JPH0445520A - Vapor growth method - Google Patents

Abstract

PURPOSE:To efficiently grow a thin film in a state where the speed and remaining element concentration in a concentration boundary layer are reduced in a moment and the occurrence of surface roughening is prevented by tentatively reducing the pressure in a reactive container when the raw material gas fed to the container is switched to another. CONSTITUTION:When an AlGaAs layer is formed on a GaAs layer, the AlGaAs layer is formed by successively supplying each raw material gas of trimethyl aluminum, trimethyl gallium, and arsine from each raw material container 5-7 after pressure control is made by means of a rotary pump 13 and pressure regulating valve 14 so that the growing pressure in a reactive container 1 can become 100Torr. When the raw material gases are supplied, a valve 14 is fully opened and the pressure in the container 1 is reduced to 50Torr. Since the pressure in the container 1 is reduced to 50Torr and returned to the 100Torr immediately before the next raw material is supplied in such way, the thickness of the boundary surface between both layers can be reduced to about 3Angstrom from about 16Angstrom in a several seconds of growth stopping time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a vapor phase growth method for forming a thin film on the surface of a substrate by sending a source gas.

[Prior Art] In a vapor phase growth method, a thin film is generally grown on the substrate by supplying a raw material gas together with a carrier gas to a substrate that is heated within a reaction vessel. The vapor phase growth method is classified into horizontal, vertical, chimney, etc. depending on the shape of the reaction vessel and the method of supplying raw material gas.

FIG. 1 shows an example of a horizontal vapor phase growth apparatus.

In the figure, 1 is a reaction vessel installed horizontally, 2
3 is a susceptor installed in the reaction vessel 1, 3 is a substrate supported on the susceptor 2, 4 is a heating coil that heats the substrate 3 together with the susceptor 2, and 5 to 7 are connected to the reaction vessel 1 through gas supply pipes 8. 9 to 11 are switching valves for switching the supply of raw material gas, 12 is an exhaust pipe for exhausting air from the reaction vessel 1, 13 is a rotary pump connected to the exhaust pipe 12, and 14 is a rotary pump connected to the exhaust pipe 12; A pressure control valve 15 is connected to the exhaust pipe 12, and a pressure gauge 15 is connected to the exhaust pipe 12.

In such a vapor phase growth apparatus, the substrate 3 in the reaction vessel 1 is heated by the heating coil 4, and the raw material gas is supplied into the reaction vessel 1 in this state from the raw material vessels 5 to 7 via the switching valves 9 to 11. , a semiconductor thin film is grown on the surface of the substrate 3.

Generally, a semiconductor thin film is formed of a plurality of layers having different compositions depending on its use. Therefore, there are multiple raw material containers, and the raw material gas necessary to form each layer is supplied to the switching valves 9 to 1.
1 is supplied to the reaction vessel 1.

In this case, a gas layer called a velocity and concentration boundary layer 16 exists on the surface of the susceptor 2 due to the raw material gas, as shown in FIG.
flows above. At this time, the source gas molecules diffuse through the velocity and concentration boundary layer 16 to reach the substrate 3 and form a thin film on the substrate 3.

If layers of thin films with different compositions are to be produced successively, this speed and the remaining elements in the concentration boundary layer 16 become a problem. That is, no matter how quickly the switching valves 9 to 11 are switched to supply a different type of raw material gas into the reaction vessel 1, the remaining raw material molecules in the velocity and concentration boundary layer 16 are not switched immediately. Normally, the switching takes 10 seconds to several tens of seconds. During this time, a thin film containing a mixture of residual elements and newly supplied elements is formed. In other words, the interface between the two layers becomes unclear, with the two elements intermingling.

This phenomenon poses a problem in terms of lifespan and reliability, especially when manufacturing light emitting/light receiving elements.

To prevent this, conventional methods have been used to stop the supply of raw material gas for several minutes when changing the composition of the thin film layer.

[Problems to be Solved by the Invention] However, with this method of stopping the supply of raw material gas, there is a problem that when a highly volatile raw material is included, the element dissociates and the surface of the thin film becomes rough. Ta. Also,
This method has the problem of poor work efficiency because it requires a long rest time each time the source gas is switched.

An object of the present invention is to provide a vapor phase growth method that does not cause surface roughness and can efficiently grow a thin film.

[Means for Solving the Problems] To explain in detail the present invention for achieving the above-mentioned object, the present invention supplies a raw material gas into a reaction vessel to a substrate supported by a susceptor within the reaction vessel. The vapor phase growth method for forming a thin film is characterized in that when switching the type of the source gas to be sent into the reaction vessel, the pressure inside the reaction vessel is once reduced, and then the heated source gas is sent.

[Function] When switching the raw material gas to be sent into the reaction vessel, once the pressure inside the reaction vessel is reduced, the velocity and concentration boundary layer are sensitive to the gas flow conditions, and therefore the velocity and concentration boundary layer are The thickness of the material decreases dramatically.

According to this method, the velocity and concentration of residual elements in the concentration boundary layer can be instantly reduced.

Thereafter, by supplying the next raw material gas into the reaction vessel, the interface layer of the thin film can be made thinner.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to FIGS. 1 and 2.

The present inventors have focused on the fact that the steepness of the interface of a thin film depends on the velocity and the amount of residual elements in the concentration boundary layer, and have been studying methods to reduce the amount.

As a result, it was found that when the pressure inside the reaction vessel 1 is reduced, the velocity and the thickness of the concentration boundary layer 16 are drastically reduced. According to this method, the residual element concentration in the velocity and concentration boundary layer 16 can be instantly reduced.

Next, a comparison of the thickness of the thin film interface between the conventional method and the method of the present invention will be described. For example, when manufacturing a GaAs-based thin film, trimethylaluminum (TMA) is supplied from raw material container 5, trimethyl gallium (TMG) is supplied from raw material container 6, and arsine (A) is supplied from raw material container 7.
s H3).

Here, when forming the AJ2GaAS layer on the GaAs layer, in the conventional method, the growth pressure in the reaction vessel 1 is 100T.
The pressure is adjusted using the rotary pump 13 and the pressure control valve 14 so that the flow rate is 10cc/min and 20cc/min, respectively, by simply switching the switching valves 9-11 to feed each raw material gas from the raw material containers 5-7.

It was supplied at 100 cc/min to form an AβGaAs layer.

In this case, in the conventional method, the GaAs layer and the AJ2GaAs
The thickness of the interface with the layer was approximately 16 mm.

In contrast, in the method of the present invention, immediately before supplying the next raw material gas by switching the switching valve, the pressure control valve 14
was fully opened, the pressure inside the reaction vessel 1 was reduced to 50 Torr, and then returned to 100 Torr before the next raw material gas was supplied.

When the A, ffGaAs layer was formed in this manner, the thickness of the interface between the GaAs layer and the A, gGaAs layer was about 3 layers. However, in this case, arsine gas was kept flowing to prevent arsine, which has a high dissociation pressure, from scattering. Further, the growth stop time for changing the pressure was about several seconds.

Note that the method of the present invention can be similarly applied to methods other than the horizontal method.

[Effects of the Invention] As explained above, in the vapor phase growth method according to the present invention, when switching the raw material gas supplied to the reaction vessel, the pressure inside the reaction vessel is temporarily reduced, so that the speed and the concentration boundary layer are reduced. The thickness can be drastically reduced, and the residual element concentration in the velocity and concentration boundary layer can be instantly reduced. Therefore, according to the present invention, the interface of the thin film can be controlled with sufficient steepness using a simple method. In particular, the method of the present invention has the advantage that sufficient steepness of the thin film interface can be obtained without reducing work efficiency, since the decompression time may be short.

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view showing a schematic configuration of an example of an apparatus for carrying out the vapor phase growth method according to the present invention, and FIG. 2 is a sectional view of the inside of a reaction vessel. 1... Reaction container, 2... Susceptor, 3... Substrate,
4... Heating coil, 5-7... Raw material container, 8...
Gas supply pipe, 9-11...Switching valve, 12...Exhaust pipe, 13...Rotary pump, 14...Pressure control valve, 15...Pressure gauge, 16...Speed and concentration boundary layer.

Claims (1)

[Claims] In a vapor phase growth method that sends a raw material gas into a reaction vessel to form a thin film on a substrate supported by a susceptor within the reaction vessel, when switching the type of the raw material gas sent into the reaction vessel, the reaction A vapor phase growth method characterized by first reducing the pressure inside the container and then sending the next raw material gas.