Amir Azordegan

Full spectral analysis of line width roughness

Various approaches can be used to quantify line width roughness (LWR). One of the most commonly used estimators of LWR is the standard deviation. However, this approach is incomplete and ignores a substantial amount of information. We propose here a full spectral analysis to investigate and monitor LWR. A variety of estimators, such as standard deviation, peak-to-valley, average, correlation length and Fourier analysis have been implemented on-line on CDSEM. The algorithms were successfully tested against e-beam written LWR patterns, both deterministic and random. This approach allows a fully automated investigation of LWR. This methodology was used to monitor LWR over a long period of time, benchmark new resists and to investigate the effect of LWR on device performance and yield.

Spectral analysis of line width roughness and its application to immersion lithography

Various approaches can be used to quantify line width rough- ness LWR. One of the most commonly used estimators of LWR is standard deviation . However, a substantial amount of information is ignored if only is measured. We use an automated approach to inves- tigate LWR, where standard deviation, correlation length, and power spectrum are measured online on critical dimension scanning electron microscopes. This methodology is used to monitor LWR, investigate the effect of LWR on critical dimension precision, and to benchmark new resists for immersion lithography. Our results indicate that online LWR metrology is a critical tool in a variety of applications, including but not restricted to process control.

Automated CD SEM tilt-ready for primetime: a fast in-line methodology for differentiating lines vs. spaces

One of many challenges the process or metrology engineers face is incorrect flagging on the process control chart. It could either be a result of an un-optimized recipe that measures the wrong feature (a space instead of line) or a feature placement error due to tool limitation. This can be a costly problem in the fab where processes are put on hold, feedback loops are corrupted and backlogs are built up unnecessarily. Often many hours must be spent by operators re-inspecting lots and process or metrology engineers re-qualifying the recipes. Most CD SEMs use algorithms employing pattern matching and contrast difference to differentiate between line and space. However, the shrinking node requirement, limited contrast between line and space images and the 1:1 line and space ratios have revealed limitations of these algorithms. Recently, a metrology solution using beam tilt on the KLA-Tencor ECD-2 has been developed to tackle the problem of dense line or dense trench array measurements. This methodology is a line vs. space detection mechanism that precedes the metrology measurement. This application is quick and oblivious to low contrast differences between line/space and to systematic errors that occur with narrow feature positioning. Whether or not the specified feature type for measurement is centered in the field of view, it always detects the requested feature type and sets the metrology measurement to be made accordingly and therefore significantly reducing false negatives and false positives. This application also allows for greater tolerance in recipe setup and placement error, and thus lightens the burden of recipe creation on the novice user. This technique can also be incorporated into waferless design based metrology where limited prior knowledge of the wafer is one of the requirements. Future potential of this metrology solution will also be discussed. This could include detecting undercut situations and possibly even correcting bottom CD based on undercut angular detection.