Abstract:
An multi-level interconnection uses a glue layer material as a via plug or contact plug. An method of forming the multi-level interconnection includes: forming a first opening and a wider second opening in a dielectric layer, whereas the first opening exposes the conductive layer and the second opening is above the first opening; and filling the first opening with titanium, titanium nitride or tungsten nitride.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 87103896, filed Mar. 17, 1998, the full disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to a structure of a multi-level interconnection and a method of fabricating the same, and more particularly to the structure and the fabrication of a multi-level interconnection without using a barrier layer. 
     2. Description of the Related Art 
     The increasing of the integration of the integrated circuited (IC) causes the insufficiency of the chip surface for formation of interconnection. To satisfy the requirement of more wiring lines as the device size is shrinking, a design of multi-level interconnection is needed for IC fabrication. The multi-level interconnection is a three-dimensional wiring line structure. To form a multi-level interconnection structure, the first or lower layer of the metal wiring line is first formed, connecting with the source/drain region of the metal-oxide semiconductor transistor (MOS) on a substrate by a contact plug through a contact hole. The second layer of the metal wiring line is then formed, connecting with the first metal wiring line by a via plug through a plug hole. The metal wiring lines can either be made from metal or any conductive material such as polysilicon. More than two layers of metal wiring lines can be formed if necessary. 
     Conventionally, there are two ways for fabricating plugs and metal lines. The first method includes two steps of forming a plug and a metal wiring line, respectively. A dielectric layer is first formed above a region desired for being coupled. After forming a opening in the dielectric layer by photolithography, a conductive material is deposited in the opening to accomplish the plug. Then, a metal layer is deposited and patterned to form a metal wiring line, connecting with the plug. Finally, an inter-metal dielectric layer is deposited. The other method utilizes a damascene technique, which accomplishes the plug and the metal wiring line simultaneously. 
     Referring to FIG. 1, which is a cross-sectional views showing the structure of the plug and the metal wiring line fabricated a conventional damascene technique. On a semiconductor substrate  10 , a conductive layer  12  is first formed. Then, a dielectric layer  14  id formed on the conductive layer, using a material such as a dielectric layer with low dielectric coefficient. In the dielectric layer  14 , an opening  15  and an opening  13  are formed successively. Next, a glue layer  16  is formed on the opening  15  and the opening  13 . Generally, the common material for the glue layer  16  includes titanium/titanium nitride (Ti/TiN), tungsten nitride (WN), tantulum or tantulum nitride (TaN). The glue layer  16  is used to enhance the adhesive force of the later deposited conductive material and obstruct the diffusion of the conductive material. Then, a conductive layer  18 , such as conductive materials of superior conductivity, tungsten or aluminum. Then, a chemical mechanical polishing (CMP) is performed to accomplish the conventional damascene process. 
     However, as the size of semiconductor devices keeps on shrinking, the width of the via hole or the contact hole is desired to be narrower and the aspect ratio becomes much higher than before. Conventionally, before filling of the conductive material, a glue layer is formed on the inner periphery of the hole so that the width of the hole will reduce. If the step coverage of the conductive material is poor, which is usually in this case and difficult to overcome, short circuit tends to occur and the difficulties in filling conductive layer into the hole becomes even greater. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a metal damascene process without a glue layer but filling metal material directly into the contact hole or via hole. 
     An multi-level interconnection using a glue layer material as a via plug or contact plug is disclosed. 
     An method of forming the multi-level interconnection is further disclosed, which includes: forming a first opening and a wider second opening in a dielectric layer, whereas the first opening exposes the conductive layer and the second opening is above the first opening; and filling the first opening with titanium, titanium nitride or tungsten nitride. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The description is made with reference to the accompanying drawings in which: 
     FIG. 1 is a cross-sectional view showing a structure of a plug and a metal wiring line according to a conventional process; 
     FIGS. 2A to  2 D are cross-sectional views showing the damascene process steps of fabricating a plug and a metal wiring line in accordance with a preferred embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 2A, the area numbered as  22  represents a conductive layer  22 , which can be one of the source/drain regions of a transistor device, the metal layer of a gate structure or a metal layer of an interconnection, whereas the MOS device on the substrate  20  is not completely shown. On the substrate  20 , a dielectric layer  24  is formed to cover the conductive layer  22 . The dielectric layer  24  is further processed to form an opening  23  and an opening  25  therein. The opening  23  exposes the conductive layer  22 . The opening  25  is above the opening  293  and has a width larger than the opening  23 . The material of the dielectric layer  24  is preferrably dielectric of relatively low dielectric coefficient. 
     Referring to FIG. 2B, a conductive layer  32  is formed over the surface of the substrate  20 . The material of the conductive layer  32  is preferrably titanium, tiatnium nitride, tungsten nitride or the other material suitable for glue layers. The conductive layer  32  is formed until at least the opening  23  is completely filled and the conductive layer  32  is formed to be coupled with the exposed portion of the conductive layer  22 . The portion of the conductive layer  32  in the opening  23  serves as a conventional via plug or contact plug. The thickness of the conductive layer  32  is substantially larger than the radius of the opening  23 . For example, if the conductive layer  32  is made of titanium, the conductive layer  32  can be formed by magnetic DC sputtering. The technique of magnetic DC sputtering provides the conductive layer  32 , such as titanium, titanium nitride or tungsten nitride, with excellent step coverage and superior density. 
     Conventionally, a glue layer is formed on the inner periphery of the opening before the formation of a metal layer in order to enhance the adhesive force between the metal layer and the dielectric layer. However, the formation of the glue layer even further increase the aspect ratio of the opening and causes difficulties in the continuous process of metal deposition. According to the invention, the conventional glue layer is formed thicker to fill the opening to serve as a via plug or a contact plug, which therefore overcome the problems coming with higher aspect ratio. Even more, the conductive layer  32  not only has the function of the glue layer but also has the advantage of higher transmission rate. 
     Next, referring to FIG. 2C, a metal layer  42  is further deposited on the conductive layer  32  to completely fill the opening  25 . The previously formed conductive layer  32  on the inner periphery of the opening  25  functions as a glue layer to increase the adhesive force between the dielectric layer  24  and the conductive layer  32 . The material of the metal layer  42  can be aluminum, copper, tungsten or the like. 
     Next, referring to FIG. 2D, an etching back process, preferrably a chemical mechanical polishing (CMP) process, is performed to remove the additional metal layer  42  and conductive layer  32 , using the dielectric layer  24  as an etching stop. Consequently, a portion of the conductive layer  32   a  and the metal layer  42   a  are at about the same level as the surface of the dielectric layer  24 . The metal layer  42   a  and a portion of the conductive layer  32   a  in the opening  25  together form the metal wiring line of the damascene structure. 
     It is therefore clear that the present invention has the following characteristics: 
     (1) The plug of the damascene structure is directly formed by using the conventional glue layer. 
     (2) The thickness of the conductive layer for a plug is substantially larger than the radius of the plug opening. 
     (3) Titanium plugs titanium nitride plugs or tungsten nitride plugs can all be formed according to the present invention. 
     (4) The conductive material formed to be a contact plug can functions as the glue layer of the via plug. 
     While the invention has been described by way of example and in terms of a preferred embodiment it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements and procedures such as the formation of a multiple voltage transistor. The scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.