Photomask and reticle defect detection : Peter H. Singer. Semiconductor Int. 66 (April 1985)

Abstract

In DUV lithography, hydrocarbon contaminants on surfaces cause transmission loss. During illumination of the reticle, heavy hydrocarbons will be slowly removed, causing transmission instability. Therefore, the reticles need to be cleaned before use. ASML has commissioned us to perform a feasibility study into reticle cleaning and storage. The reticle cleaning process must reduce transmission loss to <0.4% per reticle, do so within 2 min and without heating the reticle more than 2 K or damaging it. A combined experimental and modeling approach was used to solve this problem. It was concluded that UV cleaning at 172 nm combined with purging can be designed such that the requirements on cleanliness, cleaning time, heating and repeated cleaning can be met.