Process and Resist Parameters Influencing the MEEF Values for Sub-90nm Cntact Hole Patterns

Contact hole patterns are becoming one of the most challenging lithographic process for 45nm node and below. In this study, we first screen some 193nm resist formulations to achieve 80nm contact holes with a DOF superior to 250nm for dense pitches, 150nm for isolated with immersion lithography and focus scan option. In addition to this process window requirement, we also consider the MEEF behaviour of these resist samples as a function of the lithographic process. We encountered a trade-off between DOF performance and MEEF. With our best sample, large DOF is promoted by focus scan and photoacid diffusion whereas it strongly affects the MEEF value. Process tricks which tend to enhance chemical contrast within the resist, such as overbaking PEB and double PEB step have thus been applied. First results are interesting though these process variations do not allow fully compensating the image blur induce by the focus scan.