The JEOL system is calibrated by staff every 7 - 21 days, with separate calibration necessary for each condition file (current). These are typically stable for 1-3 weeks. As part of this process, column shift and tilt is adjusted (similar to an SEM), current is measured (and adjusted via the column zoom lenses, if necessary), wobble is checked and minimized (via the objective aperture, again similar to an SEM), focus and astigmatism is adjusted (via the objective lens strength and stigmator correction values), and the DAILYCAL file is run to ensure everything passes.

Some particularly relevant measurements are shown below:

• Current: specified as nominal values. As part of the exposure, the machine will measure the current (by default, every 20 minutes) and automatically adjust the exposure dose based on this. As such, drifts in current will not directly affect the writing quality, but may affect user experience on the system.

  • How is this measured?

    • The system moves to the Faraday cup and takes, takes a number of instantaneous measurements of the current, and averages them together.

  • Upper specification limit: the nominal current itself

    • Via the dose equation, too high of a staff set current may cause the machine to need a clock speed higher than 125 MHz if a user chooses a typical clock speed very close to the limit (e.g. typically >=120 MHz). This would result in an error message when trying to create the magazine file. From the user standpoint, this could only be remedied by increasing the minimum dose (not usually desirable, as this may overdose your pattern) or increasing the shot pitch (which may or may not result in different pattern results, but is also generally not desirable because of the unknown effect on your results). As a result, staff endeavor to keep the actual current below the nominal current at all times.

  • Lower specification limit: 10% less than the nominal current

    • Too low of a current (within reason) will not in anyway harm the pattern, but the write will take longer than expected. If the write is limited by the beam on time, 10% lower current (90% of the specified current) will take ~11% longer to write (100%/90% ≅ 1.11). This is considered a reasonable error, but longer than ~11% may unexpectedly prolong the write, and thus staff will endeavor to keep the actual current not lower than 10% lower than the nominal current.

• Calibration measured beam size: The beam size in the X and Y directions measured by the system on a “clean” spot of the AE mark used by staff for calibration. This will always be larger than the true size of the beam, and is only useful in the context explained here.

  • How is this measured?