Kazuaki Chiba

Alternating phase-shift mask and binary mask for 45-nm node and beyond: the impact on the mask error control

For 45 nm node and beyond, the alternating phase-shift mask (alt. PSM), one of the most expected resolution enhancement technologies (RET) because of its high image contrast and small mask error enhancement factor (MEEF), and the binary mask (BIM) attract attention. Reducing CD and registration errors and defect are their critical issues. As the solution, the new blank for alt. PSM and BIM is developed. The top film of new blank is thin Cr, and the antireflection film and shielding film composed of MoSi are deposited under the Cr film. The mask CD performance is evaluated for through pitch, CD linearity, CD uniformity, global loading, resolution and pattern fidelity, and the blank performance is evaluated for optical density, reflectivity, sheet resistance, flatness and defect level. It is found that the performance of new blank is equal to or better than that of conventional blank in all items. The mask CD performance shows significant improvement. The lithography performance of new blank is confirmed by wafer printing and AIMS measurement. The full dry type alt. PSM has been used as test plate, and the test results show that new blank can almost meet the specifications of pi-0 CD difference, CD uniformity and process margin for 45 nm node. Additionally, the new blank shows the better pattern fidelity than that of conventional blank on wafer. AIMS results are almost same as wafer results except for the narrowest pattern. Considering the result above, this new blank can reduce the mask error factors of alt. PSM and BIM for 45 nm node and beyond.

Study of alternating phase shift mask structures for ArF lithography

The alternating phase-shift mask (alt. PSM) is one of the most effective approaches to improve a resolution of the 65nm logic gate structure in ArF lithography. Previously we have studied the optimization of alt. PSM in 180nm gate-pitch. In this study, we evaluated various alt. PSM in the case of 160nm gate-pitch. Using a rigorous electro-magnetic field simulation of light scattering in 3D mask topographies, we evaluated CD difference between π-phase and 0-phase space size (the π-0 CD difference), resist CD through pitch and normalized image log-slope (NILS). The parameters for our simulation were mask structure (shallow trench depth (ST), undercut size (UC), space bias, Chrome (Cr) CD, pitch, phase shift depth) and ArF exposure condition (NA, sigma, defocus). From the results of simulation, it turned out that single trench structures with UC and/or space bias showed the good intensity balance through defocus. We compared the simulation results with the AIMS fab193 (Carl Zeiss) results and found there was no large difference. The combination of UC and space bias could be chosen as suitable structure for 160nm gate-pitch.

Performance study of chromeless phase lithography mask for the 65nm node and beyond

Chromeless Phase Lithography (CPL) is one of resolution enhancement technologies (RET) for 65nm node and beyond. CPL has various advantages such as no necessity of double exposure, and small pattern displacement and CD error caused by the intensity imbalance. The high resolution lithography can be expected with the combination of high NA and off-axis illumination (OAI) in 193nm lithography. It is known that CPL can flexibly change structure through gate pitch. There are various kinds of structure, such as pure CPL, Zebra, Rim, and Stripe. And there are also various kinds of scattering bar depending on the gate pitch. In this paper, we estimated normalized image log-slope (NILS), mask error enhancement factor (MEEF), depth of focus (DOF) and phase shift depth for each CPL structure by rigorous 3D mask electro-magnetic field (EMF) simulation on mask topographies. And it was found that Zebra and Stripe can improve NILS, and Stripe is most effective to improve MEEF for narrow pitch. There is no large difference in DOF between all structures, and DOF for all structures with wide pitch can be expanded by the addition of chrome scattering bar. We evaluated the impact of phase shift depth and found that the optimal phase shift depths of all structures are larger than 180degrees. The improvement of mask-making accuracy becomes more important to achieve better mask pattern resolution. Therefore, we focused on the defects of the sub-resolution chrome feature and chrome scattering bar. It was found that the defects of sub-resolution chrome feature have big influences on the lithography performance. And the defects of scattering bars become more sensitive with closer to the main feature.