JP2002050586A - Method for manufacturing semiconductor crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing semiconductor crystal, which can grow GaN crystal of high quality on various substrates. SOLUTION: The surface of the substrate 1 is once worked in a porous shape and nitride crystal 3 is grown on a porous layer 2. Thus, the GaN layer of high quality can be grown, even if there is no low-temperature buffer layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a semiconductor crystal.

[0002]

2. Description of the Related Art Group III nitride semiconductors such as gallium nitride (GaN), indium gallium nitride (InGaN), and gallium aluminum nitride (GaAlN) have been spotlighted as materials for blue light emitting diodes (LEDs) and laser diodes (LDs). I'm taking a bath. In addition to group III nitride semiconductors, elements for electronic devices have been developed in addition to optical elements, making use of the characteristics of good heat resistance and environmental resistance.

[0003] Since a group III nitride semiconductor is difficult to grow in bulk crystal, a group III nitride single crystal substrate that can be used practically has not yet been obtained. A GaN growth substrate currently in practical use is sapphire, and a method of epitaxially growing GaN on a single crystal sapphire substrate by metal organic chemical vapor deposition (MOVPE) is generally used.

Since a sapphire substrate has a different lattice constant from that of GaN, a single crystal film cannot be grown by directly growing GaN on the sapphire substrate. Therefore, a method of temporarily growing a buffer layer of AlN or GaN (low-temperature growth buffer layer) on a sapphire substrate at a low temperature, relaxing lattice distortion in the buffer layer, and then growing GaN on the buffer layer is proposed. Is disclosed (Japanese Unexamined Patent Publication No.
3-188983).

[0005]

However, the conventional low-temperature growth buffer layer described above has a very narrow setting range for the optimum growth conditions, and the fluctuation of the growth temperature and the deviation of the film thickness cause the buffer layer to have a small thickness. There is a problem that the crystallinity and the surface state of the GaN film grown thereon change greatly, and the growth reproducibility of GaN growth is poor. Also, in the growth of GaN using the low-temperature growth buffer layer, a shift between the substrate and the crystal lattice occurs, so GaN has countless defects. This defect is expected to be a hindrance in manufacturing a GaN-based LD. In addition, sapphire substrate and GaN
There is a problem that the substrate after the epitaxial growth is warped due to the difference in linear expansion coefficient from the above, and in the worst case, the substrate is cracked. For this reason, it is difficult to increase the diameter of the GaN epitaxial wafer, and a wafer having a diameter of 50 mm or more has not been put to practical use at present.

In order to solve these problems, growth using a substrate other than sapphire, for example, gallium arsenide (GaAs), silicon (Si), NGO (NdGaO ₃ ) or the like has been studied. In the case of using these substrates, a buffer layer is first grown on the substrate at a low temperature, and a Ga layer is formed on the buffer layer, as in the case of using a sapphire substrate.
Although a method of growing N has been used, there has been a problem that the problem of lattice constant difference and the problem of controlling the crystal form of GaN to be grown have not been solved yet, so that it has not been put to practical use.

It is an object of the present invention to solve the above-mentioned problems and to provide a method of manufacturing a semiconductor crystal capable of growing a high-quality GaN-based crystal on various substrates.

[0008]

In order to achieve the above object, a method of manufacturing a semiconductor crystal according to the present invention comprises forming a porous layer on the surface of a substrate other than a group III nitride, and forming a porous layer on the porous layer.
This is for growing a group III nitride single crystal layer.

In addition to the above structure, the method of manufacturing a semiconductor crystal of the present invention may use Si, Ge or GaAs as a substrate and also use its (111) plane.

[0010] In addition to the above structure, the method for manufacturing a semiconductor crystal of the present invention may use sapphire or SiC as a substrate and use the (0001) plane.

In addition to the above structure, in the method of manufacturing a semiconductor crystal according to the present invention, a porous layer may be formed on the surface of the substrate by anodic oxidation.

Further, the method for producing a semiconductor crystal according to the present invention comprises:
After forming a metal film on the surface of the substrate and turning the metal film into a porous film by anodizing, the substrate is etched using the porous film as a mask, and only the porous film is removed to form a porous layer on the surface. Is formed, and a group III nitride single crystal is grown on the substrate.

In addition to the above configuration, in the method of manufacturing a semiconductor crystal according to the present invention, aluminum may be used as the metal film.

In addition to the above structure, the method of manufacturing a semiconductor crystal according to the present invention provides a mask having stripe-shaped or dot-shaped windows on a porous layer, and grows a group III nitride single crystal layer on the mask. You may.

In addition to the above configuration, the method of manufacturing a semiconductor crystal of the present invention comprises the steps of:
Only the group III nitride single crystal layer may be separated from the porous layer.

In the method of manufacturing a semiconductor crystal according to the present invention, a substrate surface is once worked into a porous shape, and then a nitride crystal is grown on the porous layer. By making the substrate surface porous and growing GaN on the surface, a high-quality GaN layer can be grown without a low-temperature growth buffer layer.

Here, when GaN is epitaxially grown on a substrate, such as Si, having a lattice constant and a coefficient of linear expansion that are significantly different from those of GaN, the grown crystal usually becomes polycrystalline or the substrate is warped or cracked due to thermal strain. Would. However, according to the present invention, a high-quality GaN epitaxial layer can be obtained because GaN grows on the porous layer, and the porosity functions to reduce lattice distortion and thermal distortion between the substrate and GaN. In addition, the substrate does not warp or crack. Therefore, it is possible to perform a large-diameter GaN epitaxial growth of 100 mm or more, which was impossible in the past.

[0018]

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

FIG. 1 is a cross-sectional view showing one embodiment of a GaN epitaxial substrate to which a method for manufacturing a semiconductor crystal according to the present invention is applied.

This GaN epitaxial substrate is obtained by sequentially forming a porous layer and a group III nitride single crystal layer on a substrate other than a group III nitride. By making the substrate surface porous and growing GaN on the surface, a high-quality GaN layer can be grown without a low-temperature growth buffer layer.

[0021]

Next, the present invention will be described with reference to specific numerical values, but the present invention is not limited thereto.

(Example 1) Diameter 100 mm, thickness 300
An anodizing treatment was performed on a Si (111) substrate of μm in a mixed solution of hydrofluoric acid and ethanol at an electric field voltage of 20 to 2.5 V for 30 minutes. As a result, several tens to
A porous Si layer having innumerable pores of several hundred nm was formed. Next, the substrate on which the porous layer was formed was housed in an MOCVD furnace, and a GaN layer was grown on the substrate at a normal pressure of 1100 ° C. and a thickness of 2 μm using ammonia gas and trimethylgallium as raw materials. The obtained GaN had a flat mirror surface.
The obtained GaN epitaxial wafer had a sectional structure as shown in FIG. To observe the surface of the GaN epitaxial substrate by atomic force microscope (AFM), it was counted the density of pits appearing on the surface, 8 × 10 ⁶ cells / c
m ³ .

Ga grown on a sapphire substrate by a conventional method
Since the pits ¹⁰⁹ 10 ¹⁰ pieces / cm ³ is observed on the surface of the N layer, it can be said that the GaN epitaxial layer of very low defect density are obtained. Grown GaN
The half width of the rocking curve of the layer by X-ray diffraction was 24.
It was 0 sec.

Since a value of about 300 sec is generally obtained in the epitaxial substrate obtained by the conventional method, it can be said that an epitaxial layer having sufficiently high crystallinity is obtained as compared with this value. Also, the difference in height between the center and the periphery of the substrate was measured and the warpage was evaluated.
Met. In the epitaxial substrate obtained by the conventional method,
Usually, as much as 50 μm of warpage is observed, and it can be said that the warp of the epitaxial substrate according to the present invention is extremely small.

(Embodiment 2) Diameter 100 mm, thickness 350
Metal aluminum was laminated on a GaAs (111) substrate having a thickness of 1 μm by 1 μm sputtering, and the surface thereof was subjected to anodization treatment in a 3% aqueous oxalic acid solution at an electric field voltage of 12 V. As a result, metallic aluminum was oxidized, and a porous alumina layer was formed. Using the porous alumina layer formed on the surface of the substrate as a mask, the substrate was further etched in a mixed solution of sulfuric acid, hydrogen peroxide and water, and GaAs was added to the surface of the GaAs substrate.
s porous layer was formed. From this substrate, only the alumina layer was removed by hydrofluoric acid etching to produce a GaAs substrate having a porous layer on the surface.

On the GaAs substrate thus obtained, GaN was grown at a growth temperature of 750.degree.
m. The surface of this substrate was observed with an atomic force microscope, and the density of pits appearing on the surface was counted.
0 was ⁶ / cm ^3.

Example 3 50 mm in diameter and 330 μ in thickness
An SiO ₂ mask was applied to the m sapphire (0001) substrate, and windows having a diameter of 1 μm were formed on the entire surface of the mask at an interval of about 1 μm by photolithography. This substrate was etched using RIE to provide a porous layer on the sapphire substrate surface, and then the mask was removed. On this sapphire substrate, a GaN epitaxial layer was grown by 2 μm using the method of the first embodiment.

[0028] Thus the surface of the obtained GaN epitaxial layer was observed with an atomic force microscope, was counted the density of pits appearing on the surface, 1 × 10 ⁶ cells / cm ³
Met.

(Example 4) An SiO ₂ film having a thickness of 400 nm was laminated on a Si substrate having a porous layer obtained by the method shown in Example 1 by a plasma CVD method, and the diameter of the SiO ₂ film was reduced by photolithography. 1μm, pitch 5μ
m windows were formed. The masked substrate was housed in a MOCVD furnace, and a GaN layer was grown at a normal pressure of 1050 ° C. to a thickness of 2 μm. The obtained GaN layer had a flat mirror surface. The surface of the GaN layer was observed by an atomic force microscope, it was counted the density of pits appearing on the surface, 2 × 10 ⁵ cells / c
m ³ .

(Example 5) The sapphire substrate on which GaN obtained in Example 3 was grown was housed in an HVPE furnace, and decompressed at 1100 ° C using gallium chloride and ammonia as raw materials.
Then, a 200 μm GaN layer was further laminated. Next, thick film G
room temperature to 600 ° C. on the sapphire substrate on which the aN layer is formed
When the rapid heating and quenching cycles of
Due to the difference in linear expansion coefficient from aN, the porous portion of sapphire was broken, and only the GaN layer could be peeled off. G
Since porous sapphire had adhered to the aN layer, this porous sapphire was removed by polishing. In this way, a GaN free-standing substrate was obtained.

Here, the efficiency of the porous layer, the size of the pores,
The depth, the shape, and the pitch do not have a characteristic that can be uniquely defined because there are optimum values depending on the material of the substrate and the growth conditions of the nitride crystal grown on the substrate.

[0032]

In summary, according to the present invention, the following excellent effects are exhibited.

It is possible to provide a method of manufacturing a semiconductor crystal capable of growing a high-quality GaN-based crystal on various substrates.

[Brief description of the drawings]

FIG. 1 shows a Ga to which a method of manufacturing a semiconductor crystal according to the present invention is applied.
FIG. 3 is a cross-sectional view showing one embodiment of an N epitaxial substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Porous layer 3 Group III nitride single crystal layer

 ──────────────────────────────────────────────────の Continued on the front page F term (reference) 5F041 AA40 CA33 CA40 CA46 CA77 5F045 AA03 AA04 AB14 AC02 AC07 AC12 AD14 AD15 AE29 AF02 AF04 AF09 AF12 AF13 BB12 CA11 CA12 DA53 DB02 HA01 HA02 HA03 HA11 5F073 CA01 CB02 CB04 CB05 DA05

Claims (8)

[Claims] 1. A method of manufacturing a semiconductor crystal, comprising: forming a porous layer on the surface of a substrate other than a group III nitride; and growing a group III nitride single crystal layer on the porous layer. 2. The method according to claim 1, wherein the substrate is Si, Ge or GaAs.
2. The method of manufacturing a semiconductor crystal according to claim 1, wherein (111) plane is used. 3. The method of manufacturing a semiconductor crystal according to claim 1, wherein sapphire or SiC is used as the substrate and its (0001) plane is used. 4. The method according to claim 1, wherein a porous layer is formed on the surface of the substrate by an anodic oxidation method. 5. A method for forming a metal film on a surface of a substrate, forming the metal film into a porous film by anodizing, etching the substrate using the porous film as a mask, and etching only the porous film. To form a substrate having a porous layer on the surface,
2. A group III nitride single crystal is grown on the substrate.
3. The method for producing a semiconductor crystal according to item 1. 6. The method according to claim 5, wherein aluminum is used as the metal film. 7. The method of manufacturing a semiconductor crystal according to claim 1, wherein a mask having stripe-shaped or dot-shaped windows is provided on the porous layer, and a group III nitride single crystal layer is grown on the mask. 8. A method of manufacturing a semiconductor crystal, comprising separating only a group III nitride single crystal layer from a semiconductor single crystal obtained by the method according to claim 1 with a porous layer.