Method of verifying the placement of sub-resolution assist features in a photomask layout

A method for verifying the presence and the placement of sub-resolution assist features (SRAFs) in a photomask layout on an integrated circuit (IC) chip design comprising the steps of:

• generating a representative sample design of main features in the photomask layout;
• placing SRAFs into the representative sample design;
• calculating optical image properties of the main features in the presence or absence of SRAFs in the sample design in order to obtain an image profile of the main features;
• from the calculation of the optical image properties of the main features, determining a range of values of the main features in the presence or absence of SRAFs in the sample design;
• placing SRAFs into the photomask layout;
• simulating the photomask layout of the IC chip design for each of the main features of the photomask layout;
• calculating the optical image properties of each of the main features of the photomask layout considering layout details for each of the main features;
• categorizing each of the main features as a function of its proximity to adjacent features thereof;
• for each category of main features, examining their respective optical properties to determine when SRAFs are present;
• and
• in the absence of SRAFs, reporting and correcting the errors.

A method for verifying the presence and the placement of sub-resolution assist features (SRAFs) in a photomask layout of an integrated circuit (IC) chip design representing an electric circuit comprising the steps of:

• formulating an optical imaging property as differences in the photomask layout with and without SRAF placement;
• sorting geometric details of the electrical circuit into different categories;
• combining an optical image property with the geometrical details of the electrical circuit;
• and
• analyzing the quality and accuracy of the SRAFs placement.

An article of manufacture comprising a computer-usable medium having computer readable program code means embodied therein for verifying the placement of sub-resolution assist features (SRAFs) in a photomask layout of an integrated circuit (IC) chip design, the computer readable program code means in said article of manufacture comprising:

• computer readable program code means for determining selected optical image properties of main features of a sample layout in the presence or absence of SRAFs;
• computer readable program code means for analyzing the optical image properties of the main features to establish a criterion for subsequent placement of SRAFs in the photomask layout of the IC chip design;
• computer readable program code means for performing a simulation on the complete photomask layout of the IC chip design with the SRAFs;
• computer readable program code means for sorting the photomask layout geometry based on predetermined categories;
• and
• computer readable program code means for identifying, based on said established criterion, regions of the photomask layout lacking adequate placement of the SRAFs, and correcting the inadequate placement of the SRAFs.

A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to perform a method of verifying the placement of sub-resolution assist features (SRAFs) in a photomask layout of an integrated circuit (IC) chip design, said method steps comprising:

• determining selected optical image properties of main features of a sample layout in the presence or absence of SRAFs;
• analyzing the optical image properties of the main features to establish a criterion for subsequent placement of SRAFs in the photomask layout of the IC chip design;
• performing a simulation on the complete photomask layout of the IC chip deign with the SRAFs;
• sorting the photomask layout geometry based on predetermined categories;
• and
• based on the established criterion, identifying regions of the photomask layout lacking adequate placement of the SRAFs, and correcting the inadequate placement of the SRAFs.