Most of defects generated in mask fabrication processes have been mainly created during each unit process. It becomes
more important to detect and remove smaller defects on mask as pattern nodes keep shrinking. Each unit processes are
getting not only more challenging to sustain mask quality and defect level but also more influencing on other processes
for smaller pattern nodes. New type of defects based on such influences (crosstalk) between different processes is
starting to emerge, which is requesting for a revision of defect reduction strategy because dealing with crosstalk defects
is directly related with quality and TAT of mask manufacturing. It is relatively difficult to properly understand root-cause
or working mechanism of defects generated by crosstalk between different processes. This is because interaction between
different processes from defect generation perspectives has hardly been studied.
In this paper, we introduce emerging progressive defects created while etched masks are undergoing cleaning process or
subsequent events of moving to next process or temporary storage. We will investigate how etch gas residues on mask
surface remaining after etching process interact with cleaning chemicals or moisture from subsequent process or
environment to trigger defect generation and its growth. We will also examine effects of POD outgassing on generation
of crosstalk progressive defect. Based on this understanding, appropriate solutions to mitigate defects caused by crosstalk
between mask fabrication processes will be proposed.
It is believed that new type of progressive defects caused by crosstalk between different mask fabrication processes will
be more flourishing in the near future where mask blank materials, mask manufacturing processes, and chemicals need to
diversify in order to meet much tighter specifications of mask quality. Therefore, it is very crucial to have right
understandings on the interactions between various processes and eradicate possible root-causes of defect generations.
Haze issues are getting more serious since size of Haze defect printable on the water surface that could matter is
decreasing further with reduced pattern size. Many efforts have been made to reduce the contamination level on the
photomask surface by applying wet or dry processes. We have successfully reduced surface contamination down to subppb
level for organic and inorganic chemicals. No matter how well the mask surface is cleaned, chemical contaminant
cannot be perfectly eliminated from the surface. As long as contaminants exist on the surface, they are getting aggregated
around certain points with higher energy to create defects on it during laser exposure. Also, the cleaned mask surface
could be contaminated again during following processes such as shipping and storage.
Here, we propose a new paradigm for Haze retardation where we severely decelerate defect generation and growth
rather than eliminate chemical contaminants on the mask surface. We have made mask surface on which chemical
contaminants are hardly accumulated to generate Haze defects even during laser exposure. By creating mask surface
insensitive to chemical impurity level up to a certain degree, we are able to retard Haze occurrence much better than by
reducing surface impurities down to sub-ppb level. This approach has another advantage of allowing a freedom for mask
environment during the process of shipping, storage, and exposure.
We further investigate how the treated mask surface should have strong resistance against chemical contaminant
aggregation towards Haze defect generation around specific points with high energy.
It is known that PSM pattern edge (MoSiON/Qz boundary) of EA-PSM mask is the weakest point against Haze
occurrence in real mass production. Based on the understanding of these phenomena, we have developed very efficient
ways to protect PSM pattern edge from Haze defect formation even after normal SPM cleaning processes. Oxide layer
formulated on the PSM pattern (including pattern top and side) is actively trapping chemical ions existing on the surface
and inside bulk of mask substrate, preventing their motion or diffusion toward Haze defect creation during laser
exposure. As a result, we are able to reduce cleaning frequency of each EA-PSM mask set without Haze issues and
thereby dramatically expand their life time in real mass production.
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