Hi, Brad

Thanks for the suggestion. I have sent a request to make quartz mask
and hope to see an improvement of alignment accuracy. Regarding the
pressure, I use the vacuum contact mode, which apply a -0.6atm
pressure to the chunk against the mask. The wafer size is 1cmX1cm (I
think the effect of pressure also depend on wafer size, for larger
wafers, the press force will be more spread out, can cause less
bowing). I am wondering is the pressure too big under my condition
according to your experience?

Thanks,

Wei

On Tue, May 17, 2011 at 11:05 PM, Brad Cantos  wrote:
>
> 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

--
Wei Tang
Department of Materials Science and Engineering, UCLA
Cell: 310-357-0158
Website: http://tangweipku.googlepages.com