Proceedings Article | 30 October 2007
KEYWORDS: Optical proximity correction, Photomasks, Process modeling, Error analysis, Metals, Data modeling, Manufacturing, Model-based design, Lithography, Data processing
A few years ago, model-based layout verification was used primarily with mask data preparation as a safety net to predict and avoid limited printability performance prior to mask fabrication. If certain layout locations would transfer poorly onto the wafer, the mask data was intercepted, preventing yield loss associated with "mask issues."
Such mask-related issues come primarily from three sources: Mask manufacture bias, OPC limitations and intrinsic layout configurations. While mask manufacture bias and OPC limitations can be addressed during the final stages of mask synthesis and manufacture, layout configurations that exhibit poor lithographic performance for a given process cannot be modified without considering the electrical effect such new topologies will induce in the modified layout.
In principle, marginally performing layouts can be removed from the design by adequately interpreting geometric design rules. Unfortunately, while such rules are strictly defined for 1D, they are not as well-defined for arbitrary 2D configurations. For that reason, several approaches to transferring sufficient process information to the layout synthesis tools to prevent the presence of layout configurations incompatible with the production process have been attempted. However, when the production process is not fully developed, using these approaches can potentially limit the portability of the layout.
In this paper, we describe and evaluate different approaches to defining reasonable layout verification targets by exploring various methods to reduce verification time, maintain accuracy and improve layout portability. First, to reduce verification time, we implement a method to quickly scan the layout for large variations without the need to run the actual OPC recipe. This paper describes the characteristics of a model that defines a pseudo-OPC process. Next, because the pseudo-OPC process cannot be mapped exactly to the real OPC process, there are accuracy limitations when using only the pseudo-OPC process. To overcome these limitations, the verification system follows an incremental approach, in which those regions previously selected are evaluated with the full mask synthesis recipe to reduce the number of falsely detected errors. Finally, to investigate the issue of portability, we evaluate how different errors evolve with maturing process and OPC recipe conditions for different layout patterns.
