Hi everyone,

Here’s my second attempt to send you this e-mail. First attempt included SEM
pictures; which was not allowed. Some of you may have received a blank
e-mail, I’m sorry for that. If you are interested by the SEM pictures I can
send them to you directly.

We currently have some problems with the deposition of aluminium layers.
Maybe some of you already experienced that phenomenon:

Some bump-like structures appear all over the sample after the annealing of
the evaporated Al layer. These structures seem to be empty inside
(cavern-like).

The test samples are bare silicon cleaned with solvents (opticlear, acetone
and IPA, 5min each in ultra-sound). They are then immersed in a solution of
8% HF: DI to etch the native oxide (10-15sec until hydrophobicity) just
before evaporation. The aluminium is then evaporated (e-beam) at a rate of
0.3nm/sec (250nm).

The samples surface seems very clean before the evaporation. After
evaporation, the Al surface show little triangular protuberances (~100nm).

The 450°C annealing, during 30min, reveals the cavern-like structures
(~500nm-1µm). The annealing was performed under N2 atmosphere and forming
gas (N2 80%, H2 20%); both lead to the same results.

We don’t know if this comes from
- a cleaning problem (traces of water or solvent at the surface before
evaporation),
- some problem during evaporation  (contamination, non uniform deposition,
stresses) amplified during annealing,
- some contamination in the oven.
-


Does anyone have any advices or suggestions?

Thank you,

Julie