JPS6150373B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of growing semiconductor crystals, and more particularly to a method of liquid phase epitaxial growth of semiconductor crystals.

Generally, in a substrate having an epitaxially grown layer used in a semiconductor device, it is required that the interface between the epitaxially grown layer and the substrate be flat.

However, in liquid-phase epitaxial growth of - group compound semiconductor crystals, the crystal substrate is exposed to a high-temperature atmosphere before the crystal substrate and the growth melt come into contact, so that group V element components are vaporized from the surface. It is known that a thermally altered layer is formed on the surface of the substrate, resulting in a rough surface. If epitaxial growth is performed directly on this surface, the interface between the substrate and the epitaxial growth layer will be uneven, and furthermore, it will be difficult for the epitaxial growth melt to uniformly contact the rough substrate surface. This results in so-called melt contact failure, and unevenness also occurs on the surface of the epitaxially grown layer.

As described above, if the surface of the epitaxial growth layer is not flat, it becomes a serious obstacle when performing microfabrication such as photolithography on this surface. Further, if a thermally altered layer due to vaporization of Group V elements exists on the substrate surface, it will have a negative effect on the electrical and optical characteristics of the semiconductor device that is finally manufactured.

For this reason, conventionally, a method has been adopted in which a step of removing the thermally altered layer and flattening the surface is added before performing liquid phase epitaxial growth.

This method will be explained based on the drawings.

FIG. 1a is a schematic diagram showing the above planarization process. In the figure, 1 is a substrate made of - group semiconductor crystal, etc., 2 is a thermally altered layer formed on the surface of the substrate 1, and the surface 3 of this thermally altered layer 2 is uneven. Reference numeral 4 denotes an unsaturated melt for flattening, and by bringing this into contact with the surface of the thermally altered layer 2, the thermally altered layer 2 is dissolved into the melt 4 as shown by the arrow and removed. FIG. 1b is a schematic diagram showing a process of performing liquid phase epitaxial growth.
In the figure, 1 is a substrate whose surface portion has been dissolved and removed through the process shown in FIG. 1a, and 5 is a melt for epitaxial growth having a predetermined composition. As shown in the figure, by bringing this melt 5 into contact with the surface 6 of the substrate 1, components in the melt 5 are precipitated as shown by the arrows, and an epitaxial growth layer 7 is formed on the surface 6.
is formed.

According to the above method, the thermally altered layer 2 can be easily removed before epitaxial growth, but there is a tendency that the dissolution progresses excessively and an unnecessarily thick layer is removed, and that the dissolution is not uniform. Don't proceed, 2nd
An undulating pattern is likely to occur as shown by surface 6 in Figure b. The excessive progress of dissolution and the occurrence of wavy patterns are caused by the difficulty in controlling the amount of dissolution, that is, the degree of saturation of the melt 4. This degree of saturation is determined by the amount of solute dissolved in the melt 4, but if it takes time to uniformly dissolve the solute into the melt and the solute contains Group V elements, this may cause volatilization. Because of this, it vaporizes during the melting process and the concentration in the melt decreases, making it difficult to control the melt 4 to a constant degree of saturation with good reproducibility.

This invention was made in view of the above-mentioned drawbacks of the prior art, and the solubility of the constituent elements of a crystal substrate in a melt containing a predetermined solute at a constant temperature is
Focusing on the fact that it differs depending on the plane orientation of the crystal substrate,
By utilizing this difference in solubility, a melt with a predetermined degree of saturation is formed, and by performing gentle dissolution with this melt, the thickness of the melt can be controlled.
Furthermore, the purpose is to flatten the interface between the epitaxial growth layer and the substrate.

Hereinafter, for convenience of explanation, a case will be described in which an InP crystal with a plane orientation of (100) is used as the crystal of the substrate.

At a constant temperature, the solubility of P atoms in In melt varies depending on the plane orientation of the InP crystal, as reported in, for example, Telecommunications Research Institute, Research Application Report, Vol. 26, (1979) 6. On page 1029 of the issue, Oe et al. report. Here, as shown in Fig. 2, under the conditions that the temperature is 650°C and the As mole fraction in the In melt is constant (0.045), the temperature in the In melt corresponding to each concentration of Ga in the melt is It has been shown that the solubility of P atoms in InP varies depending on the plane orientation of the InP crystal. In other words, Ga in the In melt and
Assuming that the mole fraction of As is 0.006 and 0.045, and the melt temperature is 650℃, the temperature of the melt saturated with InP on the 111B plane is equivalent to about 3℃ for 100 planes. It can be seen from Fig. 2 that only 0.2% is unsaturated.

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 3 shows a commonly used slide boat method. In the figure, 8 is a slide boat, 9 is a melt reservoir, and this slide boat 8
An InP crystal substrate 1 with a plane orientation of (100) is set at the substrate setting position. 10 is an InP crystal with plane orientation (111) B, 11 is a predetermined amount of InAs in the In melt.
12 is a melt for epitaxial growth. Such a slide boat 8 is placed in a reaction furnace (not shown), heated to 650° C. in a hydrogen atmosphere, and held for a predetermined time (about 1 hour). During this holding, InP from the surface of the InP crystal 9 having the plane orientation (111)B dissolves into the flattening melt 11 to the extent that it reaches saturation with the InP having the plane orientation (111)B. After doing this,
When the melt reservoir 9 is moved to the left and the melt 11 is brought into contact with the InP crystal substrate 1 having the plane orientation (100), the melt 11 becomes the InP crystal having the plane orientation (100) as described above. On the other hand, since it is unsaturated by a temperature corresponding to about 3° C., the surface portion of the substrate 1 gently dissolves into the melt 11. At this time, since the melt 11 becomes a supersaturated melt with respect to the crystal 10 having the plane orientation (111)B, it goes without saying that InP is precipitated onto the crystal 10. When the thermally altered layer disappears after contact for a predetermined period of time, the melt reservoir 9 is moved to the left one more step, and the epitaxial growth melt is applied to the surface of the flat crystal substrate 1 where the thermally altered layer is no longer present. The liquid 12 is brought into contact to start epitaxial growth. At the stage where the epitaxial growth layer with the desired thickness is obtained by lowering the temperature to a predetermined temperature, the growth melt 1 is
Excluding 1.

As described above, according to the present invention, the thermally altered layer on the surface of the InP crystal with the plane orientation (100) can be gently dissolved in the melt, which is unsaturated by several degrees Celsius in terms of temperature. The amount of dissolution can be controlled with good reproducibility,
Furthermore, since a surface with good flatness is obtained, a smooth epitaxial growth layer can be grown thereon.

In the above embodiment, the case where an InP crystal substrate having a plane orientation (100) is used as the crystal substrate is explained, but the present invention is applicable to liquids of other compound semiconductor crystals in which the solubility in the melt is dependent on the plane orientation. It can also be used for phase epitaxial growth.

[Brief explanation of the drawing]

Figures 1a and b are schematic diagrams showing the steps of the conventional liquid phase epitaxial growth method, and Figure 2 shows the solubility of P atoms and Ga dissolved in the In melt at a given temperature.
FIG. 3 is a schematic diagram illustrating an embodiment of the present invention. 1...Substrate [InP with plane orientation (100)], 10...
Crystal with a plane orientation that has lower solubility than the crystal of the substrate [InP with plane orientation (111)B], 11... Melt for flattening (In melt containing InAs and GaAs), 12... Melt for epitaxial growth liquid. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. After the surface of a substrate made of compound semiconductor crystal is planarized by melting it with a melt containing a predetermined solute,
In the method of forming an epitaxial growth layer on this surface in a liquid phase, a compound semiconductor crystal and a melt are combined in such a manner that the solubility of the constituent elements of the crystal in the melt differs depending on the plane orientation of the crystal. A liquid phase epitaxial growth method characterized in that a melt is saturated with a crystal whose plane orientation is smaller than that of a substrate, and the saturated melt is used to melt and flatten the surface of a substrate. 2 Inp in the plane orientation (100) as the substrate crystal,
The liquid phase according to claim 1, wherein an In melt containing a predetermined amount of InAs and GaAs is used as the melt, and Inp with a plane orientation of (111)B is used as a crystal with a plane orientation smaller than that of the crystal of the substrate. Epitaxial growth method.