Abstract:
An integrated circuit including a substrate; a circuit pattern formed over the substrate; and one or more fences formed around edges of the circuit pattern, each of the one or more fences having a determined electrical resistance which is used to detect the addition of malicious circuitry. Each fence has a determined electrical resistance which is used to monitor the validity of the fence.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a non-provisional application claiming priority to U.S. Provisional Patent Application Ser. No. 60/925,519 filed Apr. 20, 2007. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to integrated circuits, and in particular to security features applied to an integrated circuit that detects alteration of the integrated circuit. 
       BACKGROUND OF THE INVENTION 
       [0003]    If left unprotected, integrated circuits (ICs) are subject to alteration, by either deletion of design data or insertion of such data. Such alteration may be particularly unwanted when the IC is used in sensitive applications. Conventionally, a determination of whether an IC has been altered by deletion of design data can be done using built-in self-testing (BIST). However, detecting the addition of malicious circuitry poses a more challenging problem. Further, even when checking for deletions using BIST, each device in the IC must be checked. Thus, conventional methods, such as BIST, are not optimally effective in securing ICs against alteration. 
       SUMMARY OF THE INVENTION 
       [0004]    An integrated circuit according to an exemplary embodiment of the present invention comprises a substrate; a circuit pattern formed over the substrate; and one or more fences formed around edges of the circuit pattern, each of the one or more fences having a determined electrical resistance. 
         [0005]    In at least one embodiment, the circuit pattern comprises one or more layers, and at least one of the one or more fences is formed at each layer. 
         [0006]    A method of securing an integrated circuit having a circuit pattern according to an exemplary embodiment of the present invention comprises the steps of: analyzing design data for the circuit pattern to determine edges of the circuit pattern; determining a route that surrounds the edges of the circuit pattern; and forming a fence along the route, wherein the fence has a determined electrical resistance. 
         [0007]    In at least one embodiment, the step of analyzing comprises dividing the design data into partitions. 
         [0008]    In at least one embodiment, the step of analyzing comprises determining which partitions are too close together to accommodate circuitry. 
         [0009]    In at least one embodiment, the method further comprises a step of merging the partitions that are too close together to accommodate circuitry. 
         [0010]    In at least one embodiment, the step of merging comprising polygon merging. 
         [0011]    In at least one embodiment, the step of determining the route comprises applying a set of rules to ensure that the route provides at least a minimum clearance from the edges of the circuit pattern. 
         [0012]    In at least one embodiment, the step of forming a fence comprises forming the fence in a polygon format. 
         [0013]    In at least one embodiment, the step of forming a fence further comprises generating layout data for the fence. 
         [0014]    In at least one embodiment, the layout data is generated using a set of rules. 
         [0015]    In at least one embodiment, the step of forming a fence comprises maintaining a running sum of resistances for the fence. 
         [0016]    A method of testing an integrated circuit comprising a substrate, a circuit pattern formed over the substrate, and one or more fences formed around edges of the circuit pattern, each of the one or more fences having a determined electrical resistance, according to an exemplary embodiment of the present invention comprises the steps of: measuring electrical resistance of the one or more fences; and comparing the measured electrical resistance to the determined electrical resistance. 
         [0017]    In at least one embodiment, the circuit pattern comprises one or more layers, at least one of the one or more fences is formed at each layer, and the method further comprises: measuring inter-layer capacitance of the fences formed at each layer; and comparing the inter-layer capacitance to a determined inter-layer capacitance of the fences at each layer. 
         [0018]    These and other features of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of this invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Various exemplary embodiments of this invention will be described in detail, with reference to the following figures, wherein: 
           [0020]      FIG. 1  is a block diagram of a system for generating a fence for an integrated circuit according to an exemplary embodiment of the present invention; and 
           [0021]      FIGS. 2A-2C  are plan views of a circuit pattern showing a process of applying a fence to the circuit pattern according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0022]    The present invention is directed to a system and method of securing an integrated circuit against alteration. It should be appreciated that the term “integrated circuit” as used herein is intended to cover any device that includes an electric circuit pattern, having semiconductor components or otherwise, including but not limited to display devices, such as liquid crystal displays and plasma displays, microcontrollers, memory devices, processors, sensors, power management circuits and amplifiers. 
         [0023]    More particularly, various exemplary embodiments of the present invention are directed to systems and methods for securing an IC by forming a fence around edges of the various components of the IC pattern. The fence has known electrical characteristics, such as, for example, resistance and, in the case of multiple fences formed within individual layers of the IC, inter-layer capacitance. Thus, any alteration to the fence can be detected by detecting changes in the electrical characteristics of the fence. The fence may be generated using an algorithm that has a spatial based solution so as to divide design data from white space (i.e., space in which no circuit pattern is formed). 
         [0024]      FIG. 1  is a block diagram of a system, generally designated by reference number  1 , for generating a fence for an integrate circuit according to an exemplary embodiment of the present invention. The system  1  includes a circuit pattern analyzer  10 , a route calculator  20 , and a fence generator  30 . 
         [0025]    The circuit pattern analyzer  10  determines the edges of a circuit pattern. According to an embodiment of the invention, the circuit pattern analyzer  10  divides the design data into manageable partitions, and analyzes the data to determine which areas, known as small area sections, are too small to accommodate circuitry. This is shown in  FIG. 2A , which shows a plan view of a circuit pattern  100  with a small area section  110 . Small area section  110  is an example of an area too small to accommodate circuitry, and thus would not need a fence. Then, as shown in  FIG. 2B , the circuit pattern analyzer  10  merges the small area sections  98  into the remaining partitions to define edges  112  of the circuit pattern  100  which need to be secured. Any suitable data merging technique may be used to merge the small area sections with the remaining partitions, such as, for example, polygon merging. 
         [0026]    The route calculator  20  uses the edges  112  of the circuit pattern  100  to determine a route that surrounds the circuit pattern  100 . In this regard, the route calculator  20  may use minimum width and spacing rules to ensure that the route provides adequate clearance from the edges  112  of the circuit pattern  100 . 
         [0027]    The fence generator  30  calculates layout data for the fence which follows the route generated by the route calculator  20 . The fence generator  30  preferably calculates the layout data in a polygon format using a set of rules as a guide. The rules may include minimum width, desired width, maximum width, minimum space, desired space and maximum space. As the fence layout data is generated, a running sum of the resistance may be maintained, so that the overall resistance of the completed fence may be determined. Once generation of the fence layout data is complete, as shown in  FIG. 2C , the data can be used to form a fence  114  around the edges  112  of the circuit pattern  100  having the determined resistance. The fence may be formed of any suitable material having effective electrical characteristics, such as, for example, metal, semiconductor material, polysilicon and doped silicon. 
         [0028]    Preferably, a fence is built on all interconnect layers of the IC, including active layers, polysilicon layers and metal layers. Capacitances can be extracted from adjacent layers, and these capacitances and the resistances of the fences can be used to detect whether the fence has been altered. For example, according to an exemplary embodiment of the present invention, an IC including a fence may be tested by slight modifications of a conventional BIST (built-in self-test) algorithm to compensate for the fence. In particular, the BIST algorithm would need to be processed at least twice, once with the fence at ground and again with the fence at a high potential. If any unwanted circuitry crosses the fence and connects to the IC design data, the resulting short would be detectable though one of the BIST tests. 
         [0029]    For large designs, it might be impractical to guard the entire circuit with one fence. The shorter the fence, the higher sensitivity is for detecting fence alterations. Thus, to increase sensitivity, multiple short fences may be used for a particular circuit pattern. If many fences are needed, a multiplexed input system may be required. However, this will not effect the BIST time, as it is only necessary to detect changes to electrical characteristics of the fence. 
         [0030]    A capacitance test offers a safe guard against massive fence alterations. Someone could try to reverse engineer the fence, matching its resistance, but placing it in a different location. However, doing this on multiple layers, while also trying to match inter-level fence capacitance would prove to be nearly impossible. 
         [0031]    While this invention has been described in conjunction with the exemplary embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.