JP2011181762A - Method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor device, in which the semiconductor device having high quality is obtained by crystal-growing group-III nitride of high quality on a sapphire substrate. <P>SOLUTION: An AlN layer on the sapphire substrate 2 which has been nitrided directly is irradiated with gas including nitrogen radicals or nitrogen ions from a radial source 5 for a predetermined time. Then the group-III nitride is crystal-grown by a PLD (pulse laser deposition) method of irradiating a target 3a comprising a constituent element of the group-III nitride to be grown with pulse laser light in a nitrogen atmosphere to obtain N-polar crystal having extremely high quality. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a method for manufacturing a semiconductor device obtained by crystal growth of a group III nitride on a sapphire substrate.

Sapphire (α-Al ₂ O ₃ ), which is thermally and chemically stable, is widely used as a single crystal substrate for growing a group III nitride crystal. In addition, as a group III nitride, AlN has a band gap energy of about 6.2 eV and a lattice constant close to that of a sapphire (0001) substrate. Therefore, during the heteroepitaxial growth of other group III nitrides. It is often used as a buffer layer.

JP 2006-213586 A

Patent Document 1 reports that an AlN thin film of several atomic layers is formed on a sapphire substrate by directly nitriding the surface of the sapphire substrate. Specifically, a sapphire substrate and graphite are placed in a soaking part of a heat treatment apparatus, and the sapphire substrate is controlled in an atmosphere in which the oxygen potential and nitrogen potential are controlled by adjusting the composition of the N ₂ —CO mixed gas. And an AlN thin film having several atomic layers is formed on the sapphire substrate.

However, it is known that the AlN thin film formed by direct nitridation in Patent Document 1 is not a complete single crystal, and has grains whose c-axis is inclined by about 1 degree and grains rotated by 30 degrees in the plane. It was. For this reason, it has been difficult to grow a high-quality group III nitride crystal on an AlN thin film formed by direct nitriding.

The present invention has been proposed in view of the above circumstances, and provides a method for manufacturing a semiconductor device capable of crystal growth of a high-quality group III nitride to obtain a high-quality semiconductor device.

As a result of intensive research, the inventors of the present invention formed a direct nitridation by irradiating a directly nitrided sapphire substrate (hereinafter also referred to as a sapphire nitride substrate) with a gas containing nitrogen radicals or nitrogen ions. High quality IN thin film on sapphire substrate
It was found that group II nitride crystal growth was possible. It was also found that the obtained group III nitride was a high-quality N-polar crystal.

That is, in the method for manufacturing a semiconductor device according to the present invention, a directly nitrided sapphire substrate is irradiated with a gas containing nitrogen radicals or nitrogen ions to clean the sapphire substrate, and the cleaned sapphire A group III nitride growth step of growing group III nitride on the substrate.

The high electron mobility device according to the present invention has an N-polar AlGaN / GaN structure obtained by the above-described method for manufacturing a semiconductor device.

The light receiving element according to the present invention has an N-polarity p-GaN / i-InGaN / n-GaN / substrate structure obtained by the above-described method for manufacturing a semiconductor device.

In addition, the light-emitting element according to the present invention is an Al obtained by the method for manufacturing a semiconductor device described above.
It has N buffer layers.

According to the present invention, a very high quality several atomic layer AlN thin film can be obtained by irradiating a directly nitrided sapphire substrate with a gas containing nitrogen radicals or nitrogen ions.
The mechanism is unknown, but by irradiation with a gas containing nitrogen radicals or nitrogen ions,
It is considered that the altered layer of the AlN thin film on the sapphire substrate has been removed or repaired. Therefore, the group III nitride crystal grown on the AlN thin film of the sapphire substrate also becomes high quality by taking over the crystallinity of the AlN thin film, and a high quality semiconductor device can be obtained.

It is a figure which shows the structural example of the PLD apparatus in one embodiment of this invention. 4 is a flowchart showing a method for manufacturing a semiconductor device in an embodiment of the present invention. It is sectional drawing of the laminated structure which formed the group III nitride film on the sapphire nitride substrate. It is a figure which shows the structural example of a high electron mobility transistor. It is a figure which shows the structural example of a light receiving element. It is a figure which shows the structural example of a light emitting element. It is a figure which shows the rocking curve of AlN0002 diffraction in the AlN thin film on a nitride sapphire substrate. It is a figure which shows the rocking curve of AlN00-11 diffraction in the AlN thin film on a nitride sapphire substrate. It is a figure which shows the rocking curve of AlN10-10 diffraction in the AlN thin film on a sapphire nitride board | substrate. It is a laser microscope image of the surface of a sapphire nitride substrate. It is a laser microscope image of the surface of a sapphire nitride substrate. It is a RHEED image of the sapphire nitride substrate before annealing. It is a RHEED image of the sapphire nitride substrate before annealing. It is a RHEED image of the sapphire nitride substrate after annealing. It is a RHEED image of the sapphire nitride substrate after annealing. It is a figure which shows the rocking curve of AlN1-102 diffraction of the sample from which the irradiation time (nitriding time) of a nitrogen radical beam differs. It is a {0001} EBSD pole figure of an AlN thin film when the irradiation time (nitriding time) of a nitrogen radical beam is 0 min. It is a {10-11} EBSD pole figure of an AlN thin film when the irradiation time (nitriding time) of a nitrogen radical beam is 0 min. It is a {0001} EBSD pole figure of an AlN thin film when the irradiation time (nitriding time) of a nitrogen radical beam is 30 min. It is a {10-11} EBSD pole figure of an AlN thin film when the irradiation time (nitridation time) of a nitrogen radical beam is 30 min. It is a SEM image when the irradiation time (nitriding time) of a nitrogen radical beam is 0 min. It is a SEM image when the irradiation time (nitriding time) of a nitrogen radical beam is 30 minutes. It is an AFM image when the irradiation time (nitriding time) of a nitrogen radical beam is 0 min. It is an AFM image when the irradiation time (nitriding time) of a nitrogen radical beam is 30 min. It is a figure which shows the rocking curve of AlN (0002) diffraction in the AlN thin film formed into a film by PLD method. It is a figure which shows the rocking curve of AlN (1-102) diffraction in the AlN thin film formed into a film by PLD method. AlN (0002) diffraction before and after growth and Sapp. FIG. 2 is a diagram showing a 2θ / ω curve of diffraction. It is a figure which shows the simulation structure of a high electron mobility transistor. It is a figure which shows the simulation result of the energy band diagram of the perpendicular direction in a high electron mobility transistor of N polarity. It is a figure which shows the simulation result of the energy band diagram of the orthogonal | vertical direction in the high electron mobility transistor of a group III polarity. It is a figure which shows the simulation structure of a light receiving element. It is a figure which shows the p-GaN / i-InGaN / n-GaN / substrate structure of group III polarity and N polarity. Is a diagram illustrating a simulation result of the conversion efficiency with respect to the polarity of the light receiving element having an In _0.5 Ga _0.5 N light receiving layer. It is a figure which shows the simulation result of the energy band diagram of the orthogonal | vertical direction in the light receiving element of N polarity. It is a figure which shows the simulation result of the energy band diagram of the perpendicular direction in a nonpolar light receiving element. It is a figure which shows the simulation result of the energy band diagram of the orthogonal | vertical direction in the light receiving element of group III polarity. It is a diagram illustrating a simulation result of the conversion efficiency with respect to the polarity of the light receiving element having an In _0.12 Ga _0.88 N light-receiving layer. It is a figure which shows the simulation result of the energy band diagram of the orthogonal | vertical direction in the light receiving element of N polarity. It is a figure which shows the simulation result of the energy band diagram of the perpendicular direction in a nonpolar light receiving element. It is a figure which shows the simulation result of the energy band diagram of the orthogonal | vertical direction in the light receiving element of group III polarity.

Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.

In the method for manufacturing a semiconductor device according to an embodiment of the present invention, an apparatus used when a directly nitrided sapphire (α-Al ₂ O ₃ ) substrate (0001) is irradiated with a gas containing nitrogen radicals or nitrogen ions is provided. Even a dedicated device may be provided in a group III nitride crystal growth device.

Further, the group III nitride crystal growth process in the present embodiment is not particularly limited, and metal organic chemical vapor deposition (MOCVD) is not limited.
Deposition), molecular beam epitaxy (MBE), pulsed excitation deposition (PXD), etc. can be used.

Fig. 1 shows a pulsed laser deposition method (PLD: Pulsed Laser Depo), one of the pulsed excitation deposition methods.
It is a figure which shows the structural example of the crystal growth apparatus applied to (sition).

The PLD apparatus 1 includes a chamber that maintains a constant pressure and temperature of a gas filled therein and forms a sealed space, and a substrate 2 and a target 3 are disposed facing each other in the chamber. Also,
The PLD apparatus 1 includes a KrF excimer laser 4 that emits a high-power pulse laser having a wavelength of 248 nm, a radical source 5 that radicalizes nitrogen gas injected into the chamber, and a reflection high-energy electron beam analyzer (RHEED: Reflection). High Energy Electron Diffraction) 6.

In the KrF excimer laser 4, F ₂ is decomposed and excited by discharging in a mixed gas of Kr and F ₂ , and an unstable KrF excimer is formed by combining with Kr. Stimulated emission is generated in another excimer by light (wavelength 248 nm) emitted when a certain excimer decomposes and falls to the ground state, and is further amplified by a resonator to output high-energy laser light.

The radical source 5 is made to be a gas containing nitrogen radicals or nitrogen ions by once exciting nitrogen gas using a high frequency, and the surface of the substrate 2 can be irradiated with this gas. The radical source 5 includes a hollow discharge chamber and a high-frequency coil (RF coil) wound around the outer periphery of the discharge chamber, and the like, to the nitrogen gas supplied to the discharge chamber from a nitrogen source such as a liquid nitrogen cylinder, A high frequency is applied by a coil to generate a gas containing charged particles (charged particles) in which nitrogen atoms called plasma are generated by ionization.

The reflection high-energy electron diffraction apparatus 6 accelerates electrons with an electron gun in a vacuum, and emits the accelerated electrons to the surface of the substrate 2 at a very shallow angle. The electron beam is reflected from the surface of the substrate 2 and the fluorescent screen 7
And appear as a diffraction pattern. According to the reflection high-energy electron diffraction apparatus 6, in-situ observation of the surface of the substrate 2 or the surface of the thin film is possible.

The PLD apparatus 1 includes a pressure valve and a rotary pump for controlling the pressure in the chamber. The pressure in the chamber is determined in consideration of the PLD process for forming a film under reduced pressure.
It is controlled so as to be a predetermined pressure in a nitrogen atmosphere by a rotary pump.

Further, the PLD device 1 includes a rotating shaft that rotates the targets 3a to 3d irradiated with the pulse laser, a revolver that switches the targets 3a to 3d irradiated with the pulse laser,
A lamp heater 8 for heating the substrate 2 is provided, and a multilayer film made of different materials can be grown.

In the PLD apparatus 1 having the above-described configuration, when the pulse laser beam is intermittently irradiated while rotating the target 3 while the chamber is filled with nitrogen gas, the temperature of the surface of the target 3 rapidly increases, An ablation plasma containing three target atoms is generated. The target 3 atoms contained in the ablation plasma move to the substrate 2 while gradually changing the state while repeating collision reaction with nitrogen gas and the like. And substrate 2
The particles containing the target 3 atoms that have reached the surface diffuse as they are on the substrate 2 and are thinned in the most stable state of lattice matching.

Next, with reference to FIGS. 1 and 2, a method for manufacturing a semiconductor device in one embodiment of the present invention will be described. A manufacturing method of a semiconductor device shown as a specific example is a cleaning step of cleaning a sapphire substrate by irradiating a directly nitrided sapphire substrate (hereinafter also referred to as a sapphire nitride substrate) with a gas containing nitrogen radicals or nitrogen ions. Step S1), a group III nitride growth step (step S2) for crystal growth of group III nitride on the cleaned sapphire substrate, and a device processing step (step S3) for forming an electrode on the group III nitride. Have

How nitriding the sapphire substrate directly, as described in JP 2006-213586, the sapphire substrate using the N ₂ -CO mixed gas under carbon saturated, precisely control the nitrogen and oxygen potential The nitridation reaction proceeds gently. Thereby, an AlN thin film of several atomic layers can be formed on the sapphire substrate. However, this AlN thin film is not a complete single crystal, and there are grains whose c-axis is inclined by about 1 degree and grains rotated by 30 degrees in the plane.

Therefore, in step S1, a gas containing nitrogen radicals or nitrogen ions is irradiated onto the directly nitrided sapphire substrate. Specifically, in FIG. 1, a sapphire nitride substrate in which nitrogen atoms called plasma are generated from a radical source 5 containing charged particles (charged particles) generated by ionization, and this plasma is used as a substrate 2. Feed on. Thereby, a single domain AlN film can be formed on the sapphire substrate. The mechanism is unknown, but the nitrogen plasma irradiation removes or repairs the altered layer such as grains with c-axis tilting about 1 degree and grains rotating 30 degrees in the plane, which exists in the AlN thin film on the sapphire substrate. It is thought that.

The time of irradiation with nitrogen plasma is desirably 30 minutes or more. 3 nitrogen plasma
Irradiation for 0 minute or longer can reduce the altered layer of the AlN thin film on the sapphire substrate.

Further, the nitrogen plasma irradiation is preferably performed in a temperature range of 500 to 1200 ° C. as in the annealing treatment performed before or simultaneously with the nitrogen plasma irradiation. By irradiating with nitrogen plasma in this temperature range, the substrate surface can be planarized at the atomic level and the altered layer of the AlN thin film can be removed. Furthermore, by irradiating nitrogen plasma after annealing the substrate, the substrate surface is flattened and charged up, so that the effect of irradiation can be increased.

In step S2, I is formed on the AlN thin film of the sapphire nitride substrate according to the device to be manufactured.
II-nitride _{(In x Al y Ga z N} , where 0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1, x +
A multilayer film of y + z = 1) is grown. Here, AlN of the sapphire nitride substrate 10 (FIG. 3)
As In _x Al _y Ga _1-xy N grown on the thin film, AlN (x = 0, y = 1,
It is preferable that z = 0).

Specifically, in FIG. 1, polycrystalline AlN is installed as the target 3, and pulsed laser light is intermittently applied to the target 3 from the KrF excimer laser 4, and ablation plasma containing target 3 atoms from the surface of the target 3. Is generated. The AlN atoms contained in this ablation plasma and the gas containing nitrogen radicals or nitrogen ions irradiated from the radical source 5 gradually change its state while repeating a collision reaction, etc., and move to the sapphire nitride substrate for lattice matching. AlN is thinned in the most stable state.

FIG. 3 is a cross-sectional view of a laminated structure in which a group III nitride film is formed on a sapphire nitride substrate. This laminated structure includes a sapphire substrate 10, an AlN thin film 11 formed directly on the (0001) plane of the sapphire substrate 10, an AlN buffer layer 12 formed on the AlN thin film, and a group III nitride film. 13. As described above, AlN is homoepitaxially grown as the buffer layer 12 on the AlN thin film 11 formed by direct nitridation of the sapphire substrate 10 to grow the group III nitride thin film 13 while taking over the good crystallinity of the buffer layer 12. be able to.

In step S3, an electrode is formed by photolithography on a group III nitride thin film grown on a sapphire nitride substrate, and processed into a device as described later.

Group III nitride has strong piezo polarization and spontaneous polarization, and AlG
c-axis direction relative to the aN / GaN heterojunction interface, ie, (0001) and (000−
According to 1), the induction of carriers at the AlGaN / GaN heterojunction interface is promoted or inhibited. In addition, since the group III nitride has a wurtzite structure, the III-nitride is III in the c-axis direction.
Although it has either group polarity or N polarity, according to the manufacturing method in the present embodiment, an extremely high quality N polarity group III nitride can be obtained. The polarity is determined by, for example, irradiating the sample with low energy He ⁺ ions of about 2 keV, and measuring the kinetic energy of the He particles that collide with the sample and scatter and the scattering intensity with respect to the sample crystal axis, thereby forming atoms constituting the sample. Information on the type and sequence of By utilizing this heterojunction interface with controlled polarity, an excellent device as described below can be provided.

<High electron mobility element>
FIG. 4 shows a high electron mobility transistor (HEMT).
FIG. The high electron mobility transistor includes a sapphire substrate 10 and
The AlN thin film 11, the AlN buffer layer 12, the channel layer 21, the barrier layer 22, the source electrode 23, the drain electrode 24, the gate electrode 25, and the SiO ₂ layer 26 are included.

As described above, the sapphire nitride substrates 10 and 11 control the oxygen potential and the nitrogen potential by adjusting the composition of the N ₂ —CO mixed gas under carbon saturation, nitride the sapphire substrate 10, and A few atomic layer AlN thin film 11 is formed.

The AlN buffer layer 12 includes a channel layer 21 and a barrier layer 22 formed on the AlN thin film 11.
In order to improve the crystal quality, the AlN layer is formed to a thickness of about several hundred nm.

The channel layer 21 is a GaN layer formed of N-polar GaN with a thickness of about several μm.

The barrier layer 22 is a group III nitride thin film layer made of Al _y Ga _z N (where 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, y + z = 1).

The source electrode 23 and the drain electrode 24 are ohmic contacts with the barrier layer 22 and are, for example, multilayer metal electrodes made of Ti / Al / Ni / Au. The gate electrode 25 has a Schottky contact with the barrier layer 22 and is a multilayer electrode made of, for example, Pd / Au. The SiO ₂ layer 26 is formed immediately below the gate electrode 25, and the charge generated by the SiO ₂ traps electrons to suppress leakage at the time of turning off, thereby realizing a high breakdown voltage.

In the high electron mobility device having such a configuration, since the interface between the channel layer 21 and the barrier layer 22 is an AlGaN / GaN heterojunction, spontaneous polarization due to crystallinity and Al _y Ga
and a piezoelectric polarization exists by distortion _{z N} and GaN, the channel layer by the polarization
Even without doping with n-type impurities, a two-dimensional electron gas is induced at the AlGaN / GaN interface,
A high electron mobility transistor is realized.

In the method for manufacturing a semiconductor device in the present embodiment, high-quality N-polar group III nitride grows, and thus the high electron mobility element has an N-polar AlGaN / GaN junction interface. Thereby, a high electron mobility element capable of a normally-off operation as described later can be realized.

<Light receiving element>
FIG. 5 is a diagram illustrating a configuration example of the light receiving element. The light receiving element includes a sapphire substrate 10 and
AlN thin film 11, AlN buffer layer 12, n-type GaN layer 31, light-receiving layer 32, p-type GaN layer 33, translucent electrode 34, p-electrode 35, n-electrode 36, and back reflective layer 37.

As described above, the sapphire nitride substrates 10 and 11 control the oxygen potential and the nitrogen potential by adjusting the composition of the N ₂ —CO mixed gas under carbon saturation, nitride the sapphire substrate 10, and A few atomic layer AlN thin film 11 is formed.

The AlN buffer layer 12 includes an n-type GaN layer 31 and a light receiving layer 3 formed on the AlN thin film 11.
2 and an AlN layer formed to improve the crystal quality of the p-type GaN layer 33.

The n-type GaN layer 31 is made to be n-type by doping GaN with a donor impurity such as Si, Ge, or Sn.

The light receiving layer 32 is non-doped In _x Ga _z N (where 0 ≦ x ≦ 1, 0 ≦ z ≦ 1, x + z =
1). Note that since non-doped In _x Ga _z N is n-type and has a small number of carrier electrons, an acceptor impurity may be doped as long as the carrier electron concentration is reduced.

The p-type GaN layer 33 is formed by doping GaN with acceptor impurities such as Zn, Mg, and Ca.

The translucent electrode 34 and the p electrode 35 are made of Au, Pt, pd, Co, Ni, or an alloy thereof. The n electrode 36 is made of Al, V, Au, Rh, or an alloy thereof. The back surface reflection layer 37 is intended to reflect the light that has passed without contributing to power generation and introduce it into the light receiving layer 32 to contribute to power generation, and includes Ag, Ti, Al, and the like.

In the light receiving element having such a configuration, when light is irradiated, electrons and holes are generated in the light receiving layer 32, and the electrons and holes are supplied to the n-type GaN layer 31 and the p-type GaN layer 33, respectively, and a current flows. .

In the method for manufacturing a semiconductor device according to the present embodiment, since a high-quality N-polar group III nitride grows, the light receiving element has an N-polar p-GaN / i-InGaN / n-GaN / substrate structure. . As a result, a light receiving element having high energy conversion efficiency can be realized as will be described later.

In addition, since sapphire is translucent, light can be incident from the sapphire substrate 10 side. In this case, the back surface reflection layer 37 is unnecessary, and an electrode material having a high reflectance may be used instead of the translucent electrode 34 in order to increase the conversion efficiency.

<Light emitting element>
FIG. 6 is a diagram illustrating a configuration example of a light-emitting element. The light emitting element includes a sapphire substrate 10 and
AlN thin film 11, AlN buffer layer 12, base layer 41, and n-type GaN cladding layer 42
A multiple quantum well (MQW) structure layer 43, a p-type AlGaN cladding layer 44, a p-type GaN contact layer 45, a p-type electrode 46, and an n-type electrode 47.

As described above, the sapphire nitride substrates 10 and 11 control the oxygen potential and the nitrogen potential by adjusting the composition of the N ₂ —CO mixed gas under carbon saturation, nitride the sapphire substrate 10, and A few atomic layer AlN thin film 11 is formed.

The AlN buffer layer 12 includes an undoped GaN layer 41 formed on the AlN thin film 11, n
Type GaN cladding layer 42, MQW structure 43, p-type AlGaN cladding layer 44, and p-type G
This is an AlN layer formed in order to improve the crystal quality of the aN contact layer 45.

The underlayer 41 is made of undoped GaN and reverses from N polarity to Group III polarity.

The n-type GaN clad layer (= contact layer) 42 is made to be n-type by doping GaN with a donor impurity such as Si, Ge, or Sn. The contact layer 42 is partially exposed, and an n-type electrode 47 is formed on the exposed surface.

The multi-quantum well structure 43 layer includes, for example, GaN barrier layer / InGaN well layer / GaN barrier layer / InGaN well layer / GaN barrier layer, includes InGaN capable of emitting ultraviolet light, and has 2 to 20 well layers. is there.

The p-type AlGaN cladding layer 44 is made to be p-type by doping AlGaN with acceptor impurities such as Zn, Mg, and Ca.

The p-type GaN contact layer 45 is formed by doping GaN with acceptor impurities such as Zn, Mg, and Ca. A p-type electrode 46 is formed on the upper surface of the p-type GaN contact layer 45.

In the light emitting device having such a configuration, when a current is applied by applying a voltage, holes are supplied from the p-type GaN cladding layer 42 and electrons are supplied from the n-type AlGaN cladding layer 44 to the MQW structure layer 43, and the MQW structure layer At 43, carriers (electrons and holes) are confined, and ultraviolet rays are efficiently emitted.

In the method of manufacturing a semiconductor device in the present embodiment, high-quality N-polar group III nitride grows. In the light emitting element described above, for example, it is necessary to reverse the polarity to the group III polarity in the base layer 41. However, since the N polarity AlN buffer layer 12 is extremely high quality, a high output light emitting element can be realized. is there.

Hereinafter, the present invention will be specifically described with reference to examples. The present invention is not limited to these examples.

<Homoepitaxial growth of AlN>
First, a 2-inch c-plane sapphire substrate was directly nitrided at 1500 ° C. for 6 hours. The first treatment was performed in a gas atmosphere of N ₂ /CO=0.9/0.1 for the first 5 hours, and N ₂ / CO = 1.
Processing was performed in a 0 / 0.0 gas atmosphere. The sapphire nitride substrate was measured by an X-ray diffractometer (D8system manufactured by Brucker), and the surface state was observed by a laser microscope.

FIGS. 7 to 9 show AlN0002 in an AlN thin film on a sapphire nitride substrate, respectively.
It is a figure which shows the rocking curve of diffraction, AlN (00-11) diffraction, and AlN (10-10) diffraction. AlN (0002) diffraction representing tilt distribution and AlN representing twist distribution
The full width at half maximum of the (10-10) diffraction rocking curve is 104 arcsec and 1008, respectively.
arcsec.

10 and 11 are laser microscope images of the surface of the sapphire nitride substrate. From observation of these laser microscope images, it was found that the sapphire nitride substrate has a columnar surface state of about several hundred nm.

Next, the sapphire nitride substrate was annealed at 800 ° C. in an ultra vacuum chamber. In order to charge up the substrate surface, the electron beam was defocused, and the sapphire nitride substrate was observed with a reflection high energy electron diffraction (RHEED) apparatus.

12 and 13 are RHEED images of the sapphire nitride substrate before annealing, and FIGS. 14 and 15 are RHEED images of the sapphire nitride substrate after annealing. An AlN (0001) RHEED pattern was confirmed before annealing. RHEE after 800 ° C vacuum annealing
Although the D image was unclear due to charge-up, a diffraction pattern from the c-plane AlN surface having a different period from the c-plane sapphire substrate was observed. In addition, AlN (0
(001) A thin sapphire pattern was confirmed in the pattern.

Next, the surface of the sapphire nitride substrate was irradiated with nitrogen plasma in an ultra-vacuum chamber at 900 ° C. to clean the substrate surface. Irradiation time (nitriding time) is 0 min, 5 min, 15
Four types of samples were prepared by changing the values to min and 30 min. An RF plasma radical source (UNI-Bulb manufactured by Veeco) was set to 400 W, 5.0 × 10 ⁻⁶ Torr, and irradiated onto the substrate surface. These samples were analyzed using an X-ray diffractometer (D8system manufactured by Bruker), EBSD (E
lectron Back Scatter Diffraction Patterns (Oxford Instruments, INCA Cr)
ystal EBSD system), SEM (Scanning Electron Microscope) equipment (JEOL, JSM-650
0F) and an AFM (Atomic Force Microscope) apparatus (manufactured by JEOL Ltd., JSPM-4210).

FIG. 16 shows AlN (1) of samples having different nitrogen radical beam irradiation times (nitriding times).
-102) It is a figure which shows the rocking curve of diffraction. When the irradiation time (nitriding time) of the nitrogen radical beam was 0 min, cracking of the (1-102) diffraction peak was observed. By irradiating with a nitrogen radical beam for 30 minutes or more, no peak cracking was observed. Also,
It was found that the crystallinity of AlN evaluated from this rocking curve does not depend on the nitriding time.

In FIGS. 17 and 18, the irradiation time (nitriding time) of the nitrogen radical beam is 0 min.
It is the {0001} EBSD pole figure and {10-11} EBSD pole figure of the AlN thin film at the time of. 19 and 20 show the irradiation time (nitriding time) of the nitrogen radical beam, respectively.
{0001} EBSD pole figure and {10-11} EB of AlN thin film when is 30 min
It is an SD pole figure.

As shown in FIGS. 17 and 18, when the nitriding time is 0 min, the c-axis tilted domain corresponding to the cracking of the (1-102) diffraction peak and the domain rotated about 30 degrees in the plane are mixed. Observed. On the other hand, as shown in FIGS. 19 and 20, when the nitriding time is 30 min,
(1-102) No inclusion of domains with tilted c-axis corresponding to cracking of the diffraction peak or domains rotated about 30 in the plane was observed. That is, it was found that the irradiation of the nitrogen radical beam for 30 minutes or more can suppress the mixing of the domain in which the c-axis is inclined and the domain rotated about 30 in the plane.

In FIGS. 21 and 22, the irradiation time (nitriding time) of the nitrogen radical beam is 0 min.
And an SEM image at 30 min. FIG. 23 and FIG. 24 are AFM images when the irradiation time (nitriding time) of the nitrogen radical beam is 0 min and 30 min, respectively.
It was found that when the nitriding time was 0 min, it was a columnar surface form of several hundred nm, whereas when the nitriding time was 30 min, it was a relatively smooth surface form.

Next, AlN was homoepitaxially grown about 300 nm by PLD on the substrate cleaned by irradiation with a nitrogen radical beam for 30 minutes as described above. The growth temperature is 900 ° C.
AlN crystals were grown for 60 minutes. Polycrystalline AlN is used as the target material, and RF plasma radical source (UNI-Bulb manufactured by Veeco) is used as the N source at 400 W, 1.0 × 10 ⁻⁶ T
The orr setting was used. Further, the KrF excimer laser was emitted to the target 3 at a setting of 3 J / cm ² and 30 Hz. The crystallinity of AlN deposited under these conditions is XRD.
Evaluation was made by measurement.

FIGS. 25 and 26 show AlN (AlN in AlN thin films formed by the PLD method, respectively.
It is a figure which shows the rocking curve of 0002) diffraction and AlN (1-102) diffraction. The full width at half maximum of the rocking curve was 27 arcsec for 0002 diffraction and 590 arcsec for 1-102 diffraction, which was found to be a very high quality AlN thin film.

FIG. 27 shows AlN (0002) diffraction and Sapp. (0006
FIG. 2 is a diagram showing a 2θ / ω curve of diffraction. From this 2θ / ω curve, it was found that a high-quality AlN thin film that inherited the crystallinity of the substrate can be grown by irradiation with a nitrogen radical beam.

From the above results, the sapphire nitride substrate that does not irradiate the nitrogen radical beam before the growth of the group III nitride has a columnar surface morphology, but by irradiating the nitrogen radical beam, It has been found that a flat sapphire nitride substrate can be realized.

In addition, it was found that the irradiation of the nitrogen radical beam before the growth of the group III nitride can suppress the mixing of the domain with the tilted c-axis.

<Simulation of high electron mobility device>
A high electron mobility transistor (HEMT) was simulated using a device simulator (trade name: ATLAS, manufactured by Silvaco International).

FIG. 28 is a diagram illustrating a simulation configuration of a high electron mobility transistor. This high electron mobility transistor includes a GaN layer 51 as a channel layer and Al _{0.3 as a} barrier layer.
Ga _0.7 N layer 52, source electrode 53, drain electrode 54, gate electrode 55, S
and an iO ₂ layer 56. The thickness of the barrier layer was set to 0.02 micrometers, and simulation evaluation was performed with a group III nitride crystal having N polarity and a group III polarity.

FIG. 29 and FIG. 30 are diagrams showing simulation results of energy band diagrams in the vertical direction in high electron mobility transistors of N polarity and Group III polarity, respectively. In the group III polarity energy band diagram shown in FIG. 30, Al _0.3 Ga _0.
7 There is an accumulation of electrons at the N / GaN heterojunction interface. On the other hand, in the N-polar energy band diagram shown in FIG. 29, there is no accumulation of electrons at the Al _0.3 Ga _0.7 N / GaN heterojunction interface. Therefore, a normally-off type high electron mobility transistor in which no current flows when no gate voltage is applied can be realized.

<Simulation of light receiving element>
The light receiving element was simulated using a device simulator (trade name: ATLAS, manufactured by Silvaco International).

FIG. 31 is a diagram showing a simulation configuration of the light receiving element. This light receiving element is an n-type G
It has an aN layer 61, an InGaN layer 62 that is a light receiving layer, and a p-type GaN layer 63. That is, it has a double hetero structure in which the InGaN layer 62 is sandwiched between the n-type GaN layer 61 and the p-type GaN layer 63. Here, the thickness of the p-type GaN layer 63 is set to 1 in consideration of piezo polarization and spontaneous polarization.
The thickness of 50 nm and the InGaN layer 62 was 200 nm. AM (air mass)
The light receiving element was simulated using a light source of 0.1 W / cm ² referred to as “5”.

FIGS. 32 (a) and 32 (b) show group III polar and N polar p-GaN / i, respectively.
It is a figure which shows -InGaN / n-GaN / substrate structure. As shown in FIG. 32, the group III polar face and the N polar face are affected by the electric field generated by the piezo polarization / spontaneous polarization of the group III nitride. Simulation evaluation was performed for the case of group polarity.

FIG. 33 is a diagram illustrating a simulation result of conversion efficiency with respect to polarity in a light receiving element having an In _0.5 Ga _0.5 N light receiving layer. 34 to 36 are diagrams showing simulation results of energy band diagrams in the vertical direction in light receiving elements of N polarity, nonpolarity, and group III polarity, respectively.

FIG. 37 is a diagram illustrating a simulation result of conversion efficiency with respect to polarity in a light receiving element having an In _0.12 Ga _0.88 N light receiving layer. FIGS. 38 to 40 are diagrams showing simulation results of energy band diagrams in the vertical direction in light receiving elements of N polarity, nonpolarity, and group III polarity, respectively.

From these results, it can be seen that high conversion efficiency can be obtained with the nonpolar plane and the N-polar light receiving element, whereas in the group III polar light-receiving element, the conversion efficiency is greatly reduced due to carrier confinement by the piezoelectric polarization electric field. Therefore, in order to obtain a high-efficiency solar cell, p-GaN / i-
InGaN having an N polarity range from a nonpolar plane in the InGaN / n-GaN / substrate structure may be grown.

Claims (6)

Irradiating a gas containing nitrogen radicals or nitrogen ions to a directly nitrided sapphire substrate, and cleaning the sapphire substrate,
A group III nitride growth step for crystallizing group III nitride on the cleaned sapphire substrate;
A method for manufacturing a semiconductor device, comprising: 2. The method of manufacturing a semiconductor device according to claim 1, wherein in the cleaning step, the gas is irradiated for 30 minutes or more. 3. The method of manufacturing a semiconductor device according to claim 1, wherein, in the cleaning step, the cleaned sapphire substrate is annealed and then irradiated with the gas. N-polar Al obtained by the method for manufacturing a semiconductor device according to claim 1.
A high electron mobility device having a GaN / GaN junction interface. 4. An N-polarity p− obtained by the method for manufacturing a semiconductor device according to claim 1.
A light-receiving element having a GaN / i-InGaN / n-GaN / substrate structure. A light emitting device comprising an AlN buffer layer obtained by the method for manufacturing a semiconductor device according to claim 1.

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