We have developed a mask pattern optimization technology that improves the accuracy of LSI lithography by approximately 20 %. 30-nanometer generation lithography with ArF laser uses various technologies for achieving higher resolution such as immersion lithography in which liquid is filled between lens and wafers to enhance the resolution, but it is approaching its limit. The purpose of this research project is to extend the lifetime of ArF immersion lithography by improving the LSI photomask.

The Sub Resolution Assist Feature (SRAF), which modulates printed images of the main pattern, has been used to improve the resolution and the accuracy of the main circuit patterns. However, optimization of SRAF placement is becoming increasingly difficult as lithographic exposure approaches its resolution limits.

Our new technology applies an adaptive search algorithm based on the optimal gradient method to optimize the placement of SRAF which improves positioning and enhances critical dimension (CD) accuracy by approximately 20 %. The developed technology opens the door to extending the life of current ArF immersion lithography to the next generation and beyond.