JPH045819A - Method and apparatus for molecular-beam epitaxy - Google Patents

Abstract

PURPOSE:To obtain a good epitaxial film in which a film composition and a film quality are changed little in the film-thickness direction by a method wherein, after the cracking characteristic of a gas has reached a stationary state, a cracked gas is spouted onto a substrate and an epitaxial growth operation is started. CONSTITUTION:The temperature of a GaAs substrate 15 is raised; a surface oxide is removed; a clean GaAs surface is obtained. Then, the temperature of the substrate 15 is lowered and kept. Then, a valve 9 is opened; arsine is introduced into a gas-cracking cell 17 and is spouted into a crystal growth chamber 12 through an orifice 21. A valve 19 is opened after about one hour; triethylgallium is introduced into a gas jet zone 5 and is spouted into the crystal growth chamber 12. Thereby, Ga atoms and As atoms reach the substrate 15; they are bonded on the substrate; an epitaxial growth operation of GaAs is started. When a cracking characteristic inside the cell 17 is set to a stationary state and the epitaxial growth operation is started, the epitaxial growth operation can be executed in a state that the cracking characteristic is not changed with the passage of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to molecular beam epitaxial growth (hereinafter referred to as gas source MBE) using a gas as a raw material, in which a substrate is irradiated with a molecular beam to epitaxially grow a crystal.

) concerning laws and devices.

[Prior Art] A gas source MBE method is one of the methods of irradiating a substrate with a molecular beam and epitaxially growing constituent elements of the molecular beam on the substrate.

This method uses gas as a molecular beam raw material, and the raw material gas whose flow rate is controlled is introduced into a high vacuum container through a molecular beam cell and irradiated onto a heated substrate.

For example, when growing GaAs, a compound semiconductor, epitaxially, triethylgallium (G a (C2Hs) 3 ) is used as the Ga raw material.
However, as a raw material for As, arsine (As Ha), which is a hydride, is used for boat fishing. The substrate temperature is 500°C to 600°C.

Triethylgallium is a liquid at room temperature, so in order to use it as a molecular beam material, it must be heated to produce vapor.
Directly control the flow rate with a mass flow controller [・roller and guide it to the molecular beam cell, or use hydrogen gas whose flow rate is controlled with a mass flow controller as a carrier gas.
Triethylgallium is blown into triethylgallium, and triethylgallium is introduced into a molecular beam cell using hydrogen as a carrier gas. The resulting triethylgallium is then irradiated onto the substrate.

It is decomposed on a substrate heated to 500°C to 600°C.

On the other hand, like triethyl gallium, arsine is introduced into the molecular beam cell by controlling its flow rate with a mass flow controller, but since it does not decompose on a substrate heated to 500°C to 600°C, it decomposes before being irradiated. Therefore, it is necessary to form arsenic dimer or tetramer.

For this purpose, arsine is heated and decomposed using a special molecular beam cell called a gas cracking cell.

Thereafter, the substrate is irradiated with light, and as a result, Ga obtained by decomposing triethyl gallium and As obtained by decomposing arsine combine to grow a crystal of Ga As.

Next, a conventional gas cracking cell for decomposing gas will be described.

FIG. 5 is a cross-sectional view showing an example of a conventional gas cracking cell.

The gas cracking cell 100 has a cylindrical 7-shaped tantalum dilation shield 102, 103 that provides heat insulation.
, a tungsten heater 104 disposed inside the tungsten heater 104 that heats the gas, a molybdenum cracking zone 117 where the gas decomposition occurs and whose tip is an orifice 118 , and a molybdenum cracking zone 117 that is a place where gas decomposition occurs. Therein, a plurality of tantalum baffle plates 106 and 107 are installed at predetermined intervals.

This tantalum baffle play 1~106°107 is
As shown in the figure, each plate is provided with a plurality of gas passage holes, and the positions of the gas passage holes are different between the tantalum baffle plates 106 and 107. Moreover, the diameter of this hole is 1 to 21 m1. A plurality of tantalum baffle plates 106 and 107 are alternately installed in the molybdenum cracking zone 117.

In addition, making a baffle plate using tantalum is
This is because tantalum's catalytic action in gas decomposition is utilized. In addition, molybdenum, tungsten, and the like are known as substances that perform a catalytic action.

Further, the gas cracking cell 100 has a vacuum flange 1
It is connected to the raw material gas introduction line 101 via 08.

A case in which gas flows through the gas cracking cell 100 having the above configuration will be briefly described.

The raw material gas passes through the raw material gas introduction line 101, enters the cracking zone 117 heated to a predetermined temperature using the heater 104, passes through the gas passage holes of the baffle plates 106 and 107, and passes through the cracking zone 117 while being decomposed. It passes through and becomes a molecular beam.

When gas passes through the baffle plates 106 and 107, these baffle plates have gas passage holes at different positions, so the gas passes through the raw material gas introduction line 10.
1 and exit the cracking zone 117 while colliding with the baffle plates 106 and 107 instead of heading straight toward the substrate.

As a result, the time the gas stays in the cracking zone 117 becomes longer than in the case where there are no baffle plates 106, 107, and the gas is sufficiently decomposed.

Incidentally, related to this type of gas source MBE method, for example, Applied Physics Letter 51 (19
1109-1111 (Applie
d Physics Letter 51 (1
987) ppH09-1111).

The above literature states that the purity of the epitaxial layer produced using the above cracking cell depends on the decomposition efficiency of arsine,
It is stated that this is affected by the substrate temperature.

[Problem to be solved by the invention] The epitaxial film produced using the above conventional technology is
There is a problem in that the composition changes in the thickness direction within the epitaxial film.

This has not been known in the past, and in the prior art, there is a problem in that the cracking property is persistent and no consideration is given to its change over time.

In other words, the decomposition products generated by cracking of the hydride source gas in the gas cracking cell change over time, and as a result, the composition of the molecular beam irradiated to the substrate also changes over time, which affects the composition and film quality of the epitaxial layer. There is a problem that the values change over time.

In order to clarify this problem, we determined the change over time when arsine gas was decomposed using a conventional gas cracking cell.

Figure 6 shows a conventional method (using a gas cracking cell to heat and decompose arsine and then immediately irradiating it onto a substrate) using a conventional gas cracking cell (shown in Figure 5). 2 is a graph showing the results of measuring the change in molecular beam intensity of arsenic dimer As2 over time using a quadrupole mass spectrometer when arsine gas is decomposed using a quadrupole mass spectrometer.

In the figure, the vertical axis represents the molecular beam intensity of As2 in arbitrary units, and the horizontal axis represents the introduction time (minutes) of arsine.

The temperature of the gas cracking cell is 700°C, and the arsine flow rate is 0.83 CCM.

As shown in the figure, the As2 molecular beam intensity increases with the introduction time of arsine and is saturated in about 1 hour.

In other words, it can be seen that there is a change over time in the cracking characteristics of arsine gas.

In the gas source MBE method, the intensity of each molecular beam is controlled by each gas flow rate, but if there is a change over time as described above, the molecular beam intensity will change even if the gas flow rate is constant. .

As a result, even if the gas flow rate is set so that the composition of the epitaxial film becomes a desired composition, the composition deviates from the desired composition over time.

Incidentally, the above-mentioned experiment has not been conducted in the past, and was conducted for the first time as an experiment for the present invention.

A first object of the present invention is to provide a method for producing crystals by gas source MBE (even if the cracking characteristics of the above-described raw material gas change over time, this does not affect the composition or film quality of the epitaxial film). It's about doing.

A second object of the present invention is to provide a gas source MBE apparatus that does not affect the composition, film quality, etc. of an epitaxial film even if the cracking characteristics of the source gas change over time.

A third object of the present invention is to provide a molecular beam cell suitable for the above gas source MBE apparatus.

[Means for Solving the Problems] A first object of the present invention is to charge a raw material gas whose cracking characteristics change over time into a gas cracking cell in advance,
This can be achieved by a crystal manufacturing method using a molecular beam epitaxial method in which the substrate is decomposed and, after a predetermined period of time has elapsed, the substrate is irradiated with molecular beams of other raw material gases to start epitaxial growth.

A second object of the present invention is to provide a space between at least one of the molecular beam cells and the crystal growth chamber so that the molecular beam generated in the molecular beam cell is irradiated into the crystal growth chamber. This can be achieved by using a molecular beam epitaxial apparatus provided with a molecular beam blocking means that can block the

Further, the third object of the present invention is to provide a molecular beam cell in which a molecular beam blocking means is provided in the gas cracking cell to block source gas decomposed in the gas cracking zone from being irradiated as a molecular beam onto the substrate surface. It can be achieved.

[Production use] First, the crystal manufacturing method according to the present invention will be explained.

The temperature of the substrate is raised to a predetermined temperature and held for about 10 minutes to remove surface oxides and obtain a clean surface. Next, the temperature of the substrate is lowered to the temperature during epitaxial growth and maintained.

Next, a raw material gas whose cracking properties change over time is introduced into a gas cracking cell, decomposed, and ejected as a molecular beam into the crystal growth chamber through an orifice.

At this time, raw material gas whose cracking properties do not change over time is not introduced into the gas emission zone.

Note that the molecules of the source gas whose cracking characteristics change over time do not grow crystals by themselves.

Further, the molecular beam of the raw material gas, which is ejected into the crystal growth chamber and whose cracking characteristics change over time, is exhausted using a vacuum pump.

After a predetermined time has elapsed since the introduction of a raw material gas whose cracking characteristics change over time into a gas cracking cell, a raw material gas whose cracking characteristics do not change over time is introduced into a gas ejection zone and is ejected into a crystal growth chamber.

In this way, the raw material gas whose cracking characteristics change over time is passed through the gas cracking cell for a predetermined period of time, but
During this period, the composition of the decomposition gas is not in a steady state where it is constant, but is changing over time, so the decomposition gas during that period does not contribute to crystal growth.

As a result, the atoms of the decomposition gas of the raw material gas whose cracking characteristics change over time reach a steady state, and the atoms of the raw material gas whose cracking characteristics do not change over time arrive on the substrate, and these atoms reach the substrate. By bonding above, epitaxial growth of the crystal is initiated and a homogeneous crystal is obtained.

Next, the operation of the molecular beam epitaxial apparatus of the present invention will be explained.

The molecular beam blocking means provided between the crystal growth chamber in which the substrate is placed and the molecular beam cell is kept open when a source gas whose cracking properties change over time contributes to crystal growth.

On the other hand, it is closed when it does not contribute to crystal growth, but this raw material gas is always allowed to flow through the gas cracking cell.

As a result, the cracking properties of a raw material gas whose cracking properties change over time can be kept in a steady state whenever this gas contributes to crystal growth, allowing epitaxial growth to occur without any change in cracking properties over time. homogeneous crystals are obtained.

Next, the operation of the molecular beam cell of the present invention will be explained.

The molecular beam blocking means provided in the gas cracking zone is kept open when a source gas whose cracking characteristics change over time contributes to crystal growth. On the other hand, when this raw material gas does not contribute to crystal growth, it is closed, but this raw material gas is always allowed to flow through the gas cracking cell.

As a result, the cracking properties of a raw material gas whose cracking properties change over time can be kept in a steady state whenever this gas contributes to crystal growth, allowing epitaxial growth to occur without any change in cracking properties over time. homogeneous crystals are obtained.

[Example] Next, various embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory diagram for explaining a method of epitaxially growing GaAsM on a GaAs substrate according to a first embodiment of the present invention.

This embodiment will be explained using the figure.

First, the structure of the device for this example will be explained.

This apparatus is roughly divided into a crystal growth chamber 12, a molecular beam cell 10 for triethyl gallium, a molecular beam cell 11 for arsine, and a vacuum pump 16.

Inside the crystal growth chamber 12 is a GaAs substrate 15 mounted on a molybdenum substrate holder 14 and heated by a tungsten heater 13 .

Molecular beam cell 1-0 for triethyl gallium.

It is comprised of a gas emission zone 5 made of stainless steel, a tungsten heater 4 arranged around it, and dilation shields 2 and 3 made of tantalum for heat insulation. Further, the temperature of the gas emission zone 5 is maintained at 100° C., and the tip thereof serves as an orifice 20 for ejecting molecular beams.

Triethylgallium is introduced into the molecular beam cell 10 through a gas introduction line 18. Introducing and shutting off I. ethyl gallium to the molecular beam cell 10 is performed by opening and closing a valve 19 provided in the gas introduction line 18.

The molecular beam cell 11 for arsine has an internal gas cracking cell having the same structure as the conventional gas cracking cell shown in FIG. 5, and the temperature of the molybdenum gas cracking zone 17 inside the cell is It can be maintained at 700°C.

Arsine is introduced into the gas cracking cell 17 through the gas introduction line]. Introduction and shutoff of arsine to the gas cracking cell 17 is performed by opening and closing a valve 9 provided in the gas introduction line 1.

Next, using this device, GaA was deposited on a GaAs substrate.
A method for epitaxially growing the s-layer will be explained.

The temperature of the GaAs substrate 15 is raised to 600° C. and held for about 10 minutes to remove surface oxides and obtain a clean GaAs surface. Next, the temperature of the G a A, s substrate 15 is lowered to the temperature during epitaxial growth and maintained. In this example, the temperature was maintained at 580'C.

Next, the valve 9 is opened, and 38 CCH of arsine is introduced into the gas cracking cell 17 and ejected into the crystal growth chamber 12 through the orifice 21.

At this time, since the valve 19 is closed, the crystal growth chamber]-
2 contains only arsine decomposition gas, and no GaAs crystal growth occurs on the GaAs substrate 15''.

Further, the arsine decomposition gas is exhausted using the vacuum pump 16.

Approximately 1 hour after the introduction of arsine into the gas cracking cell 17, the valve 19 was opened and 0.65 CCH was introduced.
of triethyl gallium is introduced into the gas emission zone 5,
It is ejected into the crystal growth chamber 12.

As a result, Ga atoms and As atoms arrive on the Ga As substrate 15 and are combined on the substrate, thereby starting epitaxial growth of Ga As.

The effects of epitaxially growing GaAs using the above method will be explained with a focus on cracking of arsine.

First, the effect of flowing arsine into the gas cracking cell 17 for at least one hour before epitaxial growth will be explained.

As already shown in FIG. 6, when the temperature of the gas cracking cell is 7000 C and the arsine flow rate is 0.83 CCM, the As2 molecular beam intensity increases with the arsine introduction time and is saturated in about 1 hour.

That is, it can be seen that approximately 1 hour is required for the composition of the cracked gas to become constant after the start of decomposition of arsine.

Next, the cracking characteristics of arsine at several temperatures will be explained using FIGS. 7 and 8.

Figure 7 at several temperatures. It is a graph showing the cracking characteristics of arsine at the initial stage of decomposition.

Figure 8 shows arsine at 0°8 at several temperatures.
It is a graph showing cracking characteristics after flowing at a flow rate of 8 CCM for 1 hour.

In both figures, the vertical axis is the molecular beam intensity of various cracked gases measured using a quadrupole mass spectrometer, and the horizontal axis is the temperature of the cracking cell.

In addition, in both figures, 500 and 600 represent the molecular beam intensity of As+, and 501 and 601 represent the molecular beam intensity of As;
503 and 603 indicate the molecular beam intensities of As 3, and 504 and 604 indicate the molecular beam intensities of As+4, respectively.

As can be seen from these figures, even if the temperature of the cracking cell is the same, the composition of the cracked gas is completely different between the initial stage of cracking and one hour later.

For example, the molecular beam intensity (A) of As+ at 900°C
is 6X10''11 at the initial stage of cracking, but 2.5X after 1 hour of gas flow.
10-”.

In other words, if arsine is decomposed by flowing it through a cracking cell and then immediately irradiated to the substrate as a molecular beam to grow a crystal, the composition of the decomposed gas will change, so the composition of the crystal will change depending on the gas. You can see that there is a difference between the initial stage and after a certain period of time.

Therefore. By flowing arsine into the gas cracking cell 17 for at least one hour before epitaxial growth, the cracking characteristics within the gas cracking cell 17 can be brought to a steady state, and then by starting epitaxial growth, the cracking characteristics can be adjusted over time. Epitaxial growth can be performed without any change.

In the above embodiment, arsine may be introduced into the gas cracking cell 17 by opening the valve 9 while removing surface oxides from the GaAs substrate 15.

Further, in the above embodiment, arsine used for epitaxial growth of a GaAs film was shown, but In
Phosphine (PH3) used for P epitaxial growth
) is also the case.

Next, a second embodiment of the present invention will be described using FIG. 2.

FIG. 2 is an explanatory diagram of the gas source MBE apparatus of the present invention.

This gas source MBE apparatus is roughly divided into two crystal growth chambers.
12, a molecular beam cell 210 for triethyl gallium,
It is configured to include molecular beam cells 1 and 1 for arsine, a molecular beam cell 260 for phosphine, and a vacuum pump 16.

Inside the crystal growth chamber 212, a molybdenum substrate holder 21 is installed.
There is a GaAs substrate 215 mounted on 4, which is heated by a tungsten heater 213.

The structure of the molecular beam cell 210 for triethyl gallium is the same as the structure of the molecular beam cell 10 for triethyl gallium in the first embodiment, so its explanation will be omitted.

The molecular beam cell 250 for arsine has almost the same structure as the molecular beam cell for arsine of the first embodiment shown in FIG. 1, and the differences between the two are as shown in FIG. The molecular beam cell 250 for arsine of this embodiment has molecular beam blocking means such as a gate valve 230 that can block molecular beam irradiation of the decomposed gas, and when the gas valve 230 is closed, the decomposed gas is exhausted. The present invention is equipped with decomposition product gas exhaust means such as a gas exhaust pipe 220, and a valve 231 attached to the gas exhaust pipe 220. Note that a gas exhaust pump (not shown) is connected to one end (not shown) of the gas exhaust pipe 220.

The molecular beam cell 260 for phosphine has the same structure as the molecular beam cell 250 for arsine described above.

Next, using this device, Ga
A case where an A s P layer is epitaxially grown will be described.

First, in the molecular beam cell 250 for arsine, the valve 209 is opened and 38 CCM of arsine is introduced into the gas cracking zone 217 heated to 700°C.
Disassemble. At this time, the gate valve 230 is closed,
The gas decomposed in the gas cracking zone 217 is exhausted through the gas exhaust pipe 220.

The same operation as above is performed for the molecular beam cell 260 for phosphine.

Continue the above two operations for about 1 hour.

During this approximately one hour period, the following operations are performed.

The temperature of the GaAs substrate 215 is raised to 600°C, and the temperature of about 10
to remove surface oxides and clean Ga A
Obtain the s surface. Next, the temperature of the GaAs substrate 215 is lowered to the temperature during epitaxial growth and maintained at 580° C. in this embodiment.

As in Kaminuki, arsine and phosphine are decomposed in their respective molecular beam cells, exhaust is started, and after about an hour, the next operation is performed.

Open the valve 219 and add 0.68 CC of triethyl gallium to the gas emission zone 205 which is heated to 100°C.
M is introduced, decomposed, and the GaAs substrate 215 in the crystal growth chamber 212 is irradiated with its molecular beam.

At the same time, the following operations are performed in the arsine molecular beam cell 250 and the phosphine molecular beam cell 260.

In the molecular beam cell 250 for arsine, the valve 231
is closed, the gate valve 230 is opened, and the GaAs substrate 215 is irradiated with arsine decomposition gas.

Similarly, in the phosphine molecular beam cell 260, the valve 225 is closed, the goo-1 valve 224 is opened, and the GaAs substrate 215 is irradiated with the phosphine decomposition gas.

By performing the above operation, GaJM atoms, As atoms, and P atoms arrive on the GaAs substrate 215,
By combining these on the GaAs substrate 215, epitaxial growth of GaAsP is started.

By the above operation, the epitaxially grown Ga
The characteristics of the A s P crystal will be explained in comparison with a conventional example using FIGS. 9 and 10.

FIG. 9 is a graph showing the atomic concentration of each element when a GaAsP crystal is epitaxially grown using the conventional technique.

In the figure, the vertical axis indicates the atomic concentration of each element of Ga, As, and P measured using Auger electron spectroscopy in percentage, and the horizontal axis indicates the distance from the GaAs substrate interface.

FIG. 10 shows that using the apparatus of this embodiment, G a A s
This is a graph showing the atomic concentration of each element when a P crystal is epitaxially grown, and the vertical and horizontal axes are as shown in the 9th graph.
Same as in the figure.

Note that in both figures, the atomic concentration of P shows a value five times the measured value.

Using both figures, calculate G with respect to the distance from the GaAs substrate interface.
The atomic concentrations of each element of a, As, and P are compared.

First, a comparison will be made regarding Ga.

The atomic concentration of Ga is almost the same whether the conventional technique is used or the apparatus of this embodiment is used.

The reason for this is that the molecular beam cell for triethyl gallium is the same for both, and the molecular beam irradiation method is also the same.

Next, a comparison will be made regarding As.

In FIG. 9, the atomic concentration of As is about 39% at a distance of 0.10 μm from the Ga As substrate, but as it moves away from the Ga As substrate, the value gradually decreases. At a distance of 0.95 μm, approximately 35%
It is the atomic concentration. On the other hand, in FIG. 10 using the apparatus of this embodiment, 0.10
At a distance of 35 μm, or at a distance of 0 and 95 μm, approximately 35
% atomic concentration.

Next, P will be compared.

In FIG. 9, the atomic concentration of P is approximately 9% atomic concentration at a distance of 0.10 μm from the Ga As substrate, but the value gradually increases as the distance from the Ga As substrate increases. At a distance of 0.95 μm, the atomic concentration is approximately 12%. On the other hand, the first
In Figure 0, 0.10 μm from the GaAs substrate.
The atomic concentration is approximately 12% at a distance of 0.95 μm and at a distance of 0.95 μm.

As described above, GaAsP crystals produced using conventional techniques have different atomic concentration ratios of As and P within the crystal. As a result, the composition of the GaAsP crystal and its properties are not uniform. On the other hand, in the GaAsP crystal produced using the apparatus of this example, the A
The ratio of the atomic concentrations of s and P is the same. As a result, Ga
The composition and properties of the A s P crystal become uniform,
A compound semiconductor thin film with stable properties can be obtained.

In addition, in this embodiment, during the removal of the surface oxide of the GaAs substrate 215, the gate valve 230 and the valve 209 are removed.
is opened, valve 231 is closed, and the As molecular beam is
The light may be irradiated onto the As substrate 15.

In this case, the time when the valve 219 is opened and the introduction of triethyl gallium into the molecular beam cell begins must be at least one hour after the introduction of arsine into the gas cracking zone 217.

Furthermore, using the apparatus of this embodiment, the GaAs substrate 2
A GaAs crystal thin film can be formed on the GaAs crystal thin film 15, and a GaA, sP crystal thin film can be further formed on the GaAs crystal thin film.

In this case, the operation is performed as in the case of Shin.

During the formation of the GaAs crystal thin film, the gate valve 24 is kept closed, the valves 223 and 225 are opened, and 33 CCM of phosphine is introduced into the gas cracking zone 222. At this time, phosphine passes through the gas introduction line 227, enters the gas cracking zone 222, and enters the gas exhaust line 222.
26 and is exhausted to the outside. In this way, after more than one hour has passed since the introduction of phosphine into the gas cracking zone 222, the valve 225 is closed, the gate valve 224 is opened, and the phosphorus molecular beam is irradiated onto the GaAs epitaxial film to form a GaAsP crystal thin film. form.

Moreover, when the molecular beam cell for arsine and the molecular beam cell for phosphine of this embodiment are used, molecular beams unnecessary for crystal growth do not enter the crystal growth chamber, so the inside of the crystal can be kept clean.

Next, the gas cracking cell and gas piping of the third embodiment will be explained using FIG.

FIG. 3 is a sectional view showing the gas cracking cell and gas piping of this example.

The structure of the gas cracking cell and gas piping of this example will be explained using the same figure.

The gas cracking cell of this embodiment has tantalum dilation seals l<332, 333, molybdenum cracking zone 317, and tungsten heater 3.
04 and Baaful Play I, 340 are the same as in the second embodiment.

A feature of the gas cracking cell 300 of this embodiment is that the cell includes a molybdenum shutter 328 and a molybdenum shutter receiver 329. Also,
A molybdenum shutter support rod 330 for supporting the molybdenum shutter 328 is provided below the molybdenum shutter 328. It is connected to an air cylinder 332 supported by.

Next, the structure of the gas piping will be explained.

Gas pipe 301 is connected to gas cracking cell 300 via vacuum flange 338. In addition, the gas pipe 30
1 is divided into two parts at the end of the gas supply valve 334, one of which is connected to the gas cracking cell 300, and the other is connected to an exhaust pump (not shown) via a gas exhaust valve 335.

Next, using the gas cracking cell 300 and gas pipe 301 of this embodiment, gas is introduced, exhausted and decomposed,
The operating procedure for performing epitaxial growth will be explained.

When the raw material gas is not used for epitaxial growth,
The force of the air cylinder 332 presses the shutter 328 against the shutter receiver 329 to prevent gas from coming out of the gas cracking cell 300. At the same time, the gas supply valve 334 is opened to supply gas to the cracking zone 3.
17 Introduced. At this time, the gas exhaust valve 33
5 is closed.

Next, after a predetermined period of time has elapsed, the gas supply valve 334 is closed, the gas exhaust valve 335 is opened, and the gas accumulated in the cracking zone 317 is exhausted.

Then, after a predetermined period of time has passed, the gas supply valve 3
34 and close the gas exhaust valve 335.

As described above, the gas supply valve 334 and the gas exhaust valve 335 are repeatedly opened and closed until the gas is decomposed and used for epitaxial growth.

Next, when the cracking characteristics of the gas are stabilized and the decomposed gas is used for epitaxial growth, the shutter 328 is moved to the shutter receiver 329 by the force of the air cylinder 332.
away from. At the same time, the gas exhaust valve 335 is closed.

In this way, the substrate is irradiated with a gas having stable cracking characteristics, and atoms of the decomposed gas are epitaxially grown on the substrate.

Gas cracking cell 300 and gas pipe 301 of this embodiment
We will explain the effect when using .

As described above, impurities in the gas pool inside the gas cracking cell 300 are removed by repeatedly opening and closing the gas supply valve 334 and the gas exhaust valve 335 until the gas is decomposed and used for epitaxial growth. This makes it possible to obtain a gas with more stable cracking characteristics than the gas cracking cell used in the second embodiment.

In addition, the inside of the crystal growth chamber can be kept clean by
This is the same as in the second embodiment.

As a result, an epitaxially grown crystal with stable film quality is obtained on the substrate.

Next, a fourth embodiment of the present invention will be described using FIG. 4.

FIG. 4 is a sectional view showing the gas cracking cell and gas piping of this example.

The structure of the gas cracking cell and gas piping of this example will be explained using the same figure.

The structure of the gas cracking cell 400 of this embodiment is as follows:
Since the structure is the same as that of the gas cracking cell of the third embodiment shown in the figure, a description of the structure will be omitted.

Next, the structure of the gas piping will be explained.

The gas pipes include two gas supply pipes 401 and a gas exhaust pipe 436, both of which are connected to the gas cracking cell 400 via a vacuum flange 408.

Note that the gas exhaust pipe 436 is connected to the gas cracking cell 4.
Connect to the location where gas pools occur in the 00 (for example, near the bottom outer periphery of the gas cracking cell).

Further, the gas supply pipe 401 is connected to a gas supply valve 434.
The gas exhaust pipe 436 is connected to an exhaust pump (not shown) through a gas exhaust valve 435.

The following describes operations for introducing, exhausting, and decomposing gas to perform epitaxial growth using the gas cracking cell 400, gas supply pipe 401, and gas exhaust pipe 436 of this embodiment.

When the raw material gas is not used for epitaxial growth,
The force of the air cylinder 432 presses the shutter 428 against the shutter receiver 429 to prevent gas from coming out of the gas cracking cell 400. At the same time, the gas supply valve 434 is opened to supply gas to the cracking zone 4.
It will be introduced within 17 days. At this time, the gas exhaust valve 435 is also opened to exhaust the gas at the same time.

In particular, when the cracking characteristics of the gas are stable and the decomposed gas is used for epitaxial growth, the shutter 428 is moved to the shutter receiver 429 by the force of the air cylinder 332.
away from. At the same time, the gas exhaust valve 435 is closed.

In this way, the substrate is irradiated with a gas with stable cracking characteristics, and the decomposed gas atoms are epitaxially grown on the substrate.

Gas cracking cell of this example 4. The effects of using OO, the gas supply pipe 401, the gas exhaust pipe 436, etc. will be explained.

Since the gas supply pipe 401 and the gas exhaust pipe 436 are provided, impurities in the gas pool inside the gas cracking cell 400 can be efficiently removed, and the cracking characteristics are improved compared to the gas cracking cell used in the third embodiment. A more stable gas is obtained.

As a result, an epitaxially grown crystal with stable film quality is obtained on the substrate.

[Effects of the Invention] According to the present invention, after the cracking characteristics of the gas in the gas cracking cell reach a steady state, the decomposition gas is irradiated onto the substrate and epitaxial growth is started.
This has the effect of providing a good epitaxial film with little change in film composition or film quality in the thickness direction of the epitaxial film.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram for explaining the gas source MBE method of the first embodiment, FIG. 2 is an explanatory diagram for explaining the gas source MBE apparatus of the second embodiment, and FIG. 3 is an explanatory diagram for explaining the gas source MBE method of the second embodiment. FIG. 4 is a sectional view showing the gas cracking cell and gas piping of the fourth embodiment, FIG. 5 is a sectional view showing an example of the gas cracking cell of the prior art, and FIG. Figure 6 is a graph showing the temporal change in the molecular beam intensity of arsenic dimer when arsine gas is decomposed using a conventional gas cracking cell, and Figure 7 is a graph showing the cracking characteristics at the initial stage of decomposition of arsine at several temperatures. Figure 8 is a graph showing the cracking characteristics after flowing arsine at a flow rate of 0.88 CCM for 1 hour at several temperatures;
Figure 10 is a graph showing the atomic concentration of each element when a GaAsP crystal is epitaxially grown using the apparatus of the second embodiment. be. 1.18...Gas introduction line, 2,3,103゜104
．． 202,203,332,333゜403.4-02
．． ...Radiation Shield, 4.104,20
4,304,404--Tungsten heater, 5...
・Gas emission zone, 6,7°106.107,251,
340,4.40...Baffle plate, 8,108
,208,338゜408...vacuum flange, 9.1
9.209°219...Valve, 334,434...
・Gas supply valve, 335,435... Gas exhaust valve, 10° 210... Molecular beam cell for triethyl gallium, 11.250... Molecular beam cell for arsine,
260・Molecular beam cell for phosphine, 12,212...
・Crystal growth chamber, 13,213...Tungsten heater, 14.214...Substrate holder, 15,215...G
a A s board, 16,216 ==- vacuum pump, 1
7゜217.222,117,317,417...Gas cracking zone, 220,226...Gas exhaust pipe, 328,428...Shutter, 329,429...
...Shutter holder, 330,430...Shutter support rod, 331,431...Bellows, 332,432...
Air cylinder, 338, 433... Air cylinder support fitting.

Claims (1)

[Claims] 1. In a method for producing crystals by a molecular beam epitaxial method using a molecular beam cell having a cracking cell, a raw material gas whose cracking properties change over time is introduced into the gas cracking cell in advance and decomposed. , after a predetermined period of time, either alone or together with other source gas molecular beams,
A crystal manufacturing method using a molecular beam epitaxial method characterized by irradiating a substrate and starting epitaxial growth. 2. The crystal manufacturing method according to claim 1, wherein the predetermined time is a time during which cracking characteristics of the raw material gas are stabilized. 3. In a method for producing crystals by a molecular beam epitaxial method using a molecular beam cell having a cracking cell, a raw material gas whose cracking properties change over time among the raw material gases of at least one type of hydride is used in a gas cracking cell. alone after running for at least 1 hour,
Or, by irradiating the substrate with molecular beams of other source gases,
A crystal manufacturing method using a molecular beam epitaxial method characterized by starting epitaxial growth. 4. A vacuum vessel is equipped with at least one molecular beam cell that decomposes a source gas and generates molecular beams, and a crystal growth chamber having a substrate holder that holds a substrate, and the molecular beams generated from the molecular beam cell are In a molecular beam epitaxial apparatus for epitaxially growing crystals on a substrate by irradiating the surface of the substrate, molecules generated in the molecular beam cell are placed between at least one of the molecular beam cells and the crystal growth chamber. A molecular beam epitaxial apparatus characterized by being provided with a molecular beam blocking means capable of blocking the irradiation of the beam into a crystal growth chamber. 5. The above-mentioned molecular beam cell is characterized in that, when the molecular beam generated in the molecular beam cell is not irradiated into the crystal growth chamber, a means is provided for exhausting the decomposition product gas generated by decomposition of the source gas. The molecular beam epitaxial apparatus according to claim 4. 6. In a molecular beam cell having a gas cracking cell of a molecular beam epitaxial apparatus, the source gas decomposed in the gas cracking zone is
A molecular beam cell characterized in that a gas cracking cell is provided with a molecular beam blocking means capable of blocking irradiation of a substrate surface as a molecular beam. 7. As the molecular beam blocking means, a shutter that prevents molecular beam irradiation is provided in the gas cracking cell, and a shutter receiver that receives the shutter is placed on the molecular beam exit side of the gas cracking cell, and the molecular beam is irradiated. When the crystal growth chamber is prevented from being irradiated with molecular beams, the shutter is separated from the shutter holder, and when the irradiation of the molecular beam is prevented, the shutter is brought into contact with the shutter holder so that the molecular beam is not irradiated into the crystal growth chamber. Molecular beam cell according to item 6. 8. The above-mentioned gas cracking cell is equipped with a means for exhausting the decomposition gas generated by decomposition of the source gas when the molecular beam generated in the molecular beam cell is not irradiated into the crystal growth chamber. The molecular beam cell according to claim 6 or 7, characterized in that: 9. A molecular beam epitaxial apparatus comprising the molecular beam cell according to claim 6, 7 or 8. 10. In the molecular beam epitaxial method using a molecular beam cell having a cracking cell, a raw material gas whose cracking properties change over time is introduced into the gas cracking cell in advance, decomposed, and after a predetermined period of time, it is used alone or with other gases. Along with the molecular beam of the raw material gas,
A molecular beam epitaxial method characterized by irradiating a substrate and starting epitaxial growth. 11. A compound semiconductor manufactured by the crystal manufacturing method according to claim 1, 2 or 3.