JP7157953B2 - Nitride-based thin film composite structure and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a nitride-based thin film composite structure and a manufacturing method thereof.

With the reduction of carbon dioxide emissions and the ban on the use of mercury under the Minamata Treaty, nitride semiconductors are expected to be applied to power devices for power control and light-emitting devices for general lighting.

Since there is no lattice-matched initial substrate for nitride semiconductors, nitride semiconductor crystals are formed on heterogeneous bulk single crystals such as Sapphire (α-Al ₂ O ₃ ), SiC, Si, and ScAlMgO ₄ regardless of whether they are thin films or bulk crystals. is produced. Commonly known crystal growth techniques include metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), and sputtering.

However, regardless of which technique is used to form the nitride semiconductor crystal, when the bulk crystal described above is used as the initial substrate, the lattice constant differs from that of the nitride semiconductor, and the difference in lattice constant poses a problem. A large number of defects are generated in the nitride semiconductor crystal due to the lattice mismatch, which is the main cause of deterioration of the efficiency and life of the device due to deterioration of the quality of the nitride semiconductor crystal. In order to solve such problems, epitaxial lateral overgrowth (hereinafter referred to as "ELO method") is well known, which is a method of selectively growing a nitride semiconductor containing no crystal defects by lateral growth. ing.

Therefore, the ELO method will be described with reference to FIGS. 6A and 6B showing the substrate viewed from the cross-sectional direction. FIG. 6A is a cross-sectional view of the sample before crystal growth by the ELO method, and FIG. 6B is a cross-sectional view of the sample during growth. In the ELO method, a base layer (buffer layer) processed on a seed crystal substrate is used. Specifically, as shown in FIG. 6A, a mask having periodic openings made of an amorphous material such as SiO ₂ or SiN is placed on a crystalline thin film 602 formed on a bulk single crystal wafer 601 . The underlying layer provided with 603 is used as the initial substrate.

FIG. 7A shows a plan view of the cross-sectional view shown in FIG. 6A viewed from above. The mask 702 may have openings 701 in a stripe pattern as shown in FIG. 7A, or may have openings 701 in a dot pattern as shown in FIG. 7B. The size and pitch of mask openings are often 2 μm or more and 10 μm or less. When crystal growth is performed on a mask-processed substrate as shown in FIG. 6A, adsorption of raw material molecules on the amorphous mask 603 becomes unstable, so that crystal growth does not progress starting from right above the mask. Instead, crystal growth progresses starting only from the mask opening. As the crystal growth progresses, a crystal 604 grown starting from the mask opening grows laterally to cover the mask 603 as shown in FIG. 6B. Finally, the crystals 604 completely cover the mask 603 to form a uniformly continuous crystal film on the substrate. At this time, the crystal defect is taken over from the mask opening and propagates in the grown crystal, but the propagation direction is bent from the direction perpendicular to the substrate surface to the direction parallel to the substrate surface due to the lateral growth, and the adjacent opening The dislocations annihilate by associating with more laterally grown crystals and forming dislocation loops. The nitride crystal produced by using the ELO method in this way has a dislocation density of about 10 ⁶ cm ⁻² to 10 ⁷ cm ⁻² , compared to 10 ⁹ cm ⁻² when the ELO method is not used. can be reduced by two orders of magnitude or more.

An important point in the ELO method is that masks 702 and openings 701 are periodically formed on the substrate surface, such as the line and space pattern shown in FIG. 7A and the dot pattern shown in FIG. 7B. is to use the initial substrate. The exposed opening 701 on the substrate surface whose size and pitch are controlled and the amorphous mask 702 which prevents crystal growth promote lateral growth, making it possible to grow high-quality nitride crystals. .

Japanese Patent No. 3189877

The ELO method is a useful technique for producing crystals with a low dislocation density, but many film formations and processes are required to prepare a base substrate for use in the ELO method. For this reason, there are problems in terms of productivity due to the cost of introducing and maintaining facilities for film formation and processing, and the inclusion of a large number of processes. First, with regard to equipment costs, equipment for fabricating the underlying crystalline thin film 602 by MOCVD or MBE, equipment for CVD or sputtering for forming the mask 702 made of SiO ₂ or SiN, and equipment for the mask 702 . Equipment for lithography for creating the opening 701 and etching using hydrofluoric acid or the like is essential. In addition to being dangerous and expensive because many of the raw materials used in CVD are flammable, CVD equipment equipped with abatement equipment, such as exhaust gas treatment equipment, and exposure equipment for lithography are also extremely expensive, increasing production costs. cause to raise. Next, in terms of productivity, since the ELO method includes many steps such as film formation, exposure, and etching, it greatly increases the time required for production.

The present invention solves the problems of the conventional methods as described above, and a nitride-based thin film composite having the same function as the processing substrate used in the ELO method is manufactured by a one-step process using an inexpensive sputtering method. An object of the present invention is to provide a structure and a method for forming the same.

A nitride-based thin film composite structure according to the present invention is a nitride-based thin film composite structure including a nitride thin film formed on a bulk single crystal wafer,
Nitride microcrystals provided on the bulk single crystal wafer in a specific orientation relationship with the crystal structure of the bulk single crystal wafer;
an amorphous nitride thin film surrounding the nitride crystallites and covering the surface of the bulk single crystal wafer;
Consists of

In addition, a method for manufacturing a nitride-based thin film composite structure according to the present invention includes the steps of preparing a bulk single crystal substrate and a target material in a vacuum chamber of a sputtering apparatus;
A gas containing 30% or more nitrogen is introduced into the vacuum chamber, the pressure is set to 0.1 Pa or more and 0.5 Pa or less, the temperature of the substrate is 25 ° C. or more and 1000 ° C. or less, and electric power is applied at a frequency of 1 kHz or more and 100 kHz or less. applying a power pulse with a time rate of 0.1% or more and 30% or less to generate plasma, surround the nitride microcrystals on the substrate and the nitride microcrystals by a reactive sputtering method, and forming an amorphous nitride thin film covering the entire surface of the bulk single crystal substrate;
including.

The nitride-based thin film composite structure and the method for manufacturing the same according to the present invention provide a crystal quality equal to or higher than that obtained when nitride crystals are manufactured using the ELO method without using film formation and exposure processes such as CVD and lithography. It is possible to provide a base substrate for producing a nitride crystal of.

1 is a schematic cross-sectional view showing a cross-sectional structure of a nitride-based thin film composite structure according to Embodiment 1; FIG. 1B is a plan view of the nitride-based thin film composite structure of FIG. 1A; FIG. FIG. 2 is a diagram showing the orientation relationship between a bulk single crystal wafer and nitride microcrystals; FIG. 2B is a diagram showing the crystallographic axis when the bulk single crystal wafer is sapphire in FIG. 2A. FIG. 2B is a view showing the crystallographic axis when the nitride microcrystal is AlN in FIG. 2A. FIG. 2C is a schematic diagram showing the orientation relationship between the [1-100] axis of sapphire and the [1-100] axis of AlN of FIGS. 2B and 2C; 1 is a schematic diagram showing the configuration of a sputtering apparatus according to Embodiment 1; FIG. 4 is a diagram showing X-ray rocking curve reflection of the AlN (0002) plane, which is the microcrystal of the nitride-based thin film composite structure according to Embodiment 1. FIG. 4 is an optical microscope image of GaN grown by MOCVD on the nitride-based thin film composite structure according to Embodiment 1. FIG. It is a schematic cross-sectional view showing a cross-sectional structure of a substrate used in a conventional ELO method. 6B is a schematic cross-sectional view showing a state in which crystal growth is performed on the substrate of FIG. 6A; FIG. It is a top view which shows an example of the mask processing pattern used by the conventional ELO method. FIG. 10 is a plan view showing another example of a mask processing pattern used in the conventional ELO method;

A nitride-based thin film composite structure according to a first aspect is a nitride-based thin film composite structure including a nitride thin film formed on a bulk single crystal wafer,
Nitride microcrystals provided on the bulk single crystal wafer in a specific orientation relationship with the crystal structure of the bulk single crystal wafer;
an amorphous nitride thin film surrounding the nitride crystallites and covering the surface of the bulk single crystal wafer;
Consists of

In the nitride-based thin film composite structure according to the second aspect, in the first aspect, the upper surface may be flat.

In the nitride-based thin film composite structure according to the third aspect, in the second aspect, the upper surface may have an arithmetic mean roughness of 0.1 nm or more and 10 nm or less.

A nitride-based thin film composite structure according to a fourth aspect is a nitride-based thin film composite structure according to any one of the first to third aspects, wherein the nitride-based thin film composite structure contains one or more of Al, Ga, and In. It may be composed of binary or ternary elements obtained by nitriding the metal element.

In a nitride-based thin film composite structure according to a fifth aspect, in any one of the first to fourth aspects, the distance between the nitride microcrystals may be 5 nm or more and 50 μm or less.

A nitride-based thin film composite structure according to a sixth aspect may be the nitride-based thin film composite structure according to any one of the first to fifth aspects, and may have a film thickness of 5 nm or more and 100 nm or less. .

A nitride-based thin film composite structure according to a seventh aspect is the nitride-based thin film composite structure according to any one of the first to fourth aspects, wherein the nitride-based thin film composite structure comprises Sapphire (α-Al ₂ O ₃ ), Si, It may be formed on any one bulk single crystal wafer selected from the group of SiC, GaP, GaAs, ZnO, MgO, _ScAlMgO4 .

A method for manufacturing a nitride-based thin film composite structure according to an eighth aspect comprises the steps of preparing a bulk single crystal substrate and a target material in a vacuum chamber of a sputtering apparatus;
A gas containing 30% or more nitrogen is introduced into the vacuum chamber, the pressure is set to 0.1 Pa or more and 0.5 Pa or less, the temperature of the substrate is 25 ° C. or more and 1000 ° C. or less, and electric power is applied at a frequency of 1 kHz or more and 100 kHz or less. applying a power pulse with a time rate of 0.1% or more and 30% or less to generate plasma, surround the nitride microcrystals on the substrate and the nitride microcrystals by a reactive sputtering method, and forming an amorphous nitride thin film covering the entire surface of the bulk single crystal substrate;
including.

A method for manufacturing a nitride-based thin film composite structure according to a ninth aspect is the reactive sputtering according to the eighth aspect, in which a target material and a gas are reacted to form a thin film on the substrate. A direct current may be supplied in a pulsed manner to generate a plasma when performing the step.

Hereinafter, a nitride-based thin film composite structure and a method for manufacturing the same according to an embodiment will be described in detail with reference to the drawings. In addition, the same code|symbol is attached|subjected about the substantially same member in drawing.

(Embodiment 1)
<Nitride thin film composite structure>
First, a nitride-based thin film composite structure 100 of Embodiment 1 will be described mainly with reference to FIGS. 1A and 1B. FIG. 1A is a schematic cross-sectional view showing a cross-sectional structure of a laminate obtained by laminating a nitride-based thin film composite structure 100 on a bulk single crystal wafer 101 of Embodiment 1. FIG. FIG. 1B is a plan view of the nitride-based thin film composite structure 100 of FIG. 1A. This nitride-based thin film composite structure 100 is formed on a bulk single crystal wafer 101, and includes nitride microcrystals provided on the bulk single crystal wafer in a specific orientation relationship with the crystal structure of the bulk single crystal. 102 and an amorphous nitride thin film 103 made of the same material as the nitride microcrystals. A plurality of nitride crystallites 102 are arranged on a bulk crystal wafer 101 . Each of the plurality of nitride microcrystals 102 is, for example, a single crystal. Each of the plurality of nitride microcrystals 102 is provided on the bulk single crystal wafer with a specific orientation relationship with the crystal structure of the bulk single crystal. That is, the crystal axes of the plurality of nitride microcrystals 102 are aligned with each other.

Here, with reference to FIGS. 2A to 2D, nitride microcrystals provided on the bulk single crystal wafer having a specific orientation relationship with the crystal structure of the bulk single crystal wafer will be described. FIG. 2A is a schematic diagram showing the orientation relationship between a single crystal bulk wafer and microcrystals when a Sapphire (0001) substrate is used as a bulk single crystal wafer and AlN (aluminum nitride) is used as nitride microcrystals. FIG. 2B is a diagram showing crystal axes when the bulk single crystal wafer is sapphire. FIG. 2C is a diagram showing crystal axes when the nitride crystallites are AlN.
Sapphire has a corundum-type crystal structure, and its unit cell 201 can be represented by a hexagonal prism. AlN has a wurtzite crystal structure, and its unit cell 202 can also be represented by a hexagonal prism. FIG. 2A and FIG. 2D show plan views viewed from above, with the [0001] axes of the hexagonal prisms of the respective unit cells overlapping. Here, the specific orientation relationship means that the Sapphire crystal axis [0001] and the AlN crystal axis [0001] have the same orientation relationship. Next, it has an orientation relationship in which the [1-100] axis of AlN is rotated by 30° with respect to the [1-100] axis of Sapphire. That is, as shown in FIG. 2D, the Sapphire unit cell is placed on the AlN unit cell with the [0001] axis rotated by 30° with the central axis aligned with the AlN unit cell.

As another example of the orientation relationship, there is a case where a combination of wurtzite structures is selected, such as using the (0001) plane of ZnO (zinc oxide) as a single crystal bulk wafer and selecting AlN as a nitride microcrystal. mentioned. In this case, the [0001] direction and the [1-100] axis of each wurtzite have the same orientation relationship. That is, each unit cell has the [0001] axis and the [1-100] axis aligned and is placed on top without rotating (not shown).

Furthermore, the amorphous nitride thin film made of the same material as the nitride crystallites is a compound composed of the same composition as the specific crystallites, but it has an amorphous structure that does not have a specific crystal structure. Refers to a nitride thin film.

Since the microcrystals 102 are spontaneously formed during the film formation process, the spacing and size of the microcrystals can be controlled by the process conditions in the method for manufacturing a nitride-based thin film composite structure, which will be described later. This nitride-based thin film composite structure can also be formed by the MOCVD method, the MBE method, and the HVPE method. However, the MOCVD method, MBE method, and HVPE method are methods in which the substrate temperature is high and crystals grow due to migration on the substrate. For this reason, in the above method, the surface roughness of a crystal formed on a single crystal bulk wafer, which is a substrate, changes sensitively depending on the growth rate, substrate temperature, and other formation conditions, and the crystal state and flatness are affected. difficult to control at the same time. On the other hand, in the sputtering method, the substrate temperature is relatively low, so the distance of migration is small and a flat film can be easily formed. Although affected by the surface roughness of the substrate, it is possible to form a thin film having an arithmetic mean roughness Ra of 0.1 nm or more and 10 nm or less by the sputtering method. That is, the nitride-based thin film composite structure of the present disclosure preferably has a flat upper surface. Furthermore, the nitride-based thin film composite structure of the present disclosure preferably has an upper surface with an arithmetic mean roughness of 0.1 nm or more and 10 nm or less. In particular, the formed thin film has excellent in-plane uniformity and flatness of the film thickness, and the cost of production equipment is low, so it is desirable that the film formation of the nitride-based thin film composite structure is performed by a sputtering method. .

<Sputtering device>
Next, a sputtering apparatus 300 for forming a nitride-based thin film composite structure according to Embodiment 1 will be described. FIG. 3 is a schematic diagram showing the configuration of a sputtering apparatus 300 according to Embodiment 1. As shown in FIG. This sputtering apparatus 300 includes a vacuum chamber 301, a vacuum pump 302, a gas supply source 304, a backing plate 308, a DC power supply 330, a pulsing unit 332, and a power supply controller 340 functioning as an example of a control section. , a pulse controller 341 and a substrate holder 305 .

The vacuum chamber 301 can be evacuated to a vacuum state by exhausting with a vacuum pump 302 connected via a gate valve 303 .

A gas supply source 304 can supply a gas required for sputtering to the vacuum chamber 301 at a constant rate. The gas supplied by the gas supply source 304 is selected from, for example, a gas having reactivity with the target material, such as nitrogen or oxygen, or a mixed gas of a reactive gas and a rare gas such as inert argon. can.

The gate valve 303 can control the degree of vacuum in the vacuum chamber 301 to a desired gas pressure by changing its opening/closing ratio.

In FIG. 3, a target material 307 is arranged in the upper part of the vacuum chamber 301 . The target material 307 is any sputter material, but an inorganic material, such as a metallic material that forms a nitride or a semiconductor material. In the case of the first embodiment, Al of high purity (6N: 99.9999%) is used.

The backing plate 308 is arranged in the upper part of the vacuum chamber 301 and supports the target material 307 so as to face the substrate holder 305 which will be described later.

A DC power supply 330 is electrically connected to the target material 307 via the pulsing unit 332 and the backing plate 308 and can apply a voltage to the target material 307 . The pulsing unit 332 can store the DC current generated by the DC power supply 330 in a built-in capacitor or the like, turn it on or off by a built-in semiconductor switching element or the like, and turn it into a pulse. The pulsing unit 332 is controlled by a pulse controller 341 , and the DC power supply 330 and the pulse controller 341 are controlled by the power supply controller 340 . Also, the current from the DC power supply 330 to the pulsing unit 332 is measured by an ammeter 331 and the measured current value is fed back to the power supply controller 340 . That is, the power supply controller 340 feedback-controls the DC power supply 330 so that the current value measured by the ammeter 331 becomes a predetermined value.

A magnet 309 and a yoke 310 are arranged behind the backing plate 308 in the upper part of the vacuum chamber 301 and can generate a magnetic field on the surface of the target material 307 . One or more magnets 309 may be provided. Note that the magnet 309 may be either a permanent magnet or an electromagnet. The yoke 310 is connected to one end of the magnet 309 , forms a magnetic circuit, and can suppress unnecessary magnetic field leakage to the side opposite to the target material 307 .

In FIG. 3, a substrate holder 305 that supports a substrate 306 is arranged in the lower part of the vacuum chamber 301 . The substrate holder 305 is arranged below the substrate 306 and supports the substrate 306 so that the surface of the substrate 306 faces the surface of the target material 307 supported by the backing plate 308 .

<Manufacturing method of nitride-based thin film composite structure>
Next, a method for manufacturing a nitride-based thin film composite structure according to Embodiment 1, that is, a film formation procedure for a nitride-based thin film composite structure will be described.
(1) First, the board is loaded. A substrate 306 on which a film is to be deposited, for example, a Sapphire (0001) substrate (“bulk single crystal wafer”) is placed at the position of the substrate 306 in FIG. The substrate 306 may be placed directly by hand after opening the vacuum chamber 301 to the atmosphere, or may be placed mechanically from a load lock chamber using a robot arm or the like without opening to the atmosphere.
(2) Subsequently, the vacuum pump 302 is operated to reduce the pressure so that the inside of the vacuum chamber 301 becomes a vacuum state, and after reaching a predetermined degree of vacuum, a gas is introduced from the gas supply source 304, The opening degree of the gate valve 303 is adjusted so as to obtain the pressure.
(3) When the gas flow rate and pressure are stabilized, power is applied to generate plasma to start film formation. In this case, the film formation of the nitride microcrystals and the amorphous nitride thin film is performed in one step. As film formation conditions, for example, a gas containing 30% or more of nitrogen is introduced into a vacuum chamber, and the pressure is set to 0.1 Pa or more and 0.5 Pa or less. Also, the temperature of the substrate is 25° C. or higher and 1000° C. or lower. Furthermore, plasma is generated by applying a power pulse with a frequency of 1 kHz or more and 100 kHz or less and a power application time ratio of 0.1% or more and 30% or less. Under the above conditions, film formation is performed for an arbitrary time so as to obtain a desired film thickness, and then the substrate is taken out to complete a series of operations.
As described above, a nitride-based thin film structure can be formed on the substrate 306, which is a bulk single crystal wafer.

Next, a method for evaluating the nitride-based thin film composite structure formed by the sputtering method described above will be described. Evaluation of the composite of microcrystals 102 and amorphous 103 in the nitride-based thin film composite structure was carried out by X-ray structural analysis and the observation of GaN grown by MOCVD using the nitride-based thin film composite structure as an initial substrate using an optical microscope. by observing by

Details of X-ray evaluation will be described. Structural analysis by X-ray was carried out using the method described in the literature (Journal of Crystal Growth, 268 (2004), 1-7), and the peak of the X-ray rocking curve reflection of AlN (0002) was separated from the width derived from the crystallites. Assuming that a narrow peak and a wide peak derived from amorphous overlap, and separating the peak derived from the crystallite and the peak derived from the amorphous using a Gaussian function, the crystallite 102 and the amorphous The presence of each with crystalloid 103 can be confirmed. Here, the width of the X-ray peak cannot be represented by a specific numerical value, but among the two separated peaks, the relatively narrow peak is related to microcrystal origin, and the wide peak is related to amorphous origin. ing.

Next, evaluation by an optical microscope will be described. Since the distance between microcrystals 102 cannot be evaluated by X-rays, GaN is grown by MOCVD using a nitride-based thin film composite structure as an initial substrate, and the positions where crystal growth has progressed are evaluated by observing with an optical microscope. If the entire surface of the nitride thin film formed by the sputtering method is crystalline or amorphous, layered GaN or polycrystalline GaN should grow, respectively. On the other hand, when a composite of microcrystals and amorphous is grown, the microcrystals serve as crystal nuclei in the microcrystal portion, and crystal growth proceeds easily. is observed. On the other hand, nothing should be observed in the amorphous portion because crystal growth does not proceed. Therefore, if the thin film formed by the sputtering method is a composite of microcrystals and amorphous, an optical microscope image of hexagonal prisms arranged at certain intervals can be observed.

(Example 1)
The examination result in Example 1 of Embodiment 1 is described below. In Example 1, a sputtering method was used, Al was used as a target material, and nitrogen was used as a reactive gas to form a nitride-based thin film composite structure. The nitrogen gas flow rate was controlled so that the deposition pressure was 0.45 Pa, and the substrate temperature was kept constant at 400° C. by lamp heating. The power applied to the target for plasma discharge was 0.15 kW, the pulse condition was a frequency of 10 kHz, and the duty ratio of power application was 5%. The film formation time was adjusted so that the film thickness of the formed nitride-based thin film composite structure was 20 nm.

Here, the film formation pressure may be any pressure at which plasma discharge occurs, and may be 0.1 Pa or more and 1 Pa or less. Desirably, it is 0.1 Pa or more and 0.5 Pa or less. If the pressure is less than 0.1 Pa, it is difficult to maintain the plasma discharge, and discharge failure may occur. When it exceeds 1 Pa, the nitriding reaction by the reactive gas becomes insufficient, and the film quality may be deteriorated such as deposition of metal Al. Although the above film formation is performed in a complete nitrogen system, Ar may be added as a sputtering gas, and the nitrogen content in the gas species to be supplied is desirably in the range of 30% to 100%. If the proportion of nitrogen is less than 30%, the nitriding reaction becomes insufficient, and problems such as precipitation of metal Al and oxidation when taking out the sample after film formation are caused by insufficient nitriding. The substrate temperature may be 25° C. or higher and 1000° C. or lower, preferably in the range of 25° C. or higher and 600° C. or lower. If the temperature is higher than 1000° C., excessive crystallization occurs, making it difficult to form a composite structure of microcrystals and amorphous. The lower limit temperature of 25° C. is a guideline for room temperature, and the temperature may be lower than this as long as it is room temperature.
Further, in the study of the present inventors, the plasma discharge becomes extremely unstable when the frequency of the power pulse applied to the target for plasma discharge is on the low frequency side, for example, less than 1 kHz. On the high frequency side, for example, when the frequency exceeds 100 kHz, one cycle is about 10 microseconds, and the duty ratio cannot be lowered to a desired value due to limitations of the power supply. Therefore, the appropriate frequency is considered to be 1 kHz or more and 100 kHz or less.

In addition, in order to achieve the purpose of instantaneously applying a large power and generating nitrogen gas with high dissociation energy into highly reactive atomic nitrogen or radical nitrogen, the time for applying power in one cycle is should be short. However, if the ratio of the power application time in one cycle is less than 0.1%, the power is in the middle of rising and the time to reach the set power is insufficient. When the duty ratio exceeds 30%, the amount of atomic nitrogen or radical nitrogen produced by the dissociation of the nitrogen gas decreases, and when the duty ratio reaches about 50%, the situation is the same as that of normal DC sputtering. Therefore, a duty ratio of 0.1% or more and 30% or less is appropriate for the ratio of time for applying power in one cycle. The film thickness may be 1 nm or more and 100 nm or less, preferably 5 nm or more and 50 nm or less. If the film thickness is less than 1 nm, the film disappears due to thermal decomposition during temperature rise during nitride semiconductor crystal growth by MOCVD or HVPE using the nitride-based thin film composite structure as a base layer. On the other hand, if it is thicker than 100 nm, the density of the microcrystals becomes excessive and the orientation of the microcrystals is disturbed, so that the nitride-based thin film composite structure loses its function as a base layer.

Next, evaluation results of the formed nitride-based thin film composite structure will be described. An X-ray rocking curve measurement was performed on the nitride-based thin film composite structure produced by the sputtering method for the purpose described above, and the obtained reflection peak of the AlN (0002) plane was attributed to microcrystals and amorphous. The separation results are shown in FIG. Since the detailed method is as described above, it will be omitted. The solid line is the raw data obtained by X-ray measurement, the one-dot chain line and the two-dot chain line are peaks derived from microcrystals and amorphous obtained by fitting, respectively, and the dotted line represents the sum of the peaks. The raw data and the dotted line are good fitting results that almost overlap, and this result supports that the nitride-based thin film composite structure formed by the sputtering method is a composite of microcrystals and amorphous.

Next, the results of forming a GaN film by the MOCVD method on the nitride-based thin film composite structure produced by the sputtering method will be described. Trimethylgallium (TMG) was used as the group III source, and _NH3 was used as the group V source. 23 sccm of TMG and 5 SLM of NH ₃ were supplied and diluted with hydrogen gas so that the total flow in the reactor was 50 SLM. The substrate temperature was set to 1050° C., and GaN was grown for 60 minutes. FIG. 5 shows the results of observation of the obtained sample with an optical microscope. According to FIG. 5, hexagonal GaN derived from the wurtzite structure was observed. Observation with a scanning electron microscope revealed that columnar crystals with a height of 1 μm or more and 20 μm or less were obtained at intervals of 50 nm or more and 20 μm or less. Since the crystal growth of GaN proceeds starting from microcrystals, the microcrystals in the nitride-based thin film composite structure formed on the bulk single crystal wafer are also scattered at intervals of 50 nm or more and 20 μm. I know there is. The interval between the microcrystals can be controlled by film formation conditions, and the interval should be 5 nm or more and 50 μm or less, preferably 50 nm or more and 20 μm or less. If it is smaller than 5 nm, when the nitride semiconductor crystal is grown by the subsequent MOCVD method or HVPE method, the bonding interface between the crystals becomes a defect, so that a high-quality crystal cannot be grown. On the other hand, when the distance between the microcrystals is 50 μm or more, the nitride semiconductor crystals grown from the microcrystals cannot be bonded when the crystal growth is performed by the MOCVD method or the HVPE method, resulting in serious defects such as pits and micropipes. cause it to generate. On the other hand, it was found that the growth of GaN was not confirmed in the regions where the hexagonal prisms were not formed, and no nucleation occurred. A result was obtained that supports the fact that the single-crystal bulk substrate is covered with an amorphous layer in this region as described above.

Therefore, the results of optical microscopic observation of a sample in which GaN was grown by MOCVD on a nitride thin film composite structure fabricated by sputtering revealed that the nitride thin film composite structure was microcrystalline and amorphous. It was a result supporting that it is a composite structure consisting of.

According to the above embodiments, it was found that a nitride-based thin film composite structure composed of microcrystals and amorphous can be formed on a single crystal bulk substrate using a sputtering method. Therefore, it is possible to provide a nitride-based thin film composite structure having the same function as a processed substrate used in the ELO method and a method for forming the same by a one-step process using an inexpensive sputtering method.

It should be noted that the present disclosure includes appropriate combinations of any of the various embodiments and / or examples described above, and each embodiment and / or The effects of the embodiment can be obtained.

A nitride-based thin film composite structure and a method for manufacturing the same according to the present embodiment provide a base layer and a base layer for growing nitride semiconductors including GaN, AlN, InN, and their mixed crystals by MOCVD or HVPE. It can be used as its manufacturing method. In addition, it is useful because it is possible to inexpensively and efficiently produce the nitride semiconductor having the same quality as high-quality crystals produced by the ELO method.

100 Nitride thin film composite structure 101 Bulk single crystal wafer 102 Nitride microcrystal 103 Amorphous nitride thin film 201 Sapphire unit cell 202 AlN unit cell 300 Sputtering device 301 Vacuum chamber 302 Vacuum pump 303 Gate valve 304 Gas supply Source 305 Substrate holder 306 Substrate 307 Target material 308 Backing plate 309 Magnet 310 Yoke 330 DC power supply 331 Ammeter 332 Pulse unit 340 Power supply controller 341 Pulse controller 601 Bulk monocrystalline wafer 602 Crystalline thin film 603 Amorphous mask 701 Aperture Part 702 mask

Claims (8)

A nitride-based thin film composite structure comprising a nitride thin film formed on a bulk single crystal wafer,
Nitride microcrystals provided on the bulk single crystal wafer in a specific orientation relationship with the crystal structure of the bulk single crystal wafer;
an amorphous nitride thin film surrounding the outer surface of the nitride crystallites and covering the surface of the bulk single crystal wafer;
with
A nitride-based thin film composite structure , wherein the distance between the nitride microcrystals is 5 nm or more and 50 μm or less, and the nitride microcrystals are exposed on the surface . 2. The nitride-based thin film composite structure according to claim 1, wherein the upper surface is flat. 3. The nitride-based thin film composite structure according to claim 2, wherein the upper surface has an arithmetic mean roughness of 0.1 nm or more and 10 nm or less. 4. The nitride-based thin-film composite structure according to any one of claims 1 to 3, wherein the nitride-based thin film composite structure is composed of binary or ternary elements obtained by nitriding one or more metal elements of Al, Ga, and In. 10. A nitride-based thin film composite structure according to claim 1. 5. The nitride-based thin film composite structure according to claim 1 , wherein the nitride-based thin film composite structure has a film thickness of 5 nm or more and 100 nm or less. The nitride-based thin film composite structure is any one bulk single crystal wafer selected from the group of Sapphire (α-Al ₂ O ₃ ), Si, SiC, GaP, GaAs, ZnO, MgO, ScAlMgO ₄ A formed nitride-based thin film composite structure according to any one of claims 1 to 5 . preparing a bulk single crystal substrate and a target material in a vacuum chamber of a sputtering apparatus;
A gas containing 30% or more nitrogen is introduced into the vacuum chamber, the pressure is set to 0.1 Pa or more and 0.5 Pa or less, the temperature of the substrate is 25 ° C. or more and 1000 ° C. or less, and electric power is applied at a frequency of 1 kHz or more and 100 kHz or less. applying a power pulse with a time rate of 0.1% or more and 30% or less to generate plasma, surround the nitride microcrystals on the substrate and the nitride microcrystals by a reactive sputtering method, and forming an amorphous nitride thin film covering the entire surface of the bulk single crystal substrate;
A method for manufacturing a nitride-based thin film composite structure, comprising: 8. The method according to claim 7 , wherein, in reactive sputtering, a direct current is supplied in a pulsed form to generate plasma when performing reactive sputtering in which a target material and a gas are reacted to form a thin film on the substrate. A method for manufacturing a nitride-based thin film composite structure.

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