JP2006004990A - Growth method of nitride semiconductor layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the growth method of a nitride semiconductor layer which is capable of reducing a pit-type crystalline defect on the surface of a nitride semiconductor layer formed on a substrate whereby capable of obtaining a high-quality nitride semiconductor layer reduced in defects across the whole surface of the substrate. <P>SOLUTION: The growth method of the nitride semiconductor layer comprises (a) a process for forming a first crystalline nitride semiconductor layer on the substrate, (b) a process for forming a nitride semiconductor buffer layer on the first crystalline nitride semiconductor layer and (c) a process for removing the obtained nitride semiconductor buffer layer and forming a second crystalline nitride semiconductor layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for growing a nitride semiconductor layer, and more particularly to a method for growing a nitride semiconductor layer capable of reducing pit-like crystal defects over the entire surface.

  2. Description of the Related Art Conventionally, as a material for forming a blue light emitting diode or the like, a technique for growing a nitride semiconductor layer, particularly a GaN layer, having high quality and few crystal defects has been actively tried.

  As an example of such a growth method, a method of forming a first buffer layer, a first GaN layer, a second buffer layer, and a second GaN layer in this order on a sapphire substrate (for example, Patent Document 1), GaN A method of growing a GaN amorphous layer and a single crystal layer in this order on a base plate made of a single crystal (for example, Patent Document 2) has been proposed.

In these methods, by alternately forming buffer layers and single crystal layers on the substrate, a high-quality GaN substrate with very few crystal defects such as dislocations can be obtained.
JP-A-11-298039 JP 2000-340509 A

  However, even when the above-described method is used, for example, pit-like defects may appear on the surface of the obtained GaN layer depending on the type and surface state of the substrate. In particular, when a sapphire substrate is used as a substrate and a nitride semiconductor layer is grown thereon, a large number of pits are generated at the end of the sapphire substrate, that is, at the end of the wafer.

  In general, in a nitride semiconductor element, the buffer layer formed on the base of the nitride semiconductor multilayer structure constituting the element and the crystallinity of the base layer greatly affect the characteristics of the element, such as output and life. Therefore, it is necessary to suppress the appearance of pits in the buffer layer and the underlayer as much as possible.

  In addition, as a substrate used for forming the nitride semiconductor element, a wafer of about 2 inches is usually used. When such a wafer is used, if one chip is a very small nitride semiconductor element, the chip can be formed by avoiding the above-described region where pits are generated. However, for example, when the size of one chip is large, such as an ultraviolet LED, the number of chips formed on one wafer is limited, and in particular, due to the presence of pits formed on the edge of the wafer, There is a problem that the number of LED chips that can be formed on one wafer is extremely reduced.

  On the other hand, it is conceivable to reduce pit-like defects by forming a thick GaN layer such as a buffer layer or an underlayer on the substrate. However, the manufacturing cost increases due to the extension of the film formation time. Furthermore, when the GaN layer is formed as a thick film, the substrate and the GaN layer such as the buffer layer and the base layer are different in thermal expansion coefficient, which causes warping of the substrate, and in subsequent electrode formation, chip formation, etc. There is a problem that a malfunction occurs.

  The present invention has been made in view of the above problems, and can reduce pit-like crystal defects on the surface of the nitride semiconductor layer formed on the substrate, and can achieve high quality with low defects over the entire surface of the substrate. It is an object of the present invention to provide a method for growing a nitride semiconductor layer capable of obtaining a nitride semiconductor layer.

  The method for growing a nitride semiconductor layer according to the present invention includes: (a) a step of forming a first crystalline nitride semiconductor layer on a substrate; and (b) a step of forming the first crystalline nitride semiconductor layer on the first crystalline nitride semiconductor layer. And a step of forming a nitride semiconductor buffer layer, and (c) removing the obtained nitride semiconductor buffer layer and forming a second crystalline nitride semiconductor layer. .

  In this method, the first crystalline nitride semiconductor layer and the nitride semiconductor buffer layer are preferably GaN.

  Further, it is preferable to further form a first buffer layer between the substrate and the first crystalline nitride semiconductor layer.

  Further, in the step (c), the nitride semiconductor buffer layer is completely removed while forming the second crystalline nitride semiconductor layer.

  According to the method for growing a nitride semiconductor layer of the present invention, at least a first crystalline nitride semiconductor layer, a nitride semiconductor buffer layer, and a second crystalline nitride semiconductor layer are formed in this order on a substrate. In addition, by forming the second crystalline nitride semiconductor layer and simultaneously removing the nitride semiconductor buffer layer, cracks and pits are formed over the entire surface of the second crystalline nitride semiconductor layer. Thus, a nitride semiconductor layer free from defects such as the above can be obtained.

  In particular, when the first crystalline nitride semiconductor layer and the nitride semiconductor buffer layer are GaN, the above effect can be made more remarkable.

  In addition, by further forming a first buffer layer between the substrate and the first crystalline nitride semiconductor layer, the lattice constant of the substrate and the first crystalline nitride semiconductor layer can be more matched. Therefore, a nitride semiconductor layer having better crystallinity can be obtained as the second crystalline nitride semiconductor layer.

  Furthermore, in the step (c), when the nitride semiconductor buffer layer is completely removed while forming the second crystalline nitride semiconductor layer, the second crystalline nitride semiconductor layer is formed of the first crystal nitride semiconductor layer. By integrating with the crystalline nitride semiconductor layer, pit-like defects can be reliably repaired even at the edge of the substrate (wafer) without increasing crystal defects, and a good crystalline surface can be obtained.

  In the method for growing a nitride semiconductor layer of the present invention, first, in step (a), a substrate is prepared, and a first crystalline nitride semiconductor layer is formed on the substrate.

As the substrate, for example, an insulating substrate such as sapphire or spinel (MgAl ₂ O ₄ ) having any one of the C-plane, R-plane, and A-plane as a main surface, a crystalline or amorphous nitride semiconductor described later. Examples thereof include oxide substrates (for example, SiO ₂ , MgO, ZnO, NdGaO _3, etc.) lattice-matched with layers, and conductive substrates such as ZnS, GaAs, Si, SiC, AlN, GaN, AlGaN, and GaP. Further, a sapphire or the like is laminated on a heterogeneous substrate such as sapphire and then sapphire or the like is removed (for example, JP 2001-102307 A, JP 11-4048 A, Jpn. Appl. Phys. Vol.39 (2000) p647-650 etc.) may be used. Of these, sapphire and spinel substrates are preferable.

In addition, the substrate has a region where the crystal defects are small, for example, about 1 × 10 ⁷ cm ⁻² or less, preferably about 1 × 10 ⁶ cm ⁻² at least on the surface portion, or partially small. What you have is appropriate. Further, it may have an off-angle angle of about 0.01 to 0.3 °, and further a step-like off-angle angle. This prevents the occurrence of fine cracks in the first crystalline nitride semiconductor layer and / or the nitride semiconductor buffer layer described later and further on the nitride semiconductor layer constituting the device. Can do.

  A first buffer layer may be further formed on the substrate before forming the first crystalline nitride semiconductor layer, that is, between the substrate and the first crystalline nitride semiconductor substrate. Good. Here, the first buffer layer is, for example, a nitride semiconductor layer in which the state of not taking a crystal structure is dominant over the entire film thickness direction of this layer, or has a crystal structure. A crystalline nitride semiconductor layer means a layer in which a different crystal structure is dominant. Among them, those having an amorphous structure that does not take a crystalline state over the entire first buffer layer, those having a partially polycrystalline and / or monocrystalline region, polycrystalline over the entire first buffer layer, or It is appropriate that the crystal structure of the single crystal is dominant.

  The material of the first buffer layer is not particularly limited, and is preferably a semiconductor layer, particularly a nitride semiconductor layer. Especially, it is preferable to form by AlN, GaN, AlGaN, InGaN etc., and it is more preferable that it is GaN.

  The first buffer layer is, for example, 900 ° C. or less, preferably about 900 to 300 ° C., about 900 to 400 ° C., about 900 to 500 ° C., about 800 to 400 ° C. Thus, vapor phase growth can be performed on the substrate. That is, the first buffer layer can be formed at a temperature lower than the film formation temperature of the first and second crystalline nitride semiconductor layers described later. In addition, as vapor phase growth, various methods, such as MOCVD (metal organic chemical vapor deposition method), HVPE (halide vapor phase growth method), MBE (molecular beam epitaxy method), are usually mentioned. Although a film thickness is not specifically limited, For example, about 10 to 0.5 micrometer is mentioned. By forming the first buffer layer, crystal defects in the first crystalline nitride semiconductor layer can be further reduced. This is considered to be because the mismatch of the lattice constant between the substrate and the first crystalline nitride semiconductor layer described later can be alleviated.

  The first crystalline nitride semiconductor layer formed on the substrate means a nitride semiconductor layer having a crystal structure in which polycrystal or single crystal is dominant over the entire film thickness direction of this layer. In particular, it is preferable that the nitride semiconductor layer has a single crystal structure over the entire nitride semiconductor layer, but the polycrystalline or amorphous regions are partially unevenly distributed to such an extent that various properties of the crystalline nitride semiconductor are not lost. May be.

  The first crystalline nitride semiconductor layer can be of the same composition as the nitride semiconductor exemplified in the first buffer layer, and is preferably GaN.

The first crystalline nitride semiconductor layer has, for example, a high temperature, that is, a temperature higher than the film formation temperature of the first buffer layer and a nitride semiconductor buffer layer described later, specifically, a temperature higher than 900 ° C. , About 950 to 1200 ° C., about 1000 to 1150 ° C., preferably about 1050 ° C., and can be vapor-phase grown on the substrate. Examples of the vapor phase growth include the same ones as described above. The first crystalline nitride semiconductor layer and the second crystalline nitride semiconductor layer described later may be usually formed undoped (in a state where impurities are not doped), or Si, Ge, Sn, S Alternatively, a nitride semiconductor layer doped with an IV group or VI group element such as O, Ti, or Zr as an n-type impurity may be formed. In particular, if the impurity concentration is 5 × 10 ¹⁷ / cm ² or less, more preferably 1 × 10 ¹⁷ / cm ² or less even if the impurity is not doped or doped, the crystallinity of each layer grown on this is further increased. Can be improved. The film thickness is not particularly limited, but for example, it is preferably 100 Å or more, about 0.01 to 10 μm, and more preferably about 1 to 5 μm.

  In the case where the first buffer layer and the first crystalline nitride semiconductor layer are formed in this order on the substrate, the first buffer layer is not necessarily formed after the first crystalline nitride semiconductor layer is formed. It is not necessary to exist in an amorphous state or the like, and the crystal state is changed during the formation of the first crystalline nitride semiconductor layer, so that it is completely or partially crystalline, or the first crystal It may be converted to a crystal structure equivalent to the crystal structure of the crystalline nitride semiconductor layer.

  Next, in the step (b), a nitride semiconductor buffer layer is formed on the obtained first crystalline nitride semiconductor layer.

  The nitride semiconductor buffer layer here can be formed of the same material, for example, in the same manner as the method of forming the first buffer layer described above. Moreover, the crystal structure can mention what was illustrated with the 1st buffer layer. The film thickness can be appropriately adjusted depending on the material of the second crystalline nitride semiconductor layer to be formed later, film formation conditions, and the like, and is preferably about 5 to 100 nm, and more preferably about 10 to 20 nm.

  Subsequently, in the step (c), a second crystalline nitride semiconductor layer is formed.

  The second crystalline nitride semiconductor layer is a film having a thickness of, for example, about 500 to 10000 nm, more preferably about 1000 to 5000 nm, by the same material and the same film formation method as the first crystalline nitride semiconductor layer described above. It can be formed with a thickness. However, when the second crystalline nitride semiconductor layer is formed, the above-described nitride semiconductor buffer layer is removed, and as a result, the second crystalline nitride semiconductor layer becomes the first crystal. It is formed so as to be disposed on the quality nitride semiconductor layer. The film formation conditions in this case can be appropriately set depending on the film formation method, the material and film thickness of the nitride semiconductor buffer layer, and the like. For example, a method of setting the film formation temperature so that the nitride semiconductor buffer layer does not crystallize and reacts with the supplied gas to evaporate, or is physically removed by the supplied gas. Is mentioned. Further, a method of selecting or changing the type of supply gas during film formation, a method of controlling the flow rate or pressure of the supply gas during film formation, and the like may be used.

  The nitride semiconductor buffer layer may be slightly left depending on the region, for example, as a thin film as a whole or as an island, but is preferably removed completely. As described above, by removing the nitride semiconductor buffer layer, it is possible to stack the second crystalline nitride semiconductor with good crystallinity and surely reduced pit-like crystal defects. Become. This is because the surface of the substrate obtained, in particular, the supply gas is not sufficiently supplied and reacted, and even at the edge of the substrate (wafer), for example, the supply state and reaction of the supply gas by evaporation and removal of the nitride semiconductor buffer layer It is considered that a change occurs in the state and the like, and pits can be reduced.

  In addition, when the dislocations and the plane density of the pits in the first and second crystalline nitride semiconductors were actually observed, both were the same for the dislocations, but the second crystalline nitride semiconductor was about the pits. Was definitely reduced. In the present specification, the dislocation means a linear defect in the semiconductor cross section, and the pit means a hole-like defect having a diameter of 0.5 to 3 μm, for example, mainly resulting from the dislocation.

  Further, the first buffer layer, the first crystalline nitride semiconductor layer, the nitride semiconductor buffer layer, and the second crystalline nitride semiconductor layer need to be nitride semiconductors having the same composition ratio and the same composition ratio. However, it is preferable to use nitride semiconductors having the same composition ratio and the same composition, particularly GaN.

  In the present invention, step (b) and / or (c) may be performed a plurality of times. That is, after performing the steps (a), (b) and (c), only the step (b), the steps (b) and (c), the step (c) and the like are further performed once or plural times. Also good.

  In the nitride semiconductor layer stacked structure thus obtained, for example, a part of the substrate and / or the first buffer layer and / or the first crystalline nitride semiconductor layer in the film thickness direction is removed. Without being removed, it can be used as it is as a nitride semiconductor substrate.

  In the present invention, a so-called ELOG substrate structure may be adopted for the nitride semiconductor substrate. That is, in the middle of forming the first crystalline nitride semiconductor layer directly on the substrate, directly on the first buffer layer, on the surface after forming the first crystalline nitride semiconductor layer, or A protective film may be formed during the formation of the second crystalline nitride semiconductor layer. The protective film is formed on the substrate, on the first buffer layer, on the surface of the first crystalline nitride semiconductor layer (which may be located inside the first crystalline nitride semiconductor layer as a result), or on the first 2 on the surface of the crystalline nitride semiconductor layer 2 (which is consequently located inside the second crystalline nitride semiconductor layer), for example, in the form of stripes, grids, dots (round, square) , Polygons, etc.), mesh shapes, etc., can be formed regularly, periodically or randomly. When the protective film is larger than the surface area on which the protective film is not formed, dislocation can be prevented and good crystallinity can be obtained. The protective film is preferably formed on the surface with a material having a property that amorphous or crystalline nitride semiconductor does not grow or is difficult to grow.

Examples of the material for the protective film include oxides such as silicon oxide (SiO _x ), titanium oxide (TiO _x ) and zirconium oxide (ZrO _x ), nitrides such as silicon nitride (Si _x N _y ) and titanium nitride, and nitriding In addition to silicon oxide or these multilayer films, refractory metals having a melting point of 1200 ° C. or higher, such as tungsten, titanium, and tantalum, can be given. Such a protective film can withstand the growth temperature of the nitride semiconductor, for example, up to about 1200 ° C., and has a property that the nitride semiconductor does not grow on the surface or is difficult to grow.

  For example, the protective film is formed by vapor deposition such as vapor deposition, sputtering, or CVD, a resist film is formed thereon, and is patterned into a desired shape such as a stripe shape using photolithography and etching processes. Can be formed.

  The protective film is, for example, about 3 μm or less, preferably about 1 μm or less, more preferably about 0.1 μm or less in consideration of the film formation time and the ease of growth of the nitride semiconductor layer formed thereon. A film thickness is appropriate. When the protective film is formed in a stripe shape, for example, it is appropriate that the stripe width is about 5 to 20 μm and the stripe interval is about 2 to 10 μm.

  By forming such a protective film, crystal defects such as threading dislocations can be further reduced with respect to the semiconductor layer formed thereon.

  The nitride semiconductor substrate obtained by forming the protective film in this way can also be used as a nitride semiconductor substrate with or without removing the protective film, together with the substrate and / or the first buffer layer. Can do.

  In addition, a nitride semiconductor element can be formed by laminating a nitride semiconductor layer constituting the element on the nitride semiconductor substrate. The nitride semiconductor substrate thus obtained should have a film thickness that can fulfill sufficient strength and function (resistivity, current injection amount, mobility, etc.) as a substrate of a subsequent nitride semiconductor element. The total film thickness is, for example, about 2 to 10 μm.

  The nitride semiconductor element is formed of a nitride semiconductor layer that functions as an element known in the art, such as an LED or a laser diode, and includes, for example, a first conductivity type semiconductor layer, an active layer, and a second layer. One in which conductive type semiconductor layers are stacked in this order can be given.

The semiconductor layers in the first and second conductivity type semiconductor layers and the active layer are not particularly limited, and include elemental semiconductors such as silicon and germanium, III-V group, II-VI group, VI-VI group, etc. A compound semiconductor etc. are mentioned. Nitride semiconductor, among others _{In X Al Y Ga 1-X} -Y N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1) gallium nitride-based compound such as a semiconductor is preferably used. The terms “first conductivity type” and “second conductivity type” in the first and second conductivity type semiconductor layers are used for the sake of convenience to distinguish between the substrate side (lower side) and the upper side of the active layer. In some cases, the first conductive semiconductor layer and the second conductive semiconductor layer may not be positively imparted with conductivity. Normally, in order to show n-type and p-type conductivity, the first and second conductive semiconductor layers, and further the active layer, include p-type impurities such as Mg, Zn, Cd, Be, Ca, Ba, etc. However, Si, Sn, Ge, Se, C, Ti or the like may be doped as an n-type impurity. The doping concentration is, for example, about 1 × 10 ¹⁸ cm ⁻³ or more, preferably about 1.5 × 10 ²⁰ to 1 × 10 ²² cm ⁻³ .
Each of the first and second conductive semiconductor layers and the active layer may have a single layer structure, but may have a laminated structure of layers having different compositions and film thicknesses, a superlattice structure, or the like. In particular, the active layer preferably has a single quantum well or multiple quantum well structure in which thin films that produce quantum effects are stacked. Thereby, element performance can be improved. By forming an element structure having such a layer structure on a substrate with few crystal defects obtained by the growth method of the present invention, the element performance can be further improved.

Specific examples of the laminated structure of the nitride semiconductor layer include the following.
First, an n-type contact layer is arbitrarily grown on the surface of the obtained nitride semiconductor substrate (second crystalline nitride semiconductor layer). The n-type contact layer has a composition that is larger than the band gap energy of an active layer that will be formed later, and is preferably Al _j Ga _1-j N (0 ≦ j <0.3). The film thickness of the n-type contact layer is not particularly limited, and is preferably 1 μm or more, more preferably 3 μm or more. The impurity concentration of the n-type contact layer is not particularly limited, and is preferably 1 × 10 ¹⁸ to 1 × 10 ²⁰ / cm ³ , more preferably 5 × 10 ^{18 to} 5 × 10 ¹⁹ / cm ³ . is there. The n-type impurity concentration may be inclined in the film thickness direction. In addition, by tilting the Al composition in the film thickness direction, it also functions as a cladding layer for confining carriers. The n-type contact layer may have either a single layer or a multilayer (including a superlattice) structure.

  In addition, although the n-type contact layer is directly formed on the second crystalline nitride semiconductor of the obtained nitride semiconductor substrate here, the n-type contact layer can be formed via another layer. When forming an n-type contact layer made of a nitride semiconductor or the like on the second crystalline nitride semiconductor, AlGaN containing Al is preferably formed with a single layer thickness of 0.5 to 3 μm, for example. That is, if AlGaN containing Al is formed on the second crystalline nitride semiconductor, pits can be reduced compared to, for example, forming AlGaN containing Al on the first crystalline nitride semiconductor. In the case where GaN is formed on the second crystalline nitride semiconductor, it is possible to form AlGaN containing Al on the second crystalline nitride semiconductor, considering that such a reduction in pits is not observed. It can be seen that this is particularly effective in reducing pits. This effect can be obtained not only at the wafer edge but at the entire wafer. Further, although the reason why the above effect is obtained is not clear, at present, the dislocation in the first crystalline nitride semiconductor and the second crystalline nitride semiconductor formed at least once through the nitride semiconductor buffer layer are present. It is considered that the dislocation states in are different, and the second crystalline nitride semiconductor is in a dislocation state in which pits are hardly generated.

After forming the n-type contact layer, a light emitting layer (active layer) is formed. The active layer includes at least _{a well} layer composed of Al _a In _b Ga _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, a + b ≦ 1), and Al _c In _d Ga _{1-c d} N A quantum well structure including a barrier layer made of (0 ≦ c ≦ 1, 0 ≦ d ≦ 1, c + d ≦ 1) is preferable. The thickness of the light emitting layer is not particularly limited, and can be appropriately set in consideration of the wavelength, impurity concentration, and the like intended by the nitride semiconductor element. Specifically, it is several nm or more and several hundred nm or less.

The thickness of the well layer is preferably 1 nm to 30 nm, more preferably 2 nm to 20 nm, and still more preferably 3.5 nm to 20 nm. The number of well layers is not particularly limited, and can be set as appropriate in consideration of the minority carrier diffusion length. The well layer may be doped with p-type impurities or n-type impurities, or may be undoped. For example, when p-type or n-type impurities are doped in the well layer, the concentration is preferably 5 × 10 ¹⁶ / cm ³ or more, and more preferably 1 × 10 ²⁰ / cm ³ or less.

Further, the barrier layer may be doped with a p-type impurity or an n-type impurity as in the case of the well layer, or may be undoped. The impurity concentration is preferably 5 × 10 ¹⁶ / cm ³ or more, and more preferably 1 × 10 ²⁰ / cm ³ or less. The barrier layer is made of a nitride semiconductor having a band gap energy larger than that of the well layer. In particular, when the emission wavelength of the well layer is in the region of 380 nm or less, the barrier layer has a general formula Al _c In _d Ga ₁₋ it is preferable to use a _{c-d N (0 <c} ≦ 1,0 <d ≦ 1, c + d <1) 3 -element mixed crystal of quaternary mixed crystal or AlGaN of AlInGaN represented by. The thickness of the barrier layer is not particularly limited, and is, for example, 1 nm to 100 nm, preferably 3 nm to 50 nm.

Further, a p-type nitride semiconductor layer is formed on the active layer. The p-type nitride semiconductor layer may be either a single layer or a multilayer.
For example, first, a layer having a composition larger than the band gap energy of the active layer (well layer) is formed. This layer may be either a single layer or a multilayer (including a superlattice) structure. This layer is preferably formed of, for example, Al _k Ga _1-k N (0 ≦ k <1), particularly Al _k Ga _1-k N (0 <k <0.4). In the case of a multilayer structure, a multilayer film composed of Al _k Ga _1-k N (0 ≦ k <1) and a nitride semiconductor layer having a smaller band gap energy may be used. For example, examples of the nitride semiconductor layer having a small band gap energy include In _l Ga _1- N (0 ≦ l ≦ 1) and Al _m Ga _1-m N (0 ≦ m <1, m> 1). .

  The film thickness of this layer is not particularly limited, and is preferably 0.005 to 0.3 μm, more preferably 0.01 to 0.2 μm. In particular, when this layer has a superlattice structure, the thickness of one layer is preferably 10 nm or less, more preferably 7 nm or less, and still more preferably 1 to 4 nm.

The p-type impurity concentration of this layer is preferably 1 × 10 ¹⁸ to 1 × 10 ²¹ / cm ³ , more preferably 1 × 10 ^{19 to} 5 × 10 ²⁰ / cm ³ . When the p-type impurity concentration is in the above range, the bulk resistance can be reduced without reducing the crystallinity. In particular, in the case of a multilayer structure composed of a layer having a large band gap energy and a layer having a small band gap energy, the doping amount of both may be the same or different, and only one of them may be doped with impurities. May be.

Next, a p-type contact layer is formed. p-type contact _{layer, Al f Ga 1-f N} (0 ≦ f <1) is used, than to constitute particularly in _{Al f Ga 1-f N (} 0 ≦ f <0.3), later formed It is possible to make a good ohmic contact with the p-electrode which is an ohmic electrode. Note that the p-type contact layer may be either a single layer or a multilayer (including a superlattice) structure. The p-type impurity concentration of the p-type contact layer is preferably 1 × 10 ¹⁸ / cm ³ or more.

  After obtaining such a laminated structure of nitride semiconductor layers, a part of the n-type contact layer is exposed by etching away a part from the p-type contact layer side, and an n-electrode is formed on the exposed surface, Get the LED. Alternatively, when a layer on the side opposite to the p-type contact layer can be used as the n-type contact layer, an electrode may be formed directly on the layer on the side opposite to the p-type contact layer.

As electrode materials, nickel (Ni), platinum (Pt) palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os), iridium (Ir), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), cobalt (Co), iron (Fe), manganese (Mn), molybdenum (Mo), chromium (Cr), tungsten (W), lanthanum (La), copper (Cu), silver (Ag), metal containing at least one selected from the group consisting of yttrium (Y), an alloy, a laminated structure, and their compounds (for example, conductive oxide) , Nitride, etc.), conductive metal oxide (oxide semiconductor, for example, tin-doped indium oxide having a thickness of 50 to 10 μm (Indium Tin) Oxide; ITO), ZnO, In ₂ O ₃ or SnO ₂ ).

  The formation of the nitride semiconductor layer is not limited to the metal organic chemical vapor deposition (MOCVD) method, but can be performed using a halide vapor phase epitaxy (HVPE) method, a molecular beam epitaxy (MBE) method, or the like. The metalorganic chemical vapor deposition method is more preferable.

  Furthermore, for a light-emitting element having an emission spectrum in the ultraviolet region, for example, Daisuke Morita et. Al, “High Output Power 365 nm ULTRAVIOLET Light Emitting Diode of GaN-Free Structure” ipn. J. Appl. Phys. Vol. 41 (2002 ) The structure described in pp. L 1434-L 1436 and a structure similar thereto may be used.

Below, the growth method of the nitride semiconductor layer of this invention is demonstrated in detail based on drawing.
Example 1
(Nitride semiconductor substrate)
First, as shown in FIG. 1A, the temperature is set to 900 ° C. on the entire surface of the sapphire substrate 1 having a 2 inch φ and C-plane as a main surface, and TMG (trimethylgallium) and NH ₃ are used. The first buffer layer 2 made of GaN was formed with a thickness of 500 mm.
Next, as shown in FIG. 1B, the temperature is set to 1050 ° C., and the high-temperature buffer layer 3 made of GaN using TMG (trimethylgallium) and NH ₃ is used as the first crystalline nitride semiconductor layer. And a film thickness of 30000 mm.
Further, as shown in FIG. 1C, the temperature was returned to 900 ° C., and the low temperature buffer layer 4 made of GaN was formed as a nitride semiconductor buffer layer with a thickness of 200 mm by the same method as described above.
Subsequently, as shown in FIG. 1 (d), the flow rate of each gas, temperature, etc. are adjusted so that the temperature is raised and the low temperature buffer layer 4 can be completely removed from the surface of the high temperature buffer layer 3. However, the high-temperature buffer layer 5 made of GaN was formed as a second crystalline nitride semiconductor layer with a film thickness of 30000 mm.
As for the surface of the obtained second crystalline nitride semiconductor layer, pit-like defects are reduced on the entire surface over the end portion, and good crystallinity is obtained, and a high-quality nitride semiconductor substrate is obtained. It was.

(Nitride semiconductor layer)
On the nitride semiconductor substrate thus obtained, first, an n-type Al _0.07 Ga _0.93 N layer was formed to a thickness of 2.5 μm. Here, the n-type impurity is Si.
Next, an active layer (MQW active layer) having a multi-quantum well (MQW) structure composed of five pairs of a well layer and a barrier layer is formed. Here, the well layer is undoped In _0.01 Ga _0.99 N and has a thickness of about 5 nm. The barrier layer was Si—Al _0.09 Ga _0.91 N and had a thickness of 20 nm.
Subsequently, a p-type Al _0.38 Ga _0.62 N layer was formed with a thickness of 30 nm. Here, the p-type impurity was Mg.
Next, a p-type ohmic contact electrode was formed by vapor deposition. At this time, by using Rh so that the p-type ohmic contact electrode has high reflection characteristics, a high reflectivity was obtained at the interface with the p-type AlGaN layer for an emission wavelength of 365 nm.
Further, a thin Au / Sn film was formed on the p-type ohmic contact electrode.

(Nitride semiconductor devices)
Subsequently, the M-plane of the nitride semiconductor layer was divided into bars in the direction perpendicular to the p-electrode and n-electrode, and the bar-shaped wafer was further divided into 1000 × 1000 μm sized chips.
Next, for each chip, the p-type ohmic contact electrode side was bonded to a substrate having high thermal conductivity (for example, a CuW substrate) through an Au / Sn film.
Thereafter, for example, laser irradiation was performed from the back side of the sapphire substrate to remove the sapphire substrate and the buffer layers 2, 3, and 5 to expose the n-type Al _0.07 Ga _0.93 N layer. After the exposed surface of the n-type Al _0.07 Ga _0.93 N layer was polished by, for example, CMP (Chemical Mechanical Polishing), an n electrode was formed on the polished surface, for example, in a predetermined mesh shape.
Then, the CuW substrate was mounted on a lead frame having a low thermal resistance.

The nitride semiconductor device thus obtained had good heat dissipation by the CuW substrate, and a high light emission output was obtained.
Further, when the nitride semiconductor substrate formed by the above method for producing a nitride semiconductor layer is used, as a comparative example, the first buffer layer 2 and the high-temperature buffer are formed on the sapphire substrate when the nitride semiconductor substrate is formed. Compared to the case where the nitride semiconductor device is formed in the same manner as described above except that the layer 3 is formed with 200 mm and 30000 mm, respectively, and the low temperature buffer layer 4 and the high temperature buffer layer 5 are not formed, The number of chips that can be taken is improved by about 40%. That is, the yield was improved by about 40%. This is because, in the method of the example, the pit-like crystal defects were effectively prevented until the end of the nitride semiconductor substrate, whereas the first buffer layer and the first crystalline material as in the comparative example. This is because, when only the nitride semiconductor layer is formed, the generation of pit-like crystal defects over the edge of the substrate of the nitride semiconductor layer could not be prevented even if the film thickness thereof was increased. .
Example 2
The nitride semiconductor layers shown in the following (1) to (5) are respectively formed on the nitride semiconductor substrate formed in the same manner as the nitride semiconductor substrate obtained in Example 1, and the nitride semiconductor element is obtained. Obtained.

(1) An n-type contact layer made of Si-doped n-type GaN having a thickness of 4 μm, a light emitting layer having a single quantum well structure made of undoped In _0.2 Ga _0.8 N having a thickness of 30 μm, and a thickness of 0 A p-type layer made of Mg-doped p-type Al _0.1 Ga _0.9 N having a thickness of 2 μm and a p-type contact layer made of Mg-doped p-type GaN having a thickness of 0.5 μm.

(2) n-side contact layer made of GaN and Si having a thickness of 5μm containing 4.5 × ¹⁰ 18 / cm ^3, and a lower layer made of undoped GaN of 3000 Å, containing Si 300Å 4.5 × ¹⁰ 18 / cm ³ An n-side first multilayer film layer (total film thickness: 3350 mm) composed of an intermediate layer made of GaN and an upper layer made of 50 ア ン undoped GaN, and 40 を of undoped GaN nitride semiconductor layer made of undoped GaN _. N-side first layer of a superlattice structure in which nitride semiconductor layers made of ₁ Ga _0.9 N are repeatedly stacked in layers of 10 繰 り 返 し, and nitride semiconductor layers made of undoped GaN are formed to a thickness of 40 Å. 2 multi-film layer (total film thickness: 640Å), and a well layer having a thickness barrier layer and the film thickness made of undoped GaN of 250Å consisting _in 0.3 _{Ga 0.7} N of 30Å Laminated by six layers alternately returns Ri, further light-emitting layer having the multiple quantum well structure thickness barrier composed of undoped GaN of 250Å was formed (total film thickness: 1930Å), the Mg comprises 5 × ¹⁰ 19 / cm ³ 40 layers of nitride semiconductor layers made of Al _0.15 Ga _0.85 N and 5 layers of nitride semiconductor layers made of In _0.03 Ga _0.97 N containing 5 × 10 ¹⁹ / cm ^{3 of} Mg are repeated in 5 layers. A p-side multilayer film having a superlattice structure in which a nitride semiconductor layer made of Al _0.15 Ga _0.85 N containing Mg 5 × 10 ¹⁹ / cm ^{3 and} having a thickness of 40 mm is alternately stacked. A p-side contact layer made of GaN containing 1 × 10 ²⁰ / cm ³ of Mg (total film thickness: 365 mm) and a film thickness of 1200 mm.

(3) An undoped GaN layer with a thickness of 1 μm, an n-side contact layer made of GaN containing 4.5 × 10 ¹⁸ / cm ³ of Si with a thickness of 5 μm, a lower layer made of 3000 Å undoped GaN, and a Si layer of 300 Å. An n-side first multilayer film layer (total film thickness: 3350 mm) composed of an intermediate layer composed of GaN containing 5 × 10 ¹⁸ / cm ³ and an upper layer composed of 50 μm undoped GaN, a nitride semiconductor layer composed of undoped GaN Nitride semiconductor layers composed of 40 nm and undoped In _0.1 Ga _0.9 N were repeatedly stacked in layers of 10 layers, and a nitride semiconductor layer composed of undoped GaN was formed to a thickness of 40 mm. N-side second multilayer film layer (total film thickness) of 640 mm) having a superlattice structure, first a barrier layer made of undoped GaN having a film thickness of 250 mm, and subsequently I having a film thickness of 30 mm. _0.3 second barrier layer first barrier layer and the thickness of Ga well layers and the film thickness made of _0.7 N consists 100Å of _{an In} 0.02 _{Ga 0.98} N is made of undoped GaN of 150Å is An active layer having a multiple quantum well structure (total film thickness of 1930 mm) formed by repeatedly and alternately stacking 6 layers (preferably a layer of 3 to 6 layers is repeatedly stacked alternately), Mg is 5 × 10 ^19. 40 cm of a nitride semiconductor layer made of Al _0.15 Ga _0.85 N containing / cm ³ and 25 kg of a nitride semiconductor layer made of In _0.03 Ga _0.97 N containing 5 × 10 ¹⁹ / cm ^{3 of} Mg Of the superlattice structure in which a nitride semiconductor layer made of Al _0.15 Ga _0.85 N containing 5 × 10 ¹⁹ / cm ^{3 of} Mg and having a thickness of 40 mm is formed by alternately laminating 5 layers. Side multilayer film layer (total film thickness 365 p), a p-side contact layer made of GaN containing 1 × 10 ²⁰ / cm ³ of Mg having a thickness of 1200 Å.

Here, further, a lower layer made of 3000 Å undoped GaN provided on the n side, a first layer made of 1,500 ア ン undoped GaN from the bottom, and a second layer made of GaN containing 100 Ｓｉ Si of 5 × 10 ¹⁷ / cm ³ , By using a lower layer of a three-layer structure composed of a third layer made of 1500 ア ン undoped GaN, it is possible to suppress the variation in _{Vf with} the lapse of the driving time of the light emitting element.

(4) An n-side contact layer made of GaN containing 6.0 × 10 ¹⁸ / cm ^{3 of} Si, an undoped GaN layer (the above is an n-type nitride semiconductor layer having a total film thickness of 6 nm), and Si of 2.0 × 10 ¹⁸ An active layer of a multiple quantum well in which 5 layers of GaN barrier layers and InGaN well layers containing / cm ³ are alternately stacked, p made of GaN containing 5.0 × 10 ¹⁸ / cm ³ of Mg having a thickness of 1300 mm Type nitride semiconductor layer, InGaN layer with a thickness of 50 mm. Thus, when an InGaN layer having a thickness of 30 to 100 mm and a preferable film thickness of 50 mm is provided, this layer is in contact with the p-electrode and can be a p-side contact layer.

(5) An n-side contact layer made of GaN containing 1.3 × 10 ¹⁹ / cm ^{3 of} Si, an undoped GaN layer (the above is an n-type nitride semiconductor layer having a total film thickness of 6 nm), and Si of 3.0 × 10 ¹⁸ An active layer (total film thickness: 800 mm) of multiple quantum wells in which 7 layers of GaN barrier layers and InGaN well layers containing / cm ³ are alternately stacked, and Mg of 1300 mm thickness is 2.5 × 10 ²⁰ / A p-type nitride semiconductor layer made of GaN containing cm ^{3 and} an InGaN layer with a thickness of 50 mm. Thus, when an InGaN layer having a thickness of 30 to 100 mm and a preferable film thickness of 50 mm is provided, this layer is in contact with the p-electrode and can be a p-side contact layer.

  In any of the nitride semiconductor devices obtained in this way, the heat dissipation by the CuW substrate was good and a high light emission output was obtained. Also, the yield was improved by about 30 to 40% compared to Comparative Example 1.

  The method for growing a nitride semiconductor layer according to the present invention can be applied to the manufacture of all nitride semiconductor devices using the nitride semiconductor layer as a substrate (underlying), and in particular, has a relatively large chip size such as a UVLED. It can utilize suitably with respect to an element.

It is a schematic sectional process drawing which shows the growth method of the nitride semiconductor layer in this invention.

Explanation of symbols

1 Sapphire substrate (substrate)
2 First buffer layer 3 High temperature buffer layer (first crystalline nitride semiconductor layer)
4 Low temperature buffer layer (nitride semiconductor buffer layer)
5 Second high-temperature buffer layer (second crystalline nitride semiconductor layer)

Claims (4)

(A) forming a first crystalline nitride semiconductor layer on a substrate;
(B) forming a nitride semiconductor buffer layer on the first crystalline nitride semiconductor layer;
(C) removing the obtained nitride semiconductor buffer layer and forming at least a second crystalline nitride semiconductor layer; and a method for growing a nitride semiconductor layer, comprising: The method of claim 1, wherein the first crystalline and nitride semiconductor buffer layer is GaN. The method according to claim 1, further comprising forming a first buffer layer between the substrate and the first crystalline nitride semiconductor layer. The method according to claim 1, wherein in step (c), the nitride semiconductor buffer layer is completely removed while forming the second crystalline nitride semiconductor layer.

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