The United States Patent and Trademark Office issued a patent to Takumi Technology for effective proximity effect correction methodology. Takumi also received a corresponding patent by the State Intellectual Property Office of the People’s Republic of China. The US patent (#7,458,056) covers technology in improving the quality and accuracy of optical proximity correction (OPC).
Takumi’s OPC patent describes a methodology based on the interpolation of the correction between selected evaluation points of the target layout. By connecting these correction points, this technique also provides a mean of reducing data volume and simplifying the mask-writing, inspection and repair processes.
Proximity effect correction has become a necessary step in the fabrication of ICs in order to improve pattern fidelity of the current lithography processes. The current methodologies are limited by dramatic increases in data volume and inaccuracies due to extrapolation of the correction.
One of the primary challenges IC designers face when using current model- and rule-based OPC methodologies is the considerable increase in the number of vertices after correction, leading to much larger data volume, typically an order of magnitude larger. Larger data volume increases processing time as well as the time it takes to write the mask. In addition, the complexity of the correction can generate issues for vector-scan e-beam mask-writing tools when small slivers are created as the data is converted to the mask writer tool format. These small slivers lead to exposure dose inaccuracies when the mask is exposed, which in turn result in dimension inaccuracies.
Correction inaccuracy between evaluation points presents another issue with model-based OPC. While the correction is accurate for the evaluation points, there is no guarantee that it will be adequate for a point in-between these evaluation points since the discontinuities in the correction are introduced by the dissection points. Furthermore, correction applied to a point in-between the evaluation points is based on extrapolation, which is inherently prone to errors.
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