JPH033321A - Vapor growth method for iii-v compound semiconductor - Google Patents

Abstract

PURPOSE:To dispense with a pretreatment process for semiconductor substrates by a method wherein the substrates are heated in a superhigh vacuum container and subsequently, the substrates are placed on a substrate heating stand in a reaction container to perform a crystal growth. CONSTITUTION:Semiconductor substrates 13 are internalized in a superhigh vacuum container 5 and subsequently, the interior of the container 5 is evacuated and a heating is performed on the substrates 13 in a superhigh vacuum of at least 5X10<-9>Torr. Subsequently, the above substrates 13 are transferred from the interior of the container 5 to the interior of a reaction container 14 for vapor growth use and are placed on a semiconductor substrate heating stand 11 installed in the container 14. Moreover, raw gas for III-V compound semiconductor vapor growth use is introduced in the container 14 and a compound semiconductor crystal is grown on the above substrates 13. For example, the above raw gas is constituted of at least one kind of an organic compound consisting of a group III element and at least one kind of a hydrogen compound or an organic compound consisting of a group V element.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides m-
Vapor phase growth method of V group compound semiconductor (Metal Orga)
nic Chemical Vapor Deposit
tion method (hereinafter abbreviated as MOCVD method), and particularly relates to a vapor phase growth method of m-v group compound semiconductors that does not require a pretreatment step for a semiconductor substrate.

(Prior art) The MOCVD method is a method of growing crystals on a substrate by thermally decomposing and reacting raw material gases such as organic metal compounds and metal hydride compounds, and is easier to mass produce than the single molecular beam crystal growth method. It has attracted attention as an epitaxial crystal growth method, and has been used to grow single-layer films such as gallium arsenide (GaAs), indium phosphide (InP), and GaAs/aluminum gallium arsenide (AI).
GaAs), InP/indium gallium arsenic (I
It is used to grow crystals with different types of semiconductor junctions (peterojunctions) such as nGaAs).

These materials are used as crystals for devices such as field effect transistors (FETs) and high electron mobility transistors (HEMTs). Recently, in order to improve mass productivity, a method of growing crystals on multiple semiconductor substrates simultaneously has been developed.
No. 171 reported that seven HEMT crystals were grown simultaneously and the uniformity was good.

Normally, when performing crystal growth, the steps are: pretreatment of a semiconductor substrate, placement of the substrate on a heating table, gas replacement in the reaction tube, heating of the substrate, crystal growth, cooling of the substrate, and removal of the crystal growth wafer. proceed. Among these processes, the semiconductor substrate pretreatment process is a process used to remove a naturally deposited film formed on the surface of a substrate whose at least one side is mirror-finished. For this, use a destructive etching solution (11□So4/H, 02/H
, O mixed solution). In order to perform the simultaneous growth of multiple substrates as described above, it becomes necessary to process multiple substrates simultaneously in the substrate pretreatment step. An increase in the number of substrates in the pretreatment process results in an increase in processing time, which lengthens the entire vapor phase growth process, which is a disadvantage in improving mass productivity. In order to improve this drawback, it is desirable to omit the substrate pretreatment step and perform crystal growth.

Therefore, the present inventor proposed an MOC as shown in the schematic diagram of FIG.
GaAs crystals for FETs were grown using a VD apparatus, and it was investigated whether it was possible to omit substrate pretreatment before crystal growth.

Crystal growth was performed according to the following procedure. First, a semi-insulating GaAs substrate 101 whose one side is mirror-finished is placed on a heating table 103 in a reaction vessel 102 without any pretreatment process. Next, hydrogen as a carrier gas is introduced into the gas inlet 104.
Ga on the heating table with the RF coil 105 while introducing from a.
The As substrate is heated to 700°C, and then (CI+-) 3 Ga (trimethylgallium: abbreviated as TMG), which is the raw material for Ga, and arsine gas (AsH,), which is the raw material for As, are poured into the gas inlet to form a buffer layer. A GaAs layer with no impurities added called ``GaAs'' is formed to a thickness of 1 μI, followed by hydrogen sulfide gas (Ua) doped with n-type impurities.
S) is poured in a predetermined amount, and the electron concentration called the active layer is I.
X LO17c shoe-3 with a thickness of 0.3 μ■ n-Ga
A GaAs crystal for FET was grown by forming an As layer.

Note that 104b in the figure is a gas exhaust port.

A Schottky electrode was formed on the surface of this wafer, and the depth distribution of electron concentration was measured. FIG. 4 shows the depth distribution of electron concentration in the wafer, and the arrow in the figure represents the boundary between the substrate and the buffer layer. As can be seen from the figure, it was found that a spike-shaped n-type layer existed at the boundary between the substrate and the buffer layer. Such crystals cannot be used as GaAs crystals for FETs because they become current paths under the active layer. Therefore, in order to investigate the cause of the generation of the high electron concentration layer, we conducted an experiment in which the time from pretreatment of the GaAs substrate to its introduction into the reaction vessel of the MOCVD equipment was varied. It was found that the longer it took to enter the reaction vessel of the device, the more frequently it occurred.

Based on the above results, the present inventor came to the conclusion that the oxide film formed on the surface of the GaAs substrate is involved in the generation of the above-mentioned high electron concentration layer, and came up with the present invention.

(Problems to be Solved by the Invention) In the above conventional technology, it is necessary to perform pretreatment on the semiconductor substrate immediately before crystal growth, and as the time elapsed between this pretreatment and crystal growth increases, There is a serious problem in that a high electron concentration layer is generated at the boundary between the substrate and the crystal growth layer, making it unsuitable as a substrate for FET. Further, there are also problems such as difficulty in keeping up with improvements in efficiency of the crystal growth process.

In view of the above-mentioned conventional problems, the present invention improves the vapor phase growth method for m-v group compound semiconductors.

[Structure of the invention]

(Means for Solving the Problems) The m-v group compound semiconductor vapor phase growth method according to the present invention includes a step of placing a semiconductor substrate in an ultra-high vacuum container, and a step in which the semiconductor substrate is placed in the ultra-high vacuum container. Exhaust at least 5 x
A step of heating the semiconductor substrate in an ultra-high vacuum of 10-' Torr, and following this step, the semiconductor substrate is transferred from the ultra-high vacuum container to a reaction container for vapor phase growth and placed therein. a step of placing the semiconductor substrate on a heating table, and a step of introducing a raw material gas for vapor phase growth of an m-v group compound semiconductor into the reaction vessel to grow crystals of the compound semiconductor on the semiconductor substrate. It is characterized in that the raw material gas is composed of at least one type of organic compound consisting of a group Ⅰ element and at least one type of hydrogen compound or organic compound consisting of a group Ⅰ element.

(Function) In the ■-v group compound semiconductor vapor phase growth method according to the present invention, M
When growing an m-v group compound semiconductor crystal on a semiconductor substrate using the OCVD method, the substrate is
' To remove the oxide film formed on the semiconductor substrate by heating it in an ultra-high vacuum chamber at Torr or less, and then place it on a substrate heating table in the reaction chamber to grow the crystals of an m-v group compound semiconductor. This makes it possible to prevent the formation of a high electron concentration layer at the boundary between the substrate and the crystal growth layer.

(Example) Hereinafter, as an example of the present invention, a case in which a GaAs crystal layer for a field effect transistor (FET) is grown will be described with reference to FIG.

The procedure for growing a crystal using the vapor phase growth method according to the present invention using the apparatus shown in FIG. 1 is as follows.

First, semi-insulating GaA with a mirror finish on one side.
A s-substrate is prepared and inserted into the preliminary chamber 2 by opening the preliminary chamber door 1 for preventing air from entering the ultra-high vacuum container or the reaction vessel. Then, the door is closed, and in order to reduce the burden on the second vacuum evacuation device 6 that evacuates the inside of the ultra-high vacuum container, the first vacuum evacuation device 3 is used to
-' Torr or less Next, open the first gate valve 4, and transport the vessel to an ultra-high vacuum container 5 which is normally maintained at a vacuum level of 10-' Torr or less. Close 4 again. Then, the inside of the container whose degree of vacuum has increased to nearly 10-'Torr by opening and closing the first gate valve is evacuated by the second evacuation device 6, and the vacuum level is evacuated to 10-10 Torr.
When the temperature becomes less than Torr, the heater 7 closes the substrate holder 8.
The GaAs substrate placed in the chamber is heated to 550°C. It was heated for the specified time. After that, turn off the power to the heater and cool it down to 300℃.
When the GaA
s Transport the substrate to the preliminary chamber and close the gate valve. After this.

Nitrogen gas is introduced into the preparatory chamber 2 from the gas inlet 9 to return the pressure to atmospheric pressure, making it the same pressure as inside the reaction vessel.

At the same time, the heating table 11 for holding the GaAs substrate is lowered to the transfer chamber 12, and the GaAs substrate in the preliminary chamber is transferred to the heating table 11.
After that, the second gate valve 10 is opened and the GaAs substrate 13 is placed on the heating table 11. In the case of this example, in order to see the effect of removing the oxide film on the substrate surface, the time after the pretreatment was completed was 30 minutes.
Five substrates were placed for 2 hours, 1 day, 2 days, and 7 days. Next, the second gate valve 1O is closed, the heating table 11 is lifted to a predetermined position in the reaction vessel 14, and hydrogen, which is a carrier gas, is flowed into the vessel from the raw material gas inlet 15 while being applied to the RF coil 16. Then, trimethylgallium ((
C113)a Ga: Abbreviation TMG) and arsine gas (
AsH3) was similarly flowed into the chamber to form a 1 μm buffer layer on the GaAs substrate 13, and then hydrogen sulfide gas, which is an n-type impurity, was also flowed into the chamber to reduce the electron concentration to I.
A wafer for FET was fabricated by forming an active layer with a thickness of 0.3 μm at a thickness of 1017 cm+−′.

The GaAs substrate (epitaxial wafer: abbreviated as epi-wafer) after crystal growth was transported from the reaction vessel 14 to the preliminary chamber 2 via the transport chamber 12 in the reverse order of the above-described procedure, and the door 1 was opened to take it out.

A Schottky electrode was formed on this epitaxial wafer, and the distribution of electron concentration in the depth direction was measured in the same manner as described in the conventional example.

As a result of a series of measurements, as shown by the arrow in Figure 2, the relationship between the substrate and the buffer layer was observed for all epitaxial wafers that were grown at the same time, regardless of the time from the end of the substrate pretreatment until the substrate was placed on the heating table. The abnormal increase in electron concentration at the boundary is eliminated,
It was found that crystals of good quality for use in FETs were produced, and the effects of the present invention became clear.

Furthermore, as a result of experiments in which the degree of vacuum required to remove the oxide film in the above step was varied from IX to -' to IX 10-" Torr, it was found to be 5 X 10" Torr.
It was found that the following is sufficient.

〔Effect of the invention〕

As described above, the method of the present invention eliminates the need for pre-treatment of semiconductor substrates, and is especially applicable to vapor phase growth using a mass-produced MOCVD apparatus that can grow a large number of substrates at the same time. A suitable growth method can be provided.

Although only the growth of GaAs crystal is described in this example, the material is not limited to this, and may be an m-v group compound other than GaAs such as InP, which easily forms a natural oxide on the substrate surface. Good for use in semiconductor crystal growth.

Further, although the temperature of the semiconductor substrate in the ultra-high vacuum container was set at 550° C. in the embodiment, the optimum value varies depending on the material used, so for example, in the case of InP, it may be selected as appropriate, such as 450° C.

[Brief Description of the Drawings] Fig. 1 is a sectional view schematically showing the main parts of the ■-■ group compound semiconductor crystal growth apparatus according to the present invention, and Fig. 2 is a cross-sectional view showing the main parts of the
Figure 3 is a diagram showing the depth distribution of electron concentration in a vapor phase epitaxy wafer for ET; Figure 3 is a cross-sectional view schematically showing the main parts of the conventional ■-V group compound semiconductor crystal growth apparatus; Figure 4; 4 is a diagram showing the depth distribution of electron concentration in the FET vapor phase grown wafer using the growth apparatus shown in FIG. 3. FIG. 3.6... Vacuum exhaust device, 5... Ultra-high vacuum container, 1
3, 101-GaAs substrate (semiconductor substrate), 14, 10
2...Reaction container.

Claims (2)

[Claims] (1) A step of placing the semiconductor substrate in an ultra-high vacuum container,
Continuing from this step, there is a step of evacuating the inside of the ultra-high vacuum container and heating the semiconductor substrate in an ultra-high vacuum of at least 5 x 10^-^9 Torr; A step of transporting from a high vacuum container to a reaction container for vapor phase growth and placing it on a semiconductor substrate heating table installed therein; A III-V compound semiconductor vapor phase growth method comprising the step of growing a crystal of the compound semiconductor on the semiconductor substrate by introducing a gas. (2) Claim 1 in which the raw material gas is composed of at least one type of organic compound consisting of a group III element and at least one type of hydrogen compound or organic compound consisting of a group V element.
III-V compound semiconductor vapor phase growth method described in .