A patternable layer is formed over a substrate. A photo-sensitive layer is formed over the patternable layer. The photo-sensitive layer contains an additive. The additive contains at least a floating control chemical and a volume control chemical. A spin drying or a baking process is performed to the photo-sensitive layer. The floating control chemical causes the additive to rise upward during the spin drying or baking process. Thereafter, as a part of an extreme ultraviolet (EUV) lithography process, the photo-sensitive layer is exposed. One or more outgassing chemicals are generated inside the photo-sensitive layer during the exposing. The volume control chemical is sufficiently voluminous and dense to trap the outgassing chemicals inside the photo-sensitive layer.