Folks,

A clarification on the image reversal.  The YES oven (or another
vacuum oven) must be plumbed with anhydrous ammonia to achieve image
reversal.  It is the ammonia that enables the negative image by
neutralizing the acid component of the exposed PAC in positive
photoresists.  Many of these ovens in the field are plumbed for HMDS
and vapor prime.

As for the lift off, it is likely that the sputtering of the metals is
contributing to the difficulties in liftoff.  Sputtering deposits a
conformal coating that is generally continuous and is therefore
difficult to lift.  Most liftoff processes call for evaporated metals,
which are deposited directionally and will leave a gap between the
metal on the wafer and that on the photoresist, especially so when
image reversal is used.

Brad Cantos
[email protected]
http://holage.com


On Aug 21, 2009, at 10:53 AM, Huihang Dong wrote:

> Hi guys,
>
> I believe you could find lots of references about image reversal.
>
> First, you have to design your mask with dark field on the metal you
> want them to stay or pattern.
> Spin 1827 - soft bake - expose UV - YES oven for image reversal -
> flash expose 22 seconds with UV on the whole wafer - developer 319
> for 1 min - Descum with March RIE before sputtering your metal. Ti -
> 40 nm, Pt - 200 nm for me.
>
> That is about what I did.
>
> Thanks,
> Huihang