Ruthenium Oxide

Mary Tang mtang at
Thu Mar 4 07:07:12 PST 2004

Hi Jim --

Can we find another etch for RuO2?  A quick search turns up several references
in which RuO2 is layered with other conductive oxides to form electrodes for
ferromagnetic applications -- and it looks like Cl2/O2 is used in a couple of
them (again, this is just a quick glance-through -- I don't know what kind of
systems were used, but would imagine that this might be a more chemical than
physical etch and that they were loadlocked, as all Cl2 systems are, so there
would be little risk of exposure.)  Can the pquest be used?  (I can see the
GaAs people cringing now.)  As for the STS dep tool -- I would guess that once
the material is capped that there is little risk of forming RuO4?  If so,
would it be possible to use spin-on-glass to cap the Ru, cure at 400C, and
then use STS dep?  Or maybe use SOG instead of STS dep?  (I guess it depends
on how thick it needs to be and whether the device can handle the high stress
of SOG... This would be a wonderful use of the P5000 TEOS, don't you think?)


Jim McVittie wrote:

> All,
> A new user ( Jim Kruger) wants to dep Ru (mp 2300C) in the Metallica,
> cover it with SiO2 in the STS PECVD tool, wet etch the SiO2 and then
> sputter etch the Ru in the MRC. Ru by itself is not toxic and not a
> problem. The problem is that one of its oxides (RuO4) is very toxic and
> and a has high vapor pressure (mp 25C and BP 130C). The cas number for
> RuO4 is 20427-56-9.  However, it does not form RuO4 very easily.
> Ruthenium is largely immune to atmospheric attack. On heating with oxygen
> (800C in air), ruthenium metal gives ruthenium (IV)  oxide, RuO2. THe MDSD
> says to avoid strong oxidizers so I assume it probably form RuO4 in HNO3
> or H2SO4. Kruger's note below inducates that RuO4 is formed in a O2
> plasma.
> What do you think? Sputtering etch Ru in the MRC is problably a problem
> since a lot of O2 plasma work gets done is there. Metalica is probably not
> a problem since the Ru will be quickly buried and we are not currently
> doing any O2 reactive sputtering in it. STS dep may also be a problem
> since you use a N2/SiH4/O2 mix to deposition PECVD oxide.
>         Jim
> On Fri, 27 Feb 2004, jim kruger wrote:
> > Hello Jim,
> >
> > I am still working on the formal "New Materials
> > Request" for Ru.
> >
> > The interest in Ru is that it is used as a capping
> > layer to protect EUV mirrors from oxidation.
> >
> > I find out that Ru resists tarnishing in air , but can
> > form a highly volatile, highly toxic oxide, RuO4 in
> > for example, plasmas.  Is this going to be a
> > show-stopper?
> >
> > Briefly, I propose to:
> >
> >  deposit ~ 1000 A Ru in Metallica,
> >
> >  cap with PECVD SiO2, pattern to form a hard mask by
> > wet etching with BOE or HF
> >
> > expose to Ar or He plasmas to check erosion
> > strip the hard mask in HF
> >
> > measure erosion step with AFM
> >
> >
> > I hope to see you Monday at the group meeting.
> >
> > Jim Kruger
> >
> >
> > __________________________________
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> >
> >
> --
> --------------------------------------------------------------
> Jim McVittie, Ph.D.                     Senior Research Scientist
> Allen Center for Integrated Systems     Electrical Engineering
> Stanford University                     jmcvittie at
> Rm. 336, 330 Serra Mall                 Fax: (650) 723-4659
> Stanford, CA 94305-4075                 Tel: (650) 725-3640

Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
CIS Room 136, Mail Code 4070
Stanford, CA  94305
mtang at

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