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Sep 18

How are semiconductor process chillers and standard chillers different?

chillers for Semiconductor from BV Thermal Systems

At this time in microchip manufacturing technology most chillers for semiconductor processing and manufacturing are used on 200 and 300 MM processes.

This size of 200 and 300 MM is the size of the Silicon substrate or wafer that the microchip is made on.  The larger the substrate the more efficient the process as a larger substrate means more chips per wafer.

Semiconductor chillers have several key differences from your standard off the shelf chiller.  The key differences are found in the method of heat removal and the features and or safety mechanisms incorporated into Semiconductor chillers. 

First lets look at heat removal, chillers that use electro-mechanical refrigeration remove heat either to the air or to a water source.  Most semiconductor manufactures prefer the water-cooled chillers as these do not have fans which circulated dust and other small particulates around a clean room.  (Most semi-processes occur in a clean room).  Water cooled chillers are generally designed to use the minimum amount of facility cooling water to produce the needed cooling effect.  This is accomplished through proper sizing of the evaporator.  For any water-cooled chiller a minimum amount of water will be required to allow the refrigeration system to operate for a given heat load.  It is this low amount of water flow that is targeted to reduce water usage, energy consumption, reduce plumbing sizes and therefore material costs.

Now for the biggest difference between an “off the shelf” chiller and a chiller for semiconductor processes, the SEMI-S2-0703 code.  This is a safety code that states what a chiller must include and not include in order to maintain the high safety standard demanded from the SEMI industry.

 

The key points of this code state the following prerequisites for a semiconductor chiller:

  • A drip tray with 110% reservoir or tank containment capacity
  • Not a requirement but often instituted is a drip tray leak detector.  Due to the dielectric nature of some semiconductor heat transfer fluids optical leak detectors are often used to ensure that even non-electrically conductive fluid leaks are quickly detected and communicated to the chillers main controls.
  • An EMO or EMS with a dry contact that can be tied into the EMO circuit of the semiconductor manufacturing equipment. 
  • Safety switches such as tank level, low flow and a temperature high alarms.  The key difference here is that all safety alarms must have a hardware type switch rather than a piece of software which would say shut a chiller down and or signal a remote alarm if the chiller temperature reached a predetermined temperature setting for the high temperature alarm such as 50C.  Obviously many other safety monitoring mechanisms are used for monitoring various chiller conditions based on the needs of the customer.  Other safety monitors may be pump overload devices, water quality / purity monitors such like resistivity or conductivity monitors, monitoring of the facility cooling water among many others.
  • Electrical shock, all SEMI chillers are required to use low voltage controls, ( 5 -24VAC or VDC) on all outer panels excepting the single power cord entry. Some special provisions may be made for multiple power cord entries.
  • Seismic restraints, all SEMI chillers must be designed to have a stable non-tipping center of gravity and include previsions for mounting the chiller via seismically rated brackets and bolts to the ground.

In a nutshell, these eight differences are the main factors setting semiconductor chillers apart from standard chillers.

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