|
|
MOSIS Technical Notes
Mask Data Prep and Manhattan Layout
MOSIS strongly recommends that layout be Manhattan (all edges
parallel to either the X or the Y axis). Should non-Manhattan layout
be necessary, it should be confined to large objects, where minor
adjustments in the edges are of no consequence.
Contacts and vias, being necessarily of minimum size, should always be
Manhattan.
There are mask generation issues that make non-Manhattan layout
subject to increasing distortion as feature sizes shrink. The issues
all stem from the need to fracture the layout data, and put it on a
grid of a given spot size (the spot size that will be used to write
the mask on the e-beam or laser exposure tool). While the spot size
has been shrinking too, it has not been shrinking as fast as the
feature size, so there are fewer spots in a minimum size feature now
than there were in the past. This means that off-grid layout is
snapped by a relatively larger amount to force it onto the grid. And,
necessarily, all 45-degree contacts are off-grid.
Furthermore, when any sizing of data is required (usually to
compensate for sizing that occurs in the wafer processing), the
algorithm used (which is based on extending or contracting the number
of spots in each feature) exaggerates the sizing along 45-degree edges
by 40% (square root of 2 - 1). Increasing the size of the 45-degree
contacts is not the appropriate answer. Standing them up
straight is the only good solution.
|
Related Links
Fabrication Schedule
Customer Support
MOSIS Products
|
|
|
