JPH09180998A - Compound semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a cracking by providing anisotropy in the thermal expansion coefficient of at least one of a semiconductor substrate and semiconductor epitaxial layer, and satisfying the specific relation between the surface expansion coefficient of each layer and the temperature difference from the crystal growth temperature to the ambient temperature. SOLUTION: An AlN epitaxial layer 12 and GaN epitaxial layer 13 are sequentially grown on a 6H-SiC off substrate 11 in which the main surface of a substrate is formed off at 12 deg. from (10 to 10) surface in <000> direction. The surface expansion coefficient βof the main surface of the substrate 11 and the surface expansion coefficient α of the layer 13 opposed to the main surface of the substrate 11 satisfy the relation of (α-β).ΔT<=1.4×10<-3> , where the temperature difference from the crystal growth temperature to the ambient temperature is ΔT. Thus, the GaN compound semiconductor layer is epitaxially grown without generating cracking.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound semiconductor device, and more particularly, to a compound for heteroepitaxially growing a wurtzite compound semiconductor such as GaN on a hexagonal semiconductor substrate such as 6H-SiC with good matching. The present invention relates to a semiconductor device.

[0002]

2. Description of the Related Art Since GaN conventionally used as a blue light emitting element is a wurtzite type compound semiconductor, M is formed on a hexagonal 6H-SiC substrate having a similar crystal structure.
Epitaxial growth was carried out using the OVPE method (metalorganic vapor phase epitaxy).

For example, 6H-SiC of (0001) _Si surface
A substrate, that is, a 6H-SiC substrate having an exposed Si surface is prepared, and TMA (trimethylaluminum) is added in an amount of 20 to 200.
μmol / min, ammonia (NH ₃ ) 20000-2
00000 μmol / min (0.02-0.2 mol / min
Min) and hydrogen as a carrier gas are flown, the growth pressure is 70 to 760 Torr, and the substrate temperature is 800 to 110.
After growing an AlN intermediate layer having a thickness of 0.02 to 0.1 μm at 0 ° C., subsequently, TMG (trimethylgallium) is added at 10 to 100 μmol / min, and ammonia (NH ₃ ) is added at 0.02 to 0 μm. 0.2 mol / min, and hydrogen as a carrier gas is flown, and the growth pressure is 70 to 760.
The GaN epitaxial layer is grown under the conditions of Torr and the substrate temperature of 800 to 1100 ° C.

The growth layer velocity in this case is 0.1 to 1 μm / hour for the AlN intermediate layer and 0.5 to 5 μm / hour for the GaN epitaxial layer. In this case, G
The a-axis and the c-axis of the aN epitaxial layer are 6H-SiC.
This corresponds to the a-axis and c-axis directions of the substrate.

[0005]

However, in the conventional heteroepitaxial growth, when a GaN epitaxial layer is deposited to a thickness of about 2 μm, GaN is formed in the process of lowering the crystal growth temperature, that is, 1000 ° C. to room temperature after completion of the crystal growth. About 200-250 on the surface of the epitaxial layer
Cracking occurs at μm intervals, which hinders the formation of devices such as light emitting devices.

That is, in order to form a device, 2 μ
Although an epitaxial layer having a thickness of m or more, for example, about 4 μm is required, cracking starts to occur when the thickness exceeds about 1 μm, and as the film thickness increases, the frequency of cracking also increases. About 20 in thickness
Cracking occurs at intervals of 0 to 250 μm, and chip area, for example, 300 to 500 μm of blue light emitting diode.
This is because the gap is smaller than □, so that cracks are present in each chip, and the cracks affect the deterioration of the light emission characteristics of the device.

This situation will be described with reference to FIG. See FIG. 3. In FIG. 3, reference numeral 14 is a (0001) _Si plane, that is, a GaN epitaxial layer epitaxially grown on a 6H—SiC substrate in which the normal to the growth plane is the C-axis direction,
The shape shown by the broken line immediately after the end of crystal growth is transformed into the shape shown by the solid line during the temperature decrease process to room temperature.

This is because the linear thermal expansion coefficient of GaN is different from that of 6H-SiC. For example, the linear thermal expansion coefficient α _{a in} the a-axis direction is 5.59 × 10 ^-6 / K for GaN. On the other hand, 6H-SiC is as small as 4.2 × 10 ⁻⁶ / K, and the linear thermal expansion coefficient α _{c in} the c-axis direction is 3.17 × 10 ⁻⁶ / K for GaN. In contrast, 6H-SiC
Is as large as 4.68 × 10 ⁻⁶ / K, and both have anisotropy in the coefficient of thermal expansion.

Therefore, at the end of crystal growth, 6H--Si
GaN epitaxial layer 12 that was lattice-matched with the C substrate
In the temperature decreasing process, since the linear thermal expansion coefficient in the a-axis direction, that is, the x direction and the y direction is larger than 6H-SiC, it tries to shrink more than 6H-SiC in the x direction and the y direction. -SiC does not shrink relatively, so tensile stress acts. As a result of being pulled in the x direction and the y direction, compressive stress acts in the z direction, that is, the c-axis direction, and contracts in the c-axis direction.

The tensile stress acting in the x and y directions is
Since it causes cracking, cracking is more likely to occur as the GaN epitaxial layer 12 becomes thicker.

Therefore, it is an object of the present invention to prevent the occurrence of cracking in an epitaxial growth layer and to provide a high quality compound semiconductor device.

[0012]

FIG. 1 is an explanatory view of the principle configuration of the present invention, and means for solving the problems in the present invention will be described with reference to FIG. See FIG. 1 (1) In the compound semiconductor device in which the heterogeneous semiconductor epitaxial layer 2 is provided on the semiconductor substrate 1, at least one of the semiconductor substrate 1 and the semiconductor epitaxial layer 2 has anisotropy in thermal expansion coefficient and When the surface expansion coefficient β of the main surface of the semiconductor substrate 1 and the surface expansion coefficient α of the semiconductor epitaxial layer 2 facing this main surface are ΔT, the temperature difference from the crystal growth temperature to room temperature is (α− β) · ΔT ≦ 1.4 × 10 ⁻³ is satisfied.

Thus, even when at least one of the semiconductor substrate 1 and the semiconductor epitaxial layer 2 has anisotropy in the coefficient of thermal expansion, the coefficient of surface expansion β of the main surface of the semiconductor substrate 1
And the surface expansion coefficient α of the semiconductor epitaxial layer 2 facing this main surface is (α−β) · ΔT ≦ 1.4 × 10 ⁻³
By making the stress in at least one of the x-direction and the y-direction to be a compressive stress, the occurrence of cracking can be reduced.

(2) Further, the present invention is characterized in that, in the above (1), an intermediate layer having a thickness of 0.1 μm or less is interposed between the semiconductor substrate 1 and the semiconductor epitaxial layer 2.

Thus, by interposing an intermediate layer such as AlN having a thickness of 0.1 μm or less, G provided on the intermediate layer.
The crystallinity of the semiconductor epitaxial layer 2 such as aN can be improved.

(3) Further, according to the present invention, in the above (1) or (2), the semiconductor substrate 1 is a SiC substrate,
In addition, the semiconductor epitaxial layer 2 is II in which the group V element is N.
It is characterized in that it is composed of an IV compound semiconductor.

The above condition (1) or (2) is that a hexagonal crystal having a crystal structure different from that of the tetragonal system, SiC, and a wurtzite crystal, which is a III-V group compound in which the V group element is N. It is useful for semiconductor combination.

(4) Further, in the present invention according to the above (3), the III-V group compound semiconductor is composed of GaN, and S
The iC substrate is a 6H-SiC substrate or a 4H-SiC substrate.

The above condition (1) or (2) is
Useful for combining GaN with either a 6H-SiC substrate or a 4H-SiC substrate.

(5) Further, in the present invention according to the above (4), an angle θ formed by the main surface of the SiC substrate and the c-axis is 0 ° ≦ θ ≦.
It is characterized in that it is 53 °.

With respect to the (0001) plane of GaN, the above-mentioned (α-β) · ΔT ≦ 1.4 × 10 ⁻³ , that is, the relationship that the surface thermal expansion coefficients are substantially equal to that of the main surface of the SiC substrate. This can be satisfied by setting the angle θ formed by the c-axis to be 0 ° <θ ≦ 53 °.

(6) Further, in the present invention according to the above (5), the main surface of the SiC substrate is from [10-10] plane to [00
The surface is turned off by 12 ± 3 ° in the [01] direction.

From the {10-10} plane of this 6H-SiC substrate in the [0001] direction, that is, from the (10-10) plane
12 in the 0001> direction or the <000-1> direction
The surface turned off is (α-β) · ΔT = 0, that is, α = β
Is a surface having the same surface thermal expansion coefficient as that of the (0001) plane of GaN, and ± 3 ° is a margin for producing a surface 12 ° off. In this specification,
For convenience, an index usually represented by "1 bar" or "2 bar" is represented by "-1" or "-2".

(7) Further, in the present invention according to the above (5), the main surface of the 6H-SiC substrate is a surface off by 12 ± 3 ° from the {11-20} plane in the [0001] direction. Is characterized by.

From the {11-20} plane of this 6H-SiC substrate in the [0001] direction, that is, from the (11-20) plane
12 in the 0001> direction or the <000-1> direction
The surface turned off is (α-β) · ΔT = 0, that is, α = β
Is a surface having the same surface thermal expansion coefficient as that of the (0001) plane of GaN, and ± 3 ° is a margin for producing a surface 12 ° off.

[0026]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described with reference to FIG. See FIG. 2A. First, the main surface of the substrate is <0001> from the (10-10) plane.
Prepare a 6H-SiC off substrate 11 off by 12 ° in the direction, and add TMA (trimethylaluminum) 20 to 200
μmol / min, preferably 180 μmol / min, ammonia (NH ₃ ) 0.02 to 0.2 mol / min, preferably 0.1 mol / min, and hydrogen as a carrier gas 500 to 3000 sccm, preferably Is 1500 sccm
And a growth pressure of 70 to 760 Torr, preferably 10
The AlN epitaxial layer 12 having a thickness of 0.02 to 0.1 μm and preferably 0.05 μm is grown under the conditions of 0 Torr and the substrate temperature of 800 to 1100 ° C., preferably 1000 ° C.

Subsequently, TMG (trimethylgallium) is added in an amount of 10 to 100 μmol / min, preferably 44 μmo.
1 / min, ammonia (NH ₃ ) 0.02-0.2mo
1 / min, preferably 0.1 mol / min, and hydrogen as a carrier gas at 500 to 3000 sccm, preferably 1500 sccm, and the growth pressure at 70 to 760 To.
rr, preferably 100 Torr, substrate temperature 800-1
MOVPE under conditions of 100 ° C, preferably 1000 ° C
GaN epitaxial layer 13 with a thickness of 3 μm
Grow.

The growth rate in this case is also 0.1 to 1 μm / hour for the AlN epitaxial layer 12 and GaN.
The epitaxial layer 13 has a thickness of 0.5 to 5 μm / hour, and the GaN epitaxial layer 13 has an a-axis and a c-axis of 6
This coincided with the a-axis and c-axis directions of the H-SiC off-substrate 11, and as a result of observing the surface with an optical microscope, no cracking was observed.

See FIG. 2B. The GaN epitaxial layer 13 grown on the 6H-SiC off-substrate 11 has a coefficient of linear thermal expansion in the a-axis direction of the 6H-SiC off-substrate 11, that is, in the x direction in the figure during the temperature lowering process. Is larger than 6H-SiC, a tensile stress similar to the conventional one acts in the x direction.

On the other hand, in the y direction, that is, in the direction away from the c-axis of 6H-SiC by 12 °, the linear expansion coefficient is smaller than that of 6H-SiC, so that compressive stress acts, and the solid line shows the shape indicated by the broken line. Although it will change to the shape shown, the overall surface expansion coefficient β on the surface turned off by 12 ° is
Since the surface expansion coefficient α of the (0001) plane of GaN is approximately the same, cracking does not occur.

That is, the angle between the main surface of the 6H-SiC off-substrate 11 and the C-axis of SiC is θ, and the surface expansion coefficient of the GaN epitaxial layer 13, the linear expansion coefficient in the a-axis direction, and c
The linear expansion coefficients in the axial direction are α, α _a1 , and α _c1 , respectively, and the surface expansion coefficient of the 6H—SiC off substrate 11 is a,
The linear expansion coefficient in the axial direction and the linear expansion coefficient in the c-axis direction are
When β, α _a2 , and α _c2 , respectively, and the temperature difference from the crystal growth temperature to room temperature is ΔT, the product of the difference in surface expansion coefficient and the temperature difference (α−β) · ΔT is α-β) · ΔT ≈ (α _a1 −α _a2 ) · ΔT · (1 + si
n ² θ) + (α _c1 −α _c2 ) · ΔT · (1-sin ² θ).

If α = β, then 0 = (α _a1 −α _a2 ) · ΔT · (1 + sin ² θ) + (α
_c1− α _c2 ) · ΔT · (1-sin ² θ) becomes 0 = (5.59-4.2) × 10 ⁻⁶ × ΔT · (1 + sin ² θ) + (3.17-4.68) × 10 ^-6 × ΔT · (1-sin ² θ) ≈ (1.39) × 10 ⁻⁶ × ΔT · (1 + sin ² θ) − 1.51 × 10 ⁻⁶ × ΔT · (1-sin ² θ) ≈10 ⁻⁶ × ΔT {−0.12 + 2.9 sin ² θ}.

Therefore, sin ² θ = 0.12 ÷ 2.9≈0.0414 ∴θ≈12 °, and in the above embodiment, the off angle is set to 12 °, so that the 6H-SiC off-substrate 11 And GaN
The surface expansion coefficient of the epitaxial layer 14 can be made substantially equal.

On the other hand, θ = 90 °, that is, (0001) _Si
In the case of growing a GaN epitaxial layer on the 6H-SiC substrate of the plane, (α−β) · ΔT≈2 (α _a1 −α _a2 ) · ΔT≈2.78
× 10 ^-6 × ΔT becomes, in case of the [Delta] T ≒ 1000 °, the (α-β) · ΔT ≒ 2.78 × 10 -3 ≒ 2.8 × 10 -3.

Since cracking occurs when GaN is grown to 1 μm or more on this (0001) _Si- face 6H—SiC substrate, in order to prevent cracking at a film thickness of 2 μm or more required for a light emitting device, The relationship of the coefficient of surface expansion must be half or less than 2.8 × 10 ⁻³ , that is, (α−β) · ΔT ≦ 1.4 × 10 ⁻³ .

Here, (α-β) ΔT = 1.4 × 10
Calculating θ that is ⁻³ is (α−β) · ΔT≈10 ⁻⁶ × ΔT {−0.12 + 2.9 sin ² θ} = 1.4 × 10 ⁻³ .

When the temperature difference ΔT is set to ΔT≈800 ° which is the lower limit of the crystal growth temperature, {-0.12 + 2.9sin ² θ} = 1.4 ÷ 800 ×
10 ³ = 1.75 Therefore, sin ² θ = (1.75 + 0.12) ÷ 2.9≈0.6
448, and therefore θ≈53 °.

Therefore, the above (α-β) · ΔT ≦
To satisfy the condition of 1.4 × 10 ⁻³ , 800 to 11
Under the growth temperature condition of 00 ° C., the angle θ between the main surface of the 6H—SiC off-substrate 11 and the C axis of SiC needs to be 0 ≦ θ ≦ 53 °.

In the description of the above embodiment, only the single layer growth process is described. However, since the substrate off from the (10-10) plane in the <0001> direction is used, The substrate can be cleaved, and a blue semiconductor laser can be obtained by forming a pair of end faces that face each other by the cleavage.

In the above description of the embodiment, the off angle from the c-axis, that is, the <0001> direction is 12 degrees.
However, it does not have to be 12 ° purely, and is 12 ± 3 in consideration of the margin when the surface 12 ° off is projected.
It is sufficient if the angle is °, and the same is true in the <000-1> direction.

In the above description of the embodiment, the turning-off direction is from the (10-10) plane to <0001>.
Off in the direction, but <000 from the (11-20) plane
It may be a plane off in the 1> direction or the <000-1> direction, and may be a plane crystallographically equivalent to these crystal planes.

That is, the main surface of the 6H-SiC off substrate is
From the {10-10} plane or the {11-20} plane to [0
It is sufficient if the surface is inclined by θ in the [001] direction to satisfy 0 ° ≦ θ ≦ 53 °.

Although 6H-SiC is used as the semiconductor substrate in the above embodiment, 4H-SiC, which is one of the crystal polymorphs, may be used.

In the above-described embodiment, similarly to the conventional example, the AlN epitaxial layer 1 having a thickness of 0.02 to 0.1 μm is formed before the GaN epitaxial layer 13 is grown.
2 is grown in order to increase the generation density of crystal growth nuclei and to improve the crystallinity of the GaN epitaxial layer 13 provided thereon, which is not necessary in principle. Therefore, the growth of the AlN epitaxial layer 12 is omitted, and GaN is formed on the 6H—SiC off substrate 11.
The epitaxial layer 13 may be directly grown.

Further, in the above embodiment, the half
Although GaN is used as the conductor epitaxial layer,
Not limited to GaN, the same wurtzite crystal structure
AlN or InN having a structure may be used, and
Is Al, which is a mixed crystal of these _xGa_yIn_1-xyUse N
It is a good thing.

[0046]

According to the present invention, a GaN-based compound semiconductor layer can be epitaxially grown on a semiconductor substrate such as 6H-SiC without cracking by a metal organic chemical vapor deposition method, and a high quality blue color can be obtained. It is possible to manufacture a light emitting diode or a blue semiconductor laser.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a principle configuration of the present invention.

FIG. 2 is an explanatory diagram of an embodiment of the present invention.

FIG. 3 is an explanatory diagram of strain of a conventional epitaxial layer.

[Explanation of symbols]

 1 Semiconductor Substrate 2 Semiconductor Epitaxial Layer 11 6H-SiC Off Substrate 12 AlN Epitaxial Layer 13 GaN Epitaxial Layer 14 GaN Epitaxial Layer

Claims (7)

[Claims] 1. A compound semiconductor device in which a heterogeneous semiconductor epitaxial layer is provided on a semiconductor substrate, wherein at least one of the semiconductor substrate and the semiconductor epitaxial layer has anisotropy in thermal expansion coefficient, and the main surface of the semiconductor substrate is When the surface expansion coefficient β and the surface expansion coefficient α of the semiconductor epitaxial layer facing the main surface are ΔT, the temperature difference from the crystal growth temperature to room temperature is (α−β) · ΔT ≦ 1.4 A compound semiconductor device characterized by satisfying a relationship of × 10 ^-3 . 2. The compound semiconductor device according to claim 1, wherein an intermediate layer having a thickness of 0.1 μm or less is interposed between the semiconductor substrate and the semiconductor epitaxial layer. 3. The semiconductor substrate comprises a SiC substrate,
In addition, the semiconductor epitaxial layer has a group V element of N
3. The compound semiconductor device according to claim 1, which is made of a III-V group compound semiconductor. 4. The compound semiconductor device according to claim 3, wherein the III-V group compound semiconductor is made of GaN, and the SiC substrate is either a 6H—SiC substrate or a 4H—SiC substrate. . 5. The angle θ between the principal surface of the SiC substrate and the c-axis
Is 0 ° ≦ θ ≦ 53 °.
The compound semiconductor device described. 6. The main surface of the SiC substrate is {10-1
6. The compound semiconductor device according to claim 5, wherein the compound semiconductor device is a surface which is off by 12 ± 3 ° in the [0001] direction from the 0} plane. 7. The main surface of the SiC substrate is {11-2
6. The compound semiconductor device according to claim 5, wherein the compound semiconductor device is a surface which is off by 12 ± 3 ° in the [0001] direction from the 0} plane.