Patent Publication Number: US-2022216368-A1

Title: Semiconductor structure and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0000544, filed on Jan. 4, 2021, in the Korean Intellectual Property Office, and Korean Patent Application No. 10-2021-0029053, filed on Mar. 4, 2021, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties. 
     BACKGROUND 
     1. Field 
     Disclosed example embodiments relate to a semiconductor structure and a method of manufacturing the same. 
     2. Description of Related Art 
     Nitride semiconductors have been applied to electronic and optoelectronic devices. Nitride semiconductors are applicable to a wide range of devices, from laser diodes (LDs) to transistors capable of operating at high frequencies and high temperatures. They are also applicable to ultraviolet light detectors, surface acoustic wave devices, and light-emitting diodes (LEDs). 
     A sapphire substrate is frequently used as a substrate for forming a nitride-based semiconductor device. However, sapphire substrates are expensive and hard, and thus a chip having a sapphire substrate is difficult to manufacture, and has low electrical conductivity. In addition, when a sapphire substrate is epitaxially grown with a large diameter, warpage may occur in the substrate itself at a high temperature due to its low thermal conductivity, and thus it is difficult to manufacture the sapphire substrate in a large area. 
     In order to overcome this limitation, a nitride-based semiconductor device using a silicon substrate instead of a sapphire substrate has been developed. Because silicon substrates have higher thermal conductivity than the sapphire substrates, the degree of warpage in the silicon substrates is not large even at the growth temperature of a nitride thin film that is grown at a high temperature, and accordingly, a large-diameter thin film may be grown. However, when a nitride semiconductor layer is grown on a silicon substrate, the dislocation density increases due to the mismatch in lattice constants between the substrate and a thin film, and cracks occur due to the mismatch in thermal expansion coefficients. Therefore, a method of reducing a defect density and a method of preventing cracks are being studied. 
     In addition, a nitride semiconductor layer (e.g., a micro-LED) having a small size may be manufactured by growing a large-area nitride semiconductor layer and then performing, generally, an etching process. For example, a mask having a preset size may be manufactured, and the nitride semiconductor layer may be etched in a micro unit through a semiconductor process. However, when the nitride semiconductor layer is etched, a leakage current in a lateral surface of the nitride semiconductor layer may be caused due to etching damage. This may cause the properties of the nitride semiconductor layer to deteriorate. 
     SUMMARY 
     Provided are a method of growing a nitride semiconductor layer in a device unit, and a structure of the nitride semiconductor layer. 
     Provided are a method of growing a nitride semiconductor layer while reducing a defect density, and a structure of the nitride semiconductor layer. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented example embodiments of the disclosure. 
     In accordance with an aspect of the disclosure, a method of manufacturing a semiconductor structure includes forming, on a substrate, a sacrificial layer pattern including a plurality of sacrificial layers spaced apart from each other; forming, on the sacrificial layer pattern, a membrane bridge that covers the plurality of sacrificial layers and including an upper surface with a constant height with respect to a surface of the substrate; removing the sacrificial layer pattern from the substrate to form a plurality of cavities defined by the substrate and the membrane bridge; crystallizing the membrane bridge such that the membrane bridge and the substrate have a same crystal structure; and growing a nitride semiconductor layer on the crystallized membrane bridge. 
     A gap between adjacent sacrificial layers of the plurality of sacrificial layers may be less than a width of each of the plurality of sacrificial layers. 
     A gap between adjacent sacrificial layers of the plurality of sacrificial layers may be less than or equal to half of a width of each of the plurality of sacrificial layers. 
     A gap between adjacent sacrificial layers of the plurality of sacrificial layers may be about 500 nm or less. 
     The plurality of cavities may be in contact with the substrate. 
     The membrane bridge may include a plurality of first regions wherein each of the plurality of first regions overlaps a respective sacrificial layer of the plurality of sacrificial layers in a thickness direction of the substrate; and a plurality of second regions that do not overlap any of the plurality of sacrificial layers in the thickness direction of the substrate. 
     Each of the plurality of second regions may fill a respective space between adjacent sacrificial layers of the plurality of sacrificial layers. 
     A width of each of the plurality of second regions may be less than a thickness of the plurality of first regions. 
     A width of the plurality of first regions may be about 1 μm or less. 
     Each of the plurality of second regions may include a first sub-region and a second sub-region, wherein a first end of the first sub-region is spaced apart from a first end of the second sub-region, wherein the first end of the first sub-region and the first end of the second sub-region are in contact with the substrate, and wherein a second end of the first sub-region is in contact with a second end of the second sub-region. 
     For each second region of the plurality of second regions, a second cavity may be formed between the first sub-region and the second sub-region. 
     For each first region of the plurality of first regions, a width of a corresponding cavity of the plurality of cavities may decrease from the first region toward the substrate. 
     A size of each of the plurality of second cavities may be less than a size of each of the plurality of cavities. 
     The membrane bridge may include at least one of silica (SiO2), alumina (Al2O3), titania (TiO2), zirconia (ZrO2), yttria (Y2O3)-zirconia, copper oxide (CuO, Cu2O), tantalum oxide (Ta2O5), aluminum nitride (AlN), and silicon nitride (Si3N4). 
     In accordance with an aspect of the disclosure, a semiconductor structure includes a substrate; a membrane bridge that defines, with the substrate, a plurality of cavities, wherein the membrane bridge and the substrate have a same crystal structure and the membrane bridge includes an upper surface with a constant height with respect to a surface of the substrate; and a nitride semiconductor layer arranged on the membrane bridge. 
     The membrane bridge may include a plurality of first regions wherein each of the plurality of first regions overlaps a respective cavity of the plurality of cavities in a thickness direction of the substrate; and a plurality of second regions that do not overlap any of the plurality of cavities in the thickness direction of the substrate. 
     A width of each of the plurality of first regions may be greater than a width of each of the plurality of second regions. 
     A width of each of the plurality of second regions may be less than a thickness of each of the plurality of first regions. 
     Each of the plurality of second regions may include a first sub-region and a second sub-region, wherein a first end of the first sub-region is spaced apart from a first end of the second sub-region, wherein the first end of the first sub-region and the first end of the second sub-region are in contact with the substrate, and wherein a second end of the first sub-region is in contact with a second end of the second sub-region. 
     For each second region of the plurality of second regions, a second cavity may be arranged between the first sub-region and the second sub-region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain example embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram illustrating a structure including a nitride semiconductor according to an embodiment; 
         FIG. 2A  to  FIG. 2E  are diagrams illustrating a method of manufacturing a semiconductor structure, according to an embodiment; 
         FIG. 3A  and  FIG. 3B  are diagrams schematically illustrating defects of a nitride semiconductor layer grown on a plurality of membranes; 
         FIG. 4  is a diagram illustrating a semiconductor structure according to an embodiment; 
         FIGS. 5A to 5D  are diagrams illustrating a method of manufacturing a light-emitting diode by using a semiconductor structure, according to an embodiment; 
         FIG. 6A  is a diagram illustrating a light-emitting diode according to an embodiment; 
         FIG. 6B  is a diagram illustrating a light-emitting diode according to an embodiment; 
         FIG. 7  is a diagram illustrating a display device including a nitride semiconductor layer according to an embodiment; and 
         FIG. 8  is a diagram illustrating a display device according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, embodiments are merely described below, by referring to the figures, to explain aspects. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. The described embodiments are merely examples, and various modifications are possible from these embodiments. In the following drawings, like reference numerals refer to like elements, and sizes of elements in the drawings may be exaggerated for clarity and convenience of description. 
     An expression “above” or “on” used herein may include not only “immediately on in a contact manner” but also “on in a non-contact manner”. 
     Terms such as “first” or “second” may be used to describe various elements, but the elements should not be limited by the terms. The terms do not define that the elements have different materials or structures from each other. 
     An expression used in the singular encompasses the expression of the plural, unless it has a clearly different meaning in the context. In addition, when an element “includes” or “comprises” an element, unless there is a particular description contrary thereto, the element can further include other elements, not excluding the other elements. 
     The term “the” and other demonstratives similar thereto should be understood to include a singular form and plural forms. 
     The operations of a method can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. In addition, all example terms (e.g., “such as” or “etc.”) are used for the purpose of description and are not intended to limit the scope of the present disclosure unless defined by the claims. 
       FIG. 1  is a diagram illustrating a structure  100  including a nitride semiconductor according to an embodiment. As illustrated in  FIG. 1 , the structure  100  including a nitride semiconductor may include a substrate  110 , a membrane bridge  130  that defines, with the substrate  110 , a plurality of cavities C, and a nitride semiconductor layer  150  on the membrane bridge  130 . 
     The substrate  110  may be a monocrystalline substrate of a heterogeneous material used to grow a heterogeneous epitaxial layer of the nitride semiconductor layer  150 , such as a sapphire substrate, a silicon substrate, a SiC substrate, or a GaAs substrate 
     The membrane bridge  130  and the substrate  110  may define the plurality of cavities C to be separate from each other. That is, a part of each cavity C may be defined by the substrate  110 , and the remaining part of each cavity C may be defined by the membrane bridge  130 . 
     The membrane bridge  130  may include first regions  131  having lower surfaces defining the cavities C, respectively, and second regions  132  having lower surfaces in contact with the substrate  110 . Upper surfaces of the first regions  131  and the second regions  132  may have a preset height H with respect to a surface of the substrate  110  as shown, e.g., in  FIG. 1 . Accordingly, an upper surface of the membrane bridge  130  may have the same height H across its entirety. 
     A thickness t of the first region  131  may be less than a thickness of the substrate  110  and may be less than a thickness of the nitride semiconductor layer  150  that will be described below. A width w 1  of the first region  131  may be greater than or equal to a width w 2  (hereinafter, also referred to as the gap w 2 ) of the second region  132 . For example, the thickness t of the first region  131  may be about 500 nm or less, and the width w 1  of the first region  131  may be 1 μm or less. In addition, the width w 2  of the second region  132  may be 500 nm or less. 
     The membrane bridge  130  may include at least one of oxide or nitride, such as silica (SiO2), alumina (Al2O3), titania (TiO2), zirconia (ZrO2), yttria (Y2O3)-zirconia, copper oxide (CuO, Cu2O), tantalum oxide (Ta2O5), aluminum nitride (AlN), or silicon nitride (Si3N4). By adjusting at least one of the composition, strength, and thickness t of the membrane bridge  130 , it is possible to regulate stress applied to the nitride semiconductor layer  150  subsequently formed on a structure using the membrane bridge  130 . 
     The nitride semiconductor layer  150  may be arranged on the upper surface of the membrane bridge  130 . For example, the nitride semiconductor layer  150  may include a first semiconductor layer  151 , an active layer  152 , and a second semiconductor layer  153 . 
     The first semiconductor layer  151  may include, for example, an n-type semiconductor. However, the disclosure is not limited thereto, and in some cases, the first semiconductor layer  151  may include a p-type semiconductor. The first semiconductor layer  151  may include a III-V group n-type semiconductor, for example, n-GaN. The first semiconductor layer  151  may have a single-layer or multi-layer structure. For example, the first semiconductor layer  151  may include any one semiconductor material of InAlGaN, GaN, AlGaN, InGaN, AlN, or InN, and may include a semiconductor layer doped with a conductive dopant such as Si, Ge, or Sn. 
     The active layer  152  may be arranged on an upper surface of the first semiconductor layer  151 . The active layer  152  may generate light as electrons combine with holes, and may have a multi-quantum well (MQW) structure or a single-quantum well (SQW) structure. The active layer  152  may include a III-V group semiconductor, for example, InGaN, GaN, AlGaN, or AlInGaN. 
     The second semiconductor layer  153  may be provided on the active layer  152 , and may include a semiconductor layer of a different type from the first semiconductor layer  151 . For example, the second semiconductor layer  153  may include a p-type semiconductor layer. The second semiconductor layer  153  may include, for example, InAlGaN, GaN, AlGaN, and/or InGaN, and may be a semiconductor layer doped with a conductive dopant such as Mg. 
     In addition to the first semiconductor layer  151 , the active layer  152 , and the second semiconductor layer  153 , the nitride semiconductor layer  150  may further include a clad layer and/or a buffer layer on and/or under each layer. 
     The nitride semiconductor layer  150  may be grown directly on the membrane bridge  130 . 
       FIG. 2A  to  FIG. 2E  are diagrams illustrating a method of manufacturing the semiconductor structure  100 , according to an embodiment. 
     Referring to  FIG. 2A , a sacrificial layer pattern  120  may be formed on the substrate  110 . The sacrificial layer pattern  120  may include a plurality of sacrificial layers  122  spaced apart from each other. A thickness and a width of the sacrificial layer pattern  120  may be determined considering the cavities C to be finally formed. The gap w 2  between the sacrificial layers  122  may be less than the width w 1  of the sacrificial layer  122 . For example, the gap w 2  between the sacrificial layers  122  may be less than or equal to half of the width w 1  of the sacrificial layer  122 , or may be 1 μm or less. Because the gap w 2  between the sacrificial layers  122  is narrow, the material of the membrane bridge  130  may fill the gap w 2  between the sacrificial layers  122  when the membrane bridge  130  is formed in a subsequent process. 
     The sacrificial layer pattern  120  may be uniformly formed entirely on the substrate  110  in the same pattern. The sacrificial layer pattern  120  may be of a line-and-space type, and may have a shape extending in the y-axis direction or the x-axis direction on the substrate  110 . However, the sacrificial layer pattern  120  is not limited thereto. The sacrificial layer pattern  120  may be formed on the substrate  110  in a locally different pattern. 
     The sacrificial layer pattern  120  may be formed by various methods such as photolithography, nanoimprinting, or organic nanoparticle attachment. As described above, the method of forming the sacrificial layer pattern  120  according to an embodiment is relatively simple, and the degree of damage to the substrate  110  is relatively low and the process may be simplified compared to the case of etching the substrate  110  by conventional technology such as a patterned sapphire substrate (PSS). 
     Any monocrystalline substrate of a heterogeneous material used to grow a heterogeneous epitaxial layer of the nitride semiconductor layer  150 , such as a sapphire, silicon, SiC, or GaAs substrate, may be used for the substrate  110  on which the sacrificial layer pattern  120  is formed. 
     Referring to  FIG. 2B , the membrane bridge  130  that covers the sacrificial layer pattern  120  may be formed on the sacrificial layer pattern  120 . The membrane bridge  130  may be formed by various methods such as atomic layer deposition (ALD), wet synthesis, metal deposition and oxidation, or sputtering. The membrane bridge  130  may be a seed for growing the nitride semiconductor layer  150 . 
     The thickness t of the membrane bridge  130  (see, e.g.,  FIG. 1 ) may be about 20 nm to about 100 nm, and the thickness t thereof may be an important factor that defines crystallographic properties because of a correlation with a thickness of a semiconductor layer to be grown in a subsequent process. 
     The membrane bridge  130  subsequently defines the cavities C with the substrate  110 , and may be formed within a range of temperatures at which the sacrificial layer pattern  120  is not deformed. The thickness t of the membrane bridge  130  may be determined such that the structure thereof stably maintains its original shape after the sacrificial layer pattern  120  is removed. In order for the cavities C to be structurally stable on the substrate  110 , it is advantageous that a part of the membrane bridge  130  is in direct contact with the substrate  110  when the membrane bridge  130  is formed. 
     The membrane bridge  130  may include the first regions  131  that overlap the sacrificial layers  122 , respectively, in the thickness direction of the substrate  110  and the second regions  132  that do not overlap the sacrificial layers  122  in the thickness direction of the substrate  110 . As the upper surfaces of the first regions  131  and the upper surfaces of the second regions  132  have the same height H with respect to a surface of the substrate  110 , the nitride semiconductor layer  150  that is to be grown on the membrane bridge  130  may have similar defect densities on the first and second regions  131  and  132 . 
     The second regions  132  may be in direct contact with the substrate  110  such that the membrane bridge  130  maintains its shape even after the sacrificial layers  122  are removed. The width w 2  of the second region  132  may be less than or equal to the width w 1  of the first region  131 , and may be less than or equal to the thickness t of the first region  131 . As it may be difficult to separate the nitride semiconductor layer  150  from the substrate  110  in the case where the width w 2  of the second region  132  is large, the width w 2  of the second region  132  may be 500 nm or less. 
     The membrane bridge  130  may be an amorphous material. For example, the membrane bridge  130  may include at least one of oxide or nitride, such as amorphous silica (SiO2), alumina (Al2O3), titania (TiO2), zirconia (ZrO2), yttria (Y2O3)-zirconia, copper oxide (CuO, Cu2O), tantalum oxide (Ta2O5), aluminum nitride (AlN), or silicon nitride (Si3N4). It is preferable to form an alumina membrane bridge on a sapphire substrate. By adjusting at least one of the composition, strength, and thickness t of the membrane bridge  130 , it is possible to regulate stress applied to the nitride semiconductor layer  150  subsequently formed on a structure using the membrane bridge  130 . As illustrated in  FIG. 2B , the membrane bridge  130  may be formed on the entire surface of the substrate  110  while covering the sacrificial layer pattern  120 . 
     Alumina may be applied with a uniform thickness t on the substrate  110  and the sacrificial layer pattern  120  by a deposition method such as ALD. Wet synthesis using a wet solution may be used instead of the deposition method. The wet solution may be uniformly coated on the substrate  110  and the sacrificial layer pattern  120 , and then alumina may be synthesized by heating, drying, or a chemical reaction. For example, an alumina thin film may be coated on the substrate  110  by mixing an aluminum precursor powder such as aluminum chloride (AlCl3) with a solvent such as tetrachloroethylene (C2Cl4), applying and coating the mixture on the substrate  110  on which the sacrificial layer pattern  120  is formed, and heating the mixture under an oxygen atmosphere to cause a reaction. Alternatively, alumina may be formed by depositing a metal Al thin film by a method such as sputtering, and then performing an oxidation process. The alumina may be formed in an amorphous state or in a polycrystalline state of fine grains. 
     As illustrated in  FIG. 2C , the sacrificial layer pattern  120  may be removed from the substrate  110 . Because the sacrificial layer pattern  120  is a polymer such as a photosensitive film, a resin for nanoimprinting, or organic nanoparticles, it may be easily removed by a heating method. The photosensitive film having an autoignition temperature of about 600° C. may be easily removed by heat. Furthermore, for easier removal by burning in an oxidation manner, a chemical reaction with gas including oxygen may be added. When it is heated at high temperature under an oxygen atmosphere, polymer components may be easily removed by a thermal decomposition process, commonly called ashing. For example, the sacrificial layer pattern  120  may be removed by heat treatment under an oxygen atmosphere. In the case where the heat treatment under an oxygen atmosphere is improper, for example, in the case where the substrate  110  is a silicon substrate, and there is a concern about oxide generation, wet removal using an organic solvent may be used. After the sacrificial layer pattern  120  is removed, the cavities C defined by the substrate  110  and the membrane bridge  130  may be formed as illustrated in  FIG. 2C . Although the plurality of cavities C are formed in an example embodiment separated from each other, the shape of the cavities may vary depending on the shape of the previously formed sacrificial layer pattern  120 . The cavities C may have an inverse shape of the sacrificial layer pattern  120 . 
     The membrane bridge  130  formed on the sacrificial layer  122  is generally amorphous or has a polycrystalline structure of fine grains. After the cavities C are formed by removing the sacrificial layer pattern  120 , as illustrated in  FIG. 2D , heat treatment may be performed on the membrane bridge  130 . Accordingly, the amorphous or polycrystalline membrane bridge  130  may be crystallized. 
     The heat treatment for removing the sacrificial layer pattern  120  and the heat treatment on the membrane bridge  130  may be performed by gradually increasing the temperature or by a continuous process. In the case where the membrane bridge  130  is formed of the same material as the substrate  110  as in the case where the substrate  110  is a sapphire substrate and the membrane bridge  130  is alumina, when heated to, for example, about 1000° C., the membrane bridge  130  may be transformed into a structure having the same crystallographic direction as that of the substrate  110 , and thus may become the crystallized membrane bridge  130 . 
     Accordingly, an interface (indicated by dashed lines in the drawings) between the crystallized membrane bridge  130  and the substrate  110  may disappear. This is because, during the high-temperature heat treatment, the substrate  110  is in direct contact with the membrane bridge  130 , and solid-phase epitaxial growth occurs at the membrane bridge  130 , and thus the crystallization occurs in the crystallographic direction of the substrate  110 . The solid-phase epitaxy starts from the interface between the substrate  110  and the membrane bridge  130 , and, in the case where the membrane bridge  130  is amorphous, the finally crystallized membrane bridge  130  may become polycrystalline, or fine polycrystals may become larger in size or may be preferably changed into a single crystal like the substrate  110 . 
     Such crystallization may occur over at least a part, in particular the entirety, of the membrane bridge  130 . Because portions of the crystallized membrane bridge  130  on the cavities C subsequently act as seed portions when the epitaxial layer of the nitride semiconductor is grown, the portions of the membrane bridge  130  on the cavities C need to be crystallized. The upper surface of the membrane bridge  130  may be a substrate of the nitride semiconductor layer  150 . 
     Next, as illustrated in  FIG. 2E , the nitride semiconductor layer  150  may be further formed on the crystallized membrane bridge  130 . A width of the nitride semiconductor layer  150  may be determined based on the size of the membrane bridge  130 . For example, the width of the nitride semiconductor layer  150  may be greater than the width of the membrane bridge  130 . In addition, because the size of the membrane bridge  130  is determined depending on the number of sacrificial layers  122 , the width of the nitride semiconductor layer  150  may be estimated from the number of sacrificial layers  122  in the membrane bridge  130 . 
     The nitride semiconductor layer  150  may be formed in a multi-layer structure. The nitride semiconductor layer  150  may include the first semiconductor layer  151 , the active layer  152 , and the second semiconductor layer  153  (see, e.g.,  FIG. 1 ). The nitride semiconductor layer  150  may include a nitride semiconductor material such as GaN, InN, AlN, or GaxAlyInzN (0&lt;x, y, z&lt;1), which is a combination thereof. A band gap may be adjusted according to a material type of the nitride semiconductor layer  150  to emit light in the ultraviolet, visible, and infrared ranges. In this case, for the nitride semiconductor layer  150 , a seed may not grow from the substrate  110 , but may grow from the crystallized membrane bridge  130 . By adjusting the deposition temperature, the pressure and flow rate of gas, or the like, the nitride semiconductor layer  150  may be grown on the crystallized membrane bridge  130 . 
     In the case where the nitride semiconductor layer  150  is grown on the membrane bridge  130  as described above to manufacture a light-emitting diode, the following advantages may be obtained. First, as the membrane bridge  130  serves as a compliant substrate, the nitride semiconductor layer  150  is grown while stress is relieved, and thus, the nitride semiconductor layer  150  having various properties may be grown. Second, because the growing nitride semiconductor layer  150  naturally grows into a core-shell structure to cover both ends of the semiconductor layer, a single nitride semiconductor layer that may be independently used may be grown on a single membrane bridge  130  without an etching process. Therefore, it is not necessary to etch both ends of the semiconductor layer, and it is possible to prevent a reduction in the current injection efficiency due to etching damage. Third, although defects in the membrane bridge  130  and the nitride semiconductor layer  150  are inevitably caused by a lattice difference, because the nitride semiconductor layer  150  is laterally grown on the membrane bridge  130 , the defect density may be reduced. 
     When the nitride semiconductor layer  150  is grown on one membrane bridge  130  rather than on a plurality of patterns, line defects may be also reduced. 
       FIG. 3A  and  FIG. 3B  are diagrams schematically illustrating defects of the nitride semiconductor layer  150  grown on a plurality of membranes. 
     As illustrated in  FIG. 3A , a nitride semiconductor layer  251  is grown on each of a plurality of membranes  231 . While each portion of the nitride semiconductor layers  251  is laterally grown, as shown in  FIG. 3B , the portions are merged into one nitride semiconductor layer  250 . There is a possibility that more defects may be generated at the boundaries where the growing portions of the nitride semiconductor layer  251  are merged. 
     As illustrated in  FIG. 3B , the defects at the boundaries where the laterally growing portions are merged are clearly oriented and occur at the entire interfaces unlike the defects that occur on the membrane  231 , and thus may be referred to as line defects. Even in the case where the nitride semiconductor layer  250  has a low overall defect density, the line defects are likely to cause a reduction in the internal quantum efficiency or leakage in current injection. 
     However, because the nitride semiconductor layer  150  according to an embodiment is grown on a single membrane bridge  130 , line defects do not occur. Therefore, the nitride semiconductor layer  150  according to an embodiment may prevent current leakage due to a line defect. 
     In addition, the nitride semiconductor layer  250  as shown in  FIG. 3B  may be grown not only on the upper surfaces of the membranes on the cavities C, but also on lateral surfaces of the membranes on lateral surfaces of the cavities C or on regions of the membranes on the substrate  110 . A nitride semiconductor layer grown from the lateral surfaces of the membranes on the lateral surfaces of the cavities C or from the regions of the membranes on the substrate  110  may be referred to as a parasitic nitride semiconductor layer. The parasitic nitride semiconductor layer may be in contact with the nitride semiconductor layer  250 , and may require an additional process to be removed from the nitride semiconductor layer  250 , or may degrade the performance of the nitride semiconductor layer  250 . 
     Because the nitride semiconductor layer  150  according to an embodiment grows on a single membrane bridge  130 , the growth of a parasitic nitride semiconductor layer may be prevented. 
     In addition, one nitride semiconductor layer  150  may be formed on one membrane. As the width of the nitride semiconductor layer  150  is determined based on the width of the membrane, in the case where the size of the nitride semiconductor layer  150  is in micro units, it is preferable that the width of the membrane is also in micro units. In the case where the membrane is formed on the sacrificial layers  122  and then the sacrificial layers  122  are removed, the membrane may sag because the thickness of the membrane is low, and the width of the membrane is large. In this case, the nitride semiconductor layer  150  may not be formed on the same crystal plane. 
     The membrane bridge  130  according to an embodiment may include three or more second regions  132  that are in contact with the substrate  110 , and the upper surfaces of the first regions  131  and the second regions  132  may constitute a flat surface having the same height H with respect to the substrate  110 . Thus, the entirety of the upper surface of the membrane bridge  130  has the same crystal plane. Because the membrane bridge  130  according to an embodiment does not sag, the nitride semiconductor layer  150  may be formed on the same crystal plane of the membrane bridge  130 . 
     The crystallized membrane bridge  130  according to an embodiment may distribute and relieve stress with the nitride semiconductor layer  150  being grown thereon and thus serve as a compliant layer, and the nitride semiconductor layer  150  may be grown while the stress that may cause dislocation is relieved and thus achieve high quality with a low defect density. 
     Because of the presence of the cavities C, in the case where there is a difference in thermal expansion coefficient between the substrate  110  and the nitride semiconductor layer  150  formed thereon, the cavities C may be locally deformed, for example, stretched or compressed in a direction, thereby eliminating stress energy. Accordingly, thermal stress applied to the nitride semiconductor layer  150  may be reduced, and thus, warpage of the substrate  110  may be suppressed. 
     In particular, because the cavities C may be controlled by adjusting the shape, size, two-dimensional arrangement, or the like of the sacrificial layer pattern  120 , the optical properties, for example, the emission pattern, of an LED manufactured from the semiconductor structure  100  may be adjusted. In addition, because the sacrificial layer pattern  120  is formed by a controlled method such as etching or nanoimprinting, the cavities C are also formed by a controlled method rather than being formed irregularly or randomly, and thus, reproducibility and device uniformity are excellent. 
     Meanwhile, when the nitride semiconductor layer  150  is grown on the substrate  110 , the nitride semiconductor layer  150  and the substrate  110  are joined to each other at the atomic level, and accordingly, a special process such as laser lift-off is required to separate the nitride semiconductor layer  150  from the substrate  110 . In an embodiment, because the membrane bridge  130  is between the substrate  110  and the nitride semiconductor layer  150 , the membrane bridge  130  and the nitride semiconductor layer  150  may be easily separated from each other by collapsing the membrane bridge  130  with a small mechanical force without performing laser lift-off. Because the nitride semiconductor layer  150  may be separated by a small mechanical force such as a tensile force or a compressive force, the nitride semiconductor layer  150  may be separated from the substrate  110  without warpage, cracking, or chipping. 
     Accordingly, it is advantageous in the field of applications where the separation of the substrate  110  and the nitride semiconductor layer  150  is necessary, for example, the manufacture of a vertical LED, a horizontal LED, or a LED transferred to a certain substrate, and the substrate  110  may be reused. 
       FIG. 4  is a diagram illustrating a semiconductor structure  100   a  according to an embodiment. Comparing  FIG. 1  with  FIG. 4 , the semiconductor structure  100   a  of  FIG. 4  may include first cavities C 1  having a width that narrows toward the substrate  110 . The first cavity C 1  may be formed by using a sacrificial layer having a width that narrows toward the substrate  110 . 
     A membrane bridge  330  may include first regions  331  having lower surfaces defining the first cavities C 1 , respectively, and second regions  332  having lower surfaces in contact with the substrate  110 . Upper surfaces of the first regions  331  and the second regions  332  may have a preset height with respect to a surface of the substrate  110 . Accordingly, an upper surface of the membrane bridge  330  may have the same height H across its entirety. 
     The second region  332  may include first and second sub-regions  332   a  and  332   b  having lower regions (e.g., lower ends) spaced apart from each other and upper regions (e.g., upper ends) in contact with each other. A second cavity C 2  may be formed between the first and second sub-regions  332   a  and  332   b.  The second cavity C 2  may be formed when the membrane bridge  330  is formed. A size of the second cavity C 2  may be less than the size of the first cavity Cl. By forming the membrane bridge  330  by using a reverse sacrificial layer, the membrane bridge  330  having a smaller thickness t may be formed. 
     The semiconductor structure  100   a  of  FIG. 4  may be manufactured by the same method as the method of manufacturing the semiconductor structure  100  of  FIG. 1 . However, their sacrificial layer patterns have different structures, and the semiconductor structure  100   a  of  FIG. 4  may further include the second cavities C 2 . 
       FIGS. 5A to 5D  are diagrams illustrating a method of manufacturing a light-emitting diode by using the semiconductor structure  100 , according to an embodiment. 
     As illustrated in  FIG. 5A , the semiconductor structure  100 , in which the membrane bridge  130  and the nitride semiconductor layer  150  are sequentially formed on the substrate  110 , may be prepared. Because the method of manufacturing the semiconductor structure  100  has been described above, a detailed description thereof will be omitted. 
     As illustrated in  FIG. 5B , an insulating layer  160  and a first electrode  170  may be formed on the nitride semiconductor layer  150 . The insulating layer  160  may surround at least a part of an upper region and a lateral region of the nitride semiconductor layer  150 . The insulating layer  160  may include a hole h 1  that exposes a partial portion of the nitride semiconductor layer  150 . The insulating layer  160  may include at least one of oxide or nitride, such as silica (SiO2), alumina (Al2O3), titania (TiO2), zirconia (ZrO2), yttria (Y2O3)-zirconia, copper oxide (CuO, Cu2O), tantalum oxide (Ta2O5), aluminum nitride (AlN), or silicon nitride (Si3N4). 
     The second semiconductor layer  153  of the nitride semiconductor layer  150 , exposed by the hole h 1 , may be an n-type or p-type semiconductor layer. The first electrode  170  may be arranged on the insulating layer  160 . The first electrode  170  may be in electrical contact with the nitride semiconductor layer  150  through the hole h 1  of the insulating layer  160 . The first electrode  170  may include Al, Au, Pt, Mo, Cu, Ag, and/or Zn. The insulating layer  160  may be omitted according to the structure of the light-emitting diode. 
     As illustrated in  FIG. 5C , the nitride semiconductor layer  150 , on which the first electrode  170  is formed, may be transferred to another substrate  410  (hereinafter, referred to as the “transfer substrate”  410 ). For example, the first electrode  170  may be bonded to the transfer substrate  410 , and then the nitride semiconductor layer  150  and the substrate  110  may be separated from each other by applying a mechanical force. For example, the substrate  110  and the nitride semiconductor layer  150  may be separated from each other by collapsing the second regions  132  of the membrane bridge  130  by applying a tensile force, a compressive force, a rotating force, or the like to the membrane bridge  130 . 
     After removing the remaining membrane bridge  130 , as illustrated in  FIG. 5D , a second electrode  180  may be formed on the nitride semiconductor layer  150 . As a result, the light-emitting diode may be manufactured. The second electrode  180  may include a conductive material, and may be the same material as the first electrode  170  or may include a different material therefrom. One light-emitting diode  400  may be manufactured from a single semiconductor structure  100  without performing an etching process, and thus, performance deterioration due to the etching process may be improved. 
       FIG. 6A  is a diagram illustrating a light-emitting diode  400   a  according to an embodiment. As illustrated in  FIG. 6A , in the light-emitting diode  400   a,  only a part of the membrane bridge  130  is removed, and a partial membrane bridge  130   a  remains on the nitride semiconductor layer  150 . For example, a hole h 2  may be formed in the partial membrane bridge  130   a  to expose the nitride semiconductor layer  150 . Then, a second electrode  180   a  may be formed to be in electrical contact with the nitride semiconductor layer  150 . Because the partial membrane bridge  130   a  is also an insulating material, the partial membrane bridge  130   a  may prevent leakage current from the nitride semiconductor layer  150 . 
       FIG. 6B  is a diagram illustrating a light-emitting diode  400   b  according to an embodiment. As illustrated in  FIG. 6B , a first semiconductor layer of a nitride semiconductor layer  150   a  may include an uneven structure. A second electrode  180   b  may be arranged on the uneven structure. The uneven structure may increase a light emission area and increase a critical angle of light emission, thereby improving the light emission efficiency of the light-emitting diode. Although  FIG. 6B  illustrates that the surface of the first semiconductor layer of the nitride semiconductor layer  150   a  has an uneven structure, the disclosure is not limited thereto. A surface of the second semiconductor layer of the nitride semiconductor layer  150  may also have an uneven structure. 
       FIG. 7  is a diagram illustrating a part of a display device including a nitride semiconductor layer according to an embodiment. Referring to  FIG. 7 , a display device  500  may include a substrate  510  on which a plurality of pixels are provided. One pixel may include a first sub-pixel SP 1 , a second sub-pixel SP 2 , and a third sub-pixel SP 3  provided on the substrate  510 . 
     The first to third sub-pixels SP 1 , SP 2 , and SP 3  may be sub-pixel regions that display an image in one pixel and may be light emission regions from which light is emitted. 
     Each of the first to third sub-pixels SP 1 , SP 2 , and SP 3  may include the substrate  510 , a driving element layer  520 , a display element layer  530 , and a cover structure layer  540 . 
     The substrate  510  may include an insulating material such as glass, an organic polymer, quartz, or the like. In addition, the substrate  510  may be formed of a flexible material so as to be bendable or foldable, and may have a single-layer structure or a multi-layer structure. 
     The driving element layer  520  may include a buffer layer  521  arranged on the substrate  510 , a thin film transistor (TFT) arranged on the buffer layer  521 , and a driving voltage wiring. 
     The buffer layer  521  may prevent impurities from diffusing into the transistor TFT. The buffer layer  521  may be provided as a single layer, or may be provided as at least two layers. 
     In the case where the buffer layer  521  is provided as multiple layers, the layers may be formed of the same material or different materials. The buffer layer  521  may be omitted according to the material and process conditions of the substrate  510 . 
     The transistor TFT may drive a corresponding light-emitting diode LD among a plurality of light-emitting diodes LD 1 , LD 2 , and LD 3  included in the display element layer  530 . The transistor TFT may include a semiconductor layer SC, a gate electrode G, a source electrode S, and a drain electrode D. 
     The semiconductor layer SC may be arranged on the buffer layer  521 . The semiconductor layer SC may include a source region in contact with the source electrode S and a drain region in contact with the drain electrode D. A region between the source region and the drain region may be a channel region. 
     The semiconductor layer SC may be a semiconductor pattern formed of polysilicon, amorphous silicon, an oxide semiconductor, or the like. The channel region may be a semiconductor pattern that is not doped with impurities, and may be an intrinsic semiconductor. The source region and the drain region may be semiconductor patterns doped with impurities. 
     The gate electrode G may be provided on the semiconductor layer SC with a gate insulating layer  522  therebetween. 
     The source electrode S and the drain electrode D may be in contact with the source region and the drain region of the semiconductor layer SC, respectively, through a contact hole penetrating an interlayer insulating layer  523  and the gate insulating layer  522 . 
     A protective layer  524  may be provided on the transistor TFT. 
     The display element layer  530  may include the plurality of light-emitting diodes LD 1 , LD 2 , and LD 3  provided on the protective layer  524 . For example, the light-emitting diode LD 1  of the first sub-pixel SP 1  may emit red light, the light-emitting diode LD 2  of the second sub-pixel SP 2  may emit green light, and the light-emitting diode LD 3  of the third sub-pixel SP 3  may emit blue light. The wavelength of emitted light may be changed by adjusting the In content in a process of manufacturing the light-emitting diodes LD 1 , LD 2 , and LD 3 . 
     In  FIG. 7 , the nitride semiconductor layer  150  illustrated in  FIG. 1  is illustrated as each of the light-emitting diodes LD 1 , LD 2 , and LD 3 . Alternatively, any one of the light-emitting diodes LD 1 , LD 2 , and LD 3  of the first to third sub-pixels SP 1 , SP 2 , and SP 3 , respectively, may have any one of the semiconductor structures  100 ,  100   a.    
     The display element layer  530  may further include pixel defining layers  531 . The pixel defining layers  531  may be provided on the protective layer  524 , and may define the light emission regions in the first to third sub-pixels SP 1 , SP 2 , and SP 3 , respectively. The pixel defining layers  531  may include openings exposing the light-emitting diodes LD 1 , LD 2 , and LD 3  included the first to third sub-pixels SP 1 , SP 2 , and SP 3 , respectively. 
     Two adjacent pixel defining layers  531  may be spaced apart from each other by a preset gap on the substrate  510 . For example, two adjacent pixel defining layers  531  may be spaced apart from each other on the substrate  510  by a gap greater than or equal to the length of the light-emitting diodes LD 1 , LD 2 , and LD 3 . The pixel defining layer  531  may be, but is not limited to, an insulating material including an inorganic material or an organic material. 
     The pixel defining layer  531  may be an insulating material including an organic material. For example, the pixel defining layer  531  may include polystyrene, polymethylmethacrylate (PMMA), polyacrylonitrile (PAN), polyamide (PA), polyimide (PI), polyarylether (PAE), a heterocyclic polymer, parylene, epoxy, benzocyclobutene (BCB), a siloxane-based resin, a silane-based resin, or the like. 
     First insulating layers  532   a  may be provided on the pixel defining layers  531 . Each of the first insulating layers  532   a  may cover a part of an upper surface of each of the light-emitting diodes LD 1 , LD 2 , and LD 3  provided in the first to third sub-pixels SP 1 , SP 2 , and SP 3 , respectively. A first end and a second end of each of the light-emitting diodes LD 1 , LD 2 , and LD 3  may be exposed to the outside by the first insulating layer  532   a.    
     First and second electrodes E 1  and E 2  may be arranged on the protective layer  524 . The first electrode E 1  may include a first sub-electrode EL 1  arranged adjacent to one end (e.g., the first semiconductor layer) of the corresponding light-emitting diode LD, and a first contact electrode CNE 1  that electrically connects the first sub-electrode EL 1  to the one end of the light-emitting diode LD. The second electrode E 2  may include a second sub-electrode EL 2  arranged adjacent to the other end (e.g., the second semiconductor layer) of the corresponding light-emitting diode LD, and a second contact electrode CNE 2  that electrically connects the second sub-electrode EL 2  to the other end of the light-emitting diode LD. 
     Accordingly, a driving voltage may be applied to the corresponding light-emitting diode LD through the first electrode E 1 , and a voltage of the transistor TFT may be applied to the corresponding light-emitting diode LD through the second electrode E 2 . As a result, as certain voltages are applied to both ends of the light-emitting diode LD through the first electrode E 1  and the second electrode E 2 , the light-emitting diode LD may emit light. The wavelength of emitted light may vary depending on the content of In of the light-emitting diode. 
     A second insulating layer  532   b  and a third insulating layer  532   c  may be provided on the first and second electrodes E 1  and E 2 . 
     An overcoat layer  540  may be provided on the third insulating layer  532   c . The overcoat layer  540  may be a planarization layer that mitigates undulations formed by the elements arranged below the overcoat layer  540 . In addition, the overcoat layer  540  may be an encapsulation layer that prevents oxygen, moisture, or the like from penetrating into the light-emitting diodes. 
     In the case where the light-emitting diodes LD 1 , LD 2 , and LD 3  of the sub-pixels SP 1 , SP 2 , and SP 3  emit light of the same wavelength, the display device may further include a color conversion layer. The color conversion layer may include first to third color conversion patterns. Here, each of the first to third color conversion patterns may correspond to one sub-pixel. For example, the first color conversion pattern may correspond to the first sub-pixel SP 1 , the second color conversion pattern may correspond to the second sub-pixel SP 2 , and the third color conversion pattern may correspond to the third sub-pixel SP 3 . 
       FIG. 8  is a diagram illustrating a part of a display device according to an embodiment. Comparing  FIG. 7  with  FIG. 8 , a first semiconductor layer, an active layer, and a second semiconductor layer of a light-emitting diode LD illustrated in  FIG. 8  may be arranged in parallel to the thickness direction of the substrate  510 . 
     The display device including the light-emitting diodes described above may be employed in various electronic devices. For example, the display device may be applied to a television, a notebook, a mobile phone, a smartphone, a smart pad, a portable multimedia player (PMP), a personal digital assistant (PDA), a navigation system, various wearable devices such as a smart watch, or the like. 
     It has been described that the nitride semiconductor layers  150  and  150   a  included in the semiconductor structure may be used as components of a light-emitting device or a display device. However, the disclosure is not limited thereto. The nitride semiconductor layers  150  and  150   a  included in the semiconductor structure  100  according to an embodiment may be also used as light detection elements. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims and their equivalents.