Computational Lithography

Chapter 3

Rule-Based Resolution Enhancement Techniques

3.1 RET Types

With Moore's law, rapid trend to reduce the critical dimension (CD) in optical lithography, imaging has become a low process, where a sizable fraction of the transmitted light energy is concentrated in the high spatial frequency components of the mask spectrum. However, the low-pass filtering properties of the lens in the exposure system cuts off the high-frequency components leading to image distortion. To enhance the resolution and contrast of the circuit patterns, different types of RETs have been proposed, such as rule-based, model-based, and hybrid approaches. Conventionally, the terminologies of “rule-based,” “model-based,” and “hybrid” were only used for OPC methods. In this book, we generalize these terminologies to the entire scope of RETs, including OPC, PSM, and OAI. In the following, the concepts of these RET approaches are discussed. Subsequently, this chapter focuses on the discussion of the rule-based RETs. Model-based RETs are discussed at length in the following chapters.

3.1.1 Rule-Based RETs

In the rule-based approaches, adjustment strategies of the mask patterns are made up based on a set of locally restricted rules. The amount of correction applied to a feature or an edge is carried out in accordance with a predefined table [80, 92]. The specifics in the table can be derived from simulation, ...