Abstract:
Disclosed is a coaxial tube wiring structure (and method of making) of a semiconductor memory device for shielding a conductive film that transmits a signal. The coaxial tube structure includes: a plurality of signal conductive films formed on a substrate; and an arbitrary conductive film which shields the upper and lower surfaces and both sides of the signal conductive film, which is insulated from the signal conductive film by an insulating film, and to which ground voltage is applied.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a wiring line structure of a semiconductor, e.g., memory device and a formation method thereof for shielding a conductive film that transmits a signal of a semiconductor memory device. 
     BACKGROUND OF THE INVENTION 
     In a wiring structure of a semiconductor memory device, a wiring for transmitting a signal is composed of metal. As integration of semiconductor memory devices increases, a coupling effect between neighboring wiring increases. Therefore, a signal transmitted through the wiring loses an original shape, i.e., it becomes distorted. 
     As shown in FIG. 1, a wiring structure of a semiconductor memory device according to the conventional art includes a substrate  2  having a device (for example, a transistor, a capacitor) (not illustrated) formed on the upper surface thereof, an insulating film  3  composed of a material such as an oxide film on the upper surface of the substrate  2 , and a first conductive film  4  (which serves as wiring for transmitting a signal) formed on the insulating film  3  by a photolithography. A coupling capacitance is generated by a coupling effect with a second neighboring conductive film  4 . 
     As shown in FIG. 2A, it can be seen that there occurs a delay in a signal waveform Q 2  at a point P 2  in FIG. 1 in comparison with a signal waveform Q 1  at a point P 1 . As shown in FIG. 2B, there occurs a overshooting, that is a distortion of a signal at a point P 4  in comparison with a signal waveform Q 3  at a point P 3 . Accordingly, in a semiconductor memory device, an error is caused by the inputting of a signal waveform Q 4  at a point P 4 . For example, inverters (not illustrated) are respectively connected to either end of each conductive film  4 , and when an input voltage (Vin) is switched from high level to low level, the input voltage (Vin) is inverted from low level into high level at the point P 1 . Here, when the voltage (Vcc) is inputted, voltage ground (Vss) must be maintained at the point P 3 , but there occurs an overshooting due to a coupling capacitance between neighboring conductive films, and at the point P 4 , the effect is gradually increased, resulting in an error of the inverter receiving an input at P 4 . 
     As shown in FIG. 3, the wiring structure of a semiconductor memory device according to another embodiment of the conventional art has a similar structure to that of FIG. 1, which includes a substrate  6  having a device (for example, a transistor, a capacitor) (not illustrated) formed on the upper surface thereof, an insulating film  7  composed of a material such as an oxide film on the upper surface, and conductive films  8 , 9  formed on the insulating film  7  by photolithography to serve as wiring. The conductive films  8 , 9  are alternatingly positioned, and ground voltage (Vss) is applied to the conductive film  9  so as to reduce a coupling capacitance between the conductive films  8 , 9 . In the above structure, a distortion of a signal transmitted to the conductive film  8  can be partially reduced. However, the upper surface of the conductive film  8  is not shielded, so a capacitance caused by a coupling between the conductive films cannot be prevented. Therefore, distortion of a transmitted signal remains unimproved. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved wiring structure of a semiconductor memory device according to the present invention which is capable of reducing distortion of a transmitted signal by controlling, i.e., minimizing, a capacitance generated by a coupling between wiring. 
     It is another object of the present invention to provide an improved formation method for a wiring structure of a semiconductor memory device according to the present invention which is capable of reducing distortion of a transmitted signal by shielding a wiring. 
     To achieve the above object, there is provided an improved wiring structure of a semiconductor memory device according to a first embodiment of the present invention which includes: a plurality of first signal conductive films formed on a substrate; and a second shielding conductive film which shields a peripheral portion of the first conductive film, which is insulated from the first conductive film by an insulating film, and to which ground voltage is applied. 
     To achieve the above object, there is provided an improved method for forming a wiring structure of a semiconductor memory device according to the present invention which includes the steps of forming on a substrate a first conductive film to which a ground voltage is applied, forming a first insulating film on the first conductive film, forming a plurality of first grooves by selectively etching the first insulating film, forming a second conductive film on the first grooves and the first insulating film, forming a first pattern connected with the first conductive film and a second pattern not connected with the first conductive film, forming a second insulating film on the first insulating film including the first and second patterns, forming second grooves by selectively etching the second insulating film corresponding to the first pattern, and forming a third conductive film on the second insulating film including the second grooves. 
     These and other objects of the present invention are also achieved by providing a coaxial tube structure for a semiconductor device, the structure comprising: a substrate; a first signal conductor; a first insulator, coaxial to said first signal conductor; and a first shielding conductor structure, formed on said substrate, coaxial to said first insulator and said first signal conductor. 
     The foregoing and other objectives of the present invention will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, wherein: 
     FIG. 1 is a schematic perspective view showing a wiring structure of a semiconductor memory device according to an embodiment of the conventional art; 
     FIGS. 2A and 2B are signal waveform diagrams showing a signal waveform at each point of the conventional wiring structure in FIG. 1; 
     FIG. 3 is a schematic perspective view showing a wiring structure of a semiconductor memory device according to another embodiment of the conventional art; 
     FIG. 4 is a schematic perspective view showing a wiring structure of a semiconductor memory device according to a first embodiment of the present invention; 
     FIG. 5 is a schematic perspective view showing a wiring structure of a semiconductor memory device according to a second embodiment of the present invention; 
     FIG. 6 is a schematic perspective view showing a wiring structure of a semiconductor memory device according to a third embodiment of the present invention; 
     FIG. 7 is a schematic perspective view showing a wiring structure of a semiconductor memory device according to a fourth embodiment of the present invention; 
     FIGS. 8A through 8H are views showing a formation method for a wiring structure of a semiconductor memory device in FIG. 4; 
     FIG. 9 is a plan view of FIG. 8B; and 
     FIGS. 10A and 10B are views showing a signal waveform at each point of a wiring structure in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A wiring structure of a semiconductor memory device and a formation method thereof according to the present invention will now be described in detail with reference to the accompanying drawings. 
     As shown in FIG. 4, a wiring structure according to a first embodiment of the present invention includes: a substrate  100  having a device (for example, formed of transistors and/or capacitors) (not illustrated) formed thereon; a plurality of signal conductive films  140 , e.g., a conductor such as an aluminum, for transmitting a signal and formed on the substrate  100  by photolithography; and an arbitrary conductive film  120  connected to ground voltage (Vss) and formed, e.g., of a conductor such as an aluminum. The signal conductive film  140  is separately formed to be shielded by the arbitrary conductive film  120 . Between the signal conductive film  140  and the arbitrary conductive film  120 , an insulating film  130 , e.g., an oxide film is located so as to remove a coupling effect. 
     FIG. 5 is a schematic perspective view showing a wiring structure of a semiconductor memory device according to a second embodiment of the present invention. Since the embodiment has a structure similar to that of the first embodiment, identical numerals are put on the identical elements. In this embodiment, the signal conductive films  140  are formed to have a predetermined space therebetween, and accordingly, the arbitrary conductive film  120  for shielding a peripheral portion of the signal conductive film  140  is also formed to have a predetermined space in a central portion and only the lower surface of the film  120  is connected. Between the signal conductive film  140  and the arbitrary conductive film, the insulating film  130  is filled so as to remove a coupling effect. 
     FIG. 6 is a schematic perspective view showing a wiring structure of a semiconductor memory device according to a third embodiment of the present invention. Since the embodiment has a structure similar to that of the second embodiment, identical numerals are put on the identical elements. In this embodiment, the signal conductive films  140  are separately formed to have a predetermined space therebetween, and accordingly, the arbitrary conductive film  120  for shielding the signal conductive film  140  is also formed to have a predetermined space in a central portion, and only the upper surface of the film  120  is connected. Between the signal conductive film  140  and the arbitrary conductive film, the insulating film  130  is filled so as to remove a coupling effect. 
     FIG. 7 is a schematic perspective view showing a wiring structure of a semiconductor memory device according to a fourth embodiment of the present invention. Since the embodiment has a structure similar to that of the third and fourth embodiments, identical numerals are put on the identical elements. In this embodiment, the signal conductive films  140  are separately formed to have a predetermined space therebetween, and accordingly, the arbitrary conductive film  120  for shielding the signal conductive film  140  is also formed to have a predetermined space in a central portion. Between the signal conductive films  140  and the arbitrary conductive film  120 , the insulating film  130  is filled so as to remove a coupling effect. 
     Referring to FIGS. 8A through 8H, description of a formation method for a wiring structure of a semiconductor memory device according to the present invention will now be given in detail. 
     As shown in FIG. 8A, the substrate  100  is formed to have a device (for example, including transistors and/or capacitors) (not illustrated) formed thereon, a first conductive film  120   a  is formed on a predetermined surface of the substrate  100 , and a first insulating film  130   a , e.g., an oxide film, is formed on the first conductive film  120   a  and the substrate. 
     As shown in FIG. 8B, a plurality of first grooves  22  are formed by selectively etching a predetermined portion of the first insulating film  130   a.    
     As shown in FIG. 8C, a second conductive film  120   b  is formed on the first insulating film  130   a  including the grooves  22 . Here, the first grooves  22  are filled with the second conductive film  120   b , which is connected with the conductive film  120   a.    
     As shown in FIG. 8D, a first pattern  120   c  (connected with the first conductive film  120   a ) and a second pattern  140  (located between pairs of first patterns  120   c  and not connected with the first conductive films  120   a ), are respectively formed by selectively etching a predetermined portion of the second conductive film  120   b . The second pattern  140  is to serve as a signal conductive film. 
     As shown in FIG. 8E, a second insulating film  130   b  is formed on the first and second patterns  120   c , 140  and the first insulating film  130   a.    
     As shown in FIG. 8F, a plurality of second grooves  24  are formed by selectively etching a predetermined portion of the second insulation film  130   a  so as to expose an upper surface of the first pattern  120   c.    
     As shown in FIG. 8G, a third conductive film  120   e  is formed on the second insulating film  130   b  including the second grooves  24 . Here, the second grooves  24  are filled with the third conductive film  120   e  to be connected with each other. 
     As shown in FIG. 8H, a predetermined portion of the third conductive film  120   e  and the insulating films  130  including the first and second insulating film  130   a , 130   b  are selectively etched away, thereby resulting in forming the arbitrary conductive film  120  surrounding the second pattern  140 . 
     FIG. 9 is a plan view of FIG. 8B The first grooves  22  are formed in the shape of a strip to have a predetermined width in a length direction of the substrate  100 . 
     FIGS. 10A and 10B are views showing a signal waveform at each point of a wiring structure in FIG.  4 . As shown in FIG. 10A, it can be seen that there occurs a little delay in a signal waveform Q 6  of the first signal conductive film  140  at the point P 6  in FIG. 4 in comparison with a signal waveform Q 5  at the point P 5 . However, as shown in FIG. 10B, a signal waveform Q 7  of the second signal conductive film  140  at a point P 7  corresponds to a signal waveform Q 8  at a point P 8  without a distortion. 
     As described above, according to a wiring structure of a semiconductor memory device, a first signal conductive film for transmitting a signal is shielded by an arbitrary conductive film so as to control a capacitance generated by a coupling effect with a second neighboring signal conductive film, and thereby to prevent a distortion of a transmitted signal waveform. 
     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as recited in the accompanying claims.