JP2002037695A - Method of forming single crystal thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a single crystal thin film in which a high quality single crystal thin film having a small dislocation density can readily be produced when growing a single crystal thin film having different quality of material on a single crystal substrate. SOLUTION: This single crystal thin film is formed by the following steps of: forming a first single crystal thin film 2 having a different latice constant on a single crystal substrate 1; forming selectively many quantum dots 3 comprising single crystals having a larger latice constant than that of the thin film 2 along a dislocation line 5 of the first single crystal thin film 2; growing continuously a second single crystal thin film 4 comprising single crystals having the same quality of the first single crystal thin film 2 on the first single crystal thin film 2 in a way that the quantum dots 3 are covered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a single crystal substrate,
The present invention relates to a method for forming a single crystal thin film for growing a single crystal thin film of a material different from that of a substrate.

[0002]

2. Description of the Related Art Conventionally, single crystal thin films have been used for optical devices such as semiconductor lasers, photodetectors, optical modulators, and FEs.
It is widely used for electronic devices such as T-HEMTs and HBTs, as well as phonic crystals and micromachines.

Recently, a single crystal thin film of gallium arsenide (GaAs) has been grown on a single crystal substrate of silicon, and a single crystal thin film of gallium nitride (GaN) has been grown on a single crystal substrate of sapphire. Research on growing single-crystal thin films of different materials on single-crystal substrates, such as those, has been carried out, and if these are realized, it becomes possible to form single-crystal thin films even with materials that did not have a conventional substrate .

[0004]

However, when growing single-crystal thin films of different materials on a single-crystal substrate, if the lattice constant of the single-crystal substrate and the single-crystal thin film differ by only 1%, the single-crystal There is a disadvantage that the dislocation density of the thin film becomes large and it becomes difficult to form a high quality single crystal thin film.

For example, when a gallium arsenide single crystal thin film is grown on a silicon single crystal substrate, the difference in lattice constant between the single crystal substrate and the single crystal thin film is about 4%, and the dislocation density of the single crystal substrate is small. In contrast to (1 to 1 × 10 ² / cm ² ), that of the single crystal thin film is extremely large, about 1 × 10 ⁵ to 1 × 10 ⁶ / cm ² .

[0006] When the dislocation density is increased as described above, non-radiative recombination increases when a single crystal thin film is used as a light emitting device, and the luminous efficiency decreases. In addition, there is a disadvantage that the S / N ratio is reduced due to an increase in the S / N ratio, and further, when used as an electronic device, there is a disadvantage that the mobility of electrons is reduced and the driving frequency is reduced.

The present invention has been devised in view of the above-mentioned disadvantages, and has as its object to easily produce a high-quality single crystal thin film having a low dislocation density when growing a single crystal thin film of a different material on a single crystal substrate. It is intended to provide a method for forming a single crystal thin film which can be formed on a substrate.

[0008]

A method for forming a single crystal thin film according to the present invention comprises the steps of: growing a first single crystal thin film having a lattice constant different from that of the single crystal substrate on the single crystal substrate;
On the surface of the first single-crystal thin film, a step of selectively forming a large number of quantum dots made of a single crystal having a larger lattice constant along dislocation lines of the first single-crystal thin film,
A step of continuously growing a second single-crystal thin film made of a single crystal of the same quality as the first single-crystal thin film on the first single-crystal thin film so as to cover the quantum dots. It is characterized by including.

Further, in the method for forming a single crystal thin film according to the present invention, the formation density of the quantum dots is 1 × 10 ⁶ / cm ² to 1 ×
It is characterized by being 10 ¹⁰ pieces / cm ² .

Further, in the method for forming a single-crystal thin film of the present invention, the single-crystal substrate is made of Si, and the first single-crystal thin film and the second
Is made of GaAs, and the quantum dots are InA
s, InGaAs, InAlAs, or InAlGaAs.

Further, the method of forming a single crystal thin film according to the present invention is characterized in that the first single crystal thin film, the quantum dots and the second single crystal thin film are continuously formed in a single film forming chamber. It is assumed that.

According to the method for forming a single crystal thin film of the present invention,
Since the dislocation lines of the first single-crystal thin film were covered with a large number of quantum dots, and a high-quality second single-crystal thin film with few dislocations was formed thereon, this second single-crystal thin film was By configuring the functional elements of various devices using
High quality devices can be obtained.

Further, according to the method for forming a single crystal thin film of the present invention, the single crystal substrate is not taken out of the film forming chamber even once,
Since the first single-crystal thin film, the quantum dots, and the second single-crystal thin film can be continuously formed in the same deposition chamber, the formation of the single-crystal thin film is easy, and high productivity can be maintained. it can.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view of a single crystal thin film manufactured by a forming method according to one embodiment of the present invention, wherein 1 is a single crystal substrate, 2 is a first single crystal thin film, 2a is a dislocation line, and 3 is a quantum Dots, 4 are second single crystal thin films, and 5 are dislocations.

The single crystal substrate 1 is made of single crystal silicon, sapphire, gallium arsenide, indium phosphide (InP), silicon carbide (SiC), or the like, and has a first single crystal thin film 2 and a second single crystal It functions as a supporting base material for supporting the thin film 4.

When the single-crystal substrate 1 is made of, for example, single-crystal silicon, an ingot of single-crystal silicon is formed by adopting a conventionally known Czochralski method (pulling method), and the ingot is formed into a predetermined thickness. It is manufactured by slicing and polishing the surface.

On the upper surface of the single crystal substrate 1, a first single crystal thin film 2 and a second single crystal thin film 4 are sequentially applied.

The first single-crystal thin film 2 and the second single-crystal thin film 4 are continuously formed of the same single-crystal material without any seam. Is formed by another single crystal having a lattice constant different from that of the single crystal (silicon) that forms.

For example, when the single crystal substrate 1 is made of single crystal silicon, the first and second single crystal thin films 2 and 4 have a lattice constant of ± 3% to ± 3% with respect to the lattice constant (5.43 °) of single crystal silicon.
Single crystals having lattice constants different by 8%, such as gallium arsenide, gallium phosphide (GaP), indium phosphide (In)
P) is used.

A large number of dislocations 5 are formed in the first single crystal thin film 2, and a gap between the first single crystal thin film 2 and the second single crystal thin film 4 is formed along the dislocation line. Many quantum dots 3 are interposed.

The quantum dots 3 have a width of 1 nm to 100 nm.
It is a polyhedral or hemispherical structure having a height of 0.5 nm to 10 nm and a small density such that the density of states of electrons is discretized by the quantum effect.

The quantum dots 3 correspond to the first and second quantum dots described above.
Formed of a high-quality single crystal having a lattice constant larger than the lattice constant of the single crystal thin films 2 and 4.

These quantum dots 3 are preferably
1. 3% to 8% of the lattice constant of the second single crystal thin films 2 and 4
The single crystal material formed of a single crystal having only a large lattice constant and forming the quantum dots 3 includes, for example,
When the second single crystal thin films 2 and 4 are made of gallium arsenide,
InAs, InGaAs, InAlAs, InAlGa
As, GaSb, or the like is used.

The quantum dots 3 are formed near the dislocation lines at a density of, for example, 1 × 10 ⁶ / cm ² to 1 × 10 ¹⁰ / cm ² , and these quantum dots 3 are interposed. The dislocation density in the region above the interface, that is, in the second single crystal thin film 4 is significantly lower than that in the first single crystal thin film 2. Therefore, by constructing functional elements of various devices using the second single-crystal thin film 4, a high-quality device can be obtained. For example, when the device is used as a light-emitting device, non-radiative recombination is reduced to reduce luminous efficiency. When used as a light receiving device, the dark current can be reduced to improve the S / N ratio, and when used as an electronic device, the mobility and driving frequency of electrons can be improved. Can be done.

Next, a method of forming the above-mentioned single crystal thin films 2 and 4 will be described with reference to FIG.

(1) First, the single-crystal substrate 1 made of single-crystal silicon manufactured by the above-described manufacturing method is washed with acetone or the like, and is immersed in a phosphoric acid-based etching solution for a predetermined time to prepare a single-crystal substrate. The polishing damage layer (the part damaged by polishing) on the surface is removed.

(2) Next, the single crystal substrate 1 is placed in a film forming chamber of a molecular beam single crystal growth apparatus, and an oxide film formed on the surface of the single crystal substrate 1 is removed.

The oxide film is removed by heating the film forming chamber to a high temperature of about 850 ° C. to cause sublimation.

(3) Next, as shown in FIG. 2A, a first single crystal thin film 2 having a lattice constant different from that of the single crystal substrate 1 is formed on the upper surface of the single crystal substrate 1.

The first single crystal thin film 2 is formed to a thickness of 1 nm to 100 nm by employing a conventionally known molecular beam epitaxy (MBE) method. At this time, the single crystal substrate 1 is placed in the same film formation chamber following the above-described step (2), and the inside of the film formation chamber is ultra-high vacuum, high temperature (about 40
0 ° C. or higher).

Then, a predetermined single crystal is formed by the supplied molecules while supplying the raw material into the film formation chamber in the form of a molecule, and the crystal is grown by depositing the single crystal on the single crystal substrate 1.

For example, when the first single crystal thin film 2 is formed of gallium arsenide, a molecular beam of gallium and arsenic is irradiated on the single crystal substrate 1 to couple gallium molecules and arsenic molecules on the surface of the single crystal substrate 1. By doing so, a first single crystal thin film 2 made of gallium arsenide is formed on the single crystal substrate 1.

In this case, gallium arsenide grows in accordance with the arrangement of the silicon molecules forming the single crystal substrate 1, but the lattice constants of the two are different by about 4%. Is dislocation 5 at a density of about 1 × 10 ⁸ / cm ²
Occurs.

(4) Next, as shown in FIG.
A large number of quantum dots 3 made of a single crystal having a larger lattice constant are selectively formed on the surface of the single crystal thin film 2 along dislocation lines 5a of the first single crystal thin film 2.

As in the case of the first single crystal thin film 2 described above, each of the quantum dots 3 employs a conventionally well-known molecular beam epitaxy method to form a polyhedron having a width of 100 nm or less and a height of 10 nm or less. It is formed so as to form a hemisphere.

When these quantum dots 3 are formed, the single crystal substrate 1 is placed in the same film forming chamber following the steps (2) and (3) described above. High vacuum and high temperature (above about 400 ° C).

In this step, molecules for constituting the quantum dots 3 are supplied into the film forming chamber, and these are combined on the first single-crystal thin film 2 to be temporarily deposited in a film having a thickness of about 6 nm. However, after that, it is naturally separated and deformed into a large number of polyhedrons or hemispheres by the action of stress, and is formed so as to cover the dislocation lines 5 a of the first single crystal thin film 2.

The growth of such quantum dots 3 is based on SK (St.
This is called “ranski-krastanow” mode growth, and many portions are formed at a portion having a low surface free energy, that is, a dislocation 5 or the like at a density of, for example, 1 × 10 ⁶ / cm ² to 1 × 10 ¹⁰ / cm ^2. It is formed.

For example, when the quantum dots 3 are formed of indium arsenide, a molecular beam of indium and arsenic is irradiated onto the single crystal substrate 1 so that the indium molecules and the arsenic molecules are combined on the surface of the single crystal substrate 1. A large number of quantum dots 3 made of arsenic are formed. in this case,
Since the lattice constant of indium arsenide forming the quantum dots 3 and gallium arsenide forming the first single crystal thin film 2 are different from each other by about 7%, the stress required to cause the SK mode growth is less than that of indium arsenide. And effectively act to form a large number of quantum dots 3 along the dislocation lines 5a on the surface of the first single crystal thin film. According to such a formation method, the quantum dots 3 are formed only by one growth, and do not require any substrate processing before growth or shape processing after growth.

(5) Finally, as shown in FIG. 2 (c), a second single crystal thin film 4 made of a single crystal of the same quality as the first single crystal thin film 2 is replaced with a plurality of quantum dots 3 described above. It is grown continuously on the first single crystal thin film 2 so as to be covered.

The second single-crystal thin film 4 is also formed seamlessly on the upper surface of the first single-crystal thin film 2 where no quantum dots 3 exist by employing a conventionally known molecular beam epitaxy method.

Also in this step, the single crystal substrate 1 is placed in the same film forming chamber following the above-mentioned steps (2) to (4), and the film forming chamber is in an ultra-high vacuum and high temperature (about 400 ° C. or higher). Is kept.

Then, in the same manner as in the step (3), while supplying the raw material in the form of molecules into the film forming chamber, a predetermined single crystal is formed by the supplied molecules, and this is covered with the quantum dots 3. By depositing on the first single-crystal thin film 2 in such a manner, a crystal having few dislocations grows.

For example, when the first single crystal thin film 2 is made of gallium arsenide, the second single crystal thin film 4 is also made of gallium arsenide. In this case, the dislocation density of the second single crystal thin film 4 is, for example, 1 × 10 ^{About 4} / cm ² and the first single crystal thin film 2
And a high quality single crystal thin film can be obtained.

Therefore, by forming functional elements of various devices using the second single-crystal thin film 4, a high-quality device can be obtained. For example, when the device is used as a light-emitting device, non-radiative recombination is reduced. In the case where the device is used as a light receiving device, the dark current can be reduced and the S / N ratio can be improved.
Further, when used as an electronic device, the mobility of electrons,
Driving frequencies can be respectively improved.

In this case, the first single crystal thin film 2, the quantum dots 3 and the second single crystal thin film 4 are continuously taken in the same film forming chamber without taking out the single crystal substrate 1 from the film forming chamber. Since the single crystal thin films 2 and 4 can be formed, the single crystal thin films 2 and 4 can be easily formed, and high productivity can be maintained.

The present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the gist of the present invention.

For example, in the above embodiment, a large number of quantum dots and single crystal thin films may be alternately stacked on the second single crystal thin film 4 a plurality of times. When such a laminated structure is repeated about 10 layers, the dislocation density of the single crystal thin film as the uppermost layer becomes about 1 × 10 ⁴ / cm ² , and the dislocation density is remarkably reduced.

In the above-described embodiment, the first and second single-crystal thin films 2 and 4 and the quantum dots 3 are formed by the molecular beam epitaxy method. Instead, the MOCVD method, the hot wall method, and the electron beam method are used. It may be formed by a vapor deposition method, a sputtering method, or the like.

[0051]

According to the present invention, the dislocation lines of the first single-crystal thin film are covered with a large number of quantum dots, and a high-quality second single-crystal thin film with few dislocations is formed thereon. Therefore, high-quality devices can be obtained by forming functional elements of various devices using the second single-crystal thin film.

Further, according to the present invention, the first single crystal thin film, the quantum dots, and the second single crystal thin film are continuously formed in the same film formation chamber without taking out the single crystal substrate from the film formation chamber. Therefore, it is easy to form a single crystal thin film, and high productivity can be maintained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a single crystal thin film manufactured by a formation method according to one embodiment of the present invention.

FIGS. 2A and 2B are cross-sectional views for explaining steps of a method for forming a single crystal thin film according to one embodiment of the present invention. FIGS.

[Explanation of symbols]

1 ... single-crystal substrate, 2 ... first single-crystal thin film, 3 ...
..Quantum dots, 4 ... second single-crystal thin film, 5 ...
Dislocation

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 31/10 H01S 5/343 H01S 5/343 H01L 31/10 A

Claims (4)

[Claims] A step of growing a first single-crystal thin film having a lattice constant different from that of the single-crystal substrate on the single-crystal substrate; and forming a larger lattice on the surface of the first single-crystal thin film. Selectively forming a large number of quantum dots made of a single crystal having a constant along dislocation lines of the first single crystal thin film; and forming a second single crystal made of a single crystal having the same quality as the first single crystal thin film. Continuously growing the crystal thin film on the first single crystal thin film so as to cover the quantum dots. 2. The formation density of said quantum dots is 1 × 10 ⁶
The method for forming a single-crystal thin film according to claim 1, wherein the number is 1 / cm ² to 1 × 10 ¹⁰ pieces / cm ² . 3. The single crystal substrate is made of Si, the first single crystal thin film and the second single crystal thin film are made of GaAs, and the quantum dots are made of InAs, InGaAs, InAlAs, I
The method for forming a single crystal thin film according to claim 1, wherein the method comprises one of nAlGaAs. 4. The first single-crystal thin film, the quantum dot, and the second
The method for forming a single crystal thin film according to any one of claims 1 to 3, wherein the single crystal thin film is formed continuously in a single deposition chamber.