[labnetwork] Critical Point Dryer Problem

Fri Aug 10 01:03:41 EDT 2012

Hello Michael-

Here's some advice regarding your key points:

1. Residual Water

If there is any residual water remaining in the process chamber your design on the wafer may require additional dehydration baths and/or increasing the time in the bath so that you can be sure that all of the H20 molecules bond sufficiently with the alcohol. 
Please note that if there any residual H20 molecules in your substrate prior to going into the process chamber that regardless of how long you PURGE (exchange) the alcohol for LCO2 the H20 will never be removed as LCO2 is not miscible with H20. 
Therefore; any residual H20 will not go thru the CO2 critical point whose minimum pressure/temp. requirements is 1072psi/31C. The critical point for H20 is significantly higher which means that anywhere on the substrate that has H20 remaining during the process will not go thru critical point and will result in stiction. 

2. Residual Alcohol 

Should you have any residual alcohol remaining in the process chamber that is either a result of 1 of 3 main things:
a) Insufficient PURGE time
b) Insufficient flow (typically due to incorrect metering valve flow adjustments)
c) Flow blockage (typically due to break away debris clogging the immediate 0.5um PURGE filter) and should be changed out for a fresh one. 

3. Contamination 

This is a complex question that typically requires complete examination starting from the system environment, handling techniques and careful review of the entire pre-CPD wet process steps to see if there is a possibility of chemical reactions occurring, etc. It's good to see that you use high purity alcohol and take the time to filter it down to 0.2um. 

I hope that you find some of the above information insightful.

Please feel free to contact me direct for a more detailed conversation to better assist you.   

Best Regards-
Yianni Tousimis

Tel.# 301.881.2450
Fax.# 301.881.5374
Cell # 443.254.5423

...innovation and quality...
     www.tousimis.com 

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-----Original Message-----
From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Michael Whitley
Sent: Thursday, August 09, 2012 2:44 PM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] Critical Point Dryer Problem

We've been having an on-going problem with our Tousimis Autosamdri 815B, Series B critical point dryer. We are able to successfully run 1cm die though the system, but 100mm wafers come with parts stuck, contaminated and sometimes there are still liquid drops left on top of the water. We have shipped the system back to Tousimis and it checked out OK at their facility.

We have replaced the following filters and parts:

-  Internal Pre- Fill 0.5um Particulate Filter
-  Internal Post-Fill 0.5um Particulate Filter
-  0.5um Purge Line Filter Element
-  LCO2 Oil/Water Filter Element on LCO2 Filter Assembly, Gasket & O-Ring
-  0.5um Particulate Filter in T-Filter Element on LCO2 Filter Assembly
-  High Pressure 10ft hose changed out with 5ft hose for Chamber LCO2 Supply Only (New Cylinder)
-  Chamber O-Ring
-  Wafer basket and rings

And we have used the following solvents in the chamber:

-  2-Propanol Optima LC/MS, 99.9% - Fisher Scientific (Note:  packaged under Nitrogen, 0.2 micron filtered)
-  Ethanol - ≥99.5%, anhydrous (200 proof) - Sigma Aldrich
*Note: Both of the alcohols above have been further filtered manually with a 0.2um filter prior to processing.

After all of this we are still getting wet wafers and stuck parts. I was hoping someone might have a suggestion on something else to try.

Best Regards,

Michael

--
Michael R. Whitley, PE
Vice President of Engineering | EngeniusMicro, LLC
107 Jefferson Street N, Huntsville, AL 35801
256-261-1260x124 | michael.whitley at engeniusmicro.com

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