As semiconductor features shrink in dimension and pitch, the excessive control of critical-dimension uniformity (CDU) and pattern fidelity is essential for mask manufacturing using electron-beam lithography. Requirements of the electronbeam shot quality affected by shot unsteadiness become more important than before for the advanced mask patterning. Imperfect electron optical system, an inaccurate beam deflector, and imprecise mask stage control are mainly related to the shot unsteadiness including positioning and dose perturbations. This work extensively investigates impacts of variable shaped beam dose and positioning perturbations on local CDU using Monte Carlo simulation for various mask contrast enhancement approaches. In addition, the relationship between the mask lithographic performance and the shot count number correlated with mask writing time is intensively studied.
Charging-induced pattern positioning errors (CIPPEs) from a 50-kV variable-shape e-beam writer on an opaque-MoSi-over-glass mask has been carefully characterized by directly measuring the pattern shifts using a high-accuracy mask registration tool. In addition, the reported behaviors associated with the CIPPEs, exponentially decaying in space and sign flipping with increasing pattern density (PD), another seldom-mentioned error component, behaving like a constant offset in space and becoming stronger with increasing PD, is found. The authors repeat the experiment with a charge dissipation layer coated atop the resist to experimentally explore the origins of these two phenomena and find that the exponential components, removable by the charge dissipating layer (CDL), result from the well-known resist charging effect but the constant offset, remain existing with the CDL, does not. From the result of Monte Carlo simulations, the constant component is speculated to result from blank charging. This finding can give important insights into the model-based charging effect correction as well as the effectiveness of the CDL.
Mask profile of chromeless phase-shifting lithography (CPL) defined by OCD has been investigated. In CPL masks,
unbalanced bombardments caused by different ion accelerations lead to the formation of micro-notch structures. A better
understanding of micro-notch structures is essential for quality gating of mask processes to improve of CPL mask
profiles. By measuring 12 of 16 elements of Mueller matrix, we are able to set up a model to simulate the depth of
micro-notch structure profile which shows good correlation with TEM images. Moreover, values of CD, quartz etching
depth and side wall angle acquired by OCD are presented and compared with those obtained by SEM, TEM and AFM,
The authors present a detailed observation of the charge-induced pattern positioning errors (CIPPEs) in a variableshape
e-beam writer on an opaque-MoSi-over-glass (OMOG) mask by directly measuring the pattern shifts using a mask
registration tool. The CIPPEs are found to have one short-range, that is exponentially decaying in space, and the other
constant offset components. The exponential term that decays slowly in time, whereas the constant offset fast diminishes.
By applying a charge dissipation layer (CDL), the authors experimentally verify that the exponential component results
from the charges in resist. On the other hands, the constant offset that can not be eliminated by the CDL is speculated to
be charges in the substrate according to the Monte Carlo simulation.