JPH0779084B2 - Semiconductor crystal growth method and apparatus for implementing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to a method for growing a semiconductor crystal and an apparatus for carrying out the method, in which a compound is provided in a substrate preparation chamber in a semiconductor crystal growing apparatus capable of carrying out a molecular beam epitaxial growth method. The semiconductor crystal substrate is set, and then, among the materials constituting the compound semiconductor crystal substrate, the molecular beam of a substance which is easily desorbed and the molecular beam of hydrogen thereof are directly irradiated to the compound semiconductor crystal substrate surface, which is the most difficult to desorb. By heating at a temperature equal to or higher than the temperature at which the substance is desorbed, and then transferring the compound semiconductor crystal substrate to a growth chamber so that the required semiconductor crystal layer is subjected to molecular beam epitaxial growth. By providing an apparatus for performing such a technique, a buffer layer is provided to remove carbon from the compound semiconductor substrate surface and enhance throughput. Be comb, in the buffer layer is obtained by allowing to grow few defects of quality crystals.

[Industrial application field]

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, and an element is formed in the semiconductor layer.

In recent years, in order to grow such a compound semiconductor crystal layer,
Molecular beam epitaxy: M
BE) 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, before the actual crystal layer is grown.
In the case of GaAs, by heating to about 300 to 400 [° C.], the water adhering to the surface of the GaAs substrate is removed in the atmosphere.

[Problems to be solved by the invention]

However, in heating by the temperature of the above degree,
Molecules containing carbon, such as hydrocarbons, cannot be removed. 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.

Also, with carbon atoms etc. attached to the GaAs substrate surface,
When a semiconductor crystal layer is epitaxially grown on it, the carbon atom acts as an acceptor and forms an interface state between the GaAs substrate and the epitaxially grown semiconductor crystal layer, so in order to avoid this effect, a thick buffer layer should be used. It will need to be formed, and it will take a lot of time, so the throughput will not increase.

The present invention removes carbon such as hydrocarbons and carbon dioxide adhering to the surface of the substrate by heat treatment, and furthermore, even if the buffer layer is thin to increase the throughput,
A high-quality semiconductor crystal layer with few surface defects can be easily grown, and a semiconductor device with good characteristics can be obtained.

[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 inside of the substrate preparation chamber 2 in the semiconductor crystal growth apparatus capable of performing the molecular beam epitaxial growth method is used.
The GaAs substrate 10 is set, and the most easily desorbed while directly irradiating the surface of the GaAs substrate 10 with the molecular beam of As and the molecular beam of H ₂ which are substances that are easily desorbed among the materials forming the GaAs substrate 10. Heating for a required time (for example, for 1 [minute]) at a temperature at which Ga, which is a substance, is desorbed (for example, 750 [℃]) or more,
After that, the GaAs substrate 10 is transferred to the growth chamber 6 and a necessary semiconductor crystal layer, for example, a GaAs / AlGaAs system crystal layer is subjected to molecular beam epitaxial growth.

[Action]

By adopting the above means, the carbonaceous matter and other contaminants deposited on the GaAs substrate 10 are surely removed, so even if the GaAs buffer layer is thinned to enhance the through put, it is formed on it. Each semiconductor crystal layer 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, 2 is a substrate preparation chamber, 3 is a substrate transfer rod, 4 is a substrate holder, 5 is an As molecular beam source, 6 is a growth chamber, 7 is a substrate holder, 8 is an As molecular beam. Source, 9 Ga molecular beam source, 10 GaAs substrate, 11 In solder, 12 and 13 gate valves, 14 and 15 cut valves, 16 H ₂ molecular beam source, 17
Is an H ₂ purifier. 18 shows the H ₂ cylinders respectively. still,
In the growth chamber 6 of this embodiment, an Al molecular beam source and a Si molecular beam source are provided in addition to the As molecular beam source 8 and the Ga molecular beam source 9. Since it is provided rotationally symmetrically with respect to the central axis of the above, it does not appear in FIG. 1, which is a longitudinal sectional view.

Here, a GaAs layer and an AlGaAs layer or an n-type on the GaAs substrate 10.
The case of growing an AlGaAs layer will be described.

The GaAs substrate 10 is attached to a molybdenum (Mo) block for mounting a substrate by using In solder in the atmosphere, and then introduced into the substrate exchange chamber 1.

The inside of the substrate exchange chamber 1 is evacuated to about 10 ⁻⁷ [Torr] to 10 ⁻⁸ [Torr], and then the gate valve 12 is opened to transfer the substrate to the substrate preparation chamber 2.

The inside of the substrate preparation room 2 is maintained at about 10 ^-9 [Torr],
The As molecular beam toward the GaAs substrate 10 from the As molecular beam source 5, also to be able to emit and H ₂ molecular beams from H ₂ molecular beam source 16. When the As molecular beam and the H ₂ molecular beam are emitted, the degree of vacuum in the substrate preparation chamber 2 decreases to about 10 ⁻³ to 10 ⁻⁴ [Torr]. The exhaust gas in this case is a turbo-molecular pump (turbo-mol
ecular pump (TMP) or oil diffusion pump
pump: DP).

The GaAs substrate 10 is heated to about 750 [° C.] by the substrate holder 4 which can be heated while being irradiated with As molecular beam and H ₂ molecular beam, and after that state is maintained for, for example, 1 [minute], The temperature is naturally lowered, and when the temperature reaches about 300 ° C., the temperature is transferred to the growth chamber 6.

In the growth chamber 6, the GaAs substrate 10 is heated again to bring the temperature to about 680 [° C.] to grow a GaAs / AlGaAs semiconductor crystal layer.

FIG. 2 is a side sectional view of a main part of a wafer having a semiconductor crystal layer manufactured by the above-described process.

In the figure, 21 is a semi-insulating GaAs substrate, 22 is a GaAs buffer layer, 23 is an Al _x Ga _1-x As spacer layer, 24 is an n-type Al _x Ga _1-x As electron supply layer, and 25 is an n-type GaAs electrode. The contact layers are shown respectively. The GaAs buffer layer 22 also serves as a channel layer.

The data of each semiconductor layer in the illustrated wafer is exemplified as follows.

(1) GaAs buffer layer 22 thickness: 0.2 [μm] (2) Al _x Ga _1-x As spacer layer 23 thickness: 60 [Å] x value: 0.3 (3) n-type Al _x Ga _1-x As Electron supply layer 24 Thickness: 900 [Å] x value: 0.3 Impurity concentration: 1 x 10 ¹⁸ [cm ^-3 ] (4) n-type GaAs electrode contact layer 25 Thickness: 200 [Å] Impurity concentration: 1 x 10 ¹⁸ [cm ^-3 ] This wafer and the wafer manufactured by the conventional technique, that is, in the substrate preparation chamber 2, ~ 400 [° C], 10 [min]
The wafers that had just been subjected to the heat treatment of 1. were subjected to hole measurement, and the electron mobility and electron concentration in the two-dimensional electron gas layer at the hetero interface were compared. In addition, the GaAs of the wafer according to the conventional technology
The thickness of the buffer layer is 0.6 [μm].

FIG. 3 is a diagram showing the relationship between the thickness of the buffer layer and the electron mobility and electron concentration in the two-dimensional electron gas layer.

In the figure, the thickness of the buffer layer is plotted on the horizontal axis, the electron mobility is plotted on the left vertical axis, and the electron concentration is plotted on the right vertical axis, and □ indicates the electron mobility in one embodiment of the present invention (cm ² / V · s] and electron concentration [cm ⁻² ] are shown, and the ○ mark shows that in the conventional example.

In this embodiment, when the GaAs buffer layer 22 is 0.2 [μm], the electron mobility is 90,000 [cm ² .Vs] and the electron concentration is
5.0 × 10 ¹¹ [cm ⁻² ], which has characteristics comparable to those of the prior art having a GaAs buffer layer having a thickness of 0.6 μm, and the entire epitaxially grown semiconductor crystal layer is thin. As a result, the surface defect density is also reduced to about 1/2 of that of the conventional thickness.

The thickness of the GaAs buffer layer is 0.2 [μm as in the present invention.
m] and the heat treatment is the same as in the conventional example, the effect of electron traps appears at the interface between the semi-insulating GaAs substrate and the epitaxially grown semiconductor crystal layer, and the electron mobility is 6
A value of 0.000 [cm ² / Vs] and an electron concentration of 3.8 × 10 ₁₁ [cm ^-2 ] were obtained.

〔The invention's effect〕

According to the present invention, when a compound semiconductor crystal layer is epitaxially grown on a compound semiconductor crystal substrate, in a substrate preparation chamber, a molecular beam and a hydrogen molecule of a substance that easily separates among the materials forming the compound semiconductor crystal substrate The heat treatment is performed at a temperature higher than the temperature at which the most difficult substance to be released is released while being exposed to the rays.

By adopting this configuration, carbon-based and other contaminants can be removed without causing surface roughness of the compound semiconductor crystal substrate, and as a result, a good quality semiconductor crystal layer can be obtained with high through-put while using a thin buffer layer. It is possible to grow.

[Brief description of drawings]

FIG. 1 is an explanatory view of a main part of an embodiment of the present invention, and FIG. 2 is a side view of a main part of a wafer manufactured according to the embodiment of the present invention.
FIG. 3 is a diagram illustrating the relationship between the thickness of the buffer layer and the electron mobility and the electron concentration of the two-dimensional electron gas layer. In the figure, 1 is a substrate exchange chamber, 2 is a substrate preparation chamber, 3 is a substrate transfer rod, 4 is a substrate holder, 5 is an As molecular beam source, 6 is a growth chamber, 7 is a substrate holder, 8 is an As molecular beam. Source, 9 Ga molecular beam source, 10 GaAs substrate, 11 In solder, 12 and 13 gate valves, 14 and 15 cut valves, 16 H ₂ molecular beam source, 17
The H ₂ purifier, 18 shows of H ₂ gas cylinder, respectively.

Claims (2)

[Claims] 1. A step of setting a compound semiconductor crystal substrate in a substrate preparation chamber in a semiconductor crystal growth apparatus capable of carrying out a molecular beam epitaxial growth method, and then removing the compound semiconductor crystal substrate from the materials constituting the compound semiconductor crystal substrate. Directly irradiating the molecular beam of a substance that is easily released and the molecular beam of hydrogen to the surface of the compound semiconductor crystal substrate, and heating the compound semiconductor crystal substrate to a temperature at which the most difficult substance to be desorbed is desorbed, and then the compound semiconductor crystal substrate is heated. And a step of carrying out molecular beam epitaxial growth of a required semiconductor crystal layer by transferring the semiconductor crystal layer to a growth chamber. 2. A holder which can hold a compound semiconductor crystal substrate and can be heated to a temperature equal to or higher than a temperature at which a substance which is the most difficult to desorb among the materials constituting the compound semiconductor crystal substrate is desorbed and a substance which is easily desorbed. Preparation of a substrate in which a molecular beam source capable of directly irradiating the compound semiconductor crystal substrate surface as a molecular beam and a molecular beam source capable of directly irradiating hydrogen as a molecular beam onto the compound semiconductor crystal substrate surface are prepared. A semiconductor crystal growth apparatus comprising: a chamber; and a growth chamber connected to the substrate preparation chamber for performing molecular beam epitaxial growth of a semiconductor crystal layer.