JPH1087392A - Production of compound semiconductor single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce compound semiconductor single crystals, especially compound semiconductor single crystals of zinc-blend structure such as GaAs and InP, by a VGF method or VB method in high yield by preventing generation of twin crystals at a crystal diameter increasing part. SOLUTION: In production of the compound semiconductor single crystals, a crucible 1, which has a seed crystal setting part 1a at a center of a bottom part, a bottom surface of which inclines with a prescribed angle α of 80 deg.<= and <90 deg. to a vertical direction so that the botton surface gradually is lowered toward its center and in which a corner part between the bottom surface and a flank has radius of curvature of 0<= to <=10mm, is used. At the time of executing crystal growing by the VGF method (vertical gradient freezing method) or VB method (vertical Bridman method), the temp. gradient of a molten raw material 3 at least at an inclined bottom part of the crucible 1, that is, in a region from a solid-liquid boundary between the seed crystal 2 and the molten raw material 3 at a point of crystal growing starting to beginning of growing of a straight cylindrical part of the crystals, is set to 1<= to <5 deg.C/cm, preferably 2<= to <=4.5 deg.C/cm and more preferably 3<= to <=4 deg.C/cm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a compound semiconductor single crystal, for example, vertical gradient freezing (hereinafter referred to as VGF) in which a raw material melt of a compound semiconductor is cooled to grow a single crystal in a vertical direction. The present invention relates to a technique which is useful when applied to the method and the vertical Bridgman (hereinafter referred to as VB) method.

[0002]

2. Description of the Related Art Generally, in manufacturing a compound semiconductor single crystal ingot, a liquid-sealed Czochralski (L) is used.
The EC) method or the horizontal Bridgman (HB) method is used industrially. Although the LEC method, the cross-sectional shape with a large diameter circular wafer is obtained, which has advantages such as high purity crystals are obtained due to the use of liquid sealant (B ₂ 0 _3), crystal growth The dislocation density in the crystal increases due to the large temperature gradient in the direction, and the FE fabricated using the crystal
There is a disadvantage that electrical characteristics of electronic devices such as T (field effect transistor) are deteriorated. On the other hand, HB
The method has the advantage that a crystal having a low dislocation density can be obtained because the temperature gradient in the crystal growth direction is small, but it is difficult to increase the diameter because the raw material melt of the compound semiconductor is solidified in the crucible. In addition, there is a disadvantage that the cross-sectional shape of the wafer becomes a semi-cylindrical shape.

Therefore, as a single crystal manufacturing method having both advantages of the LEC method and the HB method, a vertical gradient freezing (VGF) method and a vertical Bridgman (VB) method have been proposed.
A law has been proposed. In these VGF and VB methods, a circular wafer is obtained because of using a cylindrical reed.
Since the temperature gradient in the crystal growth direction is small, a crystal having a low dislocation density can be easily obtained. However, VGF
Method and the VB method are susceptible to the effects of slight temperature fluctuations in the furnace or the irregularities and foreign matter on the crucible wall,
There is a disadvantage that twins and polycrystals are easily generated.

[0004] Among these drawbacks, the influence of temperature fluctuations in the furnace has been solved by the recent development of temperature control technology. Also, the generation of polycrystals from the crucible wall can be prevented by using the liquid sealant (B ₂ O ₃ ).

[0005] However, no effective preventive measures have yet been proposed for the generation of twins. In particular, the probability of twinning in the crystal diameter-increased portion from the crystal growth start point to the straight body portion is higher than that of the straight body portion of the crystal, which is a main cause of lowering the yield of single crystal production. .

When a compound semiconductor single crystal having a zinc blende structure such as GaAs, InP, or GaP is grown using a seed crystal, the angle of the diameter-increased portion from the seed crystal to the straight body and the probability of twinning are generated. It turns out that there is a close relationship between That is, when growing a crystal of (100) orientation,
A (111) facet surface appears in the diameter-increased portion, and twins are generated from the facet surface. This has been confirmed in experiments performed by the present inventors. That is, when the present inventors performed crystal growth, in the crystal in which twins were generated, all twins were generated along facet growth.

The (111) facet makes an angle of 54.7 ° with the (100) orientation. Therefore, in general, (11
1) In order to prevent the appearance of the facet surface, the angle of the increased diameter portion is set to [90 ° -54.7 °], that is, 35.3 ° or less. However, when the angle of the diameter-increased portion is reduced, the obtained crystal has a long diameter-increased portion, and the yield of the wafer is reduced, resulting in poor productivity. Therefore, attempts have been made to set the angle of the diameter-increased portion to about 40 ° to 50 °, but a sufficient effect has not been obtained in terms of suppressing the generation of twins.

In Japanese Patent Application Laid-Open No. Hei 5-194073, a crucible in which the angle of the diameter-increased portion is 80 ° to 100 ° is used, and a region near the seed crystal is locally supercooled to be substantially cooled. A crystal is grown in a horizontal direction, and the crystal is grown so as to have an upward convex shape.
A crystal production method is disclosed, which is cooled and solidified under a temperature gradient of 15 / cm to 15 ° C / cm. In this manufacturing method, in order to cool the raw material melt while maintaining a temperature gradient of 5 ° C./cm to 15 ° C./cm, a pipe for a cooling medium is provided on a heat sink, and a cooling medium is flowed through the pipe. The heat radiation of the heat sink is improved. Note that Japanese Patent Application Laid-Open
According to -194073, when the temperature gradient is less than 5 ° C./cm, it is difficult to control the temperature distribution of the melt so that the isothermal surface of the material melt is convex toward the melt, and a single crystal grows. It is difficult. Further, it is said that when the temperature gradient exceeds 15 ° C./cm, the material is rapidly solidified, dendrites are generated, and polycrystallization is likely to occur.

[0009]

However, it has been found by the present inventors that the crystal manufacturing method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 5-194073 has the following problems. That is, in Japanese Patent Application Laid-Open No. 5-194073, a temperature gradient during cooling is controlled by 5 to control the temperature distribution of the melt so that the isothermal surface of the raw material melt is convex toward the melt.
It must be at least ° C / cm. But,
When the temperature gradient is 5 ° C./cm or more, temperature fluctuation due to convection in the raw material melt is not sufficiently reduced, and twins and polycrystals are easily generated. That is, the generation of twins and polycrystals cannot be sufficiently suppressed. In addition, there is also a disadvantage that a large cost is required because the piping for the cooling medium is provided in the heat sink.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is intended to prevent twins from being generated in a crystal diameter-increased portion and to obtain a high yield of a compound semiconductor single crystal, especially GaAs or InP. It is another object of the present invention to provide a single crystal manufacturing method capable of manufacturing a compound semiconductor single crystal having a zinc blende structure by a VGF method or a VB method.

[0011]

Means for Solving the Problems To achieve the above object, the present inventors performed crystal growth by using a crucible having a substantially flat bottom surface, thereby increasing the diameter of a diameter-increased portion having a high probability of twinning. It was thought that a crystal could be grown without forming a crystal. Also, by growing the crystal from the raw material melt in a flat shape without growing in an upwardly convex shape, the temperature gradient in the raw material melt can be made less than 5 ° C./cm, and the temperature fluctuation can be reduced. Was. Furthermore, if the radius of curvature of the portion of the grown crystal that transitions from the crystal shoulder to the straight body is large, the time required for crystal growth in that portion becomes longer, and the number of facets generated increases, so twins are more likely to occur. Therefore, it was considered effective to set the radius of curvature of the transition from the crystal shoulder to the straight body to a value within a predetermined range.

The present invention has been made based on the above point of view, wherein a seed crystal is set in a seed crystal setting portion of a crucible having a seed crystal setting portion in the center of the bottom, and the raw material and sealing of the compound semiconductor are placed in the crucible. After filling the crucible into an airtight container, the crucible is placed in a vertical heating furnace, and the raw material and the sealant are heated and melted by a heater. Is gradually cooled from the lower side and solidified upward from the seed crystal to grow a single crystal of a compound semiconductor, particularly a compound semiconductor having a zinc blende type structure. 80 ° to the vertical direction so that it gradually decreases toward
In addition to using a crucible inclined at a predetermined angle of 90 ° or more and less than 90 °, the temperature gradient in the crystal growth direction at least at the bottom of the crucible at the time of crystal growth is 1 ° C./cm or more.
The temperature is controlled to be less than 2 ° C / cm, preferably 2 ° C / cm to 4.5 ° C / cm, more preferably 3 ° C / cm to 4 ° C / cm. In the present invention, the radius of curvature of the boundary between the bottom surface and the side surface of the crucible, that is, the radius of curvature of the corner corresponding to the transition from the crystal shoulder to the straight body of the grown crystal is 0 mm or more and 10 mm or less. is there.

As a result, crystals grow flat from the raw material melt without forming a diameter-increasing portion. Further, since the temperature gradient at the time of cooling and solidifying the raw material melt is small, the temperature fluctuation is reduced. Further, the crystal growth time of the transition portion of the grown crystal from the crystal shoulder portion to the straight body portion is shortened, generation of facets is suppressed, and generation of twins is prevented. According to the study of the present inventors, as a result of measuring the temperature fluctuation with a thermocouple provided in contact with the outside of the portion corresponding to the bottom of the crucible of the hermetic container in which the raw material and the sealant are sealed, the temperature fluctuation is ± 0. It is appropriate that the temperature is not more than 0.1 ° C.

[0014]

FIG. 1 shows a crucible used in the practice of the present invention. FIG. 2 schematically shows a crystal growth furnace used when the present invention is applied to the VGF method.

In the method for producing a single crystal according to the present invention, as shown in FIG. 1, a seed crystal installation portion 1a is provided at the center of the bottom of the crucible 1, and the bottom surface 1b of the crucible 1 is gradually lowered toward the center. 80 ° or more with respect to vertical direction 9
A crucible 1 formed to be inclined at a predetermined angle α of less than 0 ° is used. Angle α of bottom surface 1a of crucible 1
The reason why is less than 80 ° and less than 90 ° is that if the angle is less than 80 °, the temperature gradient of the diameter-increased portion is apt to be formed, and as a result, the temperature fluctuation becomes large and twins are generated. This is because another grain boundary grows in the portion and becomes polycrystalline.

The crucible 1 has a bottom surface 1b and a side surface 1b.
The radius of curvature of the corner portion 1d corresponding to the boundary portion with c, that is, the transition portion from the crystal shoulder portion to the straight body portion of the grown crystal is 0 mm.
It is not less than 10 mm. Crucible 1
The radius of curvature of the corner 1d between the bottom surface 1b and the side surface 1c is 0 mm.
The reason for being not less than 10 mm is that according to the study results of the present inventors, if the radius of curvature is larger than 10 mm, the probability of twinning increases, which is not preferable.
As for the lower limit of the radius of curvature, the smaller the radius of curvature, the more the occurrence of facets can be prevented.
The radius of curvature may be 0 mm, that is, the corner 1d may not be a curved surface.

Then, as shown in FIG. 2, the seed crystal 2 is put in the seed crystal setting portion 1a of the crucible 1, and the compound semiconductor raw material 3 and the sealant 4 are put in the crucible 1. The element 6 for controlling the vapor pressure is provided in the vapor pressure control section (reservoir) 5a of the airtight container 5.
The crucible 1 is placed on the susceptor 7 in the crystal growing section 5b of the hermetic container 5, and the inside of the hermetic container 5 is evacuated and sealed with the cap 5c. The vapor pressure controlling element 6 is a simple substance or a compound composed of an element that is easily volatilized among the constituent elements of the single crystal to be grown.

The hermetic container 5 is placed at a predetermined position in a vertical heating furnace 8 and heated by a heater 9 to melt the raw material 3 and the sealant 4. Although not particularly limited, for example, a cylindrical three-stage heater including at least a heater 9A for a crystal growing unit, a heater 9B for a seed crystal unit, and a heater 9C for a vapor pressure control unit may be used as the heater 9.

The outputs of the heaters 9A, 9B, and 9C are adjusted to gradually increase the temperature from the seed crystal 2 toward the upper part of the raw material melt 3 while maintaining a predetermined temperature gradient. The single crystal 10 is grown upward by cooling the raw material melt 3 from below to a temperature below the melting point. At that time, the steam pressure in the airtight container 5 is maintained at an appropriate pressure by adjusting the output of the heater 9C for the steam pressure control unit.

Here, regarding the temperature gradient during cooling, at least the inclined bottom portion of the crucible 1, that is, the growth of the straight body of the crystal from the solid-liquid interface between the seed crystal 2 and the raw material melt 3 at the start of crystal growth. The temperature gradient in the region (see FIG. 1 and region D in FIG. 1) until the start of the heating is 1 ° C./cm or more and 5 ° C.
/ Cm, preferably 2 ° C / cm or more and 4.5 ° C / cm or less,
More preferably, the temperature is 3 ° C./cm or more and 4 ° C./cm or less. The reason is that when the temperature gradient is less than 1 ° C./cm, the temperature is easily affected by the ambient temperature, and when the temperature gradient is 5 ° C./cm or more, the temperature fluctuation becomes large. Further, if the temperature gradient is 2 ° C./cm to 4.5 ° C./cm, there is an advantage that an appropriate growth rate and a single crystallization rate can be obtained, and the temperature gradient is 3 ° C./cm to 4 ° C./cm. Is more preferable.

A thermocouple 11 is provided in contact with the outside of the airtight container 5 at a position corresponding to the bottom of the crucible.
And confirm that the temperature fluctuation is within a predetermined range. The outputs of the heaters 9A, 9B, 9C may be adjusted so that the measured temperature fluctuation is within a predetermined range. The allowable range of the temperature fluctuation is obtained through preliminary experiments and the like. As a result of conducting a preliminary experiment with the configuration shown in FIG. 2, it was found that the allowable range of the temperature fluctuation was ± 0.1 ° C. or less. The reason is that if the temperature fluctuations deviate from the allowable range, twins and polycrystals are likely to be generated.

According to the above embodiment, the bottom surface 1 of the crucible 1
b is inclined at a predetermined angle α of 80 ° or more and less than 90 ° with respect to the vertical direction so as to gradually decrease toward the center thereof, and the corner 1d between the bottom surface 1b and the side surface 1c is formed. A crucible 1 having a radius of curvature of 0 mm or more and 10 mm or less is used, and at least the temperature gradient in the crystal growth direction of the inclined crucible bottom (region D) is 1 ° C./cm or more.
The raw material melt 3 is gradually cooled while controlling so as to be less than 2 ° C./cm, preferably 2 ° C./cm or more and 4.5 ° C./cm or less, more preferably 3 ° C./cm or more and 4 ° C./cm or less. Since the compound semiconductor single crystal is grown by the VGF method, the crystal 10 grows flat from the raw material melt 3 along the bottom surface 1b of the crucible 1 without forming the diameter-increased portion of the crystal 10 and then solidifies. Crystals 10 with the liquid interface still flat
Grow upward. Therefore, since there is no crystal diameter increasing part, the yield of the wafer from the obtained single crystal ingot is high and the productivity is good. In addition, the temperature gradient at the time of solidification of the raw material melt 3 is small, the temperature fluctuation is small, and the generation of facets at the transition from the crystal shoulder to the straight body is suppressed. Is suppressed, and a single crystal can be obtained with a high yield.

Furthermore, since the heating furnace 8 does not require piping for a cooling medium, a conventional heating furnace can be used as it is, and therefore, high quality without twins or polycrystals can be obtained without increasing costs. Is obtained with a high yield.

In the above embodiment, the case where the present invention is applied to the VGF method has been described, but the present invention is also applicable to the VB method.

[0025]

EXAMPLES The features of the present invention will be clarified below with reference to examples and comparative examples. The present invention is not limited by the following embodiments.

(Example 1) As a crucible, a pBN crucible 1 having a diameter of about 3 inches and a thickness of 3 mm and having a shape shown in FIG. 1 was used.
Was used. Also, the bottom surface 1b of the crucible 1 in the vertical direction
Was made to be 87 ° C. The radius of curvature of the corner 1d of the crucible 1 between the bottom surface 1b and the side surface 1c was 4 mm.

A seed crystal 2 made of GaAs single crystal is put into the seed crystal setting portion 1 a of the crucible 1, and about 3 kg of GaAs polycrystal as a raw material 3 and an appropriate amount of B ₂ O ₃ as a sealant 4 are further placed in the crucible 1. I put it. Subsequently, 8 g of arsenic is added as a vapor pressure control element 6 to the vapor pressure control unit 5 a of the quartz ampoule, which is the hermetic container 5, and the crucible 1 containing the raw material 3 and the sealant 4 is placed on the susceptor 7 in the quartz ampoule. , And vacuum sealed with a cap 5c. Then, the airtight container 5 was installed in a vertical heating furnace 8 having a three-stage heater configuration as shown in FIG. Instead of using GaAs polycrystal as the raw material 3, Ga and As may be put in the crucible 1 and they may be directly synthesized.

The upper end of the seed crystal 2 and the raw material 3 are heated to 1238 ° C. by the heater 9A for the crystal growing part and the heater 9B for the seed crystal part.
The crucible 1 was heated to a temperature of １２1255 ° C. to melt the raw material 3 and the encapsulant 4, and the vapor pressure control unit 5a was heated to 605 ° C. by the vapor pressure control unit heater 9C. Further, a region D from the inclined bottom portion of the crucible 1, that is, the solid-liquid interface between the seed crystal 2 and the raw material melt 3 at the start of crystal growth to the start of growth of the crystal straight body portion.
Was adjusted to 3.5 ° C./cm. At this time, the temperature fluctuation measured by the thermocouple 11 was ± 0.0
6 ° C.

In this state, the crystal growth was started by continuously lowering the set temperature of the heating furnace 8 so that the crystal growth rate was 2 mm / h. About 30 hours after the start of crystal growth, the raw material melt 3 was completely solidified. Then, heating furnace 8
The whole was cooled at a cooling rate of 100 ° C./hour, and when cooled to near room temperature, the airtight container 5 was taken out of the heating furnace 8, and the airtight container 5 was broken to take out a crystal. The obtained crystal has a diameter of about 3 inches and a total length of about 12 cm.
It was an aAs single crystal, and when its crystallinity was examined, no twin or polycrystal was generated. When the dislocation density was adjusted by cutting this single crystal ingot, the dislocation density was 1000 cm ⁻² or less in any region of the crystal.

When GaAs single crystal was grown 20 times under the same conditions as in the above embodiment, a single crystal without twins or polycrystals was obtained 18 times.

Example 2 A single crystal of GaAs was grown under the same conditions as in Example 1 except that the radius of curvature of the corner 1d between the bottom surface 1b and the side surface 1c of the crucible 1 was 10 mm. I went there. As a result, for four crystal growths,
A single crystal without twins or polycrystals was obtained. The radius of curvature was made slightly larger than in Example 1 above (4 mm was changed to 10 mm).
However, although the yield of the single crystal was slightly reduced, the yield was better than that of a comparative example described later.

The present invention is also effective when a compound semiconductor having a zinc blende structure such as InP or GaP is manufactured by VGF or VB method other than GaAs.

Comparative Example 1 A GaAs single crystal was manufactured in the same manner as in Example 1 above, using a pBN crucible in which the angle α formed by the bottom of the crucible with respect to the vertical direction was 30 °. Was. The conditions other than the crucible bottom angle α were the same as those in the first embodiment. In the obtained crystal, twins are generated in the crystal diameter increasing portion from the seed crystal to the straight body portion, and the orientation has changed, so that it is impossible to use the crystal as a crystal for a semiconductor substrate. It was possible. When GaAs single crystal was grown five times under the same conditions, two of the obtained five crystals were single crystals, but three crystals had twins and were unusable. It was possible.

Comparative Example 2 The same crucible 1 as in Example 1
The GaAs single crystal was manufactured in the same manner as in Example 1 except that the temperature gradient of the inclined bottom portion (the region D) of the crucible 1 was set to 15 ° C./cm. In addition, crucible 1
The conditions other than the temperature gradient at the bottom of were the same as in the above example. The temperature fluctuation during the crystal growth was measured by the thermocouple 11, and was found to be ± 0.3 ° C. In the obtained crystal, polycrystal was generated in the diameter-increased portion, and it was impossible to use the crystal as a crystal for a semiconductor substrate. When GaAs single crystal growth was performed five times under the same conditions, only one of the obtained five crystals was a single crystal, and polycrystals were generated in the other four crystals. And was unusable. In addition, only one single-crystal GaAs
When the dislocation density was examined by cutting the s crystal, the dislocation density exceeded 5000 cm ^-2 in any region of the crystal.

[0035]

According to the present invention, a seed crystal is set in a seed crystal setting portion at the bottom of a crucible, a raw material of a compound semiconductor and a sealant are put in the crucible, and the crucible is sealed in an airtight container. Placing the airtight container in a vertical heating furnace, heating and melting the raw material and the sealant with a heater, and gradually cooling the obtained raw material melt from below to upward from the seed crystal. In growing the single crystal of the compound semiconductor by solidifying the crucible, the crucible forms a predetermined angle of 80 ° or more and less than 90 ° with respect to the vertical direction such that the bottom surface gradually decreases toward the center thereof. In addition to using a crucible inclined at the time of crystal growth, crystal growth is performed by controlling the temperature gradient in the crystal growth direction at least at the bottom portion of the crucible during crystal growth to be 1 ° C./cm or more and less than 5 ° C./cm. Because, because after the crystal growth start to not formed increased diameter of the crystal is immediately the development of the straight body portion is started,
The yield of wafers from the obtained single crystal ingot is high and the productivity is good. Further, since the temperature gradient at the time of solidification of the raw material melt is small and the temperature fluctuation is small, the generation of twins and polycrystals is suppressed, and a single crystal can be obtained with a high yield. Furthermore, since a heating furnace does not require piping for a cooling medium, a conventional heating furnace can be used as it is, so that a high-quality single crystal can be obtained at a high yield without increasing costs.

Further, according to the present invention, since the radius of curvature at the boundary between the bottom surface and the side surface of the crucible is 0 mm or more and 10 mm or less, the crystal at the transition from the crystal shoulder to the straight body of the grown crystal. The growth time is shortened, generation of facets is suppressed, and generation of twins is prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a crucible used for carrying out the present invention.

FIG. 2 is a schematic view of a crystal growth furnace used when the present invention is applied to a VGF method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crucible 1a Seed crystal installation part 1b Crucible bottom 1c Crucible side 1d Crucible corner 2 Seed crystal 3 Raw material 4 Sealant 5 Airtight container 8 Heating furnace (crystal growth furnace) 9 Heater 10 Single crystal

Claims (5)

[Claims] 1. A crucible having a seed crystal setting part at the center of the bottom, a seed crystal is set in the seed crystal setting part, a raw material of a compound semiconductor and a sealant are put in the crucible, and the crucible is placed in an airtight container. Then, the hermetic container is placed in a vertical heating furnace, the raw material and the sealant are heated and melted by a heater, and the obtained raw material melt is gradually cooled from the lower side to cool the seed. When growing a single crystal of a compound semiconductor by solidifying upward from the crystal, as the crucible, the crucible has an angle of 80 ° or more and less than 90 ° with respect to the vertical direction so that the bottom surface is gradually lowered toward the center. A crucible inclined at a predetermined angle is used, and at the time of crystal growth, a temperature gradient in a crystal growth direction at least at a bottom portion of the inclined crucible is controlled to be 1 ° C./cm or more and less than 5 ° C./cm. You Method for producing a compound semiconductor single crystal. 2. The method for producing a compound semiconductor single crystal according to claim 1, wherein a radius of curvature of a boundary portion between the bottom surface and the side surface of the crucible is 0 mm or more and 10 mm or less. 3. The method according to claim 1, wherein the temperature gradient in the crystal growth direction of the crucible bottom is controlled to be 2 ° C./cm or more and 4.5 ° C./cm or less. A method for producing a compound semiconductor single crystal. 4. The compound according to claim 1, wherein the temperature gradient in the crystal growth direction of the crucible bottom is controlled to be 3 ° C./cm or more and 4 ° C./cm or less. A method for manufacturing a semiconductor single crystal. 5. A compound semiconductor single crystal having a zinc-blende structure is grown.
The production method of the compound semiconductor single crystal according to the above.