JPH0580136B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a vapor phase epitaxial growth technique for compound semiconductors, and in particular to an effective vapor phase epitaxial growth technique for gallium-silicon compound semiconductor wafers by the chloride method. Regarding technology.

[Prior Art] As a method for vapor phase growth of a GaAs (gallium arsenide) layer on a semi-insulating compound semiconductor substrate, there is a chloride method using an apparatus as shown in FIG.

That is, a raw material boat 2 containing Ga (gallium) as a raw material is placed on the starting end side of the reaction tube 1,
Hydrogen gas is appropriately introduced into the reaction tube 1 through the gas introduction tube 3, and heated in the electric furnace 4 around the outer periphery of the reaction tube 1 to raise the temperature around the boat to around 800°C.
AsCl ₃ (arsenic chloride) is supplied from the gas introduction pipe 3 using H ₂ (hydrogen) as a carrier gas. Then, AsCl ₃ decomposes in the high temperature area around the boat 2, and As dissolves into the molten Ga inside the boat 2. However, Ga
When the As dissolved in the reactor becomes saturated, the heating in the electric furnace 4 is temporarily stopped, and the pre-treated substrate 5 is placed on the support stand 6 at the end of the reaction tube 1, and then the electricity is heated again while flowing H ₂ gas. After heating the furnace 4 and controlling the temperature distribution as shown by the symbol A in FIG. 3, AsCl ₃ is introduced through the gas introduction pipe 3 using H ₂ as a carrier gas. Then, AsCl ₃ in the high temperature part
is decomposed, and the generated HCl reacts with Ga in the boat 2 to form GaCl, which is transported to the downstream side where the substrate 5 is placed. On the other hand, the decomposed and generated As is the raw material Ga
Since it is already saturated with As, it flows toward the low-temperature substrate without being dissolved in Ga, and here
A GaAs layer is grown on the substrate 5 by reacting with GaCl.

However, in the above method,
For example, an n-type impurity concentration of approximately 3×10 ¹⁷ cm ^-3 is applied to a semi-insulating substrate crystal used in field effect transistors.
When growing a GaAs layer, the region near the interface between the semi-insulating substrate and the n-type growth layer, that is, the growth region immediately after the start of growth, has a carrier density distribution with a gentle gradient as shown by the broken line a in Figure 4. Therefore, a growth layer with a steep carrier density distribution cannot be obtained. The reason for this is that part of the Ga inside the boat, which should originally be covered with a GaAs film, becomes liquid during growth. That is, in this case, the electric furnace 4 is cooled each time the substrate 5 is installed and taken out, and then heated again during growth to perform vapor phase growth by predetermined operations. Part of the surface of the raw material becomes liquid and Ga is exposed, and for several minutes after the start of growth, As should be carried toward the substrate.
This is thought to be due to dissolving into Ga, changing the ratio of Ga and As near the substrate, and changing the carrier density in the growth layer.

Therefore, before performing the vapor phase growth, as shown by the symbol B in FIG. Place the substrate in the reaction tube and achieve the temperature distribution as shown by symbol A in Figure 3.
A method using vapor phase growth was proposed (Japanese Patent Application Laid-open No. 174626/1983).

[Problems to be Solved by the Invention] However, in the above-mentioned method of covering the surface of the raw material with a GaAs film, the GaAs formed during normal growth is
The film becomes thicker than the GaAs substrate, and the amount of Ga and As transported to the GaAs substrate increases. Therefore, GaAs films are thick at the beginning of growth, and over time the thickness increases to match the normal growth temperature. On the other hand, the transport amount (growth rate) of Ga and As increases as the GaAs film becomes thicker, so if a raw material with a prearsenization temperature approximately 10°C higher than normal growth is used for normal growth, the growth rate will decrease at the early stage of growth. is early and slow in the second half. As a result, although a grown layer with a steep carrier density distribution was obtained, it was difficult to control the thickness of the grown layer and the carrier density distribution, and the reproducibility of the grown layer was poor.

In addition, in all of the above conventional methods, the raw material Ga is
After saturating with As, the substrate was cooled, placed in the reaction tube, and then heated again, which resulted in the inconvenience of slow heating and cooling, which reduced productivity. .

The purpose of this invention is to develop a GaAs vapor phase growth method that can vapor phase grow a GaAs layer with a steep carrier density distribution near the interface with a substrate with good reproducibility and improve its productivity. It is about providing.

[Means for Solving the Problems] In order to achieve the above object, the present invention connects two gas introduction pipes to the reaction tube, one of which faces the raw material boat side, and the other of which faces the substrate side. , place the substrate together with a boat filled with raw materials in a reaction tube in advance, heat the reaction tube in an electric furnace to achieve the same temperature distribution as during normal growth, and then inject gas into the substrate side from one gas introduction tube. While the etching gas is flowing, AsCl ₃ is introduced from the other gas introduction pipe to saturate the Ga in the raw material boat with As. Then, the supply of etching gas is stopped and AsCl ₃ is introduced into the raw material boat using H ₂ as a carrier gas. GaAs is poured onto the substrate.
Made the layer grow.

[Operation] According to the above-described means, the raw material before starting vapor phase growth
Since the Ga arsenization process is performed under the same temperature distribution as during growth, the GaAs film formed on the surface of the raw material Ga is kept constant during growth, and the GaAs layer grows on the substrate surface during the arsenization process. Since this is prevented, a GaAs layer with a steep carrier density distribution near the interface with the substrate can be grown in a vapor phase with good reproducibility.

In addition, the substrate was placed in the reaction tube in advance and the raw material Ga
Since the arsenizing treatment is performed and subsequent vapor phase growth is performed with the same temperature distribution, there is no need to cool the reaction tube once after the arsenizing treatment and then heat it again, so productivity can be improved.

[Example] FIG. 1 shows an example of a vapor phase growth apparatus used in the vapor phase growth method according to the present invention.

That is, this device consists of a quartz reaction tube 1 having a cylindrical shape with both ends closed, and an electric furnace 4 that heats the reaction tube 1 from the outside. It is configured so that the distribution can be controlled.

Inside the reaction tube 1, there is provided a boat 2 on the upstream side (on the left side in the figure) for storing raw materials, and a support table 6 on the downstream side for placing the substrate to be subjected to vapor phase growth. ing. Furthermore, a first gas introduction pipe 3a is connected to the starting end of the reaction tube 1, and a second gas introduction pipe 3b is connected to the starting end of the reaction tube 1 to bypass the raw material boat 2 and supply gas to the support table 6 side. has been done.

Further, a mass flow controller 8a is connected to the other end of the gas introduction pipe 3a via a bubbling device 7a, and a mass flow controller 8b is connected to the other end of the gas introduction pipe 3b via a bubbling device 7b. . In the middle of the first gas supply path 9a, switching valves 10a and 10b are provided.
Further, a switching valve 1 is provided in the middle of the second gas supply path 9b.
0c, 10d, and 10e are provided. Of these, a third mass flow controller 8c is connected to the switching valve 10e.

On the other hand, an exhaust nozzle 11 is provided at the terminal end of the reaction tube 1.

Next, the GaAs of the present invention using the above vapor phase growth deposition method will be described.
An example of a vapor phase growth method will be described.

First, a Ga lump as a raw material is placed in the raw material boat 2.
After the GaAs substrate 5 is placed on the support stand 6, it is heated in the electric furnace 4 so that the inside of the reaction tube 1 has the same temperature distribution as during normal growth as shown by reference numeral A in FIG. At this time, mass flow controller 8
The switching valves 10a to 10e are adjusted so that only _H2 gas flows into the reaction tube 1 by means of a and 8b.
After a predetermined temperature distribution is achieved, only H ₂ gas is continued to flow and this state is maintained for one hour.

After that, changeover valves 10a and 10b are switched, and H ₂
Put gas into the bubbling device 7a and convert AsCl ₃ to H ₂
As is contained in gas and introduced into the reaction tube 1 through the gas introduction pipe 3a to dissolve As in the Ga on the raw material boat. Then, As becomes saturated and completely
Arsenidation treatment is performed until the Ga surface is covered with a GaAs film. Mass flow controller 8 during this arsenization process
The H ₂ gas from b is sent to the bubbler 7b to contain AsCl ₃ , and then passed from the gas supply path 9b to the gas introduction pipe 3.
b, bypassing the boat 2 and introducing directly upstream of the substrate 5. Then, AsCl ₃ decomposes and H ₂
HCl gas is generated by reacting with the gas, and the substrate 5 is gas-etched. This gas etching process
The process continues until the Ga surface is completely covered with the GaAs film, thereby preventing the GaAs layer from growing on the substrate 5.

After that, AsCl ₃ continues from the gas supply path 9a.
and operate the switching valve 10e to stop the introduction of AsCl ₃ from the gas supply path 9b, and replace it with Si.
A gas containing a dopant such as (silicon) is supplied from the mass flow controller 8c to the gas introduction pipe 3b, and an epitaxial layer is grown on the substrate 5. As a result, as shown by the solid line b in Figure 4, the carrier density immediately after the start of growth, that is, the carrier density in the area near the interface between the substrate and the growth layer, has a steep slope, and the rest has a flat carrier density distribution. A grown layer can be obtained with good reproducibility.

The above example is just an example, and the structure is such that a high resistance buffer layer (a GaAs layer containing no dopant) is formed on a semi-insulating substrate, such as a vapor phase growth layer for a field effect transistor. ), and on top of that, n to become the active layer.
It goes without saying that the present invention can be applied to the case where a mold layer is grown, and similar effects can be obtained.

In addition, in the above embodiment, vapor phase growth was explained in which the surface of Ga on the raw material boat 2 was not covered with GaAs. The above method can also be applied to the second and subsequent growths in which vapor phase growth is performed on the substrate.

[Effect of the invention] As explained above, in this invention, two gas introduction pipes are connected to the reaction tube, one on the raw material boat side,
On the other hand, with the open end facing the substrate side, the substrate is placed together with a boat containing raw materials in the reaction tube in advance, and the reaction tube is heated by the electric furnace 4 to achieve the same temperature distribution as during normal growth. Then, while flowing etching gas from one gas introduction pipe toward the substrate side, AsCl ₃ is introduced from the other gas introduction pipe to saturate the Ga in the raw material boat with As, and then the supply of etching gas is stopped. As a result, the GaAs layer is grown on the substrate by flowing AsCl ₃ into the raw material boat using H ₂ as a carrier gas, so that the GaAs film formed on the surface of the raw material Ga remains constant during growth. , it is possible to prevent the growth of a GaAs layer on the substrate surface during arsenization treatment, and to vapor phase grow a GaAs layer with a steep carrier density distribution near the interface with the substrate with good reproducibility.

In addition, the substrate was placed in the reaction tube in advance and the raw material Ga
Since the arsenizing treatment is performed and subsequent vapor phase growth is performed with the same temperature distribution, there is no need to cool the reaction tube once after the arsenizing treatment and then heat it again, which has the effect of improving productivity. .

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional front view showing an example of a vapor phase growth apparatus used in the method of the present invention, and FIG. 2 is an example of a general vapor growth apparatus used in a conventional vapor growth method. A cross-sectional front view, FIG. 3 is a graph showing the temperature distribution in the reaction tube during vapor phase growth by the conventional method and the method of the present invention, and FIG. 4 is a distribution of carrier density in the vapor phase growth layer by the conventional method and the method of the present invention. FIG. 1... Reaction tube, 2... Raw material boat, 3a, 3b
...Gas introduction pipe, 4...Electric furnace, 5...Substrate, 6
...Support stand, 7a, 7b...Bubbling device, 8
a~8c...Mass flow controller, 10a~
10e...Switching valve.

Claims (1)

[Claims] 1. Arsenic chloride is introduced into a reaction tube using hydrogen gas as a carrier gas, and after reacting with gallium on the raw material port in the reaction tube, an epitaxial layer is grown in a vapor phase on the surface of a substrate placed on the downstream side. First, while maintaining a predetermined temperature distribution in the reaction tube in advance, etching gas is supplied to the substrate side, and while etching the substrate surface, arsenic is dissolved in the gallium on the raw material boat until it is saturated. A method for vapor phase growth of a compound semiconductor, characterized in that the supply of etching gas is stopped and arsenic chloride is supplied to a reaction tube with the same temperature distribution to grow a gallium/arsenic layer on the surface of a substrate.