Lion,

I evaporate Si02 every day on GaAs.  So things to remember:

1)  If you evaporate Si02 you get Si0x.  You need to bleed a little 02 into your
system during the deposition.
2)  Si02 likes to be evaporated at 4A/s and your substrate at 250C  (I do it at
room temp for my needs)
3)  If you heat cycle your Si02 it will oxidize any AlGaAs / InGaAs layer in
your epi
4)  If you have any metals on your wafer, AZ400K will cause electrolysis and
dissolve epi material and undercut your mask.

Good Luck

Brent

Liang Chen wrote:

> Hi,
>
> I'm trying to use SiO2 as etching mask on GaAs, so I use ebeam evaporator to
deposit a thin layer (3000A) SiO2 on it. The deposition rate is 10A/s, and very
stable. But when I dip that sample in AZ400K developer, some part of SiO2 lift
off from the substrate. The substrate is very clean, because when I took it out
from a growth chamber (we're using MBE to grow structures on GaAs substrate), I
immediately put it into evaporator chamber.
>
> So does anyone have such experience and can give me some suggestion on the
following questions?
>
> 1) Is this ebeam evaporation of SiO2 totally unsuitable for etching mask
purpose?
> 2) Do I need special treatment on GaAs surface prior to loading it into
evaporator?
> 3) Do I need post deposition treatment, like thermal curing at, for example,
400C?
>
> Thanks a lot
>
> Lion
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