JPH05267198A - Crystal growth method for compound semiconductor - Google Patents

Abstract

PURPOSE:To provide a crystal growth method which controls single atom layer and allows growth of compound semiconductor crystal of good quality. CONSTITUTION:A suscepter 8 on which a base crystal 9 is mounted is put in a quartz reaction tube 1. The suscepter 8 which is made of graphite is supported by a supporting rod 11, and the rod is movable vertically between a sample preparatory chamber 13 and the place of crystal growth through a gate valve 12, airtightness being maintained by a bellows 14. An RF coil 2 is disposed around the outer periphery of growth position. A gas supply part 15 and a manifold 5 for supplying multiple gases 6 by switching are connected to the lower part of reaction tube. An exhausting device 3 for material gas and a pressure adjusting valve 4 are connected to the upper part of the tube. In material gas generated by diluting trimethy lindium with hydrogen is flown for 15 seconds together with hydrogen at a specified flow rate over an InAs base crystal 9 heated to 300-450 deg.C, and then exhausted. Then, AsH3 is diluted with hydrogen and flown at a specified rate, and then exhausted. Gas supplying is performed in repetition and in the order of In, hydrogen, As and hydrogen, for InAs crystal growth, while mixing of both materials is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal growth method for compound semiconductors. Compound semiconductors are used, for example, as constituent materials for various electronic devices. In order to miniaturize an electronic device and improve its performance, it may be desired to grow a compound semiconductor having a desired composition at a desired location by a desired thickness. Atomic layer epitaxy (ALE), which controls the growth on an atomic layer basis, is one way to meet these requirements.

[0002]

2. Description of the Related Art Organic metal vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE), atomic layer epitaxy (ALE) and the like are known as vapor phase crystal growth methods for compound semiconductors. Among them, MOCVD has a high growth rate, but it is difficult to control the atomic layer unit. MBE uses an ultra-high vacuum device and supplies the raw material as a molecular beam into the ultra-high vacuum.
Perform crystal growth.

By the way, when a ternary compound semiconductor is grown by a general vapor deposition method, one site (group III or V) is grown.
Two kinds of elements randomly enter the (group) and cause the alloy scattering to the traveling of the carrier. Therefore, alloy scattering can be prevented by designating and aligning the sites of the three elements. In order to specify each site of these three elements, ALE that can control growth for each element is effective.

As the ALE, there is a method of evacuating the inside of the growth chamber to an ultrahigh vacuum, heating the substrate, and sequentially introducing a predetermined amount of a gas containing a constituent element for crystal growth to grow a semiconductor for each molecular layer. Known (Japanese Patent Laid-Open No. 61-3492)
No. 2). However, this method has a problem that it takes a long time to switch the source gas, and at that time, the once-deposited atomic layer is apt to change, resulting in poor controllability.

Further, various problems arise in heteroepitaxial growth by ALE. First, InAs
A case of growing an InAs epitaxial layer on a substrate will be described. The InAs substrate placed in a reaction tube such as quartz is heated to a predetermined temperature, for example, 350 ° C.
A group III element source gas and a group V element source gas are alternately supplied. The growth gas pressure is, for example, several torr to several 100 to
It is in the range of rr.

The raw material of indium is, for example, trimethylindium (CH ₃ ) ₃ In, and the raw material of arsenic is, for example, arsine AsH ₃ . In layer and As on the substrate
InA by ALE by alternately growing layers
s crystals can be grown. When growing a GaAs crystal, the growth temperature is set to 500 ° C., trimethylgallium (CH ₃ ) ₃ Ga is used as a gallium source gas, and arsine AsH ₃ is used as an arsenic source.

In the above example, the growth temperature when growing an InAs crystal is 350 ° C., and the growth temperature when growing a GaAs crystal is 500 ° C. InAs / G
When growing an aAs heterojunction, the growth temperature is 500 ° C.
Then, the temperature is too high for the growth of InAs,
The self-limiting effect is lost and monolayer growth becomes difficult.

On the other hand, when the growth temperature is 350 ° C., Ga
The temperature is too low for As crystal growth, and crystal growth does not proceed.
Frequently changing the growth temperature during crystal growth is not preferable in terms of control and efficiency. In addition, there are problems such as a difference in lattice constant between substances forming the heterojunction, a difference in thermal expansion coefficient, stability of each atom at the hetero interface, and mutual diffusion of constituent atoms at the hetero interface.

Conventionally, in ALE, the growth rate when one cycle of the raw material gas is supplied is determined by the supply concentration and the supply time of the group III or group V raw material. For the growth rate of ALE, for example, for GaAs, Applied Physics
Letters, 53, pp. 1509-1511 (1988). The dependence of the purity of GaAs crystals on the supply concentration and the supply time of the group III and V raw materials is also described in Journal of Crystal Growth, Vol. 93, 55.
7 (1988). As described above, hitherto, no influence on the growth rate and the characteristics of crystals when no raw material is supplied has been known.

[0010]

As described above,
Atomic layer growth of compound semiconductors, particularly heteroepitaxial growth, has not been fully clarified yet, and it has not been easy to obtain desired high-quality crystals. An object of the present invention is to provide a crystal growth method of a compound semiconductor, which has a controllability of a monoatomic layer and can grow a good quality compound semiconductor crystal.

Specifically, it is an object of the present invention to provide a compound semiconductor crystal growth method capable of easily producing a heterojunction of a compound semiconductor containing In as a group III element with the strictness of a monoatomic layer. Yet another object of the present invention is to
We investigated the effect of time other than III and V source materials on the process of crystal growth, improved the growth technique of the crystal growth method by alternate supply of materials, and controlled the growth at the atomic level with a higher quality hetero The purpose is to enable epitaxial growth.

[0012]

In order to achieve the above object, the present invention provides, in the first aspect, a step of heating a base crystal to a predetermined temperature, and a step of heating an organic compound of In with hydrogen at the predetermined temperature. A first group III supply step of supplying the diluted group III source gas onto the underlying crystal at a predetermined pressure without being decomposed, a step of exhausting the group III source gas, and a group V element in a first composition. A first group V supply step of supplying a first group V source material gas containing the same at a predetermined pressure onto the underlying crystal;
A step of exhausting the group III source gas; a second group III feed step of feeding a group III source gas obtained by diluting an In organic compound with hydrogen onto the underlying crystal at a predetermined pressure without being decomposed;
Exhausting the group II source gas, and supplying a second group V source gas containing a group V element in a second composition and having a different composition from the first group V source gas onto the underlying crystal at a predetermined pressure. There is provided a method for crystal growth of a compound semiconductor, which comprises a second group V supply step of: and a step of exhausting the second group V source gas.

The compound semiconductor thus grown is
Typically, those having a heterojunction of InAs / InP, InAsP / InP, or InAs / InAsP can be mentioned. In this crystal growth method, the In organic compound is not effectively decomposed until reaching the underlying crystal,
The predetermined temperature, the hydrogen dilution ratio of the In organic compound, the flow rate of the group III source gas, and the predetermined pressure are selected so as to decompose on the base crystal.

Further, the first group V raw material supply step and the second
Hydrogen is supplied during the Group III source supply process and between the second Group V source supply process and the first Group III source supply process to exhaust the source gas, and the hydrogen supply time of this hydrogen supply (purge) process Is preferably limited to such an extent that the detachment of the group V atom attached in the first and second group V source material supplying steps can be prevented.

Further, according to the present invention, in the second aspect, the step of heating the base crystal to a predetermined temperature and the following steps at the predetermined temperature, that is, the Group III source gas diluted with hydrogen at a predetermined pressure are used. A step of supplying hydrogen gas onto the base crystal without decomposition, and a step of supplying hydrogen gas onto the base crystal.
Purge step of exhausting the group II source gas, step of supplying group V source gas at a predetermined pressure onto the base crystal, and purge step of supplying hydrogen gas onto the base crystal and exhausting the group V source gas And a crystal growth method of a compound semiconductor, characterized in that the crystal growth rate is controlled by controlling a purge amount, and a step of heating a base crystal to a predetermined temperature; In the following steps, namely, a step of supplying a group III source gas diluted with hydrogen at a predetermined pressure onto the underlying crystal while undecomposed, a hydrogen gas is supplied onto the underlying crystal and the group III source gas is supplied. A purging step of exhausting, a step of supplying a group V source gas at a predetermined pressure onto the base crystal, a purge step of supplying hydrogen gas onto the base crystal and exhausting the group V source gas,
A method for growing a crystal of a compound semiconductor, comprising the step of supplying a doping gas, wherein the doping amount is controlled by controlling the purge amount in the purging step before supplying the doping gas.

[0016]

InAs has a high electron mobility, a lattice-mismatch type device or a heterojunction type device using this is highly useful, but such a hetero growth was not easy. For example, even in the GaAs / InGaAs system, the composition of In was only about 0.2 at most. Therefore, in the present invention, the first
Attention is focused on a system containing In in both heterojunctions such as InP / InAs, and a system having a small lattice mismatch between the two is selected to facilitate growth. In particular, InP and InA
At the s interface, the mutual diffusion of As and P is extremely small, which is advantageous. Further, a heterojunction containing In in both is advantageous because the ALE growth temperatures of both are close.

Secondly, by using a group III source gas obtained by diluting an In organic compound with hydrogen at a predetermined pressure, it becomes possible to grow a monoatomic layer of In on the underlying crystal.
A monoatomic layer of a Group V element can be grown relatively easily, and a hetero interface can be realized by controlling the composition thereof. By setting the base crystal to a predetermined temperature, it becomes possible to control the reaction in the gas and the reaction on the base crystal. If the temperature of the underlayer crystal is too high, not only two-dimensional growth for growing a monoatomic layer but also three-dimensional growth occurs, so the underlayer crystal is heated to a predetermined temperature that suppresses the three-dimensional growth. By supplying the source gas of the V group element on the In atomic layer, a monoatomic layer of the V group element grows.

Furthermore, the separation of the two source gases can be improved by flowing hydrogen gas between the group III element supply step and the group V element supply step. The complete separation of the two source gases in a shorter time prevents the disorder of the hetero interface, and the growth from the source gas diluted with hydrogen gas contributes to monatomic growth. Expand the controllable range of semiconductor growth conditions. Therefore, it becomes possible to realize a more complete hetero interface even between compound semiconductors under different growth conditions, a complete hetero interface at the molecular layer level, and to reduce the unit of the superlattice structure.

When hydrogen gas is supplied and purged after the supply of the group V element and before the supply of the group III element, the once grown group V atoms are desorbed if the purge time is lengthened. When the group V atom leaves, another group V atom enters there, forming a mixed crystal state, and the advantage of ALE growth is lost. Therefore, in order to form a perfect crystal and a perfect hetero interface as described above, this purging time must be shorter than a predetermined time, while the amount of group V atoms to be desorbed is equal to the purging amount (time). Therefore, it is also possible to control the purge amount (time) to control the amount of point defects and doving of the compound semiconductor crystal.

[0020]

【Example】

(1) First, the basic experimental results will be described. Figure 1
It is a sectional view showing roughly a crystal growth device which performs crystal growth. FIG. 2 shows the growth temperature dependence of the crystal growth rate. First, the crystal growth apparatus shown in FIG. 1 will be described. The reaction tube 1 is formed of a quartz tube whose one end is narrowed and has a structure capable of exhausting. Base crystal 9 for growing crystals in the reaction tube 1
A susceptor 8 for mounting the is placed.

The susceptor 8 is made of, for example, carbon (graphite) capable of absorbing high frequencies. Susceptor 8
Is supported by a support rod 11 and is movably supported between a sample preparation chamber 13 and a crystal growth site via a gate valve 12. In the figure, a bellows 14 shown on the upper side is a mechanism for moving the support rod 11 up and down while maintaining airtightness. An RF coil 2 is arranged on the outer circumference of the reaction tube 1 around the position where crystal growth is to be performed, so that the carbon susceptor 8 can be heated by high frequency.

Below the reaction tube 1, the gas flow velocity (injection velocity)
A gas supply unit 15 having a reduced diameter is connected to the gas supply unit 15, and a manifold 5 which is a valve mechanism for switching and supplying a plurality of gases is connected to the gas supply unit 15. A plurality of source gases are connected to the gas supply unit 6 of the manifold 5. The manifold 5 is also connected to a vent pipe 7 for discharging the supplied gas to the reaction tube 1 without discharging it.

To the upper part of the reaction tube 1, an exhaust device 3 for discharging the used gas raw material and a valve 4 for pressure adjustment are connected. By using such a device, it is possible to heat the underlayer crystal to a predetermined temperature, supply a desired source gas onto the underlayer crystal at a desired pressure and a desired flow rate, and switch at a desired rate. One of the features is that it supplies various gases as a high-speed air stream and switches the gas type at high speed.
Furthermore, the gas is made to flow in the same direction and discharged.

The heating means is not limited to the RF coil, and other heating methods such as resistance heating and lamp heating may be used.
Similarly, the reaction tube 1 may be made of a material other than quartz. The susceptor 8 may be any one as long as it can keep the underlying crystal at a predetermined temperature. The manifold 5 can switch the gas for about 100 msec. Using a growth apparatus as shown in FIG. 1, InAs was formed on the (100) plane InAs substrate.
InP was crystal-grown on the (100) plane InP substrate. The growth conditions are as follows.

The raw material of In is trimethylindium (T
MIn), As raw material was AsH ₃ , and P raw material was PH ₃ . For TMIn, an In material gas was obtained by keeping the container at 27.1 ° C. and passing hydrogen through the container. This raw material gas was flowed together with hydrogen gas at 60 sccm for 15 seconds. AsH ₃
Was diluted to about 10% with hydrogen gas, and a flow rate of 480 sccm was applied for 10 seconds. PH ₃ was diluted to about 20% with hydrogen gas, and flowed at a flow rate of 480 sccm for about 20 seconds. The pressure in the reaction tube was kept at about 15 torr during crystal growth.

Gas was supplied in the order of group III raw material, hydrogen, group V raw material, and hydrogen, and this was repeated as one cycle. Hydrogen functions as a purge gas and prevents mixing of the group III raw material and the group V raw material in the space. FIG. 2 is a plot of the thickness of the growth layer obtained as a function of the growth temperature when the source gas of the group III element is flown under the above conditions, and then the gas is switched to flow the group V element gas. .. The supply of the source gas of the group V element once and the supply of the source gas of the group III element once were defined as one cycle, and the number of molecular layers formed per cycle was measured.

As can be seen from the figure, when InAs is grown, it is 1 in the range of about 300 ° C to 450 ° C, more preferably in the range of about 310 ° C to 450 ° C.
A monolayer grew in the cycle. About 3 for InP
In the range of 00 ° C to 450 ° C, more preferably in the range of about 310 ° C to 425 ° C, 0.5 molecular layer was grown in one cycle. In the atomic layer growth of InP, 0.5 molecular layer grows in one cycle because I
This is a characteristic of nP growth, and it is necessary to repeat two cycles to grow an InP1 molecular layer.

As is apparent from FIG. 2, the temperature range in which InAs can be grown with good controllability and InP.
It almost overlaps with the temperature range where stable growth is possible with good controllability. Therefore, while maintaining the substrate at a predetermined constant temperature, the InAs layer and the InP layer can be grown thereon to form a heterojunction. (2) Next, using a growth apparatus as shown in FIG.
(InAs) _m (InP) on the (0) plane InAs substrate
_n Superlattice structure was grown. The growth temperature was chosen to be 365 ° C. and the growth pressure was kept constant at 15 torr during the growth period.

The manifold 5 was prepared by bubbling hydrogen gas into TMIn kept at 27.1 ° C. as a group III source gas, diluted with hydrogen gas, and diluted with AsH ₃ to about 10% with hydrogen gas. , PH ₃ diluted with hydrogen gas to about 20% was used. The flow rate is TMIn
There 60sccm, AsH ₃ is 250sccm, PH ₃ is 400sc
cm. The hydrogen gas was used as a carrier gas, and the total flow rate in the reaction tube was 2000 sccm.

Prior to the growth of the superlattice, the InAs layer and the InP layer were first grown and the time for flowing TMIn was determined.
FIG. 3 shows the dependence of the growth rate on the TMIn pulse width. In the growth of InAs, almost complete monolayer was grown if TMIn was supplied for about 4 seconds or longer.

On the other hand, in the growth of InP, TMIn
When the supply time of was about 7 seconds or more, a nearly complete semi-molecular layer grew. In InP growth, one cycle of InP grows by repeating two cycles. In addition,
As is clear from FIG. 3, if the supply time of TMIn is more than a certain value, a monomolecular layer or a ½ molecular layer grows,
Even if the feeding time is extended, the growth does not proceed any further. That is, a so-called self-limiting effect is observed.

Therefore, in order to grow the superlattice structure, TMIn
The supply time was set to 12 seconds. Under the above conditions, various (InAs) _m (InP) _n (where m and n are positive integers) superlattice structures were grown. Figure 4
FIG. 3 is an X-ray diffraction graph of a superlattice structure of (InAs) ₃ (InP) ₂ . (100), (400), (60
The peaks of 0), (900), and (1100) are so-called satellite peaks, indicating that good monolayer growth was performed.

Further, the (500) and (1000) peaks are diffraction peaks shown by the structure having five molecular layers as a unit, and the (200) and (400) peaks of InAs, which is the substrate, are superimposed. It is a thing. As described above, it is clearly understood from the X-ray diffraction peaks shown in FIG. 4 that the (InAs) ₃ (InP) ₂ superlattice is formed on the (100) plane of the InAs substrate.

FIG. 5 shows (InAs) ₃ (I
The X-ray-diffraction peak at the time of creating a nP) ₁ superlattice is shown. In the case of this configuration, the repeating period is 4 molecular layers,
The (400) peak and the (800) peak are based on this repeating period. With a monolayer (100),
Satellite peaks of (300), (500), (700) and (900) are clearly observed.

FIG. 6 shows the same procedure (InAs).
₂ shows an X-ray diffraction peak when a ₂ (InP) ₁ superlattice was created. Also in this structure, the satellite peak due to the monolayer structure is clearly recognized. 4 to 6
Each sample showing an X-ray diffraction peak at about 100 nm
Based on a grown layer having a thickness of. These X
As can be seen from the line diffraction peaks, it was confirmed that the superlattice structure as designed was created.

In the above-mentioned embodiment, it is important to supply TMIn, which is a group III raw material, with hydrogen gas as a carrier. According to the analysis based on the above experimental data and other data, the present invention is not limited to this theory, but it is considered that the growth as described below is performed. TMIn, which is a group III material, is hardly decomposed until it reaches the underlayer crystal, and adheres to the underlayer crystal while maintaining its molecular structure.

When TMIn is about to be decomposed, hydrogen becomes insufficient because the methyl group becomes methane. It is considered that hydrogen in the carrier gas supplies hydrogen when this methyl group changes to methane. This state is shown in FIG. A methyl group is indicated by R, and an indium atom is indicated by an open circle with a bond.

As shown in the right side of the figure, when the trimethylindium molecule is adsorbed on the As atomic layer, it is difficult to be desorbed, and by reacting with hydrogen, an In atom is left on the As atomic layer, and the methyl group R is It becomes methane CH ₄ and is carried away into the gas. On the other hand, as shown on the left side of the figure, when trimethylindium molecules are adsorbed on the surface to which In atoms are already attached, the adsorption energy is low and the trimethylindium molecules are desorbed into the gas again. For this purpose, it is important that the substrate temperature is not too high.

In atoms created by decomposition of trimethylindium molecules on the substrate migrate on the substrate and
Stabilize where n atoms gather. In this way
The atomic layer gradually expands, and two-dimensional growth occurs. The collision of molecules of trimethylindium with each other in the gas and on the substrate and reacting with each other to generate indium atoms disturbs the growth mechanism.

Therefore, the substrate temperature, that is, the growth temperature,
Dilution ratio of TMIn with hydrogen, time required for TMIn to reach the underlying crystal from the source, that is, flow velocity of the supply gas when the device is fixed, and collision of TMIn molecules in the gas, that is, pressure of the supply gas, etc. Is the parameter that controls the growth mechanism. In the gas phase, TMIn hardly decomposes, reaches the underlying crystal, adheres to the underlying crystal as it is on the molecule, decomposes into hydrogen atoms by supplying hydrogen, and controls these parameters to form an In atomic layer. It is desirable to do.

It should be noted that, compared with the growth of the group III atomic layer, the group V atomic layer is relatively easy to grow a monoatomic layer and has a strong self-limiting effect. In addition to the above-mentioned arsine and phosphine, it is considered that tert-butyl arsine, tert-butyl phosphine, monoethylarsine, monoethylphosphine and the like can be used as the group V raw material.

In addition to As and P, other V group elements such as Sb may be used as the V group element. By mixing Sb, it is possible to adjust the lattice constant mismatch. Further, generally, a molecule in which a group III atom and a group V atom are bonded to hydrogen, methyl, ethyl, isobutyl, tert-butyl, amino group, halogen or the like can be used as the source gas.

Further, it is desirable to maintain the pressure of each gas at a constant value in order to prevent backflow when switching the supply gas. As described above, when the InP molecular layer is formed, only 0.5 molecular layer is formed in one cycle, and therefore two cycles must be continuously performed to form one molecular layer. It would be obvious.

(3) Regarding the invention for controlling the crystallinity of the compound semiconductor crystal grown by controlling the hydrogen purge amount (time) after the group V element supply step, before describing specific examples,
With reference to FIG. 8, the principle is shown in FIG. 8 by using trimethylgallium (TMGa) and arsine (AsH ₃ ) in an H ₂ gas flow.
A case of performing homo-growth of aAs will be described. (A) is a diagram when AsH ₃ which is a raw material of As is being supplied onto a GaAs substrate. AsH ₃ is decomposed by the catalytic action on the crystal surface to become As atoms or molecules, and only one atomic layer is deposited on the crystal surface. Since As has a high vapor pressure itself or has a small As-As binding energy, two or more layers are not deposited. Then, the supply of AsH ₃ is stopped and only H ₂ gas is supplied to purge AsH ₃ molecules.
During the purging with this H ₂ gas, the As
Are desorbed (FIG. 8B), and a number of As determined by the growth temperature and the H ₂ gas purge time remain on the surface. In the atomic layer epitaxy method using TMGa, TMGa molecules are
It selectively reacts only with s atoms to generate Ga atoms (FIG. 8 (c)). Next, TMGa is purged with H ₂ as in the previous process (FIG. 8D). However, as shown by the experimental facts shown later, even when the surface on which Ga is deposited is exposed to an H ₂ atmosphere, Ga on the surface is not desorbed, and As atoms in the second surface layer and below are not desorbed. Therefore, the growth amount of AsH ₃ → H ₂ → TMGa → H ₂ shown in FIG. 8 during one cycle remained on the surface as a result of the desorption of the surface As shown in FIG. 8B. It is determined by the amount of As. Also,
According to this method, the number of vacant As sites on the surface can be controlled, so that, for example, the As sites are occupied and become donors. VII
When doping a group element, the doping amount (doping efficiency) can be controlled. Also, considering that the stoichiometry on the surface is changed, the uptake rate of other impurities (donors, acceptors), the point defect density, etc. can be controlled.

(4) An example in which the above principle is applied to atomic layer epitaxial growth of InAs will be described. Also in this example, the growth apparatus as shown in FIG. 1 was used. Growth materials are trimethylindium (TMIn) and arsine (AsH
₃ ) was used, diluted with H ₂ gas, and alternately supplied onto the InAs crystal. A 20 KHz high frequency induction coil was used to heat the substrate. The pressure during growth was 15 torr, and the total flow rate in the reaction tube was 2000 cc / min. The TMIn cylinder was kept at 27 ° C., and 60 cc / min of H ₂ was passed through the cylinder. AsH ₃ was supplied from a cylinder diluted with hydrogen to a concentration of 10% at a flow rate of 480 cc / min.

The gas supply sequence is shown in FIG. Where t ₁ is the time of H ₂ purge after AsH ₃ and t
₂ is the time of H ₂ purge after TMIn. TMIn
And AsH ₃ were alternately supplied onto the crystal by switching the manifold valve capable of high-speed operation. In order to investigate the desorption of As atoms from the crystal surface as described in the principle of (3) above, the growth rate per cycle was measured by changing t ₁ and t ₂ . FIG. 10 shows t when the growth temperature is 400 ° C.
The relationship between ₁ and t ₂ and the growth rate is shown. In this experiment, the pulse width of TMIn is 5 seconds and the pulse width of AsH ₃ is 10 seconds.
Grew in seconds. The H ₂ purging time, which is not changed, is 0.5 second.

Thus, it is clear that the growth rate per cycle decreases with the increase of the H ₂ purge time after AsH ₃ . On the other hand, it is clear that the time of H ₂ purge after TMIn does not affect the growth rate. A similar trend was observed at 365 ° C (Fig. 11). But,
The higher the growth temperature, the larger the amount of As that escapes within the same t ₁ .

FIG. 12 shows the growth rate at 400 ° C.₁The parameter
Growth rate and T supplied when ALE growth is performed
The relationship of MIn is shown. The growth rate of ALE growth is AsH₃
It can be seen that it is controlled by the purge time after. next
AsH by the sequence as shown in FIG.₃of
After H₂Purging process t₁H after the end₂Crystallize Se
It was supplied above and the doping amount was examined. H ₂Se is 10
One diluted with ppm to 30 cc / min for 1 second
Supplied for a while.

FIG. 13 shows the relationship between t ₁ and the electron concentration (Se concentration) of the crystal. It became clear that the electron concentration (Se concentration) increased with the increase of t ₁ . In general, it is preferable that the doping gas is supplied alone or as a part of the group III element source gas after the group V element is supplied after H ₂ purging to partially remove the group V atoms. (5) FIG. 14 shows that when InAs is grown by ALE, A
It is shown in relation to the crystal growth temperature as to what range the time (second) of H ₂ purge after sH ₃ supply is limited to prevent As separation. The growth conditions at this time are shown in FIG.
The same as the case of.

In the figure, the black circles indicate the purge time which is the upper limit at which As can be prevented, and the white circles indicate the purge time which is practically optimal. These are the preferred H ₂ purge times of the formula ( 1), and a more preferable H ₂ purge time can be expressed by equation (2). log t ≦ − (7.09 / 475) T + 7.33 (1) log t ≦ − (6.72 / 350) T + 7.44 (2) [wherein T is the substrate temperature (° C.) and t is H ₂ purge is time (sec)] 15 illustrates the case where H ₂ purge time is too long examples growth InPAs. P → by ALE
After the growth of In → As, if the H ₂ purge time is long, part of As is released. Next, when the In source gas (TMIn) is supplied, In adheres only on the remaining As atoms and does not adhere to the vacant As atoms that have left. After that, In is hard to be separated even if H _{2 is} purged, but when P source gas (PH ₃ ) is supplied next, P adheres on the In atom.
At this time, As also attaches to the vacant seat from which the As has left. In this way, when As sites and P sites are mixed and alloyed (mixed crystal), the significance of controlling each atomic layer by ALE is lost.

16 (a) and 16 (b), the conventional general In
The structures of a GaAs mixed crystal and an InGaAs crystal in which In, Ga and As sites are designated by the present invention are schematically shown.
In the mixed crystal of FIG. 16 (a), the position of the group III atom is irregular, so that scattering (alloy scattering) occurs with respect to carrier motion. As shown in FIG. 15, even when the H ₂ purge time is lengthened in the ALE of the present invention, a kind of mixed crystal state (positions of P and As are irregular) occurs, and alloy scattering occurs. Moreover, it becomes difficult to form a superlattice having a small number of layers. In FIG. 16 (b), the sites of each atom are aligned so as to prevent alloy scattering.

(6) An example of a device to which the semiconductor crystal growth method of the present invention is applied will be described. FIG. 17 shows a non-doped InP (100) substrate 21 over a Fe-doped semi-insulating InP (100) substrate 21 with a non-doped (InA
s) An HEM in which an electron channel of a superlattice structure 23 of _m (InP) _n is prepared and n-type InP 24 is grown on the electron channel.
It is a T-structure element. In the figure, 25 is an n ⁺ type source / drain contact region, 26 is a gate electrode, 27 is a source electrode, and 28 is a drain electrode. n-type InP layer 2
4 acts as an electron supply layer. A band diagram is shown in FIG. The electrons supplied to the channel portion are In rather than InP.
Since it flows locally in the As part, (InAs) _m (In
Although it is a P) _n channel, it is substantially close to the InAs channel and exhibits a large electron mobility. Further, since the periodic structure of (InAs) _m (InP) _n is controlled at the atomic level by atomic layer epitaxy, the scattering of electrons is extremely small. Such as dislocations since the lattice mismatch between the substrate crystal is generated, it is conceivable to degrade the crystallinity of the channel section, the average composition (InAs) _m (InP) _m of _n-channel unit, select appropriately the _n By changing it, generation of dislocation can be suppressed.

Particularly, according to the present invention, (InAs)
A superlattice structure such as _m (InP) _n can be prepared with a periodic structure of 20 molecular layers or less, particularly 10 molecular layers or less, and further 2 to 5 molecular layers. Next, an example applied to a heterojunction bipolar transistor (HBT) will be described. The structure of HBT is shown in FIG. 19 and its band diagram is shown in FIG. Emitter 31
(N-InP; up to 5 × 10 ¹⁷ cm ^-3 ) and collector 32 (n
-InP; 10 ¹⁹ to 10 ²⁰ cm ^-3 or more) is n-type InP
Was used. The base 33 is InAs, 10 ¹⁹ to 10
It is doped to about ²⁰ p-type. And in the figure, 3
4 is a semi-insulating InP substrate, 35 is p-type In _0.53 Ga _0.47
As layer (10 ¹⁹ cm ^-3 or more), 36 is n-type In _0.53 Ga
_{It is a 0.47} As layer (10 ¹⁹ cm ⁻³ or more). Since the operating speed of the HBT is determined by the time it takes for the electrons to pass through the base portion and reach the neutral region of the collector, the speed is extremely high in the InAs-based HBT shown here. At present, an HBT structure using In _0.53 Ga _0.47 As having a composition that is lattice-matched to InP is being researched, but in this structure, the operating speed is remarkably improved.

By using such an InAs / InP heterojunction, a device utilizing high electron mobility of InAs, which has not been realized so far, can be manufactured. However, the atomic layer of the present invention is used for manufacturing such a structure. Crystal growth by epitaxy is extremely effective.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a crystal growth apparatus used for atomic layer growth.

FIG. 2 is a graph showing growth temperature dependence of growth rate in atomic layer growth of InAs and InP.

FIG. 3 is a graph showing the dependence of the growth rate on the TMIn supply time width in the atomic layer growth using TMIn as an In raw material.

FIG. 4 (InAs) ₃ (I prepared on InAs substrate)
3 is a graph showing an X-ray diffraction peak of a nP) ₂ superlattice structure.

FIG. 5: (InAs) ₃ (I formed on InAs substrate)
3 is a graph showing an X-ray diffraction peak of a nP) ₁ superlattice structure.

FIG. 6 shows (InAs) ₂ (I formed on an InAs substrate).
3 is a graph showing an X-ray diffraction peak of a nP) ₁ superlattice structure.

FIG. 7 is a conceptual diagram showing a crystal growth mechanism.

FIG. 8 is a conceptual diagram showing the principle of crystal growth control by hydrogen purge.

FIG. 9 is a sequence diagram of ALE growth of InAs.

FIG. 10: H ₂ of InAs growth rate at 400 ° C. growth
It is a graph which shows purge time dependence.

FIG. 11: H ₂ of InAs growth rate at 365 ° C. growth
It is a graph which shows purge time dependence.

FIG. 12 is a diagram in which t ₁ of FIGS. 10 and 11 is used as a parameter.
It is a figure which shows the relationship between ALE growth rate and TMIn supply time.

FIG. 13 is a diagram showing a relationship between t ₁ and an electron concentration (Se concentration).

FIG. 14 is a diagram showing the growth temperature dependence of the H ₂ purge limit time for preventing the separation of As.

FIG. 15 is a diagram for explaining the disorder of the grown crystal when the H ₂ purge time is long.

FIG. 16 is a diagram showing the relationship between the structure of a ternary crystal and alloy scattering.

FIG. 17 is a cross-sectional view of HEMT.

FIG. 18 is a band gap diagram of the HEMT of FIG.

FIG. 19 is a cross-sectional view of a heterojunction bipolar transistor.

20 is a bandgap diagram of the bipolar transistor of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reaction tube 2 ... RF coil 3 ... Exhaust device 4 ... Pressure regulating valve 5 ... Manifold 8 ... Susceptor 9 ... Base crystal 11 ... Support rod 12 ... Gate valve 13 ... Sample preparation chamber 14 ... Bellows 21 ... Semi-insulating InP substrate 23 ... Non-doped (InAs) _m (InP) _n 24 ... n-InP 26 ... Gate electrode 27 ... Source electrode 28 ... Drain electrode

Front Page Continuation (72) Inventor Kunihiko Kodama 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (11)

[Claims] 1. A step of heating a base crystal to a predetermined temperature, and supplying a group III source gas obtained by diluting an organic compound of In with hydrogen at the predetermined temperature to the base crystal without decomposition at a predetermined pressure. One
Group III supply step, step of exhausting the group III source gas, first group V source gas containing a group V element in a first composition at a predetermined pressure on the base crystal A supply step, a step of exhausting the first group V source gas, and a second step of supplying a group III source gas obtained by diluting an In organic compound with hydrogen at a predetermined pressure onto the underlying crystal in an undecomposed state.
Group III supply step, step of evacuating the group III source gas, second group V source gas containing a group V element in a second composition and having a different composition from the first group V source gas at a predetermined pressure 2. A crystal growth method for a compound semiconductor, comprising the step of: supplying a second group V gas onto the underlayer crystal; and the step of exhausting the second group V source gas. 2. The crystal growth method for a compound semiconductor according to claim 1, wherein the predetermined temperature is a temperature within a range of 300 ° C. to 450 ° C. 3. The hydrogen supply step of supplying hydrogen gas onto the base crystal at a predetermined pressure in the step of exhausting the group III source gas and the first and second group V source gases. Method for growing crystal of compound semiconductor of. 4. The first and second Group III supply steps,
The predetermined pressure in the first and second group V supply steps is 5 torr
A constant pressure within the range of ~ 1000 torr.
The method for growing a crystal of a compound semiconductor according to any one of 1. 5. The organic compound of In is trimethylindium, and the group V source gas is hydride of As and P.
5. The crystal growth method for a compound semiconductor according to claim 1, wherein the compound semiconductor is a hydride. 6. The first group III supply step and the first group V supply step are repeated a predetermined number of times, and the second group III supply step and the second group V supply step are repeated a predetermined number of times. , InAs / InP, InAsP / InP or InAs / InAsP heterojunction is formed, The crystal growth method of the compound semiconductor in any one of Claims 1-5. 7. The first group V source material supplying step and the second step
The hydrogen supply time of the hydrogen supply step between the group III raw material supply step and between the second group V raw material supply step and the first group III raw material supply step of the first and second group V raw materials. 7. The crystal growth method for a compound semiconductor according to claim 3, wherein the group V atoms attached in the supplying step are limited to a degree that prevents desorption. 8. The first or second group V raw material is AsH ₃
And the hydrogen gas supply time t after the supply step is expressed by the formula (1) log t ≦ − (7.09 / 475) T + 7.33 (1) [wherein T is the substrate temperature (° C.) and t is Hydrogen supply time (sec)
The method for growing a crystal of a compound semiconductor according to claim 7, wherein 9. The crystal growth method for a compound semiconductor according to claim 8, wherein the hydrogen gas supply time t satisfies the formula (2) log t ≦ − (6.72 / 350) T + 7.44 (2). 10. A step of heating a base crystal to a predetermined temperature, a step of supplying a group III source gas diluted with hydrogen at a predetermined temperature at a predetermined pressure to the base crystal without being decomposed, and a hydrogen gas A purging step of supplying the group III source gas onto the base crystal and exhausting the group III source gas; a step of supplying a group V source gas onto the base crystal at a predetermined pressure; and a step of supplying hydrogen gas onto the base crystal. And a purge step of exhausting a group V source gas, wherein the crystal growth rate is controlled by controlling the purge amount. 11. A step of heating a base crystal to a predetermined temperature, a step of supplying a Group III source gas diluted with hydrogen at a predetermined temperature at a predetermined pressure to the base crystal without being decomposed, and a hydrogen gas A purging step of supplying the group III source gas onto the base crystal and exhausting the group III source gas; a step of supplying a group V source gas onto the base crystal at a predetermined pressure; and a step of supplying hydrogen gas onto the base crystal. The present invention is characterized by comprising a purge step of exhausting a group V source gas and a step of supplying a doping gas, wherein the doping amount is controlled by controlling the purge amount in the purging step before supplying the doping gas. Crystal growth method of compound semiconductor.