Abstract:
A method for fabricating an electrically programmable fuse structure is provided. The method includes providing a substrate. The method also includes forming an anode and a cathode on the substrate. Further, the method includes forming a fuse between the anode and the cathode and having an anode-connecting-end connecting with the anode and a cathode-connecting-end connecting with the cathode over the substrate. Further, the method also includes forming a compressive stress region in the cathode-connecting-end, wherein the anode-connecting-end has a tensile stress region.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of Chinese patent application No. 201510006081.0, filed on Jan. 6, 2015, the entirety of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention generally relates to the field of semiconductor manufacturing and, more particularly, relates to electrically programmable fuse structures and fabrication processes thereof. 
     BACKGROUND 
     In the field of integrated circuits (ICs), a fuse is referred to a fusible interconnect wire formed in an IC. Primarily, a fuse is used to connect redundant circuits in an IC. When a defect is found in the IC by a testing process, the fuse is used to repair, or substitute the circuit having the defect. Fuses usually include laser fuses and electrically programmable fuses (Efuses). With the continuous development of the semiconductor technology, Efuses have gradually substituted the laser fuses. 
     Usually, an Efuse structure is made of metal or silicon. A typical Efuse structure includes an anode, a cathode, and a fuse connecting both the anode and the cathode between the anode and the cathode. When the fuse does not blow out, the Efuse structure is at a low-resistance state. When a relatively large current is passing through the fuse from the anode to the cathode, the electro-migration is often accompanied by a mass transportation. Thus, some local regions of the fuse can have a mass accumulation or whiskers; and other local regions of the fuse can have voids. The voids can cause the fuse to blow out. When the fuse blows out, the Efuse structure is at a high-resistance state. The Efuse structure has the characteristic of being transferred from a low-resistance state to a high-resistance state by an electrically current. Such a characteristic is referred as a programmable effect. Thus, the Efuse structure is a programmable fuse. Besides being widely used in the redundant circuits, the Efuse structures also have more applications, such as one time program (OTP) circuits, etc. 
     However, the programming power consumption of the existing Efuse structure is relatively large; and the programming time is relatively long. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     One aspect of the present disclosure includes providing a method for fabricating an electrically programmable fuse structure. The method includes providing a substrate. The method also includes forming an anode and a cathode on the substrate. Further, the method includes forming a fuse between the anode and the cathode and having an anode-connecting-end connecting with the anode and a cathode-connecting-end connecting with the cathode over the substrate. Further, the method also includes forming a compressive stress region in the cathode-connecting-end, wherein the anode-connecting-end has a tensile stress region. 
     Another aspect of the present disclosure includes providing an electrically programmable fuse structure. The electrically programmable fuse structure includes a substrate having a surface. The electrically programmable fuse structure also includes an anode formed on the surface of the substrate. Further, the electrically programmable fuse structure includes a cathode formed on the surface of substrate. Further, the electrically programmable fuse structure also includes a fuse formed on the surface of the substrate and having an anode-connecting-end having a tensile stress and connecting with the anode, and a cathode-connecting-end having a compressive stress and connecting with the cathode. 
     Other aspects of the present disclosure can be understood by those skilled in the art in light of the description, the claims, and the drawings of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an existing electrically programmable fuse in operation; 
         FIGS. 2-6  illustrate structures corresponding to certain stages of an exemplary fabrication process of an electrically programmable fuse structure consistent with the disclosed embodiments; 
         FIG. 7  illustrates a relationship between a doping dose and a stress in a polysilicon layer consistent with the disclosed embodiments; 
         FIG. 8  illustrates another exemplary electrically programmable fuse structure consistent with the disclosed embodiments; and 
         FIG. 9  illustrates an exemplary fabrication process of an electrically programmable fuse consistent with the disclosed embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments of the invention, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       FIG. 1  illustrates an existing programmable fuse that is in operation. As shown in  FIG. 1 , during the blowing out of a fuse  6 , electrons  2  may migrate from a cathode A to an anode B. The electrons  2  may also push the atoms  1  to migrate along the same direction. Thus, vacancies (not labeled) may be formed in the cathode B; and the vacancies may accumulate at the cathode B to form a void  3 . When the vacancies accumulate to a certain degree, that is, the size of the void  3  increases to a certain value, the fuse  6  may blow out. 
     However, during the migration of the electrons  2 , a counter force  5 , which may prevent the migration of the electrons  2 , may be generated in the anode A. The counter force  5  may be a mechanical force. The electromigration may be described by the following equation. 
     
       
         
           
             
               J 
               a 
             
             = 
             
               
                 
                   DC 
                   a 
                 
                 
                   
                     k 
                     B 
                   
                   ⁢ 
                   T 
                 
               
               ⁢ 
               
                 ( 
                 
                   
                     
                       Z 
                       * 
                     
                     · 
                     e 
                     · 
                     ρ 
                     · 
                     j 
                   
                   - 
                   
                     Ω 
                     ⁢ 
                     
                       
                         ∂ 
                         σ 
                       
                       
                         ∂ 
                         x 
                       
                     
                   
                 
                 ) 
               
             
           
         
       
     
     J a  refers to a current density. D refers to the effective diffusion constant of the conductive material. C a  refers to the concentration of the electrons. k B  refers to the Boltzmann constant. Ω refers to the volume of the atom. 
               ∂   σ       ∂   x           
refers to a pressure gradient.
 
             Ω   ⁢       ∂   σ       ∂   x             
refers to the counter force. Other parameters may all be constants. Thus, according to such an equation, the counter force  5  is proportional to the concentration of the electrons  2 .
 
     The counter force  5  may hinder the electro-migration, or even counteract the electro-migration. Thus, it may affect the blowing out of the fuse  6 . For example, the power consumption for the fuse  6  to blow out may be increased. Accordingly, an improved fuse structure is provided. 
       FIG. 9  illustrates an exemplary fabrication process of an electrically programmable fuse structure consistent with the disclosed embodiments.  FIGS. 2-6  illustrates structures corresponding to certain stages of the exemplary fabrication process. 
     As shown in  FIG. 9 , at the beginning of the fabrication process, a substrate with certain structure is provided; and an anode and a cathode may be formed (S 101 ).  FIGS. 2-3  illustrate a corresponding structure.  FIG. 3  is a cross-sectional view of the structure illustrated in  FIG. 2  along the A-A′ direction. 
     As shown in  FIG. 2 , a substrate  33  is provided. The substrate  33  may be a material layer of an IC structure, or other appropriate structures. The material layer of the IC structure may be an insulation material layer. In certain other embodiments, an insulation layer may be formed on the substrate  33  to insulate the substrate  33  and the subsequently formed anode, cathode, and fuse. 
     Further, an anode  200  and a cathode  100  may be formed on a surface of the substrate  33 . Further, a fuse  70  may also be formed on the substrate  33  between the anode  200  and cathode  100 . The fuse  70  may also be referred as an Efuse link. 
     One end of the fuse  70  may connect with the anode  200  and the other end of the fuse  70  may connect with the cathode  100 . The portion of the fuse  70  connecting with the anode  200  may be referred as an anode-connecting-end  72 , and the portion of the fuse  70  connecting with the cathode  100  may be referred as a cathode-connecting-end  71 . 
     In one embodiment, the anode  200 , the cathode  100 , and the fuse  70  may be formed from a same material layer simultaneously. In certain other embodiments, the anode  200 , the cathode  100 , and the fuse  70  may be formed by separated steps, and may be formed from different layers. 
     Referring to  FIG. 2 , the anode  200  and the cathode  300  may all be tapered. That is, the size of a portion of the anode  200  and the size of a portion of the cathode  100  are gradually reduced along a direction close to the fuse  70 . Such a geometry may facilitate the blowing out of the fuse  70 . 
     In certain other embodiments, the anode  200  and the cathode  100  may have other appropriate shapes. For example, the anode  200  and the cathode  100  may be rectangular. 
     Referring to  FIG. 3 , in one embodiment, a process for forming the anode  200 , the cathode  100  and the fuse  70  may include forming a first material layer  74  on the substrate  33 ; and forming a second material layer  73  on the first layer  74 . The first material layer  74  may be made of any appropriate material. In one embodiment, the first material layer  74  is a polysilicon layer. The second material layer  73  may be made of any appropriate material. In one embodiment, the second layer  73  is a metal silicide layer. That is, the anode  200 , the cathode  100  and the fuse  70  may be double-layer structures. When the fuse  70  blows out, both the metal silicide layer  73  and the polysilicon layer  74  may blow out. 
     Conductive vias may be subsequently formed to electrically connect with the anode  200  and the cathode  100 . The conductive vias may electrically connect with the polysilicon layer  74  through the metal silicide layer  73 . The metal silicide layer  73  may reduce the contact resistance between the subsequently formed conducive vias and the polysilicon layer  74 . Further, in one embodiment, the metal silicide layer  73  may be used to subsequently forming a compressive stress layer and a tensile stress layer. 
     In certain other embodiments, the metal silicide layer  73  may be omitted. That is, the fuse  70  may be a single-layer structure made of polysilicon. A compressive stress layer and a tensile stress layer may be subsequently formed in the polysilicon layer; and the subsequently formed conductive vias may directly connect with polysilicon layer. 
     In one embodiment, the polysilicon layer  74  and the metal silicide layer  73  may be formed using a shadow mask. The shadow mask may define the shape of the electrically programmable fuse structure. 
     In certain other embodiments, after forming the first material layer  74  and the second material layer  73 , an etching process may be performed to define the shape of the electrically programmable fuse structure. The first material layer  74  and the second material layer  73  may be formed by any appropriate process, such as a chemical vapor deposition (CVD) process, a physical vapor deposition (PVD) process, an atomic layer deposition (ALD) process, or a flowable CVD (FCVD) process, etc. 
     Returning to  FIG. 9 , after forming the anode  200 , the cathode  100 , and the fuse  70 , a compressive stress region may be formed (S 102 ).  FIGS. 4 ˜ 5  illustrate a corresponding structure.  FIG. 5  is a three dimensional view of the structure illustrated in  FIG. 4 . 
     As shown  FIG. 4 , a tensile stress region (doted region, not labeled) is formed in the cathode-connecting-end  71  of the fuse  70 . The tensile stress region may cover one-half of the substrate  33  having the cathode  100 . 
     In one embodiment, as shown in  FIG. 5 , the tensile stress region are formed in the metal silicide layer  73 . The metal silicide layer  73  may contact with the polysilicon layer  74 . Thus, the tensile stress may transfer to the corresponding region in the polysilicon layer  74 . 
     Further, the anode-connecting-end  72  may have a tensile stress. In one embodiment, the tensile stress in the anode-connecting-end  72  may be from the fabrication process of the fuse, i.e., an intrinsic tensile stress. In certain other embodiments, a tensile stress region may be formed in the anode-connecting-end  72  to cause the anode-connecting-end to have a tensile stress. 
     The compressive stress and the tensile stress may aid the blowing out of the fuse  70 . Referring to  FIG. 5 , during the blowing out of the fuse  70 , electrons  15  may migrate from the cathode  100  to the anode  200 . During such electro-migration, the atoms  17  of the material of the fuse  70  may be pushed to the anode  200 . Thus, vacancies (not labeled) may be formed. When the vacancies are accumulated to a certain degree, voids  11  may be formed. When the size of the voids  11  increase to a certain scale, the fuse  70  may blow out. During the electro-migration process, the atoms  17  of the material of the fuse  70  may gradually accumulate at the anode  200 , a counter force, i.e., the mechanical force  12  may resist the electro-migration process. The tensile stress in the anode-connecting-end  71  may counteract a portion of the mechanical force  12 . Thus, it may make the electro-migration easier than without a tensile stress. Accordingly, the fuse  70  may be relatively easy to blow out under a same power consumption. That is, the power consumption for the fuse  70  to blow out may be reduced. 
     Further, the compressive stress in the cathode-connecting-end  71  of the fuse  70  may also aid the blowing out of the fuse  70 . The compressive stress in the cathode-connecting-end  71  may make the migration of the atoms  17  of the cathode-connecting-end to be harder than without the compressive stress. However, in the portion of the cathode-connecting-end  71  close to the anode-connecting-end  72 , the compressive stress may be counteracted partially by the tensile stress in the anode-connecting-end  72 . Thus, the compressive stress in the portion of the cathode-connecting-end  71  close to the anode-connecting-end  72  may be reduced. Therefore, it may be easier for the portion of the fuse  70  in the cathode  100  closer to the anode  200  to have an electro-migration. That is, the electro-migration may occur at the interface region between the cathode-connecting-end  71  and the anode-connecting-end  72 , i.e., the middle of the fuse  70 . The possibility for generating voids  11  at the interface region may be increased; and it may be easier for the fuse  70  to blow out at the interface region between the cathode-connecting-end  71  and the anode-connecting-end  72 . 
     Further, referring to  FIG. 5 , the atoms  17  may migrate from the portion of the cathode-connecting-end  71  in the middle of the fuse  70 , comparing with the existing techniques in which the atoms may need to migrate from an anode to a cathode, the migration path of the atoms  17  may be reduced. That is, the time for the fuse  70  to blow out may be significantly reduced. Thus, it may aid the blowing out of the fuse  70 ; and the programming time of the electrically programmable fuse structure may be reduced. 
     The compressive stress region may be formed in the cathode-connecting-end  71  by any appropriate process. In one embodiment, the compressive region may be formed by performing an ion implantation process on the cathode-connecting-end  71  of the fuse  70 . Various ions may be used for the ion implantation process, such as tin ions, lead ions, arsenic ions, phosphorous ions, antimony ions, bismuth ions, sulfur ions, selenium ions, tellurium ions, polonium ions, bromide ions, or iodine ions, etc. 
     The tensile stress region may be formed in the anode-connecting-end  72  by any appropriate process. In one embodiment, the tensile stress region may be formed by performing an ion implantation process on the anode-connecting-region  71  of the fuse  70 . Various ions may be used for the ion implantation process, such as phosphorous ions, arsenic ions, or boron ions, etc. 
     In certain other embodiments, the tensile stress in the anode-connecting-end  72  may be the intrinsic stress. Thus, the anode-connecting-end  72  may be unnecessarily doped to have the tensile stress. That is, the anode-connecting-end  72  might not be doped or may be lightly-doped. 
       FIG. 7  illustrates a relationship between the doping dose and the stress in a polysilicon layer. The polyline A refers to a relationship between the doping dose of phosphorous ions and the stress in the polysilicon layer. The polyline B refers to a relationship between the doping dose of arsenic ions and the stress in the polysilicon layer. The ordinate of the graph refers to the stress in the polysilicon layer. When the stress is a positive value, the stress may refer to a tensile stress. When the stress is a negative value, the stress may refer to a compressive stress. The abscissa of the graph refers to the doping dose. 
     As shown in the polyline A of  FIG. 7 , when the doping dose of phosphorous ions are greater than approximately 1.8E16 atom/cm 2 , the stress in the polysilicon layer may be changed from a tensile stress to a compressive stress. As shown in the polyline B of  FIG. 7 , when the doping dose of phosphorous ions are greater than approximately 1E16 atom/cm 2 , the stress in the polysilicon layer may be changed from a tensile stress to a compressive stress. 
     Such relationships may also be applicable to the metal silicide layer  73 . The doping dose may be an illustrative value, in a practical application, the threshold of the doping dose for changing a tensile stress to a compressive stress may also be dependent of other parameters. 
     Further, as shown in  FIG. 7 , in one embodiment, the doping concentration, i.e., corresponding to the doping dose, of the compressive stress region may be greater than the doping concentration of the tensile stress region. Specifically, the tensile stress region on the anode-connecting-end  72  may be undoped, or the doping concentration of the tensile stress region in the anode-connecting-end  71  may be substantially lower than the doping concentration the cathode-connection-end  71 . The tensile stress region may be referred as a lightly doped region. Comparing with the tensile stress region, the compressive stress region may be referred as a heavily doped region. In one embodiment, the doping concentration difference between the compressive stress region and the tensile stress region may be in a range of approximately 1E15 atom/cm 2 ˜1E17 atom/cm 2 . 
     In one embodiment, the tensile stress region and the compressive stress region may be formed, sequentially, by forming a first mask layer exposing the cathode-connecting-end  71  of the fuse  70  on the anode  200 , the cathode  100  and the fuse  70 ; performing the ion implantation process on the cathode-connecting-end  71  using the first mask layer as a mask to form the compressive stress region; removing the first mask layer; forming a second mask layer exposing the anode-connecting-end  72  on the anode  200 , the cathode  100  and the fuse  70 ; and performing the ion implantation process on the anode-connecting-end  72  to form the tensile stress region. Thus, the tensile stress region and the compressive stress region may be formed. 
     The first mask layer and the second mask layer may be photoresist layers, or hard mask layers, etc. The first mask layer and the second mask layer may be formed by any appropriate process, such as a spin-coating process, or a chemical vapor deposition process, etc. 
     In certain other embodiments, the tensile stress region may be formed firstly. After forming the tensile stress region, the compressive stress region may be formed. 
     In certain other embodiments, a metal silicide layer  73  having a tensile stress may be formed directly. One portion of the metal silicide layer  73  having the tensile stress may be used as the anode-connecting-end  72  having the tensile stress; and the other portion may be doped to have a compressive stress; and used as the cathode-connecting-end  71  having the compressive stress. 
     Returning to  FIG. 9 , after forming the compressive stress region and the tensile stress region, conductive vias may be formed (S 103 ).  FIG. 6  also illustrates a corresponding structure. 
     As shown in  FIG. 6 , a plurality of first conductive vias  110  and a plurality of second conductive vias  210  are formed on the cathode  100  and the anode  200 , respectively. The first conductive vias  110  and the second conductive vias  210  may be made of any appropriate material, such as Cu, Al, or W, etc. 
     A process for forming the plurality of first conductive vias  110  and the plurality of second conductive vias  210  may include forming a photoresist layer having a plurality of first openings exposing the cathode  100  and a plurality of second openings exposing the anode  200  over the substrate  33 ; and followed by forming the first conductive vias  110  in the first openings and the second conductive vias  210  in the second openings, respectively. Thus, the first conductive vias  110  may be formed on the cathode  100 ; and the second conductive vias  210  may be formed on the anode  200 . After forming the first conductive vias  110  and the second conductive vias  210 , the photoresist layer may be removed. 
     The conductive vias  110  and the second conductive vias  210  may be formed by any appropriate process, such as a physical vapor deposition process, a sputtering process, or an electroplating process, etc. The photoresist layer may be removed by any appropriate process, such as a dry etching process, a wet etching process, or a plasma ashing process, etc. 
     Thus, an electrically programmable fuse structure may be formed by the above-disclosed processes and methods; and a corresponding electrically programmable fuse structure is illustrated in  FIG. 6 . As shown in  FIG. 6 , the electrically programmable fuse structure may include a substrate  33 . The electrically programmable fuse structure may also include a tapered anode  200  and a tapered cathode  100 . Further, the electrically programmable fuse structure may include a fuse  70  having an anode-connecting-end  72  connecting with the anode  200  and a cathode-connecting-end  71  connecting with the cathode  100 . Further, the electrically programmable fuse structure may also include a tensile stress region in the anode-connecting-end  72  and a compressive stress region in the cathode-connecting-end  71 . The electrically programmable fuse structure may also include a plurality of first conductive vias  110  formed on the cathode  100  and a plurality of second conductive vias  210  formed on the anode  200 . The detailed structures and intermediate structures are described above with respect to the fabrication processes 
       FIG. 8  illustrates another exemplary electrically programmable fuse structure formed by the above-disclosed processes and methods. As shown in  FIG. 8 , the electrically programmable fuse structure may include a substrate  33   b . The electrically programmable fuse structure may also include a rectangular anode  200   b  and a rectangular cathode  100   b . Further, the electrically programmable fuse structure may include a fuse  70   b  having an anode-connecting-end (not labeled) connecting with the anode  200   b  and a cathode-connecting-end (not labeled) connecting with the cathode  100   b.    
     Further, the electrically programmable fuse structure may also include a tensile stress region (not shown) in the anode-connecting-end and a compressive stress region (not labeled) in the cathode-connecting-end. The electrically programmable fuse structure may also include a plurality of first conductive vias (not labeled) formed on the cathode  100   b  and a plurality of second conductive vias (not labeled) formed on the anode  200   b . The detailed structures and intermediate structures are described above with respect to the fabrication processes. 
     Thus, according to the disclosed embodiments, the cathode-connecting-end of the fuse in the electrically programmable fuse structure may be doped to have a compressive stress; and the anode connecting end of the fuse in the fuse structure may have a tensile stress. The tensile stress in the anode may counteract a portion of the counter force, i.e., a mechanical stress. Thus, it may make the electro-migration to be relatively easy; and the power consumption for the fuse to blow out may be reduced. 
     Further, the compressive stress in the cathode-connecting-end may cause the electro-migration to be relatively difficult. The stress at the interface region between the portion of the anode having the tensile stress and the portion of the cathode having the compressive stress may be reduced. Thus, the scale of the electro-migration at the interface region may be increased; and the possibility for forming voids at the interface region may be increased. 
     That is, the compressive stress in the cathode-connecting-end of the fuse in the electrically programmable fuse structure may cause the voids to be formed at the interface region between the portion of the anode having the tensile stress and the portion of the cathode having the compressive stress; and the fuse may blow out at the interface region. Therefore, the migration path of atoms in the fuse may be reduced; the time for the electrically programmable fuse structure to blow out may be significantly reduced. That is, the programming time of the electrically programmable fuse structure may be reduced. 
     Therefore, the compressive stress in the cathode region and the tensile stress in the anode region may aid the blowing out of the fuse. The power consumption for the electrically programmable fuse structure to blow out may be reduced. The time for the fuse to blow out may be significantly reduced; and the programming time of the electrically programmable fuse structure may be reduced. 
     The above detailed descriptions only illustrate certain exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention. Those skilled in the art can understand the specification as whole and technical features in the various embodiments can be combined into other embodiments understandable to those persons of ordinary skill in the art. Any equivalent or modification thereof, without departing from the spirit and principle of the present invention, falls within the true scope of the present invention.