JP7084805B2 - Method for Manufacturing Group III Nitride Single Crystal Substrate and Group III Nitride Single Crystal Laminate - Google Patents

Description

The present invention relates to a method for producing a high quality Group III nitride single crystal substrate. More specifically, the present invention relates to a method for producing a high-quality group III nitride single crystal substrate in which the grain region is reduced in a group III nitride single crystal substrate having a grain region whose crystal orientation is different from that of the surrounding single crystal region.

Group III nitride single crystals such as aluminum nitride, gallium nitride, and indium nitride can form mixed crystal semiconductors having any composition, and the bandgap energy can be changed depending on the mixed crystal composition. Therefore, by using a group III nitride single crystal, it is possible to manufacture a wide range of light emitting elements from infrared light to ultraviolet light in principle. In recent years, the development of light emitting devices using aluminum-based Group III nitride single crystals containing aluminum has been energetically promoted.

Currently, in the production of a light emitting element using a group III nitride single crystal, a sapphire substrate is generally adopted from the viewpoints of crystal quality as a substrate, ultraviolet light transmission, mass productivity and cost. However, when a Group III nitride single crystal is grown on a sapphire substrate, the lattice constant between the sapphire substrate and a Group III nitride single crystal layer such as aluminum gallium nitride that forms an element layer in which light emission occurs may occur. Due to the difference in the thermal expansion coefficient, stress, dislocation, cracks, etc. occur, which causes deterioration of the performance of the light emitting element. For this reason, it is desirable to use a substrate that is close to the lattice constant and thermal expansion coefficient of the element layer, and as a substrate that forms the element layer using an aluminum-based Group III nitride single crystal, III such as aluminum nitride and aluminum gallium nitride. A group nitride single crystal substrate is preferably used.

When a device layer is formed on the above-mentioned Group III nitride single crystal substrate, it is generally known that the device layer inherits the crystal quality of the substrate. For example, when dislocations are present in a group III nitride single crystal substrate, the dislocations are inherited by the element layer grown on the substrate, so that the dislocation density per unit area or unit volume is determined between the substrate and the element layer. It will be about the same. The lower the dislocation density, the higher the internal quantum efficiency of the element layer can be obtained. Therefore, it is preferable that the dislocation density of the Group III nitride single crystal substrate is as low as possible.

Further, the group III nitride single crystal substrate may have a grain region having a crystal orientation different from that of the peripheral portion due to the manufacturing process (see Patent Document 1). When the element layer is grown on the group III nitride single crystal substrate including the grain region, the element layer on the grain region grows in a state where the crystal orientation is deviated, and a large amount of dislocations occur in the element layer. Not only that, local stress is also generated due to the deviation of the crystal orientation. Therefore, the luminous element formed on the grain region has a significantly reduced luminous efficiency and element life as compared with other regions. Further, since the growth conditions of the device layer are different from the optimum growth conditions of the peripheral portion due to the difference in the crystal orientation of the growth surface on the grain region, the device layer is placed on such a group III nitride single crystal substrate. When formed, the pn junction and the quantum well structure inside the element layer to be originally formed, which are the same as those in other regions, cannot be obtained on the grain region. Then, the light emitting element formed on the grain region does not function as the element itself. Such a tendency becomes more remarkable as the degree of crystal orientation deviation and complexity of the grain region increases. For this reason, a Group III nitride single crystal substrate having no grain region is desired.

Japanese Patent No. 2017-12028

The grain region contained in the Group III nitride single crystal substrate is localized inside the bulk single crystal, which is a form before being processed into the form of the substrate. It is considered that the generation of the grain region is introduced by various causes such as foreign matter mixed from the growth system during crystal growth of the bulk single crystal, incompatibility of crystal growth conditions, and fluctuation of crystal growth conditions. If a grain region is generated on the growth front (that is, the single crystal growth surface) due to the above-mentioned cause during the growth of a group III nitride single crystal, the grain region is subsequently grown while remaining inside the bulk crystal. As a result, the grain region remains inside the bulk crystal. That is, once the grain region generated during the growth of the bulk crystal is generated, it becomes difficult to eliminate the grain region during the growth.

A bulk crystal containing such a grain region is subjected to processing steps such as cutting, grinding, and polishing to form a wafer, that is, a group III nitride single crystal substrate. Naturally, a group III nitride single crystal is obtained. A grain region will be locally present on the crystal substrate. Even if another Group III nitride single crystal layer is formed on the substrate using such a Group III nitride single crystal substrate, the grain region is inherited by another Group III nitride single crystal layer. In addition, as described above, when the element layer is formed on the group III nitride single crystal substrate, the performance is deteriorated and the failure is caused.

That is, an object of the present invention is to provide a method for manufacturing a high-quality group III nitride single crystal substrate in which the grain region that causes performance deterioration of the element formed on the group III nitride single crystal substrate is reduced. be.

In order to solve the above problems, the present inventors investigated the structure of the group III nitride crystal constituting the grain region of the group III nitride single crystal. As a result, it was found that the elements constituting the grain region were the same as those of the single crystal portion constituting the group III nitride single crystal substrate. Further, the grain region is a region in which the crystal orientation existing in the single crystal region of the group III nitride single crystal substrate with a certain section is different from the surrounding single crystal region, and is one in the grain region. It has been clarified that the crystals exhibit various forms of existence, from the case of causing the crystal orientation deviation in an arbitrary direction to the case of causing a plurality of crystal orientation deviations in an arbitrary direction. Further, the direction of the crystal orientation deviation in the grain region and the size of the partition are arbitrary, and when a large number of crystal orientation deviations are present in the grain region, it may be recognized as a polycrystal state. It became clear. In addition, it was clarified that dislocations exist at the boundary (section) between the grain region and the surrounding single crystal region due to the deviation of the crystal orientation.

As a result of further studies based on the above findings, the atomic arrangement of the group III nitride crystal in the grain region is temporarily arranged by applying a physical action from the outside to the grain region contained in the group III nitride single crystal. We have found that the crystal orientation shift of the grain region can be significantly reduced by introducing the second reforming step of further changing the atomic arrangement of the grain region after introducing the disturbing first reforming step, and completed the present invention. I came to do.

That is, in the first invention, at least a part of the grain region of the group III nitride single crystal substrate having a grain region whose crystal orientation is different from the surrounding single crystal region is irradiated with laser light to obtain the region. By heat-treating the first modification step that temporarily disturbs the atomic arrangement of the crystal and then the group III nitride single crystal substrate, the atomic arrangement temporarily disturbed by the first modification step is rearranged. This is a method for producing a Group III nitride single crystal substrate, which comprises a second reforming step of reconstructing the crystal arrangement.

The method for producing a Group III nitride single crystal substrate of the present invention preferably adopts the following aspects .
(1 ) The irradiation energy of the laser beam is smaller than the bandgap energy of the group III nitride single crystal substrate.
( 2 ) The heat treatment is performed by heating the Group III nitride single crystal substrate to 1200 ° C. or higher.
( 3 ) The total amount of silicon, carbon, and oxygen impurities contained in the group III single crystal nitride substrate having the grain region shall be 1 × 10 ¹⁶ cm ^-3 or more and 1 × 10 ²¹ cm ^-3 or less.
( 4 ) The thickness of the Group III single crystal nitride substrate having the grain region is 50 μm or more.
( 5 ) The group IIII single crystal nitride substrate having the grain region is aluminum nitride.
( 6 ) The half-value width of the X-ray locking curve in the grain region is reformed to 100 seconds or more by the first reforming step.

Further, in the second invention, the group III nitride single crystal substrate is obtained by the above-mentioned production method, and then the group III nitride single crystal layer is laminated on the obtained group III nitride single crystal substrate III. This is a method for producing a group nitride single crystal laminate. In the second production method of the present invention, it is preferable to polish the surface of the group III nitride single crystal substrate and then laminate the group III nitride single crystal layer.

According to the present invention, the grain region existing in the group III nitride single crystal substrate can be reduced, and the quality of the group III nitride single crystal layer formed on the group III nitride single crystal substrate is good. Can be. Therefore, it is possible to suppress deterioration in performance and yield of the element layer obtained by using the group III nitride single crystal layer.

It is a schematic diagram which shows the manufacturing method of this invention. This is an example of a reflected X-ray topograph image including a grain region of a group III nitride single crystal substrate (single crystal aluminum nitride substrate).

Hereinafter, a method for producing a high-quality Group III nitride single crystal substrate with a reduced grain region according to the present invention will be described in order according to one embodiment shown in FIG.

(Group III nitride single crystal substrate)
The group III nitride single crystal substrate 10 in the production method of the present invention has at least one grain region 10a in the surface of the substrate and a single crystal region 10b so as to surround the grain region 10a.

The group III nitride single crystal substrate 10 in the production method of the present invention is a nitride single crystal containing aluminum, boron, gallium, and indium in an arbitrary ratio, and contains a single group III element nitride to mixed crystals. .. It is a nitride single crystal or a gallium nitride single crystal containing aluminum as a main component that can obtain a higher effect of the present invention, and an aluminum nitride single crystal can obtain a particularly high effect.

The thickness of the Group III nitride single crystal substrate 10 is not particularly limited, but if it is too thin, stress is locally generated when a physical action is applied in the first reforming step, and the stress causes Group III. The nitride single crystal substrate may be damaged, and from the viewpoint of ensuring physical strength, it is preferably 50 μm or more, more preferably 100 μm or more, and further preferably 200 μm or more. On the other hand, if the thickness of the group III nitride single crystal substrate 10 is too thick, it tends to be difficult to apply a physical action from the front surface to the entire back surface of the grain region contained in the group III nitride single crystal substrate. Therefore, it is preferably 2000 μm or less, more preferably 1000 μm or less, and further preferably 600 μm or less.

Therefore, the thickness of the Group III nitride single crystal substrate 10 is preferably in the range of 50 μm or more and 2000 μm or less, more preferably 100 μm or more and 1000 μm or less, and particularly preferably 200 μm or more and 600 μm or less.

The size of the Group III nitride single crystal substrate 10 is not particularly limited and may be appropriately determined according to the desired application. A group III nitride single crystal layer 14 is laminated on the second modified group III nitride single crystal substrate 12 manufactured by the production method of the present invention, and an element is formed on the obtained group III nitride single crystal substrate 10. When a layer is formed to form a light emitting element, it is preferable that the size of the substrate is large from the viewpoint of productivity. Therefore, the area of the Group III nitride single crystal substrate 10 is preferably 100 mm ² or more.

As the plane orientation of the Group III nitride single crystal substrate 10, any plane orientation can be used, but in general, c-plane (Group III polar plane), −c-c plane (nitrogen polar plane), and so on. It is possible to use a Group III nitride single crystal substrate having a specific plane orientation such as m-plane or a-plane. It is also possible to use a substrate in which the crystal axis is intentionally inclined from the specific crystal plane, that is, a group III nitride single crystal substrate provided with an off angle in relation to the plane orientation.

In order to obtain the effect of the production method of the present invention, the total amount of silicon, carbon and oxygen impurities contained in the group III nitride single crystal substrate 10 is 1 × 10 ¹⁶ cm ^-3 or more and 1 × 10 ²¹ cm ^-3 or less. It is preferable to have. The details of this reason are not clear, but the lower the concentration, the more likely it is that cracks will occur in the Group III nitride single crystal substrate after the first reforming step 101. Further, the higher the concentration, the more the lattice constant is affected by the difference in impurity concentration from the group III nitride single crystal layer 14 that grows on the group III nitride single crystal substrate 12 after the second modification after the second modification step 102. Distortion due to the difference is likely to occur. Therefore, the lower limit of impurities is more preferably 5 × 10 ¹⁶ cm ^-3 or more, further preferably 1 × 10 ¹⁷ cm ^-3 or more, and the upper limit is more preferably 1 × 10 ²⁰ cm ^-3 or less, further preferably. Is 5 × 10 ¹⁹ cm ^-3 or less.

Therefore, the total amount of silicon, carbon, and oxygen impurities contained in the group III nitride single crystal substrate 10 is more preferably 5 × 10 ¹⁶ or more and 1 × 10 ²⁰ cm ^-3 or less, and particularly preferably 1 × 10 ¹⁷ cm ⁻ . It should be in the range of ³ or more and 5 × 10 ¹⁹ cm ^-3 or less.

In the production method of the present invention, the atomic arrangement in the grain region 11a after the first modification is rearranged according to the crystal arrangement of the single crystal region 10b by the second modification step described later, and the second modification It is presumed that the post-quality grain region 12a is formed. Therefore, in order to obtain the effect of the production method of the present invention, it is preferable that the crystal orientation of the single crystal region 10b around the grain region 10a of the group III nitride single crystal substrate 10 is good. The crystal orientation of the portion can be defined by the X-ray omega locking curve, and the half-value width of the X-ray omega locking curve of the (101) plane orientation of the group III nitride single crystal is 100 seconds or less, more preferably 50 seconds. Below, it is more preferably 30 seconds or less. The smaller the value of this half price width, the better the crystal orientation, and it is preferable to use an X-ray source obtained by monochromaticizing a germanium single crystal (220) by four times diffraction for this measurement. It is also possible to evaluate the orientation of crystals in the grain region by narrowing down the X-ray irradiation region. The lower limit on the measurement principle is about 10 seconds.

(Grain area)
The grain region 10a included in the group III nitride single crystal substrate 10 is a region whose crystal orientation is different from that of the surrounding single crystal region. As described above, the constituent elements of the grain region 10a are the same as those of the single crystal region 10b (that is, the surrounding single crystal region) of the group III nitride single crystal substrate. On the other hand, the grain region 10a is a region in which the crystal orientation existing in the single crystal region 10b of the group III nitride single crystal substrate 10 with a certain section is different from that in the surrounding single crystal region 10b. The shape of the grain region 10a rarely has a specific shape and is often amorphous. The inside of the grain region 10a shows various forms of existence, from the case where the crystal orientation shift in one arbitrary direction occurs to the case where the crystal orientation shift occurs in a plurality of arbitrary directions. Further, there is no specific fixed state in the direction of the crystal orientation deviation or the size of the partition inside the grain region 10a, and when a large number of crystal orientation deviations are present, it is recognized as a polycrystal state. Further, dislocations are present at the boundary (section) between the grain region 10a and the surrounding single crystal region 10b due to the deviation of the crystal orientation of the grain region 10a.

Such a grain region 10a can be easily detected by measuring an X-ray topograph image, a birefringence distribution, polarization observation, and a rear electron diffraction spectrum. Among them, the X-ray topograph image is a means for clearly confirming the grain region with good resolution in a wide field of view. FIG. 2 is an example of a reflected X-ray topograph image using (114) plane diffraction of a group III nitride single crystal substrate (single crystal aluminum nitride substrate).

The reflected X-ray topograph image is information near the surface of the group III nitride single crystal substrate, and while a uniform diffraction contrast due to X-ray diffraction is observed from the single crystal region 10b, it is observed from the grain region 10a. Due to the crystal orientation shift, the X-ray diffraction condition is not satisfied, and the diffraction contrast as in the single crystal region cannot be observed. Further, when the crystal orientation deviation is slight, diffraction from the grain region 10a can be obtained, but the diffraction has a different intensity from that of the single crystal region 10b. Therefore, the boundary between the grain region 10a and the single crystal region 10b can be detected as a contrast difference. Further, when the grain region 10a is in the state of polycrystal, the portion where the diffraction contrast can be obtained and the portion where the diffraction contrast cannot be obtained are in a complicated interlaced state. In this way, some typical observation patterns can be seen depending on the direction and size of the crystal orientation of the grain region, but by acquiring the reflected X-ray topograph image, a foreign crystal is found in the single crystal region. The grain region is recognized as a region having the state of. That is, the grain region in the manufacturing method of the present invention can be determined as a region showing a contrast different from the surrounding region in the reflected X-ray topograph image.

Regarding the area of the grain region 10a, the grain region can be specified by image analysis of the reflected X-ray topograph image on the surface of the group III nitride single crystal substrate, and the area can be easily specified. The effect of the present invention can be further obtained when the area of the individual grain region 10a is 100 mm ² or less and 50 mm ² or less. Further, when the percentage of the total area of the grain region to the total area of the surface of the Group III nitride single crystal substrate is 40% or less, the effect of the present invention can be easily obtained.

As a method of image analysis, the reflected X-ray topograph image is traced using tracing paper, a transparent resin sheet, or a commercially available image display software to trace the outer peripheral shape of the substrate and the outer peripheral shape of the grain region, and then the traced shape is obtained. A method of determining the area by image analysis can be preferably used.

(First reforming process)
In the production method of the present invention, the first modification step is an atom of the group III nitride crystal in the grain region by applying a physical action to the grain region 10a contained in the group III nitride single crystal substrate 10 from the outside. This is a process that temporarily disturbs the arrangement. Specifically, the physical action means applying physical energy to the grain region 10a and the boundary of the grain region by laser irradiation, ion injection, or the like. In the production method of the present invention, by applying a physical action to the grain region, the state in which the crystal orientation shift exists is changed to a state in which the crystal orientation is lowered or a state in which the crystal orientation is close to amorphous. When the Group III nitride single crystal substrate 10 has a plurality of grain regions, the first modification step is carried out for each grain region.

Since the grain region exists from the surface of the single crystal substrate to the inside, in order to obtain the effect of the present invention better, not only the outermost surface and the vicinity of the surface of the single crystal substrate but also a depth of 1 μm or more from the surface or more. It is preferable to disturb the atomic arrangement by applying a physical action inside the depth. Therefore, in the case of laser irradiation, the wavelength longer than the wavelength corresponding to the band gap energy of the group III nitride single crystal substrate 10 so that the laser light exerts a physical action inside the group III nitride single crystal substrate 10. It is preferable to use an optical system having an objective lens having an appropriate number of apertures so that the laser light having an appropriate number of apertures is irradiated and the laser light is appropriately focused inside the grain region. Examples of the optimum light source when the group III nitride single crystal substrate contains aluminum as a main component include a titanium sapphire laser (wavelength 800 nm), a YAG laser and its harmonic laser (basic wavelength 1064 nm, second harmonic wavelength 532 nm). , 3rd harmonic wavelength 355nm, 4th harmonic wavelength 266nm, argon laser (wavelength 514nm or wavelength 488nm), nitride solid-state laser (wavelength 405nm, etc.), XeF excimer laser (wavelength 351nm), XeCl excimer laser (wavelength 308nm) ), A known laser light source such as a KrF excimer laser (wavelength 248 nm) can be used.

Further, as the physical energy to which the above physical action is applied, it is preferable to use laser light having an energy smaller than the band gap energy of the group III nitride single crystal substrate 10. That is, since the laser light having an energy smaller than the band gap energy of the group III nitride single crystal substrate 10 is not easily absorbed by the group III nitride single crystal substrate, the focusing point of the laser light is located at a deep position in the grain region. It can be controlled to any depth from to a shallow position. Therefore, it is possible to add a physical action not only near the surface of the substrate but also inside the surface of the substrate by the multiphoton absorption mechanism. Applying this feature, at the start of laser irradiation, the grain is focused on the grain region farthest from the laser irradiation side to apply a physical action, and then the focus is gradually moved toward the laser irradiation side. It is also possible to apply physical action over the entire area.

In addition, a continuous oscillating laser and a pulse oscillating laser can be used as the laser light source without limitation, and when a pulsed laser is used, the pulse width is in millisecond units, microsecond units, nanosecond units, and picosecond units. , Femtosecond unit, etc. can be selected from any one, and the oscillation frequency can also be selected from any one. This makes it possible to increase the amount of energy given to the Group III nitride crystal per pulse per time and to appropriately adjust the release time (cooling time) of the heat energy generated after energy irradiation, and the grain region can be efficiently applied. It is possible to modify the atomic arrangement of.

The output of the laser to be irradiated varies depending on the composition of the group III nitride single crystal substrate and the irradiation area (condensing area) of the laser, but is preferably 0.1 W or more and 100 W or less. If the laser intensity is too strong, the Group III nitride crystal itself tends to evaporate (ablation) due to the momentarily applied energy, or to generate cracks in the Group III nitride single crystal substrate. Further, when the laser intensity is too weak, it tends to be difficult to obtain the effect of the first reforming step. Therefore, the output of the laser to be irradiated is more preferably in the range of 0.5 W or more and 10 W or less, and particularly preferably 1.0 W or more and 5.0 W or less.

In the case of ion injection, the energy of the ion to be injected is increased to 50 keV or more, or the injection angle is tilted in the range of 1 to 10 ° from the surface for the purpose of reaching the inside, and more preferably in the range of 5 to 8 °. Let me. However, in the case of ion implantation, the injected ions remain in the grain region, forming a region with a locally high impurity concentration, and in some cases, a region with a locally high stress due to impurities is formed. Will be done. Therefore, it is more preferable to use a laser as a means for applying a physical action.

By any of the modifying means, an object of the present invention is to provide a group III nitride single crystal substrate with a reduced grain region, and when the group III nitride single crystal substrate is viewed from the top surface, the above-mentioned grains are used. As for the range in which the physical action is applied to the region, the range in which the entire grain region is modified is added. Normally, when a physical action is applied to the grain region, the physical energy is propagated from the applied site, so it is not always necessary to directly apply the physical action to the entire grain region. From the viewpoint of reliable modification, the area of the grain region 11a after the first modification is preferably modified within the same range as the area of the original grain region 10a, but is wider or narrower than the grain region. It may be modified in the range. In this case, the first reforming step is carried out so that the area of the grain region 11a after the first reforming is preferably within ± 50% with respect to the area of the grain region 10a.

As for the depth of the grain region 11a after the first modification, as described above, it is preferable to disturb the atomic arrangement by applying a physical action not only to the surface and the vicinity of the surface but also to the inside. It is preferable to apply a physical action to a depth of 1 μm or more with respect to the area range of the first modified grain region 11a, more preferably 10 μm or more, still more preferably 100 μm or more, and the most preferable implementation. The form is to provide a grain region after the first modification so as to penetrate from the vicinity of the front surface to the opposite surface (back surface). The reason for this is that when the crystal arrangement is restored in the second reforming step, it is possible to avoid imitating a site having a crystal orientation deviation different from that of the single crystal region.

In the state of the grain region 11a after the first modification, the atomic arrangement of the group III nitride crystal is disturbed due to physical action, and the X-ray diffraction condition is not satisfied in the X-ray topograph measurement. It can be clearly detected. Further, in the case of the grain region 10a where the X-ray omega locking curve could be measured before the first reforming step, the half width of the X-ray omega locking curve becomes large after the first reforming step, and the value is approximately 100 seconds or more. However, in some cases, it becomes a broader halo-like peak. In addition, since the relevant part has a refractive index different from that of the single crystal region, it can be observed by polarization observation, and can be observed more easily by optical microscope observation in which two polarizing plates are inserted in the directions orthogonal to each other. It is possible to do.

(Second reforming process)
In the production method of the present invention, the second reforming step 102 is a step of further changing the crystal arrangement changed by the first reforming step 101. Specifically, in the first reforming step 101, the atomic arrangement of the grain region 11a after the first reforming, in which the atomic arrangement is disturbed by a physical action, is rearranged to reconstruct the crystal arrangement. By going through such a step, it is possible to reduce or eliminate the grain region 10a initially existing in the group III nitride single crystal substrate. Here, as a method for further changing the crystal arrangement in the second reforming step, a method of heat-treating the Group III nitride single crystal substrate that has undergone the first reforming step can be mentioned. By the heat treatment in the second modification step, the atomic arrangement in the grain region 11a after the first modification proceeds to follow the crystal arrangement of the single crystal region 10b, and the rearrangement of the atoms proceeds, and the grain region 12a after the second modification It becomes.

The temperature of the heat treatment in the second reforming step may be a temperature sufficient for the crystal arrangement of the group III nitride single crystal to be reconstructed, and the temperature is appropriately determined depending on the type of the group III nitride single crystal. Just do it. The heat treatment temperature is preferably in the range of 1200 ° C. or higher and 2000 ° C. or lower. If the temperature during the heat treatment is low, the effect of the second reforming step cannot be obtained, and if the temperature is high, the Group III nitride single crystal substrate may be decomposed. Therefore, the heat treatment temperature is more preferably in the range of 1300 ° C. or higher and 1800 ° C. or lower, and particularly preferably 1400 ° C. or higher and 1700 ° C. or lower. As the heating method, a known resistance heating method, high frequency induction heating method, or light heating method can be used. When the second reforming step is performed by heat treatment, the entire grain region subjected to the first reforming step may be locally heat-treated or the entire Group III nitride single crystal substrate may be subjected to a hot wall format. It may be done by heating uniformly.

The holding time of the heat treatment may be appropriately adjusted, but is in the range of 1 minute to 600 minutes. The time spent for raising and lowering the temperature is not particularly limited, but if it is a short time, a difference in thermal expansion may occur inside the Group III nitride single crystal substrate, and damage may occur. Therefore, it is preferably 1000 ° C./min or less, more preferably 100 ° C./min or less, and further preferably 50 ° C./min or less. On the other hand, if it is a long time, the risk of the breakage is reduced, but from a practical point of view, it is preferably 1 ° C./min or more, more preferably 10 ° C./min or more, still more preferably 20 ° C./min or more. do. The atmosphere of the heat treatment depends on the material of the group III nitride single crystal substrate and the material of the heat treatment furnace, but a vacuum atmosphere, a nitrogen atmosphere, an inert atmosphere such as a rare gas can be preferably used.

The grain region 12a after the second modification is in a state where the atomic arrangement of the group III nitride crystal is rearranged, and is in a state where the X-ray diffraction condition is satisfied by the X-ray topograph measurement. It can be clearly detected as an image. Further, since the portion approaches the state of the single crystal region by atomic rearrangement, it is difficult to distinguish the boundary between the grain region after the second modification and the single crystal region in the polarization observation.

Depending on the detailed X-ray topograph measurement, a region with a small strain or dislocation of 1 mm ² or less as the horizontal cross section with respect to the substrate surface may be observed inside the grain region 12a after the second modification. However, since the area is smaller than the initial grain region 10a and the crystal arrangement is improved, the group III nitride single crystal after the second modification is performed in the film forming step 103 performed after the second modification step 102. The influence on the crystal quality of the group III nitride single crystal layer 14 formed on the substrate 12 is small. Further, even if a region with a small strain or dislocation remains in the grain region 12a after the second reforming, the second reforming is performed by further repeating the first reforming step 101 and the second reforming step 102. By modifying the post-quality grain region 12a to a smaller size, it is possible to further minimize the influence on the film forming step 103.

The state of the crystal arrangement of the grain region 12a after the second modification can be quantified by measuring the X-ray omega locking curve in the local (101) plane orientation of the region, and the X-ray omega locking curve peak is also clear. Will be observed in. After the second modification, the half width of the X-ray omega locking curve of the grain region 12a becomes a value of less than 100 seconds, and in some cases, it recovers to 50 seconds or less, further to 30 seconds or less, or to the same extent as the single crystal region 10b.

The first modification step and the second modification step of the present invention contribute to the reduction of the grain region, but when there is a region where the rearrangement is concentrated on the group III nitride single crystal substrate or the grain itself is group III. Even in the region where the polarity of the nitride single crystal is inverted, the addition of the first modification step and the second modification step of the present invention contributes to the reduction of rearrangements and the improvement of the polarity inversion region.

(Film formation process)
The second modified Group III nitride single crystal substrate 12 obtained in the second modification step 102 is subjected to a film forming step of forming a Group III nitride single crystal layer 14 having good crystal quality on the substrate. Thereby, the group III nitride single crystal laminate 13 can be obtained.

Growth methods for obtaining the Group III nitride single crystal laminate 13 include physical vapor transport (Pysical Vapor Transport) method, metalorganic vapor phase growth (MOCVD) method, and hydride Vapor Phase Epitaxy. It is possible to use known methods for growing Group III nitride single crystals, such as a method, a molecular beam epitaxy method, a liquid phase method, and an amonothermal method. By appropriately selecting these methods, the group III nitride single crystal layer 14 includes light emitting devices such as light emitting diodes and laser diodes, light receiving elements such as photodiodes, field effect transistors, and high electron mobility transistors. It is also possible to form an electronic device, and further, a group III nitride single crystal thick film having a thickness of more than 100 μm. In either case, the crystal orientation shift of the grain region contained in the initially existing Group III nitride single crystal substrate has been improved by going through the first reforming step and the second reforming step. The group III nitride single crystal layer having good crystal quality can be obtained, which contributes to deterioration of element performance and yield.

(Processes that can be added)
In forming the Group III nitride single crystal layer 14 on the Group III nitride single crystal substrate 12 after the second modification obtained in the second modification step 102, the first is performed before laminating the Group III nitride single crystal layer 14. (Ii) After modification, the surface of the Group III nitride single crystal substrate 12 can be appropriately flattened, unevenly processed, or the like.

When the flattening process is carried out, it is possible to use a known polishing process such as flattening by mechanical polishing or chemical mechanical polishing (CMP) to remove the polishing damage layer on the surface. As the abrasive to be used, an abrasive containing materials such as silica, alumina, ceria, silicon carbide, boron nitride, and diamond can be used. Further, the property of the abrasive may be alkaline, neutral or acidic. Among them, aluminum nitride has a low alkali resistance on the nitrogen polar surface (-c surface), so that it is a weakly alkaline, neutral or acidic abrasive, specifically, an abrasive having a pH of 9 or less, rather than a strongly alkaline abrasive. It is preferable to use. Of course, if a protective film is installed on the polar surface of nitrogen, it is possible to use a strongly alkaline abrasive without any problem. It is also possible to add an additive such as an oxidizing agent in order to increase the polishing speed, and commercially available materials and hardness of the polishing pad can be used.

When the surface of the Group III nitride single crystal substrate after the second modification is subjected to uneven processing, the formation of a mask pattern using a general lithograph and the subsequent dry etching processing are used. Known metal masks, resist masks, imprint masks and the like can be used for these. By providing surface irregularities, the growth region of the Group III nitride single crystal layer is restricted to the convex portion of the surface of the Group III nitride single crystal substrate after the second modification in the film forming step 103, resulting in higher quality. It enables the growth of a group III nitride single crystal layer.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

(Example 1)
(Group III nitride single crystal substrate)
As the group III nitride single crystal substrate 10, a single crystal aluminum nitride substrate having a thickness of 450 μm and a diameter of 35 mm and having double-sided CMP polishing was used. The surface was a c-plane (Al polar plane) and had an off angle of 0.25 ° in the m-plane direction and 0.01 ° in the a-plane direction. The impurity concentrations of silicon, oxygen and carbon measured by secondary ion mass spectrometry are 5 × 10 ¹⁷ cm ^-3 , 1 × 10 ¹⁹ cm ^-3 and 1.5 × 10 ¹⁹ cm ^-3 , respectively. The total was 2.55 × 10 ¹⁹ cm ^-3 . Further, in a region other than the grain region of the single crystal aluminum nitride substrate, an X-ray omega locking curve measurement using a germanium single crystal (220) as an X-ray source monochromatic by diffraction four times was performed. 101) The half-price width of the X-ray omega locking curve in the plane orientation was 12 seconds.

In order to identify the position and size of the grain region contained in the single crystal aluminum nitride substrate, a reflected X-ray topograph image using (114) plane diffraction of aluminum nitride was obtained. A high-resolution thin-film X-ray diffractometer X'Pert MRD Pro manufactured by PANalytical Co., Ltd. was used for the measurement of the reflected X-ray topograph image. Characteristic X-rays were generated in an X-ray tube using a Cu target under the conditions of an acceleration voltage of 45 kV and a filament current of 40 mA, and an X-ray beam was taken out by line focus. The generated X-ray beam was monochromatic by the X-ray Goebel mirror module. At this time, a 1/2 ° divergence slit (horizontal limiting slit) and a vertical limiting slit with a width of 50 μm are attached to the entrance of the X-ray mirror module, the X-ray beam is trimmed, and then the object is installed on the measurement stage. The aluminum nitride single crystal substrate was irradiated. The CuKα1 line diffracted from the (114) plane of the single crystal aluminum nitride substrate was detected by a semiconductor two-dimensional detector (Pixcel 3D). The measurement was performed on the entire surface of the single crystal aluminum nitride substrate, and the reflected X-ray topograph image of the entire substrate was imaged. The imaged reflected X-ray topograph image was as shown in FIG.

As a result, it was confirmed that two grain regions existed in the plane of the single crystal aluminum nitride substrate. A uniform diffraction contrast due to X-ray diffraction is observed from the single crystal region 10b, whereas the first grain region does not satisfy the X-ray diffraction conditions due to the large degree of crystal orientation deviation, and reflected X-rays. The state of the topograph image was a blackout state (a state in which diffracted X-rays were missing). In the second grain region, since the degree of crystal orientation deviation was slight, diffraction contrast was observed, and the boundary between the grain region and the single crystal region could be recognized as a contrast difference. The shape of each grain region did not particularly reflect the hexagonal crystal structure of aluminum nitride, but had an amorphous shape.

Image analysis of the reflected X-ray topograph image was performed to calculate the area of the grain region. The actual reflected X-ray topograph image is an image of X-rays diffracted near the surface of the aluminum nitride substrate, and may not reflect the exact same shape as the actual shape substrate. Therefore, in the calculation of the grain region, the ratio of the area of each grain region to the whole surrounding the outermost circumference corresponding to the diameter of 35 mm of the reflected X-ray topograph image is calculated by image analysis, and then the diameter is calculated as the ratio of the grain region. This was carried out by multiplying the substrate area of 35 mm by 962 mm ² . In addition, in order to clarify the boundary between the single crystal region and the grain region in the image analysis, the contrast boundary of the topograph image was traced and then converted into the area of the grain region. In addition, when acquiring the topograph image, the regular contrast caused by the X-ray detector was excluded so as not to affect the calculation of the region. As a result, the area of the grain region at the first location was estimated to be 9 mm ² , and the area of the grain region at the second location was estimated to be 0.8 mm ² .

(First reforming process)
Next, the first modification step of the single crystal aluminum nitride substrate was carried out. A titanium sapphire laser having a wavelength of 800 nm was used in the first reforming step. The laser output was set to 2.5 mW, the frequency was set to 10 kHz, the bals width was set to 1 ns, and the condensing part spot system was set to φ20 μm. Before irradiating the single crystal aluminum nitride substrate with a laser, a laser irradiation test was conducted on another test substrate to investigate the modified region by laser irradiation. The modified region was distributed over a range of 30 μm above and below the focal position. Laser irradiation to the two grain regions is performed from the front surface (Al polar surface) side of the single crystal aluminum nitride substrate, and at the start of irradiation, the side far from the laser irradiation side, that is, 10 μm above the back surface (N polar surface). After focusing on the grain region and applying a physical action to irradiate the entire in-plane of the grain region with the laser, the focus is moved 40 μm toward the laser irradiation surface, and the laser is again applied to the entire in-plane of the grain region. Was irradiated. By repeating this cycle while moving the focal position to the surface by 40 μm, a physical action was applied over the entire grain region including the depth direction, and the atomic arrangement of the grain region was modified.

In order to specify the range of the grain region 11a after the first modification, the X-ray topograph measurement of the (114) plane diffraction of aluminum nitride was performed in the same manner as described above. It was confirmed that the diffraction of the laser irradiation region was weakened due to the disorder of the crystal arrangement in the laser irradiation region in addition to the region of. In the second grain region as well, the diffraction was weaker than before the modification, and the contrast difference with the peripheral region became clearer. On the other hand, since the laser irradiation was performed in a wider range from the grain region to the single crystal region side, the contrast difference at the boundary portion became less clear than before the modification.

Furthermore, the area of the grain region after the first modification was estimated by the same image analysis as described above. Here, the estimation was made including the region where the contrast change on the single crystal region side was observed from the original grain region. Since the boundary part was obscured by the first reforming step, when calculating the area, the boundary of the initial grain region and the part where the influence of reforming began to affect from the grain region to the single crystal region side. That is, the middle of the single crystal region where the contrast change appeared was defined as the boundary of the grain region after the first modification. As a result, the area of the first modified grain region is 24% wider than the area of the original grain region 10a for the first modified grain region, which is the second region. The area of the grain region after the first modification was 41% wider than the area of the original grain region 10a. In addition, since the area of the grain region after the first modification at the first location is large, it is possible to measure the X-ray omega locking curve by narrowing down the irradiated X-rays, which is half due to the disorder of the crystal arrangement. The price range was 4860 seconds. The area of the first modified grain region at the second location was small and it was difficult to make similar measurements.

(Second reforming process)
Next, the second reforming step was carried out using an atmosphere control electric furnace consisting of a tungsten heater wire. The single crystal aluminum nitride substrate after the first reforming step was placed on a tungsten susceptor in the electric furnace, vacuum exhausted inside the electric furnace, and then filled with nitrogen gas having a purity of 99.999%. Furthermore, vacuum exhaust and nitrogen filling were repeated three times in total to reduce oxygen and water content inside the electric furnace. A mixed gas (mixing ratio 1: 1) of nitrogen gas and argon gas (purity 99.999%) was circulated at a flow rate of 200 ml / min, and the temperature was raised from room temperature to 1650 ° C. in 60 minutes. Then, after holding at 1650 ° C. for 30 minutes, heating was stopped, the substrate was allowed to cool, and the single crystal aluminum nitride substrate after the second reforming step was taken out from the electric furnace.

Next, the reflected X-ray topograph image of the single crystal aluminum nitride substrate was measured. As a result, the first grain region obtained the same diffraction contrast as the surrounding single crystal region through the second reforming step, but the small diffraction contrast with an area of 0.3 mm ² was obtained near the center of the grain region. There was a defect. The X-ray omega locking curve of the part where the rearrangement of the crystal arrangement was observed was 15 seconds. In the second grain region, after the second modification, the entire grain region after the second modification showed diffraction similar to the diffraction contrast of the surrounding single crystal region, and the crystal arrangement was restored. It was confirmed.

(Film formation process)
Before growing a new Group III nitride single crystal layer on the surface (Al polar surface) side of the second modified single crystal aluminum nitride substrate, the surface was flattened by chemical mechanical polishing. The single crystal aluminum nitride substrate was attached to the surface plate using anti-alkali wax, and then chemically mechanically polished using a urethane polishing pad and alkaline silica slurry, without performing the grinding process immediately before chemical mechanical polishing. .. The surface of the single crystal aluminum nitride substrate after polishing had a surface state with steps and terraces as observed by an atomic force microscope with an observation field of 2 × 2 μm ² , and the arithmetic average roughness (Ra) was 0.08 nm. Next, the surface of the substrate was scrubbed while supplying a weak alkaline detergent, then rinsed with ultrapure water, and residual water was removed by spin drying.

Next, in order to form a light emitting device layer on the substrate, it is installed in an organic metal vapor phase growth apparatus, and an n-AlGaN layer, a quantum well layer, a p-AlGaN layer, and a p-GaN layer are sequentially formed on the substrate. did. Further, using a known lithograph process and dry etching process, electrode deposition and annealing process, n electrodes are placed on the n-AlGaN layer and the p-GaN layer so as to form a section of □ 1 mm × 1 mm per element. A p-electrode was formed. Since the purpose was to confirm the occurrence of LED failure due to the modification of the grain region, a probe tester was used to perform an energization test with the LED element formed on the single crystal aluminum nitride substrate formed without cutting. Was carried out. In the energization test, a current of 650 mA having a pulse width of 10 μsec was first applied to each element formed on the grain region of the substrate, and a pulse current of 1 second was applied at 1 kHz, and then DC continuous energization was performed. In continuous DC energization, a product with a current value of 10 μA or less when the applied voltage is 3 V and a current value of -1 μA or less when -5 V is applied is regarded as a non-defective product, and a good product or a defective product is discriminated. The failure rate of the above, that is, the ratio of the light emitting elements that did not deteriorate even when the pulse was applied was calculated.

As a result, one of the nine elements formed on the grain region at the first location failed, and the failure rate was 11%. In addition, no failure was found in one LED element including the grain region at the second location. The failure rate of the device formed in the single crystal region was 7%.

(Comparative Example 1)
After performing the same polishing as in Example 1 using the same single crystal aluminum nitride substrate as in Example 1 and without applying the first reforming step and the second reforming step shown in Example 1. This is a comparative example in which the LED element layer is grown by the MOCVD method in the same growth batch as in Example 1. As a result, the failure rate of the elements formed in the single crystal region was 9%, but all 10 elements formed in the grain region failed.

(Comparative Example 2)
The same single crystal aluminum nitride substrate as in Example 1 was used, and only the second reforming step was carried out without carrying out the first reforming step shown in Example 1, and the same polishing as in Example 1 was performed. This is a comparative example in which the LED element layer was grown by the MOCVD method in the same growth batch as in Example 1. As a result, the failure rate of the elements formed in the single crystal region was 8%, but all 10 elements formed in the grain region failed.

10 Group III Nitride Single Crystal Substrate 10a Grain Region 10b Single Crystal Region 101 First Modification Step 11 After First Modification Group III Nitride Single Crystal Substrate
11a First reformed grain region 11b Modification means (physical action)
102 Second reforming step 12 After second reforming Group III nitride single crystal substrate 12a After second reforming grain region 103 Formation step 13 Group III nitride single crystal laminate 14 Group III nitride single crystal layer

Claims (9)

At least a part of the grain region of the group III nitride single crystal substrate having a grain region whose crystal orientation is different from the surrounding single crystal region is irradiated with laser light to temporarily disturb the atomic arrangement of the crystal in the region. First reforming process,
Next , the group III nitride single crystal substrate is heat-treated to include a second modification step of rearranging the atomic arrangement temporarily disturbed by the first modification step to reconstruct the crystal arrangement. A method for manufacturing a group III nitride single crystal substrate. The method for manufacturing a group III nitride single crystal substrate according to claim 1 , wherein the irradiation energy of the laser beam is smaller than the band gap energy of the group III nitride single crystal substrate. The method for producing a group III nitride single crystal substrate according to claim 1, wherein the heat treatment heats the group III nitride single crystal substrate to 1200 ° C. or higher. The group III nitride according to claim 1, wherein the total amount of silicon, carbon, and oxygen impurities contained in the group III single crystal nitride substrate having the grain region is 1 × 10 ¹⁶ cm ^-3 or more and 1 × 10 ²¹ cm ^-3 or less. A method for manufacturing a single crystal substrate. The method for producing a group III nitride single crystal substrate according to claim 1, wherein the group III single crystal nitride substrate having the grain region has a thickness of 50 μm or more. The method for producing a group III nitride single crystal substrate according to claim 1, wherein the group III single crystal nitride substrate having the grain region is aluminum nitride. The method for producing a Group III nitride single crystal substrate according to claim 1, wherein the half-value width of the X-ray locking curve in the grain region is modified to 100 seconds or more by the first modification step. A group III nitride single crystal substrate is obtained by the method according to any one of claims 1 to 7 , and then a group III nitride single crystal layer is laminated on the obtained group III nitride single crystal substrate. A method for producing a group III nitride single crystal laminate. The method for producing a laminated body according to claim 8 , wherein the surface of the group III nitride single crystal substrate is polished before laminating the group III nitride single crystal layer.

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