Abstract:
A method for fabricating semiconductor device is disclosed. The method includes the steps of: providing a substrate; forming a sacrificial mandrel on the substrate, wherein the sacrificial mandrel comprises an indentation; and forming a spacer adjacent to the sacrificial mandrel.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a method for fabricating semiconductor device, and more particularly to a method of utilizing sidewall image transfer (SIT) technique for fabricating fin-shaped structures. 
         [0003]    2. Description of the Prior Art 
         [0004]    With increasing miniaturization of semiconductor devices, it is crucial to maintain the efficiency of miniaturized semiconductor devices in the industry. However, as the size of the field effect transistors (FETs) is continuously shrunk, the development of the planar FETs faces more limitations in the fabricating process thereof. On the other hand, non-planar FETs, such as the fin field effect transistor (Fin FET) have three-dimensional structure, not only capable of increasing the contact to the gate but also improving the controlling of the channel region, such that the non-planar FETs have replaced the planar FETs and become the mainstream of the development. 
         [0005]    The current method of forming the Fin FETs is forming a fin structure on a substrate primary, and then forming a gate on the fin structure. The fin structure generally includes the stripe-shaped fin formed by etching the substrate. However, under the requirements of continuous miniaturization, the width of each fin, as well as the pitch between fins have to be shrunk accordingly. Thus, the fabricating process of the Fin FETs also faces more challenges and limitations. For example, the fabricating process is limited by current mask and lithography techniques, such that it has problems to precisely define the position of the fin structure, or to precisely control the etching time, thereby leading to the fin collapse or over-etching issues, and seriously affecting the efficiency of the fin structure. 
       SUMMARY OF THE INVENTION 
       [0006]    According to a preferred embodiment of the present invention, a method for fabricating semiconductor device is disclosed. The method includes the steps of: providing a substrate; forming a sacrificial mandrel on the substrate, wherein the sacrificial mandrel comprises an indentation; and forming a spacer adjacent to the sacrificial mandrel. 
         [0007]    According to another aspect of the present invention, a semiconductor device is disclosed. The semiconductor device includes: a substrate; a fin-shaped structure on the substrate, wherein the fin-shaped structure comprises a gate structure thereon and a first epitaxial layer adjacent to two sides of the gate structure; a dummy fin-shaped structure on the substrate and adjacent to the fin-shaped structure, wherein the dummy fin-shaped structure comprises a second epitaxial layer thereon; and a contact plug on the first epitaxial layer and the second epitaxial layer. 
         [0008]    According to another embodiment of the present invention, a semiconductor device is disclosed. The semiconductor device includes: a substrate; a fin-shaped structure on the substrate; and a dummy fin-shaped structure on the substrate and adjacent to the fin-shaped structure, wherein the dummy fin-shaped structure comprises a curve. 
         [0009]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIGS. 1-5  are top views illustrating a method for fabricating semiconductor device according to a preferred embodiment of the present invention. 
           [0011]      FIG. 6  illustrates a cross-sectional view of  FIG. 5  along the sectional line AA′. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to  FIGS. 1-5 ,  FIGS. 1-5  are top views illustrating a method for fabricating semiconductor device according to a preferred embodiment of the present invention. As shown in  FIG. 1 , a substrate  12 , such as a silicon substrate is provided, and at least one sacrificial mandrel, such as sacrificial mandrels  14  and  16  are formed on the substrate  12 . In this embodiment, the formation of the sacrificial mandrels  14  and  16  could be accomplished by first covering a material layer (not shown) on the substrate  12  entirely, and then performing a pattern transfer process by using etching to remove part of the material layer for forming a plurality of patterned material layers serving as sacrificial mandrels  14  and  16  on the substrate  12 . In this embodiment, the sacrificial mandrels  14  and  16  could be selected from the group consisting of polysilicon, silicon oxide, and silicon nitride, but not limited thereto. It should also be noted that even though two sacrificial mandrels  14  and  16  are disclosed in this embodiment, the quantity of the sacrificial mandrels  14  and  16  could also be adjusted according to the demand of the product, which is also within the scope of the present invention. 
         [0013]    Next, a sacrificial mandrel cut process is conducted by first forming a patterned mask, such as a patterned resist on the sacrificial mandrels  14  and  16  to expose part of the sacrificial mandrel  16 , and then removing part of the sacrificial mandrel  16  through etching process to form an indentation  18  or opening without separating the sacrificial mandrel  16 . In this embodiment, the indentation  18  is preferably square shaped or rectangular shaped, but not limited thereto. For instance, the shape of the region exposed by the patterned resist could be adjusted according to the demand of the process to form indentation of any geometric shape, which are all within the scope of the present invention. Viewing from another perspective, each of the sacrificial mandrels  14  and  16  formed by the aforementioned cutting process preferably includes a first side  20  and a second side  22 , in which the second side  22  of the sacrificial mandrel  16  includes the aforementioned indentation  18 . 
         [0014]    Next, as shown in  FIG. 2 , a cap layer (not shown) is formed to cover the sacrificial mandrels  14  and  16  and the substrate  12 , and an etching back process is conducted to remove part of the cap layer for forming spacers  24  and  26  surrounding the sacrificial mandrels  14  and  16 . It should be noted that since the second side  22  of the sacrificial mandrel  16  includes the indentation  18 , the spacer  26  adjacent to the second side  22  preferably includes a turning point, such as a substantially c-shaped twist  48  shown in  FIG. 2 . 
         [0015]    Next, as shown in  FIG. 3 , the sacrificial mandrels  14  and  16  are removed, and the spacers  24  and  26  adjacent to the sacrificial mandrels  14  and  16  are used as mask to remove part of the substrate  12  along with a fin-cut process to form fin-shaped structures  28 ,  30 ,  32  and a dummy fin-shaped structure  34  in the substrate  12 . The spacers  24  and  26  could be removed after the fin-shaped structures  28 ,  30 ,  32  and dummy fin-shaped structure  34  are formed. 
         [0016]    In this embodiment, the fin-cut process is preferably accomplished by conducting an etching process to remove front and back ends connecting the fin-shaped structures  28 ,  30 ,  32  and dummy fin-shaped structure  34  so that the originally circular fin-shaped structures  28 ,  30 ,  32  and dummy fin-shaped structure  34  are divided and separated into individual stripe-shaped patterns without contacting each other, in which gate structures would be formed on fin-shaped structures  28 ,  30 ,  32  in the later process while no gate structures will be formed on the dummy fin-shaped structure  34  thereafter. Since the fin-shaped structures  28 ,  30 ,  32  and dummy fin-shaped structure  34  are preferably formed by the transfer of the spacers  24  and  26  pattern, the position and pattern of the fin-shaped structures  28 ,  30 ,  32  and dummy fin-shaped structure  34  preferably correspond to the position and pattern of the aforementioned spacers  24  and  26 . Specifically, the fins-shaped structures  28 ,  30 ,  32  are preferably straight rectangular patterns while the dummy fin-shaped structure  34  is a substantially rectangular pattern with a turning point, such as a substantially c-shaped twist  48  shown in  FIG. 3 . It should be noted that even though the turning point is represented by right angled curves in  FIG. 3 , the turning point under actual circumstance, such as after optical proximity effect (OPE), etching, and cleaning process, would reveal an omega shaped curve  50 , as shown in  FIG. 4 . 
         [0017]    Referring to  FIGS. 5 and 6 ,  FIG. 6  illustrates a cross-sectional view of  FIG. 5  along the sectional line AA′. As shown in  FIGS. 5 and 6 , a gate structure fabrication process is conducted by first forming a gate structure  36  on the fin-shaped structure  32  and a gate structure  38  on the fin-shaped structures  28  and  30 . The nature and composition of the gate structures  36  and  38  could vary depending on whether the gate structures are fabricated by a gate first process, high-k first process from gate last process, or high-k last process from gate last process. For instance, the gate structures  36  and  38  could include elements such as interfacial layer, high-k dielectric layer, bottom barrier metal (BBM) layer, polysilicon layer, and hard mask layer, and as the fabrication of gate structures are well known to those skilled in the art, the details of which are not explained herein for the sake of brevity. 
         [0018]    Next, a first epitaxial layer  40  and a second epitaxial layer  42  are disposed on the fin-shaped structures  28 ,  30 ,  32  and dummy fin-shaped structure  34 , in which the first epitaxial layer  40  is preferably formed on the fin-shaped structures  28 ,  30 ,  32  and adjacent to two sides of the gate structures  36  and  38  while the second epitaxial layer  42  is covered on the dummy fin-shaped structure  34  entirely. In this embodiment, the formation of the first epitaxial layer  40  and second epitaxial layer  42  could be accomplished by first selectively etching the fin-shaped structure  32  adjacent to two sides of the gate structures  36  and  38  to form recesses (not shown) or directly trimming the epitaxial layer, and then conducting a selective epitaxial growth process to grow the first epitaxial layer  40  in the recess and at the same time forming the second epitaxial layer  42  on the surface of the dummy fin-shaped structure  34 . The composition of the first epitaxial layer  40  and second epitaxial layer  42  could be adjusted according to the type of the transistor being fabricated, such as silicon germanium or silicon phosphorus, but not limited thereto. It should be noted that elements such as spacer could be formed around the gate structures  36  and  38  and lightly doped drains and source/drain regions could be formed in the fin-shaped structures  38 ,  30 ,  32  adjacent to the gate structures  36  and  38  before or after forming the first epitaxial layer  40  and second epitaxial layer  42 , and as the order and formation of these elements are well known to those skilled in the art, the details of which are not explained herein for the sake of brevity. 
         [0019]    Next, a silicide process is conducted to form a silicide  44  on the first epitaxial layer  40  and second epitaxial layer  42 , an interlayer dielectric (ILD) layer (not shown) is covered on the substrate  12  and gate structures  36  and  38 , and at least one conductive plug  46  is formed in the ILD layer to electrically connect to the silicide  44 . This completes the fabrication of a semiconductor device according to a preferred embodiment of the present invention. 
         [0020]    Overall, the present invention preferably forms sacrificial mandrel on a substrate, removes part of the sacrificial mandrel to form an indentation during a sidewall image transfer (SIT) process, and then forms a spacer on the sidewall of the sacrificial mandrel. Due to the presence of the indentation, part of the spacer formed on the sidewall of the sacrificial mandrel would be retracted inward to form a turning point or curve so that after the pattern of the spacer is transferred to the substrate to form fin-shaped structures and dummy fin-shaped structure, the dummy fin-shaped structure would reveal a substantially omega-shaped curve. According to a preferred embodiment of the present invention, the design of the curve in the dummy fin-shaped structure could be used to reduce the gap or distance between the first epitaxial layer and second epitaxial layer grown on the fin-shaped structures and dummy fin-shaped structure respectively, and also allow the contact plug formed thereafter to contact and sit on the first epitaxial layer and second epitaxial layer simultaneously. This increases the overall contact area of the contact plug and reduces the resistance between the contact plug and epitaxial layer significantly. 
         [0021]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.