Keun Kyu Kong

Implementation of KrF 0.29 k1 lithography

One of the crucial tasks of semiconductor process is reduction of manufacturing cost by shrinking the design rule with the help of fine patterning technologies. For high density DRAM application, we explored 0.29 k1 lithography with KrF 0.80NA scanner. Well-known lithography technologies such as asymmetric crosspole, dipole illumination and 6% attenuated PSMs were used for this experiment. Illumination source and mask layout optimization were carried out iteratively to meet CD target, and high contrast thin resist was applied to improve pattern fidelity. Some of the biggest challenges were coping with large MEEF and reducing simulation error. Abnormal non-open fail, probably due to large MEEF, was observed at a dense contact hole pattern. To cope with non-open fail, we tested multi-PSM which composed of alternating PSM along the x-axis direction and 6% attenuated PSM along the y-axis direction. Also we pushed sigma offset of illumination pupil more strongly than exposure tools specification and there was no serious drawbacks of partial coherency extension. Accurate partial coherence measurement was important for obtaining target CDs and reducing OPC error. For some layers, unexpected simulation error was occurred especially at the patterns of peripheral circuit, therefore we had to calibrate simulation parameters of in-house tool and commercial tool (Solid-C) for OPC simulation. Finally we successfully demonstrated 0.29k1 KrF lithography by showing process yield over 58% in 512Mb DRAM having design rule of 90nm. Based on the results we obtained, we can conclude that 0.29k1 lithography is quite feasible for mass production and 60nm design rule DRAM devices can be manufactured with ArF dry 0.93NA. Since dry 0.93NA corresponds to 1.33NA in ArF water immersion with respect to k1, we can expect that it is possible to fabricate 42nm DRAM devices with ArF immersion lithography.

Development of new BARC for immersion process using hyper NA

Most semiconductor companies are using Bottom Anti-Reflective Coating (BARC) on their lithography process to reduce bottom reflectivity, which is cause of standing wave, pattern collapse, and bad pattern profile, and to improve lithographic performance. BARC has been diversified to adapt to the wavelength of exposure light and refractive indices of photoresists and substrates. Recently, many semiconductor companies introduce new process, such as immersion process and double patterning process, to get high resolution for next generation semiconductor and they are trying to apply these processes to their mass production. Among those process solutions, a strong candidate for high resolution is introduction of hyper NA(Numerical Aperture) exposure tool, using immersion process. There is one thing to solve for BARC material when immersion process is applied. It is reflectivity. As NA of exposure tool increases, reflectivity from a substrate also increases, simultaneously. We simulated the difference of reflectivity with increasing NA and we found a proper way how to control reflectivity on immersion process with refractive indices of BARC. We will report simulation data for immersion process and introduce our new developed BARC for hyper NA process in this paper.