> Can I use PMMA as a resist when I'm etching e-beam evaporated
> SiO2 layer above the Au-layer?
> Does HF etch Au or Ti?
HF solutions etch Ti faster than SiO2.
For an adhesion layer, you can use Cr instead.

> Can I use pure dilute HF or does it have to be buffered with
> HN3F for some reason?
Either will etch SiO2.
Buffering with NH4F (ammonium fluoride) yields a more consistent etch rate over
time.
5:1 BHF (this is 5 parts by volume of 40 wt % NH4F to 1 part 49 wt % HF) is
common.

> How can I wet-etch Au slowly (~100 nm/min)?
Aqua regia is typically mixed with 3 HCl : 1 HNO3 and heated.
By diluting with water and using near room temperature, the etch rate is slowed.
I don't have a recipe for 100 nm/min, but you can use the following as a
starting point:
The mixture 3 HCl : 1 HNO3 : 2 H2O, which self heats to about 30 C,
etches gold at 500-700 nm/min, depending on the gold sample.
Dilute aqua regia is compatible with photoresist.

> Can I etch Au with RIE and with what resist?
Traditional RIE in a parallel-plate etcher won't chemically etch gold,
but it will be slowly sputtered off.
Any resist will do, but selectivity will be poor.
I have heard of work in high-density ICP etchers that etches gold faster,
but then you'd need such a tool.

> Thanks already,
>
> Sampo Tuukkanen, nanoelectronics Group, University of
> Jyväskylä, Finland

        --Kirt Williams Agilent Technologies