Patent Publication Number: US-2002003304-A1

Title: Semiconductor device having multilevel interconnection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001] This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-207330, filed Jul. 7, 2000, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates to a semiconductor device having a multilevel interconnection.  
       [0004] 2. Description of the Related Art  
       [0005] Recently, a transmission line is formed in a multilevel interconnection of a semiconductor device in order to transmit a high-speed signal at a high efficiency. In the most popular semiconductor device, a ground line is formed to make a pair with a signal wiring line as will be described below.  
       [0006] That is, as can be seen in FIG. 9, a plurality of high-speed long-distance interconnection lines  21  and a plurality of low-speed short-distance interconnection lines  22  are mixedly formed in one layer. Above these interconnection lines  21  and  22 , a first interlayer insulating film  23  is formed. A plurality of ground lines  24  are formed on the first interlayer insulating film  23 , and a second interlayer insulating film  25  is formed on the ground lines  24 .  
       [0007] Similarly, a plurality of high-speed long-distance interconnecting lines  26  and a plurality of low-speed short-distance interconnection lines  27  are mixedly formed on second interlayer insulating film  25 . Above these interconnection lines  26  and  27 , a third interlayer insulating film  28  is formed. A plurality of ground lines  29  are formed on the third interlayer insulating film  28 , and a fourth interlayer insulating film  29  is formed on the ground lines  29 .  
       [0008] With the ground lines  24  and  29  provided as above, noise created between the lines  26  and  27  is decreased, and signals are transmitted at a high speed.  
       [0009] However, in the conventional semiconductor device, the line materials and line formation process are limited to those which have been conventionally employed. Therefore, in the case where ground lines  24  and  29  having a relatively high coverage rate are formed, a problem such as the ground lines  24  and  29  being peeled off due to an uneven stress may easily occur. Or in the case where such a large-area wiring pattern as of ground lines  24  and  29  is formed by a CMP (chemical mechanical polish) method using Cu as the line material, it is difficult to suppress dishing and therefore, a part of the wiring pattern is sometimes lost.  
       [0010] As described above, the conventional semiconductor device entails the drawback that it is very difficult to achieve a high-speed signal transmission and to relax the limitation on the materials and process.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011] According to the first aspect of the present invention, there is provided a semiconductor device comprising: a first module having a first interconnection line; a second module having a second interconnection line which is shorter than the first interconnection line, the second module being formed separately from the first module, the second module being attached to the first module in a laminating direction of the first and second interconnection lines, and the second interconnection line and the first interconnection line are electrically connected to each other; and a ground line provided within the first module and paired with the first interconnection line.  
       [0012] According to the second aspect of the present invention, there is provided a semiconductor device according to the first aspect, wherein the first interconnection line is arranged between the ground line and the second interconnection line.  
       [0013] According to the third aspect of the present invention, there is provided a semiconductor device according to the first aspect, further comprising: a first pad provided in the first module and connected to the first interconnection line; a second pad provided in the second module and connected to the second interconnection line, the second pad being formed to face the first pad; and an insulating member provided between the first and second modules, the first and second interconnection lines being electrically connected to each other by a capacitance coupling consisting of the insulating member, and the first and second pads.  
       [0014] According to the fourth aspect of the present invention, there is provided a semiconductor device according to the second aspect, wherein a part of the ground line serves as a pad electrode.  
       [0015] Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
     [0016] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
     [0017]FIG. 1 is a cross sectional view showing a semiconductor device according to the first embodiment of the present invention;  
     [0018]FIGS. 2A, 2B,  2 C and  2 D are cross sectional views each showing a different version of the semiconductor device according to the first embodiment of the present invention each;  
     [0019]FIG. 3 is a cross sectional view showing a semiconductor device according to the second embodiment of the present invention;  
     [0020]FIG. 4 is a cross sectional view showing a semiconductor device according to the third embodiment of the present invention;  
     [0021]FIG. 5 is a partially enlarged view of the semiconductor device according to the third embodiment shown in FIG. 4;  
     [0022]FIG. 6 is a circuit diagram of the semiconductor device according to the third embodiment shown in FIG. 5;  
     [0023]FIG. 7 is a diagram showing a relationship of the maximum thickness of the insulating film with regard to the frequency and electrode area;  
     [0024]FIG. 8 is a cross sectional view showing a semiconductor device according to the fourth embodiment of the present invention; and  
     [0025]FIG. 9 is a cross sectional view showing a semiconductor device according to the conventional technique.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0026] Embodiments of the present invention will now be described with reference to accompanying drawings. Throughout the descriptions of the embodiments and the drawings, the like structural elements will be designated by the same reference numerals.  
     [0027] [First Embodiment] 
     [0028] The characteristic feature of the first embodiment is that the first module having a long-distance interconnection line and a ground line and the second module having a short-distance interconnection line are formed separately, and then these modules are adhered together. It should be noted that the first embodiment is the basic structure of the present invention.  
     [0029]FIG. 1 is a cross section view of a semiconductor device according to the first embodiment of the present invention. As shown in FIG. 1, various wires are divided into long-distance interconnection lines  13   a  and short-distance interconnection lines  13   b . Then, a first module  11  is formed and it includes the long-distance interconnection lines  13   a , pads  11   a  connected to the long-distance interconnection lines  13   a  and ground lines  14  each of which makes a pair with a respective one of the long-distance interconnection lines  13   a . On the other hand, separately from the first module  11 , a second module  12  is formed and it includes the short-distance interconnection lines  13   b  and pads  12   a  connected to the short-distance interconnection lines  13   b  is formed. After that, the first and second modules  11  and  12  are adhered together in the laminating direction of the interconnection lines  13   a  and  13   b , and thus the pads  11   a  and  12   a  are electrically connected to each other. Thus, the first and second modules  11  and  12  are integrated as one unit and a chip is formed.  
     [0030] Further, it is structurally allowable that circuits  41   a  and  41   b  made of active or passive elements such as MOSFETs may be present in the first and second modules  11  and  12 . Such circuits  41   a  and  41   b  in the two modules  11  and  12  function as LSI circuits, and signals are processed with use of these circuits  41   a  and  41   b.    
     [0031] It should be noted that short-distance interconnection lines  13  may be mixed in the first module  11 .  
     [0032] In the first embodiment, the separation of the long-distance interconnection lines  13   a  and the short-distance interconnection lines  13  can be carried out in the following manner. For example, where the frequency used is represented by f c , the resistance of lines separated per unit length is represented by r, the capacitance of lines separated per unit length is represented by c, and the length of an interconnection line for reference is represented by L c , the relationship expressed by the following equation (1) can be induced.  
       f   c =½ πrcL   c   2   (1)  
     [0033] Therefore, the length L c  is expressed by the following equation (2), according to which, it is understood that the length L c  varies from one frequency f c  used to another.  
       L   c ={square root}{square root over ( )}½ πrcf   c   (2)  
     [0034] From the equation (2), in the case where the length of the interconnection line to be separated is L, and if L c &lt;L, the line is regarded as a long-distance interconnection line  13   a , whereas if L&lt;L c , the line is regarded as a short-distance interconnection line  13   b.    
     [0035] For example, a long-distance interconnection line  13   a  has a length of several hundred μm or more, and is used for interconnection between a bit line and word line in a memory or interconnection between a memory and the CPU in an LSI circuit. On the other hand, a short-distance interconnection line  13   b  has a length of several to several hundred μm, and is used for interconnection between adjacent transistors.  
     [0036] According to the first embodiment, the first module  11  and the second module  12  are separately formed. In this manner, the material for the interconnection lines or for the interlayer insulating films can be changed in accordance with the performance required for each of the modules  11  and  12 , and further an optimal process for the object of each of the modules  11  and  12  can be selected.  
     [0037] More specifically, the long-distance interconnection lines  13   a  and the ground lines  14  in the first module  11  are formed of, for example, Al films, whereas the short-distance interconnection lines  13   b  in the second module  11  are formed of, for example, Cu films. With this structure, the long-distance interconnection lines  13  and the ground lines  14 , which are made of the Al films, can be patterned by RIE (reactive ion etching), and therefore it is no longer necessary to pattern it using CMP (chemical mechanical polish). Therefore, the problem of dishing, which entails to the case where CMP is employed, does not occur.  
     [0038] Further, the most appropriate interconnection material having a low stress can be selected for each of the modules  11  and  12 , and therefore the problem of peeling-off of films, which occurs due to stress, can be suppressed.  
     [0039] Furthermore, in the first module  11 , long-distance interconnection lines  13   a  which require high-speed processes are provided, and therefore it is important to decrease the capacitance of the interconnection line. Here, as an interlayer insulating film in the first module  11 , it suffices if a low dielectric constant film having a specific dielectric constant of about 4.0 or less is used. In this manner, the capacitance can be lowered in the first module  11 . On the other hand, an element which generates heat is formed in the second module  12 , and therefore as the interlayer insulating film, a material having a high heat radiating property is required. Therefore, as the interlayer insulating film of the second module  12 , it suffices if a film having a heat radiating property higher than that of a low dielectric film and having a high strength (that is, for example, a silicon oxide film) is used. In this manner, in the second module  12 , the heat radiating property can be improved while fully protecting the element.  
     [0040] As described above, the limitations of the material properties and process can be relaxed, and therefore the degree of freedom in terms of the material type as well as the process type.  
     [0041] Moreover, the structure of the first embodiment is divided into the first module  11  including the long-distance interconnection lines  13   a  and the second module  12  including the short-distance interconnection line  13   b . In this structure, it suffices if the ground lines  14  are formed only in the first module  11 . With this structure, it is possible to suppress the number of wiring layers to the minimum necessary limit, and therefore the number of steps for making multilevel interconnection can be reduced as compared to the case where the long-distance interconnection lines  13   a  and the short-distance interconnection lines  13   b  are mixedly present. Therefore, the production cost can be reduced.  
     [0042] It should be noted here that the connection between the first module  11  and the second module  12  is not limited to the type shown in FIG. 1, but may be of those shown in FIGS. 2A to  2 D.  
     [0043] For example, as shown in FIG. 2A, the modules  11  and  12  may be connected together in such a manner that pads  11   a  and  12   a  are provided such as to project from the modules  11  and  12  respectively, and a gap between the modules  11  and  12  is filled with an insulating member  40  such as a resin. In this case, a recess portion may be made in either one of the pads  11   a  and  12   b , and a projecting portion is made in the other one of these pads as can be seen in FIGS. 2A and 2C, so that the pads  11   a  and  12   a  can be easily engaged with each other.  
     [0044] Alternatively, as shown in FIG. 2D, pads  11   a  and  12   a  are provided on outer sides of the modules  11  and  12 , respectively, and a conductive connector element  15  such as a bump is provided between the pads  11   a  and  12   b . Further, a gap between the modules  11  and  12  is filled with an insulating member  40  and thus the modules  11  and  12  are connected together. Here, as the conductive connecting element  15 , an anisotropic conductive sheet may be used.  
     [0045] With the above-described interconnections as well, the same effect as that of the first embodiment can be obtained, with a further effect of easier interconnection between the modules  11  and  12 .  
     [0046] [Second Embodiment] 
     [0047] The characteristic feature of the second embodiment is that a long-distance interconnection line is formed and arranged between a ground line and a short-distance interconnection line. The parts of the structure of the second embodiment which are different from those of the first embodiment will now be described in detail.  
     [0048]FIG. 3 is a diagram showing a cross section of a semiconductor device according to the second embodiment of the present invention. As can be seen in FIG. 3, the feature different from that of the first embodiment is that a long-distance interconnection line  13   a  a is situated between a ground line  14  and a short-distance interconnection line  13   b . In other words, the ground line  14  is located on the other side of the short-distance interconnection line  13   b  with regard to the long-distance interconnection line  13   a  which makes a pair together with the ground line  14 .  
     [0049] With the second embodiment, it is possible to obtain the same effect as that of the first embodiment.  
     [0050] Further, as mentioned above, the ground line  14  in the first module  11  is located on the other side of the short-distance interconnection line  13   b  with regard to the long-distance interconnection line  13   a  which makes a pair together with the ground line  14 . With this structure, there is no ground line  14  present between the modules  11  and  12  in order to transmit signals from the second module  12  to the first module  11 . Therefore, the short-distance interconnection line  13   b  can be connected directly to the long-distance interconnection line  13   a  via the pads  11   a  and  12   a , thereby making it possible to increase the speed of signal transmission between the modules  11  and  12 .  
     [0051] [Third Embodiment] 
     [0052] The characteristic feature of the third embodiment is that an insulating film is provided between the first and second modules, and pads in the modules are capacity-coupled via the insulating film. The parts of the structure of the second embodiment which are different from those of the first embodiment will now be described in detail.  
     [0053]FIG. 4 is a diagram showing a cross section of a semiconductor device according to the third embodiment of the present invention. As can be seen in FIG. 4, the feature different from that of the first embodiment is that an insulating film  16  is provided between the first and second modules  11  and  12 , and pads  11   a  and  12   a  within these modules  11  and  12  are capacity-coupled via the insulating film  16 .  
     [0054]FIG. 5 is a partially enlarged view of the semiconductor device according to the third embodiment shown in FIG. 4. FIG. 6 is a circuit diagram of the semiconductor device shown in FIG. 5. As can be seen in FIGS. 5 and 6, with the insulating film  16  provided between the first and second modules  11  and  12 , a capacitor  20  consisting of the pads  11   a  and  12   a  and the insulating film  16  is formed. Thus, a signal is transmitted, for example, from a to b by the capacity coupling between the pads  11   a  and  12   a  via the insulating film  16 . In this manner, with use of a serial capacitor  20 , interconnection lines  13   a  and  13   b  in the modules  11  and  12  are connected together, and thus signals are transmitted between the modules  11  and  12 .  
     [0055]FIG. 7 is a diagram showing a relationship of the maximum thickness of the insulating film with regard to the frequency and electrode area. In the case where the thickness of the insulating film  16  is represented by d, the frequency employed is represented by f, the area of the electrode (pad  11   a  or  12   a ) is represented by S, and the resistance of the insulating film  16  is represented by R, the following equation (3) is obtained.  
     d=2πfεSR  (3)  
     [0056] From this equation (3), the maximum thickness d max  of the insulating film  16 , with which signals can be transmitted, can be calculated for variables such as the frequency f employed and the area S of the electrode. As can be understood from this equation, when the thickness of the insulating film  16  is set no more than the maximum thickness d max  indicated in FIG. 7, signals can be transmitted at high efficiency.  
     [0057] With the third embodiment described above, it is possible to obtain an effect similar to that of the first embodiment.  
     [0058] Further, with the insulating film  16  provided between the first and second modules  11  and  12 , a capacitor  20  is formed. The signal transmission between the modules  11  and  12  can be carried out with use of the capacitor  20 , and therefore it is no longer necessary to provide a conductive connector element. As a result, the processing step for forming a connection element can be deleted.  
     [0059] It should be further noted that the structure of the second embodiment may be applied to the third embodiment. In this case, a similar effect to that of the second embodiment can be obtained.  
     [0060] [Fourth Embodiment] 
     [0061] The characteristic feature of the fourth embodiment is that a ground pad is formed at the same time and at the same surface level as those of the ground line.  
     [0062] The fourth embodiment which will now be discussed is achieved by applying the above-described structure to the third embodiment, however it is not limited to such a structure. Only the different structural parts from those of the second or third embodiment will be discussed here in details.  
     [0063]FIG. 8 is a cross sectional diagram of a semiconductor embodiment according to the fourth embodiment of the present invention. As can be seen in FIG. 8, a ground line  14  in the first module  11  is provided in a region on an opposite side of the short-distance interconnection line  13   b  with respect to the long-distance interconnection line  13   a  which makes a pair with the ground line  14 . The different structural aspect from that of the third embodiment is that a ground pad  17  is formed at the same surface level as that of the ground line  14  and at the same time as the formation of the ground line  14 . With this structure, a part of the ground line  14  functions as the ground pad  17 .  
     [0064] Further, a pad electrode  18  connected to some other element (not shown) may be formed at a region in the same level as that of the ground line  14 . Alternatively, a pad window  19   a  is formed above the ground pad  17  and the pad electrode  19 , and further a signal retrieval window  19   b  for retrieving signals is formed independently from the pad window  19   a.    
     [0065] With the fourth embodiment described above, it is possible to obtain an effect similar to that of the second or third embodiment.  
     [0066] Further, the ground line  14  in the first module  11  is provided in a region on an opposite side of the short-distance interconnection line  13   b  with respect to the long-distance interconnection line  13   a  which makes a pair with the ground line  14 . With this structure, the ground pad  17  and the pad electrode  18  which must be provided on an outer side to the integrated modules  11  and  12  can be formed in a region at the same level as that of the ground line  14  and at the same time as the formation thereof. Therefore, the number of steps for forming the ground pad  17  and the pad electrode  18  can be reduced, and therefore the ground pad  17  and the pad electrode  18  can be easily formed.  
     [0067] Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.