The introduction of pitch splitting (Litho-Etch-Litho-Etch) at 14FDSOInm node requires the development of specific metrologies to adopt advanced process control (for CD, overlay and focus corrections). The pitch splitting process leads to final line CD uniformities that are a combination of the CD uniformities of the two exposures, while the space CD uniformities are depending on both CD and OVL variability.
In this paper, investigations of CD and OVL process control of 64nm minimum pitch at Metal1 level of 14FDSOI technology, within the double patterning process flow (Litho, hard mask etch, line etch) are presented.
Various measurements with SEMCD tools (Hitachi), and overlay tools (KT for Image Based Overlay – IBO, and ASML for Diffraction Based Overlay – DBO) are compared. Metrology targets are embedded within a block instanced several times within the field to perform intra-field process variations characterizations.
Specific SEMCD targets were designed for independent measurement of both line CD (A and B) and space CD (A to B and B to A) for each exposure within a single measurement during the DP flow.
Based on those measurements correlation between overlay determined with SEMCD and with standard overlay tools can be evaluated.
Such correlation at different steps through the DP flow is investigated regarding the metrology type. Process correction models are evaluated with respect to the measurement type and the intra-field sampling.