JPH01208389A - Growth of single crystal of compound semiconductor - Google Patents

Abstract

PURPOSE:To control impurity concentration ratio at starting of crystal growth in high accuracy, by charging a specific double crucible with impurity-containing raw material melt, further adding impurity to an inner crucible having a circulation hole, instantly dropping the inner crucible to make the height of melt level of the inner and outer crucibles coincident and growing crystal. CONSTITUTION:A double crucible having an inner crucible 1 with a circulation hole 1a supported by an auxiliary shaft 6 in an outer crucible 2 is charged with impurity- containing raw material melts 3 and 4 and a layer of a liquid-encapsulating agent 5 is formed on the melts. Then the inner crucible 1 is pulled up only by a given distance by the auxiliary shaft 6, height of the inner crucible 1 from the bottom to the melt level is changed from A to B and a seed crystal 7 is immersed in the melt 3. Then an impurity is added only to the inner crucible 1, the height of the melt level is returned to A, before the melt 3 flows from the circulation hole 1a to the outer crucible 2 by difference of the melt level, instantly the inner crucible 1 is dropped, melt levels of both the crucibles 1 and 2 are returned to the same height, both the levels of the melts 3 and 4 are made into the same height while maintaining the volume of the melt 3 in the inner crucible constant and the impurity in both the crucibles 1 and 2 is controlled in high accuracy. The seed crystal 7 is pulled up to grow crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a growth method for growing a single crystal of a compound semiconductor by the Czochralski method.

[Prior Art] The Czochralski method is the most widely used method for growing compound semiconductor single crystals. - In the case of growth of multi-component compounds such as group V compound semiconductors or group II-Vl compound semiconductors, they contain components that easily dissociate and evaporate, which tends to cause deviations in the stoichiometric composition of the crystal, so this should be prevented. One method is the liquid-enclosed Czochralski method (LEC method), in which the surface of the crystal melt is covered with a melt of boron oxide or the like to suppress dissociation and evaporation from the melt.

In such a Czochralski method, a single crystal doped with impurities may be grown.

In such cases, impurities segregate as the crystal grows, resulting in changes in the impurity concentration within the crucible, resulting in uneven concentration distribution in the growth direction, making it impossible to obtain a single crystal with a uniform concentration distribution using normal methods. I can't.

In order to solve these problems, a double crucible method and the like have been proposed. An example of applying the double crucible method to Ge is the Journal of Applied Phys.
ics.

Volume 29, No. 8.1958, pages 1241-1244.

In such a double crucible method, when the segregation coefficient of impurities is k, the ratio of the impurity concentration in the melt in the inner crucible to the impurity concentration in the melt in the outer crucible is There is a need. Therefore, it is necessary to make the impurity concentration in the melt in the inner crucible different from the impurity concentration in the melt in the outer crucible, and to do this, polycrystalline raw materials are placed in the inner and outer crucibles. Methods include adding different amounts of impurities to the inner and outer crucibles at different stages to make the impurity concentrations different, or methods of melting raw material polycrystals in the inner and outer crucibles and then adding impurities only to the inner crucible. etc. have been traditionally adopted. An example of adding impurities only to the inner crucible after melting the polycrystalline raw material is disclosed in Japanese Patent Laid-Open No. 61-266389.

[Problems to be Solved by the Invention] In the method of adding impurities at different concentrations when adding raw material polycrystals, the melt in the inner crucible is There is a problem in that impurity diffusion occurs between the liquid and the melt in the outer crucible through the communication holes, and the impurity concentration ratio deviates from k at the start of growth.

In addition, in the method of adding impurities only to the inner crucible after melting the polycrystalline raw material, the level of the melt in the inner crucible becomes higher than the level of the melt in the outer crucible due to the addition of impurities. Therefore, there was a problem in that the melt in the inner crucible flows out into the outer crucible through the flow hole, and as a result, the impurity concentration ratio deviates from 1:k.

An object of the present invention is to provide a method for growing a compound semiconductor single crystal that can accurately control the impurity concentration ratio between an inner crucible and an outer crucible at the start of crystal growth.

[Means for Solving the Problems] In the growth method of the present invention, a double crucible consisting of an outer crucible and an inner crucible having a flow hole is filled with a raw material melt containing impurities, and impurities are further added only to the inner crucible. After that, while keeping the volume of the melt in the inner crucible constant, move the inner crucible downward so that the height of the melt level in the inner crucible matches the height of the melt level in the outer crucible. crystal growth begins immediately.

[Operation] In the growth method of the present invention, after impurities are added to the inner crucible, the inner crucible is moved downward while keeping the volume of the melt in the inner crucible constant. The height of the surface is made to match the height of the melt level in the outer crucible. Therefore, the melt does not flow out from the inner crucible to the outer crucible after adding impurities to the inner crucible as in the conventional method.

[Embodiment] FIGS. 1 to 4 are cross-sectional views showing an apparatus for explaining an embodiment of the present invention.

FIG. 1 shows a state in which the inner crucible and the outer crucible are filled with raw material melt. Inside the outer crucible 2 is the inner crucible 1.
is provided, and the inner crucible 1 is supported by a subshaft 6. The outer crucible 2 is filled with a raw material melt 4, and the inner crucible 1 is filled with a raw material melt 3. The raw material melt 3 and the raw material melt 4 are allowed to flow out or flow in through a communication hole 1a formed at the bottom of the inner crucible 1. A layer of liquid sealant 5 is formed on the raw material melt 3 and the raw material melt 4. In the state shown in FIG. 1, the inner crucible 1 is positioned so that the height of the liquid level of the raw material melt 3 from the bottom of the inner crucible 1 is A.

FIG. 2 shows the state before impurities are added to the inner crucible. In this embodiment, the position of the inner crucible 1 is moved upward by the countershaft 6. This is to ensure that the volume of the melt in the inner crucible 1 after addition of impurities is the same as the volume of the raw material melt in the inner crucible 1 in the state shown in FIG. In the state shown in FIG. 2, the height of the liquid level of the raw material melt 1ff13 from the bottom of the inner crucible 1 is B. In addition, in FIG. 2, the state of the inner crucible 1 in FIG.
Illustrated with dashed dotted lines. Further, before addition of impurities, the seed crystal 7 is immersed in the raw material melt 3 in the inner crucible 1. This is to enable crystal growth to start immediately after addition of impurities.

FIG. 3 shows the state immediately after the addition of impurities to the inner crucible. Due to the addition of impurities, the volume of the raw material melt 3 in the inner crucible 1 increases, and the raw material melt 3 from the bottom of the inner crucible 1 increases.
The height of the liquid level is A, which is the same as in Fig. 1. As a result, the liquid level of the raw material melt 3 becomes higher than the liquid level of the raw material melt 4 in the outer crucible 2.

Therefore, the raw material melt 3 tends to flow out into the crucible 2 through the flow hole 1a. Before such outflow occurs, the inner crucible 1 is immediately moved downward to the state shown in FIG. 4.

FIG. 4 shows the state at the start of growth.

As described above, immediately after adding impurities to the inner crucible 1, the inner crucible 1 is immediately moved downward, and the liquid level of the raw material melt 3 is lowered while keeping the volume of the raw material melt 3 in the inner crucible 1 constant. and the liquid level of the raw material melt 4.

Thereby, the raw material melt 3 can be prevented from flowing out into the outer crucible 2. Immediately after reaching the state shown in Figure 4, the seed crystal 7
to start crystal growth.

Note that after the start of crystal growth, the raw material melt 4 in the outer crucible 2 is
Since it continuously flows into the inner crucible 1 through the communication hole 1a, no diffusion of impurities occurs between the raw material melt 3 and the raw material melt 4.

As described above, immediately after adding impurities to the inner crucible 1, the inner crucible 1 is moved downward to prevent the raw material melt 3 from flowing out from the inner crucible 1. The impurity concentration ratio of the melt 4 can be set to 1: as set. Therefore, it is possible to obtain a uniform impurity concentration over the entire region of the grown crystal.

A GaAs crystal was grown using an apparatus as shown in FIGS. 1 to 4. PBN was used as the material for the outer crucible and the inner crucible, the outer crucible had an inner diameter of 4 inches, the inner crucible had an inner diameter of 3 inches, and a GaAs crystal with a diameter of 2 inches was pulled and grown.

To explain this process below, first, about 2000 g of high-purity GaAs polycrystal, about 200 g of sufficiently dehydrated boron oxide, and high purity 1 n as impurities are placed in an outer crucible.
11g of As polycrystal was added, and heated to 12g with a carbon heater.
It was heated to 70° C. to melt GaAs and boron oxide. Next, the inner crucible was placed in the outer crucible, and the inner crucible was also filled with GaAs melt through the communication hole. The height of the GaAs melt in the inner crucible is 10 mm, and its volume is 45 mm.
．． It was 6 cm'. Next, the temperature was gradually lowered to 1250°C. After the inner crucible was moved upward by 0.5 mm to the state shown in FIG. 2, the seed crystal was brought into contact with the GaAs raw material melt through the boron oxide melt layer while rotating.

Next, 13g of high purity 1nAs polycrystal as an impurity,
It was placed in an inner crucible, and at the same time, the inner crucible was moved 0.2 mm downward, and the seed crystal was pulled up at a speed of 10 mm/hr to start crystal growth.

As a result of performing mass spectrometry on the obtained crystal, the In concentration in the crystal was approximately 330% in the axial direction as shown in Figure 5.
The concentration was 0 wt ppm, and the concentration distribution was uniform.

As a comparison, Ga
As crystal was grown (comparative example). The crystals obtained in this comparative example were also subjected to mass spectrometry in the same manner. The results are shown in FIG. 5 by dotted lines. As is clear from the comparison with the comparative example, the crystal according to the example according to the present invention has a uniform impurity concentration distribution in the axial direction. The reason why the In concentration increases at the foot of the crystal is because the raw material melt in the outer crucible decreases at the end of the growth, and the inner crucible comes into contact with the bottom of the outer crucible, and the effect of the double crucible method is reduced. Because it was lost.

In the above embodiments, the double crucible method in which the inner crucible is supported by a sub-shaft was explained as an example, but the method of this invention
This also applies to the double crucible method in which the inner crucible is suspended in the melt.

In this case, the inner crucible can be moved downward by its own weight immediately after the impurity is added to the inner crucible.

[Effects of the Invention] ' According to the growth method of the present invention, immediately after adding impurities to the inner crucible, the inner crucible is moved in the t direction to prevent melt from flowing out from the inner crucible to the outer crucible. Therefore, it becomes possible to precisely control the impurity concentration ratio between the melt in the inner crucible and the melt in the outer crucible.

Therefore, it is difficult to grow a crystal having a uniform impurity concentration distribution over the entire region. Therefore, it becomes possible to produce crystals of high quality and desired electrical properties with excellent productivity and reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an inner crucible and an outer crucible 1 filled with raw material melt in an embodiment of the present invention. FIG. 2 is a sectional view showing a state before impurities are added to the inner crucible in an embodiment of the present invention. FIG. 3 is a sectional view showing a state immediately after the addition of impurities to the inner crucible in an embodiment of the present invention. Fourth
The figure is a cross-sectional view showing the state at the start of growth in an embodiment of the present invention. FIG. 5 is a diagram showing the In concentration distribution in the axial direction of a crystal produced according to an example of the present invention. In the figure, 1 is an inner crucible, 1a is a flow hole, 2 is an outer crucible, 3 is a raw material melt, 4 is a raw material melt, 5 is a liquid sealant, 6
indicates the minor axis, and 7 indicates the seed crystal. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] (1) A double crucible consisting of an outer crucible and an inner crucible with a flow hole is filled with a raw material melt containing impurities, and after further adding impurities only to the inner crucible, crystal growth is immediately started to remove the impurities. In a method for growing a compound semiconductor single crystal, in which a single crystal doped with is grown by the Czochralski method, after adding an impurity to the inner crucible, the volume of the melt in the inner crucible is kept constant; A method for growing a compound semiconductor single crystal, wherein the inner crucible is moved downward so that the height of the liquid level of the melt in the outer crucible matches the height of the liquid level of the melt in the outer crucible.