Abstract:
A fin field-effect transistor structure includes a silicon substrate, a fin channel, a gate insulator layer and a gate conductor layer. The fin channel is formed on a surface of the silicon substrate, wherein the fin channel has at least one slant surface. The gate insulator layer formed on the slant surface of the fin channel. The gate conductor layer formed on the gate insulator layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of an application Ser. No. 13/023,581, filed on Feb. 09, 2011, now pending. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a fin field-effect transistor structure, and more particularly to a fin field-effect transistor structure applied to a semiconductor manufacturing process. The present invention also relates to a manufacturing process of such a fin field-effect transistor structure. 
       BACKGROUND OF THE INVENTION 
       [0003]    Nowadays, as integrated circuits are increasingly developed toward miniaturization, the conventional transistor structure whose channel and substrate are coplanar usually fails to meet the practical requirements. Especially, the performance of the conventional transistor structure in high-speed circuitry is unsatisfied because the current driving capability is insufficient. For solving these drawbacks, a fin field-effect transistor (FinFET) structure has been disclosed. 
         [0004]      FIG. 1  is a schematic view illustrating a FinFET structure according to the prior art. Like the typical FET structure, the FinFET structure of  FIG. 1  comprises a substrate  10 , a source  11 , a drain  12 , a gate insulator layer  13  and a gate conductor layer  14 . However, since a channel (not shown) between the source  11  and the drain  12  is covered by the gate insulator layer  13  and the gate conductor layer  14 , plural surfaces are utilized to provide more current paths. In other words, the FinFET structure has better current driving capability than the typical FET structure. However, the performance of the FinFET structure needs to be further optimized by improving the configurations and the manufacturing process of the FinFET structure. 
       SUMMARY OF THE INVENTION 
       [0005]    In accordance with another aspect, the present invention provides a fin field-effect transistor structure. The fin field-effect transistor structure includes a silicon substrate, a fin channel, a gate insulator layer and a gate conductor layer. The fin channel is formed on a surface of the silicon substrate, wherein the fin channel has at least one slant surface. The gate insulator layer is formed on the slant surface of the fin channel. The gate conductor layer is formed on the gate insulator layer. 
         [0006]    In an embodiment, the surface of the silicon substrate is a ( 100 ) crystal plane, a top surface of the fin channel is a ( 100 ) crystal plane, and the fin channel extends along a &lt; 100 &gt; direction. The slant surface is a ( 110 ) crystal plane or a ( 111 ) crystal plane, and the overall length of the slant surface is greater than the height of the fin channel. In this situation, the fin channel is a p-type fin channel. 
         [0007]    In an embodiment, the surface of the silicon substrate is a ( 110 ) crystal plane, a top surface of the fin channel is a ( 110 ) crystal plane, and the fin channel extends along a &lt; 100 &gt; direction. The slant surface is a ( 100 ) crystal plane, and the overall length of the slant surface is greater than the height of the fin channel. In this situation, the fin channel is an n-type fin channel. 
         [0008]    In an embodiment, a second fin channel with a polarity opposite to the fin structure is further formed on the silicon substrate, wherein the second fin channel has at least one vertical sidewall. 
         [0009]    In an embodiment, the fin channel has a sandglass-shaped cross section with a wide top region, a wide bottom region and a narrow middle region. 
         [0010]    In an embodiment, an included angle between the slant surface and a normal vector of the silicon substrate is 54.7 degrees. 
         [0011]    In an embodiment, the gate insulator layer and the gate conductor layer are further formed over the top surface of the fin channel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
           [0013]      FIG. 1  is a schematic view illustrating a FinFET structure according to the prior art; 
           [0014]      FIGS. 2A ,  2 B and  2 C schematically illustrate some crystal orientations; 
           [0015]      FIGS. 2D and 2E  schematically illustrate a fin channel of a FinFET structure according to the present invention; 
           [0016]      FIGS. 3A ,  3 B,  3 C and  3 D schematically illustrate some steps of a process of manufacturing a FinFET structure according to an embodiment of the present invention; and 
           [0017]      FIGS. 4A ,  4 B and  4 C schematically illustrate some steps of a process of manufacturing a FinFET structure according to another embodiment of the present invention; and 
           [0018]      FIGS. 5A ,  5 B,  5 C,  5 D,  5 E,  5 F and  5 G schematically illustrate some steps of a process of manufacturing a FinFET structure according to a further embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]    The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed. 
         [0020]    Since a silicon crystal has a diamond crystal lattice, the silicon crystal has many crystal orientations.  FIGS. 2A ,  2 B and  2 C schematically illustrate some crystal orientations. In  FIG. 2A , an equivalent crystallographic orientation of a crystal plane ( 100 ) is represented as &lt; 100 &gt;. In  FIG. 2B , an equivalent crystallographic orientation of a crystal plane ( 110 ) is represented as &lt; 110 &gt;. In  FIG. 2C , an equivalent crystallographic orientation of a crystal plane ( 111 ) is represented as &lt; 111 &gt;. 
         [0021]    As known, the highest electron mobility of the n-channel metal-oxide-semiconductor (NMOS) appears in the &lt; 110 &gt; direction on the ( 100 ) crystal plane; and the highest hole mobility of the p-channel metal-oxide-semiconductor (PMOS) appears in &lt; 110 &gt; direction of the ( 110 ) crystal plane. Since the common wafer used in the process of manufacturing a FinFET structure has a ( 100 ) crystal plane and a &lt; 110 &gt; notch direction, the wafer having the ( 100 ) crystal plane and the &lt; 110 &gt; notch direction is used for manufacturing a FinFET structure in this embodiment.  FIG. 2D  is a schematic top view illustrating a fin channel of a FinFET structure according to the present invention.  FIG. 2E  is a schematic cutaway view illustrating the fin channel of the FinFET structure taken along the dotted line. The fin channel  20  is directly formed on the ( 100 ) crystal plane of the wafer  2  by aligning the notch direction. The top surface  200  of the fin channel  20  is a ( 100 ) crystal plane, and the sidewall  201  of the fin channel  20  is a ( 110 ) crystal plane, and the fin channel  20  extends along the &lt; 110 &gt; direction. Due to the fin channel  20 , the highest hole mobility of the PMOS is achievable. However, in a case that the fin channel  20  is applied to the NMOS, the electron mobility of the NMOS is deteriorated. In other word, such fin channel needs to be further improved. 
         [0022]      FIGS. 3A ,  3 B,  3 C and  3 D schematically illustrate some steps of a process of manufacturing a FinFET structure according to an embodiment of the present invention. Firstly, as shown in  FIG. 3A , a wafer  30  having a ( 100 ) crystal plane and a &lt; 100 &gt;notch direction is provided. The wafer  30  is a silicon wafer or a silicon-on-insulator (SOI) wafer. Then, a shown in  FIG. 3B , hard masks  301  and  302  are formed on the surface of the ( 100 ) crystal plane of the wafer  30 . Then, an etching process is performed to form an n-type fin channel  303  and a p-type fin channel  304 , which extend along the &lt; 100 &gt; direction (see  FIGS. 3C and 3D ).  FIG. 3C  is a schematic cross-sectional view illustrating the fin channels of the FinFET structure of  FIG. 3B  taken along the dotted line.  FIG. 3D  is a schematic cutaway view illustrating the fin channels of the FinFET structure of  FIG. 3B  taken along the dotted line. The top surface  3031  of the n-type fin channel  303  and the top surface  3041  of the p-type fin channel  304  are ( 100 ) crystal planes. The vertical sidewall  3032  of the n-type fin channel  303  and the vertical sidewall  3042  of the p-type fin channel  304  are ( 100 ) crystal planes, and both extend along the &lt; 100 &gt; direction. By means of these fin channels, the electron mobility of the NMOS of the FinFET structure is not degraded and the improvement on the hole mobility of the PMOS is about 10%-15%. Consequently, the purpose of the present invention is achieved. Since the top surfaces  3031  and  3041  and the vertical sidewalls  3032  and  3042  are all ( 100 ) crystal planes, the manufacturing process of this embodiment is suitable to fabricate a tri-gate FinFET structure or a double-gate FinFET structure. 
         [0023]      FIGS. 4A ,  4 B and  4 C schematically illustrate some steps of a process of manufacturing a FinFET structure according to another embodiment of the present invention. The purpose of this embodiment is to further improve the n-type fin channel  303  and the p-type fin channel  304  as shown in  FIG. 3C . Firstly, as shown in  FIG. 4A , the top surface  3031  and the vertical sidewall  3032  of the n-type fin channel  303  are completely covered by a hard mask  41 . Whereas, the top surface  3041  of the p-type fin channel  304  is covered by a hard mask  42 , but the vertical sidewall  3042  is exposed. Then, as shown in  FIG. 4B , an anisotropic etching process is performed to etch the exposed vertical sidewall  3042  to form two slant surfaces  43  and  44 . In an embodiment, the anisotropic etching process is a wet etching process using an alkaline solution as an etchant. The alkaline solution is a tetramethylammonium hydroxide (TMAH) solution, an ammonium hydroxide (NH 4 OH) solution, a sodium hydroxide (NaOH) solution, a potassium hydroxide (KOH) solution, an ethylenediamine pyrocatechol (EDP) solution, or any other possible alkaline solution. By selecting a suitable etchant or adjusting the concentration of the etchant, the slant surfaces  43  and  44  may be formed at different etching rates. Since the anisotropic etching rates on the ( 110 ) crystal plane and the ( 111 ) crystal plane are different, the slant surfaces  43  and  44  may be fabricated as the ( 110 ) crystal planes or the ( 111 ) crystal planes by a well-known Wulff-Jaccodine process. 
         [0024]    After the vertical sidewall  3042  of the p-type fin channel  304  is anisotropically etched by using the hard mask  42  as an etching mask, the slant surfaces  43  and  44  are formed. In accordance with a key feature of the present invention, the overall length of the slant surfaces  43  and  44  is greater than the height of the vertical sidewall  3042 . That is, the overall length of the slant surfaces is greater than the height of the p-type fin channel  304 . Whereas, the n-type fin channel  303  maintains the original cross-sectional shape. On the other hand, due to the slant surfaces  43  and  44 , the p-type fin channel  304  has a sandglass-shaped cross section with a wide top region, a wide bottom region and a narrow middle region. In this situation, the p-type fin channel  304  has increased effective channel width. Afterward, a gate insulator layer  48  and a gate conductor layer  49  are formed on the n-type fin channel  303  and the p-type fin channel  304 , thereby producing the FinFET structure of  FIG. 4C . Moreover, due to good surface adhesive ability, an atomic layer deposition (ALD) process may be performed to successfully fill the gate insulator layer  48  and the gate conductor layer  49  in the space between the slant surfaces  43  and  44 . Since the top surface of the p-type fin channel  304  is a ( 100 ) crystal plane but the slant surfaces of the p-type fin channel  304  are ( 110 ) or ( 111 ) crystal planes, the manufacturing process of this embodiment is suitable to fabricate a double-gate FinFET structure. 
         [0025]    In such way, sufficient effective channel width will be provided without the need of increasing the height of the p-type fin channel. The lower aspect ratio is good for fabricating the gate conductor layer in the subsequent process. As a consequence, the manufacturing process is simplified. For example, the fin channel of the conventional FinFET structure has an aspect ratio greater than 1 (e.g. 2-4). Whereas, according to the present invention, the aspect ratio of the sandglass-shaped fin channel of the FinFET structure is reduced to about 0.578. Moreover, the short channel effect and the drain induced barrier lowering (DIBL) of the sandglass-shaped fin channel are reduced when compared with the conventional vertical-sidewall channel. 
         [0026]    Alternatively, a sidewall etching process may be performed to etch the n-type fin channel.  FIGS. 5A ,  5 B,  5 C,  5 D,  5 E,  5 F and  5 G schematically illustrate some steps of a process of manufacturing a FinFET structure according to a further embodiment of the present invention. Firstly, as shown in  FIG. 5A , a wafer  50  having a ( 110 ) crystal plane and a &lt; 100 &gt; notch direction is provided. The wafer  50  is a silicon wafer or a silicon-on-insulator (SOI) wafer. Then, a shown in  FIG. 5B , hard masks  501  and  502  are formed on the surface of the ( 110 ) crystal plane of the wafer  50 . Then, an etching process is performed to form an n-type fin channel  503  and a p-type fin channel  504 , which extend along the &lt; 100 &gt;direction (see  FIGS. 5C and 5D ).  FIG. 5C  is a schematic cross-sectional view illustrating the fin channels of the FinFET structure of  FIG. 5B  taken along the dotted line.  FIG. 5D  is a schematic cutaway view illustrating the fin channels of the FinFET structure of  FIG. 5B  taken along the dotted line. The top surface  5031  of the n-type fin channel  503  and the top surface  5041  of the p-type fin channel  504  are ( 110 ) crystal planes. The vertical sidewall  5032  of the n-type fin channel  503  and the vertical sidewall  5042  of the p-type fin channel  504  are ( 110 ) crystal planes, and both extend along the &lt; 100 &gt; direction. Since all of the top surface and the vertical sidewalls are ( 110 ) crystal planes, the manufacturing process of this embodiment is suitable to fabricate a tri-gate FinFET structure or a double-gate FinFET structure. 
         [0027]    However, as shown in  FIG. 5E , if the top surface  5041  and the vertical sidewall  5042  of the p-type fin channel  504  are further completely covered by a hard mask  61 . Whereas, the top surface  5031  of the n-type fin channel  503  is covered by a hard mask  62 , but the vertical sidewall  5032  of the n-type fin channel  503  is exposed. Then, as shown in  FIG. 5F , an anisotropic etching process is performed to etch the exposed vertical sidewall  5032  to form two slant surfaces  53  and  54 . In an embodiment, the anisotropic etching process is a wet etching process using an alkaline solution as an etchant. The alkaline solution is a tetramethylammonium hydroxide (TMAH) solution, an ammonium hydroxide (NH 4 OH) solution, a sodium hydroxide (NaOH) solution, a potassium hydroxide (KOH) solution, an ethylenediamine pyrocatechol (EDP) solution, or any other possible alkaline solution. By selecting a suitable etchant or adjusting the concentration of the etchant, the slant surfaces  53  and  54  may be formed at different etching rates. Consequently, the slant surfaces  53  and  54  may be fabricated as the ( 100 ) crystal planes by a well-known Wulff-Jaccodine process. 
         [0028]    After the vertical sidewall  5032  of the n-type fin channel  503  is anisotropically etched, the slant surfaces  53  and  54  are formed. In addition, the overall length of the slant surfaces  53  and  54  is greater than the height of the vertical sidewall  5032 . That is, the overall length of the slant surfaces is greater than the height of the n-type fin channel  503 . 
         [0029]    Whereas, the p-type fin channel  504  maintains the original cross-sectional shape. On the other hand, due to the slant surfaces  53  and  54 , the n-type fin channel  503  has a sandglass-shaped cross section, wherein the included angle between the slant surface and a normal vector of the silicon substrate is  54 . 7  degrees. In this situation, the n-type fin channel  503  has increased effective channel width. Afterward, a gate insulator layer  58  and a gate conductor layer  59  are formed on the n-type fin channel  503  and the p-type fin channel  504 , thereby producing the FinFET structure of  FIG. 5G . Moreover, due to good surface adhesive ability, an atomic layer deposition (ALD) process may be performed to successfully fill the gate insulator layer  58  and the gate conductor layer  59  in the space between the slant surfaces  53  and  54 . Since the top surface is a crystal plane ( 100 ) but the slant surfaces are ( 100 ) crystal planes, the manufacturing process of this embodiment is suitable to fabricate a double-gate FinFET structure. 
         [0030]    In such way, sufficient effective channel width will be provided without the need of increasing the height of the n-type fin channel. The lower aspect ratio is good for fabricating the gate conductor layer in the subsequent process. As a consequence, the manufacturing process is simplified. For example, the fin channel of the conventional FinFET structure has an aspect ratio greater than 1 (e.g. 2-4). Whereas, according to the present invention, the aspect ratio of the sandglass-shaped fin channel of the FinFET structure is reduced to about 0.578. Moreover, the short channel effect and the drain induced barrier lowering (DIBL) of the sandglass-shaped fin channel are reduced when compared with the conventional vertical-sidewall channel. 
         [0031]    While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.