US Patent 8383322 Immersion lithography watermark reduction

A method of performing immersion lithography on a semiconductor substrate includes providing a layer of resist onto a surface of the semiconductor substrate and exposing the resist layer using an immersion lithography exposure system. The immersion lithography exposure system utilizes a fluid during exposure and may be capable of removing some, but not all, of the fluid after exposure. After exposure, a treatment process is used to neutralize the effect of undesired elements that diffused into the resist layer during the immersion exposure. After treatment, a post-exposure bake and a development step are used.