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It is becoming more and more difficult to ensure robust patterning after OPC due to the continuous reduction of layout dimensions and diminishing process windows associated with each successive lithographic generation. Lithographers must guarantee high imaging fidelity throughout the entire range of normal process variations. The techniques of Mask Rule Checking (MRC) and Optical Rule Checking (ORC) have become mandatory tools for ensuring that OPC delivers robust patterning. However the first method relies on geometrical checks and the second one is based on a model built at best process conditions. Thus those techniques do not have the ability to address all potential printing errors throughout the process window (PW). To address this issue, a technique known as Critical Failure ORC (CFORC) was introduced that uses optical parameters from aerial image simulations. In CFORC, a numerical model is used to correlate these optical parameters with experimental data taken throughout the process window to predict printing errors. This method has proven its efficiency for detecting potential printing issues through the entire process window [1]. However this analytical method is based on optical parameters extracted via an optical model built at single process conditions. It is reasonable to expect that a verification method involving optical models built from several points throughout PW would provide more accurate predictions of printing errors for complex features. To verify this approach, compact optical models similar to those used for standard OPC were built and calibrated with experimental data measured at the PW limits. This model is then applied to various test patterns to predict potential printing errors. In this paper, a comparison between these two approaches is presented for the poly layer at 65 nm node patterning. Examples of specific failure predictions obtained separately with the two techniques are compared with experimental results. The details of implementing these two techniques on full product layouts are also included in this study.

At present, the question of the move from 193 to 157nm lithography is under discussion. There are still several major issues such as the development of 157nm photo-resists and pellicles, as well as calcium-fluoride lens material availability. The extension of the 193nm lithography down to the 65- and 45-nm half pitch technologies is now considered as a serious alternative. This requires several technical challenges with the use of phase shift masks (PSM), optical proximity effects corrections or liquid immersion. Simulation gives information on expected process latitudes and is an important tool to help this technical choice. Previous works [1,2] have shown that the "Diffused Aerial Image Model" (DAIM) [3] is accurate for CD prediction. Reliable process latitudes can be extracted from the simulated focus-exposure matrices (FEM). The model is used for the process latitudes evaluation of the different lithography approaches possibly used to print the 65- and 45-nm half pitches. 193nm illumination in addition to PSM is compared to 157nm lithography associated with conventional or optimized illumination schemes. This work shows that PSM at 193nm gives generally better exposure latitude for all pitches and CD, and confirms that 193nm lithography is a possible alternative to achieve 45nm and 70nm half pitches patterning. The process windows are nevertheless very small, and huge mask error factors (MEEF) are another sign that printing such small features is close to the physical limit (k1 factor close to the quarter).