JPH0465392A - Molecular beam epitaxial crystal growing device - Google Patents

Abstract

PURPOSE:To prevent growth velocity from being reduced in accordance with reduction of a raw material and to stably obtain the stable crystal in the same conditions by changing the position of a crucible according to the change in amount of the raw material in the crucible. CONSTITUTION:A raw material 3 is introduced into a first crucible 2 arranged into the heat release preventative cylinder 1 of a shell 20. The crucible 2 is heated by a heater 4 arranged to the outside of a second crucible 7. The temp. is detected by a thermocouple 5 and the crucible 2 is controlled at the prescribed temp. Thereafter a shutter 6 is opened to start epitaxial growth. When the raw material 3 is reduced as the epitaxial growth is advanced, the crucible 2 is raised by the reduced amount of the raw material 3 with a supporting rod 8. Crystal is grown while performing regulation so that the spearhead part of the liquid level of the raw material 3 always reaches the specified position.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an apparatus for growing crystals by molecular beam epitaxy, and in particular to improvements in molecular beam epitaxy cells used for growing semiconductor crystals such as GaAs. be.

[Prior Art] Conventionally, in crystal growth by molecular beam epitaxy, raw materials are supplied using PBN (Pyrolitic B
or.

For example, when growing GaAs crystals in a crucible made of
Alternatively, it is common practice to place doping materials such as Si in a crucible and keep their evaporation ratios constant to epitaxially grow a desired crystal on a substrate.

Hereinafter, a Ga cell used for crystal growth of GaAs in the conventional molecular beam epitaxy method will be explained as an example.

FIG. 6 shows a schematic diagram of this conventional Ga cell structure. In this figure, 10 is a cell for Ga, 1 is a tube for preventing heat radiation, 2 is a crucible, 3 is Ga as a material source (evaporation source),
4 is a heating heater, 5 is a thermocouple, and 6 is a shutter.

In the Ga cell 10, a crucible 2 made of PBN or the like is installed in a heat radiation prevention cylinder l, and Qa as a material source (evaporation source) is placed in the crucible 2. The crucible 2 is heated to, for example, 800 to 900° C. by a heating heater 4, and the temperature is detected by a thermocouple 5 and adjusted to a predetermined temperature.

After setting other necessary material sources such as As and doping materials to predetermined conditions, and setting the temperature of the substrate to be grown and other conditions, when the shutter 6 of the Ga cell 10 is opened, Ga3 evaporates. do.

Thus, for example, a G
Crystals of aAS grow at a rate of 0.5-1 μm/hour.

1. Problems to be Solved by the Invention] The conventional molecular beam epitaxial crystal growth apparatus grows crystals using the method described above, and when growing a crystal, Ga3 in the crucible 2 grows as it grows. It continues to decrease. This is a rate such that, for example, the weight decreases by 1 g for each crystal growth. At this time, as shown in Figure 7, the heater 4 that heats the crucible has a top heat structure in which the temperature decreases by several tens of degrees from the tip of the crucible toward the bottom, so the material source is reduced. ↓Thus, the temperature at the top of the material source becomes lower and the amount of evaporation decreases.

A decrease in the amount of evaporation leads to a decrease in the growth rate, making it impossible to obtain a growth layer of a desired thickness under the same conditions.

Therefore, in order to obtain a grown layer of the same thickness, it was necessary to either raise the temperature of the crucible or lengthen the growth time in order to maintain the original amount of evaporation.

However, in order to detect the growth rate, it is necessary to check the thickness of the growth layer that has actually grown, and from those results determine the temperature of Ga3 at which the amount of evaporation should be corrected during the next growth, which is very troublesome.

This invention was made to solve the above-mentioned problems, and is a molecular beam epitaxial crystal that prevents the growth rate from decreasing due to a decrease in material sources and can obtain stable crystals with good reproducibility under the same conditions. The purpose is to obtain a growth device.

[Means to solve the problem]

The molecular beam epitaxial crystal growth apparatus according to the present invention includes:
The crucible built into the cell for molecular beam epitaxy is double-layered, and a material source is put into the inner second crucible, and the outer first crucible is heated with a heater capable of heating to a constant temperature. As the material source placed in the crucible decreases as it grows, the temperature at the leading edge of the material source decreases, the amount of evaporation decreases, and the growth rate decreases. Either increase the temperature so that the leading edge of the material source is always at a constant W (constant temperature), or increase the The crucible is moved to a certain position.

Further, in a crucible incorporated in a cell for molecular beam epitaxy, the material source placed in the crucible decreases as the material grows, so the temperature at the leading edge of the material source decreases and the amount of evaporation decreases.

In other words, since the growth rate decreases, in order to maintain a constant growth rate, it is only necessary to increase the temperature of the material source by the amount of the decreased temperature. Therefore, the molecular beam epitaxial crystal growth apparatus according to the present invention The relationship between changes in the liquid level height (reduction in material source) and changes in growth rate is fed back to the temperature control unit, and the amount of power supplied to the heater is controlled to keep the growth rate constant. This is what I did.

Effect C] In this invention, the crucible containing the material source is made movable so that the position of the crucible can be changed according to changes in the material source, so the leading edge of the material source is always kept constant. It can be held in position.

Therefore, a crystal with constant characteristics can be stably obtained at a constant growth rate. Furthermore, since the growth rate can be changed by changing the position of the crucible during growth, the composition ratio of crystals with different compositions, for example, mixed crystals such as GaAlAs, can be easily changed with a simple operation.

In addition, in this invention, changes in the amount of liquid in the material source placed in the crucible are detected by changes in the height of the liquid level in the material source, and the amount of change is sent to the temperature control unit for the heater heating the crucible. Since the growth rate is controlled to be constant through feedback, crystals with constant characteristics can be stably obtained.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a molecular beam epitaxy cell used for crystal growth in a molecular beam epitaxial crystal growth apparatus according to a first embodiment of the present invention. Second
The figure is a temperature distribution diagram showing an example of the temperature distribution in the crucible of this cell.

Note that here, for example, Ga, which is a ■-v group compound semiconductor, is used.
A Ga cell for producing As crystal will be explained.

In FIG. 1, reference numeral 1 denotes a heat radiation prevention cylinder, in which a heating heater 4 capable of heating at a constant temperature is provided. 2 is a first crucible for containing Ga3, and 7 is a second crucible for protecting the first crucible 2.

The first crucible is supported by a support rod 8 for vertical movement, and is configured to be movable to a desired position. Note 2
0 indicates the entire Ga cell.

Next, as an example, a case where GaAs crystal is grown will be described.

Ca3, which is a material source, is put into the first crucible 2 of the cell 20 configured as shown in FIG. Heating of the Luppo 2 is performed from the outside of the second crucible 7 with a heating heater 4, the temperature is detected with a thermocouple 5, and the temperature is adjusted to a predetermined temperature. Other material sources such as As and other cells (not shown)
After the substrate (not shown) to be grown is also set at a predetermined temperature and other conditions are set, the temperature soter 6 of each cell is opened to start growth.

Since epitaxial growth is performed while consuming Ga put in the cell, the material lGa5 decreases with each growth. At this time, as shown in FIG. 2, the temperature of the crucible decreases from the tip toward the bottom of the crucible.

In other words, because it has a top human structure, GaS
As the amount decreases, the leading edge of Ga3 moves downward C,a
3 temperature decreases. That is, the growth rate becomes slower.

For this purpose, in this embodiment, the crucible is raised upward by the support rod 8 by the amount by which Ga3 is reduced, and the crucible is adjusted so that the most extreme part of the liquid level of Ga3 is always at a constant position. Thus G
The amount of evaporation of a3 is kept constant, making it possible to stably obtain epitaxial material with predetermined characteristics without changing other conditions.

Also, while heating the crucible 2 to a predetermined temperature,
Since the growth rate can be changed by arbitrarily changing the position of , it is also possible to obtain growth layers with different compositions even during growth.

Note that the height of the liquid level of the material source Ga3 can be measured using an optimal device as required, such as an optical method, a microwave method, an infrared method, or the like.

Further, FIG. 3 is a schematic configuration diagram showing an example of a cell for molecular beam epitaxy used for crystal growth by a molecular beam epitaxial crystal growth apparatus according to a second embodiment of the present invention, and FIG. 4 is a crucible incorporated in the cell. FIG. 5 is a schematic diagram of the temperature distribution in the region shown in FIG.

Note that here, for example, Ga, which is an m-v group compound semiconductor, is used.
A Ga cell for producing As crystal will be explained.

A material source Ga3 is put into the cell 1o configured as shown in FIG. Lupo 2 is heated by a heating heater 4a, the temperature is detected by a thermocouple 5, and adjusted to a predetermined temperature. Other material sources such as As or other cells (not shown) are similarly adjusted, and the substrate to be grown (not shown) is also set at a predetermined temperature.

After other conditions are set, the shutters 6 of each cell and material source Ga3 are opened to start growth.

Since the epitaxial growth is performed while consuming the Ga3 put in the material #1, the amount of Ga3 in the material #1 decreases as it grows. At this time, the temperature of the crucible 2 becomes lower than the tip of the crucible 2 toward the bottom, as shown in FIG. That is, since it has a top heat structure, as the material source Ga3 decreases, the leading edge of the material fiGa3 falls downward and the temperature decreases. That is, as shown in FIG. 3, for example, when the tip of the material @Ga3 drops from point A to point A', the growth rate slows down.

Therefore, in this example, the reduction amount of the material source is
The material source G is monitored through the Ga amount check window 17 shown in the figure, and is controlled by a temperature control section (not shown) that stores the relationship between the change in the liquid level of the material source (the amount of decrease in the material source) and the change in the growth rate.
The crucible 2 is heated by the heater 4a of the cell 10 by the amount of decrease in the liquid level of a3, that is, the decrease in the growth rate due to the decrease in temperature.
Increase the temperature.

In this way, the amount of evaporation of the material 5ca3 is kept constant, and an epitaxial layer with predetermined characteristics can be stably obtained without changing other conditions.

Note that the height of the liquid level of the material source Ga3 can be measured using an optimal device as required, such as an optical method, a microwave method, an infrared method, or the like.

〔Effect of the invention〕

As explained above, according to the molecular beam epitaxial crystal growth apparatus according to the present invention, the position of the crucible can be changed according to changes in the amount of GaO in the crucible, and the leading edge of Ga can be adjusted so that it is always at a constant position. By attaching a support rod, it is possible to evaporate a certain amount of raw material,
Therefore, since a constant growth rate can be maintained, crystals with desired characteristics can be obtained stably and with good reproducibility.

In addition, changes in the amount of Qa in the crucible are detected optically or by other methods based on changes in the height of the Ga liquid level, and the amount of power supplied to the heater is controlled according to the amount of change, which improves crystal growth. The speed can be kept constant and crystals with constant characteristics can be stably obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a Ga cell of a molecular beam epitaxial crystal growth apparatus according to a first embodiment of the present invention, FIG. 2 is a diagram showing a schematic configuration of the temperature distribution in the crucible portion in FIG. The figure is a schematic structural diagram of a Ga cell of a molecular beam epitaxial crystal growth apparatus according to a second embodiment of the present invention.
FIG. 4 is a schematic diagram showing an example of temperature distribution near the crucible of the cell; FIG. 5 is a schematic diagram showing the liquid level and growth rate of the material source Ga; FIG. 6 is a schematic diagram of a conventional cell; FIG. 7 is a schematic diagram of the temperature distribution near the crucible of the cell. In the figure, 1 is a heat radiation prevention cylinder, 2 is a crucible, 3 is a material source Qa, 4 and 4a are heaters, 5 is a thermocouple, 6 is a shutter, 7 is a second crucible, 17 is a window for checking the amount of Qa, 8
is the support rod, and 10.20 is the entire cell. In the figures, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) In an apparatus that performs crystal growth using the molecular beam epitaxial method, there is a heater that heats the crucible at a constant temperature, and a heater that heats the crucible at a constant temperature, and a device that changes the position of the crucible in response to changes in the amount of raw material in the crucible, and grows a constant amount of raw material. It is characterized by comprising either means for maintaining a constant growth rate by evaporation, or means for obtaining a crystal with desired characteristics at a desired growth rate during growth by changing the position of the crucible. Molecular beam epitaxial crystal growth equipment. (2) In an apparatus that performs crystal growth using the molecular beam epitaxial method, a means for detecting changes in the liquid level of the material source by detecting changes in the height of the liquid level of the material source, and a means for detecting changes in the liquid level of the material source, and 1. A molecular beam epitaxial crystal growth apparatus comprising means for controlling a crystal growth rate by controlling the amount of power supplied to a heater heating a crucible.