JP3255753B2 - Method of growing rutile rod-shaped single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an EFG (Edge-d
The present invention relates to a method for growing a rutile rod-shaped single crystal to which an applied film-fed growth method is applied.

[0002]

2. Description of the Related Art The EFG method as a crystal growth method is known as a method capable of pulling a crystal into a shape according to a type. This principle will be described with reference to FIG. 2. A crucible 1 is filled with a melt 2 and a die 3 having a slit 4 is mounted in the melt. In this case, melt 2
Rises to the upper surface of the die by capillary action through the slit 4 provided in the die 3. The seed crystal 5 is attached to the melt appearing on the upper surface of the die, and cooled while being pulled up at an arbitrary speed, thereby obtaining the crystal 6 according to the die (type). Further, there is no example of growing a rod-shaped crystal having the same cross-sectional shape as the top surface of a die in the EFG method accompanied by crystal rotation. Regarding the EFG method with crystal rotation, Gd2 (MoO
4) ₃ crystal growth (Journal of Crystal Growth, 104
(1990) 77-79) only shows the result of crystal growth from the upper surface of the square die under the condition that the melt meniscus is not restricted to the die shape. According to the literature, it is reported that the instability of the crystal shape varies depending on the number of rotations of the crystal, and the shape is stable when the number of rotations is low. However, the growth process of the Gd2 (MoO4) ₃ crystal is similar to that of a rutile single crystal. It has completely different properties from those of oxide single crystals, and can be grown by the Czochralski method of pulling up and growing directly from the melt without using a die. Large and difficult to grow (Journal of Crystal Growth, 112
(1991) 835-837). The present invention relates to a technique for growing a high-quality oxide rod-shaped single crystal, and it is impossible to control the shape of an oxide single crystal such as a rutile single crystal only by optimizing the crystal rotation speed. As described above, there is no example in which a material that is difficult to grow by the Czochralski method can be grown by the EFG method. Also, rutile rod-shaped crystals are grown by pulling crystals such as Bernoulli method and floating method. In the method of pulling a crystal which is advantageous for growing a large crystal, a plate-shaped crystal is grown only by an EFG method without crystal rotation, and a rod-shaped crystal which is advantageous for mass production is not obtained.

[0003]

As is apparent from the above method, since the temperature around the crystal growth interface is lower than that of the ordinary Czochralski method, the meniscus height is low in the growth by the EFG method. The temperature distribution at the crystal growth interface is susceptible to heat radiation from the top surface of the die. In the case of growing a plate-like crystal, the thickness of the growing crystal is small and the heat radiation efficiency is good, so there is almost no effect. However, when growing a rod-like crystal with a diameter of 10 mm or more, the melt in the slit portion and the die other than the slit portion are not used. Since the amount of heat radiation from the material (Ir) is different, the vicinity of the growth interface has a temperature distribution corresponding to the pattern of the slits on the upper surface of the die, and as a result, a crystal strain similar to the pattern of the slits is generated in the crystal. There was a problem. Further, since rutile has a high melting point of about 1850 ° C., the material of the crucible and the die used is iridium, and the oxygen partial pressure of the crystal growing atmosphere is generally limited to about 3% or less. As a result, the grown crystal has a large oxygen deficiency, and the grown crystal absorbs radiated light including infrared rays from the upper surface of the die. For this reason, the amount of heat radiation from the top surface of the die is significantly different from that covered by the crystal on the top surface of the die, and the temperature distribution on the top surface of the die changes depending on the grown crystal shape. In the growth, crystals easily grow in the radial direction on the upper surface of the die, and it is difficult to control the shape. Furthermore, if the temperature distribution on the upper surface of the die is large or the temperature on the upper surface of the die at the start of growth is too low, the shape of the crystal grown from the seed crystal will not be axially symmetrical according to the temperature distribution on the upper surface of the die, Immediately after contact with the melt, the crystal rapidly grows according to the temperature distribution on the die upper surface at that time, and the phenomenon that the crystal growth does not proceed in an axisymmetric manner occurs. As a result, the crystal shoulder shape does not become axisymmetric, The amount of heat radiation from the crystal interface varies depending on the location, and it is difficult to control the shape, for example, the crystal grows in a spiral shape. When growing a rod-shaped crystal with a diameter of 10 mm or more by the EFG method, the asymmetry and the size of the temperature distribution of the die top surface and the growth atmosphere in the direction perpendicular to the crystal growth direction depend on the crystallinity and growth of the grown crystal. Affects stability. That is, when the temperature distribution of the die upper surface and the growth atmosphere is asymmetric, the crystal growth rate and the crystal cooling rate after crystallization differ depending on the location, and thermal strain remains in the crystal plane corresponding to the asymmetry. When the asymmetry increases, the amount of distortion increases, causing a problem of cracking. In addition, when the asymmetry of the temperature distribution and the size thereof are large, the fluctuation of the crystal shape becomes large, and it becomes difficult to control the crystal distribution. However, there is a problem that a boundary easily occurs. The present invention has been made to solve each of the above problems, and has a good quality and a large size.
An object of the present invention is to provide a method for growing a rutile rod-shaped single crystal capable of obtaining a rutile rod-shaped crystal.

[0004]

The method for growing a rutile rod-shaped single crystal according to the present invention is to grow a good-quality rutile rod-shaped single crystal while rotating a seed crystal by applying an EFG method.
In particular, using a die having a diameter variation of 20% or less of the average diameter in a direction in which the shape of the die upper surface is circular, growing under a condition where the temperature distribution range of the die upper surface is 10 ° C. or less, and The temperature of the die upper surface is 1
It is effective that the seed crystal is brought into contact with the melt on the upper surface of the die at a temperature higher than 0 ° C. to start the growth .

According to the method for growing a rutile rod-shaped single crystal of the present invention, the seed crystal is grown while rotating the seed crystal.
The heat radiation from the upper surface of the die does not differ from place to place, and no distortion is generated in the crystal corresponding to the pattern of the slits on the upper surface of the die. Further, there is no difference in the thermal history depending on the location of the grown crystal due to the asymmetry of the temperature distribution between the upper surface of the die and the growing atmosphere. However, since a rutile crystal has a large growth rate in the radial direction on the upper surface of the die, in order to grow a rod-shaped crystal whose shape is controlled, a die having a circular upper surface shape with a small fluctuation in diameter is used. It is necessary to grow a crystal having a crystal cross-sectional shape substantially equal to the following. Further. By using such a die,
The deviation between the crystal growth interface shape and the die upper surface shape caused by the crystal rotation growth, and large temperature fluctuation and crystal shape fluctuation at the growth interface and the die upper surface due to the deviation were suppressed. However, the effect differs depending on the crystal rotation speed. Generally, when the crystal rotation speed is increased, the deviation from the horizontal surface of the die top surface greatly affects, and the fluctuation of the growth interface shape becomes large.Moreover, more melt flows through the slit. , And the crystal growth interface shape becomes largely concave with respect to the crystal side, so that the crystal growth tends to be unstable. The rotation speed at which stable crystal growth is easy to achieve depends on the crystal diameter to be grown.
As a result of examining the crystal rotation speed of not more than rpm, the crystal rotation speed at which stable crystal growth was easy to obtain was 5 rpm or less. Also, by growing the crystal under the condition that the temperature distribution range of the upper surface of the die is set to 10 ° C. or lower or the temperature of the upper surface of the die at the start of the growth is higher than the melt temperature by 5 ° C. or more, the growth from the seed crystal is rapidly increased. Instead, the crystal shoulder can be grown symmetrically with respect to the rotation axis, and the crystal shoulder can be grown axisymmetrically, and the shape of the straight body can be controlled thereafter.

[0005]

An embodiment will be described below with reference to the drawings. (Embodiment 1) FIG. 1 shows an embodiment of the present invention. In FIG. 1, the same parts as those in FIG. Reference numeral 7 denotes a cylindrical die, in which slits 4-1, 4-2, and 4-3 are provided. Numeral 8 is a seed crystal, and numeral 9 is a grown crystal in a columnar shape. And diameter 5
15 mm diameter at the center of a crucible 1 of 0 mm and height 25 mm
A rod-shaped die 7 having a slit of 25 mm in height and a height of 25 mm is placed, and 130 g of a raw material (TiO2) is melted in a crucible by high frequency induction heating. To pull up in the C-axis direction.
However, the rotation speed of the grown crystal was 0 and 5 rpm. Rod-like crystals each having a diameter of 15 mm and a length of 40 mm were grown. A wafer was cut out from these rod-shaped crystals in a direction perpendicular to the pulling direction and observed with a polarizing microscope.
In the case of, the strain was generated corresponding to the slit, and it was observed that a boundary was formed due to a difference in temperature distribution in a plane parallel to the wafer surface, whereas the crystal grown while rotating at 5 rpm was observed. Showed no such distortion and boundary.

(Embodiment 2) When two kinds of dies having a circular and square top surface are grown and a rutile rod-shaped crystal is grown while rotating the crystal at 5 rpm, a round rod-shaped crystal is obtained in the case of a circular shape. On the other hand, in the case of a square, after the formation of a crystal shoulder having a substantially square cross section was completed, the shape varied greatly, and the shape could not be controlled thereafter. Further, when the wafer was cut out from these crystals and observed with a polarizing microscope, distortion was observed from the outer periphery due to shape variation in the latter, whereas such distortion was not observed in the former. Note that, even in the case of a circular shape, when the diameter variation is larger than 20% of the average diameter, the symmetry of the crystal shoulder shape was low, and the growth results and crystallinity were the same as those in the case of the square shape.

(Example 3) In growing a rutile single crystal from the upper surface of a die having a diameter of 15 mm and having a small diameter variation, when the temperature distribution range of the upper surface of the die is 5 ° C., 10 ° C., and 15 ° C., When the growth was compared, the temperature was 5 ° C and 10 ° C.
In the case of ℃, the crystal growth from the seed crystal proceeded symmetrically, and the symmetry of the crystal shoulder was high, whereas in the case of 15 ℃, when the seed crystal adhered to the melt, the crystal growth was caused by the temperature on the top surface of the die. Proceeding in accordance with the distribution, the shape did not change with the rotation of the crystal and became elliptical, and the symmetry of the crystal shoulder was low. And in the growth from the shoulder to the torso, the former had a stable shape, whereas the latter easily raised the temperature of the die upper surface,
After the growth of about 10 mm, the shape variation became unstable, the crystal was twisted, and so-called spiral growth occurred, which was not eliminated. In addition, the crystallinity of each crystal was the same as that of Example 2, and the latter was observed to have a strain accompanying a shape change. The crystal rotation speed was 5 rpm.

(Embodiment 4) Using the same die as in Embodiment 3, the temperature distribution range of the die upper surface is set to 10 ° C., and the die upper surface temperature when the rutile seed crystal is adhered to the melt on the die upper surface is substantially reduced. A comparison of the growth of the crystal shoulder when the temperature is equal to the liquid temperature and when the temperature is higher by 10 ° C shows that the former shows that the crystal grows in the radial direction corresponding to the temperature distribution on the die upper surface at the moment when the seed crystal adheres to the melt. Spreads asymmetrically, and this asymmetry is not eliminated by crystal rotation, and a crystal shoulder with low symmetry is formed. In the latter case, this was not the case and a highly symmetrical crystal shoulder was obtained. In the subsequent growth of the straight body, the former was stable in shape due to the difference in the symmetry of the crystal shoulder shape, whereas the latter became difficult to control the shape as in Example 3. Also, the crystallinity was measured in Example 3.
In the same manner as in the above case, the latter was observed to have a distortion accompanying the shape change. The crystal rotation was 5 rpm.

[0009]

As described above, according to the present invention, E
In the FG method, a high-quality rutile rod-shaped single crystal without distortion can be grown. Further, the fluctuation of the crystal shape is suppressed, the generation of the boundary caused by the fluctuation is suppressed, and a high-quality large rutile rod-shaped single crystal can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a conventional method.

[Explanation of symbols]

 1 Crucible 2,11 Melt 3,7 type (die) 4,4-1,4-2,4-3 Slit 5,8 Seed crystal 6,9 Growing crystal

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Machida 5310 Mikajiri, Kumagaya-shi, Saitama Chichibu Cement Co., Ltd. Fine Ceramics Headquarters (56) References JP-A-54-153786 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C30B 1/00-35/00 WPI (DIALOG)

Claims (4)

(57) [Claims] 1. A raw material melt in a container whose atmosphere is controlled.
Install a die (type) with a slit in the crucible that entered,
Based on the melt that has risen to the top of the die through the slit
A method for growing a rutile rod-shaped single crystal, comprising growing a rutile rod-shaped crystal having the same cross-sectional shape as the die top shape while rotating a seed crystal. 2. The method for growing a rutile rod-shaped single crystal according to claim 1 , wherein the shape of the upper surface of the die is circular, and the crystal is grown from the upper surface of the die having a diameter variation of 20% or less of the average diameter depending on the direction. 3. A process according to claim 1, wherein the range of temperature distribution in the die top plate is characterized by growing under conditions at 10 ° C. or less
A method for growing a rutile rod-shaped single crystal. 4. The rutile rod according to claim 1 , wherein the seed crystal is attached to the melt on the die upper surface and the growth is started under the condition that the temperature of the die upper surface is higher than the melt temperature by 10 ° C. or more. A method for growing a single crystal.