JPH03266421A - Compound semiconductor growth and semiconductor device - Google Patents

Abstract

PURPOSE:To avoid the development of any crystal defects during the oxygen doping process as well as the mixture of doping oxygen gas with the growing compound semiconductor in the next stage by a method wherein an organic metal compound having direct coupling of Al atoms and O atoms is contained in a source gas in an organic metal vapor growing process. CONSTITUTION:An organic metal compound having direct coupling of Al atoms and oxygen atoms is used as a doping gas in a source gas 2 of aluminum. That is, the Al-O organic compound having initially coupled Al atoms and oxygen atoms can be efficiently absorbed into a crystal. Besides, the oxygen will not separate from Al due to the intensive coupling force with each other even if there is any residual oxygen in a reaction furnace 1 at all. Accordingly, even if high purity crystal is continuously grown, no oxygen will be mixed therewith while avoiding the production of any oxide of the other elements which develop defects.

Description

[Detailed Description of the Invention] [Summary] Regarding the high-resistance compound semiconductor growth method and semiconductor device, crystal defects are created during oxygen doping, and oxygen gas for doping remains in the furnace, causing damage to the next-stage grown compound semiconductor. In order to solve the problem that 1.1 M atoms and 0.0
Constructed to include organometallic compounds that include direct bonds with atoms.

[Industrial application field]

The present invention relates to a method for growing crystals of a high-resistance compound semiconductor and a semiconductor device having a high-resistance compound semiconductor layer grown in this manner.

In recent years, as the demand for solid-state electronic devices using compound semiconductors has increased, efforts have been made to achieve higher integration and higher performance. In the case of solid-state electronic devices, the electrical resistance of the parts where no current flows must be made as large as possible; otherwise, current will leak between the devices, leading to malfunctions or breakdowns due to poor insulation.

As the degree of integration increases, the spaces between elements become extremely narrow, making it easier for current to flow between them.

Therefore, if insulation between elements (element isolation) can be ensured, high performance and high integration can be achieved at the same time, and the emergence of such compound semiconductor devices is strongly desired. There is.

[Conventional technology]

Many studies have been conducted to date in an attempt to achieve the above objectives.

Broadly speaking, there are two methods, and devices are currently manufactured by combining these two methods.

One is to grow a high-resistance layer using a crystal growth method such as MBE or MOCVD, and the other is to implant oxygen, hydrogen atoms, etc. into the grown layer (ion implantation). However, the above implantation method is difficult because the selectivity of the layer to be made high resistance is poor (the boundary between the high resistance layer and the low resistance layer is sagging). Furthermore, since atoms are forcibly injected into the crystal, the atoms in the crystal may be disordered, which may have an adverse effect on the active layer (the layer that makes up the device).

The following four methods can be cited as methods for obtaining a high resistance layer using the crystal growth method.

(A) Growing a material with a large band gap.

(B) Doping the crystal with a transition metal.

(C) Growing crystals at low temperatures.

(D)　Aj! Dope the GaAs growth layer with oxygen.

A material with a large band gap has a low electron density (non-doped electron density) and therefore has high resistance.

Furthermore, when a compound semiconductor is doped with a transition metal, a deep level is formed and electrons are captured, resulting in high resistance.

When crystals are grown at low temperatures, the atoms that make up the crystals are no longer regularly arranged, resulting in many lattice defects within the crystals. These crystal defects become deep levels and increase the resistance of the crystal.

However, even if a material with a large band gap is grown as in A), the resistance value of the crystal decreases due to the influence of a small amount of donor impurity contained in the raw material. Further, even if a transition metal is doped as in (B), it is not possible to completely increase the resistance. This is because the amount of transition metal that can be incorporated into the crystal lattice is determined, and if more doping occurs, current will flow through the levels created by the extra doped transition metal atoms. In addition, in the method of growing crystals at low temperatures as in (C), it is necessary to optimally limit the growth conditions such as growth temperature, growth film thickness, and ■/■ ratio, and if the optimal conditions are deviated from, the resistance will increase. There are problems in that the growth layer, which is not desired, becomes highly resistive, and surface defects due to crystal defects increase.

Therefore, the above methods (A) to (C) have limited versatility and are considered impractical.

At present, as a typical method for obtaining a high-resistance compound semiconductor, an apparatus as shown in FIG. 4 is used. G
A method of doping aAs with oxygen has been put into practical use by the MOCVD method (doping with oxygen is difficult in the MBE method because crystal growth is performed in a high vacuum state).

A I GaAs has a larger band gap than GaAs and is more likely to have high resistance.

Oxygen doping also creates lattice defects within the crystal.

Normally, oxygen doping of a -V group gold compound semiconductor changes the electrical conductivity type of the semiconductor to N- type. This is because oxygen is a group 6 atom and acts as an N-type dopant regardless of whether it is placed in the lattice position of group 3 or group 5 in the -V metal compound. However, when a crystal containing Al atoms is doped with oxygen, AA and oxygen combine to form an oxide of Affi. Because it has a very strong bond (covalent bond; similar to ruby), it is easily incorporated into crystals. Therefore, when an oxide of Af coexists within the crystal, the periodicity of the crystal lattice is disturbed, and a large number of lattice defects are generated within the crystal.

The crystal defects become deep levels and make the crystal high in resistance.

[Problem to be solved by the invention]

AI! using the above MOVPE method! Oxygen doping into GaAs crystal is the most effective means for creating a high resistance layer.

However, this method also has problems.

(A) Since oxygen remains in the growth furnace, high quality crystals cannot be continuously grown.

(B) Oxygen added at the same time as the raw materials reacts with elements other than Al to form oxides, causing surface defects.

Oxygen introduced during crystal growth adheres to the chamber or susceptor in the growth furnace and slowly leaves them and is incorporated into the growth layer, allowing crystals with good electrical properties to grow on top of the high-resistance layer. It becomes difficult.

In addition, not all oxygen is selectively bonded to Al atoms. When it combines with Ga and As to form an oxide, it becomes a nucleus and defects are generated. The defect reaches the surface,
This results in surface defects. A j1 compared to GaAs! GaAs
exhibits more metallic properties, and therefore has a large elastic modulus, making it easier for the crystal to absorb strain. For this reason, it is difficult for defects to reach the surface. However, in a crystal with a small elastic modulus such as a grown layer of GaAs, the defects will reach the surface if the crystal cannot completely absorb the defects.

In addition, growth conditions for oxygen doping must be specially set (if the growth temperature is low, it is difficult to be doped; if it is high, it is easy to be doped).

Therefore, there is a strong need for a material that can dope GaAs with oxygen, that does not remain in the growth reactor, and that selectively reacts with Al, or for such a growth method.

[Means to solve the problem]

In order to solve the above problems, the present invention uses an organometallic compound having a direct bond between an aluminum atom and an oxygen atom as a doping gas in an aluminum source gas.

For example, metal organic vapor phase epitaxy (MO) of A 12 GaAs
VPli) usually contains an organic compound of Ga (TMC:)
Limethyl gallium, TEG:) ethyl gallium, etc.)
, organic compounds of Af (TMA:) rimethylaluminum, TEA:) ethylaluminum, etc.), and As
An organic compound (AsHi) is used.

Epitaxial growth is performed on the substrate by thermally decomposing these materials in a reactor, but in order to maintain the purity of the crystals, these raw materials have to be kept as low as possible in oxygen concentration. Oxygen is doped into the crystal by adding oxygen gas (a gas containing oxygen atoms) to the crystal at the same time as the substance.However, the feature of the present invention is that it does not use the conventional oxygen gas, but instead An aluminum organic compound containing oxygen in the form of a direct bond with aluminum is used.Such a substance can be obtained, for example, by adding a trace amount of oxygen to a highly purified aluminum organic compound.

Examples of organic compounds having a direct bond between aluminum and oxygen atoms include the following.

[In these formulas, each R is independently a methyl group, an ethyl group, a hydrogen atom, etc.]

The best compound semiconductor to dope with this /l-0 organometallic compound is one containing Al, such as jlGaA.
s, AfGaAsP, I/! As, ^fAs
P, InARP.

Any such as InA II AsP may be used. In this way, in the case of a compound semiconductor containing A1 as an element, when the compound semiconductor is grown by mixing a very small amount of the above-mentioned Al-○ organic compound into the Al organic compound as the aluminum source gas, the compound semiconductor becomes oxygen-doped. A grown layer similar to that of a crystal is obtained. , 1M-0, the doping amount of oxygen is generally 10"/d or more, resulting in high resistance (insulation). Normally, when doping is not done intentionally, the density of electrons and holes is ~ It is in the 10"/cd range. If this placing plate is doped with oxygen, electrons and holes will disappear, resulting in high resistance.

As mentioned above, the compound semiconductor growth method of the present invention is based on Af-
A conventional metal organic vapor phase epitaxy method can be used except that a trace amount of an organic metal compound is mixed into the source gas.

After growing a high-resistance compound semiconductor layer in this way, when growing a conductive compound semiconductor layer continuously, even if A/
! Even if the -0 organometallic compound remains in the furnace, oxygen is not released from it and mixed into the growth layer, so the resistance of the growth layer does not become high and no deterioration in electrical characteristics is observed.

Therefore, according to the present invention, a conductive compound semiconductor layer is similarly grown continuously on a high-resistance compound semiconductor layer containing aluminum and oxygen, and the conductive compound semiconductor layer substantially contains oxygen. Provided is a semiconductor device characterized in that:

Here, "substantially no oxygen" means that the amount of oxygen incorporated into the crystal is such that it does not affect the electrical characteristics of the device at all.

This semiconductor device is characterized in that a high-resistance layer and a conductive layer are continuously grown. After growing an oxygen-doped high-resistance layer by a conventional method without using the above method of the present invention, the conductive layer is grown in a separate furnace. When grown, it is possible to prevent oxygen from being mixed into this conductive layer. However, in this case, since it is necessary to take out the oxygen-doped high-resistance layer once from the reactor, defects occur on the surface and a level is formed. In the present invention, such defects and levels do not exist.

[For production]

A1-0 organic compounds such as methoxyaluminum
! Because the atoms and oxygen atoms are bonded from the beginning, they are efficiently incorporated into the crystal. Furthermore, since the bonding force between Affi and oxygen is strong, even if oxygen remains in the reactor, oxygen will not be released.

Therefore, even if high-purity crystals are continuously grown, oxygen will not be mixed into them and the resistance will not increase, so no deterioration of electrical properties will be observed. A! Since it is bonded to atoms, oxides with other elements such as Ga atoms and As atoms, which cause defects, are not generated.

〔Example〕

(2) A MOVPE apparatus as shown in FIG. 1 above was used. With this device A
I GaAs was grown. Aj! , Ga, As
trimethylaluminum (
Using TMA) 2, trimethyl gallium (TMG) 3 and alumin (Ashs) 4, hydrogen gas carrier 5
was supplied to reactor 1. TMA, TMG
The flow rate ratio of ASH3 was 0.3:0.7:10, that is, the V1m ratio was 10, and the reactor l was evacuated to 60 Torr, and the substrate temperature in the furnace was set to 680°C. thus,/
l j! o, zGao, and 7As were grown. This A f a, zGao,? The photoluminescence emission of A3 is shown in FIG. 2(b).

Next, during this time, A I GaAs was grown using the MOVPE apparatus under exactly the same conditions as above, except that TMA containing a trace amount of dimethylmethoxyaluminum was used instead of TMA. TMA containing dimethylmethoxyaluminum was obtained by blowing oxygen into high purity TMA. The concentration of dimethylmethoxyaluminum is preferably 500 PPM or more in order to increase the resistance of A 12 GaAs. More preferably, it is 4000 PPM or more.

On the other hand, 20. If you try to exceed OOOPPM, compounds other than dimethylmethoxyaluminum will be generated during oxygen injection, and the molecules of such products will gather and become large molecules (white turbidity), lowering the vapor pressure and making it difficult to stabilize the source gas. There is a risk that the supply to the reactor may become impossible. So, in this example, 1000PP? It was set as I. Further, a suitable growth temperature is 630 to 700°C. 7
When the temperature exceeds 00°C, oxygen separates and high resistance cannot be achieved. Further, if the temperature is lower than 630°C, the crystal quality deteriorates. In this example, the temperature was 680°C. In this way, Aj2o, 3Gao, and tAs doped with oxygen (high resistance) were grown by supplying Al-〇 from dimethylmethoxyaluminum. The generation of photoluminescence in this high resistance A I GaAs is shown in FIG. 2(a).

Figure 2(b) shows the photoluminescence emission in Figure 2(a).
), the emission from the band edge disappears and only emission from deep levels remains. This is because there are many deep levels in the crystal, and electrons are trapped in the deep levels. In other words, this difference in luminescence represents the electrical properties of the crystal, and crystals using methoxyaluminum are electrically This indicates that the number of electrons involved in conduction is small.

FIG. 2 shows a GaAs-FET structure prototyped as an example of the semiconductor device according to the present invention. In the figure, 11 is Ga
A4 board, 12 is an Al GaAs layer (thickness 1
000 Å or more), 13 is an N-type dopant (Si, Se.

GaAs layer doped with S, etc. (approximately 4000 1
．． Metal electrodes 14, 15, and 16 are a source electrode, a gate electrode, and a drain electrode, respectively. This structure is Ga
After a high resistance A I GaAs layer 12 was grown on an As substrate 11, an N-type GaAs layer 13 was successively grown in the same reactor.

In this depletion type FET, since the high resistance AI GaAs layer 12 does not exist in the conventional case, the GaAs
There is a problem in that leakage current flows between the source/drain electrodes 14 and 16 through disturbance of the crystal lattice formed at the interface between the substrate 11 and the N-type GaAs layer 13, and voltage changes. However, according to the present invention, the GaAs substrate 11 and the N-type G
By inserting the A I GaAs layer 12 with high resistance using methoxyaluminum between the aAs layers 13, there is no current path at the interface between the N-type GaAs layer 13 and the underlying substrate, so that the source/drain electrodes 4, It is possible to prevent leakage current flowing between the terminals 6 and 6 and voltage fluctuations.

As explained above, when the structure shown in FIG. 2 is fabricated using a conventional oxygen-doped A 12 GaAs layer as the high-resistance A I GaAs layer 12, the oxygen remaining in the reactor is absorbed into the N-type GaAs layer. N-type GaAs is also mixed in 13.
The crystal quality and electrical properties of layer 13 will deteriorate. Therefore, after growing an oxygen-doped A and GaAs layer using the conventional method, we changed the reactor and grew an N-type GaAs layer.
Although we tried to prevent oxygen from entering the aAs layer, once the substrate was removed from the reactor, crystal defects occurred at the interface between the Al GaAs layer and the N-type GaAs layer, and the source/drain electrodes 14 , 16, and the voltage fluctuated.

■-I When dimethylaluminum ether obtained by blowing water (H2O or a gas containing water vapor) into TMA (f-limethylaluminum) is grown, the same effect as when dimethylmethoxyaluminum is used can be obtained. It was done. Since the oxygen was sandwiched between aluminum sheets, the bonding force was very strong and the oxygen was incorporated into the crystal efficiently.

n-1no, 5xGao, atAs on through-hole InP substrate
When fabricating a FET with a channel of Ino, 53 (A
Grew f@, zGao, t)o, iJs. At this time/
Methoxyaluminum containing 4000 PPM of oxygen was used as the source of 1 ml. By doing this, Ino, 5sCAI
It has become clear that to, zGao, 7) o, atAs has a high resistance, eliminates leakage current, and ensures reliable insulation between elements. In this system, Ino, s+(Afo,
5Gao, 7) o, Ino with wide bandgap instead of 4Js layer, S3A ji! . , it is also possible to use an atAs layer, but in that case the surface morphology would deteriorate and this would be impractical.

■-FET with n-GaAs channel on soil GaAs substrate
When fabricating In,..., 51 (Alo, 5Gao) between the GaAs substrate and the n-GaAs channel layer.
, 7) grew O,aqP. At this time, methoxyaluminum containing 4000 PPM of oxygen was used as the source of A1. Ino, 5IGao, and aqP have a relatively large hand gap compared to GaAs (easy to increase the resistance, but not enough. Therefore, we added AN containing oxygen to increase the resistance. By creating such a structure, the source , the leakage current between the drains was eliminated, and electrical characteristics (improved blocking wavenumber, etc.) were achieved.

〔Effect of the invention〕

According to the present invention, an excellent high-resistance (insulating) compound semiconductor layer is provided, and a compound semiconductor layer with excellent crystal quality and electrical properties can be grown on this high-resistance compound semiconductor layer.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an MOCVD apparatus for carrying out the method of the present invention, and FIGS. 2(a) and 2(b) show A 12 GaAs with high resistance made with dimethylmethoxyaluminum and GaAsA without high resistance. 3 is a schematic cross-sectional view of the FET of the example, and FIG. 4 is the conventional MOCVD of oxygen-doped A 1 GaAs.
FIG. 2 is a schematic diagram of the device. 1... Reactor, 2... TMA, 3...
TMG, 4...AsH3,5.=H
t, 11...GaAs substrate, 12-...
High resistance A I GaAs layer, 13...N-type GaAs
Layer: 14...source electrode, 15...gate electrode, 16...drain electrode.

Claims (1)

[Claims] 1. In a method for growing a compound semiconductor containing aluminum by organometallic vapor phase epitaxy, the source gas contains an organometallic compound having a direct bond between an aluminum atom and an oxygen atom, thereby forming a high-resistance compound. A compound semiconductor crystal growth method characterized by growing a semiconductor. 2. The compound semiconductor crystal growth method according to claim 1, wherein the organometallic compound is methoxyaluminum. 3. A conductive compound semiconductor layer that is continuously grown on a high-resistance compound semiconductor layer containing aluminum and oxygen formed according to claim 1, and that the conductive compound semiconductor layer does not substantially contain oxygen. Characteristic semiconductor devices.