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With the continuous reduction of layout dimension, critical dimension control becomes more and more tricky. Being one contribution of critical dimension variation, etch bias correction needs to get more accurate. The correction by rule-based optical proximity correction, which only takes into account the distance to the facing outer and inner edges, is reaching its limit at 65nm node. Indeed, its found to be not accurate enough in some particular configurations. Thus, applying etch correction by model-based optical proximity correction looks like a good solution. The etch bias to correct for can be approximated by a function of the local density, obtained by convoluting the design with Kernels. However, it is found to be still not accurate enough in some configurations if the Kernels used for etch modeling are symmetrical, as for optical part. In this study, several etch models are tested to correct etch bias variations of poly layer patterning for 65nm node.

International audience; Assist features (AF) are an essential component of reticle enhancement techniques. Their use is indispensable in sub-100 nm technologies to ensure a maximum process window (PW) across chip, especially for critical levels. Indeed, AF, which can be binary, attenuated or phase-shifted, help in providing a larger PW to the features they assist when they are used in conjunction with off-axis illumination. The depth of focus (DOF) of an isolated structure is improved by the presence of AF by providing to the optical system a diffraction pattern close to the diffraction pattern of a dense structure. The resulting DOF and exposure latitude (EL) are dependent on the relative position of the AF from the main feature. Moreover, the PW varies while inserting one, two or more AF. The relative position of each influences the results. In this paper, a method will be detailed to optimise the placement of the AF. For the purpose of this study, the diffraction pattern induced by the insertion of one or several AF is analysed in frequency space. This analysis details the evolution of the intensity of even and odd orders during the insertion of AF. The calculation of the optimum placement is detailed, and the DOF resulting from the insertion of one or more AF is also presented.