New Improving Metrology For Advanced Memory Devices With High Transmission Phase Shift Mask

In order to achieve better resolution and improve lithography process window, device manufacturers are looking into or adopting high transmission attenuated phase shift mask (HTM). The critical dimension uniformity (CDU) of the device pattern can be quite a bit better with high transmission mask as compared to conventional attenuated phase shift mask, which makes it an attractive choice for advanced memory devices. However, it poses challenges on metrology targets such as alignment marks or micro diffraction-based overlay (uDBO) marks, which has different dimensions as device patterns as required by the metrology sensors. The challenges include printability, detectability, accuracy, process compatibility and defectively on the same device layer. In this paper we demonstrate solutions to address these challenges and thereby improve metrology for advanced memory devices with HTM. Without sacrificing mark contrast on wafer, the wafer quality of alignment mark is improved up to 10 times with respect to array like alignment marks and the stack sensitivity of uDBO mark can also increase more than 7 times as array like marks. Through a holistic target approach involving target design, target OPC, and recipe setup, we are able to achieve accurate metrology for optimal on-product overlay and device yield.