OverlayΒΆ

Precise overlay requires that the following conditions are met:

  • Precise Write-Read Alignment.

    Any residual shift between write and read fields causes overlay errors. During the overlay process, neither the pixel size nor the pixel timing should be changed. Otherwise, the read-write alignment will not be correct.

  • Minimization of thermal drift.

    Thermal drift is reflected in overlay error. To minimize thermal drift, avoid temperature changes of the NanoFrazor mechanics. For example, it is suggested to wait at least 10 minutes between a cantilever replacement and the execution of a demanding overlay. This because the cantilever holder is warmed up by the contact with the hands during cantilever replacement. To minimize the error induced by residual thermal drift, minimize the time between the read and the write operations.

hr_bitmap

Figure 26 Diagram of the overlay workflow: Reading-Designing/Aligning-Writing.