JP2001274093A - Semiconductor base and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor base that has a high-quality epitaxial film where dislocation density is reduced using a mask material such as SiO2 that is used for conventional selective growth, and a growth method. SOLUTION: First, a projection part 11 and a recessed part 12 are provided on the crystal growth surface of a substrate 1. After that, a feed gas for semiconductor crystal growth such as a GaN-family compound semiconductor is supplied to the substrate, and crystal growth is simply carried out from the upper part of the projection part 11, thus forming a first semiconductor layer 2. At this time, lateral direction growth occurs, thus setting the recessed part 12 to a cavity part 13 for remaining. A substance (an anti-surfactant material) for changing a surface state operates on the surface of the first semiconductor layer 2 to fix an anti-surfactant material 3. After that, the feed gas is supplied, a second semiconductor layer 4 that is generated with dot structure made of a semiconductor crystal as a new crystal growth nucleus is used, and the semiconductor base is completed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate and a method of manufacturing the same, and more particularly to a semiconductor substrate suitable for a case where a material used is a GaN-based compound semiconductor and a method of manufacturing the same.

[0002]

2. Description of the Related Art Epitaxial growth of GaN-based compound semiconductor crystals is generally performed on a sapphire substrate or the like via a buffer layer because it is difficult to obtain a lattice-matched substrate. In this case, lattice defects such as dislocations are introduced from the growth interface due to lattice mismatch between the epitaxial film and the substrate, and about 10 ¹⁰ cm
^{There are -2} order dislocations. Dislocations in the epitaxial film cause leakage current, non-light-emitting centers, and diffusion of electrode materials in the device. Therefore, a method of reducing the dislocation density has been attempted.

As one of them, for example, Japanese Patent Laid-Open No. 10-31
There is a method using selective growth as described in Japanese Patent No. 2971. According to this method, patterning is performed on a substrate by using a mask material such as SiO ₂ to perform selective growth, and further, growth is continued until the mask material is buried. The dislocation density is reduced by the effect of bending the dislocation propagation direction during the crystal growth process.

[0004]

However, in the above method, when the mask material is buried, the crystal grown on the mask in the lateral direction with respect to the growth surface has its crystal axis tilted as the growth proceeds (Tilt; A phenomenon called tilt occurs. Since the tilted crystals are united on the mask, a new defect is generated there. Although the cause of the tilt of the crystal axis is not clear, it is considered that the mask material has an effect. In addition, since the step of fabricating the mask needs to be performed once after being taken out of the epitaxial crystal growth apparatus, there are problems such as complication of the process, contamination of the substrate, or damage to the substrate surface. are doing. In particular, when multiplexing the selective growth process using the above-mentioned mask, there is a large problem in that the step of once taking out from the epitaxial growth apparatus to the outside and the possibility of contamination and surface damage are large.

In recent years, the halide vapor phase epitaxial method (H
High quality GaN substrates can be obtained using VPE). However, still 10 ⁵ -10 ⁷ cm ^-2
It is a substrate having a dislocation density of 2. Therefore, it is required and indispensable to further reduce the dislocation density in order to improve the performance of the device.

Accordingly, the present invention reduces the dislocation density in epitaxial growth of a GaN-based compound semiconductor crystal without using a mask material such as SiO ₂ used in the conventional selective growth. To provide a semiconductor substrate having a high-quality epitaxial film in which a tilt phenomenon in which a tilt is remarkably improved is improved, and a growth method in which an epitaxial film having a low dislocation density can be obtained without loading a substrate into an epitaxial growth apparatus and taking out the substrate to the outside. In particular, it is an object of the present invention to provide a growth method for obtaining a higher-quality epitaxial film by further reducing the dislocation density of a relatively high-quality GaN substrate.

[0007]

The semiconductor substrate of the present invention comprises:
The crystal growth surface of the substrate is an uneven surface, and the first semiconductor layer is formed exclusively by crystal growth from above the convex portion of the uneven surface, and the first semiconductor layer is formed thereon via an interface or region where an anti-surfactant material is fixed. And a second semiconductor layer is formed.

Further, the method for producing a semiconductor substrate according to the present invention comprises:
In vapor-phase growing a semiconductor crystal on a substrate, a raw material gas is supplied to the substrate after subjecting the substrate surface to uneven surface processing in advance, and the crystal is grown exclusively from above the convex portion on the uneven surface. Forming a first semiconductor layer, and changing a surface state of the first semiconductor layer with an anti-surfactant material, and then supplying a raw material gas from a semiconductor crystal grown on the surface of the first semiconductor layer. Generated as a new crystal growth nucleus using the dot structure
Forming a semiconductor layer.

In the above case, it is preferable to use Si as the anti-surfactant material. Also,
It is a preferable embodiment that the growth of the first semiconductor layer is stopped before the first semiconductor layer covers the concave portion of the substrate, and then the surface state is changed by the anti-surfactant material.

[0010]

The crystal growth surface of the substrate is an uneven surface, and the process of forming the first semiconductor layer by exclusively growing the crystal from above the convex portion on the uneven surface occurs only from the crystal growth portion from the convex portion. Alternatively, it has a mode of growing while inheriting dislocation lines existing in the convex portion, and a growth mode of laterally growing and substantially dislocation-free, producing an effect of reducing dislocation density by about one digit. In the present invention, the thus formed first
The surface state of the semiconductor layer is changed by an anti-surfactant material, and then the second semiconductor layer is formed. The antisurfactant material is immobilized on the surface modified by supplying the antisurfactant material, and the immobilized antisurfactant material acts to prevent dislocation lines from extending. Thus, the extension of the dislocation lines remaining in the first semiconductor layer is blocked, and the second semiconductor layer grown thereon further lowers the dislocation density.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a manufacturing process of a semiconductor substrate according to the present invention. In the figure, first, as shown in (a), a convex portion 11 and a concave portion 12 are provided on a crystal growth surface of a substrate 1. Thereafter, a source gas for growing a semiconductor crystal such as a GaN-based compound semiconductor is supplied to the substrate, and the first semiconductor layer 2 is formed by exclusively growing the crystal from above the convex portion 11 (FIG. 1B). )). At this time, the concave portion 12 becomes the hollow portion 13 due to the lateral growth and remains. Then, a substance (anti-surfactant material) that changes the surface state acts on the surface of the first semiconductor layer 2 to immobilize the anti-surfactant material 3 (FIG. 1C). Thereafter, a source gas is supplied to form a second semiconductor layer 4 that is generated using a dot structure made of a semiconductor crystal as a new crystal growth nucleus (FIG. 1D), and the semiconductor substrate of the present invention is formed. Complete.

The above semiconductor substrate will be described in detail. The convex portion 11 formed on the crystal growth surface of the substrate 1 has a shape such that crystal growth is performed exclusively from above. “Crystal growth is performed exclusively from the upper part” refers to a state in which crystal growth can be predominantly performed at the apex or top surface of the convex part 11 and in the vicinity thereof. However, it means that the crystal growth of the convex portion 11 becomes dominant eventually. In other words, if a low dislocation region is formed by lateral growth using the upper part as a new crystal growth nucleus, the same effect as the selective growth requiring a conventional mask can be obtained. This can be grown without a mask by applying the uneven portion to the substrate.

In this embodiment, the case where the projections 11 are formed in a stripe shape is shown, and depending on the shape of the projections and depressions, in this case, the source gas of the first semiconductor layer 2 can sufficiently reach the depressions 12 and its vicinity. In other words, crystal growth occurs only from the upper part of the protrusion 11. Therefore, in the initial stage of crystal growth, a crystal unit having a mushroom-shaped cross section is generated above the convex portion 11.
Under such circumstances, when the crystal growth is continued, the films grown in the lateral direction are connected starting from the upper part of the convex part 11, and eventually the cavity 13 is left in the concave part as shown in FIG.
The first semiconductor layer 12 covers the uneven surface of the substrate 1. In this case, the portion grown in the lateral direction, that is, the concave portion 12 is formed.
A low dislocation region is formed in the upper part, and the quality of the formed film is improved.

Next, an anti-surfactant material is immobilized on the surface of the first semiconductor layer 2, and a method of contacting the anti-surfactant material with the surface is exemplified. The method of contact is not limited,
For example, when the metal organic chemical vapor deposition method (MOCVD method) is used, the first semiconductor layer 2 is placed in a MOCVD apparatus.
What is necessary is just to install the substrate on which the substrate is grown, and supply the anti-surfactant material into the apparatus. As the supply method, for example, tetraethyl silane (TESi), silane method for supplying a compound containing Si (SiH ₄₎ or the like as a gaseous and the like.

By making the antisurfactant material act on the surface, a large number of minute regions having a high surface energy are present on the surface. That is, the anti-surfactant material 3 is immobilized on the substrate surface (FIG. 1C).

Subsequently, when, for example, a GaN-based compound semiconductor material is continuously supplied as the material of the second semiconductor layer 4, the GaN-based compound semiconductor hardly grows from a region having a high surface energy, and a dot structure is formed. . This phenomenon is also interpreted as that the antisurfactant material is immobilized on the substrate by adsorption or chemical bonding to cover the crystal surface and inhibit two-dimensional growth of the GaN-based crystal. That is, it acts as if it were a SiO ₂ mask used for selective growth, and such an effect can be obtained even with an anti-surfactant material such as Ge, Mg, Zn or the like. However, in avoiding the problem of crystal contamination,
It is desirable to use Si.

The dot structure according to the present invention refers to a region where an anti-surfactant material does not act,
This refers to a microstructure generated from a region that does not inhibit the growth of N, and has various shapes such as a polyhedral structure, a dome shape, a rod shape, and the like. It depends on the distribution density.

The density of the region where the anti-surfactant material acts can be controlled by the supply amount, the supply time or the substrate temperature of the anti-surfactant material.

When the GaN-based compound semiconductor is further continuously grown after the dot structure is formed, epitaxial growth occurs with the dot structure as a new crystal growth nucleus, and the second semiconductor layer 4 is formed. 1 (d)). Since the dot structure is formed by epitaxial growth from the minute opening region, the probability that dislocation lines extend through these openings is extremely low, and dislocation lines extending from the base are blocked by the action of the anti-surfactant material as a mask. The dislocation density on the surface of the epitaxial film is reduced.

According to the present invention, the first semiconductor layer 2 is grown by lateral growth by forming an uneven surface on the substrate 1,
Since the second semiconductor layer 4 is grown by lateral growth by immobilizing the anti-surfactant material 3 on the surface (it can be called an atomic level mask), dislocation lines can be cut off in two stages. In addition, the dislocation density of the grown crystal layer can be further reduced. Such multi-stage dislocation line blocking can also be achieved by applying the uneven surface applied to the substrate 1 to the surface of the first semiconductor layer 2, but in this case, the substrate is once taken out of the growth furnace and Processing must be performed, which is inconvenient from the viewpoint of workability, but the method of the present invention is preferable because these steps can be performed continuously.

In the growth of the first semiconductor layer 2,
Before the layer covers the concave portion 12, that is, at the stage of the above-mentioned mushroom-shaped crystal unit, the growth of the first semiconductor layer 2 is stopped, and the anti-surfactant material 3 is fixed on the surface of the mushroom-shaped crystal unit. You may do so. Depending on the growth conditions, the dislocation lines may extend in the lateral direction, and a plurality of such dislocation lines may merge with each other to generate a large dislocation defect. It is useful to fix the material 3 to block the dislocation lines from being stretched in order to reduce the generation of such dislocation defects.

The above-mentioned substrate 1 is a substrate serving as a base for growing various semiconductor crystal layers, and has no buffer layer or the like for lattice matching. As such a substrate, sapphire (C
Plane, A plane, R plane), SiC (6H, 4H, 3C), Ga
N, Si, spinel, ZnO, GaAs, NGO, and the like can be used, but other materials may be used as long as they correspond to the object of the invention. The plane orientation of the substrate is not particularly limited, and may be a just substrate or a substrate having an off angle. Further, a substrate in which a GaN-based semiconductor of several μm is epitaxially grown on a sapphire substrate or the like may be used.

Various semiconductor materials can be used for the semiconductor crystal grown on the substrate 1, and Al _x Ga _1-xy
For In _y N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), GaN, Al _0.5 Ga _{0.5 in} which the composition ratio of x and y is changed
N, In _0.5 Ga _0.5 N and the like can be exemplified.

Above all, in the case of a semiconductor material containing Al such as AlGaN, there is a problem that the conventional mask method grows on a SiO ₂ mask layer, but according to the present invention, such a problem is solved by maskless operation. Therefore, lateral growth of AlGaN, which could not be performed conventionally, becomes possible, and a high-quality film with low dislocations can be grown directly above the substrate. Therefore, light absorption by the GaN layer, which is a problem in an ultraviolet light emitting element or the like, is eliminated, which is particularly preferable in application.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments will be described below. Example 1 Patterning of photoresist on a c-plane sapphire substrate (width: 2 μm, period: 4 μm, stripe orientation: stripe extension direction is <11−
20> direction) and RIE (Reactive Ion Etching)
The apparatus was etched in a rectangular shape in cross section to a depth of 5 μm.
The aspect ratio at this time was 2.5. After removing the photoresist, the substrate was mounted on a MOVPE apparatus. Thereafter, the temperature was raised to 1100 ° C. in a hydrogen atmosphere, and thermal etching was performed. Then lower the temperature to 500 ° C,
Trimethylgallium (hereinafter referred to as TMG)
Ammonia was flowed as a raw material to grow a GaN low temperature buffer layer. Subsequently, the temperature was raised to 1000 ° C., TMG / ammonia was flowed as a raw material, and silane was flowed as a dopant, to grow an n-type GaN layer as a first semiconductor layer. The growth time at that time was set to a time corresponding to 4 μm in the GaN growth in the case where the normal unevenness was not applied.
Thus, as shown in FIG. 1B, the first semiconductor layer 2 made of a flat GaN film was obtained by covering the uneven portion while leaving the hollow portion 13 in the concave portion.

Next, supply of TMG and ammonia is stopped, the growth temperature is kept as it is, and subsequently, tetraethylsilane, which is a compound containing Si as an antisurfactant material, is supplied using H2 as a carrier gas, and the first semiconductor layer 2 is formed. For 10 seconds.

The supply of tetraethylsilane was stopped, and TMG and ammonia were again supplied as raw materials for forming the second semiconductor layer 4 to form a dot structure made of GaN. Thereafter, the raw material was continuously supplied, and the growth was continued until the dots were united and the surface was buried flat. Thereby, the second semiconductor layer 4 made of GaN having a thickness of 2 μm is formed.
Was formed.

The second semiconductor layer 4 thus grown
When the dislocation density on the surface was measured, it was 10 ⁵ cm ^-2 . From the cross-sectional TEM observation, no new defect was observed in the upper part of the cavity.

[Example 2] Tetraethylsilane as a source of an anti-surfactant material was supplied to the surface of the second semiconductor layer 4 in the semiconductor substrate obtained in Example 1 in the same manner as described above. The step of growing the crystal was repeated to produce a GaN semiconductor crystal in which five interfaces where the anti-surfactant material was fixed were multiplexed.
When the dislocation density of the GaN semiconductor crystal layer grown on the fifth interface was measured, it was reduced to 10 ² cm ⁻² .

[0030]

According to the semiconductor substrate and the method of manufacturing the same of the present invention as described above, the dislocation density can be reduced without using a mask material. This makes it possible to produce a high-quality GaN-based compound semiconductor crystal.
If semiconductor light-emitting elements such as LEDs and LDs, light-receiving elements, and electronic devices are fabricated thereon, the characteristics thereof are expected to be dramatically improved.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a manufacturing process of a semiconductor substrate of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 11 Convex part 12 Concavity 13 Cavity part 2 First semiconductor layer 3 Anti-surfactant material 4 Second semiconductor layer

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yoichiro Ouchi 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Cable Industry Co., Ltd. Itami Works F-term (reference) 5F041 AA40 CA33 CA40 CA65 CA74 5F045 AA04 AB14 AC01 AC08 AC09 AC12 AF02 AF04 AF09 AF12 AF14 BB12 DA52 DA53 5F073 CA01 CB05 CB19 DA05

Claims (3)

[Claims] 1. A crystal growth surface of a substrate is an uneven surface, and a crystal is exclusively grown from an upper portion of a convex portion on the uneven surface to form a first crystal.
A semiconductor substrate having a semiconductor layer formed thereon and a second semiconductor layer formed thereon via an interface or region where an anti-surfactant material is fixed. 2. In growing a semiconductor crystal on a substrate in a vapor phase, a raw material gas is supplied to the substrate after subjecting the substrate surface to an uneven surface processing in advance, and the raw material gas is exclusively supplied from an upper portion of the convex portion on the uneven surface. Forming a first semiconductor layer by crystal growth, changing the surface state of the first semiconductor layer with an anti-surfactant material, and then supplying a source gas to grow the first semiconductor layer on the surface of the first semiconductor layer Forming a second semiconductor layer generated using a dot structure made of the semiconductor crystal to be used as a new crystal growth nucleus. 3. The growth method according to claim 1, wherein the anti-surfactant material is Si.