JP6513165B2 - Method of manufacturing group III nitride semiconductor single crystal - Google Patents

Description

  The present invention relates to a method for producing a group III nitride semiconductor single crystal.

  A method of cutting a semiconductor substrate out of a semiconductor crystal epitaxially grown thick on a seed crystal substrate by HVPE (Hydride Vapor Phase Epitaxy) or the like as one of the manufacturing methods of a group III nitride semiconductor single crystal substrate represented by the conventional GaN substrate. Is known, and some commercialization has begun.

  However, according to this method, when the crystal grown on the seed crystal substrate starts to be sliced in order to slice it, a crack is generated inside the crystal and the problem that the crystal is broken often occurs. The occurrence of such a crack is more likely to occur as the density of dislocations in the crystal and defects such as polarity inversion regions is lower and the crystal characteristics are more uniform, and more easily as the diameter of the crystal is larger. For example, it is difficult to intactly slice crystals having a diameter of 50 mm or more.

  As a technique for solving such a problem, a technique of performing cylindrical grinding using a grinding wheel on a crystal before slicing is known (see, for example, Patent Document 1). According to Patent Document 1, it is said that by slicing the crystal after removing the outer peripheral portion including the strain of the crystal, it is possible to prevent the cracking of the crystal at the time of slicing.

JP, 2013-60349, A

  However, even when the technique disclosed in Patent Document 1 is used, as soon as cylindrical grinding for removing the outer peripheral portion is started, a problem that cracks occur in the crystal due to grinding often occurs.

  One of the objects of the present invention is to provide a method for producing a group III nitride semiconductor single crystal capable of obtaining a semiconductor substrate by slicing while suppressing the occurrence of cracks.

  One aspect of this invention provides the manufacturing method of the group III nitride semiconductor single crystal of [1]-[18], in order to achieve the said objective.

[1] A step of epitaxially growing a group III nitride semiconductor single crystal on the main surface of a circular substrate, removing the first region on the outer peripheral side of the group III nitride semiconductor single crystal, and removing the group III nitride Leaving a second region inside the first region of the semiconductor single crystal, wherein the removal of the first region does not disturb the balance of distortion in the group III nitride semiconductor single crystal. And the first region is formed such that the shape of the group III nitride semiconductor single crystal always maintains axial symmetry with the central axis of the group III nitride semiconductor single crystal as the axis of symmetry; A method for producing a group III nitride semiconductor single crystal, comprising a region of and a region formed by facet growth with different concentrations of impurities.

[2] The first region is formed by crystal growth having a plane having a plane orientation different from the upper surface of the second region as a growth interface during the epitaxial growth of the group III nitride semiconductor single crystal The manufacturing method of the group III nitride semiconductor single crystal as described in said [1] which contains an area | region.

[3] The method for producing a group III nitride semiconductor single crystal according to the above [1], wherein the first region includes, on an upper surface, a facet having a plane orientation different from that of the upper surface of the second region.

[4] The removal of the first region is performed such that the shape of the removed region always maintains a uniform cylindrical shape in height, in the group III nitride semiconductor single crystal according to the above [1] Production method.

[5] The production of the group III nitride semiconductor single crystal according to the above [1], wherein the removal of the first region is carried out by grinding using a grindstone, ultrasonic machining, electrical discharge machining, etching, or laser machining Method.

[6] The method for producing a group III nitride semiconductor single crystal according to the above [1], wherein the group III nitride semiconductor single crystal is a gallium nitride crystal.

[7] The method for producing a group III nitride semiconductor single crystal according to the above [1], wherein the upper surface of the second region is the c-plane of the group III nitride semiconductor single crystal.

[8] The method for producing a group III nitride semiconductor single crystal according to the above [1], wherein the group III nitride semiconductor single crystal is a gallium nitride crystal epitaxially grown by an HVPE method, and the impurity is oxygen.

[9] The method for producing a group III nitride semiconductor single crystal according to the above [1], wherein the removal of the first region is performed not to remove the region of the substrate immediately below the first region. .

[10] A step of epitaxially growing a group III nitride semiconductor single crystal on a main surface of a circular substrate, and forming a cylindrical void in the group III nitride semiconductor single crystal, the group III nitride semiconductor single crystal Separating the group III nitride semiconductor single crystal into a first region on the outer peripheral side of the second group and a second region inside the first region of the group III nitride semiconductor single crystal, The shape of the group III nitride semiconductor single crystal is always symmetrical about the central axis of the group III nitride semiconductor single crystal so that the balance of distortion in the group III nitride semiconductor single crystal is not broken in the formation of the void. A method of manufacturing a group III nitride semiconductor single crystal, implemented so as to maintain axial axial symmetry, wherein the first region includes a region formed by facet growth different in impurity concentration from the second region. Method.

[11] The first region is formed during facet growth of the group III nitride semiconductor single crystal by facet growth using as a growth interface a facet having a plane orientation different from the top surface of the second region. The method for producing a group III nitride semiconductor single crystal according to the above [10], which includes a roughened region.

[12] The method for producing a group III nitride semiconductor single crystal according to the above [10], wherein the first region includes, on an upper surface, a facet having a plane orientation different from that of the upper surface of the second region.

[13] The method for producing a group III nitride semiconductor single crystal according to the above [10], wherein the formation of the voids is performed such that the shape of the voids always maintains a uniform cylindrical shape of height.

[14] The method for producing a group III nitride semiconductor single crystal according to the above [10], wherein the formation of the void is carried out by drilling with a hole saw, grinding using a grindstone, ultrasonic machining, electric discharge machining, or laser machining .

[15] The method for producing a group III nitride semiconductor single crystal according to the above [10], wherein the group III nitride semiconductor single crystal is a gallium nitride crystal.

[16] The method for producing a group III nitride semiconductor single crystal according to the above [10], wherein the upper surface of the second region is the c-plane of the group III nitride semiconductor single crystal.

[17] The method for producing a group III nitride semiconductor single crystal according to the above [10], wherein the group III nitride semiconductor single crystal is a gallium nitride crystal epitaxially grown by an HVPE method, and the impurity is oxygen.

[18] The method for producing a group III nitride semiconductor single crystal according to [10], wherein the formation of the void is performed so as not to remove the region of the substrate immediately below the void.

  According to the present invention, it is possible to provide a method for producing a group III nitride semiconductor single crystal capable of obtaining a semiconductor substrate by slicing while suppressing the occurrence of cracks.

FIG. 1A is a vertical cross-sectional view schematically showing a process of epitaxially growing a cylindrical group III nitride semiconductor single crystal on a substrate. FIG. 1B is a vertical cross-sectional view schematically showing a process of epitaxially growing a cylindrical group III nitride semiconductor single crystal on a substrate. FIG. 1C is a vertical cross-sectional view schematically showing a process of epitaxially growing a cylindrical group III nitride semiconductor single crystal on a substrate. FIG. 2 is a top view of a group III nitride semiconductor single crystal epitaxially grown on a c-plane substrate. FIG. 3A is a vertical sectional view schematically showing a process of removing a cylindrical region by grinding using a cylindrical grindstone. FIG. 3B is a vertical cross-sectional view schematically showing a process of removing a cylindrical region by grinding using a cylindrical grindstone. FIG. 4A is a vertical sectional view schematically showing a process of removing a cylindrical region by electric discharge machining using a cylindrical die-sinking discharge electrode. FIG. 4B is a vertical cross-sectional view schematically showing a process of removing a cylindrical region by electric discharge machining using a cylindrical die-cutting discharge electrode. FIG. 5 is a vertical cross-sectional view showing a state in which the cylindrical region is removed from the side of the grown group III nitride semiconductor single crystal and the region of the substrate immediately below the cylindrical region is left. FIG. 6 is a vertical sectional view showing a substrate on which a protective film for selectively removing a cylindrical region is formed by etching and a Group III nitride semiconductor single crystal. FIG. 7A is a vertical cross-sectional view schematically showing a process of slicing a cylindrical region. FIG. 7B is a vertical sectional view schematically showing a process of slicing a cylindrical region. FIG. 8A is a vertical cross-sectional view schematically showing a process of forming a void using a hole saw and separating a cylindrical region from a cylindrical region. FIG. 8B is a vertical cross-sectional view schematically showing a process of forming a void using a hole saw and separating a cylindrical region from a cylindrical region. FIG. 9 is a vertical sectional view showing the state of a group III nitride semiconductor single crystal after separation from a cylindrical region while leaving the cylindrical region on the substrate. FIG. 10 is a vertical sectional view schematically showing the configuration of an HVPE growth apparatus used for crystal growth of a GaN crystal.

First Embodiment
Conventionally, it is known that distortion occurs in a cylindrical region on the outer peripheral side of an epitaxially grown cylindrical crystal, and a crack is generated due to the distortion at the time of slicing. And this distortion arises because the density | concentration of the impurity taken in by the crystal at the time of epitaxial growth differs in said cylindrical area | region and the area | region inside it.

  The inventors of the present invention conducted intensive investigations into the mechanism of the occurrence of the cracks, and as a result, strain distribution in the crystal is achieved by locally releasing strain in the cylindrical region distributed axisymmetrically during slicing. It has been found that the collapse of the balance is a direct cause of the occurrence of the crack, and if the processing is performed so as not to break the symmetry of the strain distribution, the occurrence of the crack can be suppressed.

  Based on the above findings, this embodiment aims to remove distortion in the crystal before slicing and removes the above cylindrical region from the crystal while maintaining the balance of distortion distribution, and then Slice processing. The details will be described below.

(Growth of group III nitride semiconductor single crystal)
FIGS. 1A, 1 B, and 1 C are vertical sectional views schematically showing the process of epitaxially growing a cylindrical group III nitride semiconductor single crystal 2 on a substrate 1. FIG. 2 is a top view of the grown III-nitride semiconductor single crystal 2. The group III nitride semiconductor single crystal 2 shown in FIGS. 1A, 1 B, 1 C and FIG. 2 is a c-plane (Ga plane) grown GaN crystal as an example of the group III nitride semiconductor single crystal 2.

  First, as shown in FIG. 1A, a circular substrate 1 to be a seed crystal is prepared. The substrate 1 is, for example, a GaN (gallium nitride) substrate having a c-plane as the main surface 1p. The GaN substrate is suitable as a seed crystal for epitaxial growth of a GaN crystal.

  Then, as shown in FIGS. 1B and 1C, the group III nitride semiconductor single crystal 2 is epitaxially grown on the major surface 1 p of the substrate 1. The group III nitride semiconductor single crystal 2 is grown in a direction perpendicular to the major surface 1 p of the substrate 1 so as to form a cylinder. In this epitaxial growth, the growth interface on the outer peripheral side of group III nitride semiconductor single crystal 2 includes facet 4p. Crystal growth in which the growth interface is a specific crystal plane is referred to as facet growth, and the specific crystal plane is referred to as a facet plane.

  Here, a cylindrical region to be removed from the group III nitride semiconductor single crystal 2 in a later step on the outer peripheral edge side of the group III nitride semiconductor single crystal 2 is referred to as a cylindrical region 4. The central axis of the cylindrical region 4 is equal to the central axis of the group III nitride semiconductor single crystal 2, and the inner diameter of the cylindrical region 4 is uniform. Then, a cylindrical region inside the cylindrical region 4 is referred to as a cylindrical region 3. The cylindrical region 4 can be set as a cylindrical region including the facet 4 p on the top surface.

  The plane orientations of the surface 3 p which is the upper surface of the cylindrical region 3 and the facet 4 p are different. For example, when the substrate 1 is a GaN substrate having the major surface 1p as a c-plane and the group III nitride semiconductor single crystal 2 is a GaN crystal, the surface 3p of the cylindrical region 3 is a c-plane. Further, the surface 4 n other than the facet 4 p of the upper surface of the cylindrical region 4 is also formed of a surface having a plane orientation different from the surface 3 p of the cylindrical region 3.

  The growth of the group III nitride semiconductor single crystal 2 proceeds while almost retaining the shapes and sizes of the facets 4p and 4n.

  As described above, the concentration of the impurity taken into a predetermined region of the crystal during epitaxial growth depends on the plane orientation of the growth interface during epitaxial growth of that region. Therefore, the region formed by crystal growth with facet face 4p and face 4n as the growth interface is a region formed by crystal growth with face 3p as the growth interface and epitaxial growth of group III nitride semiconductor single crystal 2 The concentration of impurities introduced between them is different.

  Cylindrical region 4 includes all or almost all of the region formed by crystal growth with facet 4p and surface 4n as the growth interface, and cylindrical region 3 is formed by crystal growth with surface 3p as the growth interface Match or nearly match the Therefore, the impurity concentrations of the cylindrical region 4 and the cylindrical region 3 are different.

  As a method of growing the group III nitride semiconductor single crystal 2, it is preferable to use the HVPE (Hydride Vapor Phase Epitaxy) method capable of increasing the growth rate. When using the HVPE method, the impurity that is taken into the group III nitride semiconductor single crystal 2 during epitaxial growth and causes distortion is often oxygen generated due to the quartz member used in the furnace body. .

  The substrate 1 and the group III nitride semiconductor single crystal 2 may be made of the same type of crystal (for example, in the case of a GaN substrate and a GaN crystal), or may be made of different types of crystal (for example, For example, in the case of sapphire substrate and GaN crystal). In the case of homoepitaxial growth of group III nitride semiconductor single crystal 2 on substrate 1 made of the same type of crystal, for example, it is possible to use a high VAS (Void-Assisted Separation) method disclosed in Japanese Patent No. 3631724 or the like. A uniform low dislocation density substrate may be used as the substrate 1. In the case of heteroepitaxial growth of a group III nitride semiconductor single crystal 2 on a substrate 1 composed of different crystals, cracking easily occurs when the thickness of the group III nitride semiconductor single crystal 2 increases, but some strain relaxation is caused at the hetero interface. Cracks can be suppressed by interposing and growing layers. For example, if the technique disclosed in Japanese Patent No. 3886341 is applied, it is possible to reduce the dislocation density and at the same time to prevent the cracking caused by the thick film growth.

  The distribution of the impurity concentration in the group III nitride semiconductor single crystal 2 should be easily confirmed as a contrast by observing the state of light emission of the group III nitride semiconductor single crystal 2 by irradiating excitation light such as ultraviolet light. Can. Moreover, distortion in the group III nitride semiconductor single crystal 2 can be detected by photoelastic measurement or Raman measurement.

  A region formed by crystal growth with the facet 4p and the surface 4n as a growth interface, that is, a region having an impurity concentration different from a region formed by crystal growth with the surface 3p as a growth interface is a strained region Although they often coincide with each other, the distorted region may be widely distributed. In this case, it is desirable to remove all of the strained area, but since a dedicated device is required to observe the strain field, there is a problem that the manufacturing process and the manufacturing cost increase.

  If it is a method of removing the cylindrical area 4 set as a cylindrical area including the facet 4p that can be observed visually on the upper surface, even if it is not possible to remove all of the distorted area. It is possible to remove distortion to such an extent that the occurrence of cracks in the slicing process can be prevented. Therefore, the occurrence of cracks can be prevented in a short time and at low cost.

  In the case where the cylindrical region 4 with the smallest volume satisfying the condition of “a cylindrical region including the facet 4 p on the upper surface on the outer peripheral side of the group III nitride semiconductor single crystal 2” is set as the cylindrical region 4. If any, the cylindrical region 4 includes all or almost all of the strained region. Therefore, even in such a case, by removing the cylindrical region 4 from the group III nitride semiconductor single crystal 2, all or almost all of the strained region can be removed.

  Further, by increasing the thickness of the cylindrical region 4 and including in the cylindrical region 4 up to the region where the plane orientation of the upper surface is equal to the surface 3 p of the cylindrical region 3, it is possible to more reliably remove the strained region. it can. However, since the diameter of the cylindrical region 3 is reduced by increasing the thickness of the cylindrical region 4, the diameter of the semiconductor substrate obtained from the cylindrical region 3 is reduced.

  As shown in FIG. 2, when the group III nitride semiconductor single crystal 2 is a GaN crystal having the face 3p as a c-plane, the facet 4p is a (1-10X) face (X is a natural number), On the outer peripheral side of the upper surface of the group III nitride semiconductor single crystal 2, it appears at a position of six-fold symmetry about the central axis of the group III nitride semiconductor single crystal 2. The cross sections shown in FIGS. 1B and 1C correspond to the cross sections when the substrate 1 and the group III nitride semiconductor single crystal 2 are cut along the cutting line A-A in FIG. 2.

  The c-plane of the GaN crystal is the closest dense surface, and the region where the c-plane is the growth interface is less likely to take in impurities such as oxygen compared to the region where the plane of the other orientation is the growth interface. Have.

  Further, since the HVPE method is generally used by heating a furnace member made of a quartz member to 1000 ° C. or higher, silicon or oxygen generated by the decomposition of quartz is easily taken into the group III nitride semiconductor single crystal 2 as an impurity. Among these, since silicon is less dependent on the plane orientation of the growth interface of the group III nitride semiconductor single crystal 2 and uniformly taken in the whole, it is used as a dopant for controlling the conductivity of the GaN crystal. There are many. Therefore, the strain distribution in the group III nitride semiconductor single crystal 2 does not become nonuniform due to silicon, and the background concentration in the crystal of silicon as an impurity does not often become a problem.

In the c-plane grown GaN crystal by the HVPE method, oxygen of about 10 ¹⁶ to 10 ¹⁷ cm ⁻³ is usually taken in, although it depends on the growth conditions, but planes other than the c-plane (facet 4p and Oxygen at a concentration of about 10 ¹⁸ to 10 ¹⁹ cm ⁻³ , which is one to two orders of magnitude higher than this, is taken into a region that is grown with the surface 4 n) as a growth interface. As a result, the low oxygen concentration region and the high oxygen concentration region coexist in one GaN crystal, and a cylindrical distortion field is generated on the outer peripheral side of the crystal.

(Removal of cylindrical area)
As described above, the strain in the group III nitride semiconductor single crystal 2 is cylindrically distributed on the outer peripheral side in the group III nitride semiconductor single crystal 2 because it is caused by the impurity concentration distribution, and the balance as a whole is achieved. Keep the However, if a part of the outer periphery is cut or scraped to process the group III nitride semiconductor single crystal 2 in a strained state, part of the strain is locally released, and the group III nitride semiconductor The balance of distortion in the single crystal 2 may be broken, and a crack may occur.

  Therefore, when removing cylindrical region 4 from group III nitride semiconductor single crystal 2, removal of cylindrical region 4 is performed by removing group III nitride semiconductor single crystal 2 so that the balance of distortion in group III nitride semiconductor single crystal 2 is not lost. It is required that the shape of the nitride semiconductor single crystal 2 is always kept in axial symmetry with the central axis of the group III nitride semiconductor single crystal 2 as the symmetry axis. Here, axial symmetry is synonymous with the rotational symmetry of n-fold symmetry where n is an arbitrary integer. In this case, removal processing of cylindrical region 4 proceeds in a direction parallel to the growth direction of group III nitride semiconductor single crystal 2 (direction perpendicular to main surface 1 p of substrate 1).

  For example, in the case of removing the cylindrical region 4 by grinding using a cylindrical grindstone described later, ultrasonic machining using a cylindrical tool, electric discharge machining using a cylindrical die-sinking discharge electrode, or laser processing, The removal of the cylindrical area 4 is performed such that the shape of the removed area always maintains a uniform cylindrical shape in height.

  Below, the specific example of the removal method of the cylindrical area | region 4 is demonstrated.

  FIGS. 3A and 3B are vertical sectional views schematically showing the process of removing the cylindrical region 4 by grinding using the cylindrical grindstone 10.

  The cylindrical grindstone 10 has the abrasive grain formation part 11 in the front-end | tip (bottom part). The grindstone 10 is brought into contact with the group III nitride semiconductor single crystal 2 from the top while rotating the rotation axis with the central axis of the group III nitride semiconductor single crystal 2, and the cylindrical region 4 is slowly removed. . According to this method, the cylindrical region 4 can be removed so that the shape of the removed region always maintains a uniform cylindrical shape in height. In addition, you may use the loose abrasive mixed with the liquid as an abrasive.

  FIGS. 4A and 4B are vertical sectional views schematically showing a process of removing the cylindrical region 4 by electric discharge machining using the cylindrical die-sinking discharge electrode 20. FIG.

  The cylindrical engraved discharge electrode 20 is rotated with the rotation axis aligned with the central axis of the group III nitride semiconductor single crystal 2 and discharged between the engraved discharge electrode 20 and the group III nitride semiconductor single crystal 2 Is brought into contact with the group III nitride semiconductor single crystal 2 from above, and the cylindrical region 4 is slowly removed. According to this method, the cylindrical region 4 can be removed so that the shape of the removed region always maintains a uniform cylindrical shape in height.

  In addition, the cylindrical area 4 can be removed using ultrasonic processing using a cylindrical tool or laser processing so that the shape of the removed area always maintains a uniform cylindrical shape in height.

  Although FIGS. 3A, 3B, 4A, 4B show an example in which the cylindrical region 4 is removed from above the group III nitride semiconductor single crystal 2, processing is advanced from the substrate 1 side to remove the cylindrical region 4 It is also good. However, in this case, the region directly below the cylindrical region 4 of the substrate 1 is also removed. Therefore, when the substrate 1 is to be reused as a seed crystal, the cylindrical region 4 is viewed from the side of group III nitride semiconductor single crystal 2. It is required to remove.

  FIG. 5 is a vertical sectional view showing a state in which the cylindrical region 4 is removed from the side of the group III nitride semiconductor single crystal 2 and the region immediately below the cylindrical region 4 of the substrate 1 is left. This substrate 1 is sliced in the cylindrical region 3 of the remaining group III nitride semiconductor single crystal 2 to form a semiconductor substrate, and then the main surface 1 p is subjected to polishing treatment to be reused as a seed crystal. it can.

  FIG. 6 is a vertical sectional view showing the substrate 1 and the group III nitride semiconductor single crystal 2 on which the protective film 30 for selectively removing the cylindrical region 4 is formed by etching.

First, not wishing to remove the cylindrical region 3 on the surface 3p, and protection comprising an area corresponding to the cylindrical region 3 on the Group III nitride semiconductor single crystal 2 of the substrate 1 opposite to the surface 1b of SiO ₂ or the like Cover with a membrane 30. Then, the cylindrical region 4 is removed by vapor phase etching or wet etching. As the gas phase etching, reactive ion etching using BCl gas or the like can be used. Further, as the wet etching, etching with a hot phosphoric acid sulfuric acid based etchant can be used. By appropriately controlling the etching conditions, the cylindrical region 4 can be removed so that the shape of the removed region always maintains axial symmetry.

(Slicing of cylindrical area)
Next, the cylindrical region 3 left by the removal of the cylindrical region 4 is sliced.

  FIGS. 7A and 7B are vertical cross-sectional views schematically showing the process of slicing the cylindrical area 3. Here, the dotted line shown in FIG. 7A indicates the position where the cylindrical region 3 is sliced. For slicing of the cylindrical region 3, an existing slicing technique using an inner peripheral blade slicer, an outer peripheral blade slicer, a wire saw, an electric discharge machine or the like can be used.

  After slicing the cylindrical region 3, beveling is applied to the outer peripheral edge of the obtained disk-like semiconductor substrate 5, and polishing is applied to the front and back surfaces.

  As apparent from the manufacturing process of the semiconductor substrate 5 described above, the diameter of the semiconductor substrate 5 is smaller than the diameter of the substrate 1. Therefore, it is preferable to determine the diameter of the substrate 1 in consideration of the diameter of the semiconductor substrate 5 to be obtained and the size of the cylindrical region 4 to be removed. In addition, the diameter of the group III nitride semiconductor single crystal 2 may be made smaller than the diameter of the substrate 1 by a factor of, for example, to prevent adhesion between the group III nitride semiconductor single crystal 2 and the growth jig.

Second Embodiment
The second embodiment is different from the first embodiment in the means for removing the distortion of the group III nitride semiconductor single crystal. The description will be omitted or simplified for the same points as the first embodiment.

(Separation of cylindrical area)
The cylindrical region 4 in the present embodiment is a region separated from the cylindrical region 3 before the cylindrical region 3 is sliced. By separating the cylindrical region 4 from the cylindrical region 3, it is possible to prevent the occurrence of cracks at the time of slicing of the cylindrical region 3 as in the case of removing the cylindrical region 4.

  Separation of the cylindrical region 3 and the cylindrical region 4 is carried out by forming a cylindrical void having a central axis equal to the central axis of the group III nitride semiconductor single crystal 2 in the group III nitride semiconductor single crystal 2. Ru. This void does not leave a region having a high impurity concentration that causes distortion in the cylindrical region 3, a region passing through the boundary between the facet 4 p and the face 3 p of the group III nitride semiconductor single crystal 2, or the facet 4 p Preferably, it is formed in the inner region.

  In separating the cylindrical region 4 from the cylindrical region 3 in the same manner as in the case of removing the cylindrical region 4 from the group III nitride semiconductor single crystal 2 in the first embodiment, in the group III nitride semiconductor single crystal 2 In order to prevent collapse of the balance of distortion, the formation of voids is such that the shape of group III nitride semiconductor single crystal 2 always maintains axial symmetry with the central axis of group III nitride semiconductor single crystal 2 as the axis of symmetry. It is required to be implemented. In this case, the formation of the void proceeds in the direction parallel to the growth direction of the group III nitride semiconductor single crystal 2 (the direction perpendicular to the major surface 1 p of the substrate 1).

  For example, in the case of forming a void by excavating using a hole saw, which will be described later, grinding using a cylindrical grindstone, ultrasonic processing using a cylindrical tool, electric discharge processing using a cylindrical mold electric discharge electrode, or laser processing More preferably, the formation of the air gap is performed such that the shape of the air gap always maintains a uniform cylindrical shape in height.

  Below, the specific example of the separation | isolation method of the cylindrical area | region 4 is demonstrated.

  FIGS. 8A and 8B are vertical cross-sectional views schematically showing the process of forming a void using the hole saw 40 and separating the cylindrical region 4 from the cylindrical region 3.

  The hole saw 40 has a blade 41 at its tip (bottom). The hole saw 40 is brought into contact with the group III nitride semiconductor single crystal 2 from the top while rotating with the axis of rotation aligned with the central axis of the group III nitride semiconductor single crystal 2 to form a gap slowly. According to this method, the void can be formed so that the shape of the void always maintains a uniform cylindrical shape in height.

  FIG. 9 is a vertical cross-sectional view showing the state of group III nitride semiconductor single crystal 2 after separation of cylindrical region 4 from cylindrical region 3 is completed. The cylindrical region 4 is separated from the cylindrical region 3 by the air gap 6.

  The air gap 6 may be, for example, grinding with a cylindrical grindstone having a thickness close to that of the hole saw 40, ultrasonic processing using a cylindrical tool having a thickness close to that of the hole saw 40, or the hole saw 40. It can be formed by electric discharge machining using a cylindrical discharge electrode with a near thickness or by laser machining.

  After the cylindrical region 4 is separated from the cylindrical region 3, the cylindrical region 3 is sliced after the cylindrical region 4 is removed from above the substrate 1. In addition, the cylindrical region 3 may be sliced along with the cylindrical region 4 in a state where the cylindrical region 4 is left around the cylindrical region 3. At this time, it is preferable that no damage occurs to the cylindrical region 3 even if the cylindrical region 4 is broken.

  When the substrate 1 is to be reused as a seed crystal, as shown in FIGS. 8A and 8B and FIG. 9, the air gap 6 is formed from the side of group III nitride semiconductor single crystal 2. Leave the area directly below without removal. Then, after slicing the cylindrical region 3 of the group III nitride semiconductor single crystal 2 to form a semiconductor substrate, the main surface 1 p is polished to reuse the substrate 1 as a seed crystal.

(Effect of the embodiment)
According to the first and second embodiments, the strain in the epitaxially grown group III nitride semiconductor single crystal is removed while suppressing the occurrence of cracks, whereby the group III nitride semiconductor is not generated. A single crystal can be sliced to obtain a semiconductor substrate.

  In addition, since the slice processing is performed after the strain in the group III nitride semiconductor single crystal is removed, the strain remaining in the obtained semiconductor substrate can be significantly reduced, and the warpage of the semiconductor substrate is reduced. Can. Further, as the warpage is reduced, the variation in crystal plane orientation on the surface of the semiconductor substrate is reduced, and the variation in characteristics of the device manufactured using this semiconductor substrate can be reduced. In addition, since distortion remaining in the semiconductor substrate is small, generation of defects such as cracking and chipping in the semiconductor substrate can be suppressed when manufacturing a device using the semiconductor substrate.

  The first and second embodiments are particularly effective in the manufacture of a group III nitride single crystal substrate, particularly a GaN substrate having a c-plane as a main surface. In the region where the c-plane with a dense array of atoms is the growth interface, impurity atoms are less likely to be taken in than in the region where the other surface is the growth interface, so in the c-plane grown GaN crystal, the facet is This is because the difference in impurity concentration tends to be large between the region on the outer peripheral edge side that tends to appear and the region on the inner side, and large distortion is easily accumulated.

In addition, the crystal has a large diameter, a low defect density, and is more easily broken as the crystal characteristic is uniform. This is because there are few defects such as dislocations and inversion domains which have the property of absorbing and relieving strain. Therefore, in the first and second embodiments, a semiconductor substrate having a large diameter (for example, a diameter of 50 mm or more), a small number of pits and inversion domains, and a low dislocation density (for example, 10 ⁷ cm ⁻² or less) Particularly effective in manufacturing.

  In the first embodiment, the c-plane grown GaN crystal has been described as a specific example, but if a difference occurs in the impurity concentration between the region on the outer peripheral edge side of the GaN crystal and the region inside it, It is also effective when growing a GaN crystal in a direction different from the c-plane. The semiconductor substrate can also be manufactured from a crystal other than GaN, for example, AlN, AlGaN, InGaN, AlInGaN, or a crystal having a laminated structure in which these are laminated. In addition, an off angle may be attached to the growth orientation of the group III nitride semiconductor single crystal.

  Below, the result of having manufactured and evaluated the semiconductor substrate based on the said embodiment is described.

  In the present example, a GaN crystal was epitaxially grown by the HVPE method as the group III nitride semiconductor single crystal 2 of the above embodiment. First, the process of growing a GaN crystal by the HVPE method will be described.

  FIG. 10 is a vertical sectional view schematically showing the configuration of an HVPE growth apparatus 50 used for crystal growth of a GaN crystal. The HVPE growth apparatus 50 is made of quartz in a heater consisting of two zones: a heater 51 for heating the raw material, which is about 800 ° C. during crystal growth, and a heater 52 for heating the crystal growth region, which is about 1000 ° C. The reaction tube 53 is inserted.

  A pipe for introducing a source gas is provided on the upstream side of the quartz reaction tube 53. Ammonia gas, which is a V group material, is introduced into the furnace through the ammonia gas introduction pipe 57. Metallic gallium 56 which is a Group III material is accommodated in a boat made of quartz and placed in a region heated by the heater 51 for heating the gallium material. At the time of crystal growth, a hydrochloric acid gas is allowed to flow through the boat through a hydrochloric acid gas introducing pipe 58 for producing gallium chloride made of quartz. Then, metal gallium 56 and hydrochloric acid gas react to generate gallium chloride gas, which reaches the surface of substrate 1 through piping. The gallium chloride and ammonia react on the surface of the heated substrate 1 to grow a GaN crystal. It is also possible to flow a doping gas into the furnace through the doping gas introduction pipe 59. The substrate 1 serving as a base for crystal growth is fixed to a substrate holder 54 supported by a rotating shaft 55, and is rotated during crystal growth. The gas introduced into the reaction tube is led to the abatement system by the downstream exhaust pipe 60, subjected to detoxification treatment, and then discharged to the atmosphere.

Example 1
A GaN crystal was grown using the HVPE growth apparatus 50, with the GaN substrate having a c-plane with a diameter of 62 mm as the main surface and manufactured by the VAS method as the substrate 1. As gas flow conditions for HVPE growth, hydrogen gas as carrier gas was 900 sccm, nitrogen gas was 8100 sccm, gallium chloride gas was 180 sccm, and ammonia gas was 500 sccm. The growth pressure was 100 kPa, the substrate temperature during growth was 1070 ° C., and the growth time was 15 hours. During growth, the substrate 1 was rotated at 5 rpm, and silicon was doped at about 10 ¹⁸ cm ⁻³ by supplying dichlorosilane as a doping source gas to the substrate region. As a result, a Si-doped GaN crystal having a thickness of about 4.5 mm was grown on the substrate 1.

  The surface of the GaN crystal thus obtained was irradiated with ultraviolet light from a mercury lamp to observe a fluorescent image. As a result, a ring-shaped dark area about 3 mm wide was observed at the outer peripheral edge of the crystal. Further, when the same crystal was subjected to photoelastic measurement, a high stress area was observed at the outer peripheral edge of the crystal so as to correspond to the dark area observed in the fluorescence image observation.

  Next, using the cylindrical grinding wheel 10 shown in FIGS. 3A and 3B, the cylindrical region 4 of the GaN crystal was slowly ground away, leaving a cylindrical region 3 with a diameter of 56 mm. Next, the cylindrical region 3 of the GaN crystal was sliced using a wire saw, and five GaN free-standing substrates with a thickness of 630 μm were obtained. Furthermore, the outer peripheral edge of the obtained GaN free-standing substrate is beveled to form a diameter of 50.8 mm, an orientation flat and an index flat are formed, and then the front and back surfaces are mirror-polished. , And its thickness was 400 to 450 μm.

During the above processing, defects such as cracks and chipping did not occur in the GaN crystal. In addition, the warpage (BOW) of the substrate was all suppressed within 10 μm. When the dislocation density of one of the obtained GaN free-standing substrates was counted using the cathode luminescence method, an average value of 6.2 × 10 ⁵ cm ⁻² was obtained in the plane. Moreover, when the dispersion | variation in the inclination of the c-axis in a board | substrate surface was measured by the X-ray-diffraction method, all board | substrates were settled in less than +/- 0.05 degree in surface.

(Comparative example)
When a GaN crystal grown in the same manner as in Example 1 was sliced with a wire saw without removing the cylindrical region 4, a crack was generated as soon as the wire was cut, and thus two cracks were formed. It broke and I couldn't continue working.

(Example 2)
An undoped GaN layer was grown to a thickness of 400 nm using trimethylgallium and ammonia as raw materials by MOCVD method on a single crystal sapphire substrate having a c-plane main surface having a diameter of 58 mm, and a metal titanium film was deposited 20 nm thereon. . This substrate is placed in the HVPE growth apparatus 50 as the substrate 1, and heat treatment is performed at 1050 ° C. for 30 minutes in a stream of ammonia mixed with hydrogen gas at 20% to obtain the metal titanium film on the surface of the substrate 1. It was changed to a network-like titanium nitride film, and at the same time, innumerable microvoids were generated in the GaN layer. Subsequently, ammonia and gallium chloride were supplied onto the substrate 1 in the HVPE growth apparatus 50, and dichlorosilane was used as a dopant to grow a Si-doped GaN crystal to a thickness of about 7 mm. In crystal growth, a mixed gas of hydrogen and nitrogen is used as a carrier gas, and by optimizing the composition, the GaN crystal is embedded in the void of the substrate 1 so that the GaN crystal does not separate from the substrate 1 during growth. Adjusted to

  The surface of the GaN crystal thus obtained was irradiated with ultraviolet light from a mercury lamp to observe a fluorescent image. As a result, a ring-shaped dark area about 3 mm wide was observed at the outer peripheral edge of the crystal.

  Next, using a cylindrical grinding wheel having a shape close to that of the hole saw 8 shown in FIGS. 8A and 8B, the GaN crystal was separated into a cylindrical region 3 with a diameter of 52 mm and a cylindrical region 4. Next, the cylindrical region 3 of the GaN crystal was sliced using a wire saw to obtain eight GaN free-standing substrates each having a thickness of 650 μm. Furthermore, the outer peripheral edge of the obtained GaN free-standing substrate is beveled to form a diameter of 50.0 mm, an orientation flat and an index flat are formed, and then the front and back surfaces are mirror-polished. , And its thickness was 400 to 450 μm. During the above processing, defects such as cracks and chipping did not occur in the GaN crystal.

(Example 3)
Using the GaN off-substrate whose main surface is inclined by 2 ° in the m-axis direction from the c-plane as the substrate 1, a GaN crystal in which the crystal orientation is inclined is grown by the method similar to the first embodiment. Next, the obtained GaN crystal was subjected to ultrasonic processing using an ultrasonic processing machine, and separated into a cylindrical region 3 and a cylindrical region 4 with a diameter of 56 mm. This ultrasonic processing was performed slowly while supplying a diamond slurry using a cylindrical cutter having a shape close to that of the hole saw 8 shown in FIGS. 8A and 8B.
Next, the cylindrical region 3 of the GaN crystal was sliced using a wire saw, and five GaN free-standing substrates with a thickness of 630 μm were obtained. Furthermore, the outer peripheral edge of the obtained GaN free-standing substrate is beveled to form a diameter of 50.8 mm, an orientation flat and an index flat are formed, and then the front and back surfaces are mirror-polished. , And its thickness was 400 to 450 μm.

  During the above processing, defects such as cracks and chipping did not occur in the GaN crystal. In addition, when the c-axis off angle of the obtained GaN free-standing substrate and the in-plane variation thereof were measured by the X-ray diffraction method, all the substrates were within 2 ± 0.05 ° in the plane.

(Example 4)
With the same method as in Example 1, a GaN substrate having a c-plane with a diameter of 62 mm prepared by the VAS method as the main surface was used as the substrate 1, and a Si-doped GaN crystal about 3 mm thick was grown thereon by the HVPE method. .

  Next, the cylindrical region 4 of the obtained GaN crystal was slowly removed by laser processing using a laser processing machine, leaving a cylindrical region 3 with a diameter of 55 mm. This laser processing was performed under the condition of the maximum output 5 W in the single mode of the wavelength 532 nm. The laser was irradiated to the surface of the GaN substrate, and the cylindrical region 4 was removed by rotating repeatedly at a speed of 10 mm / sec. Next, the cylindrical region 3 of the GaN crystal was sliced using a wire electric discharge machine, and three GaN free-standing substrates with a thickness of 680 μm were obtained. Furthermore, the outer peripheral edge of the obtained GaN free-standing substrate is beveled to form a diameter of 50.0 mm, an orientation flat and an index flat are processed, and the front and back surfaces are mirror-polished. , And its thickness was 400 to 450 μm. During the above processing, defects such as cracks and chipping did not occur in the GaN crystal.

(Example 5)
With the same method as in Example 1, a GaN substrate having a c-plane with a diameter of 62 mm prepared by the VAS method as the main surface was used as the substrate 1, and Si-doped GaN crystal with a thickness of about 4 mm was grown thereon by HVPE. .

  Next, the cylindrical region 4 of the GaN crystal was slowly removed using the cylindrically shaped discharge electrode 20 shown in FIGS. 4A and 4B, leaving a cylindrical region 3 with a diameter of 56 mm. Next, the cylindrical region 3 of the GaN crystal was sliced using a wire electric discharge machine, and five GaN free-standing substrates with a thickness of 630 μm were obtained. Furthermore, the outer peripheral edge of the obtained GaN free-standing substrate is beveled to form a diameter of 50.8 mm, an orientation flat and an index flat are formed, and then the front and back surfaces are mirror-polished. , And its thickness was 400 to 450 μm. During the above processing, defects such as cracks and chipping did not occur in the GaN crystal.

(Example 6)
With the same method as in Example 1, a GaN substrate having a c-plane with a diameter of 62 mm prepared by the VAS method as the main surface was used as the substrate 1, and a Si-doped GaN crystal about 3 mm thick was grown thereon by the HVPE method. .

Next, a protective film 30 shown in FIG. 6 was formed on the surface of the obtained GaN crystal and the back surface of the substrate 1. The protective film 30 is a 58 mm diameter film made of SiO ₂ . After the protective film 30 is formed, the GaN crystal is immersed in a mixed solution of phosphoric acid and sulfuric acid heated to 230 ° C. for 12 h with the protective film 30 attached, and the front and back surfaces are not covered by the protective film 30 The cylindrical region 4 was etched away from the back surface (N surface) side and disappeared. After etching, the GaN crystal was placed in dilute hydrofluoric acid to remove the protective film 30. Thus, a cylindrical region 3 having a diameter of 56 mm was obtained (the diameter of the cylindrical region 3 was one size smaller than the diameter of the protective film 30).

  Next, the cylindrical region 3 of the GaN crystal was sliced using a wire saw, and three GaN free-standing substrates with a thickness of 650 μm were obtained. Furthermore, the outer peripheral edge of the obtained GaN free-standing substrate is beveled to form a diameter of 50.8 mm, an orientation flat and an index flat are formed, and then the front and back surfaces are mirror-polished. , Its thickness was 450 μm. During the above processing, defects such as cracks and chipping did not occur in the GaN crystal.

(Example 7)
With the same method as in Example 1, a GaN substrate having a c-plane with a diameter of 62 mm prepared by the VAS method as the main surface was used as the substrate 1, and Si-doped GaN crystal with a thickness of about 4 mm was grown thereon by HVPE. .

  Next, the cylindrical region 4 of the GaN crystal was slowly ground and removed using the cylindrically shaped discharge electrode 20 shown in FIGS. 4A and 4B, leaving a cylindrical region 3 with a diameter of 56 mm. At this time, the substrate 1 was not subjected to electrical discharge machining, and a region immediately below the cylindrical region 4 was left as in the substrate 1 shown in FIG.

  Next, the cylindrical region 3 of the GaN crystal was sliced using a wire electric discharge machine, and five GaN free-standing substrates with a thickness of 630 μm were obtained. Furthermore, the outer peripheral edge of the obtained GaN free-standing substrate is beveled to form a diameter of 50.8 mm, an orientation flat and an index flat are formed, and then the front and back surfaces are mirror-polished. , And its thickness was 400 to 450 μm. During the above processing, defects such as cracks and chipping did not occur in the GaN crystal.

  Then, after obtaining a GaN free-standing substrate, the remaining surface of the substrate 1 was subjected to planarization treatment using a grinder and mirror polishing, and was reused as a seed crystal. When the same manufacturing process of the GaN self-standing substrate as described above was performed using this recycled substrate 1, it was possible to obtain a GaN self-standing substrate of the same quality as in the case of using the first-use substrate 1. Thereby, it was confirmed that the repeated use of the GaN substrate as the substrate 1 is possible.

  As mentioned above, although embodiment and Example of this invention were described, this invention is not limited to said Embodiment and Example, A various deformation | transformation implementation is possible in the range which does not deviate from the main point of invention.

  In addition, the embodiments and examples described above do not limit the invention according to the claims. Furthermore, it should be noted that not all combinations of features described in the embodiments and examples are essential to the means for solving the problems of the invention.

  Abstract: A method of manufacturing a semiconductor substrate capable of obtaining a semiconductor substrate by slicing an epitaxially grown group III nitride semiconductor single crystal while suppressing the occurrence of cracks.

Reference Signs List 1 substrate 1p main surface 2 group III nitride semiconductor single crystal 3 cylindrical region 3p surface 4 cylindrical region 4p facet 5 semiconductor substrate 6 air gap 10 grindstone 20 type engraving discharge electrode 30 protective film 40 hole saw 50 HVPE growth apparatus

Claims (2)

Epitaxially growing a group III nitride semiconductor single crystal on the main surface of a circular substrate;
Removing the first region on the outer peripheral side of the group III nitride semiconductor single crystal, and leaving a second region inside the first region of the group III nitride semiconductor single crystal;
Including
In the removal of the first region, the shape of the group III nitride semiconductor single crystal is always the center of the group III nitride semiconductor single crystal so that the balance of distortion in the group III nitride semiconductor single crystal is not broken. Implemented to maintain axial symmetry with the axis as the symmetry axis,
The first region includes a region formed by facet growth different in concentration of impurities from the second region,
Method for producing group III nitride semiconductor single crystal. Epitaxially growing a group III nitride semiconductor single crystal on the main surface of a circular substrate;
A cylindrical void is formed in the group III nitride semiconductor single crystal, and a first region on the outer peripheral side of the group III nitride semiconductor single crystal and the first region of the group III nitride semiconductor single crystal are formed. Separating the group III nitride semiconductor single crystal into an inner second region;
Including
The shape of the group III nitride semiconductor single crystal is always symmetrical about the central axis of the group III nitride semiconductor single crystal so that the balance of distortion in the group III nitride semiconductor single crystal is not broken in the formation of the void. It is carried out to maintain the axial symmetry of the axis,
The first region includes a region formed by facet growth different in concentration of impurities from the second region,
Method for producing group III nitride semiconductor single crystal.

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