JPH04265294A - Production of semiconductor crystal - Google Patents

Abstract

PURPOSE:To obtain a high-purity and large-diameter semiconductor crystal having a desired crystal type by carrying out the transformation into a desired crystal type, removal of impurities and vapor growth of the crystal in the same closed vessel out of contact with the external air. CONSTITUTION:The raw gases 3 such as SiH4 and C3H8 are passed through a CVD device with its vessel 1 enclosed by a heater 2 to form a beta-type SiC polycrystal powder 4. The powder 4 is placed in a crucible 11 arranged in a closed vessel. The crucible 11 is then high-frequency heated in an inert gas to transform the powder 4 into 6H-type SiC 51. The closed vessel is then evacuated and heated to remove the impurities 6 in the SiC 51. The crucible 11 is then heated to a high temp., vapor deposition is performed with the 6H-type SiC 52 freed of impurities as the raw material, and an SiC crystal 8 is vapor- grown on the surface of a seed-crystal substrate 12.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing semiconductor crystals used in visible light emitting devices, high temperature MOSFETs, etc.

0002

[Prior Art] Because SiC is extremely stable, it is not only being researched as an environmentally resistant element material, but also
It is attracting attention as a material for blue and violet light emitting diodes because it has various crystal structures with a wide forbidden band width of 2.39 to 3.33 eV and can be used to form pn junctions.

[0003] SiC has α (hexagonal) type and β (
Although it has a cubic (cubic) type crystal structure, it is the α type 6H type crystal that can grow large crystals with good reproducibility, and is the one that is most in practical use.

A method for producing this 6H type crystal is shown in FIG. As shown in this figure, there is a method of mixing silica sand 31 and carbon powder 33 in a container 32 and heating it, or a method of sublimating SiC powder (not shown). However, these methods had problems. In the former case, very large crystals could not be created. Although the latter produced large crystals, the characteristics of the resulting crystals varied greatly depending on the characteristics of the raw materials. This has the disadvantage that, as shown in US Pat. No. 4,866,05, it depends largely on the crystal type and grain type of the raw material crystal, and impurities in the raw material crystal determine the characteristics of the impurities in the resulting crystal. For this purpose, a method has been adopted in which the grain types of the crystals produced by the method shown in FIG. 4 are selected and used as the materials used. However, with this method, the raw material powder contained moisture from the air during the manufacturing process, so it was basically impossible to produce crystals with good purity, and the resulting crystals were not very pure. . In other words, SiC tends to react with O2 and H2O in the air and Si in this crystal to form SiO2, which becomes SiC.
This made it difficult to obtain crystal purity and increase its size.

[0005]

[Problem to be solved by the invention] In this way, conventional Si
With the C crystal production technique, it was not possible to produce a crystal with high purity and a large diameter. The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing a semiconductor crystal having a large diameter, high purity, and a desired crystal type. [Structure of the invention]

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a first step of converting a first crystal type semiconductor crystal into a second crystal type semiconductor crystal by heating, and then a reduced pressure state. a second step of removing impurities in the second crystal type semiconductor crystal by heating, and subsequently forming a vapor phase growth layer on the surface of the seed crystal using the second crystal type semiconductor crystal as a raw material; The present invention provides a method for manufacturing a semiconductor crystal, characterized in that the first to third steps are performed in a closed container.

[0007]

[Operation] With the above configuration, the series of steps of conversion to the desired crystal type → impurity removal → crystal vapor phase growth are performed in the same sealed container without exposing the material to the outside air. After conversion to the crystal form, there is no need to worry about moisture in the air being included in the crystal, and therefore a large single crystal with extremely high purity can be formed.

[0008]

[Examples] The details of the present invention will be explained based on examples. FIG. 1 shows a method for manufacturing a semiconductor crystal according to a first embodiment of the present invention. Further, FIG. 2 shows a manufacturing apparatus used in this manufacturing method. First, a CVD apparatus equipped with a heating heater 2 is prepared around a graphite container 1, and a raw material gas such as SiH4 and C3 H8 3 is flowed through the CVD apparatus, thereby depositing β-type SiC polycrystalline powder on the wall surface. β type S
iC is more easily obtained by this method than α-type (FIG. 1(a)).

Next, this β-type SiC polycrystalline powder is temporarily placed in a crucible 11. This crucible 11 is part of the crystal growth apparatus shown in FIG. This device has a structure that serves as both a heat treatment furnace and a vapor phase growth device, so that the raw materials stored inside can be processed without exposing them to outside air at all. When this powder crystal 10 is placed in a crucible 11, the SiC seed crystal 12 is placed at a position offset from the surface of the crucible 11 to prevent impurities from adhering to the surface. For this purpose, a lateral movement device 13 was used in this crystal growth apparatus. Then, inside the chambers 151 and 152, 10
A vacuum of about -5 torr is created, and then Ar gas is introduced. Thereafter, the crucible 11 is subjected to high frequency heating using the induction heating device 16. At this time, the temperature was 1600° C. and the pressure of the atmospheric gas was 1 atm. When heating is performed in this state for about 6 hours, all the raw materials 4 in the source part are 6H type SiC5
Transfer to 1. After that, the pressure inside the chamber is reduced to several To
Make it rr. After that, it is left as it is for 2 hours to perform high purification. As a result, the impurity 6 in the 6H type SiC was removed (FIG. 1(b)).

Next, the seed substrate 12 is slid and set on the source section. Furthermore, the seed substrate 12 was heated to 2300°C.
The crucible 11, which is the source part, is heated to 2400°C. Thereafter, when vapor deposition is performed for 12 hours using this 6H type SiC52 as a raw material, SiC crystal 8 grows several cm on seed crystal 12 (FIG. 1(c)).

The crystal grown in this manner was a highly pure 6H type crystal. In the manufacturing method of this example, β
The type SiC raw material is first converted into the α type by heat treatment. The quality of the final crystal can be determined by the crystal type formed at this time. Further, the crystal type can be controlled by the atmosphere, pressure and temperature of the heat treatment. This condition can be achieved by performing the process at 1500° C. in an inert gas to create the 6H type. Since the raw material is produced by the CVD method, it can be produced with high purity. By using this raw material to create crystals using the sublimation method, it is possible to create 6H type crystals with a large diameter and high purity. On the other hand, in conventional manufacturing methods, 4H type or 15R type crystals were often present in addition to 6H type crystals, but by using the present invention,
Other crystal types are less likely to be mixed.

FIG. 3 shows the probability of occurrence of polymorphism in raw materials depending on the heat treatment temperature. The vertical axis indicates the ratio of 6H type SiC to 4H type SiC. In this way, 6H-type SiC rapidly increases above 1400℃, and above 1500℃, almost 6H type SiC increases.
It can be seen that it transforms into H type. Therefore, the heat treatment temperature for crystal type conversion is preferably 1400°C or higher, preferably 1500°C or higher. This makes it possible to improve the yield of crystals after production. Using the SiC crystal thus obtained, a light-emitting element, for example, a blue light-emitting diode, was formed and a high-luminance one was obtained.

Next, a second embodiment of the present invention will be explained. This example differs from the previous example in that the vapor phase growth film was formed using a gas transport method instead of the sublimation method, and that the surface of the seed crystal was chlorinated before forming the film by the vapor growth method. This is because it was etched with a type of gas. The process up to the removal of impurities by heat treatment in vacuum is carried out in exactly the same manner as in the previous embodiment. Next, as a transport gas, H2 or an inert gas, either alone or in combination, is flowed from the raw material powder toward the seed crystal. By doing so, the evaporated gas of SiC is transported from the upstream side to the downstream side by the transport gas. Thereafter, a SiC crystal is grown on the seed crystal. The growth temperature for the seed substrate and source part is the same as in the sublimation method. By doing so, the distance between the source section and the seed crystal can be increased. Therefore, there is no limit to the capacity of the source, and the size of the crystal that can be grown can now be increased. This method also produces the same effects as the previous embodiment. Furthermore, a third embodiment of the present invention will be described. This embodiment differs greatly from the first embodiment in that ZnS is used as a raw material instead of SiC.

ZnS has a drawback in that cubic and hexagonal crystals coexist when grown by CVD in a high temperature range. Polycrystalline ZnS can be grown by mixing dimethylzinc and dimethylsulfur in a furnace similar to that shown in FIG. 1(a) and heating the mixture at a high temperature of 500° C. or higher. At this time, by increasing the temperature of the furnace, it becomes possible to produce polycrystals that do not contain sulfur alone. However, at low temperatures only cubic crystals are formed, but at high temperatures hexagonal crystals are mixed. Therefore, a polycrystal is first prepared at a temperature of about 800°C, and then placed in a crucible and heated at about 900°C in a mixed gas of Ar and H2S gas, as in FIG. 1(b). At this time, by reducing the pressure of the atmospheric gas to several tens of Torr, it becomes easier to obtain cubic crystals. After that, the pressure was further reduced in the same chamber to 110 °C in vacuum.
First, impurities are removed at 0° C., and then a cubic ZnS seed crystal is placed in the low-temperature part of the upper part of the crucible, and the crystal can be grown in about a few days. Such a method also produces the same effects as the first embodiment. The present invention is not limited to the previous embodiments, but
It may be done as follows.

1 Not only SiC and ZnS but also other compound semiconductors such as GaN and Cd of II-IV compound semiconductors.
The present invention can also be applied to the production of crystals having polymorphic structures such as Se and CdTe. 2 Here, a blue light emitting diode is applied to a device grown by a liquid layer epitaxial method on an n-type SiC crystal containing AlN on an n-type SiC crystal, and on top of which a high-concentration P-type SiC crystal is grown using a liquid layer epitaxial method. However, other light emitting devices such as green light emitting devices and other high temperature devices can also utilize the crystals formed according to the present invention. CdTe and CdS can also be applied to radiation detectors and visible light detectors. 3 Here, impurities were not added during vapor phase growth, but a light emitting element may be obtained by adding impurities at this stage to form a P-type or N-type layer. In addition, the present invention can be modified and used in various ways without departing from the spirit thereof.

[0016]

As described above, according to the present invention, a semiconductor crystal of a desired crystal type, high purity, and large diameter can be produced with high yield. Further, according to the present invention,
Since the crystal can be made highly pure, it is possible to create a substrate with higher resistance than before. This has made it easier to create high-voltage devices.

[Brief explanation of the drawing]

[Fig. 1] Cross-sectional view showing the first embodiment of the present invention

[Figure 2
] Cross-sectional view showing the first embodiment of the present invention

[Figure 3]
Diagram explaining the first embodiment of the present invention

[Figure 4] Diagram showing a conventional example

[Explanation of symbols]

1 Graphite container 2 Heater 3 Raw material gas 4 Raw material powder 11 Crucible 12 Seed substrate 13 Seed crystal transfer device 14 Insulation material 15 Quartz chamber 16 High frequency coil

Claims (1)

[Claims] 1. A first step of converting a semiconductor crystal of a first crystal type into a semiconductor crystal of a second crystal type by heating the semiconductor crystal, and then converting the inside of the semiconductor crystal of the second crystal type by heating under reduced pressure. a second step of removing impurities, and a third step of forming a vapor phase growth layer on the surface of the seed crystal using the second crystal type semiconductor crystal as a raw material; A method for manufacturing a semiconductor crystal, characterized in that the steps of (1) and (2) are performed in a closed container.