Abstract:
Structure providing more reliable fuse blow location, and method of making the same. A vertical metal fuse blow structure has, prior to fuse blow, an intentionally damaged portion of the fuse conductor. The damaged portion helps the fuse blow in a known location, thereby decreasing the resistance variability in post-blow circuits. At the same time, prior to fuse blow, the fuse structure is able to operate normally. The damaged portion of the fuse conductor is made by forming an opening in a cap layer above a portion of the fuse conductor, and etching the fuse conductor. Preferably, the opening is aligned such that the damaged portion is on the top corner of the fuse conductor. A cavity can be formed in the insulator adjacent to the damaged fuse conductor. The damaged fuse structure having a cavity can be easily incorporated in a process of making integrated circuits having air gaps.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to electrical fuses in microelectronic devices and a method of making metal fuses. In particular, the invention relates to damaging a metal structure to control the location of fuse blow. 
     2. Description of Related Art 
     In advanced technologies, e-fuses have been implemented at the gate level where a fuse structure includes a narrow, horizontal, polycrystalline silicon (herein “poly”) line topped by a silicide. During programming, a high current (i.e. high current density) is passed through the structure. High current density causes the silicide to irreversibly migrate from the top of the poly to throughout the line, causing a change in resistance and thus acting as a programmable fuse. In poly fuses, the fuse structure is often placed over oxide isolation areas. The dielectric properties of the isolation oxide keep in the heat generated by current flow, thus increasing the temperature of the structure. The increased temperature further enhances migration, thus aiding fuse blow. In addition, air cavities are sometimes formed around the poly line to further increase the heat retention because air is a better dielectric than isolation oxides. 
     As scaling progresses, it is becoming harder to implement fuses at the poly level due to drop in maximum allowable currents through the first metal layer or conductor. Also, the collateral damage (namely movement of fuse material causing neighboring dielectric material to fracture) associated with fuse blow is becoming more difficult to contain. Furthermore, the horizontal structure of the fuse consumes valuable chip real estate. As a result, there is a drive to implement fuses vertically at the metal interconnect levels and use the phenomenon of electromigration (EM) to program the fuses. 
     In a conventional metal fuse approach, as shown in  FIG. 1 , a two-level structure comprises conductor  11  embedded in dielectric layer  10 , and via  21  and line  22  embedded in dielectric layer  20 . A cap layer  23  is typically deposited over line  22  and dielectric layer  20 . Electron flow is from via  21  into line  22 . A high current is applied between the positive current connection (I+) and negative current connection (I−) to induce EM failure. Voltage across the structure is measured using the positive (V+) and negative (V−) voltage connections. The electron flow through the fuse structure is from the lower level metal, conductor  11 , to the upper level metal, line  22 . The intent is to have a failure (i.e. fuse blow) in via  21 . However, with this design, some of the failures (i.e. fuse blows) occur in via  21  while other failures occur in line  22 . The lack of control over the failure location results in variability in the final resistance of the fuse structure after programming. 
     Therefore, a structure is needed such that fuse blow occurs repeatedly and reliably at the same location. At the same time, the structure must reliably conduct current prior to fuse blow. 
     SUMMARY 
     The general principal of the present invention is to intentionally damage a portion of a fuse structure so that the fuse will blow at that damaged location. By damaging a portion of the fuse structure, the fuse will more consistently blow at a known location resulting in post-fuse-blow circuits having a more controlled and predictable final resistance. 
     One aspect of the invention is a fuse structure prior to fuse blow. The structure includes a first connection, a second connection and a conductor having a damaged portion. 
     Another aspect of the invention is a method of forming a fuse structure. The method provides a substrate having a first level which includes a first conductor and a first insulator. The method also provides a fuse level above the first level, wherein the fuse level has a fuse insulator and a fuse conductor. The method continues by forming a cap layer above the fuse insulator and the fuse conductor. The method includes forming an opening in the cap layer, and damaging a portion of the fuse conductor thereby forming a damaged portion of the fuse conductor. The method also includes forming a second level which includes a second conductor and a second insulator wherein the second insulator is aligned above at least a portion of the damaged portion of the fuse conductor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a conventional vertical fuse structure; 
         FIG. 2  illustrates a fuse structure prior to fuse blow according to an embodiment of the present invention; 
         FIG. 3  illustrates a fuse structure prior to fuse blow according to an embodiment of the present invention; 
         FIG. 4  illustrates a stacked via fuse structure prior to fuse blow according to an embodiment of the present invention; 
         FIG. 5  illustrates a stacked via fuse structure prior to fuse blow in a device having cavities in fuse bank and non-fuse bank areas according to an embodiment of the present invention; 
         FIG. 6  is a top down view of an alignment of a cap layer opening of the device of  FIG. 5  according to an embodiment of the present invention; 
         FIG. 7  illustrates a flow chart for making a fuse structure having a damaged portion according to an embodiment of the present invention. 
         FIG. 8   a  illustrates the cap layer opening step of a method of making a fuse structure having a damaged portion according to an embodiment of the present invention. 
         FIG. 8   b  illustrates damaging a portion of the fuse conductor according to an embodiment of the present invention. 
         FIG. 8   c  illustrates forming a cavity in the fuse insulator according to an embodiment of the present invention. 
         FIG. 8   d  illustrates forming an optional thin dielectric according to an embodiment of the present invention. 
         FIG. 8   e  illustrates forming a second level insulator according to an embodiment of the present invention. 
         FIG. 8   f  illustrates forming a second level conductor according to an embodiment of the present invention. 
     
    
    
     Other objects, aspects and advantages of the invention will become obvious in combination with the description of accompanying drawings, wherein the same number represents the same or similar parts in all figures. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Various embodiments of the fuse structure of the present invention are described in conjunction with  FIGS. 2-6 . Embodiments of methods of making the fuse structures of the present invention are described in conjunction with  FIGS. 7-8   f.    
     Referring to  FIG. 2 , a fuse structure  100  prior to fuse blow is illustrated. On a substrate (not shown) is a first level  110 , a second level  120  and a fuse level  130 . The fuse level  130  is between the first  110  and second  120  levels. Each level includes an insulator and a conductor. The levels are separated by a cap layer  140 . The first, second and fuse level insulators are denoted by reference numerals  112 ,  122 , and  132  respectively. The first, second and fuse level conductors are denoted by reference numerals  114 ,  124 , and  134  respectively. Each of the conductors  114 ,  124  and  134  can include a bulk conductor and a liner. In  FIG. 2 , the bulk conductor  136  and liner  138  are only shown for the fuse conductor  134  for ease if viewing. It should be understood that the first and second conductors preferably also have a bulk conductor and a liner. 
     Any suitable insulator material may be used for insulators  112 ,  122  and  132 . The material used for each of the insulators  112 ,  122  and  132  may be the same or different. Typical insulating materials include any now known or later developed porous or non-porous insulator material such as silicon containing oxides, silicon containing oxides doped with fluorine, silicon containing nitrides, silicon containing carbides, hydrogenated silicon oxycarbides (SiCOH), silsesquioxanes, carbon-doped oxides (i.e., organosilicates) that include atoms of silicon (Si), carbon (C), oxygen (O), and/or hydrogen (H), thermosetting polyarylene ethers, SiLK™ (a polyarylene ether available from Dow Chemical Corporation), spin-on silicon-carbon contained polymer material available from JSR Corporation, and low dielectric constant materials or layers thereof. Low dielectric constant materials are those materials that have a dielectric constant less than about 3.9. The insulator levels  112 ,  122  and  132  may be made from a single type of insulator material, or each insulator level  112 ,  122 , and  132  may be a series of layers of the same or different types of insulator materials. For example, but not by way of limitation, the insulator level ( 112 ,  122  and/or  132 ) may be SiO 2 ; or the insulator level ( 112 ,  122 , and/or  132 ) may be a composite including a SiO 2  layer and a fluorine doped SiO 2  layer. Other combinations of layers and materials are also possible. 
     The material used for each capping layer  140  may be the same or different. The cap layer is preferably a dielectric material (i.e. insulating layer). Typical dielectric materials for the capping layer  140  include any now known or later developed dielectric materials such silicon carbide (SiC), silicon nitride (Si 3 N 4 ), silicon dioxide (SiO 2 ), silicon oxynitrides, and nitrogen or hydrogen doped silicon carbide (SiC(N,H)). The capping layer  140  may be a single layer of a material, a series of layers of the same material (by way of example, but not limitation, a series of SiC layers with different C percentage), or a series of layers of different materials. 
     Any suitable conductive material may be used for the bulk conductor  136  of the first  114 , second  124 , and fuse  134  conductors. The material used for each of the bulk conductors may be the same or different. Typical bulk conductive materials include materials containing copper (Cu), aluminum (Al), tungsten (W), silver (Ag), gold (Au) and their alloys. 
     Any suitable liner material may be used for liner  138 , and the material used for each of liners of the first  114 , second  124  and fuse  134  conductors may be the same or different. Typical liner materials include tantalum (Ta), tantalum nitride (TaN), titanium (Ti), titanium nitride (TiN), tungsten (W), ruthenium (Ru) and ruthenium nitride (RuN). The liner may be a single layer of liner material, or preferably, is a multilayer film of liner material. For example, but not by way of limitation, the liner may be TaN/Ta, Ti/TiN, or W/Ti. 
     Continuing with  FIG. 2 , the fuse conductor  134  has a damaged portion  139 . The damaged portion  139  can include bulk conductor  136  only, liner  138  only, or as pictured in  FIG. 2 , the damaged portion  139  includes both conductor  136  and liner  138 . The damage, as way of example but not limitation, can take the form of missing material (as shown in  FIG. 2 ), as corroded material, as oxidized material, or a combination of two or more of the previously described damage. “Material” refers to the bulk conductor  136  and/or liner  138  of the fuse conductor  134 . The damaged portion  139  depicted in  FIG. 2  is at the top corner of the fuse conductor  134 . The damaged portion  139  could also be just along the top of the fuse conductor  134  or just along a sidewall  144  of the fuse conductor  134 , but in either case, should be proximate to the top corner of the fuse conductor  134 . The damaged portion  139  should be damaged to a degree needed to prompt fuse blow at the damage portion and yet still be minimal enough so that the fuse structure operates normally prior to fuse blow. The exact amount of damage (i.e. the amount of material missing, corrosion formed, oxidation occurring) will depend on many factors including, but not limited to, materials used, current load of the fuse structure, and dimensions of the fuse structure. 
     Still referring to  FIG. 2 , there is an opening  142  in the cap layer  140  above the fuse level  130 . Here, the opening  142  is aligned such that it is over the damaged portion  139  of the fuse conductor  134  and a portion of the fuse insulator  132 , thus the opening  142  straddles a sidewall  144  of the fuse conductor  134 . In alternative embodiments, the opening  142  can be aligned so as to be completely over the fuse conductor  134  or completely over the fuse insulator  132 . But in every case, the opening  142  should be proximate to the sidewall  144  so that the fuse conductor  134  will sustain damage (as explained further in the method section). 
     At least a portion of the damaged portion  139  of the fuse conductor  134  is below the second insulator  122  (as opposed to being below the second conductor  124  which is shown later in  FIG. 3 ). In the embodiment illustrated in  FIG. 2 , none of the damaged portion  139  is below the second conductor  124 , and there is an optional intervening thin dielectric  146  layer between the damaged portion  139  and the second dielectric  122 . The thin dielectric  146  can be made from any of the materials listed for the cap dielectric  140  or insulator layers ( 112 ,  122 ,  132 ). The thickness of the thin dielectric can be from about 30 A to about 500 A, and ranges therebetween. 
       FIG. 2  generally describes a fuse blow structure in which the first  114  and second  124  conductors can act as first and second connections, respectively, to the fuse structure as indicated by the current (I) and voltage (V) abbreviations. In that case, at least a portion of the fuse conductor  134  is intended to blow during fuse blow. In a specific embodiment, the first and second conductors,  114  and  124 , can be line level metallurgy and the fuse conductor  134  is a via connecting the two lines  114  and  124 . However, unlike  FIG. 1 , the second conductor  124  is offset from the via. The offset allows the via (fuse conductor) to be damaged. In a specific embodiment described later in conjunction with  FIG. 4 , the second conductor,  124 , is a via/line structure, preferably, formed by dual damascene. 
       FIG. 3  shows a slightly different embodiment of a fuse structure  101  prior to fuse blow. Here, the same reference numerals as used as in  FIG. 2 . A first difference is a cavity  150  in the fuse insulator  132 . The cavity is proximate to the damaged portion  139  of the fuse conductor  134  and proximate the sidewall  144  of the fuse conductor. The cavity  150  may be open to damaged portion  139  of the fuse conductor  134 , or as shown in  FIG. 3 , second level insulator  122  may partially fill the cavity  150 . In an alternate embodiment, second level insulator  122  completely fills the cavity. In  FIG. 3 , the optional thin dielectric  146  also lines the cavity  150 . It should be noted that a cavity  150  can also be used in the embodiment of  FIG. 2 . 
     A second difference found in  FIG. 3  is the opening  142  in the cap layer. Here, the opening still straddles the sidewall  144  of the fuse conductor  134 , but the opening extends all the way to the second conductor  124 . 
     A third difference found in  FIG. 3  is that the second conductor  124  is above a portion of the damaged portion  139 . Therefore, a portion of the damaged portion  139  is below the second conductor  124  while another portion of the damaged portion  139  is below the second insulator  122 . Alternatively, the another portion of the damaged portion is exposed to the cavity  150 . 
     As mentioned earlier,  FIG. 2  generally describes a fuse blow structure in which the first  114  and second  124  conductors can act as first and second connections, respectively, to the fuse structure as indicated by the current (I) and voltage (V) abbreviations. In that case, at least a portion of the fuse conductor  134  is intended to blow during fuse blow. In a specific embodiment shown in  FIG. 4  the fuse structure is a stacked via fuse structure prior to fuse blow in which the second conductor  124  (acting as the second connection) has a via  126  portion and a line  128  portion. Similarly, the fuse conductor  134  has a via  166  portion and a line portion  168 . Please note, the reference numerals and material descriptions used in  FIG. 2  also apply to  FIG. 4  and will not be repeated, here. 
     Referring the stacked via fuse structure  102  of  FIG. 4 , the structure is called a stacked fuse structure because the fuse via  166  and the second conductor via  126  generally form a stack. Furthermore, the fuse conductor line  168  is preferably minimal dimension; meaning is slightly larger than of the fuse conductor via  166 . Thus, in a preferred embodiment, the fuse conductor line  168  minimally, if at all, extends out of the plane of the figure. A further description of stacked via fuse structures can be found in U.S. patent application Ser. No. 13/074407 filed on Mar. 29, 2011 and herein incorporated by reference. 
     In the stacked via embodiment  102  of  FIG. 4 , The damaged portion  139  of the fuse conductor  134  is in the line level  168  of the fuse conductor  134 ; thus the intent is that the fuse will blow at the line level rather than a via level. This intent is the opposite of other fuse blow vertical structures known in the industry which intend to blow the fuse in a via. 
     Still referring to  FIG. 4 , the cavity  150  description of  FIG. 3  also applies to  FIG. 4 . The cavity as shown in  FIG. 4  extends nearly the full height of the fuse insulator  132 . In an alternate embodiment, the cavity  150  could be shorter; for example, and not by limitation, the cavity  150  may only extend to a location even with the fuse line  168  and fuse via  166  intersection. Alternatively, the cavity  150  may also extend all the way to the cap layer  140  located on top of first level  110 . 
     A fuse structure having a cavity  150  can easily be incorporated into a device which has an air gap process. In an air gap process, cavities  150  (i.e. air gaps, also known as voids) are formed in the insulator level in order to reduce the resistance capacitance delay (RC delay) of the interconnect levels.  FIG. 5  shows a cross section of an integrated circuit having a stacked via fuse bank on the left and a non-fuse bank area on the right. The non-fuse bank area practices an air gap process. In the fuse bank area the opening  142  in the cap layer  140  is aligned so as to be proximate to the fuse conductor  134 . In the non-fuse bank area, the openings  142  in the cap layer  140  are aligned so as to be roughly equidistant from consecutive conductors  170 .  FIG. 6  is a top down view of the fuse level  130  of  FIG. 5 . Here, the ovals represent the opening  142  in the cap layer and the dotted rectangles represent the fuse conductors  134  and non-fuse bank conductors  170  below the cap layer  140 . Thus, the air gap process of a non-fuse bank area and a damaged fuse (with or without a cavity) of a fuse bank area can be easily integrated by using a single mask to form openings in the cap layer  140 . 
     Returning to  FIG. 5 , a cavity  150  in the fuse bank area can be referred to as a first cavity. The first cavity, as explained above is aligned to be proximate to the fuse conductor  134 , and in particular, proximate to a damaged portion  139  of the fuse conductor  124 . A cavity  150  in the non-fuse bank area can be referred to as a second cavity. The second cavity is more or less centered in the insulator  132  between consecutive interconnects  170  of the non-fuse bank area. In  FIG. 5 , the second cavity runs the height of the fuse level  130 , but in alternative embodiments, the second cavity may only extend down to be even with the line (top, wider portion) of the interconnect  170 . 
       FIG. 7  is a flow chart  700  for making a fuse structure having a damaged portion. Initially, in step  710  a fuse level  130  is provided over a first level  110 . In step  720  a cap layer  140  is provided over the fuse level  130 . In step  730  an opening is made in the cap level. In step  740  a portion of fuse conductor  134  is damaged. In step  770  a second level  120  is formed. Opening the cap layer  730  may occur as a separate process step or in conjunction with step  740 , damaging the fuse conductor. 
     Flow chart  700  also contains optional steps denoted by dotted arrows. One optional step is forming a cavity  750  in a fuse insulator adjacent the damaged portion of fuse conductor. Cavity formation  750  may occur as a separate process step or in conjunction with step  740 , damaging the fuse conductor. Likewise, step  730  (opening the cap layer  140 ), step  740  (damaging the fuse conductor) and  750  (forming cavity  150 ) may be three separate process steps, two separate process steps or one process step. 
     Another optional step is forming a thin dielectric layer  760 . Both optional steps ( 750  and  760 ) may be performed, one of the optional steps may be performed ( 750  or  760 ), or no optional steps may be performed. In a preferred embodiment, both optional steps ( 750  and  760 ) are performed. 
       FIGS. 8   a - f  illustrate of a method of making fuse structures ( 100 ,  101 ,  102 ) having a damaged portion  139  according to an embodiment of the present invention. For ease of viewing, the figures do not show the first level  110 , but it is understood that the fuse level  130  is above a first level  110 . In addition, the reference numerals used in  FIGS. 8   a - f  are the same as those used in  FIGS. 2-6 . Accordingly, the earlier descriptions used with respect to the reference numerals also apply to  FIGS. 8   a - f.    
     Referring to  FIG. 8   a , a fuse level  130  has a fuse insulator  132  and a fuse conductor  134 . The fuse conductor  134  can include a bulk conductor  136  and a liner  144 . A cap layer  140  is above the fuse level  130 . The cap layer has an opening  142  which, in this embodiment, straddles a sidewall  144  of the fuse conductor  134 . The cap layer  142  is opened using a etch process, preferably a reactive ion etch (herein “RIE”). The cross section in  FIG. 8   a  illustrates a fuse structure being built after step  730  of  FIG. 7  (forming an opening in a cap layer) has been completed. 
     In  FIG. 8   b , the fuse level  130  material exposed by the cap opening  142  is etched. The etch damages a portion  139  of the fuse conductor  134 . In the embodiment shown, the damaged portion includes both the bulk conductor  136  and liner  138 . In addition, some of the fuse level insulator  132  is removed. The cross section in  FIG. 8   b  illustrates a fuse structure being built after step  740  (damaging fuse conductor) has been completed. 
     At this point, an etching process can continue such that step  750 , forming a cavity  150 , is preformed, or alternatively, the etching process can be stopped and the process move to the step in  FIG. 8   d  or  8   e . If the etching process is stopped, then the final fuse structure will not have a cavity (for example, see a fuse structure embodiment shown in  FIG. 2 ). 
       FIG. 8   c  illustrates the embodiment in which the optional cavity ( 150 ) formation step  750 , is performed. 
     As explained earlier steps  730  (cap open),  740  (damage) and  750  (cavity formation) can use the same or different processes. A standard RIE process that can be used in any of the steps, can be a halogen containing precursors along with oxygen containing precursors. In a preferred embodiment, the RIE process for at least the cavity formation step  750  includes an oxygen flow 5-10 sccm greater than the standard known in the art. Or, in an alternative embodiment, instead of increasing oxygen flow, the flow of polymerizing gases (fluorocarbons) can be reduced. Reducing fluorocarbons enhances lateral etching leading to sidewall  144  etching of the fuse conductor  134 . 
     In  FIG. 8   d  an optional thin dielectric  146  is deposited. In a preferred embodiment the thin dielectric covers the surface of the structure, including the damaged portion  139 , cavity  150  and cap layer  140 . Thus, the intent is for the thin dielectric to line the entire surface of the air gap region, though depending on the geometry of the cavity  150  and its relation to the cap layer  140 , there may be some discontinuities in the thin dielectric  146 . The thin dielectric  146  can be deposited by a variety of techniques including, but not limited to, Chemical Vapor Deposition (CVD), Low Pressure CVD (LPCVD), Plasma Enhanced CVD (PECVD), and Atomic Layer Deposition (ALD). The cross section in  FIG. 8   d  illustrates a fuse structure being built after optional step  760  (forming thin dielectric) has been completed in an embodiment in which optional step  750  (forming cavity) was also completed. 
     In  FIG. 8   e , a second level insulator  122  is deposited as previously described in conjunction with  FIG. 2 . The insulator can be deposited by any of the following methods, or in the case of a multilayer insulator film a combination of the following methods: CVD, LPCVD, PECVD, ALD, and spin on. 
     In  FIG. 8   f , the second level conductor  124  is deposited in a hole (not shown) etched into the second level insulator  122 . The second level conductor  124  can act as a second connection. It, combined with the damaged  139  fuse conductor  134  and first level  110  conductor (not shown) acting as a first connector form a fuse structure ( 100 ,  101  or  102 ) having a damaged portion  139 . The cross section in  FIG. 8   f  illustrates a fuse structure after step  770  (forming second level) has been completed. 
     The fuse structures of the present invention have the advantage of fuse blow in a consistent, known location. The fuse structure of the present invention uses intentionally created pre-existing damage to aid fuse blow. Some embodiments of the fuse structure of the present invention are designed so that fuse blow takes place at the line level rather than the via level. Some embodiments of the present invention provide a cavity in the insulator proximate to the damaged portion. The cavity provides a place for blown fuse material to go without damaging the structure. The cavity embodiment is also easily integrated (meaning no extra steps or masks are needed) in air gap back end of line interconnect structures. 
     While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadcast interpretation so as to encompass all such modifications and equivalent structures and functions.