JP2002338396A - Nitride semiconductor substrate and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a nitride semiconductor substrate, by which dislocations in a nitride semiconductor layer on the substrate can be reduced easily and uniformly over the whole surface of the substrate, and to provide the nitride semiconductor substrate. SOLUTION: The nitride semiconductor substrate 10 is composed of a GaN layer 2 being a first nitride layer, formed on the surface of a sapphire substrate 1 having (0001) plane or a plane direction inclined by several degrees from the (0001) plane, a plurality of protruded nuclei 5 composed of GaN being a second nitride, formed on the GaN layer 2, and a GaN layer 7 being a third nitride layer, formed on the GaN layer 2 and the protruded nuclei 5. The method of producing the nitride semiconductor substrate 10 comprises growing the GaN layer 2 on the sapphire substrate 1, then growing the protruded nuclei 5 on the GaN layer 2, and growing the GaN layer 7 on the GaN layer 2 and the protruded nuclei 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor substrate and a method for manufacturing the same.

[0002]

2. Description of the Related Art In the manufacture of a device using a nitride semiconductor substrate, there is no suitable substrate that lattice-matches with a nitride semiconductor layer grown on the substrate, and sapphire having a lattice mismatch of 13% or lattice mismatch. Substrates made of 3% SiC (silicon carbide) or the like. Then, due to lattice mismatch between the substrate and the nitride semiconductor layer and a difference in thermal expansion coefficient, the grown nitride semiconductor layer has a thickness of 10 ⁸ to 10
^Since dislocations having a high density of ¹⁰ cm ⁻² are generated, the conventional growth method has attempted to reduce the dislocation density by changing the growth conditions.

[0003]

However, in the conventional growth method, the dislocation density is 10 ⁸ cm ⁻² or more, and there is a limit in reducing the dislocation density.

[0004] Dislocations present in the nitride semiconductor substrate cause a leakage current and affect the electrical and optical characteristics of the nitride semiconductor layer, such as non-radiative recombination centers, resulting in a high dislocation density. The more the effect, the greater the effect. Accompanying this, the characteristics of the device fabricated on the nitride semiconductor substrate are deteriorated. In a nitride semiconductor device, problems such as a high laser oscillation threshold current density and a short device life are due in part to a high dislocation density.

Recently, a technique using selective growth (Epitaxial
Lateral overgrowth (ELO) was developed and found to be able to reduce the dislocation density to about 10 ⁷ cm ⁻² (A. Usui et al. Jpn. J. App1. Phys. 36 (1997) L89).
9). This is because the direction of propagation of dislocations is bent from the vertical direction to the horizontal direction by the lateral growth that appears as the selective growth.

[0006] Pendeo growth (Pendeo Epitaxy: TS Zhe1), which preferentially causes lateral growth similar to that of selective growth, thereby reducing dislocation density.
evaet a1. MRS Internet J. Nitride Semicond. Res. 4
S1, G3. 38 (1998)).

The technique is applied to the fabrication of a laser structure, and a violet laser fabricated in a low dislocation density region oscillates at a low threshold current density (about ² KA / cm ² ) and has a continuous operating life of 3000 hours. (S. Nakamura et a1.
Jpn. J. Appl. Phys. 37 (1998) L1020).

Further, a low-temperature intermediate layer deposition method (M. Iwaya et al.)
a1. Jpn. J. App1. Phys. 37 (1998) L316) has been proposed. This is because the growth of the nitride semiconductor layer is interrupted, the substrate temperature is lowered to about 500 ° C., and after depositing gallium nitride or aluminum nitride for several tens of nm, the substrate temperature is raised again and the regrowth reduces dislocations. This is a dislocation reduction growth method utilizing the above property.

FIG. 3 shows the EL device according to the first prior art.
FIG. 2 is a schematic cross-sectional view of a nitride semiconductor substrate manufactured by O.

[0010] As shown in FIG.
(Or SiC substrate), a GaN (gallium nitride) layer 32 is grown, a line and space pattern SiO ₂ mask 33 is formed thereon, and a GaN layer 3 is formed thereon.
4 is regrown, an SiO ₂ mask 33 is buried and flattened, and a nitride semiconductor substrate 35 is manufactured.

The dislocation 36 extending in the vertical direction is once bent in the horizontal direction (dislocation 37). Therefore, SiO ₂
A mask 33 is formed, and GaN is regrown thereon.
Dislocations are reduced on the surface of the aN layer 34 on the laterally grown portion on the SiO ₂ mask 33 (for example, A in the figure).
Department). However, dislocations gather in the crystal region on the SiO ₂ mask 33 (for example, portion B in the figure), extend upward, and a high-density dislocation and defect region are formed on the surface (for example, portion C in the diagram).

FIG. 4 is a schematic sectional view of a nitride semiconductor substrate manufactured by the pendeo growth in the second prior art.

As shown in FIG. 4, a GaN layer is grown on a SiC substrate 41 (or a sapphire substrate).
A GaN nucleus 42 is formed by etching away the GaN layer to the substrate interface, leaving a part of the N growth layer. in addition,
GaN layer 43 is regrown, GaN nucleus 42 is buried,
After flattening, a nitride semiconductor substrate 44 is manufactured.

In the GaN layer 43 to be regrown, lateral growth occurs, and dislocations bend in the lateral direction. However, Ga
Dislocations 45 remain on the N nuclei 42, and at the coupling portions grown in the lateral direction, the dislocations gather to form high-density dislocations and defect regions on the surface (part D in the figure).

FIG. 5 is a schematic sectional view of a nitride semiconductor substrate manufactured by the low-temperature intermediate layer deposition method according to the third prior art.

As shown in FIG. 5, the sapphire substrate 51
Growing a GaN layer 52 on the (or SiC substrate),
The growth temperature is lowered to 500 ° C., and a low-temperature intermediate layer 53 made of gallium nitride or aluminum nitride is deposited to several tens of nm. A GaN layer 54 is grown thereon, and the growth temperature is set to 50.
0 ° C., a low-temperature intermediate layer 55 of gallium nitride or aluminum nitride was deposited for several tens nm,
The layer 56 is grown.

By disposing several layers (two layers in the figure) of the low-temperature intermediate layers 53 and 55 in this way, it is possible to reduce dislocations in the entire nitride semiconductor substrate 57. However, since it is necessary to raise and lower the temperature and further repeat the process, it takes much time to manufacture the nitride semiconductor substrate 57 by this method.

As described above, the conventional low dislocation density nitride semiconductor substrate requires an increase in the number of processes and time for reducing dislocations, and a spatial distribution of dislocation density is generated spatially depending on the method. .

The present invention has been made in view of such conventional problems, and has as its object to reduce the dislocation of a nitride semiconductor layer on a substrate simply and uniformly over the entire surface of the substrate. An object of the present invention is to provide a semiconductor substrate and a method for manufacturing the same.

[0020]

In order to solve the above-mentioned problems, a nitride semiconductor substrate according to the present invention has a first nitride layer formed on a substrate and a first nitride layer formed on the first nitride layer. Second
And a plurality of protruding nuclei made of the above nitride, and the first nitride layer and a third nitride layer formed on the protruding nuclei.

Further, the nitride semiconductor substrate of the present invention has a (0
The first nitride layer is formed on the substrate having a plane orientation inclined several degrees (less than 10 degrees) from the (001) plane or the (0001) plane.

Further, the nitride semiconductor substrate according to the present invention is characterized in that the substrate is made of sapphire, SiC or GaN.

Further, according to the method of manufacturing a nitride semiconductor substrate of the present invention, a first nitride layer is grown on a substrate, and a plurality of protrusions made of a second nitride are formed on the first nitride layer. A nucleus is grown, and a third nitride layer is grown on the first nitride layer and the protruding nucleus.

Further, in the method for manufacturing a nitride semiconductor substrate according to the present invention, it is preferable that at least one of the first nitride layer, the protrusion nuclei, and the third nitride layer is grown by MOVPE. Features.

Further, the method of manufacturing a nitride semiconductor substrate according to the present invention is characterized in that the protruding nuclei are formed by switching a carrier gas in MOVPE growth from hydrogen to nitrogen.

According to the nitride semiconductor substrate and the method of manufacturing the same of the present invention, a projection nucleus made of a second nitride is formed on a first nitride layer, and a third nitride layer is formed thereon. By doing so, the third nitride layer can be grown in the lateral direction, and the propagation of the vertically extending dislocations existing in the first nitride layer can be bent in the lateral direction. It is possible to provide a low-dislocation-density nitride semiconductor substrate in which dislocations extending to the surface of the semiconductor substrate can be reduced, and dislocations in the nitride semiconductor layer can be easily and uniformly reduced over the entire surface of the substrate.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings described below, those having the same functions are denoted by the same reference numerals, and the repeated description thereof will be omitted.

FIGS. 1 (a), 1 (b), 2 (c), (d)
FIG. 3 is a schematic cross-sectional view showing a procedure of a method for manufacturing a nitride semiconductor substrate according to an embodiment of the present invention. Note that FIG.
(D) is a schematic process drawing showing the structure of the nitride semiconductor substrate in the present embodiment.

First, as shown in FIG. 1A, a GaN layer 2 is grown as a first nitride layer on a sapphire substrate 1 (or SiC substrate).

That is, MOVP which supplies ammonia and trimethylgallium with hydrogen gas as a carrier gas
Using the E method (metal organic chemical vapor deposition), a first surface is formed on a sapphire substrate 1 (or a SiC substrate) having a (0001) plane or a plane direction inclined several degrees (less than 10 degrees) from the (0001) plane. A GaN layer 2 which is a nitride layer is grown. 3 in the figure indicates a hydrogen carrier gas.

In the case of the sapphire substrate 1, first, a gallium nitride or aluminum nitride layer (not shown) is deposited as a low-temperature buffer layer at a low temperature of about 500 ° C. in a carrier gas of hydrogen gas. Thereafter, the temperature is increased to about 1000 ° C.
And a GaN layer 2 having a thickness of 2 to 3 μm is grown.

When a SiC substrate is used in place of the sapphire substrate 1, first, in a carrier gas of hydrogen gas, about 1
At 100 ° C., an aluminum nitride layer (not shown) is deposited as a low temperature buffer layer. Thereafter, the temperature is increased to about 1000 ° C.
And a GaN layer 2 having a thickness of 2 to 3 μm is grown.

In depositing the aluminum nitride buffer layer, trimethyl aluminum is used as a raw material of aluminum.

The GaN layer 2 is grown under the condition that a commonly used carrier gas is hydrogen. The GaN layer 2 has a high dislocation density due to lattice mismatch with the substrate. 4 in the figure indicates a dislocation.

Next, as shown in FIG. 1B, GaN as a second nitride is formed on a GaN layer 2 which is a first nitride layer formed on a sapphire substrate 1 (or a SiC substrate).
A plurality of protruding nuclei (that is, three-dimensional nuclei) 5 consisting of The protruding nuclei 5 can be formed by switching the carrier gas from hydrogen to nitrogen after forming the GaN layer 2. Reference numeral 6 in the figure denotes a nitrogen carrier gas. The protruding nucleus 5 has a conical shape.

Next, as shown in FIG. 2C, a plurality of protruding nuclei 5 formed on the GaN layer 2 on the sapphire substrate 1 are formed.
On top, the GaN layer 7 is grown so as to bury these protruding nuclei 5 under the condition of returning the carrier gas from nitrogen to hydrogen and further growing in the lateral direction. Reference numeral 8 in the drawing denotes a hydrogen carrier gas. The condition for lateral growth is, for example, growth in a gallium-rich state in which the ratio of trimethylgallium to ammonia is increased.

When the GaN layer 7 is grown under the condition of lateral growth by the MOVPE method, the dislocations extending upward bend laterally from the slope of the protruding nuclei 5. 9 in the figure indicates lateral growth (dislocation bending).

FIG. 2D shows the nitride semiconductor substrate 10 manufactured according to the present embodiment. Dislocation 11 from protruding nucleus 5
Are bent, dislocations do not propagate to the surface of the GaN layer 7, and a low dislocation density nitride semiconductor substrate 10 having a reduced dislocation density is manufactured.

The nitride semiconductor substrate 10 according to the present embodiment
As shown in FIG. 2D, the sapphire substrate 1 (or S
a GaN layer 2 which is a first nitride layer formed on an iC substrate) and a Ga which is a second nitride layer formed on the GaN layer 2
It has a plurality of protruding nuclei 5 made of N, and a GaN layer 7 which is a third nitride layer formed on the GaN layer 2 and the protruding nuclei 5. The (0001) plane or (0)
001) on a sapphire substrate 1 (or a SiC substrate) having a plane orientation inclined several degrees from the plane.
An aN layer 2 is formed.

Further, nitride semiconductor substrate 1 of the present embodiment
In the manufacturing method of No. 0, a GaN layer 2 as a first nitride layer is grown on a sapphire substrate 1 (or a SiC substrate).
On the GaN layer 2, a plurality of protruding nuclei 5 made of GaN, which is a second nitride, are grown, and the GaN layer 2 and the protruding nuclei 5 are grown.
A GaN layer 7 as a third nitride layer is grown thereon. The GaN layers 2 and 7 and the protruding nuclei 5 are M
It was grown by the OVPE growth method. In addition, the protruding nucleus 5
Was formed by switching the carrier gas in MOVPE growth from hydrogen to nitrogen. Then, the carrier gas is changed from nitrogen to hydrogen and grown under the lateral growth conditions, whereby the dislocations are bent in the horizontal direction to reduce the dislocations on the substrate surface. Thus, in the growth of the nitride semiconductor layer, when the protruding nuclei 5 exist on the growth surface, the GaN
By embedding layer 7 under lateral growth conditions, dislocations can be bent laterally. Therefore, it is not necessary to take the nitride semiconductor substrate 10 out of the growth apparatus to perform the process without taking time, and the dislocation is reduced simply and uniformly over the entire growth surface of the nitride semiconductor layer. The semiconductor substrate 10 can be manufactured. According to the nitride semiconductor substrate of the present embodiment and the method for manufacturing the same, the dislocation density has been reduced from the conventional 10 ⁸ to 10 ¹⁰ cm ⁻² to 10 ⁷ cm ⁻² .

Although the present invention has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments, and it is needless to say that various modifications can be made without departing from the gist of the present invention. It is. For example, in the above-described embodiment, an example in which a sapphire substrate or a SiC substrate is used as a substrate is shown. However, a low dislocation density nitride semiconductor substrate can be obtained by a similar process using a GaN substrate instead. it can. However, when this GaN substrate is used, it is not necessary to form a buffer layer.

[0042]

As described above, according to the present invention,
A low dislocation density nitride semiconductor substrate in which dislocations of a nitride semiconductor layer on a substrate are easily and uniformly reduced over the entire surface of the substrate, and a method for manufacturing the same can be provided.

[Brief description of the drawings]

FIGS. 1A and 1B are schematic process cross-sectional views showing a procedure of a method for manufacturing a nitride semiconductor substrate according to an embodiment of the present invention.

FIGS. 2 (c) and 2 (d) are schematic sectional views showing a procedure of a method for manufacturing a nitride semiconductor substrate and a structure of the nitride semiconductor substrate according to an embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of a nitride semiconductor substrate manufactured by the ELO in the first conventional technique.

FIG. 4 is a schematic cross-sectional view of a nitride semiconductor substrate manufactured by the pendeo growth according to a second conventional technique.

FIG. 5 is a schematic sectional view of a nitride semiconductor substrate manufactured by the low-temperature intermediate layer deposition method according to a third conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate, 2 ... GaN layer, 3 ... Hydrogen carrier gas, 4 ... Dislocation, 5 ... Projection nucleus, 6 ... Nitrogen carrier gas, 7 ... GaN layer, 8 ... Hydrogen carrier gas, 9 ... Lateral growth (dislocation) 10) nitride semiconductor substrate, 11
... dislocation, 31 ... sapphire substrate, 32 ... GaN layer, 33
... SiO ₂ mask, 34 ... GaN layer, 35 ... nitride semiconductor substrate, 36, 37 ... dislocation, 41 ... SiC substrate, 42 ...
GaN nucleus, 43 GaN layer, 44 nitride semiconductor substrate,
45: dislocation, 51: sapphire substrate, 52: GaN layer,
53: low temperature intermediate layer, 54: GaN layer, 55: low temperature intermediate layer, 56: GaN layer, 57: nitride semiconductor substrate, 58 ...
Dislocation.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G077 AA03 BE15 DB08 ED06 EE05 EF03 TB05 TC14 5F045 AA04 AB14 AC08 AC12 AC15 AD09 AD13 AD14 AF02 AF04 AF09 BB08 BB12 CA12 DA53 DA67 5F073 CA01 CB04 CB05 DA04 EA28

Claims (8)

[Claims] 1. A first nitride layer formed on a substrate, a plurality of protruding nuclei made of a second nitride formed on the first nitride layer, and the first nitride layer And a third nitride layer formed on the protruding nuclei. 2. The nitride semiconductor according to claim 1, wherein the first nitride layer is formed on the (0001) plane or on the substrate having a plane orientation inclined several degrees from the (0001) plane. substrate. 3. The nitride semiconductor substrate according to claim 1, wherein said substrate is made of sapphire. 4. The nitride semiconductor substrate according to claim 1, wherein said substrate is made of SiC. 5. The nitride semiconductor substrate according to claim 1, wherein said substrate is made of GaN. 6. A first nitride layer is grown on a substrate, and a plurality of protruding nuclei made of a second nitride are grown on the first nitride layer. And growing a third nitride layer on the protruding nuclei. 7. A method of growing at least one of said first nitride layer, said protruding nuclei and said third nitride layer.
7. The method for manufacturing a nitride semiconductor substrate according to claim 6, wherein the method is a growth method. 8. The method of manufacturing a nitride semiconductor substrate according to claim 6, wherein the protruding nuclei are formed by switching a carrier gas in MOVPE growth from hydrogen to nitrogen.