Tweezer Cleaning Process Generates Lots of Particles

[Nancy Latta]

Hi All,

I am all over getting tweezers that are compatible with both the 
cleaning procedure and ultra-clean cleanliness level, but did anyone 
mention  that the tweezers used in the original complaint were over a 
year old?  A bit disturbing for two reasons- they should probably been 
throw out just for being old and certainly should have recleaned in a 
years time.....

Mary Tang wrote:

> Yes, we ought to get rid of the Delrin tweezer clean.  I understand 
> that we use Delrin because they are inexpensive.  What is the cost of 
> the CTFE tweezers?  Also, I've heard some people complain that teflon 
> tweezers are "slippery".  It would be helpful to get a few samples.
>
> Mary
>
> Ed Myers wrote:
>
>> Whoops, here is the CTFE resistance.
>>
>> At 02:35 PM 11/5/2007, Ed Myers wrote:
>>
>>> 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
>>>
>
>