Patent Publication Number: US-2021167186-A1

Title: Semiconductor device fabrication method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation application of U.S. patent application Ser. No. 16/447,818, filed on Jun. 20, 2019, which is a divisional of U.S. patent application Ser. No. 15/473,164, filed Mar. 29, 2017, now U.S. Pat. No. 10,374,065, issued on Aug. 6, 2019, which priority to Chinese patent application No. 201610379438.4, filed with the State Intellectual Property Office of People&#39;s Republic of China on Jun. 1, 2016, the content of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to integrated semiconductor devices, and more particularly to methods for manufacturing a fin-type field effect transistor (FinFET) device. 
     BACKGROUND OF THE INVENTION 
     With the advance in semiconductor technology, feature sizes of complementary metal oxide semiconductor (CMOS) devices can be scaled down to 14 nm technology node and below through incorporating high-k dielectrics in the gate stack, strain engineering techniques, pocket implants and material optimization processes. However, further scaling of planar devices presents a significant challenge due to degrading short channel effects, process variations and reliability degradation. 
     The technological advance of FinFET devices enables further feature size reduction of CMOS devices beyond the 14 nm node. Through a fully depleted fin, short channel effect can be controlled, random doping fluctuation can be reduced, parasitic junction capacitance can be reduced, and area efficiency can be improved. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the present disclosure provide methods for manufacturing a semiconductor device and semiconductor devices manufactured by the provided methods. 
     According to some embodiments of the present disclosure, a method of manufacturing a semiconductor device includes providing a substrate, forming a first semiconductor layer on the substrate, forming a stack of one or more semiconductor layer structures on the first semiconductor layer, each of the semiconductor layer structures including a first insulator layer and a second semiconductor layer on the first insulator layer, the first and second semiconductor layers having a same semiconductor compound, and performing an etching process on the stack of one or more semiconductor layer structures and the first semiconductor layer to form a fin structure. 
     In an embodiment, each of the semiconductor layer structures further includes a third semiconductor layer below the first insulator layer, so that the first insulator layer is between the third semiconductor layer and the second semiconductor layer, the second and third semiconductor layers having at least a common compound element. The second and third semiconductor layers each comprise a group III-V compound. 
     In an embodiment, the second semiconductor layer includes three compound elements, and the third semiconductor layer includes two compound elements. The third semiconductor layer includes InP. 
     In an embodiment, the method may further include forming a fourth semiconductor layer on the substrate, and the first semiconductor layer is formed on the fourth semiconductor layer. The fourth semiconductor layer includes InAlAs. 
     In an embodiment, the method may further include forming a high-k dielectric layer on the substrate, wherein the first semiconductor layer is formed on the high-k dielectric layer. 
     In an embodiment, the first semiconductor layer includes InGaAs, the second semiconductor layer includes InGaAs, and the first insulator layer includes a high-k dielectric material. The high-k dielectric material includes HfO 2 . 
     In an embodiment, performing the etching process includes removing a portion of the fin structure to form a trench on opposite sides of the fin structure, and filling the trench with a second insulator layer. 
     Embodiments of the present disclosure also provide another method of manufacturing a semiconductor device. The method includes providing a substrate, forming a first semiconductor layer on the substrate, forming a stack of one or more semiconductor layer structures on the first semiconductor layer, each of the semiconductor layer structures comprising a second semiconductor layer and a third semiconductor layer on the a second semiconductor layer, the second and third semiconductor layers having at least a common compound element, and the third semiconductor layer and the first semiconductor layer having a same semiconductor compound. The method also includes performing an etching process on the stack of one or more semiconductor layer structures and the first semiconductor layer to form a fin structure, performing a selective etching process on the second semiconductor layer to form a first air gap between the first semiconductor layer and the third semiconductor layer and a second air gap between each of adjacent third semiconductor layers in the stack of one or more semiconductor layer structures, and filling the first and second air gaps with an insulator layer. 
     In an embodiment, the method further includes, prior to performing the etching process on the stack of one or more semiconductor layer structures and the first semiconductor layer to form the fin structure, etching the second semiconductor layer in each of the one or more semiconductor layer structures, and performing the selective etching process includes removing a portion of the second semiconductor layer in each of the one or more semiconductor layer structures. 
     In an embodiment, the method further includes forming a fourth semiconductor layer on the substrate, and the first semiconductor layer is formed on the fourth semiconductor layer. 
     In an embodiment, the substrate includes silicon, the first semiconductor layer includes germanium tin, the second semiconductor layer includes germanium, the third semiconductor layer includes germanium tin, and the insulator layer includes silicon oxide. 
     Embodiments of the present disclosure also provide a semiconductor device manufactured based on one of the above-described methods. The semiconductor device includes a substrate, and a fin structure. The fin structure includes a first semiconductor layer on the substrate, and a stack of one or more semiconductor layer structures, each of the semiconductor layer structures including a first insulator layer and a second semiconductor layer on the first insulator layer, and the first and second semiconductor layers have the same semiconductor compound. 
     In an embodiment, each of the semiconductor layer structures further includes a third semiconductor layer below the first insulator layer, so that the first insulator layer is between the third semiconductor layer and the second semiconductor layer, the third semiconductor layer and the second semiconductor layer have at least a common compound element. 
     In an embodiment, the third semiconductor layer comprises InP. The third semiconductor layer and the second semiconductor layer each include a group III-V compound. 
     In an embodiment, the second semiconductor layer includes three compound elements, and the third semiconductor layer includes two compound elements. 
     In an embodiment, the substrate includes a fourth semiconductor layer, and the first semiconductor layer is on the fourth semiconductor layer. 
     In an embodiment, the substrate includes a high-k dielectric layer, and the first semiconductor layer is on the high-k dielectric layer. In an embodiment, the first semiconductor layer includes InGaAs, the second semiconductor layer includes InGaAs, and the first insulator layer includes a high-k dielectric material. The high-k dielectric material includes HfO 2 , and the fourth semiconductor layer includes InAlAs. 
     Embodiments of the resent disclosure also provide another semiconductor device manufactured by a different method. The semiconductor device includes a substrate, and a fin structure. The fin structure may include a first semiconductor layer on the substrate, and a stack of one or more semiconductor layer structures, each of the semiconductor layer structures including an insulator layer and a third semiconductor layer on the first insulator layer, the first and third semiconductor layers having a same semiconductor compound. 
     In an embodiment, the substrate includes a fourth semiconductor layer, and the first semiconductor layer is on the fourth semiconductor layer. 
     In an embodiment, the first semiconductor layer includes germanium tin, the third semiconductor layer includes germanium tin, and the insulator layer includes silicon oxide. 
     The following detailed description together with the accompanying drawings will provide a better understanding of the nature and advantages of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flowchart of a method for manufacturing a semiconductor device according to an embodiment of the present disclosure. 
         FIG. 2A  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure according to one embodiment of the present disclosure. 
         FIG. 2B  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure according to one embodiment of the present disclosure. 
         FIG. 2C  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure according to one embodiment of the present disclosure. 
         FIG. 2D  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure according to one embodiment of the present disclosure. 
         FIG. 3A  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure according to another embodiment of the present disclosure. 
         FIG. 3B  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure according to another embodiment of the present disclosure. 
         FIG. 3C  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure according to another embodiment of the present disclosure. 
         FIG. 3D  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure according to another embodiment of the present disclosure. 
         FIG. 4  is a flowchart of a method for manufacturing a semiconductor device according to another embodiment of the present disclosure. 
         FIG. 5A  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure taken along the longitudinal direction according to yet another embodiment of the present disclosure. 
         FIG. 5B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 5A  taken along the line A-A′ in the traverse direction (perpendicular to the longitudinal direction). 
         FIG. 6A  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure taken along the longitudinal direction according to yet another embodiment of the present disclosure. 
         FIG. 6B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 6A  taken along the line B-B′ in the traverse direction. 
         FIG. 7A  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure taken along the longitudinal direction according to yet another embodiment of the present disclosure. 
         FIG. 7B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 7A  taken along the line C-C′ in the traverse direction. 
         FIG. 8A  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure taken along the longitudinal direction according to yet another embodiment of the present disclosure. 
         FIG. 8B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 8A  taken along the line D-D′ in the traverse direction. 
         FIG. 9A  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure taken along the longitudinal direction according to yet another embodiment of the present disclosure. 
         FIG. 9B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 9A  taken along the line E-E′ in the traverse direction. 
         FIG. 10A  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure taken along the longitudinal direction according to yet another embodiment of the present disclosure. 
         FIG. 10B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 10A  taken along the line F-F′ in the traverse direction. 
         FIG. 11A  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure taken along the longitudinal direction according to yet another embodiment of the present disclosure. 
         FIG. 11B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 11A  taken along the line G-G′ in the traverse direction. 
         FIG. 12A  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure taken along the longitudinal direction according to yet another embodiment of the present disclosure. 
         FIG. 12B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 12A  taken along the line H-H′ in the traverse direction. 
         FIG. 13A  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure taken along the longitudinal direction according to yet another embodiment of the present disclosure. 
         FIG. 13B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 13A  taken along the line I-I′ in the traverse direction. 
         FIG. 14A  is a cross-sectional view illustrating an intermediate stage in the manufacturing process of a semiconductor structure taken along the longitudinal direction according to yet another embodiment of the present disclosure. 
         FIG. 14B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 14A  taken along the line J-J′ in the traverse direction. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present disclosure now will be described more fully hereinafter with reference to the accompanying drawings. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. The features may not be drawn to scale, some details may be exaggerated relative to other elements for clarity. Like numbers refer to like elements throughout. 
     It will be understood that when an element such as a layer, region or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “lateral” or “vertical” or “bottom” and “top” may be used herein to describe a relationship of one element, layer or region to another element, layer or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. 
     The use of the terms “first”, “second”, “third”, etc. do not denote any order, but rather the terms first, second, third etc. are used to distinguish one element from another. Furthermore, the use of the terms “a”, “an”, etc. does not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “having”, “includes”, and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Embodiments of the disclosure are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments and intermediate structures) of the disclosure. The thickness of layers and regions in the drawings may be enlarged relative to other layers and regions for clarity. Additionally, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the disclosure should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a discrete change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the disclosure. 
     Embodiments of the present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
       FIG. 1  is a flowchart of a method for manufacturing a semiconductor device according to an embodiment of the present disclosure.  FIG. 2A  through  FIG. 2D  are cross-sectional views illustrating intermediate stages of a semiconductor structure in different process steps of a method of manufacturing according to an embodiment of the present disclosure. 
     Referring to  FIG. 1 , the method may include providing a substrate and forming a first semiconductor layer on the substrate in step S 101 . 
       FIG. 2A  is a cross-sectional view illustrating an intermediate stage of a semiconductor structure in step S 101  according to an embodiment of the present disclosure. As shown in FIG.  2 A, a first semiconductor layer  21  is formed on a semiconductor substrate  20  (e.g., silicon). In an embodiment, first semiconductor layer  21  may include InGaAs (indium gallium arsenide compound). In an embodiment, first semiconductor layer  21  may have a thickness in the range between 100 Å and 1000 Å, e.g., 300 Å, 500 Å, or 800 Å. 
     In an embodiment, the semiconductor substrate may include four semiconductor layers formed on semiconductor substrate  20 , and the first semiconductor layer is formed on the four semiconductor layers. 
     In an embodiment, the semiconductor substrate may include a high-k dielectric layer (not shown) formed on semiconductor substrate  20 , and the first semiconductor layer is formed on the high-k dielectric layer. 
     Referring back to  FIG. 1 , in step S 102 , a stack of one or more semiconductor layer structures is formed on the first semiconductor layer. 
       FIG. 2B  is a cross-sectional view illustrating an intermediate stage of a semiconductor structure in step S 102  according to an embodiment of the present disclosure. As shown in  FIG. 2B , a stack of one or more semiconductor layer structures  30  is formed on first semiconductor layer  21 . Semiconductor layer structure  30  may include a first insulator layer  31  and a second semiconductor layer  22  on first insulator layer  31 . First semiconductor layer  21  includes the same semiconductor compound as that of second semiconductor layer  22 . 
     It is understood that the term “semiconductor compound” used herein refers to a semiconductor compound that includes main elements from different groups of the periodic table for forming the semiconductor layer, but does not include impurity elements that may affect the conductivity type of the semiconductor layer. 
     In an embodiment, second semiconductor layer  22  includes a group III-V compound. In an embodiment, second semiconductor layer  22  may include three compound elements, e.g., InGaAs. In an embodiment, second semiconductor layer  22  may have a thickness in the range between 100 Å and 1000 Å, e.g., 300 Å, 500 Å, or 800 Å. 
     In an embodiment, first insulator layer  31  may include a high-k dielectric material, e.g., HfO 2 . For example, the high-k dielectric material may include zirconium dioxide or titanium dioxide. In an embodiment, first insulator layer  31  may have a thickness in the range between 5 Å and 50 Å, e.g., 10 Å, or 30 Å. 
     It is understood that the number of semiconductor layer structures  30  can be any integer number N. In the example shown in  FIG. 2B , two semiconductor layer structures  30  are formed on first semiconductor layer  21 . But it is understood that the number is arbitrary chosen for describing the example embodiment and should not be limiting. 
     In an embodiment, first insulator layer  31  may be formed on first semiconductor layer  21  using a deposition process. In an embodiment, second semiconductor layer  22  may be formed on first insulator layer  31  using a deposition or sputtering process. In an embodiment, first insulator layer  31  may be formed on second semiconductor layer  22  using a deposition process. Second semiconductor layer  22  and first insulator layer  31  may then be alternately formed in this order to form subsequent semiconductor layer structures. 
     Referring back to  FIG. 1 , in step S 103 , a etch process is performed on the stack of one or more semiconductor layer structures and the first semiconductor layer to form a fin structure. 
       FIG. 2C  is a cross-sectional view illustrating an intermediate stage of a semiconductor structure in step S 103  according to an embodiment of the present disclosure. As shown in  FIG. 2C , a portion of the stack of one or more semiconductor layer structures  30  and a portion first semiconductor layer  21  are removed by etching to form a fin structure. A portion of the substrate (e.g., semiconductor substrate  20 ) is also removed by the etching process, as shown in  FIG. 2C . 
     In an embodiment, performing the etching process includes forming a first patterned mask layer, e.g., photoresist (not shown) on the structure shown in  FIG. 2B . In an embodiment, performing the etching process may also include removing a portion of the structure in  FIG. 2B  using the first patterned mask layer as a mask to form the fin structure. In an embodiment, the first patterned mask layer is then removed after forming the fin structure. 
     Thus, a method of manufacturing a semiconductor device according to an embodiment of the present disclosure is provided. 
     In an embodiment, referring to  FIG. 2C , a trench  26  is formed on opposite sides of the fin structure using the above-described etching process. In an embodiment, the method may further include partially filling trench  26  with a second insulator layer  32 , as shown in  FIG. 2D . For example, second insulator material  32  may include silicon dioxide. 
     In an embodiment, the step of partially filling the trench may include depositing the second insulator layer to completely fill trench  26 , and then performing an etching process on second insulator layer  32  to remove a portion of the second insulator layer, so that second insulator layer  32  partially fills trench  26 . 
     In another embodiment, the step of forming the fin structure and the second insulator layer may include forming a patterned hardmask layer (e.g., silicon nitride) on the structure shown in  FIG. 2B . In an embodiment, the step of forming the fin structure and the second insulator layer may also include performing an etching process on the semiconductor layer structure and the first semiconductor layer using the hardmask layer as a mask to obtain the fin structure including the trench. In an embodiment, the step of forming the fin structure and the second insulator layer may also include forming the second insulator layer to fill the trench and cover the hardmask layer using a deposition process. In an embodiment, the step may also include planarizing (e.g., using a chemical mechanical polishing process) the second insulator layer to expose a surface of the hardmask layer, and removing the hardmask layer using a wet etch process (e.g., using hot phosphoric acid). In an embodiment, the step may also include performing an etching process on the second insulator layer to remove a portion of the second insulator layer, so that the second insulator layer partially fills the trench. 
     A semiconductor device is provided by the above-described method of the present disclosure. Referring to  FIG. 2D , a semiconductor device may include a substrate (e.g., semiconductor substrate  20  including silicon) and a fin structure on the substrate. 
     In an embodiment, the fin structure includes a first semiconductor layer  21  on the substrate, and a stack of one or more semiconductor layer structures  30  on first semiconductor layer  21 . Semiconductor layer structure  30  may include a first insulator layer  31  and a second semiconductor layer  22  on first insulator layer  31 . First semiconductor layer  21  includes the same semiconductor compound as that of second semiconductor layer  22 . 
     In an embodiment, first semiconductor layer  21  includes InGaAs and has a thickness in the range between 100 Å and 1000 Å, e.g., 300 Å, 500 Å, or 800 Å, etc. 
     In an embodiment, second semiconductor layer  22  includes a group III-V compound. In an embodiment, second semiconductor layer  22  may include three compound elements, e.g., InGaAs. In an embodiment, second semiconductor layer  22  may have a thickness in the range between 100 Å and 1000 Å, e.g., 300 Å, 500 Å, or 800 Å, etc. 
     In an embodiment, first insulator layer  31  may include a high-k dielectric material, e.g., HfO 2 . For example, the high-k dielectric material may include titanium dioxide or titanium dioxide. In an embodiment, first insulator layer  31  may have a thickness in the range between 5 Å and 50 Å, e.g., 10 Å, or 30 Å. 
     In an embodiment, the substrate may also include a fourth semiconductor layer, and the first semiconductor layer is formed on the fourth semiconductor layer. 
     In an embodiment, the substrate may also include a high-k dielectric layer, and the first semiconductor layer is formed on the high-k dielectric layer. 
     In an embodiment, referring to  FIG. 2D , the fin structure has a trench  26  on opposite sides thereof. The semiconductor device may include a second semiconductor layer  32  (e.g., silicon oxide) partially filling trench  26 . 
     In a semiconductor device according to some embodiments of the present disclosure, a source and a drain may be formed in second semiconductor layer (e.g. InGaAs)  22 , and a gate may be formed on the fin structure to form an NMOS device or a PMOS device, where a portion of the second semiconductor layer between the source and the drain may serve as a channel region. Comparing with conventional fin structures without the insulator layers, the fin structure of the present disclosure includes one or more insulator layers (e.g., first insulator layer  31 ) to achieve a higher ratio of an on-current to an off-current (On current/Off current ratio), thereby improving the device performance. 
       FIG. 3A  through  FIG. 3D  are cross-sectional views illustrating intermediate stages of a semiconductor structure in different process steps of a method of manufacturing according to another embodiment of the present disclosure. 
     First, referring to  FIG. 3A , a first semiconductor layer (e.g., InGaAs)  21  is formed on a substrate, which includes a semiconductor substrate (e.g., semiconductor substrate)  20  and a fourth semiconductor layer (e.g., InAlAs)  24 . In an embodiment, fourth semiconductor layer  24  includes InAlAs and has a thickness in the range between 100 Å and 1000 Å, e.g., 300 Å, 500 Å, or 800 Å, etc. 
     Next, referring to  FIG. 3B , a stack of one or more semiconductor layer structures  34  are formed on first semiconductor layer  21 . Semiconductor layer structure  34  includes a first insulator (e.g., high-k dielectric) layer  31  and a second semiconductor layer (e.g., InGaAs)  22  on first insulator layer  31 . First semiconductor layer  21  includes the same semiconductor compound as that of second semiconductor layer  22 . 
     In an embodiment, semiconductor layer structure  34  may also include a third semiconductor layer  23  below first insulator layer  31 , so that first insulator layer  31  is disposed between third semiconductor layer  23  and second semiconductor layer  22 , as shown in  FIG. 3B . Third semiconductor layer  23  and second semiconductor layer  22  include at least a common compound element. In an embodiment, third semiconductor layer  23  includes a group III-V compound. In an embodiment, third insulator layer  23  may include two compound elements, e.g., indium phosphide (InP). In an embodiment, third semiconductor layer  23  has a thickness in the range between 5 Å and 50 Å, e.g., 10 Å, 20 Å, or 40 Å. 
     In an embodiment, third semiconductor layer  23  may be formed on first semiconductor layer  21  using a molecular beam epitaxy (MBE) or a metal organic chemical vapor deposition (MOCVD) process. In an embodiment, first insulator layer  31  is formed on third semiconductor layer  23  using a deposition process. In an embodiment, second semiconductor layer  22  is formed on first insulator layer  31  using a deposition or sputtering process. In an embodiment, third semiconductor layer  23  of a next semiconductor layer structure  34  is formed on second semiconductor layer  22  of the semiconductor layer structure below using an MBE or MOCVD process. 
     Next, referring to  FIG. 3C , an etching process is performed on the stack of one or more semiconductor layer structures  34 , first semiconductor layer  21  and fourth semiconductor layer  24  to form a fin structure. The etching process forms a trench  26  on opposite sides of the fin structure. In an embodiment, the etching process also removes a portion of semiconductor substrate  20 , as shown in  FIG. 3C . 
     Next, referring to  FIG. 3D , trench  26  is filled with a second insulator layer  32 . 
     Thus, the method of the present disclosure provides a semiconductor device  3 . Referring to  FIG. 3D , semiconductor device  3  includes a substrate and a fin structure on the substrate. The substrate may include a semiconductor substrate (e.g., silicon substrate)  20  and a fourth semiconductor layer (e.g., InAlAs)  24  on semiconductor substrate  20 . In an embodiment, fourth semiconductor layer  24  includes InAlAs and has a thickness in the range between 100 Å and 1000 Å, e.g., 300 Å, 500 Å, or 800 Å. 
     In an embodiment, referring still to  FIG. 3D , the fin structure may include a first semiconductor layer (e.g., InGaAs)  21  on the substrate, a stack of one or more semiconductor layer structures  34  on first semiconductor layer  21 . Semiconductor layer structure  34  includes a first insulator layer (e.g., high-k dielectric)  31  and a second semiconductor layer (e.g., InGaAs)  22  on first insulator layer  31 . First semiconductor layer  21  includes the same semiconductor compound as that of second semiconductor layer  22 . In an embodiment, semiconductor layer structure  34  also includes a third semiconductor layer  23  below first insulator layer  31 , so that first insulator layer  31  is disposed between third semiconductor layer  23  and second semiconductor layer  22 . Third semiconductor layer  23  and second semiconductor layer  22  have at least a common compound element. 
     In an embodiment, third semiconductor layer  23  includes a group III-V compound. In an embodiment, third semiconductor layer  23  may include two compound elements, e.g., indium phosphide (InP). In an embodiment, third semiconductor layer  23  has a thickness in the range between 5 Å and 50 Å, e.g., 10 Å, 20 Å, or 40 Å. 
     In an embodiment, referring still to  FIG. 3D , a trench  26  is disposed on opposite sides of the fin structure. The semiconductor device further includes a second insulator layer  32  partially filling trench  26 . 
     Embodiments of the present disclosure also provide a semiconductor device having a source and a drain in second semiconductor layer  22  and a gate on the fin structure to form an NMOS device or a PMOS device, where a portion of second semiconductor layer  22  between the source and the drain forms a channel region. Comparing with conventional fin structures without the insulator layers, the fin structure of the present disclosure includes one or more insulator layers (e.g., first insulator layer  31 ) to achieve a higher On current/Off current ratio, thereby improving the device performance. 
     In an embodiment, the second and third semiconductor layers each include a group III-V compound. For example, the second semiconductor layer includes InGaAs, and the third semiconductor layer includes InP. The structure reduces the stress at the top portion of the fin structure and the group III-V compound has a relatively high mobility, which can improve the electrical properties of the device. 
       FIG. 4  is a flowchart of a method for manufacturing a semiconductor device according to another embodiment of the present disclosure.  FIGS. 5A, 5B, 6A, 6B, 7A, 7B, 8A, 8B, 9A , and  9 B are cross-sectional views illustrating intermediate stages of a semiconductor structure in different process steps of a method of manufacturing according to another embodiment of the present disclosure. 
     Referring to  FIG. 4 , in step S 401 , the method may include providing a substrate and forming a first semiconductor layer on the substrate. 
       FIG. 5A  is a cross-sectional view illustrating an intermediate stage of a semiconductor structure in step S 401  along the longitudinal direction according to an embodiment of the present disclosure.  FIG. 5B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 5A  taken along line A-A′ in the traverse direction (perpendicular to the longitudinal direction) of  FIG. 5A . As shown in  FIG. 5A  and  FIG. 5B , a first semiconductor layer  41  is formed on a semiconductor substrate  40 . The semiconductor substrate may include silicon, e.g., undoped silicon or boron doped silicon. For example, boron doped silicon may have a better etch selectivity than undoped silicon, i.e., the etch rate of boron doped silicon is slower than the etch rate of undoped silicon. In an embodiment, first silicon layer  41  includes germanium tin compound (Ge 1-x Sn x ). In an embodiment, first silicon layer  41  has a thickness in the range between 5 nm and 50 nm, e.g., 10 nm, 30 nm, etc. 
     In an embodiment, the substrate may include a fourth semiconductor layer on semiconductor substrate  40  (not shown), and first semiconductor layer  41  is on the fourth semiconductor layer. 
     Referring back to  FIG. 4 , in step S 402 , the method may include forming a stack of one or more semiconductor layer structures. 
       FIG. 6A  is a cross-sectional view illustrating an intermediate stage of a semiconductor structure in step S 402  along the longitudinal direction according to an embodiment of the present disclosure.  FIG. 6B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 6A  taken along line B-B′ in the traverse direction of  FIG. 6A . As shown in  FIG. 6A  and  FIG. 6B , a stack of one or more semiconductor layer structures  50  is formed on first semiconductor layer  41 . Semiconductor layer structure  50  includes a second semiconductor layer  42  and a third semiconductor layer  43  on second semiconductor layer  42 . Second semiconductor layer  42  and third semiconductor layer  43  may include at least a common compound element. First semiconductor layer  41  and third semiconductor layer  43  have the same semiconductor compound. 
     In an embodiment, second semiconductor layer  42  includes germanium (Ge) and has a thickness in the range between 5 nm and 50 nm, e.g., 10 nm, 30 nm, etc. 
     In an embodiment, second semiconductor layer  42  includes a germanium tin compound and has a thickness in the range between 5 nm and 50 nm, e.g., 10 nm, 30 nm, etc. 
     It is understood that the number of semiconductor layer structures  50  can be any integer number N. In the example shown in  FIG. 6A  and  FIG. 6B , two semiconductor layer structures  50  are formed on first semiconductor layer  41 . But it is understood that the number is arbitrary chosen for describing the example embodiment and should not be limiting. 
     In an embodiment, second semiconductor layer  42  may be formed on first semiconductor layer  41  using an epitaxial growth process. In an embodiment, third semiconductor layer  43  may be formed on second semiconductor layer  42  using an epitaxial growth process. In an embodiment, second semiconductor layer  42  of the next semiconductor layer structure may be formed on third semiconductor layer  43  of the current semiconductor layer structure using an epitaxial growth process. 
     Referring back to  FIG. 4 , in step S 403 , the method may include performing an etching process on the stack of one or more semiconductor structures and the first semiconductor layer to form a fin structure. 
       FIG. 7A  is a cross-sectional view illustrating an intermediate stage of a semiconductor structure in step S 403  along the longitudinal direction according to an embodiment of the present disclosure.  FIG. 7B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 7A  taken along the line C-C′ in the traverse direction of  FIG. 7A . As shown in  FIG. 7A  and  FIG. 7B , a portion of the stack of one or more semiconductor structures  50  and a portion of first semiconductor layer  41  are removed by etching to form a fin structure. 
     In an embodiment, as shown in  FIG. 7A  and  FIG. 7B , the fin structure includes a first portion  61  disposed in the middle portion of the fin structure, a second portion  62 , and a third portion  63  adjacent to opposite sides of first portion  61  along the longitudinal direction. In an embodiment, as shown in  FIG. 7B , the dimension of first portion  61  is smaller than the dimension of second portion  62  and smaller than the dimension of third portion  63  in the transverse direction (perpendicular to the longitudinal direction). 
     In an embodiment, the step of performing the etching process on the stack of one or more semiconductor structures and the first semiconductor layer may include forming a second mask layer, e.g., photoresist (not shown) on semiconductor layer structures  50 , and etching the stack of semiconductor layer structures  50  and first semiconductor layer  41  using the second mask layer as a mask to remove a portion of semiconductor layer structures  50  and a portion of first semiconductor layer  41  to form the fin structure. For example, the etching process may be performed using an interferometer endpoint (IEP) process based on chlorine gas (Cl 2 ) or an inductively coupled plasma (ICP) process. In an embodiment, after the etching process has been carried out, the method also includes removing the second mask layer. 
     Referring back to  FIG. 4 , in step S 404 , the method may include selectively removing the second semiconductor layer in the fin structure to form an air gap between the first semiconductor layer and the third semiconductor layer. 
       FIG. 8A  is a cross-sectional view illustrating an intermediate stage of a semiconductor structure in step S 404  along the longitudinal direction according to an embodiment of the present disclosure.  FIG. 8B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 8A  taken along the line D-D′ in the traverse direction of  FIG. 8A . As shown in  FIG. 8A  and  FIG. 8B , a portion of second semiconductor layer  42  is selectively removed by etching to form an air gap  70  between first semiconductor layer  41  and third semiconductor layer  43  and between two third semiconductor layer  43  in each of the stack of semiconductor layer structures. 
     In an embodiment, the step of selectively etching includes forming a third patterned mask layer (e.g., photoresist) covering a portion  62  and a portion  63  of the fin structure and removing a portion  61  that is not covered by the third patterned mask layer. In an embodiment, first portion in the second semiconductor layer  62  may be removed using a microwave etching process based on carbon tetrafluoride (CF 4 ). The third patterned mask layer is removed thereafter. 
     Referring back to  FIG. 4 , in step S 405 , the method may include filling the air gaps with an insulator layer. 
       FIG. 9A  is a cross-sectional view illustrating an intermediate stage of a semiconductor structure in step S 405  along the longitudinal direction according to an embodiment of the present disclosure.  FIG. 9B  is a cross-sectional view illustrating an intermediate stage of the semiconductor structure in  FIG. 9A  taken along the line E-E′ in the traverse direction of FIG.  9 A. As shown in  FIG. 9A  and  FIG. 9B , an insulator layer  71  is formed filling air gap  70 . The insulator layer may include silicon dioxide. 
     In an embodiment, the step of forming the insulator layer may include a flowable chemical vapor deposition (FCVD) process covering the air gaps that have been selectively removed by etching. In an embodiment, the step of forming the insulator layer may also include selectively removing a portion of the insulator layer using an etch-back process, while retaining the portion of the insulator layer filling the air gaps. 
     Thus, the present disclosure provides the description of another method of manufacturing a semiconductor device. 
     According to the embodiment, as shown in  FIG. 9A  and  FIG. 9B , the semiconductor device includes a substrate and a fin structure on the substrate. In an embodiment, the substrate includes silicon (e.g., undoped silicon or boron doped silicon). 
     In an embodiment, the fin structure includes first semiconductor layer  41  on semiconductor substrate  40 , and a stack of one or more semiconductor layer structures  51  on first semiconductor layer  41 . Semiconductor layer structures  51  each may include insulator layer  71  and third semiconductor layer  43  on insulator layer  71 . First semiconductor layer  41  includes the same semiconductor compound as that of third insulator layer  43 . 
     In an embodiment, first silicon semiconductor layer  41  includes a germanium tin compound and has a thickness in the range between 5 nm and 50 nm, e.g., 10 nm, 30 nm, etc. 
     In an embodiment, third silicon semiconductor layer  43  includes a germanium tin compound and has a thickness in the range between 5 nm and 50 nm, e.g., 10 nm, 30 nm, etc. 
     In an embodiment, insulator layer  71  may include silicon dioxide. 
     In an embodiment, referring to  FIG. 9A , the fin structure may include a first portion  61  disposed in the middle portion of the fin structure, a second portion, and a third portion  63  adjacent to opposite sides of first portion  61  along the longitudinal direction. Second portion  62  and third portion  63  each may include a portion of second semiconductor layer  42  disposed between first semiconductor layer  41  and third semiconductor layer  43  and a portion of second semiconductor layer  42  disposed between two adjacent third semiconductor layers  43  of each of semiconductor layer structures  50 . In an embodiment, as shown in  FIG. 9B , the dimension of first portion  61  is smaller than the dimension of second portion  62  and smaller than the dimension of third portion  63  in the transverse direction (perpendicular to the longitudinal direction) of  FIG. 9A . 
     In an embodiment, a source and a drain may be formed in third semiconductor layer (Ge 1-x Sn x  compound)  43 , and a gate on the fin structure to form an NMOS or PMOS device, wherein a portion of the third semiconductor layer between the source and the drain is the channel region of the NMOS or PMOS device. Comparing with conventional fin structures without the insulator layers, the fin structure of the present disclosure includes one or more insulator layers (e.g., insulator layer  71 ) to achieve a higher on current/off current ratio, thereby improving the device performance. 
     In an embodiment, prior to forming the fin structure, the method may include forming a second semiconductor layer on the one or more semiconductor layer structures. In an embodiment, etching process a portion of the one or more semiconductor layer structures also includes removing a portion of the second semiconductor layer. In an embodiment, selectively etching also includes the remaining portion of the second semiconductor layer on the one or more semiconductor layer structures. 
       FIGS. 10A, 10B, 11A, 11B, 12A, 12B, 13A, 13B, 14A, and 14B  are cross-sectional views illustrating intermediate stages of a semiconductor structure in different process steps of a method of manufacturing according to yet another embodiment of the present disclosure. 
     First, as shown in  FIG. 10A  and  FIG. 10B , a first semiconductor layer  41  is formed on a substrate. In the embodiment, the substrate includes a semiconductor substrate  40  (e.g., silicon substrate) and a fourth semiconductor layer (silicon germanium)  44  on semiconductor substrate  40 . That is, first semiconductor layer  41  is on fourth semiconductor layer  44 . In an embodiment, fourth semiconductor layer  44  has a thickness in the range between 5 nm and 50 nm, e.g., 10 nm, 30 nm, etc. 
     In an embodiment, fourth semiconductor layer  44  may be formed on semiconductor substrate  40  using an epitaxial growth process. In an embodiment, first semiconductor layer  41  may be formed on fourth semiconductor layer  44  using an epitaxial growth process. 
     Next, as shown in  FIGS. 11A and 11B , a stack of one or more semiconductor layer structures  50  may be formed on first semiconductor layer  41 . A semiconductor layer structure  50  is firstly formed on the first semiconductor layer and includes a second semiconductor layer (e.g., germanium)  42  and a third semiconductor layer (e.g., germanium tin)  43  on second semiconductor layer  42 . Second semiconductor layer  42  includes at least one common compound element as that of third semiconductor layer  43 . First semiconductor layer  41  includes the same semiconductor compound as that of third semiconductor layer  43 . 
     Next, referring still to  FIGS. 11A and 11B , a second semiconductor layer (e.g., germanium)  42  of a subsequent semiconductor layer structure is formed on the current semiconductor layer structure using an epitaxial growth process. Thereafter, a third semiconductor layer (e.g., germanium tin)  43  is formed on the second semiconductor layer, and the process repeats to form subsequent semiconductor layer structures. 
     Next, referring to  FIGS. 12A and 12B , an etching process is performing on second semiconductor layers  42  in the stack of semiconductor layer structures  50 , semiconductor layer structures  50 , first semiconductor layer  41 , and fourth semiconductor layer  44  to form a fin structure. The fin structure may include a first portion  61  in the middle portion of the fin structure and a second portion  62  and a third portion  63  disposed on opposite sides of first portion  61  along the longitudinal direction. 
     Next, referring to  FIGS. 13A and 13B , portions of second semiconductor layers  42  of the fin structure are selectively removed to form an air gap  70  in the second semiconductor layer between first semiconductor layer  41  and third semiconductor layer  43  and in the second semiconductor layers between two adjacent third semiconductor layers  43  in the semiconductor layer structures. 
     In an embodiment, the selective etching process step also removes a portion of fourth semiconductor layer  44  (e.g., the portion of the fourth semiconductor layer disposed in portion  61 ) to form an air gap  70 ′ between semiconductor substrate  40  and first semiconductor layer  41 . 
     In an embodiment, the selective etching process step also removes portions  61  of second semiconductor layers  42  of the stack of one or more semiconductor layer structures to form air gaps in the second semiconductor layers. 
     Next, referring to  FIGS. 14A and 14B , an insulator layer  71  is formed filling air gaps  70  and  70 ′. 
     In summary, a semiconductor device is thus provided by yet another manufacturing method according to the present disclosure. Referring to  FIGS. 14A and 14B , the semiconductor device may include a substrate and a fin structure on the substrate. In an embodiment, the substrate may include a semiconductor substrate  40  and a fourth semiconductor layer  44  on semiconductor substrate  40 . In an embodiment, fourth semiconductor layer  44  includes SiGe and has a thickness in the range between 5 nm and 50 nm, e.g., 10 nm, 30 nm, etc. 
     In an embodiment, the fin structure includes a first semiconductor layer  41  on fourth semiconductor layer  44  and a stack of one or more semiconductor layer structures  51  on first semiconductor layer  41 . Semiconductor layer structures  51  each may include an insulator layer  71  and a third semiconductor layer  43  on insulator layer  71 . First semiconductor layer  41  includes the same semiconductor compound as that of third semiconductor layer  43 . In an embodiment, referring to  FIG. 14A , an insulator layer  71  may also be formed between semiconductor substrate  40  and first semiconductor layer  41 . 
     In another embodiment, a source and a drain may be formed in third semiconductor layer (e.g., germanium tin)  43 , a gate may be formed on the fin structure to form an NMOS device or a PMOS device having a portion of the third semiconductor layer between the source and the drain as a channel region. Comparing with conventional fin structures without the insulator layers, the fin structure of the present disclosure includes one or more insulator layers (e.g., insulator layer  71 ) to achieve a higher on current/off current ratio, thereby improving the device performance. 
     Thus, embodiments of the present disclosure provide a detailed description of a method of manufacturing a semiconductor device and a semiconductor device manufactured by the described method. Details of well-known processes are omitted in order not to obscure the concepts presented herein. 
     It is to be understood that the above described embodiments are intended to be illustrative and not restrictive. Many embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the disclosure should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.