JPH07130667A - Metal organic vapor phase epitaxial growth method - Google Patents

Abstract

PURPOSE:To ensure safe n-type impurity and ensure accurate concentration control by adding a specific organic metal compound as an n-type impurity in order to epitaxially grow an n-type III-V compound semiconductor thin film on a substrate. CONSTITUTION:A bubbler 1 is provided in the course of a piping, and a mass flow controller 2 is provided on the piping. Stock gas is introduced from the upper portion of a reaction pipe 3. The substrate 5 is placed on a susceptor disposed in the reaction pipe 3, and the susceptor is rendered to rf heating by an rf coil 6 disposed outside the reaction pipe 3. In epitaxial growth of a thin film of a III-V compound semiconductor, an organic metal compound of a group IV element or a group VI element is employed as a source flow for doping of an n-type impurity. More specifically, there are employed retramethylsilane, tetraethylsilane, tetranormalpropylsilane, tetranormalbutylsilane, dimethyl tellurium, diethyl tellurium, and dinormalpropyl tellurium, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxial growth method for III-V group compound semiconductors, and more particularly to a metalorganic vapor phase epitaxial growth method.

[0002]

2. Description of the Related Art Thin films of III-V compound semiconductors can be produced by various methods. A method of vapor phase growth using an organic metal as a raw material is called a metal organic chemical vapor deposition method (MOCVD method).
Since it is vapor phase growth, all raw materials must be supplied in a gaseous state. An organic metal such as trimethylgallium (TMG) or trimethylindium (TMI) is used as the Group III material. This is called metal-organic vapor phase epitaxy because metal-organic is used as the Group III material. As the group V raw material, for example, group V hydrides such as arsine (AsH ₃ ) and phosphine (PH ₃ ) were used. Since these are gases at room temperature, they can be directly supplied to the vapor phase growth apparatus.

However, Group V hydrides are highly toxic. Both are extremely poisonous. Care must be taken when opening the vapor phase growth apparatus so that it does not leak outside. Special consideration is also required in the gas supply system and exhaust system.
There is also the problem of exhaust gas treatment. Therefore, much research is being conducted on conversion to safer group V raw materials.

The chloride method, which has an older history than the MOCVD method, uses Ga metal and As chloride as raw materials.
As is safer when it is made into chloride because it is much less toxic than hydride. However, it is difficult to control the amount of Ga because Ga metal is used as a raw material and this is reacted with As chloride to form a gas.

Improvements within the scope of organometallic growth methods are attempted. Although As and P are made into gas, there are few substances such as gas or liquid at room temperature among these compounds. However, if As and P are organometallic compounds, there are some that are liquid or gas at room temperature. Therefore, regarding Group V raw materials,
The idea is to supply it as an organic metal. For example, data - rice butyl arsine (t-BuAsH ₂₎
Has been proposed as a raw material for As.

There are other As organic metals, but at present, this is the most advanced refining technology, and the content of impurities is small. In the semiconductor material, if impurities are not mixed even slightly, the characteristics are greatly influenced. Raw materials with few impurities are essential. Only after advances in refining technology can it be used as a raw material for semiconductors. Ga
The formation of a GaAs thin film containing, as a main component, an organic metal of

RMLum, JKKlingert & FAStevie, "C
ontrolled Doping of GaAs films grown with tertiary
butylarsine "J.Appl.Phys.vol.67, No.10, p6507 (1990)

[0008] has been proposed. The problem with group V raw materials will eventually find some solution. The present invention does not concern major Group III or Group V feedstocks.

In order to grow a thin film of a III-V group compound semiconductor, it is necessary to add an element of another group as a dopant, in addition to the group III and V groups as main raw materials. To make a p-type semiconductor, a p-type dopant is added. In addition, an n-type dopant must be added to make an n-type semiconductor.

Here, the dopant and the impurity are used synonymously. As p-type impurities, Zn, Cd, H
A group IIB atom such as g must be a dopant.
There is no problem if the single atom can be doped. However, if it is not a gas by itself, it must be compounded into a liquid or gas. Even if it is a compound, the other element itself should not enter the lattice structure and become a dopant or make a trap. In this respect, the compound with hydrogen is most suitable.

Taking Zn as an example, there is no Zn hydride. There are many halides, but they are solid at room temperature.
Compounds with group VI such as O, S and Se are solid and cannot be used because group VI becomes an n-type dopant. Therefore, in the case of Zn, it is made into p-type dopant such as diethyl zinc.

That is, for the p-type, organometallic compounds are still used. The same applies to the case of the Ga and As organic metals as the main raw materials, but the organic metals include carbon and hydrogen. If these are incorporated into a thin film, a high-purity thin film cannot be obtained. The desired electrical and electro-optical characteristics cannot be obtained. Carbon acts as a p-type impurity in the III-V group compound semiconductor. Therefore, when an organometallic raw material is used, it is necessary that the bond between the metal and the carbon be broken and the remaining carbon and hydrogen structures take up hydrogen and be discharged as hydrocarbons.

As the n-type impurity, it is necessary to use Si or a group VI atom. In the case of Si, a hydride can be formed. Therefore, as a dopant, S
Gases such as monosilane (SiH ₄ ) and disilane (Si ₂ H ₆ ) which are hydroxide gas of i are used. In the case of group VI, it is Te, Se, S, etc. All of these have hydrides H ₂ Te, H ₂ Se, and H ₂ S. These are gases at room temperature. Therefore, for Group VI, hydrides are used as n-type dopants.

[0014]

When performing III-V group compound semiconductor epitaxial growth, research is being conducted in search of safer raw materials. However, the attempts are limited to Group III and Group V, which are the main raw materials. Dopants are not seen as a problem due to the small amount.

The inventor considers that there is a problem with hydrides of silicon used as n-type impurities. I see, Si
Are much less toxic than group V hydrides (arsine, phosphine). However, low toxicity does not mean high safety.

Si hydride gas is low in toxicity, but may easily ignite and explode when mixed with air. If leaked from piping system or chamber, it mixes with air and explodes. It is a dangerous gas, and many accidents have occurred in the past, resulting in many casualties. It is extremely problematic in terms of safety. When the bonding force between Si and H is weak and mixed with air, H is separated from Si and Si is oxidized to change to SiO ₂ . H becomes H ₂ O. This reaction occurs so rapidly that it explodes.

As for the Group VI dopant, Te, Se, and S were used because Te, Se, and S are hydride gas. However, all of these are extremely toxic gases. If possible, this is a substance you do not want to use.

It is an object of the present invention to provide a metal-organic vapor phase epitaxy method which allows impurities to be added by a safe raw material without using a dangerous hydride for adding impurities. Further, it is a second object of the present invention to provide a method that realizes the addition of impurities more efficiently than the conventionally used gas and that enables the concentration of n-type impurities to be accurately controlled.

[0019]

According to the present invention, an organic metal compound of a group IV element or a group VI element is used as a raw material for the addition of n-type impurities in the epitaxial growth of a thin film of a group III-V compound semiconductor. Do not use Si hydride gas, which has a high risk of explosion, or group VI hydride, which is highly toxic. A safer organometallic compound is used.

The group VI element becomes an n-type impurity in the group III-V compound semiconductor. Group IV Si is n for vapor phase growth
It becomes a type impurity. The following are organometallic raw materials that can be used as n-type impurities of III-V group compound semiconductors. Group VI has sulfur and selenium in addition to tellurium. Although these organometallic compounds can also be used as n-type impurities, only the organometallic tellurium is illustrated here.

Si organic metal: tetramethylsilane ((CH ₃ ) ₄ Si), tetraethylsilane ((C ₂ H
₅ ) ₄ Si), tetra-normal propyl silane ((n-
_{C 3 H 7) 4 Si)} , tetra-n-butyl silane _{((n-C 4 H 9} ) 4 Si) , etc.

Tellurium organometallic dimethyl tellurium ((C
H ₃ ) ₂ Te), diethyl tellurium ((C ₂ H ₅ ) ₄ T
e), di-n-propyl tellurium _{((n-C 3 H 7} ) 2
Te) etc.

Even with an organic metal, it is necessary to decompose it with a bond between metal and carbon. If it is cut off here, the remaining organic substance portion takes in hydrogen and becomes hydrocarbons, and is removed from the device as exhaust gas. If the carbon decomposes,
When it enters the semiconductor thin film, it becomes a p-type impurity, and predetermined characteristics cannot be obtained. In this respect, organic metals having too few carbon atoms are not suitable. An organic metal having a large number of carbon atoms and in which metal atoms are easily separated is used.

[0024]

FUNCTION Group VI elements (Te, Se, S) behave unconditionally as n-type impurities in III-V group compound semiconductors.
When the Si, which is a group IV element, enters the III-V group compound semiconductor, it becomes an n-type or p-type impurity depending on the conditions. However, in vapor phase growth, Si always acts as an n-type impurity in the III-V compound semiconductor.

Conventionally, Si has been used in III-V compound semiconductors.
When impurities were doped as impurities, they were always doped as hydrides, so the risk was high. However, in the present invention, Si is doped as the organometallic compound. The organometallic compound of Si does not have a bond between H and Si, which has a weak chemical bond, in the molecule. When heated, the bond between Si and C is broken, and the methyl group, ethyl group, and the like incorporate H and become an organic compound. Therefore, it is more stable than hydride.
No contact with air causes explosive reaction at room temperature. High safety.

It is also advantageous in terms of decomposition temperature. When the organic metal compound of Si is heated to 400 ° C. or higher, the bond between silicon and hydrocarbon is easily broken. This silicon atom is
It enters the III group site of III-V compound semiconductors. III
Since one electron becomes redundant when it enters the group site, it contributes an electron as an n-type impurity. In an atmosphere without oxygen, the organometallic compound of Si has a lower decomposition temperature than Si hydride. Therefore, it decomposes efficiently at low temperatures.

The use of Si organic metal as the n-type impurity increases the doping efficiency. That is, the organometallic compound of Si is superior to the hydride as an n-type impurity in both safety and doping efficiency. Such features are
The same applies to other organometallics of group IV elements (Ge, Sn, Pb).

Like the case of Si, the organometallic compound of tellurium Te does not have Te—H bond having a weak chemical bond in the molecule. Therefore, it is more stable than hydride.
There is no fear of causing an explosive reaction when exposed to air. High safety.

Another advantage is also the doping efficiency. The organometallic compound of Te also has a lower decomposition temperature than hydride. If the organometallic compound of Te is also heated to 400 ° C. or higher, the bond between Te and the hydrocarbon is broken. Disassembled T
The e atom penetrates into the V group site of the III-V group compound semiconductor. Since it is a VI group, it contributes one electron and becomes an n-type impurity.

Since it decomposes well at a lower temperature than hydrides, the use of Te organometallic compounds as impurities causes
Ping efficiency is high. The organometallic compound of Te is superior to hydrides in terms of safety and doping efficiency. Such advantages are the same for other group VI elements (Se, S) and the like.

The above-mentioned characteristics are general characteristics that can be established regardless of the kind of organometallic compound used as the starting material for the III-V compound semiconductor. Next, the special property depending on the raw material of the III-V compound semiconductor will be described. Tertiary butyl arsine (t-BuAsH)
₂ ) is used. This is an organometal in which one butyl group, two hydrogens and a trivalent As are bonded.

This is because the hydrocarbon group has a large molecular weight and is difficult to decompose. Therefore, there is no inconvenience that carbon pollution occurs in the III-V group compound semiconductor and it becomes a p-type semiconductor. Since carbon is easy to liberate in an organic metal having a small molecular weight,
This may become a p-type impurity. In this respect, tert-butyl arsine is excellent as a V group raw material. It is a promising future V group raw material.

When tertiary III-V compound semiconductor is grown using t-butylbutylarsine as a group V source and Si organic metal as an n-type impurity, an intermediate substance between Si organic metal and As organic metal is formed. It For this reason,
Ping efficiency is high. The formation of intermediates with Si organometallics is a characteristic property of tert-butylarsine with As organometallics.

When P is used as a V group like InP in a III-V group compound semiconductor, it has the same characteristics as those using tert-butylphosphine (t-BuPH ₂ ) as a raw material. That is, an intermediate substance of Si organic metal and R organic metal is formed, and the doping efficiency is improved.

[0035]

EXAMPLE Using the vapor phase growth apparatus shown in FIG.
A Si-doped GaAs thin film was grown on the substrate. Since there are three types of raw materials, three raw material supply systems are shown here. Although there is a cylinder of hydrogen gas as a carrier gas at the tip of the pipe, it is not shown for simplicity. Since the organic metal is a raw material and is a liquid in most cases at room temperature, the bubbler 1 is provided in the middle of the pipe. Further, in order to control the flow rate accurately, a pipe is provided with a mass flow controller 2. The reaction tube 3 is a container that can be evacuated. The raw material gas can be introduced from the upper part.

Gas is exhausted from the lower part of the reaction tube 3 by the reaction tube exhaust pump 7. Inside the reaction tube 3, there is a susceptor 4, on which a substrate 5 is placed. A high frequency coil 6 is provided outside the reaction tube 3 and heats the susceptor by high frequency. In this case, the reaction tube must be made of an insulator such as quartz. Instead of high frequency heating, a resistance heating heater may be built in the susceptor to heat the susceptor from the inside. Lamp heating is also available. Such MOCVD equipment is well known. The conditions and raw materials for thin film growth are as follows.

Group III Raw Material Triethylgallium (TEG: (C ₂
H _{5) 3} Ga) V group material data - rice butyl arsine (t-Bu
AsH ₂ ) n-type impurity Tetraethylsilane (TeESi:
(C ₂ H ₅ ) ₄ Si) Substrate GaAs single crystal substrate Substrate temperature 600 ° C. Pressure 76 Torr (10 ⁴ Pa) Raw material molar ratio TEG: t-BuAsH ₂ =
1: 5 Impurity to raw material molar ratio TeESi: TEG = 0.00
1 to 0.01: 1

TEG is used as the group III raw material and t is used as the group V raw material.
The -BuAsH _2, as the Si impurity is used TeESi. Hydrogen gas was used as the carrier gas. The flow rates of these raw material gas and carrier gas were controlled by a mass flow controller. The substrate temperature was kept at 600 ° C., and the pressure in the reaction tube was 76 Torr. In the examples, the amount of the group V is 5 times as much as that of the group III.

The parameter is the amount of impurities. The ratio of the compound of tetraethylsilane (TeESi) of Si to triethylgallium (TEG) of the group III material (TeESi /
TEG) in the range of 0.01 to 0.001,
A GaAs thin film was epitaxially grown under each condition. Then, the carrier concentration of the thin film was measured. This is to confirm whether TeESi is an n-type impurity in the III-V group compound semiconductor. The result is shown in FIG. The horizontal axis is tetraethylsilane (TeES)
i) and triethylgallium (TEG) molar ratio [TeE
Si] / [TEG].

The impurity / raw material molar ratio is 1.5 × 10 ⁻³
At that time, the carrier concentration was 1.2 × 10 ¹⁷ cm ⁻³ . When the molar ratio is 3 × 10 ^-3 , the carrier concentration is 2.
It was 5 × 10 ¹⁷ cm ⁻³ . When the molar ratio was 7.5 × 10 ^-3 , the carrier concentration was 6.4 × 10 ¹⁷ cm ^-3 .
When the molar ratio is 1.5 × 10 ^-2 , the carrier concentration is 1.
It was 3 × 10 ¹⁸ cm ⁻³ .

These data points are arranged on a straight line forming an angle of about 45 degrees with respect to the axis on the logarithmic graph. That is, the addition amount of the Si organometallic compound is almost proportional to the n-type carrier (electron) concentration. That is, the added S
This means that almost all i are active as n-type impurities. This means that the doping efficiency is high. Furthermore, this range (10 ¹⁷ cm -3 to 10 ¹⁸ cm
^-3 ) shows that the carrier concentration is not saturated.
It is possible to easily and accurately calculate how much Si organic metal should be added to obtain a desired impurity concentration.

When DETe (diethyl tellurium) is used as the n-type dopant, the carrier concentration of 4 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ^-3 is obtained by adding it under the same conditions as TeESi. By using diisobutyl tellurium or the like having a low vapor pressure, it is possible to control the carrier concentration in a wider range. Se and S which are the same group VI organometallic compounds
Even when the organic compound of 1 is used, controllability in almost the same range can be obtained by paying attention to the supply molar ratio of the group VI atoms.

[0043]

INDUSTRIAL APPLICABILITY The present invention does not use a highly dangerous Si hydride gas or a highly toxic Group VI hydride gas when manufacturing an n-type III-V compound semiconductor thin film. Instead, an Si- or VI-group organometallic compound is added as an n-type dopant.
Used as a punt. Organometallic gas is safer as it has less danger of explosion and toxicity.

As described above, since the organic metal is used not only for the main raw material but also for the impurity addition, safer thin film vapor phase growth can be performed. In addition, when the organic metal is used as the dopant, the doping efficiency is higher than that in the case of the hydride.

[Brief description of drawings]

FIG. 1 is a plan view of n-type on a GaAs substrate using MOCVD method.
Schematic view of an apparatus for forming a p-type GaAs thin film.

FIG. 2 is a graph showing the relationship between the ratio of TeESi added to TEG and the carrier concentration of the thin film in the GaAs thin film produced by the present invention.

[Explanation of symbols]

 1 Bubbler 2 Mass Flow Controller 3 Reaction Tube 4 Susceptor 5 Substrate 6 High Frequency Coil 7 Reaction Tube Exhaust Pump

Claims (5)

[Claims] 1. An organometallic II for epitaxially growing an n-type III-V compound semiconductor thin film on a substrate.
Using a Group I source material and an organometallic Group V source material, tetramethylsilane ((CH ₃ ) ₄ Si), tetraethylsilane ((C
₂ H ₅ ) ₄ Si), tetra-normal propyl silane ((n-C ₃ H ₇ ) ₄ Si), or tetra-n-butyl silane ((n-C ₄ H ₉ ) ₄ Si) is added. Metal-organic vapor phase epitaxial growth method. 2. An organometallic II for epitaxially growing an n-type III-V compound semiconductor thin film on a substrate.
Using Group I raw materials and organometallic Group V raw materials, as an n-type impurity, Te organometallic compounds such as dimethyl tellurium ((CH ₃ ) ₂ Te) and diethyl tellurium ((C ₂ H ₅ ).
₂ Te), di-normal propyl tellurium ((n-C ₃ H
₇ ) ₂ Te), diisopropyl tellurium ((i-C ₃ H
₇ ) ₂ Te), di-normal butyl tellurium ((n-C ₄ H
₉ ) ₂ Te), Zita-Shaributyl tellurium ((t-C ₄
A metal-organic vapor phase epitaxial growth method characterized by adding H ₉ ) ₂ Te). 3. An organometallic II for epitaxially growing an n-type III-V compound semiconductor thin film on a substrate.
Organometallic compounds of Se, such as dimethyl selenium ((CH ₃ ) ₂ Se) and diethyl selenium ((C ₂ H ₅ ), are used as n-type impurities by using a group I source material and an organometallic group V source material.
₂ Se), di-n-propyl selenium ((n-C ₃ H
₇ ) ₂ Se), diisopropyl selenium ((i-C ₃ H
₇ ) ₂ Se), di-normal butyl selenium ((n-C ₄ H
₉ ) A metal-organic vapor phase epitaxial growth method, characterized in that ₂ Se) is added. 4. An organometallic II for epitaxially growing an n-type III-V compound semiconductor thin film on a substrate.
Using Group I raw materials and organometallic Group V raw materials, n-type impurities such as dimethyl sulfur ((CH ₃ ) ₂ S) and diethyl sulfur ((C ₂ H ₅ ) ₂ which are organometallic compounds of S.
S), di-n-propyl sulfur _{((n-C 3 H 7} ) 2
S), diisopropyl sulfur _{((i-C 3 H 7} ) 2
S), di-n-butyl sulfur _{((n-C 4 H 9} ) 2
S), Sita - rice butyl sulfur _{((t-C 4 H 9} ) 2
A metal-organic vapor phase epitaxial growth method, characterized in that S) is added. 5. The organic metal raw material of Group V is tert-butyl arsine (t-BuAsH ₂ ) or tert-butyl phosphine (t-BuPH ₂ ), which is one of claims 1 to 4. The metal-organic vapor phase epitaxial growth method as described in 1.