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Patent Issued for Sum of Coherent Systems (SOCS) Approximation Based on Object Information

February 19, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventor Adam, Konstantinos (Belmont, CA), filed on November 12, 2010, was published online on February 4, 2014.

The patent's assignee for patent number 8645880 is Mentor Graphics Corporation (Wilsonville, OR).

News editors obtained the following quote from the background information supplied by the inventors: "Particular embodiments generally relate to photolithographic processing and more specifically to a sum of coherent systems (SOCS) approximation optimization.

"Lithographic and other processes often have certain signature distortions that fabricate less than optimal features in integrated microdevices. If these distortions can be modeled, the device layout or design can be compensated in anticipation of these fabrication problems. OPC (Optical and Process Correction, or sometimes Optical Proximity Correction) involves making systematic modifications to photomask geometries to increase the achievable resolution and pattern transfer fidelity for photolithography in IC manufacturing. This is accomplished by compensating mask geometry for predictable effects that will occur during imaging or subsequent processing.

"A simulation engine is used to provide an accurate simulation of the on-wafer shape, given an input shape on the mask. Conventional simulation engines use the Sum of Coherent Systems (SOCS) approximation, in which on-wafer light intensity for partially coherent illumination is decomposed into an incoherent sum of intensities from a nominally infinite number of coherent systems. The sum of coherent systems (SOCS) approximation may be used to approximate a Hopkins imaging integral. For example, a transmission cross coefficient (TCC) matrix may be decomposed via Eigenvalue decomposition (EVD) into a finite set of kernels (SOCS kernels) whose order of importance in the SOCS series coincides with the magnitude of the respective Eigenvalue. The number of kernels in a SOCS series is large and thus, the SOCS approximation uses only a finite number of kernels, N. The number N is determined to balance accuracy and time taken to compute the sum. For example, the series may be cut off after the first ten or twenty kernels.

"The transmission cross coefficients (TCCs) are generated based on the illumination source and projection system being used. Thus, no matter what mask is being used to determine the image intensity, the same finite set of kernels is used. This may be produce results that are not as accurate and/or may not be the most computationally efficient for a particular photomask layout."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventor's summary information for this patent: "In one embodiment, a method for determining kernels in a sum of coherent systems approximation is provided. Information for an object to be simulated in a manufacturing process is determined. For example, information based on geometries that are included in a layout or photomask is determined. A set of kernels from a transmission cross coefficient (TCC) matrix are also determined. The set of kernels may be weighted by importance values in an order of importance in a SOCS series. The kernels may then be re-ordered based on the information for the object. For example, the geometry information for the object is used to determine which kernels may be more relevant for the object. These kernels are then re-ordered in the SOCS series to reflect their order of importance. The SOCS series of kernels is then truncated at the number of kernels desired. Accordingly, by re-ordering the kernels that may be more relevant to the object to have higher weights, when the truncation occurs, the kernels that are most relevant may be included in the SOCS approximation. Thus, more accurate image intensities may be determined when using the SOCS approximation in a Hopkins approach.

"In one embodiment, a method for determining kernels in a sum of coherent systems (SOCS) approximation is provided. The method comprises: determining information for an object to be simulated for a manufacturing process; determining a set of kernels that represent a transmission cross coefficient (TCC) matrix, wherein the kernels in the set are associated with importance values; analyzing the set of kernels and information for the object to determine if one or more of the kernels in the set of kernels should have a different importance value; and assigning a different importance value for one or more kernels in the set of kernels based on the analysis.

"In another embodiment, a computer readable medium comprising one or more instructions for execution by the one or more processors is provided. The one or more instructions are configured to determine kernels in a sum of coherent systems (SOCS) approximation and when executed by the one or more processors operable to: determine information for an object to be simulated for a manufacturing process; determine a set of kernels that represent a transmission cross coefficient (TCC) matrix, wherein the kernels in the set are associated with importance values; analyze the set of kernels and information for the object to determine if one or more of the kernels in the set of kernels should have a different importance value; and assign a different importance value for one or more kernels in the set of kernels based on the analysis.

"In yet another embodiment, a system configured to determine kernels in a sum of coherent systems (SOCS) approximation is provided. The system comprises: an object information determiner configured to determine information for an object to be simulated for a manufacturing process; a SOCS series determiner configured to determine a set of kernels that represent a transmission cross coefficient (TCC) matrix, wherein the kernels in the set are associated with importance values; a kernel analyzer configured to analyze the set of kernels and information for the object to determine if one or more of the kernels in the set of kernels should have a different importance value; a kernel reorder configured to assign a different importance value for one or more kernels in the set of kernels based on the analysis; and a model determiner configured to generate a model for an image intensity to be used in simulating optical effects of the object in the manufacturing process.

"A further understanding of the nature and the advantages of particular embodiments disclosed herein may be realized by reference of the remaining portions of the specification and the attached drawings."

For additional information on this patent, see: Adam, Konstantinos. Sum of Coherent Systems (SOCS) Approximation Based on Object Information. U.S. Patent Number 8645880, filed November 12, 2010, and published online on February 4, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=16&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=756&f=G&l=50&co1=AND&d=PTXT&s1=20140204.PD.&OS=ISD/20140204&RS=ISD/20140204

Keywords for this news article include: Mentor Graphics Corporation.

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Source: Journal of Engineering


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