JP2004165564A - Method for manufacturing gallium nitride crystal substrate, gallium nitride crystal substrate and gallium nitride semiconductor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a gallium nitride crystal substrate whose diameter can be enlarged, whose dislocation density is low, which is superior in crystal quality and whose "warp" is sufficiently small, and to provide the gallium nitride crystal substrate obtained by the manufacturing method of the gallium nitride crystal substrate and a gallium nitride semiconductor element provided with the gallium nitride crystal substrate. <P>SOLUTION: In the manufacturing method of the gallium nitride crystal substrate, an amorphous layer formed of phosphorous boron is vapor-grown on a surface of a silicon single crystal substrate, the gallium nitride crystal layer is grown on the amorphous layer and a laminated structure is obtained. Then, the silicon single crystal substrate is removed from the laminated structure and the gallium nitride crystal substrate is manufactured by the remaining gallium nitride crystal layer. The gallium nitride crystal layer is separated from the amorphous layer and thermal treatment is performed in an atmosphere including nitrogen atoms in a temperature range of 650°C to 1,150°C. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a gallium nitride crystal substrate, a gallium nitride crystal substrate, and a gallium nitride-based semiconductor device provided with the same. In particular, the present invention relates to a method for forming a gallium nitride crystal substrate having excellent flatness on a silicon single crystal substrate. The present invention relates to a method for manufacturing from a gallium nitride crystal layer grown on a boron-based amorphous layer.
[0002]
[Prior art]
A group III nitride semiconductor crystal layer such as gallium nitride (GaN) is a light-emitting diode (LED: Light-Emitting Diode) or a laser diode (LD: Laser Diode) that emits short-wavelength light in the near ultraviolet, blue, or green band. (For example, see Non-Patent Document 1, Chapters 13 and 14). Further, it is used to constitute a high-frequency electronic device such as a Schottky junction field effect transistor (MESFET) or a hetero bipolar transistor (HBT) (for example, refer to Non-Patent Documents 1 and 16).
Conventionally, a group III nitride semiconductor crystal layer forming a laminated structure for constituting these gallium nitride based semiconductor devices has been conventionally used as a substrate for sapphire (Sapphire: α-Al). ₂ O ₃ Single crystal) or silicon carbide (SiC) single crystal is vapor-phase grown on these substrates.
[0003]
The group III nitride semiconductor layer is formed by a vapor phase growth method such as a metal organic chemical vapor deposition (MOCVD) method, a hydride vapor phase epitaxy (HVPE) method, or a molecular beam epitaxy (MBE) method. (For example, see Non-Patent Document 1, Chapters 6 to 8). However, for example, when a gallium nitride crystal layer is grown on a sapphire substrate, the degree of lattice mismatch between the sapphire substrate and the gallium nitride crystal layer is as large as about 14% (for example, Non-Patent Documents 1 and 258). Page). For this reason, the inside of the gallium nitride crystal layer grown on the sapphire substrate by vapor phase ¹⁰ cm ^-2 Alternatively, since a dislocation is contained at a density higher than that, a crystal layer having poor crystal quality is formed (for example, see Non-Patent Document 1, pages 258).
[0004]
Therefore, recently, as a substrate for growing a gallium nitride crystal layer, a crystal material excellent in lattice matching with the gallium nitride, for example, a gallium nitride single crystal has been used. Since this gallium nitride single crystal needs to have a thickness of at least several tens to several hundreds μm in order to be used as a substrate, a method of obtaining a gallium nitride single crystal of this thickness is, for example, under a high pressure environment of about 10 GPa. Gallium (Ga) and ammonia (NH ₃ ) Are synthesized to synthesize gallium nitride (for example, see Non-Patent Document 2).
[0005]
(A) A gallium nitride crystal substrate having a large diameter because of using a large diameter silicon single crystal as a base material, (b) having a low dislocation density and excellent crystal quality, and (c) having a sufficiently small "warp". Is provided. Further, the present invention provides a gallium nitride based semiconductor device using the gallium nitride crystal substrate according to the present invention.
On the other hand, as a method of using a gallium nitride crystal layer having a thickness of about several tens of μm as a substrate, a gallium nitride crystal layer is vapor-phase grown on a sapphire substrate, and the gallium nitride crystal layer is used as a base layer, and a hydride gas is formed thereon. A method has been proposed in which a gallium nitride thick film of about several tens of μm is grown by a phase growth (HVPE) method, and then the sapphire substrate is removed and the remaining gallium nitride crystal layer is used as a substrate (for example, Patent Reference 1).
[0006]
[Patent Document 1]
JP 2001-20366 A
[Non-patent document 1]
Edited by Isamu Akasaki, "Group III Nitride Semiconductor", First Edition, Baifukan Co., Ltd., December 8, 1999
[Non-patent document 2]
Sylvester Porowski, Bulk and homoepitaxial GaN-growth and characterisation, Journal of crystal gross (Journal of 98th year, Journal of Crystallography, Journal of Crystallography, Germany) 189/190, pp. 153-158
[0007]
[Problems to be solved by the invention]
By the way, for example, the size of a gallium nitride single crystal obtained by a conventional high-pressure synthesis method is a small piece of several millimeters (mm) to several centimeters (cm) (see Non-Patent Document 2), and has a large diameter and a large area. Gallium nitride crystal substrate cannot be obtained. Therefore, a technique such as a conventional high-pressure synthesis method cannot provide a gallium nitride crystal substrate having a large diameter and a large area. For this reason, for example, it has been difficult to produce gallium nitride-based LEDs inexpensively and in large quantities.
[0008]
In the conventional method of manufacturing a gallium nitride crystal substrate using the HVPE method, a gallium nitride crystal substrate containing a large amount of crystal defects such as misfit dislocations is grown on sapphire having large lattice mismatch. Only substrates can be obtained, and therefore only provide gallium nitride crystal substrates of poor crystal quality. In addition, in a method of manufacturing a gallium nitride crystal substrate using the conventional HVPE method, a “warp” easily occurs due to a large difference in thermal expansion coefficient from a sapphire substrate, and a sufficiently flat gallium nitride crystal substrate is produced. I haven't gotten it.
[0009]
The present invention has been made in order to solve the above-mentioned problems, and it is possible to increase the diameter, reduce the dislocation density, and excel in crystal quality, and furthermore, have a sufficiently small "warp" gallium nitride crystal substrate. To provide a gallium nitride crystal substrate obtained by the method for manufacturing a gallium nitride crystal substrate, and a gallium nitride-based semiconductor device provided with the gallium nitride crystal substrate.
[0010]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, when manufacturing a gallium nitride crystal substrate based on a thick gallium nitride crystal layer grown by a vapor phase growth method, The substrate to be grown is changed from a sapphire substrate to a silicon single crystal substrate, and on this silicon single crystal substrate, a boron phosphide-based amorphous layer serving as an underlayer for vapor-phase growth of a gallium nitride crystal layer; A gallium nitride crystal substrate having a large diameter, a low dislocation density, excellent crystal quality, and a sufficiently small "warp" can be obtained by sequentially forming a crystal layer and subjecting the grown gallium nitride crystal layer to a heat treatment. The inventors have found that they can be obtained, and have reached the present invention.
[0011]
The present invention provides the following means. That is,
(1) An amorphous layer containing boron and phosphorus is vapor-phase-grown on one main surface of a silicon single crystal substrate at a temperature of 250 ° C. or more and 1200 ° C. or less, and then, on this amorphous layer A gallium nitride crystal layer is grown at a temperature of 750 ° C. or more and 1200 ° C. or less to form a laminated structure. Then, the silicon single crystal substrate is removed from the laminated structure, and the gallium nitride crystal layer is formed by the remaining gallium nitride crystal layer. In the method for manufacturing a crystal substrate, the gallium nitride crystal layer is separated from the amorphous layer, and then heat-treated in an atmosphere containing nitrogen atoms in a temperature range of 650 ° C. or more and 1150 ° C. or less. Is a method for manufacturing a gallium nitride crystal substrate.
[0012]
(2) The method for manufacturing a gallium nitride crystal substrate according to the above (1), wherein the gallium nitride crystal layer is a {0001} -gallium nitride crystal layer having a {0001} plane as one principal plane. is there.
[0013]
(3) The {0001} -gallium nitride crystal layer is a {111} -silicon single crystal having the {111} plane as one main surface, and the {111} -silicon single crystal is A {111} -boron phosphide crystal layer having a {111} plane as a principal plane at a temperature of 750 ° C. or more and 1200 ° C. or less on the amorphous layer. Characterized in that gallium nitride is vapor-phase grown on the {111} -boron phosphide crystal layer, thereby producing a gallium nitride crystal substrate according to the above item (2).
[0014]
(4) The gallium nitride crystal substrate according to the above (1), (2) or (3), wherein the gallium nitride crystal layer is subjected to a heat treatment and then cooled in an atmosphere containing nitrogen atoms. It is a manufacturing method.
[0015]
(5) The cooling is performed in a temperature range from the temperature of the heat treatment to 650 ° C. in an atmosphere containing nitrogen atoms, and in a temperature range of less than 650 ° C. in an atmosphere containing nitrogen atoms and not containing hydrogen atoms. The method of manufacturing a gallium nitride crystal substrate according to any one of the above items (1) to (4), wherein the method is performed in a medium.
[0016]
(6) The atmosphere containing a nitrogen atom is an atmosphere containing one or more selected from nitrogen, ammonia, and hydrazine, any one of the above items (1) to (5). It is a manufacturing method of the gallium nitride crystal substrate described in the above.
[0017]
(7) A gallium nitride crystal substrate manufactured by the method for manufacturing a gallium nitride crystal substrate according to any one of the above items (1) to (6).
[0018]
(8) A gallium nitride based semiconductor device comprising the gallium nitride crystal substrate according to (7).
[0019]
(9) The gallium nitride based semiconductor device according to (8), wherein an ohmic electrode is formed on one main surface of the gallium nitride crystal substrate.
[0020]
(10) The gallium nitride based semiconductor device according to the above (8) or (9), wherein a light emitting layer is formed on the gallium nitride crystal substrate.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described.
According to the method for manufacturing a gallium nitride crystal substrate of the present invention, an amorphous phase containing boron (B) and phosphorus (P) at a temperature of not less than 250 ° C. and not more than 1200 ° C. Then, a gallium nitride (GaN) crystal layer is grown on the amorphous layer at a temperature of 750 ° C. or more and 1200 ° C. or less to form a laminated structure.
Next, the silicon single crystal substrate is removed from the laminated structure, and thereafter, the gallium nitride crystal layer is further separated from the amorphous layer, and the separated gallium nitride crystal layer is heated to a temperature of 650 ° C. or more and 1150 ° C. or less. Heat treatment is performed in an atmosphere containing nitrogen atoms in a temperature range.
[0022]
As the silicon single crystal substrate described above, for example, the surface of a wafer obtained by cutting out a silicon (silicon) single crystal has a crystal plane having a low-order mirror (Miller) index such as {100}, {110}, or {111}. Can be used. Also, a silicon wafer having a so-called off-cut crystal plane whose surface is inclined at an angle of several degrees to several tens of degrees with respect to the crystal plane of the above-mentioned low-order Miller index is also used as the substrate. can do.
[0023]
As the silicon single crystal substrate, a {111} -silicon single crystal substrate having a {111} plane as a surface, which is most densely filled with silicon atoms, is particularly preferred because it is a diamond-type single crystal. preferable.
The reason is that a {111} -silicon single crystal substrate having a {111} plane as a surface is an excellent substrate having a low dislocation density and no lattice defects, and was formed on the surface of the silicon single crystal substrate. Elements of the upper layer, that is, an amorphous layer containing boron (B) and phosphorus (P), ie, boron (B) and phosphorus (P), are prevented from penetrating and diffusing into the silicon single crystal substrate; This is because it prevents the regular crystal structure inside the silicon single crystal substrate from being disturbed.
[0024]
Further, the silicon single crystal substrate having a low dislocation density is superior in forming a flat junction interface between the substrate and the upper layer when the upper layer is grown on the silicon single crystal substrate.
Further, the silicon single crystal substrate having a low dislocation density is effective in reducing dislocations penetrating and propagating to the upper layer. In particular, when the dislocation density is 10 ³ cm ^-2 Below, further 10 ² cm ^-2 A silicon single crystal substrate having a low dislocation density as described below is effective for obtaining an upper layer having a low density of threading dislocations.
[0025]
In order to grow the gallium nitride crystal layer, either an undoped silicon single crystal substrate not intentionally doped with an impurity or a silicon single crystal substrate intentionally doped with an impurity can be used. As the conductivity type of the silicon single crystal substrate, any of n-type and p-type conductivity types can be used. Alternatively, a high-resistance silicon single crystal substrate or an intrinsic silicon single crystal substrate with extremely few impurities can be used.
The thickness of the silicon single crystal substrate can be appropriately selected according to the desired thickness of the gallium nitride crystal layer, and is preferably about several hundred μm.
For example, in the case of a silicon single crystal substrate having a diameter of 50 mm, a preferable thickness is approximately 250 μm to 400 μm. In the case of a silicon single crystal substrate having a diameter of 100 mm, a preferable thickness is approximately 400 μm to 700 μm.
[0026]
In this silicon single crystal substrate, as the diameter is larger and the thickness of the gallium nitride crystal layer is larger, the "warping" of the silicon single crystal substrate during the formation of the gallium nitride crystal layer is suppressed. While maintaining a uniform temperature over the entire surface. Therefore, the uniformity of the gallium nitride crystal layer to be grown is improved.
It is also useful for preventing cracks generated in the gallium nitride crystal layer due to “warpage” and non-uniform temperature distribution of the silicon single crystal substrate.
Forming a narrow groove on the back surface of the silicon single crystal substrate for relaxing thermal stress is effective in obtaining a gallium nitride crystal layer with less "warpage".
[0027]
In this embodiment, first, an amorphous layer containing boron (B) and phosphorus (P) is vapor-phase grown on the silicon single crystal substrate.
This amorphous layer can be made of a boron phosphide-based material containing boron (B) and phosphorus (P) as constituent elements. As the boron phosphide-based material, for example, B _a Al _b Ga _c In _1-abc P _1-d As _d (0 <a ≦ 1, 0 ≦ b <1, 0 ≦ c <1, 0 <a + b + c ≦ 1, 0 ≦ d <1), B _a Al _b Ga _c In _1-abc P _1-d N _d (0 <a ≦ 1, 0 ≦ b <1, 0 ≦ c <1, 0 <a + b + c ≦ 1, 0 ≦ d <1) are preferably used. More specifically, an amorphous layer made of a monomeric boron phosphide (BP), a boron phosphide-gallium (B _a Ga _c An amorphous layer composed of P (0 <a ≦ 1, 0 ≦ c <1) or the like can be exemplified.
[0028]
Further, the amorphous layer can be replaced with a mixed crystal which is a crystal phase in which two or more crystalline substances are uniformly mixed.
As mixed crystals, boron nitride phosphide (BP _1-d N _d : 0 ≦ d <1), boron arsenide (B _a As _1-d N _d : A mixed crystal containing a plurality of group V elements such as 0 <a ≦ 1, 0 ≦ d <1).
[0029]
The amorphous layer made of the boron phosphide-based material is, for example, boron trichloride (BCl ₃ ) And phosphorus trichloride (PCl ₃ ) As a starting material (see “Journal of the Japanese Society for Crystal Growth”, Vol. 24, No. 2 (1997), page 150). Borane (BH) ₃ ) Or diborane (B ₂ H ₆ ) And phosphine (PH ₃ ) And the like as raw materials (see J. Crystal Growth, 24/25 (1974), pages 193 to 196), and molecular beam epitaxy (J. Solid State chem., 133 (1997), 269 to 272). Page)).
[0030]
In addition, an organometallic chemical vapor deposition (MOCVD) method using an organic boron compound and a hydrogen compound of phosphorus as raw materials (Inst. Phys. Conf. Ser., No. 129 (IOP Publishing Ltd. UK.) (1993), (See pages 157 to 162).
In particular, the MOCVD method uses triethyl boron ((C ₂ H ₅ ) ₃ Since a readily decomposable substance such as B) is used as a boron source, it is an advantageous growth means for vapor-phase growing an amorphous layer at a low temperature.
[0031]
This amorphous layer is preferably grown in an atmosphere that does not contain a large amount of oxygen or nitrogen so that silicon oxide, silicon nitride, or the like that hinders growth is not formed on the surface. As this atmosphere, for example, hydrogen (H ₂ ) Gas atmosphere or hydrogen (H ₂ A mixed gas atmosphere of a gas and a monoatomic inert gas such as argon (Ar) is preferable. The amorphous layer has a surface temperature of the silicon single crystal substrate of 250 ° C. or more and 1200 ° C. or less, and for example, hydrogen (H) ₂ ) Gas atmosphere, triethyl boron ((C ₂ H ₅ ) ₃ B) and phosphine (PH ₃ ) As a raw material {triethyl boron ((C ₂ H ₅ ) ₃ B) / phosphine (PH ₃ ) / Hydrogen (H ₂ ) In (1), it is preferable to carry out vapor phase growth by either normal pressure (substantially atmospheric pressure) MOCVD or reduced pressure MOCVD.
[0032]
In this case, when the growth temperature is higher than 750 ° C., a polycrystalline layer containing boron and phosphorus tends to be easily formed. Even in such a high temperature region, the ratio of the supply amount of the phosphorus source to the boron source, By lowering the so-called V / III ratio, an amorphous layer can be formed. For example, in the MOCVD method using the above reaction system, the V / III ratio (= (C ₂ H ₅ ) ₃ B / PH ₃ By setting the (supply concentration ratio) to a low ratio of 0.2 to 50, the amorphous layer can be stably formed even in the high-temperature region described above.
[0033]
The layer thickness of the amorphous layer is preferably a layer thickness sufficient to cover the surface of the silicon single crystal substrate sufficiently uniformly, that is, 0.5 nm or more and 60 nm or less, more preferably 5 nm or more and It is 20 nm or less. The thickness of the amorphous layer can be controlled by adjusting the supply time of the boron source to the growth region. The thickness of the amorphous layer can be actually measured by, for example, a transmission electron microscope (TEM). In transmission electron microscopy, an electron diffraction image from an amorphous layer becomes a halo.
[0034]
A gallium nitride crystal layer is grown on the thus obtained amorphous material.
The gallium nitride crystal layer can be grown by, for example, a sublimation method (see J. Crystal Growth, 189/190, (1998), pp. 163-166). In the present embodiment, the hydride method is used. , A halogen method, a MOCVD method or the like. The reason is that these vapor phase epitaxy methods can more easily grow a gallium nitride crystal layer. In particular, the hydride vapor phase epitaxy (HVPE) method is several μm to several tens μm / hour. (See J. Crystal Growth, 189/190, (1998), pp. 61-66), which is suitable for growing a thick gallium nitride crystal layer. is there.
[0035]
When growing a gallium nitride crystal layer by hydride vapor phase epitaxy, ammonia (NH ₃ ), Dimethylhydrazine ((CH ₃ ) ₂ N ₂ H ₂ ) Etc. can be used. Ammonia (NH ₃ )), The temperature range suitable for the vapor phase growth of the gallium nitride crystal layer is 950 ° C. to 1150 ° C. In particular, in order to grow a gallium nitride crystal layer at a lower temperature range of 750 ° C. to 1000 ° C., dimethylhydrazine ((CH ₃ ) ₂ N ₂ H ₂ ) Is preferably used.
Furthermore, in order to make the crystal structure of the gallium nitride crystal layer cubic, it is necessary to use an easily thermally decomposable nitrogen-containing compound such as dimethylhydrazine as a nitrogen source and to perform vapor phase growth at a relatively low temperature. desirable.
[0036]
The total thickness of the vapor-grown gallium nitride crystal layer is determined, for example, by forming a monomeric boron phosphide amorphous layer on a silicon single crystal substrate having a diameter of 50 mm, When the gallium crystal layer is grown by vapor phase, the thickness is preferably 80 μm or more and 450 μm or less. Further, when the diameter of the silicon single crystal substrate is changed from 50 mm to 100 mm, it is preferable that the diameter be 300 μm or more and 700 μm or less.
The gallium nitride crystal layer having such a layer thickness does not necessarily need to be grown only once, but the vapor phase growth is repeated a plurality of times, for example, twice, three times, etc., so that the gallium nitride crystal layer having a desired layer thickness is obtained. A crystalline layer can be obtained.
[0037]
For example, when the gallium nitride crystal layer is vapor-grown on the amorphous boron phosphide layer until the layer thickness becomes 80 μm, the vapor-phase growth of the gallium nitride crystal layer is temporarily stopped. Thereafter, the silicon single crystal substrate on which the gallium nitride crystal layer has been formed is taken out of the vapor phase growth apparatus, and the silicon single crystal substrate is removed. As a result, only the gallium nitride crystal layer remains. Next, the remaining gallium nitride crystal layer is placed inside the vapor phase growth apparatus, and the gallium nitride crystal layer is grown again by vapor phase. As described above, by performing the vapor phase growth twice or more, the desired diameter and the desired layer thickness are reduced, for example, so that the diameter is 50 mm and the entire layer thickness is 80 μm or more and 450 μm or less. Gallium nitride crystal layer can be manufactured.
[0038]
In addition, a gallium nitride crystal layer can be vapor-phase grown on a boron phosphide-based layer containing boron (B) and phosphorus (P) as constituent elements formed on an amorphous layer. The boron phosphide-based layer may be, for example, a monomeric boron phosphide (BP) crystal layer or a boron phosphide / indium mixed crystal layer (B _a In _1-a P: 0 <a ≦ 1) or the like. In particular, the lattice spacing of {111} planes of monomeric boron phosphide (BP) having a cubic zinc blende structure (zinc-blend structure) is determined by the gallium nitride of the wurtzite structure (Wurtzite structure). The value substantially coincides with the a-axis lattice constant (a = 0.319 nm).
[0039]
Therefore, a gallium nitride crystal layer of good crystallinity with few misfit dislocations can be formed on the monomeric boron phosphide crystal layer, reflecting good lattice mismatch. The growth temperature of the boron boron phosphide crystal layer of the monomer is preferably 1200 ° C. or lower. The reason is that at a high temperature exceeding 1200 ° C., lattice mismatch does not occur with gallium nitride (GaN). _Thirteen P ₂ This is inconvenient because a multimeric boron phosphide crystal (see J. Am. Ceramic Soc., 47 (1) (1964), pp. 44-46) is formed. On the other hand, in order to obtain a single crystal monomeric boron phosphide crystal layer, the growth temperature is preferably 750 ° C. or higher. It is convenient to grow the boron phosphide crystal layer by the same growth method as in the case of the amorphous layer when manufacturing a gallium nitride crystal substrate.
[0040]
The monomeric boron phosphide crystal layer having a {111} plane as a surface can be formed using a {111} -silicon single crystal having a {111} plane as a substrate. For example, a triethyl boron ((C ₂ H ₅ ) ₃ B) / phosphine (PH ₃ ) Reactive metal organic chemical vapor deposition (MOCVD) can be performed at a growth temperature of 750 ° C or more and 1200 ° C or less.
In addition, the supply ratio between the boron source and the phosphorus source during vapor phase growth (= PH ₃ / (C ₂ H ₅ ) ₃ B) The so-called V / III ratio is 1 × 10 ³ With such a degree, a {111} -boron phosphide crystal layer having a {111} plane as a surface can be obtained.
[0041]
A {0001} -gallium nitride crystal layer can be efficiently formed on the surface of the {111} -boron phosphide crystal layer. The lattice spacing of the {110} plane of boron phosphide crossing the {111} plane of the {111} -boron phosphide crystal layer, the lattice constant of the a-axis of the surface of the {0001} -gallium nitride crystal layer, and Are approximately the same, a {0001} -gallium nitride crystal layer with less “warp” can be vapor-phase grown on the {111} -boron phosphide crystal layer. The “warp” of the gallium nitride crystal layer can be quantitatively displayed as a warp, for example, by optical measurement using interference of general laser light. In addition, due to good lattice matching, the density of misfit dislocations on the {111} -boron phosphide crystal layer is about 1 × 10 ⁵ cm ^-2 There is an advantage that a {0001} -gallium nitride crystal layer having a low dislocation density as described below can be grown.
[0042]
FIG. 1 is a schematic diagram showing the cross-sectional structure of the laminated structure 1 obtained in this manner. In the figure, reference numeral 11 denotes a silicon (Si) single crystal substrate, and reference numeral 12 denotes boron phosphide (BP) amorphous. Layer 13 is a boron phosphide (BP) crystal layer, and 14 is a gallium nitride (GaN) crystal layer. After removing the silicon (Si) single crystal substrate 11, the boron phosphide (BP) amorphous layer 12, and the boron phosphide (BP) crystal layer 13, the gallium nitride (GaN) crystal layer 14 is subjected to a heat treatment. Thereby, the gallium nitride crystal substrate 15 having excellent flatness is obtained.
[0043]
In the present embodiment, the gallium nitride crystal layer is subjected to an annealing process in order to obtain a gallium nitride crystal substrate having a small “warp”.
In general, it is difficult to obtain a gallium nitride crystal substrate having a small “warp” even if a heat treatment is performed on the gallium nitride crystal layer in a state where a silicon single crystal substrate having a different coefficient of thermal expansion is attached. Therefore, in this embodiment, the silicon single crystal substrate and the amorphous layer are removed from the gallium nitride crystal layer, and heat treatment is performed in a state where the gallium nitride crystal layer is separated therefrom.
[0044]
For example, when a gallium nitride crystal layer is formed on the above-mentioned amorphous layer via a monomeric boron phosphide crystal layer, the boron phosphide crystal layer is removed when the amorphous layer is removed. It is also preferable to remove them together. Further, the silicon single crystal substrate can be removed by a chemical method such as wet etching. In this wet etching, for example, hydrofluoric acid (HF) and nitric acid (HNO) ₃ )) Is preferably used. The approximate etching rate of a silicon single crystal using this mixed solution of hydrofluoric acid and nitric acid is known from known literature (“Semiconductor Silicon Crystal Engineering”, Maruzen Co., Ltd.), September 30, 1993. Issue, pages 113-114).
[0045]
Further, this silicon single crystal substrate can be removed by dry etching or the like. For example, boron trichloride (BCl ₃ ) Can be removed by plasma etching using halides.
In addition, diamond, silicon carbide (SiC), boron nitride (BN), alumina (Al ₂ O ₃ ) Can also be removed by grinding by mechanical polishing using a high-hardness abrasive made of an oxide such as).
In particular, the boron phosphide amorphous layer and the boron phosphide crystal layer containing boron (B) and phosphorus (P) have high chemical stability, and thus are more plasma-etched and mechanically etched than wet-etched with a chemical. It is effective to remove using a suitable polishing.
[0046]
The heat treatment temperature is preferably from 650 ° C to 1150 ° C. The reason is that at a low temperature of less than 650 ° C., the gallium nitride crystal layer cannot be annealed sufficiently to reduce “warpage”, and at a high temperature exceeding 1150 ° C., nitrogen from the gallium nitride crystal layer cannot be heated. This is because detachment becomes remarkable, which is inconvenient for manufacturing a gallium nitride crystal substrate having a smooth surface. In order to suppress the release of nitrogen from the gallium nitride crystal layer, it is effective to perform a heat treatment in an atmosphere containing nitrogen atoms.
[0047]
The atmosphere containing nitrogen atoms can be formed using a gas containing nitrogen-containing molecules that release nitrogen atoms by thermal dissociation. For example, ammonia (NH ₃ ), Hydrazine (N ₂ H ₂ ) And other hydrogen containing nitrogen-containing molecules (H ₂ ) Gas, nitrogen (N ₂ A) a mixture of gases and an inert gas such as argon (Ar) or helium (He) can be used.
[0048]
As the heat treatment temperature is increased, the mixed atmosphere in which the volume fraction of the nitrogen-containing molecules in the mixed gas is large is effective in suppressing the volatilization of nitrogen from the gallium nitride crystal layer. Therefore, good results can be obtained by using a mixed atmosphere in which the volume fraction of nitrogen-containing molecules is increased as the heat treatment temperature is increased. For example, when performing a heat treatment on the gallium nitride crystal layer at a temperature of 1000 ° C. or more, it is preferable that the volume fraction of nitrogen-containing molecules (in this case, ammonia) constituting the ammonia-argon mixed atmosphere be 50% or more. The heat treatment at a high temperature may be carried out in an atmosphere containing only nitrogen-containing molecules with the volume fraction of nitrogen-containing molecules being 100%. The above volume fraction is a ratio of the volume of the nitrogen-containing molecule to the total volume of the gas forming the mixed atmosphere. Simply, it is expressed by the ratio of the flow rate of the nitrogen-containing molecular gas to the total flow rate of the gas forming the mixed gas.
[0049]
The heat treatment time is preferably short so that the heat treatment does not impair the smoothness of the surface of the gallium nitride crystal layer. In particular, the higher the heat treatment temperature, the shorter the heat treatment time. For the atmosphere, the heat treatment time is preferably set to be shorter as the volume fraction of the nitrogen-containing molecule is smaller. For example, in an ammonia-hydrogen mixed atmosphere containing 40% by volume of ammonia, heat treatment is preferably performed at 850 ° C. for 1 hour. Also, ammonia (NH ₃ : Volume fraction = 70%)-An example in which heat treatment is performed at 1050 ° C for 30 minutes in an argon (Ar: volume fraction = 30%) atmosphere.
[0050]
The heat treatment does not necessarily need to be performed at a constant temperature, but may be performed, for example, in a temperature range of 650 ° C. or higher and 1150 ° C. or lower while increasing or decreasing the temperature.
In the case of performing the heat treatment while changing the temperature, the rate of temperature rise and the rate of temperature decrease can be appropriately selected. Note that a rapid temperature change during the heat treatment causes thermal strain in the gallium nitride crystal layer. In order to avoid the occurrence of this thermal strain, generally, a slow rate of about 1 ° C. to 5 ° C. per minute is used. It is desirable to raise or lower the temperature in the step.
[0051]
As described above, by removing the silicon single crystal substrate and the amorphous layer from the gallium nitride crystal layer and performing heat treatment on the separated gallium nitride crystal layer, deterioration of the surface state of the gallium nitride crystal layer due to release of nitrogen can be avoided. While reducing "warpage" and providing excellent flatness. Thereby, this gallium nitride crystal layer becomes a gallium nitride crystal substrate having excellent flatness.
[0052]
The gallium nitride crystal layer after the heat treatment is cooled in an atmosphere containing nitrogen-containing molecules. In particular, when cooling is performed in an atmosphere containing nitrogen-containing molecules from the heat treatment temperature to 650 ° C., release of nitrogen from the gallium nitride crystal layer can be reliably suppressed. Further, the gallium nitride crystal layer can be cooled in an atmosphere containing nitrogen-containing molecules different from the nitrogen-containing molecules used for the heat treatment.
In particular, when the gallium nitride crystal layer is cooled in the same atmosphere as the heat treatment atmosphere, the cooling operation can be easily performed, which is convenient. For example, ammonia (NH ₃ : Volume fraction = 60%)-nitrogen (N ₂ : Volume fraction = 40%) After heat treatment in a mixed atmosphere, ammonia (NH ₃ : Volume fraction = 30%)-nitrogen (N ₂ : Volume fraction = 70%) cooling from the heat treatment temperature to 650 ° C in a mixed atmosphere.
[0053]
The volume fraction of nitrogen-containing molecules constituting the atmosphere during cooling may be smaller than the volume fraction of nitrogen-containing molecules constituting the atmosphere during heat treatment. However, a mixed atmosphere in which the volume fraction of nitrogen-containing molecules is zero (= 0) is not preferable. Cooling from 650 ° C. to a predetermined temperature lower than that is performed using hydrogen (H ₂ ), Nitrogen (N ₂ ), And can be carried out in an atmosphere containing no nitrogen-containing molecules such as an inert gas. In particular, an atmosphere containing no hydrogen is effective in diffusing hydrogen to the outside of the crystal when hydrogen (hydrogen atoms) enters the gallium nitride crystal layer during heat treatment or cooling.
[0054]
After the cooling, if the gallium nitride crystal layer is subjected to chemical mechanical polishing (CMP), a gallium nitride crystal substrate having an excellent surface smoothness can be obtained. For chemical mechanical polishing of the surface of the gallium nitride crystal layer, abrasive grains of high hardness such as diamond and alumina can be used. When a conductive or high-resistance gallium nitride crystal layer having excellent flatness is used as a substrate (gallium nitride crystal substrate), a compound semiconductor element having excellent electrical characteristics can be formed.
[0055]
For example, a laminated structure having a light emitting layer is formed on the surface of a conductive gallium nitride crystal substrate, and an ohmic electrode having one polarity is provided on the back surface of the gallium nitride crystal substrate. By providing an ohmic electrode having the other polarity on the structure, a light emitting diode (LED) or a laser diode (LD) can be formed.
Further, using a high-resistance gallium nitride crystal substrate, for example, a gallium nitride-indium mixed crystal layer (Ga _x In _1-x N = 0 ≦ X ≦ 1) can be formed as a field effect transistor (FET) having an electron transit layer.
[0056]
A substrate having a low dislocation density is provided by a {0001} -gallium nitride crystal layer formed by interposing an amorphous layer on a {111} -silicon single crystal substrate and a {111} -boron phosphide crystal layer can do. Therefore, if such a gallium nitride crystal substrate having a low dislocation density is used, a gallium nitride based semiconductor device having a small local withstand voltage defect, for example, a light emitting element such as an LED with a small local withstand voltage defect, or a dark current ( An avalanche-type or pin-junction-type light-receiving element with reduced dark current can be formed.
In addition, an effect of suppressing a leakage current of a Schottky-type gate electrode can be obtained. The gate pinch-off characteristic is excellent, and a high mutual conductance, so-called g, is obtained. _m This is advantageous in forming a Schottky junction type FET.
[0057]
FIG. 2 is a cross-sectional view showing a light emitting diode (LED) (gallium nitride based semiconductor element) 21 of the present embodiment, and is an example using the gallium nitride (GaN) crystal substrate 15 obtained as described above.
In the drawing, reference numeral 22 denotes an n-type gallium nitride (GaN) crystal substrate, 23 denotes a lower cladding layer made of n-type gallium nitride (GaN), 24 denotes a light-emitting layer made of n-type gallium indium nitride (GaInN), and 25 denotes p Upper clad layer made of a type boron phosphide layer, 26 is a p-type ohmic electrode formed in the center of the surface of the upper clad layer 25, and 27 is an approximate back surface (one main surface) of the gallium nitride (GaN) crystal substrate 22. It is an n-type ohmic electrode formed on the entire surface.
[0058]
【Example】
Hereinafter, the present invention will be specifically described based on a first embodiment and a second embodiment.
[0059]
(First embodiment)
The content of the present invention will be described by taking as an example a case where a gallium nitride crystal substrate is manufactured from a gallium nitride crystal layer grown on a silicon (Si) single crystal substrate through an amorphous layer of boron phosphide and a single crystal layer. A specific description will be given.
[0060]
First, the laminated structure 1 shown in FIG. 1 was produced.
As the silicon (Si) single crystal substrate 11, a phosphorus (P) -doped n-type {111} -Si single crystal substrate was used. The specific resistance (resistivity) of the Si single crystal of the substrate 11 at room temperature is about 1 × 10 ^-3 Ω · cm. The thickness of a 50 mm-diameter circular Si single crystal whose surface is polished to a mirror surface and whose back surface is roughly polished (as-lapping) has a thickness of about 3.5 × 10 5. ^-2 cm (= 350 μm).
[0061]
An undoped boron phosphide (BP) amorphous layer 12 was deposited on the {111} plane of the substrate 11 by normal pressure (substantially atmospheric pressure) metal organic chemical vapor deposition (MOCVD).
This amorphous layer 12 is made of triethyl boron ((C ₂ H ₅ ) ₃ B) as a boron source and phosphine (PH ₃ ) Was deposited at 450 ° C. using a phosphorus source. The ratio of the supply concentration of the phosphorus source to the MOCVD reaction system per unit time with respect to the boron source (PH ₃ / (C ₂ H ₅ ) ₃ B; V / III ratio) was set to 16. The layer thickness of the boron phosphide amorphous layer 12 was 10 nm.
[0062]
After the vapor phase growth of the boron phosphide amorphous layer 12 is terminated by stopping the supply of the boron source, phosphine (PH ₃ ) And hydrogen (H ₂ ) The temperature of the substrate 11 was increased to 925 ° C. in an atmosphere of a mixed gas of gases. Thereafter, the boron source was caused to flow again, and an undoped n-type {111} -boron phosphide crystal layer 13 was deposited on the amorphous layer 12 at 925 ° C. The V / III ratio during vapor phase growth was set to 1300. The thickness of the boron phosphide crystal layer 13 was 120 nm.
[0063]
A {0001} -gallium nitride (GaN) single crystal layer 14 is formed on the boron phosphide crystal layer 13 by a gallium (Ga) / ammonia (NH) / hydrogen (H) reaction hydride vapor phase epitaxy (HVPE) method. Deposited.
This gallium nitride single crystal layer 14 was deposited at 1050 ° C. The thickness of the gallium nitride single crystal layer 14 is 1.5 × 10 ^-2 cm (= 150 μm).
After the vapor phase growth of the gallium nitride crystal layer 14 has been completed, the {111} -silicon (Si) single crystal substrate 11 / boron phosphide amorphous layer 12 / {111} -boron phosphide is cooled. The multilayer structure 1 composed of the crystal layer 13 / the gallium nitride crystal layer 14 was obtained.
[0064]
The laminated structure 1 thus obtained was taken out of the HVPE apparatus.
Thereafter, the silicon single crystal substrate 11 constituting the laminated structure 1 was removed by etching with a mixed solution of hydrofluoric acid and nitric acid containing hydrofluoric acid and nitric acid. Next, the amorphous layer 12 and the boron phosphide layer 13 were polished and removed using diamond abrasive grains. In addition, the back surface (the surface on the side of the Si single crystal substrate 11) 14b of the gallium nitride crystal layer 14 was roughly polished.
[0065]
Next, the gallium nitride crystal layer 14 separated by removing the silicon single crystal substrate 11 and the like is treated with ammonia (NH 4) at 1050 ° C. ₃ ) -Hydrogen (H ₂ The heat treatment was performed in the mixed gas atmosphere of (2). Here, ammonia (NH ₃ ) Is 3 liters per minute (l) and hydrogen (H ₂ ) Since the flow rate of the gas was 1 liter (l) per minute, the volume fraction of ammonia forming the mixed atmosphere was 75%.
The heat treatment time was 45 minutes. After the completion of the heat treatment, the gallium nitride crystal layer 14 is replaced with the above ammonia (NH ₃ ) -Hydrogen (H ₂ The mixture was cooled from 1050 ° C. to 650 ° C. in the mixed gas atmosphere of the above). When the temperature of the gallium nitride crystal layer 14 reaches 650 ° C., ammonia (NH ₃ ) And hydrogen (H ₂ ) Is stopped, and nitrogen (N ₂ ), And cooled to room temperature (25 ° C).
[0066]
After cooling, the surface of the gallium nitride crystal layer 14 that has been subjected to the above heat treatment (the surface of the growth layer opposite to the silicon single crystal substrate 11) 14a is polished to a mirror surface using diamond fine grains or the like. And
In the measurement using a general laser interferometry, the “warp” of the gallium nitride crystal substrate 15 obtained by performing the heat treatment is warped to 1 × 10 ^-3 cm (= 10 μm). The gallium nitride crystal substrate 15 exhibits n-type electric conductivity, and the carrier concentration (n) is about 2 × 10 5 by the general Hall effect method. ¹⁸ cm ^-3 Met.
[0067]
Further, a bright-field image of the inside of the gallium nitride crystal substrate 15 was taken by a general cross-sectional TEM method. From the density of the linear black contrast image inside the bright field image (LT Romano et ai., Mat. Res. Soc. Symp. Proc., Vol. 423 (1996), pp. 245-250). The obtained dislocation density is about 1 × 10 ⁵ cm ^-2 And low density.
As described above, an n-type gallium nitride crystal substrate 15 having a small amount of “warp” and a low dislocation density can be manufactured.
[0068]
(Second embodiment)
The gallium nitride based semiconductor device according to the present invention will be specifically described by taking as an example a case where a light emitting diode (LED) is formed using the n-type gallium nitride crystal substrate manufactured in the first embodiment.
[0069]
The light emitting diode (LED) 21 shown in FIG. 2 was manufactured.
First, the following layers were sequentially stacked on the n-type gallium nitride crystal substrate 22 by MOCVD.
(1) Silicon (Si) -doped n-type {0001} -gallium nitride (GaN) (n = 1 × 10 ¹⁸ cm ^-3 , Layer thickness (t) = 1 × 10 ^-4 cm (= 1 μm)).
(2) n-type gallium indium nitride (Ga _0.90 In _0.10 N) (n = 7 × 10 ¹⁷ cm ^-3 , T = 50 nm).
(3) Undoped p-type {111} -boron phosphide (p = 2 × 10 ¹⁹ cm ^-3 , T = 380 nm).
[0070]
The above-mentioned n-type gallium nitride (GaN) layer and n-type gallium indium nitride (Ga) _0.90 In _0.10 The (N) layer is composed of (CH) ₃ ) ₃ Ga / NH ₃ / H ₂ Growth was performed at 1050 ° C. and 850 ° C., respectively, by a reactive MOCVD method.
The p-type boron phosphide is (C ₂ H ₅ ) ₃ B / PH ₃ / H ₂ It was grown at 1025 ° C. by a reactive MOCVD method.
Since the upper cladding layer 25 is formed using a p-type boron phosphide layer having a band gap of about 3 eV at room temperature, a window through which light emitted from the cladding layer and the light emitting layer 24 with respect to the light emitting layer 24 can be sufficiently transmitted to the outside. It could also be used as a layer.
[0071]
At the center of the surface of the upper cladding layer 25 made of a p-type boron phosphide layer, Au.Zn / nickel (Ni) / Au. A p-type ohmic electrode 26 having a three-layer Au structure was formed.
The p-type ohmic electrode 26 was a circular electrode having a diameter of about 120 μm to also serve as a pedestal (pad) electrode for connection.
[0072]
On the other hand, a nickel oxide (NiO) / Au multilayer electrode was formed as an n-type ohmic electrode 27 on substantially the entire back surface of the n-type gallium nitride crystal substrate 22. As a result, a light emitting diode (LED) 21 having a pn junction type double hetero (DH) structure in which the n-type light emitting layer 24 was sandwiched between the n-type lower clad layer 23 and the p-type upper clad layer 25 was obtained.
When an operating current of 20 milliamperes (mA) was applied between the two ohmic electrodes 26 and 27 in the forward direction, blue-violet light having a wavelength of about 440 nm was emitted. The luminance in a chip state measured using a general integrating sphere was 8 millicandela (mcd).
[0073]
In particular, since a gallium nitride crystal layer having a low dislocation density was used as the substrate 22, a high-brightness light-emitting diode (LED) 21 having no local breakdown voltage was obtained. For this reason, the forward voltage (so-called Vf) when the forward current is 20 mA is about 3 V, and the reverse voltage (Vr) when the reverse current is 10 μA is 8 V or more. Was expressed.
[0074]
【The invention's effect】
As described above, according to the method for manufacturing a gallium nitride crystal substrate of the present invention, the gallium nitride crystal layer is separated from the amorphous layer, and then contains nitrogen atoms in a temperature range of 650 ° C. or more and 1150 ° C. or less. Since the heat treatment is performed in an atmosphere, a flat gallium nitride crystal substrate having excellent surface flatness and less warpage can be manufactured.
[0075]
According to the gallium nitride-based semiconductor device of the present invention, since the gallium nitride crystal substrate of the present invention is provided, a gallium nitride-based semiconductor device exhibiting good rectification characteristics and having no local breakdown down is provided. can do.
If this gallium nitride based semiconductor device has a light emitting layer, it can emit light with high luminance.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a cross-sectional structure of a laminated structure obtained by a method for manufacturing a gallium nitride crystal substrate according to one embodiment of the present invention.
FIG. 2 is a sectional view showing a light emitting diode (LED) according to one embodiment of the present invention.
[Explanation of symbols]
1 laminated structure
11 Silicon (Si) single crystal substrate
12. Boron phosphide (BP) amorphous layer
13. Boron phosphide (BP) crystal layer
14. Gallium nitride (GaN) crystal layer
15 Gallium nitride crystal substrate
21 Light emitting diode (LED)
22 n-type gallium nitride (GaN) crystal substrate
23 Lower cladding layer
24 Emitting layer
25 Upper cladding layer
26 p-type ohmic electrode
27 n-type ohmic electrode

Claims (10)

An amorphous layer containing boron and phosphorus is vapor-phase grown at a temperature of 250 ° C. or more and 1200 ° C. or less on one main surface of a silicon single crystal substrate, and then 750 ° C. or more is formed on the amorphous layer. A gallium nitride crystal layer is grown at a temperature of 1200 ° C. or less to form a laminated structure. Next, the silicon single crystal substrate is removed from the laminated structure, and a gallium nitride crystal substrate is formed by the remaining gallium nitride crystal layer. In the method of manufacturing,
A method for manufacturing a gallium nitride crystal substrate, comprising separating the gallium nitride crystal layer from the amorphous layer, and then performing heat treatment in an atmosphere containing nitrogen atoms in a temperature range of 650 ° C. or more and 1150 ° C. or less. . 2. The method for manufacturing a gallium nitride crystal substrate according to claim 1, wherein the gallium nitride crystal layer is a {0001} -gallium nitride crystal layer having a {0001} plane as one main surface. The {0001} -gallium nitride crystal layer is a {111} -silicon single crystal having the {111} plane as one principal plane, and the {111} -silicon single crystal is An amorphous layer is grown in a vapor phase, and a {111} -boron phosphide crystal layer having a {111} plane as a principal plane is formed on the amorphous layer at a temperature of 750 ° C. or more and 1200 ° C. or less. 3. The method according to claim 2, wherein gallium nitride is grown on the {111} -boron phosphide crystal layer in a vapor phase. 4. The method for manufacturing a gallium nitride crystal substrate according to claim 1, wherein the gallium nitride crystal layer is heat-treated and then cooled in an atmosphere containing nitrogen atoms. The cooling is performed in a temperature range from the temperature of the heat treatment to 650 ° C. in an atmosphere containing nitrogen atoms, and in a temperature range of less than 650 ° C. in an atmosphere containing nitrogen atoms and not containing hydrogen atoms. 5. The method for manufacturing a gallium nitride crystal substrate according to claim 1, wherein the method is performed. The gallium nitride crystal substrate according to any one of claims 1 to 5, wherein the atmosphere containing a nitrogen atom is an atmosphere containing one or more selected from nitrogen, ammonia, and hydrazine. Manufacturing method. A gallium nitride crystal substrate manufactured by the method for manufacturing a gallium nitride crystal substrate according to any one of claims 1 to 6. A gallium nitride-based semiconductor device comprising the gallium nitride crystal substrate according to claim 7. The gallium nitride based semiconductor device according to claim 8, wherein an ohmic electrode is formed on one main surface of the gallium nitride crystal substrate. 10. The gallium nitride based semiconductor device according to claim 8, wherein a light emitting layer is formed on the gallium nitride crystal substrate.

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