Enhanced structures for through-the-lens alignment with DUV lithography

Alignment is the dominant performance issue for photolithography tools as integrated circuit feature sizes approach 500 nm. A study is presented on two new types of alignment structures for use with scribelines of lOOjim or less using a 1X wafer stepper with through the reticle and through the lens alignment with darkfield detection. Single line alignment structures represent a continuation of prior work1 which uses system software to automatically characterize signal strength and process latitude. Multiline pseudorandom ( MPR ) alignment structures are introduced which provide increased signal intensity. Darkfield target illumination is introduced and is shown to enhance target capture. The application of these new alignment structures for use with deep UV (DUV) and other situations is reviewed.