Some years ago, the solution to voltage sags was to use vast UPS or battery systems. But with more and more 300 mm Fabs in operation (and 450mm on the horizon) maintenance and regular replacement of such costly devices is a burden to every manufacturing facility. UPS and battery systems shall not be used in any tools (exception: FAB UPS for data systems).

Due to the extreme automation in new 300 mm semiconductor Fabs and only a few people inside the Fab, end-users want to have tools that are able to continue to run even after a voltage sag occurred. This continued operation is the Pass-Fail criteria outlined in SEMI F47-0200: “Equipment must continue to operate without interrupt during conditions identified in the area above the defined line”.

The SEMI F47 standard introduced a well thought out voltage-to-time curve that most semiconductor processing, metrology, and automated test equipment will be exposed to during normal operation.

SEMI F47 requires that tools tolerate the following voltage sags:

  • 50% remaining voltage, 50% missing voltage, for 200 milliseconds
  • 70% remaining voltage, 30% missing voltage, for 500 milliseconds
  • 80% remaining voltage, 20% missing voltage for one second.

In addition, SEMI F47 recommends, but does not require, that tools tolerate:

  • 0% remaining voltage, 100% missing voltage, for 1 cycle
  • 80% remaining voltage, 20% missing voltage, for 10 seconds.