Lithography process control using in-line metrology

High volume semiconductor manufacturing yields require that critical resist feature profile is continually controlled for uniformity and centering. One reason is the small working distance of high numerical aperture lenses. Indeed, reducing process windows require more precise dimensional control. The variation of the critical dimensions can generally be attributed to the lack of the focus and/or dose control. A methodology to control the two lithographic parameters and to construct a focus and dose budget for all components (tool, layer, resist, and reticle) has been developed. This paper presents a run-to-run control called FDO1 (Focus Dose Optimization) using in-line CD metrology. We have confirmed that this method controls the photoresist shape and the photoresist width accurately and reduces the CD variation for 28 nm devices by 50%.