JP2001192290A - Device for growing single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize the distribution of electric power density in the circumferential direction of a melt zone and to obtain a steep curve in the distribution of the electric power density in the axial direction by making the width of a flat part of a peak narrow and increasing the height of the flat part, in a device for growing a single crystal by a FZ method. SOLUTION: Four spheroidal mirrors 5b having an eccentricity (e) of >0.65 and <0.80 are arranged in counter positions on the orthogonal axes. Thereby, the uniform distribution of electric power density in the circumferential direction of the melt zone can be obtained, and in the distribution of the electric power density in the axial direction, the capture rate of the light of a halogen lamp 7 is increased and the value of a peak becomes high and the width of flat part of the peak becomes narrow. Accordingly, the steep curve is obtained. At the same time, as the eccentricity of the spheroidal mirrors 5b is higher than that of the conventional device, it becomes possible to suppress the height of the device to be lower than that of the conventional device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal growing apparatus for growing a single crystal of a high melting point material by a central heating type floating zone method.

[0002]

2. Description of the Related Art A single crystal growing apparatus of the floating zone method (hereinafter referred to as FZ method) holds a raw material rod vertically at one end, and heats and melts a joint between the raw material rod and a seed crystal to form a molten zone ( A floating zone is formed, and the raw material rods are melted and solidified one by one to form a single crystal. Compared to other single crystal growth methods such as the Bridgman method and the Czochralski method in a so-called crucible, the method is not suitable for growing large-diameter single crystals, but impurities are mixed from the crucible. Can be avoided, and a high-purity single crystal can be obtained.

As the heating source, high-frequency heating, lamp heating or the like is used. In the case of lamp heating, these lamps are placed in a spheroidal mirror, and light emitted from the lamps is condensed by the spheroidal mirror to form a molten zone.

A spheroidal mirror having one form of a spheroidal mirror and a spheroidal mirror having two forms are often used. Here, the outline will be described using a single crystal growing apparatus using a bi-ellipsoidal mirror shown in FIG. FIG. 5 is a front view, partially shown in section.

The transparent quartz tube 1 is hermetically sealed on both upper and lower sides with support flanges 2a and 2b, respectively, and both support flanges are fixed to a gantry 3. A rotating bi-ellipsoidal mirror 5 is fixed to the gantry 3 around the transparent quartz tube 1, and halogen lamps 7 and 7 are disposed at one focal point of the rotating bi-ellipsoidal mirror 5, and a halogen lamp Light emitted from 7, 7 is reflected by the rotating ellipsoidal mirror 5 and condensed on the object to be heated placed at the other common focal point. The raw material rod 8 is hung on the upper main shaft 9, and the crystal rod 10 is fixed to the lower main shaft 11. The upper spindle 9 penetrates the main shaft seal flange 12a fixed to the gantry 3, while the lower main spindle 11 also penetrates the main shaft seal flange 12b fixed to the gantry 3. 15 is kept airtight with the outside air.
Although not shown, the upper main shaft 9 and the lower main shaft 11 are connected to a mechanism that can rotate and move up and down, respectively, and both main shafts can rotate and move up and down.

Further, valves V1 and V2 are connected to the support flange 2a of the quartz tube 1, and a valve V3 is connected to the support flange 2b. Here, V1 is connected to an exhaust system, V2 is connected to a gas flow system, and V3 is connected to a gas supply system.

Hereinafter, an example of an operation procedure for growing a single crystal will be introduced. While V2 and V3 are closed, V1 is opened, the inside of the sample chamber 15 is evacuated, and oxygen and active gas in the air are once removed, and then V1 is closed. Next, V3 is opened to introduce a predetermined gas such as an inert gas into the sample chamber 15, and at the same time, V2 is opened to perform a gas flow. The gas pressure or the gas flow rate in the sample chamber 15 is adjusted to a predetermined value according to the degree of opening and closing of V2 and V3. Then, the halogen lamp 7,
7, the tip of the raw material rod 8 is heated while rotating the raw material rod 8. When the tip melts, the raw material rod 8 and crystal rod 1
0 is approached, and the two are joined to form a molten zone.
Subsequently, when the raw material rod 8 and the crystal rod 10 are slowly pulled down in this state, a single crystal is formed.

[0008]

However, the conventional single crystal growing apparatus has the following problems. It concerns the power density distribution of the light energy focused on the melting zone. This will be described with reference to FIG. 6 which is an enlarged view of the fusion zone. When the power density is referred to, a method of considering the power collected around the diameter φd (φd is equivalent to the diameter of the raw material rod 8) in a circumferential direction and an axial direction (axial direction of the raw material rod 8). There is. Here, the components are equally divided in each direction, the power densities condensed on the divided fine mesh portions are obtained by simulation, and these are connected to form a power density distribution (curve) in the circumferential direction and the axial direction. Seeking. In the circumferential direction, the light energy to be condensed on each part obtained by dividing the entire circumference of φd having a width of 1 mm in the vertical direction from the focus position to the center is obtained. In addition, the axial direction was sliced in units of 1 mm in the vertical direction,
We are looking for the light energy to be focused around.

FIG. 7 shows the power density distribution of the currently used spheroid mirror, which is most frequently used, obtained by this simulation. Here, the simulation is performed on the assumption that the lamp is a halogen lamp having an output of 1500 W made of the most common cylindrical filament, and the sample diameter (corresponding to the diameter of the raw material rod) is 4 mm. As a result, with respect to the circumferential direction, the arrangement of the lamps is depicted in the drawing, but there is a peak value in the direction in which the lamps are arranged, and the two directions show an elliptical shape protruding. On the other hand, in the axial direction, the front view of the sample is depicted on the right side of the graph in comparison with the front view of the sample so that it can be easily compared with the position of the molten zone.
According to this, the flat width of the peak portion is about 4 mm centering on the in-focus position, and the upper and lower sides have a sharply falling curve.

In growing a single crystal, a molten zone is formed, and the raw material rod and the crystal rod are rotated at an appropriate temperature equal to or higher than the melting temperature (generally, reverse rotation of 20 to 30 rpm). Although the crystal has been grown, the nonuniformity of the power density in the circumferential direction as in the above-described simulation data of the rotating ellipsoidal mirror leaves room for improvement in consideration of the quality of the obtained crystal. That is, in order to further improve the quality of the single crystal, it is necessary to make the power density distribution in the circumferential direction as uniform as possible (a shape close to a circle).

At the same time, when looking at the power density distribution in the axial direction, the flat width of the peak portion relates to the formation of the molten zone and its stable maintenance. According to FIG. 6, when the length h of the molten zone becomes longer than the diameter φd of the raw material rod,
This is because the molten zone cannot withstand its own weight and drips around. (This situation is shown in FIG. 8.) From this viewpoint, the ratio between the h dimension and the d dimension is generally considered as follows. First, h / d is set to 1.3.
It is desirable to keep it below. If this exceeds 1.8, the formation of a molten zone becomes almost impossible. In addition, 1.
The ratio between 3 and 1.8 is an area that should be avoided as much as possible.

Another problem is as follows. Sintered material is used for the raw material rod, which has many pores, and when the raw material rod is heated widely, the capillary phenomenon is promoted, and the melt penetrates into the raw material rod side through the fine holes, A stable FZ cannot be formed and maintained. To prevent that,
It is necessary to keep the axial heating area within the solid-liquid interface. For this reason, in the power density curve in the axial direction, the flat width of the peak portion must be narrowed and the curve must be steep.

As described above, with respect to the power density distributions in the circumferential direction and the axial direction, the simulation results of the rotating ellipsoidal mirror will be summarized while referring to FIG. 7 again. First, in the axial direction, the flat width of the peak portion is 4 mm, which is smaller than the upper limit value h = 5.2 mm of the ideal melting zone length where h / d is 1.3 or less, and the electric power. Since the density curve is also steep, it can be said that there is no problem. However, in the circumferential direction, the power density distribution lacks uniformity, and there is room for improvement.

Therefore, as one of the solutions, a single crystal growing apparatus using a rotating ellipsoidal mirror has been proposed. FIG.
Are a plan view and a front view illustrating main parts inside the spheroid mirror 5a in the single crystal growing apparatus.
This device has a spheroid mirror 5a having an eccentricity e of about 0.44.
Are arranged facing each other on the orthogonal axis. The eccentricity e = (a ² −b ² ) ^1/2 / a, where dimension a = the length of the major axis of the ellipse, and dimension b = the length of the minor axis of the ellipse. Note that this eccentricity is equivalent to the eccentricity of the spheroid mirror 5 described above with reference to FIG.
As in the so-called bowl, the depth is not so deep, and is a generally adopted shape.

FIG. 10 is a graph showing a result of simulating the power density distribution of this device. The conditions for the lamp and the sample diameter are the same as those for the rotating ellipsoidal mirror shown in FIG. Looking at this, the following can be said. (1) The distribution in the circumferential direction has been changed from an elliptical shape in the case of a rotating bi-ellipsoidal mirror to a substantially square shape having the apex in the direction in which the lamp is arranged, but still has a full circumference. It is hard to say that it is a uniform circular shape. (2) In the distribution in the axial direction, the flat width of the peak portion is wide, which extends to 10 mm, and the h / d is 1.3.
The upper limit h = 5.2 mm, which is generally considered to be the ideal upper limit of the molten zone length, and h / d, which is the limit ratio at which the formation of the molten zone is impossible, is 1.8. H = 7.2 mm in the case of

Therefore, in order to grow a higher quality single crystal, an apparatus is developed in which the power density distribution in the circumferential direction is more uniform and the flat width of the peak portion in the power density distribution in the axial direction is narrower. Was desired.

[0017]

In order to solve the above-mentioned problems, the single crystal growing apparatus of the present invention has an eccentricity e of 0.
Four spheroidal mirrors satisfying 65 <e <0.80 are arranged facing each other on the orthogonal axis. Thus, the power density distribution in the circumferential direction can be made as uniform as possible, and the flat width of the peak portion can be narrowed and the peak value can be increased in the power density distribution in the axial direction. In addition, a shield surrounding the interface is disposed on at least one of the solid-liquid interface with the raw material rod and the solid-liquid interface with the crystal rod.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a single crystal growing apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the same reference numerals are used for the same components as those of the conventional device. FIG. 1 is a plan view and a front view illustrating main parts inside the ellipsoidal mirror. Four spheroidal mirrors 5b are arranged opposite to each other on the orthogonal axis, and the eccentricity of these spheroidal mirrors 5b is about 0.70. With a longer major axis. When four spheroidal mirrors 5b are combined, overlapping portions that interfere with each other must be cut, but in the present invention, the cut ratio is reduced. This is apparent from comparison with the conventional example shown in FIG.
This is represented by the relationship αb> αa in each of the plan views of FIGS. 1 and 9 in which the angle α formed between the position where the lamp is arranged (one focal point) and the edge of the adjacent spheroidal mirror. ing.

Therefore, the light emitted from the lamp 7 is reflected and condensed, that is, the light capturing rate is increased. Therefore, the heating efficiency is high.

FIG. 2 shows the result of simulating the power density distribution of the device of the present invention. This also applies to the lamp and the sample diameter under the same conditions as in the case of the conventional example shown in FIGS. From now on, the following can be said. (1) When four spheroidal mirrors 5a having a small eccentricity described above with reference to FIGS. 9 and 10 are combined, the distribution in the circumferential direction is changed from a square shape to a substantially circular shape. It can be seen that heating can be performed uniformly. (2) On the other hand, in the distribution in the axial direction, FIG.
As compared with the device of the rotating four-ellipsoidal mirror 5a described in FIG. 10, the flat width of the peak portion is narrow and the curve is steep, and at the same time, the peak value is 1.75 W before.
/ Mm ² , which is so high that it almost reaches 2.2 W / mm ² .

The inventors also conducted a simulation in which the sample diameter was 8 mm. 11 and 12 and FIG.
Shows the results. FIGS. 11 and 12 show the conventional eccentricity of 0.1.
44 ellipsoids and 4 ellipses, respectively, using 44 spheroidal mirrors
It is of an elliptical configuration. FIG. 3 shows a four-ellipse configuration using a spheroidal mirror having an eccentricity of 0.70 according to the present invention. Note that the halogen lamp is the same as that described above in the case where the sample diameter is φ4 mm.

The following can be understood from the results. In the case of a rotating ellipsoid, there is no problem in the power density distribution in the axial direction, but it has an elliptical shape in the circumferential direction and lacks uniformity. (See FIG. 11) In the case of a rotating 4-ellipsoidal mirror having an eccentricity of 0.44, the power density distribution in the circumferential direction is substantially circular and uniform as compared with the case where the sample diameter is φ4 mm. Distribution
Its peak value is not high. For the axial direction,
The flat width of the peak is somewhat wider. (FIG. 12
On the other hand, in the case of the present invention comprising a rotating 4-ellipsoidal mirror having an eccentricity of 0.70, the power density distribution in the circumferential direction is substantially circular and uniform, and its peak value is also 2. It shows a high value exceeding 0 W / mm2. At the same time,
The flat width of the peak portion is sufficiently narrow at 4 mm, and the curve is steep. (See Fig. 3)

From the above results, it can be seen that the single crystal growing apparatus of the present invention is suitable for growing a high quality single crystal with little change in the temperature of the irradiation distribution generated during rotation. In addition, even in the configuration of the four spheroidal mirrors, since the capturing efficiency of the lamp light is high and the heating efficiency is increased even with the same lamp, it can be said that application to higher temperature materials is possible.

Looking at the latter heating efficiency from another point of view, if the material has been grown so far, this device can be used with a reduced lamp output.
This extends the life of the lamp by several steps. Even if the lamp is made larger (increase the outer diameter of the lamp filament) and output is increased, the lamp light can be focused sharply, so that it can be used. At the same time, they can be used at low lamp power.

In the above description, an example in which the eccentricity is about 0.70 has been described as an example. However, according to the simulation results of the inventors and experimental trials, the production and the arrangement relationship between the lamp and the ellipse are considered. Then, this value is 0.65 <e <0.8
It has been found that a range of 0 is appropriate, and particularly preferable values are 0.68 or more and 0.75 or less.

Here, attention is paid to the size of the entire apparatus. As can be seen by comparing FIG. 1 and FIG. 9, the height of the spheroid mirror of the present invention can be made lower than that of the conventional spheroid mirror due to the difference in the eccentricity. This spheroid mirror is one of the key components of the apparatus, and the height of the apparatus cannot be reduced to reduce the overall height of the apparatus. Therefore, while growing a single crystal of only about 100 mm, the height of the apparatus is as high as 1800 mm. However, according to the present invention, the height of the conventional spheroidal mirror, which was 200 mm, can be reduced to 130 mm, and detailed description is omitted, but it is necessary to increase the clearance dimension when attaching and detaching the quartz core tube. The main reason for this is that it has disappeared.
It could be reduced to as low as 00 mm. From a different point of view, according to the present invention, if the height of the apparatus is set to 1800 mm as in the related art, a single crystal having a longer size can be grown.

[0027]

Embodiment 2 Next, as an embodiment different from the above,
The present invention proposes a measure for making the power density distribution in the axial direction steeper. This will be described with reference to FIG. FIG.
FIG. 3 is an enlarged front view of a molten zone portion. This feature
In the melting zone, a shield 18 surrounding the vicinity of the solid-liquid interface with the raw material rod 8 and the solid-liquid interface with the crystal rod 10 is arranged. As a result, the power density distribution in the axial direction condensed on the melting zone is regulated and narrowed by the interval between the two shields, and has a steep curve. Therefore, the raw material rod 8 and the crystal rod 10 are excessively heated. Without melting and promoting the capillary phenomenon in which the melt seeps into the pores of the raw material rod 8,
A stable FZ can be formed and maintained.

In FIG. 4, the shield 18 is arranged at the interface between the solid and the liquid. However, depending on the content of the material, there is no problem if only one of them is used. Further, it is preferable that the attachment position (axial direction) can be arbitrarily set and changed so that various conditions can be created.

[0029]

As described above, according to the single crystal growing apparatus of the present invention, since four spheroidal mirrors having an eccentricity of 0.65 <e <0.80 are employed, the molten zone However, since it is always heated uniformly over the entire circumference and the power density distribution in the axial direction can be sharpened, a more stable single crystal can be grown. Further, even with the configuration of four spheroidal mirrors, the device has a high heating efficiency. Further, the height of the spheroid mirror is reduced, and accordingly, the height of the entire apparatus can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view and a front view (partial sectional view) showing a main part of a single crystal growing apparatus of the present invention.

FIG. 2 is a power density distribution diagram when the single crystal growing apparatus of the present invention is used.

FIG. 3 is another power density distribution diagram when the single crystal growing apparatus of the present invention is used.

FIG. 4 is an enlarged front view (partially sectional view) showing a main part of another embodiment of the present invention.

FIG. 5 is a front view (partially sectional view) showing a configuration of a conventional single crystal growing apparatus.

FIG. 6 is an enlarged front view (partially sectional view) of a molten zone portion.

FIG. 7 is a power density distribution diagram when a conventional single crystal growing apparatus having a rotating ellipsoidal mirror is used.

FIG. 8 is an enlarged front view (partial cross-sectional view) of a main part showing a state in which a molten zone hangs down.

FIG. 9 is a plan view and a front view (partial cross-sectional view) showing main parts of a conventional single crystal growing apparatus having a rotating four-ellipsoidal mirror.

FIG. 10 is a power density distribution chart when a conventional single crystal growing apparatus having a rotating ellipsoidal mirror is used.

FIG. 11 is another power density distribution diagram when a conventional single crystal growing apparatus having a rotating ellipsoidal mirror is used.

FIG. 12 is another power density distribution diagram when a conventional single crystal growing apparatus having a rotating ellipsoidal mirror is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent quartz tube 5b Spheroid mirror 7 Halogen lamp 8 Raw material rod 10 Crystal rod 18 Shield

Claims (2)

[Claims] 1. A floating zone type single crystal growing apparatus in which a lamp is provided at one focal point of a spheroidal mirror and an object to be heated forming a floating zone is provided at the other focal point. Are opposed to each other on the orthogonal axis, and these spheroidal mirrors have the following formula: eccentricity e = (a ² −b ² ) ^1/2 / a (where, dimension a = long axis Length, dimension b = length of short axis)
Wherein the eccentricity e defined by the following expression is 0.65 <e <0.80. 2. The shield according to claim 1, wherein at least one of the solid-liquid interface between the raw material rod and the floating zone or the solid-liquid interface between the crystal rod and the floating zone is provided with a shield surrounding the interface. Single crystal growing equipment.