Abstract:
A method for preventing metal extrusion in a semiconductor structure is disclosed in this present invention. The point of this invention is that the first metal is suffered to a thermal process before the fabrication of a conformal glue layer into a via onto the first metal layer, and thus the first metal layer will not be extruded by thermal effect any more during the following processes. Therefore, this invention can provide a more efficient method for preventing metal extrusion in a semiconductor structure, and the phenomenon of the raising resistance caused by the metal extrusion can be avoided thereby.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This present invention relates to a method for preventing metal extrusion, and more particularly to a method for preventing metal extrusion in semiconductor structure.  
           [0003]    2. Description of the Prior Art  
           [0004]    In semiconductor structure, metal contact plays a very important role. The metal contacts can connect semiconductor device through metal layers. In the view of one having ordinary skill in the art, metal contacts are usually formed by the follow methods. One method for forming metal contact is “through ARC”. The “through ARC” means the metal via is through the anti-reflection coating (ARC) on the metal layer. As shown in FIG. 1, an anti-reflecting coating  110  is on a first metal layer  100 . A dielectric layer  120  is blanketed onto the first metal layer  100  and the anti-reflection coating  110 . After a etching step, a via  130  is fabricated through the dielectric layer  120  and the anti-reflecting coating  110 , and thus portion of the first metal layer  100  is exposed by the via  130 . Subsequently, a glue layer  140  is deposited into the via  130 , and a secondary metal layer  150  is filled filled into the via  130 .  
           [0005]    Another well-known process for fabricating a metal contact in a semiconductor structure is as shown in FIG. 2. In contrast with the above-mentioned method, the etching process for forming the via  130  is stopped on the ARC  110 , and the first metal layer  100  will not be exposed by the via  130 .  
           [0006]    However, there are many problems in the above-mentioned methods. In the method of “through ARC”, during the formation of the glue layer and the secondary metal layer, the first metal layer  100  will be extruded by the thermal effect and some unwanted reaction may be occurred. In the case of aluminum as the first metal layer  100  and tungsten as the secondary metal layer  150 , during the formation of the glue layer  140  and the secondary metal layer  150 , the first metal layer  100  will be extruded through the glue layer  140 . Moreover, when the secondary metal layer  150  is fabricated by chemical vapor deposition (CVD) with WF 4 , the side-reaction between the extruded aluminum and WF 4  will occur, as the following reaction 1, and the resistance of the semiconductor structure will be raised by the produce  160  of the reaction 1.  
           WF 4 +Al→AlF 3    (reaction 1)  
           [0007]    On the other hand, in the above-mentioned method of “stop on ARC”, the reaction 1 will not occur, but the average resistance of the semiconductor structure is higher than the resistance of the semiconductor structure employing the method of “through ARC”. Ordinarily, the method of “through ARC” is utilized wider than the method of “stop on ARC”. Hence, it is important to develop an efficient method for preventing the metal extrusion of the method of “through ARC” in a semiconductor structure.  
         SUMMARY OF THE INVENTION  
         [0008]    In accordance with the present invention, a method is provided for preventing metal extrusion during the formation of a metal contact in a semiconductor structure. The phenomenon of raising resistance in a semiconductor structure can be efficient removed by preventing the metal extrusion during the formation of a metal contact.  
           [0009]    In accordance with the above-mentioned objects, the invention provides a method for preventing metal extrusion in a semiconductor structure. Due to a thermal process before the formation of the glue layer into a metal via, the phenomenon of metal extrusion in a semiconductor structure can be precluded efficiently. Therefore, this invention provides a method for keeping a semiconductor structure from raising resistance by preventing metal extrusion during the formation of the metal contact. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0011]    [0011]FIG. 1 is a diagram showing a metal contact fabricated by the method of “through ARC” in the prior art;  
         [0012]    [0012]FIG. 2 is a diagram showing a metal contact fabricated by the method of “stop on ARC” in the prior art;  
         [0013]    [0013]FIG. 3 is a flow chart showing the method for preventing metal extrusion in a semiconductor structure according to this present invention; and  
         [0014]    [0014]FIGS. 4A to  4 C show the method for preventing metal extrusion in a semiconductor structure according to this invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    Some sample embodiments of the invention will now be described in greater detail. Nevertheless, it should be recognized that the present invention can be practiced in a wide range of other embodiments besides those explicitly described, and the scope of the present invention is expressly not limited except as specified in the accompanying claims.  
         [0016]    One preferred embodiment of this invention is a method for preventing metal extrusion. At first, a first metal layer with an anti-reflection coating layer thereon is provided on a substrate. A dielectric layer is blanketed onto the substrate and the anti-reflection coating layer. After an etching step, a via is formed through the dielectric layer and the anti-reflection coating layer, and portion of the first metal layer is exposed by the via. Subsequently, a thermal process is performed to extrude the first metal layer. The temperature of the above-mentioned thermal process is equal to/higher than the highest temperature of the following process. Following the thermal process, a conformal glue layer is formed into the via. Finally, the via is filled with a secondary metal layer. Because the thermal process is performed before the formation of the glue layer and the secondary metal layer, the first metal layer will not be extruded by thermal effect during the following processes.  
         [0017]    Another preferred embodiment according to this present invention is a method for preventing metal extrusion in a semiconductor structure. FIG. 3 is a flowchart of the above-mentioned method for preventing metal extrusion. At first, a first metal layer with an anti-reflection coating layer thereon is provided on a substrate, as the step  310 . The first metal layer may be aluminum (Al). The anti-reflection coating layer may be consisted of a Ti layer and a TiN layer. As shown in the step  320 , a dielectric layer is blanketed onto the substrate and the anti-reflection coating layer. The dielectric layer may be SiO 2 , low-K dielectric material, or other dielectric materials.  
         [0018]    Next, the dielectric layer and the anti-reflection coating layer are etched, as the step  330 , and a via is fabricated through the dielectric layer and the anti-reflection coating layer. After the formation of the via, part of the first metal layer is exposed by the via. Subsequently, a thermal process is performed as shown in the step  340 . In order to prevent the extrusion of the first metal layer by thermal effect during the following process, the temperature of the thermal process in step  340  may be equal to/or higher than the temperature while the formation of the first metal layer. Preferably, the temperature of the thermal process in step  340  is equal to/or higher than the highest temperature during the following processes.  
         [0019]    After the thermal process, a conformal glue layer is fabricated into the via, as step  350 . The glue layer may comprise a Ti layer and a TiN layer. Finally, as shown in step  260 , a secondary metal layer is filled into the via, and the unwanted secondary metal layer is removed by a ordinary technology as chemical mechanical polishing (CMP). The secondary metal layer may be tungsten (W), or other conductive materials.  
         [0020]    Another preferred embodiment of this present invention is a method for preventing metal extrusion in a semiconductor structure. Referred to FIG. 4A, a first metal layer  410  is provided on a semiconductor substrate  400 , and an anti-reflection coating layer  420  is formed onto the first metal layer  410 . A dielectric layer is blanketed onto the substrate  400  and the anti-reflection coating layer  420 . In this manner, the first metal layer  410  may be consisted of aluminum, or other conductive materials. The anti-reflection coating layer  420  may comprise a Ti layer and a TiN layer, wherein the thickness of the Ti layer is 50˜250 angstrom and the thickness of the TiN layer is 200˜400 angstrom. The dielectric layer  430  comprises SiO 2 , low-K dielectric material, or the other dielectric materials.  
         [0021]    Subsequently, the dielectric layer  430  and the anti-reflection coating layer  420  are etching for fabricating a via  440  through the dielectric layer  430  and the anti-reflection coating layer  420 , and portion of the first metal layer  410  is exposed by the via  440 . After fabricating the via  440 , an important step of this present invention is performed. In order to prevent the extrusion of the first metal layer  410  during the following process, the first metal layer  410  is suffered to a thermal process. Next, a conformal glue layer  450  is fabricated into the via  440 , as shown in FIG. 4B. The glue layer  450  may comprises a Ti layer and a TiN layer.  
         [0022]    The temperature of the above-mentioned thermal process before the formation of the glue layer  450  is a key of this present invention. Preferably, the temperature of the above-mentioned thermal process is equal to/or higher than the temperature during the formation of the first metal layer. More preferably, the temperature of the above-mentioned thermal process is equal to/or higher than the temperature of the processes after the step for forming the via. For example, if the highest temperature during the following processes is the temperature of the glue layer  450  formation at 700˜800 degree C., the temperature of the above-mentioned thermal process may be set at 700˜800 degree C. or higher.  
         [0023]    As shown in FIG. 4C, a secondary metal layer  460  is filled into the via  440 , and the unwanted secondary metal layer  460  is removed by the technology in the prior art, such as chemical mechanical polishing. The secondary metal layer  460  may be tungsten (W), or the like. The secondary metal layer  460  is formed by chemical vapor deposition (CVD), or other ordinary process.  
         [0024]    According to this preferred embodiment, because the first metal layer is suffered to a thermal process before the fabricating of the glue layer, the extrusion of the first metal layer will not occur by thermal effect during the following processes. Thus, the side-reaction between the first metal layer and the material of the secondary metal layer as above-cited in the prior art will not happen during the formation of the secondary metal layer, and the resistance of the semiconductor structure according to this present invention will not be raised.  
         [0025]    According to the preferred embodiments, this present invention discloses a method for preventing metal extrusion in a semiconductor structure. The first metal layer is suffered to a thermal process before fabricating a conformal glue layer into a via, wherein portion of the first metal layer is exposed by the via. Because the temperature of the above-mentioned thermal process is equal to or higher than the highest temperature during the following processes, the first metal layer will not be extruded any more by thermal effect during the following processes. Moreover, the method according to this present invention can keep the first metal layer from the side-reaction during the formation of the secondary metal layer into the via. Thus, this invention provides an efficient method for preventing the raising of the resistance in a semiconductor structure due to metal extrusion.  
         [0026]    Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended to be limited solely by the appended claims.