JPH01223721A - Method and device for crystal growth - Google Patents

Abstract

PURPOSE:To remove an impurity such as carbon on the surface of a substrate, and to form a thin buffer layer by heating the substrate composed of a compound semiconductor at a fixed temperature, irradiating the substrate with hydrogen molecular beams, getting rid of impurity atoms and causing a crystal growth on the substrate. CONSTITUTION:When a GaAs substrate is used as a substrate 10, an impurity such as carbon on the surface is removed when the substrate is heated at approximately 600 deg.C and the substrate is irradiated with hydrogen molecular beams. Consequently, a heating temperature is brought to approximately 600 deg.C, As, etc., on the surface are evaporated and are not etched and a surface having excellent surface morphology is acquired according to the surface treating method. The substrate is surface-treated in a substrate anteroom 2, and the substrate 10 is sent into a crystal growth chamber 1 and a crystal growth layer such as a GaAs layer is grown. Accordingly, traps on the interface are decreased, thus acquiring the excellent crystal growth layer even when a thin buffer layer is shaped.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a method for surface treatment of a substrate to be grown and an apparatus for performing the treatment. , comprising the steps of heating a growth substrate made of a compound semiconductor to a predetermined temperature, irradiating the growth substrate with a hydrogen molecular beam to remove impurity atoms, and then growing crystals on the growth substrate. The crystal growth apparatus is equipped with a substrate preparation chamber between the substrate exchange chamber and the crystal growth chamber, a heating holder that holds and heats the substrate to be grown, and a heating holder that holds and heats the substrate to be grown, and a hydrogen molecule on the surface of the substrate to be grown. The present invention is characterized in that a hydrogen molecular beam cell for irradiating a beam is provided to treat the surface of the growth substrate.

[Industrial Application Field] The present invention relates to a crystal growth method and a crystal growth apparatus, and more particularly to a method for surface treatment of a growth substrate and an apparatus for carrying out the treatment.

Recently, much research has been carried out to create high-performance semiconductor devices by epitaxially growing m-v reduced compound semiconductor layers, such as GaAs/AlGaAs.

Ultrahigh-speed devices and optical devices are being developed that form heterojunction structures such as InP/InGaAs systems and utilize this petrostructure.

As a method for epitaxially growing such a compound semiconductor layer, molecular beam crystal growth (Molecular Bea crystal growth) is used.
The MB2 method has been developed and is known as an excellent growth method that can form steep junctions. However, in order to form a thin, high-quality crystal growth layer, the quality of the surface of the crystal substrate, which is the base thereof, is extremely important.

[Prior Art] Fig. 4 shows an outline of a conventional gas source molecular beam crystal growth apparatus applying the MB2 method, in which 1 is a crystal growth chamber, 2 is a substrate (jA room, 3 is a substrate exchange room, 4.5 is a gate valve, 6 is a substrate transfer rod, 7 is a substrate manipulator, 8 is a substrate holder equipped with a heater, 9 is a molecular beam source cell, 1
0 is a substrate (a substrate to be grown; a wafer). In operation, the substrate holder 8 holding the substrate 10 is inserted into the substrate exchange chamber 3, gate valves 4 and 5 are opened and closed, and the substrate is sent into the crystal growth chamber 1 through the substrate preparation chamber 2. When transferring the substrate from the substrate preparation chamber 2 to the crystal growth chamber 1, the substrate is held by the substrate manipulator turf in the crystal growth chamber 1 by the substrate transfer rod 6, and rotated to face the molecular beam source cell 9. Note that the broken line drawn inside the substrate preparation chamber 2 indicates the locus of rotational movement of the substrate holder. The growth process in the crystal growth chamber 1 is performed on the substrate 10.
However, for example, in the case of a GaAs substrate, when heating it to 600 to 700°C and growing a GaAs device such as a HEMT on the surface, the molecular beam source cell 9 is an As molecular beam source cell,
A plurality of molecular beam source cells such as a Ga molecular beam source cell are arranged, and molecular beams are irradiated from these cells to grow a crystal growth layer.

By the way, when molecular beam crystal growth is performed on the substrate 10 in this way, a surface treatment is performed to clean the growth surface of the substrate. For example, if the substrate is a GaAs substrate, the substrate is cleaned in vacuum. The substrate is heated at 300 to 400°C to remove moisture adhering to the surface, and immediately before growth, it is heated to about 600°C for 3 to 5 minutes to remove the natural oxide film on the substrate surface. The required crystal growth layer is grown.

Conventional surface treatment methods remove such moisture and natural oxide film (film thickness of about 10 mm).

[Problem to be solved by the invention] However, although the above surface treatment method can remove moisture and oxygen, it cannot remove carbon (C) attached to the substrate surface as hydrocarbons and carbon dioxide. . Such hydrocarbons and carbon dioxide come from the atmosphere or from inside the vacuum growth chamber and adhere thereto.

In this way, when a crystal growth layer is epitaxially grown on the surface of a GaAs substrate with carbon attached to it, carbon atoms mix into the GaAs and act as acceptors (p-type), resulting in a bond between the GaAs substrate and the crystal growth layer. This results in the formation of interface states between the two, which impairs device characteristics.

Conventionally, in order to avoid the influence of this interface state, a thick buffer layer with a film thickness of nearly 1 μm is formed, but providing this thick buffer layer increases the number of steps in the crystal growth process, which reduces throughput. I will let you do it.

As a countermeasure against this problem, for example, we have previously proposed a thermal etching method (see Japanese Patent Laid-Open No. 62-030317).

According to this method, the surface of the GaAs substrate is thermally etched to remove carbon and the buffer layer can be made thinner. However, this thermal notching method is not suitable for GaAs.
Since this is a method of thermally evaporating the surface layer by heating it to 750° C. or higher under irradiation with As molecular beams in a vacuum, it is difficult to remove the surface uniformly, and the surface morphology deteriorates, resulting in surface roughness. Surface roughness causes various problems in the manufacturing process.

The present invention proposes a surface treatment method for a crystal growth method and a growth apparatus for carrying out the method, with the purpose of removing impurities such as carbon from the surface of a substrate and making it possible to form a thin buffer layer.

[Means for solving the problem] The purpose is to heat a growth substrate made of a compound semiconductor to a predetermined temperature, irradiate the growth substrate with a hydrogen molecular beam to remove impurity atoms, and then This is achieved by a crystal growth method that includes the step of growing crystals on a substrate.

In addition, the growth apparatus for carrying out this process includes a substrate preparation chamber between the substrate exchange chamber and the crystal growth chamber, and a heating holder that holds and heats the growth substrate in the substrate preparation chamber, and a heating holder that holds and heats the growth substrate. A hydrogen molecular beam cell is installed to irradiate hydrogen molecular beams,
The method is characterized in that the surface of the growth substrate is treated.

[Operation] That is, in the present invention, impurity atoms such as carbon (C) are removed while heating the growth substrate to a relatively low temperature and irradiating it with a hydrogen (H2) molecular beam. In this way, a clean surface with good surface morphology appears, and if a crystal growth layer is epitaxially grown on that surface, a growth layer with good crystal quality can be obtained. Therefore, it is sufficient to provide only a thin buffer layer.

[Example] An embodiment will be described in detail below with reference to one drawing.

Figure 1 shows an outline of a gas source molecular beam crystal growth apparatus to which the crystal growth method according to the present invention is applied. In Figure 1, the same parts as the conventional crystal growth apparatus shown in Figure 4 are designated by the same symbols. The other 11 are hydrogen molecular beam source cells, and 12 and 13 are valves.

14 is a hydrogen purifier, 15 is a hydrogen cylinder, and a hydrogen molecular beam source cell 11 is provided in the substrate preparation room 2. In addition, the heating holder in this example is the substrate holder itself, and the heating holder is the substrate holder itself.
It is configured to be transported together with the vehicle.

Now, when the substrate 10 is a 5-GaAs plate, according to the present invention, impurities such as carbon on the surface are removed by heating the substrate to about 600° C. and irradiating it with a hydrogen molecular beam.

Therefore, in the conventional thermal etching method, evaporation is performed by heating to 750°C or higher under As molecular beam irradiation, but with this surface treatment method, the heating temperature is approximately 600°C, and such 700°C or lower If the heating temperature is , the surface ^S
etc. will not evaporate and be etched, and a good surface morphology will be obtained.

After this surface treatment in the substrate preparation chamber 2, the substrate 10 is then transferred to the crystal growth chamber 1 to form a crystal growth layer, for example, G
Grow the aAs layer. Although only two molecular beam source cells are shown in the crystal growth chamber in FIG. 1, this is because the molecular beam source cells are arranged rotationally symmetrically with respect to the substrate 10. There are also other molecular beam source cells that do not appear in FIG.

Next, a detailed example of such surface treatment and its effects will be explained.

The first embodiment uses Si (silicon) at a rate of 7 x lO”/c
The same (Si 7X10
This is an example of growing a /d doped n-GaAs layer.

First, a GaAs substrate is exposed to molybdenum (Mo) in the atmosphere.
) Attach it to the block (board holder) with In solder, insert it into the board exchange chamber 3, and open the board exchange chamber from 10-'T~
After evacuation to about 10 Torr, the gate pulp 5 is opened and introduced into the substrate preparation chamber 2.

The substrate preparation chamber 2 is maintained at a vacuum level of about IQ Torr, in which the GaAs substrate is heated to about 600° C., subjected to the above hydrogen molecular beam irradiation, and held for 20 minutes.

In that case, the degree of vacuum decreases to about 10 Torr, but evacuation is continued even after the surface treatment to restore the degree of vacuum and lower the temperature of the substrate.

Next, the GaAs substrate is introduced into the crystal growth chamber 1 to a thickness of about 6
It is heated to 80 DEG C. and grown to grow an n-GaAs layer doped with 7.times.10/- Si.

Thereafter, the carrier concentration distribution near the substrate-growth layer interface of this substrate sample was examined by CV measurement. The results are shown in Figure 2, where the vertical axis is the carrier concentration and the horizontal axis is the depth from the surface.Curve I is data from a sample to which the surface treatment method according to the present invention was applied, and curve ■ is data from a conventional surface treatment method. This data is based on samples to which processing has been applied. In the same figure, the large concavity of the curve (2) of the sample obtained by the conventional method indicates that the donor impurity (St) is consumed by the acceptor impurity (C; carbon) and is reduced. On the other hand, in the curve 1 of the sample obtained by the surface treatment method according to the present invention, the dents are smaller, indicating an improvement.

From FIG. 2, when the amount of carrier depletion is determined by integral calculation, it is 1.5×10 2 /C− for the sample made by the conventional method, and about 7×10 2 /era for the sample made by the single method, which is significantly reduced. It is known that the amount of change in carrier concentration near the substrate-growth layer interface is correlated with the amount of residual carbon on the substrate surface (Japanese Jo
urnal of Applied Physics
25(8)+1986+pp1216), therefore,
It is clear that the surface treatment method according to the present invention is effective in reducing the amount of residual carbon.

Next, a second example will be described. Semi-insulating GaA
GaAs layer + AlGaAs layer + n A on s substrate
Example (H
An example of a BMT structure), whose cross-sectional view is shown in FIG.
GaAs electron supply layer.

24 is an n-GaAs contact layer.

First, the semi-insulating GaAs substrate 20 was subjected to the surface treatment according to the present invention in the same manner as described above, that is, the vacuum level was 10 Torr.
heated to about 600°C in a substrate preparation room maintained at a moderate temperature,
A process of irradiating with a hydrogen molecular beam for 20 minutes is performed, and then the above-mentioned crystal growth layer is grown in a crystal growth chamber. The detailed values of each crystal growth layer are as follows.

■GaAsGaAs buff film thickness 0.2μm ■AlxG
axAs spacer layer 22: film thickness 60mm,
o, 3■n-81xGa xAs electron supply layer 23: film thickness 900, X value 0.3, impurity concentration 1x 10 /a+! ■n-GaAs contact layer: thickness 200, impurities)
degree 1×10/cIa Then, when the electron mobility and electron concentration of this substrate sample were measured, the electron mobility was 90000cnl/VS
, the electron concentration was 5.0xlO/cd.

On the other hand, the same surface treatment as before, ie about 400°C.

A GaA film with a thickness of 0.6 μm was applied to an S plate that was heat-treated for 20 minutes.
A sample was prepared in which the s-buffer layer 21 was grown and the other crystal growth layers were grown under the same conditions as above. As a result of measuring its electron mobility and electron concentration, it was found that the values were almost the same as those of the substrate prepared by the final method, and the surface defect density was reduced by half. As a result, it is clear that the thickness of the buffer layer can be reduced to 1 (1) by applying the surface treatment according to the present invention.

Therefore, by applying the present invention, traps at the interface are reduced, and a high-quality crystal growth layer can be obtained even when a thin buffer layer is formed.For example, in electronic devices such as HEMT, two-dimensional electron gas is increased. performance is improved. Furthermore, providing a thin buffer layer has the effect of reducing the number of crystal growth processing steps, improving throughput, and reducing surface defect density.

Note that although the above example uses a GaAs substrate, the present invention is applicable to other compound semiconductor substrates, such as 1nP substrates and I
It can also be applied to an nSb substrate, and the elements that are easily evaporated in that case are W (P) and antimony (Sb).

Furthermore, although the above embodiment was explained using the gas source MBE method,
The present invention can also be applied to metal source MBE and MOCVD.

[Effects of the Invention] As is clear from the above description, according to the crystal growth method of the present invention, a thin buffer layer is provided, throughput is improved, and a high-quality crystal growth layer can be changed. Therefore, it greatly contributes to improving the performance of electronic devices and optical devices.

[Brief explanation of the drawing]

FIG. 1 shows a gas source molecular beam crystal growth apparatus according to the present invention. FIG. 2 shows a carrier concentration distribution near the substrate-growth layer interface in the first embodiment. A cross-sectional view of the heterostructure, FIG. 4, is a diagram showing a conventional gas source molecular beam crystal growth apparatus. In the figure, 1 is a crystal growth chamber, 2 is a substrate preparation room, 3 is a substrate exchange room, 4.5 is a gate valve, 6 is a substrate transfer rod, 7 is a substrate manipulator, 8 is a substrate holder, 9 is a molecular beam source cell , 10 is a growth substrate (substrate)
11 is a hydrogen molecular beam source cell, 12 and 13 are valves,
14 is a hydrogen purifier, 15 is to a hydrogen bomb, 20 is a semi-insulating GaAs plate, 21 is a GaAs bar layer, 22 is an AlGaAs spacer layer, 23 is an n-^lGaAs electron supply layer, 24 is an n-GaAs contact layer

Claims (2)

[Claims] (1) The process includes heating a growth substrate made of a compound semiconductor to a predetermined temperature, irradiating the growth substrate with a hydrogen molecular beam to remove impurity atoms, and then growing crystals on the growth substrate. A crystal growth method characterized by: (2) A substrate preparation chamber is provided between the substrate exchange chamber and the crystal growth chamber, and the substrate preparation chamber includes a heating holder that holds and heats the substrate to be grown, and a hydrogen holder that irradiates the surface of the substrate to be grown with a hydrogen molecular beam. A crystal growth apparatus characterized in that a molecular beam cell is provided to perform surface treatment on a growth substrate.