JPH05186295A - Method for growing crystal - Google Patents

Abstract

PURPOSE:To accurately form one atomic layer by depositing >=one atomic layer of a constituent element layer of a compound to be grown on the surface of a substrate, supplying a specific substance to the surface and removing the constituent element unbonded to the substrate. CONSTITUTION:A case of growing crystal of GaAs is explained. An atomic layer 2 of As is grown on a GaAs base 1, a raw material 3 of Ga is fed to the base and >=one atomic layer of Ga atoms 4 is deposited on the As atomic layer 2. Then methyl group 5 to form a substance which is bonded to Ga and has weaker bond force than one between Ga and As is supplied to a growth face, brought into contact and reacted with the Ga atom 4a having deposited >=one atomic layer and evaporated as methylated gallium. In the operation, since the Ga atom 4b of one atomic layer directly bonded to the atomic layer 2 of As has strong bond force to As, this Ga atom will not release from the surface even if the methyl group comes into contact with this Ga atom of one atomic layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to crystal growth, and more particularly to a crystal growth method capable of controlling atomic layer growth.

[0002]

2. Description of the Related Art As a crystal growth method capable of growing each atomic layer, atomic layer epitaxy using a material having a self-stopping mechanism for growth rate (self-limiting) is known. ..

For example, in the atomic layer epitaxy of GaAs, the key is to deposit only one atomic layer of Ga having an extremely low vapor pressure. As a Ga raw material, trimethylgallium (TMGa), GaCl, Ga (C ₂ H ₅ ) ₂ C
It is known that by using 1, 1, GaCl _3, etc., one atomic layer of Ga atomic layer can be deposited on the As plane, and the growth can be automatically stopped when the growth of just one atomic layer is completed.

In the case of GaAs, As ₄ is used to grow the As layer.
Although AsH _{3 and the} like are used, since the vapor pressure of As is high, self-limiting is usually established regardless of the raw material. Thus, in the III-V group compound semiconductor, III
Atomic layer epitaxy becomes possible by using a raw material having self-limiting as the raw material of the group element.

However, the raw materials having self-limiting are limited. For example, trimethylgallium has self-limiting but triethylgallium does not have self-limiting.

When the source gas used for atomic layer epitaxy is determined, the crystal growth temperature is determined. If a gas having self-limiting is used as the source gas, the temperature range that can be selected becomes narrow.

Further, for example, when a mixed crystal is to be grown, if the raw material gases having self-limiting of the two elements that constitute the mixed crystal have different decomposition temperatures,
In fact, atomic layer growth becomes extremely difficult.

The time required for the deposition of one atomic layer is determined by the decomposition rate of the source gas. If you select a source gas from only source gas with self-limiting,
The selection range is narrow, and it is difficult to shorten the time required to grow one atomic layer.

Further, if the range of selection of the source gas is narrowed, it may be difficult to avoid mixing of elements such as impurity atoms in the crystal to be grown. For example, when an ethyl compound, a methyl compound, or the like is used, it is difficult to avoid inclusion of C, but C functions as an electric impurity in a III-V semiconductor.

[0010]

As described above,
Prior art atomic layer epitaxy presents various limitations.

It is an object of the present invention to provide a crystal growth method capable of atomic layer growth and less restricted.

[0012]

According to the present invention, in the atomic layer epitaxy, when the growth of one atomic layer is completed, instead of stopping the growth at that time, the step of depositing the constituent elements and the self-limiting are performed. Separate the process that causes it.

For example, first, a step of depositing one atomic layer or more of a constituent element is carried out, and then a contact reaction step with a substance that binds to and removes the constituent element is carried out. The deposited atoms are removed, and as a result, the deposition of one atomic layer is realized.

[0014]

In the deposition process, since one atomic layer or more can be deposited, it is not necessary to require self-limiting for the raw material used. For this reason, the range of selection is expanded,
It becomes possible to select a more preferable growth temperature and growth rate.

Even if the deposition of one atomic layer or more is performed, the portion exceeding the one atomic layer is removed by combining with the methyl group or the halogen group, so that the remaining deposited layer is one atomic layer. Epitaxy can be realized.

[0016]

EXAMPLE As shown in FIG. 1 (A), after growing an atomic layer 2 of As on a GaAs substrate 1, a sufficient amount of a Ga source material 3 was supplied to the atomic layer 2 of As. Then, one or more atomic layers of Ga atoms 4 are deposited. At this stage, no atomic layer growth is apparently performed. However, a large amount of Ga atoms 4 may be deposited so that there is no portion of the As atomic layer that is not covered with Ga.

Next, as shown in FIG. 1 (B), a methyl group 5 is supplied to the growth surface to deposit one or more atomic layers of Ga on the surface.
The atoms are brought into contact with and reacted with the atoms 4a and evaporated as gallium methylate from the surface. At this time, the Ga atom 4b for one atomic layer, which is directly bonded to the atomic layer 2 of As, has a strong bonding force with As, and therefore does not separate from the surface even when the methyl group 5 contacts.

Therefore, if more than a certain amount of methyl groups are supplied to the growth surface, one or more atomic layers of extra Ga atoms 4a will be generated.
Reacts with the methyl group and is re-evaporated, leaving exactly one atomic layer of Ga atomic layer 4b on the crystal surface. This state is shown in FIG.

The Ga raw material used in the step of depositing Ga atoms 4 does not need to have self-limiting and can be selected from a wide range. For example, when it is desired to perform atomic layer epitaxy at a low temperature, a Ga raw material can be selected from raw materials having a sufficiently low decomposition temperature.

That is, as Ga raw material, metallic Ga,
A wide range of materials can be used, such as organometallic compounds such as triethylgallium, triisobutylgallium, trimethylaminegalane, and the like.

FIG. 2 shows a reduced pressure MOVPE growth system that can be used in the embodiment of the present invention. A graphite susceptor 12 is arranged in a quartz reaction tube 11, and a GaAs substrate 13 can be mounted thereon.

The graphite susceptor 12 is heated by the high frequency power supplied from the RF coil 14 to generate GaA.
The substrate 13 is heated to a predetermined temperature. The quartz reaction tube 11 is
It is connected to the auxiliary chamber 22 via the gate valve 21. Further, the quartz reaction tube 11 is connected to an exhaust pump via an exhaust port 24, and the inside of the quartz reaction tube 11 can be maintained in a predetermined reduced pressure atmosphere. The pressure is, for example, 15 to
It is about 20 Torr.

The growth raw material is supplied from the raw material supply port 15 to the raw material gas manifold valve 16 and is supplied to the GaAs substrate 13 on the susceptor 12. A case is shown in which triisobutylgallium having a low decomposition temperature is used as a source gas of Ga that is a group III element, arsine is used as a source gas of As that is a group V element, and H ₂ is used as a carrier gas.

Further, methane gas (CH ₄ ) for removing excess Ga is mixed with hydrogen (H ₂ ) to supply port 1.
It is supplied to the plasma generator 19 from 7 through the valve 18, converted into plasma, and then supplied into the quartz reaction tube 11. The plasma generator 19 generates plasma by applying an RF electric field to the gas inside. An ECR device utilizing cyclotron resonance may be used.

FIG. 3 shows a gas supply sequence for carrying out the crystal growth method shown in FIG. 1 using the crystal growth apparatus shown in FIG. As an example, the substrate crystal was a (100) plane of GaAs, and the growth temperature was 300 ° C. In addition, triisobutylgallium having a low decomposition temperature was used as a Ga raw material. As a raw material for As, arsine (AsH
₃ ) was used. The methyl group was generated by decomposing methane gas with plasma.

First, as shown in the upper part of FIG. 3, triisobutylgallium using H ₂ as a carrier gas is supplied for about 3 seconds to deposit a Ga layer of about 1.3 atomic layers on the GaAs surface. In this step, the substrate surface may be covered with Ga atoms, and the thickness is not critical. However, since only one atomic layer is finally used, the raw material is wasted and the process time becomes longer as more layers are deposited.

Next, as shown in the second step of the sequence of FIG. 3, the Ga layer is irradiated with a methyl group (methyl radical) generated by plasma. A mixed gas of CH ₄ and H ₂ is turned into plasma in the plasma generator 19 shown in FIG. 2 and supplied to the surface of the substrate to supply methyl radicals. The supply of this methyl radical is for removing the extra approximately 0.3 atomic layer of the Ga layer.

Ga atoms deposited on Ga are Ga atoms.
-Ga bonding force Ga- (CH ₃₎ weaker than _n, Ga is allowed to re-evaporate methyl gallium when coupled with the methyl group CH _3. The time of the methyl radical supply step may be a time sufficient to remove excess Ga.

After supplying the methyl radicals, as shown in the third stage of FIG. 3, hydrogen (H ₂ ) gas is flown to purge the inside of the quartz reaction tube 11. Next, as shown in the fourth row of FIG. 3, arsine (AsH ₃ ) is supplied for about 5 seconds to form an As atomic layer. That is, a Ga atomic layer is formed in the first two steps of one cycle, and an As atomic layer is formed in the last one step, so that one molecular layer of GaAs is grown. By repeating this step a required number of times, it is possible to perform atomic layer epitaxial growth with a required thickness.

FIG. 4 shows changes in the irradiation time of a methyl group (methyl radical) and the growth rate. The horizontal axis represents the CH ₃ irradiation time in seconds, and the vertical axis represents the growth rate in terms of a molecular layer. A growth rate of 1 means that one molecular layer grows in one cycle.

The quartz reaction tube 11 has a diameter of about 70 to 80 mm.
A graphite susceptor 12 having a diameter of about 60 mm was used. Triisobutylgallium (TIBGa) as a Ga raw material is bubbled at about 20 ° C.
And H ₂ gas was flowed at about 100 sccm.

As As raw material, AsH ₃ diluted to about 10% in hydrogen was used, and about 400 sccm was used.
Shed As the methyl group raw material, methane gas CH ₄ was diluted to about 2% in hydrogen and allowed to flow at about 50 sccm. In addition, the growth temperature was measured at 300 ° C.

As is apparent from FIG. 4, of the Ga of about 1.3 atomic layers formed on the substrate, the Ga layer of one atomic layer or more is gradually reduced by irradiation with CH ₃ . Under the conditions of the data shown in FIG. 4, when the methyl group was supplied for about 4 seconds or longer, the growth rate was 1 (Ga
The thickness is As1 molecule (2.83Å)).

That is, even if Ga of 1 atomic layer or more is deposited, the Ga of 1 atomic layer or more can be obtained by removing the excessive Ga of 1 atomic layer or more by subsequent irradiation with a methyl group.

Up to now, atomic layer epitaxy has been performed using trimethylgallium or the like having self-limiting, but in the case of trimethylgallium, the decomposition temperature is about 450.
C., and the growth temperature usually used is around 500.degree. Atomic layer epitaxy at temperatures below the decomposition temperature could not be realized.

According to the above-mentioned embodiment, triisobutylgallium without self-limiting can be used, and the decomposition temperature of triisobutylgallium is about 200 ° C., so that atomic layer epitaxy at a significantly low temperature can be realized. it can.

Although the case where the MOVPE growth system is used is shown in the drawing, even if the molecular beam epitaxial growth apparatus is provided with a methyl group supply means, atomic layer epitaxy using a material without self-limiting can be realized as in the above embodiments. it can.

In this case, the Ga raw material may be metallic Ga.
In the case of Ga metal, the growth temperature can be further lowered. Further, in the case of metal Ga, since there is no contamination from the organic metal raw material, the quality of the grown film can be improved.

In the embodiments described above, the methyl group was used as the substance for removing the excessively deposited group III element, but the methyl group can be used for this purpose.

It is possible to remove the layer of the constituent element of the compound semiconductor, which is deposited by using one or more atomic layers by using halogen radicals. An example in which Cl gas is used for GaAs atomic layer growth will be described with reference to FIG.

Triethylgallium (TEGa) was used as a Ga raw material, arsine (AsH ₃ ) was used as an As raw material, and H ₂ was used as a carrier gas and introduced into the reaction tube. TEGa does not have a self-limiting mechanism.

Therefore, when TEGa and arsine are simply supplied alternately for growth, when the supply pulse width of TEGa is long, the growth film thickness per cycle is GaA.
increase over a monolayer thickness of s.

In FIG. 5, following the supply of TEGa, H ₂ is purged, and then Cl radicals are supplied. Excess Ga is removed from the growth surface by this Cl radical.

After supplying Cl radicals, purging is performed again with H ₂ gas, and Arns AsH ₃ is supplied to grow a GaAs 1 molecular layer. Then, H ₂ gas purge is performed again to complete one cycle. In addition, H ₂
Part or all of the gas purging can be omitted.

FIG. 6 shows an example of means for generating chlorine (Cl) radicals. In FIG. 6A, HCl gas is used as a raw material and a high frequency is applied from the RF coil 32 in the reaction chamber 31 to generate RF plasma, and HCl is decomposed into H and Cl.

In FIG. 6B, a tungsten (W) filament 34 is placed in the reaction chamber 31 and heated to about 1000 ° C. by passing an electric current through the filament.
The raw material Cl ₂ is supplied here to generate Cl radicals by thermal decomposition.

In FIG. 6C, a transmissive window 36 having a high transmissivity for ultraviolet rays is provided in the reaction chamber 31, and ultraviolet light 37 such as an excimer laser is radiated to allow molecules such as Cl ₂ to enter. When introduced, Cl radicals are generated by photolysis.

With such a device, HCl gas or Cl
Cl radicals can be generated from a gas containing chlorine such as ₂ gases. FIG. 7 is a graph showing the result of Ga atom removal by Cl radicals when GaAs was grown according to the sequence shown in FIG. The relationship between the pulse width of Cl radical supply and the growth rate per cycle of the sequence was plotted. In the figure, the horizontal axis is Cl
The pulse width of radical supply is shown in seconds, and the vertical axis shows the GaAs growth rate by the number of grown molecular layers per cycle.

The growth experiment was carried out at a growth temperature of about 350.degree. Ga was TEGa, and a bubbler kept at 20 ° C. was bubbled with about 100 sccm of H ₂ and supplied for about 4 seconds. AsH ₃ was used as a raw material for As, diluted to approximately 10% with hydrogen gas, and was diluted to approximately 5% at a flow rate of 500 sccm.
It was supplied for 2 seconds. The hydrogen gas was purged for about 2 seconds. The pressure in the reaction tube was kept at about 20 Torr, and the total flow rate in the reactor was set at about 200 sccm.

At this time, about 1.4 molecular layers of GaAs were grown per cycle without using chlorine radicals. If a Cl radical irradiation step is performed after growing the Ga layer, the growth rate of GaAs decreases.

As shown in FIG. 7, as the pulse width of Cl radical supply was increased, the GaAs growth rate gradually decreased. When Cl radicals were supplied for more than about 4 seconds, GaA
The s growth rate was saturated in one molecular layer. In addition, about 100 sccm of Cl _{2 as} a raw material having a concentration of 5% was supplied, and FIG.
Radicals were generated by the radical generator shown in.

Although the III-V semiconductor GaAs has been described above as an example, it will be apparent to those skilled in the art that the present invention can be applied to atomic layer epitaxy of other compounds.

That is, in the crystal growth of a compound, one or more atomic layers of the constituent elements are grown, and
A portion exceeding the atomic layer can be removed by re-evaporation by reacting with another substance, leaving only one atomic layer and growing other constituent elements thereon to perform atomic layer epitaxy. ..

Particularly in the compound semiconductor, the constituent elements deposited to a thickness of one atomic layer or more can be removed by a methyl group or a halogen group. Although the present invention has been described with reference to the embodiments, the present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0055]

As described above, according to the present invention,
In atomic layer epitaxy growth, it is possible to use raw materials that do not necessarily have self-limiting properties.

Therefore, the raw material can be selected from a wide range. If an appropriate material is selected, the growth temperature can be lowered, the time required for monolayer growth can be shortened, and the quality of the grown film can be improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating atomic layer epitaxy according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a configuration example of a crystal growth apparatus for carrying out an embodiment of the present invention.

FIG. 3 is a timing chart showing a sequence of atomic layer epitaxy according to an embodiment of the present invention.

FIG. 4 is a graph showing changes in GaAs growth rate with respect to methane irradiation time.

FIG. 5 is a timing chart showing a sequence of a crystal growth method according to an example of the present invention.

FIG. 6 is a schematic view showing a means for generating chlorine radicals.

FIG. 7 is a graph showing changes in GaAs growth rate with respect to chlorine radical irradiation time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 GaAs substrate 2 As atomic layer 3 Ga raw material 4 Ga atom 5 Methyl group 11 Quartz reaction tube 12 Graphite susceptor 13 GaAs substrate 14 RF coil 15 Raw material gas supply system 16 Raw material gas manifold valve 17 Control gas supply system 18 valve 19 Plasma Generator 21 Gate valve 22 Preliminary chamber 24 Exhaust port 31 Reaction chamber 32 RF coil 34 Filament 36 Transmission window

Claims (5)

[Claims] 1. A step of growing at least one atomic layer or more of a layer (4) of a constituent element of a compound to be grown on the surface of an underlayer (1, 2); A step of removing the constituent element (4a) which is not bonded to the base in the layer of the constituent element by supplying a material (3) which forms a material having a smaller binding force between the constituent element and the base. A crystal growth method comprising: 2. The method according to claim 1, further comprising the step of removing the constituent element to obtain a monoatomic layer of the constituent element and then depositing one atomic layer of another constituent element on the monoatomic layer. Crystal growth method. 3. The substance binding to the constituent element is a methyl group or a halogen group.
The described crystal growth method. 4. The crystal growth method according to claim 3, further comprising the step of decomposing a compound containing no constituent element of the compound to generate the methyl group or the halogen group. 5. The crystal growth method according to claim 4, wherein the decomposition includes any of thermal decomposition, plasma decomposition, and photolysis.