TY - JOUR
AU1 - Kandel, Daniel
AU2 - Levinski, Vladimir
AU3 - Sapiens, Noam
AU4 - Cohen, Guy
AU5 - Amit, Eran
AU6 - Klein, Dana
AU7 - Vakshtein, Irina
AB - Currently, the performance of overlay metrology is evaluated mainly based on random error contributions such as precision and TIS variability. With the expected shrinkage of the overlay metrology budget to < 0.5nm, it becomes crucial to include also systematic error contributions which affect the accuracy of the metrology. Here we discuss fundamental aspects of overlay accuracy and a methodology to improve accuracy significantly. We identify overlay mark imperfections and their interaction with the metrology technology, as the main source of overlay inaccuracy. The most important type of mark imperfection is mark asymmetry. Overlay mark asymmetry leads to a geometrical ambiguity in the definition of overlay, which can be ~1nm or less. It is shown theoretically and in simulations that the metrology may enhance the effect of overlay mark asymmetry significantly and lead to metrology inaccuracy ~10nm, much larger than the geometrical ambiguity. The analysis is carried out for two different overlay metrology technologies: Imaging overlay and DBO (1st order diffraction based overlay). It is demonstrated that the sensitivity of DBO to overlay mark asymmetry is larger than the sensitivity of imaging overlay. Finally, we show that a recently developed measurement quality metric serves as a valuable tool for improving overlay metrology accuracy. Simulation results demonstrate that the accuracy of imaging overlay can be improved significantly by recipe setup optimized using the quality metric. We conclude that imaging overlay metrology, complemented by appropriate use of measurement quality metric, results in optimal overlay accuracy.
TI - Overlay accuracy fundamentals
JF - Proceedings of SPIE
DO - 10.1117/12.916369
DA - 2012-02-13
UR - https://www.deepdyve.com/lp/spie/overlay-accuracy-fundamentals-XVLs3KJf5W
SP - 832417
EP - 832417-10
VL - 8324
IS - 1
DP - DeepDyve
ER -