Hi Martin,

        Thank you very much for your comprehensive information. I really
appreciate your time and kindness to explain the details. Unfortunately,
our research lab does not yet have sufficient resource to build a safe
environment for dry etching with toxic gases, so we are currently relying
on non-toxic gases like CF4 and SF6. I am trying to get self-aligned
anisotropic etching of multi-layer structure composed of Mo, a-Si:H, and
a-SiNx:H with CF4/H2 mixture. Actually I do have some success with this
gas mixture, however the photoresist cannot be completely removed after
etching, both O2 plasma and hot solvent stripper doesn't work well. I
heard that the wafer electrode in RIE system should be water-cooled during
etching to prevent overheat the photoresist and carbonize it. My process
requires long etch time, more than 10 mins. It's not too much of a problem
to upgrade the RIE machine for that, if that is the way to solve the
problem. But to upgrade to "try", then it may not be justified. Do you
have any suggestions for me? Thanks a lot!


Regards,

Isaac Chan
Ph.D. candidate in a-SiDIC research group
Electrical and Computer Engineering
University of Waterloo
200 University Ave. W
Waterloo, Ontario, Canada
N2L 3G1
(529) 888-4567 ext.6014


On Tue, 18 Feb 2003 Martin.WALKER@oxinst.co.uk wrote:

> Hi Isaac, everyone
>
> There are some very toxic gases used for plasma etching, with special
> precautions needed for certain gases.  Here is a general summary.
>
> Fluorine containing gases:  Some are dangerous out of the cylinder (such as
> NF3) and need special precautions with new pipework, etc.  Many are inert
> before they go into the plasma (CF4, CHF3, SF6) but will release F2 or HF in
> the plasma.  This will go into the exhaust.  If you are using wet pumps,
> this will dissolve in the oil.  The oil (and any other residues in the
> exhaust system) should be treated in the same way as hydrofluoric acid, that
> is, with great care.  Exhaust systems should either remove this using a
> suitable absorber, or should dilute and vent to atmosphere well away from
> sensitive areas (exact details depend on the country/state/county you live
> in).  First aid precautions should include calcium gluconate gel for dealing
> with HF burns.  First aiders should be trained in how to deal with such
> injuries.
>
> Chlorine and Bromine containing gases:  These would not normally be used in
> open-load plasma chambers, due to the toxicity of the gases and of the
> residues remaining on the chamber walls.  If they are being used in a
> non-load-locked system, a glove box should be used to protect the user from
> these residues, which are produced when moisture reaches the process
> chamber.  It is normal to have a fixed point continuous monitoring system
> when these gases are in use.  Most sensors which are tuned for Cl2 or HCl
> have cross sensitivity for Br compounds too.  Fortunately, all of these can
> be smelled at very low concentrations, so are not as great a risk as gases
> such as PH3.  Where-ever possible, metal to metal seals should be used
> (including in mass flow controllers).  Where o rings are used, these would
> normally be Kalrez rather than Viton.  Again, exhaust gas treatment or
> dilution and controlled venting should be used, with the exact precautions
> depending on the quantities and the local legislation.
>
> For all plasma etch systems, the most hazardous operation is chamber
> cleaning.  Even if the feed gases are inert and the chamber has been pumping
> for a number of hours, toxic compounds can come off the walls during
> cleaning.  Often, either dust masks or even full-face respirators are
> recommended protective equipment for this operation.  A full risk assessment
> should be done before carrying out such operations.
>
> Before using (or installing) any gases, consult the relevant Material Safety
> Data Sheet (MSDS).  These should always be supplied by the gas supplier.  If
> they haven't supplied them, demand them!  Most are pretty good, but
> sometimes they err on the side of caution (usually to minimise the chance of
> litigation in the US).
>
> The semiconductor market (and the MEMS market as a spin-off) generally has a
> very good safety record.  Much of this is because people are very willing to
> share safety related information.  If you have questions about safety, never
> be afraid to ask!
>
> Regards,
>
> Martin
>
> Martin Walker B.Sc.(Tech.) M.Sc.
> Tactical Marketing Engineer
> Oxford Instruments Plasma Technology
> North End, Yatton, Bristol, BS49 4AP UK
> T.+44 (0)1934 837031  F.+44 (0)1934 837001
> E. 
> W. 
>
>
> >Dear all,
> >
> >     I have another question regarding plasma etching (please see
> >email "Subject: post-RIE photoresist residue" for the other question).
> >Besides, CF4, CHF3, C2F6, and other fluorine-contained plasmas, Cl- and
> >Br-contained plasmas, such as CF3Cl and HBr, are commonly used for
> >dry etching. However, are they very toxic and need special chamber, pump,
> >and safety conditions to use those gases for dry etching? The thin film
> >materials for etching are amorphous silicon, amorphous silicon nitride,
> >molybdenum, and (maybe) chromium. Any comments are appreciated.
> >
> >
> >Isaac
>
>
>
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