Abstract:
First and second epitaxial layers are spaced apart from one another over the surface of a semiconductor substrate. A gate electrode is formed over the surface of the substrate, and extends within a gap defined between the first and second epitaxial layers and partially overlaps each of the first and second epitaxial layers adjacent the gap. First and second impurity regions are contained at least partially within the first and second epitaxial layers, respectively, and a gate insulating layer is located between the gate electrode and the semiconductor substrate. A non-planar channel region may be defined within the portions of the first and second epitaxial layers which are overlapped by the gate electrode and within a surface portion the semiconductor substrate located between the first and second epitaxial layers.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention generally relates to semiconductor device structures and manufacturing methods thereof, and more particularly, this invention relates to semiconductor devices having non-planar channel structures which increase the channel lengths thereof, and to methods of manufacturing such devices.  
           [0003]    2. Description of Related Art  
           [0004]    Semiconductor devices such as field effect transistors (FETs) are becoming increasingly important in low power applications. As FET devices are scaled to smaller and smaller dimensions, manufacturers must refine transistor designs to maintain optimum device performance.  
           [0005]    A conventional transistor structure and manufacturing method thereof will be described below with reference to FIG. 1.  
           [0006]    Referring to FIG. 1, a device isolation layer is formed on a predetermined region of a silicon substrate  10 , and then a gate oxide layer  12  and a gate electrode  16  are formed on the silicon substrate  10 . Next, an oxide or a nitride spacer  18  is formed on the sides of the gate electrode  16 , and then, ion implantation is performed such that source/drain regions  20  having a lightly doped drain (LDD) configuration are formed.  
           [0007]    As the integration of semiconductor devices increases, it becomes necessary to reduce the size of the transistors of such devices. For example, in conventional memory cell designs that use planar transistors, such as the device shown in FIG. 1, the cell size is minimized by scaling lithographic features F, where F is the minimum line width of the feature size that can be patterned with lithography. Accordingly, if a minimum cell size is to be obtained, it is necessary to reduce the size of the transistor as much as possible. This, in turn, reduces the channel length of the device.  
           [0008]    However, when the channel length is decreased, performance degradations occur in the device. Electrical characteristics of the device, such as hot-carrier injection, drain leakage current, and punch through become poor. For a memory cell including such a device, data retention time decreases and power consumption increases due to the resultant short channel effects.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention is at least partially characterized by a transistor having a non-planar channel structure in which epitaxial layers are used to form elevated source and drain regions over a silicon subtrate, and by a method of manufacturing such a transistor.  
           [0010]    According to one aspect of the present invention, a semiconductor device includes a semiconductor substrate having a surface, and first and second epitaxial layers spaced apart from one another over the surface of a semiconductor substrate. A gate electrode is formed over the surface of the substrate, and extends within a gap defined between the first and second epitaxial layers and partially overlaps each of the first and second epitaxial layers adjacent the gap. First and second impurity regions are contained at least partially within the first and second epitaxial layers, respectively, and a gate insulating layer is located between the gate electrode and the semiconductor substrate.  
           [0011]    According to another aspect of the present invention, a method of manufacturing a semiconductor device includes selectively growing first and second epitaxial layers over a surface of a semiconductor substrate, forming a gate insulating layer over at least a portion of the first and second epitaxial layers and the surface of the semiconductor substrate, forming a gate electrode over the gate insulating layer such that the gate electrode extends within a gap defined between the first and second epitaxial layers and partially overlaps each of the first and second epitaxial layers adjacent the gap, and forming first and second impurity regions within the first and second epitaxial layers, respectively.  
           [0012]    According to the invention, a non-planar channel region may be defined within the portions of the first and second epitaxial layers which are overlapped by the gate electrode and within a surface portion the semiconductor substrate located between the first and second epitaxial layers. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    These and other features, and advantages, of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. It is important to point out that the illustrations may not necessarily be drawn to scale, and that there may be other embodiments of this invention that are not specifically illustrated but which will still fall under the scope of the present invention.  
         [0014]    [0014]FIG. 1 shows a conventional transistor structure.  
         [0015]    FIGS.  2 A- 2 J are sectional views illustrating a method of manufacturing a semiconductor device in accordance with one or more principles of the present invention;  
         [0016]    FIGS.  3 A- 3 B show a top level layout view of the semiconductor device illustrated in FIGS.  2 A- 2 J;  
         [0017]    FIGS.  4 A- 4 B are cross-section views illustrating another method of manufacturing a semiconductor device in accordance with one or more principles of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]    Hereinafter, embodiments of the present invention will be described in detail with reference to accompanying drawings.  
         [0019]    [0019]FIGS. 2A through 2J are sectional views of a device illustrating a method of manufacturing a transistor of a semiconductor device according to an embodiment of the present invention.  
         [0020]    Referring to FIGS. 2A through 2C, a device isolation layer is formed on a silicon substrate  30 , thereby defining an active region  31  and a field region  32 . Then, a sacrificial oxide layer  34  is deposited on the silicon substrate  30 . The sacrificial oxide layer  34  may be formed of tetraethylorthosilicate (TEOS). Si growth should not occur on the sacrificial oxide layer  34  during a subsequent selective epitaxial growth (SEG) process, and the etch rate of the sacrificial oxide layer  34  should be greater than a high density plasma (HDP) oxide layer used for the device isolation layer.  
         [0021]    Next, a photoresistive pattern  36  is formed by a photolithographic process on the sacrificial oxide layer  34 . Part of the sacrificial oxide layer  34  in the active region  31  on the silicon substrate  30  is etched by using the photoresistive pattern  36  as a mask, thereby forming a sacrificial oxide layer pattern  35 . In order to form the sacrificial oxide layer pattern  35 , both dry etching and wet etching methods may be used, but damage during dry etching occurs on the surface of the active region  31  on which epitaxial Si layers are to be grown. Therefore, it is preferable that the sacrificial oxide layer pattern  35  is formed using wet etching.  
         [0022]    Then, as shown in FIG. 2C, the sacrificial oxide layer pattern  35  is successively formed on the silicon substrate by removing the photoresistive pattern  36  with a photoresistive strip process.  
         [0023]    Referring to FIG. 2D, an epitaxial silicon layer  38  is selectively grown on the exposed portion of the active region  31  on the silicon substrate 30  by a low pressure chemical vapor deposition (LPCVD) method. In the selective epitaxial growth (SEG) process, epitaxial silicon layers should not be grown on the sacrificial oxide layer pattern  35  formed on the silicon substrate  30 , and on the oxide layer of an isolation region  32 .  
         [0024]    [0024]FIG.3A shows a top view of a layout of the semiconductor substrate of FIG. 2D. As shown in FIG. 3A, an epitaxial lateral overgrowth (ELO) phenomenon occurs during the SEG process such that epitaxial layer grows vertically and laterally. Therefore, even though the epitaxial layers  38  should be selectively grown only on the selected portions of the active region  31 , they extend to the field region  32 . However, the epitaxial layers  38  should not make contact with other epitaxial layers  38  in an adjacent active region  31 . Thus, the thickness of the epitaxial layers  38  is determined in consideration of an interval spacing between adjacent active regions  31  and controlled by the design rule of the device.  
         [0025]    Referring to FIG. 2E, the sacrificial oxide layer pattern  35  is removed by a wet cleaning process. When removing the sacrificial oxide layer pattern  35 , etching of a field oxide layer  32  is minimized by using wet cleaning conditions having a high etching selectivity with respect to the oxide layer of the field region  32 . Then, a gate oxide layer  40  is deposited on the exposed silicon substrate  30  and epitaxial layers  38  as a thermal oxide layer of a metal-oxide-silicon field effect transistor (MOSFET).  
         [0026]    Referring to FIG. 2F, a gate electrode layer  43  of the MOSFET is formed on the gate oxide layer  40 . The gate electrode layer  43  is formed of doped polysilicon.  
         [0027]    Referring to FIG. 2G, the surface of the gate electrode layer  43  is planarized by a chemical mechanical polishing (CMP) process. In order to obtain the margin of a depth of focus (DOF) when forming a subsequent gate electrode pattern, a curved portion of the gate electrode layer  43  is removed using the CMP process.  
         [0028]    Referring to FIG. 2H, a conductive layer  46  having low resistance, for example a metal such as tungsten (W), WSix, or CoSix, is deposited on the gate electrode layer  43 . Next, an insulating layer  48 , for example, SiN, a high temperature oxide (HTO), or a high density plasma (HDP) oxide is deposited on the conductive layer  46  to be used as a hard mask in a subsequent process of forming a pattern.  
         [0029]    Referring to FIG. 2I, a gate pattern  50  comprising the gate oxide layer  40 , the gate polysilicon layer  43 , the low resistance conductive layer  46 , and the mask insulating layer  48 , is formed in a stacked pattern on the silicon substrate  30  by a photolithographic process.  
         [0030]    Also as shown in FIG. 2I, source/drain doping layers are formed by implanting a low concentration of impurity ions in the epitaxial layers  38 , which are exposed to both sides of the gate pattern  50 .  
         [0031]    As can be seen in FIG. 3B, the epitaxial layers  38  overlap parts of the gate electrodes  43  and the field region  32 .  
         [0032]    Referring to FIG. 2J, an insulating layer of SiN or HTO is deposited on the entire surface of the silicon substrate  30 , and then etched to form sidewalls or spacers  56  on both sides of the gate pattern  50 . Next, the source/drain junctions  54  are formed by implanting a high concentration of impurity ions, thereby completing the MOSFET. In the case of an N-MOSFET, a doping layer having a high concentration is formed on the surface of the epitaxial silicon layer by using doses of arsenic (As) at a concentration 1×10 15  through 5×10 15  at an energy of 5-30 KeV. In case of a P-MOSFET, the doping layer is formed on the surface of the epitaxial silicon layer by using doses of boron difluoride (BF 2 ) or boron (B) a concentration 1×10 15  through 5×10 15  at an energy of 10-30 KeV.  
         [0033]    FIGS.  4 A- 4 B are sectional views of a device illustrating another method of manufacturing a transistor of a semiconductor device in accordance with one or more principles of the present invention. The steps shown above with respect to FIGS. 2A through 2E are the same in this alternative method, and so they are not shown again. As shown in FIG. 4A, after the gate oxide layer  40  is deposited on the exposed silicon substrate  30  and epitaxial layers  38 , a thin doped polysilicon layer  43 A is deposited on the gate oxide layer  40 , followed by a thicker, low-resistance conductive layer  46 A, such as Tungsten. Then, the conductive layer  46 A is planarized by a chemical mechanical polishing (CMP) process. Accordingly, as illustrated in the first and second embodiments, the CMP process may be performed after depositing the gate electrode layer  43 , or may be performed after depositing a conductive layer  46 A having a low resistance. The remainder of the process steps are the same as in the first embodiment.  
         [0034]    Accordingly, as shown in FIG. 2J, the FET formed according to the above-described embodiments lies in a groove which is formed by the epitaxial layers and the silicon substrate. The channel region thereby has a non-planar channel structure. That is, the channel region includes a portion in which the gate electrode overlaps the epitaxial layers grown on the silicon substrate and also includes a portion in which the gate electrode overlaps the silicon substrate. The length of the channel is the sum of the lengths of the curved portions  62  and  64  between the source/drain regions  52  and the substrate  30 , and the length of the portion  60  between the epitaxial layers  38 . Thus, where the widths of the gate electrodes are kept equal, the length of the channel region of the device of FIG. 2J is greater than the length of the channel region for a conventional device in which the gate electrodes only overlap only the flat silicon substrate.  
         [0035]    In the drawings and specification, there have been disclosed typical preferred embodiments of this invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the present invention being set forth in the following claims.