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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.

Commercially available photoresists for 193nm litho technology still suffer of undesired phenomena, which could eventually limit the stability of critical layer processing. Also standard CD-SEM inspection has its impact on the overall litho budget, as the interaction between the primary electron beam and the photoresist locally modifies target dimension. The reduction of this effect can be important to preserve geometrical and also electrical characteristics of the chip, as the local variation ofthe CD is detectable also after target etching and resist removal. In this paper different strategies to reduce its impact onto production wafers are investigated and compared. By applying a combination of these techniques, CD local modification can be lowered up to 75%.

%675$&7Double focal plane exposure technique has the property to increase greatly the depth of focus of a lithographic process and appears to be a solution to fulfil the requirements of the most aggressive lithographic targets. The purpose of this work is to investigate the performances of this technique and to understand its mechanisms, to be able to find the best conditions of use for a given process. A simple model based on aerial images considerations has been developed to determine the behaviours of the main lithographic parameters (DoFmax, Elmax, central dose, shape of the Bossung curves) for various values of the distance between the two focal planes. Comparisons with four experiments have been realized with different conditions (type of pattern, dimensions, wavelength, N.A. and coherence σ). The possibility to predict the best experimental conditions (trade-off between DoF, El, resolution and LER) has been verified..H\ZRUGV : Aerial image, Flex, multiple exposure, defocus, Bossung, CD uniformity, process windows, simulation. ,1752'8&7,21For the most aggressive lithographic targets, DOF budget is decreasing very rapidly and the standard lithographic process is hardly able to provide a process latitude wide enough to overcome the budget reduction due to chuck and wafer flatness, to image field deviation of the scanner and to focus instabilities. In particular for 193nm technology, resists don't have yet enough maturity to provide exposure latitudes comparable to 248nm although resolution requested by the roadmap is accelerating the introduction of this technology. The use of FLEX technique 1 , that consists of multiple focal plane exposures, has been already proposed in the past as a method to increase DOF although there are several other parameters (exposure latitude, resolution, CD uniformity and LER) that has to be taken into account to validate the method as a possible solution in a production environment. In this paper we evaluate how the FLEX technique could be used for 0.12-0.16um semi-dense trenches both for 248nm and 193nm technology, and for 0.18um contacts holes for 248nm technology only. A simple model, based on aerial image simulation, has been developed to estimate and predict the behaviour of the main lithographic parameters (DoFmax, Elmax, central dose, shape of the Bossung) for various values of the distance between the focal planes. The comparison with experimental results shows that prediction of best experimental conditions (trade-off between DoF, El, resolution, LER) is feasible.(;3(5,0(17$/ The Flex method consists in exposing the same mask pattern at two different focus offsets. We will call "Dflex" the focal plane separation. In order to evaluate the impact of the technique on the lithographic process we compared simulated results with experimental ones. In particular there are four possible parameters that have to be considered to perform a correct analysis: the two energy doses of the two subsequent exposures and their focus offsets. A previous study on the subject has shown that t...

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