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
substrate.

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
                   acceleration voltage
                 - development of MAN resist in MaD532, 30s, rinse with DI
                   water
                 - 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
labs

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.



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