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Current 90nm Flash memory design introduces imaging critical points in several devices levels: active, poly, contacts, and first metallization. Among standard Resolution Enhancement Techniques (RET), Off-axis illuminations play a fundamental role, because they are capable of providing better imaging contrast and improved process latitude in low K 1 regime with very dense structures. Starting from the simulation study of real device layer geometries, object of this work is to propose a solution in terms of illumination schemes and mask choice (binary or halftone) for each critical layer, considering K 1 around 0.35 in ArF lithography. Dedicated off-axis illuminations will be compared to standard illumination modes, underlining the benefits in terms of ultimate resolution, process window and line edge roughness improvement. Experimental data confirmed the predicted gain in process robustness and, as expected, showed great line edge roughness improvement and less marginality to pattern collapse.

Double patterning is the best technique which allows 193nm immersion lithography to anticipate the 32 nm node, before EUV lithography. The final device pattern is formed by two independent patterning steps where the dense pitch is doubled. This allows printing each patterning step with higher k1 imaging factor.In this paper we present the overlay and CD budget applied to a double patterning (DP) technique for the definition of a 32nm technology node device, using an immersion scanner tool. A balance among different factors which affects the final CD of the device is necessary to optimize the imaging and the alignment performances of the exposure tool. A preliminary activity is also necessary to choose the most suitable mask splitting strategy. Adopting a single mask, which is exposed twice with the appropriate shift -the final pitch -, makes the overlay between the two exposures less critical than splitting the complementary layouts on two different masks. Finally, the CD uniformity of the pooled distributions from the two exposures is evaluated in order to define the requested tool performances in terms of overlay, CD control and metrology.

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