JP2706592B2 - Crystal substrate manufacturing method - Google Patents

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. In the case where second and third crystal substrates having different lattice constants and thermal expansion coefficients from the first crystal substrate are formed by heteroepitaxial growth, various defects and lattices based on the difference between the lattice constant and the thermal expansion coefficient are formed. The method is characterized by a method for manufacturing a crystal substrate in which distortion is reduced and removed.

[0002]

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

[0003]

However, the life of the laser diode obtained by the above-mentioned method is extremely short.

[0004] The main cause is that the dislocation generated in the GaAs semiconductor crystal substrate due to the difference between the lattice constant and the thermal expansion coefficient of the GaAs semiconductor crystal and the Si semiconductor crystal substrate, and the dislocation is generated during the operation of the element by the active layer. Is the strain stress that can propagate and multiply.

[0005] The present invention is to further reduce the dislocation density and the strain stress of the epitaxially grown layer.

[0006]

According to the present invention, there is provided a method of manufacturing a crystal substrate according to the present invention, wherein a lattice constant and a thermal expansion coefficient of the first crystal substrate are different from those of the first crystal substrate. A second crystal substrate having a lattice constant and a coefficient of thermal expansion is formed so as to face a part of the second crystal substrate while being separated from the surface of the first crystal substrate, and then a third crystal substrate is formed on the second crystal substrate. When growing a substrate, a film is formed on the first crystal substrate exposed in the etching step before growth, such as silicon oxide, on which the third crystal substrate does not grow,
A part of the second and third crystal substrates is kept separated from the first crystal substrate even after the growth of the third crystal substrate.

[0007]

The crystal substrate produced by the above-described manufacturing method is
Many dislocations existing near the interface 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, the dislocations are moved and combined in the high-temperature state due to residual strain in the second crystal substrate without dislocation multiplication from near the interface, thereby reducing dislocations. Can be.

After that, by growing a third substrate layer on the second substrate with reduced distortion and defects, a third crystal layer having better crystallinity can be obtained. 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 growing the third crystal substrate, if nothing is performed on the exposed first crystal substrate, the third crystal will also grow on the first substrate, The separated state of the first and second substrates cannot be maintained. In fact, despite the fact that a region where the third crystal does not grow appears at a certain distance from the end of the second crystal substrate on the first crystal substrate, the second substrate is still at the end. It is to be bonded to the first substrate.

If the separation state is impaired, a new strain stress is formed in the process of lowering the temperature to room temperature after the crystal growth in the second and third substrates, and an element is formed on the third substrate. In that case, the deterioration of the element is accelerated.
For this reason, when growing a third crystal on the second substrate, a coating of, for example, silicon oxide is formed on the exposed first substrate so that the first substrate is not bonded to the second and third substrates. 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 the dislocation and the strain stress which hinder the operation of the element in the third crystal substrate can be reduced. An element having good characteristics can be formed on the third substrate.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, as shown in FIG.
A GaAs epitaxial layer 3 having a thickness of 0.2 μm was formed on an i-semiconductor crystal substrate 1 using a conventionally known two-step growth method. On top of that, a selective etching layer 2 of, for example, Al0.7 Ga0.3 As, which can be epitaxially grown with GaAs and can be selectively etched with respect to GaAs, is formed to have 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. 2A, 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,
Using an AlGaAs-based selective etching solution, for example, a hydrogen fluoride solution, only the Al0.7 Ga0.3 As selective etching layer 2 is partially removed by etching, and a plan view is shown in FIG. As shown, GaAs partially separated from Si semiconductor crystal substrate 1 and having relaxed strain stress
An s semiconductor crystal substrate layer was obtained. As a result of evaluating the strain in the GaAs semiconductor crystal substrate layer partially separated in such a shape by computer simulation and photoluminescence measurement, it was found that the strain in the GaAs semiconductor crystal substrate layer before separation was 1/10 in a wide range. It was found that it decreased below.

In this state, thermal annealing was performed at 800 ° C. for 10 minutes. Observation with a transmission electron microscope for examining dislocations after thermal annealing revealed that there were regions where dislocations were not observed in the partially separated GaAs semiconductor crystal substrate 3. Also, in the photoluminescence measurement, it was found that the strength was greatly increased as compared with before the annealing.

Thereafter, as shown in the cross-sectional view of FIG. 3, a vapor-deposited SiO 2 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 a thickness of about 500 angstroms. Formed. After that, reduced pressure MOCVD (metalorganic chemi
second GaAs separated by cal vapor deposition)
A GaAs epitaxial layer 5 serving as a third crystal substrate was regrown on the s substrate 3 to a thickness of 2 μm. After this regrowth, G
The boundary between the GaAs layer 3 and the Si substrate 1 was enlarged and observed using a scanning electron microscope to examine the state of separation between the aAs layer and the Si substrate, and the GaAs layer was separated from the Si substrate even after regrowth. Was kept. At this time, this SiO2
Was not formed, after growing the third GaAs layer, polycrystalline GaAs was grown on the Si substrate at a certain distance from the end of the second GaAs layer.

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

On the other hand, when the SiO 2 film was formed, the photoluminescence was measured to evaluate the strain and the crystallinity after the regrowth and the image thereof was observed. The emission intensity increased by a factor of 10 or more and the half-value width also decreased while remaining at or below 10. Further, even in the photoluminescence image, almost no dark spot due to dislocation or the like was observed. That is, it was found that the crystallinity was remarkably improved while maintaining the state where the strain was greatly reduced even after the regrowth.

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

The coating 6 for preventing crystal growth
May be used in a selective growth method, which is one of the conventional crystal growth methods. In addition to silicon oxide, silicon nitride, aluminum oxide, and the like are known.

[0019]

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

[Brief description of the drawings]

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

FIG. 2A is a plan view of a crystal substrate in one step of a method of manufacturing a crystal substrate according to an embodiment of the present invention; FIG.

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 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)

(57) [Claims] 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 on the first crystal substrate; In a process before growing a third crystal substrate on a second crystal substrate separated from the first crystal substrate surface, the second crystal substrate is formed so as to face the crystal substrate surface separated from the first crystal substrate surface.
A method of manufacturing a crystal substrate, comprising: 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 having a lattice constant and a thermal expansion coefficient different from the lattice constant and the thermal expansion coefficient of the first crystal substrate on the first crystal substrate. When a third crystal substrate is further heteroepitaxially grown thereon, a selective etching layer that can be selectively etched with respect to the first crystal substrate and the second crystal substrate is formed on the first crystal substrate. After forming the second crystal substrate on the selective etching layer, a kerf is formed from the surface of the second crystal substrate to at least the selective etching layer, and the selective etching layer is etched through the kerf. Removing the second crystal substrate so that a portion of the second crystal substrate is opposed to the first crystal substrate surface while being separated from the first crystal substrate surface, and a second crystal substrate separated from the first crystal substrate surface is formed. In the step before growing the third crystal substrate, a film on which the third crystal substrate does not grow is formed on the exposed first crystal substrate. A method for producing a crystal substrate, comprising heteroepitaxial growth.