The lack of defect-free EUV photomask blanks is one of the multiple challenges in the application of EUV lithography for high volume wafer manufacturing. In EUV photomask manufacturing, shifting the design before writing to avoid patterning over blank defects (pattern shift process) is one of the methods for defect mitigation. A reliable pattern shift process depends upon precise image placement during EUV mask writing. Specifically, accurate determinations of centrality, mean shift distances and residual image placement (IP) errors (3σ) are required and reports describing pattern shift processes1-8 echo this importance of accurate IP during EUV photomask writing. The pattern shift process detailed in this report improves IP accuracy for EUV photomasks aligned on fiducial marks (FM) and increases the budget of potential pattern shifts, while remaining within the mask centrality specification limits. Our process is demonstrated on EUV products where <5 nm 3σ of uncorrected IP error for aligned patterns was achieved.
We quantitatively evaluate Nuflare’s latest resist charging effect correction (CEC) model for advanced photomask
production using e-beam lithography. Functionality of this CEC model includes the simulation of static and timedependent
charging effects together with an improved calibration method. CEC model calibration is performed by
polynomial fitting of image placement distortions induced by various beam scattering effects on a special test design
with writing density variations. CEC model parameters can be fine tuned for different photomask blank materials
facilitating resist charging compensation maps for different product layers. Application of this CEC model into
production yields a significant reduction in photomask image placement (IP), as well as improving photomask overlay
between critical neighbouring layers. The correlations between IP improvement facilitated by this CEC model and single
mask parameters are presented and discussed. The layer design specifics, resist and blank materials, coupled with their
required exposure parameters are observed to be the major influences on CEC model performance.
The recently introduced helium ion microscope (HIM) is capable of imaging and fabrication of nanostructures thanks to
its sub-nanometer sized ion probe. The unique interaction of the helium ions with the sample material provides very
localized secondary electron emission, thus providing a valuable signal for high-resolution imaging as well as a
mechanism for very precise nanofabrication. The low proximity effects, due to the low yield of backscattered ions
and the confinement of the forward scattered ions into a narrow cone, enable patterning of ultra-dense sub-10 nm structures. This paper presents various nanofabrication results obtained with direct-write, with scanning helium ion beam lithography, and with helium ion beam induced deposition.