JPS60141695A - Method and device for growing crystal - Google Patents

Abstract

PURPOSE:To grove a bulk crystal without any crystal defect by lowering the temp. of a high-temp. part as a vessel enclosing a crystal material is sent downward from the high-temp. part to the low-temp. part in a furnace core tube of a bulk crystal device by the Bridgman growth technique. CONSTITUTION:An ampule 21 enclosing a crystal material 22 is gradually sent downward in a furnace core tube 23 provided with a heater 24 at the outer circumferential part from the high-temp. part to the low-temp. part by the operation of an ampule driving part 25 in a device for growing a bulk crystal using the Bridgman technique wherein a crystal is grown at the interface between solid and liquid. In said device, the position signal of the ampule 21 with respect to said ampule driving part 25 is inputted to a furnace control panel 26, and the temp. of the high-temp. part is lowered by controlling the plural hetaters 24 to the temp. of the central part of the ampule 21, as said ampule 21 is sent downward from the high-temp. part to the low-temp. part of the furnace core tube 23. Since the solid and luquid interface is kept flat in this way, the intrusion of g a grain boundary into a crystal is prevented, and the crystal without any crystal defect is grown.

Description

Detailed Description of the Invention (1) Technical Field of the Invention The present invention relates to crystal growth and its apparatus, specifically, in bulk crystal growth by the Bridgman growth method, grain boundaries, which are one of the crystal defects, enter the crystal. The present invention relates to a method for preventing this and a device used in the method.

(2) Background of the technology For example, cadmium telluride (Cd1'e) single crystals used as substrates for epitaxial growth of mercury cadmium telluride for infrared sensor devices are grown by the Bridgman growth method, and in order to put this method into practice, The apparatus shown in cross section in Figure 1 is used. In the figure, 1 indicates a container for enclosing a material, such as a quartz ampoule (hereinafter referred to as an ampoule) with a length of about 20 cm, and this ampoule has a capacity of About half of the material 2 is sealed in the quartz ampoule, and the tip of the quartz ampoule is pointed as shown in the figure.The ampoule 1 is lowered into the furnace core tube 3 by a drive mechanism (not shown) as shown by the arrow in the figure. A plurality of heaters are arranged around the core tube 3, and the upper heater 4a is a high temperature part, and the lower heater 4ab is a low IAIB.For example, when making a Cd-Te crystal, 1 The process requires about 1 hour, and the ampoule 1 descends about 5 cm during this time.

The relationship between the temperature inside the furnace and the position of the ampoule is shown in Figure 2.
In the diagram on the right side of the figure, the vertical axis represents the position of the ampoule 1, the horizontal axis represents the furnace temperature, and T, , l represent the melting point of the material. Curve a shows the relationship between the position in the furnace and the temperature.
When is at the left position in the figure, there is a crystal 12 at the tip of the ampoule.
This is the time when the tip begins to grow, and the line not shown with reference numeral 13 represents the solid-liquid interface, and above it is the molten material.
The temperature of the solid-liquid interface corresponds to the melting point. When the ampoule 1 is in the position shown on the right side of the figure, the amount of crystal 13 increases and the crystal is growing in the center of the ampoule, which is the central growth period.

In the diagram on the right, the heater of the upper blade mentioned above is the high temperature part,
Also note that the lower heater is a low temperature section.

(3) Conventional technology and problems In the Bridgman growth method described above, whether or not large-angle grain boundaries, which are one type of crystal defect, easily enter the crystal is related to the shape of the solid-liquid interface during growth. .

High-angle grain boundaries tend to extend from the contact area between the solid-liquid interface and the container in a direction perpendicular to the solid-liquid interface, as shown by line 14 in Figure 2, and most of them occur around the crystals. . Therefore, if the solid-liquid interface is concave, as shown in the right ampoule of FIG. 2, the grain boundary density in the crystal will be dog. In a region where the crystal diameter is constant, the solid-liquid interface (equal liquid surface at that position) is is required to be flat.

In the conventional Bridgman growth method, the temperature profile of the furnace was fixed and ζ (kept constant) was used for growth, so the interface shape was convex as seen in the ampoule on the left in Figure 2 during the growth of the tip. When growing at the center, the ampoule on the right of FIG. 2 becomes concave and has the disadvantage of increased grain boundary density.

(4) Purpose of the Invention In view of the above conventional problems, the present invention provides a crystal growth method that prevents grain boundaries, which are crystal defects, from entering the crystal in the Bridgman growth method, and an apparatus for implementing the method. The purpose is to provide

(5) Structure and object of the invention According to the present invention, in bulk crystal growth by the Bridgman growth method, as a container containing a crystal material is lowered from a high temperature part to a low temperature part of a furnace core tube, C1
In a crystal growth method characterized by lowering the temperature of the 111i hot and cold to the temperature of the center of the container, and a bulk crystal growth apparatus using the Bridgman growth method equipped with a furnace core tube having a high temperature section and a low temperature section, A drive unit for raising a crystal material enclosure container in a furnace core tube and a plurality of heaters for heating the furnace core tube are connected to a furnace control panel, and as the container is lowered, the furnace control panel lowers the temperature of the heaters. This is achieved by providing a crystal growth apparatus characterized by the following.

(6) Examples of the invention Embodiments of the present invention will be explained in detail below with reference to the drawings.

In the Bridgman growth method, the present inventor kept the shape of the solid-liquid interface flat during growth by adjusting the temperature of the furnace during growth according to the movement (change) of the position of the growth ampoule. It provides a method for growing fewer crystals.

In the prior art, the reason why the shape of the solid-liquid interface changes from convex to concave is that the shape of the portion (crystalline portion) at a temperature lower than the melting point changes, and the state of heat flow near the interface changes. This state will be explained from the change in temperature between the outside and the center of the ampoule with reference to FIG. In FIG. 3, the horizontal axis is temperature, the vertical axis is the temperature measurement position, TM is the melting point, line a is the temperature outside the ampoule, line S is the temperature at the center of the ampoule, and al and bl represent the time of growth of the tip, respectively. The ampoule outer temperature and center temperature are set and fixed so that their intersection point is below the melting point. The reason for this is that, as understood from the diagram in FIG. 4, if the outside temperature and center temperature are equal near the melting point, the solid-liquid interface becomes flat (horizontal). In addition, Figure 4 (al is a diagram similar to Figure 3 and curve a
and b indicate the temperature outside the ampoule and the temperature at the center, respectively. It corresponds to the intersection of lines a and b.

However, as the ampoule lowers and approaches the center 1B growth period (indicated by b2 in the figure), the heat radiation from the center decreases, so the temperature at the ampoule center actually rises as shown by the broken line bb, and the temperature at the ampoule center is higher than the melting point. The temperature is higher at the center than at the outside, and thus the temperature is equal to the surface (solid-liquid interface).
became concave.

Therefore, in the present invention, as shown in FIG. 5, which is similar to FIG. 3, the temperature of the high temperature part of the furnace is lowered as the ampoule descends. That is, the temperature on the outside of the ampoule and the temperature at the center are initially changed to the dotted line a, starting from al+ bt during the growth of the tip.
Set as shown in b.

However, this temperature condition is not fixed, and when the central portion grows a2. In b2, the ampoule outer temperature and center temperature are lowered so that the ampoule outer temperature and center temperature coincide around the melting point, as shown by solid lines aa and bb. In this case, as shown in FIG. 4, the liquid surface (solid-liquid interface) is kept flat, and grain boundaries are prevented from extending into the crystal.

In one example, in the growth of a CdTe crystal (melting point 1092°C), the temperature outside the ampoule was initially set at 1150°C, and during the growth of the central part, it was lowered to 11.30'C, and the ampoule was lowered by 5 cm during a descending period of 10 days. C without crystal defects
A dTe crystal was obtained.

In order to carry out the above method, an apparatus shown in FIG. 6 is used, in which 21 is an ampoule, 22 is a material sealed in the ampoule 21, 23 is a furnace core tube, 24 is a heater,
25 is an ampoule drive unit equipped with a mechanism for lowering the ampoule 21 (the above parts are the same as in the conventional example); 26
shows a furnace control panel connected to the drive section 25 and heater 24. Therefore, the illustrated embodiment differs from the conventional example in that a furnace control panel 26 and connections between it and the drive unit 25 and heater 24 are provided. When the ampoule 21 begins to descend, the furnace control panel receives a signal from the drive unit 25, and during the central region growth (the time up to that point is related to the descending distance of the ampoule 21), the two upper high temperature regions in the figure are formed. The temperature of the heater is lowered to a predetermined value, for example, as described above. After the growth is completed, the ampoule is melted with hydronic acid to take out the CdTe crystal. As mentioned above, since the ampoule unilaterally drops by 5 cm after 10 days, the temperature change can be changed to a linear type, and the furnace control panel 26 can be constructed using ordinary technology.

(7) Effects of the Invention As explained in detail above, according to the present invention, in bulk crystal growth using the Bridgman growth method, the solid-liquid interface can be kept flat during crystal growth, so large-angle grains can be formed in the crystal. This prevents the boundaries from extending and is highly effective in keeping the grain boundary density in the crystal low. In addition, in the above explanation, C
Although dTe is used as an example and an apparatus equipped with four heaters is illustrated, the scope of application of the present invention is not limited to that case, but also extends to apparatuses for growing other crystals and having heater configurations. It is something.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the equipment used in the Bridgman growth method, Figure 2 is a diagram showing the temperature profile and solid-liquid interface shape during crystal growth by the conventional method, and Figure 3 is the temperature profile in the conventional method. Figure 4 is a diagram showing the temperature profile and isotherm inside the ampoule; Figure 5 is a diagram showing the change in temperature profile when the method of the present invention is used; Figure 6 is a diagram showing the temperature profile when the method of the present invention is carried out. FIG. 21-Ampoule, 22-Material, 23-Furnace core tube, 24-
Heater, 25- Ampoule drive l111.26-Furnace control panel Fig. 1 3, Fig. 2 Fig. 3 Fig. 4

Claims (2)

[Claims] (1) In bulk crystal growth using the Bridgman growth method, a crystal growth method characterized by lowering the temperature of the high-temperature section as the container containing the crystal material is lowered from the high-temperature section of the furnace core tube to the low-temperature section. . (2) In a bulk crystal growth apparatus using the Bridgman growth method that is equipped with a furnace core tube that has a high-temperature section and a low-temperature section, there is a drive section that lowers the crystal material enclosure container within the furnace core tube, and a plurality of drive sections that heat the furnace core tube. A crystal growth apparatus characterized in that a heater is connected to a furnace control panel, and the furnace control panel lowers the temperature of the heater as the container descends.