Overlay performance has been a critical factor for advanced semiconductor manufacturing for years. Over time these
requirements become more stringent as design rules shrink. Overlay mark design and selection are the first two steps of
overlay control, and it is known that different overlay mark designs will have different responses to process conditions.
An overlay mark optimized for traditional process might not be suitable for SADP (self-aligned double patterning)
technology due to changes in lithography and etching process conditions. For instance, the traditional BIB (box-in-box)
target defined by the core mask becomes a template structure in SADP flow, the pitch and cycle of the overlay mark is
further changed after spacer formation and core film removal hence the mark recognition and robustness have been
challenging for the subsequent process layers.
The comprehensive study on the methodology of overlay mark design and selection is still not available for SADP
process. In this paper, various types of overlay marks were designed to comply with the SADP process to get rid of the
weaknesses of traditional targets. TMU (total measurement uncertainty) performance was adopted to determine the
optimal overlay marks for meeting production overlay control requirements in SADP process flow. The results have
suggested the segmented marks outperform to non-segmented marks on image contrast as well as TMU.
Contact hole within a NOR FLASH memory array is one of the most challenging features to print in the semiconductor
manufacturing. It has been the key limiter of NOR FLASH memory scaling due to the difficulties involved in patterning
the one-dimensional contact arrays and extremely stringent contact to gate overlay constraints.
In this study, DPT (Double Patterning Technology) by ArF dry process was introduced for patterning NOR FLASH
memory contact arrays. This approach has demonstrated a contact patterning with extremely low optical proximity effect
for 50nm half-pitch with satisfied lithography process latitude and especially the circular contact shape can be
maintained without compromise of NOR FLASH cell area. The novel hard mask scheme was the key enabler for this
contact double patterning and this approach can be easily extended to ArF immersion lithography as a promising option
for contact formation in leading-edge memory products.