Abstract:
A giant magnetoresistance (GMR) pad on the same level of GMR memory bit layer is used as an intermediate connection for plugs between the GMR pad and an underlying diffusion metal layer. A single large power metal plug is used to connect the GMR pad and the overlying power plane metal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the priority benefit of provisional application Ser. No. 60/721,217, filed Sep. 28, 2005, the full disclosure of which is incorporated herein by reference. 

   BACKGROUND 
   1. Field of Invention 
   The present invention relates to a static memory. More particularly, the present invention relates to a magneto resistive random access memory (MRAM). 
   2. Description of Related Art 
   MRAM is a type of non-volatile memory with fast programming time and high density. A MRAM cell of giant magneto resistance (GMR) type has two ferromagnetic layers separated by a nonmagnetic conducting layer. Information is stored as directions of magnetization vectors in the two ferromagnetic layers. 
   The resistance of the nonmagnetic layer between the two ferromagnetic layers indicates a minimum value when the magnetization vectors of the two ferromagnetic layers point in substantially the same direction. On the other hand, the resistance of the nonmagnetic layer between the two ferromagnetic layers indicates a maximum value when the magnetization vectors of the two ferromagnetic layers point in substantially opposite directions. Accordingly, a detection of changes in resistance allows information being stored in the MRAM cell. 
   In conventional MRAM process, metal plugs used to connect a diffusion metal layer under a layer of GMR memory bits and a power plane metal over the layer of GMR memory bits have high contact resistance due to the small size and high aspect ratio of the metal plugs. Hence, there is a need to develop a low-resistance metal plug to connect the diffusion metal layer and the power plane metal. 
   SUMMARY 
   A giant magneto resistance (GMR) pad on the same level of GMR memory bit layer is used as an intermediate connection for plugs between the GMR pad and an underlying diffusion metal layer. A single large power metal plug is used to connect the GMR pad and the overlying power plane metal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention can be more fully understood by reading the following detailed description of the preferred embodiment, with reference made to the accompanying drawings as follows: 
       FIGS. 1A-1C  are cross-sectional diagrams showing a method of fabricating a low-resistance metal plug for connecting a diffusion metal layer under MRAM devices and a power metal layer over the MRAM devices according to an embodiment of this invention. 
   

   DETAILED DESCRIPTION 
   Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
     FIGS. 1A-1C  are cross-sectional diagrams showing a method of fabricating a low-resistance metal plug for connecting a diffusion metal layer under MRAM devices and a power metal layer over the MRAM devices according to an embodiment of this invention. In  FIG. 1A , a substrate  100  having a peripheral area  102  and a memory area  104  is provided. A diffusion metal layer  110  and a first dielectric layer  120  are sequentially formed on the substrate  100 . After patterning the first dielectric layer  120  to form first openings  125  therein on the peripheral area  102 , metal is deposited to fill the first openings  125  to form plugs  130 . 
   A material of the diffusion metal layer  110  can be any conductive material, such as metal or metal alloy. For example, Cu or Al—Cu alloy are usually used to fabricate interconnects in semiconductor integrated circuits. A material of the first dielectric layer  120  can be, for example, silicon oxide or low-k dielectric materials. The first dielectric layer  120  can be patterned by, for example, a photolithography process and then an etching process. A material of the plugs  130  can be, for example, tungsten or other conductive metals. 
   In  FIG. 1B , a GMR stack layer is deposited, on the first dielectric layer  120  and the plugs  130 , and then patterned to form a GMR pad  140  on the peripheral area  102  and a GMR memory bit  150  on the memory area  104 . The GMR pad  140  is located on the plugs  130  to electrically connect thereto. The GMR stack layer described above comprises a first ferromagnetic layer, a nonmagnetic conducting layer, and a second ferromagnetic layer. 
   In  FIG. 1C , a second dielectric layer  160  is formed on the first dielectric layer  120 , the GMR pad  140  and the GMR memory bit  150  and then patterned to form a second opening  165  in the second dielectric layer  160  to expose the GMR pad  140  and the GMR memory bit  150  simultaneously. Next, a conductive layer is formed on the second dielectric layer  160  and in the second opening  165  and then patterned to form a power metal layer  170  having a power metal plug  170   a  and a power plane metal  170   b.    
   The material of the second dielectric layer  160  may be the same as that of the first dielectric layer  120  or not; the material can be, for example, silicon oxide or other suitable low-k dielectric material. The material of the power metal layer  170  can be, for example, metal or metal alloy, such as Cu or Al—Cu alloy. 
   According to the embodiment provided above, a GMR pad formed at the same time with the GMR memory bit serves as an intermediate connection of the power plane metal and the diffusion metal layer. Therefore, the aspect ration of the plugs can be decreased to increase the yield. Moreover, the single large power metal plug is used to connect the GMR memory bit, the GMR pad and the power plane metal to have advantages including much lower resistance and better step coverage. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.