Since sputtering can mainly be modeled as a physical process the sidewall
coverage with respect to field thickness is dependent on aspect ratio - so the
actual dimensions dont change much unless you are at the extremes. The wider
trench width would help resolve any keyhole or overhang effects. The issue with
Au and deposition into high aspect ratio that needs to be thought about
concerns the need for low pressure to increase collimation or angle of the
sputter
flux, although since Au is so heavy that can lead to issues with sticking on the
side walls or ejection of previously deposited Au by the next one incoming -
increasing pressure reduces the energy although than the aspect ratio that can
be coated is reduced.

David Metacarpa

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I have trenches in silicon with vertical sidewalls with a depth of about 70µm
and a width of about 8µm. I have sputtered 1µm of gold on the substrate and I
could see that the gold penetrates about 24µm into the trenches. There is
almost no gold below 24µm. This shows that very narrow trenches can be coated
with an aspect ratio of up to 3:1. My goal is to coat the vertical sidewalls of
the trenches with a 400-1000nm thick layer of gold. This first test shows that
an aspect ratio of 3:1 can be coated with gold very well.

What would you think if the trench width is increased to 70µm and the depth
is 250µm? (aspect ratio=3.5:1) Do you think that it will be easier to coat a
trench which has nearly the same aspect ratio (3.5:1), but which is
significantly wider (70µm)?

Any help will be greatly appreciated!

Stephan