Abstract:
A method for fabricating interconnects is provided. The method comprises forming a conducting line on a first dielectric layer; forming a first liner layer on the surfaces of the first dielectric layer and the conducting line; forming a second liner layer on the first liner layer; forming a second dielectric layer on the second liner layer, wherein the etching selectivity rate of the second dielectric layer is higher than the etching selectivity rate of the second liner; and patterning the second dielectric layer to form a contact window opening through the second liner layer and the first liner layer to expose the surface of the conducting line. Because the second dielectric layer having an etching rate higher than the etching rate of the second liner layer, the second liner layer can be used as an etch stop layer while patterning the second dielectric layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a divisional of a prior application Ser. No. 10/708,848, filed Mar. 29, 2004, which claims the priority benefit of Taiwan application serial no. 92123869, filed on Aug. 29, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention generally relates to a semiconductor device and a method for fabricating the same, and more particularly to an interconnect structure and a method for fabricating the same.  
         [0004]     2. Description of Related Art  
         [0005]     For current VLSI fabrication processes, most semiconductor devices use two or more interconnects for routing in order to achieve a higher integration level.  
         [0006]     For a conventional process for multi-level interconnects, a silicon oxide inter level dielectric (ILD) is formed on the substrate to cover the device on the substrate. Then a contact window is formed in the ILD electrically connected to the selected device. A conducting line is formed on the ILD to electrically connect to the contact window. The conducting line is formed by stacking a Ti/TiN barrier layer, an Al layer, and a Ti/TiN barrier layer. The above process is for a single-level interconnect. The multi-level interconnects can be fabricated by repeating the above steps.  
         [0007]     However, problem occurs while a contact window is formed in the second-level ILD on the first-level interconnect. Conventionally, the contact window is formed by forming an opening in ILD to expose the conducting line and then filling a conducting material into the opening. However, when etching the ILD to form the opening, over-etching may happen due to inappropriate etching control. If the etching process does not stop on the Ti/TiN barrier layer above the Al layer, the Al layer will be etched so that the resistance will increase. For a process with a line width of 0.12 μm or below, this etching process is more difficult to control. Hence, the issue of over-etching becomes more critical for a process with a line width of 0.12 μm or below.  
       SUMMARY OF THE INVENTION  
       [0008]     An object of the present invention is to provide an interconnect structure and a method for fabricating the same to prevent the Al layer form over-etching due to the difficulty to control the end point of the etching process.  
         [0009]     The present invention provides a method for fabricating interconnects, comprising: forming a conducting line on a first dielectric layer; forming a first liner on the surfaces of the first dielectric layer and the conducting line; forming a second liner on the first liner, the dielectric layer having an etching rate; forming a second dielectric layer on the second liner, the dielectric layer having an etching rate higher than the etching rate of the dielectric layer; and patterning the second dielectric layer to form a contact window opening through the second liner and the first liner to expose the surface of the conducting line.  
         [0010]     The present invention provides an interconnect structure, comprising: a first dielectric layer; a conducting line on the first dielectric layer; a first liner on the surfaces of the first dielectric layer and the conducting line; a second liner on the surface of the first liner; and a second dielectric layer covering the second liner, the second dielectric layer having a contact widow opening through the second liner and the first liner to expose the surface of the conducting line.  
         [0011]     In brief, because the etching rate of the second liner on the conducting line is lower than that of the second dielectric layer, the second liner can be a stop layer while patterning the second dielectric layer. Hence, an over-etching of the Al layer and a subsequent increased of the resistance are precluded.  
         [0012]     The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages and embodiments of the invention will be apparent to those skilled in the art from the following description, accompanying drawings and appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIGS. 1A-1E  show the cross-sectional view of a preferred embodiment for fabricating an interconnect structure in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]      FIGS. 1A-1E  show the cross-sectional view of for fabricating an interconnect structure in accordance with a preferred embodiment of the present invention.  
         [0015]     Referring to  FIG. 1A , a dielectric layer  100  having a contact window  104  is provided. The dielectric layer  100  is, for example, silicon oxide. Further, the dielectric layer  100  can be used as an ILD. The dielectric layer  100  is formed above the substrate (not shown) to cover the device structures (not shown) on the substrate. The thickness of the dielectric layer  100  is between 6000 and 7200 Å. The contact window  104  is electrically connected to the underlying selected device. The diameter of the contact window is approximately 0.35 μm. The contact window can be W or polysilicon. In a preferred embodiment of the present invention, if the material of the contact window is W, an adhesive Ti/TiN layer can be formed between the contact window  104  and the dielectric layer  100  to enhance the adhesion of W to the dielectric layer  100 .  
         [0016]     Referring to  FIG. 1A , a conducting line layer  102  is formed on the dielectric layer  100 . The conducting line layer  102  can be formed by performing physical vapor deposition to sequentially form a barrier layer  106 , a metal layer  108 , and a barrier layer  110  on the dielectric layer  100 . The total thickness of these three layers is between 2500-4000 Å. The material of the metal layer  108  is Al-dominated, such as, Al or Al—Cu alloy. The barrier layers  106  and  110  can be a single TiN layer or a stacked layer including a TiN layer and a Ti layer.  
         [0017]     In a preferred embodiment of the present invention, the barrier layer  106  is a single Ti layer, and the barrier layer  108  is a stacked Ti/TiN layer. In another preferred embodiment of the present invention, the barrier layer  106  is a stacked Ti/TiN layer, and the barrier layer  110  is a single Ti layer. In another preferred embodiment of the present invention, both of the barrier layers  106  and  110  are stacked Ti/TiN layers. In other words, the conducting line layer  102  is a four-layered or five-layered structure including a metal layer  108 , two barrier layers  106  and  110 . Further, the Ti layer is used to prevent electromigration of the metal layer  108 . The TiN layer is used to prevent the metal layer from reacting with the contact window of W so that the resistance of the metal layer and the contact window will not increase.  
         [0018]     Referring to  FIG. 1B , the conducting line layer  102  is patterned to form the conducting line  112 . The conducting line  112  is electrically connected to the contact window  104 . The conducting line  112  includes the patterned barrier layer  106 , metal layer  108   a  , and barrier layer  110   a.  The patterned conducting line layer  102  is formed by forming a patterned photoresist layer (not shown) as a mask and etching the conducting line layer  102 .  
         [0019]     Referring to  FIG. 1C , a liner layer  114  is formed on the surfaces of the dielectric layer  100  and the conducting line  112 . The liner layer  114  is, for example, silicon oxide and is formed by, for example, performing a high-density plasma chemical vapor deposition (HDPCVD) process. The thickness of the liner layer  114  is between 100-200 Å.  
         [0020]     Then, a liner layer  116  is formed on the surface of the layer  114 . The liner  116  is SiNx or SiON, and is formed by, for example, performing a CVD process at a temperature of approximately 400° C. The thickness of the liner  116  is between 110-130 Å. It should be noted that the dielectric coefficient of the silicon oxide liner layer  114  is smaller than that of the SiNx or SiON liner layer  116 . The generation of parasitic capacitance can be avoided in the subsequent process.  
         [0021]     Referring to  FIG. 1D , a dielectric layer  118  is formed on the liner layer  116 . The material of the dielectric layer  118  is the same as that of the liner layer  116 , such as, silicon oxide. The dielectric layer  118  is formed by performing a high-density plasma chemical vapor deposition (HDPCVD). Further, the height of the dielectric layer  118  is about 6000 Å above that of the liner layer  116 .  
         [0022]     It should be noted that the silicon oxide dielectric layer  118  has an etching rate higher than the etching rate of the SiNx or SiON liner layer  116 . The etching selectivity ratio of the silicon oxide dielectric layer  118  to the SiNx or SiON liner layer  116  is, for example, between 50 and 70. Hence, it is more difficult to remove the liner layer  116  than the dielectric layer  118 . Therefore, the liner layer  116  can be used for an etch stop layer for the subsequent process to pattern the dielectric layer  118 .  
         [0023]     Referring to  FIG. 1D , a patterned photoresist layer  122  is formed on the dielectric layer  118  by performing a spin coating process to form a photoresist material layer (not shown), followed by performing a photolithography process. In another preferred embodiment of the present invention, before forming the photoresist material layer, an anti-reflective coating (ARC) is formed on the dielectric layer  118  to prevent the photoresist material layer from undesired exposure in the subsequent exposure processes. The material of the ARC can be organic or inorganic.  
         [0024]     Referring to  FIG. 1E , the dielectric layer  118  is patterned to form a contact window opening  124  through the liner layer  1114   a  and the liner layer  1116   a  to expose the surface of the conducting line  112 . The dielectric layer  118  is patterned by using the photoresist layer  122  as a mask and performing a dry etching process. Then, the photoresist layer  122  is removed.  
         [0025]     It should be noted that the silicon oxide dielectric layer  118   a  has an etching rate higher than the etching rate of the SiNx or SiON liner  1116   a.  Hence, it is more difficult to remove the liner  1116   a  than the dielectric layer  1118   a.  Therefore, the liner  116  can be used for an etch stop layer for patterning the dielectric layer  1118   a.  In other words, during the etching process on the liner  1116   a,  the etching rate gradually reduces to prevent the conducting line  122  from being over-etched.  
         [0026]     After forming the contact window opening  124 , a conducting material (not shown) can be filled into the contact window opening  124  to form the contact, which is electrically connected to the conducting line  112 . The conducting material can be tungsten or polysilicon.  
         [0027]     The interconnect structure of the present invention is illustrated as follows. Referring to  FIG. 1F , the interconnect structure includes a contact  104 , dielectric layer  100  and  118   a,  a conducting line  112 , and liners  114   a  and  116   a.    
         [0028]     The contact  104  is configured in the dielectric layer  100 . The conducting line  112  is disposed on the dielectric layer  100  and is electrically connected to the contact  104 . The conducting line  1122  is a stacked structure including a barrier layer  106   a,  a metal layer  108   a,  and a barrier layer  110   a.  For example, the conducting line  112  is a four-layered or five-layered structure, which includes a metal layer  108   a,  two barrier layers  106   a  and  110   a  as mentioned above.  
         [0029]     The liner layer  114   a  is disposed on the surfaces of the dielectric layer  100  and the conducting line  112 . The liner  114   a  is, for example, silicon oxide, and the thickness of the liner layer  114   a  is between 100-200 Å. The liner layer  116   a  is disposed on the surface of the liner layer  114   a.  The liner layer  116   a  is SiNx or SiON, and the thickness of the liner layer  116   a  is between 110-130 Å. The etching selectivity ratio of the silicon oxide dielectric layer  118   a  to the SiNx or SiON liner  116   a  is, for example, between 50 and 70.  
         [0030]     Further, the dielectric layer  118   a  covers the liner layer  116   a,  and the dielectric layer  118   a  has a contact widow opening  124  formed therein, through the liner layers  114   a  and  116   a  to expose the surface of the conducting line  112 .  
         [0031]     In a preferred embodiment of the present invention, a conducting material (not shown) can be filled into the contact window opening  124  to form the contact, which is electrically connected to the conducting line  112 . The conducting material can be tungsten or polysilicon.  
         [0032]     It should be noted that the silicon oxide dielectric layer  118   a  has an etching rate higher than the etching rate of the SiNx or SiON liner layer  116   a.  Hence, it is more difficult to remove the liner layer  116   a  than the dielectric layer  118   a.  Therefore, the liner layer  116   a  can be used for an etch stop layer for patterning the dielectric layer  118   a.  In other words, during the etching process on the liner layer  116   a,  the etching rate becomes lower to prevent the conducting line  122  from being over-etched.  
         [0033]     The above description provides a full and complete description of the preferred embodiments of the present invention. Various modifications, alternate construction, and equivalent may be made by those skilled in the art without changing the scope or spirit of the invention. Accordingly, the above description and illustrations should not be construed as limiting the scope of the invention which is defined by the following claims.