Diffraction Based Overlay (DBO) is widely evaluated by numerous authors, results show DBO can provide better
performance than Imaging Based Overlay (IBO). However, DBO has its own problems. As well known, Modeling based
DBO (mDBO) faces challenges of low measurement sensitivity and crosstalk between various structure parameters,
which may result in poor accuracy and precision. Meanwhile, main obstacle encountered by empirical DBO (eDBO) is
that a few pads must be employed to gain sufficient information on overlay-induced diffraction signature variations,
which consumes more wafer space and costs more measuring time. Also, eDBO may suffer from mark profile
asymmetry caused by processes.
In this paper, we propose an alternative DBO technology that employs a dedicated overlay mark and takes a rigorous
modeling approach. This technology needs only two or three pads for each direction, which is economic and time saving.
While overlay measurement error induced by mark profile asymmetry being reduced, this technology is expected to be as
accurate and precise as scatterometry technologies.