JP3780832B2 - Manufacturing method of semiconductor crystal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor crystal.
[0002]
[Prior art]
Group III nitride semiconductors such as gallium nitride (GaN), indium gallium nitride (InGaN), and gallium aluminum nitride (GaAlN) are in the spotlight as materials for blue light emitting diodes (LEDs) and laser diodes (LDs). In addition to optical elements, Group III nitride semiconductors are also being developed for electronic device elements that take advantage of their good heat resistance and environmental resistance.
[0003]
Since group III nitride semiconductors are difficult to grow bulk crystals, a group III nitride single crystal substrate that can withstand practical use has not yet been obtained. A substrate for GaN growth that is currently in practical use is sapphire, and a method of epitaxially growing GaN on a single crystal sapphire substrate by metal organic vapor phase epitaxy (MOVPE method) is generally used.
[0004]
Since a sapphire substrate has a lattice constant different from that of GaN, a single crystal film cannot be grown by directly growing GaN on the sapphire substrate. For this reason, there is a method in which an AlN or GaN buffer layer (low temperature growth buffer layer) is once grown on a sapphire substrate at a low temperature, and the GaN is grown on the buffer layer after relaxing the strain of the lattice with this buffer layer. (Refer to Japanese Patent Laid-Open No. 63-188983).
[0005]
[Problems to be solved by the invention]
By the way, the conventional low temperature growth buffer layer described above has a very narrow range of optimum growth conditions, and the crystallinity of the GaN film grown on the buffer layer due to slight fluctuations in the growth temperature and deviations in film thickness. There is a problem that the surface state changes greatly and the growth reproducibility of GaN growth is poor. In addition, GaN has innumerable defects because a shift between the substrate and the crystal lattice occurs in the growth of GaN using the low temperature growth buffer layer. This defect is expected to be an obstacle to manufacturing a GaN-based LD. Further, there is a problem that warpage occurs in the substrate after epitaxial growth due to a difference in linear expansion coefficient between the sapphire substrate and GaN, and in the worst case, cracks occur. For this reason, it is difficult to increase the diameter of GaN epitaxial wafers, and those having a diameter of 50 mm or more have not been put into practical use at present.
[0006]
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, as in the case of using a sapphire substrate, a method of first growing a buffer layer on the substrate at a low temperature and growing GaN on the buffer layer has been used. The problem of the difference in lattice constant and the problem of controlling the crystal shape of the growing GaN have not been solved, and there has been a problem that it has not been put into practical use.
[0007]
Accordingly, an object of the present invention is to solve the above-described problems and provide a method for manufacturing a semiconductor crystal that can grow a high-quality GaN-based crystal on various substrates.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the semiconductor crystal manufacturing method of the present invention forms a porous layer on the surface of a substrate other than the group III nitride, and grows a group III nitride single crystal layer on the porous layer. after producing the semiconductor crystal by, the linear expansion coefficient difference between the group III substrate and the group III except nitride nitride single crystal layer is peeled off porous layer group III nitride single crystal layer from the semiconductor crystal Is.
[0009]
In addition to the above-described configuration, the semiconductor crystal manufacturing method of the present invention includes a group III nitride single crystal layer made of GaN. After a GaN epitaxial layer is grown on the porous layer, a sapphire substrate on which GaN is grown is converted into HVPE. It may be formed by stacking a thick film of a GaN layer on a GaN epitaxial layer using gallium chloride and ammonia as raw materials .
[0010]
In addition to the above configuration, the semiconductor crystal manufacturing method of the present invention may use Si, Ge, or GaAs as the substrate, and may use the (111) plane .
[0011]
In addition to the above-described configuration, the semiconductor crystal manufacturing method of the present invention may use sapphire or SiC as the substrate and its (0001) plane .
[0012]
In addition to the above structure, the method for producing a semiconductor crystal of the present invention may form a porous layer on the surface of the substrate by an anodic oxidation method.
[0013]
In the method for producing a semiconductor crystal of the present invention, a metal film is formed on the surface of the substrate, the metal film is made into a porous film by an anodic oxidation method, and then the substrate is etched using the porous film as a mask. Then, only the porous film is removed to form a substrate having a porous layer on the surface, and a group III nitride single crystal is grown on the substrate .
[0014]
In addition to the above structure, the semiconductor crystal manufacturing method of the present invention may use aluminum as the metal film .
[0015]
In addition to the above structure, the semiconductor crystal manufacturing method of the present invention may be provided with a mask having a stripe-like or dot-like window on the porous layer, and the group III nitride single crystal layer may be grown on the mask. .
[0016]
In the method for producing a semiconductor crystal of the present invention, a substrate surface is once processed 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.
[0017]
Here, when GaN is epitaxially grown on a substrate having a lattice constant or a linear expansion coefficient that is greatly different from that of GaN such as Si, usually, the grown crystal is polycrystallized or the substrate is warped or cracked due to thermal strain. However, according to the present invention, since GaN grows on the porous layer, the porous functions to relieve the lattice strain and thermal strain between the substrate and GaN, so that a high-quality GaN epitaxial layer is obtained. In addition, the substrate is not warped or cracked. Accordingly, large-diameter GaN epitaxial growth of 100 mm or more, which has been impossible in the past, is also possible.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0019]
FIG. 1 is a cross-sectional view showing an embodiment of a GaN epitaxial substrate to which the method for producing a semiconductor crystal of the present invention is applied.
[0020]
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 the group III nitride. Thus, 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]
【Example】
Next, specific numerical values will be described. However, the present invention is not limited to this.
[0022]
Example 1
An anodizing treatment was performed on a Si (111) substrate having a diameter of 100 mm and a thickness of 300 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, a porous Si layer having innumerable holes of about several tens to several hundreds of nanometers was formed on the surface of the Si substrate. Next, the substrate on which the porous layer was formed was housed in a MOCVD furnace, and a GaN layer was grown to 2 μm on the substrate at 1100 ° C. under normal pressure using ammonia gas and trimethyl gallium as raw materials. The obtained GaN had a flat mirror surface. The obtained GaN epitaxial substrate had a cross-sectional structure as shown in FIG. When the surface of this GaN epitaxial substrate was observed with an atomic force microscope (AFM) and the density of pits appearing on the surface was counted, it was 8 × 10 ⁶ / cm ³ .
[0023]
Since pits of 10 ⁹ to 10 ¹⁰ pieces / cm ³ are observed on the surface of the GaN layer grown on the sapphire substrate by the conventional method, it can be said that a GaN epitaxial layer having a very low defect density is obtained. The full width at half maximum of the rocking curve according to the X-ray diffraction method of the grown GaN layer was 240 sec.
[0024]
Since an epitaxial substrate obtained by a conventional method usually has a value of about 300 sec, it can be said that an epitaxial layer having sufficiently high crystallinity is obtained compared to this value. Moreover, when the difference in height between the center and the peripheral edge of the substrate was measured and the warpage was evaluated, it was 2 μm. In an epitaxial substrate obtained by a conventional method, warpage of 50 μm is usually observed, so it can be said that the warpage of the epitaxial substrate according to the present invention is remarkably small.
[0025]
(Example 2)
Metal aluminum was laminated on a GaAs (111) substrate having a diameter of 100 mm and a thickness of 350 μm by sputtering of 1 μm, and the surface was anodized in a 3% oxalic acid aqueous solution with an electric field voltage of 12 V. As a result, the 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, etching was further performed in a mixed solution of sulfuric acid, hydrogen peroxide solution, and water to form a GaAs porous layer on the surface of the GaAs substrate. Only the alumina layer was removed from the substrate by hydrofluoric acid etching to produce a GaAs substrate having a porous layer on the surface.
[0026]
On the GaAs substrate thus obtained, 1 μm of GaN was grown at a growth temperature of 750 ° C. using the MBE method. When the surface of this substrate was observed with an atomic force microscope and the density of pits appearing on the surface was counted, it was 4 × 10 ⁶ pieces / cm ³ .
[0027]
Example 3
A SiO ₂ mask was put on a sapphire (0001) substrate having a diameter of 50 mm and a thickness of 330 μm, 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 surface of the sapphire substrate, and then the mask was removed. On this sapphire substrate, the method of Example 1 was used to grow a GaN epitaxial layer by 2 μm.
[0028]
The surface of the GaN epitaxial layer thus obtained was observed with an atomic force microscope, and the density of pits appearing on the surface was counted. As a result, it was 1 × 10 ⁶ pieces / cm ³ .
[0029]
(Example 4)
The SiO ₂ film was 400nm laminated by plasma CVD on a Si substrate having a porous layer obtained by the method described in Example 1, by further photolithography form, diameter 1μm to SiO ₂ film, the window pitch 5μm did. The substrate with the mask was placed in a MOCVD furnace, and a GaN layer was grown to 2 μm at 1050 ° C. under normal pressure. The obtained GaN layer had a flat mirror surface. When the surface of this GaN layer was observed with an atomic force microscope and the density of pits appearing on the surface was counted, it was 2 × 10 ⁵ pieces / cm ³ .
[0030]
(Example 5)
The GaN-grown sapphire substrate obtained in Example 3 was placed in an HVPE furnace, and gallium chloride and ammonia were used as raw materials, and a GaN layer of 200 μm was further laminated at 1100 ° C. under reduced pressure. Next, the sapphire substrate on which the thick GaN layer was formed was subjected to rapid heating and quenching cycles of room temperature to 600 ° C. 10 times. As a result, the porous portion of sapphire was destroyed due to the difference in linear expansion coefficient between the substrate and GaN. Only the GaN layer could be peeled off. Since porous sapphire was adhered to the GaN layer, this porous sapphire was removed by polishing. In this way, a GaN free-standing substrate could be obtained.
[0031]
Here, since the multi-efficiency of the porous layer and the size, depth, shape, and pitch of the pores have optimum values depending on the material of the substrate and the growth conditions of the nitride crystal that grows on the substrate, It is not of a personality that can be specified in a specific manner.
[0032]
【The invention's effect】
In short, according to the present invention, the following excellent effects are exhibited.
[0033]
It is possible to provide a semiconductor crystal manufacturing method capable of growing a high-quality GaN-based crystal on various substrates.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a GaN epitaxial substrate to which a method for producing a semiconductor crystal of the present invention is applied.
[Explanation of symbols]
1 Substrate 2 Porous layer 3 Group III nitride single crystal layer

Claims (8)

A porous layer formed on the group III surface of the substrate other than the nitride, after producing a semiconductor crystal is grown III nitride single crystal layer on the porous layer, and the substrate other than Group III nitride A method for producing a semiconductor crystal, comprising separating a group III nitride single crystal layer from the semiconductor crystal with a porous layer based on a difference in linear expansion coefficient from the group III nitride single crystal layer . The group III nitride single crystal layer is made of GaN, and after a GaN epitaxial layer is grown on the porous layer, the sapphire substrate on which the GaN is grown is housed in an HVPE furnace, and GaN using gallium chloride and ammonia as raw materials. The method for producing a semiconductor crystal according to claim 1, wherein the semiconductor crystal is formed by laminating a thick film of a GaN layer on the epitaxial layer . Si as the substrate, the use of Ge or GaAs, the (111) A method of manufacturing a semiconductor crystal according to claim 1 or 2 using surface. With use of sapphire or SiC as the substrate, the (0001) method for producing a semiconductor crystal according to claim 1 or 2 using surface. The method of manufacturing a semiconductor crystal according to claim 1 or 2 to form a porous layer by anodic oxidation on the surface of the substrate. A metal film is formed on the surface of the substrate, and the metal film is made into a porous film by an anodic oxidation method. Then, the substrate is etched using the porous film as a mask, and only the porous film is removed to remove the surface. method for producing a porous layer to form a substrate having a semiconductor crystal according to claim 1 or 2 for growing the group III nitride single crystal on the substrate to. The method for producing a semiconductor crystal according to claim 6 , wherein aluminum is used as the metal film. A mask having a stripe-shaped or dot-shaped window on a porous layer is provided, a method of manufacturing a semiconductor crystal according to claim 1 or 2 for growing the Group III nitride single crystal layer over the mask.

Images