Abstract:
An interconnect structure and barrier layer for electrical interconnections is described incorporating a layer of TaN in the hexagonal phase between a first material such as Cu and a second material such as Al, W, and PbSn. A multilayer of TaN in the hexagonal phase and Ta in the alpha phase is also described as a barrier layer. The invention overcomes the problem of Cu diffusion into materials desired to be isolated during temperature anneal at 500° C.

Description:
This is a continuation, of application Ser. No. 08/497,065 filed Jun. 30, 1995, abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to metal interconnects and more particularly to a metal diffusion barrier and liner for VLSI and ULSI metal interconnects, studs, for CMOS gate stacks on semiconductor chips, and for electrical interconnections in packaging and display devices. 
     BACKGROUND OF THE INVENTION 
     On VLSI and ULSI semiconductor chips, Al and alloys of Al are used for conventional chip wiring material. The incorporation of Cu and alloys of Cu as a chip wiring material results in improved chip performance and superior reliability when compared to Al and alloys of Al. However, Cu must be successfully isolated from the devices formed in the silicon substrate below and from the surrounding back end of the line (BEOL) insulators. To accomplish this isolation i.e. to prevent diffusion of Cu, a thin liner material is deposited on the patterned BEOL insulator, e.g. trenches formed in the Damascene process, or unpatterned insulator e.g. Cu reactive ion etching (RIE) or through mask Cu deposition process before the Cu is deposited. The thin film liner must also serve as adhesion layer to adhere the copper to the surrounding dielectric. Adhesion of copper directly to most insulators is generally poor. 
     TiN has been evaluated as a Cu barrier and has been reported in the literature as a barrier for Cu interconnects in SiO 2 . In a publication by S-Q Wang, MRS Bulletin 19, 30, (1994) entitled “Barriers against copper diffusion into silicon and drift through silicon dioxide”, various barrier systems including TiN are shown for placement between Si/SiO 2  and Cu. TiN has good adhesion to SiO 2 . However, Cu adheres poorly to TiN. A very thin glue or adhesion layer of Ti may be used to enhance the adhesion of Cu to TiN; however, this Ti layer drastically degrades the conductivity of the copper film during subsequent thermal processing. In addition, TiN has been known to form a corrosion couple with copper in certain copper polishing slurries used in chemical mechanical polishing (CMP). 
     Unlike TiN, pure or oxygen-doped Ta adheres poorly to some insulators such as SiO 2 . It also forms the high-resistivity beta-phase Ta when deposited directly on the insulator. Furthermore, the Cu barrier properties of Ta fail when it is in contact with Al at moderate temperatures. See for example, the publication by C. -K Hu et al., Proc. VLSI Multilevel Interconn. Conf. 181, (1986) which described an investigation of diffusion barriers to Cu wherein tantalum, silicon nitride and titanium nitride were found to be the good diffusion barriers to Cu. It is reported that oxygen in the Ta films may have inhibited Cu diffusion. 
     In a publication by L. A. Clevenger et al., J. Appl. Phys. 73, 300 (1993), the effects of deposition pressure, in situ oxygen dosing at the Cu/Ta interface, hydrogen and oxygen contamination and microstructure on diffusion barrier failure temperatures for HV and UHV electron-beam deposited Ta thin films penetrated by Cu were investigated. 
     Ta 2 N has been proposed as a good copper diffusion barrier, but its adhesion to BEOL insulators and copper is relatively poor. In contrast, the adhesion of TaN (N 18  50%) is adequate, while the adhesion of Cu to TaN is poor. A thin Ta layer can be used to enhance the adhesion of Cu to TaN, without the Ta degrading the performance of Cu BEOL. Such a dual-component liner has been previously disclosed in U.S. Pat. No. 5,281,485 Jan. 25, 1994 to E. G. Colgan and P. M. Fryer. However, the resistivity of this Ta(N) is at least 1200 Micro Ohm-cm, which leads to larger vias or stud resistances, and the inability of the metal liner to act as a redundant current strap or path. 
     For deep-submicron vias (e.g. less than 0.5 um wide) with  ˜ 250 Å liner at the bottom, the series resistance of the above Ta-based liners is in the range from 1 to 5 Ohms. By contrast, the copper stud resistance would be less than 10% of the Ta based liner. Although these via resistances compare very favorably with those of Al(Cu)/W-stud values, it is desirable to reduce them below the 1 Ohm range. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a barrier layer is provided comprising a layer of TaN in the hexagonal phase positioned between a first material to be confined and a second material whereby the second material is isolated from said first material. The first material may be one or a combination of Cu, Al, W and PbSn. 
     The invention further provides a layer of TaN in the hexagonal phase which may be positioned between the gas WF6 and a second material to be isolated from the first material. 
     The invention further provides an interconnect structure comprising a first insulation layer having an upper and lower surface and having a plurality of grooves formed in the upper surface, some of the grooves having regions extending to the lower surface to expose respective conducting surfaces in a second interconnect structure below the first insulation layer, a liner including a layer of TaN in the hexagonal phase formed on the sidewalls and bottom of the plurality of grooves and on the exposed respective conducting surfaces, and a metal formed in the plurality of grooves to substantially fill the plurality of grooves. 
     The invention further provides a liner or barrier layer for VLSI/ULSI interconnects and C4 solder bumps made mostly of Pb—Sn which simultaneously achieves good diffusion barrier performance, good adhesion to BEOL insulators, good adhesion of interconnect metal to this liner, low resistivity, and good conformality in trenches and vias. The interconnects and studs may comprise aluminum, copper, tungsten, or C4 solder balls made of lead-tin alloy. 
     The invention provides a liner composed of predominately highly oriented and non-highly oriented (random) hexagonal phase TaN (30-60% nitrogen) (which may contain up to 50% cubic phase TaN) deposited alone or as a thin film laminate in combination with other suitable metal films such as Ta. Preferably, the TaN is 100% hexagonal phase. 
     The liner material described above provides a high integrity barrier, low stress, low resistivity and excellent adhesion to both metal and various dielectrics, such as polymers, silicon dioxide, BPSG, and diamond-like carbon and isolates lead-tin solder metallurgy from Cu and Al interconnects. 
     The invention further provides a thin film material for isolating Al wiring levels from an immediate Cu interconnection level above or below. 
     The invention further provides a liner which isolates a metal layer of W, Cu, alloys of Cu, Al and alloys of Al from the contact silicide (WSi 21  , CoSi 2 , TiSi 2 , TaSi 2  and PtSi) and polycrystalline silicon in a MOSFET (metal oxide semiconductor field effect transistor) gate stack. 
     The invention further provides a liner to shield existing metal from certain gases such as WF 6 , which is corrosive and used as a precursor gas for the deposition of W. 
     The invention further provides a liner which provides good contact resistance to preceding levels of metal, such as aluminum in BEOL wiring. 
     The invention further provides a liner which provides markedly better conformality than Ti-based compounds even without collimation sputtering or chemical vapor deposition (CVD). 
     The invention further provides a thin film to isolate BEOL interconnect metals from alloying or mixing with the lead-tin in for example, C4 solder balls. 
     The invention further provides a liner material exhibiting good conformality when deposited in trenches and vias of BEOL structures. 
     The invention further provides a liner material which will not form a corrosion couple with Cu, Al, or W during or after chemical mechanical polishing of the liner material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     These and other features, objects, and advantages of the present invention will become apparent upon consideration of the following detailed description of the invention when read in conjunction with the drawing in which: 
     FIG. 1 is a cross section view of one embodiment of the invention. 
     FIG. 2 is a cross section view of a second embodiment of the invention. 
     FIG. 3 is a cross section view of a third embodiment of the invention. 
     FIG. 4 is a cross section view of a fourth embodiment of the invention. 
     FIG. 5 is a graph of an X-ray diffraction pattern for a TaN (hexagonal) film. 
     FIG. 6 is a Transmission Electron Microscope (TEM) micrograph of a diffraction pattern from TaN (hexagonal) film. 
     FIG. 7A is a Transmission Electron Microscope (TEM) micrograph of the same highly oriented TaN (hexagonal) film used to provide the X-ray diffraction pattern of FIG.  5 . 
     FIG. 7B is a Transmission Electron Microscope (TEM) micrograph of non-highly oriented (random) TaN (hexagonal) film. 
     FIG. 8 is a graph of the resistance versus temperature profile of a SiO 2 /Cu/TaN (hexagonal)/Al layered structure. 
     FIG. 9 is a cross-section view of a liner of TaN (hexagonal) for isolating Cu from Al. 
     FIG. 10 is a cross section view of a fifth embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawing and more particularly to FIG. 1, a cross section view of interconnect structures  10  and  18  is shown. Interconnect structure  10  includes a layer of insulation  12  having a lower surface  13  and an upper surface  14 . A plurality of grooves or trenches  15  are formed in upper surface  14  of insulation layer  12 . The plurality of grooves  15  may correspond to a wiring layer of a semiconductor chip  16 . Additional interconnect structures may be provided to complete the interconnections for a semiconductor chip  16 . Vias or stud openings  11  are formed at the bottom  17  of grooves  15  in selected regions to make contact to conducting surfaces in a second interconnect structure  18  below the insulation layer  12 . 
     Interconnect structure  18  has a conductor  19  in a groove  20  in insulation layer  21 . A liner  22  is shown between conductor  19  and the bottom and sidewalls of groove  20 . 
     A liner  23  of TaN (hexagonal) is formed in grooves  15  on the sidewalls  27  and bottom  17  followed by formation of metal  24  in grooves  15  to substantially fill grooves  15 . Metal  24  may be Cu, Al, W and alloys thereof. Metal  24  may be formed by sputtering, physical vapor deposition (PVD), chemical vapor deposition (CVD) or electroplating. Liner  23  may be formed by sputtering in an atmosphere of nitrogen. Liner  23  may include a second layer of Ta (alpha phase) formed adjacent to such as over TaN (hexagonal). Insulation layer  12  as well as insulation layer  21  may be for example SiO 2 , Si 3 N 4 , polymer such as polyimide, diamond-like carbon (DLC) and Fluorinated diamond-like carbon (F-DLC). 
     Where liner  23  is a highly oriented layer of TaN in the hexagonal phase, the resistivity will be in the range from 150 to 300 micro ohm-cm. Where liner  23  is a non-highly oriented layer of TaN in the hexagonal phase, the resistivity will be greater than 300 micro ohm-cm. Where a layer of Ta in the alpha phase is formed adjacent the TaN (hexagonal), the resistivity of the Ta (alpha phase) will be in the range from 15 to 60 micro ohm-cm. 
     FIG. 2 is a cross section view of interconnect structure  34 . FIG. 2 shows a semiconductor substrate  16  which may be for example Si, SiGe, Ge, or GaAs. Above substrate  16  may be a layer of insulation  35  which may be for example silicon dioxide. A layer of insulation  36  may be formed over layer of insulation  35  having a groove or trench  38  formed therein filled with metal  24 . Layer of insulation  36  and metal  24  may have a coplanar upper surface  39  formed by chemical-mechanical polishing (CMP). A layer of insulation  40  is formed on upper surface  39 . A groove or trench  42  is formed in layer of insulation  40  down to metal  24 . A liner  23  is formed on the sidewalls and bottom of groove  42  and on the upper surface  43  of layer of insulation  40  (not shown). Groove or trench  42  is filled with metal  46  over liner  23  and on the liner on upper surface  43  (not shown). The excess metal  46  and liner  23  are removed by CMP to provide a planarized upper surface  43  as shown in FIG.  2 . In FIG. 2, metal  24  may be for example Al and metal  46  may be tungsten. 
     FIG. 3 is a cross section view of interconnect structure  50 . In FIG. 3, semiconductor substrate  16  has an insulation layer  52  thereover which may be formed by thermal oxidation. A layer  54  of insulation is formed on upper surface  53  on insulation layer  52 . A groove or trench  56  is formed in insulation layer  54  and filled with metal  24  and may be for example Al. Insulation layer  54  and metal  24  may have a coplanar upper surface  58  formed by CMP. A layer  12  of insulation is formed on upper surface  58 . Layer  12  has an upper surface  14 . A groove  15  and via  11  is formed in upper surface  14 . A liner  23  is formed on sidewalls  27  and bottom  17  of groove  15  and via or stud  11 . Metal  24  is formed over liner  23  in groove  15  and via or stud  11 . Upper surface  14  is planar which may be formed by CMP. A layer of insulation  62  is formed on upper surface  14 . An opening  64  is formed in layer  62  to expose metal  24 ′. Liner  23 ′ is formed on the sidewalls  65  of opening  64  and on exposed metal  24 ′. A blanket metal layer  66  is formed on upper surface  67  on insulation layer  62  and metal  24 ′. Blanket metal layer  66  is etched through a mask not shown to form a metal pattern for wiring or interconnects. In FIG. 3, metal layer  66  may be for example Al. Metal  24 ′ may be for example Cu and metal  24  may be for example Al. 
     Thus as shown in FIG. 3, liner  23  separates metal  24  and  24 ′ and liner  23 ′ separates metal  24 ′ and metal  66 . 
     FIG. 4 is a cross section view of interconnect structure  70 . In FIG. 4, substrate  16  has a layer of insulation  72  thereover which may be for example silicon dioxide. Interconnect structure  12  is formed over layer of insulation  72 . Insulation layer  62  is formed on upper surface  14 . An opening  64  is formed in layer  62  to expose metal  24 ′. Liner  23 ′ is formed on the sidewalls  65  of opening  64  and on exposed metal  24 ′. A C4 contact bump  74  of mostly Pb—Sn is formed on liner  23 ′ in opening  64 . The C4 bump is manufactured by the IBM Corp on integrated circuit chips for making interconnections. The C4 bump extends above the integrated circuit chip by about 0.125 millimeters and is round or circular in cross-section parallel to the plane of the upper surface of the integrated circuit chip and is curved from its sides to the top surface of the bump where an interconnection is made to another electrode supported by a substrate. 
     In FIGS. 2-4, like references are used for functions corresponding to the apparatus of FIG. 1 or of an earlier FIG. than the FIG. being described. 
     FIG. 5 is a graph of an X-ray diffraction pattern for a TaN (hexagonal phase) film formed by physical vapor deposition (PVD). The following PVD arrangement was used to provide highly-oriented and non-oriented TaN (hexagonal) films. The TaN (hexagonal) films were reactively sputter deposited using a magnetron system in either the direct current or radio frequency mode i.e. dc or rf mode. The highly oriented and non-oriented TaN (hexagonal) films made under the above conditions had resistivities in the range from 150 to 800 micro ohm-cm. In FIG. 5, the ordinate represents intensity and the abscissa represents two theta. Curve  76  shows the X-ray diffraction pattern for two films; the first film has a high degree of preferred orientation and the second film is a non-oriented film. Curve portion  78  shows a single peak at about 37 degrees. 
     FIG. 6 is a Transmission Electron Microscope (TEM) diffraction pattern of a TaN (hexagonal phase) highly oriented film previously measured with X-rays in FIG.  5 . The micrograph confirms the hexagonal structure of the TaN barrier showing rings indexed to the hexagonal phase. 
     FIG. 7A is a Transmission Electron Microscope (TEM) micrograph of a TaN (hexagonal phase) film previously measured with X-rays in FIG.  5 . The micrograph shows hexagonal TaN grains which are highly oriented and approximately 20-30 nm in size. 
     FIG. 7B is a Transmission Electron Microscope (TEM) micrograph of a TaN (hexagonal phase) film. The micrograph show hexagonal TaN grains which are randomly oriented and also approximately 20-30 nm in size. 
     FIG. 8 is a graph of the resistance versus temperature provided of a SiO 2 /Cu/TaN (hexagonal)/Al multilayer structure. In FIG. 8, the ordinate represents resistance in ohms/square and the abscissa represents Temperature in degrees Centigrade. Curve  80  shows the resistance with increasing temperature and curve  82  shows the resistance with decreasing temperature. Curves  80  and  82  provide evidence of the effectiveness of TaN (hexagonal) in isolating Cu from Al up to temperatures greater than 500 degrees Centigrade. 
     FIG. 9 is a cross-section view of a liner of TaN (hexagonal) to isolate Cu from Al. In FIG. 9, an interconnect structure is shown with a layer of Al(Cu)  84 , insulation layer  85  of SiO 2 , and opening or via  86  with a liner  87  on the bottom and sidewalls. Opening  86  is filled with Cu  88  inside liner  87 . The excess liner  87  and Cu  88  is removed to form upper surface  89  on insulation layer  85  and upper surface  90  of Cu  88  by CMP. After a temperature anneal at 500 degrees Centigrade for 6 hours, the integrity and the definition of liner  87  remains showing no penetration of Cu through liner  87  to the Al(Cu) layer. 
     FIG. 10 is a cross-section view which depicts the disclosed TaN(hexagonal) barrier used between the silicide gate contact and the W stud in a P-MOSFET (P-type metal oxide semiconductor field effect transistor). 
     Ta(N) has the advantage as published in U.S. Pat. No. 5,281,485 by Colgan et al. which issued Jan. 15, 1994 that it acts to seed only the low-resistivity alpha phase Ta (rho=15 to 60 micro ohm-cm), in contrast to the higher-resistivity beta phase Ta. By using TaN (hexagonal), the resulting via resistances for deep-submicron copper vias with a composite TaN (hexagonal)/ alpha phase Ta liner would be in the resistivity range from 0.25 to 1 Ohms. This resistivity is a substantial improvement, about 5 times better, over the previous copper via systems using Ta alone or another material. The resistivity is probably an order of magnitude better than the Al(Cu)/W via system presently used by some major semiconductor manufacturers. 
     While there has been described and illustrated a barrier layer and an interconnect structure containing a layer of TaN (hexagonal phase) alone or with a second layer of Ta (alpha phase), it will be apparent to those skilled in the art that modifications and variations are possible without deviating from the broad scope of the invention which shall be limited solely by the scope of the claims appended hereto.