News Column

Patent Application Titled "Integration of Optical Proximity Correction and Mask Data Preparation" Published Online

August 21, 2014

By a News Reporter-Staff News Editor at Politics & Government Week -- According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventor Sahouria, Emile Y. (Sunnyvale, CA), filed on January 30, 2013, was made available online on August 7, 2014.

The assignee for this patent application is Mentor Graphics Corporation.

Reporters obtained the following quote from the background information supplied by the inventors: "As photolithography is pushed to fabricate deep-subwavelength devices, photomask (or mask) preparation is becoming more critical than ever before. This is in part due to the fact that mask patterns have become more complex than conventional Manhattan shapes. Multi-patterning and other techniques needed to extend the 193 immersion capabilities usually depend on a large amount of decoration with optical proximity correction (OPC) shapes. Unlike simple orthogonal SRAFs, the SRAFs for 22 nm/20 nm technology nodes tend to be blobs or curvilinear lines. In the contact and via layers, and particularly for isolated features, extensive use of sub-resolution assist features (SRAFs) is needed to produce the required process window. Another source of complex mask patterns is inverse lithography. Masks computed through use of inverse lithography are known to provide significantly better lithographical performance even than conventional model-based OPC. Such masks, however, generally contain patterns with smaller segments and curved shapes.

"Masks that preserve natural output shapes from inverse lithography solutions are shown to have better lithography process window than their Manhattan counterparts. To manufacture masks with complex shapes, a straightforward approach is to represent curvilinear shapes with Manhattan segments. This may not only lead to a large number of shots, but also affect mask pattern fidelity. Model-based mask data preparation (MDP) methods may achieve shot count savings and preserve curved shapes. Some of these methods use smooth and curved contours as mask targets and adjust the numbers, positions and sizes of rectangular shots for optimization. No matter which model-based methods are employed, there will still be residue mask errors. These mask errors can be amplified upon wafer print, degrading pattern image fidelity and resulting in assist feature printing. The sensitivity of the wafer print to mask errors cannot be predicted without information about the optical configuration that will be used to print the wafer. Also the sensitivity is expected to vary so widely across the layout as to preclude the application of a single guard band specification. It is thus desirable to combine mask data preparation with optical proximity correction (OPC), at least in a refinement process."

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventor's summary information for this patent application: "Aspects of the invention relate to techniques for integrating optical proximity correction and mask data preparation. In an OPC-MDP process, according to various embodiments of the invention, first mask writer instructions for a layout design are simulated to generate a mask contour. The layout design represents at least a portion of an integrated circuit design. The first mask writer instructions may be derived from an initial MDP operation that performs a conventional fracturing process on initial layout data, from a previous iteration of the OPC-MDP process, or an MDP global operation. The initial layout data may be generated by an OPC global operation.

"Based on the generated mask contour, first layout data for the layout design are adjusted for optical proximity correction to generate second layout data. The first layout data may be the initial layout data or the layout data from a previous iteration of the OPC-MDP process. Traditional OPC or inverse lithography may be employed for this operation. Using the generated second layout data as mask target, the first mask writer instructions are adjusted to generate second mask writer instructions.

"The above OPC-MDP process may be iterated until an end condition is met. One such end condition is residue mask and wafer errors are less than threshold error values. Another end condition is the number of iterations reaches a threshold number.


"FIG. 1 illustrates an example of a computing system that may be used to implement various embodiments of the invention.

"FIG. 2 illustrates an example of a multi-core processor unit that may be used to implement various embodiments of the invention.

"FIG. 3 illustrates an OPC-MDP tool according to various implementations of the invention.

"FIG. 4 illustrates a flow chart describing an OPC and MDP integration method according to various implementations of the invention.

"FIG. 5 illustrates a flow chart describing an OPC and MDP integration method that use outputs of global operations as initial inputs to OPC/MDP local iterations according to some implementations of the invention."

For more information, see this patent application: Sahouria, Emile Y. Integration of Optical Proximity Correction and Mask Data Preparation. Filed January 30, 2013 and posted August 7, 2014. Patent URL:

Keywords for this news article include: Mentor Graphics Corporation.

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Source: Politics & Government Week

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