JPH06232045A - Manufacture of crystalline substrate - Google Patents

Abstract

PURPOSE:To obtain a third crystalline substrate which is used for reducing dislocation and strain stress which obstruct the operations of a semiconductor element so as to make the element operate excellently and has a low dislocation density and less strain stresses at the time of forming the element on the third crystalline substrate after a second and the third crystalline substrates having different lattice constants and coefficients of thermal expansions than those of a first crystalline substrate are formed on the first crystalline substrate. CONSTITUTION:A GaAs epitaxial layer 3 which is used as a second crystalline substrate is formed on an Si substrate 1 which becomes a first crystalline substrate with a selectively etched layer 2 in between. Then an etching groove section 4 is formed in the layer 3 and only part of the layer 2 is etched off. Then, after forming an SiO2 film layer 6 on the exposed surface of the substrate 1, a GaAs epitaxial layer 5 is again grown on the GaAs layer 3 as a third crystalline substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a crystal substrate used for forming various semiconductor elements such as a transistor, a laser diode, a light emitting diode, and an optical IC, and more particularly to a first crystal substrate. Various defects and lattices based on the difference between the lattice constant and the thermal expansion coefficient when the second and third crystal substrates having the lattice constant and the thermal expansion coefficient different from the first crystal substrate are formed on the top by heteroepitaxial growth It is characterized by a method of manufacturing a crystal substrate from which strain is reduced and removed.

[0002]

2. Description of the Related Art In recent years, for example, when forming a GaAs semiconductor crystal substrate, Ga is formed by heteroepitaxial growth on a Si substrate which is inexpensive and can easily obtain larger crystals.
A method of forming an As semiconductor crystal substrate has been tried, and a laser diode or the like has been tried to be manufactured using the GaAs semiconductor crystal substrate obtained by this method.

[0003]

However, the lifetime of the laser diode obtained by the above method is extremely short.

The main cause is the dislocation generated in the GaAs semiconductor crystal substrate due to the difference in the lattice constant and the thermal expansion coefficient between the GaAs semiconductor crystal and the Si semiconductor crystal substrate, and the dislocation generated in the active layer during the operation of the device. It is a strain stress that can propagate and multiply.

The present invention further reduces the dislocation density and strain stress of this epitaxial growth layer.

[0006]

A method for manufacturing a crystal substrate according to the present invention for solving the above-mentioned problems is different from the lattice constant and the thermal expansion coefficient of the first crystal substrate on the first crystal substrate. A second crystal substrate having a lattice constant and a thermal expansion coefficient is formed so as to face each other with a part of the second crystal substrate separated from the first crystal substrate surface, and then a third crystal is formed on the second crystal substrate. In the case of growing a substrate, a film such as silicon oxide which does not cause crystal growth of the third crystal substrate is formed on the first crystal substrate exposed in the etching process before the growth,
Even after the growth of the third crystal substrate, a part of the second and third crystal substrates is kept separated from the first crystal substrate.

[0007]

The crystal substrate produced by the above manufacturing method is
A large number of dislocations existing near the boundary surface between the first and second substrates are removed, and large strain stress in the second crystal substrate is relaxed. By performing thermal annealing in this state, dislocations are not propagated from the vicinity of the interface and residual dislocations in the second crystal substrate and dislocations move / bond in high temperature state to reduce dislocations. You can

After that, a third crystal layer having better crystallinity is obtained by growing a third substrate layer on the second substrate having reduced strain and defects. If a sufficient thermal annealing effect can be obtained during the growth of the third crystal substrate, the previous thermal annealing may be omitted. However, when nothing is applied to the exposed first crystal substrate when growing the third crystal substrate, the third crystal is also grown on the first substrate, The separated state of the first and second substrates cannot be maintained. In fact, although a region where the third crystal does not grow appears at a certain distance from the edge of the second crystal substrate on the first crystal substrate, the second substrate is at the edge of the region. It will be joined to the first substrate.

If this separated state is impaired, strain stress is newly formed in the second and third substrates in the process of lowering the temperature after crystal growth to room temperature, and an element is formed on the third substrate. In that case, the deterioration of the element is accelerated.
Therefore, when growing a third crystal on the second substrate, a film of, for example, silicon oxide is formed on the exposed first substrate so that the first substrate and the second and third substrates are not joined. Form. As a result, the separated state between the first and second crystal substrates is maintained even after the third crystal growth.

That is, according to the present invention, even after the third crystal substrate is grown on the second crystal substrate, both dislocations and strain stress that hinder the operation of the device in the third crystal substrate can be reduced. A device having excellent characteristics can be formed on the third substrate.

[0011]

EXAMPLE First, as shown in FIG. 1, S having a thickness of 250 μm was used.
On the i semiconductor crystal substrate 1, a GaAs epitaxial layer 3 having a thickness of 0.2 μm was formed by a conventionally known two-step growth method. On top of that, a selective etching layer 2 of, for example, Al0.7Ga0.3As, which can be epitaxially grown with GaAs and which can be selectively etched with respect to GaAs, was formed to a thickness of 0.5 μm. On the selective etching layer 2, a GaAs semiconductor substrate layer 3 serving as a second crystal substrate was epitaxially grown by 1 μm.

Next, as shown in FIG. 2 (a), a kerf 4 reaching the selective etching layer 2 is formed by etching from the surface of the GaAs semiconductor crystal substrate layer 3 so as to leave a predetermined range 3a. Later, using the kerf 4,
Partial etching is performed to remove only the Al0.7Ga0.3As selective etching layer 2 using an AlGaAs-based selective etching solution, for example, a hydrogen fluoride solution, and a plan view is shown in FIG. 2A and a sectional view is shown in FIG. As shown, GaA partially separated from the Si semiconductor crystal substrate 1 and strain stress is relaxed.
An s semiconductor crystal substrate layer was obtained. The strain in the GaAs semiconductor crystal substrate layer partially separated in such a shape was evaluated by computer simulation and photoluminescence measurement, and as a result, it was 1/10 in a wide range compared with the strain of the GaAs semiconductor crystal substrate layer before separation. It was found to be decreasing below.

In this state, thermal annealing was performed at 800 ° C. for 10 minutes. Observation with a transmission electron microscope to examine the dislocations after the thermal annealing revealed that there are some regions in which dislocations are not observed in the partially separated GaAs semiconductor crystal substrate 3. It was also found that the photoluminescence measurement showed a significant increase in strength compared to before annealing.

Thereafter, as shown in the cross-sectional view of FIG. 3, a vapor-deposited SiO2 coating layer 6 is formed on the exposed Si substrate 1 other than the partially separated GaAs semiconductor crystal substrate 3 by a lift-off method using a photoresist to about 500 angstroms. Formed. After that, reduced pressure MOCVD (metalorganic chemi
second GaA separated by cal vapor deposition method
The GaAs epitaxial layer 5 to be the third crystal substrate was regrown on the s substrate 3 to a thickness of 2 μm. After this regrowth, G
In order to investigate the separation state between the aAs layer and the Si substrate, the boundary part between the GaAs layer 3 and the Si substrate 1 was enlarged and observed using a scanning electron microscope. The GaAs layer was separated from the Si substrate even after regrowth. Was kept. At this time, this SiO2
In the case where the GaAs was not coated, the polycrystalline GaAs was grown on the Si substrate at a certain distance from the end of the second GaAs layer after the growth of the third GaAs layer.

That is, there was a region where polycrystalline GaAs did not grow at a portion spaced from the end of the second GaAs substrate by a certain distance. This phenomenon is already well known as lateral diffusion of growth raw material. Even though there is a region where the polycrystalline GaAs does not grow, the second and third Ga are grown after the growth.
The As layer and the Si substrate were joined at their ends.
When photoluminescence measurement was performed to examine the strain in the third GaAs layer after the growth, it was found that thermal strain was further generated.

On the contrary, when the SiO 2 film was formed, the photoluminescence measurement and its image were observed to evaluate the strain and crystallinity after the regrowth. The emission intensity was increased 10 times or more and the half-width was also decreased while it was decreased to 10 or less. Furthermore, dark spots due to dislocations were hardly observed in the photoluminescence image. That is, it was found that the crystallinity was remarkably improved while maintaining the state in which the strain was greatly reduced even after the regrowth.

Thereafter, a semiconductor element such as a laser diode is formed thereon by a conventionally known method. The semiconductor element such as the laser diode is the third
It may be formed continuously during the growth of the crystal substrate. Further, if a sufficient thermal annealing effect is expected during regrowth, thermal annealing may be omitted. Further, the coating material may be other than SiO2 as long as it can prevent the bonding between the GaAs layer separated from the Si substrate and the Si substrate after the GaAs is regrown after being formed on the Si substrate.

The film 6 for preventing crystal growth
Can be used in the selective growth method which is one of the conventional crystal growth methods, and silicon nitride, aluminum oxide, etc. are known in addition to silicon oxide.

[0019]

According to the present invention, on the first crystal substrate,
Even when growing second and third crystal substrates having different lattice constants and coefficients of thermal expansion, the third substrate can be grown while keeping the separated state of the second substrate from the first substrate,
A third crystal substrate having a lower dislocation density and a lower strain stress than the second crystal substrate can be obtained, and a high quality element can be formed on the third crystal substrate.

[Brief description of drawings]

FIG. 1 is a sectional view of a crystal substrate in one step of a method for manufacturing a crystal substrate according to an embodiment of the present invention.

2A is a plan view of the crystal substrate in one step of the method of manufacturing a crystal substrate according to the embodiment of the present invention, and FIG. 2B is a sectional view taken along line AA of FIG. 2A.

FIG. 3 is a cross-sectional view of the crystal substrate in one step of the method of manufacturing a crystal substrate according to the embodiment of the present invention.

[Explanation of symbols]

 1 Si substrate 2 Al0.7 Ga0.3 As selective etching layer 3 GaAs epitaxial layer 4 etching groove 5 GaAs epitaxial regrowth layer 6 SiO2 coating layer

Claims (2)

[Claims] 1. A second crystal substrate having a lattice constant and a thermal expansion coefficient different from the lattice constant and the thermal expansion coefficient of the first crystal substrate, a part of which is formed on the first crystal substrate. In a step before the third crystal substrate is grown on the second crystal substrate spaced apart from the first crystal substrate surface, the second crystal substrate and the second crystal substrate separated from the crystal substrate surface facing each other.
A method of manufacturing a crystal substrate, which comprises forming a film on which the third crystal substrate does not grow on the exposed first crystal substrate, and then growing the third crystal substrate. 2. A second crystal substrate, which has a lattice constant and a thermal expansion coefficient different from the lattice constant and the thermal expansion coefficient of the first crystal substrate, is formed on the first crystal substrate. Upon further heteroepitaxially growing the third crystal substrate, a selective etching layer capable of being selectively etched with respect to the first crystal substrate and the second crystal substrate is formed on the first crystal substrate. After the second crystal substrate is formed on the selective etching layer, a kerf extending from the surface of the second crystal substrate to at least the selective etching layer is formed, and the selective etching layer is etched through the kerf. A second crystal substrate that is removed and is formed so that a part of the second crystal substrate faces the first crystal substrate surface in a state of being separated from the first crystal substrate surface. In the step before growing the third crystal substrate, after forming a film on which the third crystal substrate does not grow on the exposed first crystal substrate, a third crystal substrate is formed. A method of manufacturing a crystal substrate, which comprises performing heteroepitaxial growth.