Pushing the boundary: low-k1 extension by polarized illumination

摘要

The introduction of polarized illumination has enabled the extension of low-k1 processes well below a k1-factor of 0.3. Previously, it has been demonstrated by simulations and early exposure results that properly polarized illumination leads to an increase of contrast and exposure latitude, resulting in reduced MEEF and better CD control. The gain of polarization is most pronounced in the hyper-NA regime of high-end immersion tools (NA > 1.0), but also 'dry' high-NA scanners (NA = 0.93) benefit significantly from polarized illumination. For volume production, polarized illumination must be fully compatible with all requirements for a lithographic step and scan system: full throughput, overlay and focus control, flexibility and ease-of-use are essential features. This is realized by employing polarization-conserving optics, and by automated in-line metrology to optimize and control the system for any selected polarization state. In this paper, experimental results will be shown demonstrating the gain of using polarized illumination on high- and hyper-NA exposure tools, of both dry and immersion types. The various imaging relevant parameters (MEEF, EL, DOF, LWR) will be addressed in relation to the use of polarization exposure conditions. The effect of polarization control on imaging performance will be presented in relation to CD control at low k1. Finally, the viability to extend the k1-value to 0.28 for a bi-directional process and 0.27 for a uni-directional process when using polarized illumination will be demonstrated.