Abstract:
Provided is a semiconductor device which prevents deterioration of the long-term reliability caused by entry of moisture owing to a fuse opening in a multilayer wiring process. In order to prevent entry of moisture through the fuse opening, interlayer insulating films which are oxide films are etched so as to leave a part of a plasma TEOS oxide film layer. After that, a passivation nitride film is deposited and patterned, and then, the passivation nitride film is partly removed, thereby obtaining a structure in which side walls and a side bottom surface of the interlayer insulating films in the fuse opening are covered with the passivation nitride film. This enables inhibition of entry of moisture through an interface among the stacked interlayer insulating films and through an SOG layer, and deterioration of the IC characteristics owing to moisture can be prevented.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a semiconductor device including a CMOS transistor, a resistor, and a fuse for laser trimming. 
         [0003]    2. Description of the Related Art 
         [0004]    In a highly accurate analog IC used for a voltage detector or the like, in order to obtain desired characteristics by combining a transistor and a resistor, a measure is generally taken that, by blowing out a fuse for laser trimming formed of, for example, a polycrystalline silicon thin film by laser radiation, the combination pattern of resistors is adjusted to adjust variations in characteristics due to variations in manufacture in the pre-process which is a process of processing a semiconductor wafer or to adjust the target value. 
         [0005]    Such a fuse for laser trimming in an analog IC is described with reference to  FIG. 4  to  FIG. 6 .  FIG. 4  is a plan view,  FIG. 5  is a schematic sectional view taken along the line C-C, and  FIG. 6  is a schematic sectional view taken along the line D-D. A fuse  206  formed of a polycrystalline silicon thin-film resistor is provided on a field insulating film  203  formed on a surface of a P-type semiconductor substrate  201 . A nitride film  220  and an oxide film  219  as protective films and interlayer insulating films  216  and  214  among multilayer wirings are partly etched from the surface thereof to form a fuse opening  222  so that a laser can be radiated to the fuse  206 . In the fuse opening  222 , side walls of the nitride film, the interlayer insulating films, and the like are exposed. In a multilayer wiring process which is a double or more metal process, as a technology for planarization, for example, a technology is used in which, after coating an SOG layer formed of spin-on-glass (SOG), etching back is performed. SOG has excellent characteristics as a material used for etching back, but, generally, has the feature of being high in hygroscopicity. Because of that, when, after the etching back, an SOG layer  217  between the stacked interlayer insulating films remains, moisture enters through the SOG layer, which may cause fluctuations in element characteristics of the IC, resulting in occurrence of a problem related to the long-term reliability. In particular, in a PMOS transistor, it is known that negative bias temperature instability (NBTI) which is caused when a negative gate bias is applied in a high temperature state causes a shift of the threshold voltage of the transistor. 
         [0006]    The fuse opening is further described below. By adjusting the thickness of an interlayer insulating film above the fuse by patterning by photolithography and then etching the fuse opening  222 , prevention of defective trimming such as insufficient cut in the laser trimming is sought. In a related-art structure, after the passivation nitride film  220  as the final protective film is deposited, the passivation nitride film  220  in the fuse opening  222  and a pad portion (not shown) is partly removed, and then, etching is performed again so that the interlayer insulating film above the fuse has a predetermined thickness. 
         [0007]    Note that, guard rings  221  formed of first and second metal wirings for preventing entry of moisture are provided between the fuse opening  222  and an IC chip. The guard rings  221  are provided, and the SOG layer  217  used as an interlayer insulating film is cut so as to be prevented from reaching the inside of the chip as illustrated in  FIG. 5 . 
         [0008]    However, an oxide film as an insulating film is exposed at the side walls of the interlayer insulating films in the fuse opening. In the insulating film layer in which etching back of the SOG is performed, the SOG layer is exposed. It follows that entry of moisture occurs, which may result in not only NBTI but also corrosion of metal wiring or the like, leading to deterioration of characteristics of the IC. 
         [0009]    For example, Japanese Published Patent Application Hei 05-63091 and Hei 07-22508 disclose measures for preventing entry of moisture by forming a guard ring using a metal as a barrier from the fuse opening to the inside of the IC, in order to prevent deterioration of the long-term reliability owing to such entry of moisture through the fuse opening. 
         [0010]    In an analog IC, size reduction of each component is indispensable for reducing the chip size. If the distance from the fuse opening is secured for the purpose of inhibiting fluctuations in element characteristics and corrosion of metal wiring owing to entry of moisture through a fuse portion, the chip size is increased to lose competitiveness. 
         [0011]    Further, with regard to a measure of forming a guard ring as a barrier using metal wiring for the purpose of preventing entry of moisture through the SOG, a shift of characteristics caused by NBTI or the like is effectively inhibited, but, because the SOG layer is exposed in the fuse opening, the guard ring of metal wiring may cause corrosion of wiring. 
       SUMMARY OF THE INVENTION 
       [0012]    Accordingly, an object of the present invention is to provide a semiconductor device which can prevent deterioration of the long-term reliability and corrosion of wiring caused by entry of moisture owing to a fuse opening. 
         [0013]    In order to achieve the object, according to the present invention, there is provided a semiconductor device, including:
       a semiconductor substrate;   a field insulating film formed on a surface of the semiconductor substrate;   a resistor and a fuse formed on the field insulating film;   a first interlayer insulating film formed on the fuse;   a second interlayer insulating film formed on the first interlayer insulating film;   a third interlayer insulating film formed on the second interlayer insulating film and including an SOG layer therein;   a passivation oxide film formed on the third interlayer insulating film;   a fuse opening formed above the fuse by removing films from the passivation oxide film to a midpoint in the second interlayer insulating film; and   a passivation nitride film covering the passivation oxide film and a side surface and a side bottom surface of the fuse opening,   in which the passivation nitride film is removed so that the second interlayer insulating film is exposed from the passivation nitride film on a bottom surface of the fuse opening.       
 
         [0024]    Further, in the semiconductor device the fuse includes a first polycrystalline silicon. 
         [0025]    Further, in the semiconductor device the resistor includes a second polycrystalline silicon which is different from the first polycrystalline silicon. 
         [0026]    Further, in the semiconductor device: the first interlayer insulating film includes a BPSG layer and an NSG layer; the second interlayer insulating film includes a plasma TEOS silicon oxide film; and the third interlayer insulating film includes a plasma TEOS silicon oxide film, an SOG, and a plasma TEOS silicon oxide film. 
         [0027]    Further, the semiconductor device further includes a guard ring including a metal wiring material, the guard ring surrounding a periphery of the fuse opening. 
         [0028]    In an IC having multilayer wiring formed therein, a moisture entry path through a side wall of the stacked interlayer insulating films from the fuse opening which may cause deterioration of the long-term reliability can be shut off without fail to prevent deterioration of characteristics of the IC due to NBTI and corrosion of wiring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a schematic plan view of a fuse portion according to a first embodiment of the present invention. 
           [0030]      FIG. 2  is a schematic sectional view taken along the line A-A of a semiconductor device including the fuse portion according to the first embodiment of the present invention. 
           [0031]      FIG. 3  is a schematic sectional view taken along the line B-B of the semiconductor device including the fuse portion according to the first embodiment of the present invention. 
           [0032]      FIG. 4  is a schematic plan view of a related-art fuse portion. 
           [0033]      FIG. 5  is a schematic sectional view taken along the line C-C of a semiconductor device including the related-art fuse portion. 
           [0034]      FIG. 6  is a schematic sectional view taken along the line D-D of the semiconductor device including the related-art fuse portion. 
           [0035]      FIG. 7  is a schematic plan view of a fuse portion according to a second embodiment of the present invention. 
           [0036]      FIG. 8  is a schematic sectional view taken along the line A-A of a semiconductor device including the fuse portion according to the second embodiment of the present invention. 
           [0037]      FIG. 9  is a schematic sectional view taken along the line B-B of the semiconductor device including the fuse portion according to the second embodiment of the present invention. 
           [0038]      FIG. 10  is a schematic plan view of a fuse portion according to a third embodiment of the present invention. 
           [0039]      FIG. 11  is a schematic plan view of a fuse portion according to a modification of the third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    Embodiments of the present invention are described in the following with reference to the attached drawings. 
       First Embodiment 
       [0041]      FIG. 1  is a plan view of a fuse portion of a semiconductor device according to an embodiment of the present invention, and  FIG. 2  and  FIG. 3  are schematic sectional views of the same semiconductor device. 
         [0042]      FIG. 2  is a schematic sectional view of the semiconductor device taken along the line A-A of  FIG. 1 .  FIG. 3  is a schematic sectional view of the semiconductor device taken along the line B-B of  FIG. 1 . An N-type well diffusion layer  102  in a PMOS region and a P-type well diffusion layer (not particularly shown) in an NMOS region are formed on a P-type silicon semiconductor substrate  101 . A field insulating film  103  which is an oxide film formed by LOCOS is formed at a thickness of, for example, about 4,000 Å to 8,000 Å. 
         [0043]    Then, a gate insulating film  104  by thermal oxidation is formed at a thickness of about 100 Å to 400 Å. After ions are implanted so as to obtain a desired threshold voltage, a polycrystalline silicon film to be a gate electrode is deposited by CVD and patterning is performed with a photoresist to form a gate electrode  105  and a fuse  106  to be cut by laser trimming. At this time, phosphorus and boron are diffused in the polycrystalline silicon film to be the gate electrode  105  and the fuse  106  by ion implantation or doped-CVD so that the polarity of the electrode is the N-type or the P-type. After that, a second polycrystalline silicon is deposited, and ion implantation of a low concentration impurity into the second polycrystalline silicon is performed so as to form a resistor. In this case, any one of a P-type resistor and an N-type resistor may be formed. Further, the formation may be performed by doped-CVD. After that, a photolithography process is performed, and then, etching is performed and a pattern is formed to form a high resistance resistor  107 . 
         [0044]    After that, a P-type high concentration impurity region  108  to be a drain and a source of a PMOS transistor and an N-type high concentration impurity region to be a source and a drain of an NMOS transistor (not particularly shown) are formed. Further, in order to cause the resistance of a contact portion of the resistor to be low, at the same time, ions of a P-type or an N-type high concentration impurity are implanted into a low concentration region  109  of the resistor, and high concentration regions  110  are formed at both ends of the resistor. 
         [0045]    Next, a first interlayer insulating film  111  is formed, for example, through deposition by atmospheric pressure CVD at a thickness of 5,000 Å to 20,000 Å. The first interlayer insulating film may have a single layer structure of a BPSG film containing boron and phosphorus, or may have a two layer structure including a non-doped NSG film and a BPSG film. After the first interlayer insulating film is stacked, planarization is performed in a CMP process so that the thickness is as desired, for example, 10,000 Å from the silicon substrate. Note that, CMP is used in the planarization in this case, but the planarization may be performed by reflowing which is conventionally used. 
         [0046]    After that, contact holes  112  are formed. After so-called plug structures in which a high-melting metal such as tungsten is embedded are formed, a first metal wiring  113  is deposited by, for example, sputtering, at a thickness of 3,000 Å to 8,000 Å. In order to prevent a spike in the contact, a barrier metal layer formed of Ti and TiN may be formed before tungsten is embedded. As the metal wiring  113 , Al—Si, Al—Si—Cu, or Al—Cu may be used. Then, the first metal wiring  113  is formed by photolithography and etching. 
         [0047]    Then, in order to form multilayer wiring, a second interlayer insulating film  114  is formed, for example, of a TEOS oxide film by plasma CVD at a thickness of 5,000 Å to 15,000 Å. Similarly to the case of the first interlayer insulating film, planarization is performed in a CMP process so that the interlayer insulating film has a desired thickness of, for example, about 5,000 Å. After that, a contact hole for connection to the first metal wiring is formed. After a plug structure in which a high-melting metal such as tungsten is embedded is formed, a second metal wiring  115  is deposited by, for example, sputtering, at a thickness of 3,000 Å to 8,000 Å. Before the plug structure is formed, a barrier metal layer formed of Ti and TiN may be formed. As the metal wiring  115 , Al—Si, Al—Si—Cu, or Al—Cu may be used. Then, a pattern of the second metal wiring  115  is formed by photolithography and etching. 
         [0048]    After the second metal wiring  115  is formed, a third interlayer insulating film  116  is deposited of a TEOS oxide film by plasma CVD. In this case, for the purpose of planarization, after coating a surface of the third interlayer insulating film with a spin on glass (SOG) layer  117 , etching back is performed, and further, the TEOS oxide film  116  is deposited. Because SOG can perform planarization more easily than a CMP process, there are cases in which SOG is used with regard to an interlayer insulating film on which the uppermost layer metal wiring is deposited in a multilayer wiring process. 
         [0049]    Then, a contact hole is formed in the third interlayer insulating film including the TEOS oxide film formed by plasma CVD and the SOG layer. After a plug structure in which a high-melting metal such as tungsten is embedded is formed, similarly to the first and second metal wirings, a third metal wiring  118  is deposited by, for example, sputtering, at a thickness of 3,000 Å to 30,000 Å. The third metal wiring  118  may be, for example, Al—Si, Al—Si—Cu, or Al—Cu. Then, a pattern of the third metal wiring  118  is formed by photolithography and etching. 
         [0050]    Then, through formation of two-layer passivation film including a passivation oxide film  119  and a passivation nitride film  120  as a final protective film and patterning of the passivation oxide film, the insulating film, and the passivation nitride film, in a pad opening and in a fuse opening  122 , the semiconductor device is manufactured. 
         [0051]    In this case, guard rings  121  formed of the first and second metal wirings are provided in the shape of a rectangle so as to surround a periphery of the fuse opening  122  for the purpose of preventing entry of moisture through the fuse opening  122  to the inside of the IC chip. As illustrated in  FIG. 2 , the guard rings  121  is provided, and the SOG layer  117  used as an interlayer insulating film can be cut so as to be prevented from directly extending to and reach the inside of the IC chip. 
         [0052]    Further, in this embodiment, as illustrated in  FIG. 1 ,  FIG. 2 , and  FIG. 3 , a side wall and a side bottom surface which is a region on the periphery of a bottom surface and at which the bottom surface and the side wall intersect each other of the fuse opening  122 , where the interlayer insulating films are exposed, are covered with the passivation nitride film  120 . The passivation nitride film  120  is removed from the bottom surface of the fuse opening  122  except for the side bottom surface. The passivation nitride film  120  has an opening  123  in a shape different from that of the fuse opening  122  on the bottom surface of the fuse opening  122 . In the fuse opening  122 , the exposed film is only the second interlayer insulating film on the bottom surface except for the side bottom surface. Such a structure enables prevention of entry of moisture through a gap formed due to reduced adhesion at interfaces among the stacked first, second, and third interlayer insulating films. Further, because the SOG layer is similarly covered with the passivation nitride film  120 , entry of moisture through the SOG layer can be inhibited. 
         [0053]    Further, the etching of the fuse opening  122  is performed to stop at a midpoint in the second interlayer insulating film. This is because, if the etching reaches the first interlayer insulating film, the hygroscopic BPSG layer is exposed, and, even if the side wall is covered with the passivation nitride film  120 , moisture can easily enter the inside of the IC chip through the BPSG layer. Further, if the etching of the fuse opening  122  stops in the third interlayer insulating film  116 , the SOG layer  117  is again exposed and can be a moisture entry path. By stopping the etching of the opening in the second interlayer insulating film which is a plasma TEOS layer through which moisture is less liable to enter compared with the cases of other oxide films, defective trimming of the fuse can be inhibited, and at the same time, deterioration of the IC characteristics owing to entry of moisture can be prevented. 
         [0054]    A method of manufacturing the semiconductor device described in this embodiment is now described. Although not illustrated in the figures, after the third metal wiring is formed, first, the passivation oxide film  119  of the two-layer passivation film is deposited by plasma CVD, and then, the fuse opening is etched at a midpoint in the second interlayer insulating film to form the fuse opening  122 . Then, after the passivation nitride film is deposited, by, for the purpose of forming the pad openings and the fuse opening, partly removing the passivation nitride film, the final form of the semiconductor device described in this embodiment is obtained. 
       Second Embodiment 
       [0055]    Next, a modification of the first embodiment described above as a second embodiment of the present invention is described with reference to  FIG. 7  to  FIG. 9 .  FIG. 7  is a plan view illustrating a fuse portion of the modification.  FIG. 8  is a schematic sectional view of the semiconductor device taken along the line A-A of  FIG. 7 .  FIG. 9  is a schematic sectional view of the semiconductor device taken along the line B-B of  FIG. 7 . 
         [0056]    As is apparent from  FIG. 7 , in this modification, the guard rings (denoted by reference numeral  121  in  FIG. 1  to  FIG. 3 ) formed of the first and second metal wirings are not provided so as to surround the periphery of the fuse opening. The second embodiment is similar to the first embodiment with regard to other points. This is because, when it is confirmed that the resistance of the passivation nitride film  120  to the entry of moisture is sufficient, the guard rings formed of the first and second metal wirings as one of the double defensive measures against entry of moisture can be eliminated. Without the guard rings around the periphery of the fuse opening, the SOG layer is not cut and the SOG layer may extend to the inside of the IC chip as illustrated in  FIG. 8  and  FIG. 9 . However, because the passivation nitride film  120  formed in the fuse opening sufficiently prevents entry of moisture, there is no necessity of concerns about the entry of moisture through the SOG layer. 
         [0057]    The structure of the second embodiment has an effect that the length of the entire fuse along the line A-A can be reduced insofar as permitted by the manufacturing process in accordance with the space of the eliminated guard rings. 
       Third Embodiment 
       [0058]    Next, a third embodiment of the present invention is described with reference to  FIG. 10  and  FIG. 11 .  FIG. 10  is a plan view illustrating a fuse portion of the third embodiment, and  FIG. 11  is a plan view of a fuse portion as a modification of the third embodiment. In the third embodiment, the opening  123  in the passivation nitride film  120  which determines the final shape of the fuse opening is shaped so as to be independent from openings of other fuses. The shape of the opening  123  in each fuse is rectangle in  FIG. 10 , and is a circle in  FIG. 11  which illustrates the modification. Because the shape of the opening  123  is determined by the patterning of the passivation nitride film  120 , no additional process is necessary. Because, by providing independent openings in the respective fuses in this way, only the portion of the fuse which is cut in laser trimming is exposed, and peripheries thereof which surround the portion are covered with the passivation nitride film  120 . Accordingly, the effect of contamination due to the residual fuse which is blown out at high temperature is reduced, and further, the effect of expansion due to raised temperature of the peripheries of the fuse which is blown out is reduced. 
         [0059]    In the embodiments described above, three-layer metal wiring processes are described by way of example, but it goes without saying that the present invention is similarly applicable to a multilayer wiring process in which there are four or more layers.