Hi Brad and Huihang

Thanks for the information and detailed explanation. To add to this
discussion, we've have been using the AZ5214E image reversal resist
and have been getting good results. AZ5214E does not require an
ammonia filled oven for the image reversal process. A bake on the
hotplate is enough.

Best
Leo

On Fri, Aug 21, 2009 at 4:01 PM, Brad Cantos wrote:
> 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
> brad.cantos@holage.com
> 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

--
Xiaoguang "Leo" Liu
Birck Nanotechnology Center,
Purdue University,
1205 W.State Street, West Lafayette, IN, 47906 USA
liu79@purdue.edu