Abstract:
A semiconductor device having metal leads 14 with improved reliability comprising metal leads 14 on a substrate 12, a low-dielectric constant material 18 at least between the metal leads 14, and dummy leads 16 proximate the metal leads 14. Heat from the metal leads 14 is transferable to the dummy leads 16, and the dummy leads 16 are capable of dissipating the heat. The low-dielectric constant material 18 has a dielectric constant of less than 3.5. An advantage of the invention is improved reliability of metal leads for circuits using low-dielectric constant materials.

Description:
This is a division of application Ser. No. 08/250,983, filed May 31, 1994, now abandoned. 
    
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     The following co-assigned U.S. patent applications are hereby incorporated herein by reference: 
     
         ______________________________________Serial No   Filing Date             Inventor Status Title______________________________________08/137,658   10/15/93  Jeng     abandoned                             Planarized Structure                             for Line-to-Line                             Capacitance                             Reduction08/280,406    7/26/94  &#34;        pending                             Planarized Structure                             for Line-to-Line                             Capacitance                             Reduction08/201,679    2/25/94  Jeng et al                      abandoned                             Selective Filling                             Narrow Gaps with                             Low-dielectric-                             constant materials08/427,631    4/21/95  &#34;        abandoned                             Selective Filling                             Narrow Gaps with                             Low-dielectric-                             constant materials08/202,057    2/25/94  Jeng     abandoned                             Planarized Multi-                             level Interconnect                             Scheme with Em-                             bedded Low-Dielec-                             tric-Constant                             Insulators08/430,095    4/26/95  &#34;        issued Planarized Multi-(U.S. Pat. No. 5,486,493)       level Interconnect                             Scheme with Em-                             bedded Low-Dielec-                             tric-Constant                             Insulators08/473,458    6/7/95   &#34;        issued Planarized Multi-(U.S. Pat. No. 5,616,959)       level Interconnect                             Scheme with Em-                             bedded Low-Dielec-                             tric-Constant                             Insulators08/455,765    5/31/95  &#34;        issued Planarized Multi-(U.S. Pat. No. 5,591,677)       level Interconnect                             Scheme with Em-                             bedded Low-Dielec-                             tric-Constant                             Insulators08/234,443    4/28/94  Cho      pending                             Low Dielectric                             Constant Insulation                             in VLSI applications08/483,591    6/7/95   &#34;        issued Low Dielectric(U.S. Pat. No. 5,512,775)       Constant Insulation                           in VLSI applications08/234,099    4/27/94  Havemann pending                             Via Formation in                             Polymeric Materials08/476,293    6/7/95   &#34;        pending                             Via Formation in                             Polymeric Materials08/247,195    5/20/94  Gnade    issued A Low Dielectric(U.S. Pat. No. 5,470,802)         et al             Constant Material                           for Electronics                           Applications08/483,029    6/7/95   &#34;        pending                             A Low Dielectric                             Constant Material                             for Electronics                             Applications08/473,701    6/7/95   &#34;        abandoned                             A Low Dielectric                             Constant Material                             for Electronics                             Applications08/735,758   10/23/96  &#34;        pending                             A Low Dielectric                             Constant Material                             for Electronics                             Applications08/246,432    5/20/94  Havemann issued Interconnect(U.S. Pat. No. 5,488,015)         et al             Structure with an                           Integrated Low                           Density Dielectric08/473,840    6/7/95   &#34;        abandoned                             Interconnect                             Structure with an                             Integrated Low                             Density Dielectric08/751,901   11/18/96  &#34;        pending                             Interconnect                             Structure with an                             Integrated Low                             Density Dielectric08/250,063    5/27/94  Havemann issued Multilevel Inter-(U.S. Pat. No. 5,461,003)         et al             connect Structure                             with Air Gaps                             Formed Between                             Metal Leads08/428,814    4/24/95  &#34;        abandoned                             Multilevel Inter-                             connect Structure                             with Air Gaps                             Formed Between                             Metal Leads08/631,437    4/12/96  &#34;        pending                             Multilevel Inter-                             connect Structure                             with Air Gaps                             Formed Between                             Metal Leads08/811,021    3/4/97   &#34;        pending                             Multilevel Inter-                             connect Structure                             with Air Gaps                             Formed Between                             Metal Leads08/250,142    5/27/94  Havemann abandoned                             Two-step Metal                             Etch Process for                             Selective Gap Fill of                             Submicron Inter-                             connects and                             Structure for Same08/606,657    2/26/96  &#34;        pending                             Two-step Metal                             Etch Process for                             Selective Gap Fill of                             Submicron Inter-                             connects and                             Structure for Same08/481,720    8/22/95  &#34;        pending                             Two-step Metal                             Etch Process for                             Selective Gap Fill of                             Submicron Inter-                             connects and                             Structure for Same08/667,774    6/21/96  &#34;        pending                             Two-step Metal                             Etch Process for                             Selective Gap Fill of                             Submicron Inter-                             connects and                             Structure for Same08/250,747    5/27/94  Gnade    pending                             Low Dielectric             et al           Constant Layers via                             Immiscible Sol-gel                             Processing______________________________________ 
    
     The following U.S. patent applications filed concurrently with the patent application for the present invention, are also incorporated herein by reference: 
     
         ______________________________________Serial No.    Inventor Title______________________________________08/251,822    Numata   Method of Making Reliable Metal Leads in(U.S. Pat. No. 5,510,293)         High Speed LSI Semiconductors using         Thermoconductive Dielectric Layer08/250,888    Numata   Method of Making Reliable Metal Leads in(U.S. Pat. No. 5,476,817)         High Speed LSI Semiconductors using both             Dummy Leads and Thermoconductive             Dielectric Layer08/486,305    Numata   Method of Making Reliable Metal Leads in(U.S. Pat. No. 5,519,200)         High Speed LSI Semiconductors using both         Dummy Leads and Thermoconductive         Dielectric Layer______________________________________ 
    
     FIELD OF THE INVENTION 
     This invention relates generally to the fabrication of semiconductor devices, and more specifically to semiconductors with submicron spacing and low-dielectric materials between the intermetallic leads. 
     BACKGROUND OF THE INVENTION 
     Semiconductors are widely used in integrated circuits for electronic applications, including radios and televisions. Such integrated circuits typically use multiple transistors fabricated in single crystal silicon. Many integrated circuits now contain multiple levels of metallization for interconnections. 
     Semiconductor devices are being scaled in the horizontal dimension to reduce wafer cost by obtaining more chips per wafer or by increasing circuit complexity by obtaining more transistors per chip. Although semiconductor devices are being scaled in the horizontal dimension, semiconductor devices are not generally being scaled in the vertical dimension (because the current density would exceed reliability limits). Thus, conductors may have a high aspect ratio (ratio of conductor height to conductor width of greater than one). With horizontal scaling, these tall metal leads are being packed closer and closer together, causing capacitive coupling between the leads to become the primary limitation to circuit speed. If line-to-line capacitance is high, a likelihood for electrical inefficiencies and inaccuracies exist. Reducing the capacitance within these multi-level metallization systems will reduce the RC time constant between the lines. 
     Typically, the material used to isolate metal lines from each other is silicon dioxide. However, the dielectric constant of dense silicon oxide grown by thermal oxidation or chemical vapor deposition is on the order of 3.9. The dielectric constant is based on a scale where 1.0 represents the dielectric constant of a vacuum. Various materials exhibit dielectric constants from very near 1.0 to values in the hundreds. As used herein, the term low-dielectric will refer to a material with a dielectric constant of less than 3.5. 
     SUMMARY OF THE INVENTION 
     Recently, attempts have been made to use low-dielectric materials to replace silicon dioxide as a dielectric material. The use of low-dielectric materials as insulating layers reduces the capacitance between the lines (or leads), thus reducing the RC time constant. An apparently heretofore-unrecognized problem (especially in high aspect ratio metal leads) is that the decreased thermal conductivity of low-dielectric constant materials may result in metal lead breakage due to the effects of Joule&#39;s heat. The present invention solves this problem by improving the thermal conductivity of the structure, resulting in improved reliability of metal leads in structures using low-dielectric materials. 
     The invention encompasses a method for manufacturing semiconductor devices having metal leads with improved reliability, and a device for same, comprising metal leads on a substrate, a low-dielectric constant material at least between the metal leads, and dummy leads proximate the metal leads. Heat from the metal leads is transferable to the dummy leads, and the dummy leads are capable of dissipating the heat The low-dielectric constant material has a dielectric constant of less than 3.5. An advantage of the invention is to improve reliability of metal leads for circuits using low-dielectric constant materials. 
     One preferred embodiment of the invention involves depositing a metal interconnect layer on a substrate and etching the metal interconnect layer in a predetermined pattern to form metal leads and dummy leads, where the dummy leads are proximate the metal leads. Then, a low-dielectric constant material is deposited between the metal leads and the dummy leads. Another embodiment involves depositing a first metal interconnect layer on a substrate and etching the first metal interconnect layer in a predetermined pattern to form metal leads. Then a low-dielectric constant material is deposited between the metal leads. A thin oxide layer is deposited over low-dielectric constant material, and a second metal interconnect layer is deposited on the thin oxide layer. The second interconnect layer is etched in a predetermined pattern to form dummy leads, wherein the dummy leads are adjacent a portion of the metal leads of the first metal interconnect layer. Heat from the metal leads is transferable to the dummy leads and dissipatable. The low-dielectric constant material has a dielectric constant of less than 3.5. 
     An advantage of the invention is to improve reliability of metal leads for circuits using low-dielectric constant materials. The invention is particularly beneficial to semiconductors having a combination of metal leads with high aspect ratios and low-dielectric constant materials which are more thermally insulating. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, which form an integral part of the specification and are to be read in conjunction therewith, and in which like numerals and symbols are employed to designate similar components in various views unless otherwise indicated: 
     FIGS. 1A-1C are three-dimensional views of a metal lead of a semiconductor wafer, showing the negative effects of Joule&#39;s heat; 
     FIGS. 2A-2C are cross-sectional views of a first embodiment of the present invention, showing dummy leads formed on a semiconductor wafer. 
     FIGS. 3A-3B are cross-sectional views of a second embodiment of the present invention, showing dummy leads formed on a semiconductor wafer. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The making and use of the presently preferred embodiments are discussed below in detail. However, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the invention. 
     The following is a description of several preferred embodiments and alternative embodiments, including manufacturing methods. Corresponding numerals and symbols in the different figures refer to corresponding parts unless otherwise indicated. Table 1 below provides an overview of the elements of the embodiments and the drawings. 
     
                       TABLE 1______________________________________  PreferredDrawing  or Specific           Generic    Other Alternate Examples orElement  Examples Term       Descriptions______________________________________10              Semiconductor           wafer12     Silicon  Substrate  May be other metal interconnect                      layers or semiconductor                      elements, (e.g. transistors,                      diodes);                      Oxides;                      Compound semiconductors (e.g.                      GaAs, InP, Si/Ge, SiC).14     Aluminum Metal leads                      Titanium trilayer (TiN/AlCu/  alloy               TiN);                      Alloys of Cu, Mo, W, Ti, Si;                      Polysilicon, silicides, nitrides,                      carbides;                      AlCu alloy with Ti or TiN                      underlayers;                      Metal interconnect layer.16     Aluminum Dummy leads                      Titanium trilayer (TiN/AlCu/  alloy               TiN);                      Alloys of Cu, Mo, W, Ti, Si;                      Polysilicon, silicides, nitrides,                      carbides;                      AlCu alloy with Ti or TiN                      underlayers.18     OSOG     Low-dielectric                      Air gap (also inert gases,  (organic constant   vacuum); silica aerogel; other  spin-on  material   aerogels or xerogels; fluorinated  glass)              silicon oxide.20     SiO.sub.2           Thin oxide Insulating layer preferably           layer      having a thickness less than the                      height of metal leads 14______________________________________ 
    
     An apparently heretofore-unrecognized problem is that the decreased thermal conductivity of low-dielectric materials may result in metal lead breakage due to the effects of Joule&#39;s heat, especially in high aspect ratio conductors with low-dielectric constant material between conductors, where the low-dielectric material is on more than half the conductor perimeter. Since all metals have a certain amount of resistance, the temperature of a metal rises as a current passes through it. Such heat through a metal lead is known as Joule&#39;s heat. As a metal lead heats locally in one portion along it, the resistance in that portion rises slightly (due to properties of the metal), causing the temperature in that portion to rise even more (although slightly). Thus, locally heated metal leads can be damaged or fractured. The thinner the metal lead, the weaker it is (which is particularly a concern in submicron circuits). The use of low-dielectric constant materials as insulative layers further present a problem, for such materials generally have poor thermoconductivity. With the use of low-dielectric constant materials, much more of the Joule&#39;s heat generated in metal leads of a circuit remains concentrated in the lead itself. 
     The effect of Joule&#39;s heat on a metal lead is shown in FIG. 1. FIG. 1A shows a metal lead 14 of a semiconductor wafer (other portions of the wafer are not shown). When current flows through metal lead 14, the metal lead is heated. In reality, a metal lead has thin and fragile portions. Such unevenness cannot be avoided because photolithography and etching processes of metal leads are not ideal. Electromigration, intensified by Joule&#39;s heat, causes the metal lead to first weaken, and then thin. Thin and fragile portions of the metal lead becomes thinner and thinner as current is cycled through the metal lead (FIG. 1B), and electromigration is even further intensified in this portion. Eventually such leads can break, as shown in FIG. 1C, resulting in device failures. 
     The present invention improves reliability of metal leads in structures using low-dielectric constant materials by using dummy leads to improve the thermal conductivity of the structure. FIG. 2A shows a cross-sectional view of a semiconductor wafer 10 having metal leads 14 formed on a substrate 12. The substrate may, for example, contain transistors, diodes, and other semiconductor elements (not shown) as are well known in the art. The substrate 12 may also contain other metal interconnect layers, and typically contains a top insulating oxide layer (to prevent leads from shorting to each other in subsequent metal layers). A first metal interconnect layer has been deposited over the substrate 12. The first metal interconnect layer may comprise, for example, aluminum or a titanium-tungsten/aluminum bilayer. The first metal interconnect layer is etched with a predetermined pattern to form etch lines, or metal leads 14. Some of the metal leads 14 may be in close proximity to each other, for example, 1 μm or less apart. 
     FIG. 2B shows the same semiconductor device as in FIG. 2A, with a first embodiment of the present invention implemented. Dummy leads 16 are formed adjacent metal leads 14 in the same metal interconnect as metal leads 14 are formed in. The dummy leads 16 diffuse some of the Joule&#39;s heat away from the metal leads 14 when the device is in operation. A low-dielectric constant material, preferably an organic spin-on glass (OSOG), is subsequently deposited between the metal leads and dummy leads, as shown in FIG. 2C. Although low-dielectric constant material 18 may be a poor thermal conductor, it is relative thin, allowing some of the Joule&#39;s heat to be diffused away from the metal leads 14 through dummy leads 16. Since dummy leads 16 are comprised of metal, they are excellent thermal conductors. The dummy leads 16 are generally spaced apart from the metal leads 14 a distance of about one lead width. A second embodiment of the present invention is shown in FIG. 3, where dummy leads 16 are formed in an adjacent parallel metal layer. Semiconductor wafer 10 comprises a substrate 12. A first metal interconnect layer is deposited over the substrate 12, and metal leads 14 are formed in the first metal interconnect layer. A low-dielectric constant material 18 is formed between the metal leads 14, as shown in FIG. 3A. Then a relatively thin oxide layer 20 (preferably having a thickness less than the height of metal leads 14) is deposited on the metal leads 14 and the low-dielectric constant material 18. A second metal interconnect layer (adjacent and parallel to first metal interconnect layer) is deposited over thin oxide layer 20, and dummy leads 16 are formed adjacent the metal leads 14 (see FIG. 3B). The thin oxide layer 20 must be thin enough to allow some of the Joule&#39;s heat from underlying metal leads 14 to migrate through the thin oxide layer 20 to reach the dummy leads 16 formed in the second metal interconnect layer. A portion of the Joule&#39;s heat from metal leads 14 is transferable through thin oxide layer 20 to dummy leads 16. Subsequent processing steps may then be performed e.g. further deposition and etching of semiconductor, insulative and metallic layers. 
     The present invention can also be used on semiconductors using other low-dielectric constant materials, such as air gaps, aerogels, xerogels, or fluorinated silicon oxide, for example. To reduce this capacitive coupling, low-dielectric constant materials are being investigated, such as pure polymers (e.g. parylene, teflon, polyimide) or organic spin-on glass (OSOG, e.g. silsequioxane or siloxane glass). Refer to U.S. Pat. No. 4,987,101 issued to Kaanta et al on Jan. 22, 1991 which describes a method for fabricating gas (air) dielectrics; and U.S. Pat. No. 5,103,288 issued to Sakamoto on Apr. 7, 1992 which describes a multilayered wiring structure which decreases capacitance by using a porous dielectric. 
     The novel method of using dummy leads to dissipate heat from metal leads is beneficial to semiconductors having submicron spacing and using low-dielectric constant materials. The dummy leads diffuse a portion of the Joule&#39;s heat generated in the metal leads, enhancing reliability of metal leads. The invention is particularly beneficial to semiconductors having a combination of metal leads with high aspect ratios (e.g. 2 or greater) and low-dielectric constant materials (especially having a low-dielectric constant of less than 2) which are more thermally insulating. 
     While the invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.