JP4422473B2 - Method for manufacturing group III nitride substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a group III nitride substrate (a substrate including a group III nitride crystal).

  Group III nitride compound semiconductors such as gallium nitride (GaN) (hereinafter sometimes referred to as group III nitride semiconductors or GaN-based semiconductors) are attracting attention as materials for semiconductor elements that emit blue or ultraviolet light. Blue laser diodes (LD) are applied to high-density optical discs and displays, and blue light-emitting diodes (LEDs) are applied to displays and lighting. Further, ultraviolet LD is expected to be applied to biotechnology and the like, and ultraviolet LED is expected to be an ultraviolet source of fluorescent lamps.

A substrate of a group III nitride semiconductor (for example, GaN) for an LD or LED is usually formed by vapor phase epitaxial growth. For example, a substrate obtained by heteroepitaxially growing a group III nitride crystal on a sapphire substrate is used. However, the sapphire substrate and the GaN crystal have a difference of 13.8% in the lattice constant and a difference of 25.8% in the linear expansion coefficient. For this reason, the GaN thin film obtained by vapor phase epitaxial growth has insufficient crystallinity. The dislocation density of the crystal obtained by this method is usually 10 ⁸ cm ⁻² to 10 ⁹ cm ⁻² , and reduction of the dislocation density is an important issue. In order to solve this problem, efforts have been made to reduce the dislocation density, and for example, an ELOG (Epitaxial Lateral Overgrowth) method has been developed. According to this method, the dislocation density can be lowered to about 10 ⁵ cm ⁻² to 10 ⁶ cm ^−2, but the manufacturing process is complicated.

  On the other hand, a method of performing crystal growth in a liquid phase instead of vapor phase epitaxial growth has been studied. However, since the equilibrium vapor pressure of nitrogen at the melting point of a group III nitride single crystal such as GaN or AlN is 10,000 atmospheres or more, conventionally, a condition of 8000 atmospheres at 1200 ° C. is required for growing GaN in a liquid phase. It has been needed. On the other hand, it has recently been clarified that GaN can be synthesized at a relatively low temperature and low pressure of 750 ° C. and 50 atm by using Na flux.

  Recently, a mixture of Ga and Na was melted at 800 ° C. and 50 atm in a nitrogen gas atmosphere containing ammonia, and a single crystal having a maximum crystal size of about 1.2 mm was grown using this melt for 96 hours. Crystals are obtained (for example, Patent Document 1).

In addition, after a GaN crystal layer is formed on a sapphire substrate by metal organic chemical vapor deposition (MOCVD), a single crystal is grown by liquid phase epitaxy (LPE). It has been reported.
JP 2002-293696 A

  A sapphire substrate or the like is usually used for manufacturing a group III nitride substrate. However, since these substrates and group III nitride crystals have different lattice constants and thermal expansion coefficients, when the group III nitride crystals are grown using these substrates, the substrates may be distorted or warped. It was. For this reason, the substrate may be damaged during crystal growth, or manufacturing may be difficult when a device is manufactured using the formed semiconductor substrate. For example, in a stepper used in a device manufacturing process, mask alignment may be difficult.

  In view of such a situation, an object of the present invention is to provide a manufacturing method capable of manufacturing a substrate made of only a high-quality group III nitride crystal and having a small warpage.

  In order to achieve the above object, the first production method of the present invention includes (i) a step of forming a group III nitride layer having voids on a substrate, and (ii) gallium, under an atmosphere containing nitrogen, By bringing the surface of the group III nitride layer into contact with a melt containing at least one group III element selected from aluminum and indium and an alkali metal, the at least one group III element and nitrogen are reacted with each other. Growing a group III nitride crystal on the group III nitride layer; and (iii) separating the portion containing the substrate and the portion containing the group III nitride crystal in the vicinity of the gap. .

Moreover, the second manufacturing method of the present invention includes (I) a step of processing the surface of the substrate to form a convex portion;
(II) forming a seed crystal substrate in which a gap is formed between the substrate and the group III nitride layer by growing a group III nitride layer from the upper surface of the convex portion;
(III) contacting the surface of the group III nitride layer with a melt containing at least one group III element selected from gallium, aluminum and indium and an alkali metal under a pressurized atmosphere containing nitrogen, Reacting at least one group III element with nitrogen to grow a group III nitride crystal on the group III nitride layer;
(IV) A method for producing a group III nitride substrate including a step of separating a portion including the substrate and a portion including the group III nitride crystal in the vicinity of the gap.

In this specification, the group III nitride is a semiconductor represented by the composition formula Al _x Ga _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) unless otherwise specified. Means. Note that since the composition ratio never becomes a negative value, it goes without saying that 0 ≦ 1-xy ≦ 1 is satisfied (the same applies to other composition formulas).

  According to the manufacturing method of the present invention, it is possible to easily manufacture a substrate made of only a high-quality group III nitride crystal and having a small warp.

  The present invention will be described in detail below.

  In the production method of the present invention, it is preferable that the at least one element is gallium and the group III nitride crystal is a GaN crystal.

  In the production method of the present invention, the nitrogen-containing atmosphere is preferably a pressurized atmosphere. The range of the said pressurization is the range of 0.1 MPa-10 MPa, for example, Preferably it is the range of 0.5 MPa-5 MPa.

  In the step (iii) of the first production method of the present invention, the separation may be performed using stress generated by the difference between the linear expansion coefficient of the substrate and the linear expansion coefficient of the group III nitride crystal. preferable.

In the first production method of the present invention, the step (i) comprises:
(I-1) A first semiconductor layer represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) is formed on the substrate. Process,
(I-2) a step of removing a part of the first semiconductor layer to form a convex portion;
(I-3) A second semiconductor layer represented by a composition formula Al _x Ga _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is defined as the first semiconductor layer. Including the step of forming the group III nitride layer in which a portion other than the convex portion becomes a void by growing from the upper surface of the convex portion,
In the step (iii), it is preferable to separate the first semiconductor layer and the second semiconductor layer on the upper surface of the convex portion.

  The upper surface is preferably a C surface.

  In the step (i-2), the convex portion is preferably formed in a stripe shape.

  In the step (i-2), it is preferable to cover a concave portion other than the upper surface of the convex portion with a mask film. The mask film is preferably silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, aluminum nitride oxide, titanium oxide, zirconium oxide and niobium oxide, tungsten, molybdenum, niobium, tungsten silicide, molybdenum silicide and niobium silicide. It may be used alone or in combination of two or more. The mask film is preferably formed of a refractory metal or a refractory metallized material.

  In the manufacturing method of the present invention, the substrate is preferably a sapphire substrate.

  In the production method of the present invention, the alkali metal is preferably at least one selected from sodium, lithium and potassium.

  In the production method of the present invention, it is preferable that the melt further contains an alkaline earth metal.

In the first production method of the present invention, the step (i)
(Ia) A step of forming a first semiconductor layer represented by a composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) on a substrate. When,
(Ib) removing a part of the first semiconductor layer until the substrate is exposed to form a concave part that becomes a void, and forming the remaining part into a convex part,
In the step (ii), it is preferable to grow a group III nitride crystal on the surface of the convex portion (ib).

In the first production method of the present invention, the step (i)
(Ic) forming a patterned mask film on the substrate;
( _Id ) Convex shape represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) on the substrate exposed from the mask film. Forming a first semiconductor layer and forming a void in which the convex first semiconductor layer is not formed,
In the step (ii), it is preferable to grow a group III nitride crystal on the surface of the first semiconductor layer (ic).

In the step (i) above for the first manufacturing method of the present invention, III-nitride layer comprising said gap, composition formula _{Al x Ga y In 1-xy} N ( However, 0 ≦ x ≦ 1,0 ≦ After forming the semiconductor layer, heat treatment is performed in a mixed atmosphere of ammonia and nitrogen to form a void in the semiconductor layer or on the surface of the semiconductor layer. It is preferable to do. In this case, it is preferable that the group III nitride layer including the voids is composed of a composition formula Ga _x In _1-x N (where 0 ≦ x ≦ 1). The temperature raising rate of the temperature raising heat treatment is preferably in the range of 50 to 100 ° C./min.

  In the production method of the present invention, the period of the gap is preferably 30 μm or more, more preferably 50 μm or more, and further preferably 100 μm or more. Note that the void indicates a space observed in a crystal cross section, and means a space (for example, sub-μm order) or more space that can be observed with an SEM (Scanning Electron Microscope). The period of the air gap is a distance between a plurality of air gaps, and means a pitch. This can be measured, for example, with an electron microscope. The period of the voids can also be expressed by, for example, the mutual distance (pitch) of the growth points of the group III nitride crystal such as the convex surface. Further, the period of the gap can be adjusted depending on how the growth points are formed (for example, size, position, mutual distance).

  Next, the group III nitride substrate of the present invention is a group III nitride substrate manufactured by the manufacturing method of the present invention.

In the substrate of the present invention, the period of the dislocation dense region is preferably 30 μm or more, more preferably 50 μm or more, and further preferably 100 μm or more. The dislocation dense region is a region where the number of edge dislocations and screw dislocations is 10 ⁷ to 10 ⁸ / cm ² or more. As the measuring method, for example, a method of obtaining the number of dark spots by observing cathodoluminescence by electron beam irradiation, or a method of observing irregularities with AFM after etching with an acid (200 ° C.) such as pyrophosphoric acid. Etc.

  Next, the semiconductor device of the present invention is a semiconductor device including a substrate and a semiconductor element formed on the substrate, and the substrate is a group III nitride substrate manufactured by the manufacturing method of the present invention. is there. The semiconductor element is preferably a laser diode or a light emitting diode.

  Hereinafter, embodiments of the present invention will be described with reference to examples.

  The method of the present invention is a method for manufacturing a group III nitride substrate. According to this method, a substrate made of only a group III nitride semiconductor single crystal can be manufactured.

  In this method, first, a group III nitride layer having voids is formed on a substrate (step (i)). As the substrate, for example, a sapphire substrate can be used. An example of a method for forming a group III nitride layer having voids will be described below.

First, a first semiconductor layer represented by a composition formula Al _u Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) is formed on a substrate (step (i) -1)). The first semiconductor layer can be formed by, for example, the MOCVD method or the MBE method.

  Next, a part of the first semiconductor layer is removed to form a convex portion (step (i-2)). The convex portion can be formed by a known method in which photolithography and etching are combined. The upper surface of the convex portion is usually a C surface. The shape of the convex portion is selected so that the substrate can be easily separated in the following steps, and can be formed in a stripe shape or a dot shape, for example. The area of the convex portion is preferably 50% or less of the entire area. When forming a stripe-shaped convex part, the width | variety of a convex part is 1 micrometer-5 micrometers, for example, and the width | variety between adjacent convex parts is 5 micrometers-20 micrometers.

In the step (i-2), it is preferable to cover a portion (concave portion) other than the upper surface of the convex portion with a mask film. The mask film can be formed of, for example, silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, aluminum nitride oxide, titanium oxide, zirconium oxide, or niobium oxide. Further, the mask film may be formed of a refractory metal or a refractory metallized material having a high melting point (melting point is 1000 ° C. or higher). Specifically, tungsten, molybdenum, niobium, tungsten silicide, molybdenum silicide, or niobium silicide may be used.
Method for forming seed layer with void layer Next, a second semiconductor layer represented by the composition formula Al _x Ga _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) Growing the group III from the upper surface of the convex portion of the first semiconductor layer, thereby forming the group III nitride layer in which a portion other than the convex portion becomes a void ((i-3)). The second semiconductor layer may have the same composition as the first semiconductor layer or a different composition. The second semiconductor layer can be formed by, for example, the MOCVD method or the MBE method. Since the second semiconductor layer grown from the upper surface (C-plane) of the convex portion grows upward and laterally, the second semiconductor layer grown from the adjacent convex portion is docked in the space to form a bridge structure. To do. In this way, a group III nitride layer in which voids are formed in portions other than the convex portions is formed. Crystal growth is performed in the following step (ii) using the crystal layer of the group III nitride semiconductor thus obtained as a seed crystal.

  Next, the group III nitride layer is added to the melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal in an atmosphere containing nitrogen (preferably a pressurized atmosphere of 100 atm or less). By bringing the surface into contact with each other, the at least one group III element and nitrogen are reacted to grow a group III nitride crystal on the group III nitride layer (step (ii)). As the atmosphere containing nitrogen, for example, a nitrogen gas atmosphere containing nitrogen gas or ammonia can be applied. As the alkali metal, at least one selected from sodium, lithium and potassium, that is, one of them or a mixture thereof is used, and these are usually used in a flux state.

  The melt is prepared, for example, by putting a material into a crucible and heating it. After producing the melt, the semiconductor crystal grows by bringing the melt into a supersaturated state. The melting and crystal growth of the material are performed, for example, at a temperature of about 700 ° C. to 1100 ° C. and a pressure of about 1 to 50 atm. The melt may further contain an alkaline earth metal. As the alkaline earth metal, for example, Ca, Mg, Sr, Ba, Be and the like can be used.

According to this method, III-nitride crystal represented by a composition formula _{Al s Ga t In 1-st} N ( provided that 0 ≦ s ≦ 1,0 ≦ t ≦ 1) is obtained. For example, a GaN crystal can be obtained by using only gallium as a group III element as a material, and a composition formula Al _s Ga _1-s N (where 0 ≦ s ≦) by using gallium and aluminum as a group III element as a material. A crystal represented by 1) is obtained.

  Next, the portion including the substrate and the portion including the group III nitride crystal are separated in the vicinity of the gap (step (iii)). This separation step may be performed mechanically or may be performed using a stress generated by the difference between the linear expansion coefficient of the substrate and the linear expansion coefficient of the group III nitride crystal. When utilizing the difference in linear expansion coefficient, for example, separation can be performed in the cooling step (including natural cooling) after step (ii). In addition, when performing the process of (i-1)-(i-3) mentioned above, in process (iii), the said 1st semiconductor layer and said 2nd semiconductor layer are formed in the upper surface of the said convex part. To separate.

  In this way, a substrate made of only a group III nitride crystal is obtained. In the example described above, the case where the convex portion is formed in the group III nitride layer has been described, but the convex portion may be formed on the substrate. A manufacturing method in this case will be described below.

  In this case, first, the surface of the substrate is processed to form convex portions (step (I)). As the substrate, for example, a sapphire substrate whose surface is a C plane can be used. The uneven portion can be formed, for example, by a photolithography process and dry etching using chlorine gas.

  Next, by growing a group III nitride layer from the upper surface of the convex portion, a seed crystal substrate in which a void is formed between the substrate and the group III nitride layer is formed (step (II)). . The group III nitride layer can be formed by MOCVD or MBE. Crystal growth is performed in the following steps using the crystal layer of the group III nitride semiconductor formed here as a seed crystal.

  Next, in an atmosphere containing nitrogen, the surface of the group III nitride layer is brought into contact with a melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal. Three group III elements and nitrogen are reacted to grow a group III nitride crystal on the group III nitride layer (step (III)). Thereafter, the portion including the substrate and the portion including the group III nitride crystal are separated in the vicinity of the gap (step (IV)). Steps (III) and (IV) are the same as steps (ii) and (iii) described above, and therefore a duplicate description is omitted. In step (III), the substrate is separated on the upper surface of the convex portion of the substrate.

  By using a substrate having a void as a seed crystal, the sapphire substrate can be separated from the GaN single crystal. This separation step may be performed mechanically or may be performed using a stress generated by the difference between the linear expansion coefficient of the substrate and the linear expansion coefficient of the group III nitride crystal. When utilizing the difference in linear expansion coefficient, for example, separation can be performed in the cooling step (including natural cooling) after step (II).

  In the above embodiment, a method for separating a liquid phase grown group III nitride crystal in the vicinity of a void using a substrate on which a group III nitride layer having voids is formed has been described. In the same manner, the group III nitride crystal can be separated.

First, a first semiconductor layer represented by a composition formula Al _u Ga _v In _1-uv N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) is formed on a substrate (step (i) )). The first semiconductor layer can be formed by, for example, the MOCVD method or the MBE method.

  Next, a part of the first semiconductor layer is removed to the upper surface of the substrate to form a convex portion (step (ii)). The convex portion can be formed by a known method in which photolithography and etching are combined. The upper surface of the convex portion is usually a C surface. As the shape of the convex portion, a shape that facilitates separation of the substrate in the following steps is selected, and for example, it can be formed in a stripe shape or a dot shape.

  In this embodiment, at least one group III element selected from gallium, aluminum, and indium in an atmosphere containing nitrogen (preferably a pressurized atmosphere of 100 atm or less) is provided on the upper surface of the convex portion of the first semiconductor layer. By bringing the surface of the first semiconductor layer into contact with a melt containing an alkali metal, the at least one group III element and nitrogen are reacted to grow a group III nitride crystal (step (iii)). .

As a result, a gap is formed between the substrate and the group III nitride crystal. In this example, the group III nitride crystal is melted in a melt containing a group III element in which nitrogen is dissolved and an alkali metal.
In order to perform the liquid phase growth, the lateral growth rate is increased as compared with the vapor phase growth such as the conventional metal organic chemical vapor deposition (MOCVD) method and the hydride vapor phase growth (HVPE) method. be able to. Therefore, the area of the convex part is preferably 10% or less of the entire area. When forming a stripe-shaped convex part, the width of a convex part is 1 micrometer-5 micrometers, for example, and the width between adjacent convex parts is 20 micrometers-500 micrometers, for example. As for the period of a convex part, 30 micrometers or more are desirable. More desirably, it is 50 μm or more, and further desirably 100 μm or more.

  In general vapor deposition methods such as MOCVD, MBE, and HVPE, the growth rate in the horizontal direction is slow, and unless the width between the protrusions is set to 20 μm or less, the crystals grown from the respective protrusions are illustrated. Cannot merge as in 1. Further, the width of the convex portion needs to be about several μm in order to grow a crystal. Therefore, the ratio of the region where the convex portion is formed to the region where the convex portion is not formed is approximately 20% or more. However, in the liquid phase growth, the lateral growth can be promoted, and a large single crystal can be grown from the convex portion, so that the ratio can be further reduced. Decreasing the ratio of the convex portion means that the area where the LPE crystal portion and the substrate are in contact with each other can be reduced, and the substrate can be stably separated in the vicinity of the gap, and its practical effect is great. Further, the period of the dislocation dense part is preferably 30 μm or more. More desirably, it is 50 μm or more, and further desirably 100 μm or more.

  Next, the substrate and the group III nitride crystal are separated in the vicinity of the gap (step (iv)). This separation step may be performed mechanically or may be performed using a stress generated by the difference between the linear expansion coefficient of the substrate and the linear expansion coefficient of the group III nitride crystal. When utilizing the difference in linear expansion coefficient, for example, separation can be performed in the cooling step (including natural cooling) after step (ii).

  Another method described below may be used as a method of forming the convex semiconductor layer on the substrate.

  First, a mask film is patterned on the substrate. The mask film can be formed of, for example, silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, or aluminum nitride oxide. The mask film may be formed of a refractory metal or a refractory metallized material having a high melting point (melting point of 1000 ° C. or higher). Specifically, titanium, tungsten, molybdenum, niobium, tungsten silicide, molybdenum silicide, or niobium silicide may be used.

Next, a semiconductor layer represented by a composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) is formed on the substrate exposed from the mask film. The semiconductor layer can be formed by, for example, the MOCVD method or the HVPE method.

  Using the seed substrate, a group III nitride crystal is grown in a melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal in an atmosphere containing nitrogen.

  Finally, the substrate and the group III nitride crystal are separated in the vicinity of the gap.

  Hereinafter, the present invention will be described in more detail using examples that can be implemented.

In Example 1, a GaN crystal is formed on a sapphire substrate by a metal organic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy (MBE) method, or an HVPE method. A method for obtaining a GaN-based single crystal substrate by an epitaxial growth (LPE: Liquid Phase Epitaxy) method will be described. The GaN group crystal here means a semiconductor represented by the composition formula _{Al s Ga t In 1-st} N ( However, 0 ≦ s ≦ 1,0 ≦ t ≦ 1). In this embodiment, a case where a GaN single crystal substrate is manufactured will be described as an example, but a single crystal substrate such as AlGaN or AlN can be manufactured by the same method.

First, as shown in FIG. 1A, a seed layer 12 made of GaN is formed on a sapphire substrate 11 made of sapphire (crystalline Al ₂ O ₃ ) by MOCVD. Specifically, after the sapphire substrate is heated so that the substrate temperature becomes about 1020 ° C. to 1100 ° C., trimethylgallium (TMG) and NH ₃ are supplied onto the substrate, whereby the seed layer 12 made of GaN is formed. Form a film. The group III element of the seed layer 12 is not limited to gallium, and may include aluminum or indium. That is, the seed layer 12 may be a semiconductor crystal represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1).

  Next, as shown in FIG. 1B, a part of the seed layer 12 on the upper surface side is etched to form stripe-shaped convex portions. Specifically, first, a resist film is applied to the upper surface of the seed layer 12, and then the applied resist film is patterned in a stripe shape by a photolithography method to form a resist pattern 13. Subsequently, dry etching is performed on the seed layer 12 using the resist pattern 13 as a mask, so that a convex portion having a cross-sectional width of about 3 μm and a concave portion having a cross-sectional width of about 12 μm are formed on the seed layer 12 in one cycle. The periodic structure is formed. In order to facilitate the separation of the substrate in the following steps, it is preferable that the width of the convex portion is narrow. In this embodiment, the convex portion has a stripe structure, but there is no problem even if it has other structures. For example, a dot-like structure may be arranged in the plane.

  Next, as shown in FIG. 1C, a mask film 14 is formed only on the concave portion. The mask film 14 may cover the entire side wall surface of the recess, or may cover only a part of the wall surface. The mask film 14 is formed as follows, for example. First, using an electron cyclotron resonance (ECR) sputtering method, a thin film made of silicon nitride (SiNx) is deposited so as to cover the seed layer 12 and the resist pattern 13. Here, solid silicon can be used as a silicon raw material, nitrogen can be used as a reactive gas, and argon can be used as a plasma gas. In this manner, a high-quality mask film can be formed at a low temperature by forming the mask film using the ECR sputtering method. Next, the resist pattern 13 and the mask film 14 on the resist pattern 13 are removed by lifting off the register pattern 13. Thus, the upper surface (C surface) of the convex portion is exposed.

  Next, as shown in FIG. 1D, the selective growth layer 15 made of GaN crystal is regrown using the exposed upper surface of the convex portion as a seed crystal. For example, GaN is formed by a low pressure MOCVD method (26600 Pa (200 Torr), 1050 ° C.). The selective growth layer 15 is selectively grown from the upper surface of the convex portion that is not covered with the mask film 14. The selective growth layer 15 grows upward from the upper surface of each convex portion, and also grows in a direction parallel to the substrate surface (lateral growth). The GaN grown laterally from the upper surface of the convex part is docked with GaN grown from the adjacent convex part in the space (substantially the central part of the concave part) to form an air bridge structure. Thereby, the dislocation density of the part grown in the lateral direction can be reduced.

By growing the selective growth layer 15 in this way, the crystal bodies grown from the upper surfaces of the plurality of convex portions are integrated, and the upper surface becomes a C plane. As a result, the seed layer 12 and the selective growth layer 15 constitute a semiconductor layer having a gap. In this way, a seed crystal substrate (air bridge structure substrate) 17 on which a semiconductor layer having voids is formed is obtained. The group III element of the selective growth layer 15 is not limited to gallium, and may include aluminum or indium. That is, the selective growth layer 15 may be a semiconductor crystal represented by the composition formula Al _x Ga _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1).

  Next, the GaN crystal 16 is grown on the selective growth layer 15 by the LPE method using the obtained seed crystal substrate 17 (FIG. 1E). Thereafter, the portion including the sapphire substrate 11 and the portion including the GaN crystal 16 are separated on the upper surface of the convex portion (FIG. 1F). In this way, a substrate consisting only of GaN crystals is obtained.

  Hereinafter, a method for growing the GaN crystal 16 will be described. FIG. 2A shows an example of the LPE apparatus used.

The LPE apparatus of FIG. 2 (a) adjusts the pressure of the growth atmosphere and the source gas tank 21 for supplying the source gas, nitrogen gas or the mixed gas of ammonia gas (NH ₃ gas) and nitrogen gas. Pressure regulator 22, leak valve 23, stainless steel container 24 for crystal growth, and electric furnace 25. FIG. 2B is an enlarged view of the stainless steel container 24, and a crucible 26 is set inside the stainless steel container 24. The crucible 26 is made of boron nitride (BN), alumina (Al ₂ O ₃ ), or the like. The crucible 26 can control the temperature to 600 ° C to 1000 ° C. The atmospheric pressure (100 atm to 150 atm) supplied from the source gas tank 21 can be controlled to a range of 100 atm or less by the pressure regulator 22.

  Hereinafter, a method for growing a GaN crystal will be described. First, a prescribed amount of Ga and Na, which is a flux, were weighed and set in a crucible 26 together with a seed crystal substrate (the substrate of FIG. 1D). In this example, the molar ratio of Ga and Na was 2.7: 7.3. For comparison, a general seed crystal substrate (substrate having a GaN layer formed on a sapphire substrate) that does not have an air bridge structure was also set at the same time for crystal growth. Next, the crucible 26 was kept at 800 ° C., and nitrogen gas mixed with ammonia (40%) was supplied at a pressure of 5 atm. By mixing ammonia, the atmospheric pressure during growth can be reduced, but it is not always necessary to mix ammonia. Even in a nitrogen gas atmosphere in which ammonia is not mixed, crystals can be grown under a pressure of 50 atm. In this state, the temperature and pressure were kept constant, and LPE growth was performed for 96 hours. The thickness of the GaN crystal 16 thus obtained was 100 μm.

The linear expansion coefficient of sapphire as a substrate is 7.5 × 10 ⁻⁶ / K, while the grown GaN has a linear expansion coefficient of 5.5 × 10 ⁻⁶ / K. Therefore, in a sample in which crystal growth was performed using a general seed crystal substrate, the growth temperature was high (for example, 800 ° C.), and thus a large warp occurred at room temperature. Such warpage is a major problem in processes such as mask alignment in the device manufacturing process. On the other hand, in the sample in which the GaN crystal was grown on the seed crystal substrate (air bridge structure substrate) of the present invention, the substrate was separated at the interface between the seed layer 12 and the selective growth layer 15 during cooling after crystal growth. This is considered to be due to the stress caused by the difference in linear expansion coefficient during cooling after crystal growth and the stress concentrated on the convex portion because the area of the convex portion is small. In this way, a GaN single crystal substrate from which only the GaN crystal was peeled was obtained.

The dislocation density was evaluated by irradiating the obtained GaN single crystal with an electron beam and observing the in-plane distribution of cathodoluminescence (CL). The dislocation part is observed as a black spot because the emission intensity is weak. In the GaN single crystal obtained in this example, the dislocation density was as low as 1 × 10 ² cm ⁻² or less. In contrast, when the seed layer 12 on the sapphire substrate 11 was measured, the dislocation density was as high as 5 × 10 ⁹ cm ⁻² . Thus, by growing a GaN single crystal by the method of this example, the dislocation density of the crystal could be reduced.

The value of dislocation density of 1 × 10 ² cm ⁻² or less is a low dislocation density comparable to that of a GaAs substrate used in the production of semiconductor lasers for reading and writing CDs and DVDs. Therefore, according to the above example, it is considered that a GaN single crystal substrate having characteristics sufficient to produce a semiconductor laser having a lifetime of 10,000 hours or longer was obtained.

A GaN crystal was produced by the above method, and its dislocation density and PL intensity were measured. The dislocation density was 1 × 10 ² cm ⁻² or less. The PL intensity spectrum is shown in FIG. The intensity of the peak near 360 nm in the spectrum of FIG. 3B was 22 (V). For comparison, FIG. 3A shows the PL intensity of a GaN thin film produced by a normal MOCVD method. Note that FIG. 3A and FIG. 3B are spectra measured under different slit width conditions. The peak intensity around 360 nm in the spectrum of FIG. 3A was 0.48 (V). The crystal obtained by the method of the present invention has a PL strength about 50 times that of the crystal produced by the conventional method.

In the present embodiment, the manufacture of a GaN single crystal substrate using gallium has been described. However, it is desirable to manufacture a substrate that absorbs less light with respect to the operating wavelength of an optical device manufactured on the substrate. Therefore, as the semiconductor laser or a light emitting diode substrate in the ultraviolet range, it is preferable to form the Al a number included light absorption in the short wavelength region is small _{Al x Ga 1-x N (} 0 ≦ x ≦ 1) single crystal . In the present invention, such a group III nitride semiconductor single crystal can be formed by replacing a part of Ga with another group III element.

  In the above embodiment, the GaN single crystal substrate is manufactured using a simple growth apparatus. However, in order to manufacture a higher quality substrate, it is possible to manufacture the substrate using a large growth apparatus. An example of the LPE apparatus in that case is shown in FIG.

  The LPE apparatus of FIG. 4 includes an electric furnace 30 including a stainless steel chamber 31 and a furnace lid 32, and can withstand an atmospheric pressure of 10 atm. A heater 33 for heating is disposed in the chamber 31. The chamber 31 includes three zones including zones 300a, 300b, and 300c, and thermocouples 34a to 34c are attached to each of the three zones. The three zones are controlled so that the temperature range is within ± 0.1 ° C., and the temperature in the furnace is uniformly controlled. The core tube 35 is disposed to improve the uniformity of the temperature in the furnace and prevent impurities from entering from the heater 33.

  A crucible 36 made of boron nitride (BN) is disposed inside the furnace core tube 35. A material 37 is charged into the crucible 36 and the temperature of the crucible is raised to prepare the melt 37. The substrate 10 serving as a seed crystal is attached to the substrate fixing portion 38. In the apparatus of FIG. 4, a plurality of substrates 10 can be fixed to the substrate fixing part 38. The substrate 10 is rotated by a rotary motor 39a. A stirring propeller 40 can be immersed in the melt 37. The propeller 40 is rotated by the rotary motor 39b. In this embodiment, since the atmospheric pressure is 10 atm or less, a normal rotary motor can be used. However, under an atmospheric pressure of 10 atm or more, an electromagnetic induction type rotating mechanism is used. The atmospheric gas (source gas) is supplied from the gas source 41. The pressure of the atmospheric gas is adjusted by the pressure regulator 42. The atmospheric gas is sent into the furnace after impurities are removed by the gas purification unit 43.

  Hereinafter, a method of crystal growth will be described.

  (1) First, Ga and Na which is a flux are weighed by a predetermined amount and set in a crucible. Ga having a purity of 99.9999% (six nines) is used. As Na, purified Na is used. Na can be purified by heating and melting Na in a He-substituted glove box to remove oxides and the like appearing on the surface layer. Further, Na may be purified by a zone refining method. By repeating melting and solidification of Na in the tube, impurities can be precipitated and removed to increase the purity of Na.

  (2) In order to melt the raw material in the crucible, the temperature in the electric furnace is raised to 900 ° C. to prepare a raw material melt. At this stage, the seed crystal substrate is not put into the crucible. In order to stir Ga and Na, a propeller is put in the melt and the melt is stirred for several hours. The atmospheric gas is, for example, nitrogen gas or nitrogen gas containing ammonia. At this stage, the pressure of nitrogen gas is set to about 1 atm in order to avoid the reaction of Ga or Na with nitrogen gas. Note that when ammonia is mixed, the reaction occurs at a lower pressure. Therefore, it is preferable to use only nitrogen gas as the atmospheric gas at this stage.

  (3) Next, the temperature of the crucible is set to 800 ° C., and the melt is brought into a supersaturated state. Also, the atmospheric pressure is increased. In this embodiment, the atmosphere is 50 atm with, for example, nitrogen gas alone. Next, the seed crystal substrate is lowered to just above the melt, and the temperature of the substrate is brought close to the temperature of the melt. After a few minutes, the seed crystal substrate is placed in the melt and GaN crystal growth is started.

  (4) During crystal growth, the substrate is rotated at a rotation speed in the range of 10 rpm to 200 rpm. Preferably, it is rotated at around 100 rpm. After growing the crystals for 24 hours, the substrate is raised and removed from the melt. After raising the substrate, the substrate is rotated between 300 rpm and 1500 rpm in order to remove the melt remaining on the substrate surface. Desirably, it is rotated at around 1000 rpm. Thereafter, the substrate is removed from the chamber. During crystal growth, the temperature of the crucible may be kept constant, but the melt temperature may be lowered at a constant rate in order to keep the supersaturation degree of the melt constant.

  In this example, since a seed crystal substrate having an air bridge structure is used, the GaN substrate is peeled off from the convex portion of the seed crystal substrate when the substrate is cooled, and a flat GaN single crystal substrate without warpage is obtained. It was.

When the obtained substrate was evaluated, the dislocation density was 1 × 10 ² cm ⁻² or less. Moreover, the PL intensity of the obtained substrate was about 50 times the PL intensity of the GaN thin film produced by the usual MOCVD method.

  In this embodiment, a flux containing only Na is used, but the same effect can be obtained by using a mixed flux with an alkaline earth metal such as Li, Na, K flux or Ca. For example, in the mixed flux of Na and Ca, the crystal can be grown at a lower pressure by mixing about 10% of Ca.

  According to the present invention, a GaN single crystal substrate that does not include a sapphire substrate, does not warp, and has a low dislocation density can be manufactured with high productivity. Therefore, a substrate capable of manufacturing a highly reliable device can be supplied at a low cost. In particular, since there is no warpage and the dislocation density is low over the entire substrate, a device manufacturing process such as a semiconductor laser can be simplified, and a device can be manufactured with a high yield.

  In Example 2, an example in which a semiconductor laser is manufactured using the substrate obtained in Example 1 will be described. The structure of the semiconductor laser 50 is shown in FIG.

First, a contact layer 52 made of n-type GaN doped with Si so as to have a carrier density of 5 × 10 ¹⁸ or less is formed on the substrate 51 obtained in the above embodiment. The substrate 51 is a substrate in which a group III nitride crystal is formed on sapphire or a substrate made of a group III nitride crystal. In a GaN-based crystal (a crystal containing Ga and N), Ga vacancies increase when Si is added as an impurity. Since these Ga vacancies diffuse easily, if a device is fabricated on this Ga, it has an adverse effect on the life and the like. Therefore, the doping amount is controlled so that the carrier density is 3 × 10 ¹⁸ or less.

Next, a clad layer 53 made of n-type Al _0.07 Ga _0.93 N and a light guide layer 54 made of n-type GaN are formed on the contact layer 52. Next, a multiple quantum well (MQW) constituted by a well layer (thickness: about 3 nm) made of Ga _0.8 In _0.2 N and a barrier layer (thickness: about 6 nm) made of GaN is formed as the active layer 55. Next, a light guide layer 56 made of p-type GaN, a clad layer 57 made of p-type Al _0.07 Ga _0.93 N, and a contact layer 58 made of p-type GaN are formed. These layers can be formed by a known method. The semiconductor laser 50 is a double heterojunction type semiconductor laser, and the energy gap of the well layer containing indium in the MQW active layer is smaller than the energy gap of the n-type and p-type cladding layers containing aluminum. On the other hand, the refractive index of light is the largest in the well layer of the active layer 55, and the light guide layer and the cladding layer are reduced in this order.

  An insulating film 59 constituting a current injection region having a width of about 2 μm is formed on the contact layer 58. On the p-type cladding layer 57 and the p-type contact layer 58, a ridge portion serving as a current confinement portion is formed.

  A p-side electrode 500 that is in ohmic contact with the contact layer 58 is formed on the upper side of the p-type contact layer 58. The p-side electrode 500 is made of a laminate of nickel (Ni) and gold (Au).

  An n-side electrode 501 that is in ohmic contact with the contact layer 52 is formed on the upper side of the n-type contact layer 52. The n-side electrode 101 is composed of a laminate of titanium (Ti) and aluminum (Al).

  The device evaluation of the semiconductor laser manufactured by the above method was performed. When a predetermined voltage in the forward direction is applied between the p-side electrode and the n-side electrode to the obtained semiconductor laser, holes are injected from the p-side electrode into the MQW active layer, and electrons are injected from the n-side electrode, Recombination occurred in the MQW active layer to generate an optical gain, and laser oscillation occurred at an oscillation wavelength of 404 nm.

Since the semiconductor laser of this example uses a substrate having a low dislocation density of 1 × 10 ² cm ⁻² or less as a substrate, the threshold is higher than that of a semiconductor laser manufactured on a GaN substrate having a high dislocation density. A decrease in value, an improvement in luminous efficiency, and an improvement in reliability were observed.

  The following is mentioned as an effect which produces LD and LED using the board | substrate obtained by this invention. By using a GaN single crystal substrate that can remove the sapphire substrate, has no warpage, and has a low dislocation density, mask alignment and the like during the LD fabrication process can be performed easily and accurately, so that a highly reliable LD can be fabricated with a high yield. be able to. Further, by using a GaN single crystal substrate having no warpage and a low dislocation density, the influence of strain on the device can be reduced, so that the reliability of the device can be improved. Since the dislocation density is low throughout the substrate, high reliability can be realized in a wide stripe LD. Furthermore, the use of a GaN substrate enables cleavage, eliminates the need for a dry etching process, simplifies the manufacturing process, and allows the device to be manufactured at low cost.

In Example 3, an example of a method for forming irregularities on a substrate will be described. First, as shown in FIG. 6A, an uneven portion serving as a void is formed on a sapphire substrate 61 made of sapphire (crystalline Al ₂ O ₃ ) having a (0001) plane. The uneven portion is formed by forming a striped resist pattern by photolithography and performing dry etching using chlorine gas.

  Next, as shown in FIG. 6B, the SiNx film 62 is formed only in the concave portion that becomes the void. Specifically, first, a resist pattern is formed on the convex portion, and then a thin film made of silicon nitride (SiNx) is deposited by using electron cyclotron resonance (ECR) sputtering. By lifting off the resist pattern, the SiNx film can be formed in the recess.

Next, a seed layer 63 made of GaN is formed on the convex portion which is a sapphire surface by MOCVD. Specifically, after heating the sapphire substrate so that the substrate temperature is about 1020 ° C. to 1100 ° C., trimethylgallium (TMG) and NH ₃ are supplied onto the substrate to form a seed layer made of GaN. Film. Note that the group III element of the seed layer is not limited to gallium but may include aluminum or indium. That is, the seed layer may be a semiconductor crystal represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1). Crystal growth is performed using the crystal layer of the group III nitride semiconductor thus obtained as a seed crystal.

  In Example 1, a GaN single crystal was formed on a seed crystal substrate having an air bridge structure by an LPE method using a flux. However, this air bridge structure substrate can also be used as a seed crystal for crystal growth by the sublimation method. As an example of the crystal growth apparatus in this case, a crystal growth apparatus is shown in FIG.

The crystal growth apparatus of FIG. 7 includes a flow rate regulator 80, an electric furnace 81, and a thermocouple 87. A quartz tube 82 is installed inside the electric furnace 81, and a boron nitride (BN) crucible 84 containing GaN powder 83 is placed therein. Nitrogen gas containing NH ₃ gas is supplied from the direction of the arrow 88 in the figure, and the inside of the electric furnace 81 is adjusted by the flow rate regulator 80 so that a nitrogen gas atmosphere containing about 10 vol% NH ₃ gas is obtained. When the temperature of the crucible 84 is raised, the GaN powder 83 reacts with nitrogen gas (NH ₃ gas) and decomposes, jumps upward, and adheres to the substrate 86 heated by the substrate heater 85. As the substrate 86 mounted on the substrate heater 85, the air bridge structure seed crystal substrate described in the first embodiment can be used. After growing the GaN single crystal on the GaN seed crystal substrate, when the temperature in the electric furnace is lowered and the temperature of the substrate heater is also lowered, the linear expansion coefficient of the sapphire substrate and the linear expansion coefficient of the grown GaN crystal Due to the difference, the grown GaN single crystal was separated from the sapphire substrate.

  The pressure in the electric furnace is preferably 1 atm or more. Increasing the pressure raises the decomposition temperature of GaN, makes it easy to decompose GaN in the crucible and generate GaN on the substrate, so that GaN crystals can be stably grown on the substrate. it can.

In the method of the above embodiment, a c-plane Al _x Ga _1-x N (where 0 ≦ x ≦ 1) substrate can be used as a seed crystal, but Al _x Ga _1-x N ( However, even when a substrate of 0 ≦ x ≦ 1) is used as a seed crystal substrate, a single crystal substrate represented by the composition formula Al _x Ga _1-x N (where 0 ≦ x ≦ 1) is obtained. For example, when an a-plane GaN substrate is used as a seed crystal, when a light emitting diode is formed using the obtained single crystal substrate, there is no piezo effect, so holes and electrons can be efficiently recombined, Luminous efficiency can be improved.
By using a substrate obtained by the production method of the present invention and epitaxially growing a group III nitride crystal on this substrate, a semiconductor device having a semiconductor element such as an LD or LED can be obtained.

First, as shown in FIG. 8A, a seed layer 92 made of GaN is formed on a sapphire substrate 91 made of sapphire (crystalline Al ₂ O ₃ ) by MOCVD. Specifically, after the sapphire substrate 91 is heated so that the substrate temperature becomes approximately 1020 ° C. to 1100 ° C., trimethylgallium (TMG) and NH ₃ are supplied onto the substrate, whereby a seed layer 92 made of GaN is formed. Is deposited. The group III element of the seed layer 92 is not limited to gallium, and may include aluminum or indium. That is, the seed layer 92 may be a semiconductor crystal represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1).

  Next, as shown in FIG. 8B, the seed layer 92 is etched up to the sapphire substrate 91 to form stripe-shaped convex portions. Specifically, first, a resist film is applied to the upper surface of the seed layer 92, and then the applied resist film 93 is patterned in a stripe shape by a photolithography method to form a resist pattern. Subsequently, by performing dry etching on the seed layer 92 using the resist pattern as a mask, convex portions having a width of about 5 μm are formed with a period of about 300 μm as shown in FIG. In this embodiment, the convex portion has a stripe structure, but there is no problem even if it has other structures. For example, a dot-like structure may be arranged in the plane.

  Next, as shown in FIG. 8D, an LPE-GaN crystal 94 made of GaN crystal is grown by liquid phase growth using the upper surface of the convex portion as a seed crystal. Liquid phase growth was performed using the LPE apparatus shown in FIG. Sodium and gallium are weighed in a crucible, and the template shown in FIG. 8 (c) is inserted into the crucible and grown in a nitrogen-pressurized atmosphere at 50 atm and 800 ° C. for 100 hours. The LPE− in FIG. GaN crystal was grown. In the liquid phase growth, since the lateral growth rate is fast, as shown in FIG. 8D, LPE-GaN crystals grown from the convex portions could be combined.

  In this example, since the contact area between the convex portion and the LPE-GaN crystal was small, the LPE-GaN crystal could be easily separated in the vicinity of the gap when the melt was cooled. Further, in the obtained LPE-GaN crystal, many dislocations were observed on the convex portion and the merged portion, but the other portions were low dislocations. In the present invention, since the period of the convex portion is 300 μm, a low dislocation region can be realized in a wide region of 100 μm or more. Therefore, when manufacturing a semiconductor laser or the like, the accuracy of mask alignment for forming a waveguide can be relaxed, and a wide stripe waveguide necessary for a high-power semiconductor laser can be formed.

  As another example, a similar LPE-GaN crystal can be produced using the template of FIG.

  As shown in FIG. 9A, first, SiNx (silicon nitride) serving as the mask film 102 is grown to 100 nm on the sapphire substrate 101 by a CVD method at atmospheric pressure. Next, a striped window (sapphire substrate exposed portion) is opened in the mask film by photolithography and etching. The window may be dot-shaped. The width of the mask film was 10 μm and the period was 500 μm.

Next, as shown in FIG. 9B, a composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦) is formed on the sapphire substrate exposed from the mask film 102 by MOCVD. The seed layer 103 represented by v ≦ 1, u + v ≦ 1) is formed. In this embodiment, the seed layer is grown by heating the sapphire substrate so that the substrate temperature is about 1020 ° C. to 1100 ° C. and supplying trimethylgallium (TMG) and NH ₃ onto the substrate.

  Next, as shown in FIG. 9C, an LPE-GaN crystal 104 made of a GaN crystal is grown on the seed crystal by liquid phase growth. Liquid phase growth was performed using the LPE apparatus shown in FIG.

  Also in this example, since the contact area between the convex portion and the LPE-GaN crystal was small, the LPE-GaN crystal could be easily separated in the vicinity of the gap when the melt was cooled. Further, in the obtained LPE-GaN crystal, many dislocations were observed on the convex portion and the merged portion, but the other portions were low dislocations. Therefore, when manufacturing a semiconductor laser or the like, the accuracy of mask alignment for forming a waveguide can be relaxed, and a wide stripe waveguide necessary for a high-power semiconductor laser can be formed.

  As shown in FIG. 10, crystal growth is performed using metal organic chemical vapor deposition (MOVPE). That is, first, prior to vapor phase growth, the sapphire C-plane substrate 111 is placed on a susceptor in a reaction furnace, evacuated, and then heated at 1050 ° C. for 15 minutes in a hydrogen atmosphere of 200 Torr to perform substrate surface cleaning.

  Next, after cooling to 600 ° C., trimethylgallium (TMG) was flowed at 20 μmol / min, ammonia at 2.5 L / min, carrier hydrogen and nitrogen at 2 L / min, respectively, as shown in FIG. A GaN buffer layer 112 in a crystalline state is deposited to 20 nm. The optimum deposition temperature at this time is 500 to 600 ° C.

  Next, only the supply of TMG is stopped, the substrate temperature is raised to 1090 ° C., and then TMG is supplied again to form the GaN single crystal layer 113 with a thickness of about 1 μm. The film thickness is desirably 0.5 μm or more in order to increase the c-axis orientation. The growth temperature range is higher than 1000 ° C. and preferably 1200 ° C. or lower.

  Next, the supply of TMI and hydrogen was stopped, and the temperature was lowered to 800 ° C. in a mixed atmosphere of ammonia and nitrogen to reach a constant temperature. Then, trimethylindium (TMI) was 200 μmol / min, and TMG was 20 μmol / min. Then, an InGaN layer 114 is deposited to a thickness of 100 nm. The mole fraction of In in the InGaN mixed crystal is about 10%. By adjusting the supply mole fraction of TMI and TMG, the mole fraction of In in the InGaN mixed crystal can be adjusted.

  Next, the supply of TMI and TMG is stopped, and the temperature is raised from 800 ° C. to 1090 ° C. in a mixed atmosphere of ammonia and nitrogen. The temperature raising time is about 3 to 5 minutes, and is performed in a relatively short time. In this case, as shown in FIG. 10B, irregularities having a diameter and a depth of the order of several tens of nanometers are generated on the entire surface of the InGaN layer 114. The reason for this is considered that InN crystals having several orders of magnitude higher vapor pressure evaporate from the InGaN active layer during the temperature rise.

  Next, after adding 20 μmol / min of TMG and 2 L / min of carrier hydrogen to grow a GaN single crystal layer 115 as shown in FIG. 10C to a thickness of about 1 μm, only the supply of TMG is stopped, Cool to room temperature in an ammonia, hydrogen, nitrogen atmosphere.

  As a result of the growth through the above steps, a void having a diameter and depth of the order of several tens of nanometers is formed at the interface between the outermost GaN single crystal layer 115 and the InGaN single crystal layer 114 as shown in FIG. it can.

  In the present invention, the heat treatment of the InGaN layer 114 is used to create a void at the substrate side interface of the GaN single crystal layer 115, but it goes without saying that the same effect can be obtained if the AlGaInN layer contains In. Yes. A method of forming irregularities on the surface of the InGaN layer 114 in order to create voids is effective for heat treatment, and particularly rapid temperature rise is effective. The In mole fraction of the InGaN layer 114 is preferably 10% or more, but it only needs to contain In. The film thickness is preferably 100 nm or more, but if it is 10 nm or more, voids can be obtained.

  In the present embodiment, the case of the reduced pressure growth is shown, but the same effect can be obtained by the growth in the atmospheric pressure or the pressurized atmosphere.

  As shown in FIG. 11, crystal growth is performed using metal organic chemical vapor deposition (MOCVD). That is, first, prior to vapor phase growth, the sapphire C-plane substrate 111 is placed on a susceptor in a reaction furnace, evacuated, and then heated at 1050 ° C. for 15 minutes in a hydrogen atmosphere of 200 Torr to perform substrate surface cleaning.

  Next, after cooling to 600 ° C., 20 μmol / min of trimethylgallium (TMG), 200 μmol / min of trimethylindium (TMI), 2.5 L / min of ammonia, and 2 L / min of carrier nitrogen were flowed. As shown in a), a polycrystalline InGaN buffer layer 116 is deposited to 20 nm to 100 nm. The optimum deposition temperature at this time is 500 to 600 ° C.

  Next, the supply of TMG and TMI is stopped, and the substrate temperature is raised to 1090 ° C. The temperature raising time is about 3 to 5 minutes, and is performed in a relatively short time. In this case, as shown in FIG. 11B, irregularities having a diameter and a depth on the order of several tens of nm are generated on the entire surface of the InGaN buffer layer 116. Next, carrier hydrogen is further added at a rate of 2 L / min, and TMG is supplied again as shown in FIG. 11C to form a GaN single crystal layer 117 of about 1 μm. The film thickness is desirably 0.5 μm or more in order to increase the c-axis orientation. The growth temperature range is higher than 1000 ° C. and preferably 1200 ° C. or lower.

  Finally, only the supply of TMG is stopped, and the mixture is cooled to room temperature in an ammonia, hydrogen, and nitrogen atmosphere.

  As a result of the growth through the above steps, a void having a diameter and depth of the order of several tens of nanometers can be produced at the interface between the outermost GaN single crystal layer 117 and the InGaN buffer layer 116 as shown in FIG. .

  In the present invention, the heat treatment of the InGaN buffer layer 116 is used to create a void at the substrate-side interface of the GaN single crystal layer 117. However, the same effect can be obtained if the AlGaInN buffer layer contains In. Needless to say. A method of forming irregularities on the surface of the InGaN buffer layer 116 in order to create a void is effective for heat treatment, and particularly rapid temperature rise is effective. The In mole fraction of the InGaN buffer layer 116 is preferably 10% or more, but it only needs to contain In. The film thickness is preferably 100 nm or more, but if it is 10 nm or more, voids can be obtained.

  According to the manufacturing method of the present invention, it is possible to easily manufacture a substrate made of only a high-quality group III nitride crystal and having a small warp.

(A)-(f) is process sectional drawing which shows an example of the manufacturing method of this invention. (A)-(b) is a schematic diagram which shows an example of the manufacturing apparatus used for the manufacturing method of this invention. (A) is a graph which shows PL intensity | strength of the GaN crystal obtained by the conventional method, (b) is a graph which shows PL intensity | strength of the GaN crystal obtained by one Example of this invention. It is a schematic diagram which shows another example of the manufacturing apparatus used for the manufacturing method of this invention. It is sectional drawing which shows an example of the semiconductor device using the board | substrate manufactured with the manufacturing method of this invention. (A)-(c) is process sectional drawing which shows the further another example of the manufacturing method of this invention. It is a schematic diagram which shows another example of the manufacturing apparatus used for the manufacturing method of this invention. (A)-(d) is process sectional drawing which shows the further another example of the manufacturing method of this invention. (A)-(c) is process sectional drawing which shows the further another example of the manufacturing method of this invention. (A)-(d) is process sectional drawing which shows the further another example of the manufacturing method of this invention. (A)-(c) is process sectional drawing which shows the further another example of the manufacturing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 11 Sapphire substrate 12 Seed layer 13 Resist pattern 14 Mask film 15 Selective growth layer 16 GaN crystal 17 Seed crystal substrate 21 Gas tank 22 Pressure regulator 23 Valve 24 Container 25 Electric furnace 26 Crucible 30 Electric furnace 31 Chamber 32 Furnace 33 Heater 34a thermocouple 34b thermocouple 34c thermocouple 35 core tube 36 crucible 37 melt 38 substrate fixing part 39a motor 39b motor 300a zone 300b zone 300c zone 40 propeller 41 gas source 42 pressure regulator 43 gas purification part 50 semiconductor laser 51 substrate 52 Contact layer 53 Clad layer 54 Light guide layer 55 Active layer 56 Light guide layer 57 Clad layer 58 Contact layer 59 Insulating film 500 Electrode 501 Electrode 61 Sapphire substrate 62 SiNx film 63 C Layer 80 flow controller 81 electric furnace 82 quartz tube 83 GaN powder 84 crucible 85 heater 86 substrate 87 thermocouple 88 supply direction 91 sapphire substrate 92 seed layer 93 resist film 94 LPE-GaN crystal 101 sapphire substrate 102 mask film 103 seed layer 104 LPE-GaN crystal 111 Sapphire substrate 112 GaN buffer layer 113 GaN single crystal layer 114 InGaN single crystal layer 115 GaN single crystal layer 116 InGaN buffer layer 117 GaN single crystal layer

Claims (25)

(I) forming a group III nitride layer having voids on the substrate;
(Ii) bringing the surface of the Group III nitride layer into contact with a melt containing at least one Group III element selected from gallium, aluminum, and indium and an alkali metal in an atmosphere containing nitrogen; A step of reacting two group III elements and nitrogen to grow a group III nitride crystal on the group III nitride layer;
(Iii) A method for producing a group III nitride substrate, comprising: separating a portion including the substrate and a portion including the group III nitride crystal in the vicinity of the gap. The method for producing a group III nitride substrate according to claim 1, wherein the at least one element is gallium and the group III nitride crystal is a GaN crystal. The method for producing a group III nitride substrate according to claim 1, wherein the atmosphere containing nitrogen is a pressurized atmosphere. 3. The group III nitriding according to claim 1, wherein in the step (iii), the separation is performed using a stress generated by a difference between a linear expansion coefficient of the substrate and a linear expansion coefficient of the group III nitride crystal. Manufacturing method of physical substrate. The step (i)
(I-1) A first semiconductor layer represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) is formed on the substrate. Process,
(I-2) a step of removing a part of the first semiconductor layer to form a convex portion;
(I-3) A second semiconductor layer represented by a composition formula Al _x Ga _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is defined as the first semiconductor layer. Including the step of forming the group III nitride layer in which a portion other than the convex portion becomes a void by growing from the upper surface of the convex portion,
The method for producing a group III nitride substrate according to claim 1 or 2, wherein in the step (iii), the first semiconductor layer and the second semiconductor layer are separated from each other on the upper surface of the convex portion. The method for producing a group III nitride substrate according to claim 5, wherein the upper surface is a C-plane. 6. The method for producing a group III nitride substrate according to claim 5, wherein, in the step (i-2), the convex portions are formed in a stripe shape. 6. The method for manufacturing a group III nitride substrate according to claim 5, wherein, in the step (i-2), a concave portion other than the upper surface of the convex portion is covered with a mask film. The group III of claim 8, wherein the mask film includes at least one selected from the group consisting of silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, aluminum nitride oxide, titanium oxide, zirconium oxide, and niobium oxide. A method for manufacturing a nitride substrate. 9. The method for manufacturing a group III nitride substrate according to claim 8, wherein the mask film is made of a refractory metal or a refractory metallized material. 9. The method for manufacturing a group III nitride substrate according to claim 8, wherein the mask film includes at least one selected from the group consisting of tungsten, molybdenum, niobium, tungsten silicide, molybdenum silicide, and niobium silicide. (I) processing the surface of the substrate to form convex portions;
(II) forming a seed crystal substrate in which a gap is formed between the substrate and the group III nitride layer by growing a group III nitride layer from the upper surface of the convex portion;
(III) contacting the surface of the group III nitride layer with a melt containing at least one group III element selected from gallium, aluminum and indium and an alkali metal under a pressurized atmosphere containing nitrogen, Reacting at least one group III element with nitrogen to grow a group III nitride crystal on the group III nitride layer;
(IV) A method of manufacturing a group III nitride substrate, including a step of separating a portion including the substrate and a portion including the group III nitride crystal in the vicinity of the gap. The method for manufacturing a group III nitride substrate according to any one of claims 1 to 12, wherein the substrate is a sapphire substrate. The method for producing a group III nitride substrate according to any one of claims 1 to 12, wherein the alkali metal is at least one selected from sodium, lithium and potassium. The method for producing a group III nitride substrate according to any one of claims 1 to 12, wherein the melt further contains an alkaline earth metal. The step (i)
(Ia) A step of forming a first semiconductor layer represented by a composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) on a substrate. When,
(Ib) removing a part of the first semiconductor layer until the substrate is exposed to form a concave part that becomes a void, and forming the remaining part into a convex part,
The manufacturing method according to any one of claims 1 to 4, wherein in the step (ii), a group III nitride crystal is grown on the surface of the convex portion (ib). The step (i)
(Ic) forming a patterned mask film on the substrate;
( _Id ) Convex shape represented by the composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) on the substrate exposed from the mask film. Forming a first semiconductor layer and forming a void in which the convex first semiconductor layer is not formed,
The manufacturing method according to any one of claims 1 to 4, wherein in the step (ii), a group III nitride crystal is grown on the surface of the first semiconductor layer (id). In the step (i), the group III nitride layer having the voids is represented by a composition formula Al _x Ga _y In _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1). 5. A void is formed in the semiconductor layer or on the surface of the semiconductor layer by forming a semiconductor layer and then heating and heating in a mixed atmosphere of ammonia and nitrogen after forming the semiconductor layer. The manufacturing method as described in. The manufacturing method according to claim 18, wherein the group III nitride layer including the void is a semiconductor layer represented by a composition formula Ga _x In _1-x N (where 0 ≦ x ≦ 1). The manufacturing method according to claim 18 or 19, wherein a temperature increase rate of the temperature increasing heat treatment is 50 to 100 ° C / min. 21. The manufacturing method according to claim 1, wherein a period of the gap is 30 μm or more. 21. The manufacturing method according to claim 1, wherein a period of the gap is 50 μm or more. 21. The manufacturing method according to claim 1, wherein a period of the gap is 100 μm or more. (I) forming a group III nitride layer having voids on the substrate;
(ii) a step of heating and sublimating a Group III nitride crystal raw material, cooling on the Group III nitride layer in an atmosphere containing nitrogen or ammonia, and recrystallizing the Group III nitride crystal again; ,
(Iii) A method of manufacturing a group III nitride substrate, including a step of separating a portion including the substrate and a portion including the group III nitride crystal in the vicinity of the gap. 25. The method for producing a group III nitride substrate according to claim 24 , wherein the step (ii) is performed at 1 atm or more.

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