I am assuming that you are having trouble removing the polymer that is
under patterned material.

One thing to look at is to see if you can get a solvent to remove the
polymer, such as NMP.

Oxygen plasma can be used quite well to get under dielectric layers as
long as there isn't some unreasonable geometry. What you need to do is
have a plamsa that is isotropic in nature or downstream from a plasma
with a lot of free radical oxygen or other reactive species.

However, what I am surprised is that you take 3 hours to remove 2,000
angstroms polymer. What polymer is this, polyimide? This suggests
perhaps your problem.

The lateral undercut of organics is going to be less than the rate of
removal in the open areas. So if you  take 3 hours to remove 2,000
angstroms, then to undercut a very small feature such as 4 microns,
would take, (20000 A/(2000/3hr) or 30 hours at least. Since you are
making MEMS devices I suspect you need to do more lateral etching than 2
microns.

It sounds like you might be using a barrel asher. I would go to a diode
plasma etcher set up. I don't think you need an inductively coupled
plasma.

So I would work to make your oxygen plasma more intense and isotropic
increasing power and pressure. Higher temperature increases reactivity
of substrates with ozone and reactive species. Gap might need to be
adjusted. Wider gap I think is less isotropic, if I remember correctly.

Be CAREFUL that you don't cure your polymer with too high a temperature
which would make removal worse.

Ed -- Independent Process Engineer


-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of onny setya
Sent: Thursday, January 29, 2009 8:23 AM
To: General MEMS discussion
Subject: [mems-talk] hard ashing polymer (if Al deposited): possible isotropic
etch by ICP?

Hello everyone,

I'm having difficulty removing the polymer under the dielectric material
whose Al is around 60nm deposited on it

We have done these steps: on the substrate: ~600nm SiO2 or SiNx are
deposited; then ~200nm polymer is applied, after that again 600nm SiO2
or SiNx layer, and the last is Al ~60-100nm (ebeam evaporation)

I removed completely the polymer, for around 3h, using an asher
(oxygen-plasma) if the samples don´t have the Al layer on it.  For the
same ashing process I didn´t get the same result for another sample
whoose Al on it.

That´s why I would like to know:  does anyone know whether it´s possible
to get isotropic etching using only oxygen gas (maybe using ICP)?  Or
any suggestion will be appreciated.

Many thanks!

Onny Setyawati