JPH01290222A - Semiconductor vapor growth method - Google Patents

Abstract

PURPOSE:To execute epitaxy of an atomic layer of a compound semiconductor at a low temperature by a method wherein a raw material gas containing a specific alkylated substance and a raw material gas of another element constituting the compound semiconductor are supplied alternately to a growth apparatus. CONSTITUTION:An alkylated substance of at least one element constituting a compound semiconductor is expressed by a formula (C4H9)nH3-nM (where M represents a metal element and n is 1 to 3); a raw material gas containing this alkylated substance and a raw material gas of another element constituting the compound semiconductor are supplied alternately to a growth apparatus. That is to say, while the gases flow continuously at a definite flow rate from individual supply sources, they are switched by means of valves 5, 5' and supplied to a reaction tube 1. By this setup, epitaxy of an atomic layer is executed at a substrate temperature; which is by several tens of deg.C lower than a conventional temperature; epitaxial growth having a steep heterointerface can be executed.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to atomic layer epitaxy of compound semiconductors, and aims to grow compound semiconductors by vapor phase epitaxial growth at lower temperatures. For example, in the m-v compound growth method, An organometallic compound containing a butyl group is used as a raw material for the group element.

[Industrial application field]

The present invention relates to vapor phase epitaxial growth of compound semiconductors, typically m-V compounds, and in particular to atomic layer epitaxy performed using alkylated metal elements constituting the compound semiconductor.

In recent years, semiconductor integrated circuits have become more dense and faster due to miniaturization of elements, but at the same time, development of high-performance elements using heterojunctions and superlattice structures is also progressing. In such devices, there is a strong demand for controlling the composition and thickness of compound semiconductors that form heterojunctions and superlattices on an atomic layer basis.

When growing a compound semiconductor epitaxially in atomic layer units, a raw material of one composition is supplied and a layer of that element is grown by one layer.
Only one atomic layer is deposited, the other source gas is switched and one atomic layer is grown, and this process is repeated to form a compound semiconductor layer of the required thickness.

Molecular beam epitaxy may be used as a method for depositing a desired atomic layer, but CVD such as MOCVD is preferable in terms of productivity.
It is desirable to realize atomic layer epitaxy by the MO method.
For example, when epitaxially growing GaAs, CVD uses trimethyl gallium (TMG) as a raw material for Ga.
Or using triethyl gallium (TEG), A
This is carried out using arsine (AsHi) as a raw material for s and H2 as a carrier gas.

When performing atomic layer epitaxy by MOCVD,
Limiting the deposition of each layer to only one layer by some method, that is, self-1 layer limiting.
) It is necessary to produce an effect.

Originally, compound semiconductors have the most stable stoichiometric composition, so they tend to exhibit a white layer limiting effect, but in a situation where only the - side of the raw material continues to be supplied, this effect can be overcome and the same atomic layer becomes Deposition of several layers occurs.

Therefore, in atomic layer epitaxy by MOCVD, the deposited layer is made into a single atomic layer by strictly controlling the raw material supply conditions, time, processing temperature, etc. Rather than decomposing the alkyl metal in the gas phase, it is more convenient to achieve atomic layer epitaxy if it is adsorbed onto the substrate without being decomposed and then decomposed in that state by heat, light, or chemical energy.

In other words, when an alkyl metal is adsorbed to a substrate, the metal is adsorbed on the substrate side and the alkyl groups are arranged on the surface side. Once this adsorption state is achieved, the alkyl groups are separated and the metal is adsorbed. By forming the metal layer into multiple layers, multilayer metal layers can be avoided. This is because when the substrate surface is covered with alkyl groups, further adsorption is difficult to proceed.

On the other hand, if the growth of the metal layer progresses in such a way that metal atoms liberated in the gas phase are deposited on the substrate, the white layer limiting effect is unlikely to appear, resulting in a situation unsuitable for atomic layer epitaxy.

Apart from these circumstances, there is a demand to lower the temperature at which a heterojunction is formed.

If the processing temperature during or after heterojunction formation is high,
- Even if a steep compositional distribution is achieved, interdiffusion of the constituent atoms will occur, making it impossible to obtain the desired interface.If the thermal expansion coefficients of the bonding constituent layers differ, the This is because warping and distortion will occur when the temperature is lowered.

In addition, in devices that use a heterojunction, there are many cases where the impurity concentration of the two layers that make up the heterojunction are different, or the conductivity types are different, which requires a sharp change in the impurity concentration distribution. It is desirable that the processing temperature be low in order to prevent impurity redistribution during formation.

On the other hand, if the substrate temperature is low, the alkyl metal becomes difficult to decompose, which reduces the growth rate and deteriorates the crystallinity of the epitaxially grown layer.

In the atomic layer epitaxy of GaAs using TMG or TEG described above, the substrate temperature is normally about 500°C, and if we focus only on crystallinity, it is desirable to raise this to about 600°C. If crystallinity is ignored, the Ga layer grows even at 350° C. in TEG and 400° C. in TMG, but the growth rate is extremely reduced.

Under these circumstances, there is a need for an atomic layer epitaxy technique that uses low processing temperatures and can obtain good crystals without reducing the growth rate.

[Problems to be solved by conventional technology and invention] For example, G
In aAs atomic layer epitaxy, the Ga source is T.
The growth is carried out by using MG or TEG and AsH3 as a raw material for As, and alternately supplying the above raw material gases at a growth temperature of 500°C.

When the growth temperature is at this level, when crystal growth with a hetero interface is performed, constituent atoms interdiffusion occurs near the hetero interface, making it difficult to obtain a steep hetero junction.

Further, due to the large temperature difference from room temperature, distortion such as warping occurs.

To avoid this, if we lower only the growth temperature and perform epitaxial growth without changing other conditions, TMG and TEG
The decomposition rate of is reduced, and crystal growth stops progressing. Even at this temperature, the deposition of the As layer proceeds, and the white layer limiting effect is not lost due to the high vapor pressure. Therefore, if the alkyl Ga is decomposed at a low temperature, low-temperature epitaxial growth of GaAs becomes possible. This situation is common to atomic layer epitaxy of m-v compound semiconductors in general.

The object of the present invention is to enable atomic layer epitaxy of m-v compound semiconductors at lower temperatures by selecting alkyl metals.

[Means to solve the problem]

In order to achieve the above object, in the atomic layer epitaxy of the present invention, which is a semiconductor vapor phase growth method in which an alkylated compound of at least one element constituting a compound semiconductor is used as a part of the raw material, the alkylated compound has a butyl group. A source gas containing the alkylated product and a source gas of another element constituting the compound semiconductor are alternately supplied to the growth apparatus.

[For production]

The alkyl group is represented by CaHxa++-, and the decomposition temperature of the metal compound becomes lower as m becomes larger. By atomic layer epitaxy, TMG'? If butylated Ga is used instead of 3TEG, it becomes possible to deposit the Ga layer at a lower substrate temperature.

Also, since butylated Ga is a liquid at room temperature, it is possible to bubble it with a carrier gas and send the vapor to the reaction tube, but when it reaches m-5 or higher, it is solid at room temperature, so the carrier gas cannot be used. It is difficult to send by

The butyl group includes n-butyl group, i-butyl group, S-butyl group, and t-butyl group, and any of them can be used in the present invention. Furthermore, epitaxial growth is possible using not only tributylated compounds but also metal compounds having two or one butyl groups.

Various Ga compounds containing such butyl groups are represented by tributyl Ga (T B G) below, and after the growth of the As surface, TBG sent to the reaction tube is first adsorbed onto the substrate surface. At this time, surface migration is also performed, but since A3 and Ga on the substrate surface are bonded, butyl groups are lined up on the outermost surface side. Furthermore, TBG is not adsorbed to the butyl base.

When energy such as heat or light is applied in this state, or when it reacts with a chemical substance such as arsine, the butyl group is removed and the substrate surface becomes a Ga surface, which then combines with the supplied As to form one molecule. A layer of GaAs is grown. Even if the substrate temperature at that time is several tens of degrees Celsius to one hundred degrees Celsius lower than when TMG or TEG is used, the butyl group is separated.

〔Example〕

An example of atomic layer epitaxy of GaAs will be explained. The vapor phase growth apparatus used has a configuration schematically shown in FIG. 1, in which 1 is a reaction tube, 2 is a substrate which is an epitaxial growth base crystal, 3 is a susceptor, 4 is an RF heating coil, and 5.
5' is a switching valve.

The raw material gases are H8 gas bubbled with isobutylated Ga for the Ga layer, and Ht gas containing arsine for the As layer, which are continuously supplied at a constant flow rate from each supply source. Switch to supply to the reaction tube. That is, T
When sending BG to the reaction tube, the valve 5 is connected to the reaction tube side, and the valve 5' is connected to the exhaust side. Note that the substrate temperature was 300°C.

Next, when arsine is supplied, the valve 5 is connected to the exhaust side and the valve 5' is connected to the reaction tube side. However, during the switching of the raw material gas, there is a period in which only Ht gas is flowed to purge the residual gas in the reaction tube. It is provided.

During this period, the supply of arsine is stopped, for example, by a device not shown, and only H□ gas is sent to the reaction tube.

TBG5H! The supply times and flow rates of , flusine, and H8 are shown in the table below.

This is repeated a number of times corresponding to a predetermined molecular layer as one cycle. FIG. 2 shows the growth thickness as a function of the gas flow rate and the X value. Note that the gas type H2 in the above table is for purging the residual gas in the reaction tube, as described above, and its flow rate is set according to the size and shape of the reaction tube. Further, in this example, the substrate temperature is 300 degrees, and the pressure inside the reaction tube is 2QTorr. Furthermore, the flow rate of arsine is the flow rate of arsine diluted to 10% with H mushrooms.

Here, with reference to FIG. 2, the growth thickness accompanying changes in the X value will be described. As the amount of HtvL that causes TBG to bubble is increased, the growth film thickness, which initially increased linearly, gradually slows down, and shows a tendency to reach a constant value when it exceeds 200 aj/s in terms of the standard state. This grown film thickness was obtained by repeating the above-mentioned cycle 177 times, and then measuring the growth step difference in a selective growth area prepared in advance using a contact film difference meter, and determining the value per cycle.

The above saturated film thickness corresponds to the thickness of a 31 molecular layer of QaA, which indicates that atomic layer epitaxy was performed. In contrast to the fact that crystal growth hardly progressed when the raw material was TMG, TF, or G under similar conditions, epitaxial growth progressed in this way at 300°C because TBG was used as the raw material. It can be said that this is due to.

〔Effect of the invention〕

As explained above, according to the present invention, atomic layer epitaxy is performed at a substrate temperature several tens of degrees lower than in conventional methods, making it possible to achieve epitaxial growth with steeper heterointerfaces, and further reducing thermal strain. Therefore, it becomes possible to form a more excellent heterojunction type device.

When the present invention is used to form a GaAs/AjGaAs-based high electron mobility transistor (HEMT), a high-purity GaAs layer serving as a channel layer is formed by the method of the present invention, and an AjGaAs layer serving as an electron supply layer is formed using a conventional method. If formed by this method, a HEMT with excellent characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the apparatus used in the present invention, Figure 2 is a diagram showing the relationship between TBG supply amount and grown film thickness. And, In the diagram 1 is a reaction tube, 2 is the board, 3 is the susceptor, 4 is an RF coil, 5.5' is a switching valve It is. National policy diagram 1 schematically showing the device used in the present invention Figure 2

Claims (1)

[Claims] In the vapor phase growth of a semiconductor using an alkylated compound of at least one element constituting a compound semiconductor as part of the raw material, the alkylated compound is (C_4H_9)_nH_3_-_
nM (where M is a metal element, n = 1, 2 or 3),
A semiconductor vapor phase growth method characterized in that a source gas containing the alkylated product and a source gas of another element constituting the compound semiconductor are alternately supplied to a growth apparatus.