Why is SEMI F47 Important?

SEMI F47 for Tool Manufacturers and End-Users


Stricter Enforcement of SEMI F47 throughout SEMI Fabs in 2010 and 2011
Voltage Sag Immunity for semiconductor manufacturing tools, sub-systems and components Every modern semiconductor manufacturing tool can be sensitive to brief disturbances on the AC power mains. Electrical systems are subject to a wide variety of power quality problems which can interrupt production processes, affect sensitive equipment, and cause downtime, scrap, and capacity losses. The most common disturbance, by far, is a brief reduction in voltage, lasting for a few hundred milliseconds. These 'voltage sags' (in American English) or 'voltage dips' (in British English) are the most common power problem encountered in semiconductor Fabs around the world.

Why SEMI F47 Voltage Sag requirements?
Some years ago, the solution to voltage sags was to use vast UPS or battery systems. But with more and more 300mm 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 300mm 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.

What are the requirements?
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 1 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.
SEMI F47 ride-through curve
Fig1 : The famous SEMI F47 ride-through curve

Who enforces SEMI F47?
Like any other SEMI standards, SEMI F47 is not a legal requirement, but required by most semiconductor manufacturers such as Intel, TI, IBM, Samsung etc. around the world. Every new semiconductor manufacturing tool that enters a SEMI Fab has to comply with the SEMI F47 Voltage Sag requirements. It is used both for semiconductor equipment, and for components and subsystems within semiconductor equipment. Enforcement is entirely customer-driven; the procurement agents of semiconductor equipment know the economic consequences of sag-induced failures, and generally refuse to pay for new equipment that fails the SEMI F47 immunity requirement. More and more tool manufacturers require the same from their component suppliers (power supplies, vacuum pumps, HF generators etc.). SEMI F47 Testing and Certification is usually an essential part of any tool purchase specification.

What are common responses to voltage sags, and how to address these problems?
  • Emergency Off (EMO) circuitry
  • Instrument and controller power supplies
  • Motion control drives
  • Voltage monitoring relays
  • Circuit breakers open due to increased current on phases without dip
  • Sensor faults or errors
  • Robot failure
  • Internal communication errors
  • Computer re-boots
  • Graceful restoration using power quality sensors
There are many low-cost solutions to these problems. Powering EMO circuits from 24 V DC instead of 24 VAC, de-rating power supplies or choosing SEMI F47 certified power supplies, inserting time delays or just a small software changes might help to solve a problem. Yet another common equipment failure mechanism involves some obscure sequence of events. For example, a voltage sag is applied to the equipment, and its main contactor opens with a bang. But further investigation reveals that a small relay connected in series with the main contactor coil actually opened, because it received an open relay contact from a stray water sensor. That sensor, in turn, opened because its small 24 VDC. supply output dropped to 18V during the voltage sag. (In this case, the solution is an inexpensive bulk capacitor across the 24 VDC supply.)

SEMI F47 was updated in 2006 and the latest version is officially called SEMI F47-0706. It will be harmonized with IEC 61000-4-34 which is the respective international Voltage Sag Immunity standard. A new revision will come up around 2011.

With the ever-increasing use of sophisticated controls and equipment in industrial, commercial, institutional, and governmental facilities, the continuity, reliability, and quality of electrical service has become extremely crucial to many power users. The power hardly gets better in the future, so the ultimate goal for any product manufacturer is to make its product immune to voltage sags