JP2879078B2 - Method for producing compound semiconductor crystal and crucible used therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for producing a crystal such as a compound semiconductor, and more particularly to a technique for growing a long crystal by bringing a seed crystal into contact with a raw material melt placed in a crucible. The present invention relates to a method for producing a compound semiconductor crystal and a crucible used for the method.

[0002]

2. Description of the Related Art As a main method for producing a single crystal of a III-V compound semiconductor such as InP or GaAs, for example, a raw material and a sealant are melted in a crucible, and a seed crystal is brought into contact with the surface of the raw material melt. An LEC (Liquid-sealed Czochralski) method is known in which a single crystal is grown by gradually pulling it up. In the LEC method, crucibles made of quartz or pyrolytic boron nitride (hereinafter referred to as "pBN") have been used, but have the following drawbacks. That is, in a crucible made of quartz, quartz contains V in the raw material melt.
Reacts with group III elements to produce silicon and oxygen, such as InP
Defects may be generated in the crystal, and high-resistance G
Production of aAs crystals was difficult. On the other hand, pBN
Crucibles do not react with the raw material melt, so the above-mentioned disadvantages are not solved, but the frequency of twinning increases and polycrystallization is easily caused, making it difficult to grow long single crystals Met.

[0003]

DISCLOSURE OF THE INVENTION The present inventors have studied the causes of the above-mentioned drawbacks in the pBN crucible to eliminate them. In general, in a crystal pulling apparatus, a heater is arranged opposite to the side plate of the crucible, so that heat generated from the heater flows into the raw material melt through the side plate of the crucible and propagates through the melt. Then, it flows out of the melt by heat radiation from the melt surface and heat conduction through the grown crystal at the center of the melt. Such a heat flow causes a temperature gradient in the raw material melt.

In a desired temperature gradient, the heat flow described above causes the crystal 2 in the crucible 1 to move as shown in FIG.
The growth interface, i.e., the solid-liquid interface, has a convex shape whose central portion swells toward the melt 3 side. In this case, a long single crystal is easily grown. At this time, it was found that if the temperature gradient was larger than the desired gradient, a large thermal stress was generated inside the grown single crystal, and a large number of dislocations were generated. That is, it was found that it is desirable to reduce the temperature gradient in order to reduce the dislocation density in the grown crystal.

However, if the temperature gradient is made smaller than the desired gradient and the temperature gradient near the growth interface of the melt 3 becomes excessively small, the shape of the growth interface of the crystal 2 becomes flat as shown in FIG. In this state, it was found that the temperature distribution in the melt 3 near the growth interface became unstable, and the balance was easily lost. As a result, it has been found that the growth rate of the crystal 2 at the interface varies, and the low growth rate region 4 in which the growth interface of the crystal 2 is concave with respect to the melt 3 tends to be formed as shown in FIG.

By the way, dislocations generated in a single crystal due to thermal stress or the like move and multiply in a state where a thermal stress is applied at a high temperature to form a network-like high dislocation density region, that is, a lineage. easy. The lineage becomes denser as the crystal grows and becomes longer, and moves toward the growth interface. Then, it was found that the moved lineage reached the growth interface in the above-mentioned low growth rate region 4 to form a crystal boundary, and the crystal grown thereafter contained a polycrystalline portion.

In the state shown in FIG. 3, the temperature gradient in the direction perpendicular to the crystal growth direction is also small, so that the temperature distribution near the outer periphery of the growth interface becomes unstable, and the growth rate on the outer periphery of crystal 2 varies. Was found to occur. Due to the variation in the growth rate, the diameter of the crystal 2 to be grown tends to fluctuate, and when the fluctuation overlaps with a specific condition, a twin boundary is generated. It was found that a part occurred.

That is, if the temperature gradient of the crystal growth direction near the growth interface of the melt 3 is excessively reduced by controlling the temperature of the heater in order to manufacture a single crystal having a low dislocation density with a good yield, conversely, Crystal generation and polycrystallization are caused, and the yield is deteriorated. In particular, when growing a long crystal, the temperature distribution in the melt 3 is more likely to fluctuate as the remaining amount of the melt 3 in the crucible 1 decreases. Then, since the twins and polycrystals described above are easily generated, it has been found that it is extremely difficult to produce a long single crystal with a low dislocation density and a good yield. The present invention has been made to solve the above problems, and an object of the present invention is to provide a method of manufacturing a compound semiconductor crystal capable of manufacturing a long single crystal with a low dislocation density with good yield, and an object of providing a crucible used for the method. And

[0009]

In order to achieve the above object, the present inventors have made the thermal conductivity of a crucible anisotropic so that the temperature gradient in the crystal growth direction near the growth interface of the raw material melt can be improved. (1) The temperature gradient in the crystal growth direction in the raw material melt is
If the slope can be higher than desired,
Extremely high thermal conductivity in the direction perpendicular to the crystal growth direction
Crucible that can mitigate excessive temperature gradient
Used, (2) when the temperature gradient may be smaller than desired slope
To reduce the temperature gradient from becoming too small.
Based on the new concept of using a button, the following configuration
Suggest crucibles. That is, the raw materials are added, and the raw materials are added.
It is heated and melted, and the seed crystal is brought into contact with the raw material melt.
Compound semiconductor crystal that grows compound semiconductor crystal
A crucible used in the method of manufacturing, wherein the crucible is
The bottom wall and the side wall are formed in a container shape, and the bottom wall is formed.
Is located first layer facing the inside of the crucible and on the outside
Has a laminated structure of at least two layers consisting of a second layer
The thermal conductivity of the second layer in the crystal growth direction is
Less than the thermal conductivity of the first layer in the crystal growth direction
Direction perpendicular to the crystal growth direction of the second layer
Has a thermal conductivity perpendicular to the crystal growth direction in the first layer.
Having a thermal conductivity greater than the thermal conductivity in the direction
Walls conduct heat more perpendicularly to their thickness than to their thickness.
The rate of heat conduction was higher. In addition,
The first layer is made of pyrolytic boron nitride, and the second layer is made of heat-decomposed boron nitride.
It can be made of decomposed graphite. Ma
The bottom wall has a third layer provided outside the second layer.
The first layer and the third layer sandwich the second layer.
A sandwich structure, wherein the first layer and the third layer
The second layer is made of pyrolytic graphite from boron nitride.
You may make it become. Further, the side wall portion is formed by thermal decomposition nitriding.
It may be formed of a laminate of boron oxide. Further
In another crucible according to another invention,
The raw material is heated and melted, and the seed crystal is brought into contact with the raw material melt
Compound semi-conductor to grow compound semiconductor crystal
A crucible used in a method for producing a conductor crystal, comprising:
The acupoint is formed in a container shape by the bottom wall portion and the side wall portion.
The bottom wall and the side wall are perpendicular to the thickness direction of each part.
Irregularities that increase the heat flow path length in the direction
It is made to be done. The bottom wall and the front
The side wall portion is a laminate of pyrolytic boron nitride having a layer structure.
It may be formed. Also, the invention according to another invention
The method of manufacturing a compound semiconductor crystal is to put raw materials in a crucible,
The crucible is heated by a heater to melt the raw materials, and
Compound by bringing a seed crystal into contact with the raw material melt
In manufacturing method of compound semiconductor crystal for growing body crystal
The temperature gradient in the crystal growth direction in the raw material melt is
When the temperature gradient becomes larger than the desired temperature gradient,
Is smaller than the desired temperature gradient.
The crucibles are used differently. This
For growing crystals under conditions of large temperature gradients
The temperature gradient in the raw material melt
The temperature in the melt under conditions where the temperature gradient is small.
Because it can prevent the degree gradient from becoming too small,
Produces low dislocation density single crystals, especially long single crystals with good yield
Can be built.

More specifically, in the case of the above (1) by setting the temperature of the heater or the like, that is, when the temperature gradient is large as shown by the line (a) in FIG. 4, a crucible as shown in FIG. 100 is used. In the crucible 100, the bottom plate portion 101 has a three-layer structure including three layers having the same thickness, and the first layer 102 includes pBN,
The second layer 103 is pG (pyrolytic graphite), the third layer 1
04 consists of pBN. pBN and pG has a layer structure, both have anisotropic thermal conductivity, a ₁ direction in it in a direction perpendicular (Fig than its thickness direction (c ₁ direction in FIG. 5) ) Has a higher thermal conductivity. Moreover, pG more anisotropy is strong as compared with pBN, is attached to the c ₁ direction of the heat conductivity pG is smaller than pBN, a
_{For one-} way thermal conductivity, pG is greater than pBN.

The side plate portion 105 of the crucible 100 is made of a laminate of pBN in the example shown in FIG. 5, and is more perpendicular to the thickness direction (the c ₂ direction in FIG. 5) than the thickness direction (the a ₂ direction in FIG. 5). Has a higher thermal conductivity. The bottom plate portion 101 and the side plate portion 1 of the crucible 100 configured as described above.
Table 1 shows the measured values of the thermal conductivity at room temperature of No. 05. From the table, the thermal conductivity of the bottom plate portion 101 in the a ₁ direction is
It can be seen that the size is much larger than that of a conventional crucible composed of a laminate of only pBN as shown in FIG.

[Table 1]

Note that the second layer 103 is not limited to pG,
The larger the a ₁ direction thermal conductivity than the material of the layer 102 may be any material. The material of the first layer 102 and the second layer 103 is not limited to pBN. Any material may be used for the first layer 102 as long as it does not react with the raw material melt at the growth temperature and does not contaminate the melt and the crystals. Well, third
The layer 104 may be made of any material as long as it has excellent heat resistance and does not contaminate the crystal. Generally, the bottom plate portion 101 and the side plate portion 105 of the crucible 100 have substantially the same thickness.

In the case of the above (2), that is, when the temperature gradient is small as shown by the line (b) in FIG. 4, a crucible 110 as an example in FIG. 6 is used. Although this crucible 110 is not particularly limited, for example, p having a layer structure
It is formed of a laminate of BN (in FIG. 6, for example, has a three-layer structure), and fine irregularities are formed on the bottom plate portion 111 and the side plate portion 115. That is, each layer of PBN forming the plate portions 111 and 115 has a finely meandering shape due to the unevenness, and the direction perpendicular to the thickness direction of each of the plate portions 111 and 115 (a ₃ in FIG. 6). path length of the heat flow in the direction, and a _4-direction) is longer than the path length of the heat flow in the corresponding portion of the crucible (conventional crucible is flatly laminated pBN) shown in FIG. Normally, a crucible 110 whose example is shown in FIG. 6 is manufactured by using a mold base having irregularities on its surface and stacking PBN with a uniform thickness on the mold base.

That is, in this crucible 110, a
₃ direction and a ₄ direction of the heat conductivity is smaller than the direction of the heat conductivity corresponds in crucible shown in FIG. Conversely, thermal conductivity in the thickness direction (c ₃ direction and c ₄ direction in FIG. 6) of the bottom plate 111 and the side plate portion 115 is larger than in the direction of the thermal conductivity corresponding in crucible shown in FIG. 8 . Table 2 shows the measured values of the thermal conductivity at room temperature of the bottom plate 111 and the side plate 115 of the crucible 110 configured as described above.

[Table 2]

In FIG. 4, the vertical axis represents the positions of the raw material melt, the liquid sealant (B ₂ O ₃ ) and the high-pressure filling gas (N ₂ ). The higher the distance, the further away from the bottom of the crucible . The horizontal axis is an axis representing temperature, and the temperature becomes higher as going to the right.

[0016]

According to the crucible 100 described above, the bottom plate 101
Since the heat conductivity in the a ₁ direction in the above is much higher than that of the conventional crucible (see FIG. 8), the heat dissipated (supplied) from the heater is more easily transmitted to the central portion of the bottom plate portion 101 than the conventional crucible. Temperature difference in the a ₁ direction in the raw material melt,
That is, the gradient becomes smaller. Further, since the bottom plate portion 101 is hotter than the bottom plate portion of a conventional crucible, a ₂ direction in the raw material melt in, that the temperature gradient in the crystal growth direction is reduced. Therefore, when a crystal is grown under conditions where the temperature gradient is large and twins and polycrystals are unlikely to occur as shown by the line (a) in FIG. 4, the use of this crucible 100 increases the temperature gradient in the melt. Not only can it be prevented from passing too far, but also the shape of the solid-liquid interface can be changed from the shape shown in FIG. 1 (a shape convex to the melt) to the shape shown in FIG. 2 (a shape flat with the melt). Can be approached moderately. Therefore, it is possible to grow a single crystal having a low dislocation density without a twin or a polycrystalline portion.

Further, according to the crucible 110 described above, the thermal conductivity in the a ₃ direction of the bottom plate portion 111 and in the a ₄ direction of the side plate portion 115 is smaller than that of the conventional crucible (see FIG. 8). since c ₄ direction of the heat conductivity in the c ₃ direction and the side plate portion 115 is larger than a conventional crucible, heat dissipated from the heater than conventional crucible not easily transmitted to the central portion of the bottom plate portion 111, thus the raw material melt The temperature gradient in the a ₃ direction inside becomes large. Further, since the heat flow is not easily transmitted to a _4-direction of the side plate portion 115,
The temperature gradient of the crystal growth direction in the raw material melt in (a ₄ direction) increases. Therefore, when a crystal is grown under conditions where the temperature gradient is small and the occurrence of dislocation due to thermal stress is easily reduced as shown by the line (b) in FIG. 4, the use of the crucible 110 reduces the temperature gradient in the melt. By preventing the size from becoming too small, the shape of the solid-liquid interface can be appropriately approximated to the shape shown in FIG. 1 (a shape that is convex with respect to the melt). Therefore, it is possible to grow a single crystal having a low dislocation density and no twin or polycrystalline portion.

[0018]

The characteristics of the method for producing a compound semiconductor crystal according to the present invention will now be described with reference to examples and comparative examples. In Examples and Comparative Examples, a liquid for growing a crystal by putting a raw material in a crucible, heating the crucible with a heater to melt the raw material, bringing a seed crystal into contact with the raw material melt, and gradually pulling up the crystal. I doped with sulfur (S) by sealed Czochralski (LEC) method
An nP single crystal was grown.

Example 1 The temperature of the heater was controlled so as to have a relatively large temperature gradient in the crystal growth direction in the liquid sealant as shown by the line (a) in FIG. Using the crucible 100 shown, 2 inches in diameter and 100-120 mm in length
Crystals of some degree were grown. In addition, in order to reduce the dissociation of the group V element, that is, P, B ₂ O ₃ was used as a liquid sealant, and argon (Ar) gas or nitrogen (N ₂ ) gas was sealed at a high pressure for growth. (Comparative Examples 1 and 2) In Comparative Example 1, a conventional quartz crucible was used, and in Comparative Example 2, a flat p-type crucible shown in FIG.
Using a conventional crucible made of a BN laminate, crystals were grown under the same conditions as in Example 1 above. Table 1 shows the thermal conductivity of the quartz crucible and the conventional pBN crucible. The crucible 10 used in the first embodiment was used.
0 and the crucibles used in Comparative Examples 1 and 2 had the same outer shape and thickness.

From the single crystals obtained in Example 1, Comparative Example 1 and Comparative Example 2, thin substrates (wafers) were cut out. FIG. 7 shows the relationship between the sulfur concentration in the crystals of each substrate and the area of the dislocation-free region at the center of the substrate. In the figure, Example 1 is indicated by a circle, Comparative Example 1 is indicated by a triangle, and Comparative Example 2 is indicated by a square. As can be seen from the figure, the sulfur concentration is 7 × 10 ¹⁸ cm ⁻³ (the upper limit measured on the substrate obtained from the crystal of Example 1). Therefore, Example 1 has a larger area of the dislocation-free region. That is, it can be seen that the crystal obtained in Example 1 is superior to the crystals obtained in Comparative Examples 1 and 2. In particular, the crystals obtained in Example 1 had a sulfur concentration of 5 × 10 ¹⁸ cm ⁻³ or less, and the crystals of Comparative Example 1 and
It turns out that it is much better than 2.

The rate at which a single crystal was obtained, that is, the rate of single crystallization was 90% or more in each case, and almost no difference was observed between the above Examples and Comparative Examples. The heat conduction in the radial direction (the direction perpendicular to the crystal growth direction) at the bottom of the crucible 100 used in Example 1 is much larger than that of the crucible used in Comparative Example 2. Therefore, in Example 1, the radial temperature gradient at the bottom of the crucible 100 is reduced, and accordingly, the radial temperature gradient in the raw material melt is also reduced. Furthermore, the radial temperature gradient in the raw material melt is reduced, so that the radial temperature gradient in the grown crystal is reduced. The increase in the area of the dislocation-free region in the crystal obtained in Example 1 is due to the fact that the temperature gradient in the radial direction of the crystal was small during the growth and the generation of dislocation due to thermal stress was suppressed. . On the other hand, the heat conduction of the side plate 105 of the crucible 100 used in Example 1 is not different from the crucible used in Comparative Example 2. Therefore, at least, the temperature gradient in the crystal growth direction in the liquid sealant located at the upper end of the raw material melt that is hardly affected by the crucible bottom is almost the same as that of Comparative Example 2 or slightly smaller than Comparative Example 2. And twins and polycrystals occur,
It can be seen that the temperature gradient in the crystal growth direction has not decreased.

(Example 2) By controlling the temperature of the heater and providing a hood for keeping the temperature, as shown by the line (b) in FIG. The crystal was grown using a crucible 110 shown in FIG. Other conditions are the same as those in Example 1 above.
Was the same as The outer shape and thickness of the crucible 110 used in the second embodiment were the same as those of the crucible 100 used in the first embodiment. (Comparative Example 3) Using the conventional pBN crucible shown in FIG. 8, a crystal was grown under the same conditions as in Example 2 above.

In each of the substrates cut out from the crystals of Example 2 and Comparative Example 3, the concentration of sulfur was 3 × 10 ¹⁸
７7 × 10 ¹⁸ cm ⁻³ (This is the upper limit measured on the substrate obtained from the crystal of Example 2.) In the following range, the areas of the dislocation-free regions were almost the same. Further, 10 crystals each grown in Example 2 and Comparative Example 3 were observed. Table 3 shows the results. As can be seen from the table,
In Comparative Example 3, twins were formed in the straight body of all the crystals,
Although a single crystal containing no twin could not be grown, in Example 2, half or more (six) single crystals could be grown. In Comparative Example 3, twins were generated in all of the grown crystals, and at least when growing the straight body, the temperature gradient in the crystal growth direction in the liquid sealant was too small. I understand. On the other hand, in Example 2, generation of twins was suppressed, and at least the temperature gradient in the crystal growth direction in the liquid sealant was kept larger than that in Comparative Example 3. On the other hand, the occurrence of dislocations due to thermal stress is kept low as in Comparative Example 3, and during the growth, the temperature gradient in the radial direction of the crystal, that is, the radial gradient in the raw material melt that determines it. It can be seen that the temperature gradient is as small as Comparative Example 3 or slightly larger than Comparative Example 3.

[Table 3]

(Embodiment 3) The temperature of the heater is controlled to have a relatively large temperature gradient in the crystal growth direction in the liquid sealant as shown by the line (a) in FIG. Using the crucible 110 shown, a crystal having a diameter of about 2 mm and a length of about 200 mm was grown. Other conditions were the same as those in Example 1. (Comparative Example 4) Using the conventional pBN crucible shown in FIG. 8, a crystal was grown under the same conditions as in Example 3 above.

Three crystals each grown in Example 3 and Comparative Example 4 were observed. Table 4 shows the results. As can be seen from the table, in Comparative Example 4, polycrystals were formed in the straight body of all the crystals, and it was not possible to grow a long single crystal. No elongation occurred, and a long single crystal could be grown.
Thus, the crucible 110 contains 100 grown crystals.
mm or more, that is, when the remaining amount of the raw material melt becomes small, there is an effect of preventing the temperature gradient in the crystal growth direction from becoming too small, and the crucible 110 grows a long crystal. It turns out that it is suitable.

[Table 4]

In the above embodiment, the growth of an InP single crystal having a diameter of 2 inches has been described as an example. However, a similar effect can be obtained even when growing a crystal having a diameter of up to about 8 inches. Also, not limited to InP, GaAs
The same effect can be obtained in crystal growth of other III-V group compound semiconductors and II-VI group compound semiconductors. further,
In addition to the LEC method, liquid-sealed chiroporous (LE
In the case of growing a crystal from a raw material melt using a crucible, such as the K) method, it is of course generally applicable.

[0027]

According to the present invention, when a crystal is grown under a condition of a large temperature gradient, the temperature gradient in the raw material melt is prevented from becoming too large. Since the temperature gradient in the liquid can be prevented from becoming too small, a single crystal having a low dislocation density, in particular, a long single crystal can be manufactured with high yield.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a growth interface of a grown crystal in a preferable state.

FIG. 2 is a schematic diagram showing a growth interface of a grown crystal in an unfavorable state.

FIG. 3 is a schematic diagram showing a growth interface of a grown crystal in an unfavorable state.

FIG. 4 is a schematic diagram showing a temperature gradient in a crucible during crystal growth.

FIG. 5 is a schematic sectional view showing an example of the crucible according to the present invention.

FIG. 6 is a schematic sectional view showing another example of the crucible according to the present invention.

FIG. 7 is a characteristic diagram illustrating a relationship between a sulfur concentration and a non-dislocation region area in Example 1 and Comparative Examples 1 and 2.

FIG. 8 is a schematic sectional view of a conventional pBN crucible.

[Explanation of symbols]

 100,110 Crucible 101,111 Bottom plate part 102 First layer 103 Second layer 104 Third layer 105,115 Side plate part

Claims (7)

(57) [Claims] 1. A raw material is charged, and the raw material is heated and melted.
And contact the seed crystal with the raw material melt.
Compound semiconductor crystal manufacturing method for growing oxide semiconductor crystal
The crucible used, The crucible is formed in a container shape by the bottom wall and the side wall.
And The bottom wall consists of the first layer facing the inside of the crucible and the outside
At least two layers consisting of a second layer located at
Having a structure, The thermal conductivity of the second layer in the crystal growth direction is
Smaller than the thermal conductivity in the crystal growth direction in one layer, and
Heat transfer in a direction perpendicular to the crystal growth direction in the second layer.
Conductivity in the direction perpendicular to the crystal growth direction in the first layer
Has a heat conduction property larger than the heat conductivity, The side wall is more perpendicular to its thickness than its thickness.
That the thermal conductivity has a larger thermal conductivity characteristic, Used in a method for producing a compound semiconductor crystal, characterized by the following:
Bo. 2. The method of claim 1, wherein said first layer comprises pyrolytic boron nitride.
The second layer is made of pyrolytic graphite.
Used in the method for producing a compound semiconductor crystal according to claim 1.
Crucible. 3. The bottom wall portion has a third layer outside the second layer.
A layer is provided, and the first layer and the third layer sandwich the second layer
Sandwich structure, The first and third layers are made of pyrolytic boron nitride,
Characterized in that the two layers are made of pyrolytic graphite
Ruth used in the method for producing a compound semiconductor crystal according to claim 1
Bo. 4. The side wall portion is a laminate of pyrolytic boron nitride.
4. The method as claimed in claim 1, wherein the second member is formed.
Ruth used in the method for producing a compound semiconductor crystal according to any of the above.
Bo. (5) Put the raw materials, heat the raw materials and melt
And contact the seed crystal with the raw material melt.
Compound semiconductor crystal manufacturing method for growing oxide semiconductor crystal
The crucible used, The crucible is formed in a container shape by the bottom wall and the side wall.
And The bottom wall and the side wall are perpendicular to the thickness direction of each part.
Irregularities that increase the path length of heat flow in various directions
Manufacture of compound semiconductor crystal characterized by being formed
Crucible used for the method. 6. The bottom wall and the side wall have a layered structure.
Characterized by being formed of a laminate of pyrolytic boron nitride
A method for producing a compound semiconductor crystal according to claim 5,
Crucible. 7. A raw material is put in a crucible, and the crucible is heated.
To melt the raw material and seed the raw material melt.
A compound semiconductor crystal by contacting the crystal
In a method for producing a compound semiconductor crystal, Desirable temperature gradient in the crystal growth direction in the raw material melt
If the temperature gradient becomes larger than
Using the crucible according to any one of claims 4 When said temperature gradient is smaller than the desired temperature gradient
Uses the crucible according to claim 5 or claim 6.
When, A method for producing a compound semiconductor crystal, comprising: