The extendibility of optical lithography using KrF and ArF exposure tools is still being investigated, even, being demanded strongly now, due to the unforeseen issues, high cost, and general difficulty of NGLs -including F 2 and immersion lithography. In spite of these challenges Moore's Law requires continued shrinks and the ITRS roadmap still keeps its aggressive timetable. In order to follow the ITRS roadmap, the resolution must keep improving by increasing the lens NA for optical exposure tools. However, the conventional limit of optical resolution (k pitch =0.5) is very close for the current technologies, perhaps limiting progress unless NGL becomes available quickly. Therefore we need to find a way to overcome this seemingly fundamental limit of optical resolution. In this paper, we propose two practical two-mask /double-exposure schemes for doubling resolution in future lithography. One method uses a Si-containing bi-layer resist, and the other method uses Applied Materials' APF TM (a removable hard mask). The basic ideas of both methods are similar: The first exposure forms 1:3 ratio L/S patterns in one resist/hard mask layer, then the second exposure images another 1:3 ratio L/S pattern in-between the two lines (or two spaces) formed by the first exposure. The combination of these two exposures can form, in theory, k pitch =0.25 patterns. In this paper, we will demonstrate 70nm L/S pattern (140nm pitch) or smaller by using a NA0.68 KrF Scanner and a strong-RET reticle, which corresponds to k pitch = 0.38 (k 1 =0.19). We will also investigate the critical alignment and CD control issues for these two-mask / dual-exposure schemes.
Here we present both simulation and experimental results that show the effect of changes in laser light source bandwidth (E95) on CD Iso-Dense Bias. For the 55nm Technology Node Device, we have shown that E95 stability of less than 0.11pm is required in order to maintain OPE variation to within 2nm. In addition, we also verified another method to adjust for OPE variations that occur when E95 fluctuates. The Contrast Adjustment method is an effective function to adjust for OPE variation due to E95 fluctuation; it has been shown to maintain OPE variation less than 1.5nm. Furthermore, for the 45nm Technology Node Device, we have demonstrated that E95 stability of less than 0.07pm is required to maintain OPE variation to within 1nm. The bandwidth performance of the latest laser light source exhibits E95 stability less than 0.03 pm, thereby showing that the OPE variation due to E95 can be kept to under 1nm.
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