Hi Wei,

The lenses won't be a problem with a contact aligner.  I had this same
experience many years ago with the MJB3, and switching to quartz masks helped
quite a bit.  Of course, it depends on how critical your alignment is, and how
much temperature variation your masks, wafers and cleanroom experience.  Another
possible cause is the pressure placed on the mask when the wafer is brought into
contact.  If the pressure is too high (check the specs), the mask could bow
considerably, causing this problem.

Brad
_________________________________

Brad Cantos
brad.cantos@holage.com
http://holage.com




On 13 May 2011, at 11:26 AM, Wei Tang wrote:

> Hi, Edouard
>
> Thanks for the reply and sharing your experience! By mentioning
> aberrations of the lenses, are you referring to a stepper? I am using
> a contact aligner (MJB3), will the lenses aberrations play a role
> here?
>
> Wei