Patent Publication Number: US-11664453-B2

Title: Semiconductor devices and method of fabricating the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit under 35 USC 119 (a) of Korean Patent Application No. 10-2020-0082374 filed on Jul. 3, 2020 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
     BACKGROUND 
     1. Field 
     Some example embodiments relate to semiconductor devices and a method of fabricating the same. 
     2. Description of Related Art 
     In recent years, down-scaling in the sizes of semiconductor devices has been rapidly progressing. In addition, since semiconductor devices require high operating speed and accuracy in operation, various studies are being conducted for optimizing the structure of transistors included in semiconductor devices. For example, as scaling technology for increasing the density of integrated circuit devices, efforts are being made to develop semiconductor devices including a FinFET having a three-dimensional structure channel in which an active fin is formed on a substrate and a gate is formed using the active fin. 
     SUMMARY 
     Example embodiments provide a semiconductor device having a channel including a three-dimensional structure, with improved electrical characteristics and reliability and a method of fabricating the same. 
     According to some example embodiments, a semiconductor device may include a substrate including a fin-type active region, the fin-type active region extending in a first direction parallel to an upper surface of the substrate; a plurality of channel layers on the fin-type active region, the plurality of channel layers including an uppermost channel layer, a lowermost channel layer, and an intermediate channel layer isolated from direct contact with each other in a direction perpendicular to the upper surface of the substrate; a gate electrode surrounding the plurality of channel layers and extending in a second direction, the second direction parallel to the upper surface of the substrate and intersecting the first direction; a gate insulating film between the plurality of channel layers and the gate electrode; and source/drain regions electrically connected to the plurality of channel layers. In a cross section taken in the second direction, the uppermost channel layer may have a width greater than a width of the intermediate channel layer. 
     According to some example embodiments, a semiconductor device may include a substrate including a fin-type active region extending in a first direction, the first direction parallel to an upper surface of the substrate; a plurality of channel layers on the fin-type active region, the plurality of channel layers isolated from direct contact with each other in a direction perpendicular to the upper surface of the substrate and including an uppermost channel layer, a lowermost channel layer, and an intermediate channel layer; a gate electrode surrounding the plurality of channel layers and extending in a second direction, the second direction parallel to the upper surface of the substrate and intersecting the first direction; a gate insulating film between the plurality of channel layers and the gate electrode; and source/drain regions electrically connected to the plurality of channel layers. In a cross section taken in the second direction, the lowermost channel layer may have a width greater than a width of the intermediate channel layer and have an upwardly inclined side surface. 
     According to some example embodiments, a semiconductor device may include a substrate including a fin-type active region extending in a first direction, the first direction parallel to an upper surface of the substrate; a plurality of channel layers on the fin-type active region, the plurality of channel layers isolated from direct contact with each other in a direction perpendicular to the upper surface of the substrate and including an uppermost channel layer, a lowermost channel layer, and an intermediate channel layer; a gate electrode surrounding the plurality of channel layers and extending in a second direction, the second direction parallel to the upper surface of the substrate and intersecting the first direction; a gate insulating film between the plurality of channel layers and the gate electrode; and source/drain regions electrically connected to the plurality of channel layers. In a cross section taken in the second direction, the uppermost channel layer and the lowermost channel layer may each have a width greater than the width of the intermediate channel layer, and an upper surface of the uppermost channel layer may have a protruding edge portion. 
     According to some example embodiments, a method of fabricating a semiconductor device may include forming a stack structure by alternately stacking a plurality of first semiconductor layers and a plurality of second semiconductor layers on an active region of a substrate; etching the stack structure to form a fin-shaped structure on the active region; forming a silicon epitaxial liner on a surface of the fin-shaped structure; forming a gap-fill insulating film on the silicon epitaxial liner to surround the fin-shaped structure; applying an annealing process to the gap-fill insulating film; and partially removing the gap-fill insulating film to expose the fin-shaped structure. 
    
    
     
       BRIEF DESCRIPTION OF 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; 
         FIG.  2    provide cross-sectional views of the semiconductor device illustrated in  FIG.  1    taken along lines D 1 -D 1 ′ and D 2 -D 2 ′; 
         FIG.  3    is an enlarged cross-sectional view of portion “A” of the semiconductor device of  FIG.  2   ; 
         FIGS.  4 A,  5 A,  6 A, and  7 A  are perspective views illustrating some processes (a fin structure formation process) in a method of fabricating a semiconductor device according to some example embodiments; 
         FIGS.  4 B,  5 B,  6 B, and  7 B  are cross-sectional views of process results of  FIGS.  4 A,  5 A,  6 A, and  7 A  taken along line D 2 -D 2 ′, respectively; 
         FIGS.  8 A,  9 A, and  10 A  are cross-sectional views illustrating some processes (forming a device isolation layer) in a method of fabricating a semiconductor device according to some example embodiments; 
         FIGS.  8 B,  9 B, and  10 B  are partially enlarged views of portions of cross sections of  FIGS.  8 A,  9 A, and  10 A , respectively; 
         FIG.  11    is a graph illustrating silicon consumption according to an annealing process; 
         FIGS.  12 A to  12 D  are perspective views illustrating some other processes (dummy gate structure and source/drain formation) in a method of fabricating a semiconductor device according to some example embodiments; 
         FIGS.  13 A,  14 A,  15 A, and  16 A and  13 B,  14 B,  15 B, and  16 B  are cross-sectional view taken along lines D 1 -D 1 ′ and D 2 -D 2 ′, respectively, illustrating some other processes (gate structure formation) in a method of fabricating a semiconductor device according to some example embodiments; 
         FIGS.  17 A and  17 B  are cross-sectional views of a semiconductor device according to some example embodiments, taken along lines D 1 -D 1 ′ and D 2 -D 2 ′; 
         FIG.  18    is a plan view illustrating a semiconductor device according to some example embodiments; 
         FIGS.  19 A to  19 C  are cross-sectional views of the semiconductor device illustrated in  FIG.  18   , taken along lines D 2   a -D 2   a ′, D 2   b -D 2   b ′, and D 2   c -D 2   c ′; and 
         FIGS.  20 A to  20 C  are cross-sectional views illustrating some processes of the method of manufacturing the semiconductor device illustrated in  FIG.  19 C . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings. 
     Hereinafter, terms such as ‘on,’ ‘upper portion,’ ‘upper surface,’ ‘below,’ ‘lower portion,’ ‘lower surface,’ ‘side surface,’ and the like can be understood as referring to the spatial relationship between elements, components, regions, layers, and/or sections, based on the orientation of those elements, components, regions, layers, and/or sections in the drawings, unless otherwise indicated. Similarly, although the terms ‘first,’ ‘second,’ ‘third,’ etc., may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections, should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section, from another region, layer, or section. 
       FIG.  1    is a plan view illustrating a semiconductor device according to an example embodiment,  FIG.  2    is a cross-sectional view of the semiconductor device illustrated in  FIG.  1    taken along lines D 1 -D 1 ′ and D 2 -D 2 ′, and  FIG.  3    is an enlarged cross-sectional view of portion “A” of the semiconductor device of  FIG.  2   . 
     Referring to  FIGS.  1  to  3   , a semiconductor device  100  according to some example embodiments may include a substrate  101 , an active region  105  disposed on the substrate  101 , a plurality of channel layers CH disposed on the active region  105 , and a gate structure GS surrounding the plurality of channel layers CH. 
     The active region may be a fin-type active region (hereafter referred to as a fin-type active region  105 ) and may be provided on the substrate  101 . The substrate  101  may be a semiconductor substrate. For example, the substrate  101  may be an elemental semiconductor (e.g., silicon (Si) and/or a germanium (Ge)) substrate, a compound semiconductor substrate (e.g., SiGe), and/or a semiconductor on insulator (e.g., silicon on insulator (SOI)) substrate. The fin-type active region  105  may have a fin structure. The fin structure may protrude from an upper surface of the substrate  101  in a direction perpendicular to the upper surface of the substrate  101  (e.g., a Z direction) and extend in a first direction parallel to the upper surface of the substrate  101  (e.g., an X Direction). In the illustrated example embodiment, the fin structure of the fin-type active region  105  is illustrated as one, but may be provided as a plurality of fin structures arranged in parallel in a second direction (e.g., a Y direction) intersecting the first direction (e.g., the X direction). 
     Device isolation layers  110  may be provided on the substrate  101  on both sides of the fin-type active region  105 . The device isolation layer  110  may define the fin-type active region  105 . For example, the device isolation layer  110  may include an electrically insulating material. The device isolation layer  110  may include, for example, an oxide, a nitride, and/or an oxynitride. In some embodiments, the device isolation layer  110  may expose upper sidewalls of the fin-type active region  105 . The upper surface of the device isolation layer  110  may be located on a level lower than the upper surface of the active region  105 . 
     The plurality of channel layers CH may be spaced apart from each other in a direction (e.g., Z direction) perpendicular to the upper surface of the substrate  101 . The plurality of channel layers CH may include a first channel layer CH 1  located as an uppermost layer, a fourth channel layer CH 4  located as a lowermost layer, and second and third channel layers CH 2  and CH 3  sequentially disposed between the first channel layer CH 1  and the fourth channel layer CH 4 . In this case, the second and third channel layers are referred to as intermediate channel layers. The lowermost fourth channel layer CH 4  is provided as an upper region of the fin-type active region  105 , and the remaining channel layers, for example, the first to third channel layers CH 1 , CH 2  and CH 3 , respectively, may be disposed to be spaced apart from each other from the fin-type active region  105  in the direction perpendicular to the upper surface of the substrate  101  (e.g., the Z direction). Each of the first to third channel layers CH 1 , CH 2  and CH 3  may be formed of a nanosheet and/or may include a semiconductor material that is the same as or similar to semiconductor material of the fin-type active region  105 . For example, the plurality of channel layers CH and the fin-type active region  104  may both share a type of semiconductor (e.g., Group IV elemental (e.g., Si, and/or Ge) and/or compound semiconductors (e.g., SiGe)), and/or may include the same semiconductor material (e.g., Si and/or Ge) but with different types and/or concentrations of impurities (e.g., dopants). 
     The first and fourth channel layers CH 1  and CH 4  disposed at the top and bottom, respectively, may have a width greater than that of the intermediate channel layers in a first direction parallel to the upper surface of the substrate  101  (e.g., the X direction). For example, the first and fourth channel layers CH 1  and CH 4  may be wider than the second and third channel layers CH 2  and CH 3 . This difference in width may appear in a cross section taken in the second direction (e.g., the Y direction), as illustrated in  FIG.  3    and the right cross section of  FIG.  2   , but may not appear in the cross section in the first direction (e.g., the X direction) illustrated in the left cross section of  FIG.  2   . Even if a difference appears, in the cross section in the first direction (refer to the left cross section of  FIG.  2   ), a difference between, the widths of the second and third channel layers CH 2  and CH 3 , and the widths of the first and fourth channel layers CH 1  and CH 4 , may be less than a difference in width in the cross section taken in the second direction (refer to the right cross section in  FIG.  2   ). For example, in the cross section in the first direction, the first to fourth channel layers CH 1 , CH 2 , CH 3 , and CH 4  may have substantially the same width. For example, the difference in the width of the channel layer in the cross-section in the second direction (refer to the right cross-section in  FIG.  2   ) may range from about 1 nm to about 10 nm, but is not limited thereto. 
     As illustrated in  FIG.  3   , the first channel layer CH 1 , which is an uppermost channel layer, may have protruding portions PT on both sides of the upper surface thereof. The protruding portion PT may have a relatively pointed end toward an upper portion. This protruding portion PT may extend in the first direction (see  FIGS.  12 A and  12 B ). As such, in the cross section taken in the second direction (refer to the right cross section in  FIG.  2   ), the upper surface of the first channel layer CH 1  has the protruding portion PT, but a cross section in the first direction (refer to the left cross section in  FIG.  2   ), the first channel layer CH 1  may have a substantially flat upper surface. 
     The first and fourth channel layers CH 1  and CH 4  have a greater width (Wa, Wb) than widths (W 1 , W 2 ) of the second and third channel layers CH 2  and CH 3  disposed therebetween, and the volume of the channel region of the first channel layer CH 1  may be increased by the protruding portion PT, and as a result, direct current (“DC”) performance of the semiconductor device may be improved. 
     In addition, as illustrated in  FIG.  3   , the first channel layer CH 1  may have downwardly inclined side surfaces EC 1 . Similarly, the fourth channel layer CH 4  may have upwardly inclined side surfaces EC 2 . On the other hand, both side sectional surfaces of the second and third channel layers CH 2  and CH 3  may have a convex shape. 
     The width and shape of the channel layers CH 1 , CH 2 , CH 3  and CH 4  may be determined by the result of a partial encroachment of a sacrificial layer (such as SiGe) located between the channel layers CH 1 , CH 2 , CH 3  and CH 4  during an annealing process for forming a gap-fill insulating film (see  FIGS.  8 B and  9 B ) after the introduction of the silicon epitaxial liner, and may be determined by the result that, in this process, the portion of the channel layers CH 1 , CH 2 , CH 3  and CH 4  adjacent to the encroached portion of the sacrificial layer is also encroached. 
     For example, the plurality of channel layers CH may include at least one of silicon (Si), silicon germanium (SiGe), and germanium (Ge). The channel layers CH employed in this embodiment are illustrated as introducing three nanosheets for the first to third channel layers CH 1 , CH 2 , and CH 3 , but the number of nanosheets introduced as the channel layers is not limited thereto, and may be changed to a plurality of different numbers. 
     The gate structure GS may be disposed on the fin-type active region  105  and may intersect the fin-type active region  105 . 
     The gate structure GS includes a gate electrode GE surrounding the plurality of channel layers CH and extending in the second direction (e.g., the Y direction) intersecting the first direction (e.g., the X direction). The gate electrode GE may surround the first to third channel layers CH 1 , CH 2 , and CH 3  in the second direction (e.g., the Y direction) and cover the fourth channel layer CH 4 , as illustrated in  FIG.  2   . The gate electrode GE may include a main portion covering the upper surface of the first channel layer CH 1  (also referred to as the “uppermost channel layer”), and a sub-portion connected to the main portion and located in a space between the plurality of channel layers CH. The main portion of the gate electrode GE may extend in the second direction (e.g., the Y direction) and cover an upper surface of the device isolation layer  110  along both side surfaces of the plurality of channel layers CH. The gate electrode may include a conductive material. For example, the gate electrode GE may include a doped semiconductor, a conductive metal nitride, and/or a metal. 
     A gate insulating film GI may be disposed between the plurality of channel layers CH and the gate electrode GE. The gate insulating film GI may be disposed to surround each of the plurality of channel layers CH in the second direction (e.g., the Y direction). The gate insulating film GI may extend on an upper surface of the device isolation layer  110  in the second direction (e.g., Y direction) and may be disposed between the gate electrode GE and the device isolation layer  110 . The gate insulating film GI may include an electrically insulating material. For example, the gate insulating film GI may include at least one of a silicon oxide layer, a silicon nitride layer, a silicon oxynitride layer, and/or a high dielectric layer. The high dielectric layer may include a material having a high dielectric (e.g., a higher dielectric constant than a silicon oxide film) and, for example, may include a hafnium oxide film (HfO), an aluminum oxide film (AlO), and/or a tantalum oxide film (TaO). 
     The gate structure GS may include gate spacers GSP on side surfaces of the gate electrode GE, and a gate capping pattern GP on the gate electrode GE. The gate insulating film GI may extend between the gate electrode GE and the gate spacers GSP, and an uppermost surface of the gate insulating film GI may be substantially coplanar with the upper surface of the gate electrode GE. The gate spacers GSP and gate capping pattern may include an electrically insulating material. For example, each of the gate spacer GSP and the gate capping pattern GP may include at least one of a silicon oxide layer, a silicon nitride layer, and a silicon oxynitride layer. 
     In this manner, the gate electrode GE may be provided to surround the channel layers CH to provide a gate-all-around (GAA) type field effect transistor. 
     Source/drain regions SD may be disposed on fin-type active regions  105  on both sides of the gate structure GS, to be connected to both sides of the plurality of channel layers CH, respectively. The source/drain regions may be regrowth layers selectively regrown from sidewalls of the plurality of channel layers. For example, the source/drain regions SD may be epitaxial layers selectively regrown on sidewalls of the plurality of channel layers CH and the recessed surface of the fin-type active region  105 . In this case, the source/drain regions SD may share a similar crystalline structure and/or orientation to the plurality of channel layers CH. The source/drain regions SD may include at least one of SiC, Si, SiGe, or SiP. 
     An interlayer insulating film  123  may be provided on the source/drain regions SD. The gate structure GS may be located in the interlayer insulating film  123 . The upper surface of the interlayer insulating film  123  may be substantially coplanar with the upper surface of the gate capping pattern GP. The interlayer insulating film  123  may include an insulating material, for example at least one of a silicon oxide layer or a silicon oxynitride layer. 
     The semiconductor device  100  may include contact plugs CT that penetrate through the interlayer insulating film  123  and connect to the source/drain regions SD. The contact plugs CT may include a conductive material, for example a conductive metal nitride such as TiN, WN, and TaN, and/or a metal such as Ti, W, and Ta. 
       FIGS.  4 A,  5 A,  6 A, and  7 A  are perspective views illustrating some processes (fin structure forming process) in a method of fabricating a semiconductor device according to some example embodiments, and  FIGS.  4 B,  5 B,  6 B, and  7 B  are cross-sectional views taken along line D 2 -D 2 ′ of  FIGS.  4 A,  5 A,  6 A, and  7 A , respectively. 
     Referring to  FIGS.  4 A and  4 B , a stack structure ST in which a first semiconductor layer  111  and a second semiconductor layer  112  are alternately stacked is formed on a substrate  101 . 
     The second semiconductor layers  112  and the first semiconductor layers  111  may be alternately formed on the first semiconductor layer  111  in contact with the substrate  101 . An uppermost layer of the stack structure ST may be the second semiconductor layer  112 . The first semiconductor layers  111  and the second semiconductor layers  112  may be formed using, for example, an epitaxial growth method, but the example embodiment is not limited thereto. In this case, the first semiconductor layers  111  and the second semiconductor layers  112  may share a similar crystalline structure and/or orientation. 
     The first semiconductor layers  111  and the second semiconductor layers  112  may include materials having different etch selectivity. The first semiconductor layers  111  may refer to sacrificial semiconductor layers, and the second semiconductor layers  112  may refer to nanosheet semiconductor layers. For example, the first semiconductor layers  111  may be used as sacrificial layers for forming a gate structure, and the second semiconductor layers  112  may be used as a channel layer. The first semiconductor layers  111  may include SiGe. The second semiconductor layers  112  may include, for example, at least one of Si, Ge, and/or a group III-V compound semiconductor. 
     Subsequently, a first mask pattern M 1  extending in the first direction (e.g., the X direction) may be formed on the stack structure ST. The first mask pattern M 1  may include, for example, a silicon nitride film and/or a silicon oxynitride film. Before the first mask pattern M 1  is formed, a buffer oxide layer  180  may be formed on the stack structure ST (e.g., on an uppermost second semiconductor layer  112 ) to mitigate a difference in the coefficients of thermal expansion between the materials of the stack structure ST and the first mask pattern M 1 , thereby reducing and/or preventing the first mask pattern M 1  from detaching from the stack structure ST during a subsequent thermal process. 
     Subsequently, referring to  FIGS.  5 A and  5 B , a fin-shaped structure AF may be formed by etching the stack structure ST using the first mask pattern M 1 . 
     For example, a protruding fin-type active region  105  corresponding to the fin-shaped structure AF may be provided by etching a portion of the upper surface of the substrate  101 . The fin-shaped structure AF may include first semiconductor patterns  151  and second semiconductor patterns  152  alternately stacked on the fin-type active region  105  of the substrate  101 . The fin-shaped structure AF may have a structure extending in the second direction (e.g., the Y direction). 
     In this etching process, an edge portion of the buffer oxide layer  180  may be partially removed by over-etching, and an edge portion OE of an upper surface of the uppermost second semiconductor layer  152  may be exposed. The exposed edge portion OE may extend in the second direction (e.g., the Y direction). The exposed edge portion OE may be provided as a growth surface (e.g., a nucleation and/or seed surface) of the silicon epitaxial growth in a subsequent silicon epitaxial liner forming process. As a result, the uppermost second semiconductor layer  152 , for example, the uppermost channel layer, may have a different shape (e.g., a protruding portion PT), which will be described in detail in subsequent processes. 
     Next, referring to  FIGS.  6 A and  6 B , the silicon epitaxial liner  160  may be conformally formed on the surface of the fin-shaped structure AF. 
     Before the silicon epitaxial liner  160  is formed, a process of cleaning the etched surface of the preceding process, using a cleaning solution such as HF or SC-1, may be performed. Oxide-based and/or carbon-based impurities and particles remaining may be removed from the etched surface to prepare the surface for epitaxial growth. 
     Alternatively, even in the case in which the precleaning process is not sufficiently performed, the protruding portion PT (e.g., a conical producing portion) may be formed in the process in which an amorphous portion  160 T is crystallized on the first mask pattern M 1  from a portion  160 E of a silicon epitaxial liner  160  on the side surface of the fin-shaped structure AF. 
     The silicon epitaxial liner  160  may be formed by performing a general epitaxial growth process for the entire area including a peripheral circuit area (e.g., I/O circuit area) (not illustrated) and/or a selective epitaxial growth (SEG) for only the cell area. In the case of general epitaxial growth, polysilicon and/or amorphous silicon, rather than the epitaxial layer, may be formed in the transistor in the peripheral circuit area, depending on the growth surface conditions (see  FIG.  20 B ). Selective epitaxial growth (SEG) may be performed by applying an etchback process to remove a material (e.g., polysilicon) formed in another area (e.g., peripheral circuit area) along with general epitaxial growth. 
     The silicon epitaxial liner formation is not limited thereto, and may be performed at a relatively low temperature. For example, the silicon epitaxial liner formation may be performed in the range of 300° C. to 700° C. Unlike a silicon nitride (SiN) liner, the silicon epitaxial liner  160  may reduce a well leakage problem caused by the charge of the nitrogen element. 
     In addition, unlike a polysilicon liner, the silicon epitaxial liner  160  may suppress intermixing of Ge elements in the second semiconductor layers  152 , which may include, for example, SiGe. For example, as illustrated in  FIG.  11   , in the subsequent annealing process, polysilicon may be relatively rapidly oxidized and/or consumed, whereas the oxidization and/or consumption of silicon epitaxial liner is relatively delayed, and therefore is used herein as a liner to prevent intermixing. 
     In the silicon epitaxial liner  160  formed in this process, the surfaces of the fin-type active region  105  and the portion  160 E grown on the side of the fin-shaped structure AF are grown to have a required (and/or otherwise desirable) epitaxial shape, but the portion  160 T grown on the surface of the first mask pattern M 1 , which is an amorphous surface, is therefore not epitaxially grown, but may be formed of amorphous or polysilicon. 
     On the other hand, in the process of forming the silicon epitaxial liner, the edge portion OE of the upper surface of the second semiconductor layer  152  exposed by removing the buffer oxide layer  180  is provided as an epitaxial growth surface, and the silicon epitaxial portion ET may also be grown on the edge portion OE. 
     In this process, the silicon epitaxial liner  160  may be conformally formed to have a relatively constant thickness ts. For example, those regions of the silicon epitaxial liner  160  that were epitaxially grown may have a constant thickness ts within manufacturing or operational tolerance. The thickness ts of the silicon epitaxial liner  160  may be oxidized and consumed in a subsequent annealing process, and may be appropriately determined as an intermixing control factor of germanium (Ge). For example, the thickness ts of the silicon epitaxial liner  160  may range from 5 Å to 50 Å. 
     In this process, after formation of the silicon epitaxial liner, a process of nitriding the surface of the silicon epitaxial liner using plasma may be selectively performed to form a nitridation-processed surface  165 . For example, a plasma nitridation process may be applied to the surface of the silicon epitaxial liner  160 . The oxidation rate of the silicon epitaxial liner  160  in a subsequent process may be controlled by the nitridation-processed surface  165 . 
     Next, a process of forming the device isolation layer ( 110  in  FIG.  2   ) may be performed. A process of forming the device isolation layer according to the present embodiment will be described in detail with reference to  FIGS.  7 A to  10 B . 
     First, referring to  FIGS.  7 A and  7 B , a first gap-fill insulating film  110 A′ may be formed on the silicon epitaxial liner  180  to surround the fin-shaped structure AF. 
     The first gap-fill insulating film  110 A′ may include an oxide layer formed by deposition process like a flowable chemical vapor deposition (FCVD) process and/or a spin coating process. A device isolation layer ( 110  of  FIG.  3   ) may be form in a process including forming the gap-fill insulating film  110 A′ and performing an annealing (e.g. a wet annealing) process multiple times (e.g., two or more times), and thus, the first gap-fill insulating film  110 A′ provided primarily in this process may be sufficiently hardened in a subsequent process. 
     Next, referring to  FIGS.  8 A and  8 B , the first gap-fill insulating film  110 A′ may be strengthened by using an annealing process. 
     Through this process, the gap-fill insulating film  110 A′ may be oxidized, and therefor changed to a first insulating layer  110 A of, for example, SiO 2 . This process may be performed by wet annealing and/or dry annealing (indicated by black arrows). For example, the wet annealing process may be performed at 300° C. to 1100° C. in an H 2 /O 2  atmosphere. The H 2 /O 2  atmosphere may, for example, include H 2 O vapor. In this process, at least a portion of the silicon epitaxial liner  160  is oxidized, and thus, the volume of the liner  160  may increase (marked by white arrows). Due to the increase in volume of the silicon epitaxial liner  160 , compressive stress is applied to the first gap-fill insulating film  110 A′, so that the first gap-fill insulating film  110 A′ may be more effectively strengthened. In this manner, the silicon epitaxial liner  160  provides an effect that may contribute to the robustness of the first gap-fill insulating film  110 A′. 
     In this process, compared to a polysilicon liner, the encroachment of the second semiconductor layers  152  (e.g., Si) is greatly alleviated, whereas as illustrated in  FIG.  8 B , the first encroachment of the semiconductor layers  151  (e.g., SiGe) may occur partially. 
     Next, referring to  FIGS.  9 A and  9 B , a second gap-fill insulating film  110 B may be formed, and an annealing process may be additionally applied. 
     The gap-fill insulating film formation and annealing process may be repeated until the space between the fin structures AF is sufficiently gap-filled. In this annealing process, the silicon epitaxial liner  160  may be oxidized to generate compressive stress to further strengthen the gap-fill insulating film  110 . In addition, a difference in the amount of encroachment between the first and second semiconductor layers  151  and  152  may be amplified during an additional annealing process, so that a change in width and shape of the first and second semiconductor layers  151  and  152  may occur. 
     On the other hand, a silicon epitaxial portion ET grown on the edge portion OE of the upper surface of the second semiconductor layer  152  from which the buffer oxide layer  180  has been removed may remain as a protruding portion PT on both edges of the upper surface of the uppermost second semiconductor layer  152  even after this process. 
     In some example embodiments, before forming the second gap-fill insulating film  110 B, a polysilicon layer (not illustrated) may be formed on the first gap-fill insulating film  110 A. The polysilicon layer may generate a greater compressive stress by contributing as a point and/or region that the oxidation consumption is much larger (see  FIG.  11   , about 3 times) than that of the silicon epitaxial during the annealing process, thereby greatly contributing to the hardening of the gap-fill insulating film. For example, the polysilicon layer may be deposited at a temperature ranging from 300° C. to 600° C. using Di-IsoPropyl-Amino-Silane (DIMS) as a seed layer. 
     Next, referring to  FIGS.  10 A and  10 B , a device isolation layer may be formed by partially removing the gap-fill insulating film so that the fin-shaped structure AF is exposed. 
     This process may be performed by removing the first mask pattern M 1  using a process such as chemical-mechanical polishing (“CMP”) and/or performing an etch back process for the gap-fill insulating film  110 ′. In the etch back process, the fin structure AF and some of the fin-type active areas may be exposed. The silicon epitaxial liner  160  oxidized in this process may remain without being removed, but is omitted for convenience of description. In an actual process, the oxidized liner  160  may be removed together in a process of removing an oxide layer used for a selective process used in forming a gate structure and forming a source/drain. 
     As described above, in the annealing process described above, a significant amount of encroachment is generated on both sides of the first semiconductor layers  151  in the second direction (e.g., the Y direction), while the second semiconductor layers  152  may hardly be encroached. However, an edge region adjacent to the first semiconductor layers  151  may be partially encroached, and the second semiconductor layers  152  located between the first semiconductor layers  151  have a slightly reduced width in the process in which upper and lower edge regions are encroached. 
     As a result, as illustrated in  FIG.  2   , widths Wa and Wb of the first semiconductor layers  152  located at the top and bottom may be greater than widths W 1  and W 2  of the first semiconductor layers  151  located therebetween. For example, this difference in width may range from about 1 nm to about 10 nm. 
     In addition, the second semiconductor layer  152  disposed at the top may have protruding portions PT on both sides of the upper surface thereof. The protruding portion PT may have a relatively pointed end toward the top. As illustrated in  FIG.  12 A , the protruding portion PT may extend in the first direction (e.g., the X direction). 
     The second semiconductor layers  152  are provided as channel layers, and the uppermost and lowermost second semiconductor layers  152  have a relatively large width. For example, the uppermost second semiconductor layer  152  may increase the volume of a channel region by the protruding portion PT, and thus, the DC performance of the semiconductor device may be improved. 
     On the other hand, as illustrated in  FIG.  10 B , the uppermost second semiconductor layer  152  may have downwardly inclined side surfaces EC 1 . Similarly, the lowermost second semiconductor layer  152  may have upwardly inclined side surfaces EC 2 . Both side end surfaces of the second semiconductor layers  152 , which are disposed between the first semiconductor layers  151  and of which widths are reduced by encroaching both upper and lower edge regions, may have a convex shape. 
     Next, a process of forming a gate structure and forming a source/drain may be performed. As described above, an oxidized silicon epitaxial liner  160 ′ may be removed together during the deposition and removal process of the mask (e.g., an oxide film) used for a selective processes (e.g., a P-type transistor region and an N-type transistor region, and/or a cell area and a peripheral circuit area) during gate structure formation and source/drain formation. 
       FIGS.  12 A to  12 D  are perspective views illustrating some other processes (dummy gate formation and source/drain formation) in a method of fabricating a semiconductor device according to an example embodiment. 
     Referring to  FIG.  12 A , a dummy gate electrode DG extending in a second direction (e.g., the Y direction) on the fin-shaped structure AF may be formed. 
     An etch stop layer  131  and a dummy gate layer (not illustrated) are sequentially formed on the fin structure AF, and an etching process is performed using a second mask pattern M 2  to form the dummy gate electrode DG. The dummy gate electrode DG may intersect a partial region of the fin-shaped structure AF, thereby forming the dummy gate electrode DG extending in the second direction (e.g., the Y direction). In this etching process, a semiconductor cap layer  155  and the etch stop layer  131  may also be patterned together with the dummy gate layer. For example, the dummy gate layer and/or the dummy gate electrode DG may include polysilicon and/or amorphous silicon. For example, the etch stop layer  131  may include silicon oxide, silicon nitride, or silicon oxynitride. 
     Next, referring to  FIG.  12 B , a gate spacer GSP may be formed on a sidewall of the dummy gate electrode DG. 
     For example, a spacer layer (not illustrated) covering the dummy gate electrode DG and the fin-shaped structure AF may be formed on the substrate  101 . Subsequently, the spacer layer may be etched back to form the gate spacer GSP remaining on the sidewall of the dummy gate electrode DG. The gate spacer GSP may include an oxide, nitride, oxynitride, oxycarbonitride, or a combination thereof. For example, gate spacer GSP may include silicon nitride (SiN), silicon oxynitride (SiON), silicon oxide (SiO 2 ), silicon oxycarbonitride (SiOCN), or combinations thereof. Each of the gate spacers GSP may include a single layer, but is not limited thereto, and may, for example, have a multilayer structure. 
     Next, referring to  FIG.  12 C , a recess R is formed on the fin-type active region  105  by removing regions of the fin-shaped structure AF exposed on both sides of the dummy gate electrode DG and the gate spacer GSP. 
     After the recess R is formed, a portion of the fin-type active region  105  in contact with the substrate  101  may remain, and may be provided as a lowermost channel region. The alternately stacked first semiconductor layers  151  and second semiconductor layers  152  may be exposed through the side surface of the recess R. In some embodiments, a selective etching process for forming an inner spacer may be additionally performed (see  FIGS.  17 A and  17 B ). 
     Next, referring to  FIG.  12 D , the source/drain regions SD may be formed by performing a selective epitaxial regrowth process on the surface exposed by the recess R. 
     The epitaxial structures grown on both sides of the dummy gate electrode DG may be provided as source/drain regions SD. The regrowth epitaxial layer may be grown from the semiconductor surface exposed on the bottom surface of the recess R and the first semiconductor layers  151  and the second semiconductor layers  152  exposed on the side surface of the recess R. As a result, the source/drain regions SD may share a similar crystalline structure and/or orientation to the first semiconductor layers  151  and/or the second semiconductor layers  152 . For example, the crystal structures of the source/drain regions SD, the first semiconductor layers  151  and/or the second semiconductor layers  152  may include the same crystalline structure and/or orientation within tolerances due to lattice mismatch and/or the production of real, non-ideal materials. The source/drain regions SD may have various shapes defined as crystallographically stable surfaces during a growth process. For example, the source/drain regions SD may have a pentagonal cross section. On the other hand, when the source/drain regions SD include silicon (Si) and/or silicon carbide (SiC) doped with n-type impurities, the cross section of the source/drain regions SD may have a hexagonal shape and/or a polygon having a gentle angle. 
       FIGS.  13 A and  13 B  are cross-sectional views of a portion illustrated in  FIG.  12 D , taken along lines D 1 -D 1 ′ and D 2 -D 2 ′. 
     Referring to  FIGS.  13 A and  13 B , the source/drain regions SD may contact side surfaces of the fin-shaped structure AF disposed below the dummy gate electrode DG and the gate spacer GSP, for example, the first semiconductor layers  151  and the second semiconductor layers  152 . 
     Next, a process of forming the gate structure GS by replacing the dummy gate electrode DG with a real gate electrode may be performed.  FIGS.  14 A to  16 B  are cross-sectional views respectively illustrating a process of forming a gate structure in a method of fabricating a semiconductor device according to some example embodiments. 
     Referring to  FIGS.  14 A and  14 B , an interlayer insulating film  123  is formed on the substrate  101  to cover the source/drain regions SD, the dummy gate electrode DG, and the gate spacer GSP, and subsequently, the interlayer insulating film  123  is planarized until the dummy gate electrode DG is exposed. 
     In this planarization process, the second mask pattern M 2  may be removed. The interlayer insulating film  123  may include at least one of a low dielectric constant material (e.g., a material with a dielectric constant lower than SiO 2 ), an oxide layer, a nitride layer, and an oxynitride layer. Examples of the low dielectric constant material include, for example, silicone dielectrics (e.g., Flowable Oxide (FOx)), polysilazane (e.g., Tonen® SilaZen (TOSZ)), Undoped Silica Glass (USG), Borosilica Glass (BSG), PhosphoSilaca Glass (PSG), BoroPhosphoSilica Glass (BPSG), Plasma Enhanced Tetra Ethyl Ortho Silicate (PETEOS), Fluoride Silicate Glass (FSG), High Density Plasma (HDP) oxide, Plasma Enhanced Oxide (PEOX), Flowable CVD (FCVD) oxide, and/or combinations thereof. 
     Subsequently, referring to  FIGS.  15 A and  15 B , the dummy gate electrode DG may be removed through the exposed area, and the etch stop layer  131  may be selectively removed. 
     By this process, an open region H may be formed between the gate spacers GSP. Side surfaces of the first semiconductor layers  151  and the second semiconductor layers  152  of the fin-shaped structure AF may be exposed in the second direction (e.g., the Y direction) through the open region H. 
     The first semiconductor layer  151  may be removed using an etchant having a higher etch rate for the second semiconductor layers  152  than for the first semiconductor layers  151 . A plurality of spaces H respectively corresponding to the first semiconductor layers  151  may be formed. As a result, the second semiconductor layers  152  may be provided as a plurality of channel layers by being connected to the source/drain regions SD in the first direction (e.g., the X direction). The width and shape of the second semiconductor layers  152  may have unique characteristics described in  FIG.  10 B . 
     Next, referring to  FIGS.  16 A and  16 B , a gate insulating film GI may be formed along the peripheries of the second semiconductor layers  152 , sidewalls of the gate spacer GSP, and the exposed source/drain regions SD. 
     The gate insulating film GI may be conformally formed, and the formation thereof may be performed by another insulating film forming process. Subsequently, the gate electrode GE may be formed on the gate insulating film GI to extend in the second direction (e.g., the Y direction), and may be formed in a space between the gate spacers GI, a space between the channel layers CH, and a space between the channel layer CH and the fin-type active region  105 . Accordingly, a required gate structure GS may be formed. 
       FIGS.  17 A and  17 B  are cross-sectional views taken along lines D 1 -D 1 ′ and D 2 -D 2 ′ of a semiconductor device according to another example embodiment. 
     A semiconductor device  100 A according to an example embodiment may be understood as being similar to the semiconductor device  100  illustrated in  FIG.  2   , except that an internal spacer IS included and the shape of the first channel layer CH 1 , which is the uppermost channel layer, is different. In addition, the components of the present embodiment may be understood with reference to the description of the same or similar components of the semiconductor device  100  illustrated in  FIG.  2    unless otherwise specified. 
     Although the first channel layer CH 1  of the semiconductor device  100  employed in the previous example embodiments has protruding portions (“PT” in  FIGS.  2  and  3   ) on both sides of the upper surface thereof, the first channel layer CH 1  of the semiconductor device  100 A employed in this example embodiment may have a relatively flat surface. As described in  FIGS.  5  and  6   , the protruding portion (“PT” in  FIGS.  2  and  3   ) is a mask structure, for example, a structure provided by partial etching of the buffer oxide layer, and therefore, depending on the mask formation process and the mask material, the over-etched portion may not be generated, and in this case, as illustrated in  FIG.  17 B , the upper surface of the first channel layer CH 1  may not have a protruding portion. Alternatively, in another example embodiment, when the over-etched portion of the buffer oxide layer is relatively large, the protrusion structure may have a relatively large size. 
     As illustrated in  FIG.  17 A , the semiconductor device  100 A may include internal spacers IS provided between the source/drain regions SD and the gate electrode GE. The internal spacers IS may be provided on one side of the gate electrode GE. The internal spacers IS and the channel layers CH may be alternately disposed in a direction perpendicular to the upper surface of the substrate  101 . The source/drain region SD may contact the channel layer CH, and may be spaced apart from the gate electrode GE with the internal spacers IS interposed therebetween. The gate insulating film GI may be interposed between the gate electrode GE and each of the channel layers  104 , and may extend between the gate electrode GE and each of the internal spacers IS. Each of the internal spacers IS may contact the gate insulating film GI. 
     After forming the recess (see  FIG.  12 C ) and before forming the source/drain regions SD (see  FIG.  12 D ), portions of side surfaces of the first semiconductor layers  151  in the first direction (e.g., the X direction) may be selectively etched, and internal spacers IS may be formed by filling the etched space with an insulating material. For example, the internal spacers IS may include SiN, SiCN, SiON, SiBN, SiOCN, SiBCN and/or SiOC. 
       FIG.  18    is a plan view illustrating a semiconductor device according to some example embodiments, and  FIGS.  19 A to  19 C  are cross-sectional views illustrating the semiconductor device of  FIG.  18   , taken along lines D 2   a -D 2   a ′, D 2   b -D 2   b ′, and D 2   c -D 2   c′.    
     Referring to  FIGS.  19 A and  19 B  together with  FIG.  18   , first and second transistors TR 1  and TR 2  are provided in a first region (I) of the substrate  101 , and the first region (I) of the substrate  101  may be a memory cell area in which a plurality of memory cells are formed and/or a logic cell area in which logic transistors are disposed. For example, the first and second transistors TR 1  and TR 2  may be portions of a memory cell transistor constituting a plurality of SRAM cells and/or of logic transistors constituting a processor core. 
     Referring to  FIGS.  18  and  19 C , third transistors TR 3  are provided in a second region (II) of the substrate  101 , and the second region (II) of the substrate  101  may be a peripheral circuit area constituting a power supply circuit or the like. In some embodiments, the third transistor TR 3  comprises an input/output device, for example, and may be configured to operate at a higher voltage than the first and second transistors TR. 
     First, referring to  FIGS.  19 A and  19 B , the first and second transistors TR 1  and TR 2  are illustrated as transistors of different conductivity types formed in different conductivity type wells W 1  and W 2 . For example, the first transistor TR 1  may be a P-MOSFET formed in the n-type well W 1 , and the second transistor TR 2  may be an N-MOSFET formed in the p-type well W 2 , and/or the inverse. However, the example embodiments are not limited thereto, but in another embodiment, the first and second transistors TR 1  and TR 2  may include the same conductivity type transistors formed in the same conductivity type well. 
     As illustrated in  FIGS.  19 A and  19 B , respective channel layers CH_A and CH_B of the first and second transistors may have different widths. For example, the channel layer CH_A of the first transistor TR 1  may have a width greater than that of the channel layer CH_B of the second transistor TR 2 . In this case, even when the first and second transistors TR 1  and TR 2  have different widths, in the introduction of the silicon epitaxial liner and the annealing process for forming the device isolation layer, as described above, the width and shape of each channel layer may have specific characteristics thereof. 
     For example, in the first transistor TR 1 , first and fourth channel layers CH 1   a  and CH 4   a  may have widths greater than that of second channel layers CH 2   a  and CH 3   a  disposed therebetween, and also, similarly in the second transistor TR 2 , first and fourth channel layers CH 1   b  and CH 4   b  have widths greater than the widths of second channel layers CH 2   b  and CH 3   b  disposed therebetween. In addition, the first channel layers CH 1   a  and CH 1   b  of the first and second transistors TR 1  and TR 2  may have portions protruding upwardly on both edges of the upper surfaces, and may have downwardly inclined side surfaces. Similarly, the fourth channel layers CH 4   a  and CH 4   b  of the first and second transistors TR 1  and TR 2  may have upwardly inclined side surfaces. On the other hand, both side end surfaces of the second and third channel layers CH 3   a , CH 3   b , CH 4   a , and CH 4   b  may have a convex shape. 
     The first and second source/drain regions SD 1  and SD 2  may be epitaxial layers regrown from the channel layers CH_A and CH_B on the bottom and side surfaces of the fin-type active region  105 . When the first transistor TR 1  is a P-MOSFET, the first source/drain regions SD 1  may include a material that provides compressive strain to the channel layers CH_A. For example, the first source/drain regions SD 1  may include a SiGe layer having a lattice constant greater than that of Si. The first source/drain regions SD 1  may have a P-type impurity region. Inversely, when the second transistor TR 2  is an N-MOSFET, the second source/drain regions SD 2  may include a semiconductor material that provides stretchable strain to the channel layers CH_B. For example, the second source/drain regions SD 2  may include a SiC layer having a lattice constant smaller than that of Si, or a Si layer having substantially the same lattice constant as the substrate  101 . The second source/drain regions SD 2  may have an N-type impurity region. 
     Referring to  FIG.  19 C , as described above, the third transistors TR 3  may constitute a peripheral circuit such as an input/output device, and may employ a channel structure having a single active fin FA instead of a stacked channel structure using multi-nanosheets.  FIGS.  20 A to  20 C  are cross-sectional views illustrating some processes of the method of fabricating the semiconductor device illustrated in  FIG.  19 C . 
     First, referring to  FIG.  20 A , an insulating film  171  may be formed on the surface of the active fin FA. The insulating film  171  may include an amorphous material and/or an oxide. For example, a section of a substrate  101  may be etched so that a fin structure is formed, the fin structure may correspond to the active fin FA and/or the active region  105 . The etching process forming the active fin FA may be the same or a different etching process illustrated in  FIGS.  5 A and  5 B . After the formation of the fin structure the insulating film  171  may be deposited on the substrate layer. Next, referring to  FIG.  20 B , a liner  175  including polysilicon and/or amorphous silicon is formed on the insulating film  171 . This liner forming process may be performed together with the silicon epitaxial liner process illustrated in  FIGS.  6 A and  6 B . In the process of forming the silicon epitaxial liner  160  described in  FIGS.  6 A and  6 B , a liner  175  formed of polysilicon or amorphous silicon, not silicon epitaxial, may be formed on the amorphous insulating film  171  in the second region. Next, referring to  FIG.  20 C , subsequent processes such as a gap-fill insulating film  110  and a device isolation layer forming process such as an annealing process may be performed on the liner  175 . 
     As set forth above, according to some example embodiments, a semiconductor device having a channel having a three-dimensional structure, with improved electrical characteristics and reliability, may be provided. 
     While some 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.