Abstract:
A method for reducing leakage current in a semiconductor structure is disclosed. One or more dielectric layers are formed on a semiconductor substrate, on which at least one device is constructed. A hydrogen-containing layer is formed over the dielectric layers. A silicon nitride passivation layer covers the dielectric layers and the hydrogen-containing layer. The hydrogen atoms of the hydrogen-containing layer are introduced into the dielectric layers without being blocked by the silicon nitride layer, thereby reducing leakage current therein.

Description:
BACKGROUND 
   The present invention relates generally to an integrated circuit (IC) design, and more particularly to a method for reducing leakage current in an IC chip. 
   In semiconductor technology, it is important to protect devices from mechanical damage and environmental contamination which may affect the proper operation of the devices. A conventional method commonly used for providing such protection is to directly coat the devices with a thin film of silicon nitride. Silicon nitride is commonly used since it provides resistance against wear and serves as a good barrier to sodium ions, which can penetrate into oxide layers of an IC chip and destroy their insulating properties. This layer of passivation silicon nitride is usually deposited at relatively low temperatures using a technique known as plasma enhanced chemical vapor deposition (PECVD). Under certain circumstances, a nitride layer alone is not enough for protecting its underlying devices. For instance, in physiological saline solution, under an applied electric field created from active components on an IC chip, the property of silicon nitride rapidly degrades. For this reason, in conventional methods, laminated layers of silicon oxide and silicon nitride may be used, wherein the silicon oxide can provide insulation to keep the current flow from the silicon nitride, while allowing the silicon nitride to protect the silicon oxide from sodium ions. 
   After formation of the silicon nitride and silicon oxide, a hydrogen-forming gas-annealing process is performed for driving hydrogen atoms into inter-metal dielectric layers of the IC chip to fix dangling bonds therein, thereby reducing their leakage current. However, the layer of silicon nitride acts as a barrier against the hydrogen diffusion, thereby lessening the effectiveness of the hydrogen-forming gas annealing process. For this reason, multiple stages of hydrogen-forming gas annealing process are often required in order to reduce the leakage current to an acceptable level. The multiple-stage annealing process is time-consuming and costly. 
   Therefore, desirable in the art of semiconductor manufacturing are methods for effectively and efficiently fabricating a semiconductor device with reduced leakage current. 
   SUMMARY 
   The present invention discloses a method for reducing leakage current in a semiconductor structure. In one embodiment, a semiconductor substrate, on which at least one device is constructed, is provided. One or more dielectric layers are formed on the semiconductor substrate. A hydrogen-containing layer is formed over the dielectric layers. A silicon nitride passivation layer covers the dielectric layers and the hydrogen-containing layer. The hydrogen atoms of the hydrogen-containing layer are then introduced into the dielectric layers. 
   The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a cross section of a semiconductor device fabricated by a conventional method. 
       FIG. 2  illustrates a cross section of a semiconductor device with reduced leakage current fabricated by a method in accordance with one embodiment of the present invention. 
   

   DESCRIPTION 
     FIG. 1  illustrates a cross section  100  of a semiconductor device  101  fabricated by a conventional method. Multiple layers of dielectric are typically formed on top of the semiconductor device  101 . An interlayer dielectric (ILD)  102  is deposited on a semiconductor substrate. The ILD  102  is then covered by several layers of inter-metal dielectric (IMD) such as IMDs  104  and  106  where the contacts therein may be coupled together to provide connection between various metal layers. A layer of passivation silicon oxide  108  covers the IMD  106  to provide a layer of insulation. To protect the semiconductor device  101 , a layer of passivation silicon nitride (SiN)  110  is overlaid above the layer of passivation oxide  108  and the IMDs  104  and  106 . The passivation SiN  110  provides resistance to wear and serves as a barrier against sodium ions, which can penetrate into the passivation oxide  108  and IMDs  104  and  106 , thereby destroying their insulating properties. A hydrogen-forming gas annealing process is performed to reduce the leakage current in the IMDs  104  and  106 . Generally, several stages of hydrogen-forming gas annealing are required before the leakage current is reduced to an acceptable level. 
   The hydrogen-forming gas annealing process can be ineffective and inefficient, since the passivation SiN is a barrier to hydrogen diffusion that is desired for reducing the leakage current in an IC chip. 
     FIG. 2  illustrates a cross section  200  of a semiconductor device  201  with reduced leakage current fabricated by a method in accordance with one embodiment of the present invention. The semiconductor device  201  is formed in a fashion similar to that of the semiconductor device  101  (see  FIG. 1 ), except that a layer of hydrogen-containing layer  202  is inserted between a layer of passivation silicon oxide  204  and a layer of passivation silicon nitrite (SiN)  206 . The layer of passivation oxide  204  is deposited to cover one or more layers of inter-metal dielectric  208  and  210  for providing necessary insulation. The hydrogen-containing layer  202  is deposited on the layer of passivation oxide  204 . To protect the semiconductor device  201  from outside environment, the layer of passivation SiN  206  is overlaid above the hydrogen-containing layer  202 . The passivation SiN  206  can provide resistance to wear and serves as a good barrier to prevent sodium ions from penetrating into the passivation oxide  204  or the hydrogen-containing layer  202 . A hydrogen-forming gas annealing process is performed to drive hydrogen atoms from the hydrogen-containing layer  202  into the layers of inter-metal dielectric  208  and  210  for fixing dangling bonds therein, thereby effectively reducing the leakage current thereof. 
   The hydrogen-containing layer  202  is made substantially of oxide and can be formed by using technology, such as PECVD and high density plasma chemical vapor deposition (HDPCVD), low pressure chemical vapor deposition (LPCVD), atmospheric pressure chemical vapor deposition (APCVD), and spin-on coating. Besides oxide, it can also be made of materials, such as low K dielectric materials. The thickness requirement for the hydrogen-containing layer  202  can also be widely ranged from a few hundred angstroms to thousands of angstroms. In this embodiment, the thickness of the hydrogen-containing layer is between about 500 and 20,000 angstroms. The hydrogen-containing layer has a density of hydrogen between about 5 atom % and 40 atom %, such that it provides sufficient a hydrogen source during the later annealing process. 
   In another embodiment, the hydrogen-containing layer  202  replaces the entire layer of passivation oxide  204 . In such case, no deposition of the passivation oxide  204 , independent from the formation of the hydrogen-containing layer  202 , is needed. The passivation SiN  206  still remains on top of the hydrogen-containing layer  202 . The hydrogen-forming gas annealing process is still performed for reducing the leakage current in the inter-metal dielectric layers  208  and  201 . 
   In another embodiment, the hydrogen-containing layer can also be inserted within the dielectric layers such as between the layers of inter-metal dielectric  210  and interlayer dielectric  212  to provide effective hydrogen penetration for the semiconductor device  201  during the hydrogen-forming gas annealing process. By implementing the extra layer of hydrogen-containing layer  202 , the hydrogen-forming gas annealing process would only need to be performed once to effectively reduce the leakage current for the semiconductor device  201 . 
   Table I provides a set of leakage current data resulted from a first stage of hydrogen annealing process: 
   
     
       
             
           
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
             
           
         
             
               TABLE I 
             
           
           
             
                 
             
             
               Leakage Current Mean (mV/sec) 
             
           
        
         
             
                 
                 
               Type-A 
               Type-A 
               Type-B 
               Type-B 
             
             
                 
               Without 
               hydrogen- 
               hydrogen- 
               hydrogen- 
               hydrogen- 
             
             
                 
               hydrogen- 
               containing 
               containing layer 
               containing layer 
               containing layer 
             
             
                 
               containing 
               layer of 500 A 
               of 1,000 A 
               of 500 A 
               of 1,000 A 
             
             
                 
               layer 
               thickness 
               thickness 
               thickness 
               thickness 
             
           
        
         
             
                 
               Leakage 
               Leakage 
                 
               Leakage 
                 
               Leakage 
                 
               Leakage 
                 
             
             
               Size 
               current 
               current 
               Δ% 
               current 
               Δ% 
               current 
               Δ% 
               current 
               Δ% 
             
             
                 
             
           
        
         
             
               2.8 μm 
               18.49 
               17.63 
               −4.64% 
               15.38 
               −16.83% 
               14.64 
               −20.82% 
               14.92 
               −19.34% 
             
             
               3.0 μm 
               18.12 
               17.98 
               −0.78% 
               16.30 
               −10.06% 
               15.24 
               −15.88% 
               14.70 
               −18.85% 
             
             
               3.3 μm 
               15.85 
               14.77 
               −6.82% 
               13.04 
               −17.76% 
               12.75 
               −19.55% 
               12.58 
               −20.65% 
             
             
               4.0 μm 
               18.57 
               16.63 
               −10.44% 
               14.62 
               −21.26% 
               15.14 
               −18.44% 
               14.40 
               −22.45% 
             
             
                 
             
           
        
       
     
   
   Table II provides a set of leakage current data resulted from a second stage of hydrogen annealing process: 
   
     
       
             
           
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
             
             
             
           
         
             
               TABLE II 
             
           
           
             
                 
             
             
               Leakage Current Mean (mV/sec) 
             
           
        
         
             
                 
                 
               Type-A 
               Type-A 
               Type-B 
               Type-B 
             
             
                 
                 
               hydrogen- 
               hydrogen- 
               hydrogen- 
               hydrogen- 
             
             
                 
               Without 
               containing layer 
               containing layer 
               containing layer 
               containing layer 
             
             
                 
               hydrogen- 
               of 500 A 
               of 1,000 A 
               of 500 A 
               of 1,000 A 
             
             
                 
               containing 
               thickness 
               thickness 
               thickness 
               thickness 
             
           
        
         
             
               Size 
               layer 
                 
               Δ% 
                 
               Δ% 
                 
               Δ% 
                 
               Δ% 
             
             
                 
             
           
        
         
             
               2.8 μm 
               16.77 
               15.83 
               −14.37% 
               15.09 
               −18.41% 
               13.51 
               −26.91% 
               13.87 
               −24.99% 
             
             
               3.0 μm 
               17.58 
               17.35 
               −4.24% 
               16.15 
               −10.85% 
               14.48 
               −20.10% 
               14.26 
               −21.30% 
             
             
               3.3 μm 
               14.57 
               13.65 
               −13.89% 
               12.99 
               −18.02% 
               11.59 
               −26.85% 
               11.79 
               −25.59% 
             
             
               4.0 μm 
               17.08 
               15.38 
               −17.19% 
               14.24 
               −23.31% 
               13.88 
               −25.24% 
               12.88 
               −30.63% 
             
             
                 
             
           
        
       
     
   
   As shown in Tables I and II, both type A and B are hydrogen-containing layers where type B has a higher hydrogen density than that of type A. Four different device sizes (column  1 ) have been tested. Each semiconductor device within all size categories was tested under five different scenarios: a set of semiconductor devices not implemented with any hydrogen-containing layer (column  2 : control), and the application of two different types of hydrogen-containing layer under two different thicknesses (columns  3 ,  5 ,  7 ,  9 ). For example, column  3  shows the leakage current data resulted from a set of semiconductor devices that are implemented with a predetermined type of hydrogen-containing layer (type A) that has a thickness of 500A, while column  5  shows the leakage current data resulted from another set of semiconductor devices that are implemented the same type of hydrogen-containing layer (type A) with a thickness of 1000A. Similarly, tests were performed with another type of hydrogen-containing layer (type B) under two different thicknesses 500A (column  7 ) and 1000A (column  9 ). Columns  4 ,  6 ,  8 , and  10  correspond to the reduction in leakage current for the data presented in columns  3 ,  5 ,  7 , and  9 , compared against the control test (column  2 ). For example, after the first stage of annealing process, the application of a type B hydrogen-containing layer with a thickness of 500A provides an 18.44% reduction in current leakage given a device size of 4.0 μm. As another example, after the second stage of annealing process, the application of a type A hydrogen-containing layer with a thickness of 1000A provides a 10.85% reduction in current leakage given a device size of 3.0 μm. 
   With the implementation of the hydrogen-containing layer, the leakage current can be reduced. The leakage current can be further reduced by repeating the hydrogen-forming gas annealing process (improvement of the results in Table II over the results in Table I). 
   In this invention, an additional hydrogen-containing layer film is implemented within the passivation layers. Prior to the hydrogen-forming gas annealing process, by inserting a hydrogen-containing layer film between a layer of passivation oxide and a layer of passivation nitride or directly replacing the layer of passivation oxide with hydrogen-containing layer, the passivation SiN is less likely to block hydrogen penetration, thus allowing reduction in leakage current. 
   The above illustration provides many different embodiments or embodiments for implementing different features of the invention. Specific embodiments of components and processes are described to help clarify the invention. These are, of course, merely embodiments and are not intended to limit the invention from that described in the claims. 
   Although the invention is illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention, as set forth in the following claims.