Overlay and CD uniformity variation due to wafer thermal deformation caused by EUV exposure

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The extreme ultraviolet lithography (EUVL) process allows for the manufacturing of better-performance chips. However, the EUVL exposure process might contribute to significant variations in the patterns of circuits, which can cause serious image placement and flatness change. Especially during the exposure, the EUV absorption might cause local wafer thermal deformation that might cause overlay and local critical dimension (CD) variation. In this study, we investigated wafer thermal deformation with different CDs and pitches with EUV exposure and thermo-mechanical behavior of the photoresist using the finite element method simulation. It is found that the thermal deformation caused during EUV exposure is different inside a die. In the direction along the scan, thermal deformation increases as it is near the center of the slit. The deformation in the perpendicular direction increases as it approaches the edges and deforms in the opposite direction relative to the center of the slit. In both directions, the thermal deformation increases gradually as the scan progresses, and it could be as large as ∼1.5 nm in a die. There was no difference in thermal deformation by CD change, but it changed with pitch.