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Critical Point Dryer

Critical Point Dryer (CPD)

Contact Information

Maintenance RequestFaculty Contact: Aaron Hawkins
Staff Contact: Jim Fraser
Student Contact: none
General Information
Operating Procedure
  1. Critical point drying is a method of drying wafer stucture without collapsing or deforming the structure of wet, fragile specimens(sample), it is also a part of the sample preparation process for scanning electron microscopy (SEM). The occurrence known as the continuity of state for which there is no apparent difference between the liquid and gas state of a medium, the surface tension between this interface reducing to zero. This occurs at a specific temperature and pressure with resulting density, and is known as the Critical Point.
  2. The purpose of the this Critical Point Dryer is to dry the sample


  1. Before using the Critical Point Dryer, prepare your sample and make sure they fit in the holder.
  2. Check the CO2 gas tank and make sure the valve is open and have enough gas.

Start UP Procedure

  1. Turn power switch "ON". "ON/OFF" power switch is located on right side panel. Green LED on VENT button will light up. This indicates the power is ON and the unit is in standing by in the VENT mode.
  2. Let the Critical Point Dryer(CPD) 815B stand for 3-5 minutes. This initial wait period will allow all internally heated plumbing components to warm-up and will operate smoothly.
  3. Open process chamber by carefully lifting Chamber Lid and placing aside onto soft surface (Lint free wipes provide a convenient surface to place chamber lid).
  4. Now, press the VENT button once. The VENT LED will begin to blink. This indicates that the VENT solenoid is closed and in the "STAND-BY" mode. You may now introduce ultra-pure alcohol into the chamber.
  5. At this point, fill the process chamber with enough high purity alcohol (I.P.A., Methanol, or Ethanol) to cover your wafer(s) or die. NEVER EXPOSE CHAMBER TO ANY ACIDS!
  6. Carefully and quickly transfer your wafer(s) from your wafer container into the 81 5B process chamber. For best results, minimize any exposure time to air.
  7. Carefully align and place the chamber lid on top of the chamber.

Tighten Up the Lid

  1. Note: A "Star-Pattern" is the sequence necessary to properly secure chamber lid prior to initiating a process run
  2. Notice there is number around the 6-Knurl Nuts around the chamber lid. (Like putting the care wheel cover back up)You can use your hand to first slightly tighten up each nut in the sequence. Tighten the knurl nuts in the numbered sequence. Repeat this rotation sequence until the knurl nuts are unable to tighten further by hand.(Don't try to break it though!)
  3. Then, use the spanning wrench to start tightening the knurl nuts in the same sequence starting at position #1. (again, don't try to break it!)
  4. Once the nuts are tight enough, set aside the wrench and move on to the Set Purge Timer Procedure

Set Purge Timer procedure

  1. In the Purge Timer Knob, each position number increment will give you 5mins time increament. For example, setting the "purge timer" indicator arrow to the #1 position will give you a 5-minute purge time. The #2 position will give you a 10-minute purge time... Correspondingly, the #9 position will give you the maximum purge time capable of 45 minutes.
  2. The "Purge Time" setting is best determined by the individual process engineer. General Purge Time guidelines for various chamber alcohol/I.P.A levels are the following:
    1. 1/4 chamber = 10 minute purge time (indicator arrow = #2)
    2. 1/2 chamber = 15 minute purge time (indicator arrow = #3)
    3. 3/4 chamber = 20 minute purge time (indicator arrow = #4)

Press the COOL Button

  1. Press cool and wait till it stop
  1. After the 5 mins warm up time, Press COOL button. the CPD will automatically continue cooling until the chamber temperature reaches 0°C (�5°C). At this point, the cooling will automatically stop.

Press the FILL Button

  1. Press the fILL button and the 815B will begin to fill the process chamber with LCO2. From this point, it will automatically advance through all process modes sequentially until completion. During the FILL mode, the LCO2 will enter and fill the chamber for 8 minutes. You may hear the COOL cycle ON/OFF during the FILL mode as the chamber temperature is automatically maintained below 10°C.

Wait Until Automatic Sequence Completion

  1. After FILL mode, it will automatically avdance to PURGE MODE -> HEAT MODE -> BLEED MODE -> VENT MODE and the sequence is done.

Remove Sample Procedure

  1. After the sequence is done, wait for approximate 5 mins in the VENT MODE.
  2. Reverse the Tighening nut sequence, remove the chamber by alternatively and evenly loosening all of the knurl nuts using the spanning wrench. (Pressure Gauge should be in the 0 psi range, Never attempt to 'force' opening).
  3. The wafer(s) or chip(s) can then be removed from the chamber for further processing. Seal the chamber with the lid to help keep it clean and moisture free.

Shut Down Procedure

  1. Turn the power off using the ON/OFF SWITCH located on the right-hand side of the tool. You will notice that it will take a few seconds for the VENT LED to turn off.
  2. Turn the power strip power switch into the OFF position when finished processing your samples. This will shut down the power to both the SOTBR Condenser and the 815B.


If any question concerning about the Critical Point Dryer, please email the staff locating on the top of the page.