Abstract:
Described is a metal fuse in a semiconductor device that can be readily blown up without compromising device reliability, as well as methods of manufacturing thereof. In one embodiment, a metal fuse structure according to the disclosed principles comprises a semiconductor substrate, and an interconnect layers located on the semiconductor substrate, where the interconnect layer has metal contacts formed through the interconnect layer. In addition, the structure includes a metal fuse formed over the interconnect layer and in electrical contact with the metal contacts. Furthermore, the structure includes a polymeric coating formed over the metal fuse and the interconnect layer, where the polymeric coating is selected to allow radiation to pass therethrough.

Description:
TECHNICAL FIELD  
       [0001]     This disclosure relates in general to semiconductor devices, and more particularly to a metal fuse structure for semiconductor devices and fabrication methods thereof.  
       BACKGROUND  
       [0002]     Metal fuses are used in repairing semiconductor circuits and devices. Often times, the repair process involves breaking, severing, or vaporizing metal fuses with a laser beam. For example, there can be multiple memory and redundant cells within a memory device, and when defective memory cells are detected, metal fuses in redundant cells may be “blown” in order to repair the defective memory cells by isolating functional parts of the circuit(s). Metal fuses in redundant cells may also be opened or blown to re-route circuitry along alternative pathways in the event of a memory cell failure. In addition, it is also common to design and fabricate a generic logic chip having a large number of logic gate interconnects. Subsequently, the chip can be customized to perform the desired circuitry by severing the necessary metal fuses after the final processing steps. For additional information on metal fuses in semiconductor devices, please refer to U.S. Pat. Nos. 6,835,642; 6,753,210; 6,613,612; 6,831,349; and 6,784,516.  
         [0003]     Metal fuses are typically formed within dielectric materials such as silicon oxide, fluorinated silicon oxide, or other low-K dielectric materials, and can be manufactured from aluminum, copper, or gold. Within the dielectric material, an opening or “window” is normally defined in order to facilitate penetration of the high-energy laser beam used to vaporize the underlying metal fuse. As feature sizes become smaller, the thickness of the dielectric material causes difficulty in blowing conventional metal fuse structures using known lithographic and etching techniques. One solution is to increase the energy of the laser beam during the blowing process, but this approach often comes at the expense of micro-cracking and device reliability. Therefore, there exists a need to be able to blow metal fuses without compromising the overall device reliability.  
       SUMMARY  
       [0004]     Described is a metal fuse in a semiconductor device that can be readily blown without compromising device reliability and methods of manufacturing thereof. Integrated circuits are initially formed on a semiconductor substrate, where the integrated circuits can include multiple interconnect layers. Metal fuses are subsequently formed over the interconnect layers. A polymeric layer is then formed over the metal fuses. The polymeric coating allows an external radiation source to penetrate and “blow up” the underlying metal fuses with less energy than typically required by conventional techniques. As a result, when less energy is used, the likelihood of damaging other circuit components decreases, while the likelihood of properly carrying out the blowing process increases.  
         [0005]     In one embodiment, a metal fuse structure according to the disclosed principles comprises a semiconductor substrate and an interconnect layer located above the semiconductor substrate, the interconnect layer having metal contacts formed through the interconnect layer. Additionally, the structure includes a metal fuse formed over the interconnect layer and in electrical contact with the metal contacts. Furthermore, the structure includes a polymeric layer formed over the metal fuse, the polymeric layer being selected to have a high transmittance to allow radiation to pass through, and to protect the metal fuse from moisture penetration.  
         [0006]     In an embodiment of a method of forming a metal fuse in a semiconductor device, the method includes providing a semiconductor substrate, and forming an interconnect layer above the semiconductor substrate. In such an embodiment, the method also includes forming metal contacts through the interconnect layer. Also, the method includes forming a metal fuse over the interconnect layer and in electrical contact with the metal contacts. Furthermore, this embodiment of the method includes forming a polymeric layer over the metal fuse, the polymeric layer allowing radiation to pass therethrough. 
     
    
     BRIEF DESCRIPTION  
       [0007]      FIG. 1  illustrates a conventional metal fuse structure in a semiconductor device;  
         [0008]      FIG. 2  illustrates one embodiment of the presently disclosed metal fuse structure; and  
         [0009]      FIGS. 3A-3C  illustrate the mechanism behind the presently disclosed metal fuse structure embodiment of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0010]     Initial reference is made to  FIG. 1 , which illustrates a conventional metal fuse within a semiconductor device  100 . A plurality of integrated circuit (IC) interconnect layers  104  are formed on a semiconductor substrate  102  utilizing known materials and methods. The semiconductor substrate  102  is preferably silicon, although silicon-on-insulator (SOI) and gallium arsenide (GaAs) substrates may also be utilized. The various interconnect layers  104  include but are not limited to interlevel metal dielectrics, gate electrodes, interlevel dielectrics, isolation regions, active and passive devices, capacitors and other features. The various interconnect layers  104  may also contain metal contacts (not shown) that electrically connected one layer to another.  
         [0011]     An overlying intermetal dielectric (IMD) layer  106  is subsequently formed over the plurality of interconnects  104  using known materials and methods. The IMD layer  106  may include doped or undoped silicon oxide, fluorinated silicon oxide, silicon nitride, silicon oxynitride, low-K dielectric materials, or mixtures thereof. Openings are subsequently defined within the IMD layer  106  and metal contacts  108  are then formed within these openings. The metal contacts  108  provide vertical electrical connections between the underlying interconnect layers  104  and any subsequent overlying layers yet to be fabricated. The metal contacts  108  may be copper, aluminum, gold, titanium, silver or tungsten.  
         [0012]     A metal fuse  112  is subsequently formed over and provides an electrical connection for the two metal contacts  108 , as illustrated in the figure. A dielectric layer  110  is then formed over the entire wafer that provides added passivation and protection for the metal fuse  112 , as well as the underlying materials  102 ,  104 ,  106 ,  108 . The dielectric layer  110  may include doped or undoped silicon oxide, fluorinated silicon oxide, silicon nitride, silicon oxynitride, low-K dielectric materials, or mixtures thereof, while the metal fuse  112  is typically copper, aluminum, gold, titanium, silver or tungsten.  
         [0013]     A fuse window  114  within the dielectric layer  110  is subsequently defined by known lithographic techniques. After photo-defining the fuse window  114 , dielectric materials may be removed from the dielectric layer  110  by known etching processes. The etch process also controls the depth  116  of the fuse window  114 . The longer the etch time, the more dielectric material  110  is removed, and less dielectric material  110  will remain over the metal fuse  112 . Consequently, a laser beam  118  may be directed through the fuse window  114  to break or vaporize the metal fuse  112  (i.e., “blow”) through the fuse window  114  in order to make repairs to the integrated circuit. In addition to laser beams  118 , other sources of photonic radiation, such as a general light source or a broadband lamp, may also be directed through the window  114  to accomplish the repair. Furthermore, electromagnetic radiation, such as electron beam, ion beam, or an electromagnetic source, may also be utilized.  
         [0014]     Although an external laser beam  118  may sufficiently penetrate the dielectric material  110  that remains over the metal fuse  112  through the fuse window  114 , processing controls can cause uniformity issues across a wafer and lead to failures in blowing some metal fuse  112 . For example, deviations during dielectric deposition can give rise to areas of thick and thin dielectric materials  110 . The poor uniformity can be further exacerbated during the dielectric etch when the fuse window  114  is formed in the dielectric layer  110 . As a result, some fuse windows  114  may be deeper than others. Consequently, metal fuses  112  with larger window depths  116  may be blown at lower laser beam energy  118 , while blowing metal fuses with smaller window depths  116  may require higher laser beam energy  118 . Accordingly, not all metal fuses  112  will be properly blown.  
         [0015]     Reference is now made to  FIG. 2 , which illustrates one embodiment of a metal fuse structure constructed according to the disclosed principles.  FIG. 2  is similar to  FIG. 1  in many respects, except that a polymer layer  220  is formed over the metal fuse  212 . As illustrated in  FIG. 2 , interconnect layers  204  are formed on a semiconductor substrate  202  using the same or similar materials and methods as those discussed in the previous figure. An IMD layer  206  and metal contacts  208  are subsequently formed over the interconnect layers  204 , also using the same or similar materials and methods discussed with respect to the previous figure. A metal fuse  212  providing electrical connection is subsequently formed over the two metal contacts  208 , also as described above.  
         [0016]     Instead of forming a layer of dielectric material  110  directly over the metal fuse  112  as illustrated in  FIG. 1 , the disclosed technique employs a polymeric material  220  deposited or formed over the metal fuse  212 . In one embodiment, the polymeric material  220  is polyimide or benzocyclobutene (BCB). In another embodiment, the polymeric material  220  is a photoresist of either positive or negative tone. Although illustrated as rectangular in shape, the polymeric coating  220  can take on a variety of shapes and sizes. If the polymer  220  is processed on a track coater, the coating  220  will have improved uniformity and consistency compared to that of a deposition tool typically used for forming the conventional dielectric layer  110  found in conventional structures. In a preferred embodiment, the polymer  220  has a thickness in the range of 0.5 to 10 micron. Factors that may affect the thickness of the polymeric layer  220  includes but are not limited to the type of polymeric coating employed, the type of radiation source used to ablate the metal fuse(s), and the energy of the radiation source.  
         [0017]     Polymers  220  are preferred overlayer materials for metal fuses  212  because polymers  220  have, in general, lower mechanical strength than traditional dielectric material  110  of  FIG. 1 , such as glass or silicon oxide. Therefore, polymers  220  are easier to crack and remove by an external source of radiation  218 , such as a laser beam. Additionally, the transmittance of polyimide  220  decreases with increasing laser energy. In other words, polyimide  220  is transparent at longer wavelengths (900 nm-1500 nm) and becomes more absorbing at shorter wavelengths (500 nm-900 nm). This indicates that polyimide  220  is easier to remove with a laser beam of less than 900 nm wavelength, whereas silicon oxide is more difficult to remove because most dielectric material  110  is transparent at all wavelengths (500 nm-1500 nm).  
         [0018]     As a result of the difference in transmittance, laser ablation of the metal fuse  212  through the polymeric coating  220  is easier than through the traditional dielectric material  110 . In addition, there is less of a thickness and uniformity concern with polymeric coating  220 . The idea is to use an initial laser beam  218  of lower energy to penetrate through the polymeric material  220 , followed by a final laser beam  218  of higher energy to blow away the metal fuse  212 . The laser beams  218  of different energy may be tuned to specifically remove the type of material involved, such as the polymeric coating  220 , and the metal fuse  212 . Accordingly, there is little concern for uniformity or fuse windows  114  as a result of the polymer coating  220 .  
         [0019]      FIGS. 3A-3C  illustrate the mechanism behind blowing the metal fuse according to the presently disclosed principles. In  FIG. 3A , a laser beam  218  of lower energy may be tuned to specifically penetrate and remove the polymeric coating  220 . As the laser beam  218  heats the polymeric coating  220 , the polymeric coating  220  slowly transforms from a solid phase to a liquid or gaseous phase. Subsequently, the polymeric coating  220  is expelled in its liquid or gaseous phase. Residual polymer  220  may also be dislodged from the semiconductor device  200 . The underlying metal fuse  212  may or may not be substantially damaged depending on the energy of the laser beam  218  and the amount of time.  
         [0020]      FIG. 3B  illustrates the subsequent step in vaporizing the metal fuse structure, whereby the laser beam  218  is now tuned to output a higher energy level. As a result of the increase in energy, the metal fuse  212  can be heated from a solid phase directly into the vapor phase  230 . Eventually, all the metal fuse  212  is ablated into the vapor form  230 , and all that remains is a completely blown metal fuse structure  200  as illustrated in  FIG. 3C .  
         [0021]     Other benefits of the presently disclosed embodiments realized include that by using a polymeric coating  220 , there is no longer a need to photo define a fuse window  114 . Secondly, there is no longer a need to etch the fuse window  114  to a certain desirable depth  116 . The presently disclosed polymeric coating  220  provides a simple and inexpensive technique for blowing metal fuses  212  in semiconductor devices  200 , and does not suffer disadvantages associated with conventional techniques. This is because the polymeric coating  220  can be removed by an external radiation source  218  at a lower energy level thereby facilitate vaporizing the underlying metal fuse  212  with minimal resistance. In addition, since the polymeric coating  220  can be performed on a coater track, the coating  220  across a wafer is far more uniform when compared to the uniformity of a conventional dielectric material  110  formed in the typical deposition chamber. Furthermore, other benefits of the coating  220  may also be realized, such as ease of processing, reduced number of processing steps, and expediting the manufacturing process, any one of which can translate into decreased overall manufacturing costs.  
         [0022]     It will be appreciated by those of ordinary skill in the art that the invention can be embodied in other specific forms without departing from the spirit or essential character thereof. For example, the metal fuse  212  may take on a variety of shapes and sizes. In one case, the metal fuse  212  may be formed in the shape of a “T”. In other cases, the metal fuse  212  may be formed from or within multi-layers of interconnects. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than the foregoing description, and all changes that come within the meaning and ranges of equivalents thereof are intended to be embraced therein.  
         [0023]     Additionally, the section headings herein are provided for consistency with the suggestions under 37 C.F.R. § 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings refer to a “Technical Field,” the claims should not be limited by the language chosen under this heading to describe the so-called technical field. Further, a description of a technology in the “Background” is not to be construed as an admission that technology is prior art to any invention(s) in this disclosure. Neither is the “Summary of the Invention” to be considered as a characterization of the invention(s) set forth in the claims found herein. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty claimed in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims associated with this disclosure, and the claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of the claims shall be considered on their own merits in light of the specification, but should not be constrained by the headings set forth herein.