Note to Lab Members regarding Contamination
Vinny.Pici at asml.com
Wed Apr 6 07:33:42 PDT 2011
SNF Lab Members:
I have been following the issue related to contamination and the impacts it's having on the ASML stepper. I feel a need to express some concern. Although I'm sure many of you are aware of the risk in bringing contaminated wafers into the stepper, I just want to re-enforce some points.
Exposing wafers with contamination on the wafers or on the e-table (exposure-table, which holds the wafer during exposure) will degrade the imaging performance of the tool. Areas of the wafer with a particle beneath it will be exposed out of focus. This is called a HotSpot and will diminish yield.
Wafers are transported through the Stepper in several steps within the Wafer Handler and Wafer Stage subsystems. The wafer is held in place by vacuum as it travels through the stepper. The presence of particles often cause a leak in the vacuum seal. This leak could potentially cause the wafer to fall off at unpredictable times. This alone could cause damage to the stepper if it hits something or if the wafer breaks and contaminates the system. In addition, depending on where the wafer is lost. it may require opening up the stage cavity. This procedure is intrusive and could also lead to damage.
Another concern of mine is the type of e-table installed on the ASML stepper at SNF. This e-table is a 3DAlign version. This means there are very expensive optics embedded in the e-table to allow Backside Alignment. Recently a table similar to this was sent back to our Vendor for repair and they found a great deal of contamination. This will cost ASML a huge sum of money to repair this, not to mention the downtime incurred.
I would like to say a quick thanks to the Lab Members who have told me how much they appreciate having the stepper available for their work. ASML also feels there is a great benefit to working along side with the Stanford staff and Lab Members. So in order for all of us to get the most benefit from having the stepper at Stanford, please take all necessary pre-cautions to avoid contaminating the system and use all defined protocols to ensure we all can realize the benefit of having an ASML advance Stepper for our use.
US Demo Manager
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