JP2520617B2 - Semiconductor crystal growth method and apparatus for implementing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In the present invention, a compound semiconductor crystal substrate is set in a substrate pretreatment chamber in a semiconductor crystal growth apparatus capable of carrying out a molecular beam epitaxial growth method, and the inside of the substrate pretreatment chamber is elevated. It is evacuated to a vacuum, and a predetermined amount of oxygen is supplied into the substrate pretreatment chamber to maintain the oxygen partial pressure that is sufficiently low compared to the atmospheric pressure while decomposing in the material forming the compound semiconductor crystal substrate. An oxide film is formed by heating at a temperature that does not exceed the temperature at which the easily detachable substance is desorbed, and the compound semiconductor crystal substrate is transferred to a growth chamber while maintaining a high vacuum to remove the molecular beam of the easily detachable substance. A method of performing molecular beam epitaxial growth of a target semiconductor crystal layer by heating while irradiating to remove the oxide film and maintaining the compound semiconductor crystal substrate at a required temperature, and such a method are implemented. And a carbon semiconductor contaminant can be sufficiently removed from the surface of the compound semiconductor substrate. Therefore, even if the buffer layer is thinned to enhance the throughput, defects are not formed on the buffer layer. It is possible to grow a good quality crystal with less.

[Industrial applications]

The present invention relates to a semiconductor crystal growth method that can be applied to a semiconductor device formed on a compound semiconductor substrate via a buffer layer to obtain a favorable result, and an apparatus for implementing the method.

[Conventional technology]

Generally, when manufacturing a compound semiconductor device, a semiconductor layer is grown on a compound semiconductor substrate via a buffer layer,
The element is built in the semiconductor layer.

In recent years, in order to grow such a compound semiconductor crystal layer, molecular beam epitaxy has been used.
taxy: MBE) method is often applied.

In the apparatus for carrying out this MBE method, a substrate preparation chamber is provided as a front chamber of the growth chamber, in which a compound semiconductor substrate is, for example, GaAs before growing an actual crystal layer, By heating to about 300 to 400 [° C.], the moisture adhering to the surface of the GaAs substrate is removed in the atmosphere.

[Problems to be solved by the invention]

However, heating by the above-mentioned temperature cannot remove molecules such as hydrocarbons containing carbon. When the GaAs substrate is heated at a high temperature of 600 ° C. or higher in a high vacuum, As having a high vapor pressure is desorbed and the surface is roughened.

When a semiconductor crystal layer is epitaxially grown on a GaAs substrate surface with carbon atoms and the like attached thereto, the carbon atom acts as an acceptor to form an interface level between the GaAs substrate and the epitaxially grown semiconductor crystal layer. Therefore, in order to avoid the influence, it is necessary to form a thick buffer layer, and it takes a lot of time, so the through put cannot be increased.

In order to solve the above problems, the present inventor has conducted a thermal etching substrate pretreatment method (if necessary, "J. Saito et al.
l., Jpn.J.Appl.Phys., vol.25, No.8, Aug.1986, pp1216-1
220 ”).

According to this technique, the interface state between the substrate and the epitaxially grown semiconductor crystal layer can be reduced and the buffer layer can be thinned. However, when carrying out this, for example, in the case of a GaAs substrate, it was necessary to carefully control so that As would not be desorbed to cause surface roughness.

The present invention removes carbonaceous substances such as hydrocarbons and carbon dioxide adhering to the substrate surface by heat treatment, and
Even if the buffer layer is thin to enhance the through put,
In addition, a good quality semiconductor crystal layer with few surface defects can be grown, and a semiconductor device with good characteristics can be easily manufactured without requiring difficult control of surface roughness.

[Means for solving problems]

An embodiment of the present invention will be described with reference to FIG. 1, which is a drawing for explaining the embodiment.

In the present invention, the substrate pretreatment chamber 3 in the semiconductor crystal growth apparatus capable of carrying out the molecular beam epitaxial growth method is used.
Set the GaAs semiconductor crystal substrate in the substrate pretreatment chamber 3
The inside is evacuated to a high vacuum (about 10 ^-7 [Torr] to 10 ^-9 [Torr]), and a predetermined amount of oxygen is supplied into the substrate pretreatment chamber 3 to maintain a constant level sufficiently lower than atmospheric pressure. Oxygen partial pressure (eg 10
^-4 [Torr]) while maintaining the temperature of the semiconductor crystal substrate and heating at a temperature that does not exceed the temperature at which easily desorbable substances such as As are desorbed (for example, a temperature of about 400 [℃]) A film is formed, the compound semiconductor crystal substrate is transferred to the growth chamber 5 while maintaining a high vacuum, and is heated (for example, at a temperature of about 600 [° C.]) while being irradiated with the molecular beam of the easily desorbable substance. The oxide film is removed and the compound semiconductor crystal substrate is maintained at a required temperature to grow a target semiconductor crystal layer by molecular beam epitaxial growth.

[Action]

By adopting the above means, the carbonaceous matter and other contaminants adhering to the compound semiconductor crystal substrate can be reliably removed.
Even if you thin the buffer layer to increase the through put,
Each compound semiconductor crystal layer formed thereon has high quality with few defects.

〔Example〕

FIG. 1 shows an explanatory view of a main part of a semiconductor crystal growth apparatus for explaining one embodiment of the present invention.

In the figure, 1 is a substrate exchange chamber, 1A is a substrate inlet / outlet, 1B is an exhaust pipe, 2 is a gate valve, 3 is a substrate pretreatment chamber, 3A is an exhaust pipe, 4 is a gate valve, 5 is a crystal growth chamber. , 5A is an exhaust pipe, 6 is an oxygen supply source, 7 is a valve, 8 is an oxygen cylinder,
9 is a turbo molecular pump, 10 is a substrate holder, 11 is a substrate heater, 12 is a Si molecular beam source, 13 is a Ga molecular beam source, 14 is an As molecular beam source, 15 is a substrate holder, and 16 is a substrate heater. Shows.

Here, the case of growing an n-type GaAs layer on a GaAs substrate will be described.

The GaAs substrate is attached to a molybdenum (Mo) block for mounting a substrate in the atmosphere using In solder, and is introduced into the substrate exchange chamber 1 through the substrate inlet / outlet port 1A, and high vacuum exhaust is performed. To do.

After the inside of the substrate exchange chamber 1 is evacuated to about 10 ^-7 [Torr] to 10 ^-9 [Torr], the gate valve 2 is opened to transfer the GaAs substrate to the substrate pretreatment chamber 3 and to the substrate holder 10. After mounting, close the gate valve 2. The substrate heater 11 in the substrate holder 10 has the ability to heat the GaAs substrate up to 800 [° C.].

The inside of the substrate pretreatment chamber 3 is previously operated by the action of the turbo molecular pump 9.
It is evacuated to a vacuum of about 10 ⁻⁷ [Torr] to 10 ⁻⁹ [Torr], and is in a state where oxygen can be fed from the oxygen supply source 6.

While supplying and exhausting oxygen, the oxygen partial pressure is reduced to 10
^While keeping at ^-4 [Torr], the GaAs substrate is heated to about 400 [° C], and the state is maintained for about 30 [minutes] to form an oxide film on the surface of the GaAs substrate.

When the substrate heater 11 is turned off and the temperature is naturally lowered to about 200 [° C], the gate valve 4
Is opened to transfer the GaAs substrate to the growth chamber 5 which is evacuated to a high vacuum, which is attached to the substrate holder 15 having the substrate heating heater 16, and the gate valve 4 is closed.

In the growth chamber 5, the GaAs substrate is heated again while irradiating the As molecular beam from the As molecular beam source 14 to raise the temperature to about 600.
By keeping the temperature at about [° C.] or higher for about 10 [minutes], the oxide film on the surface is removed. As a result, carbon-based contaminants on the GaAs substrate surface are also removed at the same time.

Epitaxial growth is performed while maintaining the temperature of the GaAs substrate at a temperature required for growing the GaAs layer, that is, 550 [° C.]. At this time, Si from the Si molecular beam source 12 is doped to a concentration of about 1 × 10 ¹⁷ [cm ⁻³ ] which is the same as that of the GaAs substrate. In this case, the growth rate is 1 [μm / hour] and the growth layer thickness is 0.5 [μm].

FIG. 2 is a diagram showing the carrier concentration profile in the vicinity of the interface between the GaAs substrate and the epitaxially grown GaAs layer.

In the figure, the horizontal axis shows the depth from the surface of the GaAs layer, and the vertical axis shows the carrier concentration. The solid line is the characteristic line relating to one embodiment of the present invention, and the broken line is It is a characteristic line regarding the conventional example, and these data are CV
The samples were obtained by the measurement method, and the samples used were those pretreated according to the present invention and those subjected to thermal cleaning in the growth chamber 5 at a temperature of 600 ° C.

As can be seen from the figure, in the embodiment of the present invention, the carrier concentration is substantially uniform in the depth direction and there is no carrier depletion region, but in the prior art,
There is an obvious depletion region, which is considered to be due to the contamination of carbonaceous materials.

From the above, it can be seen that according to the present invention, the contaminants on the surface of the substrate were removed well, and no crystal defects were introduced.

〔The invention's effect〕

According to the present invention, when the compound semiconductor crystal layer is epitaxially grown on the compound semiconductor crystal substrate, the substrate pretreatment chamber is evacuated to a high vacuum and then an oxygen partial pressure that is much lower than atmospheric pressure and constant is maintained. Meanwhile, a thermal oxide film is formed on the surface of the compound semiconductor crystal substrate, and then the compound semiconductor crystal substrate is transferred to a growth chamber while maintaining a high vacuum, and the thermal oxide film is removed and contaminants such as carbonaceous substances are also removed. I try to remove them at the same time.

By adopting this configuration, it is possible to remove carbonaceous substances and other contaminants without causing the surface roughness of the compound semiconductor crystal substrate, and therefore, even if a thin buffer layer is used, a high quality semiconductor crystal layer can be obtained. Can be grown in through put.

In particular, regarding the removal of contaminants, since the substrate pretreatment chamber was initially evacuated to an ultrahigh vacuum of 10 ^-7 [Torr] to 10 ^-9 [Torr], oxygen was introduced, The gas is sufficiently discharged, and an oxide film can be formed in an oxygen atmosphere of high purity. Therefore, the contamination of the substrate surface in this step is small and the cleaning effect is large.

In addition, since it is oxidized by heating at about 400 [° C] in an oxygen partial pressure atmosphere of 10 ^-4 [Torr], which is sufficiently lower than atmospheric pressure, the moisture adhering to the substrate surface is In this step, the compound semiconductor crystal substrate is completely removed, and the compound semiconductor crystal substrate is transferred to the crystal growth chamber while maintaining a high vacuum, so that impurities can be remarkably reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view of a main part of one embodiment of the present invention, and FIG. 2 is a diagram showing a carrier concentration profile in the vicinity of an interface between a GaAs substrate and an epitaxially grown GaAs layer. In the figure, 1 is a substrate exchange chamber, 1A is a substrate inlet / outlet, 1B is an exhaust pipe, 2 is a gate valve, 3 is a substrate pretreatment chamber, 3A is an exhaust pipe, 4 is a gate valve, 5 is a crystal growth chamber. , 5A is an exhaust pipe, 6 is an oxygen supply source, 7 is a valve, 8 is an oxygen cylinder, 9
Is a turbo molecular pump, 10 is a substrate holder, 11 is a substrate heater, 12 is a Si molecular beam source, 13 is a Ga molecular beam source, 14 is an As molecular beam source, 15 is a substrate holder, and 16 is a substrate heater. ing.

Claims (2)

(57) [Claims] 1. A step of setting a compound semiconductor crystal substrate in a substrate pretreatment chamber in a semiconductor crystal growth apparatus capable of performing a molecular beam epitaxial growth method, and a step of evacuating the substrate pretreatment chamber to a high vacuum. And then desorbing in the material constituting the compound semiconductor crystal substrate while supplying a predetermined amount of oxygen into the substrate pretreatment chamber and maintaining a constant oxygen partial pressure sufficiently lower than atmospheric pressure. A step of forming an oxide film by heating at a temperature that does not exceed the temperature at which the easy substance desorbs, and then transferring the compound semiconductor crystal substrate to a growth chamber while maintaining a high vacuum to remove the easily desorbable substance. A step of removing the oxide film by heating while irradiating with a molecular beam, and then maintaining the compound semiconductor crystal substrate at a required temperature to form a target semiconductor crystal layer by molecular beam epitaxial growth. And a step of lengthening the semiconductor crystal. 2. An oxygen supply system capable of supplying a predetermined amount of oxygen to maintain a constant oxygen partial pressure sufficiently lower than atmospheric pressure, a high vacuum exhaust system, and a compound semiconductor crystal substrate. A substrate pretreatment chamber provided with a holder for heating to a temperature that does not exceed the desorption temperature of a substance that is the most difficult to desorb among the materials that form the compound semiconductor crystal substrate, and the substrate pretreatment chamber A molecular beam source capable of irradiating a molecular beam of a substance that is easily desorbed among the materials constituting the continuous high vacuum exhaust system and the compound semiconductor crystal substrate and the oxide film by holding and heating the compound semiconductor crystal substrate And a growth chamber provided with a holder for molecular beam epitaxial growth of a semiconductor crystal layer under necessary molecular beam irradiation.