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Device modeling for proximity effectsRelated Patent Categories: Data Processing: Design And Analysis Of Circuit Or Semiconductor Mask, Circuit Design, Optimization (e.g., Redundancy, Compaction)Device modeling for proximity effects description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080022237, Device modeling for proximity effects. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention generally relates to device modeling and to an improved model that simulates proximity effects from adjacent structures. DESCRIPTION OF THE RELATED ART [0002] Today's fast-paced product development cycles necessitate that design tools such as device models that simulate the performance of integrated circuit structures be as accurate as possible. Simulator tools have been created that determine the device parametrics of a given integrated circuit structure as a function of the process utilized to form it. See for example U.S. Pat. No. 5,761,481, "Semiconductor Simulator Tool for Experimental N-Channel Transistor Modeling" and "Influence of High Substrate Doping Levels on the Threshold Voltage and the Mobility of Deep-Submicrometer MOSFET's," 1992 IEEE Transactions on Electron Devices, Vol. 39, No. 4, pp. 932-938. This is particularly true for compact models (e.g., the physics-based subroutines used in numerical simulation codes for larger entities such as circuits, mechanical systems, etc.). To create accurate compact models, measured data are needed from hardware to calibrate the model. Compact models are further discussed and described in patent application Ser. No. 10/023,235, "System and Method For Target-Based Compact Modeling" filed Jan. 7, 2002 and assigned to the assignee of the present invention. [0003] In the art, it is known that "proximity effects" can alter one or more parameters of integrated circuit structures that are adjacent (in "proximity") to one another. Examples of three different types of proximity effects are described below. [0004] A first proximity effect is the lateral scattering of implanted dopants from a masking image placed nearby the feature of interest. A specific example is the formation of the implanted well regions for CMOS devices. When a well is implanted during manufacturing, implanted ions are scattered laterally across the wafer surface. This unwanted doping can be detected as far from the mask edge as two microns. Design rules allow for FETs to be placed well within this affected area and the result is a FET with a substantially altered threshold of voltage (Vt). Depending on the proximity, the Vt can be altered by as much as 100 mV. This effect can cause performance problems and in worst case scenarios, circuit failure. See e.g. U.S. patent Ser. No. 10/063,406, entitled "Method of Forming Retrograde N-Well and P-Well", filed Apr. 19, 2002 and assigned to the assignee of the present invention, for a further discussion of this problem. [0005] A second proximity effect is the proximity of an FET to an isolation edge (such as an edge of a shallow trench isolation, or STI), which can modify the strain (and hence mobility of carriers) in the portion of substrate that provides the channel of the FET. See for example Frim et al, "Strained Si NMOSFETs for High Performance CMOS Technology," 2001 Symposium on VLSI Technology Digest of Technical Papers, 5B-4, page 59. [0006] A third proximity effect is the differential in integrity of the depth of focus (DOF) of an image printed by a photoexposure tool between a pattern of structures that are wider apart and a pattern of structures that are closer together. Typically this problem is corrected by adding serifs or other sub-resolution "dummy" structures to the photomask. See for example U.S. Pat. No. 5,447,810, "Masks for Improved Lithographic Patterning for Off-Axis Illumination Lithography," and U.S. Pat. No. 5,821,014, "Optical Proximity Correction Method For Intermediate-Pitch Features Using Sub-Resolution Scattering Bars on a Mask." [0007] The foregoing and other proximity effects will only become more pervasive as circuit groundrules continue to shrink. A need exists in the art to develop a device modeling and simulation methodology that takes these and other proximity effects into account. SUMMARY OF THE INVENTION [0008] In view of the foregoing and other problems, disadvantages, and drawbacks of the conventional modeling systems, the present invention has been devised, and it is an object of the present invention to provide a structure and method for an improved modeling system. [0009] Acccordingly, in a first aspect the invention comprises programmable storage device having a computer readable program stored thereon executable by a computer to carry out a method of calibrating a software model for a given structure of interest for a variable imposed by an adjacent structure, comprising the steps of determining the spatial extent of the variable imposed by the adjacent structure; assigning a value to the spatial extent, which varies as a function of distance from the adjacent structure to the given structure; and attaching that value to the model of the given structure. [0010] In a second aspect, the invention comprises a method for providing proximity effect information to a model of a given device structure, comprising the steps of determining a spatial extent and variation of the a given proximity effect produced by a proximity feature; determining a location and orientation of the modeled device relative to the proximity feature; generating a variable arising from the proximity effect that is assigned to a modeled parameter; and applying the variable to the device model. [0011] In a third aspect, the invention is a method of calibrating a software model for a given structure of interest for a variable imposed by a proximity feature, comprising the steps of creating a model for the proximity feature, the model being segmented with a proximity value assigned to each segment; determining an area of the given structure within each segment of the model for the proximity feature; assigning a proximity value to each area of the given structure within each segment; integrating the proximity values for each area across the total area of the given structure; and applying the integrated shift parameter to the software model. DESCRIPTION OF THE DRAWINGS [0012] The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of a preferred embodiment(s) of the invention with reference to the drawings, in which: [0013] FIG. 1 is a flowchart of the method in accordance with a first embodiment of the invention; [0014] FIG. 2 is a flowchart of the method in accordance with a second embodiment of the invention; [0015] FIG. 3 is a top view of a proximity feature and a modeled feature illustrating step 21 of the method of FIG. 2; [0016] FIG. 4 is a flowchart of the method in accordance with a third embodiment of the invention; [0017] FIG. 5 is a top view of a proximity feature and a modeled feature illustrating steps 101 and 102 of FIG. 4; and [0018] FIG. 6 is a hardware embodiment in which the invention is carried out. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION [0019] In the description to follow, reference will be made to "devices" and "products". In the preferred embodiment, "device" refers to an active or passive integrated circuit component, such as a transistor, capacitor, resistor, or the like (most preferably, it refers to a transistor), and "product" refers to the overall integrated circuit chip. However, it is to be understood that the invention is also applicable to any component of any product, where the performance attributes of that component may be varied by proximity effects. Continue reading about Device modeling for proximity effects... Full patent description for Device modeling for proximity effects Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Device modeling for proximity effects patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. 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