For advance semiconductor manufacturing, patterning contact and via mask layers continue to be major challenge. As a result, RET's beyond the current standard 6% attPSM technology are being pursued with a goal of reducing the k1 for hole patterning to the range of 0.35 - 0.40. IML Technology has shown promising results as a possible solution which employs strong off axis illumination (OAI) to achieve the resolution for the dense pitch contacts and the use of sub-resolution scattering bars (SB) for the semi dense to isolated contacts. At the 45nm node, placing SB by simply applying a set of rules is not sufficient for deriving the correct assist feature placements for the entire range of pitches and for the complex, randomly placed contacts that occur in actual device patterns. IML Technology utilizes modeling to locate where SB should be placed and in the case of high transmission ternary PSM (HTPSM) and CPL, defines the phase of the SB relative to the contacts being imaged. To generate such reticle designs, highly complex interference maps are calculated and from this optical interference behavior, the reticle pattern is derived. Previously, the reticle pattern derived in such a manner was extremely complex raising a question as to how feasible such an approach would be in a manufacturing environment. New algorithms which simplify the mask pattern while maintaining the resolution enhancement capability of IML have been developed.
The objective of this work is to demonstrate a manufacturing methodology that utilizes IML Technology and is capable of meeting the requirements for the 45nm node designs. We will explore the application of this method 6% attPSM and CPL reticle designs which containing contact patterns that are representative of production devices. To define the SB for what are effectively randomly placed contacts over a wide range of pitches from dense to isolated, IML Technology is used. This modeling algorithm is based on mapping out the interference that occurs at the image plane as a result of the proximity effects of the target contact pattern. This technique provides a model-based approach for placing all types of assist features on both clear field and dark field patterns for the purpose of enhancing the printing resolution of the target pattern and it can be applied to any reticle type including binary, attPSM, altPSM, ternary HTPSM, and CPL. By implementing newly developed algorithms, simplified reticle patterns are generated which maintain the optimum SB placements determined by the IML process.