In 32nm/22nm advanced technology node, double patterning lithography is considered for semiconductor manufacturing.
It necessitates tightened requirement of overlay measurement, i.e. to measure the position of a pattern with respect to that
of a pattern in the underlying layer. The measurement target design plays a fundamental role in overlay precision and
accuracy. Typical alignment target, such as bar-in-bar or box-in-box (BIB), has precision, accuracy, and size restrictions.
This prompts us to look into better alignment targets. Recently, scatterometry-based metrology and profile model
capability have been extended to measure multi-level grating structures. In addition, scatterometry has been shown to be
the best choice for integrated metrology to perform wafer-to-wafer control. Therefore, it makes sense to consider using
scatterometry for overlay measurement.
In this research, the modeling analysis is performed on the spectra taken directly from a real pattern area with grating-ongrating
structure. The critical dimension (CD) at the grating on top and the lateral shift between the top and the bottom
gratings can be detected simultaneously. The lateral shift between the layers can be verified with the traditional overlay
box. Unlike the traditional BIB target that has micrometer CD size, the CD size of the scatterometry overlay (S_OVL)
target is much closer to that on the real device. So, it can much better reflect the overlay (OVL) shift on real devices. We
also studied the non-model-based S_OVL measurement using a 673-nm semiconductor laser with a 10μm x 20μm target
size, wafer-to-wafer control of CD and lateral shifts on some critical layers with grating-on-grating structure, as well as
the CD and OVL variations within layer and from layer to layer for double patterning.