. The four spheroidal reflecting mirrors had an eccentricity of 0.55, an opening diameter of 220 mm, and a ratio of the depth of the reflecting mirror to the opening diameter was 0.6. As the halogen lamp, a lamp with an output of 1000 W having a filament shape of a double helix structure was used.

  The sintered sample rod is supported from above by the sample rod support so that the sample rod is arranged vertically in the center of the elliptical mirror furnace, and the seed crystal is supported by the growth crystal support from below. The tip and the tip of the seed crystal were made to face each other.

After installing the quartz tube around the elliptical mirror furnace, the halogen lamp was turned on, the voltage applied to the halogen lamp was gradually increased while rotating the sample rod and the seed crystal, and each of these tips was melted. . At the stage where both tips were melted, the two were brought close together to merge the melted parts.
After the stable melt was formed, melting of the sample and growth of the crystal were continued while slowly moving the sample rod and the seed crystal downward at a constant speed to grow a rod-shaped single crystal. The melt could be easily held and stable crystal growth was possible.

  FIG. 5 shows the temperature distribution in the vertical direction (bar axis direction) in the melting part. In this example, the temperature distribution became curve B in the figure, and the maximum temperature reached about 1000 ° C., and the temperature rapidly decreased from the maximum temperature position toward the rod axis. Further, the difference between the maximum temperature and the minimum temperature in the circumferential direction of the melted portion was 30 ° C. or less.

The temperature distribution in the vertical direction was measured using various quartz glass ellipsoidal mirrors in which the ratio of the reflector depth to the opening diameter was changed, but when this ratio was 0.38 to 0.75, the same applies. A high maximum temperature was maintained and the vertical temperature gradient was steep.
[Comparative Example 1]
An elliptical furnace was constructed under the same conditions as in Example 1 except that four spheroidal reflecting mirrors having an eccentricity of 0.35 and a ratio of the reflecting mirror depth to the opening diameter of 0.8 were used. Then, an attempt was made to melt the sintered sample rod having a diameter of 10 mm to hold the melt, but the melt immediately dropped and a stable melt could not be formed.

FIG. 5 shows the temperature distribution in the vertical direction (bar axis direction) in the melting part. In this comparative example, the temperature distribution is the curve C in the figure, and the highest temperature reached as high as about 1000 ° C., but the temperature at a position away from the highest temperature position in the vertical direction is also high, and the temperature gradient is It became moderate.
[Comparative Example 2]
An elliptical furnace was constructed under the same conditions as in Example 1 except that four spheroidal reflecting mirrors having an eccentricity ratio of 0.8 and a ratio of the reflecting mirror depth to the opening diameter of 0.3 were used. However, although the single crystal was grown, the temperature in the melting part was low, and a stable melt could not be obtained, and a high quality single crystal could not be obtained.

FIG. 5 shows the temperature distribution in the vertical direction (bar axis direction) in the melting part. In this comparative example, the temperature distribution was the curve A in the figure, and the maximum temperature reached was greatly reduced.
[Example 2]
In the apparatus of Example 1, four spheroid reflectors were arranged so as to be inclined downward as shown in FIG. The angle θ with respect to the horizontal direction of the straight line from one focal point of the spheroid reflecting mirror to the other focal point is set to 30 degrees, and infrared rays reflected from the reflecting surface of the spheroid reflecting mirror are irradiated obliquely from above to the melting portion of the sample. did.

  A sintered sample rod having a diameter of 25 mm is supported from above by a sample rod support portion so that the sample rod is arranged in the vertical direction in the center of the elliptical mirror furnace, and a seed crystal is supported from below on the grown crystal support portion, A melt was formed in the same manner as in Example 1. While the elliptical mirror furnace was slowly raised at a constant speed, the sintered sample rod was moved slowly downward at a constant speed to continue the sample melting and crystal growth, and the shape of the solid-liquid interface between the grown crystal and the molten part Therefore, a single crystal having a diameter of 40 mm could be stably grown.

FIG. 1 is a view showing an elliptic mirror furnace of a floating zone melting apparatus according to an embodiment of the present invention, in which FIG. 1 (a) is a longitudinal sectional view and FIG. 1 (b) is a transverse sectional view. FIG. 2 is a sectional view showing a spheroidal reflecting mirror of the elliptical mirror furnace of FIG. It is the figure which showed the temperature distribution of the circumferential direction of the fusion | melting part at the time of using the elliptical mirror furnace of FIG. 3, FIG. 4A and 4B are diagrams showing an elliptic mirror furnace of a floating zone melting apparatus according to another embodiment of the present invention. FIG. 4A is a longitudinal sectional view, and FIG. 4B is a transverse sectional view. FIG. 5 is a graph showing the temperature distribution in the vertical direction when the ratio between the depth of the reflecting mirror and the opening diameter of the reflecting mirror is changed. FIG. 6A is a diagram for explaining a conventional infrared concentrated heating type floating zone melting apparatus using a single elliptical mirror furnace, and shows a state in which a sample rod is heated in the single elliptical mirror furnace. FIG. 6B is a diagram showing the temperature distribution in the circumferential direction of the melted part when this apparatus is used. FIG. 7A is a view for explaining a conventional infrared concentrated heating type floating zone melting apparatus using a double elliptical mirror furnace, and shows a state in which a sample rod is heated in the double elliptical mirror furnace. FIG.7 (b) is the figure which showed the temperature distribution in the circumferential direction of the fusion | melting part at the time of using this apparatus. FIG. 8 is a graph showing the temperature distribution in the circumferential direction of the fusion zone in the single and double elliptical furnaces. FIG. 9 is a diagram for explaining the relationship between the eccentricity and the focus size.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ellipsoidal mirror furnace 2 Elliptical mirror 2a Elliptical mirror 2b Elliptical mirror 3 Infrared lamp 4a Sample rod 4b Growth crystal 4c Melting part 5 Position adjustment mechanism 6 High temperature area 7 Isothermal line 8 Equidistant line from focus center 9 Focusing part 10 Opening part 11 Single elliptical mirror furnace 12 Elliptical mirror 21 Double elliptical mirror furnace

Claims (3)

An infrared lamp is provided at one focal point of four spheroid reflecting mirrors arranged opposite to each other on the orthogonal axis with the inner surface as a reflecting surface, and the sample reflected by the infrared ray reflected from the reflecting surface is collected at the other focal point. An infrared concentration heating type floating zone melting device for heating,
The spheroid reflecting mirror has an eccentricity of 0.40 to 0.65, and a ratio of a depth of the reflecting mirror to an opening diameter is 0.38 to 0.75 ,
The spheroid reflecting mirror is arranged such that a straight line from the one focal point to the other focal point is inclined downward by 25 to 35 degrees with respect to the horizontal direction, and the infrared ray reflected by the reflecting surface is obliquely upward A floating zone melting apparatus characterized by irradiating a sample from   The floating zone melting apparatus according to claim 1, wherein the spheroidal reflecting mirror is a glass mirror. The floating zone melting apparatus according to claim 1 , further comprising a position adjusting mechanism that horizontally moves the spheroid reflecting mirror in a radial direction around a position where the sample is arranged.

Images