CPD Critical Point Dryer Tousimis 915B, cpd
The Automegasamdri-915B Critical Point Drying (CPD) tool is used for carbon dioxide (CO2) drying after release of bulk or surface micromachined devices. Critical point drying is an efficient method of drying delicate samples without damaging it's structure by surface tension that occurs when changing from the liquid to the gaseous phase. The release is usually performed by immersion of the device in hydrofluoric acid followed by subsequent immersions in several beakers of DI water. The CPD requires that the device be completely free of acid or water before introducing it to the chamber. To avoid this, the device should be placed in isopropyl alcohol for at least one hour.
Contact List and How to Become a User
Picture and Location
The tool is located at CD45 on the SNF Cleanroom Map.
Background
The Automegasamdri-915B Critical Point Drying(CPD) tool is used for the MEMS carbon dioxide (CO2) dry release typically after wet etching. Critical point drying is an efficient method of drying delicate samples without damaging it's structure by surface tension that occurs when changing from the liquid to the gaseous phase. Critical point drying is usually performed release of bulk or surface micromachined devices. This release is usually performed by immersion of the device in hydrofluoric acid followed by subsequent immersions in several beakers of DI water. The CPD requires that the device be completely free of acid or water before introducing it to the chamber. To avoid this, the device should be placed in Isopropyl Alcohol for at least one hour. The CPD achieves a phase change from liquid to dry gas without the effects of surface tension. The critical constants for carbon dioxide are 31.1C and 1070 psi.
Process Capabilities
Cleanliness Standard
The Tousimis 915B Critical-Point Dryer system is in the flexible equipment group.
Performance of the Tool
- The critical constants for carbon dioxide are 31.1°C and 1070 psi.
- Pieces and wafers (up to five 6" wafers)
- Isopropyl Alcohol only
- Operating time for one run is two hours
How to Become a User
Read all material on the SNF website concerning the CPD
Operating Procedures
Sample Preparation:
- Rinse sample at least 3x in DI water.
This can be done at the wet benches flexible corrosive.
- Place sample in Isopropyl Alcohol for at least one hour!
This can be done at the wet bench flexible solvent.
Never expose chamber to any acids or water!
Don't leave the system while processing!
- Contact staff in charge and ask about availability of LCO2 (99.99%).
- Enable cpd.
- Record LCO2 weight in log sheet. One run uses 3 to 4 pounds of LCO2.
- If 'full bottle weight' minus 30 pounds: Shutdown CPD and contact Maintenance.
- Check valves:
- Fill 1.1
- Bleed 0.14
- Purge-Vent 0.15
- “Main Power Breaker” is always on (right side of machine).
- “Chiller Power” press ON, wait for 30 minutes.
- Press “Condenser Power” ON.
- Press “Chamber Power” ON (VENT light on), wait for 3 – 5minutes.
- Remove chamber lid and place it on aluminum foil or stack of thin clean room wipes.
- Check inside of chamber lid, o-ring, inserts, and baskets for particles. Rinse off particles using IPA at the solvent bench, wbflexsolv, or use IPA on a thin cleanroom wipe!
- Check o-ring, if the o-ring is flat, shutdown the system and contact maintenance.
- Place inserts or basket in chamber.
- Press VENT (VENT light will blink).
- Fill sufficient Isopropanol (Methanol or Acetone are not allowed) in chamber to cover your wafers.
- Transfer wafer or die directly from beaker (filled up with IPA) in chamber.
- Lower chamber lid onto chamber and use fingers to evenly tighten the 8 nuts.
- Tighten 8 nuts in numbered sequence using the wrench and repeat until nuts are unable to tighten further. Don't overdue it!
- Set PURGE time (15 minutes is max!)
- Press COOL (VENT light goes off, COOL light goes on), Temperature drops to 10°C within 4 minutes.
- Once Temperature reaches 10°C press FILL (COOL light off, FILL light on). Noice, hissing sound! Pressure goes up to 800 to 900 psi.
- LCO2 will enter chamber within 8 minutes.
- Automatic switch to PURGE (FILL light off, PURGE light on), LCO2 will continue to fill chamber, preset purge time will run.
- Automatic switch to POST-PURGE-FILL (FILL and PURGE lights on), 4 minutes, LCO2 will continue to fill chamber.
- Automatic switch to HEAT. HEAT light will be on until system reaches Critical Point, pressure rises above 1072 psi and temperature above 31°C. Pressure goes up to 1400 psi and temperature can reach up to 40°C.
- Heat will blink for 4 minutes.
- Automatic switch to BLEED (HEAT blinking light off, BLEED light on), pressure drops in a rate of 100 – 150 psi/min, ~ 10 minutes.
- Around 360 psi, automatic switch to VENT (BLEED light off, VENT light on), ~ 3 minutes.
- Open chamber at 0 psi and loosen 8 nuts in reverse pattern (8,7…1).
- Remove wafer, wafer should be dry, if not, contact SNF staff.
Shutdown Procedures:
- Clean chamber, lid, inserts, and basket with IPA and blow dry.
- Place lid back on chamber, don’t tighten nuts.
- Press “Chiller Power” OFF
- Press “Condenser Power” OFF
- Press “ Chamber Power” OFF
- Fill out log sheet.
- Disable cpd.
Helpful Hints:
If all the LED's begin to blink during a process run, either the temperature or the pressure has failed to reach the critical point. Turn "Chamber Power " OFF, shutdown CPD, and contact Maintenance!