JP2002329665A - Method for manufacturing unit substrate composed of nitride semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grow a nitride semiconductor thick on a different type substrate, and to obtain the nitride semiconductor in which a penetration dislocation is decreased. SOLUTION: The nitride semiconductor is grown on a different type substrate, to form a growth interface within the nitride semiconductor, and thereafter a unit nitride semiconductor is obtained by a wire-saw.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light emitting diode,
Light emitting element such as a laser diode or a solar cell, a nitride semiconductor device which is used a light receiving element such as an optical sensor, or the like to the electronic device (In _x Al _y Ga,
_1-xy N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) A method of manufacturing a nitride semiconductor substrate, particularly a method of obtaining a single nitride semiconductor substrate by removing a heterogeneous substrate from a nitride semiconductor About.

[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.
Among them, there is a growing demand for LDs to be used for disk systems, such as DVDs, capable of recording and reproducing large-capacity, high-density information. Therefore, such LE
Various methods have been studied for obtaining single-crystal nitride semiconductor substrates that are expected to be used for light-receiving elements and electronic devices in addition to applications to D and LD.

As a method for obtaining, for example, gallium nitride as a bulk single crystal as the nitride semiconductor substrate, there is a high pressure method or the like, but it has not been put to practical use. Therefore, a heterogeneous substrate such as sapphire, which is different from a nitride semiconductor, is used, and a nitride semiconductor is grown on the heterogeneous substrate to form a nitride semiconductor substrate, which is used for LEDs, LDs, and electronic devices.

In order to use a heterogeneous substrate such as sapphire or the like different from a nitride semiconductor and use it as a nitride semiconductor substrate, a nitride semiconductor is directly grown on the substrate due to a difference in lattice constant between the substrate and the nitride semiconductor. When a semiconductor element such as an LED or LD is grown on a nitride semiconductor substrate having such poor crystallinity, the lifetime characteristic is high because the threading dislocation density is as high as 10 ¹⁰ cm ⁻² per unit area. And device characteristics are degraded. Therefore, a method of growing a buffer layer made of a nitride semiconductor on a substrate at a low temperature of 900 ° C. or lower has been used to improve crystallinity. 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.

Also, as a vapor phase epitaxial growth method capable of growing a thick film at a high growth rate, there is a hydride vapor phase epitaxial growth method. 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.

Furthermore, if a nitride semiconductor substrate can be obtained by itself, cleavage can be facilitated, and a light emitting device or the like having an n-side electrode formed on the back surface can be provided. Therefore, a method of removing a heterogeneous substrate in a post-process is being studied. As a specific example, there has been reported a method for producing a single crystal by growing a thick gallium nitride on a sapphire substrate, which is a heterogeneous substrate, and then removing the heterogeneous substrate by polishing.

[0007]

However, since sapphire substrates and the like have high hardness, large stress is applied during polishing. For this reason, it is difficult to form a single substrate of a nitride semiconductor such as gallium nitride since the nitride semiconductor is chipped or cracked by the stress during polishing. Further, in the case of a nitride semiconductor grown by a thick film method such as a hydride vapor phase epitaxy method, specifically, when a film thickness of 100 μm or more is grown, such problems as chipping and cracking during polishing are caused. Was prominent.

On the other hand, as a method of separating nitride semiconductor such as gallium nitride and sapphire except for polishing, a Krf pulse excimer laser is irradiated from the sapphire side to separate the sapphire and the gallium nitride at a common surface. However, a method of separating sapphire from gallium nitride has been reported. According to this method, gallium nitride absorbs laser light on a shared surface where gallium nitride and sapphire are in contact with each other by laser irradiation, thereby decomposing gallium nitride and separating sapphire from gallium nitride. According to this method, sapphire is cracked by the gas pressure of nitrogen gas generated by the decomposition of gallium nitride, and the crack causes a defect on the gallium nitride surface in contact with the sapphire. If such a defect is present on the gallium nitride surface, a fine crack such as a micro crack may occur. When the microcracks are generated, it is conceivable that, in a light emitting device or the like, device characteristics such as life characteristics are reduced, a yield is reduced, and the like.

In view of the above problems, an object of the present invention is to provide a method for producing a single substrate of a nitride semiconductor by removing a heterogeneous substrate from a nitride semiconductor substrate having a nitride semiconductor grown on the heterogeneous substrate. To provide. Furthermore, the nitride semiconductor single substrate obtained here is a low-dislocation, thick-film nitride semiconductor for the purpose of improving electrical characteristics by increasing hole mobility.

[0010]

The object of the present invention can be achieved by the following constitutions (1) to (7). (1) In a method of manufacturing a single substrate made of a nitride semiconductor by removing a heterogeneous substrate from a nitride semiconductor substrate grown on a heterogeneous substrate by a vapor phase epitaxial growth method, a nitride semiconductor is formed on a heterogeneous substrate in two stages. Forming a nitride semiconductor substrate having a growth interface in the nitride semiconductor by growing, and after forming the growth interface,
Removing the heterogeneous substrate by cutting the nitride semiconductor substrate in a direction parallel to the growth interface with a wire saw. (2) The step of cutting the nitride semiconductor substrate with a wire saw is performed after fixing the surface of the nitride semiconductor to a base with wax, metal, or epoxy resin. Manufacturing method. (3) The method for manufacturing a single substrate made of a nitride semiconductor according to (1), wherein in the step of forming the growth interface, the nitride semiconductor substrate has at least two or more growth interfaces. (4) The method for producing a single substrate made of a nitride semiconductor according to (1), wherein in the step of removing the heterogeneous substrate, the nitride semiconductor substrate is cut at a growth interface in the nitride semiconductor to be a single substrate. (5) From the nitride semiconductor according to (3), a wire saw cuts at two or more places in a direction parallel to the growth interface with respect to the nitride semiconductor substrate on which at least two or more growth interfaces are formed. A method for manufacturing a single substrate. (6) The method for manufacturing a single substrate made of a nitride semiconductor according to (1), wherein a blade is used as the method for cutting the nitride semiconductor. (7) The method according to (1), wherein the vapor-phase epitaxial growth method is a hydride vapor-phase epitaxial growth method.

That is, according to the present invention, a nitride semiconductor substrate obtained by growing a nitride semiconductor on a heterogeneous substrate is cut by a wire saw at or near a growth interface within the nitride semiconductor, and a single nitride semiconductor is cut. Is formed. In addition, the cutting with a wire saw is performed for a nitride semiconductor substrate having a plurality of growth interfaces by growing a thick film.
By simultaneously cutting with a plurality of wire saws, a single substrate of a nitride semiconductor can be mass-produced.

The wire saw according to the present invention is a wire saw which presses a workpiece against a row of wires running at a high speed, supplies a slurry which is a working liquid mixed with abrasive grains, and cuts the slurry by a lapping effect of the slurry. It is. Here, the workpiece in the present invention is a nitride semiconductor substrate, and a piano wire or the like can be used as the wire. In order to fix the nitride semiconductor substrate to the base at the time of cutting, wax, metal, epoxy resin, or the like is used. The thickness of the wire saw is 80 μm to 20 μm.
0 μm. If the wire saw is too thin, the wire saw deteriorates quickly and the wire breaks. Also,
As the wire saw becomes thicker, the amount of nitride semiconductor removed at the time of cutting increases, and it becomes difficult to obtain a thick nitride semiconductor. Therefore, it is preferable to use a wire saw having a thickness within the above range. This wire saw can obtain many single substrates at one time, and is preferable for mass production.

Further, as a method for cutting the nitride semiconductor substrate, there is a method using a blade. In this method, a growth interface formed in a nitride semiconductor is cut by a cutting blade rotating in parallel to obtain a single substrate. Cutting with this blade is accurate and a short-term version can be obtained in a short time.

The growth interface formed in the nitride semiconductor according to the present invention refers to a two-stage growth after forming a crater or a convex slope on the surface of the first nitride semiconductor 3 grown on a heterogeneous substrate. Is a nitride semiconductor substrate having a growth interface formed by growing a second nitride semiconductor 4. The convex slope which is the growth interface may be present continuously.

The crater in 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 3. The size and depth of the dent are not particularly limited, but the size and depth of the dent are preferably 5 μm or more and 100 μm or less. Also, this depth is the height difference of the growth interface at the same growth interface. The height difference at the growth interface may be formed continuously. Further, a region having a height difference of 100 μm from the vicinity of the growth interface is defined as a growth interface.
A range of 00 μm, preferably 100 μm is defined as the vicinity of the growth interface.

Further, the convex slope in the present invention refers to a surface shape in which the surface of the first nitride semiconductor formed after growing the first nitride semiconductor 3 has a height difference from a horizontal plane. is there. The convex slope may have a wave-like or dot-like convex portion with respect to the horizontal plane.

The condition for forming the growth interface by the two-stage growth described above is to change the growth rate of the first nitride semiconductor and the second nitride semiconductor. This growth rate difference forms a growth interface in the nitride semiconductor. The growth rate of the first nitride semiconductor is 0.2 mm / hour.
Or more, preferably 0.5 mm / hour or more. Although the growth rate of the second nitride semiconductor is not particularly limited, preferably, the growth rate of the first nitride semiconductor is set to the second rate.
Is to be faster than the growth rate of the nitride semiconductor.
Further, the first nitride semiconductor may be grown on a heterogeneous substrate via an underlayer. Further, as a preferable growth method for the high-speed growth as described above, there is a hydride vapor phase growth method capable of growing a thick film in a short time.

Another condition for forming the growth interface is to dope the nitride semiconductor with an n-type impurity or a p-type impurity. The impurity doping amount of the first nitride semiconductor and the second nitride semiconductor is changed, or different impurities are doped. For example, by doping the first nitride semiconductor with Si as an n-type impurity,
Promotes vertical growth. Next, the second nitride semiconductor is doped with Mg as a p-type impurity to promote lateral growth. By changing the growth direction in this manner, a growth interface can be formed, and at the same time, there is an effect of reducing dislocations. Also, the growth interface can be formed by adjusting the above-described conditions of the growth rate and the conditions of the impurity doping.

When the growth interface is formed under the above conditions, a threading dislocation can form a loop near the interface of the first nitride semiconductor which is the contact surface with the second nitride semiconductor. This is because the growth interface has a height difference, and 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. 6, the threading dislocations in which the traveling direction is bent may form dislocation loops between the bent threading dislocations, and then converge to reduce threading dislocations during the growth of the nitride semiconductor. it can. As a result, the dislocation density per unit area at the growth interface is 1 × 10 ⁷ per unit area /
cm ² or less. The growth interface formed in the nitride semiconductor in this way has low crystallinity, becomes a uniform and non-uniform interface, reduces stress, and allows a thick nitride semiconductor to grow on a heterogeneous substrate. . In addition, cutting with a wire saw can be easily performed at or near a growth interface having low crystallinity, which is preferable.

Here, the underlayer is a buffer layer made of a nitride semiconductor grown at a low temperature of 900 ° C. or less on a heterogeneous substrate in order to improve the crystallinity. This underlayer is A
1N, GaN, AlGaN, InGaN, etc., and grows with a thickness of 100 to 50 μm. In addition, it may be omitted depending on the type of substrate. FIG. 1 and FIG. 3 are schematic diagrams in which a nitride semiconductor is grown via the underlayer 2. 2 and 4 are schematic diagrams in which a nitride semiconductor is grown not through the underlayer 2 but through a nitride semiconductor grown as a nucleus.

Further, by repeating the step of forming a growth interface in the nitride semiconductor, a plurality of growth interfaces can be formed, and threading dislocations can be further reduced. As a specific example, in a nitride semiconductor substrate having two growth interfaces, the threading dislocation density per unit area is 1 × 10 ⁶ / cm ² or less,
Preferably, it can be 7 × 10 ⁵ particles / 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. Also, by having a plurality of (two or more) growth interfaces, the stress generated between the heterogeneous substrate such as sapphire and the nitride semiconductor can be dispersed not only at the interface between the heterogeneous substrate and the nitride semiconductor but also in several stages. it can.
This stress is a difference in thermal expansion coefficient, and the stress cannot be sufficiently reduced only by the growth interface between the heterogeneous substrate and the nitride semiconductor. For this reason, the nitride semiconductor substrate is warped, and furthermore, cracks and chips are generated in the nitride semiconductor.
Therefore, such a problem can be solved by forming at least two growth interfaces in the nitride semiconductor.

By growing a thick film and having a plurality of growth interfaces in the nitride semiconductor as described above, cutting by a wire saw can be performed simultaneously by the number of growth interfaces. Therefore, a single substrate of a nitride semiconductor can be mass-produced at a time.

Here, the heterogeneous substrate may be any substrate different from the nitride semiconductor. This heterogeneous substrate includes sapphire or SiC (6) having any one of the C plane, the R plane, and the A plane as a main surface.
H, 4H, 3C), spinel, ZnS, ZnO, Si,
GaAs and the like. Also, as in gallium nitride, the general formula I
_{n x Al y Ga 1-x} + y N (0 ≦ X ≦ 1,0 ≦ Y ≦
1, 0 ≦ X + Y ≦ 1) may be used as the substrate. The size of the heterogeneous substrate is not particularly limited, but a wafer having a diameter of 1 to 5 inches is used, and the thickness of the substrate may be any range as long as it can be formed into chips by cleavage or dicing. Specifically, the thickness of the heterogeneous substrate is 0.1 mm or more. These heterogeneous substrates have a flat surface, but if a nucleus or a layer made of a nitride semiconductor can be grown, the growth surface of the nitride semiconductor has a fine roughness by, for example, etching, The substrate may have irregularities, slopes, or steps on the growth surface of the nitride semiconductor of the heterogeneous substrate, or may have irregularities, grooves, etc. on the back surface of the nitride semiconductor on the growth surface of the heterogeneous substrate.

By having the growth interface in the nitride semiconductor as described above, cutting with a wire saw becomes possible. If there is no growth interface in the nitride semiconductor, cutting with a wire saw cuts a nitride semiconductor grown directly on a heterogeneous substrate. The semiconductor was also cracked. Therefore, it was difficult to obtain a nitride semiconductor single substrate by cutting with this wire saw. Therefore, in the present invention, a nitride semiconductor substrate having a growth interface that can be cut with a wire saw under the above conditions is provided. Further, by providing a plurality (two or more) of the growth interfaces in the nitride semiconductor, it is possible to reduce a stress caused by a difference in lattice constant and a difference in thermal expansion coefficient between the different types of substrates. Therefore, the nitride semiconductor needs to be thicker than the thickness of the wire saw on the heterogeneous substrate, but can be grown to a thickness of 300 μm or more. Therefore, a thick film required for cutting with a wire saw can be grown, and cutting with a wire saw can be performed. In addition, by providing a plurality (two or more) of growth interfaces in the nitride semiconductor, the nitride semiconductor can be cut at once with the same number of wire saws as the growth interface, and a single nitride semiconductor can be mass-produced.

As described above, the present invention is to form a growth interface having crystal non-uniformity in a nitride semiconductor by growing nitride semiconductors having different growth conditions on a heterogeneous substrate, and cutting with a wire saw. It is. As described above, cracks or chips generated by stress on the nitride semiconductor generated when cutting with a wire saw do not affect the different types of substrates to the nitride semiconductor, and the different types of substrates can be easily removed, and the film thickness is 100 μm. A single substrate made of the above nitride semiconductor can be formed.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION A single substrate made of a nitride semiconductor according to the present invention is obtained by forming a nitride semiconductor substrate having a growth interface having a crater or a convex slope in a nitride semiconductor on a heterogeneous substrate by using a wire saw. And cut at the growth interface. Hereinafter, an embodiment of the present invention will be described based on a manufacturing process based on FIG.

As a first step, a base layer 2 is grown on a heterogeneous substrate 1, and then a first nitride semiconductor 3 is grown by two-stage growth, and a second nitride semiconductor 3 is grown thereon. By growing the semiconductor 4, a nitride semiconductor substrate having a growth interface between the first nitride semiconductor 3 and the second nitride semiconductor 4 is formed.

The heterogeneous substrate 1 in the present invention is a C-plane,
Sapphire or S whose main surface is either R surface or A surface
iC (6H, 4H, 3C), spinel, ZnS, Zn
O, GaAs, Si, a nitride semiconductor, or the like is used as the substrate. Preferred examples of the heterogeneous substrate 1 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 2 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 dissimilar substrates have a flat surface, but if a nucleus or a layer made of a nitride semiconductor can be grown, the substrate may have fine roughness by etching or the like, or the substrate may have irregularities, slopes, or steps. May be provided.

Next, an underlayer 2 is grown on the heterogeneous substrate 1 by a vapor deposition method. The underlayer 2 has an effect as a buffer layer, and can reduce lattice constant mismatch between the heterogeneous substrate 1 and the nitride semiconductor. 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). As a manufacturing method, hydrogen is used as a carrier gas, and trimethylgallium, trimethylaluminum, trimethylindium, or the like is used as a source gas, and grown at a temperature of 300 ° C. to 900 ° C. and a film thickness of 10 Å to 10 μm. Further, an n-type impurity or a p-type impurity may be doped. still,
The underlayer 2 may be a plurality of layers, or may be omitted.

When the underlayer has a two-layer structure, for example, a nitride semiconductor comprising a nucleus and a thin film is grown as a first underlayer, and then the second underlayer is formed on the first underlayer. Thus, the underlayer 2 having excellent C-axis alignment characteristics can be obtained.

Growth when this underlayer is grown in two layers
The conditions are, for example, the first underlayer using the MOCVD method.
And the second underlayer using the same carrier gas,
Hydrogen is used for Agus. Trimethyl gully as source gas
, Trimethylaluminum, trimethylindium
The composition of the first underlayer and the second underlayer is changed by using
Can be obtained. 300 ° C. or higher 900 for the first underlayer
At a low temperature of not more than 10 ° C., the thin film should have a thickness of 10 Å or more.
After growing to a thickness of 5 μm or less, the second underlayer is grown
Set the temperature to 900 ° C to 1100 ° C and higher than the first underlayer.
Grow at warm. This second underlayer is grown as a nucleus.
Those that make growth stop the growth in the middle,
The surface is mirror-formed by continuing to grow on the second base
The layer has a thickness of 5 μm or less. Such a two-layer structure
In order to mirror the surface by
M that facilitates control of orientation characteristics, size, and layer thickness
It is preferable to use the OCVD method.
It can also be used. As described above, the underlayer is formed on the heterogeneous substrate 1.
Of heterogeneous substrates by growing
Alleviates lattice mismatch with nitride semiconductor grown on top
Can be made. For example, gallium nitride and sapphire
Is very large, about 14%.
By growing the layer, good surface morphology
A nitride semiconductor substrate having crystallinity can be obtained.
The underlayer 2 is a nucleus or layer made of a nitride semiconductor.
The composition formula is not particularly limited, and the general formula In_xAl
_yGa _1-xyN (0 ≦ x, 0 ≦ y, x + y <1)
Therefore, it can be expressed. Growing with underlayer as core
In the case of stopping the growth in the middle and growing it as a layer
Is the nitride half that formed the mirror by continuing to grow further
Conductor layer. The underlayer depends on the type of the heterogeneous substrate, etc.
It can be omitted.

Next, a first nitride semiconductor 3 and a second nitride semiconductor 4 are grown on the heterogeneous substrate 1 on which the base layer 2 has been grown. As the first nitride semiconductor 3, the growth interface is a crater or a convex slope, and preferably, the convex slope is formed continuously. The height difference at the interface is preferably 5 μm to 1 μm.
00 μm, more preferably 5 μm to 50 μm,
Since the growth direction of threading dislocations can be bent in the direction of slope growth, the threading dislocations can be joined together during the growth of second nitride semiconductor 4 and the threading dislocations 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 such growth interfaces, a third nitride semiconductor 5 is grown on the second nitride semiconductor 4, and a fourth nitride semiconductor 6 is grown thereon. Thereby, a growth interface is formed between the first nitride semiconductor 3 and the second nitride semiconductor 4, and the third nitride semiconductor 5
And a fourth nitride semiconductor 6 to form a growth interface.

The conditions for forming such a growth interface include:
The growth rate, which is the growth condition of the first nitride semiconductor and the third nitride semiconductor, is 0.2 mm / hour or more, preferably 0.5 mm / hour or more, and the upper limit is 100 mm
/ Hour or less. I do. If the first nitride semiconductor is grown at this growth rate, a crater or a convex slope can be continuously formed on the surface, and the second nitride semiconductor or the fourth nitride semiconductor grown thereon can be formed. A growth interface can be formed with the semiconductor. As a condition for obtaining such a nitride semiconductor substrate, a ratio (R1 / R2) of a growth rate (R1) of the first nitride semiconductor to a growth rate (R2) of the second nitride semiconductor is 1 or more. That is, it is preferable that the growth rate of the second nitride semiconductor be lower than the growth rate of the first nitride semiconductor. The same applies to the third nitride semiconductor and the fourth nitride semiconductor. The third nitride semiconductor growth rate (R3) and the fourth nitride semiconductor growth rate (R4) Ratio (R3 / R4)
Is preferably 1 or more, and the growth rate of the fourth nitride semiconductor is preferably lower than the growth rate of the third nitride semiconductor.

As another condition for forming the growth interface, the first to fourth nitride semiconductors may be doped with an n-type impurity or a p-type impurity. The impurity doping amount of the first nitride semiconductor and the second nitride semiconductor is changed, or different impurities are doped. For example, the first
By doping the nitride semiconductor and the third nitride semiconductor with Si as an n-type impurity, vertical growth can be promoted to form craters and convex slopes. Next, the second nitride semiconductor and the fourth nitride semiconductor are doped with Mg as a p-type impurity to promote lateral growth. Further, an n-type impurity and a p-type impurity may be simultaneously doped. By changing the growth direction in this manner, a growth interface can be formed, and at the same time, there is an effect of reducing dislocations. Furthermore, the growth interface can be formed by matching the above-described growth rate conditions and impurity doping conditions. Here, the n-type impurities are Si, Ge, Sn
And at least one of S, S, and the like, and Mg, Be, Cr, Mn, Ca, Zn, or the like can be used as the p-type impurity. In order to form a growth interface, other reaction conditions include the first nitride semiconductor and the second nitride semiconductor.
It is also conceivable to provide a growth temperature difference with respect to the nitride semiconductor.

As described above, if a growth interface is formed, cutting with a wire saw in a subsequent step can be easily performed. In addition, it becomes possible to grow a nitride semiconductor having a different lattice constant and a different thermal expansion coefficient on a heterogeneous substrate in a thick film. Furthermore, threading dislocations are bent in multiple directions by forming craters and convex slopes, and threading dislocations that are bent in multiple directions join together to form a loop and converge. Can be reduced to provide a nitride semiconductor substrate. By stacking a second nitride semiconductor having a growth rate lower than that of the first nitride semiconductor on the first nitride semiconductor, reduction of defects is promoted, and low-defect nitride having mirror flatness is obtained. A semiconductor substrate can be obtained.

The thickness of the first nitride semiconductor is not particularly limited, but is preferably 20 μm to 1 mm, more preferably 50 μm to 200 μm. The first nitride semiconductor is grown under normal pressure or slightly reduced pressure. The second and fourth nitride semiconductors are preferably grown at a temperature equal to or higher than the first and third nitride semiconductors, and the temperature is set to 1000 ° C. or higher. However, if the temperature difference between the first nitride semiconductor 3 and the second nitride semiconductor 4 is large, the substrate is warped, so that the difference in growth temperature is preferably small. The thickness of the second nitride semiconductor 4 is not particularly limited as long as the uppermost surface is a mirror surface, and has a thickness within a range in which a height difference between a crater and a convex slope in the first nitride semiconductor is filled. I just need.
For this reason, the second nitride semiconductor can be grown by a MOCVD method or an MBE method if it can be grown to a film thickness of about 30 μm.
It can also be performed by a method or the like.

[0038] As the composition formula of the first to fourth nitride semiconductor is not particularly limited, the general formula _In x _Al y Ga
_1-xyN (0 ≦ x, 0 ≦ y, x + y <1). However, the first nitride semiconductor 3 and the second nitride semiconductor 3
The composition is not limited to the nitride semiconductor 4 and may be different from each other. These nitride semiconductors include:
Undoped nitride semiconductor, Si, G as n-type impurity
e, a nitride semiconductor doped with at least one kind of Sn and S, or Mg, Be, Cr,
A nitride semiconductor doped with Mn, Ca, Zn, or the like can be used.

The first layer thus grown on the underlayer 2
When the nitride semiconductor 3 and the second nitride semiconductor 4 are grown at a high growth rate and in a thick film, the hydride vapor phase epitaxial growth method is preferably used. In the case of a nitride semiconductor substrate having a growth interface, it is possible to obtain a nitride semiconductor substrate on which a nitride semiconductor having a thickness of 300 μm or more is grown by relaxing the stress generated on the substrate.

The growth conditions when the HVPE apparatus is used are shown below. In the present invention, a hydride vapor phase epitaxial growth method can be used as the first to fourth nitride semiconductor growth methods. 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. Then, the halide is reacted with an N source such as ammonia or hydrazine at a high temperature to obtain a nitride semiconductor.

In order to grow gallium nitride as a nitride semiconductor, a quartz boat containing gallium metal is installed in an HVPE apparatus, and a wafer which is a heterogeneous 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 gallium metal and the halogen gas supply pipe. The halogen gas includes HCl and the like, and is introduced from a halogen gas pipe together with the carrier gas. The halogen gas reacts with a metal such as gallium 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 a heterogeneous substrate via an underlayer.
When doping a nitride semiconductor with an n-type impurity, for example, dichlorosilane, trichlorosilane, or monosilane can be used as a source gas in the case of Si.

In the nitride semiconductor substrate formed as described above, the second nitride semiconductor 4 has a crystal nonuniformity at the growth interface with the first nitride semiconductor 3. Further, it is preferable that the dislocation density is significantly different at the growth interface. By having a dislocation density difference at the interface between the first nitride semiconductor and the second nitride semiconductor, the second nitride semiconductor can be easily broken without causing cracks when cutting with a wire saw in a later step. Dissimilar substrates can be removed.

In the second step, the nitride semiconductor substrate having the growth interface formed in the first step in the nitride semiconductor is fixed by attaching the uppermost surface of the second nitride semiconductor to the base. Next, the slurry is supplied by a high-speed traveling wire saw, and cut near the growth interface by the lapping effect of the slurry. This slurry is a working liquid in which abrasive grains are mixed. The obtained nitride semiconductor single substrate has a thickness of 50 μm or more, preferably 100 μm or more.

Here, examples of the eutectic material used for bonding for fixing to the base include wax and metal. This metal includes an Au alloy.
u-Sn, Au-Si, Au-Ge, and other Zn can be used, and further, the substrate is suppressed from being warped by pressing with a jig or the like. In addition, an epoxy resin or the like can be used for fixing the nitride semiconductor substrate.

The cut surface of the obtained second nitride semiconductor is polished to make it flat and mirror-finished, and the eutectic material used above is removed by heating, followed by acid washing, thereby removing the nitride semiconductor. It can be obtained as a single substrate.
The obtained single substrate is a nitride semiconductor having a film thickness of 50 μm or more and a low dislocation density of 1 × 10 ⁷ / cm ² or less per unit area.

[0046]

Embodiments of the present invention will be described below with reference to the drawings. [Example 1] As shown in FIG.
Using a sapphire substrate having the main surface as the main surface and the orientation flat surface as the A surface, the sapphire substrate was set in an MOCVD apparatus,
A minute of thermal cleaning was performed to remove moisture and attached substances on the surface.

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.
The film was formed at 0 ° C. with a thickness of 2.5 μm. In this embodiment, hydrogen is used as a carrier gas during growth at 20.5 L /
As a raw material gas, ammonia was flowed at 5 L / min and trimethylgallium at 25 cc / min.

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 0.2 mm
/ Hour to grow with a film thickness of 100 μm.

Next, a second nitride semiconductor layer 3 is formed on the first nitride semiconductor layer 3.
Is 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.
At r, the film is grown at a thickness of 50 μm. The second obtained here
The surface of the nitride semiconductor layer 4 is flat and mirror-
According to observation, the threading dislocation density is about 7 × 10 ⁵ / cm ² .

Next, the second nitride semiconductor surface, which is the uppermost surface of the nitride semiconductor, is bonded to a base sapphire substrate using Au—Sn as a eutectic material, and cut by a 160 μm wire saw. A single substrate with reduced warpage can be obtained. Thereafter, the sapphire substrate was removed by performing polishing from the nitride semiconductor sapphire substrate side. Since layered cracks in the C-plane direction of GaN generated during polishing are suppressed at the interface between the first nitride semiconductor and the second nitride semiconductor, after the sapphire substrate is removed, further polishing is performed, and By removing the nitride semiconductor, an interface side of the second nitride semiconductor with the first nitride semiconductor (hereinafter, referred to as a second surface of the second nitride semiconductor) is planarized to obtain a mirror surface. Can be.

[Embodiment 2] In Embodiment 1, as shown in FIG. 3, the step of forming a growth interface is repeatedly performed. A third nitride semiconductor 5 is formed on the second nitride semiconductor 4 under the same conditions as the first nitride semiconductor 3, and a fourth nitride is formed thereon under the same conditions as the second nitride semiconductor 4. The semiconductor 6 is grown to form a nitride semiconductor substrate having two growth interfaces formed in the nitride semiconductor. Otherwise, a nitride semiconductor substrate is obtained by growing under the same conditions as in Example 1. Thereafter, two single substrates can be obtained by cutting at the growth interface with a wire saw. The obtained nitride semiconductor had crystal defects per unit area of 1 × 10 ⁶ / cm, as in Example 1.
It is a single substrate of a nitride semiconductor having ² or less defects.

Example 3 The procedure of Example 1 was repeated, except that the underlayer 2 was grown on the sapphire substrate 1 having the C-plane as the main surface and the film thickness was 0.5 μm, as shown in FIG. First nitride semiconductor 3 and second nitride semiconductor 4 according to Example 1
And a nitride semiconductor substrate is obtained.

Next, the obtained nitride semiconductor substrate is bonded to a base and cut by a wire saw.
As in the first embodiment, a single substrate having a mirror surface on the second surface is obtained. The obtained nitride semiconductor single substrate is a nitride semiconductor having a crystal defect of as low as about 4 × 10 ⁶ / cm ² .

Example 4 A nitride semiconductor substrate was grown under the same conditions as in Example 1 except that a blade was used for cutting the nitride semiconductor to obtain a single substrate. Also in this method, a nitride semiconductor having a thickness of 50 μm can be obtained.

Fifth Embodiment In the first embodiment, the first nitride semiconductor layer 3 is grown at a growth rate of 0.2 mm / hour to a thickness of 200 μm, and then the second nitride semiconductor layer 4 is grown. The growth rate is 50 μm / hour and the film thickness is 3
By growing at a thickness of 00 μm, a single substrate of a nitride semiconductor having the same crystallinity as in Example 1 and a thickness of 200 μm can be obtained.

[0057]

As described above, according to the present invention, it is possible to provide a single substrate made of a nitride semiconductor with reduced threading dislocations over the entire surface of a heterogeneous substrate. Further, according to the present invention, the single substrate can be formed as a thick film, and a plurality of single substrates can be mass-produced at a time.

[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 sectional view of a nitride semiconductor showing one embodiment of the present invention.

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

FIG. 5 is a schematic sectional view of a single nitride semiconductor formed according to the present invention.

FIG. 6 is a schematic cross-sectional view showing a growth direction of threading dislocations at a growth interface according to the present invention.

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 1 ... Different substrate 2 ... Underlayer 3 ... 1st nitride semiconductor 4 ... 2nd nitride semiconductor 5 ... 3rd nitride semiconductor 6 ... 4th nitride Semiconductor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01S 5/323 610 H01S 5/323 610 F term (Reference) 5F041 CA34 CA40 CA46 CA65 CA77 5F045 AA02 AA04 AB09 AB14 AC01 AC08 AC19 AD14 AD15 AD16 AD17 AD18 AF02 AF04 AF09 AF12 AF13 BB12 DA53 DA67 GH08 5F052 DA04 DB01 GC06 GC07 GC10 HA03 JA07 KA02 5F073 BA05 BA06 CA17 CB02 CB05 DA05 DA07 EA29

Claims (7)

[Claims] 1. A method for manufacturing a single substrate made of a nitride semiconductor by removing a heterogeneous substrate from a nitride semiconductor substrate grown by a vapor phase epitaxial growth method on a heterogeneous substrate, comprising: A step of forming a nitride semiconductor substrate having a growth interface in the nitride semiconductor by performing two-stage growth; and, after forming the growth interface, cutting the nitride semiconductor substrate with a wire saw in a direction parallel to the growth interface. Removing a heterogeneous substrate by performing the method. 2. The nitride semiconductor substrate according to claim 1, wherein the step of cutting the nitride semiconductor substrate with a wire saw is performed after fixing the nitride semiconductor surface to a base with wax, metal, or epoxy resin. A method for manufacturing a single substrate. 3. In the step of forming a growth interface,
2. The method according to claim 1, wherein the nitride semiconductor substrate has at least two or more growth interfaces. 4. In the step of removing the heterogeneous substrate,
The method for manufacturing a single substrate made of a nitride semiconductor according to claim 1, wherein the nitride semiconductor substrate is cut at a growth interface in the nitride semiconductor to be a single substrate. 5. The nitride according to claim 3, wherein the cutting with a wire saw is performed at two or more places in a direction parallel to the growth interface with respect to the nitride semiconductor substrate on which at least two or more growth interfaces are formed. A method for manufacturing a single substrate made of a semiconductor. 6. The method according to claim 1, wherein a blade is used as the nitride semiconductor cutting method. 7. The method according to claim 1, wherein the vapor phase epitaxial growth method is a hydride vapor phase epitaxial growth method.