anisotropic sputter etching of ZnSe/GaAs in MRC tool
Kristiaan De Greve
kdegreve at stanford.edu
Thu Apr 5 23:27:43 PDT 2007
Dear Madam or Sir,
after having discussed with Jim McVittie about the possibility of doing
anisotropic etching/sputter etching-ion milling at Stanford, I would like
to file a request to use the MRC Argon plasma.
The basic thing I am looking for is anisotropic etching of ZnMgSe (up to 18%
Mg) MBE grown epilayers on GaAs substrates, in order to make freestanding
mesas and microdisks. Mesas and microdisks (resp. sizes: 50-200 nm and ~1
um) are lithographically defined by e-beam writing on negative e-beam
resist layer of ~ 200 nm (MAN 2403).
In the official SpecMat form:
1) name: Kristiaan De Greve, kdegreve in coral, 650 283 0803 (cell),
kdegreve at stanford.edu, EE PhD student in Yoshi Yamamoto's group.
2) * material: zincselenide(ZnSe)/zincmagnesiumselenide(ZnMgSe, ~18% Mg)
heterostrocture, epilayer (~80nm) on GaAs substrate, small pieces of 3x4mm;
covered with developed MAN2403 negative e-beam resist
* main hazards: - GaAs: toxic when inhaled/swallowed, possibly
carcinogenic, http://www.wafertech.co.uk/msds/msds_gaas.html for the MSDS
- ZnSe: toxic when inhaled, swallowed,
http://ptcl.chem.ox.ac.uk/MSDS/ZI/zinc_selenide.html for the MSDS
* storage group: it's not really a chemical, I don't see any category
under which it would fall
3) 'supplyer': MBE grown at the university of Paderborn, Germany, by Dr.
Alex Pawlis in the group of prof. Klaus Lischka (apawlis at mail.upb.de)
4) reason for request: in order to isolate small ZnSe mesa structures, we
need a dry etching (preferrably) or sputter etching process that can
anisotropically transfer patterns written into negative e-beamresist into
the ZnSe/GaAs; the mesa height is about 100 nm, i.e. into the GaAs
After talking with Jim McVittie, the option of sputter etching was withheld
(the alternative, dry etching in the PQuest - a tool initially purchased by
the Yamamoto group! - meeting resistance from GaAs III-V laser processors
who fear contamination of Zn into their processes). As the Ar plasma is
essentially non reactive, this tool has been used in the past for ion
milling/sputter etching of all kinds of materials, including Zn compounds.
No other tools are available for anitropic etching of these ZnSe epilayers;
wet etching loses quite some resolution, and the MRC plasma, although
second to the PQuest, would be of tremendous help with our experiments.
5) process flow: - spin coating of MAN 2403 resist, 3000 rpm 30s, curing
@90deg C, 1' @Ginzton cleanroom (3x4 mm pieces)
- e-beam writing in Raith 150, 360 uC dose, 10 kV
- development of MAN resist in MaD532, 30s, rinse with DI
- sputter etching in MRC, negative e-beam resist as mask
- resist stripping in MAN resist stripper (remover 1165)
in Ginzton cleanroom
6) amount and form: 3x4 wafer pieces, 3-4 pieces in a run
7) storage: in sample holders and subsequently vacuum chambers in Ginzton
8) disposal: these samples are actively measured and remeasured (optical,
cryogenic experiments); left-over pieces are disposed of as hazardous waste
in Ginzton labs.
Many thanks and best regards,
Kristiaan De Greve.
More information about the specmat