Managing the total CD error in advanced mask manufacturing requires that error contributions from writing, process and
metrology are minimized. This paper describes how both the writing and process contributions have been addressed in
the Sigma7500 DUV laser pattern generator, which prints masks by imaging a programmable spatial light modulator
(SLM). System enhancements have reduced the writing contribution to global CD uniformity to 5 nm (3s). Process-related
CD error sources, such as the signatures from mask developing and etching can be significant contributors to the
total CD error in mask manufacturing. These errors are classified as being either pattern-independent or pattern-dependent,
and the effects of both can be reduced using the ProcessEqualizer feature of the Sigma7500. This software
tool performs CD sizing during writing based on pattern density maps derived during mask data preparation, along with
tunable parameters that are determined experimentally. The CD sizing function has no effect on system throughput and
does not require flattening and re-fracturing of the pattern data.
Photomask CD control requirements continue to tighten due to inevitable device scaling, in addition to the increasing
mask error enhancement factor (MEEF). Managing the total CD error on production masks requires not only that the error contributions from the pattern generator should be minimized, but also that there is a way to handle errors due to
the mask process. This paper addresses process-related contributions such as the CD signatures from mask developing
and etching, and how their impact on the total CD error range can be reduced. This is accomplished using the on-line
ProcessEquilizerTM function in the Sigma7500 DUV laser pattern generator.
Long range and medium range process CD errors are major contributors to the total CD error range. These errors can be
classified as being either pattern-independent or pattern-dependent. Pattern-independent errors may occur in the bake,
develop and etch process steps. These errors are by definition static from mask to mask, and can therefore be mapped
and compensated by local sizing of the mask pattern data. Pattern-dependent errors typically originate from loading
effects, for example, in plasma etching. If such errors can be predicted from the pattern density variation across the
mask, then they can also be corrected for with local sizing.
The on-line ProcessEqualizerTM function performs local sizing, and offers a significant advantage over off-line solutions
that have the drawback of requiring flattening and refracturing of the pattern data. Local sizing is performed in parallel
with writing in the Sigma7500, and has no effect on throughput. In this paper the ProcessEqualizerTM function is
described, including how it is operated in the maskshop. Results are presented demonstrating the performance of the
ProcessEqualizerTM for handling global CD error signatures.
Mask cost is a key challenge for the semiconductor industry and a major issue is the write times of e-beam pattern generators. DUV pattern generators can provide high throughput, but there is a cost and time involved in qualifying these tools for IC production. To minimize this time and cost, the masks from the DUV tool should have pattern fidelity similar to that of e-beam tools. This can be done with corner enhancements on an imaging DUV mask writer. Here, we describe such a corner enhancement scheme and present results for the 65-nm-node requirements. We demonstrate how the corner radius can be tuned in a range of radii with a negligible effect on the process latitude.