JP3906739B2 - Manufacturing method of nitride semiconductor substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention has the general formula In_xAl_yGa_1-xyThe present invention relates to a method for manufacturing a nitride semiconductor substrate represented by N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1).
[0002]
[Prior art]
In recent years, various studies for growing a nitride semiconductor on a different substrate from a nitride semiconductor such as sapphire, silicon carbide, and spinel have been studied. This is because it is difficult to obtain a bulk single crystal of nitride semiconductor with good crystallinity that can be used for a light emitting device or the like. If a nitride semiconductor is grown on the heterogeneous substrate, the crystallinity of the nitride semiconductor is lowered due to a difference in lattice constant and thermal expansion coefficient.
[0003]
As a method of reducing dislocation defects, a method of forming a nitride semiconductor substrate using lateral growth is disclosed in Japanese Patent Laid-Open No. 10-312971. This is SiO₂Patterning on the substrate using a mask material such as a protective film, and growing until the protective film is embedded by lateral growth, thereby reducing the dislocation density by bending the dislocation propagation direction during the crystal growth process on the protective film. Is to be made.
[0004]
[Problems to be solved by the invention]
However, in the above method, when the nitride semiconductor is laterally grown to embed the protective film, the crystal axis is inclined as the crystal grows laterally with respect to the growth surface on the protective film. Therefore, tilt occurs. When the tilted crystals are combined, a new dislocation defect is generated. Further, if a nitride semiconductor is grown with a protective film, it is necessary to grow a thicker film than when no protective film is provided to fill the nitride semiconductor and planarize the surface. If a nitride semiconductor film is grown on a different type of substrate, the nitride semiconductor substrate warps and cracks tend to occur. Further, contamination due to decomposition of the protective film occurs during growth of the nitride semiconductor, and the crystallinity of the nitride semiconductor is deteriorated.
[0005]
Accordingly, an object of the present invention is to produce a nitride semiconductor substrate with good crystallinity that has reduced dislocation defects without laterally growing a nitride semiconductor on the protective film as described above, that is, without covering the protective film. It is to provide a method.
[0006]
[Means for Solving the Problems]
The method for producing a nitride semiconductor substrate according to the present invention is a method for producing a nitride semiconductor substrate utilizing lateral growth, wherein a release film is formed on the substrate and at least one molecular layer of the release film is formed on the substrate. A first step of chemically bonding on the surface, and a release film chemically bonded to the substrate surface,By forming a region where the substrate surface is exposed by dry etching using plasmaPattern formationThe film thickness of the release film is 1 molecular layer or more and 3 μm or less.And a second step of growing a first nitride semiconductor on the patterned substrate of the release film,A release film chemically bonded to the substrate surface;First nitride semiconductor on release filmWhen,And a third step of laterally growing a second nitride semiconductor using the first nitride semiconductor as a growth nucleus.Further, the method for forming the chemically bonded release film is preferably a plasma CVD method or an ECR sputtering method. The release film is preferably selected from the group consisting of silicon oxide, silicon nitride, silicon nitride oxide, titanium oxide, and zirconium oxide. The substrate surface subjected to the dry etching is preferably formed with a recess. The second nitride semiconductor is preferably grown at a higher temperature than the first nitride semiconductor. In the lift-off, the ambient temperature of the nitride semiconductor substrate is preferably set to 900 ° C. or higher.
[0007]
Thus, in the method for manufacturing a nitride semiconductor substrate according to the present invention, a release film is formed and a pattern is formed, but the release film is removed during the lateral growth of the nitride semiconductor. The release film in the present invention is intended to remove the nitride semiconductor by lift-off, and does not laterally grow the nitride semiconductor on the release film. For this reason, the tilt generated when the nitride semiconductor is laterally grown on the protective film as in the prior art is suppressed in the present invention. Further, since the present invention does not cover the protective film and flatten the nitride semiconductor substrate, the nitride semiconductor substrate can be formed as a thin film, and the warpage of the substrate is alleviated, thereby preventing the occurrence of cracks. You can also. Here, the lateral growth in the present invention means not only lateral growth but also vertical growth, and has an effect of bending dislocation defects in the lateral direction.
[0008]
According to the present invention, after a release film chemically bonded to the substrate surface is patterned, a first nitride semiconductor is grown on the substrate in a third step. The first nitride semiconductor is laterally formed on the release film. It does not grow. In contrast, in the second nitride semiconductor, the nitride semiconductor on the chemically bonded release film is removed by lift-off, and then lateral growth is performed using the first nitride semiconductor other than the lift-off region as a growth nucleus. . The first nitride semiconductor on the release film is removed together with the chemically bonded release film during the growth of the second nitride semiconductor. This lift-off cuts and removes the chemical bonds of the chemically bonded release film. The lift-off conditions for cutting the chemical bond between the substrate surface and the release film interface will be described later. In the present invention, since the third step can be a continuous reaction, it is possible to simplify the steps such as taking out from the reaction apparatus and reacting with another apparatus. In addition, the nitride semiconductor does not react when dust or dirt adheres to the substrate. In the third step, first, a first nitride semiconductor is grown on a substrate having the patterned release film. Next, the nitride semiconductor on the release film selectively patterned using lift-off is removed. In the region where the release film is not formed, the first nitride semiconductor remains as a growth nucleus. By having this growth nucleus, lateral growth of the second nitride semiconductor to be grown next becomes possible. In order to grow a nitride semiconductor on a substrate, it is first necessary to form a growth nucleus for growing the nitride semiconductor. The reason is as follows. Without this growth nucleus, the nitride semiconductor has a slow growth rate, and even if it grows, it has poor crystallinity and becomes polycrystalline. Therefore, the growth nucleus is partially formed on the substrate. If a nitride semiconductor grows selectively from this growth nucleus, it becomes a single crystal. The first nitride semiconductor is not formed as a growth nucleus in the region where the release film is removed by lift-off. In this region, the second nitride semiconductor does not grow, and the second nitride semiconductor does not grow. It grows selectively from the growth nucleus. By continuously growing the second nitride semiconductor from the growth nucleus, the second nitride semiconductor can be laterally grown, and a nitride semiconductor substrate having a flat and mirror surface can be obtained.
[0009]
As a method for forming the release film, it is sufficient that at least one molecular layer of the release film is chemically bonded to the substrate surface. Preferably, a plasma CVD method or an ECR sputtering method is used. As this condition, for example, in the plasma CVD method, the pressure is 20 Pa, the RF is 120 W, the SiH₄5 sccm, N₂O is 200 sccm, and the temperature is 360 ° C. In the ECR sputtering method, Ar is 20 sccm, N₂5 sccm, RF 500 W, microwave 500 W, target Si, and temperature at room temperature.
[0010]
The pattern formation of the chemically bonded release film is performed by etching the release film with energy capable of breaking the chemical bond on the substrate surface. Here, the method of etching the release film is not only to remove the release film formed on the substrate but also to remove the release film chemically bonded on the substrate surface. Etching with an energy capable of breaking the chemical bond is dry etching using plasma. Also, a combination with wet etching or heating may be used.
[0011]
In the second step, the substrate surface is exposed or recessed. This is because the substrate surface in the region where the release film is removed is exposed by patterning the release film. By partially removing the release film in this way, it is possible to provide a nitride semiconductor growth nucleus formation region to be grown in a later step. Further, if the etching is performed for a long time or the substrate surface is exposed and then the substrate is preferentially etched by an etching method having a large etching selectivity between the substrate and the release film, a recess can be formed in the substrate. The first nitride semiconductor may be formed as a growth nucleus in this recess.
[0012]
The third step is shown in FIG. A substrate on which a release film chemically bonded to the substrate surface is patterned is prepared (FIG. 2-a). Here, it is preferable that the release film leaves only a chemically bonded monomolecular layer on the substrate surface. This is to facilitate lift-off in the third step performed in a continuous reaction. Therefore, the release film is adjusted to a single molecular layer by wet etching or the like. The above is the second step. Next, the third step is performed as a continuous reaction in the apparatus. First, a first nitride semiconductor is grown on a substrate on which the release film is patterned. Here, the growth temperature of the first nitride semiconductor is such that the chemical bond is not broken, and is preferably a low temperature growth of 900 ° C. or lower, more preferably 700 ° C. or lower. Here, the first nitride semiconductor is grown on the substrate surface in the region having no release film (A region) and on the release film (B region) (FIG. 2-b). Next, the first nitride semiconductor on the release film is removed by lift-off. This lift-off only needs to grow the second nitride semiconductor at a higher temperature than the first nitride semiconductor. This reduces the reaction time. Here, the high temperature is a temperature at which the chemical bond of the release film of one molecular layer on the substrate surface can be cut. Specifically, it is 900 ° C. or higher, preferably 1000 ° C. or higher. Since the chemically bonded release film and the first nitride semiconductor on the protective film are removed during the growth of the second nitride semiconductor, the first nitride semiconductor has a growth nucleus only in the A region after lift-off. Form (FIG. 2-c). Further, after growing the first nitride semiconductor, the ambient temperature of the nitride semiconductor substrate may be raised. Thereafter, a second nitride semiconductor is grown. As a result, when the second nitride semiconductor is grown, the release film is completely removed, so even if it is a single molecular layer release film, it is mixed as an impurity during the growth of the second nitride semiconductor. There is no. The growth temperatures of the first nitride semiconductor and the second nitride semiconductor may be the same. If a nitride semiconductor is grown thereon, the crystallinity is improved. Further, the second nitride semiconductor is laterally grown by selectively growing the partially formed first nitride semiconductor as a growth nucleus (FIG. 2D). If the lateral growth is further continued, a nitride semiconductor substrate made of a nitride semiconductor that is flattened and mirror-finished is obtained (FIG. 2E). Even if the temperature necessary for breaking the chemical bond is about 300 ° C. if it is heated for a long time. However, it is not desirable for industrial use to remove the release film at such a low temperature for a long time.
[0013]
As described above, in the present invention, dislocation defects are greatly reduced, and the dislocation density per unit area on the surface of the nitride semiconductor substrate after growing the second nitride semiconductor is 10⁷Piece / cm²It can be as follows. This nitride semiconductor substrate with reduced dislocation defects also suppresses tilts, steps, and other stresses that occur at the junction between nitride semiconductors when the nitride semiconductor is laterally grown on the protective film. it can. Furthermore, since the nitride semiconductor is not laterally grown on the protective film, the nitride semiconductor substrate can be thinned. The reason for this is that the growth of the nitride semiconductor is not forcibly laterally grown on the protective film, but is laterally grown without stress from the growth nucleus. Therefore, the surface shape of the nitride semiconductor can be flat and mirror-like, and the yield and reliability of LED elements, LD elements, etc. formed on this nitride semiconductor substrate are improved.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The nitride semiconductor substrate in the present embodiment is manufactured using lateral growth, and has no tilt because it is formed without a protective film. By forming a nitride semiconductor as a growth nucleus and performing regrowth of the nitride semiconductor from the growth nucleus, the nitride semiconductor grows in the vertical direction and the horizontal direction. Therefore, dislocation defects can be bent by lateral growth, and a low dislocation region can be formed. If this lateral growth is further continued, the laterally grown nitride semiconductors are joined together to form a nitride semiconductor substrate having a flat and mirror surface.
[0015]
The number of dislocation defects in the nitride semiconductor substrate is shown below. According to the CL (cathode luminescence) method, dislocation defects per unit area on the surface of the nitride semiconductor are 1 × 10⁷Piece / cm²Or less, more preferably 1 × 10⁶Piece / cm²It becomes as follows. In addition, since the threading dislocations proceeding in the vertical direction remain in the A region, the number of dislocations is 1 × 10⁸~ 1x10¹⁰Piece / cm²It will be about.
[0016]
[Embodiment 1]
The manufacturing process of the nitride semiconductor substrate in the embodiment of the present invention includes a first step of forming a release film on the substrate and chemically bonding at least one molecular layer of the release film on the surface of the substrate; A second step of patterning a release film chemically bonded to the surface; and a first first nitride semiconductor grown on a substrate on which the release film is patterned, and then a second step on the chemically bonded release film. And a third step of laterally growing a second nitride semiconductor using the first nitride semiconductor as a growth nucleus.
[0017]
Hereafter, each said process is demonstrated in detail using FIG. First, in the first step, a release film 2 is formed on the substrate 1 (FIG. 1-1). In this film formation, at least one molecular layer of the release film is chemically bonded on the surface of the substrate 1. This may be chemically bonded on the surface of the substrate when the release film is formed, or may be newly provided with energy sufficient to allow the chemical bond after the release film is formed.
[0018]
For chemical bonding at the time of forming the release film, a film forming method using plasma is preferable, and there are a plasma CVD method and an ECR sputtering method. The simple principle of the plasma CVD method is to excite the source gas in the plasma state of a high-energy gas, or to decompose chemical bonds, create atomic or molecular radicals, and deposit a thin film by reaction between active particles. Is the method. As a simple principle of ECR sputtering, electron cyclotron resonance (ECR) is caused in a plasma generation chamber, and a sample to which DC or RF is applied is sputtered by a plasma derived along a magnetic field emanating from the plasma chamber. This is a technique for forming a thin film on a substrate in a chamber, and a ring-shaped target is installed between a plasma generation chamber and a sample chamber. As other methods, CVD, sputtering, and vapor deposition are also conceivable.
[0019]
In order to give a new energy after the formation of the release film to such an extent that the release film and the substrate can be chemically bonded (at least an energy that allows a single molecular layer of the release film to be chemically bonded to the substrate surface), annealing is specifically performed. is there.
[0020]
As the substrate 1, sapphire, spinel (MgAl) having any one of the C-plane, R-plane, and A-plane as the main surface.₂O₄An insulating substrate such as SiC (6H, 4H, 3C), ZnS, ZnO, GaAs, Si, and an oxide substrate lattice-bonded to a nitride semiconductor can be used. These substrates may have an off-angle.
[0021]
The release film 2 only needs to be chemically bonded on the substrate surface. Specific examples of the release film 2 include silicon oxide (SiO 2_x), Silicon nitride (Si_xN_y), Silicon nitride oxide (SiO_xN_y), Titanium oxide (TiO_x), Zirconium oxide (ZrO)_x) Or the like, or a metal having a melting point of 1200 ° C. or higher. The thickness of the release film is not particularly limited as long as at least one molecular layer of the release film is chemically bonded. However, in order to cut the chemical bond in a subsequent step, the release film is preferably thin to some extent. The film thickness is from 1 molecular layer to 30 μm, preferably from 1 molecular layer to 3 μm. If the film is formed in this range, it is possible to easily remove the release film (cut the chemical bond) in a later step.
[0022]
Next, as a second step, the release film 3 chemically bonded on the substrate surface is patterned (FIGS. 1-3). This pattern formation is to create a removal region of the release film. The release film 2 is patterned (FIGS. 1-2). Thereafter, the release film 3 in which one molecular layer is chemically bonded is left on the substrate surface, and the other release film is removed (FIGS. 1-3). Here, the removal region of the release film is a region where the chemical bond on the substrate surface is cut and the substrate surface is exposed. Although this region is formed by etching, the cross-sectional shape of the substrate surface may be formed in the recess by continuing the etching after the substrate surface is exposed. In addition, the patterned release film may have a single molecular layer chemically bonded on the substrate surface. By using a single molecular layer, the release film can be easily removed when lift-off is performed in a later step. Furthermore, contamination due to decomposition of the release film is also suppressed. Therefore, wet etching using buffered hydrofluoric acid (BHF) or the like is performed in order to leave only one molecular layer having a release film chemically bonded to the substrate surface.
[0023]
As a specific method for forming this pattern, there is a dry etching method, and an apparatus such as reactive ion etching (RIE), ICP, reactive ion beam etching (RIBE), electron cyclotron etching (ECR), or asher is used.
[0024]
Further, the planar shape on which the pattern of the release film is formed can be a stripe shape, a lattice shape, an island shape, a circle shape, a polygonal shape, or the like. Further, some have circular or polygonal openings. A nitride semiconductor growth nucleus is formed in the opening of the release film 2 in a later step. For example, when the release film 2 is patterned in a stripe shape, the region where the release film exists is a region where the nitride semiconductor is laterally grown in a later step. If this region is wide, a low dislocation region can be formed widely. The width of the existing region of the release film is 1 to 100 μm, preferably 5 to 15 μm.
[0025]
Further, when the release film 2 is formed in a stripe shape, if the substrate 1 is a sapphire substrate, the orientation flat surface is the A surface of sapphire and the release film 2 is shifted to the left or right with respect to the vertical axis of the orientation flat surface. May be formed. Specifically, the nitride semiconductor is grown by setting the angle θ = 0 ° to 5 ° to the left and right with respect to the vertical axis of the orientation flat surface, preferably θ = 0.001 ° to 0.5 °. It is possible to further flatten the surface after finishing.
[0026]
Next, as a third step, a nitride semiconductor composed of at least two layers is grown on the pattern forming surface of the release film of the substrate (FIGS. 1-6). This third step is a continuous reaction, and one of the layers is laterally grown to form a nitride semiconductor substrate having a planarized surface. The nitride semiconductor includes a first nitride semiconductor that forms a growth nucleus and a second nitride semiconductor that is laterally grown. A third nitride semiconductor may be grown as a single layer or a plurality of layers between the first nitride semiconductor and the second nitride semiconductor. The first nitride semiconductor may be a buffer layer in which single crystal and polycrystal are mixed.
[0027]
The first nitride semiconductor is grown at a low temperature of 900 ° C. or lower (FIGS. 1-4). Preferably, the growth is performed at 700 ° C. or less and with a film thickness of 10 Å or more and 0.5 μm or less. This is to alleviate the lattice constant irregularity with the substrate 1 and has an effect as a buffer layer for reducing dislocation defects. After the first nitride semiconductor is grown, lift-off is performed to cut the chemical bond on the substrate surface of the release film, and the release film is removed to pattern growth nuclei in the A region. This lift-off increases the ambient temperature of the nitride semiconductor substrate. As conditions for breaking the chemical bond on the substrate surface of the release film, the ambient temperature is set to 700 ° C. or higher, and H₂Hold the atmosphere for at least 10 minutes. NH₃1.0 liter / min or less, preferably 0.5 liter / min or less, and about 0.1 liter / min. As described above, the release film chemically bonded to the substrate surface is removed (FIGS. 1-5). Thereafter, a second nitride semiconductor is grown. This forms a nitride semiconductor substrate by laterally growing in the removal region of the release film using the first nitride semiconductor as a growth nucleus (FIGS. 1-6). Moreover, it has a lift-off action by growing the second nitride semiconductor under the temperature conditions shown below.
[0028]
As a growth condition of the second nitride semiconductor, a nitride semiconductor substrate having a flat surface can be formed if the growth temperature is 900 ° C. or more and the film thickness is 3 μm or more. A nitride semiconductor substrate can also be formed by selectively performing this lateral growth and flattening. By prioritizing lateral growth, the nitride semiconductor substrate can be made thinner. The conditions include reducing the V / III ratio, which is the ratio of the Group V (nitrogen) source material to the Group III source material, or setting the pressure condition to a reduced pressure condition, or otherwise doping Mg at a high concentration.
[0029]
Examples of the nitride semiconductor include undoped nitride semiconductors, nitride semiconductors doped with n-type impurities such as Si, Ge, Sn, and S, and nitride semiconductors doped with p-type impurities such as Mg and Zn, Alternatively, a nitride semiconductor in which an n-type impurity and a p-type impurity are simultaneously doped can be used. All of the nitride semiconductors have the general formula In_xAl_yGa_1-xyN (0 ≦ x, 0 ≦ y, x + y ≦ 1). However, these may have different compositions. As a method for growing a nitride semiconductor, MOVPE (metal organic vapor phase epitaxy), HVPE (halide vapor phase epitaxy), MBE (molecular beam epitaxy), MOCVD (metal organic chemical vapor deposition), etc. A vapor phase growth method can be applied.
[0030]
Further, dislocation defects can be further reduced by growing a nitride semiconductor on the nitride semiconductor substrate in a thick film and converging the dislocation defects during the growth of the thick film. Usually, when a nitride semiconductor is grown on a laterally grown nitride semiconductor substrate, the surface after the thick film growth is not flat due to the influence of tilt. However, in the nitride semiconductor substrate of the present invention, there is no step in the stress or the junction between the nitride semiconductors due to tilt or lateral growth, so that the surface becomes flat and mirror-like even after the thick film growth. When this thick film growth is performed by the HVPE method, for example, for GaN, HCl gas and Ga metal react to react with GaCl or GaCl.₃Further, the Ga chloride reacts with ammonia to cause low dislocation, and deposits GaN of 100 μm or more on the substrate. When a nitride semiconductor is grown on a different substrate different from the nitride semiconductor, a single substrate consisting only of the nitride semiconductor is formed by removing the heterogeneous substrate from the thick nitride semiconductor substrate. Can do. A single substrate made of a nitride semiconductor can form an LED, LD, or the like having a back electrode structure.
[0031]
[Embodiment 2]
Next, a nitride semiconductor laser element formed on the nitride semiconductor substrate is shown (FIG. 3). Al doped with an n-type impurity as the n-side contact layer 101 on the nitride semiconductor substrate (the nitride semiconductor 10 is formed on the substrate 1) formed in the first embodiment._xGa_1-xN (0 ≦ X <1) is grown at about 5 μm. An n-type impurity-doped In as an anti-cracking layer (not shown) on the n-side contact layer_xGa_1-xN (0 ≦ X <1) is grown at about 0.2 μm. This crack prevention layer can be omitted. Subsequently, the n-side cladding layer 102 is grown on the crack prevention layer. The n-side cladding layer preferably has a superlattice structure, and is undoped Al._xGa_1-xAn n-side cladding layer having a superlattice structure with a total film thickness of about 1.2 μm is formed by alternately stacking layers made of N (0 ≦ X <1) and layers made of n-type GaN doped with n-type impurities. Grow. Subsequently, an n-side light guide layer 103 made of undoped GaN is grown to a thickness of about 0.1 μm. This n-side light guide layer may be doped with n-type impurities.
[0032]
Next, the barrier layer is non-doped In_xGa_1-xN (0 ≦ X ≦ 1) and n-type impurity doped In in the well layer_xGa_1-xAn active layer 104 having a single quantum well structure or a multiple quantum well structure made of N (0 ≦ X ≦ 1) is grown. If it is a multiple quantum well structure, a barrier layer and a well layer are laminated | stacked alternately by the same temperature about 2-5 times, and it is set as a barrier layer at the end, and makes the total film thickness 200-500 mm.
[0033]
Next, p-type Al doped with a p-type impurity as a p-side cap layer (not shown) on the active layer_xGa_1-xN (0 ≦ X <1) is grown. The p-side cap layer is grown with a film thickness of about 50 to 500 mm. Subsequently, a p-side light guide layer 105 made of undoped GaN is grown to a thickness of about 0.05 to 0.5 μm. The p-side light guide layer 105 may be doped with a p-type impurity. Next, the p-side cladding layer 106 is grown on the p-side light guide layer. The p-side cladding layer preferably has a superlattice structure as in the case of the n-side cladding layer._xGa_1-xP composed of a superlattice structure having a total film thickness of about 0.3 to 0.8 μm by alternately laminating layers composed of N (0 ≦ X <1) and layers composed of p-type GaN doped with p-type impurities. A side cladding layer is grown. Finally, Al doped with p-type impurities on the p-side cladding layer_xGa_1-xA p-side contact layer 107 made of N (0 ≦ X ≦ 1) is grown.
[0034]
Here, the impurity concentration is not particularly limited, but preferably n-type impurities and p-type impurities are 1 × 10.¹⁸/ Cm³~ 1x10²⁰/ Cm³And Examples of the n-type impurity include Si, Ge, Sn, S, O, Ti, Zr, and Cd. Examples of the p-type impurity include Be, Zn, Mn, Mg, Ca, and Sr.
[0035]
Next, after forming the nitride semiconductor laser element on the nitride semiconductor substrate, when the p electrode and the n electrode are formed on the same surface side, the n-side contact layer is etched to form the n electrode. Expose. Next, a ridge is formed by etching to form a stripe-shaped optical waveguide region. Here, the etching is preferably anisotropic etching to form a ridge. For example, an RIE (reactive ion etching) apparatus or the like is used. The width of the ridge formed here can be as wide as 1.0 to 3.0 [mu] m, although it depends on the buried layer and output formed in a later step in the present invention. In addition, as an etching depth, etching is performed up to at least the p-side cladding layer in the nitride semiconductor element. Furthermore, the ridge shape includes a forward mesa type, a reverse mesa type, and a vertical type, and these shapes are preferable because they can confine light in the lateral direction.
[0036]
After forming the ridge, an embedded film (eg, ZrO, diamond-like carbon, glass, etc.) made of an insulator is formed on the nitride semiconductor layers on both side surfaces of the ridge from the exposed side wall of the ridge by sputtering or the like. Form. The effects of this buried film are current confinement and lateral light confinement. In order to confine light in the lateral direction, it is necessary to provide a difference in refractive index between the nitride semiconductor layer and to confine light in the core region, a buried layer made of a material having a refractive index smaller than that of the nitride semiconductor. Used for. Further, in the optical confinement in the vertical direction, light is confined in the core by providing a refractive index difference between the core region having a high refractive index and the p and n-side cladding layers having a low refractive index.
[0037]
Thereafter, the buried layer formed on the top surface of the ridge is removed by lift-off or the like in order to form the p-electrode 201. Next, after removal, a p-electrode made of Ni / Au is formed in a stripe shape on the exposed surface of the p-side contact layer. After forming the p-electrode, the n-electrode 202 made of Ti / Al is formed on the surface of the n-side contact layer. Are formed in parallel with the ridge stripe. Next, a pad electrode 203 as an extraction electrode is formed on the p electrode and the n electrode.
[0038]
Further, the p electrode may be Ni / Au / RhO and the p-side pad electrode may be RhO / Pt / Au. Before forming the pad electrode, SiO₂TiO₂A dielectric multilayer film made of the same may be formed on the resonator surface (light emission end face side). By having this dielectric multilayer film, it is possible to suppress end face deterioration of the light emitting end face at the time of high output. Further, a buried film 301 and a damage protective film 302 are formed.
[0039]
Further, after forming the resonator surface, a dielectric multilayer film is formed on the resonator surface, cut in a direction parallel to the electrodes, and formed into a chip to obtain a nitride semiconductor laser element. The nitride semiconductor laser element is placed on a heat sink, wire-bonded, and sealed with a cap to obtain a nitride semiconductor laser diode.
[0040]
When laser oscillation was attempted at room temperature using the nitride semiconductor laser diode obtained as described above, the oscillation wavelength was 400 to 420 nm, the threshold current density was 2.9 kA / cm.²In the case of, continuous oscillation is exhibited, and kink does not occur not only at a low output of about 5 mW but also at an output of 30 mW or more, preferably about 50 mW, and has a life characteristic of 3000 hours or more.
[0041]
【Example】
Although the Example of this invention is shown below, this invention is not limited to this.
[Example 1]
Using a sapphire substrate 1 with the C-plane as the main surface and the orientation flat surface as the A-plane, using a plasma CVD apparatus, pressure 20 Pa, RF 120 W, SiH₄5 sccm, N₂SiO is set at 200 sccm and temperature at 360 ° C.₂A release film made of is formed with a film thickness of 0.1 μm. Thereafter, the pattern width is formed in the A region 6 μm and the B region 14 μm. Next, wet etching is performed with BHF so that the release film has only one molecular layer chemically bonded to the substrate surface. At this time, the etching rate is SiO.₂Is etched at 0.3 μm / min.
[0042]
Next, using a MOCVD apparatus, the temperature is 500 ° C., hydrogen is used as the carrier gas, ammonia and TMG (trimethyl gallium) are used as the source gas, and a first nitride semiconductor made of GaN is formed on the sapphire substrate 1 to a thickness of 200 Å. Grow with film thickness.
[0043]
Furthermore, lift-off is performed by setting the atmospheric temperature in the MOCVD apparatus to 1060 ° C. by continuous reaction. Then, using the first nitride semiconductor (A region) as the growth nucleus, the second nitride semiconductor is laterally grown using the ambient temperature of 1070 ° C., the carrier gas as hydrogen, and the source gas as ammonia and TMG (trimethylgallium). Let
[0044]
The nitride semiconductor substrate obtained as described above has a total thickness of 5 μm of nitride semiconductor, the surface is mirror-like and flat, has no tilt, and the number of dislocations per unit area on the surface is 1 × 10.⁷Piece / cm²The following nitride semiconductor substrate can be obtained.
[0045]
[Example 2]
In Example 1, growth is performed in the same manner as in Example 1 except that silane gas is added to the growth conditions of the nitride semiconductor. The obtained nitride semiconductor substrate has low dislocation defects, and an Si-doped n-type nitride semiconductor substrate can be obtained.
[0046]
[Example 3]
In Example 1, a nitride semiconductor is grown in the same manner as in Example 1 except that SiC is used for the substrate. The resulting nitride semiconductor substrate is a nitride semiconductor substrate having substantially the same function and effect as in the first embodiment.
[0047]
【The invention's effect】
As described above, according to the method for manufacturing a nitride semiconductor substrate of the present invention, it is possible to provide a nitride semiconductor substrate having low dislocation defects without growing a nitride semiconductor on a protective film in a stressed state. it can. In addition, a light-emitting element, a light-receiving element, and an electronic device with good characteristics can be realized using this nitride semiconductor substrate.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of a nitride semiconductor substrate obtained in each step of the present invention.
FIG. 2 is a schematic cross-sectional view showing the structure of a nitride semiconductor substrate obtained in each step in the present invention.
FIG. 3 is a schematic cross-sectional view showing a nitride semiconductor laser substrate according to an embodiment of the present invention.
[Explanation of symbols]
1 ... Board
2 ... Release film
3 ... Release film chemically bonded on substrate surface
4 ... 1st nitride semiconductor
5 ... Second nitride semiconductor

Claims (6)

A method of manufacturing a nitride semiconductor substrate using lateral growth,
A first step of forming a release film on the substrate and chemically bonding at least one molecular layer of the release film on the surface of the substrate;
The release film chemically bonded to the substrate surface is patterned by forming a region where the substrate surface is exposed by dry etching using plasma, and the thickness of the release film is set to be not less than 1 molecular layer and not more than 3 μm . And the process of
Wherein after the growth of the first nitride semiconductor on the release film of the patterned substrate, and the release layer bonded the substrate surface and the chemical, the first and the nitride semiconductor on said release layer, it was removed by lift-off And thereafter, a third step of laterally growing a second nitride semiconductor using the first nitride semiconductor as a growth nucleus, and a method for manufacturing a nitride semiconductor substrate. 2. The method of manufacturing a nitride semiconductor substrate according to claim 1, wherein the method of forming the chemically bonded release film is a plasma CVD method or an ECR sputtering method. The method for manufacturing a nitride semiconductor substrate according to claim 1, wherein the release film is selected from the group consisting of silicon oxide, silicon nitride, silicon nitride oxide, titanium oxide, and zirconium oxide. The method for manufacturing a nitride semiconductor substrate according to claim 1 , wherein the substrate surface subjected to the dry etching is formed with a recess. 2. The method of manufacturing a nitride semiconductor substrate according to claim 1, wherein the second nitride semiconductor is grown at a higher temperature than the first nitride semiconductor. The method of manufacturing a nitride semiconductor substrate according to claim 3 , wherein the lift-off is performed by setting the ambient temperature of the nitride semiconductor substrate to 900 ° C. or higher .

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