As pattern density and OPC complexity grow, photomask write times on electron beam tools increase in proportion.
Reducing the write time would decrease mask-making costs, but the performance of any alternative mask writer must
meet all of the technical requirements on both mask and wafer. In addition, it is desirable to use existing OPC models in
order to avoid the costs of developing and maintaining separate OPC models for each writer. The Sigma7500 deep-UV
pattern generator provides the highest resolution available from a laser-based tool, and it has the advantage of
maintaining about a 3 hour write time even as the feature count increases.
In this study, the Sigma7500 and a variable shaped e-beam (VSB) tool are compared on 65nm metal1 and via1 layers.
In the first phase, the Sigma pattern positioning was matched to a SMIC reference grid and a registration value of
10 nm (3s) was achieved with scales removed. In the second phase, M1 and V1 masks were printed with both laser and
e-beam writers using the same pattern data and compared on CD uniformity, linearity and proximity. The Sigma7500
met all of the photomask requirements for these layers. The masks were then printed on wafers and the wafer data was
evaluated. The results were comparable to those for the e-beam masks and were within the requirements, indicating that
the Sigma7500 can handle these layers without the need to revise the e-beam mask OPC models.