In advanced technology nodes, due to accuracy and computing time constraint, OPC has shifted from discrete simulation
to pixel based simulation. The simulation is grid based and then interpolation occurs between grid points. Even if the
sampling is done below Nyquist rate, interpolation can cause some variations for same polygon placed at different
location in the layout. Any variation is rounded during OPC treatment, because of discrete numbers used in OPC output
file. The end result is inconsistency in post-OPC layout, where the same input polygon will give different outputs,
depending on its position and orientation relative to the grid. This can have a major impact in CD control, in structures
like SRAM for example, where mismatching between gates can cause major issue.
There are some workarounds to minimize this effect, but most of them are post-treatment fix. In this paper, we will try to
identify and solve the root cause of the problem. We will study the relationship between the pixel size and the
consistency of post OPC results. The pixel size is often set based on optical parameters, but it might be possible to
optimize it around this value to avoid inconsistency. One can say that the optimization will highly depend on design and
not be possible for a real layout. As the range of pitch used in a design tends to decrease, thanks to fix pitch layouts, we
may optimize pixel size for a full layout.