Abstract:
A semiconductor integratd circuit device includes fuse elements formed on an element isolation insulating film, and an insulating film, an interlayer insulating film and a silicon nitride film successively formed over the fuse elements. An opening region extends through the silicon nitride film into the interlayer insulating film above the fuse elements, and openings formed in the interlayer insulating film are positioned on both sides of middle portions of the fuse elements. The openings facilitate blowing off of the insulating film during laser cutting of the fuse elements, reducing physical damage to the element isolation insulating film under the fuse elements.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor integrated circuit device including a fuse element. 
     2. Description of the Related Art 
     In a semiconductor integrated circuit device manufacturing process there is a method of setting elements for circuit configuration by cutting a fuse element formed of polysilicon, metal, and the like by using, for example, a laser after a wafer manufacturing process is finished. With the use of this method, a resistance value can be corrected to obtain desired characteristics after electrical characteristics of the semiconductor device are measured. The method is thus effective particularly for a semiconductor device that places emphasis on its analog characteristics. 
     A conventional semiconductor integrated circuit device is illustrated in  FIG. 5  and  FIG. 6 .  FIG. 5  is a plan view of fuse elements  103 , and  FIG. 6  is a sectional view taken along the line A-A? of  FIG. 5 . As illustrated in  FIG. 6 , the fuse elements  103  are formed on an element isolation insulating film  102 , and are formed of a polycrystalline Si film doped with impurities, which is the same conductive material as that of a gate electrode (not shown) of a MOS transistor. 
     Further, an opening region  108  that is used for cutting middle portions of the fuse elements  103  with a laser is formed above the fuse elements  103 . The opening region  108  is hitherto formed by selectively etching an interlayer insulating film  105  formed for the purpose of metal lamination and a silicon nitride film  106  formed for the purpose of protecting an internal element from moisture coming in from the outside respectively using a mask. At that time, the insulating film on the fuse element  103  should be adjusted to have a thickness in a certain range, taking into consideration variations that occur in a process such as deposition or etching of the insulating film and variations in laser intensity during cutting of the fuse elements  103 . The reason is that, if a fuse element  103  is exposed, the fuse element  103  expands under the influence of the moisture and a crack may develop along an interface between the exposed fuse element  103  and a fuse element  103  covered with the insulating film, which may adversely affect the internal element. Meanwhile, when the fuse element  103  is cut with a laser, it is necessary to blow off the insulating film simultaneously with the fuse element  103 . At this time, if the insulating film on the fuse element  103  is too thick, the insulating film on the fuse element  103  is not blown off so easily, and thermal energy for the blowing off is transferred to the element isolation insulating film  102  under the fuse element  103  to physically damage the element isolation insulating film  102 , which results in generation of a crack. If a residue of the scattered fuse element  103  enters the crack, the residue and a silicon substrate  101  may be electrically connected to each other, leading to abnormal electrical characteristics. 
     In order to deal with the problem described above, various devices for alleviating damage to a base film have been made that includes measurement and strict control of a film thickness of a fuse opening, increasing the thickness of the insulating film under the fuse element  103  with respect to other element isolating film thicknesses, and laying a damage block material on the base film (for example, Japanese Patent Application Laid-open No. 2010-056557). 
     However, when the thickness of the insulating film  102  under the fuse element  103  is increased with respect to other element isolating film thicknesses or a material for blocking damage is laid on the base film, there is apprehension that the level difference between the silicon substrate  101  and the element isolation insulating film  102  may be increased. Therefore, the aspect ratio of a contact of an element formed on the silicon substrate  101  becomes very high, and there is a possibility that the contact is not formed or electrical connection is made that exhibits an unusually high contact resistance value. Meanwhile, even if the contact of the element formed on the silicon substrate  101  is electrically connected, a contact to the fuse element  103  may pierce the film of the fuse element  103  to cause a quality abnormality. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a semiconductor integrated circuit device that enables stable cutting of a fuse without the apprehension described above and without causing abnormal quality when the fuse is cut. 
     In order to solve the above-mentioned problem, the following means is taken in one embodiment of the present invention. 
     First, provided is a semiconductor integrated circuit device, including: 
     a semiconductor substrate; 
     an element isolation insulating film formed on a surface of the semiconductor substrate; 
     a plurality of fuse elements, each of which is formed of first polycrystalline silicon, and are arranged on the element isolation insulating film at intervals; 
     an insulating film formed on the plurality of fuse elements; 
     an interlayer insulating film formed on the insulating film; 
     a silicon nitride film formed on the interlayer insulating film; 
     an opening region formed above the plurality of fuse elements, the opening region being formed by removing part of the silicon nitride film and part of the interlayer insulating film; and 
     concaves formed by removing a remaining portion of the interlayer insulating film under the opening region, the concaves being formed in the vicinity of both sides of each of fuse middle portions of the plurality of fuse elements at regular intervals. 
     Further, in the semiconductor integrated circuit device, the concaves formed in the vicinity of both sides of each of the fuse middle portions of the plurality of fuse elements at regular intervals have slit-like shapes. 
     Further, in the semiconductor integrated circuit device, the concaves formed in the vicinity of both sides of each of the fuse middle portions of the plurality of fuse elements at regular intervals have small square shapes. 
     Further, in the semiconductor integrated circuit device, the number of the concaves formed in the vicinity of both sides of each of the fuse middle portions of the plurality of fuse elements at regular intervals is one between adjacent fuse elements. 
     According to the present invention, even when the thickness of the insulating film on the fuse elements is set to be large, the slit-like concaves are formed in the vicinity of both sides of each of the fuse middle portions of the fuse elements at regular intervals, and thus, the insulating film can be blown off more easily when cut with a laser. As a result, physical damage to the element isolation insulating film under the fuse elements can be reduced to prevent electrical connection with the semiconductor substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic plan view of a semiconductor integrated circuit device according to a first embodiment of the present invention. 
         FIG. 2  is a schematic sectional view of the semiconductor integrated circuit device taken along the line A-A′ of  FIG. 1 . 
         FIG. 3  is a schematic plan view of a semiconductor integrated circuit device according to a second embodiment of the present invention. 
         FIG. 4  is a schematic plan view of a semiconductor integrated circuit device according to a third embodiment of the present invention. 
         FIG. 5  is a schematic plan view of a related-art semiconductor integrated circuit device. 
         FIG. 6  is a schematic sectional view of the related-art semiconductor integrated circuit device taken along the line A-A′ of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention are described below with reference to the attached drawings. 
       FIG. 1  is a schematic plan view of a semiconductor integrated circuit device according to a first embodiment of the present invention.  FIG. 2  is a schematic sectional view of the semiconductor integrated circuit device according to the first embodiment of the present invention taken along the line A-A? of  FIG. 1 . First, a structure of a fuse region in plan view is described with reference to  FIG. 1 . A plurality of fuse elements  103  are arranged in spaced-apart side-by-side relationship on a surface of an element isolation insulating film formed on a silicon semiconductor substrate. A fuse middle portion of the fuse element  103  is thinner than both end portions thereof so as to be easily cut with a laser. Slit-like openings such as concaves  201  are formed in the vicinity of both sides of each of fuse middle portions of the fuse elements  103  at regular intervals. Further, an opening region  108  in which a polyimide  107 , a silicon nitride film  106  serving as a protective film, and an interlayer insulating film  105  are etched partway for the purpose of cutting with a laser is formed above the middle portions of the plurality of fuse elements  103  as shown in  FIG. 2 . Therefore, the concaves  201  are formed so as to be exposed at the bottom of the fuse opening region  108 . The present invention has a feature in that the slit-like concaves  201  are formed so as to be adjacent to the fuse elements  103 , respectively, in the interlayer insulating film  105  above the fuse element  103 . In this embodiment, the slit-like concaves  201  are rectangular in plan view. 
       FIG. 2  is a schematic sectional view of the semiconductor device taken along the line A-A′ of  FIG. 1 . The element isolation insulating film  102  at a thickness of from 4,000 Å to 7,000 Å, for example, is formed on the silicon semiconductor substrate  101 . The fuse elements  103  on the element isolation insulating film  102  are formed of a polycrystalline Si film doped with impurities that is the same layer and the same conductive material as those of a gate electrode (not shown) of a MOS transistor. The fuse elements  103  have a thickness of from about 2,000 Å to about 4,000 Å. An insulating film  104  for insulating an element formed on the silicon substrate  101  and metal wiring from each other, for example, a BPSG film is formed on the fuse elements  103 , and the metal wiring and the interlayer insulating film  105  for the purpose of metal wiring lamination are formed on the insulating film  104 . Further, the silicon nitride film  106  is laminated for the purpose of protecting an internal element from moisture coming in from the outside. Finally, the polyimide  107  for alleviating stress on a package is laminated, and after that, the opening region  108  is formed in the polyimide  107 . Then, part of the silicon nitride film  106  and part of the interlayer insulating film  105  are etched subsequently with the remaining polyimide  107  itself being used as a mask, thereby forming the opening region  108 . Then, another mask is used for patterning and the rest of the interlayer insulating film  105  is etched to form the slit-like concaves  201 : At this time, etching selectivity between the interlayer insulating film  105  and the insulating film  104  thereunder is small, and thus, it is difficult to stop the etching at an interface therebetween. The insulating film  104  may be etched to some extent. 
     With such a structure, the slit-like concaves  201  are on both sides of each of the fuse elements  103 , and adjacent concaves  201  of adjacent fuse elements  103  are spaced apart and separated from one another. Thus the interlayer insulating film  105  is separated along the fuse elements  103 , which facilitates blowoff of the interlayer insulating film  105  when laser light is radiated even when the interlayer insulating film  105  above the fuse elements  103  is thick. Therefore, even when the interlayer insulating film  105  above the fuse elements  103  is thick, it is not necessary to increase the output of the laser, and physical damage to the element isolation insulating film  102  under the fuse elements  103  can be reduced. In this embodiment, the concaves are rectangular in plan view, but it goes without saying that the concaves may be polygonal or oval. 
       FIG. 3  is a schematic plan view of a semiconductor integrated circuit device according to a second embodiment of the present invention. While the concaves (openings)  201  are rectangular slits in the first embodiment, in the second embodiment, the concaves (openings)  201  are a plurality of small square concaves  201 . A plurality of square concaves  201  are on both sides of a fuse element  301 , and thus, the interlayer insulating film  105  is partly separated along the fuse elements  103 , which facilitates blowoff of the interlayer insulating film  105  when laser light is radiated. Note that, the small concaves may be rectangular or circular. 
       FIG. 4  is a schematic plan view of a semiconductor integrated circuit device according to a third embodiment of the present invention. While two lines of concaves  201  are formed between adjacent fuse elements  103  in  FIG. 1  and in  FIG. 3 , as illustrated in  FIG. 4 , one line of concave (openings)  201  may be formed between adjacent fuse elements  103 . In this case, the concaves  201  can have an increased width (width in a direction of intervals of adjacent fuse elements  103 ), which is advantageous in that fuse cutting is further facilitated and in that the possibility is further reduced that the interlayer insulating film  105  damages the element isolation insulating film  102  under the adjacent fuse elements  103  when blown off by radiated laser light. 
     In the above description, part of the polyimide  107 , part of the silicon nitride film  106 , and part of the interlayer insulating film  105  are etched in succession using the first mask to form the opening region  108 , and then, the rest of the interlayer insulating film  105  is etched using the second mask to form the concaves  201 . Alternatively, the polyimide  107  and the silicon nitride film  106  may be etched in succession using the first mask to form the opening region  108 , and then, the interlayer insulating film  105  may be etched using the second mask to form the concaves  201 . Forming of the concaves  201  as in the present invention facilitates blowoff of the interlayer insulating film  105 , and thus, such a process can be set. Further, there is a case in which the polyimide  107  is not used, but it goes without saying that the present invention can be completely similarly applied to such a case. 
     As described above, even when the thickness of the insulating film  104  on the fuse elements  103  is set to be large, the concaves  201  are formed in the interlayer insulating film  105  in the vicinity of both sides of each of the fuse middle portions of the fuse elements  103  at regular intervals, and thus, the insulating film can be blown off more easily when cut with a laser. As a result, physical damage to the element isolation insulating film  102  under the fuse elements  103  can be reduced to prevent electrical connection with the silicon substrate  101 .