Abstract:
A new method is provided for the creation of copper interconnects. A pattern of copper interconnects is created, a protective layer of semiconductor material is deposited over the surface of the created copper interconnects. The protective layer is patterned and etched, exposing the surface of the pattern of copper interconnects. The exposed copper surface is Ar sputtered after which a first barrier layer is deposited. The patterned and etched layer of protective material is removed, leaving in place overlying the pattern of copper interconnects a protective layer of first barrier material. A dielectric barrier layer, in the form of a layer of etch stop material, is deposited after which additional layers of dielectric interspersed with layers of etch stop material are deposited. Via and trench patterns are etched aligned with a copper pattern to which an electrical contact is to be established, the copper pattern being protected by the first layer of barrier material. A second barrier layer is deposited, the via and trench pattern is filled with copper after which excess copper is removed by polishing the surface of the deposited layer of copper.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    (1) Field of the Invention  
           [0002]    The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method for providing a protective layer over the surface of a created copper interconnect.  
           [0003]    (2) Description of the Prior Art  
           [0004]    An important aspect in the creation of semiconductor devices is the interconnect metal that is provided between elements of semiconductor devices or between semiconductor devices. Interconnect metal typically comprises metal conductive lines and vias that provide the interconnection of integrated circuits in semiconductor devices and/or the interconnections in a multilayer substrate over the surface of which semiconductor devices are mounted. Frequently used processes for the creation of conductive interconnects are the single damascene and the dual damascene processes. In fabricating Very and Ultra Large Scale Integration (VLSI and ULSI) circuits with the dual damascene process, a layer of insulating or dielectric material, comprising for instance silicon oxide, is patterned with several thousand openings. These openings form the pattern for the conductive lines and vias, which are filled at the same time with metal, such as typically aluminum but more recently copper. The pattern of conductive lines and vias serves to interconnect active and passive elements of an integrated circuit. The dual damascene process also is used to form multilevel conductive lines of metal, such as copper, in layers of insulating material, such as polyimide, using therewith multi-layer substrates over the surface of which semiconductor devices are mounted.  
           [0005]    Single damascene is an interconnection fabrication process in which grooves are formed in an insulating layer and filled with metal to form the conductive lines. Dual damascene is a multi-level interconnection process in which, in addition to forming the grooves of the single damascene process, conductive via openings also are formed. In the standard dual damascene process, the insulating layer is coated with a layer of photoresist. The coated layer of photoresist is first exposed through a first mask with an image pattern of the via openings, the via pattern is anisotropically etched in the upper half of the insulating layer. The photoresist now is second exposed through a second mask with an image pattern of conductive lines after the second exposure has been aligned with the first exposure pattern in order to encompass the via openings. In anisotropically etching the openings for the conductive lines in the upper half of the insulating material, the via openings that have previously been created in the upper half of the insulating layer are simultaneously etched and replicated in the lower half of the insulating material. After the etching of the conductive lines and the vias is complete, both the vias and line openings are filled with metal.  
           [0006]    The dual damascene process is an improvement over the single damascene process because the dual damascene process permits the filling of both the conductive grooves and vias with metal at the same time, thereby eliminating processing steps. Although the standard damascene process offers a number of advantages over other processes for forming interconnections, it has a number of disadvantages. For instance, the dual damascene process requires two masking steps to form the pattern, a first mask for the vias and a second mask for the conductive lines. Further, the edges of the via openings in the lower half of the insulating layer, after the second etching, tend to be poorly defined because of the two etchings. In addition, since alignment of the two masks is critical in order for the pattern of the conductive lines to be aligned with the pattern of the vias, a relatively large tolerance is provided resulting in via openings that do not extend over the full width of the conductive line.  
           [0007]    Copper is gaining increased use as an interconnect metal due to its low cost and low resistivity. Copper however has a relatively large diffusion coefficient into a surrounding dielectric material such as silicon dioxide and silicon. Copper, which is used as an interconnect medium, therefore readily diffuses into the silicon dioxide layer causing the dielectric to become conductive and decreasing the dielectric strength of the silicon dioxide layer. Copper interconnects are therefore typically encapsulated by at least one diffusion barrier to prevent diffusion into the surrounding silicon dioxide layer. Copper is also well known to be very sensitive to surface exposure, typically resulting in oxidation of the exposed copper surface.  
           [0008]    The invention addresses concerns of creating copper interconnects and, more specifically, the negative impact that is experienced by an exposed surface of created copper interconnects.  
           [0009]    U.S. Pat. No. 6,180,516 B1 (Hsu) shows a lift off process for a barrier layer in a dual damascene process.  
           [0010]    U.S. Pat. No. 5,689,140 (Shoda) shows a lift off process for a barrier layer in a dual damascene process.  
           [0011]    U.S. Pat. No. 6,202,191 (Filippi et al.) shows a lift off process for an inductor.  
           [0012]    U.S. Pat. No. 6,281,127 B1 (Shue) shows a self passivation process for a dual damascene interconnect.  
           [0013]    U.S. Pat. No. 6,274,499 (Gupta et al.) shows a cap over an interconnect.  
           [0014]    U.S. Pat. No. 6,258,713 B1 (Yu et al.) discloses a dual damascene with a cap.  
         SUMMARY OF THE INVENTION  
         [0015]    A principle objective of the invention is to provide a method of creating copper interconnect metal whereby the created interconnect metal is not affected by chemicals or other elements that are present in the environment.  
           [0016]    Another objective of the invention is to provide a protective cap of semiconductor material over the surface of a created copper interconnect metal.  
           [0017]    In accordance with the objectives of the invention a new method is provided for the creation of copper interconnects. A pattern of copper interconnects is created, a protective layer of semiconductor material is deposited over the surface of the created copper interconnects. The protective layer is patterned and etched, exposing the surface of the pattern of copper interconnects. The exposed copper surface is Ar sputtered after which a first barrier layer is deposited. The patterned and etched layer of protective material is removed, leaving in place overlying the pattern of copper interconnects a protective layer of first barrier material. A dielectric barrier layer, in the form of a layer of etch stop material, is deposited after which additional layers of dielectric interspersed with layers of etch stop material are deposited. Via and trench patterns are etched aligned with a copper pattern to which an electrical contact is to be established, the copper pattern being protected by the first layer of barrier material. A second barrier layer is deposited, the via and trench pattern is filled with copper after which excess copper is removed by polishing the surface of the deposited layer of copper.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a cross section of the surface of a semiconductor substrate over the surface of which copper points of electrical contact have been provided in a layer of dielectric.  
         [0019]    [0019]FIG. 2 is a cross section after a layer of semiconductor material has been deposited over the surface of the layer of dielectric.  
         [0020]    [0020]FIG. 3 shows the formation of a photoresist mask.  
         [0021]    [0021]FIG. 4 show the result of etching the layer of semiconductor material in accordance with the photoresist mask, the photoresist mask has been removed.  
         [0022]    [0022]FIG. 5 shows a cross section during the process of argon sputter.  
         [0023]    [0023]FIG. 6 shows a cross section after deposition of a layer of barrier material.  
         [0024]    [0024]FIG. 7 shows a cross section after lift-off of the patterned and etched layer of semiconductor material.  
         [0025]    [0025]FIG. 8 shows a cross-section after deposition of a layer of etch stop material.  
         [0026]    [0026]FIG. 9 shows a cross section after deposition of additional layers of dielectric and etches stop material.  
         [0027]    [0027]FIG. 10 shows a cross section after patterning and etching of the deposited additional layers of dielectric and etch stop material, creating an opening there through.  
         [0028]    [0028]FIG. 11 shows a cross section after deposition of a second layer of barrier material.  
         [0029]    [0029]FIG. 12 shows a cross section after the opening has been filled with metal, the excess metal and the second barrier material have been removed from the surface of the upper layer of dielectric. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    Using the current copper dual damascene process, the surface of the copper to which damascene interconnect plugs must be formed is exposed after via and trench etch. This exposed copper surface, when exposed to the processing environment and the therein present elements, is attacked by components of the etching chemistry, by photoresist strip, by post-etch via/trench cleaning chemistry and by oxidation in the air. This exposure of the copper surface results in a deterioration of the copper surface, having a negative impact on the performance of the copper interconnect metal. In addition, conventional argon (Ar) sputtering that precedes the deposition of copper barrier and the copper fill, removes copper atoms from the exposed copper surface resulting in copper deposits over the lower extremities of the openings that have been created for the vias and interconnect trenches. These copper deposits readily diffuse into surrounding dielectrics and form a source of leakage currents from the copper interconnect metal to surrounding circuit or device elements.  
         [0031]    The invention provides a process that first covers the surface of a pattern of copper interconnect with a layer of barrier material after which overlying layers of metal interconnect are formed. This process will now be explained in detail using FIGS. 1 through 12 for this purpose.  
         [0032]    Referring now specifically to FIG. 1, there is shown a cross-section of a semiconductor substrate  10  over the surface of which a pattern of copper interconnect metal has been formed. Specifically highlighted in the cross section of FIG. 1 are a layer  13  of dielectric through which the pattern  12 / 14  of copper interconnect metal has been formed. The surface of layer  13  has been polished after the copper for pattern  12 / 14  has been deposited.  
         [0033]    The invention continues, FIG. 2, with the deposition of a layer  16  of semiconductor material over the surface of the layer  13  of dielectric, including the surface of the interconnect pattern  12 / 14 .  
         [0034]    Preferred materials for the layer  16  of semiconductor material are photoinimide, polyimides, polymers or other dielectric materials. It is well known in the art that organic polymer is taken from the group consisting of poly(arylene ether) and a polyimide, and is used as an inter-metal-dielectric. As an example of the deposition of a layer  16  can be cited depositing a layer of polymer at a pressure of between about 25 and 2.75 Torr in a plasma containing CHF 3  at a flow rate of about 18 sccm, CF 4  at a flow rate of about 72 sccm and He at a flow rate of about 165 sccm, deposited for a time of about 10 seconds and to a thickness between about 200 and 300 Angstrom.  
         [0035]    For layer  16  for instance can be used a low-k polymer material including polyimides, fluorinated polyimides, polysilsequioxane, benzocyclobutene (BCB), parlene F, parlene N and amorphous polytetrafluorothylene. A polymer film can be spun onto the wafer and can contain polycarbonate (PC), polystyrene (PS), polyoxides (PO), polymethylmethacrylate (PPMA) and poly-polyoxides (PPO). It is important to use a material for the polymer film that can be applied by spin coating and that can, at a later date, be easily removed by dipping the coated semiconductor package in a solvent. Solvents that can be used for this purpose include acetone, THF and trichloro-methane.  
         [0036]    The layer  16  of semiconductor material is next patterned and etched, using for this purpose a photoresist mask  18 , FIG. 3, having a pattern that exposes the surface of layer  16  by means of openings  15 / 17  there-through, opening  15 / 17  align with the interconnect pattern  12 / 14 . Conventional methods of photolithographic exposure and development are applied for the creation of the photoresist mask  18  shown in cross section in FIG. 3.  
         [0037]    The layer  16  of semiconductor dielectric is now etched, FIG. 4, after which the photoresist mask  18  is removed from the surface of the patterned and etch layer  16  using methods of photoresist ashing following by a thorough surface clean.  
         [0038]    The etching of layer  16  of dielectric such as polysilicon can be accomplished by using an anisotropic plasma etch, for example a Reactive Ion Etch (RIE), using as etchant gasses a gas such as hydrogen bromide (HBr) or chlorine (Cl 2 ) and a carrier gas such as argon (Ar) with as preferred gasses SF 6  and HBr.  
         [0039]    Conventional processing parameters for the etch of layer  16  of dielectric can be applied: etchant comprising a mix of C 4 F 8  to CO with the C 4 F 8  being provided at a temperature of between about 50 and 70 degrees C. and a pressure between about 50 and 60 mTorr and a flow rate of between about 12 and 16 sccm. The CO gas is processed at a temperature of between about 50 and 70 degrees C. and a pressure of between about 50 and 60 mTorr and a flow rate of between about 300 and 400 sccm. The mix of C 4 F 8  to CO has a ratio of between about 1/20 and 1/30.  
         [0040]    The surface of the structure shown in cross section in FIG. 4 is now ion bombarded (pre-barrier metal argon sputter  20 , FIG. 5), using Ar as sputtering ions at a temperature of about 25 to 150 degrees C. and a pressure of about 100 to 150 mTorr for a time duration of about 5 to 10 seconds, the sputter process being time controlled. This Ar ion bombardment dislodges a number of copper atoms from the exposed surface of copper pattern  12 / 14 , these dislodged copper atoms form thin layers of copper deposits  21  over the lower extremities of sidewalls of the openings  15 / 17  created through the layer  16  of dielectric material.  
         [0041]    This deposition of barrier material over the surface areas of openings  31  results in improved adhesion of the thereover deposited metal that is deposited to fill openings  31 , facilitating this process of metal deposition. The Ar sputter is therefore followed by the deposition of a layer  22  of barrier material as shown in cross section in FIG. 6.  
         [0042]    Barrier layer  22  is formed of a material selected from the group consisting of without however being limited thereto tungsten, Ti/TiN:W (titanium/titanium nitride:tungsten), titanium-tungsten/titanium or titanium-tungsten nitride/titanium or titanium nitride or titamium nitride/titanium, tantalum, tantalum nitride, tantalum silicon nitride, niobium, molybdenum, aluminum, aluminum oxide (Al x O y )  
         [0043]    As a material for the layer  22  of barrier material is selected a material that is:  
         [0044]    electrically conductive  
         [0045]    copper compatible  
         [0046]    isolation dielectric compatible  
         [0047]    chemically stable, and  
         [0048]    resistant to interaction with processing chemicals.  
         [0049]    As an example of the creation of layer  22  can be cited depositing a layer of SiN using PECVD in a temperature range of between 200 and 500 degrees C. to a thickness of between about 50 and 1000 Angstrom. Another example of depositing a barrier layer over a damascene structure by depositing a layer of SiN under a temperature between about 200 and 500 degrees C., a pressure between about 1 mTORR and 100 TORR, a time between about 2 and 100 seconds, an environment of SiH 4 +NH 3 +N 2  or Si 2 H 6 +NH 3 +N 2  or SiH 4 +N 2 +Ar using a plasma or thermal process.  
         [0050]    Next, the layer  16 , FIG. 6, of semiconductor material is removed (“polymer lift-off”) from the surface of the layer  13  of dielectric, the results of which are shown in cross section in FIG. 7. Remaining in place are the layers  22  of barrier material overlying the copper pattern  12 / 14 , these layers  22  form protective layers of the surface of the copper interconnect pattern  12 / 14 .  
         [0051]    The lift-off the polymer and the Ta that is overlaid over the polymer, acetone or any other solvent may be used.  
         [0052]    A layer  24 , FIG. 8, of etch stop material is then deposited over the surface of the structure shown in cross section in FIG. 7. Etch stop layers, typically comprising silicon nitride, are used to control the depth of the etch that is performed through a layer of dielectric. The method of choice that is most frequently used to create openings uses photolithography whereby a pattern that is contained in an exposure mask is transferred to a radiation sensitive medium, such as photoresist.  
         [0053]    Layer  24  of etch stop material may for instance comprise oxynitride or silicon nitride and is preferably deposited using methods of LPCVD or PECVD or HDCVD or sputtering or High Density Plasma CVD (HDPCVD). An etch stop layer  24  of silicon nitride (Si 3 Ni 4 ) can be deposited using PECVD procedures at a pressure between about 200 mTorr and 400 mTorr, at a temperature between about 350 and 450 degrees C., to a thickness of about 1,000 to 5,000 Angstrom using NH 3  and SiH 4  or SiC 12 H 2 . A silicon nitride layer  24  can also be deposited using LPCVD or PECVD procedures using a reactant gas mixture such as dichlorosilane (SiC 12 H 2 ) as a silicon source material and ammonia (NH 3 ) as a nitrogen source, at a temperature between about 600 and 800 degrees C., at a pressure between about 300 mTorr and 400 mTorr, to a thickness between about 1,000 and 5,000 Angstrom.  
         [0054]    Next, layers of dielectric interspersed with etch stop material are deposited as shown in the cross section of FIG. 9. Specifically shown in the cross section of FIG. 9 are a first layer  26  of dielectric, a second layer  27  of etch stop material (with layer  24  being a first layer of etch stop material) and a second layer  28  of dielectric. For the layers  26  and  28  of dielectric can be used conventional materials used for the isolation of conductors from each other and from underlying conductive elements, a suitable dielectric being, for instance silicon dioxide (“oxide”, doped or undoped) or silicon nitride (“nitride”), silicon oxynitride, fluoropolymer, parylene, polyimide, tetra-ethyl-ortho-silicate (TEOS) based oxides, boro-phosphate-silicate-glass (BPSG), phospho-silicate-glass (PSG), boro-silicate-glass (BSG), oxide-nitride-oxide (ONO), plasma enhanced silicon nitride (PSiNx), oxynitride. A low dielectric constant material, such as hydrogen silsesquioxane. HDP-FSG (high-density-plasma fluorine-doped silicate glass) is a dielectric that has a lower dielectric constant than regular oxide.  
         [0055]    The most commonly used and therefore the preferred dielectrics of layers  26  and  28  are silicon dioxide (doped or undoped), silicon oxynitride, parylene or polyimide, spin-on-glass, plasma oxide or LPCVD oxide.  
         [0056]    Layers  26 ,  27  and  28  are deposited in preparation for the creation of a contact opening through these layers, the created contact opening is aligned with copper pattern  14  as shown in the cross section of FIG. 10. Conventional methods of photolithographic exposure and development are applied for the etch of the opening  29  through the layers  28 ,  27 ,  26  and  24 . Shown in the cross section of FIG. 10 are deposits  30  created in this instance by the etch for the creation of opening  29 , which dislodges a number of copper atoms from the exposed surface of copper pattern  14 . These dislodged copper atoms form thin layers  30  of copper deposits over the lower extremities of sidewalls of the opening  29 .  
         [0057]    A second barrier layer  30 , FIG. 11, is next deposited over inside surfaces of opening  29  and the surface of layer  28  of dielectric, using the same criteria of material selection and deposition conditions as previously have been highlighted for the creation of the first barrier layer  22 , FIG. 6. This is followed by, FIG. 12, the deposition using methods of Electro Chemical Plating (ECP) copper and copper Chemical Mechanical Polishing (CMP).  
         [0058]    Typical ECP processing parameters are as follows: temperature between about 25 and 50 degrees, the source of deposition of the H 2 SO 4  is the dilution of H 2 SO 4 , CuSO 4  and HCl with a deposition flow rate of between about 15K and 20 K sccm and a deposition time of between about 1 and 10 minutes, the voltage applied to the anode between about 0.1 and 2 volts and the voltage applied to the cathode between about 0.1 and 2 volts.  
         [0059]    The ECP process creates the metal plug in a well-controlled manner due to the fact that ECP Cu deposits Cu only on places that have a Cu seed, without the Cu seed the ECP bath does not deposit Cu. It may therefore be of advantage to the process of the invention to further deposit a seed layer (not shown) over the layer  30 , FIG. 11, of copper barrier material.  
         [0060]    From the above detailed description of the invention, it is clear that the invention has provided a method for the protection of a copper surface during processing steps of creating an opening overlying the copper surface. Barrier layer  22 , FIG. 7, serves this function of copper surface protection. The method of polymer lift-off has been used for the creation of the barrier layer overlying the copper surface.  
         [0061]    Although the invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended that the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the spirit of the invention. It is therefore intended to include within the invention all such variations and modifications which fall within the scope of the appended claims and equivalents thereof.