JP4178936B2 - Group III nitride free-standing substrate, semiconductor device using the same, and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a group III nitride free-standing substrate, a semiconductor device using the same, and a method for manufacturing the same.
[0002]
[Prior art]
Nitride semiconductor materials have a sufficiently large forbidden band width and a direct transition type between band transitions. Therefore, application to a short wavelength light emitting element has been actively studied. In addition, application to electronic devices is also expected due to the high saturation drift velocity of electrons and the use of two-dimensional carrier gas by heterojunction.
[0003]
The nitride semiconductor layers constituting these elements are formed using a vapor phase growth method such as metal organic vapor phase epitaxy (MOVPE), molecular beam vapor phase epitaxy (MBE), or hydride vapor phase epitaxy (HVPE). It is obtained by performing epitaxial growth on the substrate. However, since there is no underlying substrate having a lattice constant matching with this nitride semiconductor layer, it is difficult to obtain a high-quality growth layer, and the obtained nitride semiconductor layer contains many crystal defects. . Since this crystal defect becomes a factor that hinders improvement in device characteristics, techniques for reducing crystal defects in the nitride semiconductor layer have been actively studied so far.
[0004]
One such technique is known in which a thick GaN layer is used as an underlayer for crystal growth, and a semiconductor multilayer film constituting an element portion is formed on the GaN layer. An ELO (Epitaxial Lateral Overgrowth) technique is known as a technique for forming a small number of GaN underlayers. ELO is a crystal growth method that covers a part of the base with a mask and prevents the propagation of threading dislocations extending vertically from the base. In this method, the crystal grows laterally from the mask opening, and finally a continuous film covering the entire mask is formed. In Japanese Patent Application Laid-Open No. 11-251253 (Patent Document 1), by using this ELO technique, a crystal defect in the vicinity of the wafer surface is 1 × 10 6. ^Five Piece / cm ² It is said that the following GaN substrate was obtained. However, when ELO is used, it is difficult to reduce the crystal defect density over the entire surface of the wafer. In ELO, GaN selectively grows laterally from the opening of the mask. In the region where the mask is formed, dislocations are prevented from proceeding upward, but in the opening, the dislocations are inherited as they are from the underlayer, and the upper region has a structure including many threading dislocations. Therefore, in the crystal growth by ELO, a portion with few crystal defects is formed, while a region with many threading dislocations is formed at the same time, and it is difficult to reduce crystal defects over the entire surface of the wafer. In the example of the above publication, when the crystal defect density near the surface was observed by TEM, 1 × 10 ^Four Although described as having been described below, such a region having a low crystal defect is formed, while a region including a large number of crystal defects is formed at the same time. Actually, “Applied Physics Letter Volume 71 1997 pp.2472-2474” (Non-patent Document 1) includes SiO 2 ₂ Almost no dislocation is observed on the mask, but 10 at the mask opening. ⁸ ~Ten ⁹ cm ^-2 It has been reported that dislocations are observed.
[0005]
On the other hand, the present inventors have developed FIELO (Facet-Initiated Epitaxial Lateral Overgrowth) technology, which is a further development of the ELO technique (Non-patent Document 2: “Applied Physics” (Vol. 68, No. 7, 1999, pp. 774-779)). This technology uses SiO ₂ Although it is common with ELO in that selective growth is performed using a mask, it is different in that a facet is formed in the mask opening. By forming facets, the propagation direction of dislocations is changed, and threading dislocations reaching the upper part of the epitaxial growth layer are reduced. By using this method, a high-quality GaN substrate with relatively few crystal defects can be obtained by growing a thick GaN layer on a base substrate such as sapphire and then removing the base substrate. By utilizing the above, it is possible to obtain an element having a performance superior to that of the prior art.
Japanese Patent Laid-Open No. 2002-33288 (Patent Document 2) describes a crystal growth method in which the ELO method is improved. This publication discloses a technique for reducing a dislocation density by exposing a semiconductor layer having a concavo-convex portion in a mask opening and crystal growth using this layer as a base. This document discloses a method of forming crystal irregularities inside a mask opening, starting crystal growth from the irregularities, and laterally growing on the mask. In the concavo-convex portion, the concave portion is left unfilled by growing in the lateral direction, and a void is left in that portion, thereby causing discontinuity with the base crystal and reducing threading dislocations. In FIG. 8 and paragraphs 0050 to 0051 of the publication, a technique is described in which the entire surface of the mask opening is covered with an anti-surfactant that inhibits crystal growth and crystal is grown from the pinhole portion. In this opening, a process is described in which the GaN layer expands so that the growth starts in an island shape from the pinhole portion, and further grows and extends onto the mask. According to this method, it is described that threading dislocations extending vertically can be surely interrupted and the dislocations can be reduced.
[0006]
However, at present, a higher level of reduction in dislocations is desired from the viewpoint of improving the performance of the device, and the above-described conventional technology does not sufficiently meet the demand.
The ELOs shown in Patent Documents 1 and 2 prevent the propagation of threading dislocations by covering the base with a mask, and high-density dislocations are generated above a portion where no mask exists. Therefore, it is difficult to form a low dislocation region with a large area as an element formation region. In order to form a low dislocation region with a large area, it is conceivable to increase the mask width, but in that case, the crystal axis (c-axis) is disturbed, and it becomes difficult to obtain a crystal of good quality. In mask growth, it is well known that the c-axis orientation deteriorates as the mask width increases. For example, FIG. 4. In addition, these conventional techniques are basically based on the idea of blocking the progress of dislocations with a mask, and include the concept of reducing dislocations reaching the surface by bending the dislocations as in FILEO. Absent.
[0007]
On the other hand, FIELO shown in Non-Patent Document 2 is effective in reducing dislocations, and a low dislocation region can be formed with a relatively large area as an element formation region. However, in order to realize a high level of crystal quality as currently desired, it is necessary to make the crystal layer on the mask thick to some extent, and it is not always necessary to meet the demand for a large area of the low dislocation region. It was not enough, and there was still room for improvement.
[0008]
[Patent Document 1]
JP-A-11-251253
[Patent Document 2]
JP 2002-33288 A
[Non-Patent Document 1]
Applied Physics Letter Volume 71 1997 pp.2472-2474
[Non-Patent Document 2]
"Applied Physics" (Vol. 68, No. 7, 1999, pp. 774-779)
[Non-Patent Document 3]
2nd Intern. Symp. On Blue Laser and Light Emitting Diodes, Chiba, Japan, Sept. 29-Oct. 2, 1998, P488-491 (FIG. 4)
[0009]
[Problems to be solved by the invention]
In view of the above circumstances, an object of the present invention is to provide a group III nitride free-standing substrate in which dislocations are significantly reduced. Another object of the present invention is to form a low dislocation region with a large area. Another object of the present invention is to form such a large-area low dislocation region without disturbing the crystal axis orientation. Another object of the present invention is to form such a large-area low dislocation region without growing a thick semiconductor layer to reduce dislocation.
[0010]
[Means for Solving the Problems]
According to the present invention, a free-standing substrate including a group III nitride semiconductor layer, A substrate, a plurality of first masks extending in a stripe shape formed on the surface of the substrate, a second mask formed between adjacent first masks and having a plurality of openings, A plurality of small facet structures formed in the opening and a facet structure including the plurality of small facet structures, and the width of the second mask in a direction perpendicular to the stripe direction of the first mask is Narrower than the width of the first mask stripe, Dislocations propagating upward from the base material in the group III nitride semiconductor layer are And water In a flat direction, bending is caused at each of the facet surfaces of the plurality of small facet structures and the facet surfaces of the facet structures that include the small facet structures. By There is provided a self-supporting substrate characterized in that the group III nitride semiconductor layer includes dislocations that are bent a plurality of times.
[0011]
In this self-supporting substrate, dislocations propagating from the substrate are bent by the facet surfaces that are oblique to the substrate horizontal plane, so that the dislocation density in the group III nitride semiconductor layer is significantly reduced. The “facet structure” refers to a polyhedral structure whose side face is a facet surface located obliquely with respect to the substrate horizontal plane. The facet structure and the external crystal layer are usually formed in a continuous process and are semiconductor layers having the same composition. However, they have different growth rates, and the impurity concentrations differ accordingly. Therefore, the contour of the facet structure can be clearly grasped by a predetermined method. This point will be described later in the section of the embodiment.
[0013]
This self-supporting substrate is bent in a direction parallel to the base material a plurality of times. Since the number of dislocations propagating in the layer growth direction is reduced by changing the dislocation progress direction, according to the present invention, a remarkable dislocation reduction effect can be obtained. In the FIELO described in the section of the prior art, dislocations are bent once, whereas in the method of the present invention, the dislocation reduction effect is remarkably improved because a plurality of times bending occurs. In the above-described FIELO, as shown in the cross-sectional TEM image of FIG. 5 of Non-Patent Document 2, the bending of the dislocation in the horizontal direction is only once. On the other hand, in the present invention, a significant reduction in dislocation is realized by bending a plurality of times.
[0016]
Further, according to the present invention, a base material, a mask pattern having a predetermined opening provided on the surface of the base material, and a group III nitride formed so as to grow from the opening and cover the mask pattern A plurality of first masks extending in stripes, and a second mask that is positioned between the adjacent first masks and is narrower than the first mask. A self-supporting substrate is provided.
In this free-standing substrate, a small facet structure grown from the second mask and a facet structure formed between the adjacent first masks and including the small facet structure are stably formed. Therefore, a region having a low dislocation and a good crystal orientation is formed in a large area.
[0017]
According to the present invention, there is provided a semiconductor element characterized in that any one of the above-mentioned free-standing substrates is used as a substrate, and an element structure is provided on the substrate. The element structure can be, for example, a laser structure including at least an active layer.
[0018]
According to the present invention, there is also provided a method for manufacturing the above-mentioned free-standing substrate, wherein a plurality of first masks extending in a stripe shape on the surface of a base material Forming process And between the adjacent first masks Forming a plurality of openings by forming a second mask whose width in the direction perpendicular to the stripe direction of the first mask is narrower than the width of the stripe of the first mask; Opening In A step of growing a group III nitride semiconductor to form a small facet structure; I Further growth of Group II nitride semiconductors ,in front Incorporate the storage facet structure Rufu Forming a facet structure; The group III nitride semiconductor is further grown, and dislocations propagating upward from the base material in the group III nitride semiconductor are in a direction parallel to the base material in the small facet structure and the facet structure. Forming multiple dislocations by bending at each facet surface; and A method for manufacturing a self-supporting substrate is provided.
[0019]
In this growth method, a stripe-shaped facet structure including a small facet structure is formed. For this reason, the direction of dislocation propagating from the base material in the vertical direction is changed by both the side face of the small facet structure and the side face of the stripe-shaped facet structure. Since the number of dislocations propagating in the layer growth direction is reduced by changing the dislocation progress direction, according to the present invention, a remarkable dislocation reduction effect can be obtained. In the FIELO described in the section of the prior art, dislocations are bent once, whereas in the method of the present invention, the dislocation reduction effect is remarkably improved because a plurality of times bending occurs.
[0020]
Further, according to the present invention, there is provided a method for manufacturing the above-mentioned self-supporting substrate, wherein a plurality of first masks extending in a stripe shape on a surface of a base material and between the adjacent first masks Further, the width of the first mask in the direction perpendicular to the stripe direction is narrower than the width of the stripe of the first mask. Second mask By forming , Multiple openings A step of forming a mask pattern, and a step of epitaxially growing a group III nitride semiconductor on the base material while forming a facet surface that forms an acute angle with respect to the horizontal surface of the base material, with the opening of the mask pattern as a growth region. A method for manufacturing a self-supporting substrate is provided.
[0021]
According to this growth method, a small facet structure is formed from the growth region of the opening between the second masks, and then a striped facet structure including the small facet is formed between the adjacent first masks. The dislocation propagating in the vertical direction from the base material is converted in its direction by the side face of the small facet structure, the side face of the stripe-shaped facet structure, etc., so that a remarkable dislocation reduction effect is obtained.
[0023]
In addition, although the self-supporting substrate in the present invention includes the group III nitride semiconductor layer having the above-described configuration, it may have a configuration in which other semiconductor layers are appropriately stacked.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
The facet structure in the present invention refers to a structure having a crystal-specific shape in which a crystal plane having a specific low plane index with the slowest growth rate is left during crystal growth. In the case of GaN having a Wurtzite structure as in the present embodiment, when the mask stripe direction is the <11-20> direction of GaN, the growth rate of the {1-101} plane is the slowest in the opening, and this plane is In order to form an angle of 62 ° with the (0001) plane parallel to the substrate surface, a facet structure having a triangular cross section is formed. The growth rate of the surface differs depending on the growth method and growth conditions in addition to the intrinsic properties of the crystal, and not only the triangle consisting of {1-101} as in the present embodiment, but also a triangle with a different angle. Structures, facet structures with vertical sides, and trapezoidal shapes may appear. As the growth continues, the facet structures merge to form a large triangular facet, and by continuing further growth, a large triangular facet structure is formed between the masks A. Such facet formation process can be observed, for example, by a fluorescence micrograph of a cross section shown in FIG. This fluorescence microscope uses ultraviolet light as a light source and captures light emission in the visible light band from the growth layer. The way in which impurities are incorporated varies depending on the plane orientation, and can be observed as a contrast corresponding to such a growth pattern. From this photograph, it can be seen that a small triangular facet structure is first formed in the opening, and finally a large facet structure is formed in the region between the wide masks.
[0025]
FIG. 12 schematically shows an example of a cross-sectional structure of a self-supporting substrate according to the present invention and the movement of dislocation accompanying facet multiplexing. In this cross-sectional structure, a GaN film 1002 is provided on a sapphire substrate 1000, and a mask 1003 having a predetermined opening is formed thereon. As illustrated, the mask 1003 includes a narrow mask and a wide mask. A thick GaN layer 1004 is grown from the surface of the GaN film 1002 through the opening of the mask 1003.
[0026]
The facet structure grown from the opening of the mask 1003 and the facet structure formed by combining these are shown as a small facet structure 1007 in FIG. The larger facet structure 1007 of the larger ones is combined to form a giant facet structure 1008. This huge facet is stably formed by the presence of a wide mask.
[0027]
The GaN layer 1004 includes many dislocations indicated by arrows in the figure. These dislocations are bent in the direction of dislocation by the small facet structure 1007 and the giant facet structure 1008. As a result, dislocations 1006 reaching the surface of the GaN layer 1004 are more dislocated than dislocations existing near the surface of the GaN film 1002. It is greatly reduced.
[0028]
By forming the facets, the edge dislocations occupying 70 to 80% of the threading dislocations and the mixed dislocations of 20 to 30% change the direction in the direction parallel to the substrate surface as described above. As a result, the density of threading dislocations is greatly reduced. However, particularly at the meeting portion between facets, a part of the mixed dislocation rises again toward the growth surface. In the above structure, the dislocation is further reduced by bending the dislocation at the next facet structure or the next facet structure. The dislocation is driven to the end of the huge facet that is finally formed.
[0029]
As described above, the example of the structure of the free-standing substrate according to the present invention has been described. For the purpose of understanding the mechanism of reducing the dislocation, the layer growth process by FIELO will be described as a comparison. FIG. 13 is a process sectional view showing a layer growth process by the conventional FIELO. First, a base crystal film 202 containing GaN is grown on a sapphire substrate 201, and a striped mask 204 is formed on the surface by using a photolithography method and a wet etching method to form a growth region 203 (FIG. 13 (a)). A crystal is grown on the facet surface 205 starting from the growth region 203 (FIGS. 13B to 13D), and finally a flat GaN layer is formed (FIG. 13E). In this process, the dislocation is bent only once by the facet surface 205 shown in FIG. The mask width is usually about 2 μm and the opening width is about 5 μm. In this case, it is difficult to obtain a large area low dislocation region. Although it is conceivable to increase the mask width in order to obtain a large area low dislocation region, in such a case, disorder of the crystal axis of the GaN layer tends to occur. The present invention solves these problems and realizes a free-standing substrate or crystal film of good quality.
[0030]
The “small facet structure” in the present invention refers to one having a smaller size than the “facet structure”. For example, in the case of using a mask pattern in which a second mask is provided between first masks, a facet structure formed from the opening of the second mask or a plurality of facet structures formed by combining them are formed. This is called a “small facet structure”, and a facet structure including this “small facet structure” and formed between adjacent first masks is called a “facet structure”. The “small facet structure” can have any shape, but the “facet structure” preferably has a stripe shape. Since the upper part of the facet structure is a low dislocation density region, a low dislocation density region having a shape and area suitable for forming an element region can be obtained in this way. When the facet structure is a stripe shape, the stripe width is preferably 20 μm or more. In this way, a large area low dislocation density region can be obtained. Note that when both the “small facet structure” and the “facet structure” are formed in a stripe shape, a large area low dislocation density region can be more suitably formed.
[0031]
In the present invention, the facet structure preferably includes a plurality of small facet structures smaller than the facet structure. In this way, the dislocations can be bent a plurality of times, and a more remarkable dislocation reduction effect can be obtained.
[0032]
The cross-sectional shape of the facet structure is arbitrary, but for example, it can be a shape having a triangular or trapezoidal cross section with a base of 20 μm or more. When the cross section is triangular, since there is no flat portion on the upper surface, propagation of dislocations from the base to the layer growth direction is further suppressed, which is preferable. Even in the case of a trapezoidal cross section, the propagation of dislocations can be remarkably suppressed by reducing the width of the upper base. For example, when the facet structure is formed by mask growth, dislocations traveling upward from the mask opening can be more effectively reduced by making the width of the upper base smaller than the mask width.
[0033]
The facet structure is preferably formed periodically in a direction perpendicular to the stripe direction. In this way, a low dislocation density region where an element region should be formed can be stably formed, and the yield in the element formation process is improved.
[0034]
In the present invention, 50% or more of the dislocations contained in the low dislocation density region can be composed of mixed dislocations. Although there are edge dislocations and mixed dislocations as types of dislocations, it is important to significantly reduce edge dislocations in the upper part of the facet formation region from the viewpoint of improving the characteristics of the element structure formed on the free-standing substrate. . The reason for this will be described below with reference to an example of a semiconductor laser. As is well known in semiconductor lasers, the conditions for obtaining optical gain for guided light in the active layer must be achieved. However, the edge dislocation is a cause of generation of a low-angle grain boundary in the crystal, and light scattering is likely to occur at the low-angle grain boundary. For these reasons, it is desirable that edge dislocations be reduced in semiconductor lasers.
[0035]
In the present invention, both the first mask and the second mask have a stripe shape extending in substantially the same direction, and the second mask is formed with a period smaller than the period of the first mask. Can do. By doing this, a small facet structure is formed from the growth region of the opening between the second masks, and a facet overlapping structure in which a stripe facet structure including the small facets is formed between the adjacent first masks is preferable. Can be formed. Thereby, the remarkable dislocation reduction effect is acquired.
In the present invention, the width of the first mask is made wider than the width of the second mask. The width of the first mask is set to be larger than 1 time of the width of the second mask, preferably 1.2 times or more, more preferably 1.5 times or more. By doing so, a large facet structure growing between the first masks can be formed more stably, and as a result, a more remarkable dislocation reduction effect can be obtained.
The first mask and the second mask need not all have the same mask width. For example, by using a plurality of types of widths for the second mask, multiplexing of facet structures can be further promoted, and the dislocation reduction effect can be made more remarkable.
[0036]
Here, the stripe direction of the first mask is a [11-20] direction, a [1-100] direction, or a direction that forms a deviation angle within 30 degrees from these directions with reference to the crystal structure of the group III nitride semiconductor. It can be. By doing so, a facet structure exhibiting an excellent dislocation reducing effect is stably formed.
[0037]
The interval between the adjacent first masks is, for example, 20 μm or more, preferably 30 μm or more. By doing so, a facet structure having a bottom surface width of 20 μm or more, or 30 μm or more is formed, and a large area low dislocation density region can be obtained.
[0038]
When the self-standing substrate of the present invention is used, an excellent crystal quality element structure can be formed on the upper part. When a light emitting device is formed by forming a device structure including an active layer, a device having excellent light emission characteristics can be obtained.
[0039]
In the method for manufacturing a self-supporting substrate of the present invention, the base material includes a dissimilar material substrate made of a material different from the group III nitride semiconductor, and after the step of forming the group III nitride semiconductor layer, the dissimilar material substrate is It can be set as the structure which further implements the process to remove. According to this configuration, it is possible to suitably form a free-standing substrate made of a group III nitride semiconductor.
[0040]
In the present invention, various base materials can be employed as the base material for forming the facet structure. Examples of base materials are sapphire, SiC, Si, GaAs, GaP, LGO, NGO, ZrB ₂ , ZnO, MgAl ₂ O _Three And the like, a group III nitride semiconductor substrate, and a substrate in which a group III nitride semiconductor layer is formed on these substrates. The surface shape of the underlayer is not particularly limited, and may be a flat surface or an uneven surface. Further, a groove may be formed in the substrate, and a facet structure may be formed thereon. For example, it is also effective to use a combination of techniques such as PENDEO and LEPS to obtain a synergistic effect of the dislocation reduction effect due to the facet structure and the dislocation reduction effect such as PENDEO.
[0041]
Next, a method for evaluating a free-standing substrate will be described.
[0042]
The simplest method for measuring the distribution of surface dislocation density on a free-standing substrate is to selectively etch a portion where dislocations protrude from the surface with a chemical solution, and measure the density of the formed depression (this is called an etch pit) using an optical microscope, Alternatively, counting is performed using a scanning electron microscope. Thereby, the dislocation density and distribution can be easily measured. Moreover, the distinction between mixed dislocations and edge dislocations can be easily grasped by the size and shape of the etch pits. Note that these types of dislocations can also be determined by TEM observation.
[0043]
The crystallinity can be evaluated by using the half width of the X-ray rocking curve by the double crystal method in addition to the observation of the etch pits. This half width is effective as a method for evaluating crystallinity because it becomes smaller by improving crystallinity, particularly by reducing dislocations.
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0044]
FIG. 1 is a process sectional view showing an example of a method for manufacturing a self-supporting substrate according to the present invention. Here, as an example, an example of a manufacturing process of a GaN film on a (1000) plane sapphire substrate crystal is given. First, a first GaN film 12 including a low-temperature buffer layer is formed on a (1000) plane sapphire substrate 11 as an example of a group III nitride by MOVPE (Metal Organic Vapora Phase Epitaxy). Here, GaN is used, but this layer contains at least one of group III elements such as gallium (Ga), aluminum (Al), boron (B), and indium (In), and at least N as a group V element. Is included. In addition, the MOVPE can use any method of normal pressure, reduced pressure, and increased pressure. Furthermore, an HVPE (Hydride Vapor Phase Epitaxy) method using chloride as a raw material, a sublimation method formed by sublimating Ga, or the like can also be used.
Next, silicon oxide (SiO 2) is formed on the crystal film by a CVD (chemical vapor deposition) method. ₂ Or an insulating film made of silicon nitride. This insulating film is made of silicon oxide (SiO ₂ ) And a silicon nitride multilayer film. Furthermore, it is possible to use a refractory metal such as titanium or tungsten. Next, an opening is formed in this insulating film or refractory metal film by lithography and wet etching techniques. As an example, the mask material is SiO ₂ A mask pattern having a period of 60 μm was formed between the masks A having a width of 9 μm and six masks B having a width of 5 μm between the masks A having a width of 3 μm. The stripe direction was the <11-20> direction of the GaN film 12. Here, it is desirable that the opening width is 0.5 to 10 μm, but it is also possible to set the opening width to several nm to several hundred nm by using electron beam exposure or the like. The width of both mask A and mask B is preferably 0.5 to 20 μm. In this example, a 9 μm width mask is used as the mask A, and a 5 μm width mask is used as the mask B. However, the width is not limited to this width as long as the relationship of A> B can be satisfied. The stripe direction of the mask is preferably the <11-20> direction or a direction within 30 degrees from the <1-100> direction perpendicular to this direction, more preferably the <11-20> direction or the <1-100> direction. . Particularly, the growth method is preferably the <11-20> direction or the <1-100> direction in the HVPE method, and the <11-20> direction in the MOVPE method.
[0045]
Next, the substrate crystal on which the mask pattern is formed is set in a reaction tube of an HVPE growth apparatus, and GaN is grown. The growth of GaN starts from the surface of the GaN film 12 exposed at the opening 14. First, as shown in FIG. 1B, a GaN crystal having a facet structure having a triangular cross section with the (1-101) plane as a side surface is formed in the opening.
[0046]
In this embodiment, the period of the mask A is 60 μm, and the facet formed between the masks A is a huge facet structure that is finally formed. After the formation of the huge facet structure, further growth was performed by the HVPE method, and finally a flattened GaN crystal film having a thickness of 200 μm was produced. FIG. 7 shows the result of measuring the distribution of dislocation density on the surface of the crystal film. A dislocation distribution with a period of 60 μm is observed, and at the center where the facet structure is formed, 1.5 × 10 ^Five cm ^-2 The low value is obtained. Compared with conventional techniques such as ELO and PENDEO, dislocation reduction is realized in a wide area. This is extremely convenient when an element structure such as a laser diode is manufactured.
[0047]
In addition to the plane (0001) plane parallel to the substrate as in this embodiment, a crystal plane such as (1-101) is formed, so that, for example, an impurity such as silicon (Si) is taken in. It depends on. Specifically, (1-100) is easier to take in impurities such as Si, and accordingly, when a facet structure is formed, the carrier concentration in this region increases and the resistance value decreases. Therefore, when an element structure is created above the region where the facets are formed, it is possible to suppress the generation of heat with a low electrical resistance and improve the performance of the element.
[0048]
FIG. 6 is a diagram showing another embodiment. Here, a PENDEO type substrate is used. This substrate can be obtained, for example, by etching the opening in FIG. 1 to the sapphire substrate. For this etching, for example, reactive etching using chlorine gas can be used. Using this substrate, for example, when GaN is grown by the HVPE method, the growth starts laterally only from the side wall of the GaN layer remaining on the pillar, and gradually merges with the adjacent growth layer, and at the same time, a facet structure is formed at the top. Is formed. If the growth is continued, the facets merge with each other, and gradually a large facet structure grows, eventually resulting in a facet structure defined by the widest mask period, dislocations similar to those shown in the first embodiment. A reduction effect is obtained. Furthermore, in this case, since the initial growth is started only from the lateral growth, the influence of threading dislocations is reduced, and lower dislocations can be achieved.
[0049]
As the growth method in the above embodiment, it is preferable to use a method with a high growth rate such as the HVPE method. This is because it is necessary to grow to a thickness of 100 μm to 1 mm in order to obtain a flat film by embedding the final facet structure. As a raw material for the HVPE method, a group III element B, Al, Ga, In metal alone, a halide compound thereof, or an organometallic compound is used. When a group III metal element is used, hydrogen chloride (HCl), hydrogen bromide (HBr), and hydrogen iodide (HI) are used to generate a group III element halide compound in the reaction tube. Further, ammonia, hydrazine-based materials, organic amines, etc. are used as nitrogen materials. In addition, it is desirable to dope impurities to control conductivity. For example, as the n-type impurity, at least one element of C, Si, Ge, Sn, S, Se, and Te is used. In addition, as the p-type impurity, at least one element of C, Si, Ge, Sn, Be, Mg, Ca, Zn, and Cd is used. As these impurity raw materials, a single element, a hydride, a halide such as chloride, or an organic metal can be used.
[0050]
In the above embodiment, the back surface of the sapphire substrate 11 may be irradiated with a laser to perform a substrate peeling process. By selecting the wavelength of this laser so that it passes through the sapphire substrate and is absorbed by the group III nitride semiconductor crystal film, a part of the group III nitride layer in contact with the sapphire substrate can be melted, and only the sapphire substrate can be easily obtained. Can be peeled off. Examples of such a laser include a KrF excimer laser with an oscillation wavelength of 248 nm, and an Nd with an oscillation wavelength of 355 nm. ³⁺ : 3rd harmonic of YAG laser. Further, only the substrate crystal can be dissolved by mechanical polishing of the substrate or solution etching to separate only the group III nitride crystal film.
[0051]
The manufacturing method of the group III nitride crystal film described in this embodiment makes it possible to manufacture a gallium nitride substrate having a low dislocation density. Using this gallium nitride substrate, LEDs (Light Emitting Diodes), LDs (Laser Diodes), FETs (Field Effect Transistors), etc. can be fabricated, compared to those fabricated on previous sapphire and SiC substrates. Thus, higher performance functions can be obtained.
[0052]
In the above embodiment, the shape of the mask can be variously changed. For example, in addition to the stripe pattern used in the present embodiment, the same result can be obtained with respect to the reduction of the dislocation density even in the case of a triangle, a quadrangle, and various polygons, circles, ellipses, and the like. However, as in this embodiment, for manufacturing a laser using a stripe-type active layer, a crystalline film in which a region having a low dislocation density exists in a stripe shape is finally preferable.
[0053]
The width of the low dislocation density region is desirably sufficiently wide with respect to the laser stripe width. When the conventional PENDEO or ELO technique is used, the width of the low dislocation density region is about several μm, and the width of the low dislocation region cannot be sufficiently obtained for the laser stripe width of about 2 μm. For this reason, the high dislocation regions existing on both sides of the low dislocation region may affect the laser structure and deteriorate the device characteristics.
[0054]
【Example】
Example 1
In this example, a GaN crystal was grown on a sapphire substrate to obtain a group III nitride free-standing substrate.
[0055]
FIG. 1 shows a schematic cross-sectional view of a production process of a GaN film on a (1000) plane sapphire substrate crystal. A (1000) plane sapphire substrate is used as the substrate 11, and this is used as a base substrate for crystal growth to grow a group III nitride semiconductor layer, thereby obtaining a group III nitride free-standing substrate. In forming the GaN film 12, trimethylgallium (TMGa) is used as a group III material, and ammonia gas (NH is used as a group V material. _Three The metal organic chemical vapor deposition method (MO-VPE method) was used. In addition, SiO ₂ The film 13 is made of disilane (SiH _Four ) And oxygen (O ₂ The opening 14 was formed using a lithography technique. The GaN film 15 is formed by gallium chloride (GaCl), which is a reaction product of gallium (Ga) and hydrogen chloride (HCl), as a group III material, and NH as a group V material. _Three Hydride vapor deposition (HVPE method) using gas was used.
[0056]
Details of the manufacturing process are as follows.
[0057]
First, the growth surface of the sapphire substrate 11 is cleaned and set in the reaction tube of the MO-VPE apparatus. Hydrogen (H ₂ ) And nitrogen (N ₂ ) Using a gas mixture gas, the sapphire substrate 11 is heated to a temperature of about 1050 ° C., heat-treated for about 10 minutes, and then the sapphire substrate 11 is cooled to a temperature of 500 ° C. After the temperature stabilizes, TMGa and NH _Three To form a GaN film having a thickness of 350 nm, and the sapphire substrate 11 is heated again to a temperature of 1050 ° C. NH during temperature rise _Three Supply gas. After the temperature was stabilized, TMG was supplied to form a flattened GaN film 12 having a thickness of about 2 μm. After the GaN film 12 is formed, the supply of TMG is stopped, and the temperature is lowered to room temperature and taken out from the growth apparatus. Next, the sapphire substrate 11 on which the GaN film 12 is formed is made of SiO. ₂ Set in the film forming apparatus. N ₂ When the temperature is raised to 450 ° C. in a gas atmosphere and the temperature stabilizes, SiH _Four Gas and O ₂ A gas is supplied to form a 0.5 μm thick SiO 2 film on the GaN film 12. ₂ A film 13 was formed. SiO ₂ After forming the film 13, SiH _Four Gas and O ₂ The gas supply is stopped, the temperature is lowered to room temperature, and the gas is taken out from the forming apparatus. Next, patterning is performed using a lithography technique, and SiO 2 is formed by wet etching. ₂ Striped openings 14 are formed in the film 13. All the opening widths are 3 μm. SiO between openings ₂ A pattern consisting of six masks each having a width of 5 μm as a film (referred to as a mask) and two masks each having a width of 9 μm on both sides was formed as one cycle, and this pattern was formed on the entire surface of the GaN crystal. The stripe direction of the opening 14 is the <1-100> direction of the GaN film 12 (FIG. 1A).
[0058]
Next, the sapphire substrate 11 in which the opening 14 is formed is set in a reaction tube of a growth apparatus of the HVPE method. H for carrier gas ₂ Using a gas, the sapphire substrate 11 was heated to a temperature of 1040 ° C. while supplying a flow rate of 3000 cc / min. NH of sapphire substrate with flow rate of 1500cc / min from around 600 ° C _Three Gas was added to suppress decomposition of the surface of the GaN film 12 exposed at the opening 14. The Ga source in the reaction tube was heated to a temperature of 850 ° C. After the temperature of the entire reaction tube has stabilized, GaCl generated by reacting by supplying HCl gas at a flow rate of 10 cc / min onto the Ga source is supplied to the growth region, _Three React with gas to grow GaN. The growth of GaN starts from the surface of the GaN film 12 exposed at the opening 14 and grows for about 5 minutes. As shown in FIG. The GaN film 15 having the first facet structure is grown. When the growth is continued, the adjacent facet structures are merged in a growth of about 20 minutes, and a GaN film 15 having a second facet structure having a triangular cross section as shown in FIG. 1C grows. When the growth is further continued for about 120 minutes, adjacent facet structures are united, and a third facet structure (giant facet structure) having a triangular cross section is grown as shown in FIG. In this embodiment, since a wide mask having a width of 9 μm is provided, the third facet structure is stably formed.
Thereafter, the growth is continued by increasing the flow rate of HCl supplied onto the Ga source to 50 cc / min, and the growth is continued until the GaN film 15 having the third facet structure is united and a GaN film 15 having a flat surface appears. It was. The thickness of the planarized GaN film 15 is about 250 μm. After the growth of the GaN film 15, the HCl gas supplied onto the Ga source was stopped and the temperature of the reaction tube was lowered. NH _Three While supplying gas, the substrate was cooled to room temperature, and the substrate was taken out.
[0059]
The group III nitride free-standing substrate obtained as described above was evaluated as follows.
[0060]
Etch pits were measured by etching the surface of the formed GaN film 15 with a mixture of phosphoric acid and sulfuric acid. When the etch pit density was measured at intervals of 10 μm in the <1-100> direction of the GaN film 15, the distribution as shown in FIG. 8 was shown. In the area where the facet structure is formed, the etch pit density is 1.2 × 10 ^Five / Cm ² A low value was obtained. In contrast, in the meeting region of the GaN film 15 having the facet structure having the third cross-sectional triangle shape, 1.5 × 10 5 ⁶ / Cm ² And the dislocation density increased. That is, in the region where the third facet structure (giant facet structure) was formed, a defect density lower by one digit or more was obtained compared to the facet meeting portion. Further, it was found that 50% or more of mixed dislocations in the region with few dislocations.
[0061]
Further, it was found that the tilt angle of the C axis obtained from the (0002) reflection X-ray rocking curve measurement of the growth surface was as small as 80 seconds. Without using the technique of the present invention, the normal ELO pattern (mask width 40 μm, opening width 20 μm) shown in FIG. 13 having a substantially equivalent mask width within the same 60 μm period as in this embodiment is used. In a GaN film grown using the HVPE method for thickness, the dislocation density is 5 × 10 5 on the surface above the opening. ⁷ cm ^-2 3 × 10 on the surface of the mask ⁸ cm ^-2 It was found that the tilt angle was as large as 10 degrees above the mask. Further, due to the inclination of the C axis, a film having a flat surface could not be obtained.
[0062]
Example 2
In this example, a group III nitride semiconductor layer was grown on a GaN substrate as a base substrate for crystal growth to obtain a group III nitride free-standing substrate. The surface dislocation density of the GaN substrate used was 1 × 10 in terms of etch pit density. ⁷ / Cm ² It was about. Hereinafter, a description will be given with reference to FIG.
[0063]
First, the surface of the GaN substrate 21 is treated with an organic solvent or an acid, and the SiO used in Example 1 is used. ₂ 1 μm thick SiO in film forming equipment ₂ A film 22 is formed. Next, the SiO and wet etching techniques are used for SiO. ₂ A part of the film 22 is removed to form an opening 23. The widths of the openings 23 are all 5 μm. SiO between openings ₂ A pattern consisting of four masks each having a width of 5 μm as a film (called a mask) and two masks each having a width of 15 μm on both sides of the mask was formed as one cycle, and this pattern was formed on the entire surface of the GaN crystal. The stripe direction of the opening was a direction inclined by 5 degrees from the <1-100> direction of the GaN film 12 (FIG. 2A).
[0064]
Next, the GaN substrate 21 in which the opening 23 is formed is set in the reaction tube of the HVPE growth apparatus used in Example 1 above. H with a flow rate of 3000cc / min ₂ Gas and N of 500cc / min ₂ The temperature of the GaN substrate 21 is raised while supplying the gas. NH at a flow rate of 2000 cc / min when the substrate region of the reaction tube reaches a temperature of around 600 ° C. _Three Add gas to a temperature of 1060 ° C. The temperature of the Ga source in the reaction tube was raised to 850 ° C. After the temperature in the reaction tube becomes stable, HCl gas at a flow rate of 10 cc / min is supplied onto the Ga source to supply GaCl produced by the reaction to the growth region. _Three The GaN film 24 is grown by reacting with the gas.
[0065]
The GaN film 24 grows from the surface of the GaN substrate 21 in the opening 23. With the growth for about 6 minutes, as shown in FIG. 2B, the GaN film 24 having the first facet structure having a triangular cross section is grown. When the growth is further continued, two to three adjacent first facet structures are merged in a growth of about 35 minutes, and as shown in FIG. 2C, a GaN film having a second facet structure having a triangular cross section. 24 grows. Continue to grow and after 100 minutes of growth, the adjacent second facet structure is 20 μm wide SiO 2 ₂ As shown in FIG. 2D, a third facet structure having a triangular cross section is grown on the film 22. Further, the flow rate of HCl supplied onto the Ga source is increased to 50 cc / min, and NH _Three The growth is continued by reducing the flow rate to 1000 cc / min, and the adjacent third facet structure is united to form a flat GaN film 24 (FIG. 2E). The planarized GaN film 24 was formed to a thickness of 300 μm. After the formation of the GaN film 24, the HCl gas supplied onto the Ga source is stopped and the temperature of the reaction tube is lowered. When the temperature of the reaction tube is around 500 ° C., NH _Three The gas supply was stopped and the system was cooled to room temperature, and the GaN substrate 21 was taken out from the reaction tube.
[0066]
The group III nitride free-standing substrate obtained as described above was evaluated as follows.
[0067]
Etch pit density in the flat region on the GaN film 24 having the third facet structure in which the surface of the formed GaN film 24 is etched with a mixed solution of phosphoric acid and sulfuric acid as in Example 1 and the etch pits are measured. Is 8 × 10 ^Four / Cm ² A low value was obtained.
[0068]
In the present embodiment, the direction of the opening is formed to be inclined by 5 degrees from the <11-00> direction. However, as long as it can be merged after the facet structure having the third cross-sectional triangle shape is formed, it is limited to the above stripe direction. However, the same effect can be obtained even when tilted at an arbitrary angle.
[0069]
Example 3
In this example, a SiC substrate 31 on which a GaN film 32 having a thickness of 5 μm is formed is used as a substrate crystal (FIG. 3), and a group III nitride semiconductor layer is grown by using this as a base substrate for crystal growth. A group nitride free-standing substrate was obtained. Hereinafter, a description will be given with reference to FIG.
[0070]
First, the SiO used in Example 1 was formed on the surface of the GaN film 32. ₂ SiO film with a thickness of 0.2 μm using a film forming apparatus ₂ A film 33 is formed. Next, by lithography and wet etching techniques, SiO ₂ An opening 34 is formed in the film 33. The width of the opening 34 was 2 μm, and the mask width (interval between the openings) was 10 μm, 4 μm, 4 μm, 7 μm, 4 μm, 4 μm, 10 μm,. The stripe direction of the opening 54 was formed to be inclined by 2 degrees in the <1-100> direction of the sapphire substrate 51 (FIG. 5A).
Next, the SiC substrate 31 in which the opening 34 is formed is set in the reaction tube of the HVPE growth apparatus used in the first embodiment. H with a flow rate of 3000cc / min ₂ While supplying the gas, the temperature of the GaN substrate 21 is raised, and the substrate region of the reaction tube is heated from a temperature of about 600 ° C. to a flow rate of 2000 cc / min. _Three Gas is added to reach a temperature of 1050 ° C. The temperature of the Ga source in the reaction tube is raised to 800 ° C. After the temperature in the reaction tube becomes stable, HCl gas at a flow rate of 5 cc / min is supplied onto the Ga source, and GaCl generated by the reaction is supplied to the growth region. _Three Gas is reacted to grow GaN. The growth of GaN is performed from the surface of the GaN film 32 in the opening 34, and is grown for about 10 minutes. As shown in FIG. 3B, the GaN film 35 having the first facet structure having a triangular cross section is formed. grow up. If the growth is further continued, after the adjacent facet structures are merged, a GaN film 35 having a second facet structure having a triangular cross section as shown in FIG. 3C grows. Further, when the growth is continued by increasing the flow rate of HCl supplied onto the Ga source to 50 cc / min, the adjacent facet structures are united and flattened (FIG. 3D). The planarized GaN film 35 was formed to have a thickness of 270 μm. After the formation of the GaN film 35, the HCl gas supplied onto the Ga source is stopped as in the above embodiment, and the temperature of the reaction tube is lowered. When the temperature of the reaction tube is around 500 ° C., NH _Three Stop the gas supply and H at around 200 ℃ ₂ N from gas ₂ The gas was cooled to room temperature and the substrate was taken out from the reaction tube.
[0071]
A group III nitride free-standing substrate was obtained as described above. The obtained substrate was of good crystal quality with few dislocations.
[0072]
Example 4
In this example, a group III nitride semiconductor layer was grown on a GaN substrate as a base substrate for crystal growth to obtain a group III nitride free-standing substrate. The surface dislocation density of the GaN substrate used was 1 × 10 in terms of etch pit density. ⁷ / Cm ² It was about. Hereinafter, a description will be given with reference to FIG.
[0073]
First, after cleaning the surface of the GaN substrate 41, the SiO shown in the above embodiment is used. ₂ 1 μm thick SiO film forming device ₂ A film 42 is formed. Next, SiO ₂ An opening 43 is formed in the film 42. The opening 43 was formed by a lithography technique and a wet etching technique. The opening 43 width is 3 μm and SiO ₂ The width of the film 42 was periodically changed to 4 μm, 6 μm, 4 μm, 8 μm, 4 μm, 6 μm, 4 μm, and 10 μm to form a mask pattern on the entire surface of the GaN substrate 41. The direction of the opening 43 was the <11-20> direction (FIG. 4A).
[0074]
Next, the GaN substrate 41 in which the opening 43 is formed is set in the reaction tube of the growth apparatus of the HVPE method as in the above-described embodiment. H with a flow rate of 2000cc / min ₂ And 1000cc / min N ₂ While supplying the gas, the temperature of the GaN substrate 41 is raised, and the sapphire substrate is NH at a flow rate of 1000 cc / min from around 600 ° C. _Three Gas is added and the temperature is raised to 1020 ° C. The temperature of the Ga source in the reaction tube was raised to 860 ° C. After the temperature in the reaction tube stabilizes, GaCl generated by reacting by supplying HCl gas at a flow rate of 20 cc / min onto the Ga source is supplied to the growth region, and NH _Three React with gas to grow GaN. The growth of GaN occurs from the surface of the GaN substrate 41 in the opening 43. With the growth for about 3 minutes, as shown in FIG. 4B, a GaN film 44 having a first facet structure having a triangular cross section is grown. As the growth continues further, adjacent first facet structures are merged in a growth of about 15 minutes, and a GaN film 44 having a second facet structure having a triangular cross section as shown in FIG. 4C grows. The growth is further continued, and the adjacent second facet structure is merged in the growth for 40 minutes, so that a GaN film 44 having a third facet structure having a triangular cross section as shown in FIG. 4D is grown. Further, the growth is continued, and in the growth for 80 minutes, the adjacent third facet structure is united, and as shown in FIG. 4E, the GaN film 44 having the fourth facet structure having a triangular cross section is grown. To do. Thereafter, the flow rate of HCl supplied onto the Ga source is increased to 70 cc / min, and the growth is continued. The adjacent GaN films 44 having the fourth facet structure are combined to form a flat GaN film 44 (FIG. 4). (F)). The planarized GaN film was formed to a thickness of 350 μm. After the GaN film 44 is formed, the supply of HCl gas is stopped and the temperature of the reaction tube is lowered. Until the temperature of the reaction tube reaches around 500 ° C, NH _Three Supply gas and H around 200 ℃ ₂ N from gas ₂ The sapphire substrate 11 was taken out from the reaction tube after the gas was cooled to room temperature.
[0075]
Etch pits were measured by etching the surface of the formed GaN film 44 with a mixture of phosphoric acid and sulfuric acid in the same manner as in Example 1. In a flat region on the GaN film 44 having the fourth facet structure, the etch pit density is 2 × 10 ^Four / Cm ² A low value was obtained.
[0076]
Example 5
In this example, a GaN crystal was grown on a sapphire substrate to obtain a group III nitride free-standing substrate. Hereinafter, a description will be given with reference to FIG.
[0077]
In this example, a (1000) plane sapphire substrate with the c-axis tilted by 0.15 degrees was used as the substrate. For the formation of the GaN film, trimethylgallium (TMGa) is used as a group III material, and ammonia gas (NH is used as a group V material. _Three The metalorganic chemical vapor deposition method (MO-VPE method) is used. In addition, SiO ₂ For the formation of the film 53, dichlorosilane (SiH _Four ) And oxygen (O ₂ The opening 54 was formed by using a lithography technique.
[0078]
Details of the process will be described below. First, the growth surface of the sapphire substrate 51 is cleaned, and the sapphire substrate 51 is made of SiO. ₂ Set in the film forming apparatus. Sapphire substrate 51 is N ₂ The temperature is raised to 450 ° C. in a gas atmosphere. 0.04% SiH after temperature stabilizes _Four Gas and 0.4% O ₂ A gas is supplied to form a 0.5 μm thick SiO 2 film on the GaN film 52. ₂ A film 53 is formed. SiO ₂ After forming the film 53, SiH _Four Gas and O ₂ The gas supply is stopped, the temperature is lowered to room temperature, and the gas is taken out from the growth apparatus.
[0079]
Next, SiO ₂ An opening 54 is formed in the film 53. The width of the opening 54 was 3 μm, and the mask width (interval between openings) was 3 μm, 5 μm, 3 μm, 7 μm, 3 μm, 5 μm, 3 μm, and 9 μm, respectively. The stripe direction of the opening 54 was formed to be inclined by 2 degrees in the <1-100> direction of the sapphire substrate 51 (FIG. 5A).
[0080]
Next, the sapphire substrate 51 in which the opening 54 is formed is set in the reaction tube of the MO-VPE apparatus. Hydrogen (H ₂ ) And nitrogen (N ₂ ) While supplying the gas mixture gas, the sapphire substrate 51 is heated to a temperature of about 1050 ° C., heat-treated for about 10 minutes, and the sapphire substrate 51 is cooled to a temperature of 520 ° C. After the temperature stabilizes, TMGa and NH _Three To form a GaN film having a thickness of 300 nm. Again, NH _Three The temperature of the sapphire substrate 51 is raised to a temperature of 1050 ° C. while supplying gas. The heating time is about 12 minutes. In this temperature raising step, SiO ₂ The GaN on the film 53 evaporates. After the temperature is stabilized, TMG is supplied to form a GaN film 55 having a facet structure with the (1-101) plane as a side wall on the opening 54 (FIG. 5B).
[0081]
Further, as shown in FIG. 5C, the GaN film 55 having the adjacent facet structure is united to form the GaN film 55 having the second facet structure. Further, the growth is continued, and the adjacent second facet structure is united to form the GaN film 55 having the third facet structure (FIG. 5D).
[0082]
The growth is further continued, and the adjacent third facet structure is united to form the GaN film 55 having the fourth facet structure having the flat surface 56 (FIG. 5E). Thereafter, the supply of TMG was stopped, the temperature was lowered to room temperature, and the TMG was taken out from the growth apparatus. Until the temperature during temperature drop reaches around 500 ° C, NH _Three Gas was supplied.
[0083]
Etch pits were measured by etching the surface of the formed GaN film 55 with a mixture of phosphoric acid and sulfuric acid in the same manner as in Example 1. In the flat region of the GaN film 55 having the fourth facet structure, the etch pit density is 2 × 10 ^Five / Cm ² A low value was obtained.
[0084]
Example 6
In this example, a GaN crystal was grown on a sapphire substrate to obtain a group III nitride free-standing substrate. Hereinafter, a description will be given with reference to FIG.
[0085]
Details of the manufacturing process are as follows. As the substrate, a (1000) plane sapphire substrate 61 inclined by 0.2 degrees was used, trimethyl gallium (TMGa) as the group III material, and ammonia gas (NH) as the group V material. _Three GaN film 62 having a thickness of about 1 μm was formed on the surface by using a metal organic chemical vapor deposition method (MO-VPE method). Next, dichlorosilane (SiH _Four ) And oxygen (O ₂ ) With a thickness of 0.5 μm by thermal CVD using ₂ A film 63 was formed. SiO by dry etching ₂ After providing an opening 64 in the film 63, SiO ₂ Using the film 63 as a mask, the GaN film 62 and the sapphire substrate 61 were dry-etched by 0.5 μm or more (FIG. 6A). Etching gas is Cl ₂ Gas was used. Here, the width of the opening 64 was 4 μm, and the mask width (interval between the openings) was 6 μm, 6 μm, 6 μm, 10 μm, 6 μm, 6 μm, 6 μm, 10 μm,. That is, this pattern was formed on the entire surface of the GaN crystal, with a pattern consisting of three 6 μm wide masks and two 10 μm wide masks on both sides of each mask. The stripe direction of the opening 64 was formed in the <1-100> direction of the sapphire substrate 61.
[0086]
Next, the substrate subjected to the above treatment is set in a reaction tube of an HVPE growth apparatus. H with a flow rate of 2000cc / min ₂ And 1000cc / min N ₂ The temperature of the sapphire substrate 61 is raised while supplying gas, and NH is supplied at a flow rate of 1000 cc / min from around 600 ° C. _Three Gas is added and the temperature is raised to 1020 ° C. The temperature of the Ga source in the reaction tube was raised to 860 ° C. After the temperature in the reaction tube has stabilized, GaCl generated by reacting by supplying HCl gas at a flow rate of 5 cc / min onto the Ga source is supplied to the growth region, and NH _Three React with gas to grow GaN. The growth of GaN is performed from the side wall surface of the GaN film 62 in the trench 65, and the first facet structure made of GaN is grown in the opening as shown in FIG. To do. Next, the flow rate of HCl supplied onto the Ga source is increased to 50 cc / min, and SiH ₂ Cl ₂ When the GaN growth is continued by supplying the gas, as shown in FIG. ₂ A GaN film 66 having a second facet structure having a triangular cross section is grown between the films 63. Further, the growth is continued, and the growth is continued until the adjacent GaN films 66 having a triangular facet structure are combined to form a flat surface GaN film 66 as shown in FIG. After the GaN film 66 having a flat surface is formed, the supply of HCl gas is stopped and the temperature of the reaction tube is lowered. NH _Three While supplying the gas, it was cooled to room temperature, and the sapphire substrate was taken out.
[0087]
Etch pits were measured by etching the surface of the formed GaN film 66 with the mixed solution of phosphoric acid and sulfuric acid used in Example 1 above. In the central region where the GaN film 66 finally forms a facet structure in the <1-100> direction, the etch pit density is 4 × 10 ^Five / Cm ² And a low value was obtained. ¹⁸ / Cm ^Three The carrier concentration was obtained.
[0088]
After the GaN film 66 is formed, the sapphire substrate 61 is removed, and the back surface of the GaN film 66 is planarized by polishing or the like, so that a single GaN substrate 66 can be manufactured. For removal of the sapphire substrate 61, methods such as polishing, laser peeling, and etching can be used.
[0089]
Example 7
In this example, a GaN crystal was grown on a sapphire substrate to obtain a group III nitride free-standing substrate. Hereinafter, a description will be given with reference to FIG.
[0090]
As the substrate, a (1000) plane sapphire substrate 71 inclined by 0.15 degrees was used. A resist film 72 having a thickness of 4 μm or more was formed on the sapphire substrate 71, and an opening 73 was formed in the resist film 72 by a lithography technique.
[0091]
Here, the width of the opening 73 is 4 μm, and the mask width (interval between the openings) is 6 μm, 6 μm, 6 μm, 6 μm, 8 μm, 6 μm, 6 μm, 6 μm, 6 μm, 8 μm,. That is, a mask pattern was prepared with a pattern consisting of four 6 μm wide masks and two 8 μm wide masks on both sides of each as one cycle. The stripe direction of the opening 73 was formed in the <1-100> direction of the sapphire substrate 71 (FIG. 7A).
[0092]
Next, Cl ₂ The surface of the sapphire substrate 71 in the opening 73 was etched by a dry etching method using gas to form a groove 74 having a depth of 4 μm or more (FIG. 7B).
[0093]
Next, the resist film 72 is removed and set in the reaction tube of the MO-VPE apparatus. Hydrogen (H ₂ ) And nitrogen (N ₂ ) While supplying the gas mixture gas, the sapphire substrate 71 is heated to a temperature of about 1070 ° C., heat-treated for about 15 minutes, and the sapphire substrate 71 is cooled to a temperature of 520 ° C. After the temperature stabilizes, TMGa and NH _Three To form a GaN film having a thickness of 250 nm. Again, NH _Three The temperature of the sapphire substrate 71 is raised to a temperature of 1050 ° C. while supplying gas. After the temperature is stabilized, TMG is supplied to grow GaN. As shown in FIG. 7C, the GaN film 75 is formed on the surface of the sapphire substrate 71 and the growth of GaN 76 occurs on the bottom surface of the groove 74 after the growth for 20 minutes.
[0094]
After the GaN film 75 having the facet structure is formed, the supply of TMG is stopped, the temperature is lowered to room temperature, and the substrate is taken out from the growth apparatus. Until the temperature during cooling is around 500 ° C, NH _Three Supply gas.
[0095]
Next, it is set in the reaction tube of the growth apparatus of the HVPE method used in the above embodiment. H for carrier gas ₂ And N ₂ The sapphire substrate 71 is heated to a temperature of 1060 ° C. while supplying a flow rate of 4000 cc / min using a mixed gas (flow rate ratio 1: 2). NH with a flow rate of 1500 cc / min after the sapphire substrate 71 reaches a temperature from around 600 ° C. _Three Supply gas. The Ga source in the reaction tube was heated to a temperature of 840 ° C. After the temperature of the entire reaction tube is stabilized, GaCl generated by reacting by supplying HCl gas at a flow rate of 50 cc / min onto the Ga source is supplied to the growth region, and NH _Three React with gas to grow GaN. In order to dope Si impurities, SiH ₂ Cl ₂ The gas was supplied at a flow rate of 0.015 cc / min. The growth of GaN occurs from the surface of the GaN film 75. The growth of the GaN film at the bottom of the groove 74 is slow, and the state shown in FIG.
[0096]
If the growth is continued, a GaN film 75 including a huge facet structure is formed (FIG. 7D), and then a GaN film 75 having a flat surface is formed when grown for 200 minutes (FIG. 7E). ). The film thickness of the GaN film 75 was flattened to a thickness of 320 μm. After the formation of the GaN film 75, the HCl gas supplied onto the Ga source is stopped and the temperature of the reaction tube is lowered. Until the temperature of the reaction tube reaches around 500 ° C, NH _Three Supply gas and H around 200 ℃ ₂ N from gas ₂ The gas was switched to room temperature and the substrate was taken out.
[0097]
The surface of the formed GaN film 75 was etched with the mixed solution of phosphoric acid and sulfuric acid used in Example 1, and the etch pit was measured. Measurements were made at 10 μm intervals in the <1-100> direction. The GaN film 65 is 2 × 10 at the etch pit density in the central region on the facet structure. ^Five / Cm ² A low value was obtained.
[0098]
In this embodiment, dry etching is used to form the groove of the sapphire substrate 71. However, the same effect can be obtained even when the phosphoric acid-based mixed solution is used.
[0099]
Example 8
In this example, a semiconductor laser structure was produced using the group III nitride free-standing substrate produced in Example 1. Hereinafter, a description will be given with reference to FIG.
[0100]
For the production of the laser structure, metal organic chemical vapor deposition (MO-VPE) using an organic metal as a group III material was used. The group III nitride free-standing substrate produced in Example 1 was set in an MO-CVD apparatus. H ₂ Gas and NH _Three The temperature was raised to 1050 ° C. while supplying the gas. After the temperature was stabilized, an n-type GaN layer 91 having a thickness of 1 μm to which Si was added was formed. Furthermore, 0.4 μm thick n-type Al doped with Si _0.15 Ga _0.85 An N clad layer 92 and a 0.1 μm thick n-type GaN light guide layer 93 to which Si was added were formed. Subsequently, at a temperature of 790 ° C., an undoped In of 2.5 nm thickness _0.2 Ga _0.8 N quantum well layer and 5nm thick undoped In _0.05 Ga _0.95 A three-cycle multi-quantum well structure active layer 94 made of an N barrier layer was formed. Then at a temperature of 1000 ° C
A p-type GaN light guide layer 95 having a thickness of 0.1 μm to which Mg is added;
0.4μm thick p-type Al with Mg added _0.1 Ga _0.9 N clad layer 96,
A p-type GaN contact layer 97 having a thickness of 0.5 μm to which Mg is added;
Were sequentially formed to form a laser element structure (FIG. 9A).
[0101]
After making the laser structure, NH _Three Cooling to a temperature of 500 ° C. while supplying gas, ₂ While supplying gas, it was cooled to room temperature.
[0102]
After cooling, the substrate on which the laser structure has been formed is taken out of the apparatus, and a 0.5 μm thick SiO ₂ A film 98 was formed. Further, an opening 99 having a width of 1.8 μm was formed in a region where the facet structure was formed by lithography. Further, a p-type electrode 100 of palladium (Pd) having a thickness of 50 nm and gold (Au) having a thickness of 0.3 μm is formed on the p-type GaN contact layer 97 of the opening 99, and N ₂ Heat treatment was performed at a temperature of 450 ° C. in a gas atmosphere.
[0103]
Next, the sapphire substrate 11, the GaN film 12, and the GaN film 15 were polished from the back surface so that the total film thickness was about 100 μm. After the polished back GaN film 15 is etched with a phosphoric acid-based solution, an n-electrode 101 made of 50 nm thick Ti and 0.3 μm thick aluminum (Al) is formed (FIG. 9B). Subsequently, the cavity surface of the GaN film 15 was cleaved to form a cavity mirror surface having a laser structure.
[0104]
The semiconductor laser fabricated as described above is oscillated at room temperature (25 ° C.). The threshold was measured. The laser obtained has a threshold current of 20 mA (current density: ~ 3.5 KA / cm). ² ) Good value before and after. Further, the laser lifetime exceeded 5000 hours at 60 ° C. and 30 mW output, and it was confirmed that it was a practical level as a light source for optical disc pickup.
[0105]
It is considered that the reason why the excellent light emission performance was obtained in this example is that dislocations introduced into the laser element structure including the active layer are greatly reduced. In particular, the reduction in edge dislocation is considered to be one of the causes of the improvement in characteristics. As described above, the edge dislocation is a cause of generation of a low-angle grain boundary in the crystal, and light scattering is likely to occur at the low-angle grain boundary. In this example, since the edge dislocations are remarkably reduced in the active layer, it is considered that the laser characteristics are remarkably improved.
[0106]
Example 9
In this example, a GaN substrate was used as a base substrate for crystal growth, and a group III nitride semiconductor layer was grown thereon using various mask patterns to obtain a group III nitride free-standing substrate. The surface dislocation density of the GaN substrate used was 1 × 10 in terms of etch pit density. ⁷ / Cm ² It was about.
[0107]
FIG. 10 is a schematic diagram of the mask pattern used in this example. Both masks are SiO ₂ A film was used, and the film thickness was 0.5 μm.
[0108]
In FIG. 10, SiO ₂ The width of the film 110 is 10 μm and other SiO ₂ The films 112, 113, 114, 115, 116, and 117 were formed so as to be wider than the width. SiO ₂ The distance between the films 110 was 20 μm or more. The width of the opening 111 from which the substrate surface is exposed was set to 1.5 μm or more. SiO ₂ The direction of the film 110 was the <1-100> direction of the underlying GaN substrate.
[0109]
In the mask pattern shown in FIG. ₂ SiO between the films 110 ₂ A film 112 is formed. SiO ₂ The film 112 has a width of 5 μm and a length of 5 μm to 50 μm.
[0110]
In the mask pattern shown in FIG. ₂ SiO between the films 110 ₂ A film 113 is formed. SiO in the horizontal plane of the substrate ₂ The shape of the film 113 is a triangle and a rhombus.
[0111]
In the mask pattern shown in FIG. ₂ SiO between the films 110 ₂ A film 114 is formed. SiO in the horizontal plane of the substrate ₂ The shape of the film 114 is a rectangle including a hollow portion. The width (short side) of the rectangle was about 1 μm.
[0112]
In the mask pattern shown in FIG. ₂ SiO between the films 110 ₂ A film 115 is formed. SiO in the horizontal plane of the substrate ₂ The film 115 is a parallelogram having a width of 5 μm and a length of 20 μm.
[0113]
In the mask pattern shown in FIG. ₂ SiO between the films 110 ₂ A film 116 is formed. SiO in the horizontal plane of the substrate ₂ The film 116 is a triangle having a side of about 7 μm.
[0114]
In the mask pattern shown in FIG. ₂ SiO between the films 110 ₂ A film 117 is formed. SiO in the horizontal plane of the substrate ₂ The film 117 is circular with a diameter of about 10 μm.
[0115]
Next, using the substrate on which the mask patterns having the shapes shown in FIGS. 10A to 10F were formed, the GaN film was epitaxially grown by the HVPE method or the MOVPE method in the same manner as in the above example.
[0116]
In the growth process, a GaN film is grown from the opening 111 to form a facet structure as in the above embodiment. By continuing the growth, the coalescence of adjacent facet structures is repeated, and SiO 2 is formed on the substrate crystal. ₂ A GaN film having a huge triangular facet structure is formed between the films 110. As the growth continues, a GaN film having a flat surface area is formed by combining the GaN films having a huge triangular facet structure.
[0117]
The surface defects of the GaN film formed using each mask pattern were measured. In either case, the etch pit density is 2 × 10 in the region where the huge facet structure is formed. ^Five / Cm ² We were able to reduce to.
[0118]
The present invention has been described above based on the embodiments. Each of the free-standing substrates obtained in Examples 1 to 8 has a structure in which the large facet structure includes a plurality of small small facet structures. The facet structure has a triangular or trapezoidal cross-sectional shape with a base of 20 μm or more, and in the formed group III nitride semiconductor layer, dislocations propagating from the substrate toward the top are substantially horizontal to the substrate. It is bent several times in various directions.
In addition, the self-standing substrates obtained in Examples 1 to 8 above are all observed by etching pits.
(i) Surface average dislocation density of 10 ^-6 cm ^-2 Less than a low dislocation density region is periodically formed in one direction in the substrate horizontal plane.
(ii) The width of the low dislocation density region is 20 μm or more.
(iii) 50% or more of the dislocations included in the low dislocation density region are mixed dislocations.
Was confirmed.
[0119]
Further, when the tilt angle of the low dislocation density region was measured by the method described in Example 1, it was confirmed that all were 1 degree or less.
[0120]
As described above, the present invention has been described based on the embodiments, but the present invention is not limited thereto, and various configurations can be changed.
[0121]
For example, in the above embodiment, 0.5 μm thick SiO as a mask. ₂ A film was used but SiO ₂ Any thickness that can form a facet structure without epitaxially growing GaN on the film may be used. The mask material is also SiO ₂ In addition to the film, SiN (x) film, Al ₂ O _Three A film or the like can be used. Further, the mask opening width and the stripe direction can be appropriately changed.
[0122]
Also, a substrate other than those described in the above embodiment can be used as the base substrate.
[0123]
【The invention's effect】
As described above, according to the present invention, a group III nitride free-standing substrate in which dislocations are remarkably reduced can be obtained. The low dislocation density region formed on this free-standing substrate has a large area, and an element structure can be suitably formed thereon.
[Brief description of the drawings]
FIG. 1 is a process cross-sectional view illustrating an example of a method for manufacturing a self-supporting substrate according to the present invention.
FIG. 2 is a process cross-sectional view illustrating an example of a method for manufacturing a self-supporting substrate according to the present invention.
FIG. 3 is a process cross-sectional view illustrating an example of a method for manufacturing a self-supporting substrate according to the present invention.
FIG. 4 is a process cross-sectional view illustrating an example of a method for manufacturing a self-supporting substrate according to the present invention.
FIG. 5 is a process cross-sectional view illustrating an example of a method for manufacturing a self-supporting substrate according to the present invention.
FIG. 6 is a process cross-sectional view illustrating an example of a method for manufacturing a self-supporting substrate according to the present invention.
FIG. 7 is a process cross-sectional view illustrating an example of a method for manufacturing a self-supporting substrate according to the present invention.
8 is a diagram showing the measurement results of etch pit density in Example 1. FIG.
FIG. 9 is a process cross-sectional view of the method for manufacturing the semiconductor laser shown in the embodiment.
FIG. 10 is a diagram illustrating an example of a mask pattern used in an example.
FIG. 11 is a diagram showing a faceted multiple structure observed by an electron microscope.
FIG. 12 is a schematic diagram showing a state of dislocation bending due to a facet structure;
FIG. 13 is a diagram showing a process of crystal growth by FIELO.
[Explanation of symbols]
11 Sapphire substrate
12 GaN film
13 SiO ₂ film
14 opening
15 GaN film
21 GaN substrate
22 SiO ₂ film
23 opening
24 GaN film
31 SiC substrate
32 GaN film
33 SiO ₂ film
34 opening
35 GaN film
41 GaN substrate
42 SiO ₂ film
43 opening
44 GaN film
51 Sapphire substrate
52 GaN film
53 SiO ₂ film
54 opening
55 GaN film
56 flat surface
61 Sapphire substrate
62 GaN film
63 SiO ₂ film
64 opening
65 groove
66 GaN film
71 Sapphire substrate
72 resist film
72 groove
73 opening
74 Groove
75 GaN film
91 GaN layer
92 Clad layer
93 n-type GaN light guide layer
94 Multiple quantum well structure active layer
95 p-type GaN optical guide layer
96 Clad layer
97 Contact layer
98 SiO ₂ film
99 opening
100 p-type electrode
101 n-type electrode
110 SiO ₂ film
111 opening
112 SiO ₂ film
113 SiO ₂ film
114 SiO ₂ film
115 SiO ₂ film
116 SiO ₂ film
117 SiO ₂ film
201 Sapphire substrate
202 Underlying crystal film
203 Growth area
204 mask
205 Faceted surface
1000 Sapphire substrate
1002 GaN film
1003 Mask
1004 GaN layer
1006 dislocation
1007 Small facet structure
1008 Giant facet structure

Claims (17)

A free-standing substrate including a group III nitride semiconductor layer,
A substrate;
A plurality of first masks extending in a stripe shape formed on the surface of the substrate;
A second mask formed between adjacent first masks and having a plurality of openings;
A plurality of small facet structures formed in the opening;
A facet structure containing the plurality of small facet structures,
The width of the second mask in a direction perpendicular to the stripe direction of the first mask is narrower than the width of the stripe of the first mask,
Facet dislocations propagating toward the top from the substrate in the III nitride semiconductor layer is, the substrate and the horizontal direction, enclosing a facet surface and the small facet structures of said plurality of small facet structure the Rukoto Oremaga in each of the facets of the structure, self-supporting substrate having the group III nitride semiconductor layer is characterized in that it comprises a dislocations are bent multiple times. In the self-supporting substrate according to claim 1 ,
The facet structure has a triangular or trapezoidal cross-sectional shape with a base of 20 μm or more, and is a self-supporting substrate. In the self-supporting substrate according to claim 1 or 2 ,
Said first mask and said second mask, each have a stripe shape extending in the same direction, said second mask and characterized by being formed with a smaller period than the period of the first mask A self-supporting board. In free-standing substrate according to any one of claims 1 to 3,
The stripe direction of the first mask is a [11-20] direction, a [1-100] direction, or a direction that forms a deviation angle within 30 degrees from these directions with respect to the crystal structure of the group III nitride semiconductor. A self-supporting board characterized by that. In free-standing substrate according to any one of claims 1 to 4,
The self-supporting substrate, wherein an interval between the adjacent first masks is 20 μm or more. In free-standing substrate according to any one of claims 1 to 5, a plurality of the small facet structure is periodically formed in the extending direction perpendicular to the direction of the first mask and the second mask A self-supporting board characterized by that. In free-standing substrate according to any one of claims 1 to 6,
A self-supporting substrate comprising a stripe-shaped facet structure whose bottom is a region partitioned by the adjacent first mask. The semiconductor device characterized by claim using the free-standing substrate according to any one of claim 1 to 7 as a substrate, provided with a device structure on the substrate. The semiconductor device according to claim 8 ,
A semiconductor device, wherein the device structure is a laser structure including at least an active layer. A method for manufacturing the self-supporting substrate according to claim 1, comprising:
Forming a plurality of first masks extending in stripes on the substrate surface;
Forming a plurality of openings between adjacent first masks by forming a second mask whose width in the direction perpendicular to the stripe direction of the first mask is narrower than the width of the stripe of the first mask; When,
Grown Oite III nitride semiconductor prior Symbol opening, forming a small facet structure,
Further growing the I II-V nitride semiconductor, forming a full Asetto structure you containing the previous SL small facet structure,
The group III nitride semiconductor is further grown, and dislocations propagating upward from the base material in the group III nitride semiconductor are in a direction parallel to the base material in the small facet structure and the facet structure. Forming multiple dislocations by bending at each facet surface; and
A method for manufacturing a self-supporting substrate, comprising: The method of manufacturing a self-supporting substrate according to claim 10 ,
Said first mask and said second mask, each have a stripe shape extending in the same direction, said second mask and characterized by being formed with a smaller period than the period of the first mask A method for manufacturing a self-supporting substrate. In the method of manufacturing the self-supporting substrate according to claim 10 or 11 ,
The stripe direction of the first mask is a [11-20] direction, a [1-100] direction, or a direction that forms a deviation angle within 30 degrees from these directions with respect to the crystal structure of the group III nitride semiconductor. A method for manufacturing a self-supporting substrate. A method for producing a self-supporting substrate according to any one of claims 10 to 12,
A method for manufacturing a self-supporting substrate, wherein an interval between adjacent first masks is 20 μm or more. A method for manufacturing the self-supporting substrate according to claim 1, comprising:
A width in a direction perpendicular to the stripe direction of the first mask between the plurality of first masks extending in a stripe shape on the substrate surface and the adjacent first mask is larger than the stripe width of the first mask. Forming a mask pattern including a plurality of openings by forming a narrow second mask ; and
And a step of epitaxially growing a group III nitride semiconductor on the base material while forming a facet surface having an acute angle with respect to a horizontal surface of the base material with the opening of the mask pattern as a growth region. A method for manufacturing a substrate. The method of manufacturing a self-supporting substrate according to claim 14 ,
Said first mask and said second mask, each have a stripe shape extending in the same direction, said second mask and characterized by being formed with a smaller period than the period of the first mask A method for manufacturing a self-supporting substrate. A method for manufacturing a self-supporting substrate according to claim 14 or 15 ,
The stripe direction of the first mask is a [11-20] direction, a [1-100] direction, or a direction that forms a deviation angle within 30 degrees from these directions with respect to the crystal structure of the group III nitride semiconductor. A method for manufacturing a self-supporting substrate. A method for producing a self-supporting substrate according to any one of claims 14 to 16,
A method for manufacturing a self-supporting substrate, wherein an interval between adjacent first masks is 20 μm or more.

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