Hi,

I want to realise FBAR (thin film bulk acoustic resonator) device with 2µm c
oriented ALN film.
I plan to deposit AlN on a silicon membrane (10µm thick) obtained by anisotropic
etching (20% KOH, 80-90°C) of (100) Si covered by a 100nm metallic layer. An
another metallic layer is then deposited on the AlN film. Then I want to remove
the Si membrane by an isotropic etching (probably a mixture of HF, HNO3,
CH3COOH).

So, I'm searching for:

1/ HF, HNO3 and CH3COOH resistant metals (and if possible KOH resistant metals)
for masks
2/ a recipe for isotropic Si etchant (with etching rate and selectivity or
etching rate of possible mask metals)
    I've been told that Au, Cr, W, Ni are resistant against KOH.
3/ What are their etching rate in KOH solution?

I wish your advices. Thank everybody in advance for any suggestion and help.

Best regards,
    Vincent Mortet.