Julie,

-it seems to me, you have adhesion/out gassing or
spikes problems. Some SEMs would
help to localize.

-Are u using 100% Al? AlSi or AlSiCu were better choice.

good luck
Ngo

At 19:31 29.09.2008, you wrote:
>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

Dr. Ha-Duong Ngo
Microsensor and Actuator Technology
Research Center of Microperipheric Technologies
Technical University
TiB3.1
Gustave-Meyer-Allee 25, Geb. 17a
13355 Berlin
Tel:+49 30 314 72 522
Fax:+49 30 314 72 603
Email:ngo@mat.ee.tu-berlin.de
http://www-mat.ee.tu-berlin.de