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.
With reduction of design rules, a number of corresponding new technologies, such as i-HOPC, HOWA and DBO
have been proposed and applied to eliminate overlay error. When these technologies are in use, any high-order error
distribution needs to be clearly distinguished in order to remove the underlying causes. Lens aberrations are normally
thought to mainly impact the Matching Machine Overlay (MMO). However, when using Image-Based overlay (IBO)
measurement tools, aberrations become the dominant influence on single machine overlay (SMO) and even on stage
repeatability performance. In this paper, several measurements of the error distributions of the lens of SMEE SSB600/10
prototype exposure tool are presented. Models that characterize the primary influence from lens magnification, high
order distortion, coma aberration and telecentricity are shown. The contribution to stage repeatability (as measured with
IBO tools) from the above errors was predicted with simulator and compared to experiments. Finally, the drift of every
lens distortion that impact to SMO over several days was monitored and matched with the result of measurements.
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