JPH0529228A - Atomic layer crystal growth method and its apparatus - Google Patents

Abstract

(57) [Abstract] [Purpose] To widen the rate margin of atomic layer crystal growth. [Structure] When trimethylaluminum is passed through the quartz tube 3 at 400 ° C., it is thermally dissociated into dimethylaluminum, monomethylaluminum, and Al atoms, and the Al atoms adhere to the inner wall of the quartz tube 3 and do not come out from the quartz tube 3. . Hydrogen atoms are bonded to the remaining bonds of dimethylaluminum to form dimethylaluminum hydride. Hydrogen atoms bond to the remaining two bonds in monomethylaluminum, but this compound is unstable and easily becomes stable dimethylaluminum hydride. Therefore, the molecules supplied to the substrate 7 are dimethyl aluminum hydride. The hydrogen of dimethylaluminum hydride that has reached the surface of the substrate 7 dissociates during the reaction between Al and As on the substrate surface, so that the chemical bonding between Al and As is easily performed at a relatively low temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an atomic layer crystal growth method and an apparatus thereof, and more particularly to an atomic layer crystal growth method and an apparatus thereof using a compound semiconductor in which a molecule having a self-stopping mechanism is used as a part of a raw material. is there.

[0002]

2. Description of the Related Art In the conventional atomic layer crystal growth method, for example, Ga
When growing As crystals, trimethylgallium ((CH ₃ ) ₃ Ga: TMG), which is an organometallic gas, is used as a Ga raw material, and arsine (AsH ₃ ) is used as an As raw material, and these gases are alternated on the substrate crystal. To obtain a GaAs crystal layer. In this atomic layer crystal growth method, TM
When G is supplied, a part of the alkyl group of TMG is chemically deviated and chemically bonded to As on the substrate surface to form a Ga layer on the As substrate crystal. At this time, the TMG which has further flown onto this layer cannot be adsorbed, and the growth of the Ga layer stops at one layer. This mechanism is called a self-stopping mechanism, and atomic layer crystal growth is achieved by utilizing this mechanism. Such a conventional atomic layer crystal growth method has a relatively low substrate temperature (about 5
(00 ° C.) and under the condition that the growth temperature margin is extremely narrow.

The reason is that if TMG is thermally dissociated into Ga atoms in the vapor phase before reaching the substrate surface, Ga is further attached on Ga and growth for each atomic layer cannot be realized. Is. That is, in the conventional method, the high temperature side of the growth temperature is limited by the temperature Th at which thermal dissociation of the raw material occurs in the vapor phase. On the other hand, if the growth temperature is too low, the raw material gas cannot chemically bond with the surface of the substrate, and the growth does not reach the atomic layer. That is, the low temperature side of the growth temperature is determined by the temperature Tl at which the raw material is chemically bonded to the surface atoms of the substrate to grow (bond) the atomic layer. Further, the values of the temperature Th and the temperature Tl described above depend on the source gas. TM as an example
In the case of GaAs growth using G, the temperature Th is about 500 ° C. and the temperature Tl is about 490 ° C., and the difference, that is, the growth temperature range in which atomic layer crystal growth is possible is only 10 ° C. This is the reason why the growth temperature margin of the atomic layer crystal growth method is narrow.

[0004]

Conventionally, the growth of GaAs has been realized although the growth temperature range is narrow as described above. However, it has been difficult to realize a compound semiconductor containing Al atoms such as AlAs or AlGaAs. This is because an organic metal in which three methyl groups or ethyl groups are bonded to Al metal has been usually used, but since there is no difference between the temperatures Th and Tl, atomic layer growth cannot be performed.
In order to solve this, a raw material such as diethyl aluminum chloride ((CH ₃ ) ₂ AlCl) in which a part of the alkyl group bonded to Al chloride or Al metal is replaced with chlorine has been used. At this time, a method is also used in which the methyl group is removed by thermal dissociation in advance before supplying to the substrate to supply. However, since the product AlCl is unstable, AlCl chemically reacts with each other to generate Al metal, and atomic layer crystal growth has not been realized. This means that hetero crystal growth (eg GaAs / AlGaAs,
It means that atomic layer crystal growth of (GaAs / AlAs) is impossible. In addition, in the atomic layer crystal growth method, as described above, the source gas contains an alkyl group, and it is finally decomposed on the substrate surface, so that carbon in the alkyl group is taken into the crystal as an impurity. . This concentration reaches, for example, 10 ¹⁸ / cm ³ or more in the case of a normal GaAs crystal. Therefore, this method makes it difficult to grow high-purity crystals, which hinders the practical application of the atomic layer crystal growth method.

Therefore, a main object of the present invention is to provide an atomic layer crystal growth method and an apparatus therefor capable of making a growth temperature margin wider than ever. Another object of the present invention is to provide an atomic layer crystal growth method and apparatus capable of growing a composition which has been impossible in the past. Further, another object of the present invention is to provide an atomic layer crystal growth method and an apparatus therefor capable of realizing a high-purity crystal having a lower carbon impurity concentration than ever before.

[0006]

In order to achieve such an object, according to one embodiment of the present invention, an atomic layer crystal of a compound semiconductor which alternately supplies an organic metal having a self-growth stopping mechanism composed of a metal and an alkyl group. In the growth method, before the organometallic molecule reaches the substrate surface, at least one alkyl group bond bonded to the metal is thermally dissociated, and one or more alkyl group bonds are left on the substrate. It is characterized in that an atomic layer is supplied to form an atomic layer or is thermally dissociated in a hydrogen atmosphere, and hydrogen atoms are bonded to the dissociated bonds to be supplied onto the substrate to form an atomic layer.
This is different from the conventional atomic layer crystal growth method in that it is supplied to the substrate surface in a state of being bonded only to undecomposed alkyl groups.

[0007]

With this structure, at least one of the alkyl group bonding hands bonded to the metal is thermally dissociated before the growing molecule reaches the surface of the substrate, and the alkyl radical molecule is supplied to the growing substrate. , Reduce the binding energy with the substrate atoms. Alternatively, by thermally dissociating in a hydrogen atmosphere, it is supplied to the substrate to be grown as a relatively stable hydride, and the thermal decomposition temperature on the substrate surface is made different due to the difference in bond species. By these actions, the temperature range in which atomic layer crystal growth is possible can be increased and the carbon impurity concentration in the crystal can be reduced.

[0008]

EXAMPLES Next, examples of the present invention will be described. Figure 1
Shows a block diagram of an apparatus for realizing the atomic layer crystal growth of GaAs as the first embodiment of the atomic layer crystal growth method according to the present invention. In the figure, 1 is trimethyl which is a group III raw material. Tank containing gallium, 2 is a tank containing arsine which is a group V raw material, 3 is a quartz tube which is individually temperature-controlled for thermally dissociating a part of alkyl groups of trimethylgallium, and 4 is for temperature control Heater 5 wound around the quartz tube 3 of the above, 5 is a thermocouple for monitoring the temperature inside the quartz tube 3, and 6 is a carrier gas for carrying trimethylgallium and controlling the atmosphere inside the quartz tube 3. Tank, 7 is a substrate to be grown on a suitable support, 8 is a reaction tube, and 9 is RF for controlling the substrate temperature.
The (high frequency) coils 10a and 10b are stop valves that control the supply of raw materials.

FIG. 2 shows the results of examining the thermal decomposition characteristics of trimethylgallium in a nitrogen atmosphere with a quadrupole mass spectrometer. The figure shows the change in Ga peak intensity generated by the decomposition of trimethylgallium. In the figure, the horizontal axis represents the substrate temperature and the vertical axis represents the Ga ion current. In the figure, the region where the peak intensity is constant represents the amount of Ga decomposed in the quadrupole mass spectrometer. The decrease in peak intensity at 520 ° C. or higher indicates that trimethylgallium is decomposed in a nitrogen atmosphere. Part of the decomposed molecular species adheres to the wall surface of the quartz tube and the like, and the amount of trimethylgallium analyzed by the quadrupole mass spectrometer decreases, so the peak intensity decreases.

In FIG. 3, the temperature inside the quartz tube 3 in FIG. 1 is controlled to 540 ° C. at which trimethylgallium decomposes,
The carrier gas from the tank 6 is nitrogen, the flow rate is 2 liters per minute, the flow rate of trimethylgallium in the quartz tube 3 is 1.6 × 10 ⁻⁶ mol / cycle, and the flow rate of arsine from the tank 2 is 7 × 10 ^−6. In the condition of mol / cycle, trimethylgallium supply per cycle: Purge: Arsine supply: Purge = 1 second: 3 seconds: 1 second: 3 seconds in a sequence
FIG. 6 is a diagram showing the relationship between the growth rate and the substrate temperature when GaAs is grown. In the figure, the horizontal axis represents the substrate temperature and the vertical axis represents the growth rate. In the figure, the ● marks show the results of growth according to the present invention, and the ○ marks show the results of growth by a conventional method (supplying trimethylgallium using hydrogen carrier gas without decomposing). As shown by ●, the substrate temperature is from 460 ℃ to 5
In the region of 20 ° C, the growth rate becomes constant at 2.8Å / cycle. This value corresponds to the thickness of one atomic layer of GaAs, and it can be seen that atomic layer crystal growth is realized. On the other hand, in the conventional method, the area that becomes constant is 490 ° C to 500 ° C, which is only 1
Only 0 ° C.

Next, an example in which atomic layer crystal growth of AlAs is realized is shown as an example in which the source gas in the second embodiment is thermally decomposed and then supplied as hydride onto the substrate. FIG. 4 shows the decomposition characteristics of trimethylaluminum in a hydrogen atmosphere, which is the basis for obtaining the set temperature of the quartz tube 3 in FIG.
In the figure, the horizontal axis represents the temperature of the quartz tube and the vertical axis represents the ion current. This figure is the result of measurement with a quadrupole mass spectrometer similar to that described with reference to FIG.
Decomposition of trimethylaluminum begins to occur at 80 ° C. In this embodiment, the temperature inside the quartz tube 3 is set to 400 ° C. In the figure, DMAl is dimethylaluminum, MMAl is monomethylaluminum, Al is aluminum, CH4 is methane, and TMAl is trimethylaluminum. The numerical value on the right side of each material name shows the magnified magnification of the measured value. .

FIG. 5 is a diagram for realizing atomic layer crystal growth of AlAs according to the present invention. In the figure, the horizontal axis represents the substrate temperature and the vertical axis represents the growth rate. The growth conditions at this time are
The carrier gas from the tank 6 in FIG. 1 is hydrogen, the flow rate is 2 liters per minute, the group III raw material from the tank 1 is trimethylaluminum, and the flow rate is 1 × 10 ⁻⁶ mol / min.
Cycle, 7 × arsine flow from the tank 2 10 ^{@ 6} mo
Trimethylaluminum supply per cycle under the condition of l / cycle: Purge: Arsine supply: Purge = 1
It is the figure which showed the growth rate at the time of growing AlAs in the sequence of second: 3 second: 1 second: 3 second, and the substrate temperature. In the figure, ● indicates the result of growth according to the present invention, and ○ indicates the result of growth according to the conventional method (supplied without decomposing trimethylaluminum). ● Board temperature is 460 ℃
The growth rate becomes constant at 2.8 Å / cycle in the range from 480 ° C to 480 ° C. This value corresponds to the thickness of one AlAs atomic layer,
It can be seen that atomic layer growth has been realized. On the other hand, in the conventional method, there is no constant region, and atomic layer crystal growth cannot be performed.

FIG. 6 is a diagram for explaining the reason why the atomic layer crystal growth of AlAs shown in FIG. 4 was realized, and shows the change in the molecular state of trimethylaluminum before and after passing through the quartz tube 3 in FIG. Represent Trimethylaluminum 400 ℃
When it is passed through the quartz tube 3 of
Thermally dissociated into monomethylaluminum and Al atoms. Al atoms adhere to the inner wall of the quartz tube 3 and do not go out of the quartz tube 3. In addition, hydrogen atoms are bonded to the remaining bonds of dimethylaluminum to form dimethylaluminum hydride (H (CH ₃ ) ₂ Al). This reaction can easily occur because the bond energy between Al and hydrogen is larger than the bond energy between Al and a methyl group, and dimethylaluminum hydride is a stable compound. Hydrogen atoms bond to the remaining two bonds in monomethylaluminum, but this compound is unstable and easily changes to stable dimethylaluminum hydride. Therefore, the molecules supplied to the substrate are dimethyl aluminum hydride. The hydrogen of dimethylaluminum hydride reaching the substrate surface is dissociated during the reaction between Al and As on the substrate surface, so that the chemical bond between Al and As easily occurs even at a relatively low temperature. A method of using dimethylaluminum hydride itself instead of trimethylaluminum is also conceivable. However, compared with trimethylaluminum, the vapor pressure is less than one digit, so it is difficult to obtain a sufficient flow rate, and it is necessary to keep the raw material gas cylinder and the piping to the reaction tube at a high temperature of about 90 ° C at all times. , There is a problem in the reliability of the liquefaction in the piping and the stop valve and the mass flowmeter. The present invention can completely solve this problem.

The reason for expanding the temperature region toward the low temperature side of the atomic layer crystal growth of GaAs shown in FIG. 3 of the present invention will be explained by substituting FIG. 6, and trimethylgallium is decomposed in the quartz tube 3,
Radicals such as dimethylgallium and monomethylgallium
Ga is generated. Ga atoms are adsorbed on the quartz tube wall and do not go out from the quartz tube. The radicals do not bond with nitrogen in the atmosphere and reach the surface of the substrate. Since these radicals have dangling bonds, they do not require adsorption energy with As and are adsorbed even at low temperatures.

FIG. 7 shows an embodiment in which the carbon concentration is reduced by the present invention. In the apparatus shown in FIG.
It shows the carbon concentration of AlAs grown by supplying trimethylaluminum to. The growth conditions of the examples show the results obtained under the same conditions as those shown in FIG. The carbon concentration is reduced by about 2 to 3 digits as compared with the conventional method, and the remarkable effect of the present invention can be confirmed. Molecules that have passed through the quartz tube 3 become dimethyl aluminum hydride, which is supplied to the surface of the substrate and then dissociates hydrogen atoms. This dissociated hydrogen atom reacts with the methyl group that causes carbon bonded to Al and is removed as methane, so that a crystal with less carbon can be grown.

In the above example, an organic metal gas of trimethylgallium and trimethylaluminum is used.
II-VI such as organometals or dimethylzinc bound to other alkyl groups and sulfur compounds or Se compounds
It goes without saying that the same effect can be expected with the raw material species of the group.

FIG. 8 shows an apparatus for realizing a photodissociation method for dissociating a bond of a group III organometallic gas. A halogen lamp 21 is used as a light source, and TMA reaches the surface of the substrate 7 through the quartz tube 3 irradiated with light. By setting the other conditions to the same conditions as described in FIG. 5, atomic layer crystal growth of AlAs was realized as in the second embodiment of the present invention.

FIG. 9 shows an apparatus for realizing a dissociation method by an electron beam in dissociating a bond of a group III organometallic gas. Only TMA from tank 1 electron gun 31
The positions of the electron gun 31 and the TMA introducing tube 32 are set so as to reach the surface of the substrate 7 across the electron beam emitted from. The acceleration voltage of the electron beam from the electron gun 31 is set to 20 KeV, and the flow rate of TMA from the tank 1 is 1.5 sc
cm, the supply amount of arsine from the tank 2 is 2 sccm, the pressure in the reaction tube 8 is 8 × 10 ⁻⁵ Torr, the source gas of TMA is supplied for 5 seconds, and the time for purging each gas is 10
By setting to seconds, the atomic layer crystal growth of AlAs as shown in FIG. 5 was realized. In this example, the substrate heater 33 for controlling the substrate temperature is installed below the substrate 7.

[0019]

As described above, the present invention promotes the adsorption efficiency at low temperature by changing the molecular state to be easily chemisorbed on the surface of the substrate and supplying it, and as a result, the compound which could not be realized conventionally. Enables atomic layer crystal growth of semiconductors. Further, the carbon concentration in the crystal can be reduced, and high-purity crystal growth becomes possible. This has the effect of enabling the growth of various compound semiconductors, the growth of structures essential for device realization such as the hetero-growth structure, and the significant promotion of the practical application and application of the atomic layer crystal growth method. In other words, the present invention can precisely control the composition and film thickness uniformity at the hetero-interface that affects the device characteristics in atomic layer units in the crystal growth technology that realizes a fine electronic device structure expected to operate at ultra-high speed. It can be used for expanding the crystal composition that can be realized by the crystal growth method and reducing the concentration of carbon impurities contained in the crystal.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the results of examining the thermal decomposition characteristics of trimethylgallium in a nitrogen atmosphere with a quadrupole mass spectrometer.

FIG. 3 is a graph showing the effect of the first embodiment and showing the relationship between the growth rate of GaAs crystals and the substrate temperature according to the present invention and the conventional example.

FIG. 4 is a diagram showing decomposition characteristics of trimethylaluminum in a hydrogen atmosphere.

FIG. 5 is a graph showing the effect of the second embodiment and showing the relationship between the growth rate of AlAs crystals and the substrate temperature according to the present invention and the conventional example.

FIG. 6 is a diagram for explaining the reason why atomic layer growth of AlAs is realized.

FIG. 7 is a graph showing the effects of the present invention, showing the carbon impurity concentration of ALAs crystals according to the present invention and a conventional example.

FIG. 8 is a block diagram of an apparatus showing another embodiment of the present invention.

FIG. 9 is a block diagram of an apparatus showing still another embodiment of the present invention.

[Explanation of symbols]

1 tank 2 tanks 3 Quartz tube 4 heating heater 5 thermocouple 6 tanks 7 Growth substrate 8 reaction tubes 9 RF coil 10a stop valve 10b stop valve 21 Halogen lamp 31 electron gun 32 TMA introduction tube 33 Substrate heating heater

Claims (10)

[Claims] 1. An organic metal having a self-growth stopping mechanism composed of a metal and an alkyl group is used, and at least one bond between the metal of the organic metal and the alkyl group is thermally dissociated,
Atoms on the substrate by alternately supplying an organometallic molecule consisting of the metal and an alkyl group with one or more bonds left, and a hydride or an organometallic molecule different from the metal on the substrate. Atomic layer crystal growth method characterized in that a layer is grown. 2. The organic metal according to claim 1, wherein the organic metal is II
It is one selected from Group I and Group II metals, and the hydride or organometallic molecule contains at least one element selected from Group V and Group VI elements related to the organometal. Atomic layer crystal growth method characterized by the above. 3. The organic metal according to claim 1, wherein the treatment for thermally dissociating at least one bond between the metal and the alkyl group is carried out in a hydrogen gas atmosphere, and the dissociated bond has a hydrogen atom. The atomic layer crystal growth method is characterized in that the following treatment is carried out after the bonding. 4. An organic metal having a self-growth stopping mechanism composed of a Group III or Group II metal and an alkyl group is thermally dissociated from at least one bond between the Group III or Group II metal and an alkyl group, And after leaving one or more bonds,
An organometallic molecule containing a Group III or Group II metal,
An atomic layer crystal growth method characterized in that an atomic layer is grown by alternately supplying a hydride containing a group V or group VI element or an organic metal molecule onto a substrate. 5. An organic metal having a self-growth stopping mechanism composed of a group III or group II metal and an alkyl group is prepared by using at least one bond between the group III or group II metal and the alkyl group in a hydrogen gas atmosphere. Is thermally dissociated, and a hydrogen atom is bonded to the dissociated bond, and then the organometallic molecule containing the group III or II metal and the hydride or organometallic molecule containing the group V or VI element are alternated. Atomic layer crystal growth method characterized in that the atomic layer is grown on the substrate to grow the atomic layer. 6. A reaction chamber, a substrate arranged in the reaction chamber and having an atomic layer formed on the surface thereof, means for controlling the temperature of the substrate, and a metal and an alkyl group connected to the reaction chamber. A means for supplying a first raw material having a self-growth stopping mechanism to the reaction chamber, a first valve means for stopping the supply of the first raw material to the reaction chamber, and a connection to the reaction chamber Means for supplying a second raw material containing hydride or organometallic molecules to the reaction chamber, second valve means for stopping the supply of the second raw material to the reaction chamber, and the reaction Means for thermally dissociating at least one bond in the state where one or more bonds of the organic metal and the alkyl group of the first raw material supplied to the chamber are left, and the first valve means And the second valve means to control the inside of the reaction chamber. An atomic layer crystal growth apparatus characterized in that organometallic molecules consisting of the metal and an alkyl group and the hydride or organometallic molecules are alternately supplied to the substrate on the substrate. 7. The atomic layer according to claim 6, wherein the means for thermal dissociation comprises a quartz tube to which the first raw material is supplied and a heating means arranged on the outer periphery of the quartz tube. Crystal growth equipment. 8. The atomic layer crystal growth apparatus according to claim 6, wherein the heating means is a heater. 9. The atomic layer crystal growth apparatus according to claim 6, wherein the heating means is a lamp. 10. The atomic layer crystal growth apparatus according to claim 6, further comprising means for supplying hydrogen gas to the thermal dissociation means to perform thermal decomposition in a hydrogen gas atmosphere.