JP2002338398A - Method for producing nitride semiconductor substrate and method for producing nitride semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of cracks or fractures in a method for producing a nitride semiconductor substrate or a nitride semiconductor device by growing a nitride semiconductor layer on a mother substrate and separating the mother substrate and the nitride semiconductor layer by laser irradiation. SOLUTION: A GaN layer 2 is grown until the thickness of the layer becomes 150 μm by a hydride vapor-phase epitaxy (hereinafter referred to as HVPE) in which ammonia and GaCl formed by reacting metal Ga and HCl at a high temperature of about 900 deg.C are used as raw materials. After the completion of crystal growth, the temperature of the substrate is lowered to a temperature close to the room temperature, and the substrate is taken out of a HVPE device. Thereafter, the GaN layer 2 is heated to 500 deg.C and irradiated with laser light 10 being scanned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a nitride semiconductor substrate, and a method for manufacturing a nitride semiconductor substrate on which a nitride semiconductor device such as a visible light emitting diode device, a blue-violet laser device, and a high-speed transistor is formed. .

[0002]

2. Description of the Related Art Nitride semiconductors such as GaN, InN, and AlN are suitable as materials used for blue and green LEDs, blue semiconductor lasers, high-speed transistors that can operate at high temperatures, and the like.

[0003] A nitride semiconductor layer is grown on a sapphire substrate, and a strong laser beam is applied to the interface between the sapphire substrate and the nitride semiconductor layer, whereby the nitride semiconductor layer is locally heated at the interface of the base material substrate, Technology for decomposing and separating the nitride semiconductor layer from the base material substrate (hereinafter referred to as laser lift-off)
Is being considered.

For example, Japanese Patent Application Laid-Open No. 2000-25222 discloses a method of transferring a nitride semiconductor device onto a host substrate such as silicon using laser lift-off. Hereinafter, a conventional transfer technique will be described with reference to FIG. The base material substrate 1 in FIG. 22A is sapphire. A GaN layer 2 is grown on the base material substrate 1 (FIG. 22B).
Note that a semiconductor device may be formed by growing a stacked structure of a nitride semiconductor instead of the GaN layer 2. GaN layer 2
It is bonded to the host substrate 36 via the adhesive 35 (FIG. 2).
2 (c)). The GaN layer 2 is irradiated with the laser beam 10 through the base material substrate 1. The laser beam 10 has a wavelength that can be transmitted through the sapphire of the base material substrate 1 and absorbed by the GaN layer 2. As the laser light 10, for example, third or higher order harmonic light of a Nd: YAG laser or KrF excimer laser light can be used. The irradiated part generates metal Ga11, and the base material substrate 1 and the GaN layer 2 are separated (FIG. 22).
(D)). When the laser light 10 is scanned and irradiated on the entire surface of the nitride semiconductor layer, the GaN layer 2 and the base material substrate 1 are separated on the entire surface, and the GaN layer 2 can be transferred from the base material substrate 1 to the host substrate 36 (FIG. 22). (E)).

[0005] Also, Japanese Journal of Japan
Applied Physics, vol. 38, page L217-L
219 pages (Japanese Journal of Japan)
fApplied Physics Vol. 38, L
217-L219) has a thickness of 20
A method is described in which laser lift-off is performed from 0 μm to 300 μm without using a host substrate or the like to obtain a single GaN substrate.

[0006]

When the nitride semiconductor layer is decomposed by applying a laser beam to the interface between the sapphire substrate and the nitride semiconductor layer, a very strong light of 0.3 J / cm ² or more is irradiated. Therefore, the temperature of the interface between the sapphire substrate and the nitride semiconductor layer becomes extremely high. For example, the specific heat of GaN is 3.8 J / mol / K,
e (e is the natural logarithm base) has a thickness of about 0.1 μm, so that the heat capacity of a region where GaN absorbs light (hereinafter simply referred to as a light absorption region) is approximately 7 × 10 −
⁷ J / K. If all the irradiated laser light is used to raise the heat in the light absorption region, the temperature rise will be about 10,000 ° C
Also reach. Actually, since the pulse of the laser beam has a finite width, heat is dissipated into the sapphire substrate and the nitride semiconductor layer in addition to the light absorption region, and heat is consumed for decomposition of GaN. Therefore, the temperature in the vicinity of the interface is about several thousand degrees Celsius.

Since the melting point of the sapphire substrate is 2046 ° C., the sapphire substrate may be melted at a temperature higher than that, and may adhere to the GaN layer when it is solidified after irradiation. In this case, the separation of the GaN layer is not performed smoothly, and the stress due to the difference in thermal expansion coefficient concentrates on the locally attached portion. As a result, cracks occur in the GaN layer and the sapphire substrate, and large areas cannot be separated. In addition, the adhesion between the sapphire substrate and the GaN layer when solidifying and adhering after melting is non-uniform. Therefore, after irradiation,
Stress due to the difference in thermal expansion coefficient between the sapphire substrate and the GaN layer is unevenly applied to the GaN layer and the sapphire substrate, and G
Cracks may occur in the aN layer.

When GaN is decomposed, metallic Ga and nitrogen gas are generated. At this time, when the interface is heated to a temperature higher than the boiling point of Ga, high-pressure Ga gas and nitrogen gas are generated. The boiling point of Ga at one atmospheric pressure is 240
3 ° C. For example, at 1 atmosphere and 2500 ° C., 1 cm ³
When GaN is decomposed, about 16000 cm ³ of metal G
a gas and about 8000 cm ³ of nitrogen gas are generated. Thus, the total amount of generated gas is about 2% of the decomposed GaN.
Since it reaches 0000 times or more, the interface expands and cracks may occur in the nitride semiconductor layer or the sapphire substrate, which has been a problem when transferring a semiconductor device or manufacturing a substrate.

In view of the above, it is an object of the present invention to provide a means for performing a laser lift-off without causing cracks or the like in a nitride semiconductor layer in manufacturing a nitride semiconductor substrate by laser light irradiation.

[0010]

Means for Solving the Problems In order to solve the above problems, a method for manufacturing a nitride semiconductor substrate of the present invention has the following configuration.

The method for manufacturing a nitride semiconductor substrate according to the present invention comprises:
Forming a nitride semiconductor layer on the base material substrate; and forming the nitride semiconductor layer on the nitride semiconductor layer such that an interface temperature between the base material substrate and the nitride semiconductor layer is lower than a melting point of the base material substrate. Irradiating light to separate the base material substrate and the nitride semiconductor layer.

With this configuration, the base material substrate is prevented from melting and re-adhering to the nitride semiconductor layer, and the nitride semiconductor layer can be efficiently separated from the base material substrate.

The method for manufacturing a nitride semiconductor substrate according to the present invention comprises:
Forming a nitride semiconductor layer on the base material substrate; and irradiating the nitride semiconductor layer with light such that the temperature of the interface between the base material substrate and the nitride semiconductor layer is lower than the boiling point of Ga. And separating the base material substrate and the nitride semiconductor layer.

With such a configuration, the generated G
Since a is a liquid or a solid, the gas generated is remarkably reduced to only nitrogen, and cracks generated in the nitride semiconductor layer can be prevented.

The method for manufacturing a nitride semiconductor substrate according to the present invention comprises:
Forming a nitride semiconductor layer on a base material substrate; and irradiating the nitride semiconductor layer with light while cooling the base material substrate or the nitride semiconductor layer. And a step of separating

With this configuration, generated Ga becomes a liquid or a solid, and the volume of nitrogen generated by cooling is reduced, so that cracks generated in the nitride semiconductor layer can be prevented.

The method for manufacturing a nitride semiconductor substrate according to the present invention comprises:
Further, in the step of separating the base material substrate and the nitride semiconductor layer, it is preferable that the base material substrate or the nitride semiconductor layer is provided under a condition in which nitrogen is liquefied.
According to this preferred configuration, the generated Ga is a solid, and the generated nitrogen is also liquefied. Therefore, the volume can be significantly reduced, and cracks generated in the nitride semiconductor layer can be prevented.

The method for manufacturing a nitride semiconductor substrate according to the present invention comprises:
Forming a nitride semiconductor layer on a base material substrate; and irradiating the nitride semiconductor layer with light under a condition that a pressure applied to the base material substrate and the nitride semiconductor layer is greater than 1 atm. Separating the substrate from the nitride semiconductor layer.

With such a configuration, the generated G
Since the volume of a and nitrogen can be reduced, cracks generated in the nitride semiconductor layer can be prevented.

The method for manufacturing a nitride semiconductor substrate according to the present invention comprises:
Further, the base material substrate is composed of a first material having a thermal expansion coefficient smaller than that of the nitride semiconductor layer, and a second material having a thermal expansion coefficient larger than that of the nitride semiconductor layer. It is preferable that both of the second materials transmit the light. According to this preferred configuration, it is possible to prevent generation of cracks in the nitride semiconductor layer during light irradiation.

The method for manufacturing a nitride semiconductor device according to the present invention comprises:
Further, the step of forming a nitride semiconductor layer on the base material substrate,
Preferably, the method is a step of forming one or more nitride semiconductor layers to form a semiconductor device. According to this preferred configuration, the nitride semiconductor layer can be efficiently separated from the base material substrate.

The method for manufacturing a nitride semiconductor device according to the present invention comprises:
Forming one or more nitride semiconductor layers on a base material substrate to form a semiconductor device, and a temperature at which an interface temperature between the base material substrate and the nitride semiconductor device is lower than a melting point of the base material substrate. The nitride semiconductor layer is irradiated with light so that the base material substrate and the nitride semiconductor device are separated from each other.

With this configuration, the base material substrate is prevented from melting and re-adhering to the nitride semiconductor device, and the nitride semiconductor device can be efficiently separated from the base material substrate.

Here, the term “nitride semiconductor substrate” means not only a simple single crystal substrate such as a GaN substrate, but also a nitride semiconductor device such as a visible light emitting diode device, a blue-violet laser device, or a high-speed transistor. Refers to a nitride semiconductor substrate on which is formed.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) A method of manufacturing a nitride semiconductor substrate according to a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a diagram showing the first half of the manufacturing process of the nitride semiconductor substrate according to the first embodiment of the present invention.

The base material substrate 1 shown in FIG.
It is a sapphire (single crystal of aluminum oxide) with a thickness of 400 microns, and both the front and back surfaces are mirror-finished. The plane orientation of the surface is the (0001) plane.

The base material substrate 1 is made of sapphire. Since the band gap of sapphire is 8.7 eV, the energy corresponding to the band gap is 142.5 eV.
Light having a wavelength longer than nm is transmitted. Therefore, the wavelength 248
nm KrF excimer laser light or 355 nm wavelength N
d: Third harmonic light of a YAG laser can be transmitted.

First, a nitride semiconductor layer is grown.

Ammonia, metal Ga and HCl are mixed for about 90 minutes.
GaN was grown by hydride vapor phase epitaxy (hereinafter referred to as HVPE) using GaCl produced by reacting at a high temperature of about 0 ° C. as a raw material. The pressure was grown at atmospheric pressure. The growth method is not particularly limited,
The above-mentioned HVPE method can achieve a growth rate of about 50 μm / h, and is therefore suitable for growing a nitride semiconductor of several tens μm to several hundred μm.

In order to increase the nucleation density of GaN on sapphire, the substrate temperature must be increased by 100% prior to GaN growth.
Keep at 0 ° C. and supply only GaCl for 15 minutes (hereinafter, referred to as
This process is called GaCl treatment). For the purpose of increasing the nucleation density, a process of nitriding sapphire with a low-temperature buffer layer or ammonia may be performed instead of the GaCl process, or a combination thereof.

After the GaCl treatment, ammonia is introduced and G
The growth of the aN layer 2 is started. Since the main surface of sapphire constituting the base material substrate 1 is the (0001) plane, the GaN layer 2
Grows with the (0001) plane as the main surface.

The growth was performed until the thickness of the GaN layer 2 became 150 μm (FIG. 1B).

The substrate temperature is lowered to around room temperature and HVP
The substrate was taken out of the E apparatus, and a laser irradiation step was performed.

For the laser irradiation, an apparatus as shown in FIG. 2 was used. The laser beam 10 emitted from the laser device 3 is two-dimensionally scanned by the scan mirror 4. The GaN layer 2 is formed by the light condensing means 5 and the opening 6.
The diameter of the laser beam can be adjusted. The substrate temperature can be adjusted by the cooling means 7 and the heating means 8.
The cooling means can be, for example, a pipe for circulating a refrigerant, and a wide temperature range can be realized by using liquid helium, liquid nitrogen, ammonia, chlorofluorocarbon, water, or the like as the refrigerant. As the heating means 8, for example, a resistance wire heater or the like can be used. Alternatively, a Peltier element serving both as the cooling means 7 and the heating means 8 may be used. The laser device 3 is a third harmonic of Nd: YAG having a wavelength of 355 nm. The pulse width is 5 ns and the pulse period is 10 Hz. Since the laser beam 10 is transparent to sapphire, the GaN layer 2 is irradiated with the laser beam 10 through the base material substrate 1. The laser beam 10 is condensed to form a circle having a diameter of 2 mm at the position of the GaN layer 2. The laser beam 10 is applied to the base material substrate 1
0.2 J / cm ² to ² J /
The light density is in the range of cm ² .

The base material substrate 1 and the GaN layer 2 are warped at room temperature due to different thermal expansion coefficients.
Therefore, in the present embodiment, in order to reduce warpage due to a difference in thermal expansion coefficient between base material substrate 1 and GaN layer 2, base material substrate 1 and GaN layer 2 are heated to 500 ° C. by heating means 8 and irradiated. Do.

The GaN layer 2 is heated to 500 ° C. and irradiated while scanning the laser beam 10 (FIG. 1C).
FIG. 3 shows a schematic diagram of the scanning method. In FIG. 3, the overlap of the spots 37 is depicted away from reality in order to make the figure easier to understand. Only the outermost periphery of the spot 37 is shown, and only the locus of the optical axis is schematically shown. GaN layer 2
Then, the laser light is scanned circularly so that the adjacent irradiation spots 37 overlap each other by 1.5 mm, and the irradiation is performed from the outside to the inside, whereby the entire surface of the GaN layer 2 can be irradiated with the laser light.

With the laser power set to 0.5 J / cm ² ,
The GaN layer 2 is irradiated with a laser beam 10. By the irradiation of the laser beam 10, the interface between the GaN layer 2 and the base material substrate 1 is decomposed, and metal Ga11 and nitrogen gas (not shown) are generated (FIG. 1D). The nitrogen gas is radiated through the region where the surrounding GaN layer 2 and the base material substrate 1 are separated because the substrate is irradiated from the surroundings. Since FIG. 1D is a cross-sectional view, the periphery of the gap between the base material substrate 1 and the GaN
Although the figure is closed by a11, when observed from the top surface, the metal Ga11 is scattered, so that nitrogen can be diffused. The state of the metal Ga11 is liquid at the time of irradiation. Therefore, when the entire GaN layer 2 is irradiated, the GaN layer 2 is
(FIG. 1 (e)).

After the irradiation, the base material substrate 1 and the GaN layer 2
Even if the temperature is lowered to about ° C., since the metal Ga11 is a liquid, the GaN layer 2 is separated from the base material substrate 1 only by holding the base material substrate 1 and lifting the GaN layer 2 by vacuum suction or the like (FIG. 1). (F)). When the temperature is set to 25 ° C. or lower, the metal Ga
Although 1 becomes a solid, Ga is a very soft material even if it is a solid. Therefore, the thickness of the GaN layer 2 is about 50 μm
If it is greater than or equal to the above, even if Ga becomes solid, no crack is generated when it is lifted.

The metal Ga11 adheres to each of the GaN layer 2 and the base material substrate 1, but can be removed using an acid such as hydrochloric acid (FIG. 1 (g)).

Since there is no crack or the like in the GaN layer 2, the GaN layer 2 has a size substantially equal to that of the base material substrate 1.
It can be used as an inch freestanding GaN substrate. Further, the sapphire substrate from which the metal Ga11 has been removed is free from damage and the like, so that it can be used again for growing the GaN layer, thereby reducing the material cost and producing the GaN substrate at low cost.

The appropriate range of the power of the laser beam for separating the base material substrate 1 and the GaN layer 2 is 0.3 J /
cm ² or more and less than 1.5 J / cm ² .

Hereinafter, a case where the laser power is out of the above-described range will be described.

FIG. 4 is a view showing a case where the laser beam is irradiated with a power density of less than 0.3 J / cm ³ , and shows an irradiation step when the laser power is low. At a power density of less than 0.3 J / cm ³ , the GaN layer 2 does not decompose even when irradiated with the laser beam 10. The temperature rise in the laser-irradiated part is G
Since the temperature does not reach the decomposition temperature of aN of about 1000 ° C., no decomposition occurs. Therefore, base material substrate 1 and GaN
Layer 2 cannot be separated.

FIG. 5 shows that the laser power is 1.5 J / cm ^2.
This is the above case, and shows an irradiation step when the laser power is high. FIG. 5A is a diagram during irradiation. Laser light 10
, The GaN layer 2 is decomposed, metal Ga11 and nitrogen (not shown) are generated, and a part of the interface of the base material substrate 1 is also melted by the generated heat, so that the molten sapphire 1
2 has occurred. The generation of alumina 13 in FIG. 5A will be described. When the irradiation spot moves, the temperature of the molten sapphire 12 decreases and solidification starts. At this time,
Since there is metal Ga11 and nitrogen gas generated by the decomposition of the GaN layer 2 around the molten sapphire 12, the metal Ga11 is mixed into the molten sapphire 12, or a part thereof reacts with nitrogen to become AlN. Further, it reacts partially with the metal Ga11 to form an AlGa alloy or an oxide of Ga. Further, part of oxygen in sapphire is decomposed and diffused. Therefore, when the molten sapphire 12 is re-solidified, it does not become a single crystal, but becomes a polycrystalline alumina 13 containing many impurities such as Ga and nitrogen. Alumina 13 takes in metallic Ga11 and nitrogen and increases in volume, and adheres and deposits on base material substrate 1 and GaN layer 2. FIG. 5 (a)
The alumina 13 in the inside is formed in this manner.

Since the alumina 13 is deposited on the base material substrate 1 and the GaN layer 2 from the liquid phase, it has a strong adhesive force. Also, alumina itself is hard and does not easily deform. In addition, the GaN layer 2 and the base material substrate 1 are unevenly attached via the alumina 13. For this reason, in the step of lowering the temperature to room temperature after irradiation, stress is unevenly applied to the base material substrate 1 and the GaN layer 2. In the present embodiment, since the GaN layer 2 is thinner than the base material substrate 1, cracks occur in the GaN layer 2 (FIG. 5B). Moreover, since the alumina layer 13 is formed on the surface of the base material substrate 1, the alumina layer 13 cannot be removed by a treatment such as an acid treatment, and the base material substrate 1 can be easily reused for GaN growth. Can not. Note that hatching is omitted in the GaN layer 2 of FIG. 5B to show the appearance of cracks.

The above result is briefly described as follows.
/ Cm ² at 500 ° C. decomposed,
If the decomposition temperature of N is 1000 ° C., 0.3 J / cm ²
Is believed to cause a temperature rise of about 500 ° C.
At 1.5 J / cm ² , the temperature rises by about 2500 ° C. Therefore, it is considered that the interface of the base material substrate 1 in contact with the GaN layer 2 is heated to the melting point of sapphire of 2046 ° C. or more.

According to the manufacturing method of the present embodiment described above, the temperature of the interface between the base material substrate and the nitride semiconductor layer, which rises by laser irradiation, is set to be equal to or lower than the melting point of the base material substrate.
It has been shown that a standard GaN substrate having a large area of 2 inches can be manufactured at low cost without lowering the yield due to cracks or the like.

The range of power at which a GaN substrate without cracks can be obtained is when the transmittance of laser light changes due to a rough back surface of the sapphire substrate or a layer formed on the back surface. It goes without saying that it changes.

The range of power that can provide a crack-free GaN substrate depends on the laser pulse width, pulse waveform,
Needless to say, it changes depending on the laser beam shape.

In the first embodiment, the base material substrate 1
Instead of sapphire, a substrate that transmits the laser beam 10 can be used. Examples of such a substrate include a spinel substrate and an AlN substrate. When the material of the substrate changes, the melting point of the material changes, and it goes without saying that the upper limit of the light density that can be irradiated changes. At this time, it is needless to say that the melting point of the surface of the base material substrate is preferably higher than the decomposition temperature of GaN.

(Embodiment 2) FIG. 6 is a diagram showing a manufacturing process of a nitride semiconductor device according to a second embodiment of the present invention. The second embodiment of the present invention is a case where a semiconductor device is formed on the GaN substrate of the first embodiment.

The base material substrate 1 shown in FIG.
It is sapphire with a thickness of 400 microns and has a mirror-finished surface on both sides. The plane orientation of the surface is (000
1) Surface.

A nitride semiconductor layer is grown in the same manner as in the first embodiment.

Ammonia, metal Ga and HCl are mixed for about 90 minutes.
GaN is grown by a hydride vapor phase epitaxy method (hereinafter referred to as an HVPE method) using GaCl produced by a reaction at a high temperature of about 0 ° C. as a raw material.

Prior to the growth of GaN, the substrate temperature was set at 100
Hold at 0 ° C. and perform GaCl treatment for 15 minutes. After the GaCl treatment, ammonia is introduced to start the growth of the GaN layer 2. In order to make the GaN layer 2 n-type, H
A silane gas is introduced at a flow rate of about 1/100 to 1 / 10,000 of Cl. Growth is performed until the thickness of the GaN layer 2 becomes 150 μm (FIG. 6B).

Next, the substrate temperature is lowered to around room temperature,
The substrate is taken out from the HVPE apparatus, and a laser irradiation step is performed.

The laser irradiation step, the apparatus used and the method of scanning the laser beam 10 are exactly the same as those in the first embodiment.

The GaN layer 2 is heated to 500 ° C. and irradiated while scanning the laser beam 10 from the surroundings (FIG. 6).
(C)).

By irradiating a laser beam 10 with an appropriate laser power of 0.5 J / cm ^2, the base material substrate 1 of the GaN layer 2
Decomposes to generate metallic Ga and nitrogen gas. The appropriate laser power is a power that makes the temperature at the interface between the GaN layer 2 and the base material substrate 1 equal to or lower than the melting point of the base material substrate 1. G
When the entire aN layer 2 is irradiated, the GaN layer 2 becomes
And only weakly adhere via the metal Ga11 (FIG. 6D). In addition, the power range of the laser beam suitable for performing the separation is determined in exactly the same manner as in the first embodiment.
0.3 J / cm ² or more and less than 1.5 J / cm ² .

After the irradiation, the base material substrate 1 and the GaN layer 2 are cooled to room temperature, and while holding the base material substrate 1,
When the layer 2 is lifted, the GaN layer 2 is separated from the base material substrate 1 (FIG. 6E). Through the above steps, a self-supporting GaN layer 2 having a diameter of 2 inches is obtained. The base material substrate 1 is removed, and only the GaN layer 2 is used below. The base material substrate 1 can be cleaned and polished to remove Ga on the surface, and can be applied to the growth of the GaN layer again.

Metal Ga 11 adhered to GaN layer 2
Is removed using an acid such as hydrochloric acid (FIG. 6 (f)).

Next, a nitride semiconductor device is grown. Metal organic chemical vapor deposition (hereinafter abbreviated as MOCVD) is used for the growth. The Ga source is trimethylgallium (hereinafter abbreviated as TMG), the Al source is trimethylaluminum (hereinafter abbreviated as TMA), and the In source is trimethylindium (hereinafter abbreviated as TMI). The N raw material is ammonia. The transport gas for the raw material is hydrogen or nitrogen. The pressure is 0.1 atm. During the growth of GaN and AlGaN, the transport gas is hydrogen, the molar flow ratio of the group V source to the group III source is 4000, and the growth temperature is 1050 ° C. The mixed crystal ratio of AlGaN was controlled by controlling the flow ratio of TMG and TMA. During the growth of InGaN, the transport gas is nitrogen, and the molar flow ratio between the group V material and the group III material is 100.
00, and the growth temperature is 750 ° C. The mixed crystal ratio of InGaN is controlled by controlling the flow ratio of TMG and TMI.

First, an undoped In _0.2 Ga _0.8 N active layer 23 having a thickness of 50 nm is formed on the GaN layer 2 using nitrogen as a transport gas. Next, using a transport gas of hydrogen, a Mg-doped p-type Al _0.05 Ga _0.95 N clad layer 24 is formed to a thickness of 1 μm, and a Mg-doped p-type GaN contact layer 25 is formed to a thickness of 0.1 μm.
It grows to a thickness of 1 μm (FIG. 6 (g)).

An n-electrode 26 having a multilayer structure of Ti and Al is in contact with the GaN layer 2, and a p-electrode 27 having a multilayer structure of Ni and Au is in contact with the p-type GaN contact layer 25.
Are formed by vapor deposition (FIG. 6 (h)). Note that the n-electrode 26 or the p-electrode 27 may be a thin electrode capable of transmitting light with a thickness of about 100 nm for the purpose of improving light extraction efficiency.

Finally, G is obtained by cleavage or dicing.
When the layer structure formed on the aN layer 2 and the GaN layer 2 is divided, an LED chip is obtained (FIG. 6 (i)).

In the above steps, the GaN layer 2 and the base material substrate 1
Cracks do not occur. Therefore, an LED can be obtained from almost the entire surface of the GaN layer 2 having a diameter of 2 inches.
Since the LED completed as described above does not have a sapphire substrate and has electrodes disposed on both sides, the area of the entire semiconductor device can be reduced with the same light emitting layer area as compared with the related art. Therefore, it is advantageous for miniaturization of a semiconductor device. Further, since a larger number of semiconductor devices can be formed from a single wafer than in the past, it is advantageous in terms of cost.

That is, according to the present embodiment, it is possible to provide a method capable of manufacturing an LED advantageous for miniaturization and cost reduction without lowering the yield due to cracks.

In the second embodiment, it goes without saying that other nitride semiconductor devices such as lasers and FETs can be formed in exactly the same manner instead of LEDs. In particular, when the nitride semiconductor device to be formed is a laser, the above-described LE
In addition to the advantage of D, there is an advantage that the cavity end face can be formed by cleavage.

In the second embodiment, the GaN layer 2
It is needless to say that the LED can be completed without increasing the necessary equipment even if a nitride semiconductor device is formed by MOCVD after the growth of the semiconductor device and a laser irradiation step is performed thereafter.

(Embodiment 3) A method of manufacturing a GaN substrate according to a third embodiment of the present invention will be described with reference to FIGS.

FIG. 7 is a diagram showing the first half of the manufacturing process of the nitride semiconductor substrate according to the third embodiment of the present invention.

The substrate shown in FIG. 7A has a diameter of 2 inches and a thickness of 3 inches.
An AlN layer 21 made of aluminum nitride single crystal is formed on a base material substrate
It was grown to a thickness of μm. The single crystal of aluminum nitride can be formed, for example, by growing it at 1000 ° C. by MOCVD or the like. The base material substrate 1 is mirror-finished on both the front and back surfaces. The plane orientation of aluminum nitride on the surface is the (0001) plane.

The band gap of aluminum nitride is 6.
Since the energy is 2 eV, light having a wavelength greater than 193 nm having energy corresponding to the band gap is transmitted. Therefore, a KrF excimer laser beam having a wavelength of 248 nm or a wavelength of 3
It can transmit the third harmonic light of a 55 nm Nd: YAG laser.

First, the GaN layer 2 is grown. Growth is
The HVPE method is the same as in the first embodiment. The pressure was grown at atmospheric pressure.

AlN and GaN are the same nitride.
Since the adhesion between 1N and GaN is good, single crystal GaN can be directly grown at 1000 ° C. without performing GaCl treatment or the like.

Then, the GaN layer 2 was grown directly on the AlN layer 21 and was grown until the film thickness became 150 μm (FIG. 7B).

Next, laser light irradiation was performed. The irradiation apparatus and irradiation conditions are the same as those in the first embodiment.
The layer 2 was heated to 500 ° C. and irradiated while scanning with the laser beam 10 (FIG. 7C). As in FIG. 3 of the first embodiment, a laser beam was scanned from the outside of the GaN layer 2 so that adjacent irradiation spots overlap by 1.5 mm.

The power of the laser beam 10 is set to 0.5 J / cm ²
The laser light 10 is transmitted through the base material substrate 1 and the AlN layer 21 to irradiate the GaN layer 2. By the irradiation of the laser beam 10, the interface between the GaN layer 2 and the AlN layer 21 is decomposed, and metal Ga11 and nitrogen gas (not shown) are generated (FIG. 7D). When the entire GaN layer 2 is irradiated, the GaN layer 2 and the AlN layer 21 only weakly adhere via the metal Ga11 (FIG. 7E). After the irradiation, the GaN layer 2 is lowered to around room temperature, and the GaN layer 2 is held while holding the base material substrate 1.
The GaN layer 2 is separated from the AlN layer 21 only by lifting (FIG. 7F).

The metal Ga11 adheres to the GaN layer 2 and the AlN layer 21, but can be removed using an acid such as hydrochloric acid (FIG. 7 (g)). The GaN layer 2 has no cracks or the like, and has a size of about 2 inches, which is almost the same size as the base material substrate. The GaN layer 2 can be used as a self-standing GaN substrate. Since no damage or the like is introduced into the AlN layer 21 from which the metal Ga11 has been removed, it can be used again for growing the GaN layer, and a GaN substrate can be manufactured at low cost.

The appropriate range of laser power for separating the GaN layer 2 and the AlN layer 21 is 0.3 J / c
m ² or more and less than 1.7 J / cm ² . Since the melting point of single crystal AlN is 2450 ° C., which is higher than the melting point of sapphire, the upper limit of the appropriate laser power is wider than in the first embodiment.

Hereinafter, the case where the laser power is in the range other than the above will be described.

FIG. 8 is a view showing a case in which a power density of less than 0.3 J / cm ³ is applied, and shows an irradiation step when the laser power is low. At a power density of less than 0.3 J / cm ³ , the GaN layer 2 does not decompose even when irradiated with the laser beam 10 as in the first embodiment. Therefore, Al
The N layer 21 and the GaN layer 2 cannot be separated.

FIG. 9 shows that the laser power is 1.7 J / cm ^2.
This is the case described above, and shows a diagram during irradiation when the laser power is high. The GaN layer 2 is decomposed to generate metal Ga11 and nitrogen (not shown), but as the irradiation reaches the center of the wafer, the GaN layer 2 blows off along the shape of the irradiation spot. Therefore, a free standing GaN substrate having a diameter of 2 inches cannot be obtained. The AlN layer 21
No polycrystalline precipitation was observed on the top. 1.7J /
If it is less than 1.7 cm ² , no cracking occurs and 1.7 J
The phenomenon that the GaN layer 2 blows off was observed with the threshold value of / cm ² .

This phenomenon will be described below. Estimating from the result of the first embodiment, it is considered that the temperature of the GaN layer 2 is heated to about 2500 ° C. when the laser beam of 1.7 J / cm ² is irradiated. Therefore, it is considered that the generated Ga11 is a gas exceeding the boiling point of the metal Ga11 of 2403 ° C. Since the gas to be generated includes not only nitrogen but also gaseous Ga, if the temperature of the interface exceeds the boiling point of Ga, the pressure of the generated gas is significantly increased and G
It is considered that the aN layer 2 blows away. Therefore, the metal Ga
The GaN layer 2 is used as a threshold for the laser power at which
It is considered that the phenomenon of blowing away is observed. In addition, since the metal gas has a high viscosity, laser irradiation is performed from the surroundings. However, the generated gas does not easily diffuse from the gap between the GaN layer 2 and the AlN substrate 1, and cracks occur due to pressure.

According to the manufacturing method of the present embodiment described above, the temperature of the interface between the base material substrate and the nitride semiconductor layer, which is raised by laser irradiation, is set to be equal to or lower than the boiling point of Ga. It has been shown that a GaN substrate can be manufactured at low cost without lowering the yield due to cracks or the like.

(Embodiment 4) FIG. 10 shows a fourth embodiment of the present invention.
FIG. 10 is a diagram illustrating a manufacturing process of the nitride semiconductor device according to the embodiment. The fourth embodiment of the present invention is the same as the third embodiment.
In this case, a semiconductor device is formed on the GaN substrate according to the embodiment.

The substrate shown in FIG. 10A is formed on a base material substrate 1 made of sapphire having a diameter of 2 inches and a thickness of 300 microns.
An AlN layer 21 made of a single crystal of aluminum nitride is grown. Both the front and back are mirror-finished. The plane orientation of aluminum nitride on the surface is (000
1) Surface.

First, the GaN layer 2 is grown. The GaN layer 2 is grown directly on the AlN layer 21 and has a thickness of 150
The growth was performed until the thickness reached μm (FIG. 10B).

Next, laser light irradiation was performed. The irradiation apparatus and irradiation conditions are the same as those in the third embodiment.
The layer 2 was heated to 500 ° C. and irradiated while scanning the laser beam 10 (FIG. 10C). As in FIG. 3 of the first embodiment, the laser beam was scanned from the outside of the GaN layer 2 so that adjacent irradiation spots overlap by 1.5 mm.

The power of the laser beam 10 is set to 0.5 J / cm ²
The laser light 10 is transmitted through the base material substrate 1 and the AlN layer 21 to irradiate the GaN layer 2. By the irradiation of the laser beam 10, the interface between the GaN layer 2 and the AlN layer 21 is decomposed, and metallic Ga and nitrogen gas are generated. When the entire GaN layer 2 is irradiated, the GaN layer 2 is made of AlN layer 21 and metal Ga11.
(FIG. 10 (d)). After the irradiation, the GaN layer 2 is lowered to about 30 ° C.
Only by lifting the GaN layer 2 while maintaining the AlN
The GaN layer 2 is peeled from the layer 21 (FIG. 10E). G
The aN layer 2 has no cracks and the like, and has a size of 2 inches which is almost the same size as the base substrate. On the other hand, since no damage or the like has been introduced into the AlN layer 21, the metal Ga11 can be removed and used again for growing the GaN layer. Hereinafter, only the GaN layer 2 is used.

The range of the appropriate laser power for separating the GaN layer 2 and the AlN layer 21 is described in Embodiment 3.
0.3J / cm ² or more and 1.7J
/ Cm ² .

Metal Ga 11 adhered to GaN layer 2
Is removed using an acid such as hydrochloric acid (FIG. 10 (f)).

Next, a nitride semiconductor device was grown. The growth method of each nitride semiconductor layer and the structure of the nitride semiconductor device are as follows.
This is the same as in the second embodiment.

That is, when the transport gas is nitrogen and GaN
An undoped In _0.2 Ga _0.8 N active layer 23 is formed on
A thickness of nm is formed. Next, using hydrogen as the transport gas, Mg
1 μm of doped p-type Al _0.05 Ga _0.95 N clad layer 24
Mg-doped p-type GaN contact layer 25
Is grown to a thickness of 0.1 μm (FIG. 10 (g)).

An n-electrode 26 having a multilayer structure of Ti and Al is in contact with the GaN layer 2, and a p-electrode 27 having a multilayer structure of Ni and Au is in contact with the p-type GaN contact layer 25.
Is formed by vapor deposition (FIG. 10 (h)).

Finally, G is obtained by cleavage or dicing.
When the layer structure formed on the aN layer 2 and the GaN layer 2 is divided, an LED chip is obtained (FIG. 10 (i)).

In the above steps, the GaN layer 2 and the base material substrate 1
Cracks do not occur. Therefore, 2 inch diameter GaN
An LED can be obtained from almost the entire surface of the layer 2. The LED completed as described above does not have a sapphire substrate, and electrodes are arranged on both sides.
Conventionally, the area of the entire semiconductor device can be reduced. Therefore, it is advantageous for miniaturization of a semiconductor device. Further, since a larger number of semiconductor devices can be formed from one wafer than in the past, it is advantageous in terms of cost.

That is, by setting the temperature of the interface between the base material substrate and the GaN layer at the time of laser irradiation to be equal to or lower than the boiling point of Ga as in this embodiment, an LED advantageous for miniaturization and cost reduction can be obtained. A method that can be manufactured without lowering the yield due to the above.

In the fourth embodiment, it goes without saying that other nitride semiconductor devices such as lasers and FETs can be formed in exactly the same manner instead of LEDs. In particular, when the nitride semiconductor device to be formed is a laser, the above-described LE
In addition to the advantage of D, there is an advantage that the cavity end face can be formed by cleavage.

In the fourth embodiment, the GaN layer 2
It is needless to say that the LED can be completed without increasing the necessary equipment even if a nitride semiconductor device is formed by MOCVD after the growth of the semiconductor device and a laser irradiation step is performed thereafter.

(Embodiment 5) FIGS. 11 to 13 are views showing a method of manufacturing a nitride semiconductor device according to a fifth embodiment of the present invention.

The wafer 14 shown in FIG. 11A is a sapphire wafer having a diameter of 2 inches and a thickness of 150 microns. The wafer 15 is a quartz glass wafer having a diameter of 2 inches and a thickness of 600 microns. In the following figures, the reason why the wavy lines are provided on the left and right of the layer is to show that the figure is an enlarged view of the vicinity of one semiconductor device in the wafer and that there are layers on the left and right.

A quartz glass wafer 15 is placed between two sapphire wafers 14, and heated at about 1800 ° C., which is higher than the softening point of quartz glass and lower than the melting point of sapphire. Then, the quartz glass wafer 15 and the sapphire wafer 14 can be fused together without damaging the sapphire wafer 14, and one base material substrate 1 can be obtained (FIG. 11B).

This base material substrate 1 is made of quartz glass wafer 15
By disposing the sapphire wafer 14 on both sides of the main surface,
The thermal expansion coefficient distribution in the direction perpendicular to the direction is symmetric. So
Therefore, warpage occurs even at room temperature and during heating.
Does not occur. The coefficient of thermal expansion of sapphire is 7.8 ×
10^-6K^-1The thermal expansion coefficient of quartz glass is 0.5 × 10 ^-6
K^-1And the thermal expansion coefficient of GaN is 5.6 × 10^-6K^-1
It is. Quartz glass with smaller thermal expansion coefficient than GaN and G
Appropriate thickness for sapphire with a larger coefficient of thermal expansion than aN
Because they are bonded, the thermal expansion coefficient in the plane direction is
Almost the same. Therefore, the thermal expansion
GaN can be grown without adding distortion due to number difference
You.

Next, a nitride semiconductor device is grown. The MOCVD method is used for the growth. The raw materials and growth conditions are the same as in the second embodiment.

First, an AlN layer 21 having a thickness of 80 nm is formed on the base material substrate 1 at a temperature of 600 ° C. before forming a semiconductor device structure by using hydrogen as a transport gas. Next, a Si-doped n-type GaN contact layer 22 is formed to a thickness of 3 μm. Subsequently, the transport gas was changed to nitrogen and undoped In _0.2
The Ga _0.8 N active layer 23 is formed to a thickness of 50 nm. Again using the transport gas as hydrogen, Mg-doped p-type Al _0.05 Ga
_{A 0.95} N cladding layer 24 is formed to a thickness of 1 μm, and a Mg-doped p-type GaN contact layer 25 is grown to a thickness of 0.1 μm (FIG. 11C).

A part of n-type GaN contact layer 22 is exposed by reactive ion etching using chlorine gas, and Ti and Al are brought into contact with n-type GaN contact layer 22.
And a p-electrode 27 having a multilayer structure of Ni and Au in contact with the p-type GaN contact layer 25 is formed by vapor deposition and photolithography. The size of the semiconductor device is approximately 500 μm square.

Thus, an LED semiconductor device structure can be formed (FIG. 11D).

Next, a fusion step is performed.

The AuSn solder 28 is previously arranged on the Si submount 29 in substantially the same shape as the LED electrode pattern. By mounting the AuSn solder 28 and the n-electrode 26 and the p-electrode 27 in close contact and heating to 350 ° C., the LED semiconductor device is fused to the Si submount 29 (FIG. 12E). The thickness of the AuSn solder is 1
If the thickness is set to 0 μm or more, the difference in height between the n-electrode 26 and the p-electrode 27 hardly affects the fusion.

Next, a transfer step by laser irradiation is performed.

Laser irradiation is performed under the same apparatus and conditions as in the first embodiment. The diameter of the laser beam is 2 mm, while the size of the semiconductor device is 500 μm. Therefore, when transferring only one semiconductor device as in this embodiment, it is not necessary to scan with a laser, and it is only necessary to irradiate once so that the semiconductor device is included.

Since the base material substrate 1 is made of sapphire and quartz glass transparent to the third harmonic laser light of Nd: YAG, it transmits the laser light. Also, the AlN layer 21
Since almost no laser light is absorbed, the laser light is n-type G
It is absorbed near the interface between the aN contact layer 22 and the AlN layer 21.

In this embodiment, since the thickness of the semiconductor device layer structure is as thin as about 4 μm, the decomposition temperature at the time of laser irradiation must be lowered to prevent generation of Ga gas. It is necessary to pay attention to the amount of gas generated. This will be described below.

In the present embodiment, the light density of the laser is set to 0.1.
And 4J / cm ^2, the area where the n-type GaN contact layer at this time is decomposed is about 40 nm.

At the time of laser irradiation, n-type GaN contact layer 22 floats from base material substrate 1 due to nitrogen generated. Assuming that the substrate temperature at the time of laser irradiation is 500 ° C., the distance that the n-type GaN contact layer 22 floats from the base material substrate 1 due to the generated nitrogen is 120 μm assuming that no crack occurs.
To the extent. Actually, it cannot withstand a deformation of 120 μm, and cracks occur in the nitride semiconductor.

Therefore, at the time of laser irradiation, cooling water is introduced into the cooling means 7 to cool the substrate to about 10 ° C. Thus, the amount of n-type GaN contact layer 22 floating from base material substrate 1 can be reduced, and cracks can be prevented. At this time, since the distance between the AlN layer 21 and the n-type GaN contact layer 22 is as small as about 40 μm as compared with the irradiation size of 2 mm in diameter, the nitride semiconductor layer only bends and no crack occurs (FIG. (F)). Note that metal Ga11 is generated between the AlN layer 21 and the n-type GaN contact layer 22. The voids other than the metal Ga11 are filled with nitrogen gas generated by decomposition.

To satisfactorily separate the nitride semiconductor device,
The nitride semiconductor around the submount 29 is scribed with a diamond scriber (FIG. 13G). Submount 2
When the substrate 9 is detached from the base material substrate 1, the LED chips are divided along the markings, and the LEDs adhere to the submount 29 and can be separated from the base material substrate 1 (FIG. 13 (h)). LE
The metal Ga11 attached to the D chip may absorb the light of the LED and reduce the luminous efficiency, so that the metal Ga11 may be removed by immersing it in hydrochloric acid or the like for a short time. At this time, if the time of the treatment with hydrochloric acid is set to be long, care must be taken because Al of the n-electrode 26 is corroded.

When a nitride semiconductor grown on a sapphire substrate is irradiated with a laser at room temperature, cracks occur in the sapphire substrate and the nitride semiconductor, which may cause a reduction in yield. This is because stress due to the difference in thermal expansion coefficient is concentrated at the boundary between the laser irradiation part and the non-irradiation part. On the other hand, in the present embodiment, the base material substrate 1 made of a composite material having a thermal expansion coefficient substantially equal to that of the nitride semiconductor is used as the base material substrate for forming the GaN semiconductor device. No cracks or the like occur in the base material substrate 1 or the GaN semiconductor device without the stress due to the concentration. Also, after forming an LED on the entire surface of the base material substrate 1 and performing a transfer process, the base material substrate 1
Can be used again for the growth of the nitride semiconductor layer, and the cost of raw materials can be reduced and the LED can be manufactured at low cost.

As in the present embodiment described above, by cooling the substrate at the time of laser irradiation, the thin film GaN can be separated without cracks, and can be used for transferring a GaN semiconductor device. It is possible. In addition, due to the composite substrate whose coefficient of thermal expansion is controlled, even during cooling,
Laser irradiation is possible without generating stress due to the difference in thermal expansion coefficient.

When the laser irradiation size is reduced, the floating amount of the n-type GaN contact layer must be reduced, so that the substrate must be cooled to a lower temperature. On the other hand, when the irradiation size of the laser increases, the temperature of the substrate may be increased. However, since laser irradiation raises the temperature of the nitride semiconductor layer and the entire base material substrate, even when the substrate is irradiated at a temperature of several hundred degrees Celsius, depending on conditions such as laser power, the gas may be directly above the substrate. Needless to say, a mechanism for maintaining the temperature of the substrate uniformly at the set temperature within the plane by an effective cooling means such as by flowing is required.

When cooling is performed in the air, water droplets and the like adhere to the substrate 1 and the like and refract the laser beam, which may adversely affect laser irradiation. In order to prevent this, it is preferable to install the substrate 1 in an atmosphere such as dry air or dry nitrogen.

Although the LED structure is used in the fifth embodiment, it goes without saying that a similar effect can be obtained with another semiconductor device structure or a nitride semiconductor thin film.

(Embodiment 6) FIGS. 14 and 15 are views showing a method of manufacturing a nitride semiconductor substrate according to a sixth embodiment of the present invention.

The wafer 14 shown in FIG. 14A is a sapphire wafer having a diameter of 2 inches and a thickness of 150 microns. The wafer 15 is a quartz glass wafer having a diameter of 2 inches and a thickness of 600 microns.

As shown in FIG. 14B, the fifth embodiment
In exactly the same manner as described above, the quartz glass wafer 15 and the two sapphire wafers 14 are heated and fused at about 1800 ° C.
A base material substrate 1 is manufactured.

Next, G is applied by the same MOCVD method as in the second embodiment.
An aN layer is grown. The growth conditions are the same as in the fifth embodiment except that doping is not performed.
Then, the GaN layer 2 is grown to 5 μm (FIG. 14).
(C)).

Next, a laser irradiation step is performed.

In this embodiment, the light density of the laser is set to 0.1.
And 4J / cm ^2, the area where the n-type GaN contact layer at this time is decomposed is about 40 nm. In the present embodiment, the entire surface of the substrate is scanned with the laser beam 10 by the same method as in FIG.

By introducing cooling water into the cooling means 7 at the time of laser irradiation and cooling the substrate temperature to about 10 ° C., the amount of floating of the GaN layer 2 from the base material substrate 1 due to the generated nitrogen is reduced. 2 to prevent cracks.

The laser irradiation causes the AlN layer 21 and Ga
A metal Ga11 is generated between the metal layer 11 and the N layer 2. AlN layer 21
And the GaN layer 2 are weakly attached via the soft solid metal Ga11 (FIG. 14D).

Since the GaN layer 2 is very thin, about 5 μm, it is preferable that the metal Ga 11 be liquefied by heating to about 30 ° C. at the time of peeling. A holding jig 31 having an appropriate mechanism such as electrostatic suction so that the GaN layer 2 can be uniformly sucked.
By using GaN, the GaN layer 2 can be separated from the AlN layer 21 (FIG. 15E).

Metal Ga 11 adhered to GaN layer 2
Is preferably a holding jig 3 so that the GaN layer 2 is not broken.
While holding at 1, it can be removed with hydrochloric acid or the like (FIG. 15 (f)).

The GaN layer 2 separated by the above method can be used as a substrate. For example, a 5 μm GaN layer 2
Can be used as an underlayer substrate on which GaN can be grown thick without stress.

In this embodiment, since the base material substrate for forming a GaN semiconductor device is base material substrate 1 having a thermal expansion coefficient substantially equal to that of a nitride semiconductor, stress due to the thermal expansion coefficient is concentrated by laser irradiation. Thus, no cracks or the like occur in the base material substrate 1 or the GaN layer 2. Therefore, G
The aN layer 2 has a large area of about 2 inches, which is almost the same as that of the base material substrate 1, and has a fixed shape.

As described above, by cooling the substrate at the time of laser irradiation, cracks do not occur, and it is possible to form a thin-film large-area GaN substrate, which is extremely difficult to manufacture by the conventional method.

When the laser irradiation size is reduced, the amount by which the GaN layer 2 floats must be reduced, so that the substrate must be cooled to a lower temperature. On the other hand, when the irradiation size of the laser increases, the temperature of the substrate may be increased. However, since laser irradiation raises the temperature of the nitride semiconductor layer and the entire base material substrate, even when the substrate is irradiated at a temperature of several hundred degrees Celsius, depending on conditions such as laser power, the gas may be directly above the substrate. Needless to say, a mechanism for maintaining the temperature of the substrate uniformly at the set temperature within the plane by an effective cooling means such as by flowing is required.

When cooling is performed in the air, water droplets and the like adhere to the substrate 1 and the like, refracting the laser light, which may adversely affect laser irradiation. In order to prevent this, it is preferable to set the base material substrate 1 in an atmosphere such as dry air or dry nitrogen.

(Seventh Embodiment) A method for manufacturing a nitride semiconductor device according to a seventh embodiment of the present invention will be described with reference to FIGS. The seventh embodiment is substantially the same as the fifth embodiment except that the separation conditions are different from those of the fifth embodiment.

The wafer 14 in FIG. 16A is a sapphire wafer having a diameter of 2 inches and a thickness of 150 microns. The wafer 15 is a quartz glass wafer having a diameter of 2 inches and a thickness of 600 microns.

As shown in FIG. 16B, the third embodiment
In exactly the same manner as described above, the quartz glass wafer 15 and the two sapphire wafers 14 are heated and fused at about 1800 ° C.
A base material substrate 1 is manufactured.

Next, the same nitride semiconductor device as that of the fifth embodiment is grown. The growth conditions and the like are the same as in the fifth embodiment.
The 1N layer 21 is 80 nm, the Si-doped n-type GaN contact layer 22 is 3 μm, the undoped In _0.2 Ga _0.8 N active layer 23 is 50 nm, the Mg-doped p-type Al _0.05 Ga _0.95 N clad layer 24 is 1 μm, and the Mg-doped p-type GaN contact A layer 25 is sequentially grown to a thickness of 0.1 μm (FIG. 16)
(C)).

A portion of the n-type GaN contact layer 22 is exposed by reactive ion etching,
6. A p-electrode 27 is formed. The size of the semiconductor device is approximately 500 μm square.

Thus, an LED structure can be formed (FIG. 16).
(D)).

The subsequent fusing step is the same as in the fifth embodiment. That is, the AuSn solder 28 patterned on the Si submount 29, the n-electrode 26, and the p-electrode 27 are placed in close contact with each other, and heated to 350 ° C. to fuse the Si submount 29 and the LED semiconductor device. I do.

Next, a scribe for effectively separating the nitride semiconductor device is formed on the n
17 is formed on the p-type GaN contact layer 22 (FIG. 17).
(E)).

Next, a transfer step by laser irradiation is performed.

In the present embodiment, the following replacement is made to the fifth embodiment. As the laser, a low-output laser that is easy to handle is used. Since the laser has a low output, the irradiation size is focused to 50 μm, and the light density of the laser is set to 0.4 J / cm ² . Since the irradiation size is smaller than the semiconductor device size, the entire semiconductor device is irradiated using the scan mirror 4.

The amount of GaN decomposed by laser irradiation,
The ratio to the amount of generated nitrogen is the same regardless of the spot diameter, as long as the temperature and pressure are the same. Therefore, when the spot size is reduced, the ratio between the spot size and the distance at which the n-type GaN contact layer 22 floats from the AlN layer 21 due to nitrogen becomes larger. As a result, since the n-type GaN contact layer 22 is deformed with a larger curvature, cracks are very likely to occur.

For this reason, in this embodiment mode, the substrate is cooled and irradiated under a condition where nitrogen is liquefied.

When liquid nitrogen is used as the refrigerant, the temperature of the n-type GaN contact layer 22 becomes slightly higher because cold air is diverged. Then, the liquid nitrogen is sent to the cooling pipe at approximately atmospheric pressure, and the substrate 1 on which the nitride semiconductor layer is formed
Is introduced into a container 33 having a window 32 through which a Nd: YAG laser is transmitted, and is pressurized to 10 atm and irradiated with a laser beam 10 (FIG. 17F).

By applying pressure in this manner, it is possible to reduce the volume of generated nitrogen. For example, when laser irradiation is performed in a pressurized atmosphere of 10 atm, the volume of generated nitrogen can be reduced to one tenth in the case of 1 atm.
Furthermore, when the temperature is equal to or lower than the critical temperature of nitrogen as in the present embodiment, the conditions for liquefying the nitrogen can be obtained by appropriately setting the pressurizing pressure. In an atmosphere containing nitrogen, nitrogen may be liquefied and adhere to the base material substrate 1 in some cases. Also,
A gas having a boiling point higher than the temperature of the base material substrate 1 may also adhere to the base material substrate 1. In order to prevent them, irradiation is performed in an atmosphere having a low boiling point, such as a pure hydrogen atmosphere.

By the irradiation of the laser beam 10, the n-type GaN
Between the contact layer 22 and the AlN layer 21, a region 34 made of liquefied nitrogen and metallic Ga is formed.

In the present embodiment, since the substrate is cooled under the condition where the nitrogen is liquefied, when the GaN is decomposed by the irradiation of the laser beam, the generated nitrogen quickly becomes a liquid. The decomposition products of GaN are solid Ga and liquid nitrogen, and the volume is about twice the original GaN volume. At this time, the distance between the n-type GaN contact layer 22 and the AlN layer 21 is about 80 nm, which is much smaller than the spot size of 50 μm. Therefore, the deformation of the nitride semiconductor growth layer can be significantly reduced. As a result, it is possible to prevent the occurrence of cracks (FIG. 18).
(G)).

Then, the temperature of the liquid nitrogen is maintained, or
After the temperature is slowly increased so that nitrogen does not rapidly evaporate, the submount 29 is detached from the base material substrate 1 using an appropriate jig such as vacuum suction. Can be separated from the material substrate 1 (FIG. 1)
8 (h)). In the region 34 composed of liquefied nitrogen and metallic Ga attached to the LED, nitrogen evaporates in the process of returning to normal temperature. The metal Ga may be removed with hydrochloric acid after reaching room temperature.

As described above, by cooling the substrate during laser irradiation, it is possible to transfer a thin-film GaN semiconductor device without generating cracks. Further, since the base material substrate 1 is a composite substrate made of sapphire and quartz glass, laser irradiation can be performed without generating cracks due to stress due to a difference in thermal expansion coefficient even during cooling near liquid nitrogen temperature. .

In order to perform the irradiation under the condition that the nitrogen is liquefied, in addition to pressurizing the substrate, a method using a lower temperature refrigerant such as liquid helium, or maintaining the liquid nitrogen at 77 K or less at a high pressure is used. It is also possible to use a method in which the liquid is sent as it is, the pipe diameter is increased just before the substrate, and a low temperature is achieved by adiabatic expansion.

(Embodiment 8) FIGS. 19 to 21 show a method of manufacturing a nitride semiconductor substrate according to an eighth embodiment of the present invention.

The wafer 14 shown in FIG. 19A is a sapphire wafer having a diameter of 2 inches and a thickness of 150 microns. The wafer 15 is a quartz glass wafer having a diameter of 2 inches and a thickness of 600 microns.

As shown in FIG. 19B, the fifth embodiment
In exactly the same manner as described above, the quartz glass wafer 15 and the two sapphire wafers 14 are heated and fused at about 1800 ° C.
A base material substrate 1 is manufactured.

Next, G is applied by the same MOCVD method as in the second embodiment.
An aN layer is grown. The growth conditions are the same as in the fifth embodiment except that doping is not performed.
Then, the GaN layer 2 is grown to 5 μm (FIG. 19C).

Next, a laser irradiation step is performed.

In this embodiment, the same low-output laser as in Embodiment 7 which is easy to handle is used. Since the laser has a low output, the irradiation size is focused to 50 μm, and the light density of the laser is set to 0.4 J / cm ² . Since the irradiation size is smaller than the semiconductor device size, the entire GaN layer 2 is irradiated from the periphery to the inside by using the scan mirror 4.

In this embodiment mode, irradiation is performed by cooling the substrate under the condition that nitrogen is liquefied.

Liquid nitrogen is sent to the cooling pipe at approximately atmospheric pressure, and the substrate 1 on which the nitride semiconductor layer is formed is subjected to Nd: YAG
It is introduced into a container 33 having a window 32 through which the laser is
Pressurize to 0 atm and irradiate laser beam 10 (FIG. 20)
(D)).

By applying pressure as described above, the volume of generated nitrogen is reduced, and more preferably, conditions for liquefying nitrogen can be set. During the irradiation, the irradiation in the container 33 is performed in an atmosphere containing almost no nitrogen such as a pure hydrogen atmosphere.

The irradiation of the laser beam 10 causes the GaN layer 2
A region 34 made of liquefied nitrogen and metal Ga is generated between the AlN layer 21 and the GaN layer 2 and the AlN layer 21 through the region 34 made of liquefied nitrogen and metal Ga without generating cracks. It can be in a state of weakly attaching (FIG. 21E). Then, the temperature of the GaN layer 2 is kept at the liquid nitrogen temperature or slowly raised so that the nitrogen does not rapidly evaporate.
And the AlN layer 21 can be separated. G separated
On the aN layer 2 and the AlN layer 21, nitrogen diverges near room temperature to form metal Ga11.
(F)).

The metal Ga11 can be removed with an acid such as hydrochloric acid (FIG. 21 (g)).

As described above, by cooling the substrate at the time of laser irradiation, a thin-film, large-area GaN
It is possible to obtain a substrate. Further, since the base material substrate 1 is a composite substrate made of sapphire and quartz glass, laser irradiation can be performed without generating cracks due to stress due to a difference in thermal expansion coefficient even when cooling near liquid nitrogen temperature. Is possible.

In the first to eighth embodiments, the layer decomposed by the laser is a GaN layer.
It goes without saying that the same applies even when an AlGaN layer capable of absorbing laser light is used instead of the N layer. In this case, since an AlGa alloy is formed instead of metal Ga, it goes without saying that the temperature rise of the AlGaN layer due to laser irradiation must be lower than the boiling point of the AlGa alloy.

[0173]

As described above, according to the method for manufacturing a nitride semiconductor substrate of the present invention, it is possible to provide a method for peeling a nitride semiconductor layer from a base material substrate without cracks by laser irradiation. There is an effect that a method for manufacturing a substrate or a nitride semiconductor device with good mass productivity can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a manufacturing process of a nitride semiconductor substrate according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an apparatus for laser irradiation according to an embodiment of the present invention.

FIG. 3 is a diagram showing a laser irradiation method according to the first embodiment of the present invention.

FIG. 4 is a diagram showing an irradiation step when the laser power is low in the first embodiment of the present invention.

FIG. 5 is a diagram showing an irradiation step when the laser power is high in Embodiment 1 of the present invention.

FIG. 6 is a diagram showing a manufacturing process of the nitride semiconductor device according to the second embodiment of the present invention.

FIG. 7 is a diagram showing the first half of the manufacturing process of the nitride semiconductor substrate according to the third embodiment of the present invention.

FIG. 8 is a diagram showing an irradiation step when the laser power is low in Embodiment 3 of the present invention.

FIG. 9 is a diagram showing an irradiation step when laser power is high in Embodiment 3 of the present invention.

FIG. 10 is a diagram showing a manufacturing process of the nitride semiconductor device according to the fourth embodiment of the present invention.

FIG. 11 is a diagram showing a manufacturing process of the nitride semiconductor device according to the fifth embodiment of the present invention.

FIG. 12 is a diagram showing a manufacturing process of the nitride semiconductor device according to the fifth embodiment of the present invention.

FIG. 13 is a diagram showing a manufacturing process of the nitride semiconductor device according to the fifth embodiment of the present invention.

FIG. 14 is a view showing a manufacturing process of the nitride semiconductor substrate according to the sixth embodiment of the present invention.

FIG. 15 is a diagram showing a manufacturing process of the nitride semiconductor substrate according to the sixth embodiment of the present invention.

FIG. 16 is a diagram showing a manufacturing process of the nitride semiconductor device in the seventh embodiment of the present invention.

FIG. 17 is a view showing a manufacturing process of the nitride semiconductor device in the seventh embodiment of the present invention.

FIG. 18 is a diagram showing a manufacturing process of the nitride semiconductor device in the seventh embodiment of the present invention.

FIG. 19 is a view showing a manufacturing process of the nitride semiconductor substrate according to the eighth embodiment of the present invention.

FIG. 20 is a view showing a manufacturing process of the nitride semiconductor substrate in the eighth embodiment of the present invention.

FIG. 21 is a diagram showing a manufacturing process of the nitride semiconductor substrate according to the eighth embodiment of the present invention.

FIG. 22 is a view showing a manufacturing process of a conventional nitride semiconductor device.

[Explanation of symbols]

Reference Signs List 1 base material substrate 2 GaN layer 3 laser device 4 scan mirror 5 focusing means 6 opening 7 cooling means 8 heating means 10 laser beam 11 metal Ga 12 fused sapphire 13 alumina 14 sapphire wafer 15 quartz glass wafer 21 AlN layer 22 n-type GaN Contact layer 23 In _0.2 Ga _0.8 N active layer 24 p-type Al _0.05 Ga _0.95 N clad layer 25 p-type GaN contact layer 26 n-electrode 27 p-electrode 28 AuSn solder 29 Si submount 31 holding jig 32 window 33 container 34 liquid nitrogen Region consisting of metal and metal 35 adhesive 36 host substrate

Claims (8)

[Claims] A step of forming a nitride semiconductor layer on the base material substrate, wherein the temperature of the interface between the base material substrate and the nitride semiconductor layer is lower than the melting point of the base material substrate. Irradiating the nitride semiconductor layer with light to separate the base material substrate and the nitride semiconductor layer from each other. 2. A step of forming a nitride semiconductor layer on a base material substrate, and the step of forming a nitride semiconductor layer such that a temperature of an interface between the base material substrate and the nitride semiconductor layer is lower than a boiling point of Ga. Irradiating light to the layer to separate the base material substrate and the nitride semiconductor layer. Forming a nitride semiconductor layer on the base material substrate; and irradiating the nitride semiconductor layer with light while cooling the base material substrate or the nitride semiconductor layer. Separating the nitride semiconductor layer from the nitride semiconductor layer. 4. The method according to claim 1, wherein, in the step of separating the base material substrate and the nitride semiconductor layer, the base material substrate or the nitride semiconductor layer is set under a condition in which nitrogen is liquefied. 3. The method for manufacturing a nitride semiconductor substrate according to item 3. 5. A step of forming a nitride semiconductor layer on a base material substrate, and irradiating the nitride semiconductor layer with light under a condition that a pressure applied to the base material substrate and the nitride semiconductor layer is higher than 1 atm. Separating the base material substrate and the nitride semiconductor layer. 6. The base material substrate comprises a first material having a thermal expansion coefficient smaller than that of the nitride semiconductor layer, and a second material having a thermal expansion coefficient larger than that of the nitride semiconductor layer. 6. The method for manufacturing a nitride semiconductor substrate according to claim 1, wherein said material and said second material both transmit said light. 7. The method according to claim 1, wherein the step of forming a nitride semiconductor layer on the base material substrate is a step of forming one or more nitride semiconductor layers to form a semiconductor device. 6. The method for manufacturing a nitride semiconductor substrate according to 5. 8. A step of forming one or a plurality of nitride semiconductor layers on a base material substrate to form a semiconductor device, and controlling a temperature of an interface between the base material substrate and the nitride semiconductor device by the base material substrate. A step of irradiating the nitride semiconductor layer with light so as to have a temperature lower than the melting point of the semiconductor substrate to separate the base material substrate and the nitride semiconductor device from each other. .