Abstract:
A semiconductor device comprises a semiconductor layer including a plurality of paralleled linear straight sections extending in a first direction. The layer also includes a plurality of connecting sections each having a width in the first direction sufficient to form a wire-connectable contact therein and arranged to connect between adjacent ones of the straight sections in a second direction. The connecting sections have respective ends formed aligned with a first straight line parallel to the second direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2007-98227, filed on Apr. 4, 2007, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor device and method of manufacturing the same. In particular, it relates to a semiconductor device and method of manufacturing the same using the so-called sidewall transfer process to etch an etching target member. 
   2. Description of the Related Art 
   In a semiconductor manufacturing process to form a wiring pattern (line-and-space), generally, a photolithography mask is used to develop a resist to transfer the pattern to the resist, which is then used as a mask to etch an etching target member. 
   As semiconductor devices have been fine-patterned in recent years, EEPROMs with a reduced number of bit lines and drain contacts have been proposed (see, for example, Patent Document 1: JP 2-74069A). Associated with the reduced number of bit lines and drain contacts, there are technologies for solving the problem about injection of electrons (failed write) due to occurrences of electron-hole pairs in a Si substrate (see, for example, Patent Document 2: JP 6-275800A). 
   The technologies as in the above Patent Documents 1, 2 require a semiconductor device that allows a common contact to be formed in a set of two source/drain diffusion layer portions (semiconductor layer portions). Such the common contact-formable semiconductor device is structured to have H-shaped source/drain diffusion layer portions partly connected seen from above. 
   Formation of the above H-shaped source/drain diffusion layer portions leaves a problem associated with the lithography resolution limit caused in accordance with downsizing of semiconductor devices. Specifically, if a contact fringe is formed in a portion of source/drain diffusion layer portions aligned at a smallest pitch, the interval between contact fringes in adjacent source/drain diffusion layer portions can not be formed by the lithography at a sufficient resolution. In this case, the interval becomes narrow, which may establish a short circuit possibly. An etching also can not form the interval. In a word, the above problem lowers the yield as well. 
   In the method of forming a contact at the center of two diffusion layer portions as disclosed in the Patent Document 2, the contact area between the source/drain diffusion layer portion and the contact is small. Therefore, it causes an increase in contact resistance as a problem. If the contact is shifted to one side by misalignment or the like, an open failure may arise. 
   On the other hand, there is a technology for forming a pattern below the lithography resolution limit using the so-called sidewall transfer process. The use of this technology to form source/drain diffusion layer portions and form a contact fringe spanning two source-drain diffusion layer portions, however, additionally requires a lithography step and an etching step. Further, as for lithography, the problem about the narrow space associated with an adjacent pattern and the problem about the misalignment with the source/drain diffusion layer portions may occur similarly as can be predicted. 
   SUMMARY OF THE INVENTION 
   In one aspect the present invention provides a method of manufacturing a semiconductor device including a first region formed of a plurality of paralleled semiconductor layer portions extending linearly in a first direction and a second region formed of two adjacent ones of the semiconductor layer portions connected in a second direction, the method comprising: forming a first hard mask on an etching target member; forming on the first hard mask a second hard mask having paralleled portions extending straight in the first direction at plural locations; executing ion implantation into the second hard mask in the second region while protecting the first region from the ion implantation with a mask, thereby reforming the second region for changing an etching rate for wet etching in the second region from that in the first region; etching the first hard mask with a mask of the second hard mask; removing the second hard mask from the first region selectively by wet etching while leaving the second hard mask in the second region; forming sidewall films on sidewalls of the first hard mask; etching off the first hard mask selectively to remove a portion thereof having an upper part not covered with the second hard mask but exposed in the first region; and etching off the etching target member with a mask of the sidewall films and the first hard mask. 
   In one aspect the present invention provides a semiconductor device, comprising: a semiconductor layer including a plurality of paralleled linear straight sections extending in a first direction and a plurality of connecting sections each having a width in the first direction sufficient to form a wire-connectable contact therein and arranged to connect between adjacent ones of the straight sections in a second direction, wherein the connecting sections have respective ends formed aligned with a first straight line parallel to the second direction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a semiconductor device according to an embodiment of the present invention. 
       FIG. 2A  shows a step in a method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 2B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 2C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 3A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 3B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 3C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 4A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 4B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 4C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 5A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 5B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 5C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 6A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 6B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 6C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 7A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 7B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 7C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 8A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 8B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 8C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 9A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 9B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 9C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 10A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 10B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 10C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 11A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 11B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 11C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 12A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 12B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 12C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 13A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 13B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 13C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 14A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 14B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 14C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 15A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 15B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 15C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 16A  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 16B  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 16C  shows a step in the method of manufacturing the semiconductor device according to the embodiment of the present invention. 
       FIG. 17  shows a shape of source/drain diffusion layer portions  1 ′ in a semiconductor device according to another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The embodiments of the present invention will now be described in detail with reference to the drawings. 
   A structure of a semiconductor device according to an embodiment of the present invention is described with reference to  FIG. 1 . As shown in  FIG. 1 , the semiconductor device according to the embodiment includes plural source/drain diffusion layer portions  1  linearly extending in the X-axis direction on a semiconductor substrate; word lines  2  extending over the source/drain diffusion layer portions  1  in the Y-axis direction (a direction orthogonal to the X-axis direction); and selection gate lines  3  extending over the source/drain diffusion layer portions  1  in the Y-axis direction. 
   The source/drain diffusion layer portion  1  is formed in an H-shape. Each source/drain diffusion layer portion  1  includes two straight sections  11  extending parallel in the X-axis direction and a connecting section  12  extending in the Y-axis direction to connect between adjacent straight sections  11 . In the semiconductor device according to the present embodiment, the location of forming the straight sections  11  serves as a memory cell array region M. In addition, the location of forming the connecting section  12  serves as a fringe region H for connecting the source/drain diffusion layer portions  1  to a bit line (not shown). The connecting section  12  has a width in the X-axis direction, which is a bit line contact-formable width. All ends in the X-axis direction are formed in parallel with the Y-axis direction and aligned with a straight line. The connecting section  12  has a width in the Y-axis direction, which is formed wider than the straight section  11 . 
   In the semiconductor device shown in  FIG. 1 , the straight sections  11  are formed as derived from linear sidewall films along sidewalls of a hard mask formed in parallel as described later. The connecting section  12  is formed after mask formation through a step of implanting impurity ions into a hard mask in a rectangular ion implantation region I aligned with the connecting section  12 . The connecting section  12  is formed as derived from the hard mask and sidewall films. The hard mask is provided with an etching rate for wet etching different from that in the straight section  11  through the step of ion implanting. The ion implantation region I has the same width as the width of the connecting section  12  in the X-axis direction. Namely, the width of the connecting section  12  in the X-axis direction is based on boundaries of masks formed in other regions than the ion implantation region I and of the hard mask. 
   A method of manufacturing the semiconductor device according to the embodiment of the present invention is described next with reference to  FIGS. 2A  ( 2 B,  2 C) through  15 A ( 15 B,  15 C).  FIGS. 2A-15A  are top views of the semiconductor device in manufacturing steps.  FIGS. 2B-15B  are cross-sectional views taken along A-A′ of  FIGS. 2A-15A .  FIGS. 2C-15C  are cross-sectional views taken along B-B′ of  FIGS. 2A-15A . In the following example, a silicon nitride film (SiN)  50  formed on a pad oxide film  42  on a semiconductor substrate  41  is etched as an etching target member. In the memory cell array region M, with the use of the sidewall transfer process, the straight sections  11  in the source/drain diffusion layer portion  1  below the lithography resolution limit are formed of the silicon nitride  50 . In the fringe region H, the connecting section  12  is formed of the silicon nitride  50  at the same time with an arbitrary width for connecting between the straight sections  11  in the source/drain diffusion layer portion  1 . 
   First, as shown in  FIGS. 2A-2C , a first hard mask  60  composed of TEOS (Tetra Ethyl Ortho Silicate) for use in etching the etching target member or the silicon nitride  50  is deposited thereon. This is just an example and the first hard mask  60  in various types (the number of layers, the thickness of each layer, the material and so forth) may be used in consideration of etching conditions and mask materials. 
   The first hard mask  60  serves as a sidewall formation material for forming sidewalls  80  as described later. A second hard mask  70  composed of amorphous silicon is further formed on the first hard mask  60 . The second hard mask  70  is formed to etch the first hard mask  60  composed of TEOS into a desired pattern. The second hard mask  70  may also be composed of a material that changes the etching rate for wet etching on receipt of ion implantation, such as polysilicon, instead of amorphous silicon. 
   Next, as shown in  FIGS. 3A-3C , an antireflective film  91  is applied over the entire second hard mask  70  and then a resist is applied on the upper surface of the antireflective film  91 . Thereafter, a lithography method is used to develop the resist to form a resist  92  having a desired pattern form. The resist  92  has plural paralleled rectangular pattern forms extending in the X-axis direction. The resist  92  has a line-and-space of the minimum line width W, and the width W of the lines is almost equal to that of the spaces. The minimum line width W herein means a width determined from the lithography resolution limit. 
   Next, as shown in  FIGS. 4A-4C , an anisotropic etching is used to etch the antireflective film  91  and slim the resist  92  at the same time to bring the resist  92  to a slimmed width below the resolution limit of photolithography. Then, an anisotropic etching with a mask of the slimmed resist  92  is used to etch the second hard mask  70 . In a word, plural paralleled portions extending in the X-axis direction are formed in the second hard mask  70 . After the etching, the antireflective film  91  and the resist  92  are peeled off as shown in  FIGS. 5A-5C . The resist  92  is herein controlled to have a line width of ½W and a space width of 3/2W. 
   Then, as shown in  FIGS. 6A-6C , a resist  93  is formed on the second hard mask  70  only in regions (the memory cell array regions M in this example) desired to form line-and-space patterns therein below the lithography resolution limit through the sidewall transfer process. 
   Subsequently, as shown in  FIGS. 7A-7C , with the use of the resist  93  as a mask, impurity ions (preferably, boron (B), phosphorous (P), arsenic (As) and boron difluoride (BF 2 )) are implanted into the second hard mask  70 . In an example, the ion implantation condition is adjusted such that the ion-implanted second hard mask  70 B has an impurity concentration of 1×10 20  cm −3 . The ion-implanted second hard mask  70 B not covered with the resist  93  is lower in etching rate for wet etching with an alkaline solution than the second hard mask  70  covered with the resist  93  and not ion-implanted. 
   Subsequently, after the resist  93  is peeled off as shown in  FIGS. 8A-8C , an anisotropic etching with a mask of the second hard masks  70 ,  70 B is used to etch the first hard mask  60  serving as a sidewall formation material as shown in  FIGS. 9A-9C . 
   Thereafter, as shown in  FIGS. 10A-10C , a wet etching with an alkaline solution is applied to remove the never-ion-implanted second hard mask  70  selectively and leave the ion-implanted second hard mask  70 B. The alkaline solution-used wet etching also etches the oxide and nitride films at a higher selection ratio. Accordingly, it exerts no ill effect on the first hard mask  60  serving as the sidewall formation material and the silicon nitride  50  in the underlying layer (the etching target material). This method makes it possible to remove only the second hard mask  70  in the memory cell array region M with ease and without exerting any side-effect on others. 
   Thereafter, as shown in  FIGS. 11A-11C , a CVD method is applied to deposit an amorphous silicon film over the entire first hard mask  60  including the upper surface of the second hard mask  70 B. Then, an anisotropic etching is used to etch the amorphous silicon film so as to remain only on the sidewalls of the first hard mask  60  and on the sidewalls of the second hard mask  70 B. The remaining films are used as sidewall films  80  (amorphous silicon films). The sidewall films  80  are desired to reach the upper part of the sidewalls of the second hard mask  70 B to prevent the first hard mask  60  from being etched in the next step ( FIGS. 12A-12C ). The first hard mask  60  is etched to a width of around ½W, or one-half of the minimum line width W in accordance with the resolution limit. Therefore, the thickness of the deposited amorphous silicon, the etching condition and so forth are set such that the sidewall films  80  have a width of around ½W. 
   Subsequently, as shown in  FIGS. 12A-12C , a wet etching with, for example, a dilute hydrofluoric acid is used to etch off the first hard mask  60  sandwiched between the sidewall films  80  and having exposed upper parts in the memory cell array region M. On the other hand, the first hard mask  60  covered with the second hard mask  70 B in the fringe region H is not etched and remains. As a result, in the memory cell array region M, only the ½W-wide sidewall films  80  remain on the silicon nitride  50  at a space width of ½W. An etching with a mask of only such the sidewall films  80  can form a pattern of the semiconductor layer with a line width of ½W and a space width of ½W below the lithography resolution limit in the memory cell array region M. On the other hand, in the hinge region H, the first hard mask  60  covered with the second hard mask  70 B and the sidewall films  80  is not etched and remains, and is used as an etching mask together with the sidewall films  80 . 
   Thereafter, as shown in  FIGS. 13A-13C , an anisotropic etching with a mask of the sidewall films  80  composed of amorphous silicon and the second hard mask  70 B similarly composed of amorphous silicon is applied to etch the silicon nitride  50 . Preferably, the second hard mask  70 B is set to have such a thickness that the second hard mask  70 B can be etched off completely. 
   The etching is further continued with a mask of the sidewall films  80  to etch the first hard mask  60  as shown in  FIGS. 14A-14C . In this step, the silicon nitride  50  becomes a closed-loop form seen from above as shown in  FIG. 14A . Subsequently, as shown in  FIGS. 15A-15C , both ends of the silicon nitride  50  in the X-axis direction are lithographed and then etched off. As a result, the both ends of the silicon nitride  50  in the X-axis direction become in the form of lines as shown in  FIG. 15A . 
   Then, as shown in  FIGS. 16A-16C , with a mask of the silicon nitride  50 , the pad oxide  42  and the semiconductor substrate  41  in the underlying layers are etched. Through these steps, the H-shaped source/drain diffusion layer portions  1  each having the straight sections  11  and the connecting section  12  shown in  FIG. 1  are finally formed in the underlying layer below the silicon nitride  50 . 
   As described above, the method of manufacturing a semiconductor device according to the present embodiment includes forming plural paralleled linear portions of the second hard mask  70  on the first hard mask  60 , and implanting ions of an impurity such as boron linearly as spanning the portions of the second hard mask  70  for reforming. Thus, the present embodiment is possible to form the straight sections  11  below the lithography solution limit and the connecting section  12  for connecting between the straight sections  11  in the source/drain diffusion layer  1  through an identical lithography step. Therefore, it is possible to reduce the difficulty of lithography particularly in comparison with the prior art. 
   One embodiment of the invention has been described above though the present invention is not limited to this embodiment but rather can be given various modifications, additions and so forth without departing from the scope and spirit of the invention. For example, the sidewall film  80  is formed of amorphous silicon as exemplified in the above embodiment though, depending on the etching condition and others, it may be composed of other materials such as a silicon oxide or the like. The silicon nitride  50  is formed in an H-shape seen from above in the above embodiment though the silicon nitride  50  may be formed in a closed-loop as shown in  FIG. 14A  without the use of the step shown in  FIGS. 15A-15C . The source/drain diffusion layer  1  is described as H-shaped in the above embodiment though the source/drain diffusion layer according to the present invention is not limited to the H-shape. In a word, a source/drain diffusion layer  1 ′ as shown in  FIG. 17  may also be available, which has straight sections  11 ′ linearly extending in the X-axis direction, and connecting sections  12 ′ for connecting between the straight sections  11 ′ at plural locations in the X-axis direction.