JP3654242B2 - Manufacturing method of nitride semiconductor substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nitride semiconductor (In) used in a light-emitting element such as a light-emitting diode or a laser diode, or a light-receiving element such as a solar cell or an optical sensor._xAl_yGa_1-xyThe present invention relates to a method for manufacturing a nitride semiconductor substrate having N, 0 ≦ X, 0 ≦ Y, and X + Y ≦ 1) in a nitride semiconductor element.
[0002]
[Prior art]
In recent years, there has been an increasing demand for semiconductor lasers using nitride semiconductor substrates for use in disk systems capable of recording and reproducing information with a large capacity and high density, such as DVDs. In addition, since there is a great demand for high-brightness LEDs, white LEDs, and the like, various methods for obtaining a nitride semiconductor substrate used for such LEDs and LDs as bulk single crystals have been studied in recent years.
However, in order to obtain a single crystal, it is not at a level that can be mass-produced in spite of the necessity of high-pressure and other dangerous reaction conditions and expensive equipment. Growth methods are being considered.
[0003]
When a nitride semiconductor is grown on a heterogeneous substrate, crystal defects are generated when the nitride semiconductor is grown on the heterogeneous substrate due to an irregular lattice constant or a difference in thermal expansion coefficient between the heterogeneous substrate and the nitride semiconductor. Therefore, an ELOG (Epitaxially Lateral OverGrowth GaN) growth method using a method of growing a nitride semiconductor laterally with respect to the substrate has been reported. According to this method, in the region where the nitride semiconductor grows, the generated crystal defects proceed only in the vertical direction along with the growth of the nitride semiconductor from the window portion of the protective film. A nitride semiconductor having a low defect can be obtained.
[0004]
For example, Jpn. J. et al. Appl. Phys. Vol. 37 (1998) p. L309-L312 includes SiO2 on gallium nitride grown on a sapphire substrate.₂It is disclosed that a protective film such as the above is partially formed and gallium nitride is grown thereon. SiO₂Since gallium nitride does not grow directly on the protective film, gallium nitride having a low defect density can be grown on the protective film by lateral growth of gallium nitride grown from a portion without the protective film.
Therefore, according to the ELOG growth, the defect density in the low defect region can be reduced by two orders of magnitude or more compared to a nitride semiconductor grown using a conventional buffer layer.
[0005]
[Problems to be solved by the invention]
In such a method, although a nitride semiconductor substrate having a low defect in which threading dislocations are partially reduced can be obtained, a crystal defect propagated from a seed part is present at a junction between nitride semiconductors on a protective film. Since large crystal defects occur, device characteristics such as leakage and electrostatic breakdown are deteriorated.
In addition, SiO₂When the nitride semiconductor element is grown on the nitride semiconductor substrate having the protective film, the protective film may be decomposed. The decomposed Si, O, or the like contaminates the nitride semiconductor element and lowers the crystallinity.
Furthermore, it reacts with an etchant such as an etching gas or an acid at the time of forming the resonator surface or forming an electrode, and becomes a contamination source when it is formed into a chip, thereby reducing the life characteristics.
In addition, since the ELO method has large irregularities, it is difficult to create a device.
[0006]
Therefore, in view of the above circumstances, the present invention provides a method for growing a nitride semiconductor on a heterogeneous substrate, a method for growing a nitride semiconductor substrate that has good crystallinity, relaxes stress, and suppresses warpage of the substrate, and nitride semiconductor. The object is to provide a semiconductor device having a substrate.
[0007]
[Means for Solving the Problems]
(1) Growing a first nitride semiconductor layer on a heterogeneous substrate made of a material different from that of a nitride semiconductor, and then forming a protective film having a window on the first nitride semiconductor layer,SaidBy growing the second nitride semiconductor layer laterally from the window and stopping the growth in a state where the adjacent second nitride semiconductor layers are not joined together, and then removing the protective film,SaidFirst nitride semiconductor layerIs partExposureExposureForming partAs well as,SaidA cavity is formed under the laterally grown second nitride semiconductor layer.Forming,An exposed portion of the first nitride semiconductor layer; andSaidSecond nitride semiconductor layerFromA third nitride semiconductor layerGrowing and bonding the second nitride semiconductor layer laterally grown by the third nitride semiconductor layer and the first nitride semiconductor layer of the exposed portion to form a mirror surface on the substrate surface A method for manufacturing a nitride semiconductor substrate.
(2)(3) The third nitride semiconductor layer is grown below the second nitride semiconductor layer grown in the lateral direction after the third nitride semiconductor layer is grown. Of manufacturing a nitride semiconductor substrate.
(3) The distance between the second nitride semiconductor layers after lateral growth is not less than 1 μm and not more than 1000 μm.The method for producing a nitride semiconductor substrate according to (1) or (2)
(4) The protective film is formed in a stripe shape, a lattice shape, or an island shape.(1)-(3) The manufacturing method of the nitride semiconductor substrate.
(5) The protective film has a planar shape that is polygonal or circular.The manufacturing method of the nitride semiconductor substrate as described in (1)-(4).
(6) The planar shape of the protective film is a hexagon.(1)-(5) The manufacturing method of the nitride semiconductor substrate.
(7) The ratio Ws / Ww between the width (Ws) of the protective film and the width (Ww) of the window is 1000 or less.The manufacturing method of the nitride semiconductor substrate as described in (1)-(6).
(8) The protective film is made of at least one selected from the group consisting of silicon oxide, silicon nitride, titanium oxide, zirconium oxide, a metal having a melting point of 1200 ° C. or higher, and a multilayer film thereof.The manufacturing method of the nitride semiconductor substrate as described in (1)-(7).
(9) The protective film is removed by growing or etching the second nitride semiconductor layer until the first nitride semiconductor layer is exposed.The manufacturing method of the nitride semiconductor substrate as described in (1)-(8).
(10) In a state where the growth of the second nitride semiconductor layer is stopped, the shape of the second nitride semiconductor layer in the laterally grown portion has a taper type, a reverse taper type, a vertical type, or a polygon. It is trapezoid typeThe manufacturing method of the nitride semiconductor substrate as described in (1)-(9).
(11)On the nitride semiconductor substrate manufactured by the method according to any one of (1) to (10),At least an n-type nitride semiconductor, an active layer,as well asA nitride semiconductor device, wherein p-type nitride semiconductors are stacked.
  (12)On the nitride semiconductor substrate manufactured by the method according to any one of (1) to (10)At least an n-type nitride semiconductor, an active layer, and a p-type nitride semiconductor.LaminatedAndfurtherOptical waveguideBecomeStripe shape or ridge shape formedWasA nitride semiconductor laser device characterized by the above.
[0008]
That is, in the method of the present invention, the laterally grown portion of the nitride semiconductor is not bonded on the protective film, but the laterally grown second nitride semiconductor layer and the exposed portion of the first nitride semiconductor layer are Since the third nitride semiconductor layers grown from above are joined together and grown in the vertical direction, they are nitride semiconductors having a low-defect portion and eliminate crystal defects and undulations that occur at the junction between the lateral growths. be able to. Further, the restriction of the off angle between the crystal direction and the side direction of the protective film can be eliminated. Here, the swell is a step formed when the nitride semiconductors grown in the lateral direction are joined together. The cross-sectional shape of the joint is a step because of the difference in height, and the planar shape is not a stripe but a wave. If this undulation (step) is large, the influence is inherited to the formation of the nitride semiconductor device, and the characteristics of the nitride semiconductor device are deteriorated.
[0009]
In addition, the method of the present invention removes the protective film so that the nitride semiconductor device is grown later in the step of growing the nitride semiconductor device.₂Such a protective film decomposes during the reaction, contaminates the nitride semiconductor, lowers the crystallinity, and prevents the deterioration of the life characteristics due to the device etchant contamination.
Furthermore, since there is a cavity under the second nitride semiconductor layer grown laterally by removing the protective film, the second nitride semiconductor layer and the third nitride from the first nitride semiconductor layer are provided. The dislocation propagation in the vertical direction to the semiconductor layer can be suppressed, and the warpage of the substrate can be reduced.
[0010]
In the method of the present invention, since the distance between the laterally grown portions of the adjacent second nitride semiconductor layers is 1 to 1000 μm, the second nitride semiconductor layer is earlier than the growth of the third nitride semiconductor layer. It can prevent joining together. The distance between the laterally grown portions of the second nitride semiconductor layer can be rephrased as the distance between the pillar portions (vertically grown regions) of the second nitride semiconductor layer. In this case, an LD element can be formed in the laterally grown portion. Further, when forming an LD element, it is sufficient that at least a ridge region (that is, a waveguide region) is formed in a laterally grown portion, and the above range may be 100 μm.
[0011]
In addition, the shape of the protective film is as described above, and if the ratio of the width of the protective film (Ws) to the width of the window (Ww) is within the above range, a low defect due to lateral growth is formed on the protective film. It is possible to reduce the number of defect dislocations from the window portion.
[0012]
Moreover, dry etching or wet etching can be used as a method for removing the protective film, and these methods remove the protective film until the nitride semiconductor is exposed without reducing the crystallinity of the nitride semiconductor. The depth to be removed can be easily and accurately controlled. By this control, the protective film can be left with a film thickness of 1 μm or less, and further, the protective film can be left under the lateral growth of the second nitride semiconductor layer. Thus, after the third nitride semiconductor layer is grown, a protective film and a cavity can be provided under the laterally grown second nitride semiconductor layer.
[0013]
In the present invention, a nitride semiconductor obtained by the nitride semiconductor growth method of the present invention is used as a substrate, and at least an n-type nitride semiconductor, an active layer, and a p-type nitride semiconductor forming an element structure are formed thereon. By doing so, a nitride semiconductor device with good lifetime characteristics can be obtained.
Furthermore, in the present invention, a laser device having good lifetime characteristics can be manufactured by forming an optical waveguide of a nitride semiconductor laser device having a ridge-shaped stripe on a second nitride semiconductor layer grown in the lateral direction. it can.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
As an embodiment of the nitride semiconductor growth method of the present invention, first, in a first step, a first nitride semiconductor layer 2 is grown on a heterogeneous substrate 1 and a protective film having a window portion thereon. In the second step, the second nitride semiconductor layer is grown in the lateral direction from the window, and the growth is stopped in a state where the second nitride semiconductor layers grown in the lateral direction are not joined together, Subsequently, in the third step, the protective film is removed to expose the first nitride semiconductor layer, and there is a cavity under the laterally grown second nitride semiconductor layer, and in the fourth step, A third nitride semiconductor layer is grown from the exposed portion of the first nitride semiconductor layer and the second nitride semiconductor layer, so that the second nitride semiconductor layer grown in the lateral direction and the exposed first nitride semiconductor layer are exposed. Nitride semiconductor layer is bonded to grow a nitride semiconductor substrate having a mirror surface It can be.
[0016]
Below, it demonstrates in detail for every said process.
(First step)
FIG. 1 is a schematic cross-sectional view in which a first step of growing a first nitride semiconductor layer 2 on a heterogeneous substrate 1 and forming a protective film 3 having a window portion thereon is performed.
In the first step, as a heterogeneous substrate that can be used, sapphire (Al) whose main surface is any one of the C-plane, R-plane, and A-plane is used.₂O₃), Spinel (MgAl₂O₄Insulating substrate such as SiC (including 6H, 4H, and 3C), ZnS, ZnO, GaAs, Si, and an oxide substrate that is lattice-bonded to a nitride semiconductor. This heterogeneous substrate may be removed before and after the formation of the nitride semiconductor device. Further, a bulk crystal such as GaN can be used as the substrate.
[0017]
Next, a buffer layer (not shown) is grown on the heterogeneous substrate 1 by MOCVD. This buffer layer has an effect of relaxing the lattice constant irregularity and the difference in thermal expansion coefficient with the nitride semiconductor grown on the heterogeneous substrate 1. Specific examples include AlN, GaN, AlGaN, and InGaN, and the growth temperature is not particularly limited, but is preferably 300 ° C. or higher and 900 ° C. or lower.
The buffer layer is grown to a thickness of 10 angstroms to 0.5 μm. The first nitride semiconductor may be omitted depending on the nitride semiconductor growth method and the type of substrate.
[0018]
Next, the first nitride semiconductor layer 2 to be grown thereon is doped with undoped GaN, GaN doped with at least one of Si, Ge, Sn and S as n-type impurities, or p-type impurities. GaN or the like can be used. The first nitride semiconductor layer 2 is grown on the heterogeneous substrate 1 at a temperature higher than that of the buffer layer and at 900 ° C. to 1100 ° C., preferably about 1050 ° C. The film thickness of the first nitride semiconductor 2 is not particularly limited, and is 1 to 30 μm, preferably 2 to 20 μm.
[0019]
Thereafter, protective film 3 having a window portion is formed on the surface of first nitride semiconductor layer 2. The shape of the protective film 3 may be a stripe shape, a lattice shape, an island shape, and a planar shape as long as the nitride semiconductor grows laterally from the window portion of the protective film and reduces crystal defects of the nitride semiconductor. However, there are polygons and circles, and hexagonal patterns that allow easy crystal growth can be used.
[0020]
As a material of the protective film 3, a material having a property that a nitride semiconductor does not grow or is difficult to grow on the surface of the protective film is selected._x), Silicon nitride (Si_xN_y), Silicon nitride oxide (SiON), titanium oxide (TiO 2)_x), Zirconium oxide (ZrO)_xIn addition to oxides, nitrides, and multilayer films of these, metals having a melting point of 1200 ° C. or higher can be used.
[0021]
The width of the protective film 3 is 5-1000 μm, the width of the protective film window is 1-1000 μm, and the ratio Ws / Ww of the protective film width (Ws) to the window width (Ww) is 1000 or less. And preferably 0.005 to 1000, more preferably 0.01 to 500, and most preferably 1 to 20.
[0022]
Further, the thickness of the protective film is not particularly limited as long as the nitride semiconductor can be grown in the lateral direction on the protective film. Therefore, the preferable film thickness is 0.1 to 3 μm, more preferably 0.3 to 1 μm.
Here, the protective film 3 can be formed using, for example, CVD, vapor deposition, or sputtering. The protective film 3 can be selectively formed in a predetermined region by forming a photoresist having a predetermined shape.
[0023]
When the protective film 3 is formed in the above range, a nitride semiconductor substrate whose uppermost surface is a mirror surface can be grown in a later step.
The growth rate of the nitride semiconductor grown on the protective film can be controlled by the thickness of the protective film.
[0024]
(Second step)
Next, as shown in FIG. 2, the second nitride semiconductor 4 is grown laterally from the window portion of the protective film 3, and the growth is stopped in a state where the adjacent second nitride semiconductors are not joined together. .
As the second nitride semiconductor 4, for example, undoped GaN, n-type impurities such as Si, GaN doped with p-type impurities, or GaN doped with p-type impurities such as Mg can be used. The film thickness of the second nitride semiconductor 4 is not particularly limited as long as the uppermost surface is a mirror surface, and is 1 to 50 μm, preferably 3 to 20 μm.
[0025]
In addition, if the distance between the second nitride semiconductor layers in the laterally grown portion is 1 to 1000 μm, the adjacent second nitride semiconductor layers are joined together by the growth of the nitride semiconductor in a later step. Can be prevented.
[0026]
(Third step)
Next, as shown in FIG. 3, the protective film 3 is removed so that the first nitride semiconductor layer 2 is exposed.
If nitride semiconductor elements or the like for forming a laser are stacked in a later process with this protective film left, contamination of the nitride semiconductor due to decomposition of the protective film, and crystallinity may be reduced. It is most preferable to completely remove the protective film. For example, the protective film may remain somewhat if it is durable at high temperature, does not decompose, and is not contaminated in the device process.
[0027]
(Fourth process)
Next, as shown in FIG. 7, a nitride semiconductor substrate is formed by growing a third nitride semiconductor layer from the exposed portion of the first nitride semiconductor layer and the second nitride semiconductor layer.
In the third nitride semiconductor layer 5, the nitride semiconductor grown from the exposed portion of the first nitride semiconductor layer and the nitride semiconductor grown from the second nitride semiconductor layer 4 in the laterally grown portion are joined. It is formed by. That is, if the adjacent second nitride semiconductor layers 4 grow directly bonded to each other, or the third nitride semiconductor layers 5 grown from the exposed first nitride semiconductor layer 2 directly bond to each other. The third nitride semiconductor layer 5 is selectively formed after the nitride semiconductor grown from the second nitride semiconductor layer 4 and the nitride semiconductor grown from the first nitride semiconductor layer 2 are joined. By growing in the vertical direction, the third nitride semiconductor layer is formed as a nitride semiconductor substrate having a mirror surface.
Further, after the third nitride semiconductor layer 5 is grown, warping of the substrate can be reduced if the shape has a cavity under the laterally grown portion of the second nitride semiconductor layer.
[0028]
The third nitride semiconductor layer 5 is not particularly limited in the same manner as the first nitride semiconductor layer 2 and the second nitride semiconductor layer 4, and has the general formula In_xAl_yGa_1-xyN (0 ≦ x, 0 ≦ y, x + y ≦ 1).
[0029]
The film thickness of the third nitride semiconductor 5 is 5 to 40 μm, preferably 10 to 20 μm. Within this range, warpage of the wafer due to a difference in thermal expansion coefficient between the substrate and the nitride semiconductor can be prevented, and a good nitride semiconductor element can be grown on this substrate.
[0030]
The third nitride semiconductor 5 obtained by the above process is a nitride semiconductor substrate having a top surface as a mirror surface and having a wide range of low-defect portions with suppressed warpage of the substrate.
[0031]
In the present invention, the first nitride semiconductor layer 2, the second nitride semiconductor layer 4, and the third nitride semiconductor layer 5 are all represented by the general formula In._xAl_yGa_1-xyN (0 ≦ x, 0 ≦ y, x + y ≦ 1). However, these may have different compositions, or may be nitride semiconductors doped with undoped, n-type impurities, or p-type impurities. Examples of the n-type impurity include Si, Ge, and S, and examples of the p-type impurity include Mg, Be, Cr, Mn, Ca, and Zn.
[0032]
In the method for growing a nitride semiconductor according to the present invention, a method for growing a nitride semiconductor such as the first nitride semiconductor layer, the second nitride semiconductor layer, and the third nitride semiconductor layer is not particularly limited. However, methods such as MOVPE (metal organic chemical vapor deposition), HVPE (halide vapor deposition), MBE (molecular beam epitaxy), MOCVD (metal organic chemical vapor deposition) can be applied.
[0033]
As an etching method for removing the protective film, there are methods such as wet etching and dry etching, and dry etching is preferably used to form a smooth surface. Dry etching includes, for example, isotropic plasma etching, reactive ion etching (RIE), reactive ion beam etching (RIBE), electron cyclotron etching (ECR), etc., all of which appropriately select an etching gas. Thus, the nitride semiconductor can be etched.
[0034]
【Example】
Although the Example of this invention is shown below, this invention is not limited to this.
[Example 1]
Each process in Example 1 is shown using FIGS. Moreover, although Example 1 uses the MOCVD method, it is not particularly limited as long as it is a method capable of growing a nitride semiconductor.
[0035]
As the heterogeneous substrate 1, a sapphire substrate with the C-plane as the main surface and the orientation flat surface as the A-plane is set in a reaction vessel, the temperature is set to 510 ° C., the carrier gas is hydrogen, the source gas is ammonia and TMG (trimethyl). A buffer layer (not shown) made of GaN is grown on the sapphire substrate to a thickness of 200 Å.
[0036]
After growing the buffer layer, only TMG is stopped, the temperature is increased to 1050 ° C., and when it reaches 1050 ° C., TMG and ammonia are used as the source gas, and the first nitride semiconductor layer 2 made of undoped GaN is 2.5 μm. Growing with a film thickness of
[0037]
After the growth of the first nitride semiconductor layer 2, the wafer is taken out of the reaction vessel, and a SiO 2 having a stripe width of 14 μm and a stripe interval (window portion) of 6 μm is formed on the surface of the first nitride semiconductor 2 by a CVD apparatus.₂A protective film 3 is formed with a thickness of 0.4 μm.
[0038]
Thereafter, the wafer is set again in a MOCVD reaction vessel, the temperature is set to 1050 ° C., ammonia is 0.27 mol / min, and TMG is 225 μmol / min (V / III ratio = 1200). The nitride semiconductor layer 4 is grown to a thickness of 20 μm.
At this time, the second nitride semiconductor layer 4 is laterally grown on the protective film 3, but the growth is stopped midway so that the second nitride semiconductor layers are not joined to each other on the protective film 3. The distance between the second nitride semiconductor layers 4 grown on the protective film 3 is 20 μm.
[0039]
Next, the protective film 3 is completely removed by wet etching to expose the first nitride semiconductor layer 2.
[0040]
Next, after removing the protective film 3, the wafer is transferred to a reaction vessel, and TMG and ammonia are used as source gases at 1050 ° C. to expose the second nitride semiconductor layer 4 and the first nitride semiconductor layer 2. A third nitride semiconductor 5 is grown from the portion.
The film thickness of the third nitride semiconductor layer 5 is 15 μm.
[0041]
The surface of the obtained third nitride semiconductor layer 5 becomes a mirror surface, and a nitride semiconductor having a low defect portion and suppressing warpage can be provided.
[0042]
[Example 2]
In Example 1, the same process is performed except that only the protective film 3 under the window portion of the adjacent second nitride semiconductor layers is removed until the first nitride semiconductor layer is exposed in the step of removing the protective film 3. A nitride semiconductor substrate is grown.
The resulting nitride semiconductor substrate has a protective film under the laterally grown second nitride semiconductor layer, but the nitride semiconductor is not bonded on the protective film during the growth of the third nitride semiconductor layer. Therefore, it is possible to eliminate a larger defect that occurs in the joint, and it is possible to eliminate the restriction of the off angle.
[0043]
[Example 3]
In Example 1, a nitride semiconductor substrate is grown in the same manner except that a silane gas is used during the growth of the third nitride semiconductor layer 5 and an Si-doped n-type nitride semiconductor substrate is used.
The resulting nitride semiconductor substrate is a good surface state similar to that of Example 1, and is a substrate with low defects and reduced warpage.
[0044]
[Example 4]
In Example 1, the protective film 3 is formed in a hexagonal shape, and a nitride semiconductor is grown in the same manner except that the second nitride semiconductor layer 4 is laterally grown. Similar to Example 1, the nitride semiconductor substrate has low defects and suppresses warpage of the substrate.
[0045]
[Example 5]
Example 5 uses the MOCVD method, but is not particularly limited as long as it is a method capable of growing a nitride semiconductor. As the heterogeneous substrate 1, a sapphire substrate with the C-plane as the main surface and the orientation flat surface as the A-plane is set in a reaction vessel, the temperature is set to 510 ° C., hydrogen as the carrier gas, ammonia and TMG (trimethyl) as the source gas A buffer layer (not shown) made of GaN is grown on the sapphire substrate to a thickness of 200 Å. After growing the buffer layer, only TMG is stopped, the temperature is increased to 1050 ° C., and when it reaches 1050 ° C., TMG and ammonia are used as the source gas, and the first nitride semiconductor layer 2 made of undoped GaN is 2.5 μm. Growing with a film thickness of
[0046]
After the growth of the first nitride semiconductor layer 2, the wafer is taken out of the reaction vessel, and a SiO film having a protective film stripe width of 25 μm and a stripe interval (window portion) of 5 μm is formed on the surface of the first nitride semiconductor 2 by a CVD apparatus.₂A protective film 3 is formed to a thickness of 0.3 μm.
[0047]
Thereafter, the wafer is set again in a MOCVD reaction vessel, the temperature is set to 1050 ° C., ammonia is 0.27 mol / min, and TMG is 225 μmol / min (V / III ratio = 1200). The nitride semiconductor layer 4 is grown to a thickness of 7 μm. At this time, the second nitride semiconductor layer 4 is laterally grown on the protective film 3, but the growth is stopped midway so that the second nitride semiconductor layers are not joined to each other on the protective film 3. The distance between the second nitride semiconductor layers 4 grown on the protective film 3 is 7 μm.
[0048]
Next, the surface of the second nitride semiconductor layer and the protective film 3 is removed using chlorine gas by an RIE apparatus. Etching is stopped when the thickness of the second nitride semiconductor layer is 2 μm, and then the protective film is completely removed to expose the first nitride semiconductor layer 2.
[0049]
After removing the protective film 3, the wafer is transferred to a reaction vessel, and at 1050 ° C., TMG and ammonia are used as source gases, and the second nitride semiconductor layer 4 and the first nitride semiconductor layer 2 are exposed from the exposed portion. 3 nitride semiconductor 5 is grown. The film thickness of the third nitride semiconductor layer 5 is 15 μm, and the surface of the obtained third nitride semiconductor layer 5 is a mirror surface.
[0050]
The nitride semiconductor substrate obtained as described above has a dislocation defect of 5 × 10 5 by CL measurement.⁶Piece / cm²As described below, a nitride semiconductor substrate having low defects and suppressing dislocation propagation and warping because the substrate has a cavity can be provided.
[0051]
[Example 6]
In Example 5, a nitride semiconductor substrate is formed under the same conditions except that only the protective film in the surface exposed region is removed after the second nitride semiconductor layer is grown in the lateral direction. The third nitride semiconductor layer is grown using the exposed first nitride semiconductor layer and second nitride semiconductor layer as growth starting points, and the resulting nitride semiconductor substrate exhibits substantially the same characteristics as in the fifth embodiment.
[0052]
[Example 7]
Example 5 showing the structure of a laser device using the nitride semiconductor obtained in Example 1 as a substrate will be described below.
[0053]
(Undoped n-type contact layer 101)
The wafer obtained in Example 1 was set in a reaction vessel of an MOCVD apparatus, and TMG (trimethylgallium), TMA (trimethylaluminum), ammonia was used as a nitride semiconductor at 1050 ° C., and Al was used._0.05Ga_0.95An undoped n-type contact layer 101 made of N is grown to a thickness of 1 μm. This layer functions as a buffer layer between the nitride semiconductor substrate made of GaN and the semiconductor element including the n-type contact layer.
[0054]
(N-type contact layer 102)
Next, TMG, TMA, ammonia, Si-doped Al at 1050 ° C. using TMG, TMA, ammonia and silane gas as impurity gas on the obtained buffer layer 101_0.05Ga_0.95An n-type contact layer 102 made of N is grown to a thickness of 4 μm.
[0055]
(Crack prevention layer 103)
Next, using TMG, TMI (trimethylindium), and ammonia, the temperature is set to 900 ° C. and In_0.07Ga_0.93A crack prevention layer 103 made of N is grown to a thickness of 0.15 μm. This crack prevention layer can be omitted.
[0056]
(N-type cladding layer 104)
Next, the temperature is set to 1050 ° C., TMA, TMG, and ammonia are used as source gases, and undoped Al_0.05Ga_0.95A layer of N is grown to a thickness of 25 mm, then TMA is stopped, silane gas is used as impurity gas, and Si is 5 × 10 5¹⁸/ Cm³A B layer made of doped GaN is grown to a thickness of 25 mm. This operation is repeated 200 times to form a laminated structure of the A layer and the B layer, and an n-type cladding layer made of a multilayer film (superlattice structure) having a total film thickness of 1 μm is grown.
[0057]
(N-type guide layer 105)
Next, at the same temperature, an n-type guide layer 105 made of undoped GaN is grown to a thickness of 0.15 μm using TMG and ammonia as source gases. The n-type guide layer 105 may be doped with n-type impurities.
[0058]
(Active layer 106)
Next, the temperature is set to 900 ° C., TMI (trimethylindium), TMG, and ammonia are used as source gas, silane gas is used as impurity gas, and Si is 5 × 10 5.¹⁸/ Cm³Doped In_0.05Ga_0.95The barrier layer made of N is 140 mm thick, the silane gas is stopped, and undoped In_0.13Ga_0.87A well layer made of N is stacked in a thickness of 40 mm in the order of barrier layer / well layer / barrier layer / well layer, and finally, TMI, TMG and ammonia are used as a barrier layer, and undoped In_0.05Ga_0.95Grow N. The active layer 106 has a multiple quantum well structure (MQW) with a total film thickness of 500 mm.
[0059]
(P-type electron confinement layer 107)
Next, at the same temperature as the active layer, TMA, TMG and ammonia are used as source gases and Cp is used as impurity gas.₂Mg (cyclopentadienylmagnesium) is used and Mg is 1 × 10¹⁹/ Cm³Doped Al_0.3Ga_0.7A p-type electron confinement layer 107 made of N is grown to a thickness of 100 mm.
[0060]
(P-type guide layer 108)
Next, the temperature is set to 1050 ° C., TMG and ammonia are used as the source gas, and the p-type guide layer 108 made of undoped GaN is grown to a thickness of 0.15 μm. This p-type guide layer may be doped with p-type impurities.
[0061]
(P-type cladding layer 109)
Next, undoped Al at 1050 ° C._0.05Ga_0.95A layer of N is grown to a thickness of 25 mm, then TMA is stopped, Cp₂Using Mg, a B layer made of Mg-doped GaN is grown to a thickness of 25 mm, and this is repeated 90 times to grow a p-type cladding layer 109 made of a superlattice layer having a total thickness of 0.45 μm. The p-type cladding layer has a superlattice structure in which GaN and AlGaN are stacked. By making the p-type cladding layer 109 a superlattice structure, the Al mixed crystal ratio of the entire cladding layer can be increased, so that the refractive index of the cladding layer itself is reduced and the band gap energy is increased. It is very effective in reducing the value.
[0062]
(P-type contact layer 110)
Finally, at 1050 ° C., on the p-type cladding layer 109, TMG, ammonia, Cp₂Mg is used, and Mg is 1 × 10²⁰/ Cm³A p-type contact layer 110 made of doped p-type GaN is grown to a thickness of 150 mm.
After the completion of the reaction, the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.
[0063]
After the annealing, the nitride semiconductor laminated wafer is taken out of the reaction vessel, and the top surface of the p-type contact layer is made of SiO.₂A protective film is formed, and SiCl is formed using RIE (reactive ion etching).₄Etching with a gas exposes the surface of the n-type contact layer 102 where the n-electrode is to be formed.
[0064]
Next, SiO₂A protective film is formed and CF is used using RIE.₄Etching with gas forms a ridge stripe as a striped waveguide region.
[0065]
Next, after ridge stripe formation, Zr oxide (mainly ZrO₂Is formed on the p-type guide layer 108 exposed by etching to a thickness of 0.5 μm.
[0066]
A p-type electrode is formed from Ni and Au on the p-type contact layer, and an n-type electrode is formed from Ti and Al on the n-type contact layer exposed by etching. The p-electrode is formed in stripes on the ridge, and is formed in a direction parallel to the n-electrodes that are also formed in stripes.
[0067]
Next, SiO₂And TiO₂Then, a pad electrode made of Ni—Ti—Au (1000Ｔｉ-1000Å-8000Å) was provided on each of the p and n electrodes. At this time, SiO is also applied to the resonator surface (reflection surface side).₂And TiO₂A dielectric multilayer film is provided.
[0068]
The laser element obtained as described above has a threshold value of 2.8 kA / cm at room temperature.²Thus, a continuous wave laser element with an oscillation wavelength of 405 nm can be obtained at an output of 5 to 30 mW. The element lifetime of the obtained laser element is 3000 to 20000 hours.
[0069]
【The invention's effect】
INDUSTRIAL APPLICABILITY The present invention can provide a method for growing a nitride semiconductor with good crystallinity in which warpage and undulation of the substrate are suppressed and dislocations of crystal defects are reduced.
Further, by using the nitride semiconductor obtained according to the present invention as a substrate and growing the element structure, a nitride semiconductor having good element performance such as life characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a nitride semiconductor showing an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view of a nitride semiconductor showing an embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view of a nitride semiconductor showing one embodiment of the present invention.
FIG. 4 is a schematic cross-sectional view of a nitride semiconductor showing an embodiment of the present invention.
FIG. 5 is a schematic cross-sectional view of a nitride semiconductor showing one embodiment of the present invention.
FIG. 6 is a schematic cross-sectional view of a nitride semiconductor showing one embodiment of the present invention.
FIG. 7 is a schematic cross-sectional view of a nitride semiconductor showing one embodiment of the present invention.
[Brief description of symbols]
1 ... Different substrates
2... First nitride semiconductor layer
3 ... Protective film
4 ... Second nitride semiconductor layer
5 ... Third nitride semiconductor layer
101: Undoped n-type contact layer
102: n-type contact layer
103 ... Crack prevention layer
104 ... n-type cladding layer
105 ... n-type guide layer
106 ... Active layer
107 ... p-type electron confinement layer
108 ... p-type guide layer
109 ... p-type cladding layer
110 ... p-type contact layer

Claims (12)

Growing a first nitride semiconductor layer on a heterogeneous substrate made of a different material from the nitride semiconductor;
Thereafter, a protective film having a window is formed on the first nitride semiconductor layer,
Wherein the second nitride semiconductor layer from the window portion is grown in the lateral direction, and stop growing in the state in which the second nitride semiconductor layer adjacent to each other is not Awa joined,
Thereafter, by removing the protective layer, together with the first nitride semiconductor layer forms an exposed portion exposed portion to form a cavity under the second nitride semiconductor layer above the lateral growth,
Wherein the first exposed portion of the nitride semiconductor layer and the second nitride semiconductor layer is grown a third nitride semiconductor layer,
The second nitride semiconductor layer laterally grown by the third nitride semiconductor layer and the first nitride semiconductor layer in the exposed portion are joined to form a mirror surface on the substrate surface. A method for manufacturing a nitride semiconductor substrate. The third nitride semiconductor layer is grown below the second nitride semiconductor layer grown in the lateral direction after the third nitride semiconductor layer is grown. Of manufacturing a nitride semiconductor substrate. 3. The method for manufacturing a nitride semiconductor substrate according to claim 1 , wherein a distance between adjacent ones of the second nitride semiconductor layers after lateral growth is 1 μm or more and 1000 μm or less. 4. The method of manufacturing a nitride semiconductor substrate according to claim 1 , wherein the protective film is formed in a stripe shape, a lattice shape, or an island shape. 5. 5. The method for manufacturing a nitride semiconductor substrate according to claim 1 , wherein the protective film has a polygonal or circular planar shape. 6. The method for manufacturing a nitride semiconductor substrate according to claim 1, wherein the protective film has a hexagonal planar shape. The nitride semiconductor substrate according to any one of claims 1 to 6, wherein a ratio Ws / Ww between the width (Ws) of the protective film and the width (Ww) of the window portion is 1000 or less. Manufacturing method . The protective layer may be silicon oxide, silicon nitride, titanium oxide, zirconium oxide, melting point 1200 ° C. or more metals, and to claim 1, characterized in that comprises at least one selected from the group consisting of multilayer films 8. The method for manufacturing a nitride semiconductor substrate according to claim 7 . The protective film of any one of claims 1 to 8, characterized in that it is removed by etching or stripping until after growing a second nitride semiconductor layer, the first nitride semiconductor layer is exposed A method for producing a nitride semiconductor substrate as described in 1. above . In a state where the growth of the second nitride semiconductor layer is stopped, the shape of the second nitride semiconductor layer in the laterally grown portion is a taper type, a reverse taper type, a vertical type, or a trapezoidal type having a polygon. The method for manufacturing a nitride semiconductor substrate according to claim 1, wherein the method is provided . 11. At least an n-type nitride semiconductor, an active layer, and a p-type nitride semiconductor are stacked on the nitride semiconductor substrate manufactured by the method according to any one of claims 1 to 10. A featured nitride semiconductor device. At least an n-type nitride semiconductor, an active layer, and a p-type nitride semiconductor are stacked on the nitride semiconductor substrate manufactured by the method according to any one of claims 1 to 10 , and an optical waveguide nitride semiconductor laser device, wherein a stripe shape or a ridge shape which is formed.

Images