Tweezer Cleaning Process Generates Lots of Particles

Ed Myers edmyers at stanford.edu
Mon Nov 5 14:35:50 PST 2007


I've looked over a number of web sites related to chemical resistance 
of plastics.  Jim is right, Delrin does not fit with our cleaning 
procedure.  It has low chemical resistance to most acids, but is fine 
with our solvents.  Looking for an alternative, the leading 
candidates come from the fluorocarbon plastics such as CTFE.  It so 
happens we stock a CTFE tweezers.

567 Fluorocarbon (CTFE) for use in Chemical Processing of 
semiconductors. Withstands Hydrofluoric and other acid,.
Resists radiation. 6-3/8"x15/32" body
tapering down to .009" by 3/32" at Tweezer Tips Extra long with 
line-up pin guide.
[]


We should review the cost of these tweezers and decide if we want to 
stock CTFE exclusively or make not of appropriate cleans and 
applications for the different wafer types.  At the very least we 
need to stop the mentioned cleaning procedure on the Delrin version.

Regards,
Ed



At 02:50 PM 9/10/2007, Jim McVittie wrote:
>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
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