JPH0444222A - Manufacture of algaas monocrystalline substrate - Google Patents

Abstract

PURPOSE:To eliminate the need of removing substrate, reduce the epitaxial growing time and semiconductor device manufacturing cost, and prevent semiconductor wafers from bending by bringing a solid matter containing GaAs, Al, and impurities into contact with a Ga solution containing GaAs, Al, and impurities and a seed crystal into contact with the solution so as to allow an Al GaAs crystal to grow on the seed crystal. CONSTITUTION:A discoid single GaAs crystal having a diameter of about 4 cm is used as a seed crystal. By using a Ga as a solvent and a single GaAs crystal and Al as a solute, and Si as a dopant for imparting n-type conductivity to the crystal, the solute is dissolved in the Ga solution. A used solid matter composed of GaAs crystal and Al added with Si as a dopant is used. By bringing the solid matter, solution, and seed crystal into contact with each other and respectively heating the upper and lower sections of the solution to 900 deg.C and 950 deg.C with a temperature difference, a single AlGaAs crystal is grown on the seed crystal by utilizing the differences in specific gravity and temperature. At the time of growing the AlGaAS, the seed crystal is gradually pulled up. Therefore, a bulk crystal is grown on the seed crystal and an ingot is obtained. Thereafter, AlGaAs crystal substrates are obtained by slicing the ingot into pieces.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing an AlGaAs single crystal substrate.

[Conventional technology]

When epitaxially growing an AlGaAs crystal, which is a ternary mixed crystal of the (1)-V group compound semiconductor, GaAs, which is a binary compound of the (1)-V group, is generally used as a substrate due to the requirement of lattice matching. In this GaAs substrate, the thickness of the epitaxial layer grown by epitaxy is usually several tens of μm.
This is necessary because the epitaxial layer as it is has low mechanical strength. 20 GaA
Generally, substrates, not just S-substrates, are obtained by producing an ingot in which bulk crystals are grown by a pulling method or the like, and slicing the ingot into plate shapes. The wafer cut into thin plates by slicing is used as an epitaxial substrate, and further epitaxial layers are stacked thereon.

[Problem to be solved by the invention]

By the way, since the GaAs crystal substrate exhibits light absorption properties,
In order to increase the light extraction efficiency or to extract light from the GaAs substrate side, the GaAs substrate must be removed, and a substrate removal step is required during the device fabrication process.

In addition, in connection with this substrate removal, since the substrate is removed in the step after epitaxy, the AlGaAs layer epitaxially grown on the substrate must be thick to ensure mechanical strength. This takes a long time, which is one of the reasons for the high cost of semiconductor devices.

Furthermore, when growing an AlGaAs layer on a GaAs substrate, a slow cooling method using liquid phase epitaxy or a temperature difference method is usually used. For example, in the slow cooling method, Ga
AlGaAs crystal is epitaxially grown on an As substrate. However, if the crystal growth starts at a high temperature and the growth ends at a low temperature, a semiconductor wafer with an AlGaAs layer on a GaAs substrate will have a thermal expansion coefficient (generally is Ga at room temperature
As is 7.3X10-', AlGaAs is 5.2XIO
-') warping has already occurred.

Semiconductor wafers in such a warped state become difficult to perform subsequent processing processes. occurs frequently.

If it is known in advance that the GaAs substrate will be removed at the design stage of the semiconductor device, or if AlG is removed on the GaAs substrate.
In order to avoid the problem of warping of semiconductor wafers provided with an aAs layer, AlGaAs substrates should be used rather than GaAs substrates from the beginning.
Although it is sufficient to use an AlGaAs substrate, which is advantageous in terms of lattice matching, for the layer, it is difficult to grow a bulk crystal of AlGaAs as a substrate using a normal bulk crystal growth technique such as a pulling method. Therefore, it is unavoidable to use a GaAs substrate and epitaxially grow an AlGaAs layer thereon.

Therefore, an object of the present invention is to provide a novel method for manufacturing an AlGaAs single crystal substrate that solves the above problems at once.

[Means to solve the problem]

The purpose is to contact a solid material containing GaAs, Al, and impurities with a GafJ liquid containing GaAs, Al, and impurities, and then contact a seed crystal with the solution to form A on the seed crystal.
This is achieved by a method for manufacturing an AlGaAs single crystal substrate, which is characterized by having a step of growing an IGaAs crystal.

According to the manufacturing method of the present invention, a bulk crystal of AlGaAs for a substrate can be grown, and an ingot of AlGaAs single crystal can be obtained. If this ingot is sliced into thin plates and used as an AlGaAs crystal substrate, AlGaAs
Since the S substrate is optically transparent, there is no need to remove it.Moreover, even if the As layer on the A substrate is epitaxially grown on the AlGaAs base, both the substrate and the epitaxial layer are Al.
Since it is GaAs, there is no difference in thermal expansion coefficient, so no warpage occurs, and if the AlGaAs substrate according to the manufacturing method of the present invention is used, there is no need for a substrate removal process, so the epitaxial layer grown on the substrate can be a thin film. Therefore, Ga
The growth time can be shorter than the time required to form a thick AlGaAs layer on the As substrate with consideration given in advance to the removal of the substrate, and as a result, the manufacturing cost of the semiconductor element can be reduced.

In addition to these advantages, as will be described later, in the production method of the present invention, crystal growth is performed using a Ga solution using Ga, a low melting point metal (melting point: approximately 30°C), as a solvent, so there is no difference in stoichiometric composition. There are few structural defects in crystals such as.

Next, the three elements of the seed crystal, solution, and solid substance used in the production method of the present invention, which provide the various advantages described above, will be explained.

First, as is well known, a seed crystal is a crystal that becomes the first nucleus of a growing crystal, and there are no particular limitations on the seed crystal used in the present invention as long as it can be used as a nucleus to grow an AlGaAs crystal. The size of the 0 seed crystal, which is usually preferably made of monocrystalline or polycrystalline GaAs as in the case of obtaining conventional Ga^3 bulk crystals, depends on the size and shape of the ingot to be obtained, but for example, An example is a disk-shaped one with a diameter of about 1.5 to 2 inches (approximately 3.8 to 5.1 C11). During AlGaAs crystal growth, the seed crystal may be gradually pulled up as the crystal grows, or it may be left standing. Of course, if it is left standing, the AlGaAs crystal will grow in the solution. Furthermore, in either case of pulling or standing still, the seed crystal may be rotated slowly during crystal growth, if necessary.

The solution with which the seed crystal is brought into contact is a melt containing Ga as a solvent and monocrystalline or polycrystalline GaAs, Al, and impurities as solutes. Impurities (dopants) are added to control the conductivity of AlGaAs crystals.In the case of AlGaAs, in order to obtain n-type crystals, Sl,
SSn, Se, S, etc. are doped with Zn, Mg, Cd, etc. to obtain a p single crystal. The mixing ratio of each component in the solution depends on the composition of the AlGaAs crystal to be grown, but the ratio of GaAs to 100 parts by weight of Ga
1 to 14 parts by weight, preferably 3 to 10 parts by weight, AIo,
2 to 0.9 fi parts, preferably 0.5 to 0.8 parts by weight, dopant I X I (1-3 to 5 X 10-'
Parts by weight, preferably 3xl O-” to 2.5xl O
−' parts by weight.

The solid material to be brought into contact with the solution contains GaAs (single or polycrystalline), A1, and impurities. This is to compensate for f'Jf equivalent to the decrease in solubility (Al, As, )--Punt) in the solution as the AlGaAs crystal grows on the seed crystal. Therefore, the composition of the solid substance is almost the same as that of the AlGaAs crystal, and the impurities doped into the solid substance are Si, Te, and S in the n-type AlGaAs crystal, similar to the impurities in the solution.
n, Se.

S, etc., but P-type AlGaAs crystal contains ZnSMg, C
d etc. Each composition in the solid substance is AlGaAs
Although it depends on the composition of the crystal and the components in the solution for precipitating the crystal, it may be substantially the same as in the case of the solution described above.

That is, for 100 parts by weight of GaAs, All0 to 1
6 parts by weight, preferably 1 to 14 parts by weight, dopant I
X 10-' ~ I x 10-' parts by weight, ffi
L<I-! lXl0-' to lXl0-' parts by weight. However, it is important that each composition in the solid substance contains sufficient amounts of solutes in the solution necessary for AlGaAs crystal growth.

In the present invention, A
To grow a lGaAs crystal, a solid and a solution, and a solution and a seed crystal are placed in contact with each other.

With this arrangement, the AlGaAs bulk crystal grows thickly on the seed crystal. To explain the principle of this growth, first, elements (Al, ^S) that are lighter than the solvent (Ga) become highly concentrated in the solution due to the difference in specific gravity, and Al
GaAs crystals precipitate. On the other hand, as the crystal grows, the solution near the interface between the solid and the solution becomes unsaturated, resulting in a shortage of solutes A1 and As. moves toward the growing crystal due to the difference in specific gravity. In this way, by paralleling the growth of the AlGaAs crystal and the supply of the solute necessary for the crystal, a thick AlGaAs single crystal of a constant composition grows on the seed crystal.

However, the distribution of seed crystals, solutions, and solids! There is no particular limitation as long as the above-mentioned crystal growth process is repeated spontaneously. However, since the movement of solutes is due to the difference in specific gravity, it is usually a solid state in a suitable bulk crystal growth container 30 as shown in FIG. It is most preferable in terms of crystal growth efficiency to arrange substance 1, solution 2, and seed crystal 3 in this order in the vertical direction.If the seed crystal is left as it is or slowly pulled up in arrangement B, the specific gravity difference will be reduced. AlGaA on the seed crystal based on the principle
The s-crystal grows, and by creating a temperature difference between the upper and lower parts of the solution, the growth rate is further accelerated. In other words, if the upper part of the solution that comes into contact with the seed crystal is kept at a lower temperature, and the temperature is increased as it moves downwards (the solid material placed at the bottom of the solution is also brought to the same temperature), the solution containing a high concentration of solute will be In combination with density diffusion due to the density difference with the low temperature side (seed crystal side), thermal diffusion due to the temperature difference, and the aforementioned specific gravity difference, the movement of the solute supplied from the solid and crystal precipitation are promoted. This temperature difference varies somewhat depending on the composition of the AlGaAs crystal to be grown, but specifically, the temperature difference at the top of the solution is 800 to 1000°C1.
Preferably 850 to 950” C1, particularly preferably 90
At about 0℃, the lower part is 850-1200℃, preferably 9
00 to 1000''C1, particularly preferably about 950°C. This temperature difference is maintained during crystal growth.

When the temperature difference is not used, crystal growth is performed only by the difference in specific gravity, but in that case, it is preferable to keep the temperature of the entire solution as the same as possible.The same temperature is 700-1100. "C, preferably 850-1000"
C2 is particularly preferably about 900°C.

The bulk crystal-grown AlGaAs ingot is sliced into thin plates to obtain AlGaAs crystal substrates, and an AlGaAs epitaxial thin film is grown on the substrates by epitaxy (usually liquid phase epitaxy). At this time, as mentioned earlier, the epitaxial growth layer and the substrate are made of the same material and there is no difference in thermal expansion coefficient, so no warping occurs, but since the GaAs substrate is optically transparent, there is no need to remove it. Even if the epitaxial layer grown thereon is thin, it has sufficient mechanical strength as a semiconductor wafer.

An example of an LED chip manufactured using a ^1GaAs crystal substrate obtained by the manufacturing method of the present invention is shown in Figs.
The LEDs shown in C) and (a) have a simple structure consisting of an n-type AlGaAs substrate 10 manufactured according to the above manufacturing method, and a p-type AlGaAs layer 11 epitaxially grown on the substrate 10. A pn junction 12 is formed at the interface with 11. Further, on the upper surface of the layer 11, for example, CrAu, Zn-Au,
Alternatively, the electrode E1 made of 5i-Au or the like is made of, for example, AuGe or 5n-A as the n-side electrode material on the lower surface of the substrate 10.
An electrode E2 made of U or the like is provided by means such as vacuum evaporation.

The LED shown in [Yes]) has a P-type AlGaAs substrate 20,
P-type AlG grown epitaxially on the substrate 20
A pn junction 23 is formed at the interface between the 0 layer 21 and the layer 22, which are composed of an aAs layer 21 and an n-type AlGaAs layer 22. The layer 22 has an n-side electrode E2, and the substrate 20 has a p-side electrode E1. is provided. (C) LED is P-type AlG
aAs substrate 30, n-type AlGaAs layer 31, p-type AlG
Consisting of an aAs active layer 32 and an n-type AlGaAs layer 33,
An electrode E2 is formed on the layer 33, and an electrode E1 is formed on the substrate 30.

〔Example〕

Specific examples of the production method of the present invention will be described below.

In this embodiment, a disk-shaped single crystal GaAs having a diameter of about 4C11 is used as a zero seed crystal whose solid phase A1 of the A] GaAs crystal substrate to be manufactured is 0.7 and whose conductivity type is n type.

The solution uses Ga as a solvent and single crystal GaAs as a solute, A
1, Sl is used as a dopant to obtain n-type conductivity, and these solutes are dissolved in a Ga solvent. The mixing ratio of each component in the solution is 100 parts by weight of Ga to 100 parts by weight of GaAs.
Single crystal 6.08 parts by weight, AIo, 90 parts by weight, Te5X
It is 10-3 parts by weight. Solids are crystalline GaAs, AI
The material used is made of the following materials and is doped with Si as a dopant. The mixing ratio in the solid substance is 114 parts by weight of A1 and 10 parts by weight of Te1X with respect to 100 parts by weight of GaAs.

The above solid matter, solution, and seed crystal are brought into contact and distributed as shown in Part 1, and the upper part of the solution is 900°C and the lower part is 950°C, creating a temperature difference in the solution and utilizing the specific gravity difference and temperature difference. Then, an AlGaAs single crystal is grown on the seed crystal. In addition, AlG
During the growth of the aAs crystal, the seed crystal was gradually pulled up. As a result, a bulk crystal of AlGaAs grew on the seed crystal, and an ingot was obtained.

After that, slice this ingot into 1ill pieces.A
A GaAs crystal substrate can be provided.

[Effects of the Invention] Since the method for manufacturing an AlGaAs epitaxial crystal substrate of the present invention is configured as described above, it produces the effects as described below.

i) Since the aAs substrate is optically transparent to Al, Ga
There is no need to remove it unlike the As substrate.

11) Even if an AlGaAs layer is epitaxially grown on a ^1GaAs substrate, it is still the same AlGaAs crystal, so
There is no difference in thermal expansion coefficient, and no warpage occurs in the semiconductor wafer consisting of the substrate and epitaxial layer.

ii) Since the AlGaAs substrate does not need to be removed, the epitaxial layer grown on the substrate can be a thin film. Therefore, compared to the case where a GaAs substrate is used, the epitaxial layer growth time is shortened and the manufacturing of semiconductor devices is Cost can be reduced.

iv) Since the bulk crystal growth of AlGaAs is carried out in a state of thermal equilibrium, the resulting crystal does not have a non-stoichiometric composition;
Fewer structural defects.

[Brief explanation of drawings]

1st Fg:J is a cross-sectional view showing the arrangement of solids, solutions, and seed crystals for growing AlGaAs bulk crystals in the manufacturing method of the present invention, and Figures 2 (a) to (C) are respectively FIG. 2 is a cross-sectional view showing an example of an LED manufactured using the obtained AlGaAs substrate. 1. Solid 2: Solution 3 M crystal 10.20.30: AlGaAs crystal substrate 11.
21.31: p1AIGaAs layer 12.23
: pn junction 22.33 : n-type AlGaAs layer 32
:P-type AlGaAs active layers E1, E2
:@Pole Figure 1 El (a) Figure 2 (C) Figure 2

Claims (1)

[Claims] GaAs, Al, solid material containing impurities, GaAs,
AlGaAs characterized by having a step of contacting a Ga solution containing Al and impurities and further contacting a seed crystal with the solution to grow an AlGaAs crystal on the seed crystal.
Manufacturing method of As single crystal substrate.