JPS6272116A - Doping method - Google Patents

Abstract

PURPOSE:To perform a uniform doping with excellent reproducibility by a method wherein the raw material of organic tin, which is diluted with carrier gas to the desired concentration, is prepared and placed in a container in advance, and it is used with gas supplied in the controllable quantity without performing a bubbling. CONSTITUTION:When Sn is doped using an MOCVD (metal oxide chemical vapor deposition) method which is a vapor-phase growth method, an organic tin compound is used as a precursor. An organic tin compound vapor of dopant material is placed in a container, and it is used after dilution with diluting gas. (CH3)4Sn and (C2H5)4Sn are desirable as the above-mentioned organic tin compound, and the inert gas such as H2, N2, Ar, He and the like which do not react with the organic tin compound is considered suitable as the organic tin compound to be used for doping. The degree of dilution can be arbitrarily determined in the range of dilution wherein the materials of organic tin compound is not liquefied. However, the range of several - several tens of ml/min of MFC (flow rate regulator) is set as the quantity of supply which can be controlled easily, and the practical concentration of the organic tin compound in the container is in the range of 0.2-200ppm. The control of the feeding quantity of the organic tin material can be accomplished by merely feeding the diluted gas of fixed concentration to the reaction chamber with an MFC.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a doping method for metal-organic chemical vapor deposition (hereinafter abbreviated as MOCVD) for m-v group compound semiconductors, and particularly to a method for supplying an organometallic compound as a doping raw material. Regarding.

When epitaxially growing an n-type single crystal thin film of a [1-V group compound semiconductor represented by GaAs], impurities such as sulfur (S), selenium (Se), silicon (Si),
It is usually doped with tin (Sn) or the like.

Among these impurities, Sn has a particularly small diffusion coefficient in the GaAs crystal, which makes it difficult to cause phenomena such as "sag" in the doped impurity profile even if it is subjected to heat treatment in the device fabrication process after epitaxial film formation. Exists. Therefore, in epitaxial growth by the liquid phase method, Sn has been used for a long time.

On the other hand, in the MOCVD method, which is a vapor phase growth method, when doping Sn, which has such advantages, it is necessary to use an organic tin compound as a precursor, and tetrameltin (TMSn) is used as a precursor.
) and tetraethyltin (TESn) are effective, as reported in the Journal of Gysta! Growth
68 (1984), pp. 60-64 and 65-70.

However, as is clear from the above literature, it is necessary to transport this compound in the form of vapor to the growth reaction chamber.

That is, as shown in FIG. 1, a liquid organic tin compound 1 as a raw material is filled into a bubbler (T generator) 4 placed in a constant temperature chamber 3 containing a refrigerant 2, and this is filled with a carrier gas such as hydrogen. is adjusted to a predetermined flow rate using a flow fft controller (MFC) 6 and introduced into the bubbler 4. At this time, the switching valves 7.8 are kept open and the switching valves 9 are kept closed. Saturated vapor of an organic tin compound by bubbling is supplied to the reaction chamber (not shown) through line 10, but it is mixed in advance with a gas containing trimethyl gallium (TMG), arsine (Asf13), etc., and then supplied to the reaction chamber. do.

In this case, the supply amount of Sn is determined by strictly controlling the carrier gas amount and bubbler temperature.

However, it has been found that it is very difficult to achieve uniform doping with good reproducibility using such a conventional supply method, and in reality, only unsatisfactory results can be obtained as shown in the comparative example below.

The following are generally thought to be the causes of this. In other words, the normal doping concentration should be at most 10 to 1
Since the level is 0'9 pieces/cI113, if the difference in decomposition efficiency is ignored, trimethyl gallium (TMGa
) etc. 1/1000 to 1/10000 of 4 degrees of group ■ side raw materials
It is necessary to control the four main characters.

In the normal MOCVD method, TMGa is ~10-'mol
Since the supply amount is e/min, the dopant amount is 10
-8 to 10- It is necessary to control to "mole/win."

Is this amount current? This is almost impossible to achieve with the combined use of an R quantity controller (MFC) and a temperature-controlled bubbling system. This is because, for example, when supplying, the carrier flow rate is substantially set to 0.01 m1/min.
This is not possible with normal MFC. Conversely, within the control range of the MFC, for example,
To obtain a carrier supply amount of 1 ml/win, the bubbler temperature must be cooled to -80°C, and TMSn
If the temperature drops below the freezing point of the liquid, bubbling becomes inconvenient.

Furthermore, since the supply of bubbling gas at 1 ml/min is too small for the practical diameter of the dip tube of the bubbler, the intervals between bubbling gases are several times 7 ml/min.
This is the cause of pulsating currents.

This pulsating flow is Journal of Crystal G
Rowth, Vol. 68, p. 412 (1984).

The present invention was made in view of the current situation and aims to improve the above-mentioned drawbacks.

That is, the present invention is a MOCVD method characterized by preparing an organic tin raw material diluted in advance with a carrier gas to a desired /a concentration in a container, and supplying a predetermined amount of the raw organic tin compound from the cylinder to a reaction chamber by NFC. A doping method is provided.

According to the present invention, since bubbling is not performed, there is no concern about pulsating current, and since the sulfur gas method is not used, the organic tin raw material can be diluted with a carrier gas at a sufficiently dilute concentration. Therefore, it is possible to supply the gas in an amount that falls within the controllable range of NFC, and it is possible to easily control i:llI and to perform doping uniformly and with excellent reproducibility.

Another advantage is that there is no need for temperature control and it is only necessary to control the amount of gas at a fixed temperature using NFC, which simplifies the g setting.

The present invention will be explained in detail below.

The doping method of the present invention can be applied to conventionally known ■-■ group semiconductors, namely GaAs, GaAlAs, InP, and InAI.
It can be suitably employed in the production of P and the like by the MOCVD method.

In the present invention, the organic tin compound used is (C
lli)4Sn, (Czlls)aSn are preferable, and the carrier gas for dilution is H2, N2, Ar,...
An inert gas that does not react with organotin compounds such as He is preferred.

However, when gas-mixing H2 or He gas and the organic tin compound raw material in a container, some care must be taken, and a long aging time is essential to achieve a uniform mixed state. If this is not done, the 4-degree analysis value in the container will not be constant and the reproducibility will be unstable. Therefore, to avoid this, it is preferable to mix with N8 gas.

The concentration of dilution can be arbitrarily determined within a range that does not liquefy the organic tin compound of raw material 4.
Assuming that the supply amount is realistically easy to control in the range of min to several tens of ml/win, the normal doping level is 10 to 101 impurities/cII+3 in the crystal, so the organotin compound concentration in the container is 0.2ppm~200
A range of ppm is practical.

Unlike the bubbling method, strict temperature control of the cylinder is not required to control the supply amount of the raw material organic tin compound, and it is only necessary to send a constant amount of diluent gas at a constant temperature of 7 degrees to the reaction chamber using the MFC. .

In other words, an expensive thermostat and its control system to strictly control the temperature, such as the one illustrated in Figure 1? jl H
It also eliminates the need for a bubbler with a unique shape and the accompanying gas switching valves.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

Embodiment A T for doping was placed in the cylinder container 11 shown in FIG.
MSn was diluted with nitrogen gas and TMSn i: rf-2,
The gas 12 with a concentration of 5 ppm is passed through the pressure reducing valve 13 to the MFC 6.
G
Carrier hydrogen for aAs growth (9000ml/m1n
), Arsine (Asll*, 15m1/m1n)
evaporation 2= as shown in Figure 1.
(Bubbler) TMGa using bubbler temperature -10
7 saturated with bubble hydrogen (15 ml/+in) at °C.
Mix MGa gas TMSn, AsL, TMGa
A mixed raw material gas is introduced upward into a vertical reaction growth chamber (not shown).

In the center of the reaction chamber, there is a graphite support stand capable of high-frequency induction heating, on which a (100)-plane GaAs 1ij crystal substrate is placed, heated to 650°C for one growth period, and the introduced raw material gas is blown to perform Evita growth. was carried out. The film was grown to a thickness of about 6 μm in a growth time of 2 hours.

Figure 3a shows the horizontal profile of the impurity l4 degrees in the Evita kinial grown film obtained in this way.
The results obtained by C-■ measurement using the electrolytic polishing method are shown. It is well understood that a very uniform profile is obtained.

Comparative Example Growth was carried out under exactly the same conditions as in the Example, except that a conventional reactor (FIG. 1) was used to transport the TMSn dopant to the reaction chamber. The evaporation conditions for TMSn were as follows: The bubbler temperature was -80°C to make the supplied TMSn the same as in the example.
, Hz gas introduction for bubble f! tO, was regulated using an MFC that flows from 2 ml/+in up to 10 ml/min.

The impurity 7 degree profile of the grown film was determined using the same method,
It is shown in Figure 3b.

It can be seen that, unlike the films of Examples, uniform doping did not occur.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an example of a liquid dopant supply section (evaporation bubbler) of a conventional MOCVD apparatus, FIG. 2 is a block diagram of an embodiment of the present invention, and FIGS. It is a profile of the impurity concentration in the GaAs film obtained in a comparative example in the direction of thickness. 4... Bubbler (evaporator) 6... Flow controller (MFC) 11... Cylinder container Figure 2 Figure 3 Figure procedure amendment (method) % formula % 2. Invention Name Doping Method 3, Relationship with the Amendment Case Patent Applicant Address 5-15 Kitahama, Higashi-ku, Osaka Address Inside Sumitomo Chemical Co., Ltd., 5-15 Kitahama, Higashi-ku, Osaka +i
``'''': 5. I 5. Date of amendment order January 28, 1985 (shipping date) 6. Column 7 of "Brief explanation of drawings" of the specification subject to amendment 7. Description of contents of amendment Page 9, pages 19 to 10, line 2, ``Figure 3 a and b are profiles.'' was changed to ``Figure 3 shows CaAs obtained in the examples and comparative examples.
In the diagram showing the distribution of impurity concentration in the film in the depth direction, the vertical axis shows the impurity level, and the horizontal axis shows the depth. ” is corrected. that's all

Claims (3)

[Claims] (1) In the organometallic chemical vapor deposition method of group III-V compound semiconductors, a doping method characterized in that the vapor of an organotin compound as a dopant raw material is diluted in advance with a diluent gas in a container. (2) The organotin compound is (CH_3)_4Sn or (
Claim No. (1) which is C_2H_3)_4Sn
Doping method described in section. (3) The doping method according to claim (1) or (2), wherein the diluent gas is N_2, Ar, H_2 or He.