Patent Publication Number: US-2023139447-A1

Title: Semiconductor devices having asymmetrical structures

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/180,989, filed on Feb. 22, 2021, which claims benefit of priority, under 35 U.S.C. § 119, to Korean Patent Application No. 10-2020-0088637, filed on Jul. 17, 2020 in the Korean Intellectual Property Office, the disclosure of each of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates to semiconductor devices. 
     As demand for high performance, high speed, multifunctionality, and the like, in semiconductor devices increases, a degree of integration of semiconductor devices is increasing. In manufacturing a semiconductor device having a fine pattern corresponding to the trend of a high degree of integration of the semiconductor device, patterns having a fine width or a fine spacing distance may be implemented. In addition, in order to overcome limitations of operation characteristics due to a reduction in a size of a planar metal oxide semiconductor FET (MOSFET), efforts are being made to develop semiconductor devices including a FinFET having a three-dimensional channel. 
     SUMMARY 
     An aspect of the present inventive concepts is to provide semiconductor devices having improved reliability. 
     According to some example embodiments, a semiconductor device may include a substrate including first and second active regions extending in a first direction and isolated from direct contact with each other in the first direction. The semiconductor device may include a device isolation layer in a trench region of the substrate between the first and second active regions, and including a liner layer and an isolation insulating layer, the liner layer between an inner wall that at least partially defines the trench region and the isolation insulating layer. The semiconductor device may include a plurality of channel layers on the first and second active region, respectively, and isolated from direct contact with each other in a vertical direction perpendicular to the first direction. The semiconductor device may include gate structures extending in a second direction on the substrate and intersecting the first and second active regions and the plurality of channel layers. Each of the gate structures may include a gate electrode surrounding the plurality of channel layers. The second direction may be different from the first direction. The first direction and the second direction may both be parallel to an upper surface of the substrate. The semiconductor device may include source/drain regions on the first and second active regions on at least one side of each of the gate structures, and contacting the plurality of channel layers. The semiconductor device may include contact plugs connected to the source/drain regions. The gate structures may include first and second gate structures respectively intersecting end portions of the first and second active regions contacting the device isolation layer, the first gate structure including a first gate electrode, the second gate structure including a second gate electrode. The first gate structure and the second gate structure may have an asymmetrical disposition with respect to the device isolation layer, such that first gate structure and the second gate structure do not have reflective symmetry with respect to each other in the first direction. 
     According to some example embodiments, a semiconductor device may include a substrate including first and second active regions extending in a first direction and isolated from direct contact with each other in the first direction, a device isolation layer between the first and second active regions in the substrate, and first and second gate structures extending in a second direction on the substrate while respectively intersecting end portions of the first and second active regions. The first gate structure may include a first gate electrode. The second gate structure may include a second gate electrode. The second direction may be different from the first direction. The first direction and the second direction may both be parallel to an upper surface of the substrate. The first gate structure may protrude further toward the device isolation layer as compared to the second gate structure in a vertical direction that is perpendicular to the first and second directions, and a lower end of the first gate electrode may be located on a lower height level than a lower end of the second gate electrode. 
     According to some example embodiments, a semiconductor device may include a substrate including first and second active regions extending in a first direction and isolated from direct contact with each other in the first direction, a device isolation layer between the first and second active regions in the substrate, the device isolation layer including a liner layer and an isolation insulating layer, sequentially stacked, gate structures extending in a second direction on the substrate and intersecting the first and second active regions, and source/drain regions on the first and second active regions on at least one side of each of the gate structures. The gate structures may include a first gate structure intersecting an end portion of the first active region contacting the device isolation layer and including a first gate electrode, a second gate structure intersecting an end portion of the second active region contacting the device isolation layer and including a second gate electrode, and a third gate structure isolated from direct contact with the device isolation layer and including a third gate electrode. The first gate structure may have a shape, different from shapes of the second and third gate structures, and the second gate electrode may have a width, different from a width of the third gate electrode in the first direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of the present inventive concepts will be more clearly understood from the following detailed description, taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a plan view illustrating a semiconductor device according to some example embodiments. 
         FIGS.  2 A and  2 B  are cross-sectional views illustrating a semiconductor device according to some example embodiments. 
         FIG.  3    is a partially enlarged view illustrating a portion of a semiconductor device according to some example embodiments. 
         FIGS.  4 A and  4 B  are plan and cross-sectional views illustrating a semiconductor device according to some example embodiments. 
         FIGS.  5  and  6    are cross-sectional views illustrating a semiconductor device according to some example embodiments. 
         FIGS.  7 A and  7 B  are cross-sectional views illustrating a semiconductor device according to some example embodiments. 
         FIGS.  8 A and  8 B  are plan and cross-sectional views illustrating a semiconductor device according to some example embodiments. 
         FIGS.  9 A,  9 B,  9 C,  9 D,  9 E,  9 F,  9 G, and  9 H  are views illustrating a process sequence for explaining a method of manufacturing a semiconductor device according to some example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, example embodiments of the present disclosure will be described with reference to the accompanying drawings. 
     It will be understood that elements and/or properties thereof (e.g., structures, surfaces, directions, or the like), which may be referred to as being “perpendicular,” “parallel,” “coplanar,” or the like with regard to other elements and/or properties thereof (e.g., structures, surfaces, directions, or the like) may be “perpendicular,” “parallel,” “coplanar,” or the like or may be “substantially perpendicular,” “substantially parallel,” “substantially coplanar,” respectively, with regard to the other elements and/or properties thereof. 
     Elements and/or properties thereof (e.g., structures, surfaces, directions, or the like) that are “substantially perpendicular” with regard to other elements and/or properties thereof will be understood to be “perpendicular” with regard to the other elements and/or properties thereof within manufacturing tolerances and/or material tolerances and/or have a deviation in magnitude and/or angle from “perpendicular,” or the like with regard to the other elements and/or properties thereof that is equal to or less than 10% (e.g., a. tolerance of ±10%)). 
     Elements and/or properties thereof (e.g., structures, surfaces, directions, or the like) that are “substantially parallel” with regard to other elements and/or properties thereof will be understood to be “parallel” with regard to the other elements and/or properties thereof within manufacturing tolerances and/or material tolerances and/or have a deviation in magnitude and/or angle from “parallel,” or the like with regard to the other elements and/or properties thereof that is equal to or less than 10% (e.g., a. tolerance of ±10%)). 
     Elements and/or properties thereof (e.g., structures, surfaces, directions, or the like) that are “substantially coplanar” with regard to other elements and/or properties thereof will be understood to be “coplanar” with regard to the other elements and/or properties thereof within manufacturing tolerances and/or material tolerances and/or have a deviation in magnitude and/or angle from “coplanar,” or the like with regard to the other elements and/or properties thereof that is equal to or less than 10% (e.g., a. tolerance of ±10%)). 
     It will be understood that elements and/or properties thereof may be recited herein as being “the same” or “equal” as other elements, and it will be further understood that elements and/or properties thereof recited herein as being “the same” as or “equal” to other elements may be “the same” as or “equal” to or “substantially the same” as or “substantially equal” to the other elements and/or properties thereof. Elements and/or properties thereof that are “substantially the same” as or “substantially equal” to other elements and/or properties thereof will be understood to include elements and/or properties thereof that are the same as or equal to the other elements and/or properties thereof within manufacturing tolerances and/or material tolerances. Elements and/or properties thereof that are the same or substantially the same as other elements and/or properties thereof may be structurally the same or substantially the same, functionally the same or substantially the same, and/or compositionally the same or substantially the same. 
     It will be understood that elements and/or properties thereof described herein as being the “substantially” the same encompasses elements and/or properties thereof that have a relative difference in magnitude that is equal to or less than 10%. Further, regardless of whether elements and/or properties thereof are modified as “substantially,” it will be understood that these elements and/or properties thereof should be construed as including a manufacturing or operational tolerance (e.g., ±10%) around the stated elements and/or properties thereof. 
     When the terms “about” or “substantially” are used in this specification in connection with a numerical value, it is intended that the associated numerical value include a tolerance of ±10% around the stated numerical value. When ranges are specified, the range includes all values therebetween such as increments of 0.1%. 
     As described herein, an element that is “on” another element may be above, beneath, and/or horizontally adjacent to the other element. Additionally, an element that is “on” another element may be directly on the other element such that the elements are in direct contact with each other or may be indirectly on the other element such that the elements are isolated from direct contact with each other. 
       FIG.  1    is a plan view illustrating a semiconductor device according to some example embodiments. 
       FIGS.  2 A and  2 B  are cross-sectional views illustrating a semiconductor device according to some example embodiments.  FIGS.  2 A and  2 B  are cross-sectional views of the semiconductor device of  FIG.  1    taken along cut lines I-I′ and II-II. For convenience of description, only major components of a semiconductor device are illustrated in  FIGS.  1 ,  2 A , and  2 B. 
       FIG.  3    is a partially enlarged view illustrating a portion of a semiconductor device according to some example embodiments.  FIG.  3    is an enlarged view illustrating portion ‘A’ of  FIG.  2 A . 
     Referring to  FIGS.  1  to  3   , a semiconductor device  100  may include a substrate  101 , first and second active regions  105 A and  105 B on the substrate  101  (e.g., on, including being direct on, the upper surface of the substrate  101 ), channel structures  140  including a plurality of channel layers  141 ,  142 , and  143  arranged perpendicularly to the first and second active regions  105 A and  105 B, respectively, and spaced apart from each other, gate structures  160  intersecting the first and second active regions  105 A and  105 B and extending in a direction (e.g., the y direction, also referred to herein as a second direction), source/drain regions  150  contacting the plurality of channel layers  141 ,  142 , and  143 , and contact plugs  180  connected to the source/drain regions  150 . The semiconductor device  100  may further include a device isolation region IR including a device isolation layer  110 , internal spacer layers  130 , and an interlayer insulating layer  190 . The gate structures  160  may include a gate dielectric layer  162 , a gate electrode  165 , gate spacer layers  164 , and a gate capping layer  166 , respectively. 
     It will be understood that elements described herein to be “spaced apart” from each other may be interchangeably referred to as being isolated from direct contact with each other (e.g., by one or more interposing structures and/or spaces). 
     As shown in at least  FIGS.  1 - 2 A , in the semiconductor device  100 , the first and second active regions  105 A and  105 B may each extend in a first direction (e.g., the x direction), for example such that the length of each of the first and second active regions  105 A and  105 B in the first direction (e.g., x direction, is greater than the length of the first and second active regions  105 A and  105 B in a perpendicular direction (e.g., the y direction). The first direction (e.g., x direction) and a second direction (e.g., y direction) may each be parallel to an upper surface of the substrate  101 . The first and second active regions  105 A and  105 B may be spaced apart from each other (e.g., isolated from direct contact with each other) in the same first direction (e.g., the x direction). In the semiconductor device  100 , the first and second active regions  105 A and  105 B may have a fin structure, and the gate electrode  165  may be disposed between the first and second active regions  105 A and  105 B and the channel structures  140 , between the plurality of channel layers  141 ,  142 , and  143  of the channel structures  140 , and on the channel structure  140 . Therefore, the semiconductor device  100  may include a transistor having a multi-bridge channel field effect transistor (MBCFET) structure, which may be a gate-all-around type field effect transistor. 
     The substrate  101  may have an upper surface extending in x and y directions. The substrate  101  may include a semiconductor material, such as a group IV semiconductor, a group III-V compound semiconductor, or a group II-VI compound semiconductor. For example, the group IV semiconductor may include silicon, germanium, or silicon-germanium. The substrate  101  may be provided as a bulk wafer, an epitaxial layer, a silicon on insulator (SOI) layer, a semiconductor on insulator (SeOI) layer, or the like. 
     The device isolation region IR may define the first and second active regions  105 A and  105 B in the substrate  101 . The device isolation region IR may be formed by, for example, a shallow trench isolation (STI) process. According to some example embodiments, the device isolation region IR may further include a region having a step difference in a lower portion of the substrate  101  and extending deeper thereinto. The device isolation region IR may expose upper surfaces of the first and second active regions  105 A and  105 B, and may partially expose upper portions of the first and second active regions  105 A and  105 B. In some example embodiments, the device isolation region IR may have a curved upper surface to have a higher height level, as the device isolation region IR is adjacent to the first and second active regions  105 A and  105 B. 
     The device isolation region IR may include a liner layer  112  and an isolation insulating layer  114 . The liner layer  112  may be located along an inner wall of a trench in which the device isolation region IR is located, and may have a relatively thin thickness, as compared to the isolation insulating layer  114 . The liner layer  112  may be, for example, a layer for curing an exposed surface of the substrate  101  (which may include an exposed portion of the upper surface of the substrate  101 ) after the trench is formed. The liner layer  112  may include an insulating material different from the isolation insulating layer  114 , and may include, for example, silicon nitride or silicon oxynitride. The isolation insulating layer  114  may be stacked on the liner layer  112 , and may be disposed to fill the trench. The trench may be referred to as a trench region of the substrate  101 , such that the inner wall may be understood to at least partially define the trench region. In some example embodiments, the exposed surface of the substrate  101  may define at least a portion of the inner wall. As a result, the device isolation layer  110  may be understood to be in a trench region of the substrate  101  (e.g., in trench as defined at least in part by the inner wall and in some example embodiments further defined by the exposed surface) between the first and second active regions  105 A and  105 B, where the device isolation layer includes the liner layer  112  and the isolation insulating layer  114 , where the liner layer  112  and the isolation insulating layer  114  are sequentially stacked, for example as shown in  FIGS.  2 A and  2 B , such that the liner layer  112  may be between (e.g., directly between and directly contact each of) the inner wall and the isolation insulating layer  114 . The isolation insulating layer  114  may include, for example, a silicon oxide. 
     The device isolation layer  110  may refer to a region of the device isolation region IR. As illustrated in  FIG.  1   , the device isolation layer  110  may refer to a region of the device isolation region IR located between the first and second active regions  105 A and  105 B (e.g., between the first and second active regions  105 A and  105 B in the substrate  101 ). For example, the device isolation layer  110  may refer to a region located between the first and second active regions  105 A and  105 B in a direction in which the first and second active regions  105 A and  105 B extend, for example, in the x direction. The device isolation layer  110  may electrically isolate the first and second active regions  105 A and  105 B from direct contact with each other. 
     The device isolation layer  110  may have an asymmetrical disposition with respect to a center along the x direction, for example such that the device isolation layer  110  does not have reflectional symmetry (also referred to as line symmetry, reflective symmetry, or mirror symmetry) in the x direction, and/or does not have reflectional symmetry across a y-z plane CP extending through the device isolation layer  110  at a position in the x direction that is between (e.g., equidistant in the x direction between) the first and second active layers  105 A and  105 B. The y-z plane CP may be understood to extend through, and thus represent the center along the x direction, of the device isolation layer  110 . Specifically, in the device isolation layer  110 , both upper end portions of the liner layer  112  may be located on different height levels. As shown in  FIG.  2 A , for example, an upper end portion of the liner layer  112  adjacent to a second gate structure  160 B (second end portion  112 B) may be located on a higher height level (e.g., height distance in the z direction from the substrate  101  and/or upper surface of the substrate  101 ) than an upper end portion of the liner layer  112  adjacent to a first gate structure  160 A (first end portion  112 A). Accordingly, both (e.g., opposite) end portions of the liner layer  112  in the x direction may be located on different height levels. This shape may be formed according to asymmetrical dispositions of the first and second gate structures  160 A and  160 B in an upper portion of the liner layer  112 , which will be described below. 
     As illustrated in the enlarged view of  FIG.  3   , a corner of the second active region  105 B contacting the end portion of the liner layer  112  may have a rounded shape. This shape may be formed according to, for example, a process of forming the liner layer  112 . The liner layer  112  may have a shape such that a lateral surface of the liner layer  112  contacting the isolation insulating layer  114  is obliquely extended and connected to an upper surface of the liner layer  112 , to reduce a width of the liner layer  112  as being closer to the end portion of the liner layer  112 . For example, the liner layer  112  may have an upper surface inclined toward the second active region  105 B in the second end portion  112 B. The liner layer  112  may have a similar shape in an end portion on the other side contacting the first active region  105 A (e.g., first end portion  112 A), but is not limited thereto. For example, as shown in  FIG.  2 A , one end portion of the liner layer (e.g., one of the first or second end portions  112 A or  112 B) has an upper surface inclined toward the first or second active region  105 A or  105 B. Additionally, as shown in  FIGS.  2 A and  3   , at least one active region of the first active region  105 A or the second active region  105 B, contacting one end portion of the liner layer  112 , may have a rounded corner. 
     The first and second active regions  105 A and  105 B may be defined by the device isolation region IR in the substrate  101 , and may be disposed to extend in a first direction, for example, in the x direction. The first and second active regions  105 A and  105 B may be disposed to be spaced apart from each other and side by side, with the device isolation layer  110  interposed therebetween, in the x direction. 
     The first and second active regions  105 A and  105 B may have a structure protruding from the substrate  101 . According to some example embodiments, upper ends of the first and second active regions  105 A and  105 B may be disposed to protrude from the upper surface of the device isolation layer  110  to a predetermined height. For example, in  FIG.  2 B , the liner layer  112  may be disposed to cover a lateral surface of the first active region  105 A, but an arrangement of the liner layer  112  is not limited thereto. For example, the liner layer  112  may be located to partially expose the lateral surface of the first active region  105 A. Further, according to some example embodiments, corners of an upper end of the first active region  105 A illustrated in  FIG.  2 B  may also have rounded shapes. 
     The first and second active regions  105 A and  105 B may be formed as a portion of the substrate  101 , or may include an epitaxial layer grown from the substrate  101 . On both sides of the gate structures  160 , the first and second active regions  105 A and  105 B on the substrate  101  may be partially recessed, and the source/drain regions  150  may be disposed on the recessed first and second active regions  105 A and  105 B. In some example embodiments, the first and second active regions  105 A and  105 B may include impurities. 
     The channel structures  140  may include the first to third channel layers  141 ,  142 , and  143 , which may be a plurality of, e.g., two or more channel layers arranged to be spaced apart from each other, in a direction, perpendicular to the upper surfaces of the first and second active regions  105 A and  105 B, for example in a vertical direction perpendicular to the direction in which the first and second active regions  105 A and  105 B extend, for example, in the z direction on the first and second active regions  105 A and  105 B. As shown in  FIGS.  2 A and  2 B , the first to third channel layers  141 ,  142 , and  143  may at least partially (or entirely) overlap with each other in the vertical direction (e.g., the z direction), also referred to herein as being at least partially aligned with each other in the vertical direction, and the first to third channel layers  141 ,  142 , and  143  may be isolated from direct contact with each other in the same vertical direction (e.g., z direction). The first to third channel layers  141 ,  142 , and  143  may be connected to the source/drain regions  150  and may be spaced apart from the upper surfaces of the first and second active regions  105 A and  105 B at the same time. The first to third channel layers  141 ,  142 , and  143  may have the same width as or a width similar to the first and second active regions  105 A and  105 B in the y direction, and may have the same width as or a width similar to the gate structure  160  in the x direction. According to some example embodiments, the first to third channel layers  141 ,  142 , and  143  may have a reduced width such that lateral surfaces of the first to third channel layers  141 ,  142 , and  143  are located below the gate structure  160  in the x direction. 
     The first to third channel layers  141 ,  142 , and  143  may be made of a semiconductor material, and may include at least one of silicon (Si), silicon germanium (SiGe), or germanium (Ge). The first to third channel layers  141 ,  142 , and  143  may be made of the same material as the substrate  101 , for example. According to some example embodiments, the first to third channel layers  141 ,  142 , and  143  may include an impurity region located in a region adjacent to the source/drain regions  150 . The number and shape of the channel layers  141 ,  142 , and  143  constituting a single channel structure  140  may be variously changed in some example embodiments. For example, according to some example embodiments, the channel structure  140  may further include a channel layer disposed on the upper surfaces of the first and second active regions  105 A and  105 B. 
     The source/drain regions  150  may be disposed on the first and second active regions  105 A and  105 B on both sides of the channel structure  140 . The source/drain regions  150  may be disposed to cover a lateral surface of each of the first to third channel layers  141 ,  142 , and  143  of the channel structure  140  and the upper surfaces of the first and second active regions  105 A and  105 B. The source/drain region  150  may be disposed in a region in which upper portions of the first and second active regions  105 A and  105 B are partially recessed, but in some example embodiments, whether or not a recess is formed and, when present, a depth of the recess may be variously changed. Upper surfaces of the source/drain regions  150  may be located on the same height level or a height level similar to lower surfaces of the gate structures  160 , and may be variously changed in some example embodiments. According to some example embodiments, the source/drain regions  150  may be connected to each other or may be merged on two or more active regions adjacent in the y direction, to form a single source/drain region  150 . 
     The source/drain regions  150  may be formed as an epitaxial layer, and may include impurities. For example, the source/drain regions  150  may be a semiconductor layer including silicon (Si) or silicon germanium (SiGe), and may include impurities of different types and/or concentrations depending on regions of the source/drain regions  150 . 
     The gate structures  160  may be disposed on (e.g., directly on) the first and second active regions  105 A and  105 B and the channel structures  140 , to intersect (e.g., overlap in the z direction) the first and second active regions  105 A and  105 B and the channel structures  140  and may extend in a second direction, for example, in the y direction. As shown, the second direction may be different from (e.g., perpendicular) to the first direction (e.g., x direction) in which the first and second active regions  105 A and  105 B extend, and both the first and second directions (e.g., x and y directions) may be parallel to the substrate  101  and/or a upper surface of the substrate  101 , and the vertical direction (e.g., z direction) may be perpendicular to the first and second directions and/or may be perpendicular to the substrate  101  and/or an upper surface of the substrate  101 . Channel regions of transistors may be formed in the first and second active regions  105 A and  105 B and/or the channel structures  140 , intersecting the gate electrode  165  of the gate structure  160 . 
     The gate structures  160  may include first to third gate structures  160 A,  160 B, and  160 C. As illustrated in  FIG.  1   , the first gate structure  160 A may intersect (e.g., overlap in the z direction) an end portion of the first active region  105 A adjacent to the second active region  105 B, and the second gate structure  160 B may intersect (e.g., overlap in the z direction) an end portion of the second active region  105 B adjacent to the first active region  105 A. The end portions may be in contact with the device isolation layer  110  (e.g., in contact with the device isolation layer  110  in the first direction, or x direction). The third gate structures  160 C may be located to be spaced apart from end portions of the first and second active regions  105 A and  105 B and may be located to be isolated from direct contact with the device isolation layer  110 . The first to third gate structures  160 A,  160 B, and  160 C may have different shapes. As shown in  FIGS.  2 A- 2 B , the first to third gate structures  160 A,  160 B, and  160 C may each include a gate electrode  165  that surrounds the channel layers  141 ,  142 , and  143 , for example at least surrounding the channel layers  141 ,  142 , and  143  in the z direction (e.g., the vertical direction) and the y direction (e.g., the second direction) as shown. For example, as shown in  FIG.  2 B , a gate electrode  165  of the third gate structure  160 C may surround the channel layers  141 ,  142 , and  143  in the z direction and the y direction (e.g., in a y-z plane). As further shown in at least  FIGS.  1  and  2 A , the source/drain regions  150  are on the first and second active regions  105 A and  105 B on at least one side of each of the first to third gate structures  160 A to  160 C, and the source/drain regions  150  are contacting (e.g., in direct contact with) the plurality of channel layers (e.g., channel layers  141 ,  142 , and  143 ). 
     The first and second gate structures  160 A and  160 B may have different widths, intersecting each of the first and second active regions  105 A and  105 B. For example, the gate electrode  165  of the first gate structure  160 A may overlap the first active region  105 A (e.g., overlap in the z direction) by a first length L1 in the x direction, and the gate electrode  165  of the second gate structure  160 B may overlap the second active region  105 B (e.g., overlap in the z direction) by a second length L2, longer than the first length L1 in the x direction. The first length L1 may be, for example, in a range of about 30% to 80% of an entire width of the gate electrode  165  of the first gate structure  160 A in the x direction. The first gate structure  160 A may protrude from an end portion of the first active region  105 A toward the device isolation layer  110  in the x direction by a first distance D1, and the second gate structure  160 B may protrude from an end portion of the second active region  105 B toward the device isolation layer  110  in the x direction by a second distance D2, shorter than the first distance D1. The first and second gate structures  160 A and  160 B may be adjacent to the device isolation layer  110 . At least a portion of each of the first and second gate structures  160 A and  160 B may be in contact with the device isolation layer  110 . 
     As illustrated in  FIG.  2 A , the first gate structure  160 A and the second gate structure  160 B may have an asymmetrical disposition with respect to the device isolation layer  110 , for example such that the first and second gate structures  160 A and  160 B do not have mirrored shapes in the x direction, have shapes that do not have reflectional symmetry (also referred to as line symmetry, reflective symmetry, mirror symmetry, etc.) with respect to each other in the x direction, and/or have shapes that do not have reflectional symmetry across a y-z plane CP extending through the device isolation layer  110  at a position in the x direction that is between (e.g., equidistant in the x direction between) the first and second active layers  105 A and  105 B. Restated, the first gate structure  160 A, second gate structure  160 B and device isolation layer  110  may collectively not have reflective symmetry, for example may not have reflective symmetry across a center in the x direction of the collective device isolation layer  110  and first and second gate structures  160 A and  160 B, where said center may be represented by the y-z plane CP. The gate electrode  165  of the first gate structure  160 A (e.g., a first gate electrode) may have a first width W1 in the x direction (e.g., the first direction), and the gate electrode  165  of the second gate structure  160 B (e.g., a second gate electrode) may have a second width W2 in the x direction, the second width W2 being narrower (e.g., smaller in magnitude of width) than the first width W1 in the x direction. The second width W2 may be narrower than a third width W3 of the gate electrode  165  of the third gate structures  160 C (e.g., a third gate electrode) in the x direction. Restated, the third width W3 may be wider than the second width W2 in the x direction. The first width W1 may also be narrower than the third width W3, but is not limited thereto. In this case, the ‘width’ may refer to a maximum width. Relationship between the relative widths of the gate electrodes  165  may be equally applied to widths of the first to third gate structures  160 A,  160 B, and  160 C. As shown in at least  FIG.  2 A , the first gate structure  160 A may have a shape that is different from shapes of the second and third gate structures  160 B and  160 C. 
     The gate electrode  165  of the first gate structure  160 A may have a first region having a shape similar to a shape of the gate electrode  165  of the third gate structure  160 C, and a second region continuously extending from an upper portion of the first gate structure  160 A, and the first and second regions may be arranged to be adjacent to each other in the x direction. As shown in  FIG.  2 A , the first region may include regions that are isolated from direct contact with each other in the z direction with channel layers  141 - 143  interposed therebetween, and second region continuously extending in the z direction. In the second region, the gate electrode  165  of the first gate structure  160 A may have a shape in which regions of the first region that are between the first to third channel layers  141 ,  142 , and  143  and a region of the second region on or above the channel structure  140  are connected to each other. Restated, the gate electrode  165  of the first gate structure  160 A may have a shape in which regions between the plurality of channel layers and a second region on the plurality of channel layers are connected to each other in the x direction. In the second region, the gate electrode  165  of the first gate structure  160 A may have a region protruding toward the device isolation layer  110  in a downward, or vertical direction (e.g., the z direction). The first gate structure  160 A may protrude further toward the device isolation layer  110  in the z direction, as compared to the second gate structure  160 B. Therefore, a lower end of the gate electrode  165  of the first gate structure  160 A may be located on a first height level HL1, lower than a second height level HL2, which may be a height level of a lower end of the gate electrode  165  of the second gate structure  160 B. As referred to herein, a height level may be a distance in the vertical direction (e.g., the z direction) from the substrate  101 , for example from the upper surface of the substrate  101 . 
     The second gate structure  160 B may have a shape in which a portion of the gate spacer layer  164  and a portion of the gate electrode  165  protrude toward the device isolation layer  110 . For example, in an upper portion of the channel structure  140 , the gate electrode  165  of the second gate structure  160 B may have an inclined lower surface lowering toward the device isolation layer  110 . 
     In the first and second gate structures  160 A and  160 B, each of the gate spacer layers  164  on one side, adjacent to the device isolation layer  110 , may extend along the lateral surfaces of the channel structure  140 , may extend in a downward direction, and may be at least partially in contact with the device isolation layer  110 . Therefore, the first and second gate structures  160 A and  160 B may not only have an asymmetrical disposition with respect to each other, but also each may have an asymmetrical disposition with respect to the center in the x direction. Restated, and as shown in at least  FIG.  2 A , the first gate structure  160 A may not have reflective symmetry (e.g., bilateral symmetry, mirror symmetry, line symmetry, etc.) in the x direction, and the second gate structure  160 B may not have reflective symmetry (e.g., bilateral symmetry) in the x direction. In the first and second gate structures  160 A and  160 B, the internal spacer layers  130  may not be disposed on lateral surfaces of the gate electrodes  165  adjacent to the device isolation layer  110 . 
     The semiconductor device  100  may optimize circuit design characteristics by including the first to third gate structures  160 A,  160 B, and  160 C having different shapes as described above. For example, widths of the first and second gate structures  160 A and  160 B overlapping the first and second active regions  105 A and  105 B may be controlled to have the above-described shapes, to control characteristics of transistors constituting the semiconductor device  100  according to its purpose. 
     The gate structure  160  may include a gate electrode  165 , a gate dielectric layer  162  between the gate electrode  165  and a plurality of channel layers  141 ,  142 , and  143 , a gate spacer layer  164  on lateral surfaces of the gate electrode  165 , and a gate capping layer  166  on an upper surface of the gate electrode  165 . 
     The gate dielectric layer  162  may be disposed between the first and second active regions  105 A and  105 B and the gate electrode  165  and between the channel structure  140  and the gate electrode  165 , and may be disposed to cover at least a portion of surfaces of the gate electrode  165 . For example, the gate dielectric layer  162  may be disposed to surround all surfaces of the gate electrode  165  except for an uppermost surface of the gate electrode  165 . The gate dielectric layer  162  may extend between the gate electrode  165  and the gate spacer layers  164 , but is not limited thereto. The gate dielectric layer  162  may include an oxide, a nitride, or a high dielectric constant (high-k) material. The high-k material may refer to a dielectric material having a dielectric constant, higher than a dielectric constant of the silicon oxide (SiO 2 ) The high-k material may include, for example, aluminum oxide (Al 2 O 3 ), tantalum oxide (Ta 2 O 3 ), titanium oxide (TiO 2 ), yttrium oxide (Y 2 O 3 ), zirconium oxide (ZrO 2 ), zirconium silicon oxide (ZrSi x O y ), hafnium oxide (HfO 2 ), hafnium silicon oxide (HfSi x O y ), lanthanum oxide (La 2 O 3 ), lanthanum aluminum oxide (LaAl x O y ), lanthanum hafnium oxide (LaHf x O y ), hafnium aluminum oxide (HfAl x O y ), and praseodymium oxide (Pr 2 O 3 ). According to some example embodiments, the gate dielectric layer  162  may be formed as a multilayer film. 
     The gate electrode  165  may fill between the plurality of channel layers  141 ,  142 , and  143  on the first and second active regions  105 A and  105 B, and may be disposed to extend onto the channel structure  140 . The gate electrode  165  may be spaced apart from the plurality of channel layers  141 ,  142 , and  143  by the gate dielectric layer  162 . The gate electrode  165  may include a conductive material, and may include, for example, a metal nitride such as a titanium nitride (TiN), a tantalum nitride (TaN), or a tungsten nitride (WN), and/or a metal material such as aluminum (Al), tungsten (W), molybdenum (Mo), or the like, or a semiconductor material such as doped polysilicon. The gate electrode  165  may be formed as two or more layers. 
     The gate spacer layers  164  may be disposed on both lateral surface of the gate electrode  165 . The gate spacer layers  164  may insulate the source/drain regions  150  and the gate electrodes  165 . The gate spacer layers  164  may have a multilayer structure according to some example embodiments. The gate spacer layers  164  may be made of an oxide, a nitride, and an oxynitride, and in particular, may be formed as a low dielectric constant (low-k) film. In the first and second gate structures  160 A and  160 B, gate spacer layers  164  adjacent to the device isolation layer  110  may have a relatively long length, and may have lower end positions located on a lower height level than other gate spacer layers  164 . 
     The gate capping layer  166  may be disposed on the gate electrode  165 , and a lower surface and lateral surfaces of the gate capping layer  166  may be surrounded by the gate electrode  165  and the gate spacer layers  164 , respectively. 
     The internal spacer layers  130  may be disposed in parallel with the gate electrode  165  between the channel structures  140 . The gate electrode  165  may be stably spaced from the source/drain regions  150  by the internal spacer layers  130 , and may be electrically isolated. The internal spacer layers  130  may have a shape in which lateral surfaces of the internal spacer layers  130  facing the gate electrode  165  may be convexly rounded medially toward the gate electrode  165 , but are not limited thereto. The internal spacer layers  130  may be made of an oxide, a nitride, and an oxynitride, and in particular, may be formed as a low-k film. According to some example embodiments, the internal spacer layers  130  may be omitted. 
     The contact plugs  180  may pass through the interlayer insulating layer  190  to be connected to the source/drain regions  150 , and may apply an electric signal to the source/drain regions  150 . The contact plugs  180  may have inclined lateral surfaces in which a width of a lower portion becomes narrower than a width of an upper portion according to an aspect ratio, but is not limited thereto. The contact plugs  180  may extend from an upper portion of the semiconductor device  100  to a height level below the third channel layer  143 , for example. For example, the contact plugs  180  may extend to a height level corresponding to an upper surface of the second channel layer  142 . In some example embodiments, the contact plugs  180  may be disposed to contact the source/drain regions  150  along upper surfaces of the source/drain regions  150  without recessing the source/drain regions  150 . The contact plugs  180  may include, for example, a metal nitride such as a titanium nitride (TiN), a tantalum nitride (TaN), or a tungsten nitride (WN), and/or a metal material such as aluminum (Al), tungsten (W), molybdenum (Mo), or the like. In some example embodiments, the contact plugs  180  may further include a barrier metal layer disposed along an outer surface and/or a metal-semiconductor compound layer disposed in a region contacting the source/drain regions  150 . The metal-semiconductor compound layer may be, for example, a metal silicide layer. 
     The interlayer insulating layer  190  may be disposed to cover the source/drain regions  150  and the gate structures  160  and to cover the device isolation layer  110 . The interlayer insulating layer  190  may include at least one of an oxide, a nitride, or an oxynitride, and may include, for example, a low dielectric constant material. 
     Hereinafter, the same description as described above with reference to  FIGS.  1  to  3    will be omitted. 
       FIGS.  4 A and  4 B  are plan and cross-sectional views illustrating a semiconductor device according to some example embodiments.  FIG.  4 B  illustrates a cross-section along the cut line I-I′ of  FIG.  4 A . 
     Referring to  FIGS.  4 A and  4 B , in a semiconductor device  100   a , one end of a second gate structure  160 B may be located on an end portion of a second active region  105 B. For example, some example embodiments in which the second distance D2 of  FIG.  1    is substantially zero or close to zero are illustrated. Therefore, the second gate structure  160 B may not protrude from the end portion of the second active region  105 B toward a device isolation layer  110  in the x direction. 
     In the semiconductor device  100   a , a first gate structure  160 A may have a shape different from shapes of second and third gate structures  160 B and  160 C. The second gate structure  160 B may have a structure corresponding to the third gate structure  160 C. In this case, the expression ‘a structure corresponding to . . . ’ may refer to a structure in which components of the second gate structure  160 B may be arranged in the same shape as or a shape similar to components of the third gate structure  160 C in positions corresponding to the components of the third gate structure  160 C. For example, a structure of the second gate structure  160 B may be similar to a structure of the third gate structure  160 C, but, in the x direction, a width of the second gate structure  160 B may be narrower than a width of the third gate structure  160 C. In the first to third gate structures  160 A,  160 B, and  160 C, a relationship between first to third widths W1, W2, and W3 of the gate electrodes  165  may be the same as described above. According to some example embodiments, the second gate structure  160 B may have substantially the same structure and substantially the same size as the third gate structure  160 C. 
       FIGS.  5  and  6    are cross-sectional views illustrating a semiconductor device according to some example embodiments.  FIGS.  5  and  6    illustrate cross-sections corresponding to  FIG.  2 A . 
     Referring to  FIG.  5   , in a semiconductor device  100   b , a device isolation layer  110   b  may have first insulating regions SR1 having a first depth SR1D, and a second insulating region SR2 having a second depth SR2D, greater than the first depth, between the first insulating regions SR1. 
     The second insulating region SR2 may be disposed in a partial region within a device isolation region IR (refer to  FIG.  1   ). The second insulating region SR2 may be formed in a deep trench region between the first insulating regions SR1 to enhance electrical isolation between portions of transistors of the semiconductor device  100   b  according to an arrangement of the transistors. For example, the second insulating region SR2 may be disposed in a region between PMOS and NMOS. 
     The second insulating region SR2 may be formed by an additional process after the first insulating regions SR1 is formed. Therefore, even when a liner layer  112  is disposed along sidewalls of the trench of the first insulating regions SR1, the liner layer  112  may not be disposed in the second insulating region SR2 as illustrated. Restated, in the device isolation layer  110 , the liner layer  112  may be located only in the first insulating regions SR1 without extending to the second insulating region SR2. At a boundary between the first insulating region SR1 and the second insulating region SR2, an end portion of the liner layer  112  may have a shape protruding in an upward direction, but is not limited thereto. 
     Referring to  FIG.  6   , in a semiconductor device  100   c , a device isolation layer  110   c  may not include a liner layer  112 . Therefore, the device isolation layer  110   c  may be formed as a single insulating material layer. In this case, height levels of both end portions of the device isolation layer  110   c  may be the same or similar, and may be variously changed according to a length of a gate electrode  165  extending from a first gate structure  160 A in a downward direction. 
     As such, a structure of the device isolation layer  110   c  from which the liner layer  112  is omitted may be applied to other example embodiments. 
       FIGS.  7 A and  7 B  are cross-sectional views illustrating a semiconductor device according to some example embodiments.  FIGS.  7 A and  7 B  illustrate cross-sections corresponding to  FIGS.  2 A and  2 B , respectively. 
     In some example embodiments, including the example embodiments illustrated in  FIGS.  7 A and  7 B , and unlike some example embodiments, including the example embodiments illustrated in  FIGS.  1  to  3   , a semiconductor device  100   d  may not include channel structures  140 , and shapes of gate structures  160   d  and an arrangement of a liner layer  112  may be different from that in the above embodiments. In the semiconductor device  100   d , a channel region of transistors may be limited to the first and second active regions  105 A and  105 B having a fin structure. According to some example embodiments, the semiconductor device  100   d  may be additionally disposed in regions of semiconductor devices of other embodiments. 
     As illustrated in  FIG.  7 A , a first gate structure  160 Ad and a second gate structure  160 Bd may have an asymmetrical disposition with respect to a device isolation layer  110 . A gate electrode  165  of the first gate structure  160 Ad may have a fourth width W4 in the x direction, and a gate electrode  165  of the second gate structure  160 Bd may have a fifth width W5, narrower than the fourth width W4 in the x direction. The fifth width W5 may be equal to or narrower than a sixth width W6 of a gate electrode  165  of a third gate structures  160 Cd. The fourth width W4 may be equal to or narrower than the sixth width W6, but is not limited thereto. A relationship between relative widths of the gate electrodes  165  may be equally applied to widths of the first to third gate structures  160 Ad,  160 Bd, and  160 Cd. 
     The gate electrode  165  of the first gate structure  160 Ad may have a first region having a shape similar to a shape of the gate electrode  165  of the third gate structures  160 Cd, and a second region continuously extending from an upper portion of the first gate structure  160 Ad, and the first and second regions may be arranged to be adjacent to each other in the x direction. In the second region, the gate electrode  165  of the first gate structure  160 Ad may extend along a lateral surface of the first active region  105 A in a downward direction. In the second region, the gate electrode  165  of the first gate structure  160 Ad may have a region protruding toward the device isolation layer  110  in a downward direction. Therefore, a lower end of the gate electrode  165  of the first gate structure  160 Ad may be located on a first height level HL1, lower than a second height level HL2, which may be a height level of a lower end of the gate electrode  165  of the second gate structure  160 Bd. In the first gate structure  160 Ad, a gate spacer layer  164  adjacent to the device isolation layer  110  may extend along a lateral surface of the first active region  105 A, may extend in a downward direction, and may be in contact with the device isolation layer  110 . Therefore, the first gate structures  160 Ad may have asymmetrical dispositions with respect to a center in the x direction. 
     The second gate structure  160 Bd may have the same structure as or a structure similar to the third gate structure  160 Cd. For example, the second gate structure  160 Bd may differ only in width from the third gate structure  160 Cd. According to some example embodiments, the second gate structure  160 Bd may have a shape in which a portion of the gate spacer layer  164  and a portion of the gate electrode  165  protrude toward the device isolation layer  110 . 
     An end portion of the liner layer  112  adjacent to the second gate structure  160 Bd may be located on a height level spaced from an upper surface of the second active region  105 B in a downward direction. In some example embodiments, upper portions of the first and second active regions  105 A and  105 B may be exposed to a predetermined height from the device isolation layer  110  including the liner layer  112  as described above. The height on which the first and second active regions  105 A and  105 B are exposed may be variously changed in some example embodiments. According to an arrangement of the liner layer  112 , as illustrated in  FIG.  7 B , the gate electrode  165  have a region extending along the first active region  105 A from the upper surface of the first active region  105 A in a downward direction, and being then curved along the liner layer  112 . Even in this case, in the device isolation layer  110 , both upper end portions of the liner layer  112  may be located on different height levels in a cross-section in the x direction. An arrangement of the liner layer  112  may be applied to other embodiments. 
       FIGS.  8 A and  8 B  are plan and cross-sectional views illustrating a semiconductor device according to some example embodiments.  FIG.  8 B  illustrates a cross-sectional view taken along the cut line Ie-Ie′ of  FIG.  8 A . 
     Referring to  FIGS.  8 A and  8 B , a semiconductor device  100   e  may have first and second regions R1 and R2. The first and second regions R1 and R2 may include first and second active regions  105 A and  105 B, respectively, channel structures  140 , source/drain regions  150 , and gate structures  160 . The first region R1 may have the same cross-sectional structure as described with reference to  FIG.  2 A , and the description with reference to  FIG.  2 A  may be applied in the same manner. The second region R2 may include first and second gate structures  160 Ae and  160 Be having a symmetrical shape with respect to a device isolation layer  110   e , as illustrated in  FIG.  8 B . 
     The first and second gate structures  160 Ae and  160 Be may have substantially the same width intersecting each of the first and second active regions  105 A and  105 B. For example, a gate electrode  165  of each of the first and second gate structures  160 Ae and  160 Be may overlap each of the first and second active regions  105 A and  105 B by a third length L3 in the x direction. The third length L3 may be equal to or longer than a first length L1 of the first region RE The first and second gate structures  160 Ae and  160 Be may protrude from end portions of the first and second active regions  105 A and  105 B toward the device isolation layer  110   e  in the x direction by a third distance D3, respectively. The third distance D3 may be equal to or shorter than a first distance D1 of the first region R1. 
     As illustrated in  FIG.  8 A , the first gate structure  160 Ae and the second gate structure  160 Be may have a symmetrical shape with respect to the device isolation layer  110   e . The gate electrode  165  of the first gate structure  160 Ae may have a seventh width W7 in the x direction, and the gate electrode  165  of the second gate structure  160 Be may have an eighth width W8 that may be substantially equal to the seventh width W7 in the x direction. The seventh width W7 and the eighth width W8 may be narrower than a ninth width W9 of a gate electrode  165  of each of third gate structures  160 C, but are not limited thereto. A relationship between relative widths of the gate electrodes  165  may be equally applied to the widths of the first to third gate structures  160 Ae,  160 Be, and  160 C. 
     The gate electrode  165  of the first gate structure  160 Ae may have the same structure as or a structure similar to the first gate structure  160 A in the first region R1, as described above with reference to  FIG.  2 A . For example, the first gate structure  160 Ae may differ only in width from the first gate structure  160 A in the first region R1. The gate electrode  165  of the second gate structure  160 Be may have a structure symmetrical to the gate electrode  165  of the first gate structure  160 Ae. 
       FIGS.  9 A,  9 B,  9 C,  9 D,  9 E,  9 F,  9 G, and  9 H  are views illustrating a process sequence for explaining a method of manufacturing a semiconductor device according to some example embodiments.  FIGS.  9 A to  9 H  illustrate some example embodiments of a method for manufacturing the semiconductor device of  FIGS.  1  to  3   , and cross-sections corresponding to  FIGS.  2 A and  2 B  are illustrated together. 
     Referring to  FIG.  9 A , sacrificial layers  120  and channel layers  141 ,  142 , and  143  may be alternately stacked on a substrate  101 . 
     The sacrificial layers  120  may be layers to be replaced with the gate dielectric layer  162  and the gate electrode  165 , as illustrated in  FIGS.  2 A and  2 B , by a subsequent process. The sacrificial layers  120  may be made of a material having etch selectivity with respect to the channel layers  141 ,  142 , and  143 , respectively. The channel layers  141 ,  142 , and  143  may include a material different from the sacrificial layers  120 . The sacrificial layers  120  and the channel layers  141 ,  142 , and  143  may include, for example, a semiconductor material including at least one of silicon (Si), silicon germanium (SiGe), or germanium (Ge), but different materials may be included, and impurities may or may not be included. For example, the sacrificial layers  120  may include silicon germanium (SiGe), and the channel layers  141 ,  142 , and  143  may include silicon (Si). 
     The sacrificial layers  120  and the channel layers  141 ,  142 , and  143  may be formed by performing an epitaxial growth process on the substrate  101 . Each of the sacrificial layers  120  and the channel layers  141 ,  142 , and  143  may have a thickness of about 1 Å to about 100 nm. The number of layers of the channel layers  141 ,  142 , and  143  alternately stacked with the sacrificial layers  120  may be variously changed in some example embodiments. 
     Referring to  FIG.  9 B , the sacrificial layers  120 , the channel layers  141 ,  142 , and  143 , and a portion of the substrate  101  may be removed to form active structures and a device isolation region IR may be formed. 
     The active structures may include the sacrificial layers  120  and the channel layers  141 ,  142 , and  143  that may be alternately stacked with each other, and may further include first and second active regions  105 A and  105 B protruding from the substrate  101  by removing a portion of the substrate  101 . The active structures may be formed in a linear shape extending in one direction, for example, in the x direction, and may be arranged to be spaced apart from each other in the y direction. 
     A liner layer  112  and an isolation insulating layer  114  may be sequentially stacked in a trench region from which a portion of the substrate  101  is removed. Next, the liner layer  112  and the isolation insulating layer  114  may be partially removed to, at least, expose upper surfaces of the first and second active regions  105 A and  105 B, to form a device isolation region IR including a device isolation layer  110 . In the device isolation region IR, an upper surface of the isolation insulating layer  114  may be, at least, formed on a lower height level than the upper surfaces of the first and second active regions  105 A and  105 B by a predetermined depth D4. The depth D4 may be variously changed in some example embodiments. The liner layer  112  may protrude from the upper surface of the isolation insulating layer  114  in an upward direction, and may remain, but is not limited thereto. Depending on materials of the liner layer  112  and the isolation insulating layer  114 , removal process conditions, or the like, an upper surface of the liner layer  112  may also have a height level similar to a height level of the isolation insulating layer  114 . In this operation, when the liner layer  112  is formed, for example, when the substrate  101  is nitrided using a nitridation process to form the liner layer  112 , corners of the first and second active regions  105 A and  105 B may be formed to have a rounded shape. 
     Referring to  FIG.  9 C , sacrificial gate structures  170  and gate spacer layers  164  may be formed on the active structures. 
     The sacrificial gate structures  170  may be sacrificial structures formed in a region in which the gate dielectric layer  162  and the gate electrode  165  are arranged on the channel structures  140  by a subsequent process, as illustrated in  FIGS.  2 A and  2 B . The sacrificial gate structure  170  may include first and second sacrificial gate layers  172  and  175 , and a mask pattern layer  176 , sequentially stacked. The first and second sacrificial gate layers  172  and  175  may be patterned using the mask pattern layer  176 . The first and second sacrificial gate layers  172  and  175  may be an insulating layer and a conductive layer, respectively, but are not limited thereto, and the first and second sacrificial gate layers  172  and  175  may be formed as a single layer. For example, the first sacrificial gate layer  172  may include a silicon oxide, and the second sacrificial gate layer  175  may include polysilicon. The mask pattern layer  176  may include a silicon oxide and/or a silicon nitride. The sacrificial gate structures  170  may intersect the active structures to have a linear shape extending in one direction. The sacrificial gate structures  170  may extend in the y direction, for example, and may be disposed to be spaced apart from each other in the x direction. 
     The gate spacer layers  164  may be formed on both sidewalls of the sacrificial gate structures  170 . The gate spacer layers  164  may be prepared by forming a film having a uniform thickness along upper and lateral surfaces of the sacrificial gate structures  170  and the active structures, and performing then an anisotropic etching process. The gate spacer layers  164  may be made of a low dielectric constant material, and may include, for example, at least one of SiO, SiN, SiCN, SiOC, SiON, or SiOCN. 
     In this operation, the sacrificial gate structures  170  adjacent to the device isolation layer  110  may be formed to have a partially extended shape onto the device isolation layer  110  or have a partially inclined shape along an end portion of the active structure. In addition, the gate spacer layers  164  on sidewalls of the sacrificial gate structures  170  may extend in a downward direction to contact the device isolation layer  110 . 
     Referring to  FIG.  9 D , exposed sacrificial layers  120  and the channel layers  141 ,  142 , and  143  may be removed to form recess regions RC between the sacrificial gate structures  170 . 
     The exposed sacrificial layers  120  and the channel layers  141 ,  142 , and  143  may be removed by using the sacrificial gate structures  170  and the gate spacer layers  164  as masks. Therefore, the channel layers  141 ,  142 , and  143  may form a channel structure  140  having a limited length in the x direction. According to some example embodiments, below the sacrificial gate structures  170 , the sacrificial layers  120  and the channel structure  140  may be partially removed from lateral surfaces thereof in a medial direction, to locate both lateral surfaces of the sacrificial layers  120  and the channel structure  140  in the x direction below the sacrificial gate structures  170  and the gate spacer layers  164 . 
     In this operation, when forming the recess regions RC, an upper portion of the device isolation layer  110  may be additionally recessed to a predetermined depth D5. The depth D5 may be variously changed in some example embodiments. 
     Referring to  FIG.  9 E , the exposed sacrificial layers  120  may be partially removed from lateral surfaces thereof in a medial direction, and internal spacer layers  130  may be formed in regions from which the sacrificial layers  120  have been removed. 
     The sacrificial layers  120  may be selectively etched with respect to the channel structures  140  by, for example, a wet etching process, to be removed from the lateral surface thereof in the x direction to a predetermined depth. The sacrificial layers  120  may have lateral surfaces that are medially concave by the lateral etching operation as described above. Shapes of the lateral surfaces of the sacrificial layers  120  are not limited to those illustrated. 
     The internal spacer layers  130  may be prepared by filling an insulating material in regions from which the sacrificial layers  120  have been removed, and removing the insulating material deposited on an outside of the channel structures  140 . The internal spacer layers  130  may be formed of the same material as the gate spacer layers  164 , but are not limited thereto. For example, the internal spacer layers  130  may include at least one of SiN, SiCN, SiOCN, SiBCN, or SiBN. 
     Referring to  FIG.  9 F , on both sides of the sacrificial gate structures  170 , source/drain regions  150  may be formed in the recess region RC. 
     The source/drain regions  150  may be formed on the lateral surfaces of the first to third channel layers  141 ,  142 , and  143 , and on the first and second active regions  105 A and  105 B on a bottom surface of the recess region RC, by a selective epitaxial growth process. The source/drain regions  150  may include impurities by an in-situ doping process, and may include a plurality of layers having different doping elements and/or different doping concentrations. 
     Referring to  FIG.  9 G , an interlayer insulating layer  190  may be formed, and the sacrificial layers  120  and the sacrificial gate structures  170  may be removed. 
     The interlayer insulating layer  190  may be prepared by forming an insulating film covering the sacrificial gate structures  170  and the source/drain regions  150 , and performing a planarization process. 
     The sacrificial layers  120  and the sacrificial gate structures  170  may be selectively removed with respect to the gate spacer layers  164 , the interlayer insulating layer  190 , and the channel structures  140 . First, the sacrificial gate structures  170  may be removed to form upper gap regions UR, and then the sacrificial layers  120  exposed through the upper gap regions UR may be removed to form lower gap regions LR. For example, when the sacrificial layers  120  include silicon germanium (SiGe) and the channel structures  140  include silicon (Si), the sacrificial layers  120  may be selectively removed by performing a wet etching process using peracetic acid as an etchant. During the removal, the source/drain regions  150  may be protected by the interlayer insulating layer  190  and the internal spacer layers  130 . 
     In this operation, when the sacrificial layers  120  and the sacrificial gate structures  170  are removed, a portion of the device isolation layer  110  including the liner layer  112  at a corner of the first active region  105 A may be removed together. 
     Referring to  FIG.  9 H , gate structures  160  may be formed in the upper gap regions UR and the lower gap regions LR. 
     Gate dielectric layers  162  may be formed to conformally cover inner surfaces of the upper gap regions UR and the lower gap regions LR. After forming gate electrodes  165  to completely fill the upper and lower gap regions UR and LR, portions of the gate electrodes  165  may be removed from an upper portion of the upper gap regions UR to a predetermined depth. A gate capping layer  166  may be formed in regions in which the portions of the gate electrodes  165  have removed from the upper gap regions UR. A shape and a thickness of the gate capping layer  166  may be variously changed in some example embodiments. Therefore, gate structures  160  including the gate dielectric layer  162 , the gate electrode  165 , the gate spacer layers  164 , and the gate capping layer  166  may be formed. 
     Next, referring to  FIGS.  2 A and  2 B  together, a contact plug  180  may be formed. 
     First, the interlayer insulating layer  190  may be patterned to form a contact hole, and a conductive material may be filled in the contact hole to form the contact plug  180 . A lower surface of the contact hole may be recessed into the source/drain regions  150  or may have a bend along upper surfaces of the source/drain regions  150 . In some example embodiments, a shape and an arrangement of the contact plug  180  may be variously changed. 
     A semiconductor device having improved reliability may be provided by including gate structures having an asymmetric shape (e.g., asymmetrical disposition) as described herein and disposed adjacent to each other with a device isolation layer interposed therebetween. 
     Various advantages and effects of the present inventive concepts are not limited to the above-described contents, and can be more easily understood in the course of describing specific embodiments of the present inventive concepts. 
     While example embodiments have been illustrated and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present inventive concepts as defined by the appended claims.