Abstract:
A method of preventing metal penetration and diffusion from metal structures formed over a semiconductor structure, comprising the following steps. A semiconductor structure including a patterned dielectric layer is provided. The patterned dielectric layer includes an opening and an upper surface. The dielectric layer surface is then passivated to form a passivation layer. A metal plug is formed within the dielectric layer opening. The passivation layer prevents penetration and diffusion of metal out from the metal plug into the semiconductor structure and the patterned dielectric layer.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to fabrication of semiconductor devices used in integrated circuits, and specifically to a method of creating copper traps during fabrication of semiconductor devices. 
     BACKGROUND OF THE INVENTION 
     Without treatment, the dielectric surface is susceptible to copper (Cu) penetration and diffusion. Thus there is potential damage to the device since Cu has a long diffusion length, especially with the number of thermal cycles present in the normal process flow. 
     U.S. Pat. No. 5,451,542 to Ashby describes a method for passivating compound semiconductor surfaces by photolytically disturbing molecular sulfur vapor with ultraviolet radiation to form reactive sulfur which then reacts with, and passivates, the compound semiconductor surfaces. 
     U.S. Pat. No. 5,953,628 to Kawaguchi describes a method for forming copper wiring for a semiconductor device within SiO 2  insulating layers. An SiO 2  insulating layer and an intermediate SiO 2  insulating layer are stacked successively. An opening is formed within the intermediate SiO 2  insulating layer and a copper wiring is formed within the opening. The copper wiring is covered with an anti-oxidation layer that is not a transition metal as in conventional semiconductor devices, but is copper sulfide (Cu x S where 0&lt;×≦2). 
     U.S. Pat. No. 5,990,008 to Koyama et al. describes a method of forming high aspect copper structures that permits a heightened degree of copper burying. For example, a fine connecting hole may be formed in a layer insulating film on a silicon substrate. A CVD-TiN barrier film is formed on the etched insulating film as an adhesive film, and a copper film having thickness of 1 μm is then formed over the TiN adhesive film. The copper film has a high level of purity with an oxygen concentration of 0.5 ppm or lower, and a sulfur concentration of 0.06 ppm or lower. A heat treatment is applied and a copper fine contact hole is formed without voids. 
     U.S. Pat. No. 5,431,774 to Douglas describes a method of dry etching metals, such as copper, using—acids in an energetic environment such as a plasma, laser, or afterglow reactor, or by using ligands forming volatiles at low temperatures within a pulsed energetic environment. 
     U.S. Pat. No. 5,821,168 to Jain describes a process for forming a semiconductor device in which an insulating layer is nitrided and then covered by a thin adhesion layer before depositing a composite copper layer. The process does not require a separate diffusion barrier as a portion of the insulating layer (SiO) is converted to form a diffusion barrier film (SiON) by performing a plasma nitriding step. 
     U.S. Pat. No. 5,831,283 to Batey et al. describes a layer for passivating copper, aluminum, or other refractory metal films using ammonia-free silicon nitride. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to prevent copper penetration and diffusion into the dielectric surface. 
     Another object of the present invention is to create a copper barrier by strong adhesion with ligand sites binding copper. 
     A further object of the present invention is to create a polymer ‘virtual’ copper barrier that is highly resistant to thermal cycles due to the stability of the polymers. 
     Other objects will appear hereinafter. 
     It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a semiconductor structure including a patterned dielectric layer is provided. The patterned dielectric layer includes an opening and an upper surface. The dielectric layer surface is then passivated to form a passivation layer. A metal plug is formed within the dielectric layer opening. The passivation layer prevents penetration and diffusion of metal out from the metal plug into the semiconductor structure and the patterned dielectric layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the method of the present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate similar or corresponding elements, regions and portions and in which: 
     FIGS. 1 and 4 schematically illustrate in cross-sectional representation structures common to the four embodiments of the present invention. 
     FIG. 2 schematically illustrates in cross-sectional representation a structure common to the first three embodiments of the present invention. 
     FIG. 3 schematically illustrates in cross-sectional representation a structure of the fourth embodiment of the present invention. 
     FIG. 5A is the chemical structure of pyridine. 
     FIG. 5B is the chemical structure of (2-pyridyl)-ethene. 
     FIG. 5C is the chemical structure of (2-pyridyl)-triofluoroethane. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Unless otherwise specified, all structures, layers, etc. may be formed or accomplished by conventional methods known in the prior art. 
     Process Common to Each of the Embodiments 
     Accordingly as shown in FIG. 1, starting semiconductor structure  10  is understood to possibly include a semiconductor wafer or substrate, active and passive devices formed within the wafer, conductive layers and dielectric layers (e.g., inter-poly oxide (IPO), intermetal dielectric (IMD), etc.) formed over the wafer surface. The term “semiconductor structure” is meant to include devices formed within a semiconductor wafer and the layers overlying the wafer. 
     The upper surface of semiconductor structure  10  can be comprised of a dielectric layer, e.g. ILD layer, an ILD layer with conductive plugs exposed, an intermetal layer (IMD), or an IMD layer with metal plugs or lines exposed (not shown). 
     Dielectric layer  12  is formed over semiconductor structure  10 . Dielectric layer  12  has a thickness from about 7000 to 16,000 Å, and more preferably from about 4000 to 8000 Å. Dielectric layer  12  includes upper, outer exposed surface  15 . 
     Dielectric layer  12  may be a CVD low-k dielectric material, a spin-on -dielectric (SOD) material, silicon dioxide (SiO 2  or “oxide”), porous oxide, fluorine-doped oxide, carbon-doped oxide, or boron-phosphosilica glass (PSG). Dielectric layer  12  is preferably porous oxide for the first embodiment, and carbon doped oxide (for example Black Diamond™ available from Applied Materials) for the second, third and fourth embodiments. 
     As shown in FIG. 2, dielectric layer  12  is patterned and etched to form opening  14  that extends to, and contacts the exposed metal plugs or lines on the upper surface of semiconductor structure  10 . Dielectric layer  12  may be patterned by an overlying layer of photoresist (not shown), for example. Upper surface  15  of dielectric layer  12  extends into opening  14 . 
     Opening  14  may be a dual damascene opening as shown in FIG. 2, or another shape such as a single damascene opening. Opening  14  has a minimum opening from about 1000 to 50,000 Å wide, more preferably from about 1000 to 10,000 Å wide, and most preferably from about 1000 to 5000 Å wide. 
     Formation of Generic Passivation Layer  18   
     Exposed surface  15  of etched dielectric layer  12  is then passivated to form passivation layer  18  over dielectric layer  12 . Passivation layer  18  may be formed by one of four methods as detailed below in the respective four embodiments of the invention. Passivation layer  18  is preferably from about 5 to 1000 Å thick, and more preferably from about 5 to 100 Å thick. 
     As shown in FIG. 4, regardless of which method is used to form passivation layer  18 ,  18 ′,  18 ″,  18 ′″, passivation layer  18 ,  18 ′,  18 ″,  18 ′″ becomes a virtual barrier to metal plug  20 . Metal plug  20  may be comprised of copper (Cu), aluminum copper alloy (Al(Cu)), gold (Au), silver (Ag) or aluminum (Al), and is preferably copper (Cu). 
     First Embodiment—Pure Sulfur Treatment 
     In the first embodiment, passivation layer  18  is formed by treating exposed surface  15  of etched dielectric layer  12  with pure sulfur in a thermal process having the parameters: 
     flow rate of sulfur gas: from about 10 to 1000 cm 3 /minute, and more preferably from about 100 to 300 cm 3 /minute; 
     temperature: from about 25 to 500° C., and more preferably from about 25 to 200° C.; and 
     time: from about 10 to 100 seconds, and more preferably from about 10 to 30 seconds. 
     Pure sulfur passivation layer  18  is formed in a separate standard passivation chemical vapor deposition (CVD) chamber with plasma enhanced RF source or remote plasma application. The pure sulfur gas may be obtained from Aldrich Chemicals or Merck. 
     Pure sulfur passivation layer  18  is comprised of SO 3 , SO 2  bonds and is from about 5 to 100 Å thick, and more preferably from about 5 to 25 Å thick. 
     Second Embodiment—Sulfur-Containing Compound Treatment 
     In the second embodiment, passivation layer  18 ′ is formed by treating exposed surface  15  of etched dielectric layer  12  with a sulfur-containing gaseous compound at the following parameters: 
     concentration of sulfur-containing compound: from about 0.5 to 100 at. %, and more preferably from about 10 to 50 at. % 
     temperature: from about 25 to 250° C., and more preferably from about 50 to 100° C.; and 
     time: from about 10 to 300 seconds, and more preferably from about 10 to 60 seconds. 
     The structure is moved to a separate, remote plasma chamber with remote RF source or downstream plasma to form pure sulfur passivation layer  18 ′. This plasma chamber may be a standard plasma asher available in manufacturing line. 
     The sulfur-containing compound may comprise a mixture of NH 4  and H 2 S, and is most preferably H 2 S. 
     Third Embodiment—(NH 4 ) 2 S Solution Treatment 
     In the third embodiment, passivation layer  18 ″ is formed by treating exposed surface  15  of etched dielectric layer  12  with a (NH 4 ) 2 S (aq) solution at the following parameters: 
     concentration of (NH 4 ) 2 S (aqueous) (standard aqueous solution) from about 0.01 to 1 moles/liter, and more preferably 0.05 to 0.5 moles/liters; 
     temperature: from about 25 to 150° C., and more preferably from about 25 to 50° C.; and 
     time: from about 10 to 200 seconds, and more preferably from about 30 to 60 seconds. 
     The structure is moved to a separate chamber for formation of (NH 4 ) 2 S treated passivation layer  18 ″. The separate chamber may be a simple and standard chemical bath with a heater block for temperature control. 
     (NH 4 ) 2 S solution treatment passivation layer  18 ″ is comprised of sulfur terminated bonds and is from about 5 to 50 Å, and more preferably from about 5 to 20 Å. 
     Fourth Embodiment—Surface Modification Through Self-Assembly Technique 
     In the fourth embodiment, the more preferred embodiment because the surface termination with ligand sites  16  has a broader application, passivation layer  18 ′″ is formed by modifying exposed surface  15  of etched dielectric layer  12  through a self-assembly technique. “Self-assembly” implies the spontaneous formation of passivation layer  18 ′″ without any additional processing or deposition. 
     Ligand sites  16  are formed on the exposed surface of etched dielectric layer  12  and within opening  14  at the following parameters: 
     ligand: pyridine (see FIG.  5 A); 
     Criteria for Selecting Ligands 
     additives: hydrogen and fluorine; 
     polymers: (2-pyridyl)-ethene (see FIG. 5B) and (2-pyridyl)-triofluoroethane (see FIG.  5 C); 
     temperature: from about 25 to 500° C., and more preferably from about 200 to 400° C.; and 
     time: from about 10 to 500 seconds, and more preferably from about 30 to 60 seconds. 
     Ligand sites  16  in conjunction with the additives with polymers form passivation layer  18 ′″ that has a strong bonding affinity with copper (Cu) to create a virtual barrier. For example, the following structures illustrate polymers with additives and ligand sites  16 :                           
     Where “L” is the ligand (i.e., e.g. pyridine as shown in FIG. 5A) attached to ligand site  16 . Also see FIGS. 5B (2pyridyl)-ethene) and  5 C (2-pyridyl)-triofluoroethane). 
     These compounds, for example, serve to form passivation layer  18 ′″ as they represent the self-assembly of the polymers on the hydrophilic surface to which the molecules (ligands) bond. These compounds may be formed by: a CVD method with direct plasma, i.e. plasma chemical vapor deposition (PECVD); remote plasma, i.e. downstream CVD; or by a reactor with a high-pressure environment to form the self-assembly of the molecules. 
     Process Common to Each of the Embodiments 
     As shown in FIG. 4, regardless of which embodiment is selected to form passivation layer  18 ,  18 ′,  18 ″,  18 ′″, a layer of metal is deposited over passivation layer  18 ,  18 ′,  18 ″,  18 ′″ and planarized to remove the excess of the metal layer and the portion of passivation layer  18 ,  18 ′,  18 ″,  18 ′″ from the upper horizontal surface of etched dielectric layer  12  to form planarized metal plug  20  within opening  14 . 
     Metal plug  20  may be formed from copper, aluminum, gold, aluminum copper alloy (Al(Cu)), or silver (Ag), and is preferably copper. For purposes of illustration, metal plug  20  will be considered to be formed of copper hereafter. 
     Passivation layer  18 ,  18 ′,  18 ″,  18 ′″ serves as a virtual barrier layer against the migration of copper from copper plug  20  into etched dielectric layer  12  and semiconductor structure  10  by, in effect, creating copper traps. 
     Advantages of the Present Invention 
     The present invention: 
     strongly passivates the exposes etch dielectric layer  12  with sulfur or sulfur containing compounds in the first, second and third embodiments to form passivation layer  18 ,  18 ′,  18 ″; 
     in the fourth embodiment, allows for strong adhesion with ligand sites  16  binding copper so as to create a virtual Cu barrier (passivation layer  18 ′″); and 
     in the fourth embodiment, the resulting structure is highly resistant to thermal cycles due to stable polymer. 
     While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.