JP2002313739A - Nitride semiconductor substrate and its growth method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor substrate wherein a thick nitride semiconductor film can be grown on a substrate and generation of penetrating dislocation is reduced. SOLUTION: In a method for growing nitride semiconductor on a substrate, at least two growing interfaces are formed in the nitride semiconductor, thereby relieving difference of stress between the substrate and the nitride semiconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light emitting diode,
Light-emitting devices such as laser diodes or solar cells, light-receiving element, or an electronic device gallium nitride compound is used in a semiconductor device such as an optical sensor (In _x Al _y G
The present invention relates to a gallium nitride-based compound semiconductor substrate having a _1-xy N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and a method for growing the same.

[0002]

2. Description of the Related Art In recent years, attention has been paid to white light emitting diodes (LEDs) and semiconductor lasers (LDs) using a nitride semiconductor substrate and having a short wavelength from blue to ultraviolet.
There is an increasing demand for semiconductor lasers for use in disk systems, such as DVDs, capable of recording and reproducing high-capacity, high-density information. Therefore, such an LED
Various methods have been studied for obtaining single-crystal nitride semiconductor substrates that are expected to be applied to light-receiving elements and electronic devices in addition to applications to LDs and the like.

As the nitride semiconductor substrate, for example, GaN
Although there are high pressure methods and the like as a method for obtaining sucrose from a bulk single crystal, it has not been put to practical use. Therefore, a substrate such as sapphire, which is different from the nitride semiconductor, is used, and a nitride semiconductor is grown on this substrate to form a nitride semiconductor substrate.
It is used for EDs, LDs, and electronic devices.

In order to form a nitride semiconductor substrate, when a nitride semiconductor is directly grown on a substrate due to a lattice constant difference between the substrate and the nitride semiconductor, threading dislocations are generated at about 10 ¹⁰ cm ⁻² . When a semiconductor device such as an LED or LD is grown on such a nitride semiconductor substrate having poor crystallinity, the life characteristics and device characteristics are poor. A method of growing a buffer layer made of a nitride semiconductor at a low temperature is used. By growing this buffer layer, threading dislocations were reduced to 10 ⁸ cm ⁻² , and a flat, mirror-finished nitride semiconductor substrate could be grown.

[0005] surface of the nitride semiconductor substrate 10 ⁸ cm
If threading dislocations of about ^-2 exist, the threading dislocations propagate to an active layer or the like in a semiconductor laser device grown on a nitride semiconductor substrate, so that a decrease in crystallinity only adversely affects the life characteristics. In addition, since the hole mobility is small, the electric characteristics are also deteriorated.

[0006] Therefore, further threading dislocations 10 ⁸ cm
ELOG (Epitaxially Laminated) using a method of growing a nitride semiconductor laterally on a substrate in order to reduce it to ^-2 or less.
teral OverGrowth GaN) growth method has been reported. In this method, a protective film having a window serving as an opening is formed in a nitride semiconductor, a nitride semiconductor is grown from the window, and a nitride semiconductor is grown on the protective film by growing the nitride semiconductor. By growing laterally, a nitride semiconductor is bonded on the protective film, and a low-dislocation nitride semiconductor substrate can be obtained. This is because the threading dislocations generated in the region where the nitride semiconductor grows progress in the vertical and horizontal directions together with the growth of the nitride semiconductor from the window of the protective film, and the threading in the laterally grown nitride semiconductor grows. Since the dislocations converge at the junction, threading dislocations on the surface of the growth region of the laterally grown nitride semiconductor are reduced to about 10 ⁶ cm ⁻² .

In this ELOG growth method, although the threading dislocations are small in the region grown in the lateral direction, threading dislocations are large in the window of the protective film, and there is a region where the crystallinity is not good on the entire surface of the nitride semiconductor substrate. It is expected that the threading dislocations are uniformly reduced on the entire surface of the nitride semiconductor substrate.

[0008] A hydride vapor phase epitaxy method is a vapor phase epitaxial growth method capable of growing a thick film at a high growth rate. This hydride vapor phase epitaxial growth method is characterized in that the growth rate is higher than that of other metal organic chemical vapor deposition (MOCVD) methods and the like, and a bulk single crystal having a thickness of several tens to several hundreds μm can be obtained. Therefore, a substrate in which a thick film is grown by the hydride vapor phase epitaxial growth method to uniformly reduce threading dislocations generated on the surface of the nitride semiconductor is expected.

[0009]

However, a nitride semiconductor substrate obtained by growing a nitride semiconductor on a substrate such as sapphire in a thick film by the hydride vapor phase epitaxial growth method described above causes cracking. For this reason, a nitride semiconductor substrate having a thick film grown thereon cannot be formed on one wafer.
You have to use divided or three-divided wafers,
The use of divided wafers increases the number of processes as compared with the use of one wafer, and lowers the overall yield. In addition, the characteristics of the nitride semiconductor device may be degraded due to cracking. Therefore, the present invention solves such a problem and, despite being a nitride semiconductor substrate having a thick film grown on the substrate, does not generate cracks and the like, and a nitride semiconductor which has reduced threading dislocations simultaneously with the thick film growth. A substrate is provided.

[0010]

In order to achieve the above object, a nitride semiconductor substrate according to the present invention is a nitride semiconductor substrate obtained by growing a nitride semiconductor on a substrate, wherein the nitride semiconductor A nitride semiconductor substrate provided with at least two craters or a growth interface having a convex slope.

[0011] The nitride semiconductor substrate is characterized in that a growth interface is formed by the continuous presence of the convex slope.

The method for growing a nitride semiconductor substrate according to the present invention is a method for growing a nitride semiconductor substrate on a substrate by using a vapor phase epitaxial growth method. A nitride semiconductor layer and a second nitride semiconductor layer grown thereon, having a crater or a convex slope at the interface between the first nitride semiconductor layer and the second nitride semiconductor layer A method for growing a nitride semiconductor substrate comprising a step of forming a growth interface.

In the method for growing a nitride semiconductor substrate, a nucleus or a layer made of a nitride semiconductor is grown on the substrate as an underlayer, and the first nitride semiconductor layer is grown through the underlayer. It is characterized by making it.

The method for growing a nitride semiconductor substrate has at least two or more steps of forming the growth interface.

The method for growing a nitride semiconductor substrate is characterized in that it is a hydride vapor phase epitaxial growth method.

Here, if the substrate is a dissimilar substrate different from the nitride semiconductor, sapphire, SiC (6H, 4H, 3C), spinel, Examples include ZnS, ZnO, Si, and GaAs.
Moreover, the general formula as gallium nitride _In x _Al y Ga
_{1−x + y} N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ X + Y ≦
The nitride semiconductor shown in 1) can be used as the substrate. The size when the substrate is used as a wafer is not particularly limited, but a substrate having a diameter of 1 to 5 inches is used, and the substrate may have any thickness as long as it can be formed into chips by cleavage or dicing. Specifically, the thickness of the substrate is 0.1 mm or more. These substrates have a flat surface, but if a nucleus or a layer made of a nitride semiconductor can be grown, for example, a substrate having fine roughness by etching or the like, or a growth surface of the nitride semiconductor of the substrate may be used. The substrate may have irregularities, slopes, or steps, or may have irregularities, grooves, and the like on the back surface with respect to the nitride semiconductor growth surface of the substrate.

The crater according to the present invention is a polygonal pyramidal or conical depression formed on the plane of the surface after the growth of the first nitride semiconductor layer. The size and depth of the depression are 5 μm or more and 100 μm or less,
This depth is the height difference of the growth interface at the same growth interface.

In the present invention, the convex slope means a surface having a height difference from a horizontal plane after growing the first nitride semiconductor layer. The convex slope may have a wave-like or dot-like convex portion with respect to the horizontal plane.

The growth interface in the present invention means that a crater or a convex slope is formed after the growth of the first nitride semiconductor layer described above, and then the second nitride is formed on the first nitride semiconductor layer. 2 shows an interface between a first nitride semiconductor layer and a second nitride semiconductor layer formed after growing a semiconductor layer. This growth interface shows a height difference of the crater, and this height difference is 5 μm or more and 100 μm or less. Further, the height difference at the growth interface is preferably formed continuously.

By using the nitride semiconductor substrate and the method for growing a nitride semiconductor substrate described above, a uniform crystalline non-uniform interface within the same composition can be formed on the growth interface formed in the nitride semiconductor. By having this, the stress is relaxed, and a nitride semiconductor can be grown on the substrate with a thickness of 30 μm or more as a specific example. Further, since the growth interface forms a continuous slope, threading dislocations are formed on the slope. The dislocation direction is bent,
The bent threading dislocations are focused in the nitride semiconductor grown on the growth interface, and threading dislocations can be reduced.

With the above-described height difference of the growth interface, the surface of the growth interface is inclined with respect to the horizontal plane, so that the traveling direction of threading dislocation can be changed. As shown in FIG. 3, the threading dislocations in which the traveling direction is bent form defect loops between the bent threading dislocations, and the threading dislocations can be reduced during the growth of the nitride semiconductor.

Further, by repeating the step of forming the growth interface of the nitride semiconductor, threading dislocations can be further reduced. In a nitride semiconductor substrate having two growth interfaces, the threading dislocation density per unit area can be reduced. 1 × 10 ⁶ / c
m ² , preferably 7 × 10 ⁵ / cm ² . This nitride semiconductor substrate does not selectively form a region having good crystallinity, but can uniformly reduce the entire surface of the nitride semiconductor substrate to low dislocations. Therefore, a stable low dislocation substrate is provided. Can be. Further, by having two growth interfaces, it is possible to disperse the stress generated between the substrate such as sapphire and the nitride semiconductor. This stress is a difference in thermal expansion coefficient, and the stress cannot be sufficiently reduced only by the growth interface between the substrate and the nitride semiconductor. Therefore, the nitride semiconductor substrate is warped, and further, cracks and chips are generated. Therefore, such a problem is solved by forming at least two growth interfaces in the nitride semiconductor. Since this growth interface converges threading dislocations, a portion having weak crystallinity, that is, threading dislocations, is present at the growth interface, and tensile strain or the like, which is a stress, can be reduced here. In the case of growing a thick film of 50 μm or more on a substrate, by having two growth interfaces,
It is possible to gradually reduce the warpage of the nitride semiconductor substrate and the stress between the substrate and the nitride semiconductor, thereby allowing the nitride semiconductor to grow on the substrate in a thick film.

As described above, according to the present invention, when a nitride semiconductor is grown on a substrate such as sapphire in a particularly thick film, the nitride semiconductor substrate may be cracked due to a difference in thermal expansion between the substrate and the nitride semiconductor. Although chipping occurs, stress can be relaxed by having a growth interface not only at the interface between the substrate and the nitride semiconductor but also within the nitride semiconductor, and having at least two growth interfaces in the nitride semiconductor 50 μm
As described above, a nitride semiconductor substrate having a thickness of preferably 500 μm or more can be provided.

Further, the method for growing a nitride semiconductor substrate according to the present invention enables continuous growth in a hydride vapor phase epitaxial growth apparatus, and therefore, the protective film is formed with a smaller thickness than the selective growth using a protective film or the like. Since a device process for forming a stripe shape or the like can be eliminated, mass production of a nitride semiconductor substrate becomes possible, and the number of processes for removing the substrate from the reaction furnace is reduced, so that contamination due to adhesion of dust or the like can be eliminated.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION A nitride semiconductor substrate according to the present invention is a nitride semiconductor substrate provided with at least two craters or a growth interface having a convex slope on a nitride semiconductor on the substrate. Hereinafter, embodiments of the present invention will be described based on a growth process.

The base layer 2 is grown on the substrate 1, then the first nitride semiconductor layer 3 is grown, and the second nitride semiconductor layer 4 is grown thereon. The nitride semiconductor substrate has an interface between the nitride semiconductor layer 3 and the second nitride semiconductor layer 4.

In the present invention, the substrate 1 has a C-plane, an R-plane, and an A-plane.
Sapphire or SiC (6H,
4H, 3C), spinel, ZnS, ZnO, GaAs,
A substrate is made of Si, nitride semiconductor, or the like. Preferred substrates include sapphire, SiC, and spinel. In addition, the substrate may be off-angled. In this case, it is preferable to use a substrate that is off-angled in a step-like manner because the underlayer made of a nitride semiconductor tends to grow with good crystallinity. The off angle at this time is 0 ° to 0 °.
5 °, preferably 0.1 ° to 0.2 °. These substrates have a flat surface, but if a nucleus or a layer made of a nitride semiconductor can be grown, for example, a substrate having fine roughness by etching or the like, or a substrate having irregularities, slopes, or steps may be used. You may have.

Next, by growing the underlayer 2 on the substrate 1 by vapor phase epitaxy, the lattice constant mismatch between the substrate 1 and the nitride semiconductor can be reduced. For example, since the lattice mismatch between gallium nitride and sapphire is as large as about 15%, it has been difficult to obtain a substrate having good surface morphology and good crystallinity. The underlayer 2 has an effect of alleviating this difference in lattice constant. As a specific example,
_{Al x Ga 1-x N (} 0 ≦ X ≦ 1), In x Ga 1-x
N (0 ≦ X ≦ 1) , and _{In x Al y Ga 1- x-} y N
(0 ≦ X ≦ 1, 0 ≦ Y ≦ 1). Hydrogen is used as a carrier gas, and trimethylgallium, trimethylaluminum, trimethylindium, and the like are used as source gases.
The film is grown at a temperature of 0 ° C. or more and 900 ° C. or less and a film thickness of 10 Å or more and 10 μm or less. The underlayer 2
Is not particularly limited, and may be a plurality of layers or may be omitted.

When the underlayer has a two-layer structure, for example, a nitride semiconductor composed of a nucleus or a thin film is grown, and then nitride semiconductors having different compositions are grown, whereby excellent C-axis orientation characteristics are obtained. The underlayer 2 can be used.

The growth condition for growing this underlayer in two layers is that the first underlayer and the second underlayer are formed by MOCVD.
Using the same carrier gas and source gas as the underlayer, hydrogen as the carrier gas, trimethylgallium as the source gas, etc., the first underlayer at a low temperature of 300 to 900 ° C. After growing to a thickness of not less than Å and not more than 0.5 μm, the second underlayer is grown at a growth temperature of 9 μm.
It is grown at a temperature higher than that of the first underlayer by setting the temperature to 00C to 1100C. In this second underlayer, a mirror is formed by stopping growth on the way for a nucleus and using it as a nucleus while continuing to grow the layer. In order to form a mirror having such a two-layer structure, it is easy to control the uniformity and orientation characteristics of the crystal nucleus density, the size, and the thickness of the layer.
Although it is preferable to use the OCVD method, other vapor phase growth methods can be used.

When the second underlayer is grown as a layer having a mirror surface, the first underlayer is grown to a thickness of 10 Å to 0.5 μm.
It is preferable that the second underlayer be grown at a thickness of 500 Å to 50 μm, because it has an effect as a buffer layer and also has an effect to reduce threading dislocations.

Next, on the substrate 1 on which the underlayer 2 has been grown,
The first nitride semiconductor layer 3 and the second nitride semiconductor layer 4 are grown. The first nitride semiconductor layer 3 has a growth interface of a crater or a convex slope, and preferably, the convex slope is formed continuously. Also, the height difference at this interface is preferably 5 μm or less.
When the thickness is 100 μm, more preferably 5 μm to 50 μm, the growth direction of threading dislocations can be bent in the direction of slope growth. Therefore, when growing the second nitride semiconductor layer 4, the threading dislocations are joined to each other, and threading dislocations are formed. Can be focused. Even if this nitride semiconductor substrate is grown to a thickness of 30 μm or more, it has a growth interface so that stress can be relaxed and threading dislocations can be focused by forming the growth interface. This also has the effect of reducing threading dislocations.

Further, in order to form two growth interfaces, a third nitride semiconductor layer 5 is grown on the second nitride semiconductor layer 4, and a fourth nitride semiconductor layer 6 is grown thereon. Thereby, a growth interface is formed between the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4, and the third nitride semiconductor layer 5 and the fourth nitride semiconductor layer 6 Can form a growth interface. In order to form such a growth interface, the growth rate, which is the growth condition of the first nitride semiconductor layer and the third nitride semiconductor layer, is 0.5 mm / hour or more, more preferably 1 to 5 mm / hour. And If the first nitride semiconductor layer is grown at this growth rate, a crater or a convex slope can be continuously formed on the surface, and the second nitride semiconductor layer or the fourth Between the substrate and the nitride semiconductor layer, a growth interface for relaxing the stress between the substrate and the nitride semiconductor can be formed.

When the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4 to be grown on the underlayer 2 are grown at a high growth rate in a short time, a hydride vapor phase epitaxial growth method is used. Preferably it is. It becomes a nitride semiconductor substrate having a growth interface, so that the stress generated on the substrate can be reduced and a thick film can be grown. Since the nitride semiconductor substrate on which the thick film has been grown can be peeled off by grinding or the like, it is effective for forming a single substrate made of a nitride semiconductor. The growth process using the HVPE apparatus and the growth conditions are described below.

In the present invention, the first to fourth nitride semiconductor layers can be grown by a hydride vapor phase epitaxial growth method. In the hydride vapor phase epitaxial growth method, a Group 3 element such as gallium, aluminum, indium or the like is reacted with a halogen gas such as hydrogen chloride to obtain a halide of the Group 3 element such as chloride, bromide or iodide. And convert the halide to ammonia,
This is a method of obtaining a nitride semiconductor by reacting with an N source such as hydrazine at a high temperature.

In order to grow GaN as a nitride semiconductor, a quartz boat containing Ga metal is installed in an HVPE apparatus, and a substrate is installed at a position away from the quartz boat. Next, an N source supply pipe is provided separately from the supply pipe of the halogen gas to be reacted with the Ga metal and the halogen gas supply pipe.

As a halogen gas, there is HCl or the like, which is introduced from a halogen gas pipe together with a carrier gas. The halogen gas reacts with a metal such as Ga to generate a halide of a Group 3 element, and further reacts with the ammonia gas flowing from the N source supply pipe to form a first to fourth nitride semiconductor layer. Is grown on the substrate via the underlayer.

Here, the growth conditions of the first and third nitride semiconductor layers are such that the growth rate is 0.5 mm / hour or more, and more preferably 1 to 5 mm / hour.
If the first and third nitride semiconductor layers are grown at this growth rate, craters and convex slopes can be continuously formed on the surface, and the second and fourth nitride semiconductor layers grown thereon can be formed. Stress between the substrate and the nitride semiconductor at the growth interface with the nitride semiconductor layer can be reduced. Therefore, it is possible to grow a nitride semiconductor having a different lattice constant and a different coefficient of thermal expansion on the substrate in a thick film. Furthermore, threading dislocations can be bent in multiple directions by forming craters and convex slopes. Therefore, the second nitride semiconductor layer was grown on the first nitride semiconductor layer, and the fourth nitride semiconductor layer was grown on the third nitride semiconductor layer. Since threading dislocations join together to form a loop and converge, a nitride semiconductor substrate with reduced dislocations can be obtained.

Changing the growth rates of the first nitride semiconductor layer and the second nitride semiconductor layer means changing the growth direction of the nitride semiconductor. Threading dislocations can be focused by growing preferentially in the lateral direction. Specifically, by stacking a second nitride semiconductor layer having a growth rate lower than that of the first nitride semiconductor layer on the first nitride semiconductor layer, the reduction of defects is promoted, and the mirror surface is flattened. It is possible to obtain a low-defect nitride semiconductor substrate having a property. As a condition for obtaining such a nitride semiconductor substrate, a ratio (R1 / R2) of a growth rate (R1) of the first nitride semiconductor layer to a growth rate (R2) of the second nitride semiconductor layer is set. It is preferable that the ratio is 1 or more, that is, the growth rate of the second nitride semiconductor layer is lower than the growth rate of the first nitride semiconductor layer. The same applies to the third nitride semiconductor layer and the fourth nitride semiconductor layer. The growth rate (R3) of the third nitride semiconductor layer and the growth rate of the fourth nitride semiconductor layer (R4)
It is preferable that the ratio (R3 / R4) is 1 or more, and the growth rate of the fourth nitride semiconductor layer is lower than the growth rate of the third nitride semiconductor layer.

The thickness of the first nitride semiconductor layer is not particularly limited, but is preferably 20 μm to 1 mm, more preferably 50 μm to 200 μm, and the pressure is grown under normal pressure or slightly reduced pressure.

The first to third nitride semiconductor layers are not limited to undoped ones and are doped with at least one type of n-type impurity such as Si, Ge, Sn and S, or M-type.
A material doped with a p-type impurity such as g, Be, Cr, Mn, Ca, or Zn can be used. Doping with such an n-type impurity promotes growth in the vertical direction. Therefore, it is preferable that the first nitride semiconductor layer and the third nitride semiconductor layer are doped with an n-type impurity to promote vertical growth and form craters and convex slopes. Further, the second nitride semiconductor layer and the fourth nitride semiconductor layer are doped with a p-type impurity or simultaneously with an n-type impurity and a p-type impurity to promote lateral and vertical growth. Thus, dislocations can be reduced by converging the growth direction of threading dislocations by bending them, which is preferable.

Next, after the growth of the first and third nitride semiconductor layers, second and fourth nitride semiconductor layers are grown thereon under the following conditions. The second and fourth nitride semiconductor layers are the first and fourth nitride semiconductor layers.
It is preferable to grow at a temperature equal to or higher than that of the third nitride semiconductor layer, and set to 1000 ° C. or higher. However, the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4
If the temperature difference is large, the substrate may be warped, so that the difference in growth temperature is preferably small. Further, the thickness of the second nitride semiconductor layer 4 is not particularly limited as long as the uppermost surface becomes a mirror surface, and a film in a range in which a height difference of a crater or a convex slope in the first nitride semiconductor layer is filled. Any thickness is acceptable. Therefore, the second nitride semiconductor layer can also be formed by a MOCVD method, an MBE method, or the like as long as it is a vapor phase growth method capable of growing the film to a thickness of about 30 μm.

The composition formulas of the first to fourth nitride semiconductor layers are as follows.
Is not particularly limited, and the general formula In _xAl_yGa
_1-xyBy N (0 ≦ x, 0 ≦ y, x + y <1)
Can be represented. However, the first nitride semiconductor layer 3 and the
2 may have different compositions from each other.
No.

Since the nitride semiconductor substrate of the present invention can grow a thick film, after forming two or more growth interfaces, ELO is performed to further reduce threading dislocations.
Threading dislocations can be further reduced by growing G.

The nitride semiconductor substrate obtained by the above growth method can be a thick film substrate. Further, a nitride semiconductor substrate having a flat top surface and a mirror surface with uniformly reduced threading dislocations is obtained. Since the nitride semiconductor substrate obtained by the present invention can grow a thick film, a single substrate obtained by growing a thick film and then removing only a substrate such as sapphire can be used. Therefore, it is also possible to form a back electrode. Note that the nitride semiconductor element grown on the nitride semiconductor substrate obtained by the present invention may be a light emitting element, a light receiving element, or an electronic device as long as it is made of a nitride semiconductor.

[0046]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 As shown in FIG. 1, a sapphire substrate having a C-plane as a main surface and an orientation flat surface as an A-plane was used as a substrate 1.
The apparatus was set in an OCVD apparatus, and thermal cleaning was performed at a temperature of 1050 ° C. for 10 minutes to remove moisture and surface deposits.

Next, at a temperature of 510 ° C., a first underlayer made of GaN was grown to a thickness of 200 angstroms using hydrogen as a carrier gas and ammonia and trimethylgallium as source gases.

Thereafter, a layer made of GaN and having flatness is formed on the first underlayer as a second underlayer at a growth temperature of 105.
It was formed at 0 ° C. with a film thickness of 20 μm. In this embodiment,
During the growth, hydrogen was flowed at 20.5 L / min as a carrier gas, ammonia at 5 L / min, and trimethylgallium at 25 cc / min as a source gas.

After the second underlayer is grown, the substrate is set in a hydride vapor phase epitaxial growth apparatus, Ga metal is prepared in a quartz boat, and GaCl ₃ is generated by using HCl gas as a halogen gas. And a first nitride semiconductor layer 3 made of GaN was grown. The growth temperature of the first nitride semiconductor layer 3 is 1000 ° C., and the growth rate is 1 mm / h.
our was grown at a film thickness of 100 μm.

Next, a second nitride semiconductor layer 3 is formed on the first nitride semiconductor layer 3.
Was grown in a hydride vapor phase epitaxial growth apparatus. As growth conditions at this time, the growth temperature is the same as that of the first nitride semiconductor layer 3,
The growth rate of the second nitride semiconductor layer 4 is 50 μm / hou.
The film thickness was grown at 50 μm at r.

Next, the above steps are repeated to form a third nitride semiconductor layer 5 on the second nitride semiconductor layer 4 under the same conditions as the first nitride semiconductor layer, and a second nitride semiconductor layer 5 on the third nitride semiconductor layer 5. The fourth nitride semiconductor layer 6 was grown under the same conditions as the nitride semiconductor layer, two growth interfaces were formed in the nitride semiconductor, and the stress was relaxed.

The surface of the fourth nitride semiconductor layer 6 obtained as described above is flat and specular, and according to CL observation, the threading dislocation density is about 7 × 10 ⁵ / cm ² . Thus, the present invention can provide a nitride semiconductor substrate which is a thick film substrate and has low defects.

Example 2 In Example 1, as shown in FIG. 2, a first nitride semiconductor layer was directly formed as a nucleus without forming an underlayer on a sapphire substrate 1 having a C-plane as a main surface. The first to fourth nitride semiconductor layers are grown under the same conditions as in Example 1 except that they are grown as above, to obtain a nitride semiconductor substrate. When the obtained nitride semiconductor substrate was observed by a CL method, crystal defects were 1 × 10 ⁶ , as in Example 1.
A nitride semiconductor substrate having a low defect density of not more than / cm ² can be expected.

[Embodiment 3] Embodiment 3 showing the structure of a laser device using the nitride semiconductor obtained in Embodiment 1 as a substrate will be described below.

(Undoped n-type contact layer 101) The wafer obtained in Example 1 was set in a reaction vessel of a MOCVD apparatus, and a nitride semiconductor was formed at 1050 ° C. using TMG.
(Trimethylgallium), TMA (trimethylaluminum) and ammonia, and Al _0.05 Ga _0.95
1 μm undoped n-type contact layer 101 made of N
It grows with the film thickness of. This layer has a function as a buffer layer between a nitride semiconductor substrate made of GaN and a semiconductor element such as an n-type contact layer.

[0056] (n-type contact layer 102) Next, the resulting TMG on the buffer layer 101, TMA, ammonia, using a silane gas as the impurity gas, from _Al 0.05 _{Ga 0.9 5} N was Si doped at 1050 ° C. The n-type contact layer 102 is grown to a thickness of 4 μm.

(Crack prevention layer 103) Next, TMG,
Using TMI (trimethylindium) and ammonia,
At a temperature of 900 ° C., a crack preventing layer 103 made of In _0.07 Ga _0.93 N is grown to a thickness of 0.15 μm.

(N-type cladding layer 104)
050 ° C., undoped Al _0.05 Ga _0.95 N using TMA, TMG and ammonia as source gases
A layer consisting of 25 .ANG. Is grown, followed by TM
A is stopped, a silane gas is used as an impurity gas, and a B layer made of GaN doped with 5 × 10 ¹⁸ / cm ^{3 of} Si is grown to a thickness of 25 °. This operation is repeated 200 times to form a laminated structure of the A layer and the B layer, and an n-type clad layer composed of a multilayer film (superlattice structure) having a total film thickness of 1 μm is grown.

(N-type guide layer 105) Next, at the same temperature, using TMG and ammonia as source gases, an n-type guide layer 105 made of undoped GaN was 0.15 μm thick.
It grows with the film thickness of. This n-type guide layer 105 may be doped with an n-type impurity.

(Active Layer 106) Next, the temperature was set to 900 ° C., and TMI (trimethyl indium), TM
G and ammonia, silane gas as an impurity gas, and Si doped at 5 × 10 ¹⁸ / cm ³
_A barrier layer made of _0.05 Ga _0.95 N is formed to a thickness of 140 ° while silane gas is stopped, and undoped In _0.13 Ga
_A well layer made of _0.87 N is formed with a thickness of 40 ° and a barrier layer /
Well layers / barrier layers / well layers are stacked in this order, and finally TMI, TMG and ammonia are used as barrier layers, and undoped In _{0 . 05} Ga _0.95 N is grown. The active layer 106 has a multiple quantum well structure (MQ
W).

(P-type electron confinement layer 107) Next, at the same temperature as the active layer, TMA, TMG and ammonia are used as source gases, Cp ₂ Mg (cyclopentadienyl magnesium) is used as an impurity gas, and Mg is added. 1 × 10 ¹⁹
Of p / cm ³ doped Al _0.3 Ga _0.7 N
Type electron confinement layer 107 is grown to a thickness of 100 °.

(P-type guide layer 108)
At 50 ° C., a p-type guide layer 108 made of undoped GaN is grown to a thickness of 0.15 μm using TMG and ammonia as source gases. This p-type guide layer may be doped with a p-type impurity.

(P-type cladding layer 109) Next, 1050
A consisting of undoped Al _0.05 Ga _0.95 N at ℃
A layer is grown to a thickness of 25 °, followed by stopping TMA and
Using p ₂ Mg, a B layer made of Mg-doped GaN is
The p-type cladding layer 109 composed of a superlattice layer having a total thickness of 0.45 μm is grown by growing the film at a thickness of 5 ° and repeating the process 90 times.
Grow. The p-type cladding layer is made of GaN and AlGaN
And a superlattice structure in which are laminated. p-type cladding layer 109
Has a superlattice structure, so that A
Since the l-mixed crystal ratio can be increased, the refractive index of the cladding layer itself decreases, and the band gap energy increases, which is very effective in lowering the threshold value.

(P-type contact layer 110)
At 50 ° C., TMG, ammonia, and Cp ₂ Mg are used to form Mg on the p-type cladding layer 109 at 1 × 10 ²⁰ / cm.
P-type contact layer 11 made of ^3- doped p-type GaN
0 is grown to a thickness of 150 °. After the reaction, the wafer is annealed at 700 ° C. in a nitrogen atmosphere in a reaction vessel to further reduce the resistance of the p-type layer.

After annealing, the wafer on which the nitride semiconductor was laminated was taken out of the reaction vessel, and a protective film made of SiO ₂ was formed on the surface of the uppermost p-type contact layer.
Etching is performed with SiCl ₄ gas using IE (Reactive Ion Etching) to expose the surface of the n-type contact layer 102 where the n-electrode is to be formed.

Next, a ridge stripe is formed as a stripe-shaped waveguide region by forming an SiO ₂ protective film and etching it by RIE using CF ₄ gas.

Next, after the formation of the ridge stripe, an insulating protective film made of Zr oxide (mainly ZrO ₂ ) is formed with a thickness of 0.5 μm on the p-type guide layer 108 exposed by etching.

On a p-type contact layer, a p-type electrode is formed of Ni and A
An n-type electrode is formed from Ti and Al on the n-type contact layer formed by u and exposed by etching.
This p-electrode is formed in stripes on the ridge,
Similarly, it is formed in a direction parallel to the stripe-formed n-electrode.

Next, after providing a dielectric multilayer film composed of SiO ₂ and TiO ₂ , Ni—Ti—Au is formed on the p and n electrodes.
(1000 ° -1000 ° -8000 °) pad electrodes were provided. At this time, a dielectric multilayer film made of SiO ₂ and TiO ₂ is also provided on the resonator surface (reflection surface side).

The laser device obtained as described above is
At room temperature, a continuous oscillation laser element having a threshold value of 2.8 kA / cm ² and an output of 30 mW and an oscillation wavelength of 405 nm can be obtained. The device life of the obtained laser device is 30
We can expect from 00 to 20000 hours. .

[0071]

According to the present invention described above, it is possible to provide a thick film substrate in which cracks and chips are suppressed, and to provide a low dislocation substrate in which threading dislocations are uniformly reduced on the entire surface of the substrate. Further, by growing an element structure on the nitride semiconductor substrate obtained by the present invention, a nitride semiconductor laser having good life characteristics and the like can be expected.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a nitride semiconductor showing one embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a nitride semiconductor showing one embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing a growth direction of threading dislocations at a growth interface according to the present invention.

FIG. 4 is a schematic sectional view of a nitride semiconductor laser device showing one embodiment of the present invention.

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Underlayer 3 ... 1st nitride semiconductor layer 4 ... 2nd nitride semiconductor layer 5 ... 3rd nitride semiconductor layer 6 ... 4th Nitride semiconductor layer 101 ... undoped n-type contact layer 102 ... n-type contact layer 103 ... crack preventing layer 104 ... n-type cladding layer 105 ... n-type guide layer 106 ... activity Layer 107: p-type electron confinement layer 108: p-type guide layer 109: p-type cladding layer 110: p-type contact layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H01S 5/323 610 H01L 29/46 GF Term (Reference) 4G077 AA03 BE15 DB05 EE05 EF03 TB03 TC14 4M104 AA04 AA09 BB05 BB14 CC01 DD23 EE06 FF13 GG04 5F041 AA40 CA05 CA34 CA40 CA46 CA65 5F045 AA02 AA04 AB14 AC08 AC12 AD06 AD07 AD08 AD09 AD10 AD11 AD12 AD13 AD14 AF04 AF09 AF13 BB12 CA11 CA12 DA53 DA63 5F073 AA11 AA07 AB AA AA AA A A A A A A A A A B A A A A A A A A A A B A A A A A A A A A A A A B A A A A A A A A A A A B A A A A A A A A A A B A A A A A A A A A A A B A A A A A A A A A A A A B A A A A A A A A A A A B A A A A A A A A A A A A A A A A A A A B A A A A A A A A A A A A A B A A

Claims (6)

[Claims] 1. A nitride semiconductor substrate having a nitride semiconductor grown on a substrate, wherein the nitride semiconductor has at least two growth interfaces having craters or convex slopes on the nitride semiconductor on the substrate. substrate. 2. The nitride semiconductor substrate according to claim 1, wherein said convex slope forms a growth interface by being present continuously in a horizontal direction. 3. A method for growing a nitride semiconductor substrate on a substrate using a vapor phase epitaxial growth method, comprising: forming a first nitride semiconductor layer on a substrate; Forming a growth interface having a crater or a convex slope at the interface between the first nitride semiconductor layer and the second nitride semiconductor layer. A method for growing a semiconductor substrate. 4. The method according to claim 1, wherein a nucleus or a layer made of a nitride semiconductor is grown on the substrate as an underlayer, and the first nitride semiconductor layer is grown through the underlayer. 4. The method for growing a nitride semiconductor substrate according to item 3. 5. The method for growing a nitride semiconductor substrate according to claim 3, comprising at least two or more steps of forming said growth interface. 6. The method for growing a nitride semiconductor according to claim 3, wherein said vapor phase epitaxial growth method is a hydride vapor phase epitaxial growth method.