In this paper, we show the characteristics of particle contamination induced defect footprints and explain the basic principles of their formation during ebeam exposure. To verify these principles, we carried out full 3D Monte Carlo Simulations of electrons impinging on the mask stack (modelled as PMMA, Cr, and SiO2), covered by a defect layer and compared the simulated contour with SEM images of real defect footprints. The relevant physical property is the deposited energy inside the PMMA layer. First, we verified in our simulations that the deposited energy is indeed antiproportional to the beam energy. In a second step we simulated scattering trajectories of electrons to quantify the nontrivial dependence of deposited energy on the size and thickness of defects as well as defect composition. We also considered shotnoise statistics due to the limited number of electrons in ebeam pattern generation accompanied by gaussian smoothing of the deposited energy representing subsequent processing and demonstrate that considerably increased energy deposition to an ebeam-active resist can occur in direct vicinity of a scattering defect when scattering widens the beam opening angle leading to longer trajectories inside the resist. The pattern generator is variable-shaped electron beam (VSB) with 50 keV energy operated in the high-volume photomask manufacturing facility at AMTC Dresden, the Monte Carlo simulation software is virtualSEM from GenISys GmbH.
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