|
The benefit of assist feature has been greatly appreciated in the aspect of bringing the process windows of isolated and semi-isolated patterns into together with that of dense patterns; hence a common process window is attainable. The width of assist feature and the distance between assist feature and main pattern are two basic, fundamental specifications from the viewpoint of lithographer. In fact, there exist other specifications that are essential to success of assist feature implementation. For instance, the distance of two adjacent assist features and the gap between ends of assist feature to main patterns are all of necessity in terms of lithographic performance. From the perspective of feasibility and ease of photomask fabrication there are some specifications and/or constraints that should be implemented and enforced. One illustrative example is the extent of assist feature end pullback as two slightly off- axis assist features either joint or separate with a distance smaller than a given minimum space. Recently, the request of multiple assist features has enormously increased. The task of implementing multiple assist features is not trivial at all; the fact is that it introduces many more specifications to be contended. Under most circumstances, the implementation of assist feature involves lithographic engineers, mask-making engineers, and CAD engineers or script implementation engineers; this brings out the importance of communication mechanism that can describe the true intention of each specification. The question is that whether the mechanism is sufficient or not. The goal of the present work is to develop templates of specifications for assist feature implementation. Currently, many conditions and constraints have been identified and collected. One example is the central-edge template, which is allowed to prioritize the 'central assist feature' vs. 'edge assist feature.' It is believed that with the presence of specification templates both CAD and script implementation engineer will have a clear and consistent guideline to achieve the true intention of each specification.
|
