CONTACT HOLE IMAGING AT THE 0.13 μm NODE USING KrF LITHOGRAPHY

In this paper we discuss possible solutions for the imaging of 0.15 μm contacts through various pitches by the use of high-NA KrF-lithography. As different pitches have there own critical points, isolated, semi-dense and fully dense contacts are addressed separately. On the way to a production worthy solution of printing contact layers at this resolution, two main obstacles have to be overcome. These are limited depth of focus for isolated features and high optical proximity effects. The established enhancement technique to widen the process latitude of isolated contacts is the use of Attenuated Phase Shift Masks (AttPSM). The necessary parameter optimization required for its application is considered. This comprises numerical aperture, phase shift error, aberrations and mask feature bias for a 6% AttPSM using a partial coherence of 0.4. The boundary conditions to prevent sidelobe printing are addressed as well. Predictions for this optimization, using the PROLITH/2 Lumped Parameter Model was verified by experimental results using ASML’s high-NA PAS 5500/750E Step & Scan system. Encouraging process latitudes of 0.45 μm DoF@10%EL were achieved for both fully isolated and semi-dense (1:2) contacts. For dense (1:1) contacts quadrupole illumination (QUASARTM) using Binary Intensity Masks (BIM) gave the best results. A full-field CD uniformity of 17 nm or better (3σ) is obtained through an 0.4 μm focus range. At least 80% of the observed variation is due to the reticle used and to the measured MEF. Therefore, we studied influences on MEF for 0.15 μm dense contacts in more detail. This revealed a high impact of non-linearities introduced by the resist process. We also analyzed the issue of closing contacts and formulated boundary conditions for its avoidance. Finally, the further potential of KrF lithography in terms of resolving “near half wavelength sized” contacts is demonstrated by cross sections of 0.13 μm contact holes.