JPS63156314A - Method of growing semiconductor crystal and apparatus therefor - Google Patents

Abstract

PURPOSE:To remove contaminants containing carbon or the like from a compound semiconductor crystal substrate without roughening the surface thereof, by heat-treating the substrate in a substrate preparing chamber at a temperature higher than a temperature at which a material that can be eliminated most hardly from among the components of the compound semiconductor crystal substrate is eliminated while irradiating the substrate with molecular beams of easily eliminable material and of hydrogen. CONSTITUTION:A substrate exchanging chamber 1 is evacuated to about 10<-7>-10<-8> torr. Then, a gate valve 12 is opened so that a GaAs substrate 10 is transferred into a substrate preparing chamber 2. The pressure in the chamber 2 is held at about 10<-9> torr and As molecular beams are emitted from an As molecular beam source 5 to the GaAs substrate 10 while H2 molecular beams are emitted by an H2 molecular beam source 16 to the substrate 10. The GaAs substrate 10 is heated to about 750 deg.C while it is irradiated with the As and H2 molecular beams. Then, the temperature is lowered spontaneously. The substrate is transferred to a deposition chamber 6, in which the GaAs substrate 10 is heated again to about 680 deg.C so that a semiconductor crystal layer of GaAs/AlGaAs is deposited on the substrate.

Description

[Detailed Description of the Invention] [Summary] The present invention provides a method for growing a semiconductor crystal and an apparatus for carrying out the method, in which a compound is grown in a substrate preparation chamber of a semiconductor crystal growth apparatus capable of carrying out a molecular beam epitaxial growth method. A semiconductor crystal substrate is set, and then a molecular beam of a substance that is easily desorbed among the materials constituting the compound semiconductor crystal substrate and a molecular beam of hydrogen are irradiated at a temperature higher than the temperature at which the substance that is most difficult to desorb is desorbed. and then transferring said compound semiconductor crystal substrate to a growth chamber for molecular beam epitaxial growth of the required semiconductor crystal layer, and also provides an apparatus for carrying out such a technique. By doing so, even if carbon is removed from the surface of the compound semiconductor substrate and the buffer layer is thinned to increase throughput, it is possible to grow high-quality crystals with few defects on the buffer layer. That is.

[Industrial application field]

The present invention relates to a semiconductor crystal growth method that can be applied to fabricate a semiconductor device in a semiconductor layer formed on a compound semiconductor substrate with a buffer layer interposed therebetween, and to obtain good results, 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 with a buffer layer interposed therebetween, and elements are built into the semiconductor layer.

In recent years, to grow such compound semiconductor crystal layers,
Molecular beam epitaxial growth
eam epitaxy (MBE) method is often used.

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

[Problem that the invention seeks to solve]

However, in heating at the above-mentioned temperature,
Carbon-containing molecules such as hydrocarbons cannot be removed. It should be noted that when a GaAs substrate is heated in a high vacuum at a high temperature of 600 ('C) or more, As having a high vapor pressure is desorbed and the surface becomes rough.

Furthermore, when a semiconductor crystal layer is epitaxially grown on the surface of a GaAs substrate with carbon atoms attached to it, the carbon atoms act as acceptors and the GaAs
Since interface states are formed between the substrate and the epitaxially grown semiconductor crystal layer, in order to avoid this effect, it is necessary to form a thick buffer layer, which requires a lot of time, so the throughput does not increase. do not have.

The present invention removes carbon such as hydrocarbons and carbon dioxide adhering to the substrate surface by heat treatment, and even if the buffer layer is thinned to increase throughput,
To easily grow a high-quality semiconductor crystal layer with few surface defects and to obtain a semiconductor device with good characteristics.

[Means for solving problems]

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

In the present invention, a GaAs substrate 10 is set in a substrate preparation chamber 2 of a semiconductor crystal growth apparatus capable of implementing the molecular beam epitaxial growth method, and a GaAs substrate 10 is set in a substrate preparation chamber 2 of a semiconductor crystal growth apparatus capable of implementing the molecular beam epitaxial growth method. While irradiating the molecular beams of As and H2, which are substances, at a temperature higher than the temperature at which Ga, which is the substance that is most difficult to desorb, desorbs (e.g. 750 ('j:)) or higher for the required time (e.g. l [min. ), and then the GaAs substrate 10 is transferred to the growth chamber 6 to form a necessary semiconductor crystal layer, for example, GaAs/
The AlGaAs crystal layer is grown by molecular beam epitaxial growth.

[Effect]

By adopting the above method, carbon-based and other contaminants deposited on the GaAs substrate 10 are reliably removed, so even if the GaAs buffer layer is made thinner in order to increase throughput, the GaAs buffer layer formed on the GaAs substrate 10 can be removed. Each semiconductor crystal layer is of good quality with few defects.

〔Example〕

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

In the figure, 1 is a substrate exchange room, 2 is a substrate preparation room, 3 is a substrate transfer ring, 4 is a substrate holder, 5 is an As molecular beam source, 6 is a growth chamber, 7 is a substrate holder, and 8 is an As molecular beam. 9 is a Ga molecular beam source, 10 is a GaAs substrate, 1) is In solder, 12 and 13 are gate valves, 14 and 15 are cut pulp, 16 is a H2 molecular beam source, 17 is an H2 purifier, 18 is H
Two cylinders are shown. Incidentally, in addition to the As molecular beam source 8 and the Ga molecular beam source 9, an A1 molecular beam source and a Si molecular beam source are also provided in the growth chamber 6 in this embodiment.
Since each molecular beam source is provided rotationally symmetrically with respect to the central axis of the growth chamber 6, it does not appear in FIG. 1, which is a longitudinal cross-sectional view.

Here, a GaAs layer and an A I
The case of growing a GaAs layer or an n-type AlGaAs layer will be described.

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

Inside the board exchange room 1 10''''7 (To r r) ~I
After exhausting to about Qe ('l''orr), the gate pulp 12 is opened and transferred to the substrate preparation chamber 2.

The inside of the substrate preparation chamber 2 is maintained at about 10-9 Torr, and an A3 molecular beam is emitted from the As molecular beam source 5 toward the GaAs substrate 10, and an 8 Torr is emitted from the H2 molecular beam source 16.
It is capable of emitting bimolecular beams. When the As molecular beam and the 82 molecular beam are radiated, the degree of vacuum in the substrate preparation chamber 2 decreases to about 10-3 to 10-' (Torr). The exhaust in this case is a turbo-molecular pump (turbo-mo
1ecular pump: TMP) or oil diffusion pump: D
P).

The GaAs substrate 10 is heated to a temperature of about 750 (
After being heated to about 'C) and maintaining that state for, for example, 1 minute, the temperature is naturally lowered, and when the temperature reaches about 300 ('C), it is transferred to the growth chamber 6.

In the growth chamber 6, the GaAs bases Fi, 1O are heated again to a temperature of about 680 [°C], and the GaAs-based
A semiconductor crystal layer of As/A It Ga As system is grown.

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

In the figure, 21 is a semi-insulating GaAs substrate, 22 is a GaAs substrate, and 22 is a GaAs substrate.
As buffer layer, 23 is Al, G'a +-*A
s spacer layer, 24 an n-type A'X Gar-x As electron supply layer, and 25 an n-type GaAs electron contact layer. Note that the GaAs buffer layer 22 also serves as a channel layer.

Examples of data for each semiconductor layer in the illustrated wafer are as follows.

(1) GaAs buffer layer 22 thickness: 70.2 Cμm] (2) A I g G a I-x A s Electron supply layer 24 thickness: 900 [people] X value: 0.3 Impurity concentration: I X 10I8 (cffi-') (4
) N-type GaAs electrode contact layer 25 thickness: 200
Person C] Impurity concentration: I x 1018 (cm-') This wafer and wafers manufactured by the conventional technology, that is, heat treated in the substrate preparation chamber 2 at ~400 (°C) for 10 (minutes). The electron mobility and electron concentration in the two-dimensional electron gas layer at the hetero-interface were compared by Hall measurements on wafers that had just been exposed to GaAs.
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. )2/■・s
The layers and electron concentrations (cm-'') are shown, and the ◯ marks represent those in the conventional example.

In this embodiment, the GaAs buffer layer 22 has a thickness of 0°2 [μm].
], the electron mobility is 90,000 (cm”
/V -s), the electron concentration is 5.0X10'1 [o4]
As a result, characteristics comparable to those of the conventional technology having a GaAs buffer layer with a thickness of 6 (μm) were obtained, and since the entire epitaxially grown semiconductor crystal layer was made thinner, the surface defect density was reduced. The thickness is also reduced to about 2 when compared with the conventional thickness.

Incidentally, the thickness of the GaAs buffer layer is set to 0.0 mm as in the present invention.
2 [μm] and the heat treatment is the same as in the conventional example, the effect of electron traps at the interface between the semi-insulating GaAs substrate and the epitaxially grown semiconductor crystal layer appears, and the electron mobility is 60.000cc+12/■. S], and the electron concentration was only 3.8×10"Ccm -").

〔Effect of the invention〕

According to the present invention, when epitaxially growing a compound semiconductor crystal layer on a compound semiconductor crystal substrate, in the substrate preparation room, molecular beams of substances that are easily separated from materials constituting the compound semiconductor crystal substrate and hydrogen molecules are used. Heat treatment is performed at a temperature higher than the temperature at which the substance that is most difficult to release leaves while being exposed to radiation.

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 high-quality semiconductor crystal layer can be formed with high throughput while using a thin buffer layer. making it possible to grow.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a main part of an embodiment of the present invention, FIG. 2 is a cutaway side view of a main part of a wafer manufactured according to an embodiment of the present invention,
FIG. 3 shows diagrams illustrating the relationship between the thickness of the buffer layer and the electron mobility and electron concentration of the two-dimensional electron gas layer. In the figure, 1 is a substrate exchange room, 2 is a substrate preparation room, 3 is a substrate transfer frame, 4 is a substrate holder, 5 is an As molecular beam source, and 6 is '
Growth chamber, 7 is a substrate holder, 8 is an As molecular beam source, 9 is a Ga
Molecular beam source, 10 is GaAs substrate, 1) is In solder, 12
and 13 are gate valves, 14 and 15 are cut pulp, 16 is an H2 molecular beam source, 17 is an H2 purifier, and 18 is an H2 cylinder, respectively. FIG. 2 is a cutaway side view of essential parts of a wafer according to the present invention.

Claims (2)

[Claims] (1) A step of setting a compound semiconductor crystal substrate in a substrate preparation chamber of a semiconductor crystal growth apparatus capable of implementing the molecular beam epitaxial growth method; a step of heating to a temperature higher than the temperature at which the substance that is most difficult to desorb desorbs while irradiating it with a molecular beam of a substance and a molecular beam of hydrogen; and then transferring the compound semiconductor crystal substrate to a growth chamber to perform the necessary A method for growing a semiconductor crystal, comprising the step of growing a semiconductor crystal layer by molecular beam epitaxial growth. (2) A holder capable of holding a compound semiconductor crystal substrate and heating it to a temperature higher than the temperature at which the substance that is most difficult to desorb among the materials constituting the compound semiconductor crystal substrate, and a holder that can hold a substance that is easy to desorb as a molecule. a substrate preparation room equipped with a molecular beam source capable of irradiating the compound semiconductor crystal substrate with hydrogen as a molecular beam; and a molecular beam source capable of irradiating the compound semiconductor crystal substrate with hydrogen as a molecular beam; 1. A semiconductor crystal growth apparatus comprising a growth chamber connected to the chamber and for growing a semiconductor crystal layer by molecular beam epitaxial growth.