There is a dire need for the removal of all printable defects on lithography masks. As the technology node advances,
smaller particles need to be efficiently removed from smaller features without any damage or adders. CO2 cryogenic
aerosol cleaning is a dry, residue-free and chemically inert technique that doesn't suffer from disadvantages of
conventional wet cleaning methods such as transmission/reflectivity loss, phase change, CD change,
haze/progressive defects, and/or limitation on number of cleaning cycles. Ultra-pure liquid CO2 when dispensed
through an optimally designed nozzle results in CO2 clusters that impart the required momentum for defect removal.
Historically nanomachining debris removal has been established with this technique. Several improvements have
been incorporated for cleaning of advanced node masks, which has enabled Full Mask Final Clean, a new capability
that has been successfully demonstrated. The properties of the CO2 clusters can be captured utilizing the Phase
Doppler Anemometry (PDA) and effect of varying process and design parameters can be verified. New nozzles
have been designed to widen the cleaning process window for advanced node optical masks, without any damage to
the weak primary features and/or sub-resolution assist features (SRAFs). This capability has been experimentally
proven for high aspect ratio SRAFs e.g. 2.79 (52nm wide by 145 nm tall) as well as SRAFs 45nm wide by 73 nm
tall. In this paper, 100% removal of soft defects that would have printed on advanced node masks is demonstrated.
No printed defects larger than 50nm is observed after the CO2 cleaning. Stability of the cleaning and handling
mechanisms has been demonstrated over the last 4.5 months in a production environment. The CO2 cleaning
technique is expected to be effective for more advanced masks and Extreme Ultra-Violet (EUV) lithography.