JPH0652718B2 - Doping method - Google Patents

Description

The present invention relates to a doping method in a metalorganic chemical vapor deposition method (hereinafter abbreviated as MOCVD method) of a III-V group compound semiconductor, and particularly to a method of supplying an organometallic compound as a doping raw material thereof. Regarding

When epitaxially growing an n-type single crystal thin film of a III-V group compound semiconductor represented by GaAs, sulfur (S), selenium (Se), silicon (Si), tin (Sn), etc. are usually doped as impurities. .

Among these impurities, especially Sn has a small diffusion coefficient in the GaAs crystal, so that even if it is subjected to heat treatment in the process of device formation after the epitaxial film is formed, the phenomenon that the profile of the doped impurities is "dull" is hard to occur. Have Therefore, Sn has been used conventionally in the epitaxial growth by the liquid phase method.

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 organotin compound as a precursor, and tetramertin (TMSn) or tetraethyltin (TESn) is effective. Is the Journal of G
It has already been reported in ystal Growth Vol. 68 (1984) 60-64 and 65-70.

However, as is apparent from the above literature, it is necessary to transport this compound as vapor to the growth reaction chamber.

That is, as shown in FIG. 1, a liquid organotin compound 1 as a raw material is filled in a bubbler (evaporator) 4 placed in a thermostat 3 containing a refrigerant 2, and a carrier gas such as hydrogen is adjusted in flow rate. The flow rate is adjusted to a predetermined value with a container (MFC) 6 and introduced into the bubbler 4. At this time, the switching valves 7 and 8 are open and 9 is closed. The saturated vapor of the organotin compound obtained by bubbling is supplied to the reaction chamber (not shown) through the line 10, or trimethylgallium (TM) is used in advance.
G), mixed with a gas containing arsine (AsH ₃ ) etc. and supplied to the reaction chamber.

In this case, the supply amount of Sn can be obtained by strictly controlling the carrier gas amount and the bubbler temperature.

However, it has been found that it is very difficult to perform uniform doping with good reproducibility by such a conventional supply method, and in reality, unsatisfactory results are obtained as mentioned in Comparative Examples below.

The following are generally considered as the causes. That is, the usual doping concentration is at most 10 ¹⁸ to 10 ¹⁹
Since it is a level of pcs / cm ³ , it is necessary to control the concentration of 1/1000 to 1/10000 of the concentration of the group III side raw material such as trimethylgallium (TMGa), ignoring the difference in decomposition efficiency.
In the usual MOCVD method, TMGa is supplied at -10 ^-5 mole / min. Therefore, it is necessary to control the dopant amount to 10 ^-8 -10 ^-9 mole / min.

Achieving this amount with a current flow controller (MFC) in combination with a temperature controlled bubbling system is nearly impossible. This is because, for example, when supplying, the carrier flow rate must be substantially controlled at 0.01 ml / min, which is not possible with a normal MFC. Conversely, MFC
Within the control range of, for example, the carrier supply amount of 1 ml / min, it is necessary to cool the bubbler temperature to −80 ° C., which is below the freezing point of TMSn, which causes inconvenience in bubbling.

In addition, since the bubbling gas is too small at a supply rate of 1 ml / min with respect to the actual diameter of the bubbler dip tube, the interval at which bubbling bubbles are generated is several times / minute, resulting in pulsation. It is the cause.

This pulsating flow is Journal of Crystal Growth Vol. 68, No. 412
As discussed in page (1984).

The present invention has been made in view of the above circumstances, and improves the above-mentioned drawbacks.

That is, the present invention prepares an organotin raw material which is diluted with a carrier gas to a desired concentration in a container in advance, and supplies a predetermined amount of the raw material organotin compound from the cylinder to the reaction chamber by MFC doping in MOCVD. It provides a method.

According to the present invention, since bubbling does not occur and there is no fear of pulsating flow, and since the saturated vapor method is not adopted, the organotin raw material can be diluted with a carrier gas in a sufficiently dilute concentration. Therefore, it is possible to supply the gas in an amount within the controllable range of the MFC, and it is possible to perform doping that is easy to control, uniform, and excellent in reproducibility.

Further, there is also an advantage that the apparatus can be simplified because it is not necessary to control the temperature and only the amount of gas whose concentration is determined by the MFC is controlled.

Hereinafter, the present invention will be described in detail.

The doping method of the present invention is based on a conventionally known III-V group semiconductor,
That is, GaAs, GaAlAs, InP, InAlP, etc. can be preferably used in the production by the MOCVD method.

In the present invention, the organotin compound used is (C
H ₃ ) ₄ Sn and (C ₂ H ₅ ) ₄ Sn are preferable, and the carrier gas for dilution is preferably an inert gas that does not react with an organotin compound such as H ₂ , N ₂ , Ar and He.

However, when mixing H ₂ or He gas and the organic tin compound raw material in a container, some care needs to be taken, and a long aging time is indispensable for achieving a uniform mixed state. If this is neglected, the concentration analysis value in the container will not be constant, resulting in indeterminate reproducibility. Therefore, in order to avoid this, it is preferable to mix with N ₂ gas.

The concentration of dilution can be arbitrarily determined within the range in which the raw material organotin compound is not liquefied, but it is several ml / min to several tens of MFC.
Assuming that the supply rate is practically easy to control in the ml / min range, the usual doping level is 10 ¹⁶ to 10 ^{19 in} terms of the impurity concentration in the crystal.
Organotin compound concentration in the container because it is pieces / cm ³ is 0.2p
The range of pm-200ppm is practical.

Unlike the bubbling method, strict temperature control of the cylinder is not necessary to control the supply amount of the raw material organotin compound,
It suffices to send a fixed amount of diluent gas with a constant concentration to the reaction chamber by MFC.

That is, it has the advantages that an expensive constant temperature bath for strictly controlling the temperature and its control system, a bubbler having a complicated shape as illustrated in FIG. 1, and gas switching valves associated therewith are unnecessary.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

EXAMPLE TM for doping in the cylinder container 11 shown in FIG.
Gas 1 in which Sn is diluted with nitrogen gas to have a TMSn concentration of 2.5 ppm
2 through the pressure reducing valve 13 to the line 14 by MFC6 at a flow rate of 10 ml / min, and carrier hydrogen (9000 m
l / min) and arsine (AsH ₃ , 15 ml / min) gas, and further using the evaporator (bubbler) 4 shown in FIG.
TMGa bubbler temperature -10 ℃ Hydrogen for bubble (15ml / min)
TMSn mixed with TMGa gas saturated in, introduced from above the mixed raw material gas AsH _3, TMGa vertical reaction growth chamber (not shown). In the center of the reaction chamber, there is a graphite support that can be heated by high frequency induction, a (100) plane GaAs single crystal substrate is placed on it, heated to a growth temperature of 650 ° C., and the introduced raw material gas is sprayed to carry out epitaxial growth. . It grew to a film thickness of about 6 μm in a growth time of 2 hours.

FIG. 3a shows the result of the CV measurement of the depth profile of the impurity concentration in the epitaxially grown film thus obtained by the wet electrolytic polishing method. It is well understood that a very uniform profile is obtained.

Comparative Example Growth was performed under exactly the same conditions as in Example except that the conventional evaporator (FIG. 1) was used as the method of transporting the TMSn dopant to the reaction chamber. The evaporation conditions of TMSn were adjusted by using a bubbler temperature of −80 ° C. and an MFC flowing from a bubble H ₂ gas introduction amount of 0.2 ml / min to a maximum of 10 ml / min in order to make the supplied TMSn the same as in the example.

The impurity concentration profile of the grown film was obtained by the same method and is shown in b of FIG.

It can be seen that unlike the films of the examples, uniform doping does not occur.

[Brief description of drawings]

FIG. 1 is a block diagram of an example of a liquid dopant supply unit (vaporizer for evaporation) of a conventional MOCVD apparatus, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is obtained in Examples and Comparative Examples. In the figure showing the distribution of the impurity concentration in the GaAs film in the depth direction, the vertical axis represents the impurity concentration and the horizontal axis represents the depth. 4 …… Bubbler (Evaporator) 6 …… Flow controller (MFC) 11 …… Cylinder container

Front page continued (72) Inventor Noboru Fukuhara 2-10-1 Tsukahara, Takatsuki City, Osaka Prefecture Sumitomo Kagaku Kogyo Co., Ltd. Within the corporation

Claims (3)

[Claims] 1. A doping method, characterized in that in a metalorganic chemical vapor deposition method of a III-V group compound semiconductor, a vapor of an organotin compound as a raw material for a toupant is preliminarily diluted with a diluent gas. 2. The organic tin compound is (CH ₃ ) ₄ Sn or (C ₂ H ₅ ) ₄ S.
The doping method according to claim (1), wherein n is n. 3. The doping method according to claim 1 or ₂ , wherein the diluent gas is N ₂ , Ar, H ₂ or He.