Abstract:
A dual damascene structure with improved profiles and reduced defects and method of forming the same, the method including forming a first dielectric over a conductive area; forming a first dielectric insulator over the first dielectric; forming a first opening in the first dielectric insulator; lining the opening with a second dielectric; forming a second dielectric insulator over the first dielectric insulator; forming a second opening in the second dielectric insulator overlying and communicating with the first opening; and, filling the first and second openings with a conductive material to electrically communicate with the conductive area.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention generally relates to semiconductor device manufacturing methods and more particularly to dual damascene interconnects formed in inter-metal dielectric (IMD) layers and a method of forming the same having a via portion lined with a dielectric via liner also functioning as a trench stop to improve a trench etching process to avoid trench etching induced defects thereby improving device performance and reliability. 
       BACKGROUND OF THE INVENTION 
       [0002]    In forming interconnect wiring structures in integrated circuit manufacturing processes, the trend has been to use low-K dielectric insulating materials together with metal damascenes to increase electrical transport speed and take advantage of the processing advantages inherent in a damascene or dual damascene process. 
         [0003]    Low-K materials are now routinely required to reduce signal delay and power loss effects as integrated circuit devices are scaled down. One way this has been accomplished has been to introduce porosity or dopants into the dielectric insulating layer, also referred to as an inter-metal dielectric (IMD) layer. 
         [0004]    As a result, the need for lower dielectric constant materials has resulted in the development of several different types of organic and inorganic low-K materials. Several different organic and inorganic low-K materials have been developed and proposed for use in semiconductor devices as insulating materials having dielectric constants less than about 3.5. 
         [0005]    One problem with low-K materials has been susceptibility of low-K materials to plasma etching damage during an interconnect formation process, where low-K materials may be damaged in terms of overetching to detrimentally alter opening etch profiles as well as degrading dielectric constant properties. The various problems included in interconnect formation processes with low-K materials are exacerbated in higher aspect ratio openings and in dual damascene formation processes where multiple etching steps are carried in the manufacturing process. 
         [0006]    To overcome these problems prior art processes have proposed partially filling the via opening with organic resinous material to form a via plug following the via etching process where the via opening extends through lower and upper dielectric insulating (ILD) layers including a middle etch stop layer. The via plug was intended to protect the via opening during the trench etching process. Several shortcomings, including process complexity and cost are associated with the foregoing process. In addition, other shortcomings such as formation of etch residue fences as the trench/via interface, undesired micro-trenching at the bottom portion of the trench, and difficulty in controlling the level of the via plug, have been associated with such a process. 
         [0007]    There is therefore a need in the integrated circuit manufacturing art to develop a more reliable and cost effective dual damascene interconnect and method of forming the same. 
         [0008]    It is therefore among the objects of the present invention to provide a more a more reliable and cost effective dual damascene interconnect and method of forming the same, in addition to overcoming other shortcomings of the prior art. 
       SUMMARY OF THE INVENTION 
       [0009]    To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a dual damascene structure with improved profiles and reduced defects and method of forming the same. 
         [0010]    In a first embodiment, the method includes forming a first dielectric over a conductive area; forming a first dielectric insulator over the first dielectric; forming a first opening in the first dielectric insulator; lining the opening with a second dielectric; forming a second dielectric insulator over the first dielectric insulator; forming a second opening in the second dielectric insulator overlying and communicating with the first opening; and, filling the first and second openings with a conductive material to electrically communicate with the conductive area. 
         [0011]    These and other embodiments, aspects and features of the invention will be better understood from a detailed description of the preferred embodiments of the invention which are further described below in conjunction with the accompanying Figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIGS. 1A-1G  are cross sectional views of a dual damascene structure at stages of manufacture according to embodiments of the present invention. 
           [0013]      FIG. 2  is a process flow diagram including several embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    The present invention is directed at a dual damascene and method of forming the same where the dual damascene is formed having a via portion in a first type of low-K IMD layer and the trench line portion is formed in a second type of low-K IMD layer. The present invention is addressed at overcoming problems of forming dual damascenes in low-K materials. The various advantages of the present invention include improving etching process windows, allowing improved control of etching profiles, as well as avoiding damage to low-K materials by plasma etching processes. The dual damascene structure of the present invention and method of forming the same thereby provides an improved dual damascene with improved performance and reliability while reducing a processing cost compared to prior art via plug formation processes. 
         [0015]    It will be appreciated that although the dual damascene structure and method of the present invention is particularly beneficial in forming copper filled dual damascenes, other metals may be used as well, such as tungsten, aluminum, and alloys thereof. 
         [0016]    For example, referring to  FIGS. 1A-1F , in an exemplary embodiment, are shown cross sectional views of a portion of a multi-level semiconductor device at stages in an integrated circuit manufacturing process. 
         [0017]    Referring to  FIG. 1A , a conductive region  10  is provided as an uppermost material layer in an integrated circuit manufacturing substrate, for example a metal or semiconductor, formed on a semiconductor wafer, formed by conventional processes known in the micro-electronic integrated circuit manufacturing process. An overlying etch stop layer (first dielectric)  12 A, is formed on the conductive region  10 , for example an upper the etch stop layer preferably formed of silicon nitride (e.g., SiN, Si 3 N 4 ), silicon carbide (e.g., SiC), carbon doped silicon oxide, and combinations thereof. In one embodiment, the first dielectric is preferably a nitrogen containing dielectric. The etch stop layer is typically formed to a thickness of about 300 Angstroms to about 700 Angstroms by a conventional CVD, LPCVD, PECVD, or HDP-CVD process. 
         [0018]    Still referring to  FIG. 1A , formed over first etch stop layer  12 A is a first insulating dielectric layer  14 A, also referred to as an inter-metal dielectric (IMD) layer, preferably formed of an organic or inorganic silicon oxide based material, more preferably inorganic. For example, preferred materials include fluorinated silicate glass (FSG) and carbon doped silicon oxide. In one embodiment, the first dielectric insulating layer  14 A preferably has a dielectric constant of less than about 3.2, e.g., a low-K inorganic silicon oxide based material. In another embodiment, the first insulating dielectric layer  14 A is preferably formed by a chemical vapor deposition (CVD) method such as CVD, LPCVD, PECVD, or HDP-CVD process. For example, the first dielectric insulating layer  14 A may be formed of BLACK DIAMOND™ (manufactured by Applied Materials) or other inorganic CVD low-K material. Other, suitable, but less preferred low-K inorganic materials include methyl silsesquioxane (MSQ), hydrogen silsesquioxane (HSQ), and fluorine tetra-ethyl-orthosilicate (FTEOS). In one embodiment, the first dielectric insulating layer  14 A is preferably FSG for enhanced mechanical strength. An optional organic or inorganic uppermost anti-reflectance coating (ARC), e.g.,  13  may be formed over the first dielectric insulating layer  13 . 
         [0019]    Referring to  FIG. 1B , a first photoresist layer  16 A is formed over the first IMD layer  14 A. The photoresist layer is patterned by a conventional photolithographic patterning process to form a via etching mask. A conventional plasma etching process, such as a reactive ion etch (RIE) process, is then carried out to form a via opening  18 A by etching through the first IMD portion  14 A to stop on the first etch stop layer  12 A, which may include partially etching through a thickness portion of the first etch stop layer  12 A. It will be appreciated that the via may be a circular (i.e., a hole), or rectangular (e.g., a slot). Following via etching, the first photoresist layer  16 A is removed according to a conventional chemical stripping or plasma ashing process. 
         [0020]    Referring to  FIG. 1C , in an important aspect of the invention, following removal of the photoresist layer  16 A, and optionally, the ARC layer  13 A, an etch stop layer/via liner (second dielectric)  12 B is formed over the IMD layer  14 A to include lining the sidewalls and bottom portion of the via opening  18 A. Preferably, the second etch stop layer/via liner  12 B is formed of silicon nitride (e.g., SiN, Si 3 N 4 ), silicon oxynitride (e.g., SiON), carbon doped silicon oxide, silicon oxide, and combinations thereof. In one embodiment, the second etch stop layer/via liner  12 B is preferably formed of a nitrogen containing dielectric. Preferably, the second etch stop layer/via liner  12 B is formed having a thickness of from about 20 Angstroms to about 200 Angstroms and is preferably formed by a chemical vapor deposition (CVD) process, most preferably an atomic layer CVD (ALCVD) process. 
         [0021]    Referring to  FIG. 1D , a second dielectric insulating layer (IMD layer)  14 B is formed on the process surface including second etch stop layer/via liner  12 B. Preferably, the second dielectric insulating layer is formed over the process surface by covering the via opening  18 A without filling the opening. For example, a small upper portion of the via opening may be filled by the deposition process of the IMD layer  14 B, for example a CVD, PECVD, or HDP-CVD deposition process. The second dielectric insulating layer  14 B may be formed of the same or different materials of the preferred materials outlined for the first dielectric insulating layer  14 A. In one embodiment, the second dielectric insulating layer is preferably a low-K organic or inorganic material, preferably inorganic, having a dielectric constant of less than about 3.2, for example, carbon doped oxide having a dielectric constant of about 2.4 to about 3.2. By the term ‘low-K’ is meant a dielectric constant of less than or equal to about 3.2. In one embodiment, only the second dielectric insulating layer  14 B is a low-K dielectric material. 
         [0022]    Referring to  FIG. 1E , an ARC layer  13 B is preferably formed over the second IMD layer  14 B. The ARC layer  13 A may be formed of an organic or inorganic material but is preferably and inorganic material, for example, formed of one or more of SiN, SiON, SiC, and SiOC. A second photoresist layer  16 B is then formed over the process surface and patterned by a conventional photolithographic process to form a trench line etching mask. A trench line opening  18 B is the then etched by a conventional plasma etching process (e.g., RIE), through the thickness of the second IMD portion  14 B, to stop on the upper portion of the second etch stop/via liner layer  12 B. It will be appreciated that the trench line opening  18 B may be formed to overlie and encompass more than one via opening. 
         [0023]    Referring to  FIG. 1F , following removal of the second photoresist layer  16 B by a stripping process, for example, an in-situ ashing process, the via liner dielectric  12 B is plasma etched (e.g., reactive ion etch) to remove the liner portion at the via bottom to expose the underlying conductive region  10 . During the photoresist ashing process and the etching process, the first dielectric insulating layer  14 A, including the via etch profile is protected and preserved by the via liner  12 B. In addition, the etch stop/via liner  12 B at the bottom portion of the trench line opening  18 B is partially or fully etched through during removal of the liner at the via bottom portion, thereby preserving the dual damascene opening profile at the via/trench opening transition level. It will be appreciated that a portion of the dielectric via liner  12 B may remain lining the sidewall portions of the via opening  18 A. 
         [0024]    Referring to  FIG. 1G , subsequent processes are then undertaken to complete formation of the dual damascene. For example, optional formation of a barrier layer  20  lining the dual damascene opening, followed by conventional processes such as PVD, CVD, or electro-chemical deposition (ECD) methods as are appropriate to fill the dual damascene with metal layer  22 , such as aluminum, copper, tungsten, or alloys thereof. A chemical mechanical polish (CMP) process may then be performed to remove metal layer  22  above the dual damascene opening including remaining portions of overlying layers above the IMD layer  14 B, e.g., ARC layer  13 B, to complete the dual damascene formation process. 
         [0025]    Advantageously, according to the present invention, etching profile defects accompanying the trench etching process are avoided, such as formation of etching residue fences at the trench/via interface, as well as undesirable micro-trenching defects at trench bottom portion. In addition, the formation of facets, degrading the etching profile at the trench/via interface are avoided by undesirable overetching during removal of the etch stop layer at the via bottom, a problem in prior art processes. In addition, it has been found that a remaining portion of the via dielectric liner along sidewalls, has the unexpected effect of reducing via induced metal interconnect corrosion (VIMIC) of an underlying conductive material, e.g., copper. Such foregoing advantages improve the performance and device reliability of an integrated circuit semiconductor device as well as decrease processing costs compared to prior art processes including via plug formation processes. 
         [0026]    Referring to  FIG. 2  is shown a process flow diagram including several embodiments of the present invention. In process  201 , a semiconductor substrate is provided with an exposed conductor area. In process  203 , a first dielectric is formed over a conductor area. In process  205 , a first dielectric insulator is formed on the first dielectric. In process  207 , a via opening is formed through the first dielectric insulator. In process  209 , a dielectric liner is formed over the first dielectric insulator to include lining the via opening. In process  211 , a second dielectric insulator is formed over the first dielectric insulator. In process  213 , a trench opening is formed in the second dielectric insulator overlying the via opening. In process  215 , the dielectric liner is removed from a bottom portion of the via opening to expose the conductor area. In process  217 , the via and trench opening are simultaneously filled with metal in electrical contact with conductor area. 
         [0027]    The preferred embodiments, aspects, and features of the invention having been described, it will be apparent to those skilled in the art that numerous variations, modifications, and substitutions may be made without departing from the spirit of the invention as disclosed and further claimed below.