Efficient Method For Sraf Rule Determination

Depth of Focus has always been of great concern in Lithography as a result of processes optimized for specific feature dimensions and pitches. Insertion of sub-resoultion assist features(SRAFs) ([1]) ([2]) or Scatter Bars is a common technique used to equalize DOF through the variety of geometries used in a design. SRAFs can be inserted into the layout by a variety of means ranging from methods based on simple rule-tables ([3]) to full-fledged layout simulations ([4][5]). Various tools are available from electronic design automation (EDA) vendors that are capable of placing srafs based on elaborate simulations of the design layout, but, a tool that can determine a rule-table is not available. Each resolution enhancement technique (RET) engineer has his/her own methodology of extracting rules based on simulation of a large layout with design and sraf rule variations. Significant computational resources are required to carry-out these extensive simulations affecting the time required to formulate the rule table and restricting the variation that can be considered for the simulations. In this paper, we discuss an efficient method which overcomes this problem by searching in the design and sraf rule domain to obtain a comprehensive set of sraf rules, thereby resulting in a better rule-set by using significantly lesser computation resources.