JPH0247440B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for producing epitaxially grown layers, particularly liquid phase epitaxially grown layers of GaAs.

Typically, Si-doped GaAs epitaxial wafers are used for high-efficiency infrared light-emitting diodes, and the sliding board method is commonly used to manufacture these wafers.

In the liquid phase epitaxial growth method using an ordinary carbon slide board, as shown in Fig. 1, a GaAs substrate 2, which is a growth substrate, is placed on a carbon board 1.
A substrate holder 3 is provided for placing the growth material in a molten state, for example Ga as a solvent, and GaAs as a solute is placed in a solution holder 4 also made of carbon.
and Ga solution 5 containing Si as an impurity.
While holding the solution 5, the solution holder 4 is slid to reach the growth target substrate 2 in the substrate holder 3, and the substrate 2 and the solution 5 are brought into contact to form an epitaxial growth layer on the surface of the substrate 2. It is something to do.

The most important stages in the liquid phase epitaxial growth process are the growth initiation period and the growth termination period.

At the beginning of growth, it is necessary to ensure uniform and complete contact between the substrate and the solution, and to prevent the solution surface from containing particles such as microcrystals and oxides.

After the growth is completed, if the temperature is lowered to room temperature while the solution and the growth surface remain in contact, the growth layer tends to become non-uniform. For this reason, a method is usually adopted in which the solution is separated from the growth surface (referred to as wipe-off) after the growth process is finished. At this time, it is important to completely remove the solution from the growth surface.Especially in Si-doped GaAs epitaxial growth, if even a small amount of solution remains on the growth surface after wiping off, it may cause damage while cooling to room temperature. Si microcrystals precipitate on the surface of the epitaxial growth layer below the residual solution, and the surface of the epitaxial growth layer becomes rough, which greatly impedes the subsequent device fabrication process. The surface impurity concentration of the epitaxial wafer needs to be high in order to stabilize the electrode formation in the subsequent device fabrication process, and if the Si concentration in the solution is increased for this purpose,
The above-mentioned Si microcrystals are more likely to precipitate.

On the other hand, to wipe off the solution from the growth surface,
The solution holder 4 in FIG. 1 or the wipe-off slider (not shown in FIG. 1)
The solution is removed by sliding the slider, but in order to completely wipe off the solution, the gap between the slider and the growth surface must be 50 μm below. To achieve this, strict dimensional accuracy of the slide board device is required.

Furthermore, strict precision is required in the thickness of the single crystal substrate and the thickness of the epitaxially grown layer until wipe-off.

Normally, the processing accuracy of the graphite material used to make the slide board is ±10 μm at most, the accuracy of the thickness of the single crystal substrate is ±10 μm, and the control accuracy of the epitaxial growth layer pressure is ±10 μm or more in the case of Si-doped GaAs epitaxial growth layers. It is. Therefore, it is extremely difficult to make the gap between the slider and the surface of the growth layer 50 μm or less and to prevent the slider and the surface of the growth layer from coming into contact with each other.

Furthermore, during wipe-off, there is excess water on the solution surface.
Since the GaAs component is precipitated as polycrystals, it is often observed that the slider gets caught in these polycrystals.

There are various problems in industrially implementing the conventional wipe-off method as described above.

The present inventors have conducted various studies to compensate for the shortcomings of conventional methods. As a result, the thickness of the Ga solution on the GaAs single crystal substrate was reduced to 3 mm or less, and the Si in the Ga solution was reduced to 3 mm or less.
If the concentration is 0.30% or less and GaAs polycrystals are precipitated over the entire surface of the Ga solution by bringing a jig into contact with the surface of the Ga solution, an epitaxial growth layer is formed without wiping off the Ga solution. Even if the Ga solution remains on the surface and is cooled to room temperature,
Since Si microcrystals do not form in the epitaxially grown layer and the segregation coefficient of Si is small, the Si concentration increases as the layer precipitates at a lower temperature, so it is easy to improve the Si concentration on the surface of the epitaxially grown layer. The present invention was achieved based on the discovery that it is possible to maintain the concentration at 5×10 ¹⁸ atm/cm ³ or higher, which is required for forming electrodes.

The present invention will be explained in detail below.

In the GaAs liquid phase epitaxial growth process, as the Ga solution containing GaAs as the solute is cooled, the
GaAs polycrystals are easily precipitated. In this case, from experiments conducted by the present inventors, we found that Si microcrystals precipitate preferentially on the polycrystalline surface formed on the solution surface than on the single crystal surface from a solution containing Si. If the thickness exceeds 5 mm or the Si concentration
It was found that when the content exceeds 0.7%, Si microcrystals precipitate even on single crystal planes. It was also found that even when polycrystals are precipitated on the solution surface, if it is only local and small, Si microcrystals are likely to precipitate on the single crystal surface.

Therefore, if GaAs polycrystals are precipitated over the entire surface of the Ga solution and epitaxial growth is performed at the same time, Si microcrystals will be concentrated on the polycrystalline side, making it possible to make the epitaxially grown layer extremely smooth. be. By separating and removing the polycrystalline portion in the intermediate liquid phase portion after epitaxial growth, it is possible to obtain a wafer of extremely high quality for use in light emitting diodes.

In order to deposit GaAs polycrystals over the entire surface of the Ga solution, the thickness of the Ga solution on the single crystal substrate must be 5
It is effective to prepare a large number of cores for polycrystalline precipitation, in addition to making the diameter smaller than mm.

The present inventors have found that the precipitation state of GaAs polycrystals on the surface of a Ga solution is greatly influenced by the material and structure of the substance that first comes into contact with the solution.

In other words, when the Ga solution surface is in contact with the gas phase or with a substance other than the gas phase,
GaAs is a substance with poor wettability with Ga solution.
Polycrystals tend to precipitate easily.

On the other hand, to make the epitaxial growth layer uniform
Although it is necessary to keep the Ga solution thickness uniform and constant,
Since the solution has a high viscosity, in order to keep the solution thickness constant over the entire surface of the substrate, it is necessary to suppress it with the upper slider 6 as shown in FIG. 2a. The upper slider 6 is attached to the solution holder 4 as shown in Figure 2b.
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The slider 6 is made of graphite, which has poor wettability with the Ga solution, and the surface that comes into contact with the Ga solution has a rough surface.
Finishing the surface as rough as polishing it with #300 emery paper and preparing many contact points with the Ga solution is extremely effective in precipitating GaAs polycrystals.

As explained above, if GaAs polycrystals are deposited on the entire surface of the Si-doped GaAs-Ga solution placed on the GaAs single crystal substrate and an epitaxial growth layer is formed on the single crystal substrate, the surface It is possible to extremely stably obtain an epitaxially grown layer with a high Si concentration and a nearly perfect uniform smoothness.

Examples of the present invention will be described below.

Example 1 A graphite slide board device as shown in FIG. 2b was used to form a GaAs epitaxial growth layer doped with Si on a GaAs single crystal substrate.
The depth of the substrate holder 3 was 3 mm, and the size of the GaAs single crystal substrate 2 was 45 mm in diameter and 350 μm in thickness.
In addition, six parts of the back surface of the solution holder 4 were finished by polishing with No. 300 emery paper.

0.91g of GaAs for 40g of Ga as Ga solution 5
and 0.1 g of Si was added. GaAs
The amount is the saturation amount of GaAs relative to Ga at a growth temperature of 750°C. The substrate 2 and the Ga solution 5 are mounted on a slide board device, placed in an H ₂ atmosphere, and after the inside of the furnace is sufficiently replaced with H ₂ , the temperature is raised to 750° C. and held for about 1 hour. During this time, the solute in the Ga solution 5
GaAs and impurity Si dissolve to form a GaAs saturated liquid. Incidentally, until this time, the Ga solution 5 and the substrate 2 are placed at positions apart from each other. Thereafter, the solution holder 4 is operated from outside the furnace and slid to bring the Ga solution 5 into contact with the substrate 2 and further slid to fill the substrate holder 3 with the Ga solution 5a, and the upper slider 6 suppresses the liquid level.

In this state, the furnace is gradually cooled down to 500°C at a cooling rate of approximately 0.5°C/min. During this time, a GaAs layer is epitaxially grown on the surface of the substrate 2, and a GaAs layer is grown on the surface of the Ga solution.
Polycrystals precipitate. 30 minutes after epitaxial growth
After cooling to ℃, the substrate was taken out using a slide board device, and the GaAs polycrystalline portion on the surface was removed to obtain the intended GaAs wafer.

The thus obtained GaAs epitaxial growth layer had a thickness of 50 μm and a Si concentration of 7.5×10 ¹⁸ atm/cm ³ .

Example 2 A graphite slide board device shown in FIG. 2b was used in which slits having a width of 0.5 mm and a depth of 0.2 mm were provided at 0.5 mm intervals on the surface of six parts. The epitaxial growth layer was grown under the same conditions as in Example 1, and the GaAs polycrystalline portion on the surface was removed.
The GaAs epitaxial growth layer is 45 μm thick and Si
The concentration was 7.5×10 ¹⁸ atm/cm ³ .

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a conventional epitaxial growth method, and FIG. 2 is an explanatory diagram showing a method of the present invention.

Claims (1)

[Claims] 1 When forming a Si-doped epitaxial growth layer on a GaAs single crystal substrate by the slide board method, the Si concentration in the Ga melt on the substrate was set to 0.1.
~0.7% by weight, and the thickness of the Ga melt on the substrate is 1
A method for producing an epitaxially grown layer, the epitaxially grown layer being formed on the substrate while crystallizing GaAs polycrystals on the surface of the Ga melt.