JPH01224295A - Gas source molecular beam crystal growing apparatus - Google Patents

Abstract

PURPOSE:To provide the title apparatus so designed that plural gases differing in decomposition temperature from each other made up of a metal hydride gas and an organometallic gas are put to mixed reaction followed by emission, thereby reducing contamination of impurities such as carbon into a crystal growth layer. CONSTITUTION:Firstly, the temperatures of a preheating section A, a thermal cracking section C and a low-temperature heating section B are brought to 300-400 deg.C, 800-900 deg.C, and 400-500 deg.C, respectively. Then, an AsH3 gas via the inlet of a main gas introduction tube 20 is heated at the section A and enters the section C where said gas is decomposed into As and hydrogen followed by entering the section B. In the section B, a triethylgallium gas intro duced via the inlet of a sub-gas introduction tube 21 is decomposed into Ga and ethyl group, said ethyl group is allowed to react with the As to form triethylarsenic, which is then emitted. From this molecular beam source cell, As molecule, Ga molecule, ethyl group and triethylarsenic are emitted, among them, the triethylarsenic little liberates carbon on the substrate, therefore, facili tating high-purity crystal growth of low carbon impurity concentration.

Description

[Detailed Description of the Invention] [Summary] Regarding a new configuration of a molecular beam source cell that supplies gas in a gas source molecular beam crystal growth apparatus, the present invention aims to reduce the incorporation of impurities such as carbon into the crystal growth layer. For the purpose, connect the auxiliary gas introduction pipe to the main gas introduction pipe of the molecular beam source cell,
The main gas introduction pipe is divided into a plurality of heating zones, and the first heating zone, which is located closer to the raw material gas source than the connection part, is heated to a high temperature and is placed closer to the growth substrate than the connection part. The second heating zone is heated to a low temperature, metal hydride gas is introduced through the main gas introduction pipe, organometallic gas is introduced through the auxiliary gas introduction pipe, and a plurality of gases with different decomposition temperatures are mixed and reacted. It is characterized by comprising a molecular beam source cell configured to emit light.

[Industrial Application Field] The present invention relates to a gas source molecular beam crystal growth apparatus, and particularly to a novel configuration of a molecular beam source cell that supplies gas to a crystal growth chamber.

The epitaxy method (crystal growth method) in which a semiconductor film is epitaxially grown along a crystal substrate is a basic technology for semiconductor manufacturing, and gas source molecular beam epitaxy has recently been developed as a notable technology.

However, since this gas source molecular beam epitaxy method is a method of epitaxial growth by thermally decomposing a compound gas, impurities are likely to be mixed into the crystal growth layer, and it is desired to reduce the mixing of impurities as much as possible.

[Prior Art] Now, gas source molecular beam epitaxy uses a gas source instead of the metal source in conventional molecular beam epitaxy (MBE).
When growing a (gallium arsenide) layer or an AlGaAs (aluminum gallium arsenide) layer, trimethyl gallium (TMG; Ga (CH3)3), ) is used as a group ■ molecular beam source material.
ethyl gallium (TEG; Ga(C2H5)3), )
Remethylaluminum (TMA; Al (CH3)
s),) ethylaluminum (TEA;A
A gas such as t (C2H5) s ) is used, and arsine (AsHa) or the like is used as a group Ⅰ molecular beam source material.

This gas source molecular beam crystal growth method has advantages over the conventional MBE method, such as being able to reduce surface defects and easily achieving a high growth rate, and because it uses gas in the molecular beam region, The growth process is closer to the MBE method than to the MOCVD (metal-organic pyrolysis) method, and a very steep hetero-interface can be easily formed by opening and closing the gas flow.
This method is said to have a great advantage in industrial production because the source can be replaced without exposing the clean ultra-high vacuum atmosphere inside the growth container to the atmosphere.

Figure 3 shows a conventional crystal growth apparatus that performs gas source molecular beam crystal growth. is a molecular beam source cell.

6 is a valve, 7 is a liquid nitrogen shroud, and 8 is a gate valve. As shown in the figure, the substrate 2 is held by a substrate holder 3 and heated by a heater 4, so that, for example, the substrate 2 is made of Ga.
In the case of an As substrate, it is heated to 600 to 700°C. Further, a plurality of molecular beam source cells are provided, and the plurality of molecular beam source cells are arranged facing the wafer 2.

FIGS. 4(a) and 4(b) show cross-sectional views of conventional molecular beam source cells. The molecular beam source cell for high-temperature decomposition gas shown in a) uses, for example, arsine (As), a group V gas.
) 13; metal hydride gas), etc., and 80
When heated to 0 to 900℃, it decomposes into As and H2, forming A.
This is a cell that emits s toward the substrate. In the figure, 11 is a gas introduction pipe, and 12 is a heater made of Ta (Tantalum).

13 is a vacuum flange, 14 is a heat shield plate, 15 is PBN
A (sintered boron nitride) plate is provided with a thermal cracking section C that is heated to a high temperature and decomposes gas at the outlet portion having PBN15.

In addition, the molecular beam source cell for low-temperature decomposition gases shown in Figure 4(b) is used for organometallic gases such as TMG and TMA, which are easily decomposed group gases.
It is a cell that is heated to ~60°C and emits radiation. The symbols in the figure are the same parts as in Figure 4(a), but
This hot rubbing section C for low-temperature decomposition gas is not provided. Note that the gas introduction pipe 11 of these molecular beam source cells has a diameter of 174 inches.

It is made of quartz and has a length of about 30 cs, and the distance between the tip of the gas introduction tube 11 and the wafer 2 is relatively short.

[Problems to be Solved by the Invention] However, using the gas source molecular beam epitaxial growth apparatus as described above, it is difficult to grow, for example, a GaAs layer or an AlGaA layer.
When growing the s-layer, TMG or T is used as a Ga source.
EC is used and arsine is used as the As source.
In addition, arsine, a group II element, is emitted from a high-temperature molecular beam source cell heated to about 900°C (Fig. 4 (a)), and TMG, a group II element, is emitted from a low-temperature molecular beam source cell heated to about 50 to 60°C. (4th
Figure (b)), which is released from arsine at 600
Since it is not decomposed on a GaAs substrate heated to ~700°C, it is thermally decomposed in advance in a molecular beam source cell and emitted as a single As molecule.

On the other hand, since TMG can be thermally decomposed at low temperatures, it was not thermally decomposed in the molecular beam source cell, but was heated to a temperature (50 to 60°C) that would prevent the source gas from adhering to the tube wall of the molecular beam source cell. It is disassembled and deposited on a GaAs substrate.

However, when thermally decomposed on a GaAs substrate, methyl groups (CH3) and ethyl groups (CH3) and ethyl groups (
C2H! There is a drawback that 5) does not evaporate as it is, but its groups decompose and liberated carbon mixes into the crystal growth layer, becoming an impurity and reducing the purity of the crystal growth layer. For example, in extreme cases, the carbon (C) concentration may be 1011? /- level and acts as an acceptor (p type) (.

The present invention proposes a gas source molecular beam crystal growth apparatus equipped with a molecular beam source cell for the purpose of reducing the incorporation of impurities such as carbon into the crystal growth layer.

[Means for solving the problem] The purpose is to connect an auxiliary gas introduction pipe to the main gas introduction pipe of the molecular beam source cell, divide the main gas introduction pipe into a plurality of heating zones,
a first disposed closer to the raw material gas source than the connection portion;
A heating zone is heated to a high temperature, a second heating zone located closer to the growth substrate than the connection part is heated to a lower temperature, a metal hydride gas is introduced from the main gas introduction pipe, and an organometallic gas is introduced. This is achieved by a gas source molecular beam crystal growth apparatus equipped with a molecular beam source cell configured to introduce a plurality of gases with different decomposition temperatures through an auxiliary gas introduction pipe, cause a mixture reaction, and radiate the mixture.

[Function] That is, the present invention has a molecular beam source cell having a structure that combines a molecular beam source cell for high-temperature decomposition gas that decomposes metal hydride gas and a molecular beam source cell for low-temperature decomposition gas that decomposes organometallic gas. Then, the organometallic gas is decomposed into metal molecules and methyl or ethyl groups in the cell, and then this methyl or ethyl group is reacted with the metal molecules decomposed from the metal hydride gas, and the metal compound is emitted. . This makes it difficult for carbon to be liberated on the substrate, making it possible to reduce the amount of carbon mixed in.

In addition, it has been experimentally proven in the literature that methyl groups or ethyl groups react easily with As, and
ese Journal of Applied Ph.
ysics 26(3)+1987, pp419-4
It is described in 22.

[Example] An embodiment will be described in detail below with reference to one drawing.

FIG. 1 shows a cross-sectional view of a molecular beam source cell according to the present invention, in which 20 is a main gas introduction pipe, 21 is a sub-gas introduction pipe, and 22 is a sectional view of a molecular beam source cell according to the present invention.
23 is a heater made of Ta, 23 is a vacuum flange, 24 is a heat shielding plate, 25 is a PBN plate, C is a hot trough king part, A is a preheating part, and B is a low temperature heating part.

The gas inlet 26 of the gas inlet pipe 20, 21, which is close to the raw material gas source, is composed of a thin quartz tube with a diameter of 174 inches.The gas inlet pipe is expanded to a diameter of about 1 inch in the preheating section A, and a portion of that pipe diameter is A thermal graphing section C9 and a low temperature heating section B are provided. Note that the first heating zone means the preheating section A and the thermal clubbing section C, and the second heating zone means the low temperature heating section B.

The heater 22 is divided into three parts: a preheating section A, a thermal racking section C, and a low temperature heating section B.
The PBN board has a plurality of discs arranged at regular intervals (approximately 10 cranes), each disc has holes in a zigzag pattern, and the material gas hits the discs efficiently. It is well decomposed and the molecules are emitted from the tip 27 through the pores. Further, the heat shield plate 24 is made of Ta (metal) and PBN (insulator), and is intended for heat retention. The length of the entire molecular beam source cell is 30-40 cn.

Using such a molecular beam source cell, arsine (AsHa
) and triethyl gallium (TEG) are thermally decomposed and radiated.
00℃, temperature of thermal racking part C is 800~900℃
, the temperature of the low-temperature heating section B is set to about 400 to 500°C.

Then, the AsH3 gas flowing in from the gas inlet of the main gas introduction pipe 20 is heated in the preheating section A and enters the thermal cranking section C, where it is decomposed into As and hydrogen, and is decomposed into low temperature heating section B. to go into. In the low-temperature heating section B, the TEG gas flowing in from the gas inlet of the auxiliary gas introduction pipe 21 is decomposed into Ga and ethyl groups, and the ethyl groups react with As to become triethyl arsenic, which is emitted. That is, As molecules, Ga molecules, ethyl groups (unreacted), and triethyl arsenic are emitted from this molecular beam source cell, but triethyl arsenic does not liberate much carbon on the substrate, and therefore does not contain carbon impurities. Promotes growth of a highly pure crystal growth layer with low concentration.

FIG. 2 shows an example of a gas source molecular beam crystal growth apparatus according to the present invention equipped with the molecular beam source cell shown in FIG.
The same parts as in FIG. 3 are given the same symbols. The other 51.52 is a molecular beam source cell that is a feature of the present invention, 53
．． 54 indicates a conventional partial source cell.

Using the gas source molecular beam crystal growth apparatus shown in FIG. 2, 51 is a cell into which AsH3 and TEG are introduced, 53 is a cell into which only AsH3 is introduced, and 54 is a cell into which only TEG is introduced. A GaAs substrate is heated to 600° C. in a crystal growth chamber at about -s Torr, and a GaAs layer is grown using a conventional molecular beam source cell 53, 54, and a molecular beam source cell 51 according to the present invention is used. GaAs
Grew layers. The carrier concentration was investigated by Hall measurements of the GaAs layer of the substrate sample, and the results showed that the impurity concentration per unit volume could be reduced by one to two orders of magnitude by using the molecular beam source cell according to the present invention. . Therefore,
A crystal growth apparatus equipped with a molecular beam source cell according to the present invention includes:
It is effective in forming a highly pure crystal growth layer.

The above was explained using an example in which AsH3 and TEG were thermally decomposed, and PH3 (phosphine) was used as the group ①.

It is also possible to use TMG, TEA, TMA, TEL, etc. as the group (2), and it goes without saying that a highly pure AlGaAs layer can also be grown.

[Effects of the Invention] As is clear from the above description, according to the gas source molecular beam crystal growth apparatus provided with the molecular beam source cell according to the present invention, a highly pure crystal growth layer can be obtained, and it is possible to improve the performance of semiconductor devices. This significantly contributes to improved performance.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a molecular beam source cell according to the present invention, FIG. 2 is a diagram showing a gas source molecular beam crystal growth apparatus according to the present invention, and FIG. 3 is a diagram showing a conventional gas source molecular beam crystal growth apparatus. Figures 4(a) and 4(b) are cross-sectional views of conventional molecular beam source cells. In the figure, A is a preheating section, B is a low temperature heating section, C is a thermal cracking section, 1 is a crystal growth chamber, 2 is a substrate, 3 is a substrate holder, 4 is a heater, 5 is a molecular beam source cell, 6 is a valve , 7 is a liquid nitrogen shroud, 8 is a gate valve, 20 is a main gas introduction pipe, 21 is a sub-gas introduction pipe, 22 is a Ta heater, 23 is a vacuum flange, 24 is a heat shield plate,
25 is a PBN plate, 26 is a gas inlet, 27 is a tip of a gas introduction tube, 51 and 52 are molecular beam source cells according to the present invention, and 53 and 54 are conventional molecular beam source cells.

Claims (1)

[Claims] A secondary gas introduction pipe is connected to the main gas introduction pipe of the molecular beam source cell, the main gas introduction pipe is divided into a plurality of heating zones, and a first heating zone is arranged closer to the raw material gas source than the connection part. A second heating zone placed closer to the growth substrate than the connection part is heated to a high temperature, and a metal hydride gas is introduced from the main gas introduction pipe, and an organometallic gas is introduced into the subgas. 1. A gas source molecular beam crystal growth apparatus comprising a molecular beam source cell configured to introduce a plurality of gases through an introduction tube, mix and react a plurality of gases having different decomposition temperatures, and emit radiation.