Mask manufacturers are facing major reticle metrology challenges, driving the need for
cost‐effective solutions that provide tighter registration specifications and on‐device
E‐beam mask writers’ local registration error may have a critical impact on the error
contribution of the reticles to wafer overlay, as it is very local and most likely is not
revealed with standard quality control schemes and sampling. The reticle error
signatures are, of course, writing‐strategy‐dependent, but may also be caused by
residual deflector alignment issues, thus leading to a very local but potentially critical
non‐correctable overlay error on the wafer. Since the e‐beam writer strategy does not
differ significantly between ArFi masks and EUV masks, we expect a similar error
signature for both mask types.
We will present data which demonstrates local registration errors that can be correlated
to the writing swathes of state‐of‐the‐art e‐beam writers and multi‐pass strategies,
potentially leading to systematic device registration errors versus design of close to 2nm.
Furthermore, error signatures for local charging and process effects are indicated by
local registration measurements resulting in systematic error, also on the order of 2nm.
A unique measurement methodology, Local Registration Metrology, is presented that
allows for dense sampling of reticle dies to characterize the local e‐beam registration
error. Several thousand sites in a region of interest with length and width of a few
hundred microns are measured. LMS IPRO metrology algorithms enable parallel
registration measurement of all individual sites for fast and accurate metrology. High
throughput allows completion of Local Registration measurement within a few minutes
instead of exceeding a day of measurement time with conventional registration
metrology strategies. This capability enables mask users to add local registration quality
control to ensure the local wafer pattern placement error contribution by a mask is
within the acceptable tolerance.
In addition, based on the results of Local Registration Metrology, e‐beam mask writer
corrections via feed forward can now be developed to significantly reduce local overlay
error on wafer caused by the reticles.