JPS5895696A - Vapor-phase growing method with controlled vapor pressure - Google Patents

Abstract

PURPOSE:To form a growing layer of a compound semiconductor with little defects and high quality, by keeping the partial pressure of an element of high vapor pressure at an optimal vapor pressure in the vapor-phase growing method of the compound semiconductor. CONSTITUTION:In the case of the epitaxial growth of GaAs, hydrogen gas 1 is passed through a flowmeter 5, bubbled in a liquid, e.g. trimethylgallium, in a vessel 2 and fed to a reaction tube 6. On the other hand, an arsine, etc. from a gas cylinder 3 and a carrier gas 4, e.g. hudrogen gas, are fed through flowmeters 5 to the reaction tube 6 to grow GaAs epitaxially on substrate crystals 9 placed on a carbon boat 8 heated by the induction heating with a coil 7. In the process, the arsine, etc. are fed to the reaction tube 6 so that the partial pressure of As which is an element of high vapor pressure may be the optimal vapor pressure (shown in the table) corresponding to the growth temperature (the temperature of the substrate crystals 9).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vapor pressure controlled vapor phase growth method for achieving stoichiometric composition of compound semiconductors.

In conventional vapor phase growth, a method for achieving stoichiometric composition (stoichiometry) of compound semiconductors is not used. , the optimum A8 pressure required to satisfy the stoichiometry of GaAs has been reached. Usually, As is grown at a partial pressure lower than the A8 pressure that satisfies stoichiometry. The same applies to other substances, such as GaAs
If it is a l-V group such as 9, the vapor pressure of the group V element is usually high, and the partial pressure of the group V element becomes a problem. Also, ■-■ family, ■-
The elemental partial pressure of the high vapor pressure of group (3) and their mixed crystals becomes a problem.

An object of the present invention is to obtain a low-defect, high-quality compound semiconductor growth layer by adjusting the partial pressure of a high vapor pressure element to an optimum vapor pressure in the vapor phase growth of a compound semiconductor.

Another purpose is to prevent contamination of impurities such as carbon, silicon, and oxygen.

The following two inventions will be described in detail.

FIG. 1 shows a growth apparatus for vapor phase epitaxial growth of GaAs. - As an example, metal-organic vapor phase epitaxial growth will be described. In Figure 1.

1 is usually hydrogen gas (H2), which is the liquid in vessel 2.
For example, trimethyl gallium ((CH3) 3 Ga) or triethyl gallium ((C2H5) 3 Ga) is used as a valve.

The molar ratio is determined by the atmospheric pressure and gas flow rate.

Vapor pressure is determined by temperature. The supply of As is arsine (As
Cylinder 3 in which H3) etc. was diluted with hydrogen gas etc.
From there, it is directly introduced into two reaction tubes 6 through a flow meter 5.

4 is a carrier gas, H2 etc. is used! By changing these absolute flow rates and relative flow rates, the crystallinity, etc. of the produced GaAs is controlled. As the heating device, a high frequency heating method is used here, and the substrate crystal 9 is indirectly heated by inductively heating the carbon boat 8 using the coil 7, thereby performing epitaxial growth on the substrate. GaA
In compound semiconductors such as e, a slight deviation from the stoichiometric composition becomes a serious problem. For example, since the atomic density of GaA3 semiconductor is about -1 5 x 1022 atoms/d, the composition of Ga and As is not 1:1 but +lp
If it is biased toward either pm, then 5X1016
There is a difference in the number of atoms on the order of /d, which is the same condition as when a considerable amount of impurity is present. Simply assuming that all of this deviation contributes to carriers, it is equivalent to the presence of 5×10 crn of impurities.

FIG. 2 shows the temperature dependence of the vapor pressure of the simple elements of group Ⅰ and group V. In the figure, the horizontal axis represents absolute temperature ('x)+25 and antimony (Sb) 26. In the case of ~V compound-semiconductor,
The vapor pressure of group V elements is extremely high, and they become extremely easy to evaporate. At high temperatures, each crystal is exposed to vacuum, hydrogen, nitrogen,
When heat treatment is performed in a gas such as argon, the effect of this difference in vapor pressure becomes noticeable, and high vapor pressure elements are extracted from the surface, resulting in a very rough state. In l-V group semiconductors, V
The group is a high vapor pressure element.

FIG. 3 shows the temperature dependence of the vapor pressure of the Ir group and (■) group simple elements. The horizontal axis is absolute temperature ('K) and the vertical axis is vapor pressure (T
orr). In the figure, the Ir group is mercury (Hg)31,
Cadmium (Cd)32. Zinc (Zn) 33 +
The VT group is sulfur (S)34. Selenium (Ss)35. It is tellurium (Te2)36. In the group (1)-(3), mercury has the highest vapor pressure. For example, in the case of HgTe, it is necessary to pay particular attention to the vapor pressure of mercury during growth.

Taking GaA3 as an example of a 1-V compound, when the crystal grows at high temperature under conditions where the partial pressure of As is insufficient, 88 vacancies are generated. However, when a moderate A8 pressure is applied, the stoichiometric composition of Ga and As becomes equal, and when the A8 partial pressure is higher than that, a state where As is greater than G(-, a) is reached. If there is not enough or too much, various structural defects will occur due to deviation from the equilibrium state of the stoichiometric composition.The simplest of these is the point defect, and the vacancy in As is taken as an example. Figure 4 is a model diagram of defects in a crystal. 〇 is Ga and - is 80. (1) Neutral vacancy of As 41. (2) As having one electron in the vacancy of As. F 421 (3) 'θ vacancy point F'431 (4) Compound defect of neutral vacancy son and F center 44. (5) Consisting of two F centers 452 etc. As There are many different types of point defects in the vacancies. Similarly, when there is a large amount of All, various types can be considered. Also, interactions with impurities.

There are also combinations and it becomes very complicated. More stacking faults.

There are also dislocations, etc. The optimum A8 pressure point is where these various defects are minimized.

FIG. 5 shows the relationship between optimum arsenic pressure and temperature in -GaAs. The horizontal axis is the reciprocal of the absolute temperature (0K) multiplied by 1000, 1000/T, and the vertical axis is the arsenic pressure P@&
^7 (Torr). The optimum pressure for arsenic is temperature dependent; the higher the temperature, the higher the arsenic pressure required.

The arsenic pressure here is the pressure of As4. When arsenic becomes a gas, it becomes As4. The data in the figure is
This was obtained from the results of previous heat treatment experiments on GaAs substrates under arsenic pressure (.) and crystal growth experiments from a solution of As dissolved in a Ga solvent (1), but the same thing can be seen in vapor phase growth. occurs.

Vapor phase growth while also undergoing heat treatment under partial pressure of arsenic.

GaAs is formed on the surface of the substrate. Essentially, it is no different from heat treatment under arsenic pressure or liquid phase growth under arsenic pressure.7 The partial pressure of arsenic is very important. Fifth
The empirical formula for arsenic pressure obtained from the figure is.

1.05 2.6X10'e@p(--) in PGaAs (
1) T, where: Boltzmann constant, T: growth temperature (substrate temperature).

Table 1 shows the optimum arsenic pressure for each growth temperature and the molar amount of A s H3 with respect to the growth temperature for each arsenic pressure.

The optimum arsenic pressure is a calculated value based on equation (1).

The concentration of AsH3 was determined using the chemical formula: As2 also exists, but Ag3 is A
It was a small amount compared to s4, so I ignored it. However, when calculating the amount of 2 moles, use the Boyle-Chassis law.

It is assumed that Dalton's law of partial pressure holds true.

It is sufficient if the partial pressure of As4 becomes the optimum arsenic pressure shown in Table 1.

AsH3 is almost 100% at a temperature slightly higher than 500℃
It will be disassembled soon. Also, A e C13 is a little higher at 600 ~
Decomposes almost 100% at 700℃. In organometallic vapor phase epitaxy, the current growth temperature is about 600 to 700°C, and in the case of growth using a ride gas such as AaCl3.

Since it is grown at a growth temperature between 700 and 800° C., higher molar amounts must be used than those currently in use. Since higher temperatures increase the molar ratio to carrier gas, a high pressure region may be used in which the total pressure including the carrier gas is higher than 1 atmosphere within the growth tube. or.

As long as the molar amount of As4 is sufficient, it may be carried out under reduced pressure. However, since the optimum arsenic pressure is required on the growth substrate, the arsenic pressure in other parts is high due to the structure of the growth apparatus, and the molar amount of As) 13 is not close to that shown in Table 1. Cases will arise. It is only necessary that the substantially necessary As4 partial pressure be near the substrate.

That is, in actual equipment, there is a dependence on the equipment, and the optimum supply amount of As'H3, AaCl3, etc. changes. Although the above has been described regarding ()aAs, it goes without saying that the above applies to other compound semiconductors as well, but in the II-Vl group,
Both components have higher vapor pressures than group V.

In such cases, it becomes very important to control not only the vapor pressure of one element but also the vapor pressure of the other element. It is clear that in mixed crystals, the number of vapor pressures to be controlled increases.

Recently, metal-organic vapor phasing, which utilizes thermal decomposition of alkylated substances, has been developed.
e 1ptaxy.

MO-VPI) has been used in place of halide vapor phase epitaxial growth (H-4PK) due to its low growth temperature, low growth rate, and suitability for thin film growth. In pyrolytic growth, rather than surface reactions at the crystal surface.

Crystal growth occurs by reacting in space and then adhering to the crystal surface, whereas growth by hydrogen reduction of I-ride gases such as A3Cl3 involves mostly surface reactions on the crystal surface with almost no reactions in the air. It is said that the perfection of the crystals is superior to that produced by tona-sho and pyrolysis methods. Furthermore, since an organic metal is used, a large amount of carbon is introduced into the epitaxially grown layer, which poses a problem. Trimethylgallium ('
I'MG) and triethylgallium (TBG) are substances that are very easily thermally decomposed, and in the case of TMG, (CH3)3G a-+3- CH3-)-Ga
(4)・CH3 free radicals travel on the streetcar. This CH3 combines with other TMG to form intermediate products.

Usually, a hydrogen carrier is used to immediately combine CH3 resulting from thermal decomposition with hydrogen to form methane (CH4). M
In O-VPJC, 1Usually hydrogen is used as a carrier gas for the above reasons, and other inert gases (N2, Ar
, He, etc.) are not used. In the present invention.

Using an inert gas as the carrier gas, hydrogen chloride (MCI)
), hydrogen hydride (HBr), etc. as TMG-? It is supplied into the system together with AsH3, etc., and also controls the vapor pressure.

By injecting HCI, Br is added to the ride gas.
The injection of 2nd grade improves the integrity of the crystal by creating different intermediate products and increasing surface reactions. In addition, HCI, HBr, HF, etc. can be injected into the
Carbon contamination can also be suppressed by immediately converting CH3 radicals into CH4 by hydrogen radicals H during the decomposition of CI, HBr, HF, etc. Therefore,
Even when Ar, Hlil + N2 gases are used, carbon contamination can be suppressed by simultaneous injection of H(:1, etc.).Ar, He.

By using an inert gas such as Nz, the thermal decomposition rate of AsH3 is promoted and the crystal growth rate can be increased. When growing using inert gas.

As can be seen from equation (4), the molar amount of HCl, etc. to be injected at the same time must be at least three times the molar amount of 'I'MG in the case of TMG. However, in reality, A s H3 is also injected at the same time. Since hydrogen free radicals (.H) generated by decomposition of hydrogen are also present due to the injection, the amount does not need to be three times or more. By implanting MCI or the like, the growth rate becomes slower than that using only an inert gas carrier. Furthermore, by injecting a smaller amount of H2 into the inert gas, the rate of thermal decomposition of the hydride can be slowed down and the growth rate can also be changed. Depending on the device, the growth rate can vary over a fairly wide range.

Light-emitting diodes and single power devices require extremely thick growth layers, but semiconductor lasers and integrated circuits require thickness control of 1 μm or less, making it difficult for each device to grow industrially. This requires economic growth speed.

Various applications are possible using these methods. Of course, even if the amount of inert gas is reduced and the carrier becomes H2, the effect of HCI injection still exists, so the effect is better than without HCI.

If there is hydrogen, C12, B r2 as a halide
etc.

As explained above, in the present invention, by performing vapor phase growth with vapor pressure control, a stoichiometric composition of a compound semiconductor can be achieved, and a compound semiconductor crystal with low defects and high quality can be obtained. In addition, by injection of MCI etc. in pyrolysis vapor phase growth, contamination of impurities such as carbon is prevented compared to conventional techniques, and high quality crystals with high crystalline perfection can be obtained, and the growth rate can be varied over a wide range. I can do it.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a general vapor phase growth apparatus. Figure 2 shows the relationship between vapor pressure and temperature for Group ■ and Group V, and Figure 3 shows ■
Figure 4 shows the relationship between vapor pressure and temperature for the groups 2 and 3. Figure 4 shows a wedge diagram of defects in GaAs, and Figure 5 shows the relationship between optimum As pressure and temperature in GaAs.

Claims (2)

[Claims] (1) While circulating carrier gas inside the growth tube. to the compound semiconductor substrate housed within the reaction tube. A gas containing constituent elements of the compound semiconductor is supplied together with the carrier gas to maintain the substrate at a predetermined growth temperature. In vapor phase growth for forming at least one growth layer on the surface of the substrate, the partial pressure of at least one high vapor pressure element among the constituent elements of the compound semiconductor is adjusted to near the optimum vapor pressure depending on the growth temperature. A vapor pressure controlled vapor phase growth method characterized by: (2) In vapor pressure controlled vapor phase growth using organic metals,
A vapor pressure controlled vapor phase growth method characterized in that at least one of halides including hydrogen chloride (Hcffi), hydrogen bromide (HBr), etc. is mixed into a carrier gas and a gas containing constituent elements of a compound semiconductor.