Adoption of darkfield blank inspector to enhance yield of optical reticles

Blank mask quality control is vital for achieving high yield in reticle production. Various defects on blanks can be easily transferred to the final patterned mask, leading to unnecessary rework and yield loss. Insufficient attention to blank mask quality control results in significant yield reduction. The adoption of a blank inspection tool not only prevents blank defects but also monitors the process to ensure high yield in optical mask shops. KLA evaluated FlashScan^® darkfield blank inspection tool for optical mask manufacturing at various mask shops. In this paper, we will introduce how FlashScan is integrated into mask production process and highlight its applications for yield improvement. For incoming masks, the blank box opener mitigates the risk of contamination even in the cleanroom environment. The defect sizing functionality accurately reports defect size for severity determination. For process monitoring, the darkfield technology exhibits superior sensitivity and inspectability on vertical and horizontal line/space patterns. This capability allows rapid identification of root causes and addresses unpredictable process issues during production. The high sensitivity is also crucial for optical masks to detect very small defects that can be transferred to the final masks. Our study illustrates that the adoption of FlashScan significantly enhances yields in optical mask manufacturing.