Product layout induced topography effects on intrafield levelling

Abstract

International audienceWith continuing dimension shrinkage using the TWINSCAN NXT:1950i scanner on the 28nm node and beyond, the imaging depth of focus (DOF) becomes more critical. Focus budget breakdown studies [Ref 2, 5] show that even though the intrafield component stays the same, it becomes a larger relative percentage of the overall DOF. Process induced topography along with reduced Process Window can lead to yield limitations and defectivity issues on the wafer. In a previous paper, the feasibility of anticipating the scanner levelling measurements (Level Sensor, Agile and Topography) has been shown [1]. This model, built using a multiple variable analysis (PLS: Partial Least Square regression) and GDS densities at different layers showed prediction capabilities of the scanner topography readings up to 0.78 Q² (the equivalent of R² for expected prediction). Using this model, care areas can be defined as parts of the field that cannot be seen nor corrected by the scanner, which can lead to local DOF shrinkage and printing issues. This paper will investigate the link between the care areas and the intrafield focus that can be seen at the wafer level, using offline topography measurements as a reference. Some improvements made on the model are also presented

Verification and application of multi-source focus quantification

“…image plane deviation measured by FOCAL) can also effect the BF of a single pattern differently across the field [15]. The wafer topography also has an intrafield component showing non-correctable systematics that are tightly linked to the onproduct focus [2]. For a given pattern, best focus depends on the intrafield position of each of its occurrences across field.…”

“…The concept of the multi-source focus correlation method was presented in 2015 [1,2]. A more accurate understanding of real on-product focus can be obtained by gathering information from different sectors: design, scanner short loop monitoring, scanner leveling, on-product focus and topography.…”

“…In reference [1], the link between scanner monitoring and on-product focus was established as well as the correlation between design and the scanner level sensor measured intra field non-correctable errors after leveling. In [2], the on-product focus to topography correlation has been studied and the concept of smart leveling was proposed.…”