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

On Fri, May 13, 2011 at 6:01 AM, Edouard Duriau
 wrote:
> Hi Wei,
>
> Of course the baking process can have an impact, but I don't think this is
> the root cause. Bake plate and process conditions do have a specific
> fingerprint, but such big scaling error is nost likely to come from the
> exposure tool itself.
> Such scaling can arise from mask deformation itself (and I do think that
> quartz mask could help), but I doubt that this is the only root cause since
> I suspect that the exposure time is limited, right?
> In general, this is caused by aberrations of the lenses. These aberrations
> are commonly modeled by Zernike fringe polynomials. In the case of scaling,
> several zernike coefficients can impact scaling. In order to determine which
> ones (i.e. the order of the polynomial), you should check if it is
> linear/quadratic/higher order over the full wafer.
>
> Hope this helps!
>
> Kind regards,
> Edouard

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