Multilayer diffusion barrier for copper interconnections

[0001] This application is a divisional of U.S. patent application Ser. No. 09/587,465 filed Jun. 5, 2000, and entitled, “Method of Forming Multilayer Diffusion Barrier for Copper Interconnections,” which is hereby incorporated by reference in its entirety.

[0002] (1) Field of the Invention

[0003] This invention relates to a method of fabrication in the formation of an improved copper metal diffusion barrier layer, W/WSiN/WN, by a combination of a tungsten nitride bottom layer, followed by an in situ silane soak process forming a WSiN layer, and a final top layer of tungsten, in single and dual damascene interconnect trench/contact via processing with 0.10 micron nodes for MOSFET and CMOS applications.

[0004] (2) Description of Related Art

[0005] Related patents and relevant literature now follow as Prior Art.

[0006] U.S. Pat. No. 6,001,415 entitled “Via With Barrier Layer for Impeding Diffusion of Conductive Material from Via Into Insulator” granted Dec. 14, 1999 to Nogami et al. describes a method of forming various diffusion barrier layers, i.e., both pure WSiN and pure WN barrier layers, for conducting copper contact vias. The via structure described includes a barrier layer disposed between a via plug and an insulating layer surrounding a via hole to impede diffusion of conductive material from the via plug into the insulating layer. The deposition of the barrier metals described use an ion metal plasma sputtering process that is combined with a plasma etching process to remove unwanted barrier layer material from the bottom of the contact via.

[0007] U.S. Pat. No. 5,801,098 entitled “Method of Decreasing Resistivity in an Electrically Conductive Layer” granted Sep. 1, 1998 to Fiordalice et al. describes a method of decreasing resistivity in an electrically conductive, diffusion barrier layer of TiN, that includes the use of a high density plasma sputtering technique to deposit the electrically conductive TiN layer. The electrically conductive diffusion barrier layer is further exposed to a plasma anneal.

[0008] U.S. Pat. No. 5,968,333 entitled “Method of Electroplating a Copper or Copper Alloy Interconnect” granted Oct. 19, 1999 to Nogami et al. describes a process whereby copper or a copper alloy is electroplated to fill via/contact holes and/or trenches in a dielectric layer. A barrier layer is initially deposited on the dielectric layer lining the hole/trench. A thin conformal layer of copper or a copper alloy is sputter deposited on the barrier layer outside the hole/trench. Copper or a copper alloy is then electroplated on the conformal copper or copper alloy layer filling the hole/trench. During electroplating, the barrier layer functions as a seed layer within the hole/trench. The barrier layer materials include single layers of: W, WN, WSiN, TiN, TiSiN and TiW.

[0009] U.S. Pat. No. 5,907,188 entitled “Semiconductor Device with Conductive Oxidation Preventing Film and Method for Manufacturing the Same” granted May 25, 1999 to Nakajima et al. describes a semiconductor device that includes a semiconductor substrate, and a laminated film insulatively formed over the semiconductor substrate. A conductive oxidation preventing film is disposed between a refractory metal film and a semiconductor film, to prevent oxidation of the semiconductor film. Oxidation and diffusion barriers, i.e., single layers of W, WN, and WSiN, are mentioned in the specifications.

[0010] U.S. Pat. No. 5,985,762 entitled “Method of Forming a Self-Aligned Copper Diffusion Barrier in Vias” granted Nov. 16, 1999 to Geffken et al. describes a process whereby a copper diffusion barrier is formed on the side walls of vias connected to copper conductors, to prevent copper diffusion into inter-level dielectric. A thin film of copper diffusion barrier material is deposited on the wafer post via etch. A sputter etch is performed to remove barrier material from the base of via and to remove copper oxide from the copper conductor. The barrier material is not removed from the sidewall during the sputter etch. Thus, a barrier to re-deposited copper is formed on the via sidewalls to prevent copper poisoning of the dielectric. Barrier materials that are mentioned include single layers of: Ta, TiN, Si₃N₄, TaN, WN, WSiN, and TaSiN.

[0011] It is a general object of the present invention to provide an improved method of fabrication in the formation of an improved copper metal diffusion barrier layer having the structure, W/WSiN/WN, in single and dual damascene interconnect trench/contact via processing with 0.10 micron nodes for MOSFET and CMOS applications. The diffusion barrier is formed by depositing a tungsten nitride bottom layer, followed by an in situ SiH₄/NH₃ or SiH₄/H₂ soak forming a WSiN layer, and depositing a final top layer of tungsten. This invention is used to manufacture reliable metal interconnects and contact vias in the fabrication of MOSFET and CMOS devices for both logic and memory applications and the copper diffusion barrier formed, W/WSiN/WN, passes a stringent barrier thermal reliability test at 400° C. Pure single barrier layers, i.e., single layer WN, exhibit copper punch through or copper spiking during the stringent barrier thermal reliability test at 400° C.

[0012] In summary of the present invention, a process flow description follows that summarizes the necessary process steps and sequence of steps necessary for the main embodiments of the present invention, to form W/WSiN/WN barrier layer, which exhibits high diffusion resistance to both copper and silicon (at both interfaces). The necessary process steps and sequence of steps necessary to form the W/WSiN/WN are outlined, as follows. Step one is the deposition of the WN film or layer in the trench/via opening by metal-organic chemical vapor deposition (MOCVD) from the reduction of tungsten organic precursors, or deposited by plasma-enhanced chemical vapor deposition (PECVD), or by physical vapor deposition (PVD), sputtering. Step two in the process flow description is the an in situ soak process treating the WN layer with a SiH₄/NH₃ gas mixture or a SiH₄/H₂ gas mixture, at between from about 300 to 400° C. This reactive soak process forms a WSiN layer on top of the WN layer, thus a WSiN/WN barrier. Following the silane soak treatment, is step three, the final top barrier deposition by chemical vapor deposition (CVD) or physical vapor deposition (PVD), sputtering, of a tungsten layer. Thus, a W/WSiN/WN barrier layer is formed. Next, step four is the copper seed layer deposition with improved adhesion and copper crystal texture, preferred dense <111>, upon the rigid diffusion the barrier layer, W/WSiN/WN. This fine crystal texture is important for subsequent electrochemical deposition (ECD) of copper, which subsequently fills the trench/via cavity. The copper seed layer, deposited over the tungsten layer, exhibits fine, highly dense grains, as studied by scanning electron microscopy (SEM). The subsequent process step, the electrochemical deposition (ECD) of copper, is used to fill the trench cavity, upon the copper seed layer. The kinetics of the electrochemical copper deposition process are based on a uniform, defect-free seed layer and barrier layer with good adhesion properties. The underlying layers improve and make wider the process window for the deposition of copper to fill both single and dual damascene structures.

[0013] The final processing step in building of the single and dual damascene structure is the chemical mechanical polishing (CMP) back of the excess electrochemical deposited copper metal. The copper is chem-mech polished back without dishing. In addition, any excess seed layer and barrier layer are removed from the top substrate surface. The copper is polished back so that only the copper that lies in the openings is left to form single and dual inlaid structures that include via and interconnect portions. Device applications include MOSFET and CMOS devices.

[0014] This invention has been summarized above and described with reference to the preferred embodiments. Some processing details have been omitted and are understood by those skilled in the art. More details of this invention are stated in the “DESCRIPTION OF THE PREFERRED EMBODIMENTS” section.

[0021] It is a general object of the present invention to provide an improved method of fabrication in the formation of an improved copper metal diffusion barrier layer having the structure, W/WSiN/WN, in single and dual damascene interconnect trench/contact via processing with 0.10 micron nodes for MOSFET and CMOS applications. The diffusion barrier is formed by depositing a tungsten nitride bottom layer, followed by an in situ SiH₄/NH₃ or SiH₄/H₂ soak forming a WSiN layer, and depositing a final top layer of tungsten. This invention is used to manufacture reliable metal interconnects and contact vias in the fabrication of MOSFET and CMOS devices for both logic and memory applications and the copper diffusion barrier formed, W/WSiN/WN, passes a stringent barrier thermal reliability test at 400° C. Pure single barrier layers, i.e., single layer WN, exhibit copper punch through or copper spiking during the stringent barrier thermal reliability test at 400° C.

[0022] It has been found that one reason that just a WN layer alone does not work, as well as, a W/WSiN/WN composite barrier layer is the possibility of pin holes in the WN layer. Pin holes facilitate the movement (through fast surface diffusion) of copper through the WN layer, during subsequent thermal processing, resulting in copper spiking or punch through of the barrier.

[0023] Referring to FIG. 1 illustrated in cross-sectional drawing, for completeness provided by the present invention, is a semiconductor substrate 10 with an insulating layer 12. A copper metal interconnect 16 is patterned within an insulating layer 14. In addition, a layer of low dielectric constant material 17 is deposited and patterned into a trench 18 (gap) opening in FIG. 1. Provided is a single damascene structure 18 and/or a dual damascene structure (not shown in Figs.). The typical insulator material is silicon oxide type compounds. Also, polysilicon gate structures (with silicides) and source/drain diffusions are typically upon or in a single crystal silicon substrate or IC module (not shown in figures).

[0024] Referring again in more detail to FIG. 1, which is a cross-sectional representation shows the first embodiment of the present invention, a trench structure filled with the first layer of the copper metal barrier layer, WN (19), deposited by metal-organic chemical vapor deposition (MOCVD) from the reduction of tungsten organic precursors, or deposited by plasma-enhanced chemical vapor deposition (PECVD), or by physical vapor deposition (PVD), sputtering.

[0025] Referring to FIG. 2, which in cross-sectional representation illustrates one of the main embodiments of the current invention, an in situ soak process treating the WN layer (19) with a SiH₄/NH₃ gas mixture (20) or a SiH₄/H₂ gas mixture (20), at between from about 300 to 400° C. This reactive soak process forms a WSiN layer (22) on top of the WN layer (19), thus forming a WSiN/WN barrier. Silicon atoms diffuse between the grains and into the grain boundaries of the WN film. Therefore, the silicon atoms block the diffusion path of deleterious copper atoms.

[0026] Referring to FIG. 3, illustrated in cross-sectional drawing is shown the result of the main embodiments of the current invention, the final top barrier deposition by chemical vapor deposition (CVD) or physical vapor deposition (PVD), sputtering, of tungsten (30). Thus, a W/WSiN/WN barrier layer is formed. The top tungsten barrier layer (30) is deposited over the WSiN layer (22) and the bottom WN layer (19). This top tungsten barrier layer yields better copper seed layer properties in the next process step.

[0027] FIG. 4, which in cross-sectional representation illustrates another embodiment of the present invention, the copper seed layer (40) deposition with improved adhesion and copper crystal texture, preferred dense <111>, upon the rigid diffusion barrier layer, W/WSiN/WN. This fine crystal texture is important for subsequent electrochemical deposition (ECD) of copper, which subsequently fills the trench/via cavity. The copper seed layer (40) deposited over the tungsten layer (30) exhibits fine, highly dense grains, as studied by scanning electron microscopy (SEM). The trench or channel and the via hole contact is lined with the adhesive copper seed layer on the diffusion barrier layer. The copper seed layer can be deposited by several methods: electrochemical deposition (ECD), or by physical vapor deposition (PVD) sputtering, and the seed layer material is comprised of a copper metal layer, thickness from about 1,000 to 2,200 Angstroms by PVD, and thickness from about 200 to 500 Angstroms by chemical vapor deposition (CVD).

[0028] FIG. 5, includes a process flow diagram summarizes the necessary process steps and sequence of steps necessary for an embodiment of the present invention, to form W/WSiN/WN barrier layer, which exhibits high diffusion resistance to both copper and silicon (at both interfaces). The necessary process steps and sequence of steps necessary to form the W/WSiN/WN are outlined in FIG. 5. Step one (1) is the deposition of the WN film or layer in the trench/via opening by metal-organic chemical vapor deposition (MOCVD) from the reduction of tungsten organic precursors, or deposited by plasma-enhanced chemical vapor deposition (PECVD), or by physical vapor deposition (PVD), reactive sputtering. Step two (2) in the flow diagram is an in situ soak process treating the WN layer with a SiH₄/NH₃ gas mixture or a SiH₄/H₂ gas mixture, at between from about 300 to 400° C. This reactive soak process forms a WSiN layer on top of the WN layer, thus a WSiN/WN barrier. Following the silane soak treatment, is step three (3), the final top barrier deposition by chemical vapor deposition (CVD) or physical vapor deposition (PVD), sputtering, of a tungsten layer. Thus, a W/WSiN/WN barrier layer is formed. Next, step four (4) is the copper seed layer deposition with improved adhesion and copper crystal texture, preferred dense <111>, upon the rigid diffusion the barrier layer, W/WSiN/WN. This fine crystal texture is important for subsequent electrochemical deposition (ECD) of copper, which subsequently fills the trench/via cavity. The copper seed layer, deposited over the tungsten layer, exhibits fine, highly dense grains, as studied by scanning electron microscopy (SEM). Not shown in the FIGS., is the subsequent process step, the electrochemical deposition (ECD) of copper, used to fill the trench cavity, upon the copper seed layer. The kinetics of the electrochemical copper deposition process are based on a uniform, defect-free seed layer and barrier layer with good adhesion properties. The underlying layers improve and make wider the process window for the deposition of copper to fill both single and dual damascene structures.

[0029] The final processing step in building of the single and dual damascene structure is the chemical mechanical polishing (CMP) back of the excess electrochemical deposited copper metal. The copper is chem-mech polished back without dishing. In addition, any excess seed layer and barrier layer are removed from the top substrate surface. The copper is polished back so that only the copper that lies in the openings is left to form single and dual inlaid structures that include via and interconnect portions. Device applications include MOSFET and CMOS devices. Robust diffusion barriers are critical to these technologies since copper is an excellent mid-band gap, recombination center in semiconductor material and minor carrier lifetime, retention time, is severely reduced by copper contamination in the semiconductor device regions.

[0030] Some of the process details and specifications for the in situ soak process, are as follows. The in situ soak process treats the WN layer with a SiH₄/NH₃ gas mixture or a SiH₄/H₂ gas mixture, at between from about 300 to 400° C. This reactive soak process forms a WSiN layer on top of the WN layer, thus forming a WSiN/WN barrier. Gas pressure ranges from about 1 to 10 Torr. Gas flows are, with a SiH₄/NH₃ gas mixture, SiH₄ gas flow from about 40 to 60 sccm and NH₃ gas flow from about 5 to 10 sccm. Gas flows are, with a SiH₄/H₂ gas mixture, SiH₄ gas flow from about 40 to 60 sccm and H₂ gas flow from about 2 to 3 sccm. Reaction time at processing temperature ranges from about 6 to 60 seconds. The WSiN layer thickness, formed by the above process, is from approximately 30 to 60 Angstroms. (Note, the in situ soak process that treats the WN layer, as specified above, is intentionally not a plasma process.)

[0031] Some of the specifications for the sandwich barrier structure or barrier layer W/WSiN/WN, are as follows. For a 300 Angstrom barrier layer of W/WSiN/WN, W thickness is approximately 40 Angstroms, WSiN thickness is from approximately 30 to 60 Angstroms, and WN thickness is approximately 200 Angstroms. If the total barrier layer W/WSiN/WN thickness is made to be thicker or thinner than 300 Angstroms, this has the effect of either increasing or decreasing only the WN thickness, as shown in the following example. For example, for a total barrier layer W/WSiN/WN thickness of 200 Angstroms, the W thickness is still approximately 40 Angstroms, WSiN thickness is still from approximately 30 to 60 Angstroms, but the affected WN thickness is now approximately 100 Angstroms. In general terms, the trench or channel and via hole contact is lined with a diffusion barrier layer comprised of a composite barrier with top layer of W thickness from about 30 to 50 Angstroms, interposed or intervening layer of WSiN thickness from about 30 to 60 Angstroms, and bottom layer of WN thickness from about 60 to 400 Angstroms.

[0032] One process variation or process option of the present invention, is as follows. The tungsten layer of the W/WSiN/WN barrier layer can be omitted to form a WSiN/WN barrier layer. Omitting the tungsten layer and the associated processing to deposit that layer, has the following affects on the barrier layer properties. Comparing the top of the barrier layer, W versus WSiN, W has a better crystal texture than WSiN. More specifically, WSiN is an amorphous phase or “nano-crystalline” phase (very small crystals or grains, close to amorphous). The properties of the conducting copper metal, that is deposited upon the barrier layer, are dependent upon the baffler layer material that is on the top surface of the barrier layer. A specific example of this barrier layer surface affect on the deposited copper layer properties is as follows. A barrier layer with W on top has the following properties: the tungsten layer has a better grain or crystal texture (finer texture) than a top layer of WSiN layer. Furthermore, the if copper is directly deposited on a layer of WSiN, the copper grains exhibit less of the desirable preferred crystal orientation <111>/<200>. However, if copper is directly deposited on a layer of W, the copper grains exhibit more of the desirable preferred crystal orientation <111>/<200>. This effect is attributed to the better crystal texture of the tungsten layer. In cases where the process variation or process option of omitting the W top layer is exercised, the trench or channel and via hole contact is lined with a diffusion barrier layer comprised of a composite barrier with a top layer of WSiN thickness from about 30 to 60 Angstroms, and a bottom layer of WN thickness from about 60 to 400 Angstroms.

[0033] While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.