Patent Publication Number: US-8536638-B2

Title: Method of manufacturing a semiconductor device having lower leakage current between semiconductor substrate and bit lines

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/712,299, filed on Feb. 27, 2007, entitled “Semiconductor Device and Method of Manufacturing the Same,” which is a continuation in part of international patent application number PCT/JP2006/303702, filed Feb, 28, 2006 which are hereby incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a semiconductor device and a method of manufacturing the semiconductor device, and more particularly, to a semiconductor device that has bit lines formed in a semiconductor substrate and a method of manufacturing the semiconductor device. 
     2. Description of the Related Art 
     In recent years, non-volatile memories that are data-rewritable semiconductor devices are often used. In a flash memory, which is a typical non-volatile memory, each transistor forming a memory cell has a floating gate or an insulating film called a charge accumulating layer. As charges are accumulated in the charge accumulating layer, data is stored. An example of a flash memory having an insulating film as a charge accumulating layer is a SONOS (Silicon Oxide Nitride Oxide Silicon) flash memory that accumulates charges in the trapping layer in an ONO (Oxide/Nitride/Oxide) film. As a SONOS flash memory, U.S. Pat. No. 6,011,725 discloses a flash memory having virtual ground memory cells. Each of the virtual ground memory cells replaces the source and the drain with each other, and operates them in a symmetrical fashion. 
       FIG. 1  is a plan view of a memory cell of a conventional flash memory. It should be noted that an ONO film is not shown in  FIG. 1 . Bit lines  12  are formed with diffusion layers buried in a semiconductor substrate  10  extend in the vertical direction of  FIG. 1 , and word lines  23  extend in the width direction of the bit lines  12 . Contact portions  42  are provided for each of the bit lines  12  at intervals of every several word lines  23  (every eight or sixteen word lines  23 , for example). The contact portions  42  connect to wiring layers that are formed on the bit lines  12  and extend in the same direction as the bit lines  12 . 
     Since the bit lines  12  are formed with diffusion layers, the resistivity of the bit lines  12  is high. If the bit lines  12  have high resistance, the write and erase characteristics of the charges (or data) accumulated in the trapping layer in the ONO film deteriorate. Therefore, the bit lines  12  are connected to the wiring layers formed with metal layers via the contact portions  42 . In this manner, the resistance of the bit lines  12  can be made lower, and deterioration of the write and erase characteristics can be restrained. 
     As described above, a large number of contact portions  42  connecting to the bit lines  12  are provided, so as to obtain more uniform write and erase characteristics. However, the contact portions  42  add to the area. Therefore, the upper face of each of the bit lines  12  is silicided, so as to form a silicide layer  22   a , as shown in  FIG. 2A . Referring to  FIG. 2A , an ONO film  20  formed with a tunnel oxide film  14 , a trapping layer  16 , and a top oxide film  18  is formed on the semiconductor substrate  10 . Openings for forming the bit lines  12  are formed in the ONO film  20 . With the openings serving as masks, the bit lines  12  and the silicide layers  22   a  are formed. In this manner, the resistance of the bit lines  12  can be made lower, and uniform write and erase characteristics can be obtained without a large number of contact portions  42 . It should be understood here that, in this specification, “the resistance of the bit lines” is the resistance of the bit lines  12  and the silicide layers  22 . 
     However, in a case where the silicide layers  22   a  are in contact with any portion of the semiconductor substrate  10  other than the bit lines  12 , as shown in  FIG. 2A , a current flows between the p-type semiconductor substrate  10  and the n-type bit lines  12  via the silicide layers  22   a . Japanese Patent Application Publication No. 2005-57187 discloses a technique by which silicide layers  22   b  in the bit lines  12  are not in contact with the semiconductor substrate  10 , as shown in  FIG. 2B . By the technique disclosed in Japanese Patent Application Publication No. 2005-57187, the leakage current between the semiconductor substrate  10  and the bit lines  12  can be restrained, and accordingly, the resistance of the bit lines can be made lower. 
     Japanese Patent Application No. 10-284627 discloses a technique by which silicon oxide films including phosphorus (P) are formed on both sides of a gate insulating film. 
     However, in the flash memory disclosed in Japanese Patent Application Publication No. 2005-57187, the trapping layer  16  in the ONO film  20  is contaminated by the slurry that is used for polishing the interlayer insulating film and the metal material of the contact portions  42 . When the trapping layer  16  is contaminated by organic matters such as Na and K included in the slurry, the charges accumulated in the trapping layer  16  are lost (the charge loss). 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-described circumstances and it is an object of the present invention to provide a semiconductor device that has lower leakage current between the semiconductor substrate and the bit lines, so as to reduce the resistance of the bit lines and restrain the charge loss through the trapping layer, and to provide a method of manufacturing the semiconductor device. 
     According to a first aspect of the present invention, there is provided a semiconductor device including: a bit line that is provided in a semiconductor substrate; a silicide layer that has side faces and a bottom face surrounded by the bit line, and is provided within the bit line; an ONO film that is provided on the semiconductor substrate; and sidewalls that are in contact with side faces of a trapping layer in the ONO film over portions of the bit line located on both sides of the silicide layer, the sidewalls being formed with silicon oxide films including phosphorus. In accordance with this embodiment, the silicide layer is not in contact with the semiconductor substrate. Accordingly, the leakage current between the semiconductor substrate and the bit line can be restrained, and the resistance of the bit line can be made lower. Also, the silicon oxide films including phosphorus getter the contaminants in the trapping layer, so as to restrain the charge loss. 
     According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device including: forming a trapping layer on a semiconductor substrate; forming an opening in the trapping layer; forming a bit line in a portion of the opening located within the semiconductor substrate; forming sidewalls on side faces of the opening, the side walls being formed with oxide silicon films including phosphorus; and forming a silicide layer in the bit line, with the sidewalls serving as masks. In accordance with this embodiment, the silicide layer is not in contact with the semiconductor substrate, as the sidewalls serve as masks when the silicide layer is formed. Accordingly, leakage current between the semiconductor substrate and the bit line can be restrained, and the resistance of the bit line can be made lower. Also, the sidewalls having the silicon oxide films including phosphorus getter the contaminants in the trapping layer, so as to restrain the charge loss. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a conventional flash memory; 
         FIGS. 2A and 2B  illustrate the problems with the conventional flash memory; 
         FIGS. 3A through 3D  are cross-sectional views showing procedures for manufacturing a flash memory in accordance with a first embodiment of the present invention; 
         FIGS. 4A through 4D  are cross-sectional views also showing procedures for manufacturing the flash memory in accordance with the first embodiment; 
         FIGS. 5A and 5B  are cross-sectional views also showing procedures for manufacturing the flash memory in accordance with the first embodiment; 
         FIG. 6  is a cross-sectional view showing a procedure for manufacturing the flash memory in accordance with the first embodiment; 
         FIGS. 7A through 7D  are cross-sectional views showing procedures for manufacturing a flash memory in accordance with a second embodiment of the present invention; 
         FIGS. 8A through 8D  are cross-sectional views also showing procedures for manufacturing the flash memory in accordance with the second embodiment of the present invention; 
         FIGS. 9A and 9B  are cross-sectional views also showing procedures for manufacturing the flash memory in accordance with the second embodiment of the present invention; 
         FIGS. 10A through 10C  are cross-sectional views also showing procedures for manufacturing the flash memory in accordance with the second embodiment of the present invention; 
         FIGS. 11A through 11C  are cross-sectional views also showing procedures for manufacturing the flash memory in accordance with the second embodiment of the present invention; 
         FIG. 12  illustrates a block diagram of a portable phone, upon which embodiments may be implemented. 
         FIG. 13  illustrates a block diagram of a computing device, upon which embodiments may be implemented. 
         FIG. 14  illustrates an exemplary portable multimedia device, or media player, in accordance with various embodiments of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the claims. Furthermore, in the detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention. 
     First Embodiment 
     A first embodiment of the present invention is an example case where word lines also serving as gates are formed. Referring to  FIGS. 3A through 6 , a method of manufacturing a flash memory in accordance with the first embodiment is described.  FIGS. 3A and 4A  are cross-sectional views, taken along the lines equivalent to the lines A-A, B-B, and C-C of  FIG. 1 .  FIG. 4B  is a cross-sectional view, taken along the lines equivalent to the lines A-A and C-C of  FIG. 1 .  FIGS. 4C and 4D  are cross-sectional views, taken along the line equivalent to the line A-A of  FIG. 1 .  FIGS. 5A and 5B  are cross-sectional views, taken along the line equivalent to the line B-B of  FIG. 1 .  FIG. 6  is a cross-sectional view, taken along the line equivalent to the line C-C of  FIG. 1 . 
     As shown in  FIG. 3A , a tunnel oxide film  14  that is a silicon oxide film is formed on a p-type silicon semiconductor substrate (or a p-type well in a semiconductor substrate)  10  by a thermal oxidation method, for example. A trapping layer  16  of a silicon nitride film is then formed on the tunnel oxide film  14  by CVD. As shown in  FIG. 3B , a photoresist  50  is formed on the trapping layer  16 . Openings  51  for forming bit lines are then formed in the photoresist  50 . The openings  51  extend in the direction in which the bit lines should extend. With the photoresist  50  serving as a mask, etching is performed on the trapping layer  16  and the tunnel oxide film  14 . In this manner, the openings  51  are formed in the trapping layer  16  and the tunnel oxide film  14 . With the photoresist  50  serving as a mask, arsenic (As) ions are implanted, for example. In this manner, bit lines  12  are formed in the respective openings  51  of the semiconductor substrate  10 . After the photoresist  50  is removed, a heat treatment is carried out, so that the bit lines  12  formed with n-type diffusion layers are formed in the semiconductor substrate  10 . 
     Referring now to  FIG. 3C , a PSG (phosphosilicate glass) film that is a silicon oxide film including phosphorus (P) is then formed on the bit lines  12  and the trapping layer  16  by CVD, for example. Etching is then performed on the surface such that sidewalls  24  made of PSG are formed on the side faces of the trapping layer  16  and the tunnel oxide film  14  (or the side faces of the opening  51 ). A cobalt (Co) film is then formed on the trapping layer  16 , the sidewalls  24 , and the bit lines  12  by a sputtering technique. After that, a heat treatment is carried out, so that the Co on each of the bit lines  12  is silicided to form a silicide layer  22  made of CoSi (cobalt silicide). The Co on the trapping layer  16  and the sidewalls  24  is not silicided and is removed later. The silicide layers  22  extend within the respective bit lines  12  in the direction in which the bit lines  12  extend. The silicide layers  22  may be made of another silicide metal such as TiSi (titanium silicide). 
     Referring now to  FIG. 4A , a top oxide film  18  such as a silicon oxide film is formed on the trapping layer  16 , the sidewalls  24 , and the silicide layers  22  by CVD, for example. In this manner, an ONO film  20  formed with the top oxide film  18 , the trapping layer  16 , and the tunnel oxide film  14  is produced on the semiconductor substrate  10 . Referring now to  FIG. 5A , a polysilicon film is formed as a conductive layer to be word lines on the top oxide film  18 . Etching is performed on predetermined regions of the polysilicon film, so as to form word lines  26  extending in the width direction of the bit lines  12 . 
     Referring now to  FIG. 4B , a BPSG (borophosphosilicate glass) film is formed on the top oxide film  18  and the word lines  26 . After that, flattening is performed by CMP, so as to form an interlayer insulating film  40 . Referring to  FIG. 4C , contact holes connecting to the respective silicide layers  22  are formed in the interlayer insulating film  40 . A metal layer made of tungsten (W), for example, is formed in each of the contact holes and on the interlayer insulating film  40 . Polishing is then performed by CMP, so as to form contact portions  42  that are made of W, for example, and electrically connect to the respective silicide layers  22 . Referring to  FIG. 4D , wiring layers  44  connecting to the respective contact portions  42  are formed on the interlayer insulating film  40 . A protection film  46  is formed to cover the wiring layers  44 . Referring to  FIG. 5B , the interlayer insulating film  40  is formed on the word lines  26 , while the wiring layers  44  and the protection film  46  are formed on the interlayer insulating film  40 . Referring to  FIG. 6 , the interlayer insulating film  40  is formed on the top oxide film  18  between the word lines  26  on which the contact portions  42  are not formed, while the wiring layer  44  and the protection film  46  are formed on the interlayer insulating film  40 . In this manner, the flash memory in accordance with the first embodiment is produced. 
     In accordance with the first embodiment, as shown in  FIGS. 4D ,  5 B, and  6 , the bit lines  12  are formed in the semiconductor substrate  10 , and the silicide layers  22  that have side faces and a bottom face surrounded by the bit lines  12  and extend in the direction in which the bit lines  12  (the longitudinal direction of the bit lines  12 ) are formed successively. Furthermore, the ONO film  20  is formed on the semiconductor substrate  10 , and the sidewalls  24  formed with silicon oxide films including P are provided on the bit lines  12  on both sides of the respective silicide layers  22 . The sidewalls  24  are in contact with the side faces of the trapping layer  16  in the ONO film  20 . Since the side faces and the bottom face of each of the silicide layers  22  are surrounded by the bit lines  12  in this structure, current flow between the semiconductor substrate  10  and the bit lines  12  via the silicide layers  22  can be restrained. Accordingly, the silicide layers  22  successively provided in the extending direction of the bit lines can lower the resistance of the bit lines. Further, the sidewalls  24  formed with insulating films are formed on the side faces of the trapping layer  16 . The P in the silicon oxide films getters the Na and K in the trapping layer  16 . Accordingly, even if the trapping layer  16  is contaminated with organic matters such as Na and K included in the slurry used for the polishing of the interlayer insulating film  40  and the contact portion  42 , the amount of Na and K in the trapping layer  16  can be reduced. Thus, the charge loss due to the contamination can be restrained. 
     Further, the sidewalls  24  are in contact with the side faces of the tunnel oxide film  14  and the trapping layer  16  in the ONO film  20 . The top oxide film  18  in the ONO film  20  is provided on the trapping layer  16 , the sidewalls  24 , and the silicide layers  22 . Since the sidewalls  24  are covered with the top oxide film  18 , contamination of the trapping layer  16  can be restrained when the interlayer insulating film  40  and the contact portions  42  are polished. Thus, the charge loss can be further reduced. Also, as the word lines  26  are formed on the ONO film  20  as shown in  FIG. 5B , the silicide layers  22  can be insulated from the word lines  26  by the top oxide film  18 . 
     Further, the interlayer insulating film  40  is provided on the ONO film  20 , and the contact portions  42  connecting to the silicide layer  22  are provided in the interlayer insulating film  40 . When the interlayer insulating film  40  and the contact portions  42  are polished, contamination of the trapping layer  16  due to the organic matters such as Na and K included in the slurry used for the polishing can be restrained. 
     Second Embodiment 
     A second embodiment of the present invention is an example case where word lines are formed on gate electrodes. Referring to  FIGS. 7A through 11C , a method of manufacturing a flash memory in accordance with the second embodiment is described.  FIGS. 7A through 8D  are cross-sectional views, taken along the lines equivalent to the lines A-A, B-B, and C-C of  FIG. 1 .  FIG. 9A  is a cross-sectional view, taken along the lines equivalent to the lines A-A and C-C of  FIG. 1 .  FIGS. 10A and 11A  are cross-sectional views, taken along the line equivalent to the line A-A of  FIG. 1 .  FIGS. 9B ,  10 B, and  11 B are cross-sectional views, taken along the line equivalent to the line B-B of  FIG. 1 .  FIGS. 10C and 11C  are cross-sectional views, taken along the line equivalent to the line C-C of  FIG. 1 . 
     As shown in  FIG. 7A , a tunnel oxide film  14  that is a silicon oxide film, a trapping layer  16  that is a silicon nitride film, and a top oxide film  18  that is a silicon oxide film are formed as an ONO film  20  on a semiconductor substrate  10 . As shown in  FIG. 7B , a first conductive layer  27  that is made of polysilicon and is to be gate electrodes is formed on the ONO film  20 . An insulating film  34  that is a silicon nitride film is formed on the first conductive layer  27 . As shown in  FIG. 7C , a photoresist having openings for forming bit lines is formed on the first conductive layer  27 . With the photoresist serving as a mask, etching is performed on the insulating film  34 , the first conductive layer  27 , and the ONO film  20 . As a result, openings  52  for forming bit lines are formed in the insulating film  34 , the first conductive layer  27 , and the ONO film  20 . The openings  52  extend in the direction in which the bit lines should extend. Arsenic ions are then implanted, so as to form the bit lines  12  in the openings  52  in the semiconductor substrate  10 . As shown in  FIG. 7D , a PSG film is formed, and etching is performed on the PSG film. In this manner, sidewalls  24  are formed on the side faces of the first conductive layer  27 , the ONO film  20 , and the openings  52 . 
     As shown in  FIG. 8A , a cobalt (Co) film  36  is formed on the insulating film  34 , the sidewalls  24 , and the bit lines  12  in the openings  52 . As shown in  FIG. 8B , a heat treatment is carried out so that the Co film  36  is silicided with the silicon in the bit lines  12 , and silicide layers  22  are formed. Since the insulating film  34  and the sidewalls  24  cover the first conductive layer  27  at this point, the first conductive layer  27  is not silicided. As shown in  FIG. 8C , an insulating layer  30  made of silicon oxide is formed in the openings  52  and on the insulating film  34  by high-density plasma CVD, for example. The insulating layer  30  is then polished by CMP until reaching the first conductive layer  27 . In this manner, the insulating layer  30  remains in the openings  52 , and the first conductive layer  27  and the insulating layer  30  are leveled with each other. The insulating film  34  is removed by the polishing, or is removed before the polishing. As shown in  FIG. 8D , a second conductive layer  31  made of polysilicon is formed on the first conductive layer  27  and the insulating layer  30 . 
     As shown in  FIG. 9A , the portions of the first conductive layer  27  and the second conductive layer  31  that are not located in the regions in which word lines are to be formed are removed by etching. As shown in  FIG. 9B , gate electrodes  28  are formed from the first conductive layer  27  on the ONO film  20 , and word lines  32  are formed from the second conductive layer  31 . 
     As shown in  FIGS. 10A through 10C , an interlayer insulating film  40  made of BPSG is formed on the ONO film  20 , the insulating layers  30 , and the word lines  32 . As shown in  FIG. 10A , contact portions  42  that are made of W or the like and connect to the silicide layers  22  are formed in the interlayer insulating film  40 . 
     As shown in  FIGS. 11A through 11C , wiring layers  44  connecting to the respective contact portions  42  are formed on the interlayer insulating film  40 . A protection film  46  is then formed on the wiring layers  44  and the interlayer insulating film  40 . In this manner, a semiconductor device in accordance with the second embodiment is completed. 
     In accordance with the second embodiment, as shown in  FIG. 11B , the word lines  32  that extend in the width direction of the bit lines  12  are formed above the ONO film  20 , and the gate electrodes  28  are provided between the ONO film  20  and the word lines  32 . The sidewalls  24  are in contact with the side faces of the gate electrodes  28  and the ONO film  20 . Accordingly, in the flash memory having a double-layer structure of the gate electrodes  28  and the word lines  32 , the resistance of the bit lines  12  can also be lowered, and the charge loss can be reduced. 
     By the manufacturing method in accordance with the second embodiment, the top oxide film  18  is formed on the trapping layer  16 , as shown in  FIG. 7A . The openings  52  are formed in the top oxide film  18  and the trapping layer  16 , as shown in  FIG. 7C . The sidewalls  24  are formed on the side faces of the openings  52  in the top oxide film  18  and the trapping layer  16 , as shown in  FIG. 7D . In a case where the top oxide film  18  is formed by the thermal oxidation method, for example, after the bit lines  12  and the silicide layers  22  are formed as in the first embodiment shown in  FIG. 4A , diffusion of the bit lines  12  and the silicide layers  22  is caused. In accordance with the second embodiment, the top oxide film  18  is formed before the bit lines  12  are formed. Accordingly, diffusion of the bit lines  12  and the silicide layers  22  due to the formation of the top oxide film  18  can be prevented. 
     Also, the first conductive layer  27  to be the gate electrodes is formed on the top oxide film  18 , as shown in  FIG. 7B . The openings  52  are formed in the first conductive layer  27 , the top oxide film  18 , and the trapping layer  16 , as shown in  FIG. 7C . The sidewalls  24  are formed on the side faces of the openings  52  in the first conductive layer  27 , the top oxide film  18 , and the trapping layer  16 . With this arrangement, the sidewalls  24  cover the side faces of the first conductive layer  27 . Accordingly, in the procedures for forming the silicide layers  22  shown in  FIGS. 8A and 8B , a metal layer such as a Co layer can be prevented from covering the side faces of the first conductive layer  27 . Particularly, in a case where the first conductive layer  27  is made of polysilicon, silicidation of the first conductive layer  27  can be prevented. 
     Further, the second conductive layer  31  to be the word lines is formed on the first conductive layer  27 , as shown in  FIG. 8D . The predetermined portions of the second conductive layer  31  and the first conductive layer  27  are removed, so as to form the word lines  32  from the second conductive layer  31  and the gate electrodes  28  from the first conductive layer  27 , as shown in  FIGS. 9A and 9B . Through those procedures, a flash memory having a double-layer structure of the gate electrodes  28  and the word lines  32  can be produced. 
     Further, the insulating film  34  is formed on the first conductive layer  27 , as shown in  FIG. 7B . When the silicide layers  22  are formed, a metal layer such as a Co film  36  is formed on the insulating film  34  and the bit lines  12  in the respective openings  52 , as shown in  FIG. 8A . The metal layer is silicided through a heat treatment, so as to form the silicide layers  22 , as shown in  FIG. 8B . In those procedures, the insulating film  34  prevents the metal layer from covering the first conductive layer  27 . Particularly, in a case where the first conductive layer  27  is made of polysilicon, silicidation of the first conductive layer  27  can be prevented. 
     Further, the insulating layers  30  are formed in the respective openings  52 , as shown in  FIG. 8C . The second conductive layer  31  is formed on the first conductive layers  27  and the insulating layers  30 . In this manner, the openings  52  are filled with the insulating layers  30 , so that the second conductive layer  31  can be formed on a flatter surface, as shown in  FIG. 8D . Furthermore, since the sidewalls  24  are covered with the insulating layers  30 , contamination of the trapping layer  16  can be more effectively restrained. 
     Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents. 
     Finally, various aspects of the present invention are summarized in the following. 
     According to a first aspect of the present invention, there is provided A semiconductor device including: a bit line that is provided in a semiconductor substrate; a silicide layer that has side faces and a bottom face surrounded by the bit line, and is provided within the bit line; an ONO film that is provided on the semiconductor substrate; and sidewalls that are in contact with side faces of a trapping layer in the ONO film over portions of the bit line located on both sides of the silicide layer, the sidewalls being formed with silicon oxide films including phosphorus. 
     In the above-described semiconductor device, the sidewalls may be in contact with side faces of a tunnel oxide film and the trapping layer in the ONO film; and the ONO film may have a top oxide film formed on the trapping layer, the sidewalls, and the silicide layer. The top oxide film restrains contamination of the trapping layer, and the charge loss can be more effectively restrained. 
     The above-described semiconductor device may further include a word line that extends in a width direction of the bit line and is provided on the ONO film. 
     The above-described semiconductor device may further include: a word line that extends in a width direction of the bit line and is provided on the ONO film; and a gate electrode that is provided between the ONO film and the word line, and the sidewalls may be in contact with side faces of the gate electrode and the ONO film. The resistance of the bit line can be made lower, and the charge loss can be restrained also in a semiconductor device having a double-layer structure of the gate electrode and the word line. 
     The above-described semiconductor device may further include: an interlayer insulating film that is provided on the ONO film; and a contact portion that is provided in the interlayer insulating film and connects to the silicide layer. The charge loss caused by the trapping layer contaminated when the interlayer insulating film and the contact portion are formed can be restrained. 
     According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device including: forming a trapping layer on a semiconductor substrate; forming an opening in the trapping layer; forming a bit line in a portion of the opening located within the semiconductor substrate; forming sidewalls on side faces of the opening, the side walls being formed with oxide silicon films including phosphorus; and forming a silicide layer in the bit line, with the sidewalls serving as masks. 
     The above-described method may further include forming a top oxide film on the trapping layer, the sidewalls, and the silicide layer. The top oxide film restrains contamination of the trapping layer, and the charge loss can be more effective restrained. 
     The above-described method may further include forming a word line on the top oxide film, the word line extending in a width direction of the bit line. 
     The above-described method may further include forming a top oxide film on the trapping layer, and forming the opening may include forming the opening in the top oxide film and the trapping layer; and forming the sidewalls may include forming the sidewalls on side faces of the opening formed in the top oxide film and the trapping layer. 
     The above-described method may further include forming a top oxide film on the trapping layer, and forming the opening may include forming the opening in the top oxide film and the trapping layer; and forming the sidewalls may include forming the sidewalls on side faces of the opening formed in the top oxide film and the trapping layer. The top oxide film is formed before the bit line is formed. Accordingly, diffusion of the bit line and the silicide layer due to the formation of the top oxide film can be prevented. 
     The above-described method may further include forming a first conductive layer to be a gate electrode on the top oxide film, and forming the opening may include forming the opening in the first conductive layer, the top oxide film, and the trapping layer; and forming the sidewalls may include forming the sidewalls on side faces of the opening formed in the first conductive layer, the top oxide film, and the trapping layer. The side faces of the first conductive layer can be protected by the sidewalls. 
     The above-described method may further include: forming a second conductive layer to be a word line on the first conductive layer; and forming the word line from the second conductive layer and the gate electrode from the first conductive layer by removing predetermined regions of the second conductive layer and the first conductive layer. The resistance of the bit line can be made lower, and the charge loss can be restrained also in a semiconductor device having a double-layer structure of the gate electrode and the word line. 
     The above-described method may further include forming an insulating film on the first conductive layer, and forming the silicide layer may include: forming a metal layer on the insulating film and the bit line located in the opening; and siliciding the metal layer through a heat treatment. The insulating film prevents the metal layer from directly covering the first conductive layer. Accordingly, silicidation of the top face of the first conductive layer can be prevented when the metal layer is silicided. 
     The above-described method may further include forming an insulating layer in the opening, and forming the second conductive layer may include forming the second conductive layer on the first conductive layer and the insulating layer. The insulating layer is formed in the opening, so that the second conductive layer can be formed on a flatter surface. 
     The above-described method may further include: forming an interlayer insulating film on the trapping layer; and forming a contact portion in the interlayer insulating film, the contact portion connecting to the silicide layer. The charge loss caused by the trapping layer contaminated when the interlayer insulating film and the contact portion can be restrained. 
     Embodiments generally relate to semiconductor devices. More particularly, embodiments allow for a semiconductor device that has lower leakage current between the semiconductor substrate and the bit lines, so as to reduce the resistance of the bit lines and restrain the charge loss through the trapping layer. In one implementation, the various embodiments are applicable to flash memory and devices that utilize flash memory. Flash memory is a form of non-volatile memory that can be electrically erased and reprogrammed. As such, flash memory, in general, is a type of electrically erasable programmable read only memory (EEPROM). 
     Like Electrically Erasable Programmable Read Only Memory (EEPROM), flash memory is nonvolatile and thus can maintain its contents even without power. However, flash memory is not standard EEPROM. Standard EEPROMs are differentiated from flash memory because they can be erased and reprogrammed on an individual byte or word basis while flash memory can be programmed on a byte or word basis, but is generally erased on a block basis. Although standard EEPROMs may appear to be more versatile, their functionality requires two transistors to hold one bit of data. In contrast, flash memory requires only one transistor to hold one bit of data, which results in a lower cost per bit. As flash memory costs far less than EEPROM, it has become the dominant technology wherever a significant amount of non-volatile, solid-state storage is needed. 
     Exemplary applications of flash memory include digital audio players, digital cameras, digital video recorders, and mobile phones. Flash memory is also used in USB flash drives, which are used for general storage and transfer of data between computers. Also, flash memory is gaining popularity in the gaming market, where low-cost fast-loading memory in the order of a few hundred megabytes is required, such as in game cartridges. Additionally, flash memory is applicable to cellular handsets, smartphones, personal digital assistants, set-top boxes, digital video recorders, networking and telecommunication equipments, printers, computer peripherals, automotive nagivation devices, and gaming systems. 
     As flash memory is a type of non-volatile memory, it does not need power to maintain the information stored in the chip. In addition, flash memory offers fast read access times and better shock resistance than traditional hard disks. These characteristics explain the popularity of flash memory for applications such as storage on battery-powered devices (e.g., cellular phones, mobile phones, IP phones, wireless phones, etc.). 
     Flash memory stores information in an array of floating gate transistors, called “cells”, each of which traditionally stores one bit of information. However, newer flash memory devices, such as MirrorBit® Flash Technology from Spansion Inc., can store more than 1 bit per cell. The MirrorBit cell doubles the intrinsic density of a Flash memory array by storing two physically distinct bits on opposite sides of a memory cell. Each bit serves as a binary bit of data (e.g., either 1 or 0) that is mapped directly to the memory array. Reading or programming one side of a memory cell occurs independently of whatever data is stored on the opposite side of the cell. 
     With regards to wireless markets, flash memory that utilizes MirrorBit® technology has several key advantages. For example, flash memory that utilizes MirrorBit® technology is capable of burst-mode access as fast as 80 MHz, page access times as fast as 25 ns, simultaneous read-write operation for combined code and data storage, and low standby power (e.g., 1 μA). 
       FIG. 12  shows a block diagram of a conventional portable telephone  2010  (e.g., cell phone, cellular phone, mobile phone, interne protocol phone, wireless phone, etc.), upon which embodiments can be implemented. The cell phone  2010  includes an antenna  2012  coupled to a transmitter  2014  and a receiver  2016 , as well as a microphone  2018 , a speaker  2020 , a keypad  2022 , and a display  2024 . The cell phone  2010  also includes a power supply  2026  and a central processing unit (CPU)  2028 , which may be an embedded controller, conventional microprocessor, or the like. In addition, the cell phone  2010  includes integrated, flash memory  2030 . Flash memory  2030  includes a bit line that is provided in a semiconductor substrate, a silicide layer that has side faces and a bottom face surrounded by the bit line, and is provided within the bit line, an ONO film that is provided on the semiconductor substrate, and sidewalls that are in contact with side faces of a trapping layer in the ONO film over portions of the bit line located on both sides of the silicide layer, the sidewalls being formed with silicon oxide films including phosphorus. According to various embodiments, it is possible to provide a semiconductor device, such as flash memory, that has lower leakage current between the semiconductor substrate and the bit lines, so as to reduce the resistance of the bit lines and restrain the charge loss through the trapping layer. The present invention also provides a method of manufacturing such a semiconductor device. As a result, the flash memory  2030  operates much more efficiently that conventional flash memory. This increased efficiency for the flash memory translates into increased efficiency and reliability for various devices, such as mobile phones, cellular phones, internet protocol phones, and/or wireless phones. 
     Flash memory comes in two primary varieties, NOR-type flash and NAND-type flash. While the general memory storage transistor is the same for all flash memory, it is the interconnection of the memory cells that differentiates the designs. In a conventional NOR-type flash memory, the memory cell transistors are connected to the bit lines in a parallel configuration, while in a conventional NAND-type flash memory, the memory cell transistors are connected to the bit lines in series. For this reason, NOR-type flash is sometimes referred to as “parallel flash” and NAND-type flash is referred to as “serial flash.” 
     Traditionally, portable phone (e.g., cell phone) CPUs have needed only a small amount of integrated NOR-type flash memory to operate. However, as portable phones (e.g., cell phone) have become more complex, offering more features and more services (e.g., voice service, text messaging, camera, ring tones, email, multimedia, mobile TV, MP3, location, productivity software, multiplayer games, calendar, and maps.), flash memory requirements have steadily increased. Thus, a more efficient flash memory will render a portable phone more competitive in the telecommunications market. 
     Also, as mentioned above, flash memory is applicable to a variety of devices other than portable phones. For instance, flash memory can be utilized in personal digital assistants, set-top boxes, digital video recorders, networking and telecommunication equipments, printers, computer peripherals, automotive navigation devices, and gaming systems. 
       FIG. 13  illustrates a block diagram of a computing device  2100 , upon which embodiments of the present invention can be implemented. Although computing device  2100  is shown and described in  FIG. 13  as having certain numbers and types of elements, the embodiments are not necessarily limited to the exemplary implementation. That is, computing device  2100  can include elements other than those shown, and can include more than one of the elements that are shown. For example, computing device  2100  can include a greater number of processing units than the one (processing unit  2102 ) shown. Similarly, in another example, computing device  2100  can include additional components not shown in  FIG. 13 . 
     Also, it is appreciated that the computing device  2100  can be a variety of things. For example, computing device  2100  may be, but is not limited to, a personal desktop computer, a portable notebook computer, a personal digital assistant (PDA), and a gaming system. Flash memory is especially useful with small-form-factor computing devices such as PDAs and portable gaming devices. Flash memory offers several advantages. In one example, flash memory is able to offer fast read access times while at the same time being able to withstand shocks and bumps better than standard hard disks. This is important as small computing devices are often moved around and encounter frequent physical impacts. Also, flash memory is more able than other types of memory to withstand intense physical pressure and/or heat. Thus, portable computing devices are able to be used in a greater range of environmental variables. 
     In its most basic configuration, computing device  2100  typically includes at least one processing unit  2102  and memory  2104 . Depending on the exact configuration and type of computing device, memory  2104  may be volatile (such as RAM), non-volatile (such as ROM, flash memory, etc.) or some combination of the two. This most basic configuration of computing device  2100  is illustrated in  FIG. 11  by line  2106 . Additionally, device  2100  may also have additional features/functionality. For example, device  2100  may also include additional storage (removable and/or non-removable) including, but not limited to, magnetic or optical disks or tape. In one example, in the context of a gaming system, the removable storage could a game cartridge receiving component utilized to receive different game cartridges. In another example, in the context of a Digital Versatile Disc (DVD) recorder, the removable storage is a DVD receiving component utilized to receive and read DVDs. Such additional storage is illustrated in  FIG. 13  by removable storage  2108  and non-removable storage  2110 . Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Memory  2104 , removable storage  2108  and non-removable storage  2110  are all examples of computer storage media. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory  2120  or other memory technology, CD-ROM, digital video disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can accessed by device  2100 . Any such computer storage media may be part of device  2100 . 
     In the present embodiment, the flash memory  2120  comprises: a bit line that is provided in a semiconductor substrate, a silicide layer that has side faces and a bottom face surrounded by the bit line, and is provided within the bit line, an ONO film that is provided on the semiconductor substrate, and sidewalls that are in contact with side faces of a trapping layer in the ONO film over portions of the bit line located on both sides of the silicide layer, the sidewalls being formed with silicon oxide films including phosphorus. According to various embodiments, it is possible to provide a semiconductor device, such as flash memory, that has lower leakage current between the semiconductor substrate and the bit lines, so as to reduce the resistance of the bit lines and restrain the charge loss through the trapping layer. The present invention also provides a method of manufacturing such a semiconductor device. As a result, the flash memory  2030  operates much more efficiently that conventional flash memory. This increased efficiency for the flash memory translates into increased efficiency and reliability for various devices, such as personal digital assistants, set-top boxes, digital video recorders, networking and telecommunication equipments, printers, computer peripherals, automotive navigation devices, gaming systems, mobile phones, cellular phones, interne protocol phones, and/or wireless phones. Further, in one embodiment, the flash memory  2120  utilizes MirrorBit® technology to allow storing of two physically distinct bits on opposite sides of a memory cell. 
     Device  2100  may also contain communications connection(s)  2112  that allow the device to communicate with other devices. Communications connection(s)  2112  is an example of communication media. Communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. The term computer readable media as used herein includes both storage media and communication media. 
     Device  2100  may also have input device(s)  2114  such as keyboard, mouse, pen, voice input device, game input device (e.g., a joy stick, a game control pad, and/or other types of game input device), touch input device, etc. Output device(s)  2116  such as a display (e.g., a computer monitor and/or a projection system), speakers, printer, network peripherals, etc., may also be included. All these devices are well known in the art and need not be discussed at length here. 
     Aside from mobile phones and portable computing devices, flash memory is also widely used in portable multimedia devices, such as portable music players. As users would desire a portable multimedia device to have as large a storage capacity as possible, an increase in memory density would be advantageous. Users would also benefit from reduced memory read time and reduced cost. 
       FIG. 14  shows an exemplary portable multimedia device, or media player,  3100  in accordance with an embodiment of the invention. The media player  3100  includes a processor  3102  that pertains to a microprocessor or controller for controlling the overall operation of the media player  3100 . The media player  3100  stores media data pertaining to media assets in a file system  3104  and a cache  3106 . The file system  3104  is, typically, a storage medium or a plurality of storage media, such as disks, memory cells, and the like. The file system  3104  typically provides high capacity storage capability for the media player  3100 . Also, file system  3104  includes flash memory  3130 . In the present embodiment, the flash memory  3130  comprises: a bit line that is provided in a semiconductor substrate, a silicide layer that has side faces and a bottom face surrounded by the bit line, and is provided within the bit line, an ONO film that is provided on the semiconductor substrate, and sidewalls that are in contact with side faces of a trapping layer in the ONO film over portions of the bit line located on both sides of the silicide layer, the sidewalls being formed with silicon oxide films including phosphorus. According to various embodiments, it is possible to provide a semiconductor device, such as flash memory, that has lower leakage current between the semiconductor substrate and the bit lines, so as to reduce the resistance of the bit lines and restrain the charge loss through the trapping layer. The present invention also provides a method of manufacturing such a semiconductor device. As a result, the flash memory  2030  operates much more efficiently that conventional flash memory. This increased efficiency for the flash memory translates into increased efficiency and reliability for various devices, such as personal digital assistants, set-top boxes, digital video recorders, networking and telecommunication equipments, printers, computer peripherals, automotive navigation devices, gaming systems, mobile phones, cellular phones, internet protocol phones, and/or wireless phones. However, since the access time to the file system  3104  is relatively slow, the media player  3100  can also include a cache  3106 . The cache  3106  is, for example, Random-Access Memory (RAM) provided by semiconductor memory. The relative access time to the cache  3106  is substantially shorter than for the file system  3104 . However, the cache  3106  does not have the large storage capacity of the file system  3104 . Further, the file system  3104 , when active, consumes more power than does the cache  3106 . The power consumption is particularly important when the media player  3100  is a portable media player that is powered by a battery (not shown). The media player  3100  also includes a RAM  3122  and a Read-Only Memory (ROM)  3120 . The ROM  3120  can store programs, utilities or processes to be executed in a non-volatile manner. The RAM  3122  provides volatile data storage, such as for the cache  3106 . 
     The media player  3100  also includes a user input device  3108  that allows a user of the media player  3100  to interact with the media player  3100 . For example, the user input device  3108  can take a variety of forms, such as a button, keypad, dial, etc. Still further, the media player  3100  includes a display  3110  (screen display) that can be controlled by the processor  3102  to display information to the user. A data bus  3124  can facilitate data transfer between at least the file system  3104 , the cache  3106 , the processor  3102 , and the CODEC  3112 . The media player  3100  also includes a bus interface  3116  that couples to a data link  3118 . The data link  3118  allows the media player  3100  to couple to a host computer. 
     In one embodiment, the media player  3100  serves to store a plurality of media assets (e.g., songs, photos, video, etc.) in the file system  3104 . When a user desires to have the media player play/display a particular media item, a list of available media assets is displayed on the display  3110 . Then, using the user input device  3108 , a user can select one of the available media assets. The processor  3102 , upon receiving a selection of a particular media item, supplies the media data (e.g., audio file, graphic file, video file, etc.) for the particular media item to a coder/decoder (CODEC)  3110 . The CODEC  3110  then produces analog output signals for a speaker  3114  or a display  3110 . The speaker  3114  can be a speaker internal to the media player  3100  or external to the media player  3100 . For example, headphones or earphones that connect to the media player  3100  would be considered an external speaker. 
     In a particular embodiment, the available media assets are arranged in a hierarchical manner based upon a selected number and type of groupings appropriate to the available media assets. For example, in the case where the media player  3100  is an MP3-type media player, the available media assets take the form of MP3 files (each of which corresponds to a digitally encoded song or other audio rendition) stored at least in part in the file system  3104 . The available media assets (or in this case, songs) can be grouped in any manner deemed appropriate. In one arrangement, the songs can be arranged hierarchically as a list of music genres at a first level, a list of artists associated with each genre at a second level, a list of albums for each artist listed in the second level at a third level, while at a fourth level a list of songs for each album listed in the third level, and so on. 
     As described above, the present invention provides a semiconductor device that has lower leakage current between the semiconductor substrate and the bit lines, so as to reduce the resistance of the bit lines and restrain the charge loss through the trapping layer, and also provides a method of manufacturing the semiconductor device. 
     Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.