JPH07291782A - Method for growing compound semiconductor single crystal - Google Patents

Abstract

PURPOSE:To prevent useless crystal growth and improve the yield of single crystal production by observing the state of a melt surface in growth of a compd. semiconductor single crystal by a perpendicular gradient freezing method. CONSTITUTION:A crucible 4 contg. a raw material 5 of the compd. semiconductor is arranged into a quartz ampoule 2 and after this quartz ampoule is vacuum sealed, the quartz ampoule 2 is heated in a heating furnace 1 to melt the raw material 5. While the temp. distribution in the perpendicular direction of the heating furnace 1 is so controlled that the temp. on the bottom side of the raw material melt is kept higher than the temp. on the front surface side of the raw material melt, the temp. of the heating furnace 1 is gradually lowered and the compd. semiconductor single crystal is grown downward from the surface of the raw material melt. At this time, the crystal is grown while the state of the raw material melt surface in the crucible 4 before and after generation of the nucleus on the front surface of the raw material melt is observed from the upper part of the heating furnace 1. For example, the raw material melt state is photographed by a video camera 8 and is observed by connecting this video camera to a video tape recorder 10 and/or a monitor television 9.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a vertical gradient freezing method (VGF method, Vertical Gadient Freezing).
And a method of growing a compound semiconductor single crystal according to
The present invention relates to a method for growing a compound semiconductor single crystal such as Te or CdZnTe.

[0002]

2. Description of the Related Art The VGF method grows a crystal with a smaller temperature gradient than the LEC method (liquid-encapsulated Czochralski method), so that the thermal stress of the crystal is small and crystal defects such as dislocations can be suppressed. Have an advantage. However, since the crystal is grown in the crucible, there is a problem that crystal defects such as twin crystals and lineage are likely to occur due to the stress with the crucible wall. In particular, in the general VGF method, a crystal is grown from the seed crystal side installed at the lower end of the crucible with a temperature distribution set so that the temperature is vertically higher than the lower end of the crucible, and the crucible wall at the bottom of the crucible is grown. Since the angle between the growth axis and the growth axis is large, the above-mentioned crystal defects are likely to occur in the initial stage of growth, which causes polycrystallization.

Therefore, the Japanese Patent Publication No.
As described in Japanese Patent Publication No. 59873, the temperature distribution is set so that the temperature is vertically lower than the lower end of the crucible, and the crystal is grown downward from the melt surface. Since the portion in contact with the crucible wall is limited to the peripheral portion of the crystal, the generation of crystal defects can be limited to the edge of the crystal. As described in Japanese Examined Patent Publication No. 5-59873, the temperature gradient is 0.1 to 10 ° C./c.
m, the cooling rate is 0.01 to 1 ° C./h, the temperature of the center of the melt surface is lower than that of the periphery, and the crystal gradually grows from the center to the periphery to become a single crystal. The present inventors have grown crystals by this method with relatively high crystal quality and high single crystal yield.

[0004]

When, for example, a CdZnTe single crystal is grown by the above-described conventional crystal growth method, it takes 2 to 3 weeks to grow, although it depends on the length of the single crystal. In addition, not all crystals are always single crystals, but they may become polycrystals, which results in unnecessary crystal growth for 2-3 weeks, which causes a cost increase. It was

[0005]

Means for Solving the Problems The inventors of the present invention have made earnest studies to solve the above-mentioned problems, and as a result, by observing the state of the surface of the melt, a state in which polycrystallization occurs when crystal growth is continued as it is Then, the inventors have found a method of judging whether or not it is, and if it is in such a state, redo the crystal growth, and otherwise continue the crystal growth.

That is, according to the present invention, a crucible containing a raw material for a compound semiconductor is placed in a quartz ampoule, the quartz ampoule is vacuum-sealed, and then the quartz ampoule is heated in a heating furnace to melt the raw material. Then, while controlling the temperature distribution in the vertical direction of the heating furnace so that the temperature of the raw material melt bottom side is higher than the temperature of the raw material melt surface side, gradually lowering the temperature of the heating furnace, In the method of growing the compound semiconductor single crystal downward from the surface of the raw material melt, the state of the raw material melt surface in the crucible before and after nucleation on the raw material melt surface from the upper part of the heating furnace The present invention provides a method for growing a compound semiconductor single crystal, which is characterized in that the crystal is grown while observing.

The condition of the surface of the raw material melt is the presence or absence and the degree of convection of the raw material melt, and / or the position or spreading of solidification, and the method of observing the surface state of the raw material melt is The present invention provides a method for growing a compound semiconductor single crystal, which is a method of taking an image with a video camera and connecting to a video tape recorder and / or a monitor TV for observation.

Further, according to the present invention, a crucible containing a raw material for a compound semiconductor is placed in a quartz ampoule, the quartz ampoule is vacuum-sealed, and the quartz ampoule is heated in a heating furnace to melt the raw material. , While controlling the temperature distribution in the vertical direction of the heating furnace so that the temperature of the raw material melt bottom side is higher than the temperature of the raw material melt surface side, gradually lowering the temperature of the heating furnace, In the method of growing the compound semiconductor single crystal downward from the surface of the raw material melt, the state of the raw material melt surface in the crucible before and after nucleation on the raw material melt surface from the upper part of the heating furnace A method for growing a compound semiconductor single crystal, which comprises observing and growing a crystal while measuring the temperature distribution on the surface of the raw material melt.

The surface state of the raw material melt is the convection and / or solidification start position of the raw material melt, and the method of observing the surface state of the raw material melt is videotaped by a video camera. A method of observing by connecting to a recorder and / or a monitor TV, and further, the method of measuring the temperature distribution on the surface of the raw material melt is such that a video signal from a video camera is input to a computer via an image processing board, A method for growing a compound semiconductor single crystal, which is a method for measuring a temperature distribution on the surface of the raw material melt by converting a video signal in the visible region into a temperature.

First, the inventors of the present invention installed a crucible containing a raw material for a compound semiconductor in a quartz ampoule, vacuum-sealed the quartz ampoule, and then heated the quartz ampoule in a heating furnace. And gradually lowering the temperature of the heating furnace while controlling the temperature distribution in the vertical direction of the heating furnace so that the temperature of the raw material melt bottom side is higher than the temperature of the raw material melt surface side. Then, the state of the surface of the raw material melt in the crucible when the compound semiconductor single crystal was grown downward from the surface of the raw material melt was observed from the upper part of the heating furnace.

As a result, when convection of the raw material melt is large before and after the nucleation of the surface of the raw material melt and solidification of the surface, polycrystallization tends to occur, and when the convection is little or very small. It has been found that a single crystal is formed, and when the solidification start position on the surface of the raw material melt comes into contact with the crucible wall, polycrystallization occurs.

Therefore, when a compound semiconductor single crystal is grown, by observing the state of the surface of the raw material melt (the size of convection and the solidification start position) before and after the generation of nuclei, when it is in a state where it is likely to become polycrystalline, By raising the temperature of the heating furnace again and performing crystal growth again, wasteful crystal growth for 2-3 weeks can be avoided.

Further, the present inventors have studied not only observing the surface of the raw material melt but also measuring the temperature distribution on the surface of the raw material melt.

The distribution of an electromagnetic field radiated when an object has a certain temperature is represented by Planck's law of the following equation 1.

[0015]

[Formula 1] I (λ, T) = C ₁ · ε (λ, T) / {λ ⁵ ·
[exp (C ₂ / λT) -1]}

Here, I is the intensity of light, T [K] is the temperature of the object, λ [μm] is the wavelength of light, ε is the emissivity, and C ₁ and C ₂ are constants. From this equation, the wavelength dependence of the electromagnetic field radiated from an object at a certain temperature is obtained as shown in FIG. Generally, in order to measure the temperature distribution, a camera including an element having sensitivity in the infrared region is often used. This is Figure 1
This is because the peak of light emitted from an object having a temperature of 3600 ° C. or lower is in the infrared region as can be seen from.

However, visible light having a brightness that can be perceived by the naked eye is emitted from an object having a temperature of about 1000 ° C. Since the radiation intensity of light from an object changes depending on the temperature, the light intensity in the visible region also changes when the temperature of the object changes. Therefore, if the temperature has a distribution, the light intensity can also have a distribution.

Therefore, considering that the temperature of the surface of the raw material melt is measured by the light intensity in the visible region, the video signal from the video camera is input to the computer through the image processing board, and the video signal in the visible region is heated. The method of measuring the temperature distribution on the surface of the raw material melt by converting into

A specific method of converting a video signal into temperature uses an integrated value of luminance in a wavelength range of 580 to 700 nm of red (R) among the three primary colors (R, G, B),
This is a method in which the absolute value is calibrated in advance at the temperature measured with a thermocouple and conversion is performed.

According to this method, there is an advantage that an infrared camera for measuring temperature is not newly required, a video camera for observing the surface of the raw material melt can be used together, and the apparatus can be simplified.

Further, by measuring the temperature of the surface of the raw material melt, it is possible to more accurately estimate the crystal growth state, and it is possible to expect an advantage that wasteful growth time can be shortened.

[0022]

EXAMPLE The crystal growth according to the present invention will be described with reference to the schematic view of the crystal growth apparatus of FIG. 2 using an example of a CdZnTe crystal. A quartz ampoule 2 having an outer diameter of 110φ is installed in a heating furnace 1, and a 4-inch diameter pBN crucible 4 containing a CdZnTe polycrystalline raw material 5 is placed in the ampoule 2. In order to control the stoichiometry of the crystal, Cd6 is stored in the reservoir part of the ampoule. At the entrance of the crystal growth furnace, there is a viewing window 6 made of quartz, and a heat-resistant mirror 13 is placed on top of it, which horizontally reflects the image inside the furnace,
The picture is taken with the video camera 8 installed outside the furnace. The reason why the mirror is installed at the entrance of the furnace is that the heat radiated from the furnace causes the temperature near the furnace opening to become high temperature and the video camera cannot be installed. The temperature of the crystal growth part is raised to 111 by heating the heating furnace 1.
Hold at 0 ° C and hold Cd reservoir at 800 ° C. The temperature gradient on the side wall of the ampoule at the pBN crucible is 0.1 ° C / cm or less, with the temperature of the lower part being higher than that of the upper part.
The melt is solidified from the surface by slow cooling at a rate of / h. At this time, the image signal captured by the video camera 8 is input to the personal computer 12 via the television monitor 9, the video tape recorder 10, and the image processing board,
Computer monitor 11 at the same time as TV monitor
The temperature distribution on the surface was displayed on.

Crystal growth was carried out while successively observing an actual image, a temperature distribution image, and a thermocouple arranged on the side wall of the ampoule.

Crystal growth is carried out while observing in this manner,
As a result of re-melting and re-growing the growth conditions and re-growing the crystal that seems to be likely to be polycrystallized from the state of convection and solidification position before and after nucleation, polycrystallized crystal was found to be 1 out of 5 times. However, if it is allowed to grow as it is without performing such an observation, about 80% of what seems to be polycrystal was not wasted.

The reason why the mirror is installed at the entrance of the furnace in the above-described embodiment is that the heat radiated from the furnace causes the temperature near the furnace to become high and the video camera cannot be installed. Any device may be installed directly.

Further, although CdZnTe single crystal has been described in the above embodiment, the present invention is not limited to this, but can be applied to other compound semiconductor single crystals, but CdTe single crystal with small stacking fault energy and crystal defects easily enter. CdZ
It is most effective when applied to nTe single crystals.

[0027]

According to the present invention, by performing crystal growth while observing the surface of the melt, it is possible to quickly find a state in which polycrystallization is likely to occur, so that unnecessary crystal growth can be avoided.
There is an advantage that the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a wavelength distribution of temperature and radiant energy of an object.

FIG. 2 is a conceptual diagram of a crystal growth apparatus for explaining an example of the present invention.

[Explanation of symbols]

 1 Heating Furnace 2 Quartz Ampoule 3 Quartz Cap 4 pBN Crucible 5 CdTe Raw Material 6 Reservoir Cd 7 Quartz Viewing Window 8 Video Camera 9 TV Monitor 10 Video Tape Recorder 11 Monitor 12 Personal Computer 13 Mirror

Claims (7)

[Claims] 1. A quartz ampoule is provided with a crucible containing a raw material of a compound semiconductor, the quartz ampoule is vacuum-sealed, and the quartz ampoule is heated in a heating furnace to melt the raw material, and the heating is performed. While controlling the temperature distribution in the vertical direction of the furnace so that the temperature of the raw material melt bottom side is higher than the temperature of the raw material melt surface side, the temperature of the heating furnace is gradually lowered to obtain the raw material melt. In the method of growing the compound semiconductor single crystal downward from the surface of the, while observing the state of the raw material melt surface in the crucible before and after nucleation on the raw material melt surface from the upper part of the heating furnace A method for growing a compound semiconductor single crystal, which comprises growing a crystal. 2. The compound semiconductor according to claim 1, wherein the state of the surface of the raw material melt is the presence or absence and the degree of convection of the raw material melt, and / or the position or spread of solidification. Single crystal growth method. 3. The method for observing the surface state of the raw material melt is the method of photographing with a video camera, a video tape recorder, and / or
Alternatively, the method for growing a compound semiconductor single crystal according to claim 1 or 2, which is a method of observing by connecting to a monitor television. 4. A quartz ampoule is provided with a crucible containing a raw material of a compound semiconductor, the quartz ampoule is vacuum-sealed, the quartz ampoule is heated in a heating furnace to melt the raw material, and the heating is performed. While controlling the temperature distribution in the vertical direction of the furnace so that the temperature of the raw material melt bottom side is higher than the temperature of the raw material melt surface side, the temperature of the heating furnace is gradually lowered to obtain the raw material melt. In the method of growing the compound semiconductor single crystal downward from the surface of, the state of the raw material melt surface in the crucible before and after nucleation on the raw material melt surface is observed from the upper part of the heating furnace, A method for growing a compound semiconductor single crystal, which comprises growing a crystal while measuring the temperature distribution on the surface of the raw material melt. 5. The compound semiconductor according to claim 4, wherein the state of the surface of the raw material melt is the presence or absence and the degree of convection of the raw material melt, and / or the position where the solidification starts and the way the compound semiconductor spreads. Single crystal growth method. 6. The method of observing the surface state of the raw material melt, comprising: photographing with a video camera;
Alternatively, the method for growing a compound semiconductor single crystal according to claim 4 or 5, which is a method of observing by connecting to a monitor television. 7. The method for measuring the temperature distribution on the surface of the raw material melt comprises the steps of inputting a video signal from a video camera to a computer via an image processing board and converting the video signal in the visible region into temperature. 5. A method for measuring a temperature distribution on the surface of a raw material melt, 5.
7. The method for growing a compound semiconductor single crystal according to 5 or 6.