Abstract:
A method for manufacturing a semiconductor device improves hot carrier characteristic in a device having a thick gate insulating film without being affected by short channel effect, thereby improving reliability of the device. The method for manufacturing a semiconductor device includes the steps of forming gate electrodes having gate insulating films of different thicknesses on a semiconductor substrate, implanting a low-concentration impurity ion into the semiconductor substrate at both sides of the gate electrodes, implanting a nitrogen ion into a portion, where the low-concentration impurity ion is implanted, in the gate insulating film relatively thicker than the other gate insulating film, forming sidewall spacers at both sides of the gate electrodes, and implanting a high-concentration source/drain impurity ion into the semiconductor substrate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing MOSFET. 
     2. Background of the Related Art 
     Generally, with high packing density of a semiconductor device, there has been provided a method for simultaneously manufacturing devices having different functions or a method for forming a dual gate having gate insulating films of different thicknesses. 
     In manufacturing a device having gate insulating films of different thicknesses, it is most preferable that both a device having a thin gate insulating film and a device having a thick gate insulating film have desired characteristics at the same time. 
     A related art method for manufacturing a semiconductor device will be described with reference t o the accompanying drawings . 
     FIGS. 1 a  to  1   d  are sectional views illustrating a related art method for manufacturing a semiconductor device. 
     As shown in FIG. 1 a , dual gate insulating films  13  and  13   a  are formed by a typical dual gate oxidation process and then gate electrodes  14  and  14   a  are formed. That is to say, a gate electrode  14  having a thin gate insulating film  13  and a gate electrode  14   a  having a relatively thick gate insulating film  13   a  are formed on a semiconductor substrate  11 . A reference numeral  12  which is not described denotes a device isolation film. 
     Afterwards, as shown in FIG. 1 b , lightly doped drain (LDD) regions  15  and  15   a  are formed into the semiconductor substrate  11  by low-concentration impurity ion implantation using the gate electrodes  14  and  14   a  as masks. 
     As shown in FIG. 1 c , an insulating film is deposited on an entire surface of the semiconductor substrate  11  including the gate electrodes  14  and  14   a . The insulating film is then etched back to form sidewall spacers  16  and  16   a  at both sides of the gate electrodes  14  and  14   a.    
     As shown in FIG. 1 d , source/drain impurity regions  17  and  17   a  are formed by high-concentration impurity ion implantation using the gate electrodes  14  and  14   a  and the sidewall spacers  16  and  16   a  as masks. As a result, the related art method for manufacturing a semiconductor device is completed. 
     However, the related art method for manufacturing a semiconductor device has several problems. 
     In case that the thin gate insulating film and the thick gate insulating film are formed at the same time, hot carrier life time characteristic becomes poorer in the device having the thick gate insulating film than the device having the thin gate insulating film, thereby reducing reliability of the device. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a method for manufacturing a semiconductor device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a method for manufacturing a semiconductor device which improves hot carrier characteristic in a device having a thick gate insulating film without being affected by short channel effect, thereby improving reliability of the device. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or ray be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method for manufacturing a semiconductor device according to the present invention includes the steps of forming gate electrodes having gate insulating films of different thicknesses on a semiconductor substrate, implanting a low-concentration impurity ion into the semiconductor substrate at both sides of the gate electrodes, implanting a nitrogen ion into a portion, where the low-concentration impurity ion is implanted, in the gate insulating film relatively thicker than the other gate insulating film, forming sidewall spacers at both sides of the gate electrodes, and implanting a high-concentration source/drain impurity ion into the semiconductor substrate. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
     In the drawings: 
     FIGS. 1 a  to  1   d  are sectional views illustrating a related art method for manufacturing a semiconductor device; 
     FIGS. 2 a  to  2   c  are sectional views illustrating a method for manufacturing a semiconductor device according to the first embodiment of the present invention; 
     FIGS. 3 a  to  3   c  are sectional views illustrating a method for manufacturing a semiconductor device according to the second embodiment of the present invention; 
     FIGS. 4 a  to  4   c  are sectional views illustrating a method for manufacturing a semiconductor device according to the third embodiment of the present invention; and 
     FIG. 5 shows graphs illustrating hot carrier life time according to a method for manufacturing a semiconductor device of the present invention in comparison with the related art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     In a method for manufacturing a semiconductor device according to the present invention, in order to form a device having a thin gate insulating film and a device having a thick gate insulating film, ion implantation is performed to form an LDD region and then a nitrogen ion is implanted into a semiconductor substrate at both sides of a gate electrode having a thick gate insulating film. 
     A method for manufacturing a semiconductor device according to the embodiments of the present invention will be described in detail. 
     FIGS. 2 a  to  2   c  are sectional views illustrating a method for manufacturing a semiconductor device according to the first embodiment of the present invention. 
     As shown in FIG. 2 a , gate electrodes  24  and  24   a  having different gate insulating films are formed on a semiconductor substrate  21 . That is to say, a gate electrode  24  having a gate insulating film  23  of a first thickness and a gate electrode  24   a  having a gate insulating film  23   a  of a second thickness thicker than the first thickness are formed. At this time, the gate insulating films  23  and  23   a  of the first and second thicknesses are formed by a typical dual gate oxidation process. A reference numeral  22  which is not described denotes a device isolation film. 
     As shown in FIG. 2 b , LDD regions  25  and  25 a are formed into the semiconductor substrate  21  at both sides of the respective gate electrodes  24  and  24   a  by low-concentration impurity ion implantation using the gate electrodes  24  and  24   a  as masks. 
     Afterwards, a photoresist is deposited on an entire surface of the semiconductor substrate  21  including the gate electrodes  24  and  24   a . The photoresist is then patterned to expose the gate electrode  24   a  having the gate insulating film  23   a  of the second thickness and the semiconductor substrate  21  at both sides of the gate electrode  24   a , so that a mask pattern  26  is formed. A nitrogen ion is implanted into the exposed substrate  21  using the mask pattern  26  as a mask. 
     Subsequently, as shown in FIG. 2 c , the mask pattern  26  is removed and then an insulating film is deposited on the entire surface of the substrate  21  including the respective gate electrodes  24  and  24   a . The insulating film is then etched back to form sidewall spacers  27  and  27   a  at both sides of the respective gate electrodes  24  and  24   a.    
     Finally, source/drain impurity regions  28  and  28   a  are formed by high-concentration impurity ion implantation using the gate electrodes  24  and  24   a  and the sidewall spacers  27  and  27   a  as masks. As a result, the method for manufacturing a semiconductor device according to the first embodiment of the present invention is completed. 
     In the aforementioned first embodiment of the present invention, the nitrogen ion implantation may be performed before forming the LDD regions  25  and  25   a  (not shown). That is to say, the gate electrodes  24  and  24   a  are formed and then the mask pattern  26  is formed to expose the gate electrode  24   a  having the gate insulating film  23   a  of the second thickness and the substrate  21  at both sides of the gate electrode  24   a . The nitrogen ion is implanted into the exposed substrate  21  using the mask pattern  26  as a mask. Subsequently, the mask pattern  26  is removed and then an impurity ion is lightly implanted into the semiconductor substrate  21  at both sides of the respective gate electrodes  24  and  24   a  to form LDD regions  25  and  25   a.    
     Meanwhile, FIGS. 3 a  to  3   c  are sectional views illustrating a method for manufacturing a semiconductor device according to the second embodiment of the present invention. 
     In the first embodiment of the present invention, nitrogen ion implantation is performed after forming the LDD regions. While, in the second embodiment of the present invention, nitrogen ion implantation is performed after forming source/drain impurity regions. 
     That is, as shown in FIG. 3 a , a gate insulating film  33  of a first thickness and a second gate insulating film  33   a  of a second thickness are formed on a semiconductor substrate  31  by a typical dual gate oxidation process. Then, gate electrodes  34  and  34   a  are respectively formed on the gate insulating films  33  and  33   a.    
     Afterwards, LDD regions  35  and  35   a  are formed by low-concentration impurity ion implantation using the gate electrodes  34  and  34   a  as masks. 
     A reference numeral  32  which is not described denotes a device isolation film. 
     As shown in FIG. 3 b , an insulating film is deposited on an entire surface of the substrate  31  including the respective gate electrodes  34  and  34   a . The insulating film is then etched back to form sidewall spacers  36  and  36   a  at both sides of the respective gate electrodes  34  and  34   a . Source/drain impurity regions  37  and  37   a  are formed by high-concentration impurity ion implantation using the gate electrodes  34  and  34   a  and the sidewall spacers  36  and  36   a  as masks. 
     Subsequently, as shown in FIG. 3 c , a photoresist is deposited on the entire surface of the semiconductor substrate  31  including the gate electrodes  34  and  34   a . The photoresist is then patterned to form a mask pattern  38  for masking both the gate electrode  34  having the insulating film  33  of the first thickness and the substrate  31  at both sides of the gate electrode  34 . 
     A nitrogen ion is implanted into the substrate  21  at both sides of the gate electrode  34   a  having the gate insulating film  33   a  of the second thickness using the mask pattern  38  as a mask. As a result, the method for manufacturing a semiconductor device according to the second embodiment of the present invention is completed. 
     In the aforementioned second embodiment of the present invention, the nitrogen ion implantation may be performed before forming the source/drain impurity regions  37  and  37   a  (not shown). That is to say, the sidewall spacers  36  and  36   a  are formed and then the mask pattern  38  for masking the gate electrode  34  having the gate insulating film  33  of the first thickness and the substrate  31  at both sides of the gate electrode  34  is formed. The nitrogen ion is implanted into the substrate  31  at both sides of the gate electrode  34 a having the gate insulating film  33   a  of the second thickness using the mask pattern  38  as a mask. Subsequently, the mask pattern  38  is removed and then the source/drain impurity regions  37  and  37   a  are formed by high-concentration impurity ion implantation. 
     FIGS. 4 a  to  4   c  are sectional views illustrating a method for manufacturing a semiconductor device according to the third embodiment of the present invention. 
     In the third embodiment of the present invention, nitrogen ion implantation is twice performed. 
     As shown in FIG. 4 a , a gate insulating film  43  of a first thickness and a second gate insulating film  43   a  of a second thickness are formed on a semiconductor substrate  41  by a typical dual gate oxidation process. Then, gate electrodes  44  and  44   a  are respectively formed on the gate insulating films  43  and  43   a.    
     Afterwards, LDD regions  45  and  45   a  are formed into the substrate  41  at both sides of the respective gate electrodes  44  and  44   a  by low-concentration impurity ion implantation. 
     A reference numeral  42  which is not described denotes a device isolation film. 
     As shown in FIG. 4 b , a photoresist is deposited on an entire surface of the semiconductor substrate  41  including the gate electrodes  44  and  44   a . The photoresist is then patterned to form a first mask pattern  46  for masking both the gate electrode  44  having the insulating film  43  of the first thickness and the substrate  41  at both sides of the gate electrode  44 . 
     A nitrogen ion is primarily implanted into the substrate  41  at both sides of the gate electrode  44   a  having the gate insulating film  43   a  of the second thickness using the first mask pattern  46  as a mask. 
     Afterwards, as shown in FIG. 4 c , the first mask pattern  46  is removed and an insulating film is deposited on the entire surface of the substrate  41  including the respective gate electrodes  44  and  44   a . The insulating film is then etched back to form sidewall spacers  47  and  47   a  at both sides of the respective gate electrodes  44  and  44   a . Source/drain impurity regions  48  and  48   a  are formed into the substrate  41  at both sides of the respective gate electrodes  44  and  44   a  by high-concentration impurity ion implantation using the gate electrodes  44  and  44   a  and the sidewall spacers  47  and  47   a  as masks. 
     Subsequently, a photoresist is deposited on the entire surface of the semiconductor substrate  41  including the gate electrodes  44  and  44   a . The photoresist is then patterned to form a second mask pattern  46   a  for masking both the gate electrode  44  having the insulating film  43  of the first thickness and the substrate  41  at both sides of the gate electrode  44 . 
     The nitrogen ion is secondarily implanted into the substrate  41  at both sides of the gate electrode  44   a  having the gate insulating film  43   a  of the second thickness using the second mask pattern  46   a  as a mask. As a result, the method for manufacturing a semiconductor device according to the third embodiment of the present invention is completed. 
     In the third embodiment of the present invention, the primary nitrogen ion implantation may be performed before forming the LDD regions  45  and  45   a  and the secondary nitrogen ion implantation may be performed before forming the source/drain impurity regions  48  and  48   a . That is to say, before forming the LDD regions  45  and  45   a , the first mask pattern  46  is formed to expose the gate electrode  44   a  having the gate insulating film  43   a  of the second thickness and the substrate  41  at both sides of the gate electrode  44   a . Then, the nitrogen ion is primarily implanted into the exposed substrate  41 . Thereafter, the first mask pattern  46  is removed and then the LDD regions  45  and  45   a  are formed into the substrate  41  at both sides of the respective gate electrodes  44  and  44   a  by low-concentration ion implantation. The sidewall spacers  47  and  47   a  are formed and the second mask pattern  46   a  is formed to expose the gate electrode  44   a  having the gate insulating film  43   a  of the second thickness and the substrate  41  at both sides of the gate electrode  44   a . The nitrogen ion is then secondarily implanted into the exposed substrate  41 . 
     Afterwards, the second mask pattern  46   a  is removed and then source/drain impurity regions  48  and  48   a  are formed into the substrate  41  at both sides of the respective gate electrodes  44  and  44   a  by high-concentration ion implantation (not shown). 
     Meanwhile, FIG. 5 shows comparisons between the related art and the present invention in hot carrier generating time by normalizing hot carrier generating time in particular, in hot carrier life time of the device in which the thick gate insulating film is formed. 
     As shown in FIG. 5, in the present invention, if the nitrogen ion is implanted into the substrate in which the thick gate insulating film is formed, it is noted that hot carrier characteristic occurs later than the related art. 
     In other words, in case of characteristic deterioration by about 10%, characteristic deterioration occurs on the temporal axis less than  10   3  in the related art while characteristic deterioration occurs on the temporal axis more than 10 3  in the present invention. 
     Accordingly, in view of normalized hot carrier generating time, it is noted that life time of the device in the present invention become longer than that in the related art. 
     As aforementioned, the method for manufacturing the semiconductor device has the following advantages. 
     Since the nitrogen ion is implanted into the LDD regions and source/drain regions of the device having the thick gate insulating film, it is possible to improve hot carrier life time by the nitrogen ion, thereby increasing life time of the device. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the method for manufacturing a semiconductor device according to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of the invention provided they come within the scope of the appended claims and their equivalents.