Abstract:
A method for post-etch copper cleaning uses a hydrogen plasma with a trace gas additive constituting about 3-10 percent of the plasma by volume to clean a copper surface exposed by etching. The trace gas may be atomic nitrogen or other species having an atomic mass of 15 or greater. The trace gas adds a sputtering aspect to the plasma cleaning and removes polymeric etch by-products and polymeric and other residuals formed during the deposition of dielectric materials or etch stop layers over the copper surface. An anti-corrosion solvent may be used to passivate the copper surface prior to formation of the dielectric materials or etch stop layers.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates most generally to semiconductor devices and methods for their fabrication. More particularly, the present invention is directed to a cleaning method and structure that provide copper contact structures with low contact resistance.  
       BACKGROUND  
       [0002]     The use of copper as a conductive interconnect material is favored in semiconductor devices because of the high speed that copper provides. Copper is difficult to pattern and therefore copper interconnect leads are typically formed using damascene processing technology whereby an opening is formed in a dielectric, copper is deposited over the dielectric and within the opening, then a polishing/planarization process is used to remove copper from over the dielectric, leaving the copper inlaid within the opening. The inlaid copper includes an upper surface that is essentially co-planar with the top surface of the dielectric in which the copper is disposed. A shortcoming associated with the use of copper interconnect technology is that the exposed copper surfaces are prone to oxidation. Thus, according to conventional processing technology, a passivation or other oxidation-prevention operation is carried out after the copper surface is formed by polishing. The materials conventionally used to passivate the copper surface after polishing, however, may complex with species used in the formation of further materials over the passivated copper surface, to form undesirable contaminants.  
         [0003]     Contact may be made to the copper surface by forming a further dielectric and further optional materials over the copper surface then etching an opening through the dielectric and the further optional materials that exposes the copper surface. In one exemplary embodiment after the polishing process forms copper interconnect structures inlaid within a dielectric, a further dielectric is formed over the structure. An etch stop layer may optionally be formed between the overlying further dielectric and the polished surface. During the deposition of such an etch stop layer, organosilicate (SiOCH) contaminants may be formed at the interface between the etch stop layer and the passivated copper surface. SiC used during the initial deposition of an etch stop layer may complex with the anti-corrosion passivated surface of copper to form the organosilicate. When the optional etch stop layer is not used, contaminants may be formed during the initial stages of the further dielectric deposition. An etching operation is then carried out to etch through the further dielectric and the optional etch stop layer exposing portions of the copper surface for the purpose of providing contact to the copper surface. Applicants have noted that, regardless of the condition of the copper surface prior to the formation of the subsequent film such as the optional etch-stop film and/or the overlying dielectric, the plasma etching processes used to etch the opening that exposes the copper surface leave contaminating etch residuals and by-products that degrade the quality of the exposed copper surface and result in undesirably increased contact resistance. It would therefore be desirable to address the integrity of the copper surface after the etching operation. The etch residuals are generally polymeric in nature and difficult to remove.  
         [0004]     The polymeric etch residuals and by-products may include fluorine, F, carbon, C, copper, Cu and other species in various combinations. Hydrogen, H 2 , plasmas are conventionally used in the art of semiconductor manufacturing to remove polymeric etch by-products and residuals such as those formed due to the deposition of the etch stop layer or dielectric or during the etching operation that exposes the copper surface. Hydrogen plasmas, however, are extremely sensitive to the condition of the plasma chamber and therefore run-to-run repeatability is difficult to achieve. The via resistance for the vias formed to contact the copper surface, is dependent upon the hydrogen plasma clean and is therefore also susceptible to changes in chamber conditions and therefore unstable. Often, when a hydrogen plasma is used for cleaning, a further cleaning operation must be used due to the aforementioned shortcomings.  
         [0005]     It would therefore be desirable to provide a robust cleaning procedure that insures that the copper surfaces upon which further conductive materials are formed, are clean, and that via resistance is thereby minimized.  
       SUMMARY OF THE INVENTION  
       [0006]     To address these and other needs and in view of its purposes, an aspect of the invention provides a method for providing contact to copper in a semiconductor device. The method comprises providing a copper surface, treating the copper surface with an anti-corrosion element, forming a dielectric layer over the copper surface, etching an opening through the dielectric layer and exposing the copper surface, and cleaning in a plasma that includes a plasma gas comprising hydrogen and a further component having an atomic mass of 15 or greater. The further component comprises about 3 to 10 percent by volume of the plasma gas and provides a sputtering aspect to the cleaning method.  
         [0007]     Another aspect of the invention provides a method for providing contact to copper in a semiconductor device. The method comprises providing a copper surface, treating the copper surface with an anti-corrosion element, forming a dielectric layer over the copper surface, etching an opening through the dielectric layer and exposing the copper surface, and cleaning in a plasma that includes a plasma gas comprising hydrogen and nitrogen, with the nitrogen comprising about 3-10 percent by volume of the plasma gas. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0008]     The present invention is best understood from the following detailed description when read in conjunction of the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not necessarily to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Like numerals denote like features throughout the specification and drawing.  
         [0009]      FIG. 1  is a cross-sectional view showing a copper structure inlaid within a dielectric;  
         [0010]      FIG. 2  is a cross-sectional view showing the structure  FIG. 1  after an etch stop layer and dielectric have been formed over the structure;  
         [0011]      FIG. 3  is a cross-sectional view showing the structure of  FIG. 2  after an opening has been formed to expose a surface of the copper; and  
         [0012]      FIG. 4  is a cross-sectional view showing the structure of  FIG. 3  after the opening has been filled with an conductive material. 
     
    
     DETAILED DESCRIPTION  
       [0013]      FIG. 1  is a cross-sectional view showing copper structure  2  inlaid within dielectric  4  according to damascene processing technology. A polishing operation such as chemical mechanical polishing may be used to form the structure which includes top surface  6  of copper structure  2  and top surface  8  of dielectric  4  which are substantially co-planar. Dielectric  4  may be any of various suitable dielectrics used in semiconductor manufacturing, including low-k dielectric materials and various oxides and oxynitrides. After the structure shown in  FIG. 1  is formed, top surface  6  of copper structure  2  may be passivated using conventional techniques. According to one exemplary embodiment, the passivation process may include treating with an anti-corrosion solvent such as BTA (Benzotriazole) using conventional methods, but other anti-corrosion solvents and other passivation techniques may be used in other exemplary embodiments. In still further exemplary embodiments, the passivation technique may not be used.  
         [0014]      FIG. 2  shows the structure of  FIG. 1  after optional etch stop layer  10  and upper dielectric  12  having been formed, using conventional methods, over top surface  8  and top surface  6 . CVD, chemical vapor deposition, or other formation techniques, may be used to form optional etch stop layer  10  and upper dielectric  12 . Upper dielectric  12  may be any of various suitable dielectrics such as silicon oxides, silicon oxynitrides, silicon nitrides, or various low-k dielectric materials. Etch stop layer  10  is chosen to have different etching characteristics than upper dielectric  12 , in particular, etch stop layer  10  is chosen to be resistant to the etching characteristics used to etch upper dielectric  12 . According to one exemplary embodiment, etch stop layer  10  may be silicon carbide but other materials such as silicon nitride may be used in other exemplary embodiments. In some exemplary embodiments, organosilicate (SiOCH) species may undesirably form at interface  14  formed between top surface  6  of copper structure  2  and etch stop layer  10 , during the formation of etch stop layer  10 . According to the embodiments in which etch stop layer  10  is not used, other contaminating species may form on top surface  6  during the formation of upper dielectric  12 . In each of the aforementioned exemplary embodiments, the contaminating species may be a product of species used to passivate the copper surface complexing with the species used to form upper dielectric  12  or optional etch stop layer  10 .  
         [0015]     Photoresist film  16  is formed over upper dielectric  12  according to conventional techniques and includes opening  18  aligned over top surface  6  of copper structure  2 . Conventional etching techniques are then used to form an opening that exposes top surface  6  for the purpose of providing an electrical connection to top surface  6 .  
         [0016]      FIG. 3  shows the structure of  FIG. 2  after a conventional plasma etching operation or a sequence of plasma etching operations, has been carried out to etch through upper dielectric  12  and optional etch stop layer  10  to expose a portion of top surface  6  of copper structure  2 , and after the subsequent removal of the photoresist film shown in  FIG. 2 . Opening  20  is formed by plasma etching and often results in polymeric residual materials and etch by-product materials formed on top surface  6  and which can increase the resistance of a contact formed by forming a conductive material within opening  20  that contacts top surface  6 . The polymeric etch residuals and by-products may include fluorine, F, carbon, C, copper, Cu and other species in various combinations. For example, various CF x  compounds may be produced. Opening  20  may be a via in an exemplary embodiment or it may be single or dual damascene trench, but other openings that expose top surface  6  of copper structure  2  may be used in other exemplary embodiments.  
         [0017]     After the structure shown in  FIG. 3  is formed by etching, an aspect of the present invention provides a cleaning operation that effectively removes residual and by-product material from opening  20  and from top surface  6 . The cleaning operation effectively removes organosilicate (SiOCH) species which may have formed at interface  14  and which may still undesirably exist on top surface  6 . The cleaning operation also capably removes etch residuals and by-products such as CF x  and others that may include fluorine, F, carbon, C, copper, Cu or various other species. The cleaning procedure is a plasma cleaning operation that includes hydrogen and a trace gas that has an atomic mass of 15 or greater. In an exemplary embodiment, the trace gas may be atomic nitrogen, N 2  but other suitable trace gasses may be used in other exemplary embodiments. The hydrogen:trace gas ratio may range from 10:1 to 50:1 by volume but other ratios may be used in other exemplary embodiments. The trace gas may represent 2-10% or 3-10%, by volume, of the plasma gas. The atomic mass of 15 or greater provides a sputtering aspect of the cleaning operation. In one exemplary embodiment, the cleaning operation may include a ratio of hydrogen:nitrogen of 20:1. In an exemplary embodiment, a gas flow of 400 sccm H 2  and 20 sccm N 2  may be used at a pressure of 60 millitorr and at a source power of 400 watts and a bias power of 150 watts of an inductively coupled plasma. In other exemplary embodiments, the pressure used in the cleaning chamber may range from 10 mT to 200 mT. Also in other exemplary embodiments, the power for performing the cleaning operation may range from 100 W to 2000 W. Due to the sputtering aspect provided by the trace gas, the cleaning operation is not very sensitive to the condition of the cleaning chamber.  
         [0018]     After the plasma cleaning operation is concluded, a conductive material is formed within opening  20  to contact cleaned top surface  6 .  FIG. 4  shows conductive material  22  filling opening  20  shown in  FIG. 3 . Copper or other suitable conductive materials may be used. The exemplary structure shown in  FIG. 4  also shows top surface  24  of conductive material  22  being substantially co-planar with upper surface  26  of upper dielectric  12  such as may be produced after a polishing operation such as used in damascene processing technology, but other methods for forming a conductive structure within opening  20  ( FIG. 3 ) and contacting top surface  6  of copper structure  2 , may be used in other exemplary embodiments.  
         [0019]     The preceding merely illustrates the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes and to aid the reader in understanding the principles of the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.  
         [0020]     This description of the exemplary embodiments is-intended to be read in connection with the figures of the accompanying drawing, which are to be considered part of the entire written description. In the description, relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation.  
         [0021]     Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.