JPH11340147A - Manufacture of nitride semiconductor wafer and element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the optimum nitriding condition by a simple method by specifying the nitriding time at a specific temperature in a nitriding process and, in addition, the ruggedness of AlN crystalline nuclei formed on the surface of a sapphire substrate. SOLUTION: A buffer layer 2 is deposited on a nitriding sapphire substrate 4 and a GaN crystalline layer 3 is grown on the layer 2. The nitriding time (t) (sec) of the substrate 4 is set at 4.7×10<-4> × exp (1.5×10<4> /T) when the nitriding temperature is T (k). In addition, the nitriding time (t) is set so that the ruggedness of AlN crystalline nuclei formed on the surface of the substrate 4 may not exceed 10 nm. Consequently, a crystalline layer 3 having high crystallinity can be obtained easily. When the temperature T is 1,000 deg.C, the nitriding time (t) is calculated to be about 62 seconds from the relation. Therefore, the productivity of a nitride semiconductor wafer 11 and, in addition, the crystallinity of a nitride semiconductor can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used as a light source for picking up an optical disk, a nitride semiconductor wafer which is a material for a light emitting diode used for a display device, a white light and the like, and a method for manufacturing a nitride semiconductor device. It is about.

[0002]

2. Description of the Related Art Nitride semiconductors do not have a thick film wafer. Conventionally, a sapphire substrate is used as a substrate and a thin film grown by vapor phase is used as a wafer. In such a crystal growth process, due to differences in the lattice constant between the substrate and the crystal to be grown, differences in the coefficient of thermal expansion, differences in the chemical surface state, etc., the substrate is used as a device material unless surface treatment is performed properly. I cannot make crystals. In particular, when growing a nitride crystal on a sapphire substrate, the difference in the chemical surface state becomes a more serious problem than the difference in the lattice constant and the coefficient of thermal expansion. For example, in the case where GaN is grown on a sapphire substrate, the crystallinity of GaN is best at 1000 ° C.
In the vicinity, the amount of GaN crystal attached to the sapphire substrate becomes very small, and a continuous crystal film cannot be obtained.

[0005] To solve this problem, FIG.
As shown in FIG. 1, after a buffer layer 2 made of AlN or GaN is deposited on a sapphire substrate 1 at a low temperature of about 600 ° C., a GaN crystal layer 3 is grown at 1000 ° C.
With this method, the GaN crystal layer 3 can be grown as a continuous film on the buffer layer 2 even at around 1000 ° C.

[0004] However, the crystallinity of the GaN crystal layer 3 depends on the unevenness of the buffer layer 2 as the base. The irregularities on the surface of the buffer layer 2 are caused by the lack of adhesion caused by attaching the buffer layer 2 on the sapphire substrate 1 at a low temperature.

In order to improve the adhesion of the buffer layer 2 on the sapphire substrate 1 at a low temperature, Japanese Patent Laid-Open Publication No.
No. 03388, before starting the crystal growth of the GaN crystal layer 3, the sapphire substrate 1 was heated at 1000 ° C. in an NH ₃ atmosphere.
Temperature, and heat-treated for 10 minutes to cover the surface of the sapphire substrate 1 with a thin Al film. Thereafter, a nitriding treatment was performed to lower the temperature of the sapphire substrate 1 to 950 ° C. It is disclosed that a 0.5 μm AlN film is grown.

According to this method, a nitride semiconductor wafer and a nitride semiconductor element which can be used as a device material can be manufactured.

[0007]

However, since the nitriding treatment of the sapphire substrate 1 is sensitive to temperature, it has been difficult to find optimal nitriding conditions by the above-described conventional method. That is, there is a problem in that it takes time to set the nitriding conditions, and the productivity is reduced.
An object of the present invention is to provide an optimum nitriding condition by a simple method to solve this problem.

[0008]

According to a first aspect of the present invention, there is provided a method for manufacturing a nitride semiconductor wafer, comprising the steps of: nitriding a sapphire substrate; and forming a buffer layer on the nitrided sapphire substrate. And forming a nitride-based crystal on the buffer layer in the method for manufacturing a nitride semiconductor wafer, wherein the nitriding time t is defined as T (K) in the nitriding process.
(Seconds) is 6.1 × 10 ⁻⁵ × exp (1.7 × 10 ⁴ /
T) or more. With this configuration, the optimum nitriding conditions can be obtained by a simple method, so that the productivity of the nitride semiconductor wafer and the nitride semiconductor element can be improved.

According to a second aspect of the present invention, in the method for manufacturing a nitride semiconductor wafer, the AlN crystal nuclei formed on the surface of the sapphire substrate have irregularities in the nitriding step, and the irregularities are 10 nm or less. It is characterized by the following. With this configuration, the optimum nitriding conditions can be obtained by a simple method, so that the productivity of the nitride semiconductor wafer and the nitride semiconductor element can be improved.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a manufacturing process of a nitride semiconductor wafer according to an embodiment of the present invention.

First, as shown in FIG. 1 (a), a sapphire substrate having a sapphire C-plane as a substrate is loaded into a MOCVD crystal growth furnace and heated to 1000 ° C. in a hydrogen atmosphere. At this time, the pressure in the furnace was 760 Torr, and the flow rate of hydrogen was 8 liters per minute. Sapphire substrate temperature is 10
When the temperature reaches 00 ° C., a sapphire substrate 1 is nitrided by flowing 3.8 liters of ammonia gas per minute. After nitriding,
A nitride layer (not shown) is formed in the sapphire substrate 4.

Thereafter, as shown in FIG. 1B, the substrate temperature is lowered to 550 ° C., and trimethylgallium (TMG
a) was supplied at a rate of 13.5 μmol / min, and a buffer layer 2 made of GaN was deposited on a sapphire substrate 4 having been subjected to a nitriding treatment.
Deposit for a minute. By this nitriding process, the surface state of the sapphire substrate 4 can be adjusted to the buffer layer 2.

Thereafter, as shown in FIG. 1C, the substrate temperature is raised again to 1000 ° C., and the crystal layer 3 made of GaN is formed.
Is grown on the buffer layer 2 for one hour. With this configuration, the manufacture of the wafer of the GaN-based nitride semiconductor device can be completed. Here, the wafer refers to a crystal serving as a base when manufacturing an element, and includes a crystal composed of several layers.

Here, the inventors paid attention to this nitriding step and conducted a detailed investigation on the nitriding step of the sapphire substrate. As a result, they have found that the sapphire substrate nitridation process consists of two steps.

The first step is to form an amorphous AlO by diffusing nitride species such as N, NH and NH ₂ into the sapphire substrate 4.
N is formed, and in the second step, AlN crystal nuclei are generated by nitriding the amorphous AlON. Here, the amorphous AlO
When N was formed, it was found that the surface was flat, and if the nitriding treatment was continued as it was, AlN crystal nuclei were generated, and the AlN crystal nuclei gradually increased, and irregularities exceeding 10 nm occurred.

The surface condition of the nitrided sapphire substrate 4 and the crystallinity of the crystal layer 3 grown via the buffer layer 2 formed thereon are investigated.
The crystallinity of the crystal layer 3 was the best when the surface of the substrate was amorphous AlON. In other words, it is necessary to perform a nitriding treatment so that the surface of the sapphire substrate 4 fits into the buffer layer 2. However, if the nitriding treatment is performed too much, AlN crystal nuclei are formed, so that the irregularities become large, and the crystallinity of the crystal layer 3 deteriorates. Become.

Further, the diffusion constant D and the temperature T of the nitride species in the sapphire substrate during the formation of the amorphous AlON
I came to understand the relationship. The diffusion constant D (cm ² / s) of the nitride species in sapphire is D = 2.5 × 10 ⁻¹³ × exp (−1.5 × 10 ⁴ / T), where T is the temperature. . From the diffusion constant D, the thickness of the amorphous AlON when sapphire is nitrided for t seconds is calculated as 2 × (D × t) ^1/2 . Since amorphous AlON which have minimum atomic layer of the sapphire substrate 4 (2.16 Å) or more even, minimum required nitridation time t (in seconds) is ^{t = (2.16 × 10 -8)} 2/4 / D Thus, t = 4.7 × 10 ⁻⁴ × exp (1.5 × 10 ⁴ / T).

On the other hand, if the nitriding time is too long, AlN crystal nuclei grow and the surface irregularities become large. As a result of the investigation, it was found that if the roughness exceeds 10 nm, the crystallinity of the crystal layer 3 deteriorates.

Therefore, when the temperature for nitriding the sapphire substrate 4 is T (K), the nitriding time t (second) is 4.7 ×
The nitriding time should be set to 10 ⁻⁴ × exp (1.5 × 10 ⁴ / T) or more and within a time such that the AlN crystal nuclei formed on the surface of the sapphire substrate 4 do not generate irregularities exceeding 10 nm. It can be seen that the crystal layer 3 having good crystallinity can be easily obtained.

In this embodiment, since the temperature T is 1000 ° C., it can be calculated as about 62 seconds by applying the above relational expression. Here, in consideration of the fact that the unevenness of the AlN crystal nucleus does not exceed 10 nm, a nitriding treatment was performed for 100 seconds to form a nitrided layer.

In the two-crystal X-ray rocking curve measurement of the GaN nitride semiconductor crystal fabricated as described above, G
The half value width of the diffraction peak from the aN (0002) plane is 60 (a
rcsec).

FIG. 2 shows the change in the half width of the X-ray rocking curve of the two-crystal method when the nitriding time (t) is changed from 10 seconds to 600 seconds.

It can be seen that when the nitriding time (t) is 10 seconds or 30 seconds, the crystallinity of the GaN nitride semiconductor is poor due to insufficient nitriding. That is, if the nitriding treatment is insufficient, the adhesion density of the crystal layer 3 when depositing the buffer layer 2 is low, and the grain size of the buffer layer 2 is large. In such a buffer layer 2 having a large grain size, during crystal growth of the crystal layer 3, distortion due to lattice mismatch with the sapphire substrate 4 and a difference in thermal expansion coefficient cannot be relaxed, and crystallinity deteriorates. Although the crystallinity is deteriorated even when the nitriding time (t) is 300 seconds or longer, since the sapphire substrate 4 is excessively nitrided, the generation of AlN crystal nuclei increases and the sapphire crystal before the buffer layer 2 is deposited. This is because large irregularities occurred on the surface of the substrate 4.

Next, a light emitting diode will be described as an example of a nitride semiconductor device manufactured using the nitride semiconductor wafer according to the embodiment of the present invention.

FIG. 3 is a sectional view of a light emitting diode manufactured on a nitride semiconductor wafer according to an embodiment of the present invention.

First, on the crystal layer 3 of the nitride semiconductor wafer of the present invention, an n-type GaN contact layer 5 and an undoped InG
Active layer 6 made of aN and p-type GaN contact layer 7
Grow sequentially. Next, in order to form an n-electrode, the p-type GaN contact layer 7 and the active layer 6 are shaved by dry etching, and a part of the n-type GaN contact layer 5 is shaved by dry etching. Next, an n-electrode 8 and a p-electrode 9 were deposited on the n-type GaN contact layer 5 and the p-type GaN contact layer 7, respectively, to produce a light emitting diode.

FIG. 4 is a diagram showing the relationship between the external quantum efficiency (%) and the nitriding time (second) of the light emitting diode formed on the nitride semiconductor wafer of the present invention.

In the case where the nitride semiconductor device of the light emitting diode is not subjected to the nitriding treatment or the nitriding time is short (a)
Has a small number of irregularities on the crystal surface, but has low luminous efficiency because the crystal has many crystal transitions and the like. In the case where the nitriding time is 300 seconds or longer (b), the electron concentration of the crystal layer 3 increases due to the unevenness formed on the substrate surface, and p
Since a mold layer cannot be obtained, the luminous efficiency is extremely low.

As described above, it is understood that it is very important to perform a nitriding treatment with an appropriate nitriding time using the present invention in manufacturing a GaN-based semiconductor device.

In the present embodiment, the nitriding temperature (T)
Was set to 1000 ° C., but the minimum time t (second) of the nitriding treatment was 4.7 × 10 ⁻⁴ × exp (1.5 × 10 ⁴ ) even at other temperatures.
/ T), an appropriate nitriding condition can be obtained by calculation.

In this embodiment, the steps of manufacturing a nitride semiconductor wafer and a nitride semiconductor device by MOCVD have been described.
The same effect can be obtained by growing a GaN crystal by a BE method, a plasma MOCVD method, or the like. Similar effects can be obtained irrespective of the source gas, carrier gas, growth pressure and the like.

In this embodiment, GaN is used as the buffer layer 2, but Al _x Ga ₁ -xN (0 ≦ x ≦ 1), that is, the same effect can be obtained by using AlN or AlGaN.

[0034] In the present embodiment uses a GaN crystal as the crystal layer 3 grown on the buffer layer 2, B _{x
Al y Ga z In 1-xyz} N (0 ≦ x ≦ 1,0 ≦ y ≦ 1,
0 ≦ z ≦ 1) That is, the same effect can be obtained with AlN crystal, InN crystal, BN crystal, and a mixed crystal thereof.

In the present embodiment, an n-type GaN contact layer 5, an active layer 6, and a p-type GaN contact layer 7 are sequentially grown on the crystal layer 3 of the nitride semiconductor wafer to manufacture a light emitting diode. An n-type cladding layer such as AlGaN may be provided between the n-type GaN contact layer 5 and the active layer 6, and a p-type cladding layer such as AlGaN may be provided between the p-type GaN contact layer 7 and the active layer 6. Good.

Although an example in which a light emitting diode is manufactured using the nitride semiconductor wafer of the present invention has been described, a semiconductor laser, a transistor, or the like may be formed as another element using the nitride semiconductor wafer. Similarly, the characteristics can be improved.

By growing the crystal layer 3 shown in the present embodiment to a greater thickness and removing the sapphire substrate 4, a similar effect can be obtained even when a nitride semiconductor wafer is manufactured.

[0038]

According to the present invention, since the optimum nitriding conditions can be obtained by a simple method, the productivity of the nitride semiconductor wafer can be improved. Furthermore, by using the nitride semiconductor wafer obtained by the method of the present invention, the crystallinity of the nitride semiconductor can be improved, so that the characteristics of the nitride semiconductor element and the like can be improved.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of a nitride semiconductor wafer according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between nitriding time and X-ray rocking curve half width.

FIG. 3 is a sectional view of a light emitting diode formed on a nitride semiconductor wafer according to an embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between nitriding time and external quantum efficiency of a light emitting diode.

FIG. 5 is a sectional view of a conventional nitride semiconductor device.

[Explanation of symbols]

 Reference Signs List 1 sapphire substrate 2 buffer layer 3 crystal layer 4 sapphire substrate nitrided 5 n-type GaN contact layer 6 active layer 7 p-type GaN contact layer 8 n-electrode 9 p-electrode

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masahiro Ishida 1-1, Sachimachi, Takatsuki-shi, Osaka Matsushita Electronics Corporation

Claims (5)

[Claims] 1. A nitriding step of nitriding a sapphire substrate, a step of forming a buffer layer on the nitrided sapphire substrate, and a step of forming a crystal layer made of nitride on the buffer layer. In the method of manufacturing a nitride semiconductor wafer having the above, the nitriding time t (second) when the temperature in the nitriding treatment step is T (K) is 4.7 × 1.
A method for producing a nitride semiconductor wafer having a density of 0 ⁻⁴ × exp (1.5 × 10 ⁴ / T) or more. 2. In the nitriding step, an AlN crystal nucleus formed on the sapphire substrate surface has irregularities,
2. The method for manufacturing a nitride semiconductor wafer according to claim 1, wherein the unevenness is 10 nm or less. 3. The method according to claim 1, wherein the buffer layer is made of Al _x Ga ₁ -xN (0 ≦
3. The method for manufacturing a nitride semiconductor wafer according to claim 1, wherein x ≦ 1). Wherein said crystal layer _{B x Al y Ga z In 1} -xyz
4. The method for producing a nitride semiconductor wafer according to claim 1, wherein N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1). 5. An n-type contact layer, an active layer and a p-type contact layer are sequentially formed on the nitride semiconductor wafer according to claim 1, wherein the n-type contact layer and the p-type contact layer are formed. A method for manufacturing a nitride semiconductor device, wherein an n-electrode and a p-electrode are respectively formed on a mold contact layer.