Tweezer Cleaning Process Generates Lots of Particles

[Jim McVittie]

Hi,

I have a problem with our recommended cleaning procedure for Delrin 
tweezers.  It attacks the Delrin surface and causes the tweezers to leave 
particles on the wafers.  Today, I was helping a student do a TEL plasma 
oxidation. When he loaded his wafer, we spotted particles. We traced the 
particles to his Delrin tweezers. On quizzing him, I found that he had 
followed the cleaning procedure on our website. 

Here is the procedure in question:
Delrin (plastic) Tweezers: 

1. Remove trace metals for 5 min in unheated 5:1:1 H2O:H2O2:HCl.

2. Rinse for 4 min in DI water.

3. Remove organics for 5 min in unheated 5:1:1 H2O:H2O2 :NH4OH

4. Rinse for 4 min in DI water.

5. Blow dry using N2 gun at the wetbench.

6. Place tweezers in a clean storage box with the tips oriented toward the
end of the box marked TIPS. This will insure that comtaminates from gloved
hands and fingers will not transfer to the ends of the tweezers which will
be in contact with the wafers.

There are a number of problems with this clean. For one a standard clean
should always start with an organic clean step to expose the metal
contamination so the following HCl step can remove the metal. Another
problem is that it dose not address the issue that Delrin is an organic
and is attacked by the H2O2 and most acids. Although it can stand up to
bases, such as NaOH and KOH, it does not hold up well to NH4OH.

Since Delvin is compatible with most solvents, I suggest we limit our 
Delrin cleaning to solvent rinses. In addition, I suggest we look for 
plastic tweezers which are compatible with some of our standard acid, such 
as HF and HCl. 

The chemical compatibility of Delvin can be found at:
http://www.ronningen-petter.com/images/Literature/Chemical-Compatability-MCF-Filter-Diagram.pdf


	Jim 
--------------------------------------------------------------
Jim McVittie, Ph.D.    			Senior Research Scientist 
Allen Center for Integrated Systems     Electrical Engineering
Stanford University             	jmcvittie at stanford.edu
Rm. 336, 330 Serra Mall			Fax: (650) 723-4659
Stanford, CA 94305-4075			Tel: (650) 725-3640