Crystal growth vessel and crystal growth method

Details Crystal growth vessel and crystal growth method Crystal growth vessel and crystal growth method

2002-04-25

2004-07-06

Hiteshew, Felisa C. (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Processes of growth from liquid or supercritical state

Havin growth from molten state

C117S083000

Reexamination Certificate

active

06758899

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crystal growth vessel and crystal growth method for growing crystals of compound semiconductors such as GaAs and InP used in microwave devices and the like.
2. Related Background Art
Bridgeman method has conventionally been known as a technique for growing crystals of compound semiconductors and the like. In the Bridgeman method, there is a process which does not employ seed crystals, in order to grow a large amount of crystals inexpensively. More specifically, this process comprises the steps of combining Ga and As within a growth vessel not provided with seed crystals so as to generate a GaAs melt and then rapidly lowering the temperature of the growth vessel from its side where the growth is to be started (e.g., at the bottom part of the growth vessel), so as to grow crystals toward the other side (e.g., the opening part of the growth vessel). Though impurities usually accumulate in the finally grown area of generated crystals, they can be kept at an end part of crystals when the crystals are unidirectionally grown from the bottom part of the growth vessel toward the opening part as such, for example. When the end part where the crystals have finished growing is cut off, then crystals free of impurities can be obtained.
SUMMARY OF THE INVENTION
In the conventional technique in which crystals are grown with a temperature gradient without using seed crystals, however, there have been problems as follows. Namely, in the above-mentioned conventional technique, since no seed crystals are installed within the growth vessel, nuclei are hard to generate, so that the material melt would not solidify until the degree of supercooling enhances to a certain extent. If the temperature of the growth vessel is kept lowering, a large amount of melt which has not solidified although the temperature was lowered to its melting point or lower rapidly solidifies at the instant when a certain degree of supercooling is exceeded. As a result, there have been problems in the generated crystals, such as occurrences of so-called compositional misalignment, in which Ga and As are not combined one to one, and voids. Since polycrystals which have generated voids or compositional misalignment allow impurities to mix therein at the time of processing, they have to be discarded, which lowers the yield. On the other hand, there is an idea of slowing the cooling rate of the growth vessel in order to restrain the solution from rapidly solidifying, which lowers the productivity of crystals, however.
Also, since no seed crystals are disposed within the growth vessel, crystals do not always start growing from desirable places, so that there are cases where the material melt starts solidifying at a plurality of unexpected sites within the growth vessel. In such cases, the crystal growth does not always terminate at the end part of crystals, whereby there is a possibility of impurities accumulating at the center part of crystals. If impurities accumulate at the center part of crystals, then the yield becomes lower.
In view of such circumstances, it is an object of the present invention to provide a crystal growth vessel and crystal growth method which can unidirectionally grow high-quality crystals from a desirable site within the growth vessel at a low cost without lowering the cooling rate.
The present invention provides a crystal growth vessel for growing a crystal within a main container, the crystal growth vessel having a crystal growth starting portion in which the crystal starts to grow, the crystal growth starting portion being formed from a material having a thermal conductivity higher than that of a material of the main container.
For growing a crystal by using the crystal growth vessel in accordance with the present invention, the main container is started to cool after a material melt for the crystal is introduced into the main container. Here, since the crystal growth starting portion has a thermal conductivity higher than that of the main container, the temperature of the crystal growth starting portion becomes lower than that of the main container surrounding it. Therefore, the material melt can start to solidify from the crystal growth starting portion, whereby crystals can easily be grown uniaxially. Upon growing crystals, the material melt is cooled in a direction away from the crystal growth starting portion, so as to be solidified. Hence, even if the cooling rate is similar to that in the case where crystals are grown by a conventional growth vessel not equipped with the crystal growth starting portion, the material melt will solidify in a shorter period of time since the temperature of the crystal growth starting portion is lower than that of the main container. Consequently, as compared with the case where crystals are grown by a conventional growth vessel not equipped with the crystal growth starting portion, the amount of rapidly solidifying material melt becomes lower, whereby occurrences of compositional misalignment and voids can be reduced. Also, since there is no need to use seed crystals, the cost can be suppressed.
In this case, it is preferred that the main container comprise pBN, whereas the crystal growth starting portion comprise SiC, SiN, carbon, or sapphire.
The present invention provides another crystal growth vessel for growing a crystal within a main container, the crystal growth vessel having a crystal growth starting portion in which the crystal starts to grow, the crystal growth starting portion being formed from a material which is more wettable than a material of the main container.
For growing a crystal by using the crystal growth vessel in accordance with the present invention, the main container is started to cool after a material melt for the crystal is introduced into the main container. Here, since the crystal growth starting portion is formed from a material which is more wettable than the main container, nuclei are more likely to be generated therein. Therefore, the material melt can start to solidify from the crystal growth starting portion, whereby crystals can easily be grown uniaxially. Also, since nuclei are more likely to be generated in the crystal growth starting portion, the degree of supercooling of the material melt in the vicinity of the crystal growth starting portion becomes lower. Consequently, as compared with the case where crystals are grown by a conventional growth vessel not equipped with the crystal growth starting portion, the amount of rapidly solidifying material melt becomes lower, whereby occurrences of compositional misalignment and voids can be reduced. Also, since there is no need to use seed crystals, the cost can be suppressed.
In this case, it is preferred that the main container comprise pBN, whereas the crystal growth starting portion comprise quartz, pBN having a surface rougher than the main container, pBN-coated carbon having a surface rougher than the main container, or cBN having a surface rougher than the main container.
The present invention provides a crystal growth method for growing a crystal within a main container without using a seed crystal, the method comprising the steps of installing within the main container a crystal growth starting member having a thermal conductivity higher than that of the main container, and then generating a material melt for the crystal within the main container.
In the crystal growth method in accordance with the present invention, a crystal growth starting member having a thermal conductivity higher than that of the main container is initially installed within the main container without accommodating a seed crystal therein. Subsequently, a material melt for the crystal is generated within the main container, and then the main container is started to cool. Here, since the crystal growth starting member has a thermal conductivity higher than that of the main container, its temperature becomes lower than that of the main container surrounding it. Consequently, the material melt can start to solidify f

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