There are two main technologies commercially available to write photomasks: Raster Scanning and Variable Shape
Beam (VSB). For masks with features sizes that can be written on either kind of machine, it is advantageous to estimate
the write time on both kinds of machines. The machine that is expected to have a faster Turn Around Time could be
chosen. It is trivial to estimate how much time a design would take to be written by using a Raster Scanning machine.
Since this kind of machine scans the whole design area, its TAT depends mainly on the size of the design and the size of
the pixel. The write time is therefore mostly independent of the number of figures composing the design data.
Estimating how long the same design would take to be written by a VSB machine is more involved, since its TAT
depends greatly on how data is organized and fractured. In other words, there is a direct relation between number of
elementary data figures (rectangles and trapezoids) and writing time.
In VSB machines, data with curvilinear geometries can produce a huge increase in the amount of shots needed to write a
design, which in turn directly affects TAT.
This paper presents a novel technique used to provide the user with relevant information to aid with deciding which
technology is to be used for writing the mask. The technique yields two vital pieces of information:
a) An estimation of the amount of VSB Shots needed by a VSB Machine to write the design data into a
b) A map of where curvilinear geometries are located throughout the design.