JP2003142404A - Method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device by which a high-quality III group nitride semiconductor crystal such as a cubic crystal GaN can be produced. SOLUTION: This method for manufacturing a semiconductor device is used to epitaxially grow a III group nitride semiconductor singlecrystal thin film provided with a substrate made of a GaAs single crystal. It includes a first process where each of material elements such as In, Ga, As, and N is alternately supplied onto the surface of the substrate in order of In, Ga, As, and N by a RF plasma source molecular-beam epitaxial method, to form an InGaAsN single crystal thin film; a second process where a III group element and N are alternately supplied onto the InGaAsN single crystal thin film by an migration enhanced epitaxy method, to a III group nitride single crystal thin film; and a third process where a III group nitride semiconductor crystal is grown on the III group nitride single crystal thin film by the molecular epitaxial method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device such as a light emitting diode or a semiconductor laser, and more specifically, gallium nitride (GaN) or aluminum nitride (Al).
N), indium nitride (InN) and other epitaxial technology for crystal growth of group III nitride semiconductors.

[0002]

2. Description of the Related Art Crystal growth of group III nitride semiconductors
As a technology, metal organic chemical vapor deposition (MOCVD method),
There is a line epitaxial method (MBE method). like this
When growing GaN by technology, cubic GaN is
It is a metastable phase mechanically and is more stable than hexagonal GaN which is a stable phase.
It is known that it becomes a low quality crystal. Its growth
Substrates for use are usually made of GaAs (001) or cubic SiC (001).
A substrate with a cubic structure is used. This board is hexagonal
Sapphire (Al
₂O₃Cleaving property is better than that of
It is advantageous for production. Furthermore, make the substrate itself conductive
It is also possible.

Regarding the growth method, light emitting diodes and semiconductor lasers have been realized (hexagonal GaN) by the MOCVD method. On the other hand, with respect to the growth of cubic GaN, a high quality crystal has not been obtained by either growth method, but it is considered that the MBE method is more advantageous than the MOCVD method. The reason is MOCVD and M
The optimum growth temperature for the group III nitride semiconductor crystal differs between the BE growth methods. That is, MOCVD
The method is 1000-1100 [℃], while the MBE method is 600
It is as low as ~ 800 [℃]. Cubic GaN which is a metastable phase
It is considered that the growth temperature by the MBE method is more suitable for the growth of GaN (group III nitride semiconductor: Isamu Akasaki).

In the MBE method, RF (Radio Frequency) is used.
-There is the MBE method. The RF-MBE method is performed by an MBE device using an RF plasma cell. RF-MBE
In the method, a high-frequency magnetic field is applied to molecular nitrogen (N ₂ ) to generate excited plasma (hereinafter referred to as plasma nitrogen).

[0005]

The conventional RF-MBE growth technique has the following three problems.

(1) First, as shown in FIG. 13, when cubic GaN is grown on a GaAs (001) substrate 101, G
The lattice mismatch between aAs and GaN is as large as about 20%, and the buffer layer 102 has a mosaic amorphous structure. Therefore, the stable layer, hexagonal GaN 103, grows predominantly,
Cubic GaN does not grow.

(2) The second is, as shown in FIG.
The flatness of the N growth surface is slightly broken, and it is a GaN (111) surface G
When the aN (111) facet surface 104 is formed, c
Hexagonal GaN 105 with oriented axes grows. In FIG. 14, reference numeral 106 is cubic GaN.

(3) Third, as shown in FIG. 15 (a), high-energy plasma-like nitrogen 107 is generated by the substrate 101.
As a result, the substrate surface is roughened as shown in FIG. In FIG. 15B, reference numeral 109 is
Ga. Then, as in the case where the GaAs (111) facet surface 108 is formed, as shown in FIG.
GaN105 grows.

As described above, according to the conventional growth technique, (1) the buffer layer has a mosaic amorphous structure, and (2) the GaN (111) facet is formed during GaN growth.
Growth of cubic GaN with c-axis oriented N (111) facets hinders growth of cubic GaN (3) Substrate is damaged by plasma nitrogen, resulting in irregularities and accompanying GaAs (111) facets Hexagonal G
There is a problem that aN grows and hinders the growth of cubic GaN.

The present invention solves the above three problems,
An object of the present invention is to provide a method for manufacturing a semiconductor device capable of realizing a high-quality group III nitride semiconductor crystal such as cubic GaN.

[0011]

In order to solve the above-mentioned problems, the invention of claim 1 epitaxially grows a group III nitride semiconductor single crystal thin film using a GaAs single crystal as a substrate.
In a semiconductor device manufacturing method, In, Ga, As, and N source materials are alternately supplied to the substrate surface in the order of In and Ga, As, and N by an RF plasma source molecular beam epitaxy method, and InGaAsN A first step of forming a single crystal thin film and a second step of forming a group III nitride single crystal thin film by alternately supplying a group III element and N onto the InGaAsN single crystal thin film by a migration enhanced epitaxy method. And a third step of growing a group III nitride semiconductor crystal on the group III nitride single crystal thin film by molecular beam epitaxy.

According to a second aspect of the present invention, in a method of manufacturing a semiconductor device, in which a group III nitride semiconductor single crystal thin film having a GaAs single crystal as a substrate is epitaxially grown, the substrate cleaned by an RF plasma source molecular beam epitaxial method. On the GaAs (001) surface of the substrate, the substrate temperature is 350-450 [℃]
In, Ga, As, and N are used as raw material elements for In, Ga, As, and
The first process of alternately supplying N in order to form an InGaAsN single crystal thin film, and the migration enhanced epitaxy method are used to alternately mix Ga and N on the InGaAsN single crystal thin film at a substrate temperature of 450 to 550 [° C.]. Supply to Ga
The second step of forming the N single crystal thin film and the substrate temperature on the GaN single crystal thin film by the molecular beam epitaxial method.
And a third step of growing a group III nitride semiconductor crystal at 600 to 700 [° C.].

According to a third aspect of the present invention, in the method of manufacturing a semiconductor device according to the first or second aspect, N is made into a plasma state in the first step, the second step and the third step. It is characterized by supplying.

When crystal growth of a cubic group III nitride semiconductor is performed on a GaAs (001) substrate, control at the initial stage of growth is extremely important. InGaAsN is used as the first growth layer by MBE method (formation of one atomic layer of InGaAs) and substitution of As and N (nitriding treatment)
When the growth is performed by alternately repeating and, unevenness at the interface between the substrate and the growth layer is suppressed, and a cubic crystal and single crystal buffer layer is realized. Using this as a template for growth of cubic GaN, GaN is grown as the second layer by the migration enhanced epitaxy method, and GaN is further grown thereon as the third layer by the MBE method.

As a result, hexagonal GaN, which has been a problem in the past,
It is possible to significantly reduce the inclusion of Cu, to inherit the cubic structure of the GaAs substrate in the growth layer, and to improve the proportion of cubic GaN in the crystal to 98%.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail. In this embodiment, a group III nitride semiconductor single crystal thin film using a gallium arsenide (GaAs) single crystal as a substrate is epitaxially grown. For this,
A GaAs (001) substrate is used. On the cleaned GaAs (001) surface,
At a substrate temperature of 350 to 450 [℃], indium (I
n), gallium (Ga), arsenic (As), and nitrogen (N) are alternately supplied in the order of (In + Ga), As, N, and InGa
An AsN single crystal thin film is formed. On top of that, 450-550 [℃]
A GaN single crystal thin film is formed by alternately supplying Ga and N at the substrate temperature of. On top of that, 600
A Group III nitride semiconductor crystal is grown at a substrate temperature of ℃ to 700 ℃.

Specifically, a group III element such as Ga and In, As, and plasma-like nitrogen are supplied on a GaAs single crystal substrate by RF-MBE to grow epitaxially. Nitrogen molecules are chemically very stable and have poor reactivity.
In MBE growth of N, how to supply nitrogen is
It becomes a big problem. In this embodiment, nitrogen (N ₂ )
Was activated by being made into a plasma state and used.

First, GaAs (001) surface is irradiated with (In + Ga or Ga) and As in this order at a substrate temperature of 350 to 450 [° C.],
About 1 atomic layer of InGaAs is formed. Subsequently, the nitriding treatment of irradiating plasma nitrogen is repeated several times to form an InGaAsN primary buffer layer. The above is the first process. By the nitriding treatment, some of the As atoms on the surface are replaced with N atoms.

Next, the substrate temperature is raised to 450 to 550 [° C.] while irradiating the As beam, and the irradiation of the As beam is stopped at the same time when the temperature rise is completed. Then, while maintaining the substrate temperature of 450 ° C. to 550 [° C.], the irradiation of the source beam is repeated alternately in the order of Ga and plasma nitrogen by the migration enhanced epitaxy method (MEE method) to form a cubic crystal.
Form a GaN secondary buffer layer. The above is the second process.

Subsequently, the substrate temperature is set to 600 to 700 [° C.].
The temperature rises to. While maintaining this temperature, the substrate is simultaneously irradiated with Ga and a plasma-like nitrogen beam to epitaxially grow GaN as a group III nitride semiconductor crystal by the MBE method. The above is the third process.

By taking these first to third steps, cubic GaN containing less hexagonal GaN is realized.

The following effects are produced by the above embodiment.

The main causes of the deterioration of the crystallinity of cubic GaN and the incorporation of hexagonal GaN in the conventional method are the formation of GaAs (111) facets and the formation of GaN (111) facets. That is, the flatness of the interface between the substrate and the growth layer is deteriorated by the damage of the plasma nitrogen, and the buffer layer is made amorphous due to the large lattice mismatch between the substrate and the epitaxial layer. What can be said from these facts is that the control of the initial stage of growth is extremely important for the production of cubic GaN which is a metastable layer.

First, the effect of the primary buffer layer will be described.

In order to solve the above-mentioned damage to the substrate and the problem of formation of the amorphous buffer layer at the same time, and to realize a buffer layer having a single crystal and cubic structure,
Raw material elements were alternately supplied onto the substrate at a substrate temperature of 0 to 450 [° C.] to grow crystals. By supplying the raw materials in the order of group III element and As, and growing only one atomic layer of group III arsenic compound such as GaAs, AlAs, and InAs, and irradiating it with plasma-like nitrogen alone, The process of nitriding for substituting parts with N atoms is alternately repeated several times.

As a result, a single crystal buffer layer was realized, and at the same time, substrate damage that promotes the formation of hexagonal GaN was successfully suppressed. Group III elements are Ga, In, A
As a result of growing with l and mixed crystals, high energy backscattered electron diffraction (Rheed: Reflection high-e
From the observation of energy electron diffraction), it was found that the case of InGaAsN has the highest single crystallization and a buffer layer having a cubic crystal structure can be obtained.

Normally, the nitriding phenomenon is negative for a substrate such as GaAs (001), which is easily damaged.
By this method, one atomic layer of flat InGaAs is formed at the atomic layer level by the method, and this is used as a template for nitride formation to perform nitriding treatment. As a result, the interface flatness between the substrate and the epitaxial layer was improved, the buffer layer was single-crystallized, and the obtained single-crystal buffer layer was used as a template for cubic GaN to maintain the cubic structure of the substrate in the epitaxial layer. And high quality cubic GaN can be realized. In other words, it is the key technology of the present invention in which the formation of the arsenic compound by the MEE method and the nitriding treatment are integrated.

Next, the effect of the secondary buffer layer will be described.

In the RF-MBE method, the optimum growth temperature of nitride is known to be 600 to 800 [° C]. However, even if As is always supplied in the temperature rising process after the growth of the above InGaAsN primary buffer layer, if the substrate temperature exceeds 600 [° C.], the epitaxial film peels off. The cause is In
It is thought that this is due to the desorption of As from the GaAsN surface.

At the substrate temperature of 450 to 550 [° C.], the GaN layer is inserted to prevent the desorption of As and to stabilize the InGaAsN layer. As a result, the substrate temperature is raised to 700 [° C.]. However, peeling from the substrate did not occur. Furthermore, this Ga
By growing the N secondary buffer layer by the MEE method, the symmetry of the Rheed diffraction image was improved and the crystallinity of the subsequent epitaxial layer was also improved as compared with the sample grown by the MBE method.

As described above, cubic crystals are formed on the GaAs substrate according to the present invention.
The structure in which GaN is formed has excellent cleaving properties and is effective in manufacturing a device using a cleaved surface such as a semiconductor laser.

[0032]

Embodiments of the present invention will be described in detail below. In this example, an InGaAsN primary buffer layer was grown on a GaAs (001) substrate, a GaN secondary buffer layer was grown on the GaAs (001) substrate, and a cubic GaN layer was grown on the InGaAsN primary buffer layer.

The MBE device contains the raw material elements and the substrate.
The container is ^-7[Torr] to 10
^-TenExhausted to [Torr]. In addition, such as Ga, In and As
The metal element is heated by an electric furnace,
Is irradiated as a dome. And the temperature of the electric furnace is changed
By doing so, the beam intensity can be adjusted.
The flow rate of nitrogen is adjusted by the mass flow controller.
And irradiate the substrate as plasma-like nitrogen on the substrate
To be done.

First, in order to grow the InGaAsN primary buffer layer, the substrate is heated to 400 ° C. The irradiation dose of each raw material was 6.5 × 10 ^-8 [Torr] for In and 3.6 × 10 ^{-8 for} Ga.
[Torr], As is 1 × 10 ⁻⁵ [Torr], N ₂ is 2 [sccm], R
The F output is 300 [W]. The MEE method was adopted in which the crystallinity of the epitaxial layer was dramatically improved by alternately opening and closing the shutters for supplying the group III element and the group V raw material.

According to the time chart shown in FIG. 1, the source element supplying method is such that (In + Ga) is irradiated for 10 seconds, As is irradiated for 5 seconds, and plasma-like nitrogen is irradiated for 2 seconds in this order. went. The supply amount of In atoms and Ga atoms was adjusted to an amount corresponding to 90% to 100% of the amount required to form one atomic layer of InGaAs per cycle. III
The amount equivalent to one atomic layer of group element is MB of GaAs (InGaAs)
It was determined from the Rheed intensity oscillation of E growth. The Rheed image after the growth of the InGaAsN layer is shown in FIG. For comparison, FIG. 5 shows a Rheed image after MBE growth of 15 atomic layers of GaN at a substrate temperature of 550 [° C.]. A raw material supply time chart for growing GaAsN by the MEE method at a substrate temperature of 400 ° C. is shown in FIG. Rhee after growth
The d image is shown in FIG. However, the irradiation amounts of Ga and plasma-like nitrogen, which are the raw materials, are the same as when the InGaAsN layer was grown.

Comparing FIGS. 4 to 6, the Rheed pattern (FIG. 4) after the growth of the InGaAsN layer is the best and shows the single crystallization of the grown layer. On the other hand, the substrate temperature
Rheed image of GaN layer grown by MBE at 550 [℃] (Fig. 5)
Shows a mosaic pattern, indicating that the crystallinity is poor. Here, GaN is used as the substrate temperature of 550 [° C.]
The substrate temperature is 400 by the MBE method.
When grown at [° C], the crystal further deteriorates and Rheed diffraction does not occur. GaAsN grown by MEE at a substrate temperature of 400 ° C. shows the just intermediate Rheed pattern of the previous two examples (FIG. 6). Although the crystallization is relatively advanced, the deterioration is unavoidable as compared with FIG. 4, and it can be imagined that it is amorphous.

Further, FIG. 7 shows an electron micrograph (SEM) image of a sample in which an InGaAsN layer was inserted as a buffer layer. In particular, the MBE-grown Ga showing a remarkable difference was observed.
FIG. 8 shows a cross-sectional SEM image of the sample with the N layer inserted. Then, compare these. In FIG. 8, remarkable unevenness is observed at the substrate-growth layer interface. However, in FIG. 7, the unevenness is eliminated by inserting the InGaAsN layer. "ME
It was verified that the combination of E method (InGaAs growth) + nitridation (substitution of As and N) ”drastically reduces damage to the substrate by plasma nitrogen.

Subsequently, As was grown on the InGaAsN primary buffer layer-formed sample and the GaAsN primary buffer layer-formed sample to grow a GaN secondary buffer layer, 1 × 10 ⁻⁵ [Torr] was used. ] The substrate temperature was raised to 500 [° C] while irradiating the substrate with the beam intensity. Irradiated A
Although s does not participate in growth, it has the effect of preventing As from desorbing from the substrate surface and preventing crystal deterioration.

After the temperature rise, according to the raw material supply time chart shown in FIG. 3 for growing GaN by the MEE method, Ga was irradiated for 4 seconds and plasma nitrogen was irradiated for 2 seconds in this order, and this was set as one cycle, 400 cycles, 80
Atomic layer was grown. The raw material supply conditions are Ga of 3.6 × 10 ^-8
[Torr], N ₂ is 2 [sccm], RF output is 300 [W],
The supply amount of Ga atoms was adjusted to an amount corresponding to 20 [%] of the amount required to form a GaN atomic layer per cycle.

Subsequently, the substrate temperature of these two samples was set to 650.
After heating to [℃], Ga was 1 × 10 ^-6 [Tor
r], N ₂ is 3 [sccm], and RF output is 350 [W], the GaN is supplied at a rate of 0.3 [μm] per hour.
Has grown up. InGaAsN primary buffer layer followed by GaN
Fig. 9 shows the Rheed image after growing the secondary buffer layer.
FIG. 9B shows a Rheed image shown in FIG. 9A, and then after MBE growth of GaN at a substrate temperature of 650 ° C.
Shown in. For comparison, MEE as the primary buffer layer
Rh after adopting the grown GaAsN layer and performing similar growth
The eed images are shown in FIGS. 10 (a) and 10 (b), respectively (a GaN secondary buffer layer at a substrate temperature of 500 [° C.], a substrate temperature of 6).
GaN growth layer at 50 [℃] is common to both samples. 9 and 10, the left side is <-110> incident and the right side is <110>.
The incident Rheed image is shown. In addition, "-1" in <-110>
Represents a bar of 1.

A four-fold streak pattern was confirmed in the Rheed image (FIG. 9B) when InGaAsN was used as the primary buffer layer. On the other hand, in the sample in which GaAsN was adopted as the primary buffer layer, as shown in FIG. 10B, an oblique pattern showing the formation of facet planes and the formation of twin defects was shown. 500 [℃] for both samples
The conditions of the GaN secondary buffer layer of No. 2 and the GaN growth layer of 650 [° C.] are common, so the results of FIGS. 9B and 10B show the effect of the primary buffer layer. That is, it means that the crystallinity control in the initial stage of growth greatly influences the crystallinity of the growth layer thereafter.

Here, the verification will be advanced by measuring the X-ray diffraction reciprocal lattice map. 11 and 12 show the results of the X-ray diffraction reciprocal lattice map measurement performed on the samples in which the InGaAsN layer and the GaAsN layer were inserted as the primary buffer layers, respectively. 11 and 12, peaks 10 and 11 are diffraction peaks by the GaAs (002) plane and the cubic GaN (002) plane, respectively. Further, although peak 12 and peak 13 are present in FIG. 12, hexagonal GaN (00
02) and hexagonal GaN (10-11) planes are diffraction peaks. The former is GaN (111) facets and the latter is hexagonal GaN grown from twin defects. In addition, in (10-11), "-1" represents the bar of 1. Cubic hexagonal GaN (0002)
Plane, GaN (10-11) plane peak intensity is calculated,
The ratio of cubic GaN in the growth layer was calculated. As a result, 60 samples with GaAsN primary buffer layer were inserted.
In contrast, the sample having the InGaAsN primary buffer layer inserted was as large as 98%, and the effect was confirmed.

Although the embodiments and examples of the present invention have been described in detail above, the present invention is not limited to these embodiments and examples, and changes and the like within the scope not departing from the gist of the present invention. Even if it exists, it is included in this invention. For example, in this embodiment and example, GaN is formed on the substrate.
However, the present invention can be applied to other group III nitride compound semiconductors such as AlN and InN.

[0044]

As described above, according to the present invention, a high quality cubic crystal by the RF plasma source MBE method is used.
Group III nitrides can be grown on GaAs (001) substrates.

Further, according to the present invention, InGaAsN is
When the first growth layer is grown by alternately repeating the E method (formation of one atomic layer of InGaAs) and the substitution of As and N (nitriding treatment), unevenness of the substrate-growth layer interface is suppressed, A cubic and single crystal buffer layer is realized. This is cubic Ga
As a template for N growth, GaN is grown as the second layer by the MEE method, and then GaN is grown as the third layer by the MBE method, so that the problem of the conventional mixture of hexagonal GaN is eliminated. It is possible to greatly reduce the crystal structure of the GaAs substrate to be inherited in the growth layer, and to increase the ratio of cubic GaN in the crystal to 98%.

[Brief description of drawings]

FIG. 1 is a supply chart showing supply of raw material elements in an example of the present invention.

FIG. 2 is a supply chart showing supply of raw material elements in an example of the present invention.

FIG. 3 is a supply chart showing supply of raw material elements in an example of the present invention.

FIG. 4 is a photograph showing a Rheed image after growth of an InGaAsN buffer layer according to an example of the present invention.

FIG. 5 is a photograph showing a Rheed image of a comparative sample with the sample of FIG.

FIG. 6 is a photograph showing a Rheed image of a comparative sample with the sample of FIG.

FIG. 7 is a cross-sectional electron micrograph (cross-section SEM) of a sample on which crystal growth was performed according to an example of the present invention.

8 is a cross-sectional electron micrograph (cross-section SEM) of the comparative sample of FIG.

FIG. 9 is a photograph showing an electron beam diffraction image after the growth of the secondary buffer layer and the growth of the GaN layer (third layer) according to the example of the present invention.

10 is a photograph showing an electron diffraction image of a comparative sample corresponding to the configuration of FIG.

FIG. 11 is a photograph showing an X-ray reciprocal lattice map of a sample on which crystal growth was performed according to an example of the present invention and a comparative sample.

12 is a photograph showing an X-ray reciprocal lattice map of the comparative sample of FIG.

FIG. 13 is a schematic diagram showing a conventional problem.

FIG. 14 is a schematic diagram showing a conventional problem.

FIG. 15 is a schematic diagram showing a conventional problem.

[Explanation of symbols]

10 XRD diffraction peak of GaAs (002) XRD diffraction peak of 11 GaN (002) XRD diffraction peak of 12 GaN (0002) XRD diffraction peak of 13 GaN (1011)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoki Fujiwara             3-4-1 Okubo, Shinjuku-ku, Tokyo Waseda Univ.             Faculty of Science and Engineering (72) Inventor Kaji Horikoshi             3-4-1 Okubo, Shinjuku-ku, Tokyo Waseda Univ.             Faculty of Science and Engineering F-term (reference) 5F041 AA40 CA34 CA40 CA66                 5F103 AA04 DD01 GG01 HH03 LL02                       LL03 RR06

Claims (3)

[Claims] 1. A method of manufacturing a semiconductor device, comprising epitaxially growing a group III nitride semiconductor single crystal thin film using a GaAs single crystal as a substrate, comprising: an RF plasma source molecular beam epitaxial method.
The first step of forming InGaAsN single crystal thin film by alternately supplying In, Ga, As, and N source materials to the substrate surface in the order of In and Ga, As, and N, and by the migration enhanced epitaxy method. A second step of alternately supplying a group III element and N on the InGaAsN single crystal thin film to form a group III nitride single crystal thin film; and a group III nitride single crystal by a molecular beam epitaxial method. And a third step of growing a group III nitride semiconductor crystal on the thin film. 2. A method for manufacturing a semiconductor device, comprising epitaxially growing a group III nitride semiconductor single crystal thin film using a GaAs single crystal as a substrate, comprising: an RF plasma source molecular beam epitaxial method.
On the GaAs (001) surface of the cleaned substrate, the substrate temperature of 350 ~
First step of forming InGaAsN single crystal thin film by alternately supplying In, Ga, As, and N source materials at 450 [° C] in the order of In, Ga, As, and N, and migration enhanced epitaxy method The substrate temperature is 450-550 on the InGaAsN single crystal thin film.
The second step of alternately supplying Ga and N at [° C] to form a GaN single crystal thin film, and a molecular beam epitaxial method on the GaN single crystal thin film at a substrate temperature of 600 to 700 [° C]. And a third step of growing a group III nitride semiconductor crystal. 3. The method of manufacturing a semiconductor device according to claim 1, wherein N is supplied in a plasma state in the first step, the second step and the third step.